Physics doi: 10.3390/physics8040082

Authors: Aleksander V. Postnikov Pavel S. Shlepakov Ilia V. Uvarov Vitaly B. Svetovoy

Measurement of Casimir–Lifshitz forces with high enough precision at separations below 50 nm is problematic due to the snap-in instability. The method of the adhered cantilever is not influenced by this problem. This method has demonstrated a relative precision of 10%, mostly because of systematic errors related to inhomogeneous thickness and the twisting of the cantilever. In this paper, we measure the thickness along the length of the cantilever and reduce the effect of twisting by modifying the measuring chip. It is demonstrated that the adhesion energy between Si and Ru can be measured with a precision of about 1%, which is comparable to the best experiments at distances of 100–200 nm. Only dispersion and, to a lesser degree, electrostatic forces contribute to the adhesion energy. A standard way to discriminate between these forces is the application of a compensating electric potential; however, for the present setup, this is not possible. To separate the forces, a method based on elastoplastic mechanics is proposed. In spite of its lower precision, it gives quite a strong restriction on the electrostatic interaction. The average distance between contacting surfaces is not measured directly but predicted using the distance dependence for electrostatic and Casimir–Lifshitz forces. The combination of the two measurements allows for quite a narrow range of parameters in the distance-potential plane. At a fixed potential, an unprecedented precision for Casimir-type experiments of −0.15 nm in the determination of the average separation distance can be reached.

Physics doi: 10.3390/physics8040081

Authors: David Joffe Thi Tran

We report the results of a study of orbital and stellar parameters of the short-period eclipsing binaries TIC 53847727 and TIC 29914740 using TESS data and Gaiadatasets. The photometric transit data was analyzed in a two-stage process, first with the Lightkurve package to obtain the basic transit properties, and then with the allesfitter software package, using Markov Chain Monte Carlo. Results are reported for the stellar radii and brightness ratios, the orbital semi-major axes and inclinations, and the period and durations of the transits. Limb-darkening coefficient results are also reported for TIC 53847727. Uncertainties in the results are given for fits with a fixed value of the mass ratio q=0.6 and do not include the uncertainty on the q value itself, which may be substantial. We show that the eclipse signal observed in the aperture of TIC 29914747 is diluted light originating from the nearby binary TIC 29914740, and we present a joint Gaia–TESS solution for the true source.

Physics doi: 10.3390/physics8040080

Authors: Mahdi Kourehpaz Dima L. Shepelyansky

The Boltzmann–Loschmidt dispute in 1876–1877 concerned the problem of the time reversal of thermalization in time-reversible classical equations of motion. Here, 150 years later, we revisit this problem in the context of quantum computing. We propose a quantum protocol that allows us to perform a time reversal of complex evolution in the regime of many-body quantum chaos with many qubits. The system consists of qubits evolving on a square lattice with inter-qubit next-nearest-neighbor static couplings and a driven pulsed magnetic field. The system entropy grows quite rapidly to maximal values but returns to its initial comparably small values after time reversal. This time reversal is shown to be stable with respect to quantum gate imperfections. However, similar to the Lorenz butterfly effect, there is a butterfly effect of a qubit in which the inversion of only one qubit breaks the time reversibility of the whole system. We argue that this protocol is accessible to current quantum computers and annealers with hundreds of qubits.

Physics doi: 10.3390/physics8040079

Authors: Michael Bordag Irina G. Pirozhenko

We reconsider the vacuum (Casimir) energy of a massive scalar field obeying Dirichlet boundary conditions inside a spherical cavity. Using zeta-function regularization, we carefully recalculate the analytic part of the zeta function via the uniform asymptotic expansion of the modified Bessel functions. We correct a sign error present in an earlier calculation that affected the large-mass behavior. The renormalized vacuum energy is shown to vanish as m→∞, as required on physical grounds. Numerical results reveal that the energy changes sign several times as a function of the cavity radius.

Physics doi: 10.3390/physics8040078

Authors: Dmitry Kaparulin Nikita Levin Mikhail Malev

In this paper, we investigate the thermodynamics of an ideal gas of classical particles with continuous helicity in three-dimensional Minkowski space. Using the one-particle distribution function for a particle with continuous helicity, we derive expressions for the chemical potential, angular momentum, and entropy of the gas. We show that such a system, when placed in a rotating container, can exist in two phases: rotating and non-rotating. We describe the conditions for the phase transition and examine the phase diagram of the gas. It is found that at comparably low angular velocities the rotating phase can exist only in the form of metastable states. A distinctive feature of these metastable states at such low angular velocities is a negative angular momentum.

Physics doi: 10.3390/physics8040077

Authors: Norio Inui Shido Mikawa

We investigate the Casimir energy between a magnetodielectric plate and a metallic plate in a liquid and show that the Casimir repulsion is enhanced compared with that in vacuum when the metal is described by the plasma model. This enhancement occurs because the attractive transverse magnetic (TM) mode contribution depends on the dielectric contrast between the magnetodielectric plate and the liquid. At large enough separations, exact dielectric matching completely suppresses the attractive TM mode, maximizing repulsion. Using an yttrium iron garnet (YIG)–gold system, we analyze the distance dependence and the effect of imperfect dielectric matching to assess the experimental observability of liquid-mediated repulsion. Observation of this repulsive force provides a practical scheme to address the long-standing Drude–plasma controversy.

Physics doi: 10.3390/physics8040076

Authors: Mikhail Piotrovich Stanislava Buliga Tinatin Natsvlishvili

We present a phenomenological study of a hypothetical compact object with a traversable Kerr-type wormhole geometry connecting two asymptotically distinct regions. One mouth of the wormhole is assumed to reside in an active galactic nucleus (AGN) environment with ongoing accretion, while the second mouth is located in a comparatively quiescent galactic nucleus without accretion activity. In such a configuration, matter accreted near the AGN-side mouth may traverse the wormhole throat and emerge from the opposite mouth. Because the inflowing matter possesses angular momentum, the resulting outflow is expected to be predominantly equatorial, producing a disk-like structure fundamentally different from a conventional accretion disk around a black hole. Several dynamical regimes are considered depending on the outflow velocity relative to the local escape and orbital velocities. Possible observational manifestations, thermal properties, recombination signatures, and magnetic field effects are discussed. Special attention is given to the possibility of jet formation in the absence of a conventional accretion disk. We explicitly distinguish the weak-field, large-radius Newtonian classification used for the outer flow from the strong-field region near the throat, where the dynamics should be treated in a general-relativistic and magnetohydrodynamic framework. We further discuss the specific energy and angular momentum inherited from the inner edge of the accretion flow, the possible modification of these quantities by magnetic stresses and energy-extraction processes, and the effects of an intrinsic dipolar magnetic field of the wormhole.

Physics doi: 10.3390/physics8040075

Authors: Nouha Mastour Said Ridene

In this paper, a numerical investigation of an organic light-emitting diode (OLED) based on a bilayer architecture is presented, with particular emphasis on the influence of ZnO nanoparticles (ZNPs) concentration on charge transport, recombination dynamics, exciton formation, and luminescence performance. The studied device consists of a hole injection layer combined with an electron transport and emissive layer based on Alq3 doped with ZNPs. The impact of ZNPs concentration has been explicitly investigated with respect to carrier mobility, dielectric permittivity, Langevin recombination rate, and radiative exciton decay. The simulation results show that increasing ZNPs concentrations enhances charge balance, recombination efficiency, exciton density, and luminescence power. Furthermore, the variation in the ZNPs concentration, from 0% to 10% in the Alq3 layer, increases the electron charge density from 1.00 × 1015 cm−3 to 1.81 × 1015 cm−3, the recombination rate from 2.48 × 1020 cm−3 s−1 to 6.10 × 1020 cm−3 s−1, the exciton density from 0.16 × 1015 cm−3 to 0.42 × 1015 cm−3, and the power of luminescence from 0.23 W/μm2 to 0.45 W/μm2. The performance of Alq3–ZNPs–OLED is tenfold higher than that of pure Alq3–OLED. These findings demonstrate that the incorporation of ZNPs is a key parameter for ameliorating and optimizing OLED performance, which can serve various optoelectronic designs.

Physics doi: 10.3390/physics8040074

Authors: Fabio Siringo

A novel introduction to gauge invariance is provided by basic pedagogical arguments. A standard problem on Doppler effect leads to a deep insight into the nature of the field theory which describes the photon. The gauge invariance emerges as a nontrivial symmetry which is necessary for the Lorentz invariance of local field theories, and some general properties of photons are recovered without any explicit use of Maxwell equations. The consequent local U(1) symmetry of all charged particles is then highlighted.

Physics doi: 10.3390/physics8040073

Authors: Ludwig Schulz Max Best Carsten Henkel

We investigate interacting spinless electrons on finite molecular networks described by a tight-binding Hubbard Hamiltonian. The interplay between network geometry, Coulomb interactions and discrete symmetries is analysed for rings with L=3,4,5, and 6 nodes, filled with one, two or three electrons. Special attention is devoted to the role of the network symmetries in determining the structure of the many-body spectrum and the Mulliken classification of the eigenstates. Using group-theoretical methods, we examine the evolution of the spectra in the presence of an external magnetic flux. The Zeeman effect lifts degeneracies and results in combination with the Coulomb interaction to avoided crossings in symmetry sectors. We identify a qualitative distinction between systems with an even and odd number of particles. At half-filling, particle–hole symmetry (duality) protects selected symmetry sectors against Zeeman splitting.

Physics doi: 10.3390/physics8040072

Authors: Brian Jonathan Wolk

This paper presents a quantized dynamic lattice model for space–time from which is derived a higher-derivative, gauge-invariant Lagrangian which belongs to a class of actions known to admit perturbative renormalization and which yields the Einstein–Hilbert Lagrangian at the first order.

Physics doi: 10.3390/physics8040071

Authors: Galina L. Klimchitskaya Alexander S. Korotkov Vera V. Loboda Vladimir M. Mostepanenko

We present the theoretical description of a resistive nanoswitch designated for a change-over between the two operation modes by calculating the electric, elastic, dispersion (van der Waals and Casimir), and also exchange repulsive forces in its configuration with an account of surface roughness. The dispersion forces are described by means of the Lifshitz theory and, at the shortest separations between the interacting bodies, where this theory is inapplicable, by the method of additive summation of the interatomic potentials corrected for the role of the effects of nonadditivity. The exchange repulsion is also found by a summation of the interatomic potentials and using the proximity force approximation. It is shown that the nanoswitch possesses the equilibrium closest separation between a cantilever tip and a ground plate calculated as a function of the actuation voltage and operates in a cyclic manner with no pull-in when this voltage is switched on and off. We find the tunnel current between a cantilever tip and a plate and investigate distortions appearing in the signal transmitted through a nanoswitch. According to the results obtained, the amplitude distortions arising in the low-frequency information signal can be made sufficiently small by increasing a difference between the amplitudes of the carrier and information signals. Possible applications of the obtained results are discussed.

Physics doi: 10.3390/physics8040070

Authors: Evgeny Nikulchev

A method for reconstructing dynamical systems from a scalar time series is proposed, based on replacing delay coordinates with jet-space coordinates—the signal and its time derivatives. A theorem is proved establishing a Lie algebra isomorphism under jet prolongation, which ensures equivariance under the full symmetry group of the original system. Unlike Takens embedding, which provides only topological equivalence, jet-space reconstruction preserves not the visual appearance of the attractor, but its fundamental properties: the symmetry group and the differential structure. This is demonstrated numerically on the Lorenz and Rössler systems, where jet space faithfully reproduces the geometry, group invariants, and correlation dimension, while Takens embedding introduces severe distortions. An additional experiment on a symmetric modification of the Rössler system shows that integrating the reconstructed derivatives in jet space recovers the original signal with near-zero error, whereas the same operation in Takens space fails dramatically. This confirms that jet space preserves the differential structure of the system, making it suitable for data-driven equation identification, in contrast to Takens space, where such identification is inherently biased. The method requires no parameter tuning, applies to systems with arbitrary symmetries.

Physics doi: 10.3390/physics8030069

Authors: Márius Pavlovič Ivan Strašík Mauro T. F. Pivi

Modern ion-therapy facilities are commonly equipped with rotating gantries to achieve higher dose conformity to the tumor. The gantry is the terminating part of the beamline from the accelerator to a gantry treatment room. The gantry is mechanically rotated around the patient. In synchrotron-based facilities, the slowly extracted beams have different emittance patterns in the two transverse planes (such beams will be referred to as asymmetric beams). Several matching techniques were developed in the past to remove the angular dependence of the beam parameters at the gantry isocenter on the gantry rotation angle. Recently, a novel so-called rotatorlike gantry optics has been introduced. In this concept, all existing matching techniques are integrated into the gantry optics and the gantry nozzle. The underlying theoretical description of its working principle is presented in this paper. The description is based on the first-order matrix analysis of the transport of asymmetric beams in rotating ion-optical systems, in general. The results are formulated in terms of ion-optical constraints imposed on the fixed incoming beamline, and the gantry transfer matrix. Theoretical matrix analysis is followed by a design study applied to the MedAustron proton-gantry layout as a typical representative of an isocentric gantry equipped with a pencil-beam scanning system.

Physics doi: 10.3390/physics8030068

Authors: Hui-Min Tang Yong Yang Yoshiyuki Kawazoe

We investigated the electronic structures of the wide-bandgap semiconductor Ta2O5 in the presence of oxygen vacancies using standard density functional theory. The emergence of flat bands is observed in certain structural phases due to these vacancies. For instance, when the concentration of oxygen vacancies reaches 10% in the γ1, B, and δ phases of Ta2O5, a flat band appears near the Fermi energy. Further analysis reveals that in certain regions within the Brillouin zone, electrons in flat bands exhibit effective masses 103 times larger than that of free electrons, with some locations even being 104 times higher, thus demonstrating pronounced heavy-fermion-like behavior. Experimental schemes based on electron cyclotron resonance for the detection of such behavior are suggested.

Physics doi: 10.3390/physics8030067

Authors: Romel Rubicel Flores Gámez José Trinidad Guillen Bonilla Héctor Guillen Bonilla Alex Guillen Bonilla Cuauhtémoc Acosta Lúa Maricela Jiménez Rodríguez Mónica Vázquez Gutiérrez María Eugenia Sánchez Morales

In this paper, a Michelson interferometer was employed to generate interference patterns, the modulated function was extracted by digital filtering and the Laplace transform was subsequently applied to obtain the complex function F(s)=F(σ+ωi), which changes its zero structure in response to physical perturbations. This study presents a novel method for detecting millimetric displacements based on analyzing the movement of zeros in the complex s-plane. The proposed technique demonstrates that an unperturbed system displays two zeros on the imaginary axis, whereas the introduction of a displacement ∆x generates a third zero with a real component. The position of this third zero in the s-plane directly correlates with the magnitude of the perturbation. Finally, the measurement vector smeas, calculated as the vector difference between reference and perturbed zeros, quantifies the displacement with high precision. Experimentally, displacements ranging from 0.8 mm to 8.8 mm were introduced into one of the interferometer arms, allowing for the systematic observation of the zero migration within the complex plane. The obtained results demonstrate that this methodology transforms the displacement measurement problem into a singularity localization task in the complex domain, offering enhanced robustness against intensity fluctuations compared to conventional techniques based on Fourier analysis or fringe counting.

Physics doi: 10.3390/physics8030066

Authors: Aleksei P. Kiselev Alexandr B. Plachenov

A review of simple solutions to the linear wave equation in three spatial variables, involving arbitrary functions, is given. Physicists’ interest in these solutions is primarily motivated by the need for a convenient description of spatiotemporally localized wave beams and packets. Four families of closed-form solutions with arbitrary functions—relatively undistorted waves—and some of their applications, particularly in optics, are examined within a unified framework. These are classical plane waves and their simple generalizations, classical and complexified spherical waves known as “complex source fields”, the Bateman wave and its various generalizations, and quasi-spherical waves, which have recently been introduced into consideration. In connection with the latter, we discuss the relatively new concept of the unidirectionality of solutions. We also briefly review families of solutions generated from spherical, quasi-spherical, and Bateman-type waves by Lorentz transformations. The review updates literature from the past two decades to assist in modeling spatiotemporally localized wave phenomena, such as laser pulses, using arbitrary functions instead of complex simulations. The review focus on few-cycle pulses and localized beams matches crucial ongoing developments in laser physics. It also bridges the gap between recent exact solutions and modern paraxial and non-paraxial optics and fills a significant literature void.

Physics doi: 10.3390/physics8030065

Authors: Jarunee Sanongkhun Ekkachai Martwong Daengdesh Naenkieng Akom Hayeeuma

Low-cost and accessible laboratory experiments remain important in physics education, particularly in school and undergraduate laboratories where sophisticated commercial instrumentation is not always available. This study presents the development of a low-cost falling-ball viscometer using an Arduino platform and infrared sensors for viscosity experiments based on Stokes’ law. An automated start–stop timing mechanism was implemented to reduce human reaction errors during measurements. The system was evaluated using glycerin and cooking oil, and the measured viscosities were compared with reference measurements from a Brookfield viscometer. The developed apparatus yielded viscosity values of (0.81 ± 0.04) N·s/m2 for glycerin and (0.117 ± 0.006) N·s/m2 for cooking oil, corresponding to percentage errors of 3.5% and 9.4%, respectively. The present study focuses on the educational implementation of a sensor-based experimental system that enables students to explore viscosity measurement, experimental uncertainty, calibration procedures, and the practical application of Stokes’ law to laboratory data. Despite limitations related to temperature control, optical sensing conditions, and simplifying experimental assumptions, the developed system shows practical potential for physics laboratories and STEM (science, technology, engineering, and mathematics education.

Physics doi: 10.3390/physics8030064

Authors: Jerry Va’vra

The paper investigates the possibility of small hydrogen (SH) formation in the early Universe during an interval of about 10–80 s after the Big Bang. Assuming that SH exists as proposed by the author earlier, the current study examines the cosmological conditions under which the SH can be formed and survive. The photon, baryon, and electron–positron pair densities are estimated, together with the corresponding thermal energies and temperatures, and the formation cross section required to obtain a specified SH abundance and the maximum destruction cross section consistent with SH survival are derived. Although the microscopic formation and destruction cross sections are not presently known, phenomenological constraints the cross sections must satisfy are derived for a given SH abundance. The study suggests that, if SH exists and has negligible nuclear interactions, it would not significantly participate in the standard Big Bang nucleosynthesis reaction network. The possibility that SH can undergo early cosmological decoupling, subject to the presently unknown momentum-transfer cross sections, is also discussed. If SH is formed in sufficient abundance and decouples sufficiently early, it can provide an interesting mechanism for early structure formation and may potentially contribute to the formation of black-hole seeds. This study does not establish the existence of SH, but rather examines whether the conditions in the early Universe present immediate cosmological obstacles to SH formation and survival.

Physics doi: 10.3390/physics8030063

Authors: Norma Susana Mankoč Borštnik

The description of the internal spaces of fermion and boson fields with “basis vectors”, which are the superpositions of odd and even products of the operators γa, with the index a running in internal and external space-time, suggests in d=2(2n+1)-dimensions in internal space, such as d=(13+1), and d=(3+1) in external space-time, a unified picture of all so far observed fermions and bosons. Quarks, leptons, antiquarks, and antileptons appear in families - each family contains fermions and antifermions. Bosons—gravitons, photons, weak bosons, gluons, and scalars, which carry the spatial index α (for tensors and vectors α=n=(0,1,2,3) and for scalars α≥5)—appear in two orthogonal groups. All fields are assumed to have non-zero momenta and angular momenta only in the d=(3+1), SO(3,1), of ordinary space-time. In any d=2(2n+1)-dimensional space, the number of internal states of fermions in all families and their Hermitian conjugate partners is equal to the number of internal states of bosons. The article presents general properties of massless fermion and boson fields and their mutual interactions in this theory, which determine the Lagrangian density of both fields and their interactions. It particularly illustrates “basis vectors” and their properties in d=(13+1) and d=(5+1). The article presents new results and discusses open problems with this theory.

Physics doi: 10.3390/physics8030062

Authors: Mohammad Mobassir Ameen Ganapati Dash Anushree Vijay Theertha Chembakan Prafulla Kumar Behera

Recent developments in particle physics require cost-effective pixel detectors capable of operating under increased energy and luminosity conditions foreseen in future collider experiments. In response, monolithic CMOS pixel sensors incorporating modern readout architectures have emerged, combining high-rate capability with substantial radiation tolerance. To optimize the performance of these sensors for application in tracking detectors, a comprehensive characterization has been done focusing on threshold and noise behavior as a function of front-end DAC tuning parameters. The effect of radiation damage has been investigated using high-intensity X-ray irradiation, followed by a detailed comparison of sensor performance before and after irradiation. The threshold distribution is observed to be uniform across the pixel matrix. Irradiation introduces a systematic shift in the threshold, with a larger impact at low-threshold configurations, while overall uniformity is preserved. In contrast, the noise remains largely stable across the parameter space. The correlation between threshold and noise is used to identify optimal operating regions, demonstrating that stable, efficient performance can be achieved across quite a wide range of configurations. These results confirm the robustness of the sensor under irradiation and its suitability for operation in radiation environments relevant to future high-energy physics experiments.

Physics doi: 10.3390/physics8030061

Authors: Igor Yu. Skobelev Sergey N. Ryazantsev Sergey S. Makarov Roman K. Kulikov Maxim V. Sedov Hui-Tong Zhai Xi-Chen Hu Ming-Yang Zhu Bing-Zhan Shi Yi-Fei Li Jin-Guang Wang Xin Lu Jie Feng Li-Ming Chen

Relativistic interaction of ultra-intense laser pulses with cluster targets is of particular interest for high-energy-density physics, compact X-ray source development, and laboratory astrophysics. Understanding the dynamics of such plasmas requires precise control of their parameters, in particular temperature, on subpicosecond timescales. In this study, X-ray spectral methods were used to diagnose the laser plasma of krypton cluster targets, created at laser pulse intensities of the order of 1020–1021 W/cm2. The use of a time-dependent detailed radiation-collisional kinetic model made it possible to describe the results of the observed X-ray spectra in the femtosecond laser plasma of a cluster target. We present a method for diagnosing the non-stationary plasma of high-atomic-number (krypton) clusters using resonance spectral lines 1s22s22p53s 1P1–1s22s22p6 1S0 and 1s22s22p53s 3P1–1s22s22p6 1S0 of the Ne-like Kr XXVII ion, allowing one to determine the plasma temperature at the moment of “plasma channel” formation. In the experiment, this temperature was shown to be 55 ± 5 eV. The same spectroscopic approach can be extended to other cluster species (for example, Ar, Xe) for non-stationary plasma diagnostics in the relativistic regime.

Physics doi: 10.3390/physics8030060

Authors: Bhimsen K. Shivamoggi

The role of Chapman’s hydrostatic solar wind model (based on a hydrostatic force balance condition) in Parker’s hydrodynamic solar wind theory is investigated by invoking the de Laval nozzle analogy for the production of flow acceleration in the latter model. The action of solar gravity in Parker’s hydrodynamic solar wind model is shown to be geometrically equivalent to a renormalization of the actual wind channel area and the renormalization factor is exactly Chapman’s hydrostatic radial density profile, which is totally predicated on the hydrostatic force balance condition. This result appears to be traceable to the encapsulation of the solar gravity effects in Parker’s hydrodynamic solar wind model by Chapman’s hydrostatic corona model, even beyond the coronal base. Furthermore, this result is shown to be robust by considering both isothermal gas and polytropic gas models as well as an n-dimensional (n= 1, 2, or 3) underlying space for the solar wind.

Physics doi: 10.3390/physics8030059

Authors: Gerardo Alfonso Perez Jaime Virgilio Colchero Paetz

The dynamic critical exponent z describes the divergence of correlation times near a continuous phase transition. Obtaining accurate estimates of z from noisy time series is complex, especially when computational resources are limited. We compare machine learning approaches for estimating z in the three-dimensional Ising model. Data are generated from Monte Carlo simulations on a standard laptop computer, requiring 15 to 20 min of runtime. Twelve time-series features are extracted from the simulation output. We compare linear regression, simple scaling, and ensemble methods. Linear regression achieves a root mean square error of 0.0164 on the validation set with a coefficient of determination R2=0.974. The integrated autocorrelation time logτ shows a near-perfect correlation with z (the correlation value r=0.992), consistent with the system linear size scaling relation τ∼Lz. Autocorrelation features at three lags considered show correlations with z between 0.72 and 0.87. Standardised coefficient analysis indicates that the standard deviation of successive differences and the standard deviation of magnetisation are the dominant predictors in the standardised model, with coefficients of −0.246 and 0.239, respectively. Accurate exponent estimation is possible with minimal computational resources, and fluctuation-based features capture critical slowing down effectively.

Physics doi: 10.3390/physics8030058

Authors: Alessandro Sergi Agostino Migliore Antonino Messina

Quantum mechanics is among the most successful physical theories, yet its formulation and empirical testing rely on classical structures. Following Lev Landau and Niels Bohr, this reliance is not merely pragmatic: quantum observables acquire empirical meaning only relative to classical reference frames, and, in practice, quantization starts from classical models. At the same time, the two domains display forms of mutual irreducibility: intrinsically quantum features (that is, spin and exchange statistics) have no counterpart in the phase-space ontology of classical point-particle mechanics, while classical trajectory chaos does not arise straightforwardly from unitary quantum evolution in closed systems. A hierarchy is commonly established between classical and quantum theories, namely, a claim of ontological and explanatory priority according to which quantum mechanics is fundamental and classical mechanics is only a limiting case. This claim is less secure than is often assumed; therefore, the traditional hierarchy deserves to be examined. In this paper, we argue that a quantum–classical framework provides an effective and structurally faithful representation of empirically accessible physical systems in regimes where quantum and classical degrees of freedom coexist within a single, consistent effective dynamical description. To give this point of view a firm theoretical basis, we discuss the quasi-Lie formal structure underlying quantum–classical hybrid dynamics, with applications ranging from gravity and condensed matter to open, driven systems in biology and complex media.

Physics doi: 10.3390/physics8030057

Authors: Margarita A. Man’ko Vladimir I. Man’ko

The general problem of describing quantum states not only by wave functions and density operators but also by probability distribution functions is discussed in this paper. The qubit-state density-matrix elements expressed in terms of probability distributions are connected with the irreducible representation of group SU(2). The transform of the probability distributions corresponding to the unitary transform of the qubit state of the spin-1/2 system is obtained and expressed in terms of matrix elements of the group SU(2). The possibility to extend the introduced formalism to other quantum states is suggested. For qubit systems, the notion of density operators algebra and the relation with the probability representation of quantum states are discussed. The Schrödinger equation for qubit states is obtained as an equation for probabilities.

Physics doi: 10.3390/physics8030056

Authors: Imane Salhi Yassine Tabbai Abdelhadi Mortadi Hajar Rejdali Fouad Belhora Abdelowahed Hajjaji

A significant amount of mechanical and thermal energy is lost when typing on a laptop keyboard. To address this, hybrid energy harvesters must increase the generated power density and mitigate energy fluctuation issues. This paper explores the potential enhancement of energy harvesting by combining thermoelectric and piezoelectric effects within a multilayered structure integrated into a laptop keyboard button. Through numerical simulation, the study assesses how these two behaviors can synergistically increase the power density generated by the hybrid device. The focus is on optimizing energy efficiency by harnessing the heat losses from integrated circuits and the mechanical stresses due to the act of typing. The point is to refine the design of such a system to maximize the conversion of ambient energy into electricity. The findings indicate that the hybrid structure combining both piezoelectric and thermoelectric effects, effectively captures energy from a laptop keyboard, producing a substantial amount of electricity. This investigation shows that the generator can produce up to 2.07 mW of power using PU-40%PZT as piezoelectric material and an additional 71.93 μW through the PEDOT: PSS as thermoelectric material from a single keystroke when pressed and heated. This study underscores the potential for improving energy-harvesting efficiency in laptop keyboards, contributing to more sustainable and energy-efficient electronic devices.

Physics doi: 10.3390/physics8030055

Authors: Jan Novák Oem Trivedi

It has been known for about hundred years that the universe is expanding, but an impressive discovery came at the end of 20th century, when it was found that the universe is expanding with acceleration. Since then, many models have been developed in cosmology to explain this phenomenon. One of the possible elucidations is that the theory of gravity must be modified at the classical level. However, many such models have already been excluded by gravitational wave experiments. Therefore, one must put a more critical question: could accelerated expansion of the universe be a phenomenon of quantum gravity? Here, we review the basic models of how one explains the origin of dark energy or the cosmological constant in metastring theory, discrete approaches to quantum gravity, group field theory, non-commutative geometry, causal dynamical triangulation, asymptotic safety, and models based on holography and entropic gravity. At the end of a newly formed approach to the quantization of gravity, we mention the ring paradigm, which may, after application to cosmology, naturally model the late-time accelerated expansion epoch in the universe. What is most remarkable, though, is that the final formulation of this theory may ultimately solve the old problem of the cosmological constant.

Physics doi: 10.3390/physics8030054

Authors: Evangelos Georgios Filothodoros

A formal thermodynamic mapping is established between the attractive Fermi–Hubbard model and the repulsive Bose–Hubbard model at finite temperature and at imaginary chemical potential μ=iθ. By utilizing a large N-expansion, it is shown that the partition functions of the two models are related by a plain shift θ→θ+π. This condition maps the BCS–BEC crossover of attractive fermions to a Bose–Fermi crossover (fermion-like occupation) of repulsive bosons. A central feature of this correspondence is the thermal kernel g(βE,ϕ) (with β the inverse absolute temperature, E the energy scale, and ϕ the phase angle), whose analytic continuation gB(βE,ϕ)=gF(βE,ϕ+π) governs the bosonic (B) and fermionic (F) sectors. Interestingly, the particular angles ϕ=2π/3 and 4π/3 for fermions correspond to ϕ=π/3 and 5π/3 for bosons, marking the boundaries of an universal thermal window. It is further argued that the present mechanism shows how an emergent, fermionization-like phenomenon can occur at finite interaction strength through a thermodynamic effect induced by the imaginary chemical potential. It is emphasized that this does not imply a transmutation of quantum statistics at the operator level, but rather a thermodynamic exclusion-like behavior driven by the imaginary chemical potential, unlike the Tonks–Girardeau limit, where fermionization arises from an infinite repulsive interaction and anyonic or Floquet-engineered systems where transmutation emerges from modified statistics or dynamics. Effectively, the phase ϕ is a statistical parameter; by twisting the thermal phase, it generates fermion-like behavior without hard-core constraints or infinite repulsion through purely thermodynamic mechanisms. The gap equation and number equation for the bosonic model are derived, highlighting the role of the imaginary chemical potential as a statistical regulator. The results obtained here provide a unified framework for understanding crossovers in interacting lattice systems.

Physics doi: 10.3390/physics8020053

Authors: Sebastiano Ettore Spoto

Deep gas emissions in volcanic and tectonic environments are commonly interpreted as the surface expression of localized deep emitters. This representation is adequate for first-order description, but it is not physically complete. Deep degassing is more appropriately represented as a coupled source–storage–pathway system in which volatile generation, compressible accumulation, phase change, hydraulic communication, and permeability evolution are dynamically linked. Starting from phase-wise mass conservation in deformable porous–fractured media, reduced equations for gas migration, pore-pressure diffusion, and thermo-poro-mechanical coupling are derived, showing how the distinction between gas-mass transport and pressure propagation provides a unified framework for volcanic and tectonic degassing. Deep pressure gradients are shown to arise from the competition between volatile supply and pathway leakance, while episodic discharge can occur when permeability evolves under effective stress, sealing, and failure. A minimal analytical source–storage–pathway model is further derived, yielding explicit criteria for valve onset, source charging and discharge times, and the distinction between pressure-led and mass-led responses. The framework is then applied to the published Campi Flegrei carbon dioxide (CO2) diffuse total output record, providing a real-data illustration of slow storage loading and rapid transient discharge. The analysis considers magmatic exsolution, hydrothermal mediation, metamorphic devolatilization, advective–diffusive near-surface filtering, and the inverse problem through which surface fluxes and gas compositions are used to infer deep source properties. The formulation links magmatic degassing, hydrothermal pressurization, tectonic fluid ascent, and fault-valve behavior within a common continuum-physics perspective and identifies the constitutive assumptions that most strongly control interpretation.

Physics doi: 10.3390/physics8020052

Authors: Lorenzo Albanese

Possible violations of the no-signaling constraint in Weinberg-type nonlinear extensions motivate the question of whether entanglement could, under suitable conditions, become a resource for operational signaling. A minimal binary model is introduced in which, in each run, a sender selects a binary input bit and a receiver locally records a binary output bit. Signaling is defined operationally as a dependence of the local output statistics on the remote input and is summarized by a single channel parameter that can be estimated from data. An estimator and a corrected confidence interval are then introduced to assess this dependence quantitatively, while transmission reliability is expressed through the minimum decision error. On this basis, a conservative criterion is formulated, using an upper bound on the error and a threshold fixed in advance, to characterize a near-identity channel regime. Minimal reporting requirements are also proposed to document the conditions under which artifacts and classical leakage may reasonably be excluded.

Physics doi: 10.3390/physics8020051

Authors: Ximena Jocelyn Téllez-Tovar Félix Sánchez-De Jesús Claudia Alicia Cortés-Escobedo María Isabel Reyes-Valderrama Ana María Bolarín-Miró

This study investigates the modulation of coercivity and magnetodielectric coupling in heat-treated, nickel-substituted lanthanum ferrite. LaFe0.7Ni0.3O3 samples were synthesized by high-energy ball milling and sintered at temperatures between 1073 and 1473 K. Chemical composition, crystalline structural evolution, surface morphology, magnetic, dielectric, and electrical properties, as well as magnetodielectric coupling, were analyzed. The XPS spectra revealed the presence of adsorbed oxygen, associated with the high oxygen affinity of the material. This behavior is interpreted as a charge-compensation mechanism, related both to the formation of oxygen vacancies and to the partial oxidation of Fe3+ to Fe4+. XRD and Rietveld refinement confirmed a single-phase orthorhombic Pnma structure, and structural simulations revealed progressive octahedral distortions with increasing temperature, affecting the octahedral tilting and electronic bandwidth. Magnetic characterization revealed that thermal processing modifies the magnetic behavior, inducing weak ferromagnetism and a significant increase in coercivity, correlating with progressive densification, greater domain stability, and reduced microstrain. Impedance measurements revealed magnetodielectric coupling, the Maxwell–Wagner interfacial polarization mechanism, and reduced dielectric losses. These findings demonstrate that the coercivity and magnetodielectric response in cationic nickel-substituted lanthanum ferrite can be tuned through thermal processing. A semi-empirical magnetocrystalline anisotropy model is proposed to explain the coercivity evolution and associated multiferroic behaviors, thus contributing to the study of functional ferrites as sustainable alternatives to rare-earth magnetic materials with potential in sensors and memory devices.

Physics doi: 10.3390/physics8020050

Authors: Eugene O. Kamenetskii

Quantum bianisotropy and chirality are fundamental concepts in light–matter interaction that describe how materials with broken symmetries respond to electromagnetic fields at the level of macroscopic quantum electrodynamics. In quantum bianisotropy, magnetoelectric (ME) energy plays a critical role in mediating and enhancing light–matter interactions. This concept is essential for bridging the gap between classical electromagnetics (where bianisotropy often involves field non-locality) and quantum mechanics in metamaterials. The precise manipulation of a quantum emitter’s properties at a subwavelength scale is due to near fields, which effectively function as a tunable environment. In this paper, it is shown that the ME near field, interpreted as a structure combining the effect of bianisotropy/chirality with a quantum atmosphere, is a non-Maxwellian field with space–time symmetry breaking. Quantum ME fields arise from the dynamic modulation and topological coupling of magnetization and electric polarization within ME meta-atoms—specific subwavelength structural elements with magnetic and dielectric subsystems in magnetic insulators, which are assumed to have quantum properties.

Physics doi: 10.3390/physics8020049

Authors: Florian Neukart Eike Marx Valerii Vinokur

We investigatewhether a finite local information capacity of spacetime can account for the gravitational phenomena commonly attributed to cold dark matter. Starting from a covariant effective-field-theory description, we modelcoarse-grained entropy deposition as a dynamical scalar field S(x) whose stress–energy tensor contributes to structure formation. The macroscopic action contains a single dimensionless coupling λ multiplying the canonical kinetic term, ensuring ghost-free dynamics and conservation of the associated stress–energy tensor. In a slow-roll regime, defined by a covariant source term Γ≡S¨+3HS˙=0, where H is the Hubble parameter and overdot denotes derivative with respect to cosmic time, and |S¨|≪H|S˙|, the entropy sector behaves as pressureless dust at background and in linear order. Implemented in a modified Cosmic Linear Anisotropy Solving System (CLASS) Boltzmann solver, the entropy component fits Planck satellite 2018 cosmic microwave background (CMB) data, baryon acoustic oscillation (BAO) measurements, and the Pantheon + Type Ia supernova sample for 0.5≲λ≲2, while preserving the linear growth factor to within 0.2% over Euclid space telescope scales. To regulate ultraviolet contributions, we introduce a holographically motivated prescription in which gravitationally active entropy deposition is confined to causal two-surfaces, yielding a ρ∝r−2 halo envelope with a finite-density core determined by local entropy saturation. Fixing the flux scale A from astrophysical entropy budgets reproduces Milky-Way-mass halos without introducing fine-tuned length scales. Pilot N-body simulations that evolve the entropy field on a staggered grid reproduce the halo mass function down to 1010.5M⊙, mitigate the cusp–core and missing-satellite tensions, and remain consistent with cluster lensing constraints. On linear scales, the model predicts percent-level, scale-dependent deviations in the lensing convergence and matter power spectra, testable by Euclid space telescope, the Roman Space Telescope High Latitude Survey, and the CMB-S4 experiment.

Physics doi: 10.3390/physics8020048

Authors: Soon-Tae Hong Bum-Hoon Lee

We construct the strong energy conditions (SECs) for both massive and massless stringy extended objects in the higher dimensional cosmology (HDC) with cosmological constant Λ. Exploiting these conditions, we find the equation of state (EoS) parameters w≥−(D−4)/D for both the massive and massless stringy extended objects in D (D≥5) dimensional cosmology. The stringy SECs impose a universal constraint on w that remains valid across both radiation- and matter-dominated eras. We elucidate the relations between the EoS parameter in the HDC with cosmological constant and that of Hawking–Penrose limit for the massive and massless point particles in the four dimensions. We evaluate the EoS parameters in terms of the contributions from the point particle property, cosmological constant, and extended object degrees of freedom, respectively. We also investigate the weak energy condition for the massive and massless stringy extended objects in the HDC, and those for the massive and massless point particles in the four dimensions, respectively.

Physics doi: 10.3390/physics8020047

Authors: Helena Cristina Vasconcelos Reşit Özmenteş Maria Meirelles

We develop a leading-order continuum framework for thin-film hydrodynamics on inclined solid substrates, integrating capillarity, intermolecular forces, gravitational symmetry breaking, confined transport, and stochastic wetting into a single formulation. Starting from lubrication theory with capillary curvature and disjoining-pressure interactions, we obtain a lubrication-scale thin-film equation that incorporates inclination-driven advection, nanoscale stabilization, and humidity-controlled source–sink fluxes. A dimensionless analysis shows that, within the long-wave lubrication approximation, inclination induces a coordinated leading-order coupling among the Bond (Bo), Péclet (Pe), and Damköhler (Da) numbers. This coupling defines a characteristic inclination-angle-dependent scaling trajectory Γ(θ) in the (Bo, Pe, Da) space: material parameters set the system’s position along this curve, while the geometric constraint organizes the ordering of hydrodynamic, transport, and confinement regimes. We further derive leading-order crossover criteria associated with transport transitions (Pe ≃ 1) and reactive-confinement loss (Da ≃ 1), providing explicit regime boundaries that can be evaluated for representative parameter ranges. A representative parameterization of an ultrathin atmospheric electrolyte film is then used to make these crossovers explicit, yielding illustrative inclination thresholds that depend on the chosen parameter set. Coupling the deterministic structure to a minimal stochastic closure captures intermittent wet–dry dynamics under environmental forcing. In this closure, inclination selectively accelerates the drying pathway through the drainage time (and thus drying rate λdry), while rewetting remains primarily humidity-controlled, to leading order, providing a scaling-based description of wet-state persistence and time-of-wetness versus θ. The resulting framework provides a continuum-scale physical description of confined films under geometric asymmetry, relevant to wetting, interfacial drainage, confined transport, and thin-film systems in which symmetry breaking and coupled interfacial–transport processes coexist.

Physics doi: 10.3390/physics8020046

Authors: Juan A. Lazzús

This study investigates the thermodynamic consequences of substitutional doping in bilayer graphene using a minimal tight-binding model in which doping is encoded as a reduction in the intralayer hopping amplitude α in one sheet. The interlayer coupling Δ fixes the low-energy window, while 0<α<1 introduces spectral asymmetry without generating new energy scales. The results show that decreasing α redistributes the density of states toward the Fermi level, producing an enhancement of the low-energy density of states within the hybridized inner branches. As a consequence, the total electronic entropy vanishes in the limit of zero temperature (T→0) and increases smoothly with temperature for all α, consistent with the third law of thermodynamics. Layer-resolved analysis reveals that the doped sheet acquires a larger electronic entropy than the pristine one for 0<α<1, giving rise to a finite entropic polarization. The maximum polarization follows a linear scaling, demonstrating that the entropy imbalance is continuously controlled by the hopping asymmetry and does not involve critical behavior. These results establish a direct connection between doping-induced spectral redistribution and thermodynamic layer polarization in bilayer graphene.

Physics doi: 10.3390/physics8020045

Authors: J. Va’vra

This paper examines whether a compact electron–proton configuration (“small hydrogen”) with a characteristic radius of a few femtometers is excluded by basic relativistic kinematics and simple stationarity constraints. Motivated by earlier discussions of formally deep relativistic energy scales in Dirac-based treatments, a phenomenological, virial-inspired energy-balance framework that incorporates relativistic kinetic energy, finite-size regularization of the central field, and order-of-magnitude spin–magnetic and spin–orbit contributions is developed in this paper. Within this framework, self-consistent characteristic scales associated is obtained with a hypothetical compact configuration without invoking Dirac or quantum-electrodynamics (QED) bound-state eigenvalues. The resulting scales—namely, a central energy scale of about 260 keV and a characteristic spin-dependent scale of order ΔEspin ≈ 100 ± 20 keV—define concrete experimental and observational energy ranges of interest. The present study does not establish the existence, formation probability, lifetime, or dynamical stability of such states. Rather, it shows that relativistic kinematics, finite-size effects, and virial-inspired stationarity constraints do not, by themselves, rule out compact stationary electron–proton configurations within the assumptions of the model. If such states were realized in nature and possessed radiative or interaction channels, those states may have implications for astrophysics, fusion concepts, and dark-matter phenomenology.

Physics doi: 10.3390/physics8020044

Authors: Diana Deară Oana Ristea Cătălin Ristea Alexandru Jipa

We present a study of the mean transverse momentum pT of identified strange hadrons (KS0,Λ,Λ¯,Ξ−,Ξ¯+,ϕ,Ω−,Ω¯+) produced in Au+Au collisions at RHIC-BES energies (the nucleon–nucleon center-of-mass energy sNN=7.7 GeV,11.5 GeV,19.6 GeV,27 GeV and 39 GeV). The mean transverse momentum is obtained from transverse momentum spectra of the strange hadrons as measured by the STAR experiment and its dependence on the number of participants Npart is studied. For RHIC-BES energies, experimental data indicate a centrality dependence of pT, with an increase towards central collisions. This dependency is described using a power-law function to fit the data. The power-law exponent α is used to characterize the degree of flattening of pT with respect to Npart and its dependency on the collision energy and particle mass is studied. Special emphasis is placed on ϕ-meson that has a smaller interaction cross-section, thus reflecting the properties of the early stages of the system’s evolution. The pT of ϕ-mesons produced in Au+Au collisions at RHIC-BES energies are compared with the results obtained in Au+Au collisions at higher RHIC energies and in Pb+Pb collisions at SPS and LHC energies. A distinct energy dependence of ϕpT values is identified. Furthermore, data indicate, when comparing peripheral and central heavy-ion collisions, that ϕ-meson pT increases with system size, following two distinct trends. The results are compared with the predictions of the default and string-melting versions of the AMPT generator. We observe that the string-melting AMPT version describes the strange meson pT, but underpredicts the strange baryon pT centrality dependence. The default AMPT overpredicts the KS0 and ϕ meson pT centrality dependence, while the strange baryon data are in general better described by this version of the model. The exponent α obtained from AMPT-simulated results does not describe the measurements satisfactorily.

Physics doi: 10.3390/physics8020043

Authors: Bing He Shengyu Peng Nan Sun Guoliang Li Xiaofei Zhu Peng Xu Xiaowei Shen

As a foundation for numerical solvers in computational electromagnetics, particularly for multiphysics and electromagnetic compatibility applications, Jefimenko’s equations offer a generalized solution to Maxwell’s equations, enabling the direct computation of electromagnetic fields from time-dependent source distributions without the boundary-condition artifacts inherent to grid-based methods. However, the numerical integration of these equations is computationally intensive, typically scaling as O(NsNo) for Ns source points and No observation points. In this paper, we present JefiFast, a highly optimized graphics processing unit (GPU) implementation that significantly outperforms the state-of-the-art JefiGPU algorithm. We identify that previous implementations are strictly memory-bound due to inefficient global memory transactions and a lack of data reuse. JefiFast addresses these bottlenecks through four key optimizations: (i) a packed memory layout (PML) using an array-of-structures approach to ensure coalesced memory access for source densities and their derivatives; (ii) geometry-aware shared memory tiling strategies that maximize L2 (level-2) cache hit rates and on-chip data reuse; (iii) pre-computation of time derivatives to minimize redundant arithmetic operations; and (iv) a robust observation domain decomposition strategy that enables linear scaling across multiple GPUs. Benchmarks demonstrate that JefiFast achieves speedups ranging from 4.08 times (for 303 grids on a single NVIDIA V100 graphic processor) to 84.51 times (for 503 grids on 4 NVIDIA V100 processors) compared to the baseline. Notably, for a 503 grid on a single GPU, JefiFast reduces execution time from about 51 min to just about 2.6 min (19.54 times speedup). These performance advances make high-resolution relativistic heavy-ion collision simulations feasible in near real-time.

Physics doi: 10.3390/physics8020042

Authors: Elmo Benedetto

General relativity is often perceived by undergraduate and advanced high-school students as conceptually and mathematically inaccessible. This paper does not provide new results in gravitation but rather introduces a lucid pedagogical framework for understanding gravitomagnetic effects in rotating systems. Starting from the Langevin metric, which describes flat spacetime in a uniformly rotating reference frame, the paper considers an apparent paradox: two clocks moving with identical velocities in an inertial frame but located at different radii on a rotating platform. While the equality of proper time of the clocks is expected in the inertial frame, its reconstruction in the rotating frame is not immediately transparent. It is shown here that this equality emerges from an exact compensation between three distinct contributions: a centrifugal potential term, a kinematic time dilation term, and a velocity-dependent term being formally analogous to a gravitomagnetic potential. The explicit identification and interpretation of these contributions constitute the pedagogical significance of this paper. Although the consideration presented is performed in flat spacetime, the formal analogy with gravitomagnetic effects provides students with an accessible pathway to more advanced concepts such as frame-dragging and the Sagnac effect, while highlighting the importance of velocity-dependent interactions in relativistic physics.

Physics doi: 10.3390/physics8020041

Authors: M. Shahbaz Ullah M. Javed Idrisi Sergey Ershkov

In this paper, the circular Sitnikov three-body problem is studied under the combined influence of radiation pressure and albedo. The model consists of two equal-mass primaries moving in circular orbits about their center of mass and an infinitesimal body constrained to oscillate along the perpendicular axis. The radiative emission from one primary and the reflected radiation from the other are incorporated into the effective potential through radiation and reflectivity parameters. Using the Jacobi integral, we determine the energetically admissible region for vertical motion and examine how radiative effects modify the accessible phase space. The study shows that the system admits a single vertical equilibrium point at the origin, which remains linearly stable within the physically admissible parameter range. Radiation and albedo reduce the effective restoring force and increase the oscillation period, producing a measurable rescaling of the physical time without altering the geometrical structure of the phase trajectories. The phase-space dynamics are further explored by means of Poincare (first-return) maps obtained from numerical integration of the nonlinear equation of motion. The resulting invariant curves confirm that the motion remains regular and bounded, while their progressive contraction reflects the reduction in the oscillation amplitude with increasing radiative effects. Overall, the results show that albedo acts as a quantitative modifier of the vertical Sitnikov dynamics by changing the effective potential, the admissible energy domain, and the observable time scale, without generating new qualitative phase-space structures.

Physics doi: 10.3390/physics8020040

Authors: Larissa Inácio Felipe S. S. Rosa Astrid Lambrecht Paulo A. Maia Neto Serge Reynaud

The Casimir interaction in salted water contains a universal contribution of electromagnetic fluctuations that makes it of a longer range than previously thought. The universal contribution dominates non-universal ones at the distances relevant for actin fibers inside the cell. We discuss universal and non-universal contributions with a model mimicking biological matter. We also show that the universal Casimir effect should have crucial implications at the cell scale.

Physics doi: 10.3390/physics8020039

Authors: Nikolay V. Sidorov Mikhail N. Palatnikov Alexander Y. Pyatyshev Alexander V. Skrabatun

It is found that the speckle structure of the photoinduced light scattering indicatrix of the LiNbO3:Y3+(0.46 wt%) crystal and its behavior with the time of crystal irradiation with a laser undergo an atypical behavior caused by the features of the dissipation processes of laser-induced defects in the crystal. In the frequency range of 100–4000 cm−1, the Raman spectra of the LiNbO3:Y3+(0.46 wt%) single crystal were recorded upon excitation by visible (532 nm) and near-IR (785 nm) laser radiation. Five second-order Raman scattering lines were detected in the frequency range of 1000–2100 cm−1, with the frequencies of two of them (of about 1790 cm−1 and 1940 cm−1) somewhat exceeding the doubled value of the frequencies of fundamental vibrations of the 4A1(z)LO (longitudinal optical) and 9E(x,y) symmetry types, which allows us to attribute these lines to the overtones of the fundamental vibrations of 4A1(z)LO and 9E(x,y). It is found that only one Raman scattering line is observed in the region of stretching vibrations of OH-groups (3200–3800 cm−1). The frequency of this line is found to depend on the scattering geometry, varied within 3431–3438 cm−1, and to be shifted to the low-frequency region by about 30–50 cm−1 relative to the frequencies in the IR absorption spectrum. This finding may be due to the alternative prohibition rule due to the presence of the center of symmetry of the oxygen octahedra O6 of the crystal structure.

Physics doi: 10.3390/physics8020038

Authors: Anatoly A. Gurchenkov Ivan A. Matveev

The evolution of the flow of a viscous, electrically conductive, incompressible fluid on a rotating wall in the presence of a magnetic field is studied. The wall forms an arbitrary angle with the axis of rotation. The unsteady flow is induced by longitudinal oscillations of the wall and a suddenly applied magnetic field directed normal to the wall. An analytical solution to the three-dimensional unsteady magnetohydrodynamic equations is presented for the case of infinitely high fluid conductivity. The velocity field and induced magnetic field in the flow of a viscous, electrically conductive fluid are determined. A number of special cases of wall motion are considered. Based on the obtained results, the influence of the magnetic field on the characteristics of the waves emitted by the wall is investigated.

Physics doi: 10.3390/physics8020037

Authors: Alfred Wünsche

The Wigner quasiprobability, along with some of its essentialproperties, is introduced and discussed in two versions, first covering real canonical variables such as W(q,p) and second a pair of complex conjugate coordinates such as W(α,α*). The reconstruction of the density operator ϱ of states is also given. Building upon the Susskind–Glogower concept of quantum phase operators, further aspects of phase operator algebras in the quantum optics of a harmonic oscillator are discussed in relation to the realization of the su(1,1) Lie algebra. Coherent phase states |ε⟩ are introduced in analogy to the common coherent states |α⟩ in two ways, as both eigenstates of certain operators and as states generated from a ground state |0⟩ by operators of the Lie group SU(1,1). The limiting transition to the non-normalizable Fritz London phase states |eiφ⟩ on the unit circle and an (over)-completeness relation for the coherent phase states are derived. The Wigner quasiprobability W(q,p) for the coherent phase states is calculated and graphically represented. From the Wigner quasiprobability, a phase distribution W(φ) is calculated by integrating over the radius, and its uncertainty is defined and presented. The Hilbert–Schmidt distance is discussed as a measure of the non-classicality of states, where most of our with Viktor Dodonov work was carried out.

Physics doi: 10.3390/physics8020036

Authors: José Holanda

This paper investigates the control of magnetic energy confinement in one- and three-dimensional magnetic systems by systematically accounting for magnetic interactions. The analysis provides new insight into magnetic behavior at the nanoscale and introduces a simulation-based framework that clearly distinguishes between magnetizing and demagnetizing interaction regimes. Within this framework, magnetic energy confinement is rigorously defined and can be quantitatively controlled through the underlying interaction landscape. To validate this approach, extensive numerical simulations were performed on representative one- and three-dimensional nanostructures, including individual nanowires and hexagonal arrays of nanowires. Each nanowire was modeled as a chain of interacting ellipsoidal grains, enabling an accurate description of the complex magnetic interactions governing energy confinement in these systems.

Physics doi: 10.3390/physics8020035

Authors: Alexander Breev Dmitry Gitman

The relationship between states obtained by the non-commutative integration method of the Schrödinger equation on Lie groups and generalized coherent states is investigated. It is shown that such solutions belong to the class of generalized coherent states when the corresponding λ-representation is real.

Physics doi: 10.3390/physics8020034

Authors: Fernando M. O. Moucherek Ricardo L. L. Vitória

We investigate the effects of Lorentz symmetry violation (LSV) on a scalar particle via a non-minimal coupling in the Klein–Gordon equation within the charge–parity–time CPT-odd gauge sector. Through an analytical approach, we derive bound-state solutions for two distinct anisotropic backgrounds: time-like and space-like. In the time-like case, the LSV induces an effective centrifugal potential, modifying the angular momentum spectrum. When a hard-wall confining potential is included, discrete energy levels emerge, explicitly dependent on the LSV parameters. In the space-like scenario, the particle becomes confined by a Coulomb-type potential induced by the LSV, leading to a quantized energy spectrum that reduces to the free-particle limit when the LSV parameters vanish. Our results illustrate how spacetime anisotropies, encoded in a background vector field, can significantly alter the quantum dynamics of scalar particles in the presence of a magnetic field.

Physics doi: 10.3390/physics8020033

Authors: Galina L. Klimchitskaya Constantine C. Korikov Vladimir M. Mostepanenko

We consider the Casimir force in configurations with magnetic metal plates and analyze the reasons why the predictions of the Lifshitz theory using the dielectric permittivity of the Drude model are inconsistent with the measurement data. For this purpose, the contributions of the electromagnetic waves with the transverse magnetic and transverse electric polarizations to the Casimir force are computed using the Lifshitz theory expressed in terms of the pure imaginary Matsubara frequencies. Furthermore, the fractions of the evanescent and propagating waves in these contributions are found using the equivalent formulation of the Lifshitz theory along the real frequency axis. All computations are performed for Au–Ni and Ni–Ni plates using the Drude model and the experimentally consistent plasma model over the separation region from 0.5 to 6 μm, where the total force value is determined by the conduction electrons. It is shown that the transverse magnetic contribution to the Casimir force does not depend on the model of the dielectric permittivity used, allowing the total difference between the predictions of the Lifshitz theory using the Drude model and the measurement data to be determined by the transverse electric contribution. In doing so, as opposed to the case of nonmagnetic metals, both fractions of the evanescent and propagating waves in this contribution depend on the model of the dielectric permittivity used in computations, whereas the magnetic properties of the plate metal influence the Casimir force solely through the fraction of the propagating waves in the transverse electric contribution. The issue of a more adequate theoretical description of the electromagnetic response of magnetic metals is discussed.

Physics doi: 10.3390/physics8010032

Authors: Grigoris Panotopoulos

The paper investigates the structural properties of self-gravitating fluid spheres composed of a dilute, homogeneous, and ultracold Bose gas, assuming repulsive, short-range interactions. For the first time, the Lee–Huang–Yang (LHY) correction is incorporated to the standard polytropic equation-of-state with index n=1, which extends beyond the Hartree mean-field approximation by accounting for quantum fluctuations. The findings indicate that this correction significantly affects the mass–radius relationships and other properties of condensate dark stars, such as the compactness factor and tidal Love numbers. Notably, the impact of the LHY correction is more pronounced for equations of state that support higher maximum stellar masses.

Physics doi: 10.3390/physics8010031

Authors: Mohamed Babiker

The turning point that sparked the initiation of quantum theory was the Planck–Einstein postulate that the energy of a monochromatic radiation field is quantized in terms of photons, and this was followed by the development of the principles of quantum mechanics. Although some conceptual issues remain to be resolved, quantum mechanics is regarded as a well-established discipline which may lead to the unraveling of the nature of matter in general. Today, the influence of quantum mechanics is evident in its applications, with remarkable technological advances involving diverse aspects of the physical world. What appears to need particular attention, however, (after a hundred years have elapsed since the birth of quantum mechanics) is the impact that the concept of the ‘quantum’ has had beyond traditional quantum mechanics. The paper describes how the ‘quantum’ concept has influenced and continues to influence developments in physical systems, which are essentially classical, in that they are basically governed, entirely, or in part, by non-quantum laws, but in which, the physics is distinguished by its own special quantum—the photon analogue. The paper illustrates this by considering, as prototype examples, bulk plasmons and phonons. The study outlines the systematic quantization of plasmons and phonons, both of the polariton (transverse) forms and their longitudinal forms, and discusseshow these interact with quantum systems such as electrons, atoms, and condensed matter. It is demonstarted using one case, namely, involving longitudinal plasmons, how utilizing quantum concepts and techniques facilitate their interaction with matter, as in electron energy loss spectroscopy.

Physics doi: 10.3390/physics8010030

Authors: Santosh Kumar Kudtarkar

The paper develops a coarse-grained framework for computing mean extinction times in multi-metastable systems modeled as one-step continuous-time Markov chains with an absorbing state. At the microscopic level, backward equations on finite corridors are solved to obtain closed-form series for committors, mean first-passage times, and intrawell (basin) waiting times. A renewal–reward construction then yields effective interwell transition rates written as a success probability divided by a mean cycle duration, providing an interpretable effective rate constant. These rates define a reduced Markov chain on the wells together with extinction; mean extinction times follow from a linear system, and the associated fundamental matrix quantifies pre-extinction residence times in each coarse state. This framework makes explicit how multiple escape pathways and intrawell dwell times contribute to extinction statistics in finite systems. The method is illustrated on a double-well landscape with an extinction state, using a reversible potential-to-rates mapping for the numerical example. Comparisons of alternative intrawell models and validation against exact one-step computations demonstrate accuracy at finite system sizes, including regimes where diffusion approximations are unreliable. The resulting formulas require only local rate data, remain numerically stable under strong bias, and extend directly to multiple wells and flexible boundary conditions.

Physics doi: 10.3390/physics8010029

Authors: Merab Gogberashvili Tinatin Tsiskaridze

We investigate a possible resolution of the dark energy problem within a pair-universe framework, in which the universe emerges as an entangled pair of time-reversed sectors. In this setting, a global zero-energy condition allows vacuum energy contributions from the two sectors to cancel, alleviating the need for extreme fine-tuning. We propose that the observed dark energy does not originate from vacuum fluctuations but instead arises as an effective entanglement energy between the visible universe and its mirror counterpart. Treating the cosmological constant as an integration constant fixed by boundary conditions rather than a fundamental parameter, we show that the cosmological equations can be formulated without explicitly introducing vacuum energy. By imposing physically motivated boundary conditions at the cosmological event horizon, we obtain an integration constant consistent with the observed dark energy density. The parallel mirror world scenario thus provides a unified framework that may simultaneously explain the origins of dark energy and dark matter.

Physics doi: 10.3390/physics8010028

Authors: Yuriy G. Gubarev Jingyue Luo

The problem of controlling plasma is one of the most essential challenges in the creation of experimental facilities for thermonuclear fusion. In this study, a mathematical model of a two-component Vlasov–Poisson plasma is used to study the stability of spatial dynamic equilibria in this plasma. Applying the direct Lyapunov method, we obtain results that demonstrate that three-dimensional (3D) dynamic equilibrium states of the Vlasov–Poisson plasma are absolutely unstable with respect to small spatial perturbations. The sufficient conditions for linear practical instability are obtained for the 3D dynamic equilibria of a two-component Vlasov–Poisson plasma. An a priori exponential lower estimate is constructed, and initial data are found for small spatial perturbations that grow with time. Finally, analytical examples are presented for exact stationary solutions to the mathematical model of Vlasov–Poisson plasma and the growing small 3D perturbations superimposed on these solutions.

Physics doi: 10.3390/physics8010027

Authors: Dmitry Kalashnikov Konstantin Belotsky

As is known, the standard cosmological model (ΛCDM ) demonstrates reasonable agreement with observations of the large-scale structure of the Universe. However, the model shows significant differences between observations of individual galaxies and numerical simulations. To address these discrepancies, various extensions of ΛCDM are being explored, one of which is self-interacting dark matter (SIDM). We employ a SIDM model characterized by a dark Coulomb-like interaction between dark electrons and dark protons and mediated by a dark photon. An essential feature of such models is recombination—the formation of ‘dark atoms’, which can be part of dark matter (DM). The spatial distributions of two-component DM that may explain the positron anomaly have been studied in earlier studies. Our contribution is to calculate three-body recombination rates and the resulting neutral fraction of ‘dark atoms’, as well as to show that the recombination process provides a natural mechanism for generating such two-component DM during the evolution of the Universe.

Physics doi: 10.3390/physics8010026

Authors: Annabel Kropf Ivo Schulthess

This review serves as a conceptual and practical introduction to strong-field quantum electrodynamics (SFQED), written from the standpoint of experimental physicists. Rather than providing a comprehensive theoretical review, the paper focuses on the core ideas, terminology, and challenges in SFQED that are most relevant to experimental design and interpretation. The review serves as a first point of contact with the subject, bridging the gap between foundational theory and hands-on experimental investigations, and complementing more formal literature in the field.

Physics doi: 10.3390/physics8010024

Authors: Carlos Rodriguez-Benites Sergio Santa-María Nelson Mechán-Zurita Kenyi Llauce-Baldera Arnhol Campos-Bocanegra Cristhian Nunura-Cotrina Manuel Gonzales-Hernandez Vaukelyn Viloria-León Moises Barrios-Cespedes Fredy Medina-Gamboa Antonio Rivasplata-Mendoza

We investigate cosmological scenarios in a spatially flat Friedmann–Lemaître–Robertson–Walker (FLRW) universe containing Ricci-type holographic dark energy within the framework of general relativity. The cosmic fluid is composed of baryonic matter, radiation, cold dark matter, and dark energy. We consider three phenomenological interaction schemes in the dark sector and derive analytic expressions for the standard cosmological quantities in each case. Using observational data from cosmic chronometers and Type Ia supernovae (Pantheon sample), we constrain the parameters of the interacting models and determine their best-fit values. Finally, we compare the interacting holographic scenarios with the concordance ΛCDM (Λ cold dark matter) model at the background level, displaying contour plots for the cosmological and interaction parameters and discussing the performance of the models in light of earlier results in the literature.

Physics doi: 10.3390/physics8010025

Authors: Yuan Shi John D. Moody

Magnetic fields, either imposed externally or produced spontaneously, are often present in laser-driven high-energy-density systems. In addition to changing plasma conditions, magnetic fields also directly modify laser–plasma interactions (LPI) by changing the participating waves and their nonlinear interactions. In this paper, we use two-dimensional particle-in-cell (PIC) simulations to investigate how magnetic fields directly affect crossbeam energy transfer (CBET) from a pump to a seed laser beam when the transfer is mediated by the ion-acoustic wave (IAW) quasimode. Our simulations are performed in the parameter space where CBET is the dominant process and in a linear regime, where pump depletion, distribution function evolution, and secondary instabilities are insignificant. We use a Fourier filter to separate out the seed signal and project the seed fields onto two electromagnetic eigenmodes, which become nondegenerate in magnetized plasmas. By comparing the seed energy before CBET occurs and after CBET reaches quasi-steady state, we extract the CBET energy gains for both eigenmodes in lasers that are initially linearly polarized. Our simulations reveal that, starting from a few MG fields, the two eigenmodes have different gains, and magnetization alters the dependence of the gains on laser detuning. The overall gain decreases with magnetization when the laser polarizations are initially parallel, while a nonzero gain becomes allowed when the laser polarizations are initially orthogonal. These findings qualitatively agree with theoretical expectations.

Physics doi: 10.3390/physics8010023

Authors: Slobodan Radošević Sonja Gombar Milica Rutonjski Petar Mali Milan Pantić Milica Pavkov-Hrvojević

We discuss the geometry behind the classical Heisenberg model at the level suitable for third- or fourth-year students who did not have the opportunity to take a course on differential geometry. The arguments presented here rely solely on elementary algebraic concepts such as vectors, dual vectors and tensors, as well as Hamiltonian equations and Poisson brackets in their simplest form. We derive Poisson brackets for classical spins, along with the corresponding equations of motion for the classical Heisenberg model, starting from the two-sphere geometry, thereby demonstrating the relevance of standard canonical procedures in the case of the Heisenberg model.

Physics doi: 10.3390/physics8010022

Authors: Alexei D. Chepelianskii Dima L. Shepelyansky

The quantum dissipative time evolution of a fluxonium under a pulsed field (kicks) is studied numerically and analytically. In the classical limit, the system dynamics is converged to a strange chaotic attractor. The quantum properties of this system are studied using the density matrix within the framework of the Lindblad equation. In the case of dissipative quantum evolution, the steady-state density matrix is converged to a quantum strange attractor that is similar to the classical one. It is shown that depending on the dissipation strength, there is a regime when the eigenstates of the density matrix are localized at a strong or moderate dissipation. At weak dissipation, the eigenstates are argued to be delocalized, which is linked to the Ehrenfest explosion of the quantum wave packet. This phenomenon is related to the Lyapunov exponent and Ehrenfest time for the quantum strange attractor. Possible experimental realizations of this quantum strange attractor with fluxonium are discussed.

Physics doi: 10.3390/physics8010021

Authors: Boris A. Malomed Gennadiy Burlak Gustavo Medina-Ángel Yuri Karlovich

We systematically investigate semiclassical dynamics of the optical field produced by quantum nanoemitters (NEs) embedded in a periodic lattice of conducting nanorings (NRs), in which plasmon polaritons (PPs) are excited. The coupling between PPs and NEs through the radiated optical field leads to establishment of a significant cross-correlation between NEs, so that their internal dynamics (photocurrent affected by the laser irradiation) depends on the NR’s plasma frequency ωp. The transition to this regime, combined with the nonlinearity of the system, leads to a quite increase in the photocurrent in the NEs, as well as to non-smooth (chimera-like or chaotic) behavior in the critical (transition) region, where considerably small variations in ωp lead to significant changes in the level of the NE pairwise cross-correlations. The chimera-like state is realized as coexistence of locally synchronized and desynchronized NE dynamical states. A fit of the dependence of the critical current on ωp is found, being in agreement with results of numerical simulations. The critical effect may help to design new optical devices, using dispersive nanolattices which are made available by modern nanoelectronics.

Physics doi: 10.3390/physics8010020

Authors: R. Guy Woolley

This review explores the foundations of non-relativistic quantum electrodynamics (QED) and its application to atoms and molecules. It follows the traditional route of placing classical electrodynamics in an Hamiltonian framework, followed by Dirac’s canonical quantisation algorithm. The properties of the resulting quantum Hamiltonian are reviewed from a non-perturbative perspective. It discusses the gauge invariance of the S-matrix, the Coulomb interaction, and the challenges posed by infinities in classical and quantum electrodynamics. The paper examines the mathematical frameworks used to address these issues, including the use of distributions and the Colombeau algebra. The review also highlights the limitations of the Coulomb Hamiltonian in explaining molecular structure and chemistry, emphasizing the need for additional theoretical modifications to bridge quantum mechanics and chemical phenomena.

Physics doi: 10.3390/physics8010019

Authors: Vladimir M. Mostepanenko Galina L. Klimchitskaya

We address the spatially nonlocal dielectric functions of graphene at any frequency derived starting from the first principles of thermal quantum field theory using the formalism of the polarization tensor. After a brief review of this formalism, the longitudinal and transverse dielectric functions are considered at any relationship between the frequency and the wave vector. The analytic properties of their real and imaginary parts are investigated at low and high frequencies. Emphasis is given to the double pole at zero frequency, which arises in the transverse dielectric function. The role of this unusual property in solving the problem of disagreement between experiment and theory in the Casimir effect is discussed. We believe that a more complete dielectric response of ordinary metals should also be spatially nonlocal and its transverse part may possess the double pole in the region of evanescent waves.

Physics doi: 10.3390/physics8010018

Authors: Igor Kaganovich Michael Tendler

Partially ionized plasma physics has attracted increased attention recently due to numerous technological applications made possible by the increased sophistication of computer modelling, the depth of the theoretical analysis, and the technological applications to a vast field of manufacturing for computer components. Partially ionized plasma is characterized by a significant presence of neutral particles in contrast to the fully ionized plasma. The theoretical analysis is based upon solutions of the kinetic Boltzmann equation, yielding the non-Maxwellian electron energy distribution function (EEDF), thereby emphasizing the difference with a fully ionized plasma. The impact of the effect on discharges in inert and molecular gases is described in detail, yielding the complex nonlinear phenomena resulting in plasma selforganization. A few examples of such phenomena are given, including the non-monotonic EEDFs in the discharge afterglow in a mixture of argon with the molecular gas NF3; the explosive generation of cold electron populations in capacitive discharges, hysteresis of EEDF in inductively coupled plasmas. Recently, highly advanced computer codes were developed in order to address the outstanding challenges in plasma technology. These developments are briefly described in general terms.

Physics doi: 10.3390/physics8010017

Authors: Evgenii Yu. Prosviryakov Evgenii S. Baranovskii Sergey V. Ershkov Alexander V. Yudin

Polynomial exact solutions of the Navier–Stokes equations for describing micropolar incompressible fluid flows with energy dissipation are reported. The transformation of mechanical energy into thermal energy is taken into account. The heat equation for the Rayleigh function contains the sum of the squares of the components of the Cauchy velocity tensor (the main component for the dissipative function). Unidirectional homogeneous and non-homogeneous fluid flows with moment stresses are considered. The solvability of overdetermined systems for studying homogeneous and non-homogeneous shear flows is studied. The paper pays attention to the exact integration of equations for three-dimensional flows. The construction of classes of exact solutions is carried out first using the Lin–Sidorov–Aristov solution family. In other words, the velocity field depends linearly on part of the coordinates. The coefficients of the linear forms of the velocity field depend on the third coordinate and time. The pressure field and the temperature field are quadratic forms with similar functional arbitrariness. In addition, exact solutions for the velocity field with a nonlinear dependence on part of the coordinates are considered.

Physics doi: 10.3390/physics8010016

Authors: Khakimjan Butanov Maksudbek Baydjanov Hammid Yusupov Komiljon Bobojonov Maksudbek Yusupov Andrey Chaves Khamdam Rakhimov

We investigate time-resolved wave-packet transport in monolayer graphene patterned with asymmetric arrays of circular electrostatic scatterers. Using the Dirac continuum model with a split-operator scheme, we track how transmission evolves with scatterer radius and polarity sequence. To this end, we consider three potential configurations (Samples 1–3). The results reveal a geometry-controlled crossover from near-ballistic propagation at small radii to interference-dominated backscattering at large radii. Sample 1, where the potential exhibit two parallel lines of circles, each line sharing the same potential sign, preserves the highest transmission. Conversely, in Sample 3, where potential signs are intercalated between circles of the same line, the dwell time increases, which produces stronger confinement. As the radius increases, pronounced temporal oscillations emerge due to repeated internal reflections (similar to Fabry–Pérot interferometer), and the radius dependence of the saturated transmission probability exhibits anti-resonant dips that are tunable by geometry and potential magnitude. These behaviors establish simple design rules for graphene nanodevices: small-radius Sample 1 for high-throughput transport, Sample 2 (with inverted potential signs as compared to Sample 1) for broadband suppression, and Sample 3 for finely tunable, interference-based confinement.

Physics doi: 10.3390/physics8010015

Authors: José Tito Mendonça Kyriakos Hizanidis

We compare two different approaches to turbulence: the kinetic theory of solitons and the kinetic theory of quasi-particles. Using the same model equation as the starting point of both descriptions, we compare their properties, advantages, and limitations. We also address the question of whether a gas of solitons be seen as a particular case of a gas of quasi-particles and propose possible strategies leading to a more general theoretical model of wave turbulence.

Physics doi: 10.3390/physics8010014

Authors: Sukhendu Das Adhikary Amar Prasad Misra

We employ a two-dimensional fluid simulation approach to study the nonlinear turbulent dynamics of internal gravity waves (IGWs) in the weakly ionized Earth’s ionospheric F-layer with the effects of Pedersen conductivity. We observe that the presence of Pedersen conductivity leads to the formation of intermediate-scale structures in the velocity potential, along with the development of small-scale density fluctuations. The characteristic turbulent energy spectrum exhibits a non-Kolmogorov scaling of k−2.40 in the presence of Pedersen conductivity, while a Kolmogorov-like k−5/3 scaling is observed when it is absent, where k denotes the wave number. Due to energy loss caused by Pedersen conductivity, the wave’s amplitude reduces gradually with time. The cross-field diffusion coefficient related to the velocity potential also reduces as Pedersen conductivity increases. The results in the F-layer are compared with those in the literature, where the Ampère force and hence the Pedersen conductivity effect were ignored compared to the pressure gradient and gravity forces, as relevant in the Earth’s D-layer.

Physics doi: 10.3390/physics8010013

Authors: Mitsuo Kono Hans L. Pécseli

Models for dual cascades in power-spectra for fully three-dimensional (3D) incompressible turbulence are reviewed and summarized. Special attention is given to analyses where the basic equations for 3D incompressible flows are expanded in terms of the eigenfunctions for the curl-operator. The possibilities for forward and inverse cascades in 3D fluid turbulence are illustrated and quantified. Conditions for dual- and forward-energy cascades in wavenumber space are presented. The forward or unidirectional cascade is found to dominate, a result consistent with the basic physical arguments formulated by vortex-line stretching. The analysis gives additional details to quantify the cascade conditions including dual cascades. Selected initial or boundary value conditions can give transient space or time intervals, where a dual cascade is dominating.

Physics doi: 10.3390/physics8010012

Authors: Jan Weiland Tariq Rafiq

We show how a source-aware fluid closure framework for turbulent transport performs well on the confinement timescale in magnetically confined plasmas. A central result is that whether a source is resonant with the turbulence determines which fluid moments must be retained. Using a nonlinear current formulation, we show that resonance broadening—the dominant kinetic nonlinearity—cancels linear resonances and thereby justifies a quasilinear fluid closure already on the turbulence timescale. We derive a practical negative-energy criterion and identify parameter regimes satisfied by ion-temperature-gradient (ITG) modes (slab and toroidal), with parallel ion compressibility and magnetic curvature controlling the sign. The framework clarifies when velocity-space dynamics must be retained in the kinetic Fokker–Planck equation (for example, for fast-particle instabilities at frequencies about 102 higher than drift-wave frequencies). The present study provides additional support for our model by predicting transport that increases with radius and by showing—consistent with nonlinear kinetic simulations—that the diamagnetic flow dominates the Reynolds stress. Altogether, the results obtained provide a consistent, reduced-cost path to fluid closures that retain the essential kinetic physics while remaining tractable on confinement timescales.

Physics doi: 10.3390/physics8010011

Authors: Suman Kumar Panja Mathias Boström

We present a brief review of a nontraditional but significant application for a high-temperature charged plasma. The unorthodox proposition was made by Barry Ninham concerning a contribution from Casimir forces across high-temperature electron–positron plasma in nuclear interactions. The key message in this review is that high temperatures (about 1011 K) are found to be essential. Certainly, classical, semi-classical, and quantum considerations for the background media impact both the Casimir effect and the physics of stars and the Universe.

Physics doi: 10.3390/physics8010009

Authors: Alexandra V. Rogachevskaya Vasily N. Lednev Pavel A. Sdvizhenskii Igor Y. Savin Sergey V. Gudkov Alexey S. Dorohov Andrey Y. Izmaylov

Laser-induced breakdown spectrometry (LIBS), known as an express analysis technique, is for the first time applied in this study for determining selenium in soil. Modern agriculture requires elemental analysis methods to perform the continuous automated online control of microelement content in soil. However, selenium has never been quantitatively determined in soil by LIBS so far. Different sample preparation techniques (loose soil powder, mounted on adhesive tape and tableted soil) are employed here for LIBS determination of selenium in soil. The optimal choice of analytical line is challenging for selenium because of spectral interference with the minor and major soil components (Fe, Si, Zn, Al, Sb), but the Se I 196.09 nm line has the lowest spectral interference. A limit of detection of 3 mg/kg for selenium in soil is achieved in the present study using LIBS. The analytical performance of tape-mounted and loose soil powder samples with appropriate data averaging is found to be comparable to that achieved for tablets.

Physics doi: 10.3390/physics8010010

Authors: Fernando C. Lombardo Francisco D. Mazzitelli

We analyze shortcuts to adiabaticity (STA) and their completions for the quantum harmonic oscillator (QHO) with time-dependent frequency, as well as for quantum field theory (QFT) in non-stationary backgrounds. We exploit the analogy with one-dimensional quantum mechanics, and the known correspondence between Bogoliubov coefficients in the QHO and transmission/reflection amplitudes in scattering theory. Within this framework, STA protocols for the QHO are equivalent to transmission resonances, while STA in QFT with homogeneous backgrounds correspond to reflectionless potentials. Moreover, using the connection between particle creation and squeezed states, we show how STA completions can be understood in terms of the anti-squeezing operator.

Physics doi: 10.3390/physics8010008

Authors: Alan C. Maioli Evaldo M. F. Curado Jean-Pierre Gazeau Tomoi Koide

We present two complementary approaches to the Gorini–Kossakowski–Sudarshan–Lindblad equation for an open qubit. First, based on linearity, yields solutions illustrated by mixed-state trajectories in the Bloch ball, including non-random asymptotic fixed points and exceptional points. Second, exploiting the SU(2) symmetry, leads to a nonlinear dynamical system that separates angular dynamics from radial dissipation. This symmetry-based perspective presents a promising route toward generalization to open qudits.

Physics doi: 10.3390/physics8010007

Authors: Nuno Crokidakis

The Spanish conquest of the Inca empire in the early 16th century stands as one of the most striking examples of asymmetric historical collapse. In this paper, a simplified mathematical formulation is developed being inspired by Lotka–Volterra dynamics to describe, in a stylized quantitative manner, the interactions between the Inca state and the invading Spanish forces. The model is not intended to explain the historical events in a causal or predictive sense, but rather to capture and represent key mechanisms commonly identified in historical analyses. These include the demographic and political weakening caused by smallpox epidemics prior to direct contact, the internal fragmentation produced by the civil war and the introduction of external shocks such as the capture of Atahualpa and the fall of Cusco. Although intentionally minimalistic, the framework provides a dynamical illustration of how combined internal and external pressures can destabilize a complex society. This descriptive perspective situates the Inca collapse within the broader conceptual language of complex systems, emphasizing how nonlinear interactions, feedback and structural asymmetry shape trajectories of resilience and failure.

Physics doi: 10.3390/physics8010006

Authors: Shuwen Cao Jinhong Yang Shun Lei

Polyurea, a novel spray-applied composite polymer, is of high application importance for rapid roadway support in coal mines. The current study investigates the dynamic process and mechanisms governing the impact and spreading of polyurea droplets on rough surfaces through experimental and theoretical approaches. The key novelty lies in revealing how spontaneously varying viscosity couples with surface microstructure to produce novel scaling laws distinct from classical Newtonian behavior. The droplet impact and wetting process can be divided into three stages. In the pinning stage, droplet behavior is dominated by kinetic energy, leading to inertia-driven spreading in which the contact line radius increases quite slowly with time. In the penetration stage, the apparent three-phase contact line (TPCL) is pinned by surface microstructures, while the real TPCL evolves with time following a temporal scaling law t3/2. In the spreading stage, surface roughness becomes decisive. On low-roughness substrates, limited pinning allows the real and apparent TPCLs to spread synchronously, with TPCL evolution governed by surface tension and viscous forces, following a t1/8 scaling law. As roughness increases, pinning effects strengthen, causing divergence: the real TPCL is driven by surface tension and viscous dissipation between microstructures, whereas the apparent TPCL is additionally influenced by pinning and reaction-induced viscosity, scaling as t1/24. This t1/24 scaling for the apparent contact line on relatively high-roughness surfaces represents a significant deviation from established scaling relations. Experiments on rock-like substrates confirm these mechanisms for polyurea droplets. These findings provide theoretical and engineering guidance for optimizing spray-coating parameters in coal mines, with the goal of improving coating uniformity and interfacial adhesion.

Physics doi: 10.3390/physics8010005

Authors: Erik O. Shalenov Yerkhan A. Tashkenbayev Yeldos S. Seitkozhanov Karlygash N. Dzhumagulova

We present the effective optical potential describing the interaction between an electron and a neon atom in a dense plasma. This potential accounts not only for the screening effect but also for the quantum non-locality and electronic correlation effects, which lead to an increase in the interaction energy between the electron and the neon atom. Within this framework, differential and momentum transport cross-sections for elastic electron–neon scattering are determined. The obtained results are compared with the available experimental data and theoretical predictions, showing exceptionally good agreement.

Physics doi: 10.3390/physics8010004

Authors: Grégoire Salomon Mathias Rapacioli J. Christian Schön Nathalie Tarrat

The environmental pollution caused by emerging organic contaminants—such as ibuprofen—is becoming increasingly a cause for alarm. New treatments for their removal are currently being developed, but the nature and toxicity of the transformation products (TPs) formed during the processes cannot be readily assessed experimentally. Atomistic simulations are thus of high interest in predicting the chemical structure of these TPs. In this paper, we demonstrate that the transformation of a contaminant molecule under irradiation can be studied using the threshold algorithm combined with the density functional-based tight-binding (DFTB) method. The fragmentation pathways of an ibuprofen molecule under irradiation are studied as a function of the energy added to the system. Specifically, the chemical structures of ibuprofen’s TPs, the paths between them, their stabilities, probabilities of occurrence, and the related mass spectra were obtained as a function of the amount of energy absorbed. We also simulated the evolution of the ibuprofen molecule as a function of the number of pulses, i.e., for a sequence of energy depositions. A dominant fragmentation scheme is identified, where first the OH group is released, followed by the loss of the CO group. The photon energy and the number of pulses are found to be key parameters for the selection of this degradation route among all identified fragmentation pathways.

Physics doi: 10.3390/physics8010003

Authors: Svetlana Sofronova Artem Chernyshev Anna Selyanina Aleksandr Krylov Timofey Tislenko

First-principles calculations of the structural and magnetic properties of kotoite Ni2Co(BO3)2 are carried out. The minimization of the lattice parameters shows the values to be in good agreement with the experimental data (the difference is less than 1%). The atomic coordinates are calculated. Cobaltions are found tending to occupy position 2a and nickel ions tending to occupy position 4f. The same magnetic cell as in Ni3(BO3)2, but quadrupled in size (2a × b × 2c), found having the minimum exchange energy for Ni2Co(BO3)2. In Ni2Co(BO3)2, the magnetic moments are obtained oriented along the baxis, similar to that in Co3(BO3)2.

Physics doi: 10.3390/physics8010002

Authors: Andrea Addazi Salvatore Capozziello Giuseppe Meluccio

The cosmological constant (CC, Λ) problem stands as one of the most profound puzzles in the theory of gravity, representing a remarkable discrepancy of about 120 orders of magnitude between the observed value of dark energy and its natural expectation from quantum field theory. This paper synthesizes two innovative paradigms—holographic naturalness (HN) and pre-geometric gravity (PGG)—to propose a unified and natural resolution to the problem. The HN framework posits that the stability of the CC is not a matter of radiative corrections but rather of quantum information and entropy. The large entropy SdS∼MP2/Λ of the de Sitter (dS) vacuum (with MP being the Planck mass) acts as an entropic barrier, exponentially suppressing any quantum transitions that would otherwise destabilize the vacuum. This explains why the universe remains in a state with high entropy and relatively low CC. We then embed this principle within a pre-geometric theory of gravity, where the spacetime geometry and the Einstein–Hilbert action are not fundamental, but emerge dynamically from the spontaneous symmetry breaking of a larger gauge group, SO(1,4)→SO(1,3), driven by a Higgs-like field ϕA. In this mechanism, both MP and Λ are generated from more fundamental parameters. Crucially, we establish a direct correspondence between the vacuum expectation value (VEV) v of the pre-geometric Higgs field and the de Sitter entropy: SdS∼v (or v3). Thus, the field responsible for generating spacetime itself also encodes its information content. The smallness of Λ is therefore a direct consequence of the largeness of the entropy SdS, which is itself a manifestation of a large Higgs VEV v. The CC is stable for the same reason a large-entropy state is stable: the decay of such state is exponentially suppressed. Our study shows that new semi-classical quantum gravity effects dynamically generate particles we call “hairons”, whose mass is tied to the CC. These particles interact with Standard Model matter and can form a cold condensate. The instability of the dS space, driven by the time evolution of a quantum condensate, points at a dynamical origin for dark energy. This paper provides a comprehensive framework where the emergence of geometry, the hierarchy of scales and the quantum-information structure of spacetime are inextricably linked, thereby providing a novel and compelling path toward solving the CC problem.

Physics doi: 10.3390/physics8010001

Authors: Kalamkas Astemessova Medeu Abishev Nurzada Beissen Tursynbek Yernazarov Daulet Berkimbayev Sulukas Sarsenbayeva Nurkamal Shynggyskhan Bekzat Zhumabay Gulzhan Turlybekova

We consider a model problem of polarization-dependent light bending and time delays in the vicinity of neutron stars endowed with magnetar-strength magnetic fields (B∼1015G), combining an effective-metric formulation of Heisenberg–Euler nonlinear electrodynamics with general-relativistic ray tracing. The spacetime geometry is analyzed using both the Kerr metric and a quadrupole-deformed q-metric, characterized by a quadrupole parameter varying in the range q∈[10−3,0.5]. In addition, the impact of complex magnetic-field topologies is examined by introducing a magnetic quadrupole component alongside the dipole configuration. The simulations performed in this study demonstrate that the inclusion of the quadrupole deformation parameter significantly modifies photon trajectory deflections compared to the standard Kerr solution. We further quantify the geometric dilution of the photon beam, finding a cross-section expansion ratio of approximately 4.7×1013 for rays reaching Earth. This strong dilution imposes stringent constraints on the detectability of polarization-dependent signatures and time-delay echoes. Finally, characteristic illustrations are presented for trajectory distortions, bending-angle distributions, and intensity valleys produced by the combined gravitational and magnetic lensing effects.

Physics doi: 10.3390/physics7040068

Authors: Nabil Benzerroug Karim Choubani Mohamed Ben Rabha Mohsen Choubani

By solving the three-dimensional Schrödinger equation with a second-order implicit Finite Difference Method (FDM), the combined effects of temperature, morphology, hydrostatic pressure, and transverse electric field on the nonlinear optical rectification (NOR) of GaAs/AlεGa1−εAs elliptical quantum rings are examined. The NOR amplitude is twelve times enhanced and a noticeable blue shift is induced in the THz region when the electric field is increased. Consequently, with the electric field of 1 × 105 V/m, the NOR magnitude achieves its maximum value of 17.116 × 105 m/V. Additionally, when the electric field is aligned along one side of the system’s in-plane cross-section, the strongest amplification takes place. However, with corresponding spectrum shifts, the NOR intensity rises with temperature and falls with hydrostatic pressure. Additionally, changing the transverse profile of the quantum ring from triangular to parabolic broadens the carrier wave functions and has a considerable impact on the NOR coefficient. These findings provide important information for the construction of high-performance, tunable THz optoelectronic devices by demonstrating effective external and structural tuning of NOR.

Physics doi: 10.3390/physics7040067

Authors: Uriel Rivera-Ortega Antonio Barcelata-Pinzon Griselda Saldaña-Gonzalez

In this study, we present the custom development and implementation of a mobile application designed specifically to experiment with Malus’s law, leveraging the integration of a LEGO EV3 and the light sensor of a mobile device. Unlike previous studies that utilize pre-designed mobile applications, our approach focuses on creating a tailored solution that meets the unique requirements of this optical experiment. Using MIT App Inventor, we developed a customized interface that allows for the rotation of polarizers controlled by motors connected to a LEGO EV3 while simultaneously measuring the light intensity using the mobile’s light sensor. The block-based programming in App Inventor facilitates the application of programming concepts in creating physics experiments in a straightforward manner. This innovative approach not only facilitates the understanding of fundamental optical concepts but also integrates accessible technology to enrich the educational experience in physics, offering a customizable solution adaptable to various educational settings. Preliminary results indicate a significant improvement in students’ comprehension of optical polarization principles, demonstrating the effectiveness of our approach.

Physics doi: 10.3390/physics7040066

Authors: Olga V. Man’ko

The quantizer–dequantizer method is employed. Using the construction of probability distributions describing density operators of a quantum system states, the connection between the Feynman path integral and the time evolution of the density operator (Landau density matrix) as well as the wave function of the stateconsidered. For single–mode systems with continuous variables, a tomographic propagator is introduced in the probability representation of quantum mechanics. An explicit expression for the probability in terms of the Green function of the Schrödinger equation is obtained. Equations for the Green functions defined by arbitrary integrals of motion are derived. Examples of probability distributions describing the evolution of state of a free particle, as well as states of systems with integrals of motion that depend on time (oscillator type) are discussed.

Physics doi: 10.3390/physics7040065

Authors: Alexander Volyar Mikhail Bretsko Yana Akimova

Over the past thirty years, the focus in singular optics has been on structured beams carrying orbital angular momentum (OAM) for diverse applications in science and technology. However, as practice has shown, the OAM-free structured Gaussian beams with several degrees of freedom are no worse than the OAM beams, especially when propagating through turbulent flows. In this paper, we partially fillthis gap by theoretically and experimentally mapping cyclic changes in vortex-free states (including OAM) as a phase portrait of the beam evolution in an astigmatic optical system. We show that those cyclic variations in the beam parameters are accompanied by the accumulation of the geometric Berry phase, which is an additional degree of freedom. We find also that the geometric phase of cyclic changes in the intensity ellipse shape does not depend on the radial numbers of the Laguerre–Gaussian mode with zero topological charge and is always set by changing the shape of the Gaussian beam. The Stokes parameter formalism was developed to map the beam states’ evolution onto a Poincaré sphere based on physically measurable second-order intensity moments. Theory and experiment are found to be in a good enough agreement.

Physics doi: 10.3390/physics7040064

Authors: Sayabek Sakhiyev Kylyshbek Turlybekuly Asset Shaimerdenov Darkhan Sairanbayev Avganbek Sabidolda Zhanibek Kurmanaliyev Akzhol Almukhametov Olzhas Bayakhmetov Ruslan Kiryanov Ekaterina Korobkina Egor Lychagin Alexey Muzychka Valery Nesvizhevsky Cole Teander Khac Tuyen Pham

We present the concept of an ultracold neutron (UCN) source with a superfluid He-4 (SF 4He) converter located in the thermal column of the WWR-K research reactor at the Institute of Nuclear Physics (INP) in Almaty, Kazakhstan. The conceptual design is based on the proposal of accumulating UCNs in the source and effectively transporting them to experimental setups. We propose to improve the UCN density in the source by separating the heat and UCN transport from the production volume and decreasing the temperature of the SF 4He converter to below about 1 K. To obtain operation temperatures below 1 K, we plan to use a He-3 pumping cryogenic system and minimize the thermal load on the UCN accumulation trap walls. Additional gain in the total number of accumulated UCNs can be achieved through the use of a material with a high critical velocity for the walls of the accumulation trap. The implementation of such a design critically depends on the availability of materials with specific UCN and cryogenic properties. This paper describes the conceptual design of the source, discusses its implementation methods and material requirements, and plans for material testing studies.

Physics doi: 10.3390/physics7040063

Authors: Helena Cristina Vasconcelos Maria Gabriela Meirelles

We establish a general, device-oriented procedure to extract absolute pump-band metrics from room-temperature UV–Vis (ultraviolet–visible) absorbance—including the absorption coefficient α(λ), per-active-ion cross-section σeffλ, the effective per-active-ion absorption cross section σeffλ and derivative-based line-shape descriptors. As a representative case study, the procedure is applied to nanocrystalline Er3+/Ho3+:Y3Ga5O12 over the 350–700 nm spectral range. After baseline correction and line-shape inspection assisted by the numerical second derivative of the absorbance, we extract conservative peak positions and the full width at half maximum across the visible 4f–4f manifolds. At the technologically relevant pump wavelengths near 406 nm (Er-addressing) and 473 nm (Ho-addressing) bands, resulting absorption coefficients are α = 0.313 ± 0.047 cm−1 and α = 0.472 ± 0.071 cm−1, respectively. The corresponding per-active-ion σeff of (3.62 ± 0.54) × 10−22 cm2 and (5.46 ± 0.82) × 10−22 cm2, referenced to the measured optical path length L = 0.22 ± 0.03 mm (approximately 15% propagated relative uncertainty; explicit 1/L rescaling). Cross sections are reported per total active-ion density (Er3+ + Ho3+). The spectra exhibit Stark-type substructure only partially resolved at room temperature; the second derivative highlights hidden components, and we report quantitative descriptors (component count, mean spacing, curvature-weighted prominence, and pump detuning) that link line-shape structure to absolute pump response. These device-grade metrics enable rate-equation modelling (pump thresholds, detuning tolerance), optical design choices (path length, single/multi-pass or cavity coupling), and host-to-host benchmarking at 295 K. The procedure is general and applies to any rare-earth-doped material given an absorbance spectrum and path length.

Physics doi: 10.3390/physics7040062

Authors: Min-Chang Lee

BU–MIT whistler wave injection experiments, which were conducted at Arecibo Observatory, started with the joint US–USSR Active Space Plasma Program Experiment on 24 December 1989. In this experiment, a satellite-borne VLF transmitter injected radio waves at the frequency and power of 10 kHz and 10 kW. A series of controlled whistler wave experiments with the Arecibo HF heater were subsequently carried out during 1990–1998 until the HF heater was damaged by Hurricane Georges in 1998. In these ionospheric HF heating experiments, 28.5 kHz whistler waves were launched from the nearby naval transmitter (code-named NAU) located at Aguadilla, Puerto Rico. HF heater waves were used to create ionospheric ducts (in the form of parallel-plate waveguides) to facilitate the entry of NAU whistler waves from the neutral atmosphere into the ionosphere. Conjugate whistler wave propagation experiments were conducted between Arecibo, Puerto Rico and Trelew, Argentina in 1997. After 1999, whistler wave experiments in the absence of an HF heater had been conducted. Naturally-occurring large-scale ionospheric irregularities due to spread F or Traveling Ionospheric Disturbances (TIDs) were relied on to guide NAU launched 40.75 kHz whistler waves to propagate from the ionosphere further into the radiation belts, to cause 390 keV charged-particle precipitation. A train of TIDs, resulting from the 9.2 Mw earthquake off the west coast of Sumatra, Indonesia, was observed in our 26 December 2004 Arecibo experiments, about a day after the earthquake-launched tsunami waves traveled across the Indian Ocean, then into remote parts of the Atlantic Ocean. The author’s recent research efforts, motivated by Arecibo experiments, focus on Solar Powered Microwave Transmitting Systems, to simulate Solar Energy Harvesting via Solar Power Satellite (SPS) (also known as Space Based Solar Power (SBSP)) These experiments involved a large number of the author’s BU and MIT students working on theses and participating in the Undergraduate Research Opportunities Program (UROP), in collaboration with other colleagues at several universities and national laboratories.

Physics doi: 10.3390/physics7040061

Authors: Lucas Veneziani de Toledo Breno Justen de Castro Moreira Leonardo Rodrigues Cadorim Edson Sardella

This study investigates the influence of inelastic electron–phonon collision time (τe-ph) on the behavior of the resistive state of three-dimensional superconducting systems. Using the generalized time-dependent Ginzburg–Landau formalism, we model the interplay between vortex dynamics, energy dissipation, and thermal effects across varying values of the dimensionless parameter γ proportional to τe-ph and different values of the Ginzburg–Landau parameter. The results show that larger values of γ enhance the superconducting state by delaying the transition to the normal state, modulating critical currents, and altering differential resistance. An exponential relationship between the upper critical current and γ is observed, indicating prolonged resistive states as the inelastic electron–phonon collision time becomes larger. Furthermore, the study investigates the maximum local peaks in the differential resistance curves, revealing their exponential decay with increasing γ.

Physics doi: 10.3390/physics7040060

Authors: Simon Gluzman

Scaling of the cost-functional and its violations are discussed with regard to their application to the summation of asymptotic truncated expansions. A new family of cost-functionals dependent only on amplitudes is considered, allowing for a continuous breaking of scaling. Cost-functionals can be a homogeneous function of the second order with respect to the scaling of all amplitudes with the same multiplicative factor. However, non-homogenous cost-functionals do violate scaling. A robust and accurate calculation of amplitudes emergent at quite a large value of the variable from the truncated series obtained for relatively small values of the variable is performed using the cost-functional technique with varying degrees of scaling violation. Various physical examples from field theory, quantum mechanics, and statistical physics are considered. Certain parallels with complex systems are noticed and discussed.

Physics doi: 10.3390/physics7040059

Authors: Spencer Kuo Min-Chang Lee Arnold Snyder Brenton Watkins

Analysis of nonlinear plasma waves, formulated and applied for ionospheric HF heating experiments, indicates that Langmuir/upper hybrid waves excited by parametric instabilities can evolve into traveling solitary waves accompanied by self-induced cavitons. To explore these cavitons, a digisonde operating in fast mode was utilized. Significant results were observed in ionograms recorded two minutes after the activation of the O-mode heater. These ionograms displayed two distinct bumps in the virtual height spread, located slightly below both the HF reflection height and the upper hybrid resonance height. It is notable that these heights are also slightly below the excitation regions where Langmuir/upper hybrid Parametric Decay Instabilities (PDIs) are typically generated by an O-mode HF heater. These observations correlate with the theory and provide valuable insights into the dynamics of nonlinear plasma waves and their interaction with the ionosphere during HF heating experiments.

Physics doi: 10.3390/physics7040058

Authors: Yuefeng Li Benchu Lu Huijie Xue Ning Wang Dongmei Cai

The Zernike polynomial method is extensively used for atmospheric phase screen generation but is limited by insufficient high-frequency components. Calculating higher-order terms introduces challenges in computational efficiency and numerical instability when using the direct method. This paper analyzes these issues and proposes replacing the direct method with recursive radial formulas. We evaluate four recursive algorithms (Barmak’s, q-recursive, Prata’s and Kintner’s) for their performance in phase screen generation, focusing on computational speed and numerical stability. Our results demonstrate that recursive methods achieve a 10–20-times improvement in computational efficiency and maintain numerical stability even for high-order expansions. The main novelty of this study lies in the comprehensive comparison and validation of these recursive strategies for high-accuracy atmospheric phase screen simulation.

Physics doi: 10.3390/physics7040057

Authors: Henrique R. Martins-Fontes Fernando S. Navarra

The multiplicity distributions measured in proton–proton collisions at the LHC exhibit appealing new features. One of them is the appearance of a substructure—the so-called “shoulder”—at relatively large multiplicities. The most natural interpretation of this behavior is the existence of two particle-production mechanisms. The final result is then a superposition of two distributions. In our recent paper, we assumed that the two production mechanisms are soft and semihard partonics scatterings. In this paper, we further discuss this assumption, and, in particular, we study the dependence of the results on the scale that separates soft from hard events.

Physics doi: 10.3390/physics7040056

Authors: Luiz Augusto Stuani Pereira Carlos Alberto Tello Sáenz

We investigate the dependence of the maximum etched track length (Lmax) on alpha-particle energy and incidence angle in LR-115 type II nuclear track detectors by combining Geant4 Monte Carlo simulations with controlled chemical etching experiments. The bulk (VB) and track (VT) etch rates were determined under standardized conditions, yielding VB=(3.1±0.1) µm/h and VT=(5.98±0.06) µm/h, which correspond to a critical detection angle of about (58.8±1.2)°. Simulations covering initial energies spanning 1 MeV to 5 MeV and incidence angles up to 70° confirmed that the maximum etched track length varies quadratically with particle energy E and depends systematically on incidence angle θ. Empirical parameterizations of Lmax(E,θ) were obtained, and energy thresholds for complete track registration within the 12 µm sensitive layer were established. The angular acceptance predicted by the VT/VB ratio was validated, and the results demonstrate that Lmax provides a monotonic and more reliable observable for energy calibration compared to track diameter. These findings improve the quantitative calibration of LR-115 detectors and strengthen their use in environmental radon monitoring, radiation dosimetry, and alpha spectrometry. In addition, they highlight the utility of Geant4-based modeling for refining solid state nuclear track detector response functions and guiding the development of optimized detector protocols for nuclear and environmental physics applications.

Physics doi: 10.3390/physics7040055

Authors: Riasat Ali Tiecheng Xia Rimsha Babar

This paper analyzes how the generalized uncertainty principle (GUP) affects the thermodynamic properties in a regular black hole spacetime in the context of f(Q,BQ) symmetric teleparallel gravity, with an arbitrary action f as a function of non-metric scalar Q and the boundary BQ. We analyze a GUP-influenced semi-classical technique in regular black hole spacetime that incorporates the quantum tunneling mechanism. The GUP-influenced temperature results show that the GUP term reduced the vector particles’ radiation in the context of f(Q,BQ) gravity. Moreover, we explore the GUP-influenced entropy as well as the GUP-influenced emission energy, it can help to explain the complex interactions between quantum gravity and astrophysics and highlights the important role of GUP-influenced thermodynamic properties (Hawking temperature, entropy and emission energy) in regular black hole spacetime in the context of f(Q,BQ) gravity. We graphically analyze the effects of different parameters on black hole geometry.

Physics doi: 10.3390/physics7040054

Authors: Alexander R. Karimov Grigoriy O. Buyanov

Based on the hydrodynamic description, the dynamics of nonlinear cylindrical waves in an isentropic plasma are investigated. The problem is considered in an electrostatic formulation for a two-dimensional plasma medium where ions form a stationary background. Proceeding from the particular, exact solution of hydrodynamic equations, we obtain the system of differential equations which describes the electron’s dynamics, taking into account the finite temperature of electrons. Moreover, we find the conditions when this system is reduced to the generalized Ermakov–Pinney equation which was used for analyzing electron dynamics. In the present calculations, a parabolic-in-radius temperature profile was used, associated with an electron density varying only with time. In the framework of the model that worked out, the influence of initial conditions and thermal effects on the regular and singular dynamics of excited waves are discussed. It is shown that the development of singular behavior due to intrinsic nonlinearity is avoided by taking into account thermal effects and the initial rotation of the electron flow.

Physics doi: 10.3390/physics7040053

Authors: Oleg M. Gradov

The effect of the curvature of the boundary of semi-infinite cold plasma on the parameters and properties of surface oscillations localized near this boundary is considered. An analytical description of various cases of the impact of static deformation of the plasma boundary on the characteristics of the oscillating surface charge is obtained, and the results of the exact numerical solution of the initial equations are found to confirm the reliability of the derived analytical formulas. A significant role of the boundary perturbation shape in the formation of the spatial distribution of surface oscillation parameters is revealed. With the help of analytical formulas and precise numerical calculations, a description of this nonlinear interaction is presented. The availability of such a description is crucial both for determining the possibility of using the examined effect for specific applications and, on the other hand, for exciting it in plasma, which requires knowledge of the field structure features.

Physics doi: 10.3390/physics7040052

Authors: Abdel Nasser Tawfik Salah G. Elgendi Sameh Shenawy Mahmoud Hanafy

By extending the four-dimensional semi-Riemann geometry to higher-dimensional Finsler/Hamilton geometry, the canonical quantization of the fundamental metric tensor of general relativity, i.e., an approach that tackles a geometric quantity, is derived. With this quantization, the smooth continuous Finsler structure is transformed into a quantized Hamilton structure through the kinematics of a free-falling quantum particle with a positive mass, along with the introduction of the relativistic generalized uncertainty principle (RGUP) that generalizes quantum mechanics by integrating gravity. This transformation ensures the preservation of the positive one-homogeneity of both Finsler and Hamilton structures, while the RGUP dictates modifications in the noncommutative relations due to integrating consequences of relativistic gravitational fields in quantum mechanics. The anisotropic conformal transformation of the resulting metric tensor and its inverse in higher-dimensional spaces has been determined, particularly highlighting their translations to the four-dimensional fundamental metric tensor and its inverse. It is essential to recognize the complexity involved in computing the fundamental inverse metric tensor during a conformal transformation, as it is influenced by variables like spatial coordinates and directional orientation, making it a challenging task, especially in tensorial terms. We conclude that the derivations in this study are not limited to the structure in tangent and cotangent bundles, which might include both spacetime and momentum space, but are also applicable to higher-dimensional contexts. The theoretical framework of quantization of general relativity based on quantizing its metric tensor is primarily grounded in the four-dimensional metric tensor and its inverse in pseudo-Riemannian geometry.

Physics doi: 10.3390/physics7040051

Authors: Krzysztof Stasiewicz

The applicability of the first-order Fermi mechanism—a cornerstone of the diffusive shock acceleration (DSA) model—in explaining the cosmic ray spectrum is reexamined in light of recent observations from the Magnetospheric Multiscale (MMS) mission at Earth’s bow shock. It is demonstrated that the Fermi and DSA mechanisms lack physical justification and should be replaced by the physically correct ballistic surfing acceleration (BSA) mechanism. The results show that cosmic rays are energized by the convection electric field during ballistic surfing upstream of quasi-perpendicular shocks, independently of internal shock processes. The spectral index of cosmic rays is determined by the magnetic field compression and shock geometry: the acceleration is strongest in perpendicular shocks and vanishes in parallel shocks. The BSA mechanism reproduces the observed spectral indices, with s=−2.7 below the knee at 1016 eV and s=−3 above it. It is suggested that the spectral knee may correspond to particles whose gyroradii are comparable to the characteristic size of shocks in supernova remnants. The acceleration time to reach the knee energy, as predicted by the BSA, is in the order of 500 years.