Search Results (221)

The extraordinary mechanical flexibility, high electrical conductivity, and nanoscale instability of freestanding graphene make it an excellent candidate for vibration energy harvesting. When freestanding graphene is stretched taut and subject to external forces, it will vibrate like a drum head. Its vibrations occur at a fundamental frequency along with higher-order harmonics. Alternatively, when freestanding graphene is compressed, it will arch slightly out of the plane or buckle under the load. Remaining flat under compression would be energetically too costly compared to simple bond rotations. Buckling up or down, also known as ripple formation, naturally creates a bistable situation. When the compressed system vibrates between its two low-energy states, it must pass through the high-energy middle. The greater the compression, the higher the energy barrier. The system can still oscillate but the frequency will drop far below the fundamental drum-head frequency. The low frequencies combined with the large-scale movement and the large number of atoms coherently moving are key factors addressed in this study. Ten ripples with increasing compressive strain were built, and each was studied at five different temperatures. Increasing the temperature has a similar effect as increasing the compressive strain. Analysis of the average time between curvature inversion events allowed us to quantify the energy barrier height. When the low-frequency bistable data were time-averaged, the authors found that the velocity distribution shifts from the expected Gaussian to a heavy-tailed Cauchy (Lorentzian) distribution, which is important for energy harvesting applications. Full article

Magnetic tunnel junctions (MTJs) are pivotal for spintronic applications such as magneto resistive memory and sensors. Two-dimensional van der Waals heterostructures offer a promising platform for miniaturizing MTJs while enabling the twist-angle engineering of their properties. Here, we investigate the impact of twisting the insulating barrier layer on the performance of a van der Waals MTJ with the structure graphene/1T-VSe₂/h-BN/1T-VSe₂/graphene, where 1T-VSe₂ serves as the ferromagnetic electrodes and the monolayer h-BN acts as the tunnel barrier. Using first-principles calculations based on density functional theory (DFT) combined with the non-equilibrium Green’s function (NEGF) formalism, we systematically calculate the spin-dependent transport properties for 18 distinct rotational alignments of the h-BN layer (0° to 172.4°). Our results reveal that the tunneling magnetoresistance (TMR) ratio exhibits dramatic, rotation-dependent variations, ranging from 2328% to 24,608%. The maximum TMR occurs near 52.4°. An analysis shows that the twist angle modifies the d-orbital electronic states of interfacial V atoms in the 1T-VSe₂ layers and alters the spin polarization at the Fermi level, thereby governing the spin-dependent transmission through the barrier. This demonstrates that rotational manipulation of the h-BN layer provides an effective means to engineer the TMR and performance of van der Waals MTJs. Full article

This paper refers to fast and accurate electric servo control in the presence of position and velocity constraints. This problem, one of the most common nowadays in industrial automation, is often addressed by controllers derived using barrier Lyapunov functions (BLFs). This popular and effective technique is burdened with several difficulties, such as complex feasibility conditions and the inapplicability of the derived controller because of control constraints. In this contribution, we propose a novel, BLF-based, adaptive controller for an electric servo (linear or rotational) with modeling uncertainties, solving a tracking problem. The controller derivation is completed by the tuning procedure, which enables safe system operation in the presence of active control constraints, measurement errors, and noise. The selection of the best combination of BLFs is a part of this procedure. Also, all feasibility issues are solved by the proposed approach. The derivation is completed by extensive numerical simulations and real-life implementation using two different servo systems—the first with a linear permanent magnet motor and the second with a rotational PMSM. Full article

This study investigated the hydraulic characteristics of a self-rotating flood barrier (SRFB) by performing laboratory experiments. The SRFB is proposed as a secure solution to withstand both waves and sudden water level rise, thereby protecting the coastal area behind it. The SRFB is designed to rotate and rise automatically by buoyancy when the water level exceeds a certain threshold or waves start to overtop the crest level of the caisson, where the barrier is enclosed. The barrier begins to rise when the chamber is filled with enough water for the buoyancy force to exceed its own weight. The performance of the structure was tested under various regular wave conditions at different water depths. Pressure transducers were placed along the front face of the barrier to measure the wave pressures acting on it. The barrier’s angular displacement was also identified using synchronized video footage during the measurements. The results showed that the overall magnitude of the measured pressures increased with water depth due to the larger volume of water inflow from overtopping waves. During the rise in the barrier, the pressure profiles dynamically varied with the rotation angle as the pattern of water flow into the chamber changed depending on the test cases. Analysis results showed how the pressures are distributed along the barrier at the moment of peak wave force. These findings would provide fundamental information for estimating design wave forces on the structure. Full article

The tribological performance of a novel nonmetallic composite casing coating is investigated under dry wear conditions and different side loads and rotational speeds. The coating is composed of a short-glass-fiber-reinforced epoxy matrix with silicon carbide, aluminum oxide, and calcium carbonate nanofillers to provide a protective barrier against contact with hardened drill pipe tool joints. The results revealed that the wear behavior was highly dependent on the applied side load and rotational speed. Under high-load conditions, the formation of a compacted tribofilm significantly reduced the coefficient of friction and specific wear factor by limiting direct surface contact. Lower rotational speeds and moderate side loads resulted in adhesive wear with formation of stable tribofilms that mitigated material loss. Full article

Regenerative agriculture has emerged as a new organic farming movement, initially difficult to distinguish from similar approaches. Its core concerns, such as ecosystem degradation caused by intensive farming, align with those of many other organic systems. However, regenerative agriculture prioritizes soil health, biodiversity, and social equity, setting itself apart through its scalability and flexibility. Unlike other ecological farming methods, often limited to smaller scales, regenerative agriculture aims to be implemented on large farms, typically major contributors to pollution due to reliance on external inputs like fertilizers and pesticides. Notably, regenerative certification standards are more flexible, allowing the use of industrially synthesized inputs under specific conditions, provided that regenerative principles are upheld. This review systematically examines seven core regenerative practices: no-tillage farming, crop rotation, cover cropping, green manures, intercropping, perennial cover systems, and integrated crop-livestock systems. It outlines the practical advantages and ecological benefits of each, while identifying key adoption challenges, including costs, farm size, and institutional barriers. The paper argues that addressing these issues, particularly concerning scale and socio-economic constraints, is essential for broader adoption. By synthesizing recent evidence, this review clarifies the distinctiveness of regenerative agriculture and highlights pathways for its scalable implementation. Full article

Floating offshore wind turbines (FOWTs) unlock superior wind resources and reduce operational barriers. The dynamics of FOWT platforms present added engineering challenges and opportunities. While the motion of the floating platform due to wind and wave disturbances can worsen power quality and increase structural loading, certain movements of the floating platform can be exploited to improve power capture. Consequently, active FOWT platform control methods using conventional and innovative actuation systems are under investigation. This paper develops a novel framework to design nonlinear control laws for six degrees-of-freedom platform motion. The framework uses simplified rigid-body analytical models of the FOWT. Lyapunov’s direct method is used to develop actuator-agnostic unconstrained control laws for platform translational and rotational control. A model based on the NREL-5MW reference turbine on the OC3-Hywind spar-buoy platform is utilized to test the control framework for an ideal actuation scenario. Possible applications using traditional and novel turbine actuators and future research directions are presented. Full article

We use Co doping to alter the magnetic relaxation dynamics in superparamagnetic nanofluids made of 18 nm average diameter Fe₃O₄ nanoparticles immersed in Isopar M. Ac-susceptibility data recorded at different frequencies and temperatures, χ″vs. T|_f, reveals a major (~100 K) increase in the superspin blocking temperature of the Co_0.2Fe_2.8O₄-based fluid (CFO) compared to its Fe₃O₄ counterpart (FO). We ascribe this behavior to the strengthening of the interparticle magnetic dipole interactions upon Co doping, as demonstrated by the relative χ″-peak temperature variation per frequency decade $\mathsf{\Phi }={\displaystyle \frac{∆\mathrm{T}}{\mathrm{T}·∆\mathrm{l}\mathrm{o}\mathrm{g}\left(\mathrm{f}\right)}}$, which decreases from Φ~0.15 in FO to Φ~0.025 in CFO. In addition, χ″vs. T|_f datasets from the CFO fluid reveal two magnetic events at temperatures T_p1 = 240 K and T_p2 = 275 K, both above the fluid’s freezing point (T_F = 197 K). We demonstrate that the physical rotation of the nanoparticles within the fluid, the Brown mechanism, is entirely responsible for the collective superspin relaxation observed at T_p1, whereas the Néel mechanism, the superspin flip across an energy barrier within the particle, is dominant at T_p2. We confirm this finding through fits of models that describe the temperature dependence of the relaxation time via the two mechanisms: ${\mathsf{\tau }}_{\mathrm{B}}(\mathrm{T})={\displaystyle \frac{3{\mathsf{\eta }}_0{\mathrm{V}}_{\mathrm{H}}}{{\mathrm{k}}_{\mathrm{B}}\mathrm{T}}}\exp \left[{\displaystyle \frac{{\mathrm{E}}^{\prime }}{{\mathrm{k}}_{\mathrm{B}}\left(\mathrm{T}-{{\mathrm{T}}_0}^{\prime }\right)}}\right]$ and ${\mathsf{\tau }}_{\mathrm{N}}\left(\mathrm{T}\right)={\mathsf{\tau }}_0\exp \left[{\displaystyle \frac{{\mathrm{E}}_{\mathrm{B}}}{{\mathrm{k}}_{\mathrm{B}}\left(\mathrm{T}-{\mathrm{T}}_0\right)}}\right]$. The best fits yield ${\mathsf{\gamma }}_0={\displaystyle \frac{3{\mathsf{\eta }}_0{\mathrm{V}}_{\mathrm{H}}}{{\mathrm{k}}_{\mathrm{B}}}}$= 1.5 × 10⁻⁸ s·K, E′/k_B = 7 03 K, and T₀′ = 201 K for the Brown relaxation, and E_B/k_B = 2818 K and T₀ = 143 K for the Néel relaxation. Full article

The prevalence of end-stage renal disease has surged significantly in recent decades, with an 88% increase reported in the United States between 2002 and 2022. Peritoneal dialysis and home hemodialysis offer numerous advantages over in-center hemodialysis, including improved quality of life, increased treatment flexibility, and reduced healthcare costs. Despite strong preferences among healthcare professionals and the documented benefits of home-based therapies, utilization remains limited in the U.S. One of the many factors that play a role in the underutilization of home therapies is inadequate training and perceived incompetence among nephrology fellows in initiating and managing home dialysis patients. Here in this article, we highlight the current educational gaps in home dialysis training and ways to overcome the barriers. There is a need for a multifaceted approach that includes home dialysis rotations and continuity clinics; a dedicated one-year Home Dialysis Fellowship; and continued medical education through didactics, symposiums, and conferences. Here we emphasize the need for structured, longitudinal programs that combine didactic learning with hands-on clinical in fellowship trainings and the importance of dedicated one-year fellowships in cultivating future leaders and experts in the field. By enhancing training pathways and expanding fellowship opportunities, nephrology education can better equip physicians to meet the growing demand for home dialysis, ultimately improving patient outcomes and advancing public health objectives. Full article

Transdermal drug delivery offers a non-invasive route for the systemic and localized administration of therapeutics; however, the skin’s barrier function limits its efficiency. This study investigates the application of various electromagnetic field (EMF) configurations to enhance the transdermal delivery of salicylic acid, a model compound with moderate lipophilicity and ionizability. Samples were exposed to pulsed, oscillating, static, and rotating magnetic fields, and their effects on physicochemical properties, thermal stability, skin permeation, and accumulation were evaluated. Structural analyses (FTIR, XRD) and thermal assessments (TGA, DSC) confirmed that EMF exposure did not alter the chemical structure or stability of salicylic acid. In vitro transdermal studies using porcine skin and Franz diffusion cells revealed that pulsed magnetic fields—especially with a 5 s on/5 s off cycle—and rotating magnetic fields at 30–50 Hz significantly enhanced drug permeation compared to controls. In contrast, static fields of negative polarity increased skin retention, suggesting their potential for controlled, localized delivery. These findings demonstrate that EMFs can be used as tunable, non-destructive tools to modulate drug transport across the skin and support their integration into transdermal delivery systems aimed at optimizing therapeutic profiles. Full article

The rotational spectra of xanthene and its oxidation product xanthone were investigated by combining quantum chemical calculations with Fourier transform microwave spectroscopy in a jet-cooled environment. Xanthone was unexpectedly generated in the experiment when water was present in the reservoir of xanthene leading to the total disappearance of xanthene after few hours. Structurally, xanthone shows a near planar disposition, whereas xanthene exhibits a non-planar geometry with both benzene rings twisted out of the molecular plane. This geometry enables an inversion motion between two equivalent conformers, giving rise to a splitting in the ground vibrational state. A two-state analysis of the vibration–rotation interaction for the $v=0$ and $v=1$ states gives an energy separation between these states (inversion splitting) of $\Delta E_{01}=4689.7095\left(10\right)\mathrm{MHz}$. This large-amplitude motion leads to vibration–rotation coupling of energy levels. A symmetric double-minimum inversion potential function was determined, resulting in a barrier of about 45 cm⁻¹ in good agreement with that obtained by DFT quantum chemical calculations. Full article

Sotolon is a chiral furanone derivative featuring three distinct oxygen atoms at carbonyl, hydroxyl, and cyclic ether groups that can serve as hydrogen-bond acceptor sites, making it an ideal model system for probing water’s preferential interactions with competing functional groups. In this study, the rotational spectrum of sotolon and its microsolvated complexes, representing the early stages of hydration, was investigated using chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy. The conformational landscape of sotolon is dominated by a single conformer stabilized by an intramolecular O–H···O=C hydrogen bond. During hydration, water molecules disrupt this interaction by forming closed hydrogen-bonded cycles, resulting in mono- and dihydrated complexes. High-level theoretical calculations underscore the central role of electrostatic interactions in stabilizing these hydrated structures. Furthermore, A/E splittings observed in the rotational spectrum, arising from the internal rotation of one of sotolon’s methyl groups, provide insight into how hydration modulates the methyl internal rotation barrier. Full article

Water scarcity is a critical challenge in arid and semi-arid regions, where agricultural water consumption accounts for a significant portion of freshwater use. Conventional agriculture (CA) methods with high reliance on chemical and mechanical inputs often exacerbate this issue through soil degradation and water loss. This review aims to examine how different organic practices, such as mulching, cover cropping, composting, crop rotation, and no-till (NT) in combination with precision technologies, can contribute to water optimization, and it discusses the opportunities and challenges for the adoption and implementation of those practices. Previous findings show that organic agriculture (OA) may outperform CA in drought conditions. However, the problems of weed management in organic NT, trade-offs in cover crop biomass and moisture conservation, limited access to irrigation technologies, lack of awareness, and certification barriers challenge agricultural resilience and sustainability. Since the outcomes of OA practices depend on the crop type, local environment, and accessibility of knowledge and inputs, further context-specific research is needed to refine a scalable solution that maintains both productivity and resilience. Full article

Background/Objective: Early mobilization (EM) of critically ill patients is a feasible and safe intervention that limits the implications of bed rest and improves lung function. However, its limited implementation suggests a gap between the research evidence and clinical practice. It is widely accepted that early mobilization faces a variety of barriers. This study aimed to investigate the perceptions of Greek physiotherapists on EM barriers and record their knowledge and practices. Methods: We conducted an electronic survey using the online platform “Microsoft Forms”, among critical care physiotherapists in 66 hospitals that had an Intensive Care Unit (ICU) department in Greece in 2024. We administered a questionnaire, developed based on valid and reliable international questionnaires, with the following domains: education and knowledge on early mobilization, practices, perception regarding EM, and perceived barriers to early mobilization. Results: A total of 126 Greek physical therapists participated. The majority of them worked in urban area hospitals and in a rotation schedule around all departments. Most physical therapists stated that early mobilization is a priority for the patient’s rehabilitation and an important factor in preventing the complications of bed rest. Yet, they do not use specific protocols. Most had knowledge of what EM involved and the international guidelines. The most common barriers reported were the hemodynamic instability and the incoherence with the ventilator. Dedicated physiotherapists singled out certain barriers like the presence of delirium and the lack of communication among ICU staff. Additionally, physiotherapists with more years of experience did not acknowledge tubes, connections, femoral lines and Body Mass Index (BMI) as barriers. Conclusions: Most Greek physiotherapists believe that early mobilization is crucial for the rehabilitation of critically ill patients. A significant percentage know the guidelines, yet they do not follow a specific protocol. Various barriers prevent its implementation, which depends on the patients, healthcare providers, and the overall process. Yet, It is recognized that practices and perceived barriers are influenced by experience and work schedule. Establishing clinical protocols is essential to facilitate the implementation of early mobilization and support patient rehabilitation. Future efforts should focus on designing strategies and EM protocols for physiotherapy in Greek ICUs. Also, we need to monitor changes in perceived barriers across other countries as focus on the matter via published studies and clinical seminars could lead to significant changes. Full article

The morphotropic phase boundary (MPB) with multiphase coexistence serves as a critical region for piezoelectric materials, but the individual contributions of various microscopic mechanisms to the overall electromechanical response remains a challenge for further subdivision. Here, we systematically investigate the microscopic origins of outstanding piezoelectricity in <001>-oriented Pb(Mg_1/3Nb_2/3)O₃-30PbTiO₃ (PMN-30PT) single crystals and quantitatively identify the dominant factors for giant electrostrain and ultrahigh piezoelectric coefficient. Large electrostrain arises predominantly from polarization rotation within the easily distorted monoclinic phase and the high-energy-barrier monoclinic-to-tetragonal phase transition, enabled by a synergistic interplay of broad electric field adaptability and high strain sensitivity. In contrast, the peak piezoelectric coefficient (d₃₃ > 2100 pC/N) is attributed to the low-energy-barrier rhombohedral-to-monoclinic phase transition, which facilitates polarization rotation. Furthermore, the critical yet distinct roles of monoclinic phase compared to piezoelectric and electrostrain have been confirmed. By the quantitative segmentation of various microscopic factors, this work provides fundamental insights into the design of high-performance piezoelectrics. Full article