Physical Sciences Forum

Better understanding of the fitness and flexibility of microbial platform organisms is central to biotechnological process development. Live-cell experiments uncover the phenotypic heterogeneity of living cells, emerging even within isogenic cell populations. However, how this observed heterogeneity in growth relates to the variability of intracellular processes that drive cell growth and division is less understood. We here approach the question, how the observed phenotypic variability in single-cell growth rates links to metabolic processes, specifically intracellular reaction rates (fluxes). To approach this question, we employ the Maximum Entropy (MaxEnt) principle that allows us to bring together the phenotypic solution space, derived from metabolic network models, to single-cell growth rates observed in live-cell experiments. We apply the computational machinery to first-of-its-kind data of the microorganism Corynebacterium glutamicum, grown on different substrates under continuous medium supply. We compare the MaxEnt-based estimates of metabolic fluxes with estimates obtained by assuming that the average cell operates at its maximum growth rate, which is the current predominant practice in biotechnology. Full article

In Bayesian analysis, testing for linearity requires placing a prior to the entire space of potential regression functions. This poses a problem for many standard tests, as assigning positive prior probability to such a hypothesis is challenging. The Full Bayesian Significance Test (FBST) sidesteps this issue, standing out for also being logically coherent and offering a measure of evidence against H 0 , although its application to nonparametric settings is still limited. In this work, we use Gaussian process priors to derive FBST procedures that evaluate general linearity assumptions, such as testing the adherence of data and performing variable selection to linear models. We also make use of pragmatic hypotheses to verify if the data might be compatible with a linear model when factors such as measurement errors or utility judgments are accounted for. This contribution extends the theory of the FBST, allowing for its application in nonparametric settings and requiring, at most, simple optimization procedures to reach the desired conclusion. Full article

This paper explores the application of the Value of Information, (VoI), based on the Claude Shannon/Ruslan Stratonovich framework within economic contexts. Unlike previous studies that examine circular settings and strategic interactions, we focus on a non-strategic linear setting. We employ standard economically motivated utility functions, including linear, quadratic, constant absolute risk aversion (CARA), and constant relative risk aversion (CRRA), across various priors of the stochastic environment, and analyse the resulting specific VoI forms. The curvature of these VoI functions play a decisive role in determining whether acquiring additional costly information enhances the efficiency of the decision making process. We also outline potential implications for broader decision-making frameworks. Full article

Using Bayesian inference to calibrate constitutive model parameters has recently seen a rise in interest. The Markov chain Monte Carlo (MCMC) algorithm is one of the most commonly used methods to sample from the posterior. However, the choice of which MCMC algorithm to apply is typically pragmatic and based on considerations such as software availability and experience. We compare three commonly used MCMC algorithms: Metropolis-Hastings (MH), Affine Invariant Stretch Move (AISM) and No-U-Turn sampler (NUTS). For the comparison, we use the Kullback-Leibler (KL) divergence as a convergence criterion, which measures the statistical distance between the sampled and the ‘true’ posterior. We apply the Bayesian framework to a Newtonian squeeze flow problem, for which there exists an analytical model. Furthermore, we have collected experimental data using a tailored setup. The ground truth for the posterior is obtained by evaluating it on a uniform reference grid. We conclude that, for the same number of samples, the NUTS results in the lowest KL divergence, followed by the AISM sampler and last the MH sampler. Full article

When the quantities of interest remain underdetermined a posteriori, we would like to draw inferences for at least one particular solution. Can we do so in a Bayesian way? What is a probability distribution over an underdetermined quantity? How do we get a posterior for one particular solution from a posterior for infinitely many underdetermined solutions? Guided by discrete invariant underdetermined ill-posed inverse problems, we find that a probability distribution over an underdetermined quantity is non-absolutely continuous, partially improper with respect to the initial reference measure but proper with respect to its restriction to its support. Thus, it is necessary and sufficient to choose the prior restricted reference measure to assign partially improper priors using e.g., the principle of maximum entropy and the posterior restricted reference measure to obtain the proper posterior for one particular solution. We can then work with underdetermined models like Hoeffding–Sobol expansions seamlessly, especially to effectively counter the curse of dimensionality within discrete nonparametric inverse problems. We show Singular Bayesian Inference (SBI) at work in an advanced Bayesian optimization application: dynamic pricing. Such a nice generalization of Bayesian–maxentropic inference could motivate many theoretical and practical developments. Full article

Of the three major axion search experimental strategies, light-shining-through-wall experiments, haloscopes, and helioscopes, this paper focuses on the latter. IAXO, the International AXion Observatory, will be a next-generation helioscope following in the footsteps of previous experiments like SUMICO and CAST. Helioscopes aim to detect axions produced in the Sun, utilizing a magnetic field to couple them to X-ray photons. BabyIAXO represents a near-term step toward IAXO, designed to test custom components while delivering competitive results in axion searches. The experimental components are currently under development and construction. Further research into the applications of BabyIAXO beyond baseline axion searches is being conducted. Full article

Exchange-biased specimens were produced by molecular beam epitaxy (MBE) of ferromagnetic (FM) Co-on-CoO substrates after the substrates had been irradiated by heavy ions to induce defects in the antiferromagnet (AFM). Measurements were obtained at different temperatures for different sample orientations with respect to the external magnetic field. While the EB was relatively small, measurements of the bulk magnetization at low temperatures revealed unusually shaped hysteresis loops. The surface magnetization, however, showed simple, nearly rectangular hysteresis loops. This study focuses on the advantage of complementary information on surface and bulk magnetization from optical and non-optical measurement methods. Full article

We report a graded index chalcogenide glass (As₂Se₃)-based photonic crystal fiber having a solid core. The proposed PCF has ultra-high numerical aperture value reaching up to 1.82 for the explored wavelength range of 1.8–10 μm in the mid-infrared region. The value of numerical aperture increases as the pitch increase from 0.92 to 0.96 to 1 micrometer, at a particular value of wavelength. With this high value of numerical aperture, a PCF is capable of gathering a high amount of light in its core. With negative dispersion reaching up to −2000 ps/km/nm at 4.8 µm, the fiber acts as a dispersion-compensating fiber, with confinement loss being close to zero for higher values of wavelength. The confinement loss of the designed PCF is also significantly less and it decreases as the wavelength increases. Also, the value of dispersion is significantly less due to the regular variation in the size of the holes in the transverse direction, as compared to the design when there is no gradation. The design has been optimized with an appropriate value of the perfectly matched layer to achieve the best results. Full article

The 1st International Online Conference on Photonics, centered around the theme of optics and photonics, was held from 14 to 16 October 2024. This conference aimed to highlight and facilitate the utilization of recent advancements in all areas related to optics and photonics, as well as to address complex issues, exchange the latest scientific breakthroughs, and guide the development of future technologies and processes in these fields. Full article

Since the early 20th century, dimensional analysis and similarity arguments have provided a critical tool for the analysis of scientific, engineering, and thermodynamic systems. Traditionally, the resulting dimensionless groups are categorized into those defined by (i) geometric similarity, involving ratios of length scales; (ii) kinematic similarity, involving ratios of velocities or accelerations, and (iii) dynamic similarity, involving ratios of forces. This study considers an additional category based on entropic similarity, with three variants defined by the following: (i) ratios of global or local entropy production terms Π entrop = σ ˙ 1 / σ ˙ 2 or Π ^ entrop = σ ˙ ^ 1 / σ ˙ ^ 2 ; (ii) ratios of entropy flow rates Π entrop = F S , 1 / F S , 2 or magnitudes of entropy fluxes Π ^ entrop = | | j S 1 | | / | | j S 2 | | ; and (iii) the ratio of a fluid velocity to that of a carrier of information Π info = U / c . Given that all phenomena involving work against friction, dissipation, spreading, chemical reaction, mixing, separation, or the transmission of information are governed by the second law of thermodynamics, these are more appropriately analyzed directly in terms of competing entropic phenomena and the dominant entropic regime, rather than indirectly using ratios of forces. This work presents the entropic dimensionless groups derived for a wide range of diffusion, chemical reaction, dispersion, and wave phenomena, revealing an entropic interpretation for many known dimensionless groups and many new dimensionless groups. Full article

In this paper, a novel single-layer dual-band orbital angular momentum (OAM) multiplexed reflective metasurface array antenna is proposed, which can independently generate OAM beams with different modes in the C-band and Ku-band, and complete flexible beam control in each operating band, achieving the generation of an OAM beam with mode l = −1 under oblique incidence at 7G with 94.4% mode purity, and having a wider usable operating bandwidth at 12G with a wide operating bandwidth, and an OAM beam with mode l = +2 is generated under oblique incidence, achieving 82.5% mode purity, which verifies the performance of the unit, makes preparations for the next research, and provides new possibilities for communication in more transmission bands and larger channel capacity. Full article

Electrospinning can be used to prepare nanofiber mats from diverse polymers and polymer blends. A large area of research is the application of nanofibrous membranes for tissue engineering. Typically, cell adhesion and proliferation as well as the viability of mammalian cells are tested by seeding the cells on substrates, cultivating them for a defined time and finally dyeing them to enable differentiation between cells and substrates under a white light or fluorescence microscope. While this procedure works well for cells cultivated in well plates or petri dishes, other substrates may undesirably also be colored by the dye. Here we show investigations of the optical contrast between dyed CHO DP-12 (Chinese hamster ovary) cells and different electrospun nanofiber mats, dyed with haematoxylin-eosin (H&E), PromoFluor 488 premium, 4,6-diamidino-2-phenylindole (DAPI) or Hoechst 33342, and give the optimum dyeing parameters for maximum optical contrast between cells and nanofibrous substrates. Full article

In this paper we demonstrate a new approach to the measurement of dispersion of light reflected in integrated optical devices. The approach utilizes the fact that light reflected from the end facet of an integrated waveguide will interfere with light reflected from points inside the device under test (DUT), effectively creating a Michelson interferometer. The distance between the measured fringes of this interferometric signal will depend directly on the group delay experienced in the device under test, allowing for fast and easy measurement of waveguide dispersion. This approach has been used to determine the dispersion of a fabricated linearly chirped Bragg gratings waveguide and the result agrees well with the designed value. Full article

Public touchscreens, such as those used in automated teller machines or ticket payment systems, which are accessed by different people in a short period of time, could transmit pathogens and thus spread infections. Therefore, the aim of this study was to develop and test a prototype of a touchscreen system for the public sector that disinfects itself quickly and automatically between two users without harming any humans. A quartz pane was installed in front of a commercial 19” monitor, into which 120 UVC LEDs emitted laterally. The quartz plate acted as a light guide and irradiated microorganisms on its surface, but—due to total reflection—not the user in front of the screen. A near-infrared commercial touch frame was installed to recognize touch. The antibacterial effect was tested through intentional staphylococcus contamination. The prototype, composed of a Raspberry Pi microcomputer with a display, a touchscreen, and a touch frame, was developed, and a simple game was programmed that briefly switched on the UVC LEDs between two users. The antimicrobial effect was so strong that 1% of the maximum UVC LED current was sufficient for a 99.9% staphylococcus reduction within 25 s. At 17.5% of the maximum current, no bacteria were observed after 5 s. The residual UVC irradiance at a distance of 100 mm in front of the screen was only 0.18 and 2.8 µW/cm² for the two currents, respectively. This would allow users to stay in front of the system for 287 or 18 min, even if the LEDs were to emit UVC continuously and not be turned off after a few seconds as in the presented device. Therefore, fast, automatic touchscreen disinfection with UVC LEDs is already possible today, and with higher currents, disinfection durations below 1 s seems to be feasible, while the light guide approach virtually prevents the direct irradiation of the human user. Full article

The intrinsic third-order nonlinearity in silicon has proven it to be quite useful in the field of quantum optics. Silicon is suitable for producing time-correlated photon pairs that are sources of heralded single-photon states for quantum integrated circuits. A quantum signal source in the form of single photons is an inherent requirement for the principles of quantum key distribution technology for secure communications. Here, we present numerical simulations of a silicon ring with a 6 μ m radius side-coupled with a bus waveguide as the source for the generation of single photons. The photon pairs are generated by exploring the process of degenerate spontaneous four-wave mixing (SFWM). The free spectral range (FSR) of the ring is quite large, simplifying the extraction of the signal/idler pairs. The phase-matching condition is considered by studying relevant parameters like the dispersion and nonlinearity. We optimize the ring for a high quality factor by varying the gap between the bus and the ring waveguide. This is the smallest ring studied for photon pair generation with a quality factor in the order of 10 5 . The width of the waveguides is chosen such that the phase-matching condition is satisfied, allowing for the propagation of fundamental modes only. The bus waveguide is pumped at one of the ring resonances with the minimum dispersion (1543.5 nm in our case) to satisfy the principle of energy conservation. The photon pair generation rate achieved is comparable to the state of the art. The photon pair sources exploiting nonlinear frequency conversion/generation processes is a promising alternative to atom-like single-photon emitters in the field of integrated photonics. Such miniaturized structures will benefit future on-chip architectures where multiple single-photon source devices are required on the same chip. Full article

The recently much noticed Far-UVC spectral range offers the possibility of inactivating pathogens without necessarily posing a major danger to humans. Unfortunately, there are various Far-UVC sources that differ significantly in their longer wavelength UVC emission and, subsequently, in their risk potential. Therefore, a simple assessment method for Far-UVC sources is presented here. In addition, the temporal intensity stability of Far-UVC sources was examined in order to reduce possible errors in irradiation measurements. For this purpose, four Far-UVC sources and a conventional Hg UVC lamp were each spectrally measured for about 100 h and mathematically evaluated for their antimicrobial effect and hazard potential using available standard data. The two filtered KrCl lamps were found to be most stable after a warm-up time of 30 min. With regard to the antimicrobial effect, the radiation efficiencies of all examined (Far-) UVC sources were more or less similar. However, the calculated differences in the potential human hazard to eyes and skin were more than one order of magnitude. The two filtered KrCl lamps were the safest, followed by an unfiltered KrCl lamp, a Far-UVC LED and, finally, the Hg lamp. When experimenting with these Far-UVC radiation sources, the irradiance should be checked more than once. If UVC radiation is to be or could be applied in the presence of humans, filtered KrCl lamps are a much better choice than any other available Far-UVC sources. Full article

Since its inception in 2004, nested sampling has been used in acoustics applications. This work applies nested sampling within a Bayesian framework to the detection and localization of sound sources using a spherical microphone array. Beyond an existing work, this source localization task relies on spherical harmonics to establish parametric models that distinguish the background sound environment from the presence of sound sources. Upon a positive detection, the parametric models are also involved to estimate an unknown number of potentially multiple sound sources. For the purpose of source detection, a no-source scenario needs to be considered in addition to the presence of at least one sound source. Specifically, the spherical microphone array senses the sound environment. The acoustic data are analyzed via spherical Fourier transforms using a Bayesian model comparison of two different models accounting for the absence and presence of sound sources for the source detection. Upon a positive detection, potentially multiple source models are involved to analyze direction of arrivals (DoAs) using Bayesian model selection and parameter estimation for the sound source enumeration and localization. These are two levels (enumeration and localization) of inferential estimations necessary to correctly localize potentially multiple sound sources. This paper discusses an efficient implementation of the nested sampling algorithm applied to the sound source detection and localization within the Bayesian framework. Full article

This work introduces a new method for the exploration of solutions space in complex problems. This method consists of the build of a latent space which gives a new encoding of the solution space. We map the objective function on the latent space using a manifold, i.e., a mathematical object defined by an equations system. The latent space is built with some knowledge of the objective function to make the mapping of the manifold easier. In this work, we introduce a new encoding for the Travelling Salesman Problem (TSP) and we give a new method for finding the optimal round. Full article