bluuebunny/crossref_metadata_2025 huggingface dataset:
Electroproduction of Hypernuclei
Authors: Denisova Daria , Bydžovský Petr , Veselý Petr , Skoupil Dalibor
Published: February 2024

Abstract. The electroproduction of hypernuclei initiates a captivating domain of study, offering great insights into the characteristics of composite nucleon-hyperon systems. This inquiry assumes prime significance as it displays critical features of nuclear matter structure and tests the interactions between hyperons and nucleons. In this paper, we unveil the distorted-wave impulse approximation (DWIA) approach, aimed at explaining the cross sections in electroproduc-tion of Λ-hypernuclei. Our investigation examines how various model assumptions affect the results we get. We focus on two important factors: influence of the proton Fermi motion and description of the various models of nuclear and hypernuclear structure.
Multidimensional listener perception of speaker gender reflects spectrum of gender diversity
Authors: Shapiro Maura
Published: February 2024

Without a forced gender binary, listeners organize speaker characteristics differently.
Estimating solar irradiance to predict crop yield on northern agrivoltaic farms
Authors: Johnson-Groh Mara
Published: February 2024

Improved model can guide development of mixed-use farms with solar panels.
Phase field crystal models with applications to laser deposition: A review
Authors: Burns Duncan , Provatas Nikolas , Grant Martin
Published: February 2024

In this article, we address the application of phase field crystal (PFC) theory, a hybrid atomistic-continuum approach, for modeling nanostructure kinetics encountered in laser deposition. We first provide an overview of the PFC methodology, highlighting recent advances to incorporate phononic and heat transport mechanisms. To simulate laser heating, energy is deposited onto a number of polycrystalline, two-dimensional samples through the application of initial stochastic fluctuations. We first demonstrate the ability of the model to simulate plasticity and recrystallization events that follow laser heating in the isothermal limit. Importantly, we also show that sufficient kinetic energy can cause voiding, which serves to suppress shock propagation. We subsequently employ a newly developed thermo-density PFC theory, coined thermal field crystal (TFC), to investigate laser heating of polycrystalline samples under non-isothermal conditions. We observe that the latent heat of transition associated with ordering can lead to long lasting metastable structures and defects, with a healing rate linked to the thermal diffusion. Finally, we illustrate that the lattice temperature simulated by the TFC model is in qualitative agreement with predictions of conventional electron–phonon two-temperature models. We expect that our new TFC formalism can be useful for predicting transient structures that result from rapid laser heating and re-solidification processes.
Relationship between magnetic rigidity cutoff and chaotic behavior in cosmic ray time series using visibility graph and network analysis techniques
Authors: Sierra-Porta D.
Published: February 2024

Cosmic rays are highly energetic particles originating from astrophysical events outside the Solar System. In this study, we analyze the time series of cosmic ray flux measured by neutron detectors at 16 monitoring stations distributed worldwide. By applying visibility graph analysis, we explore the relationship between the magnetic rigidity cutoff (Rc) and the fractality exhibited from topology of the cosmic ray time series. Our results reveal a significant association between the magnetic rigidity cutoff and the fractality of the cosmic ray time series. Specifically, the analysis of visibility graphs and network properties demonstrates that the magnetic rigidity is inversely related to the magnetic rigidity cutoff. The identified relationship between magnetic rigidity and fractality provides insights into the chaotic nature of cosmic ray variations and their potential uses for predictability.
Predicting wind farm wake losses with deep convolutional hierarchical encoder–decoder neural networks
Authors: Romero David A. , Hasanpoor Saeede , Antonini Enrico G. A. , Amon Cristina H.
Published: February 2024

Wind turbine wakes are the most significant factor affecting wind farm performance, decreasing energy production and increasing fatigue loads in downstream turbines. Wind farm turbine layouts are designed to minimize wake interactions using a suite of predictive models, including analytical wake models and computational fluid dynamics simulations (CFD). CFD simulations of wind farms are time-consuming and computationally expensive, which hinder their use in optimization studies that require hundreds of simulations to converge to an optimal turbine layout. In this work, we propose DeepWFLO, a deep convolutional hierarchical encoder–decoder neural network architecture, as an image-to-image surrogate model for predicting the wind velocity field for Wind Farm Layout Optimization (WFLO). We generate a dataset composed of image representations of the turbine layout and undisturbed flow field in the wind farm, as well as images of the corresponding wind velocity field, including wake effects generated with both analytical models and CFD simulations. The proposed DeepWFLO architecture is then trained and optimized through supervised learning with an application-tailored loss function that considers prediction errors in both wind velocity and energy production. Results on a commonly used test case show median velocity errors of 1.0%–8.0% for DeepWFLO networks trained with analytical and CFD data, respectively. We also propose a model-fusion strategy that uses analytical wake models to generate an additional input channel for the network, resulting in median velocity errors below 1.8%. Spearman rank correlations between predictions and data, which evidence the suitability of DeepWFLO for optimization purposes, range between 92.3% and 99.9%.
Prestress effect on friction reduction of multilayer suspended h-BN
Authors: Zhang Xiushuo , Lang Haojie , Xu Peipei , Zou Kun , Peng Yitian
Published: February 2024

Prestress manifests on multilayer suspended two-dimensional materials, significantly influencing their friction characteristics. Here, friction of multilayer suspended h-BN to varying prestress levels was quantified through atomic force microscopy (AFM). Friction diminishes as prestress escalates from the center to the edge and the time after the suspended h-BN is prepared. Finite element simulation figures out that prestress broads the contact geometry of multilayer suspended h-BN. Synchronous reduction of the contact area and the interfacial shear strength results in friction reduction. The depressed strengthening effect and stick-slip asymmetry confirm that prestress regulated the contact quality. This work demonstrates that the prestress can provide an additional strategy for friction modulation of two-dimensional materials.
Adaptation rules inducing synchronization of heterogeneous Kuramoto oscillator network with triadic couplings
Authors: Emelianova Anastasiia A. , Nekorkin Vladimir I.
Published: February 2024

A class of adaptation functions is found for which a synchronous mode with different number of phase clusters exists in a network of phase oscillators with triadic couplings. This mode is implemented in a fairly wide range of initial conditions and the maximum number of phase clusters is four. The joint influence of coupling strength and adaptation parameters on synchronization in the network has been studied. The desynchronization transition under variation of the adaptation parameter occurs abruptly and begins with the highest-frequency oscillator, spreading hierarchically to all other elements.
Spherical Langmuir probes in magnetized plasma. A model based on particle-in-cell simulations
Authors: Brask S. M. , Mishra R. , Holen G. , Miyake Y. , Usui H. , Miloch W. J.
Published: February 2024

We present a new model for current collected by a spherical Langmuir probe in magnetized plasmas. Data are obtained using state-of-the-art fully 3D kinetic particle-in-cell simulations. We perform a dimensional analysis and use it to determine the appropriate model function. The model is then empirically derived based on the simulation data for a range of probe potentials and magnetic field values with respect to the Debye length. The final model function is applicable to most space plasmas and can easily be generalized.
Charge photogeneration dynamics in non-fullerene polymer solar cells with fluorinated and non-fluorinated acceptors
Authors: Cai Zekai , Hu Rong , Xiao Zijie , Feng Junyi , Zou Xianshao , Wen Guanzhao , Dong Geng , Zhang Wei
Published: February 2024

In this work, charge photogeneration and recombination processes of PM6:IDIC-4F and PM6:IDIC blend films were investigated by the steady-state and time-resolved spectroscopies, as well as the time-dependent density functional theory calculations. The peaks in absorption and photoluminescence (PL) spectra of IDIC and IDIC-4F solutions were assigned by combining the experiment and the simulation of UV–vis absorption and PL spectra. For neat acceptor films, the exciton diffusion length of neat IDIC and IDIC-4F films was estimated as ∼28.9 and ∼19.9 nm, respectively. For PM6-based blend films, we find that the fluorine substitution engineering on the IDIC acceptor material can increase the phase separate size of acceptor material in blend films, resulting in the reduction of dissociation efficiencies of acceptor excitons. In addition, we find that the charge recombination in PM6:IDIC-4F is dominated by bimolecular recombination, in comparison to geminate type carrier recombination in PM6:IDIC blend films. In addition, we find that thermal annealing treatment has a weak influence on carrier recombination but slightly reduces the exciton dissociation efficiency of acceptor in PM6:IDIC blend films, leading to a slightly reduced power conversion efficiency of PM6:IDIC solar cells. These results may shed light on the design of high-performance semiconductor molecules for application in solar cells.
Glass spectrum, excess wing phenomenon, and master curves in molecular glass formers: A multi-method approach
Authors: Rössler Ernst A. , Becher Manuel
Published: February 2024

The relaxation spectra of glass formers solely displaying an α-peak and excess wing contribution collected by various methods are reanalyzed to pin down their different spectral evolution. We show that master curve construction encompassing both α-peak and emerging excess wing works for depolarized light scattering (DLS) and nuclear magnetic resonance (NMR) relaxometry. It reveals the self-part of the slow dynamics’ spectrum. Master curves are to be understood as a result of a more extensive scaling covering all temperatures instead of strict frequency–temperature superposition. DLS and NMR display identical relaxation spectra; yet, comparing different systems, we do not find a generic structural relaxation at variance with recent claims. Dielectric spectroscopy (DS) spectra show particularities, which render master curve construction obsolete. The DS α-peak is enhanced or suppressed with respect to that of DLS or NMR, yet, not correlated to the polarity of the liquid. Attempting to single out the excess wing from the overall spectrum discloses a stronger exponential temperature dependence of its amplitude compared to that below Tg and a link between its exponent and that of the fast dynamics’ spectrum. Yet, such a decomposition of α-peak and excess wing appears to be unphysical. Among many different glasses, the amplitude of the excess wing power-law spectrum is found to be identical at Tg, interpreted as a relaxation analog to the Lindemann criterion.
Effect of higher-order interactions on chimera states in two populations of Kuramoto oscillators
Authors: Kar Rumi , Yadav Akash , Chandrasekar V. K. , Senthilkumar D. V.
Published: February 2024

We investigate the effect of the fraction of pairwise and higher-order interactions on the emergent dynamics of the two populations of globally coupled Kuramoto oscillators with phase-lag parameters. We find that the stable chimera exists between saddle-node and Hopf bifurcations, while the breathing chimera lives between Hopf and homoclinic bifurcations in the two-parameter phase diagrams. The higher-order interaction facilitates the onset of the bifurcation transitions at a much lower disparity between the inter- and intra-population coupling strengths. Furthermore, the higher-order interaction facilitates the spread of breathing chimera in a large region of the parameter space while suppressing the spread of the stable chimera. A low degree of heterogeneity among the phase-lag parameters promotes the spread of both stable chimera and breathing chimera to a large region of the parameter space for a large fraction of the higher-order coupling. In contrast, a large degree of heterogeneity is found to decrease the spread of both chimera states for a large fraction of the higher-order coupling. A global synchronized state is observed above a critical value of heterogeneity among the phase-lag parameters. We have deduced the low-dimensional evolution equations for the macroscopic order parameters using the Ott–Antonsen Ansatz. We have also deduced the analytical saddle-node and Hopf bifurcation curves from the evolution equations for the macroscopic order parameters and found them to match with the bifurcation curves obtained using the software XPPAUT and with the simulation results.
An efficient quantum circuit implementation of Shor’s algorithm for GPU accelerated simulation
Authors: Tan XinJian , Gao Peng
Published: February 2024

In this study, we introduce a novel implementation of Shor’s algorithm specifically designed for the Graphics Processing Unit (GPU) acceleration framework. Our focus lies on achieving efficient execution of the modular multiplication circuit through GPU simulation. To seamlessly integrate our design into the PyQPanda library framework, we made necessary modifications, making a deliberate trade-off by sacrificing a small number of quantum resources to leverage the advantages of GPU acceleration. Subsequently, we conducted simulations and rigorously validated the functionality of our circuit using the PyQPanda library, resulting in a significant speedup compared to a central processing unit-only mode.
Transition to period-3 synchronized state in coupled gauss maps
Authors: Gaiki Pratik M. , Deshmukh Ankosh D. , Pakhare Sumit S. , Gade Prashant M.
Published: February 2024

We study coupled Gauss maps in one dimension with nearest-neighbor interactions. We observe transitions from spatiotemporal chaos to period-3 states in a coarse-grained sense and synchronized period-3 states. Synchronized fixed points are frequently observed in one dimension. However, synchronized periodic states are rare. The obvious reason is that it is very easy to create defects in one dimension. We characterize all transitions using the following order parameter. Let x∗ be the fixed point of the map. The values above (below) x∗ are classified as +1 (−1) spins. We expect all sites to return to the same band after three time steps for a coarse-grained periodic or three-period state. We define the flip rate F(t) as the fraction of sites i such that si(3t−3)≠si(t). It is zero in the coarse-grained periodic state. This state may or may not be synchronized. We observe three different transitions. (a) If different sites reach different bands, the transition is in the directed-percolation universality class. (b) If all sites reach the same band, we find an Ising-type transition. (c) A synchronized period-3 state where a new exponent is observed. We also study the finite-size scaling at critical points. The exponents obtained indicate that the synchronized period-3 transition is in a new universality class.
The power-extraction regime of a figure-eight trajectory flapping-foil turbine
Authors: Zheng Min , Yao Huimin , Bai Yalei , Bo Qin , Chi Xu , Chen Jinyan
Published: February 2024

At specified Reynolds numbers Re=ρvc/μ=5×105, this study investigates the power-extraction regime of a flapping-foil turbine executing a figure-eight trajectory. This study thoroughly explored the impacts of trajectory shape, heave and pitch amplitudes, phase difference, and pitch axis location on the power-extraction regime of a flapping turbine. A figure-eight trajectory substantially bolsters the energy harvesting capacity, achieving a peak efficiency of up to 50%. This trajectory capitalizes on the energy generated from the drag encountered by the flapping foil, thereby marking a significant efficiency breakthrough. This could denote a considerable progression for flapping foils tailored for heave and pitch motions since the free stream can be optimally harnessed by the trajectory we have established. In scenarios where the flapping foil undergoes the same maximum effective angle of attack, a wake diffusion spectrum aligns with the Betz limit threshold. Crucially, the closeness to this efficiency frontier suggests a universal maximum effective angle of attack—a consistent law that remains valid for the conventional flapping turbine design. It implies that selections for stroke and pitch amplitudes should be methodical rather than arbitrary. In addition, the positioning of the pitch axis ought to be modified in tandem with phase difference adjustments to bolster the synchronization between heaving motions and resultant lift. The ideal phase difference is variable, contingent on pitch amplitude and pitch axis position. Even with low pitch amplitudes, fine-tuning the phase difference guarantees that the energy harvesting efficiency does not fall below 30%. Such an enhancement would significantly broaden the operational envelope and the parameter space for flapping turbines.
Comparing the influence of cation order and composition in simulated Zn(Sn, Ge)N2 on structure, elastic moduli, and polarization for solid state lighting
Authors: Cordell Jacob J. , Lany Stephan , Tellekamp M. Brooks
Published: February 2024

Alloying and site ordering play complementary roles in dictating a material’s properties. However, deconvolving the impacts of these separate phenomena can be challenging. In this work, we simulate structures of Zn(Sn,Ge)N2 with varied Sn content and site ordering to determine the impacts of order and composition on structural and electronic properties. We assess the formation enthalpy, lattice parameters, elastic constants, spontaneous polarization, and piezoelectric coefficients. In mostly disordered structures (order parameters ranging from 0.2 to 0.4), the formation enthalpy exhibits local extrema as a function of the order parameter, deviating from the more linear trends seen in both fully disordered and fully ordered systems. This anomalous deviation from the otherwise linear trend in formation enthalpy with order manifests in each of the other properties calculated. This range of order parameters of interest may be caused by a transition in the ordering of the quaternary material similar to phase changes seen in ternary compounds but stretched over a region inclduing 20% of the order parameter range. Most parameters calculated are more sensitive to order than to composition in the limited composition range tested; however, the lattice parameter c, piezoelectric coefficient e33, and elastic moduli C12, C13, and C23 are more sensitive to composition. Of the properties compared, the piezoelectric coefficients are influenced most significantly by changes in both the composition and order parameter. Lattice parameters undergo the smallest changes with order and composition, but these small differences appear to impart large trends in the other properties. Better understanding the effects of disorder and group IV alloying in Zn(Sn,Ge)N2 allows for more accurate modeling of characteristics of this material system for solid state lighting and other applications.
Study on the effect of Bi/Sr ratio on the device characteristics of high-Tc superconducting terahertz wave emitters made of Bi2Sr2CaCu2O8+δ single crystals
Authors: Nakayama M. , Nakagawa S. , Yamaguchi T. , Minami H. , Kadowaki K. , Nakao H. , Mochiku T. , Tsujimoto M. , Ishida S. , Eisaki H. , Kashiwagi T.
Published: February 2024

To obtain high-performance THz-wave-emitting devices made of single crystals of Bi2Sr2CaCu2O8+δ (Bi2212), a high-temperature superconductor, an understanding of the device characteristics based on crystal characteristics can be a key issue because, in principle, the electrical properties of the intrinsic Josephson junctions (IJJs) constructed in Bi2212 crystals highly depend on crystal conditions, such as carrier concentration, crystal homogeneities, and crystal defects. To evaluate the tendencies of the device characteristics associated with crystal characteristics, we prepared Bi2212 crystals with different Bi/Sr ratios (x=0.05, 0.15, and 0.25) and δ values (annealed under N2 or O2 gas flow conditions). The unit cell parameter c decreased as the Bi/Sr ratio or δ increased. For the same annealing conditions under N2 gas flow, the superconducting transition temperature as well as the size of the hysteresis loop of the current–voltage characteristics and emission characteristics were significantly suppressed for the sample with x=0.25 compared with the corresponding values for the samples with x=0.05 and 0.15. The experimental results clearly indicate that parameters, such as the Bi/Sr ratio and annealing conditions, are crucial factors in determining the electrical characteristics of a device. This information can be a useful guide for the preparation of crystals for IJJ THz-wave devices that can be fine-tuned according to the desired device characteristics.
Log-periodic oscillations as real-time signatures of hierarchical dynamics in proteins
Authors: Dorbath Emanuel , Gulzar Adnan , Stock Gerhard
Published: February 2024

The time-dependent relaxation of a dynamical system may exhibit a power-law behavior that is superimposed by log-periodic oscillations. D. Sornette [Phys. Rep. 297, 239 (1998)] showed that this behavior can be explained by a discrete scale invariance of the system, which is associated with discrete and equidistant timescales on a logarithmic scale. Examples include such diverse fields as financial crashes, random diffusion, and quantum topological materials. Recent time-resolved experiments and molecular dynamics simulations suggest that discrete scale invariance may also apply to hierarchical dynamics in proteins, where several fast local conformational changes are a prerequisite for a slow global transition to occur. Employing entropy-based timescale analysis and Markov state modeling to a simple one-dimensional hierarchical model and biomolecular simulation data, it is found that hierarchical systems quite generally give rise to logarithmically spaced discrete timescales. By introducing a one-dimensional reaction coordinate that collectively accounts for the hierarchically coupled degrees of freedom, the free energy landscape exhibits a characteristic staircase shape with two metastable end states, which causes the log-periodic time evolution of the system. The period of the log-oscillations reflects the effective roughness of the energy landscape and can, in simple cases, be interpreted in terms of the barriers of the staircase landscape.
Solving the time-dependent protein distributions for autoregulated bursty gene expression using spectral decomposition
Authors: Wu Bingjie , Holehouse James , Grima Ramon , Jia Chen
Published: February 2024

In this study, we obtain an exact time-dependent solution of the chemical master equation (CME) of an extension of the two-state telegraph model describing bursty or non-bursty protein expression in the presence of positive or negative autoregulation. Using the method of spectral decomposition, we show that the eigenfunctions of the generating function solution of the CME are Heun functions, while the eigenvalues can be determined by solving a continued fraction equation. Our solution generalizes and corrects a previous time-dependent solution for the CME of a gene circuit describing non-bursty protein expression in the presence of negative autoregulation [Ramos et al., Phys. Rev. E 83, 062902 (2011)]. In particular, we clarify that the eigenvalues are generally not real as previously claimed. We also investigate the relationship between different types of dynamic behavior and the type of feedback, the protein burst size, and the gene switching rate.
Numerical analysis of horizontal bearing capacity of pile in clay slope
Authors: Ma Jian , Xu Junyue , Fan Zhenkai , Xu Gang , Yu Yi
Published: February 2024

In this study, a series of numerical calculations were performed to investigate the lateral behavior of piles in slopes and in horizontal ground. First, a numerical model is created and then verified by comparing the numerical results with the results of model tests. The numerical results agree well with the results of model tests. Second, numerical calculations of different slopes were conducted to explore the effect of slope angle on the horizontal displacement of pile and bending moment. Then, the effect of slope angle on the foundation stiffness proportional coefficient m is investigated. The stress distribution of soil around the pile and the deformation of pile at different slope angles are also compared. Finally, the p–y curves of the different slope angles are compared. An improved p–y method is proposed to consider the effect of slope angle based on the numerical results. The results show that the bearing capacity of piles decreases with an increase in slope angle. The horizontal displacement of pile nonlinearly decreases along the pile body with the depth of pile. The bending moment of piles increases along the pile body with an increase in pile depth, and until 0.5 times of the pile length, the bending moment reaches the maximum value. As the slope angle increases, the maximum of bending moment tends to decrease. The distance from the slope toe to the pile section has a little influence on the pile bending moment and horizontal displacement. With an increase in slope angle, the horizontal foundation coefficient m gradually decreases.
High-precision ground simulator for laser tracking of gravity satellite
Authors: Zhao Menghao , Hong Wei , Xiao Chunyu , Ma Yun , Bai Yanzheng , Zhou Zebing
Published: February 2024

Inter-satellite laser ranging is a key technology to improve the measurement precision of gravity satellites in future missions. However, it requires a stable laser link between satellites, which would be affected by external disturbances in space and internal couplings of satellite components. This paper presents a dynamic model to describe the tracking error and proposes a high-precision satellite simulator for the validation of inter-satellite laser tracking. Then, the noises of the sensors and actuators are tested to give the theoretical tracking performance of the simulator. Finally, the laser tracking performance is validated through two experiments: fixed-position tracking and motion tracking. The experimental results show that the measured tracking error of the satellite platform is better than 10 mrad/Hz in the fixed-position tracking and 50 mrad/Hz in the motion tracking. Furthermore, the optical platform can reduce the measured tracking error to 80 μrad/Hz in both two experiments. This work provides a theoretical foundation for optimizing laser tracking performance in space missions, and the proposed simulator has demonstrated a potential for mission simulation with laser tracking.
Disorder enhanced relative intrinsic detection efficiency in NbTiN superconducting nanowire single photon detectors at high temperature
Authors: Ma Ruoyan , Huan Qingchang , Huang Jia , Zhang Xingyu , Xiao You , Xu Hongxing , Han Hailong , Liu Xiaoyu , Peng Wei , Li Hao , Zhang Xiaofu , You Lixing
Published: February 2024

The intrinsic detection performance of superconducting nanowire single photon detectors (SNSPDs) is highly dependent on the superconducting properties of underlying thin films. This report outlines the enhancement of detection performance for single telecom wavelength photons in disordered NbTiN SNSPD at 4.2 K. By increasing the nitrogen content and deposition pressure, the NbTiN films show suppression in critical temperature and an increase in sheet resistance. Notably, the resulting SNSPDs display a broader saturation plateau at 2.2 K, leading to superior detection performance at 4.2 K. With the disordered 7-nm-thick NbTiN films, we fabricated SNSPDs with system detection efficiency up to 83% for 1550 nm photons at 4.2 K. Moreover, these devices also show saturated intrinsic detection efficiency for 2000 nm photons. With the features outlined, the devices can be integrated into the idle 4.2 K stage of the dilution refrigerator for applications in optical quantum information processing or utilize for detecting laser radar signals in airborne platforms.
Filling fraction measurement around a drying drop onto nanoporous silicon using digital holographic microscopy
Authors: Martínez M. F. , Sallese M. D. , Psota P. , Berli C. L. A. , Urteaga R. , Budini N. , Monaldi A. C.
Published: February 2024

In this work, we implemented an off-axis digital holographic microscopy (DHM) setup to study the behavior of liquid drops on nanostructured porous silicon (PS) membranes. When a liquid comes into contact with the PS structure, capillary action and surface tension give rise to imbibition of the liquid into the intricate volume of the pores. At the same time, the vapor field developed around the drop enhances liquid condensation and evaporation into and from the pores. The complex interplay between these phenomena (capillary driven internal flows, condensation, and evaporation) is not yet fully understood but the methods we propose can provide new insights. We demonstrate how DHM allows determining the filling fraction of the porous membrane around drying drops of water and isobutyl alcohol. The phase information obtained from registered holograms provides quantitative information that permits to reconstruct the filling fraction along the porous membrane and its evolution during the drying process. Additionally, relevant parameters such as speed and contact angle during retraction of the drops can be measured. These methods can be further extended to other porous materials, such as porous alumina, micro- and macro-PS, to develop better fluid-dynamic models for describing fluid behavior in highly confined structures.
Low-threshold single ternary GaAsSb nanowire lasers emitting at silicon transparent wavelengths
Authors: Schmiedeke P. , Doganlar C. , Jeong H. W. , Döblinger M. , Finley J. J. , Koblmüller G.
Published: February 2024

Conventional binary III–V nanowire (NW) lasers face substantial challenges in tuning their lasing emission to silicon transparent wavelengths and require complex quantum heterostructure designs for realizing on-chip integrated nanolasers. Here, an alternative and straightforward approach is reported by developing ternary III–V NW-lasers in the form of surface-passivated GaAsSb NW-lasers grown on silicon. High-quality GaAsSb NW-cavities with high Sb-content (>20%) and extended lengths (>5 μm) are shown to exhibit striking radiative efficiency enhancements (∼200-fold) when passivated by closely lattice-matched InAlGaAs shell layers. Utilizing this core–shell approach, optically pumped lasing is then demonstrated from single GaAsSb NW-lasers with lasing threshold as low as 3.2 μJ/cm2 at temperatures up to 250 K and emission wavelengths of ∼1.1–1.2 μm. Analysis of the optical mode spectra and mode-dependent threshold gain further shows that lasing is induced by the fundamental HE11 modes, and likely even lower thresholds may be achieved by establishing the TE01 mode at increased NW-cavity diameters.
Terahertz spectral characteristics of photosensitive resin based on microfluidic technology
Authors: Zhang Xin-Rui , Yang Hui-Yu , Peng Zhuang , Su Bo , Zhang Cun-Lin
Published: February 2024

Photosensitive resin is a kind of polymer gel material. Due to its excellent UV curing performance, it is widely used in the emerging 3D printing industry. This article combines terahertz technology with microfluidic chip technology to study the terahertz spectral characteristics of liquid and solid photosensitive resins under different electric fields. In the experiment, it was found that an electric field can also cause polymerization of photosensitive resin monomers to form cross-linked polymers, increasing their curing degree. For solid photosensitive resins, the orientation of polymer molecules is enhanced under an electric field, and the molecular arrangement changes from a disordered state to an ordered state. Meanwhile, it was found that both liquid and solid photosensitive resins subjected to electric fields exhibit absorption coefficients below zero within a very small frequency range. We explain this from two aspects: energy and the Fabry Pérot effect. This article uses terahertz spectra to study the curing and structural changes in photosensitive resins under an electric field, laying a foundation for further improving 3D printing technology.
SHE-MTJ based ReLU-max pooling functions for on-chip training of neural networks
Authors: Vadde Venkatesh , Muralidharan Bhaskaran , Sharma Abhishek
Published: February 2024

We present a detailed investigation of various routes to optimize the power consumption of the spintronic-based devices for implementing rectified linear activation (ReLU) and max-pooling functions. We examine the influence of various spin Hall effect layers, and their input resistances on the power consumption of the ReLU-max pooling functions, we also access the impact of the thermal stability factor of the free-ferromagnet layer on the power consumption and accuracy of the device. The design for ReLU-max pooling relies on the continuous rotation of magnetization, which is accomplished by applying orthogonal spin current to the free-FM layer. We also demonstrate the non-trivial power-resistance relation, where the power consumption decreases with an increase in SHE resistance. We utilize the hybrid spintronic-CMOS simulation platform that combines Keldysh non-equilibrium Green’s function (NEGF) with Landau-Lifshitz-Gilbert-Slonzewski (LLGS) equations and the HSPICE circuit simulator to evaluate our network. Our design takes 0.343 μW of power for ReLU emulation and 17.86 μW of power for ReLU-max pooling network implementation at a thermal stability factor of 4.58, all while maintaining reliable results. We validate the efficiency of our design by implementing a convolutional neural network that classifies the handwritten-MNIST and fashion-MNIST datasets. This implementation illustrates that the classification accuracies achieved are on par with those attained using the ideal software ReLU-max pooling functions, with an energy consumption of 167.31 pJ per sample.
Towards fully electrically controlled domain-wall logic
Authors: Vermeulen B. B. , Raymenants E. , Pham V. T. , Pizzini S. , Sorée B. , Wostyn K. , Couet S. , Nguyen V. D. , Temst K.
Published: February 2024

Utilizing magnetic tunnel junctions (MTJs) for write/read and fast spin-orbit-torque (SOT)-driven domain-wall (DW) motion for propagation, enables non-volatile logic and majority operations, representing a breakthrough in the implementation of nanoscale DW logic devices. Recently, current-driven DW logic gates have been demonstrated via magnetic imaging, where the Dzyaloshinskii-Moriya interaction (DMI) induces chiral coupling between perpendicular magnetic anisotropy (PMA) regions via an in-plane (IP) oriented region. However, full electrical operation of nanoscale DW logic requires electrical write/read operations and a method to pattern PMA and IP regions compatible with the fabrication of PMA MTJs. Here, we study the use of a Hybrid Free Layer (HFL) concept to combine an MTJ stack with DW motion materials, and He+ ion irradiation to convert the stack from PMA to IP. First, we investigate the free layer thickness dependence of 100-nm diameter HFL-MTJ devices and find an optimal CoFeB thickness, from 7 to 10 Å, providing high tunneling magnetoresistance (TMR) readout and efficient spin-transfer torque (STT) writing. We then show that high DMI materials, like Pt/Co, can be integrated into an MTJ stack via interlayer exchange coupling with the CoFeB free layer. In this design, DMI values suitable for SOT-driven DW motion are measured by asymmetric bubble expansion. Finally, we demonstrate that He+ irradiation reliably converts the coupled free layers from PMA to IP. These findings offer a path toward the integration of fully electrically controlled DW logic circuits.
Link prediction using low-dimensional node embeddings: The measurement problem
Authors: Menand Nicolas , Seshadhri C.
Published: February 2024

Graph representation learning is a fundamental technique for machine learning (ML) on complex networks. Given an input network, these methods represent the vertices by low-dimensional real-valued vectors. These vectors can be used for a multitude of downstream ML tasks. We study one of the most important such task, link prediction. Much of the recent literature on graph representation learning has shown remarkable success in link prediction. On closer investigation, we observe that the performance is measured by the AUC (area under the curve), which suffers biases. Since the ground truth in link prediction is sparse, we design a vertex-centric measure of performance, called the VCMPR@k plots. Under this measure, we show that link predictors using graph representations show poor scores. Despite having extremely high AUC scores, the predictors miss much of the ground truth. We identify a mathematical connection between this performance, the sparsity of the ground truth, and the low-dimensional geometry of the node embeddings. Under a formal theoretical framework, we prove that low-dimensional vectors cannot capture sparse ground truth using dot product similarities (the standard practice in the literature). Our results call into question existing results on link prediction and pose a significant scientific challenge for graph representation learning. The VCMPR plots identify specific scientific challenges for link prediction using low-dimensional node embeddings.
‘Perfectly-tuned’ planetary system found
Authors: Cooper Keith
Published: February 2024

Astronomers have discovered a new planetary treasure trove that provides one of the best opportunities for characterizing “mini-Neptunes”, as Keith Cooper reports.
Researchers build first all-electric organic laser
Authors: Dumé Isabelle
Published: February 2024

Researchers at the University of St Andrews in Scotland have made the first organic semiconductor laser that does not require a separate light source to operate.
Oppenheimer on screen
Authors: Durrani Matin
Published: February 2024

Who’d have thought a film about a physicist would be up for eight Golden Globes?
Denial of reality
Authors: Crease Robert P
Published: February 2024

Robert P Crease reviews On Disinformation: How to Fight for Truth and Protect Democracy by Lee McIntyre.
Ask me anything: Sally Oey
Authors: Harris Margaret
Published: February 2024

Sally Oey is a professor of astronomy at the University of Michigan, US, where she studies massive stars and their effects on their host galaxies. She is especially interested in how ultraviolet ionizing radiation escapes from so-called “starburst” galaxies, which contain many bright, young stars that heat interstellar gas to millions of degrees.
Ab initio study of p- and n-type doping of two-dimensional MoO2: investigation of a pn-homojunction
Authors: Ndang Amassa Kevin , Etindele Anne Justine , Douma Dick Hartmann , Kenmoe Stephane , Nithaya Chetty
Published: February 2024

Based on density functional theory, we studied the effect of p- and n-type doping on the structural and electronic properties of MoO2 monolayers and bilayers. We used niobium (Nb) and nitrogen (N) as p-type dopants, and technetium (Tc) and fluorine (F) as n-type dopants through atomic substitutions. Our study shows that the presence of a substituent in the 4 × 4 supercell of MoO2 leads to a slight distortion and negligible modification of the lattice parameter. Both p- and n-type doped monolayers exhibit a metallic character. The bilayers obtained by vertically stacking n-p doped monolayers all exhibit a metallic character, as their band diagrams do not show a band gap. The study of their charge difference highlights a physisorption phenomenon. This type of material, which features a nucleophilic site in the p-doped region and an electrophilic site in the n-doped region, is a promising candidate for catalysis. When n-type and p-type doped monolayers are horizontally joined, the resulting stack exhibits a semi-conductor behavior.The special feature of this stacking is that we obtain a true pn junction, that is a space charge zone associated with a potential jump. For its application in infrared junction diodes, we have demonstrated both quantitatively and qualitatively the existence of a potential jump at the junction.
Bifacial flexible CIGS thin-film solar cells with nonlinearly graded-bandgap photon-absorbing layers
Authors: Ahmad Faiz , Monk Peter B , Lakhtakia Akhlesh
Published: February 2024

The building sector accounts for 36% of energy consumption and 39% of energy-related greenhouse-gas emissions. Integrating bifacial photovoltaic solar cells in buildings could significantly reduce energy consumption and related greenhouse gas emissions. Bifacial solar cells should be flexible, bifacially balanced for electricity production, and perform reasonably well under weak-light conditions. Using rigorous optoelectronic simulation software and the differential evolution algorithm, we optimized symmetric/asymmetric bifacial CIGS solar cells with either (i) homogeneous or (ii) graded-bandgap photon-absorbing layers and a flexible central contact layer of aluminum-doped zinc oxide to harvest light outdoors as well as indoors. Indoor light was modeled as a fraction of the standard sunlight. Also, we computed the weak-light responses of the CIGS solar cells using LED illumination of different light intensities. The optimal bifacial CIGS solar cell with graded-bandgap photon-absorbing layers is predicted to perform with 18%–29% efficiency under 0.01–1.0-Sun illumination; furthermore, efficiencies of 26.08% and 28.30% under weak LED light illumination of 0.0964 mW cm−2 and 0.22 mW cm−2 intensities, respectively, are predicted.
Sustainable energy harvesting and breath sensing with electrospun triboelectric nylon-6
Authors: Jelmy E J , Sunil Mathew , Kandappanthodi Chitra , Rincy P , Saji K J , Pillai Suresh C , John Honey
Published: February 2024

A high-performance triboelectric nanogenerator (TENG) has been developed for breath sensing applications, utilizing tribopositive electrospun nylon-6 nanofibers and tribonegative fluorinated ethylene propylene (FEP). The optimization toward the development of electrospun nylon-6-based TENG includes a range of factors such as the applied force and frequency on tribo responses, the thickness of the fiber mat, the concentration of nylon-6 in the fiber mats, and the selection of the tribonegative material for pairing with nylon-6 nanofiber. Among these parameters, the nanofiber prepared with 18 wt% nylon-6, characterized by a uniform fiber distribution, the highest surface area of 55.69 m2 g−1, and an optimal thickness of 0.169 mm, demonstrated excellent TENG performance, among others. The TENG module constructed using nanofiber in a 4 cm2 area showed the TENG responses of more than 30 μA short-circuit current, 200 V open-circuit voltage, and 90 nC charge when hand-pressed. It achieved a substantial power density of 890 mW m−2 at 20 MΩ by applying a constant force of 10 N at a 10 Hz frequency. Charging a 1 μF capacitor to approximately 30.1 V in just 30 s highlights the potential of electrospun nylon-6 as a promising material for nanogenerator energy harvesting and sensing applications. The TENG device was found to be sufficient to power small, portable electronics such as LEDs and digital watch displays. A wearable belt was fabricated to showcase its breath-sensing capabilities by pairing it with FEP. The microcontroller connected to the TENG in the wearable belt is used to analyze the output produced through breathing patterns, subsequently activating a buzzer and LED by the nature of the breathing.
Effect of notch angle on creep deformation and rupture behavior of 304HCu SS
Authors: Sahoo Kanhu Charan , Sreevidya N , Sakthivel T , Reddy G V Prasad
Published: February 2024

Multiaxial creep deformation behaviour of U-notched 304HCu austenitic stainless steel (304HCu SS) has been studied by altering the angle of the U-notch, by 30°, 60°, 90°, and 120°, for a fixed root radius of 1.25 mm. The associated stress concentration factor for the U-notch geometry is about 1.8–1.86 with decrease in notch angle. Creep rupture lives of all notched specimens are above the un-notched specimen. However, decrease in rupture life and increase in creep rupture ductility has been observed with an increase in notch angle. At all notch angles, nearly intergranular creep cavitation failure with isolated cavities was observed at the notch center. In contrast, at the notch root, with decrease in notch angle the fracture mode changed from mixed mode to intergranular fracture. Finite element analysis (FEA) of stationary state of stress distribution indicated that von-Mises stress throughout the notch throat plane and maximum principal stress near the notch root region were found to increase with increase in notch angle. However, away from the notch root the maximum principal stress was found to decrease with increase in notch angle. Hydrostatic stress distribution remained same near the notch root at all the notch angles, but tends to increase towards the specimen center with decrease in notch angle. Similarly, at the notch throat plane, triaxiality factor (TF) was found to increase with decrease in notch angle. The creep damage evaluated through FEA coupled with continuum damage mechanics (CDM) proposed by Kachanov-Rabotov (K-R) model was found to increase with an increase in notch angle, resulting in decrease in creep rupture life. Creep damage evaluated as a function of notch depth, during initial creep exposure, revealed significant damage for 1.675 mm notch depth in comparison to 2 and 2.5 mm notch depths which resulted in lower rupture life for 1.675 mm notch depth.
A one-way street for phonon transport: past, present and future of solid-state thermal rectification
Authors: Rurali Riccardo
Published: February 2024

Thermal rectification is the dependence of the thermal conductivity on the direction of heat propagation. This fascinating effect could be exploited for the design of thermal devices, such as the thermal diode, and could find application in energy harvesting and thermal management. Where did we start from, what has been achieved and what does the future hold?