bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement and modeling of strain waves in germanium induced by ultrafast laser pulses
Authors: Aagaard Martin , Julsgaard Brian
Published: April 2024

Transient reflectivity measurements are used to probe the strain waves induced by ultrashort laser pulses in bulk [100] germanium. The measurement signals are compared to purely analytical model functions based on the known material parameters for germanium. The modeling includes (i) a derivation of analytical solutions to the wave equation for strain waves coupled to the diffusion equation for heat and charge carriers and (ii) an expression for the impact on reflection coefficients that are caused by perturbations to the dielectric function but extended to cover a non-isotropic, uniaxial dielectric tensorial form. The model is held up against transient reflectivity measurements with an s- and a p-polarized probe and with a probe wavelength in the range of 502–710 nm. Excellent agreement is found when comparing the oscillatory shape of the measurement signals to the models. As for the magnitude of the oscillations, the models reproduce the overall trends of the experiment when using the previously published values for the elasto-optical tensor measured under static strain.
Evaluating the impact of air terminal geometry on lightning intercept efficacy under a strong background electric field
Authors: Fryar N. , Stephens J. , Mankowski J. , Dickens J. , Hattz D. , Koone N. , Neuber A.
Published: April 2024

A comparative analysis of the attachment efficacy of sharpened vs blunted air terminals under a strong background DC electric field, similar to conditions found in naturally occurring lightning events, is presented. Testing was conducted using an oil-free, 17-stage, 1.4 MV bipolar Marx generator with a biased discharge plane that emulated the conditions found prior to the lightning return stroke. The biased discharge plane allowed the introduction of a strong DC electric field and subsequent corona formation on a time scale much longer than the brief duration over which the downward leader propagates. Initial observations indicate that despite a higher background electric field at the sharpened terminals, leading to pre-discharge corona formation where none is seen on the blunt terminal, both the sharpened and blunted terminals exhibit similar attachment probabilities during discharge events, with some discharge events attaching to both terminals.
Consistent c-axis orientation and reinforced magnetoelectric coupling performance in bulk BaSrCo2Fe11AlO22
Authors: Zhao Dongpeng , Li Jun , Bai Han , Wu Huantong , Chen Xiping , Sun Guangai , Zhou Zhongxiang
Published: April 2024

Consistent c-axis orientation characteristics toward the direction of applied pressure of Y-type BaSrCo2Fe11AlO22 (BSCFAO-θ) were successfully prepared by the strategy of hot pressing. The samples’ magnetoelectric coupling performance was greatly enhanced by the strategy of hot pressing than that of the traditional solid reaction method. The magnetoelectric current of BSCFAO-θ (θ = 0°) (12.06 μA/m2) was nearly 5 times higher than BSCFAO-SS (2.24 μA/m2). The magnetoelectric polarization of BSCFAO-θ (θ = 0°) (32.82 μC/m2) was nearly 4 times higher than that of BSCFAO-SS (8.31 μC/m2). The magnetoelectric coupling coefficients of BSCFAO-θ (θ = 0°) (1880 ps/m) were nearly 4 times higher than those of BSCFAO-SS (404 ps/m). The enhancement of magnetoelectric polarization of BSCFAO-θ (θ = 0°) can be attributed to the uniform c-axis orientation, which reinforced magnetoelectric polarization compared with none orientation that eliminated the magnetoelectric polarization on grain boundaries. The magnetoelectric coupling performance of BSCFAO-θ presented a gradually decreasing trend with the angle changing from 0° to 90° for the changing of orientation. Compared with traditional solid reaction methods, the strategy of hot pressing inhibits grain growth and increases grain boundaries, thus facilitating the enhancement of grain boundaries’ resistivity, and the electrical resistivity of BSCFAO-θ (3.08 × 1010 Ω cm) was nearly 10 000 times higher than that of BSCFAO-SS (2.5 × 106 Ω cm), which also benefits the magnetoelectric polarization performance of BSCFAO-θ. Therefore, the hot-pressing strategy can contribute to the forming of oriented ceramics and enhance the grain boundaries’ resistivity to improve magnetoelectric coupling performance.
Formation and growth of wipe blockages due to a vertical obstruction in sewers: Experimental analysis to policy and management strategies
Authors: Peng Xinzai , Zhu David Z. , Zhang Wenming
Published: April 2024

Improper disposal of wipes results in significant sewer blockages, especially during the COVID-19 pandemic. However, the formation and growth of wipe blockages and their backwater effect in sewers have not been studied. This study employed a vertical rod to simulate sewer obstructions such as tree root intrusion in sewers. Stochastic interactions among wipes, turbulent flow, and the obstruction were experimentally studied in a circular pipe (diameter D = 25 cm), with systematic variations in flow Froude number (Fr), wipe length (L), flow depth (H), submerged rod length (hrod), and rod diameter (drod). It was found that the mean area ratio of wipes (ratio of projected area in water to original surface area of the wipe) ranged from 0.14 to 0.30, indicating the distorted shapes in water. The entrapment probability P (ratio of entrapped to released wipes) for a single wipe was closely correlated with Fr, H/D, L/H, drod/H, and hrod/H, with a maximum value of 0.90. With the increase in the number of wipes released, the influence of the obstruction on wipe accumulation processes became negligible. New equations were developed for characterizing entrapment probability, blockage length, and backwater rise, which can be used to predict the development of wipe blockages and sewage levels. Based on the research findings, policy and management strategies were proposed for wipe blockage reduction in sewers.
Electron mobility of SnO2 from first principles
Authors: Wang Amanda , Bushick Kyle , Pant Nick , Lee Woncheol , Zhang Xiao , Leveillee Joshua , Giustino Feliciano , Poncé Samuel , Kioupakis Emmanouil
Published: April 2024

The transparent conducting oxide SnO2 is a wide bandgap semiconductor that is easily n-type doped and widely used in various electronic and optoelectronic applications. Experimental reports of the electron mobility of this material vary widely depending on the growth conditions and doping concentrations. In this work, we calculate the electron mobility of SnO2 from first principles to examine the temperature and doping concentration dependence and to elucidate the scattering mechanisms that limit transport. We include both electron–phonon scattering and electron-ionized impurity scattering to accurately model scattering in a doped semiconductor. We find a strongly anisotropic mobility that favors transport in the direction parallel to the c-axis. At room temperature and intrinsic carrier concentrations, the low-energy polar-optical phonon modes dominate scattering, while ionized-impurity scattering dominates above 1018 cm−3.
Migration trajectories and blocking effect of the fine particles in porous media based on particle flow simulation
Authors: Bai Bing , Chen Jing , Zhang Bixia , Wang Hao
Published: April 2024

The particle flow code method based on the discrete element method was used to establish the seepage migration model of fine particles [fine particles (FPs), i.e., suspended particles] in a porous medium. A series of numerical simulations were carried out by changing the particle size, seepage velocity, particle injection number, and wide particle size gradation. The research showed that large FPs play a major role in blocking porous medium channels when the injected FPs have a wide size gradation. Due to the blocking effect, small FPs that would not otherwise have deposited also deposit. Moreover, by increasing the number of large FPs in the mixed particles, the total number of particles deposited and the number of smaller FPs deposited will also increase. The distribution of FPs in porous mediums can be divided into three types: surface deposition, internal deposition, and non-deposition. When the seepage velocity increases and reaches a seepage threshold, which is the critical seepage velocity, the deposited FPs will once again be in a suspended state and undergo migration. On the contrary, the FPs will continue to maintain their sedimentary state, and the critical seepage velocity will also increase correspondingly with increasing particle size.
Optimizing blood glucose regulation in type 1 diabetes: A fractional order controller approach
Authors: Shenbagam Manikandan , Kanagaraj Ganesan , Giri Jayant , Yu Vincent F. , Qin Hong , Mallik Saurav
Published: April 2024

This study presents the design and implementation of a Fractional Order Proportional, Integral, and Derivative (FOPID) controller intended for the regulation of blood glucose levels in individuals with type 1 diabetes mellitus (T1DM). The efficacy of this controller is evaluated through its application to a nonlinear Stolwijk–Hardy model simulating T1DM patients, accounting for a range of physiological conditions. Utilizing a genetic algorithm, the parameters of the FOPID controller are fine-tuned. By conducting a comparative analysis with previously established control algorithms, the performance of the proposed controller is validated, demonstrating its superior performance. The results underscore the significant improvements achieved by the proposed controller in maintaining blood glucose concentrations within safe thresholds, particularly in scenarios involving disruptions due to meals.
Planarization of p-GaN surfaces on MOCVD grown V-defect engineered GaN-based LEDs
Authors: Tak Tanay , Quevedo Alejandro , Wu Feng , Gandrothula Srinivas , Ewing Jacob J. , Gee Stephen , Nakamura Shuji , DenBaars Steven P. , Speck James S.
Published: April 2024

The large polarization barriers between the quantum wells and quantum barriers in long-wavelength GaN-based light-emitting diodes (LEDs) inhibit their performance by requiring excess driving voltages to reach standard operating current densities. Lateral injection of carriers directly into quantum wells is required to circumvent this issue. V-defects are naturally occurring inverted hexagonal defects with semipolar 101¯1-plane sidewalls generated on surface depressions from threading dislocations. LEDs engineered to intentionally generate V-defects below the active region of the LED can achieve lateral carrier injection through the V-defect sidewalls and have already been able to demonstrate world record wall-plug efficiencies for LEDs in the green-red wavelengths. V-defects can be enlarged during kinetically limited growth where the growth rate of the c-plane GaN is faster than that of their sidewalls, leaving them unfilled. We report on the metal organic chemical vapor deposition growth conditions required to fill in V-defects with p-GaN during epitaxial growth of the LED post the active region. Circular transmission length measurements of Pd/Au contacts processed on p-GaN surfaces with various amounts of unfilled V-defects showed no significant difference in their sheet resistance and specific contact resistance. J–V measurements of LEDs grown with varying unfilled V-defect densities showed no significant difference in the forward bias regime. However, in the reverse bias regime, catastrophic breakdown occurred at markedly lower voltages for samples with larger unfilled V-defect densities. This suggests that unfilled V-defects may act as hotspots for device failure, and planarizing LED surfaces may help prevent early degradation of LED devices.
Hot carrier relaxation dynamics of an aza-covalent organic framework during photoexcitation: An insight from ab initio quantum dynamics
Authors: Ghosh Atish , Das Priya , Kumar Subhash , Sarkar Pranab
Published: April 2024

In order to develop an efficient metal-free solar energy harvester, we herein performed the electronic structure calculation, followed by the hot carrier relaxation dynamics of two dimensional (2D) aza-covalent organic framework by time domain density functional calculations in conjunction with non-adiabatic molecular dynamics (NAMD) simulation. The electronic structure calculation shows that the aza-covalent organic framework (COF) is a direct bandgap semiconductor with acute charge separation and effective optical absorption in the UV-visible region. Our study of non-adiabatic molecular dynamics simulation predicts the sufficiently prolonged electron–hole recombination process (6.8 nanoseconds) and the comparatively faster electron (22.48 ps) and hole relaxation (0.51 ps) dynamics in this two-dimensional aza-COF. According to our theoretical analysis, strong electron–phonon coupling is responsible for the rapid charge relaxation, whereas the electron–hole recombination process is slowed down by relatively weak electron–phonon coupling, relatively lower non-adiabatic coupling, and quick decoherence time. We do hope that our results of NAMD simulation on exciton relaxation dynamics will be helpful for designing photovoltaic devices based on this two dimensional aza-COF.
Large-cage occupation and quantum dynamics of hydrogen molecules in sII clathrate hydrates
Authors: Ranieri Umbertoluca , del Rosso Leonardo , Bove Livia Eleonora , Celli Milva , Colognesi Daniele , Gaal Richard , Hansen Thomas C. , Koza Michael Marek , Ulivi Lorenzo
Published: April 2024

Hydrogen clathrate hydrates are ice-like crystalline substances in which hydrogen molecules are trapped inside polyhedral cages formed by the water molecules. Small cages can host only a single H2 molecule, while each large cage can be occupied by up to four H2 molecules. Here, we present a neutron scattering study on the structure of the sII hydrogen clathrate hydrate and on the low-temperature dynamics of the hydrogen molecules trapped in its large cages, as a function of the gas content in the samples. We observe spectral features at low energy transfer (between 1 and 3 meV), and we show that they can be successfully assigned to the rattling motion of a single hydrogen molecule occupying a large water cage. These inelastic bands remarkably lose their intensity with increasing the hydrogen filling, consistently with the fact that the probability of single occupation (as opposed to multiple occupation) increases as the hydrogen content in the sample gets lower. The spectral intensity of the H2 rattling bands is studied as a function of the momentum transfer for partially emptied samples and compared with three distinct quantum models for a single H2 molecule in a large cage: (i) the exact solution of the Schrödinger equation for a well-assessed semiempirical force field, (ii) a particle trapped in a rigid sphere, and (iii) an isotropic three-dimensional harmonic oscillator. The first model provides good agreement between calculations and experimental data, while the last two only reproduce their qualitative trend. Finally, the radial wavefunctions of the three aforementioned models, as well as their potential surfaces, are presented and discussed.
Fluorite-structured high-entropy oxide sputtered thin films from bixbyite target
Authors: Kotsonis George N. , Almishal Saeed S. I. , Miao Leixin , Caucci Mary Kathleen , Bejger Gerald R. , Ayyagari Sai Venkata Gayathri , Valentine Tyler W. , Yang Billy E. , Sinnott Susan B. , Rost Christina M. , Alem Nasim , Maria Jon-Paul
Published: April 2024

The prototype high-entropy oxide (HEO) Y0.2La0.2Ce0.2Pr0.2Sm0.2O2−δ represents a particularly complex class of HEOs with significant anion sublattice entropy. The system takes either a fluorite or bixbyite-type crystal structure, depending on synthesis kinetics and thermal history. Here, we synthesize bulk ceramics and epitaxial thin films of Y0.2La0.2Ce0.2Pr0.2Sm0.2O2−δ and use diffraction to explore crystal symmetry and phase. Thin films exhibit the high symmetry fluorite phase, while bulk ceramics adopt the lower symmetry bixbyite phase. The difference in chemical ordering and observed symmetry between vapor-deposited and reactively sintered specimens suggests that synthesis kinetics can influence accessible local atomic configurations, i.e., the high kinetic energy adatoms quench in a higher-effective temperature, and thus higher symmetry structure with more configurational entropy. More generally, this demonstration shows that recovered HEO specimens can exhibit appreciably different local configurations depending on synthesis kinetics, with potential ramifications on macroscopic physical properties.
Impulse coupling measurement of metallic and carbon targets during laser ablation through ballistic pendulum experiments and simulations
Authors: Le Bras C. , Berthe L. , Videau L. , Baton S. , Boustie M. , Boyer S. , Rousseaux C. , Brambrink E. , Chevalier J.-M. , Houy J. , Aubert B. , Jodar B. , Loison D. , Hébert D.
Published: April 2024

Laser ablation propulsion and orbit cleaning are developing areas of research. The general aim of laser-based techniques applied to this field is to maximize the momentum transfer produced by a laser shot. This work presents results from ballistic pendulum experiments under vacuum on aluminum, copper, tin, gold, and porous graphite targets. The work has focused on the metrology of the laser experiments to ensure good stability over a wide range of laser parameters (laser intensity ranging from 4 GW/cm2 to 8.7 TW/cm2, pulse duration from 80 ps to 15 ns, and wavelengths of 528 or 1057 nm). The results presented compile data from three experimental campaigns spanning from 2018 to 2021 on two different laser platforms and using different pulse durations, energies, and wavelengths. The study is complemented by the simulation of the momentum from the mono-dimensional Lagrangian code ESTHER. The first part of this work gives a detailed description of the experimental setup used, the ESTHER code, and the treatment of the simulations. The second part focuses on the experimental results. The third part describes the simulation results and provides a comparison with the experimental data. The last part presents possible improvements for future work on the subject.
Rapid subsurface analysis of frequency-domain thermoreflectance images with K-means clustering
Authors: Jarzembski Amun , Piontkowski Zachary T. , Hodges Wyatt , Bahr Matthew , McDonald Anthony , Delmas William , Pickrell Greg W. , Yates Luke
Published: April 2024

K-means clustering analysis is applied to frequency-domain thermoreflectance (FDTR) hyperspectral image data to rapidly screen the spatial distribution of thermophysical properties at material interfaces. Performing FDTR while raster scanning a sample consisting of 8.6 μm of doped-silicon (Si) bonded to a doped-Si substrate identifies spatial variation in the subsurface bond quality. Routine thermal analysis at select pixels quantifies this variation in bond quality and allows assignment of bonded, partially bonded, and unbonded regions. Performing this same routine thermal analysis across the entire map, however, becomes too computationally demanding for rapid screening of bond quality. To address this, K-means clustering was used to reduce the dimensionality of the dataset from more than 20 000 pixel spectra to just K=3 component spectra. The three component spectra were then used to express every pixel in the image through a least-squares minimized linear combination providing continuous interpolation between the components across spatially varying features, e.g., bonded to unbonded transition regions. Fitting the component spectra to the thermal model, thermal properties for each K cluster are extracted and then distributed according to the weighting established by the regressed linear combination. Thermophysical property maps are then constructed and capture significant variation in bond quality over 25 μm length scales. The use of K-means clustering to achieve these thermal property maps results in a 74-fold speed improvement over explicit fitting of every pixel.
Deposition of Ca on the 2H–NbSe2 surface: Competing processes
Authors: Starnberg H. I.
Published: April 2024

The interaction of Ca evaporated in vacuum onto a 2H–NbSe2 surface held at room temperature was studied by photoelectron spectroscopy. Indications of an intercalation reaction were observed initially, but larger Ca depositions resulted in a layer-breaking reaction producing a disordered overlayer of varying compositions. The layer-breaking reaction is likely due to the intercalation compound becoming unstable as the local Ca concentration exceeds the threshold value. Continued Ca depositions eventually resulted in the growth of three-dimensional islands of Ca metal, exposing relatively unaffected NbSe2 layers between the Ca islands.
Melting evolution of phase change material in square cavity by lattice Boltzmann method
Authors: Lu Yu , Zheng Lin
Published: April 2024

Most numerical simulations for solid–liquid phase change problems are based on the melting point of phase change materials (PCMs) as the initial condition, while research with an initial temperature below the melting point is relatively scarce. In this paper, an enthalpy-based thermal lattice Boltzmann method is employed to investigate the solid–liquid melting process in a square cavity, and various factors including ambient temperature (θa= 0.0, 0.1, and 0.2), saturation temperature (θs = 0.0–0.9), Rayleigh number (Ra = 103, 104, and 105), Stefan number (Ste= 0.025, 0.05, and 0.1), and Prandtl number (Pr= 0.025, 0.05, and 0.1) of the PCMs are systematically examined for their effects on the phase change process at saturated and unsaturated conditions. The simulation results indicate that, first, increasing the ambient temperature or decreasing the saturation temperature results in an accelerated melting rate. Moreover, when the system approaches the saturated condition, achieving complete melting becomes easier. Second, an increase in the Rayleigh number has a dual effect: it enhances convective heat transfer and simultaneously accelerates the melting rate. This effect is particularly pronounced under saturated conditions. Similarly, the Stefan number plays a crucial role in promoting the melting rate, although its impact on convective intensity is minimal. Finally, increasing the Prandtl number not only intensifies convective heat transfer and accelerates the melting rate but also reduces convective disturbances.
Electronic structures of skyrmionic polycrystalline MnSi thin film studied by resonance photoemission and x-ray near edge spectroscopy
Authors: Jena S. , Urkude R. , Choi W.-Y. , Pandey K. K. , Karwal S. , Jung M. H. , Gardner J. , Ghosh B. , Singh V. R.
Published: April 2024

Magnetic nanometric skyrmions are small complex vortex-like topological defects, mainly found in non-centrosymmetric crystals such as MnSi. They have potential applications for future spintronic devices. In this article, the structural, electronic, and magnetic states of the Mn atoms in a polycrystalline MnSi thin film facing a c-sapphire substrate were studied using x-ray diffraction, x-ray photo-emission spectroscopy, resonance photoemission spectroscopy (RPES), and extended x-ray absorption fine structure (EXAFS). The valence band spectra indicate the metallic nature of the film. The RPES study reveals the presence of major itinerant Mn 3d states near EF and also the mixed Mn 3d and Si 3s–3p states from 5.3 to 11.3 eV. The EXAFS spectrum does not show the existence of oxygen vacancies in the system, and the obtained magnetic moment in the non-stoichiometric MnSi thin film is a combination of the partially itinerant and partially localized Mn 3d states.
Theory construction and computation for polymer film melt stretching by modified Leonov model
Authors: Ma Ruixue , Cao Wei , Zhang Shixun , Wang Zhen , Chang Baobao , Lu Bo , Shen Changyu
Published: April 2024

Polymer film melt stretching exhibits a unique stress–strain behavior, featuring a stress plateau followed by a sudden increase with increasing the strain. This phenomenon poses a challenge to conventional melt-extension theories and methods. To address this, we derive a simplified flow theory according to the symmetric characteristics of thin melt-stretching, and propose a modified multi-mode Leonov model (m-Leonov) that accounts for molecular orientation effects, a crucial factor in accurately simulating the process. In order to improve the computational efficiency, an iterative algorithm was developed to decouple the interdependence between governing and constitutive equations. The computational results reveal that the viscoelastic nature of the film contributes to a delay in the transformation of stretching forces, leading to the observed stress plateau. Significantly, our m-Leonov model successfully predicts both the plateau and the subsequent abrupt increase in stress, across various temperatures and stretching rates. These simulations closely agree with experimental data, underlining the robustness of our approach. Our findings would enhance the understanding of rheological complexities in film stretching, offering potential applications in various materials and polymer processing.
Ternary recombination of excited Ar+(P1/22) ions, established experimental results reinterpreted with a new extended model
Authors: Nongni F. T. , Kalus R. , Benhenni M. , Gadéa F. X. , Yousfi M.
Published: April 2024

For many years, the recombination of excited ions of argon, Ar+(P1/22), has been assumed negligible under ambient conditions as compared to the recombination of ground-state ions, Ar+(P3/22). This opinion was confronted with detailed experimental results that seem to clearly support it. Here, we propose a new interpretation in light of our recent calculations, which shows that the recombination efficiency is comparable for both fine-structure states. Noteworthily, in our model leading to a picture consistent with the experiment, residual dimer ions emerge from Ar+(P1/22) due to non-adiabatic dynamics effects and interplay in measured data.
An accurate and efficient deep learning model for spatio-temporal prediction of interfacial flows
Authors: Deng Yangyu , Zhang Di , Cao Ze , Liu Yakun
Published: April 2024

Aiming at fast and accurate spatiotemporal prediction of interfacial flow fields, a novel deep learning model combining Convolutional AutoEncoder (CAE) and long short-term memory with spatial and temporal attention (LSTM-STA) is proposed and named as CAE-LSTM-STA (hybrid model of CAE and LSTM-STA) in this article. To enable a fast calculation process, CAE is first utilized to compress the high-dimensional snapshots of flow fields into the low-dimensional latent space by its encoder. Then, the latent space serves as the input feature for LSTM-STA to temporally evolve the state of the low-dimensional latent space. Finally, the low-dimensional latent space at future time steps is fed back into the decoder of CAE to derive the full-order snapshots of the flow fields. The prediction performance of the proposed model is evaluated via two representative benchmark cases, including the dam break case and the rising bubble case. The capability of CAE in dimension reduction is found to be much better than that of the widely used Proper Orthogonal Decomposition, while LSTM-STA is observed that outperforms the original LSTM in multivariant temporal prediction. These promising results indicate that the proposed CAE-LSTM-STA model is able to effectively capture and advance the spatiotemporal characteristics of the interfacial flow fields, therefore making it an advanced surrogate model for fast and precise generation of the temporally continuous interfacial flow fields.
A hydrodynamic model of capillary flow in an axially symmetric tube with a non-slowly-varying cross section and a boundary slip
Authors: Iwamatsu Masao
Published: April 2024

The capillary flow of a Newtonian and incompressible fluid in an axially symmetric horizontal tube with a non-slowly-varying cross section and a boundary slip is considered theoretically under the assumption that the Reynolds number is small enough for the Stokes approximation to be valid. Combining the Stokes equation with the hydrodynamic model assuming the Hagen–Poiseulle flow, a general formula for the capillary flow in a non-slowly-varying tube is derived. Using the newly derived formula, the capillary imbibition and the time evolution of meniscus in tubes with non-uniform cross sections such as a conical tube, a power-law-shaped diverging tube, and a power-law-shaped converging tube are reconsidered. The perturbation parameters and the corrections due to the non-slowly-varying effects are elucidated, and the new scaling formulas for the time evolution of the meniscus of these specific examples are derived. Our study could be useful for understanding various natural fluidic systems and for designing functional fluidic devices such as a diode and a switch.
Solar energy broadband capturing by metamaterial absorber based on titanium metal
Authors: Zhu Xiaoqing , Wang Bo
Published: April 2024

In recent years, the exploration of solar absorbers has grown in favor due to the scarcity of energy. Here, we propose an absorber with an array of a circular ring surrounding disk (RSD) for solar energy capture. The novel structure keeps above 93.5% absorption with an average absorption of 96.95% in wavelengths from 300 to 4000 nm. Meanwhile, the proposed absorber is advantageous in that the structure is generalizable to other metals and dielectric materials. Furthermore, the data results show that the absorber has polarization-independent properties as well as maintaining >90% absorption in the considered wavelength range up to an incidence angle of 52° and >95% absorption at large process tolerances. Finally, the excellent absorption under the AM1.5 solar spectrum demonstrates the RSD absorber’s ability to capture solar energy. These results show the potential of the absorber for applications in electromagnetic invisibility cloaking, thermal emitters, and solar energy capture and conversion.
Multiscale simulations of viscoelastic fluids in complex geometries using a finitely extensible nonlinear elastic transient network model
Authors: Gómez-López A. , Vargas R. O. , Mil-Martínez A. , Phillips T. N.
Published: April 2024

This paper presents a novel implementation of a numerical scheme for predicting complex flows of viscoelastic fluids using a finitely extensible nonlinear elastic (FENE) transient network model. This model extends the FENE model by incorporating chain interactions and accounting for the way in which the maximum chain length, drag, and relaxation time are influenced by entanglement and disentanglement processes. Three different initial networks are considered (disentanglement, entanglement, and aleatory), and the influence of variables such as the kinetic rate constants, elasticity, and chain length on the microstate concentration, stresses, and drag force is investigated. It is shown that although the concentrations of the microstates are independent of the Weissenberg number and the maximum extension length, the stresses and hence the drag are influenced by them.
A turbulence model: Model, analysis, and algorithm
Authors: Zhang Yuanshuang , Huang Pengzhan
Published: April 2024

The standard eddy viscosity model is commonly used to simulate turbulence, but there exist difficulties in simulating the backscatter of the non-statistical equilibrium turbulence. In this work, we construct a novel modified eddy viscosity model based on a simplified Cebeci–Smith equation, which is applied to the non-equilibrium turbulence. Moreover, we analyze some properties of the model and propose a fully discrete scheme, which is proven to be stable and convergent. Finally, some numerical examples are presented to test the theoretical prediction of the proposed scheme, and intermittent backscatter is captured and observed by simulating the established model.
The bond energy of UN+: Guided ion beam studies of the reactions of U+ with N2 and NO
Authors: Bubas Amanda R. , Kafle Arjun , Stevenson Brandon C. , Armentrout P. B.
Published: April 2024

A guided ion beam tandem mass spectrometer was used to study the reactions of U+ with N2 and NO. Reaction cross sections were measured over a wide range of energy for both systems. In each reaction, UN+ is formed by an endothermic process, thereby enabling the direct measurement of the threshold energy and determination of the UN+ bond dissociation energy. For the reaction of U+ + N2, a threshold energy (E0) of 4.02 ± 0.11 eV was measured, leading to D0 (UN+) = 5.73 ± 0.11 eV. The reaction of U+ + NO yields UO+ through an exothermic, barrierless process that proceeds with 94 ± 23% efficiency at the lowest energy. Analysis of the endothermic UN+ cross section in this reaction provides E0 = 0.72 ± 0.11 eV and, therefore, D0 (UN+) = 5.78 ± 0.11 eV. Averaging the values obtained from both reactions, we report D0 (UN+) = 5.76 ± 0.13 eV as our best value (uncertainty of two standard deviations). Combined with precise literature values for the ionization energies of U and UN, we also derive D0 (UN) = 5.86 ± 0.13 eV. Both bond dissociation energies agree well with high-level theoretical treatments in the literature. The formation of UN+ in reaction of U+ with NO also exhibits a considerable increase in reaction probability above ∼3 eV. Theory suggests that this may be consistent with the formation of UN+ in excited quintet spin states, which we hypothesize are dynamically favored because the number of 5f electrons in reactants and products is conserved.
On-the-fly machine learned force fields for the study of warm dense matter: Application to diffusion and viscosity of CH
Authors: Kumar Shashikant , Jing Xin , Pask John E. , Suryanarayana Phanish
Published: April 2024

We develop a framework for on-the-fly machine learned force field (MLFF) molecular dynamics (MD) simulations of warm dense matter (WDM). In particular, we employ an MLFF scheme based on the kernel method and Bayesian linear regression, with the training data generated from the Kohn–Sham density functional theory (DFT) using the Gauss spectral quadrature method, within which we calculate energies, atomic forces, and stresses. We verify the accuracy of the formalism by comparing the predicted properties of warm dense carbon with recent Kohn–Sham DFT results in the literature. In so doing, we demonstrate that ab initio MD simulations of WDM can be accelerated by up to three orders of magnitude, while retaining ab initio accuracy. We apply this framework to calculate the diffusion coefficients and shear viscosity of CH at a density of 1 g/cm3 and temperatures in the range of 75 000–750 000 K. We find that the self- and inter-diffusion coefficients and the viscosity obey a power law with temperature, and that the diffusion coefficient results suggest a weak coupling between C and H in CH. In addition, we find agreement within standard deviation with previous results for C and CH but disagreement for H, demonstrating the need for ab initio calculations as presented here.
Magnetization switching by electric field in ZnFe2O4/ZnO heterostructure
Authors: Guchhait Suman , Aireddy H. , Singh Sudarshan , Chakraborty Sayan , Kander Niladri Sekhar , Das A. K.
Published: April 2024

We have fabricated the ZnFe2O4/ZnO (ZFO/ZnO) heterostructure on a silicon substrate by pulsed laser deposition technique and studied the magnetization switching by the electric field in the ZFO/ZnO heterostructure using an indigenously developed optical cantilever beam magnetometer setup. The magnetization (M) vs electric field (E) curve reveals that the magnetization of the ZFO film has been switched by an electric field applied along the thickness of the ZnO film. The saturation magnetization is found to be 28.77 MA/m from the M–E curve. The emergence of electric field-driven magnetization switching in the ZFO/ZnO heterostructure is attributed to the strain-mediated magnetoelectric coupling between the electric polarization of the ZnO film and the magnetization of the ZFO film as evidenced by the butterfly-type hysteresis behavior of magnetization with the applied electric field. However, the realization of electric field-controlled magnetization switching in the ZFO/ZnO heterostructure is regarded as a potential aspect for the fabrication of energy-efficient spintronic devices such as magnetoelectric random access memory cells, highly sensitive magnetic field sensors, magneto-logic devices, and neuromorphic devices.
Very-large-scale motions in open-channel flow: Insights from velocity spectra, correlations, and structure functions
Authors: Zampiron A. , Cerino B. , Berni C. , Proust S. , Nikora V.
Published: April 2024

We employ spectral-space and real-space quantities to characterize large-scale motions (LSMs) and very-large-scale motions (VLSMs) in open-channel flows (OCFs). The obtained data on velocity auto- and co-spectra, spectral correlation coefficient, and structure functions of the second and third orders are consistent with the hypothesis that VLSMs are a special type of coherent structure rather than an alignment of LSMs, even if active interactions between LSMs and VLSMs most likely take place. The Letter is concluded with a conceptual velocity spectrum for OCFs and an explanation of the mechanism of VLSMs' contribution to the Reynolds shear stress.
Controlling spatiotemporal dynamics of neural networks by Lévy noise
Authors: Rybalova E. , Nikishina N. , Strelkova G.
Published: April 2024

We explore numerically how additive Lévy noise influences the spatiotemporal dynamics of a neural network of nonlocally coupled FitzHugh–Nagumo oscillators. Without noise, the network can exhibit various partial or cluster synchronization patterns, such as chimera and solitary states, which can also coexist in the network for certain values of the control parameters. Our studies show that these structures demonstrate different responses to additive Lévy noise and, thus, the dynamics of the neural network can be effectively controlled by varying the scale parameter and the stability index of Lévy noise. Specifically, introducing Lévy noise in the multistability mode can increase the probability of observing chimera states while suppressing solitary states. Nonetheless, decreasing the stability parameter enables one to diminish the noise effect on chimera states and amplify it on solitary states.
Inhibition performances of lithium-ion battery pack fires by fine water mist in an energy-storage cabin: A simulation study
Authors: Lou Zhen , Huang Junqi , Wang Min , Zhang Yang , Lv Kefeng , Yao Haowei
Published: April 2024

Fire incidents in energy storage stations are frequent, posing significant firefighting safety risks. To simulate the fire characteristics and inhibition performances by fine water mist for lithium-ion battery packs in an energy-storage cabin, the PyroSim software is used to build a 1:1 experimental geometry model of a containerized lithium-ion energy storage cabin. The simulation reveals five stages and their characteristic parameter variations during a fire incident: initial temperature rise, flame generation, flame spread, stable combustion, and flame extinguishment. By adjusting various parameters of the fine water mist, the design of the fine water mist firefighting system for containerized energy storage units is optimized. The simulation results indicate that the optimal inhibition effect for the energy storage cabin's fine water mist firefighting system is achieved when the spray intensity is ≥24 l/min, the fog cone angle is 76°, nozzle velocity is 10 m/s, and the optimal particle size of the fine water mist is 50 μm. The research findings not only provide a rational method and theoretical guidance for the numerical simulation of thermal runaway in lithium batteries but also offer theoretical data support for the safety design and protection of future energy storage cabins.
First-principles and experimental study to investigate structural, elastic, electronic, thermal, and optical properties of KCdCl3 metal halide perovskite crystals
Authors: Sorker Md. Sunjid , Islam Md. Raihan , Chakraborty Arpon , Razzak Sarker Md. Abdur
Published: April 2024

In this research, we examine the structural, elastic, anisotropic, acoustic, electronic, thermo-physical, and optical properties of KCdCl3 using both the density functional theory method as well as experimental data characterizations. The x-ray diffraction and Fourier transform infrared spectroscopy showed that our synthesized sample was well crystalline (orthorhombic), and the values of the lattice parameters are closely matched those of the first principles study. The scanning electron microscopy measurements of our sample morphology and microstructure showed a high grain size. The elastic property indicates that the structure is both mechanically and dynamically stable. The band structures and the density of state computation assured the semiconducting nature of our sample. Mulliken atomic populations showed ionic and covalent bonding in these materials, which can also be said to be mechanical property. The negative value of Cauchy’s pressure indicates the presence of angular bonding in the structure. In addition, the structure has high machinability. The phase transitions and thermal breakdown of KCdCl3 were examined by thermo-gravimetric analysis, and we found weight loss occurs in three stages. UV–visible spectrophotometers assessed the optical absorption and transmittance, which suggests that KCdCl3 is a strong UV absorber that gradually rises with wavelength. While the elastic and mechanical characteristics are anisotropic, the optical parameters are almost isotropic. The high UV reflectivity (∼28.5%) shows the material may not be an efficient radiation reflector but has great photovoltaic and optoelectronics potential.
Cooperatively tuning magnetic anisotropy and colossal magnetoresistance via atomic-scale buffer layers in highly strained La0.7Sr0.3MnO3 films
Authors: Li Sheng , Lu Zengxing , Lao Bin , Zheng Xuan , Chen Guoxin , Li Run-Wei , Wang Zhiming
Published: April 2024

Achieving simultaneous control over multiple functional properties, such as magnetic anisotropy, magnetoresistance, and metal-insulator transition, with atomic precision remains a major challenge for realizing advanced spintronic functionalities. Here, we demonstrate a unique approach to cooperatively tune these multiple functional properties in highly strained La0.7Sr0.3MnO3 (LSMO) thin films. By inserting varying perovskite buffer layers, compressively strained LSMO films transition from a ferromagnetic insulator with out-of-plane magnetic anisotropy to a metallic state with in-plane anisotropy. Remarkably, atomic-scale control of the buffer layer thickness enables precise tuning of this magnetic and electronic phase transformation. We achieve a colossal magnetoresistance tuning of 10,000% and an exceptionally sharp transition from out-of-plane to in-plane magnetic anisotropy within just a few atomic layers. These results demonstrate an unprecedented level of control over multiple functional properties, paving the way for the rational design of multifunctional oxide spintronic devices.
Predictions of thorium super nitrides and superconductivity under pressure: Ab initio calculations
Authors: Sahoo B. D. , Joshi K. D.
Published: April 2024

Thorium nitrides have been the topic of intense studies due to their prospective applications as advanced nuclear fuels. The phase diagram of the Th–N scheme, however, continues unknown at low temperatures and extremely high pressures. In this article, we examine the Th–N system's phase diagram up to 300 GPa from the first-principle approach using universal structure predictor: evolutionary Xtallography (USPEX) method. Apart from the experimentally observed phase (ThN, Th2N3, and Th3N4), there are several unique chemical stoichiometries, i.e., ThN3, ThN4, ThN6, ThN8, ThN10, and ThN12 are found to have stability fields on the Th–N phase diagram at pressure of 3.0, 32, 100, 42, 28, and 236 GPa along with previously predicted composition ThN2 at 3.5 GPa. The structural stability of the predicted compositions is further assessed by evaluating the elastic and dynamic stability. Out of all above mentioned compositions, ThN3 is possibly a metastable one at 0 GPa. Electronic structure calculations predict that all newly discovered compositions are metallic except ThN10, which is semi-metallic at high pressures. Further, we predict that ThN4 and ThN6 have high electron–phonon coupling constant of 1.874 and 0.894 with Tc around 21.22 and 25.02 K, respectively, at 100 GPa.
A deep-learning-based compact method for accelerating the electrowetting lattice Boltzmann simulations
Authors: Zhuang Zijian , Xu Qin , Zeng Hanxian , Pan Yongcai , Wen Binghai
Published: April 2024

Research on the electrowetting of micro- and nanoscale droplets is essential for microfluidics and nanomaterials applications. A lattice-Boltzmann-electrostatics (LBES) method is an effective and accurate method for simulating this process. However, the electric potential field in each time step requires numerous iterative calculations to converge. Therefore, there is a trade-off dilemma between using high-density lattice fields to improve simulation refinement and low-density lattice fields to reduce computing costs in simulations. Fortunately, deep learning techniques can enhance the computing efficiency of electric potential fields, providing an efficient and accurate solution for electrowetting studies in fine-grained fields. In this study, a compact LBES (C-LBES), a computationally accelerated model for an electric potential field with spatiotemporal prediction capability, is developed by combining the advantages of a recurrent residual convolutional unit and a convolutional long-short-term memory unit. A loss function incorporating a geometric boundary constraint term and a self-cyclic prediction scheme are introduced according to the characteristics of the prediction task, which further improves the prediction accuracy of the model and the computing efficiency of the electric potential field. The model is validated with small datasets, and the results show that the C-LBES model with the self-cyclic prediction scheme improves the computing efficiency of the conventional LBES method by a factor of 10 and provides high-precision results when predicting a two-dimensional convergent electric potential field with a lattice size of (110, 160). In the generalization experiments, the average absolute error of the calculated results remains in the same order of magnitude as the accuracy experimental results.