bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular dynamics study of thermal transport at interface between alumina and epoxy resin
Authors: Umeno Yoshitaka , Kubo Atsushi , Kurata Yuto , Sakaniwa Daisuke , Ishikawa Fumiaki N. , Yamaguchi Kenji
Published: February 2024

The study investigates heat transfer within a composite consisting of epoxy resin and alumina filler using all-atom molecular dynamics simulations. Various models of epoxy resin–alumina filler interfaces were analyzed, both with and without silane coupling agents (SCAs), to assess thermal conductivity and resistance. The results reveal that the presence of SCAs enhances heat transfer at the resin/filler interface. Conversely, models lacking SCAs exhibit a distinct temperature gap, indicating thermal resistance. In addition, the study suggests that effective heat transfer in polymer composites is influenced not only by molecular coupling at interfaces but also by the alignment of resin polymers.
Pressure dependent structure of amorphous magnesium aluminosilicates: The effect of replacing magnesia by alumina at the enstatite composition
Authors: Mohammadi Hesameddin , Zeidler Anita , Youngman Randall E. , Fischer Henry E. , Salmon Philip S.
Published: February 2024

The effect of replacing magnesia by alumina on the pressure-dependent structure of amorphous enstatite was investigated by applying in situ high-pressure neutron diffraction with magnesium isotope substitution to glassy (MgO)0.375(Al2O3)0.125(SiO2)0.5. The replacement leads to a factor of 2.4 increase in the rate-of-change of the Mg–O coordination number with pressure, which increases from 4.76(4) at ambient pressure to 6.51(4) at 8.2 GPa, and accompanies a larger probability of magnesium finding bridging oxygen atoms as nearest-neighbors. The Al–O coordination number increases from 4.17(7) to 5.24(8) over the same pressure interval at a rate that increases when the pressure is above ∼3.5 GPa. On recovering the glass to ambient conditions, the Mg–O and Al–O coordination numbers reduce to 5.32(4) and 4.42(6), respectively. The Al–O value is in accordance with the results from solid-state 27Al nuclear magnetic resonance spectroscopy, which show the presence of six-coordinated aluminum species that are absent in the uncompressed material. These findings explain the appearance of distinct pressure-dependent structural transformation regimes in the preparation of permanently densified magnesium aluminosilicate glasses. They also indicate an anomalous minimum in the pressure dependence of the bulk modulus with an onset that suggests a pressure-dependent threshold for transitioning between scratch-resistant and crack-resistant material properties.
Reconfigurable spin wave modes in a Heusler magnonic crystal
Authors: Mantion S. , Torres Dias A. , Madami M. , Tacchi S. , Biziere N.
Published: February 2024

We report on the field evolution of the microwave spin wave modes in magnonic crystals made of square antidot lattices etched in a thin film of the Co2MnSi Heusler alloy and having a lateral size s of 200 nm and an edge-to-edge separation d of 600 or 800 nm. The spin wave modes are investigated combining ferromagnetic resonance, Brillouin light scattering experiments, and micromagnetic simulations of the static and dynamic magnetic states as a function of the applied field. We show that for applied fields ≥10 mT, when the magnetization is quasi-saturated across the crystals, the two samples show similar behavior and the two most intense modes in the spin waves spectra correspond to a mode extending in the channels comprised between the antidot and a mode localized in the region between the antidots. For smaller fields, we observe a difference of the measured spectra as a function of d. This is attributed to the fact that for d = 800 nm, the magnetization remains partially uniform in the channel between the antidots because of the Heusler cubic crystal anisotropy, while for d = 600 nm, the magnetic edge domains around the antidots spread into the channels. Moreover, this anisotropy also allows different remanent states when initializing the crystals with a small magnetic field along two perpendicular directions. This leads to an efficient excitation or extinction of the spin wave modes, making possible to achieve reconfigurable microwave devices exploiting an antidot geometry in a metallic ferromagnetic with a low damping coefficient.
Einstein–Stokes relation for small bubbles at the nanoscale
Authors: Zhou Youbin , Huang Mengyuan , Tian Falin , Shi Xinghua , Zhang Xianren
Published: February 2024

As the physicochemical properties of ultrafine bubble systems are governed by their size, it is crucial to determine the size and distribution of such bubble systems. At present, the size or size distribution of nanometer-sized bubbles in suspension is often measured by either dynamic light scattering or the nanoparticle tracking analysis. Both techniques determine the bubble size via the Einstein–Stokes equation based on the theory of the Brownian motion. However, it is not yet clear to which extent the Einstein–Stokes equation is applicable for such ultrafine bubbles. In this work, using atomic molecular dynamics simulation, we evaluate the applicability of the Einstein–Stokes equation for gas nanobubbles with a diameter less than 10 nm, and for a comparative analysis, both vacuum nanobubbles and copper nanoparticles are also considered. The simulation results demonstrate that the diffusion coefficient for rigid nanoparticles in water is found to be highly consistent with the Einstein–Stokes equation, with slight deviation only found for nanoparticle with a radius less than 1 nm. For nanobubbles, including both methane and vacuum nanobubbles, however, large deviation from the Einstein–Stokes equation is found for the bubble radius larger than 3 nm. The deviation is attributed to the deformability of large nanobubbles that leads to a cushioning effect for collision-induced bubble diffusion.
Lagrangian stochastic integrals of motion in isotropic random flows
Authors: Sirota V. A. , Il'yn A. S. , Kopyev A. V. , Zybin K. P.
Published: February 2024

A set of exact integrals of motion is found for systems driven by homogenous isotropic stochastic flow. The integrals of motion describe the evolution of (hyper-)surfaces of different dimensions transported by the flow and can be expressed in terms of local surface densities. The expression for the integrals is universal: it represents general geometric properties and does not depend on the statistics of the specific flow.
A comparative study of three modes for realizing transmedia standing-and-hovering behavior in robotic dolphins
Authors: Lei Ming , Li Zhihan , Yan Han , Cao Jiabo , Xia Dan
Published: February 2024

Three different hovering modes, namely, the caudal fin, pectoral fins, and multi fins, were utilized to achieve the standing-and-hovering behavior in robotic dolphins. A three-dimensional dolphin model, consisting of body, caudal fin, and symmetric pectoral fins, was used as the virtual swimmer to implement three hovering modes. A novel paddling motion was proposed, and a symmetric shape was designed of the pectoral fins. The hovering mechanisms of different modes were revealed, and the mapping relationships between different motion and performance parameters such as hovering height, efficiency, stability, and rapidity were established. The respective advantages of the three hovering modes were compared. The results showed that the caudal fin mode had the best hovering stability, while the pectoral fins mode had the best hovering rapidity. Moreover, it is worth noting that the multi fins mode had both the good hovering stability and rapidity. Therefore, the optimal hovering mode and motion parameters can be selected based on different expected objectives to achieve the best results. This study provides a new approach to break through the spatial barriers to movement of underwater robots and provides a solid hydrodynamic theoretical basis for the development of cross-medium robots with multiple hovering modes.
Steric repulsion introduced by loop constraints modulates the microphase separation of chromatins
Authors: Wei Jiachen , Xue Yue , Liu Yawei , Tian Hao , Shao Yingfeng , Gao Yi Qin
Published: February 2024

Within the confines of a densely populated cell nucleus, chromatin undergoes intricate folding, forming loops, domains, and compartments under the governance of topological constraints and phase separation. This coordinated process inevitably introduces interference between different folding strategies. In this study, we model interphase chromatins as block copolymers with hetero-hierarchical loops within a confined system. Employing dissipative particle dynamics simulations and scaling analysis, we aim to explain how the structure and distribution of loop domains modulate the microphase separation of chromatins. Our results highlight the correlation between the microphase separation of the copolymer and the length, heterogeneity, and hierarchically nested levels of the loop domains. This correlation arises from steric repulsion intrinsic to loop domains. The steric repulsion induces variations in chain stiffness (including local orientation correlations and the persistence length), thereby influencing the degree of phase separation. Through simulations of block copolymers with distinct groups of hetero-hierarchical loop anchors, we successfully reproduce changes in phase separation across diverse cell lines, under fixed interaction parameters. These findings, in qualitative alignment with Hi-C data, suggest that the variations of loop constraints alone possess the capacity to regulate higher-order structures and the gene expressions of interphase chromatins.
Rupture of membranous microbubbles induced by pulsed acoustic wave
Authors: Gong Menyang , Xu Xin , Fei Zhonghan , Li Yuanyuan , Gao Shenlian , Qiao Yupei , Liu Jiehui , Ma Teng , Liu Xiaozhou
Published: February 2024

Encapsulated microbubbles serve as suitable drug carriers in medicine. This paper proposes corrections for the resonance frequency of lipid-coated bubbles under various acoustic pressure levels and the critical pressure for bubble rupture based on the Marmottant model. The suggestion to induce the rupture of lipid-coated bubbles using acoustic waves leans toward utilizing pulse waves rather than continuous waves. Corresponding experiments validate the accuracy of these corrections and the rationale behind the suggestion, aligning closely with theoretical predictions. This study offers a more precise predictive framework for the behavior of lipid-coated bubbles under acoustic waves.
Evaluation of stochastic particle Bhatnagar–Gross–Krook methods with a focus on velocity distribution function
Authors: Park Woonghwi , Kim Sanghun , Pfeiffer Marcel , Jun Eunji
Published: February 2024

For precise application of Bhatnagar–Gross–Krook (BGK) methods, assessing its accuracy in non-equilibrium flows is necessary. Generally, this assessment relies on macroscopic parameters, which are moments of the velocity distribution function (VDF). However, in non-equilibrium flows, the significance of each moment diminishes as the VDF deviates from the Maxwellian VDF. This study investigates the VDF in non-equilibrium flows. Two Prandtl-corrected BGK methods, the ellipsoidal statistical BGK and Shakhov BGK (SBGK), are compared with the direct simulation Monte Carlo method. To observe the VDF while excluding the effects of convection, the homogeneous relaxation of the initial non-equilibrium state is analyzed. The VDF in Couette flow and normal shock waves, where collision and convection coexist, is then examined. When comparing the accuracy of the BGK methods using higher-order moments, inconsistencies are observed. However, when comparing the VDFs, the SBGK method reproduces the non-equilibrium VDF more accurately. The results demonstrate the importance of the VDF in the evaluation of non-equilibrium flows.
Effects of Mach and Atwood numbers on the shock-induced evolution of a double-layer gas cylinder
Authors: Li Xin , Hao Jiaao , Wen Chih-Yung , Fan E
Published: February 2024

The evolution of a double-layer gas cylinder under various Mach numbers (M = 1.27, 1.5, 1.7, and 2.1) and Atwood numbers (A = 0.504, 0.392, 0.194, and −0.202 for the first layer) are studied numerically. At M ≥ 1.5 and A = 0.504, a bulge is generated near the upstream pole of the outer cylinder due to the impingement of a reflected shock wave, which promotes the formation of an upstream jet. At a higher Mach number, the evolution of the jet is suppressed under the influence of a higher pressure upstream of the jet head. The compressibility effects are quantified by the widths and heights of the gas cylinders. The Atwood number is associated with nonlinear acoustic effects, and the sign of A results in a significant variation in the wave patterns. The development of vortex pairs slows down with the decreasing Atwood numbers in the scenario of A > 0 for the first layer gas cylinder, while vortex pairs emerge and propagate in both upstream and downstream directions from the outer interface in the scenario of A < 0 for the first layer. As the Mach numbers and the magnitude of the Atwood numbers are increased, the mixing of various gases is promoted by detecting the circulation and mixed mass. The net circulation can be predicted by the linear summation of the Picone and Boris model and the Samtaney and Zabusky model under various Mach and Atwood numbers.
On the performance of HRPA(D) for NMR spin–spin coupling constants: Smaller molecules, aromatic and fluoroaromatic compounds
Authors: Jessen Louise Møller , Sauer Stephan P. A.
Published: February 2024

In this study, the performance of the doubles-corrected higher random-phase approximation [HRPA(D)] has been investigated in calculations of nuclear magnetic resonance spin–spin coupling constants (SSCCs) for 58 molecules with the experimental values used as the reference values. HRPA(D) is an approximation to the second-order polarization propagator approximation (SOPPA) and is, therefore, computationally less expensive than SOPPA. HRPA(D) performs comparable and sometimes even better than SOPPA, and therefore, when calculating SSCCs, it should be considered as an alternative to SOPPA. Furthermore, it was investigated whether a coupled-cluster singles, doubles and perturbative triples [CCSD(T)] or Møller-Plesset second order (MP2) geometry optimization was optimal for a SOPPA and a HRPA(D) SSCC calculation for eight smaller molecules. CCSD(T) is the optimal geometry optimization for the SOPPA calculation, and MP2 was optimal for HRPA(D) SSCC calculations.
Basic fractional nonlinear-wave models and solitons
Authors: Malomed Boris A.
Published: February 2024

This review article provides a concise summary of one- and two-dimensional models for the propagation of linear and nonlinear waves in fractional media. The basic models, which originate from Laskin’s fractional quantum mechanics and more experimentally relevant setups emulating fractional diffraction in optics, are based on the Riesz definition of fractional derivatives, which are characterized by the respective Lévy indices. Basic species of one-dimensional solitons, produced by the fractional models which include cubic or quadratic nonlinear terms, are outlined too. In particular, it is demonstrated that the variational approximation is relevant in many cases. A summary of the recently demonstrated experimental realization of the fractional group-velocity dispersion in fiber lasers is also presented.
Recent developments and applications of reference interaction site model self-consistent field with constrained spatial electron density (RISM-SCF-cSED): A hybrid model of quantum chemistry and integral equation theory of molecular liquids
Authors: Imamura Kosuke , Yokogawa Daisuke , Sato Hirofumi
Published: February 2024

The significance of solvent effects in electronic structure calculations has long been noted, and various methods have been developed to consider this effect. The reference interaction site model self-consistent field with constrained spatial electron density (RISM-SCF-cSED) is a hybrid model that combines the integral equation theory of molecular liquids with quantum chemistry. This method can consider the statistically convergent solvent distribution at a significantly lower cost than molecular dynamics simulations. Because the RISM theory explicitly considers the solvent structure, it performs well for systems where hydrogen bonds are formed between the solute and solvent molecules, which is a challenge for continuum solvent models. Taking advantage of being founded on the variational principle, theoretical developments have been made in calculating various properties and incorporating electron correlation effects. In this review, we organize the theoretical aspects of RISM-SCF-cSED and its distinctions from other hybrid methods involving integral equation theories. Furthermore, we carefully present its progress in terms of theoretical developments and recent applications.
Investigation of negative differential resistance in metal-edge-contact MoS2 field effect transistor
Authors: Garg Ankur , Ehteshamuddin Mohammad , Sharma Somit , Dasgupta Avirup
Published: February 2024

Negative differential resistance (NDR) is observed in various emerging electronic devices. As compared to the conventional silicon-based field effect transistor (FET), the NDR is widely investigated in two-dimensional (2D) transition metal dichalcogenide (TMD) FETs. In this work, we study the NDR effect for the TMD-based metal-edge-contact MoS2 double-gate FET with 10 nm channel length. The multiscale atomistic simulation is demonstrated for the lateral heterostructure of a metal–semiconductor–metal FET by density functional theory, maximally localized Wannier function tight-binding Hamiltonian, and non-equilibrium Green’s function methods. The quantum transport model in the given lateral heterostructure resulted in NDR in a double-gate FET. Here, we focus on the NDR by the systematic study of the transmission spectrum of the metal-edge-contact MoS2 channel FET and finally compare it with zero NDR ideal highly doped FET. The peak-to-valley ratio in the NDR response can be modulated with the change in the gate-to-source voltage and can be used to explore various future electronic applications.
Broad luminescence from Zn acceptors in Zn doped β-Ga2O3
Authors: Hommedal Ylva K. , Frodason Ymir K. , Galeckas Augustinas , Vines Lasse , Johansen Klaus Magnus H.
Published: February 2024

Zn-related defects in β-Ga2O3 were studied using photoluminescence (PL) spectroscopy combined with hybrid functional calculations and secondary ion mass spectrometry. We have in-diffused Zn by heat treatments of β-Ga2O3 in Zn vapor to promote the formation of the ZnGaZni complex as the dominating Zn configuration. Subsequently, we did heat treatment in oxygen ambient to study the dissociation of the donor complex ZnGaZni into the ZnGa acceptor. The PL spectra revealed a broad band centered at 2.5 eV. The signature has a minor contribution to the overall emission of as-grown and Zn-annealed samples but increases dramatically upon the subsequent heat treatments. The theoretical predictions from hybrid functional calculation show emission energies of 2.1 and 2.3 eV for ZnGa10/− and ZnGa20/−, respectively, and given that the previously observed deviation between the experimental and calculated values for the self-trapped holes in β-Ga2O3 is about 0.2 eV, we conclude that the 2.5 eV emission we observe herein is due to the Zn acceptor.
Epitaxial growth and characterization of Bi1−xSbx thin films on (0001) sapphire substrates
Authors: Huang Yu-Sheng , Islam Saurav , Ou Yongxi , Ghosh Supriya , Richardella Anthony , Mkhoyan K. Andre , Samarth Nitin
Published: February 2024

We report the molecular beam epitaxy of Bi1−xSbx thin films (0 ≤ x ≤ 1) on sapphire (0001) substrates using a thin (Bi,Sb)2Te3 buffer layer. The characterization of the films using reflection high energy diffraction, x-ray diffraction, atomic force microscopy, and scanning transmission electron microscopy reveals the epitaxial growth of films of reasonable structural quality. This is further confirmed via x-ray diffraction pole figures that determine the epitaxial registry between the thin film and the substrate. We further investigate the microscopic structure of thin films via Raman spectroscopy, demonstrating how the vibrational modes vary as the composition changes and discussing the implications for the crystal structure. We also characterize the samples using electrical transport measurements.
A deep learning super-resolution model for turbulent image upscaling and its application to shock wave–boundary layer interaction
Authors: Sofos Filippos , Drikakis Dimitris , Kokkinakis Ioannis William , Spottswood S. Michael
Published: February 2024

Upscaling flow features from coarse-grained data is paramount for extensively utilizing computational physics methods across complex flow, acoustics, and aeroelastic environments where direct numerical simulations are computationally expensive. This study presents a deep learning flow image model for upscaling turbulent flow images from coarse-grained simulation data of supersonic shock wave–turbulent boundary layer interaction. It is shown for the first time that super-resolution can be achieved using only the coarsest-grained data as long as the deep learning training is performed using hundreds of fine-grained data. The unsteady pressure data are used in training due to their importance in aeroelasticity and acoustic fatigue occurring on aerospace structures. The effect on the number of images and their resolution features used in training, validation, and prediction is investigated regarding the model accuracy obtained. It is shown that the deep learning super-resolution model provides accurate spectra results, thus confirming the approach's effectiveness.
Thickness-dependent topological phases in topological magnet Fe2S2
Authors: Liang Yan , Han Xuening , Wang Qiang , Zhao Pei
Published: February 2024

Magnetic topological insulators showcase intricate interplay between nontrivial topology and magnetism, providing a fertile ground for exploring various topological quantum phenomena. A recent study reported a ferromagnetic quantum anomalous Hall (QAH) insulator Fe2S2 with huge nontrivial bandgap, but its layer-number-correlated magnetic coupling and topological phases remain unclear. Here, we identify the magnetic coupling and thickness-dependent band topology in Fe2S2 based on first-principles. The results indicate a preferential interlayer antiferromagnetic coupling in the multilayer Fe2S2, giving rise to evident alternating QAH and quantum spin Hall states for odd and even layers, respectively. Moreover, the spin Hall conductivity in even-layer Fe2S2 could be enlarged by increasing the thickness, due to the formation of multiple dissipationless spin transport channels. These findings not only promote the topological magnet Fe2S2 as a potential candidate for diverse topological phase investigations and applications but also provide an avenue to manipulate the quantum states in van der Waals QAH insulators by thickness control.
Microfluidic–nanophotonic sensor for on-chip analysis of complex refractive index
Authors: Kuzin A. , Panda K. , Chernyshev V. , Florya I. , Kovalyuk V. , An P. , Golikov A. , Chulkova G. , Kolesov D. , Gorin D. , Goltsman G.
Published: February 2024

Photonic biosensors based on photonic integrated circuits (PICs) and microfluidic channels (MFCs) have become the subject of intensive research for point-of-care (POC) device applications. In the presented work, we demonstrate the possibility of identifying the complex refractive index (RI) of analyzed liquids through the optimization of the geometry configuration of MFCs under PICs by experimental and numerical approaches. Our results suggest that the real and imaginary parts of the RI for analytes under study can be determined from spectrum of devices with optimized MFCs width. This work paves the way for promising opportunities to identify the presence and concentration of biological markers by using RI sensors for in situ POC applications.
Synthesis of two-dimensional MoO2 nanoplatelets and its multistep sulfurization into MoS2
Authors: Yan Wei , Zhang Zhi , Wan Jihong , Meng Lan , Li Xing-ao
Published: February 2024

To control the growth of layered two-dimensional structures, such as transition metal dichalcogenide materials or heterostructures, understanding the growth mechanism is crucial. Here, we report the synthesis of ultra-thin MoO2 nanoplatelets through the sublimation of MoO3. Rhombus MoO2 nanoplatelets with the P21/c space group were characterized using various microscopic and spectroscopic techniques. Introducing sulfur sources into the chemical vapor deposition system also leads to the formation of monoclinic MoO2 nanoflakes due to the incomplete sulfurization of MoO3. With a gradual increase in the vapor concentration of sulfur, MoO3 undergoes stepwise reduction into MoS2/MoO2 and eventually into MoS2. Additionally, utilizing MoO2 as a precursor for Mo sources enables the formation of monolayer MoS2 single crystals. This work provides an effective approach for growing MoO2 nanoplatelets and elucidates the mechanism behind the stepwise sulfurization of MoO3.
Direct observation of phase-change volume in contact resistance change memory using N-doped Cr2Ge2Te6 phase-change material
Authors: Shuang Yi , Ando Daisuke , Song Yunheub , Sutou Yuji
Published: February 2024

As we strive for faster and denser nonvolatile memory, a two-terminal phase-change random access memory device has been developed to fulfill this pressing need. This device utilizes a phase-change material (PCM) that experiences reversible resistive switching. Our study delved into the resistive switching behavior in a nitrogen-doped Cr2Ge2Te6 (NCrGT) contact resistance change memory, which employs a T-shape cell. The results of our study were highly promising: NCrGT memory cells showed a remarkable 90% reduction in Reset energy compared to the traditional PCM Ge2Sb2Te5. This notable reduction is attributed to the smaller phase-change volume of NCrGT, which was fine-tuned by the contact property. Moreover, we found that the N dopant was robustly distributed in the CrGT matrix during switching. Furthermore, we directly observed the phase-change area of the T-shape cell using transmission electron microscopy and energy-dispersive x-ray spectroscopy. After 104 of switching, our findings revealed that failure within the cells was caused by atom migration.
Experimental verification of the inverse anomalous spin Hall effect with perpendicular magnetic anisotropy materials
Authors: Abrão J. E. , Rodrigues A. R. , Bedanta S. , Azevedo A.
Published: February 2024

In this work, the spin pumping technique was employed to investigate the anomalous inverse spin Hall effect in BIG/NiO/Fe samples where BIG[(Bi,Tm)3(Fe,Ga)5O12] exhibits perpendicular magnetic anisotropy. Our results reveal an intriguing phenomenon: when the magnetization of both ferromagnetic layers is perpendicular to each other, a distinct spin-to-charge current conversion mechanism occurs. This conversion is intricately linked to the magnetization of the converting layer, spin polarization, and the spin current orientation.
Robust unfolding of MeV x-ray spectra from filter stack spectrometer data
Authors: Wong C.-S. , Strehlow J. , Broughton D. P. , Luedtke S. V. , Huang C.-K. , Bogale A. , Fitzgarrald R. , Nedbailo R. , Schmidt J. L. , Schmidt T. R. , Twardowski J. , Van Pelt A. , Alvarez M. Alvarado , Junghans A. , Mix L. T. , Reinovsky R. E. , Rusby D. R. , Wang Z. , Wolfe B. , Albright B. J. , Batha S. H. , Palaniyappan S.
Published: February 2024

We present an inversion method capable of robustly unfolding MeV x-ray spectra from filter stack spectrometer (FSS) data without requiring an a priori specification of a spectral shape or arbitrary termination of the algorithm. Our inversion method is based upon the perturbative minimization (PM) algorithm, which has previously been shown to be capable of unfolding x-ray transmission data, albeit for a limited regime in which the x-ray mass attenuation coefficient of the filter material increases monotonically with x-ray energy. Our inversion method improves upon the PM algorithm through regular smoothing of the candidate spectrum and by adding stochasticity to the search. With these additions, the inversion method does not require a physics model for an initial guess, fitting, or user-selected termination of the search. Instead, the only assumption made by the inversion method is that the x-ray spectrum should be near a smooth curve. Testing with synthetic data shows that the inversion method can successfully recover the primary large-scale features of MeV x-ray spectra, including the number of x-rays in energy bins of several-MeV widths to within 10%. Fine-scale features, however, are more difficult to recover accurately. Examples of unfolding experimental FSS data obtained at the Texas Petawatt Laser Facility and the OMEGA EP laser facility are also presented.
Deprotonated sulfamic acid and its homodimers: Does sulfamic acid adopt zwitterion during cluster growth?
Authors: Hu Zhubin , Shao Qiaoqiao , Li Zhipeng , Sun Zhenrong , Wang Xue-Bin , Sun Haitao
Published: February 2024

We present a joint experimental and computational study on the geometric and electronic structures of deprotonated sulfamic acid (SA) clusters [(SA)n–H]− (n = 1, 2) employing negative ion photoelectron spectroscopy and high-level ab initio calculations. The photoelectron spectra provide the vertical/adiabatic detachment energy (VDE/ADE) of the sulfamate anion (SM−) H2N●SO3− at 4.85 ± 0.05 and 4.58 ± 0.08 eV, respectively, and the VDE and ADE of the SM−●SA dimer at 6.41 ± 0.05 and 5.87 ± 0.08 eV, respectively. The significantly increased electron binding energies of the dimer confirm the enhanced electronic stability upon the addition of one SA molecule. The CCSD(T)-predicted VDEs/ADEs agree excellently with the experimental data, confirming the identified structures as the most stable ones. Two types of dimer isomers possessing different hydrogen bonding (HB) motifs are identified, corresponding to SM− binding to a zwitterionic SA (SM−●SAz) and a canonical SA (SM−●SAc), respectively. Two N–H⋯O HBs and one superior O–H⋯O HB are formed in the lowest-lying SM−●SAc, while SM−●SAz has three moderate N–H⋯O HBs, with the former being 4.71 kcal/mol more stable. Further theoretical analyses reveal that the binding strength advantage of SM−●SAc over SM−●SAz arises from its significant contributions of orbital interactions between fragments, illustrating that sulfamate strongly interacts with its parent SA acid and preferably chooses the canonical SA in the subsequent cluster formations. Given the prominent presence of SA, this study provides the first evidence that the canonical dimer model of sulfamic acid should exist as a superior configuration during cluster growth.
Low-frequency dependence of plasma characteristics in dual-frequency capacitively coupled plasma sources
Authors: Zhou Yang , Zhao Kai , Ma Fang-Fang , Liu Yong-Xin , Gao Fei , Schulze Julian , Wang You-Nian
Published: February 2024

It is commonly recognized that in radio frequency capacitive discharges, a higher excitation frequency can yield an enhanced electron heating rate and ion flux. Here, we reveal the low-frequency dependence of the plasma density and ion energy/angular distribution in a low-pressure (2 Pa), dual-frequency (DF) capacitively coupled argon plasma based on a combination of experiments and kinetic particle simulations. As the low frequency (LF, fL) is decreased from 6.8 MHz to 40 kHz, the plasma density undergoes a moderate decline initially, followed by an increase, reaching a maximum at fL=400 kHz. The enhanced plasma density is attributed to a combined effect of (i) an attenuated modulation effect of the LF source on the high-frequency electron heating and (ii) enhanced emission of electron-induced secondary electrons. At a lower fL, the ion transit time across the sheath, τion, gets comparable to or shorter than the LF period, τLF, resulting in a higher ion energy with a narrower angular spread. The enhanced ion flux and ion energy in DF discharges operated at low frequencies in the range of hundreds of kHz are beneficial for the high-aspect-ratio plasma etching extensively used in the semiconductor industry.
A three-phase model for biofilm formation on a porous solid surface
Authors: Kumar Uttam , Pushpavanam Subramaniam
Published: February 2024

We investigate the growth kinetics of bacterial biofilms on porous substrates. A three-phase model is developed, which accounts explicitly for the cell phase, extracellular matrix (ECM), and nutrient-rich aqueous phase. We use the thin-film approximation as the characteristic height of the biofilm is much smaller than its characteristic radius. We use the 2D axisymmetric model to capture biofilm growth on a porous agar substrate. Our model accounts for osmotic flux and predicts the spatiotemporal variations of the volume fractions of the different phases and the nutrient concentrations in the biofilm and the substrate. An increase in surface tension helps redistribute biomass radially. Our model captures the behavior of different kinds of biofilms: films characterized by low (yeast) and high (bacterial) ECM content. The predictions of our model are quantitatively validated with the experimental data from the literature. Our model provides insights on the role of different parameters on biofilm growth, which can be used to develop strategies to prevent or accelerate biofilm formation on surfaces.
Quantum state-to-state nonadiabatic dynamics of the charge transfer reaction H+ + NO(X2Π) → H + NO+(X1Σ+): Influence of ro-vibrational excitation of NO
Authors: Wang Zhimo , Hou Siting , Gao Hong , Xie Changjian
Published: February 2024

Quantum state-to-state nonadiabatic dynamics of the charge transfer reaction H+ + NO(X2Π, vi = 1, 3, ji = 0, 1) → H + NO+(X1Σ+) has been studied based on the recently constructed diabatic potential energy matrix. It was found that the vibrational excitation of reactant NO inhibits the reactivity, while the rotational excitation of reactant NO has little effect on the reaction probability. These attributes were also observed in the semi-classical trajectory calculations employed in the adiabatic representation. Such an inhibitory effect of the vibrational excitation of reactant NO was owing to lower accessibility of the conical intersection and avoided crossing regions, which are located in the wells with respect to the Π diabat, as evidenced by the analysis of the population of the time-independent wave functions. Calculated vibrational state distributions of the product show that the decrease of the reaction mainly leads to the less formation of low vibrational states (vf < 6), and the product vibrational state distributions are more evenly populated for vi = 1 and 3, suggesting a non-statistical behavior. However, the overall shapes of the product rotational distributions remain unchanged, indicating that the redistribution of energy into the rotation of product NO is sufficient in the charge transfer process between H+ and NO. While the reaction is dominated by the forward and backward scattering in differential cross sections (DCSs), consistent with the complex-forming mechanism, a clear forward bias in the DCSs appears, indicating that the occurrence of the reaction is not sufficiently long to undergo the whole phase space of the interaction configurations.
Enhancement of light emission of a low-resistivity silicon nanocrystal thin film: A simulational and experimental study
Authors: Ma Fengyang , Zhou Jian , Liu Kaixin , Yan Zhongyao , Dai Xiyuan , Wu Li , Yu Liang , Sun Jian , Wang Song-You , Lu Ming
Published: February 2024

A silicon nanocrystal (Si NC) white light-emitting (λ = ∼400–900 nm) thin film with a relatively low resistivity of 1.6 × 104 Ω m has been prepared as an active medium for electrically driven Si light sources. The average size of Si NC is 2.4 ± 0.4 nm. To enhance the light emission efficiency of this low-resistivity Si NC thin film, approach of hydrogen passivation suitable for the traditional high-resistivity (1.2 × 107 Ω m in this work for example) red light-emitting Si NC thin film has been tried and found unavailable unfortunately. Our first principles simulation shows that Si NCs bonded to −O, −NH2, −OH, and −H ligands are responsible for red, green, and blue (RGB) primary color emissions in this white light-emitting sample, respectively. Passivation of the sample in NH3 and H2O atmosphere is then conducted, aiming to increase the number of the RGB light emitters. The light emission is significantly enhanced, with photoluminescence intensity, photoluminescence quantum yield, electroluminescence intensity, and net optical gains increased by factors of 4.6, 4.2, 4.0, and ∼3.0, respectively, after 10-day passivation. Further enhancements are expected for longer passivation.
Polygon Boolean operations and physical unclonable functions implemented by an Ag-embedded sodium-alginate-based memristor for image encryption/decryption
Authors: Shi Jiajuan , Han Jiaqi , Bian Jingyao , Dong Yongjun , Lin Ya , Zhang Yifan , Tao Ye , Zhao Xiaoning , Xing Guozhong , Wang Zhongqiang , Xu Haiyang , Liu Yichun
Published: February 2024

In this work, we demonstrate the coexistence of nonvolatile memory (NVM) and volatile threshold switching (VTS) behaviors in an Ag-embedded sodium-alginate-based memristor using the current pulse mode. High and low compliance currents allow the device to present stable and reliable NVM and VTS behaviors, respectively. Specifically, NVM and VTS behaviors randomly occur under a compliance current of 40 μA. On this basis, four polygon Boolean operations (AND, OR, NOT, and XOR) and physical unclonable functions (PUFs) with an inter-class Hamming distance of 50.75% are demonstrated simultaneously in memristive devices. Adopting PUF keys, image encryption and decryption are implemented by executing the XOR logic operation. Our memristive devices have the ability of in-memory computing and providing PUFs simultaneously and thus great potential for hardware security applications.
Tunable broadband terahertz absorber based on graphene with bilayer hexagonal
Authors: Fu Maixia , Xia Na , Duan Yule , Zhou Fei , Li Yinsheng
Published: February 2024

An ultra-wideband absorber with an absorption rate of near unit is studied and numerically simulated in the terahertz frequency band. The proposed absorber is a stacked compact structure consisting of a double-layer patterned graphene embedded between two separated dielectric. Under normal incidence, the absorption rate exceeds 99% at 2.31–3.92 THz. The absorption bandwidth can reach 2.54 THz for absorptions greater than 90% (1.91–4.45 THz), and the relative bandwidth achieves 80%. Furthermore, the absorber is tunable, with absorption ranging from 14% to almost 99.9% by altering the Fermi energy of graphene from 0 to 1 eV. The phenomenon of ultra-wideband absorption is analyzed in relation to impedance matching and field distribution. Moreover, the absorber has high polarization-independence and can operate across a broad range of incidence angles. This tunable ultra-wideband absorber has promising functions in modulation, stealth, switching, and imaging technologies.
An AK-iDNS framework to solve the condensation-driven aggregation with realistic kernels
Authors: Pan Kejun , Wang Lian-Ping , Xie Mingliang
Published: February 2024

In this study, a concise and fast framework based on the average kernel and iterative direct numerical simulation is proposed to solve the generalized Smoluchowski coagulation equation with a physically realistic kernel. Taking advantage of the symmetry of the homogeneous collision kernel, the realistic kernel function can be represented as a simple power function through Laplace transformation under the average kernel method, and the corresponding moment model and self-preserving model can then be constructed and solved analytically. Compared with the classical Taylor-series expansion method of moments, the present moment model has the same asymptotic growth rate, but the form is more concise and the particle number density is decoupled from the other moments. To obtain a better agreement with the experimental data, the iterative direct numerical simulation can be employed to correct the similarity solution using the analytical similarity solution as the initial condition. The corrected similarity solution overcomes the inherent contradiction between the analytical solution and experimental data discussed in the literature. The results reveal that the shape of self-preserving distribution is independent of the initial distribution and that it does depend on the mechanism of coagulation. The results also show the universality, reliability, and strong robustness of the iterative direct numerical simulation algorithm.
Shape optimization of sound barriers using an isogeometric meshless method
Authors: Liu Hanqing , Wang Fajie , Cheng Suifu , Qiu Lin , Gong Yanpeng
Published: February 2024

The sound barrier is an important means to reduce noise caused by traveling vehicles on roads or railways. Structural design and optimization of the sound barrier can effectively reduce the use of materials and improve the noise reduction effect. In this paper, a new isogeometric singular boundary method is proposed and applied to the shape optimization of sound barriers. The geometric structure is accurately represented by using non-uniform rational B-splines. The acoustic shape sensitivity of the control points was calculated using the direct differentiation method and the adjoint variable method. After that, the method of moving asymptotes is adopted as an optimizer to search for the optimal layout of the design objective. In the numerical procedure, the shoelace formula is introduced to calculate the area of the closed structure, which only uses the discrete node information on the boundary. The proposed approach completely avoids the mesh division in the finite element method as well as the singular integral calculation in the boundary element method. More importantly, it can be seamlessly connected with the computer-aided design system for the subsequent treatment by engineers. Three numerical examples are provided to illustrate the accuracy and effectiveness of the proposed isogeometric method. This work provides a simple and effective way for the structural optimization design of sound barriers.
Non-linear light–matter interactions from the Bethe–Salpeter equation
Authors: Rauwolf Nina , Klopper Wim , Holzer Christof
Published: February 2024

A route to assess non-linear light–matter interactions from the increasingly popular GW-Bethe–Salpeter equation (GW-BSE) method is outlined. In the present work, the necessary analytic expressions within the static-screened exchange approximation of the BSE are derived. This enables a straightforward implementation of the computation of the first hyperpolarizability as well as two-photon absorption processes for molecular systems. Benchmark calculations on small molecular systems reveal that the GW-BSE method is intriguingly accurate for predicting both first hyperpolarizabilities and two-photon absorption strengths. Using state-of-the-art Kohn–Sham references as a starting point, the accuracy of the GW-BSE method rivals that of the coupled-cluster singles-and-doubles method, outperforming both second-order coupled-cluster and time-dependent density-functional theory.
Temperature evolution characteristics of stem root during dark period in positive long spark discharge
Authors: Cheng Chen , He Hengxin , Huang Yubin , Fu Zhong , Zhao Aihua , Xiang Nianwen , Chen Weijiang
Published: February 2024

Gas temperature plays an important role in the characterization of plasma parameters. The temperature evolution of stem roots during the dark period is at the heart of our understanding of the physical mechanism of streamer to the leader transition process in a long spark discharge. The quantitative schlieren system with high spatiotemporal resolution was designed to conduct positive leader discharge experiments with a 1.0 m rod-plate gap at atmospheric pressure, and the amplitude and rise time of positive impulse voltage waveforms were 380 kV and 200 μs, respectively. The time-resolved quantitative schlieren images of the discharge channel near the electrode tip can be captured to gather the temperature data of stem roots for case study. Further statistical tests revealed that due to the dispersion of the first streamer discharge, there were three evolutionary trends of gas temperature at the axis of the stem root in the early dark period. Interestingly, the gas temperature at the axis of the stem root was maintained at 1000–1200 K in regardless of the evolutionary trend in the early dark period. In addition, the statistical results indicate that there is a significant positive correlation between the curvature radius of the discharge electrode tip and the critical charge value Qcrit of the first streamer discharge, which leads to a transition in evolutionary trends of gas temperature at the axis of the stem root. This research has important guiding significance for understanding the physical mechanism of leader inception and the whole process modeling of long air gap discharge.
Research on cavitation bubble behaviors between a dual-particle pair
Authors: Wang Xiaoyu , Zhang Cheng , Su Hongchen , Li Shaowei , Shen Junwei , Zhang Yuning , Li Jingtao , Zhang Yuning
Published: February 2024

The interactions between particle clusters and cavitation bubbles play an important role in several industrial applications, e.g., the abrasive erosion of hydraulic machinery, the efficiency improvement of ultrasonic cleaning, and the mineral flotation. This paper explores the influence of a dual-particle pair of unequal sizes on the bubble collapse dynamics based on a Kelvin impulse model and high-speed photography. The impact of the radius ratio of the dual-particle pair (ranging from 1.0 to 3.0), defined as the ratio of the large-particle radius to the small-particle radius, on the bubble interface deformation, collapse jet, and the translational movement of the bubble is analyzed. The main findings are as follows: (1) the Kelvin impulse based on the Weiss theorem can effectively predict the asymmetric bubble behaviors in terms of the moving distance and the direction of the bubble centroid during the bubble collapse; (2) the particle radius ratio is a key parameter affecting the intensity and direction of the Kelvin impulse, as well as the bubble centroid moving distance; and (3) the zero-Kelvin-impulse point is always biased toward the smaller particle in the dual-particle pair.
The effective relativistic coupling by asymptotic representation approach for molecules with multiple relativistic atoms
Authors: Weike Nicole , Eisfeld Wolfgang
Published: February 2024

The Effective Relativistic Coupling by Asymptotic Representation (ERCAR) approach is a method to generate fully coupled diabatic potential energy surfaces (PESs) including relativistic effects, especially spin–orbit coupling. The spin–orbit coupling of a full molecule is determined only by the atomic states of selected relativistically treated atoms. The full molecular coupling effect is obtained by a diabatization with respect to asymptotic states, resulting in the correct geometry dependence of the spin–orbit effect. The ERCAR approach has been developed over the last decade and initially only for molecules with a single relativistic atom. This work presents its extension to molecules with more than a single relativistic atom using the iodine molecule as a proof-of-principle example. The theory for the general multiple atomic ERCAR approach is given. In this case, the diabatic basis is defined at the asymptote where all relativistic atoms are separated from the remaining molecular fragment. The effective spin–orbit operator is then a sum of spin–orbit operators acting on isolated relativistic atoms. PESs for the iodine molecule are developed within the new approach and it is shown that the resulting fine structure states are in good agreement with spin–orbit ab initio calculations.