bluuebunny/crossref_metadata_2025 huggingface dataset:
Infinite wall in the fractional quantum mechanics
Authors: Dong Jianping , Lu Ying
Published: March 2021

The space-fractional Schrödinger equation for a local potential is difficult to solve because the fractional Riesz operator in it is nonlocal. In fractional quantum mechanics, the infinite wall is a basic problem and has not been solved yet. In this paper, we consider a free particle in an infinite wall region. Making use of the Lévy path integral method, we derive the Lévy path integral amplitude of the particle and take advantage of it to get the solution of the fractional Schrödinger equation for an infinite wall. Then, the infinite wall potential with a delta-function perturbation is also studied. According to Fox’s H-function, we get an equation of bound state energies of a free particle moving in an infinite wall region perturbed by the δ-function for two situations, E < 0 and E > 0. We give a transcendental equation that determines energy levels when E < 0 and prove that there is no bound states when E > 0. The asymptotic behaviors of the center of the delta function approaching to the origin and the infinite are also shown. The results of this paper include special cases in standard quantum mechanics.
Agent-based modeling: Population limits and large timescales
Authors: Niemann J.-H. , Winkelmann S. , Wolf S. , Schütte C.
Published: March 2021

Modeling, simulation, and analysis of interacting agent systems is a broad field of research, with existing approaches reaching from informal descriptions of interaction dynamics to more formal, mathematical models. In this paper, we study agent-based models (ABMs) given as continuous-time stochastic processes and their pathwise approximation by ordinary and stochastic differential equations (SDEs) for medium to large populations. By means of an appropriately adapted transfer operator approach, we study the behavior of the ABM process on long time scales. We show that, under certain conditions, the transfer operator approach allows us to bridge the gap between the pathwise results for large populations on finite timescales, i.e., the SDE limit model, and approaches built to study dynamical behavior on long time scales like large deviation theory. The latter provides a rigorous analysis of rare events including the associated asymptotic rates on timescales that scale exponentially with the population size. We demonstrate that it is possible to reveal metastable structures and timescales of rare events of the ABM process by finite-length trajectories of the SDE process for large enough populations. This approach has the potential to drastically reduce computational effort for the analysis of ABMs.
Particles to partial differential equations parsimoniously
Authors: Arbabi Hassan , Kevrekidis Ioannis G.
Published: March 2021

Equations governing physico-chemical processes are usually known at microscopic spatial scales, yet one suspects that there exist equations, e.g., in the form of partial differential equations (PDEs), that can explain the system evolution at much coarser, meso-, or macroscopic length scales. Discovering those coarse-grained effective PDEs can lead to considerable savings in computation-intensive tasks like prediction or control. We propose a framework combining artificial neural networks with multiscale computation, in the form of equation-free numerics, for the efficient discovery of such macro-scale PDEs directly from microscopic simulations. Gathering sufficient microscopic data for training neural networks can be computationally prohibitive; equation-free numerics enable a more parsimonious collection of training data by only operating in a sparse subset of the space–time domain. We also propose using a data-driven approach, based on manifold learning (including one using the notion of unnormalized optimal transport of distributions and one based on moment-based description of the distributions), to identify macro-scale dependent variable(s) suitable for the data-driven discovery of said PDEs. This approach can corroborate physically motivated candidate variables or introduce new data-driven variables, in terms of which the coarse-grained effective PDE can be formulated. We illustrate our approach by extracting coarse-grained evolution equations from particle-based simulations with a priori unknown macro-scale variable(s) while significantly reducing the requisite data collection computational effort.
Micro-elastography: Toward ultrasonic shear waves in soft solids
Authors: Laloy-Borgna G. , Zorgani A. , Catheline S.
Published: March 2021

Since shear waves in soft human tissues have been used in clinics, little is known about their upper frequency behavior except that they fade out before the ultrasonic regime due to viscoelastic dissipation. Studying this upper bound has become a need in micro-elastography that aims at characterizing a single cell using shear waves. We report through phantom experiments the observation of ultrasonic shear waves at 20.4 kHz. Moreover, it is shown that the Kelvin–Voigt model can predict a frequency upper bound in good agreement with cell experiments. At last, according to this simple rheological model, the maximum error of elasticity estimation when viscosity is neglected (wide spread perfectly elastic assumption) is 40%.
Static mesh adaptation for reliable large eddy simulation of turbulent reacting flows
Authors: Agostinelli P. W. , Rochette B. , Laera D. , Dombard J. , Cuenot B. , Gicquel L.
Published: March 2021

The design challenge of reliable lean combustors needed to decrease pollutant emissions has clearly progressed with the common use of experiments as well as large eddy simulation (LES) because of its ability to predict the interactions between turbulent flows, sprays, acoustics, and flames. However, the accuracy of such numerical predictions depends very often on the user's experience to choose the most appropriate flow modeling and, more importantly, the proper spatial discretization for a given computational domain. The present work focuses on the last issue and proposes a static mesh refinement strategy based on flow physical quantities. To do so, a combination of sensors based on the dissipation and production of kinetic energy coupled to the flame-position probability is proposed to detect the regions of interest where flow physics happens and grid adaptation is recommended for good LES predictions. Thanks to such measures, a local mesh resolution can be achieved in these zones improving the LES overall accuracy while, eventually, coarsening everywhere else in the domain to reduce the computational cost. The proposed mesh refinement strategy is detailed and validated on two reacting-flow problems: a fully premixed bluff-body stabilized flame, i.e., the VOLVO test case, and a partially premixed swirled flame, i.e., the PRECCINSTA burner, which is closer to industrial configurations. For both cases, comparisons of the results with experimental data underline the fact that the predictions of the flame stabilization, and hence the computed velocity and temperature fields, are strongly influenced by the mesh quality and significant improvement can be obtained by applying the proposed strategy.
Cavitation causes brain injury
Authors: Lang Ji , Nathan Rungun , Zhou Dong , Zhang Xuewei , Li Bo , Wu Qianhong
Published: March 2021

In this study, an artificial transparent head surrogate with high-speed photography discovers the formation and collapse of cavitation bubbles near the contrecoup regions as the head is exposed to a sudden translational impact. The cavitation damages the brain surface and produces a shock wave through the brain matter. Based on a novel experimental design, this new finding uncovers the mystery of the motion and deformation of the soft brain matter, which is not visible otherwise. It suggests that current brain injury criteria may underestimate the risk of head collision.
Contribution of the carbon-originated hole trap to slow decays of photoluminescence and photoconductivity in homoepitaxial n-type GaN layers
Authors: Kato Masashi , Asada Takato , Maeda Takuto , Ito Kenji , Tomita Kazuyoshi , Narita Tetsuo , Kachi Tetsu
Published: March 2021

N-type GaN epitaxial layers grown via metal organic vapor-phase epitaxy typically exhibit a yellow luminescence (YL) band owing to carbon-related deep levels in the photoluminescence spectra. The decay of YL after pulse excitation involves a long time constant (∼0.2 ms at room temperature), whereas microwave photoconductivity decay (μ-PCD) curves show the corresponding component of the time constant. To clarify the origin of the long decay time, the temperature-dependent time constants of YL decay and μ-PCD curves are analyzed using a numerical model based on rate equations for trapping and emission through a deep level. The characteristics of the decays are well reproduced by a recombination model using a hole trap H1 at an energy of EV + 0.88 eV because of the acceptor-like state of carbon on a nitrogen site (CN) whose electron capture cross section (σn) is estimated to be 3 × 10−21 cm2. The slow decay in μ-PCD signals indicates that the electrons before being captured to H1 traps are free electrons in the conduction band. These findings indicate that the slow recombination process through CN results in tail currents in the turn-off switching periods of devices.
A single-shot measurement of time-dependent diffusion over sub-millisecond timescales using static field gradient NMR
Authors: Cai Teddy X. , Williamson Nathan H. , Witherspoon Velencia J. , Ravin Rea , Basser Peter J.
Published: March 2021

Time-dependent diffusion behavior is probed over sub-millisecond timescales in a single shot using a nuclear magnetic resonance static gradient time-incremented echo train acquisition (SG-TIETA) framework. The method extends the Carr–Purcell–Meiboom–Gill cycle under a static field gradient by discretely incrementing the π-pulse spacings to simultaneously avoid off-resonance effects and probe a range of timescales (50–500 µs). Pulse spacings are optimized based on a derived ruleset. The remaining effects of pulse inaccuracy are examined and found to be consistent across pure liquids of different diffusivities: water, decane, and octanol-1. A pulse accuracy correction is developed. Instantaneous diffusivity, Dinst(t), curves (i.e., half of the time derivative of the mean-squared displacement in the gradient direction) are recovered from pulse accuracy-corrected SG-TIETA decays using a model-free log-linear least squares inversion method validated by Monte Carlo simulations. A signal-averaged 1-min experiment is described. A flat Dinst(t) is measured on pure dodecamethylcyclohexasiloxane, whereas decreasing Dinst(t) is measured on yeast suspensions, consistent with the expected short-time Dinst(t) behavior for confining microstructural barriers on the order of micrometers.
Spontaneous imbibition in tight porous media with different wettability: Pore-scale simulation
Authors: Lin Wei , Xiong Shengchun , Liu Yang , He Ying , Chu Shasha , Liu Siyu
Published: March 2021

Spontaneous imbibition is significantly influenced by rock wettability, and it has been extensively studied in core-based experiments and numerical simulations owing to its important role in the development of oil/gas reservoir. Due to the fine pore structure and complex wettability of tight sandstone, an in-depth exploration of the effects of wettability on the pore-scale flow physics during spontaneous imbibition is of great value to complement traditional experimental studies and enhance the understanding of microscopic flow mechanisms during the development of tight oil reservoirs. Based on a X-ray computed tomography scanning experiment and a lattice Boltzmann multiphase model, in this work, we systematically investigate the effects of different hydrophilic strengths on the evolution of the imbibition fronts within the micropores and the degree of nonwetting fluid recovery during spontaneous imbibition of tight sandstone. The results show that the wettability significantly affects the morphological characteristics of the imbibition fronts. Under strong hydrophilic conditions, the wetting fluid preferentially invades the pore corner in the form of angular flow. As the contact angle increases, the hysteresis effect at the main terminal interface decreases, and the two-phase interface becomes regular and compact. Wettability also significantly affects the imbibition rate and the nonwetting fluid recovery degree. The smaller the contact angle, the faster the imbibition rate and the higher the recovery degree of nonwetting fluids during the cocurrent spontaneous imbibition.
A priori assessment of convolutional neural network and algebraic models for flame surface density of high Karlovitz premixed flames
Authors: Ren Jiahao , Wang Haiou , Luo Kun , Fan Jianren
Published: March 2021

Accurate modeling of the unresolved flame surface area is critical for the closure of reaction source terms in the flame surface density (FSD) method. Some algebraic models have been proposed for the unresolved flame surface area for premixed flames in the flamelet or thin reaction zones (TRZ) regimes where the Karlovitz number (Ka) is less than 100. However, in many lean combustion applications, Ka is large (Ka > 100) due to the strong interactions of small-scale turbulence and flames. In the present work, a direct numerical simulation (DNS) database was used to evaluate the performance of algebraic FSD models in high Ka premixed flames in the context of large eddy simulations. Three DNS cases, i.e., case L, case M and case H, were performed, where case L is located in the TRZ regime with Ka < 100 and case M and case H are located in the broken reaction zones regime with Ka > 100. A convolutional neural network (CNN) model was also developed to predict the generalized FSD, which was trained with samples of case H and a small filter size, and was tested in various cases with different Ka and filter sizes. It was found that the fraction of resolved FSD increases with increasing filtered progress variable c̃ and decreasing subgrid turbulent velocity fluctuation u′Δ. The performance of CNN and algebraic models was assessed using the DNS database. Overall, the results of algebraic models are promising in case L and case M for a small filter size; the CNN model performs generally better than the algebraic models in high Ka flames and the correlation coefficient between the modeled and actual generalized FSD is greater than 0.91 in all cases. The effects of c̃ and u′Δ on the performance of different models for various cases were explored. The algebraic models perform well with large values of c̃ and small values of u′Δ in high Ka cases, which indicates that they can be applied to high Ka flames in certain conditions. The performance of the CNN model is better than the algebraic models for a large filter size in high Ka cases.
Inner structures of Görtler streaks
Authors: Huang Ganglei , Si Wufei , Lee Cunbiao
Published: March 2021

The hypersonic boundary layer transition over a concave wall is investigated in a Mach 6.5 quiet wind tunnel using temperature sensitive paint (TSP), CO2-enhanced filtered Rayleigh scattering flow visualization, PCB fast-response pressure sensors, and a high-frequency schlieren technique. The TSP shows that low- and high-temperature streaks are distributed in the spanwise direction. The wavelengths of naturally developing Görtler streaks are randomly distributed, with an average of approximately 7 mm, and change little as the unit Reynolds number increases. More importantly, three-dimensional waves are clearly visualized and quantitatively measured inside the Görtler streaks. This is the first time that the entire evolution of the Görtler instability has been visualized using the Rayleigh-scattering flow visualization in hypersonic flow. The results demonstrate that three-dimensional waves are amplified as a result of the Görtler instability, resulting in a localized high-shear layer around the interface of the three-dimensional waves, which contributes to the formation of hairpin vortices and mushroom-like structures. The three-dimensional waves grow and play an important role in Görtler instability-induced boundary layer transitions.
High n-type conductivity and carrier concentration in Si-implanted homoepitaxial AlN
Authors: Breckenridge M. Hayden , Bagheri Pegah , Guo Qiang , Sarkar Biplab , Khachariya Dolar , Pavlidis Spyridon , Tweedie James , Kirste Ronny , Mita Seiji , Reddy Pramod , Collazo Ramón , Sitar Zlatko
Published: March 2021

We demonstrate Si-implanted AlN with high conductivity (>1 Ω−1 cm−1) and high carrier concentration (5 × 1018 cm−3). This was enabled by Si implantation into AlN with a low threading dislocation density (TDD) (<103 cm−2), a non-equilibrium damage recovery and dopant activation annealing process, and in situ suppression of self-compensation during the annealing. Low TDD and active suppression of VAl-nSiAl complexes via defect quasi Fermi level control enabled low compensation, while low-temperature, non-equilibrium annealing maintained the desired shallow donor state with an ionization energy of ∼70 meV. The realized n-type conductivity and carrier concentration are over one order of magnitude higher than that reported thus far and present a major technological breakthrough in doping of AlN.
Investigation of turbulent inflow specification in Euler–Lagrange simulations of mid-field spray
Authors: Liu K. , Huck P. D. , Aliseda A. , Balachandar S.
Published: March 2021

The process of atomization of a liquid jet by a parallel high-speed gas stream results in a spray, whose downstream development is of considerable interest to several applications. The round jet spray can be spatially divided into (i) a near-field (near-nozzle) region of liquid atomization and (ii) a downstream mid-field region of fully-dispersed droplets. In order to accurately model mid-field droplet dispersion, this work aims at developing a rigorous and robust injection model for Euler–Lagrange spray simulations. Results from experiments are used to obtain the relevant droplet number density, size distribution, and mean and standard deviation velocity distributions of the injection model, systematically in a step-by-step process. Two-phase large eddy simulations are performed by stochastically generating the Lagrangian droplets at the inlet of the mid-field region. Number flux, diameter distribution, mean velocity, and other time-averaged statistics at several downstream locations are shown to agree well with the corresponding experimental data.
A plasmonically enhanced route to faster and more energy-efficient phase-change integrated photonic memory and computing devices
Authors: Gemo E. , Faneca J. , G.-C. Carrillo S. , Baldycheva A. , Pernice W. H. P. , Bhaskaran H. , Wright C. D.
Published: March 2021

Over the past 30 years or more, chalcogenide phase-change materials and devices have generated much scientific and industrial interest, particularly as a platform for non-volatile optical and electronic storage devices. More recently, the combination of chalcogenide phase-change materials with photonic integrated circuits has begun to be enthusiastically explored, and among many proposals, the all-photonic phase-change memory brings the memristor-type device concept to the integrated photonic platform, opening up the route to new forms of unconventional (e.g., in-memory and neuromorphic) yet practicable optical computing. For any memory or computing device, fast switching speed and low switching energy are most attractive attributes, and approaches by which speed and energy efficiency can be improved are always desirable. For phase-change material-based devices, speed and energy consumption are both enhanced the smaller the volume of phase-change material that is required to be switched between its amorphous and crystalline phases. However, in conventional integrated photonic systems, the optical readout of nanometric-sized volumes of phase-change material is problematic. Plasmonics offers a way to bypass such limitations: plasmonic resonant structures are inherently capable of harnessing and focussing optical energy on sub-wavelength scales, far beyond the capabilities of conventional optical and photonic elements. In this work, we explore various approaches to combine the three building blocks of Si-photonics, resonant plasmonic structures, and phase-change materials to deliver plasmonically enhanced integrated phase-change photonic memory and computing devices and systems, underlining the inherent technical and theoretical challenges therein.
Experimental investigation on the impingement of synthetic jet vortex rings onto a porous wall
Authors: Xu Yang , Li Zhi-Yu , Wang Jin-Jun
Published: March 2021

This paper presents an experimental study on the effects of the Reynolds number (Resj = 300, 600, and 900) and porosity (ϕ = 20%–85%) on synthetic jet vortex rings impinging onto a porous wall. Laser-induced fluorescence and particle image velocimetry are used to acquire flow information qualitatively and quantitatively. When Resj is low (Resj = 300), ϕ plays a key role in determining the formation of transmitted vortex rings downstream. For the first time, a row of individual small-scale vortex rings that form at the lowest porosity (ϕ = 20%) have been observed in the synthetic jet/porous wall interaction. As Resj increases to 900, the triggered Kelvin–Helmholtz instability promotes the vorticity cancellation at a low porosity (ϕ = 30%), and thus contributes to the formation of a transmitted vortex ring. It is concluded that the vorticity cancellation is the dominant factor affecting the generation of a transmitted vortex ring. Time-averaged characteristics indicate that for a low Resj, the incoherence of the vortex ring is mainly due to the viscous effects. However, for a high Resj, it is the transition that leads to a significant enhancement in the turbulent kinetic energy. Measurements of flow macroscopic parameters show that the loss of the momentum flux exhibits a linear relationship with ϕ for all Resj, while the loss of the kinetic energy transport is nonlinearly dependent on ϕ. Incorporating ϕ, this study presents a more comprehensive similarity parameter, ϕln(Resj2dh*3), to characterize the synthetic jet/porous wall interaction.
Opaque and translucent films from aqueous microfiber suspensions by evaporative self-assembly
Authors: Mirvakili Mehr Negar , Hatzikiriakos Savvas G. , Englezos Peter
Published: March 2021

Films were prepared by casting microfiber (MF) suspensions on hydrophobic and hydrophilic substrates at controlled conditions (23 °C and 50% relative humidity). It was found that opaque films are formed on the hydrophilic surface, while translucent films are formed on the hydrophobic one. The physical and mechanical properties of the MF films were found to be comparable to those of nano-fibrillated cellulose and microfibrillated cellulose films. The observations from the microfiber film formation on the two substrates of different wettability are discussed in the context of the evaporation of water from sessile droplets containing nanoparticles.
Semiconductor-to-metal transition in bilayer MoSi2N4 and WSi2N4 with strain and electric field
Authors: Wu Qingyun , Cao Liemao , Ang Yee Sin , Ang Lay Kee
Published: March 2021

With exceptional electrical and mechanical properties and at the same time air-stability, layered MoSi2N4 has recently drawn great attention. However, band structure engineering via strain and electric field, which is vital for practical applications, has not yet been explored. In this work, we show that the biaxial strain and external electric field are effective ways for the bandgap engineering of bilayer MoSi2N4 and WSi2N4. It is found that strain can lead to indirect bandgap to direct bandgap transition. On the other hand, electric field can result in semiconductor to metal transition. Our study provides insights into the band structure engineering of bilayer MoSi2N4 and WSi2N4 and would pave the way for its future nanoelectronics and optoelectronics applications.
Fragmentation of isocyanic acid, HNCO, following core excitation and ionization
Authors: Gerlach Marius , Fantuzzi Felipe , Wohlfart Lilith , Kopp Karina , Engels Bernd , Bozek John , Nicolas Christophe , Mayer Dennis , Gühr Markus , Holzmeier Fabian , Fischer Ingo
Published: March 2021

We report a study on the fragmentation of core-ionized and core-excited isocyanic acid, HNCO, using Auger-electron/photoion coincidence spectroscopy. Site-selectivity is observed both for normal and resonant Auger electron decay. Oxygen 1s ionization leads to the CO+ + NH+ ion pairs, while nitrogen 1s ionization results in three-body dissociation and an efficient fragmentation of the H–N bond in the dication. Upon 1s → 10a′ resonant excitation, clear differences between O and N sites are discernible as well. In both cases, the correlation between the dissociation channel and the binding energy of the normal Auger electrons indicates that the fragmentation pattern is governed by the excess energy available in the final ionic state. High-level multireference calculations suggest pathways to the formation of the fragment ions NO+ and HCO+, which are observed although the parent compound contains neither N–O nor H–C bonds. This work contributes to the goal to achieve and understand site-selective fragmentation upon ionization and excitation of molecules with soft x-ray radiation.
Efficient implementation of atom-density representations
Authors: Musil Félix , Veit Max , Goscinski Alexander , Fraux Guillaume , Willatt Michael J. , Stricker Markus , Junge Till , Ceriotti Michele
Published: March 2021

Physically motivated and mathematically robust atom-centered representations of molecular structures are key to the success of modern atomistic machine learning. They lie at the foundation of a wide range of methods to predict the properties of both materials and molecules and to explore and visualize their chemical structures and compositions. Recently, it has become clear that many of the most effective representations share a fundamental formal connection. They can all be expressed as a discretization of n-body correlation functions of the local atom density, suggesting the opportunity of standardizing and, more importantly, optimizing their evaluation. We present an implementation, named librascal, whose modular design lends itself both to developing refinements to the density-based formalism and to rapid prototyping for new developments of rotationally equivariant atomistic representations. As an example, we discuss smooth overlap of atomic position (SOAP) features, perhaps the most widely used member of this family of representations, to show how the expansion of the local density can be optimized for any choice of radial basis sets. We discuss the representation in the context of a kernel ridge regression model, commonly used with SOAP features, and analyze how the computational effort scales for each of the individual steps of the calculation. By applying data reduction techniques in feature space, we show how to reduce the total computational cost by a factor of up to 4 without affecting the model’s symmetry properties and without significantly impacting its accuracy.
Artificial spin ice: Paths forward
Authors: Schiffer Peter , Nisoli Cristiano
Published: March 2021

Artificial spin ice systems are lithographically prepared arrays of interacting nanoscale magnetic moments with collective behavior resulting from the chosen array geometry. These many-body systems are unusual in that their simple constituent elements can be configured to design their interactions with exquisite control. They can then be probed experimentally over a remarkably large range of time scales and length scales, including imaging of the individual moments. The study of artificial spin ice has broadened well beyond the original focus on systems with connection to spin ice and ice models, and now the term is used in reference to many other structures that exhibit a much wider range of physical phenomena. In this Perspective, we review progress in the field of artificial spin ice since its inception more than a decade ago. We then discuss prospects for future directions—continuing the exploration of nanomagnetism, statistical spin models, and the potential for technological devices.
Fantastic n = 4: Ce5Co4+xGe13−ySny of the An+1MnX3n+1 homologous series
Authors: Weiland Ashley , Wei Kaya , McCandless Gregory T. , Baumbach Ryan E. , Chan Julia Y.
Published: March 2021

Ce-based intermetallics are of interest due to the potential to study the interplay of localized magnetic moments and conduction electrons. Our work on Ce-based germanides led to the identification of a new homologous series An+1MnX3n+1 (A = rare earth, M = transition metal, X = tetrels, and n = 1–6). This work presents the single-crystal growth, structure determination, and anisotropic magnetic properties of the n = 4 member of the Cen+1ConGe3n+1 homologous series. Ce5Co4+xGe13−ySny consists of three Ce sites, three Co sites, seven Ge sites, and two Sn sites, and the crystal structure is best modeled in the orthorhombic space group Cmmm where a = 4.3031(8) Å, b = 45.608(13) Å, and c = 4.3264(8) Å, which is in close agreement with the previously reported Sn-free analog where a = 4.265(1) Å, b = 45.175(9) Å, and c = 4.293(3) Å. Anisotropic magnetic measurements show Kondo-like behavior and three magnetic transitions at 6, 4.9, and 2.4 K for Ce5Co4+xGe13−ySny.
Universal perturbation growth of Richtmyer–Meshkov instability for minimum-surface featured interface induced by weak shock waves
Authors: Liang Yu , Liu Lili , Zhai Zhigang , Si Ting , Luo Xisheng
Published: March 2021

Experimental and theoretical investigations are performed to explore the development of Richtmyer–Meshkov (RM) instability for a minimum-surface featured (3D-) interface. The exact mathematical expression of 3D-interface perturbation is obtained for the first time by the spectrum analysis, describing as a superposition of transverse two-dimensional (2D) single-mode with three-dimensional (3D) multi-mode. In particular, the normalized 3D-interface profile is found to be solely determined by one dimensionless parameter related to the 3D-interface initial spectrum. The shock tube experiments are performed by varying the interface height to change the mode-composition of 3D-interfaces under weak shock conditions. It is found that the 3D multi-mode component of a 3D-interface promotes/suppresses the RM instability at the transverse boundary/symmetry plane in comparison with the classical 2D single-mode case. At the linear regime, the 3D perturbation growth can be well predicted by combining the amplitude growth of a 2D single-mode and a 3D dual-mode. At the nonlinear regime, as the interface height reduces, the nonlinear effect on the RM instability at the boundary plane becomes stronger. A generalized nonlinear model is established to predict the interface amplitude by considering the interface spectrum and the mode-coupling of 3D modes. It is found that the mode-coupling has an evident influence on the bubble evolution, and the first-order 3D mode leads to different behaviors for the bubble and spike width growths. This work may provide great insight into the physical mechanism of the 3D RM instability existing in practical applications.
Semi-insulating 4H-SiC lateral bulk acoustic wave resonators
Authors: Jiang B. , Opondo N. P. , Bhave S. A.
Published: March 2021

Silicon carbide (SiC) excels in its outstanding mechanical properties, which are widely studied in microelectromechanical systems. Recently, the mechanical tuning of color centers in 4H-SiC has been demonstrated, broadening its application in quantum spintronics. The strain generated in a mechanical resonator can be used to manipulate the quantum state of the color center qubit. This work reports a lateral overtone mechanical resonator fabricated from a semi-insulating bulk 4H-SiC wafer. An aluminum nitride piezoelectric transducer on SiC is used to drive the resonance. The resonator shows a series of modes with quality factors (Q) above 3000. An acoustic reflector positioned at the anchor shows a 22% improvement in Q at 300 MHz resonance and suppresses the overtone modes away from it. This monolithic SiC resonator allows optical access to the SiC color centers from both sides of the wafer, enabling a convenient setup in quantum measurements.
Simulation of photo-electron spectrum and electron scattering by dual time propagation
Authors: Bhan Luke , Covington Cody , Rivas Jason , Varga Kálmán
Published: March 2021

A dual time propagation approach is introduced to describe electron scattering and ionization. The space is divided into two regions, a central region with a full time-dependent Hamiltonian and an outer region where the kinetic operator and the laser field dominate. The two regions are connected by a source term. Time-dependent density functional theory calculations of wave packet scattering on molecules and photoelectron spectrum due to circularly polarized laser are presented to illustrate the efficiency and applicability of the approach.
Quantum dynamics of the energy transfer for vibrationally excited HF (v = 7) colliding with D2 (v = 0): Theory assessing experiment
Authors: Zhou Boyi , Yang Dongzheng , Xie Daiqian
Published: March 2021

It is still challenging to accurately qualify the rate coefficients for vibrationally excited molecules in experiment. In particular, for the energy transfer between HF (v = 7) and D2 (v = 0), which is a prototype for near resonant collisional transfer of vibrational excitation from one molecule to the other, the two available experimental results of rate coefficients contradict each other by a factor of nearly 20. In order to benchmark these data, in this work, the rate coefficients of vibration–vibration energy transfer processes of this system at temperatures ranging from 100 to 1500 K were calculated by employing the coupled-states approximation based on our recently developed full-dimensional ab initio intermolecular potential energy surface. The state-to-state rate coefficients were found to follow the general energy gap law. The calculated total vibration–vibration energy transfer rate coefficients decrease with the increase in the angular momentum of HF at most temperatures. The vibrational relaxation rate coefficient decreases monotonously with the temperature, and the calculated result of 8.1 × 10−11 cm3 mol−1 s−1 at room temperature is in very good agreement with the experimental value reported by Dzelzkalns and Kaufman [J. Chem. Phys. 77, 3508 (1982)].
Redefining southern Australia’s climatic regions and seasons
Authors: Fiddes Sonya , Pepler Acacia , Saunders Kate , Hope Pandora
Published: March 2021

Climate scientists routinely rely on averaging over time or space to simplify complex information and to concisely communicate findings. Currently, no consistent definitions of ‘warm’ or ‘cool’ seasons for southern Australia exist, making comparisons across studies difficult. Similarly, numerous climate studies in Australia use either arbitrarily defined areas or the Natural Resource Management (NRM) clusters to perform spatial averaging. While the NRM regions were informed by temperature and rainfall information, they remain somewhat arbitrary. Here we use weather type influence on rainfall and clustering methods to quantitatively define climatic regions and seasons over southern Australia. Three methods are explored: k-means clustering and two agglomerative clustering methods, Ward linkage and average linkage. K-means was found to be preferred in temporal clustering, while the average linkage method was preferred for spatial clustering. For southern Australia as a whole, we define the cool season as April–September and warm season as October–March, though we note that a three-season split may provide more nuanced climate analysis. We also show that different regions across southern Australia experience different seasons and demonstrate the changing spatial influence of weather types with the seasons, which may aid regionally or seasonally specific climate analysis. Division of southern Australia into 15 climatic regions shows localised agreement with the NRM clusters where distinct differences in rainfall amounts exist. However, the climate regions defined here better represent the importance of topographical aspect on weather type influence and the inland extent of particular weather types. We suggest that the use of these regions would provide consistent climate analysis across studies if widely adopted. A key requirement for climate scientists is the simplification of data sets into both seasonally or regionally averaged subsets. This simplification, by grouping like regions or seasons, is done for a number of reasons both scientific and practical, including to help understand patterns of variability, underlying drivers and trends in climate and weather, to communicate large amounts of data concisely, to reduce the amount of data required for processing (which becomes increasingly important with higher resolution climate model output), or to more simply draw a physical boundary between regions for other purposes, such as flora and fauna habitat analysis, appropriate agricultural practices or water management.
The Antarctic ozone hole during 2018 and 2019
Authors: Klekociuk Andrew R. , Tully Matthew B. , Krummel Paul B. , Henderson Stuart I. , Smale Dan , Querel Richard , Nichol Sylvia , Alexander Simon P. , Fraser Paul J. , Nedoluha Gerald
Published: March 2021

While the Montreal Protocol is reducing stratospheric ozone loss, recent increases in some ozone depleting substance (ODS) emissions have been identified that may impact southern hemisphere climate systems. In this study, we discuss characteristics of the 2018 and 2019 Antarctic ozone holes using surface in situ, satellite and reanalysis data to gain a better understanding of recent ozone variability. These ozone holes had strongly contrasting characteristics. In 2018, the Antarctic stratospheric vortex was relatively stable and cold in comparison to most years of the prior decade. This resulted in a large and persistent ozone hole that ranked in the upper-tercile of metrics quantifying Antarctic ozone depletion. In contrast, strong stratospheric warming in the spring of 2019 curtailed the development of the ozone hole, causing it to be anomalously small and of similar size to ozone holes in the 1980s. As known from previous studies, the ability of planetary waves to propagate into the stratosphere at high latitudes is an important factor that influences temperatures of the polar vortex and the overall amount of ozone loss in any particular year. Disturbance and warming of the vortex by strong planetary wave activity were the dominant factors in the small 2019 ozone hole. In contrast, planetary wave disturbances to the vortex in the winter–spring of 2018 were much weaker than in 2019. These results increase our understanding of the impact of Montreal Protocol controls on ODS and the effects of Antarctic ozone on the southern hemisphere climate system.
Stage-specific overcompensation, the hydra effect, and the failure to eradicate an invasive predator
Authors: Grosholz Edwin , Ashton Gail , Bradley Marko , Brown Chris , Ceballos-Osuna Lina , Chang Andrew , de Rivera Catherine , Gonzalez Julie , Heineke Marcella , Marraffini Michelle , McCann Linda , Pollard Erica , Pritchard Ian , Ruiz Gregory , Turner Brian , Tepolt Carolyn
Published: March 2021

Significance

Theoretical models of population dynamics have shown the counterintuitive conclusion that harvest can increase the equilibrium size of a population. These models of increases in response to mortality have been considered for fisheries harvest and removal of non-native species and can be driven by density-dependent overcompensation. This is the first controlled experimental field demonstration showing that harvest-driven overcompensation produced a 30-fold, single-year increase in the abundance of the invasive European green crab (Carcinus maenas), one of the world’s most invasive predators. Using multiple lines of evidence, we provide both a robust demonstration of a fundamental prediction of population models in a field population and an important cautionary message for future eradication efforts for similar invasive species.
Monitoring tumor cell death in murine tumor models using deuterium magnetic resonance spectroscopy and spectroscopic imaging
Authors: Hesse Friederike , Somai Vencel , Kreis Felix , Bulat Flaviu , Wright Alan J. , Brindle Kevin M.
Published: March 2021

Significance

There is an unmet clinical need for sensitive methods for detecting cell death in vivo, for example, in disease and following tumor treatment. We show here that deuterium magnetic resonance measurements at 7 T of labeled malate production from injected
2
H-labeled fumarate provide a sensitive method for detecting tumor cell death in vivo following treatment. Malate production was relatively slow in viable cells but was markedly increased in necrotic tissue.
Sex differences in early experience and the development of aggression in wild chimpanzees
Authors: Sabbi Kris H. , Emery Thompson Melissa , Machanda Zarin P. , Otali Emily , Wrangham Richard W. , Muller Martin N.
Published: March 2021

Significance

Chimpanzees, human’s close evolutionary relatives, are a tractable model system for understanding how physical aggression can develop in the absence of gender socialization. Here we used 13 y of behavioral data and a targeted 3-y social development study to document clear sex differences in chimpanzees’ early aggressive experiences, supporting the possibility for social experience to shape sex-typed behavior in the absence of explicitly taught gender norms. However, as young males’ own aggressive behavior provoked aggressive responses from others, experiential differences were influenced by early-emerging behavioral differences that already resembled adult patterns. By demonstrating interactions between exposure to aggression and developing behavior, our results add an important perspective to long-standing debates over the origins of gender differences in human aggression.
Diverse innate stimuli activate basophils through pathways involving Syk and IκB kinases
Authors: Pellefigues Christophe , Mehta Palak , Chappell Sally , Yumnam Bibek , Old Sam , Camberis Mali , Le Gros Graham
Published: March 2021

Significance

Basophils contribute to allergic reactions when surface-bound IgE is cross-linked by allergens. How they respond to innate stimuli to produce cytokines during tissue inflammation and homeostasis is less known. Here, we comprehensively identify and compare which innate and homeostatic stimuli, among cytokines, growth factors, hormones, metabolites, and bacterial components, can activate primary basophils. We find that activated basophils display phenotypic heterogeneity at the single-cell level, suggesting that mutually exclusive functional basophil subsets exist in vivo. Furthermore, using selective kinase inhibitors we show that distinct receptor families, including IL-1R, GPCR, FcR, CD200R, and cytokine receptors, mediate basophil activation through Syk and IκB kinases. We propose these pathways have a rheostat function controlling basophil activation to diverse stimuli.
Exposure density and neighborhood disparities in COVID-19 infection risk
Authors: Hong Boyeong , Bonczak Bartosz J. , Gupta Arpit , Thorpe Lorna E. , Kontokosta Constantine E.
Published: March 2021

Significance

We present a computational approach to measure exposure density at high spatial and temporal resolution to understand neighborhood disparities in transmission risk of COVID-19. By integrating geolocation data and granular land-use information, we are able to establish both the extent of activity in a particular neighborhood and the nature of that activity across residential, nonresidential, and outdoor activities. We then analyze the differential behavioral response to social-distancing policies based on local risk factors, built-environment characteristics, and socioeconomic inequality. Our results highlight the significant disparities in health outcomes for racial and ethnic minorities and lower-income households. Exposure density provides an additional metric to further explain and understand the disparate impact of COVID-19 on vulnerable communities.
Crystal structure of a far-red–sensing cyanobacteriochrome reveals an atypical bilin conformation and spectral tuning mechanism
Authors: Bandara Sepalika , Rockwell Nathan C. , Zeng Xiaoli , Ren Zhong , Wang Cong , Shin Heewhan , Martin Shelley S. , Moreno Marcus V. , Lagarias J. Clark , Yang Xiaojing
Published: March 2021

Significance

Phytochromes are well-known far-red-light sensors found in plants that trigger adaptive responses to facilitate competition for light capture with neighboring plants. Red- and far-red sensing are also critical for cyanobacteria living in the far-red–enriched shade of plants. This work reports the crystal structure of a far-red–sensing cyanobacteriochrome, a distant cyanobacterial relative of phytochrome. These studies shed insights into the molecular basis of far-red-sensing by phycobilin-based photoreceptors. Owing to the deep tissue penetration of far-red light, far-red–sensing cyanobacteriochromes are promising protein scaffolds for developing genetically encoded photoswitches, optoacoustic contrast agents, and fluorescent probes for in situ imaging and optogenetic applications.
ILC3s control splenic cDC homeostasis via lymphotoxin signaling
Authors: Vanderkerken Matthias , Baptista Antonio P. , De Giovanni Marco , Fukuyama Satoshi , Browaeys Robin , Scott Charlotte L. , Norris Paula S. , Eberl Gerard , Di Santo James P. , Vivier Eric , Saeys Yvan , Hammad Hamida , Cyster Jason G. , Ware Carl F. , Tumanov Alexei V. , De Trez Carl , Lambrecht Bart N.
Published: March 2021

The spleen contains a myriad of conventional dendritic cell (cDC) subsets that protect against systemic pathogen dissemination by bridging antigen detection to the induction of adaptive immunity. How cDC subsets differentiate in the splenic environment is poorly understood. Here, we report that LTα1β2-expressing Rorgt+ ILC3s, together with B cells, control the splenic cDC niche size and the terminal differentiation of Sirpα+CD4+Esam+ cDC2s, independently of the microbiota and of bone marrow pre-cDC output. Whereas the size of the splenic cDC niche depended on lymphotoxin signaling only during a restricted time frame, the homeostasis of Sirpα+CD4+Esam+ cDC2s required continuous lymphotoxin input. This latter property made Sirpα+CD4+Esam+ cDC2s uniquely susceptible to pharmacological interventions with LTβR agonists and antagonists and to ILC reconstitution strategies. Together, our findings demonstrate that LTα1β2-expressing Rorgt+ ILC3s drive splenic cDC differentiation and highlight the critical role of ILC3s as perpetual regulators of lymphoid tissue homeostasis.