bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural origin of excitations in a colloidal glass-former
Authors: Ganapathi Divya , Sood A. K. , Ganapathy Rajesh
Published: May 2022

Despite decades of intense research, whether the transformation of supercooled liquids into glass is a kinetic phenomenon or a thermodynamic phase transition remains unknown. Here, we analyzed optical microscopy experiments on 2D binary colloidal glass-forming liquids and investigated the structural links of a prominent kinetic theory of glass transition. We examined a possible structural origin for localized excitations, which are building blocks of the dynamical facilitation theory—a purely kinetic approach for the glass transition. To accomplish this, we utilize machine learning methods to identify a structural order parameter termed “softness” that has been found to be correlated with reorganization events in supercooled liquids. Both excitations and softness qualitatively capture the dynamical slowdown on approaching the glass transition and motivated us to explore spatial and temporal correlations between them. Our results show that excitations predominantly occur in regions with high softness and the appearance of these high softness regions precedes excitations, thus suggesting a causal connection between them. Thus, unifying dynamical and thermodynamical theories into a single structure-based framework may provide a route to understand the glass transition.
Characterization of trap states in AlN/GaN superlattice channel high electron mobility transistors under total-ionizing-dose with 60Co γ-irradiation
Authors: Liu Shuang , Zhang Jincheng , Zhao Shenglei , Shu Lei , Song Xiufeng , Wang Chengjie , Li Tongde , Liu Zhihong , Hao Yue
Published: May 2022

In this Letter, the effects of trap states in AlN/GaN superlattice channel HEMTs (high electron mobility transistors) under total ionizing dose with γ-irradiation have been systematically investigated. After 1 Mrad γ-irradiation with a dose rate of 50 rad/s, negative drifts in threshold voltage and C–V characteristics are observed. Simultaneously, the two-dimensional electron gas sheet density of the upper channel increases from 5.09 × 1012 to 5.47 × 1012 cm−2, while that of the lower channel decreases from 4.41 × 1012 to 3.86 × 1012 cm−2, respectively. Furthermore, frequency-dependent capacitance and conductance measurements are adopted to investigate the evolution of trap states in an electron channel. The trap state density (DT = 0.21–0.88 × 1013 cm−2 eV−1) is over the ET range from 0.314 to 0.329 eV after irradiation for the upper channel, while the trap state in the lower channel decreases from 4.54 × 1011 cm−2 eV−1 at ET = 0.230 eV to 2.38 × 1011 cm−2 eV−1 at ET = 0.278 eV. The density (1.39–1.54 × 1011 cm−2 eV−1) of trap states with faster τT (0.033–0.037 μs) generated in a lower channel is located at shallower ET between 0.227 and 0.230 eV. The results reveal the mechanism of trap states in the channel, affecting the performance of HEMTs, which can provide a valuable understanding for hardening in space radiation.
Ephemeral ice-like local environments in classical rigid models of liquid water
Authors: Capelli Riccardo , Muniz-Miranda Francesco , Pavan Giovanni M.
Published: May 2022

Despite great efforts over the past 50 years, the simulation of water still presents significant challenges and open questions. At room temperature and pressure, the collective molecular interactions and dynamics of water molecules may form local structural arrangements that are non-trivial to classify. Here, we employ a data-driven approach built on Smooth Overlap of Atomic Position (SOAP) that allows us to compare and classify how widely used classical models represent liquid water. Macroscopically, the obtained results are rationalized based on water thermodynamic observables. Microscopically, we directly observe how transient ice-like ordered environments may dynamically/statistically form in liquid water, even above freezing temperature, by comparing the SOAP spectra for different ice structures with those of the simulated liquid systems. This confirms recent ab initio-based calculations but also reveals how the emergence of ephemeral local ice-like environments in liquid water at room conditions can be captured by classical water models.
Highly conductive film of PEDOT:PSS treated with cosolvent of formamide and methanol for flexible piezoresistive sensor applications
Authors: Xia Yijie , Cui Ying , Huang Pengju , Wu Luchao , Du Shuaishuai , Zhu Yinfei , Lin Jian , Liu Xuyan , Zhong Gaoyu
Published: May 2022

Flexible and wearable piezoresistive sensors keep attracting attention in many areas due to their wide application. Flexible materials with high conductivity are crucial to be explored for flexible piezoresistive sensors. In this work, a mild treatment method utilizing a cosolvent of formamide and methanol to dramatically improve the film conductivity of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) was developed. The PEDOT:PSS film conductivity was improved from 0.3 to 1287 S/cm through double treatments with cosolvent of formamide and methanol. The enhancement of conductivity is because of reduced insulating PSS and the change of PEDOT chain conformational. The flexible piezoresistive sensor made by the formamide/methanol treated PEDOT:PSS film demonstrates good performance, especially the excellent mechanical durability in detecting finger joint movement, which suggests that the sensor developed has promising application in human motion detection.
Kinetic Monte Carlo modeling of oxide thin film growth
Authors: Purton John A. , Elena Alin M. , Teobaldi Gilberto
Published: May 2022

In spite of the increasing interest in and application of ultrathin film oxides in commercial devices, the understanding of the mechanisms that control the growth of these films at the atomic scale remains limited and scarce. This limited understanding prevents the rational design of novel solutions based on precise control of the structure and properties of ultrathin films. Such a limited understanding stems in no minor part from the fact that most of the available modeling methods are unable to access and robustly sample the nanosecond to second timescales required to simulate both atomic deposition and surface reorganization at ultrathin films. To contribute to this knowledge gap, here we have combined molecular dynamics and adaptive kinetic Monte Carlo simulations to study the deposition and growth of oxide materials over an extended timescale of up to ∼0.5 ms. In our pilot studies, we have examined the growth of binary oxide thin films on oxide substrates. We have investigated three scenarios: (i) the lattice parameter of both the substrate and thin film are identical, (ii) the lattice parameter of the thin film is smaller than the substrate, and (iii) the lattice parameter is greater than the substrate. Our calculations allow for the diffusion of ions between deposition events and the identification of growth mechanisms in oxide thin films. We make a detailed comparison with previous calculations. Our results are in good agreement with the available experimental results and demonstrate important limitations in former calculations, which fail to sample phase space correctly at the temperatures of interest (typically 300–1000 K) with self-evident limitations for the representative modeling of thin films growth. We believe that the present pilot study and proposed combined methodology open up for extended computational support in the understanding and design of ultrathin film growth conditions tailored to specific applications.
Investigation of negative-ion resonances using a subspace-projected multiconfigurational electron propagator perturbed with a complex absorbing potential
Authors: Das Subhasish , Samanta Kousik
Published: May 2022

The transient negative-ion resonances found in scattering experiments are important intermediates in many chemical processes. These metastable states correspond to the continuum part of the Hamiltonian of the projectile–target composite system. Usual bound-state electronic structure methods are not applicable for these. In this work, we develop a subspace-projection method in connection with an electron propagator (EP) defined in terms of a complete-active-space self-consistent-field initial state. The target Hamiltonian (Ĥ) is perturbed by a complex absorbing potential (CAP) for the analytical continuation of the spectrum of Ĥ to complex eigenvalues associated with the continuum states. The resonance is identified as a pole of the EP, which is stable with respect to variations in the strength of the CAP. The projection into a small subspace reduces the size of the complex matrices to be diagonalized, minimizes the computational cost, and affords some insight into the orbitals that are likely to play some role in the capture of the projectile. Two molecular (Πg2N2− and 2Π CO−) and an atomic shaperesonance (2P Be−) are investigated using this method. The position and width of the resonances are in good agreement with the previously reported values.
Effect of an applied magnetic field on Kelvin–Helmholtz instability driven by a laser under multi-mode disturbance
Authors: Sun Wei , Lei Zhu , Lv Chong , Zhong Jiayong
Published: May 2022

Kelvin–Helmholtz instability (KHI), as a fundamental physical process of fluids and plasmas, widely exists in astrophysics and physical phenomena of high energy density. In this paper, through radiation magnetohydrodynamic code, KHI is generated by the interaction between laser pulses and modulation targets in two-dimensional numerical simulations. Here, the evolution process of KHI vortices under different initial disturbance modes and with or without a horizontal external flow-direction magnetic field is investigated and compared from the perspectives of vorticity, magnetic pressure, magnetic tension, and longitudinal maximum kinetic energy. The simulation demonstrates that the external magnetic field in the horizontal flow direction inhibits the evolution of single-mode KHI vortices and the merging of multi-mode KHI vortices. The research results can provide theoretical guidance for KHI experiments using a high-energy-density laser device under a robust magnetic environment. They are also of significance to frontier research related to inertial confinement fusion.
Enhancing one-dimensional particle-in-cell simulations to self-consistently resolve instability-induced electron transport in Hall thrusters
Authors: Faraji F. , Reza M. , Knoll A.
Published: May 2022

The advent of high-power Hall thrusters and the increasing interest toward their use as a primary propulsion system for various missions have given a new boost to the efforts aiming at self-consistent predictive modeling of this thruster technology. In this article, we present a novel approach, which allows enhancing the predictive capability of one-dimensional particle-in-cell (PIC) simulations to self-consistently capture the wave-induced electron transport due to the azimuthal instabilities in Hall thrusters. The so-called “pseudo-2D” PIC scheme resulting from this approach is extensively tested in several operating conditions. The results are compared against a well-established 2D3V axial–azimuthal reference case in terms of the axial profiles of the time-averaged plasma properties, the azimuthal electric field fluctuations and their dispersion features, and the contributions of the force terms in the electron azimuthal momentum equation to the cross-field mobility. We have demonstrated that the pseudo-2D PIC provides a prediction of the above aspects that compares very closely in almost all conditions with those from the full-2D simulation. In addition, the sensitivity of the pseudo-2D simulation results to the numerical parameters associated with our approach is assessed in detail. The outcomes of these analyses have casted light on the next steps to further improve the approach.
Spectral densities and absorption spectra of the core antenna complex CP43 from photosystem II
Authors: Sarngadharan Pooja , Maity Sayan , Kleinekathöfer Ulrich
Published: May 2022

Besides absorbing light, the core antenna complex CP43 of photosystem II is of great importance in transferring excitation energy from the antenna complexes to the reaction center. Excitation energies, spectral densities, and linear absorption spectra of the complex have been evaluated by a multiscale approach. In this scheme, quantum mechanics/molecular mechanics molecular dynamics simulations are performed employing the parameterized density functional tight binding (DFTB) while the time-dependent long-range-corrected DFTB scheme is applied for the excited state calculations. The obtained average spectral density of the CP43 complex shows a very good agreement with experimental results. Moreover, the excitonic Hamiltonian of the system along with the computed site-dependent spectral densities was used to determine the linear absorption. While a Redfield-like approximation has severe shortcomings in dealing with the CP43 complex due to quasi-degenerate states, the non-Markovian full second-order cumulant expansion formalism is able to overcome the drawbacks. Linear absorption spectra were obtained, which show a good agreement with the experimental counterparts at different temperatures. This study once more emphasizes that by combining diverse techniques from the areas of molecular dynamics simulations, quantum chemistry, and open quantum systems, it is possible to obtain first-principle results for photosynthetic complexes, which are in accord with experimental findings.
Deposition temperature dependence of thermo-spin and magneto-thermoelectric conversion in Co2MnGa films on Y3Fe5O12 and Gd3Ga5O12
Authors: Mizuno Hayato , Modak Rajkumar , Hirai Takamasa , Takahagi Atsushi , Sakuraba Yuya , Iguchi Ryo , Uchida Ken-ichi
Published: May 2022

We have characterized Co2MnGa (CMG) Heusler alloy films grown on Y3Fe5O12 (YIG) and Gd3Ga5O12 (GGG) substrates at different deposition temperatures and investigated thermo-spin and magneto-thermoelectric conversion properties by means of a lock-in thermography technique. X-ray diffraction, magnetization, and electrical transport measurements show that the deposition at high substrate temperatures induces the crystallized structures of CMG, while the resistivity of the CMG films on YIG (GGG) prepared at and above 500 °C (550 °C) becomes too high to measure the thermo-spin and magneto-thermoelectric effects due to large roughness, highlighting the difficulty of fabricating highly ordered continuous CMG films on garnet structures. Our lock-in thermography measurements show that the deposition at high substrate temperatures results in an increase in the current-induced temperature change for CMG/GGG and a decrease in that for CMG/YIG. The former indicates the enhancement of the anomalous Ettingshausen effect in CMG through crystallization. The latter can be explained by the superposition of the anomalous Ettingshausen effect and the spin Peltier effect induced by the positive (negative) charge-to-spin conversion for the amorphous (crystallized) CMG films. These results provide a hint to construct spin-caloritronic devices based on Heusler alloys.
Near-exact treatment of seniority-zero ground and excited states with a Richardson–Gaudin mean-field
Authors: Fecteau Charles-Émile , Cloutier Samuel , Moisset Jean-David , Boulay Jérémy , Bultinck Patrick , Faribault Alexandre , Johnson Paul A.
Published: May 2022

Eigenvectors of the reduced Bardeen–Cooper–Schrieffer (BCS) Hamiltonian, Richardson–Gaudin (RG) states, are used as a variational wavefunction ansatz for strongly correlated electronic systems. These states are geminal products whose coefficients are solutions of non-linear equations. Previous results showed an un-physical apparent avoided crossing in ground state dissociation curves for hydrogen chains. In this paper, it is shown that each seniority-zero state of the molecular Coulomb Hamiltonian corresponds directly to an RG state. However, the seniority-zero ground state does not correspond to the ground state of a reduced BCS Hamiltonian. The difficulty is in choosing the correct RG state. The systems studied showed a clear choice, and we expect that it should always be possible to reason physically which state to choose.
Gaussian approximation of dispersion potentials for efficient featurization and machine-learning predictions of metal–organic frameworks
Authors: Choi Sihoon , Sholl David S. , Medford Andrew J.
Published: May 2022

Energy-related descriptors in machine learning are a promising strategy to predict adsorption properties of metal–organic frameworks (MOFs) in the low-pressure regime. Interactions between hosts and guests in these systems are typically expressed as a sum of dispersion and electrostatic potentials. The energy landscape of dispersion potentials plays a crucial role in defining Henry’s constants for simple probe molecules in MOFs. To incorporate more information about this energy landscape, we introduce the Gaussian-approximated Lennard-Jones (GALJ) potential, which fits pairwise Lennard-Jones potentials with multiple Gaussians by varying their heights and widths. The GALJ approach is capable of replicating information that can be obtained from the original LJ potentials and enables efficient development of Gaussian integral (GI) descriptors that account for spatial correlations in the dispersion energy environment. GI descriptors would be computationally inconvenient to compute using the usual direct evaluation of the dispersion potential energy surface. We show that these new GI descriptors lead to improvement in ML predictions of Henry’s constants for a diverse set of adsorbates in MOFs compared to previous approaches to this task.
Femtosecond ultraviolet laser absorption spectroscopy for simultaneous measurements of temperature and OH concentration
Authors: Liu Ning , Chen Timothy Y. , Zhong Hongtao , Lin Ying , Wang Ziyu , Ju Yiguang
Published: May 2022

This Letter reports a femtosecond ultraviolet laser absorption spectroscopy (fs-UV-LAS) for simultaneous in situ measurements of temperature and species. This fs-UV-LAS technique was demonstrated based on X2Π-A2Σ+ transitions of OH radicals near 308 nm generated in low temperature plasmas and flames. The fs-UV-LAS technique has revealed three major diagnostic benefits. First, a series of absorption features within a spectral bandwidth of ∼3.2 nm near 308 nm were simultaneously measured and then enabled simultaneous multi-parameter measurements with enhanced accuracy. The results show that the temperature and OH concentration could be measured with accuracy enhanced by 29–88% and 58–91%, respectively, compared to those obtained with past two-narrow-line absorption methods. Second, an ultrafast time resolution of ∼120 picoseconds was accomplished for the measurements. Third, due to the large OH X2Π-A2Σ+ transitions in the UV range, a simple single-pass absorption with a 3-cm path length was allowed for measurements in plasmas with low OH number density down to ∼2 × 1013 cm−3. Also due to the large OH UV transitions, single-shot fs absorption measurements were accomplished in flames, which was expected to offer more insights into chemically reactive flow dynamics.
Rotational state specific dissociation dynamics of D2O via the C̃(010) state: The effect of bending vibrational excitation
Authors: Wu Yucheng , Zhang Zhaoxue , Zhang Su’e , Luo Zijie , Zhao Yarui , Yang Shuaikang , Li Zhenxing , Chang Yao , Chen Zhichao , Yu Shengrui , Yang Xueming , Yuan Kaijun
Published: May 2022

The rotational state resolved photodissociation dynamics of D2O via the C̃(010) state has been investigated by using the D-atom Rydberg tagging time-of-flight technique combined with a tunable vacuum ultraviolet light source. The D-atom action spectrum of the C̃(010) ← X̃(000) band and the corresponding time-of-flight (TOF) spectra of D-atom photoproducts formed following the excitation of D2O to individual rotational transition have been measured. By comparison with the action spectrum of the C̃(000) ← X̃(000) band, the bending vibrational constant of the C̃ state for D2O can be determined to be v2 = 1041.37 ± 0.71 cm−1. From the TOF spectra, the product kinetic energy spectra, the vibrational state distributions of OD products, and the state resolved anisotropy parameters have been determined. The experimental results indicate a dramatic variation in the OD product state distributions for different rotational excitations. This illuminates that there are two distinctive coupling channels from the C̃(010) state to the low-lying electronic states: the homogeneous electronic coupling to the Ã1B1 state, resulting in vibrationally hot OD(X) products, and the Coriolis-type coupling to the B̃1A1 state, producing vibrationally cold but rotationally hot OD(X) and OD(A) products. Furthermore, the three-body dissociation channel is confirmed, which is attributed to the C̃ → 1A2 or C̃ → Ã pathway. In comparison with the previous results of D2O photolysis via the C̃(000) state, it is found that the v2 vibration of the parent molecule enhances both the vibrational and rotational excitations of OD products.
De-asymmetry of small-scale motions in wall-bounded turbulence
Authors: Zhang Qing-fu , Pan Chong , Wang Jin-jun
Published: May 2022

The present work focuses on the symmetry-breaking phenomenon in large-to-small amplitude modulation (AM) of wall-bounded turbulence. Using the recently proposed multi-component variational mode decomposition method, the volumetric velocity fields of a spatially developing turbulent boundary layer being obtained by direct numerical simulation are decomposed into four three-dimensional intrinsic mode functions (IMFs), whose spanwise length scales are fully separated from each other. It is found that the first IMF mainly characterizes the streamwise large-scale (LS) and very-large-scale turbulent motions. Splatting and sputtering events are observed in the second IMF (2IMF), leading to the biased conditional probability density functions of near-wall u2IMF and v2IMF under the condition of extreme large-scale motions. This is in distinct contrast to the hierarchical self-similarity of the wall-normal profiles of Reynolds shear stress (RSS) of the last two IMFs (3IMF and 4IMF). When treating 2IMF as components of small-scale (SS) turbulent motions, such splatting and sputtering events lead to asymmetric AM effect; that is, the AM coefficients corresponding to positive and negative LS motions are asymmetric to each other. The underlying reason is that these strong quadrant events are spatially asymmetric and are tightly coupled with local LS motions. Based on this observation, a de-spatial-asymmetry (DSA) method is proposed to obtain asymmetry-free “universal” SS turbulent motions. This method includes the removal of the transitional 2IMF from SS motions, the de-amplitude modulation, and the length-scale rescaling. Analysis of single-point velocity statistics, RSS, as well as velocity spectrum, shows that the “universality” of SS motions derived from the DSA method is remarkably improved.
Benchmarking GNOF against FCI in challenging systems in one, two, and three dimensions
Authors: Mitxelena Ion , Piris Mario
Published: May 2022

This work assesses the reliability of the recently proposed [M. Piris, Phys. Rev. Lett. 127, 233001 (2021)] global natural orbital functional (GNOF) in the treatment of the strong electron correlation regime. First, we use an H10 benchmark set of four hydrogen model systems of different dimensionalities and distinctive electronic structures: a 1D chain, a 2D ring, a 2D sheet, and a 3D close-packed pyramid. Second, we study two paradigmatic models for strongly correlated Mott insulators, namely, a 1D H50 chain and a 4 × 4 × 4 3D H cube. We show that GNOF, without hybridization to other electronic structure methods and free of tuned parameters, succeeds in treating weak and strong correlation in a more balanced way than the functionals that have preceded it.
Effects of particle size and liquid film viscosity on characteristics of particles colliding with dry and wet walls
Authors: Lin Zhe , Chen Xiaoxiao , Ye Jiahui , Zhu Zuchao
Published: May 2022

Particle-wall collisions frequently occur in fluidized beds, granulation processes, and the transportation of gas–solid two-phase flows in pipelines. Exploring the rebound characteristics of particles after colliding with the wall will enable more accurate calculation models of collision rebound, enhanced control of the collision–rebound process, and improved efficiency of industrial production. This paper studies the relationship between the energy consumed by the liquid film and the energy consumed in the collision and investigates the effects of different particle sizes and liquid film viscosities on the liquid bridge morphology, coefficient of restitution (COR), and critical capture angle (CCA). The results show that the normal COR is affected by particle size, incident velocity, and viscosity, while the tangential COR is only related to the existence of the liquid film. Additionally, the maximum size of the liquid bridge and the growth rate of COR change suddenly in a transition region. The particle size and liquid film viscosity have significant effects on the CCA of the particle. The numerical results enable us to propose a general form of the normal wet collision model.
Electric field- and strain-induced bandgap modulation in bilayer C2N
Authors: Dabsamut Klichchupong , Maluangnont Tosapol , Reunchan Pakpoom , T-Thienprasert Jiraroj , Jungthawan Sirichok , Boonchun Adisak
Published: May 2022

Recently, the C2N monolayer with an optical bandgap of 1.96 eV has emerged as a novel two-dimensional material for modern optoelectronic devices. Herein, we report its bandgap modulation by using a simple bilayer formation that includes the application of an electric field and strain. We identify four energetically favorable bilayer configurations (AA-, AB-, AB′-, and Min-stacking) by using a hybrid functional, obtaining a calculated bandgap of 1.3–1.6 eV. When subjected to a perpendicular electric field up to 4 V/nm, the bandgap decreases by as much as 0.5 eV, which correlates with the increasing energy of the valence-band maximum, where the N-px and N-py states shift closer to the N-pz state. Without the electric field, the bandgap decreases when the interlayer distance is contracted by a compressive strain. We express the strain (or interlayer distance) and the physical applied pressure via the stabilized jellium equation of state. For the Min-stacking configuration, the bandgap decreases from 1.75 to 0.9 eV upon applying a pressure of 35 GPa. The strain-induced reduction in the bandgap is similarly monitored under an applied electric field. Our theoretical work suggests that the electric field and strain (or applied pressure) can be used to tune the electronic properties of the bilayer C2N.
Changeable electroresistance in Pt/Pb(Zr,Ti)O3/(La,Sr)MnO3 tunnel junctions and memristive properties for synaptic plasticity emulation
Authors: Zhang Yuanhao , Xu Jibo , Yu Yahui , Zheng Weijie , Xu Zhiyu , Lu Lingzhi , Wang Ziyu , Lu Chaojing , Wen Zheng
Published: May 2022

Ferroelectric tunnel junctions (FTJs) are promising candidates for the next-generation memory technologies. The electroresistance mechanism, however, has been reported not only from the polarization-modulation of barrier profiles. Electrical migration of charged defects has also been observed as a possible origin for the resistive switching. Here, we achieve two kinds of electroresistance behaviors in Pt/Pb(Zr,Ti)O3/(La,Sr)MnO3 tunnel junctions by introducing oxygen vacancies in the Pb(Zr,Ti)O3 barrier. The oxygen vacancies are observed by x-ray photoelectron spectroscopy, and their effects on the widely adopted piezoresponse force microscopy characterizations of ultrathin ferroelectric films have been analyzed by AC voltage-dependent hysteresis loops. For the Pt/Pb(Zr,Ti)O3/(La,Sr)MnO3 device that is modulated by the polarization reversal, a counterclockwise resistance–voltage (R–V) relationship is observed due to the tunneling between high and low barriers, whereas the R–V hysteresis loop is changed to clockwise with the existence of oxygen vacancies, in which conductive filaments are formed in the Pb(Zr,Ti)O3 barrier. However, such an ionic electroresistance is not stable during repetitive switching. Further investigation on memristive behaviors is, thus, performed on the ferroelectric-controlled Pt/Pb(Zr,Ti)O3/(La,Sr)MnO3 tunnel junctions. An excellent linearity is achieved in continuous resistance change owing to the nucleation-limited-switching mode of domain switching in the Pb(Zr,Ti)O3 barrier, giving rise to spike-timing-dependent plasticity behaviors for the Hebbian rule of learning and memory. These results provide insight into the distinguishing of ferroelectric and ionic contributions in electroresistance of FTJ devices, facilitating deep understanding of nonvolatile resistive memories.
Ferromagnetic and nutation resonance frequencies of nanomagnets with various magnetocrystalline anisotropies
Authors: Titov Sergei V. , Dowling William J. , Kalmykov Yuri P.
Published: May 2022

Nutation and precession resonances are investigated for nanomagnets with uniaxial, biaxial, and cubic magnetocrystalline anisotropies employing the linearized inertial Landau–Lifshitz–Gilbert equation. Analytical expression analogous to the Smit–Beljers–Suhl formula for resonance frequencies is obtained. The estimated nutation resonance frequencies are compared with those obtained from the undamped inertial Landau–Lifshitz–Gilbert equation by determining numerically closed trajectories near the bottom of the deepest potential well. The good agreement of both independent estimations is demonstrated.
Effects of wall temperature on two-point statistics of the fluctuating wall shear stress and heat flux in supersonic turbulent boundary layers
Authors: Dong Siwei , Tong Fulin , Yu Ming , Chen Jianqiang , Yuan Xianxu , Wang Qian
Published: May 2022

In the present study, we investigate two-point statistics of fluctuating streamwise wall shear stress τ′x and wall heat flux q′w by exploiting a direct numerical simulation database of supersonic turbulent boundary layers over a heated wall and a cooled wall at the friction Reynolds number around 800. By separately investigating positive and negative families of τx′ and qw′ with the aid of the conditional correlation analysis, we identify the asymmetrical deformation of τ′x and q′w, reminiscent of and ascribed to the asymmetrical deformations of sweeps and ejections events. The degree of such asymmetry is alleviated by the lower wall temperature. The spatial orientation of τx′ is insensitive to the wall temperature, whereas the spanwise elongated q′w that is closely related to the wall pressure is manifested merely in the cooled-wall case. The cross correlation between τx′ and the fluctuating streamwise velocity u′ reveals that low-speed streaks related to negative τx′ are more inclined to the wall than high-speed ones related to positive τx′ by 4°–5°, and that the phase lag between negative τx′ and u′ is larger than that between positive τx′ and u′ except in the near-wall region. Such a difference is proportional to the wall distance and should be considered for models predicting near-wall and wall quantities using signals in the logarithmic layer.
Wall heat flux in a supersonic shock wave/turbulent boundary layer interaction
Authors: Tong Fulin , Yuan Xianxu , Lai Jiang , Duan Junyi , Sun Dong , Dong Siwei
Published: May 2022

The characteristics of wall heat flux (WHF) beneath a supersonic turbulent boundary layer interacting with an impinging shock wave with a 33.2° angle at Mach 2.25 are analyzed using direct numerical simulation. It is found that the QP85 scaling, defined as the ratio of the mean WHF and wall pressure, changes across the interaction. The probability density function of the WHF fluctuations normalized by the local root-mean-squared value is similar to that of wall shear stress. Comparing the WHF and wall pressure spectra shows that the low-frequency shock unsteadiness exhibits little influence on the spectrum. The space–time correlation of the fluctuating WHF reveals that both the streamwise correlation length scale and the convection velocity experience a sharp decrease in the separation region and subsequent recovery in the downstream region. Moreover, the mean WHF in an incident shock interaction is decomposed for the first time. An analysis of the velocity and temperature fluctuations based on bidimensional empirical mode decomposition is performed to evaluate the contribution of turbulent structures with specific spanwise length scales to the mean WHF generation. The decomposed results indicate that the contribution associated with the large-scale structures in the outer region is greatly amplified by the shock interaction and has the leading role in the generation downstream of the interaction.
A combined first- and second-order optimization method for improving convergence of Hartree–Fock and Kohn–Sham calculations
Authors: Kreplin David A. , Werner Hans-Joachim
Published: May 2022

In this work, we investigate the optimization of Hartree–Fock (HF) orbitals with our recently proposed combined first- and second-order (SO-SCI) method, which was originally developed for multi-configuration self-consistent field (MCSCF) and complete active space SCF (CASSCF) calculations. In MCSCF/CASSCF, it unites a second-order optimization of the active orbitals with a Fock-based first-order treatment of the remaining closed-virtual orbital rotations. In the case of the single-determinant wavefunctions, the active space is replaced by a preselected “second-order domain,” and all rotations involving orbitals in this subspace are treated at second-order. The method has been implemented for spin-restricted and spin-unrestricted Hartree–Fock (RHF, UHF), configuration-averaged Hartree–Fock (CAHF), as well as Kohn–Sham (KS) density functional theory (RKS, UKS). For each of these cases, various choices of the second-order domain have been tested, and appropriate defaults are proposed. The performance of the method is demonstrated for several transition metal complexes. It is shown that the SO-SCI optimization provides faster and more robust convergence than the standard SCF procedure but requires, in many cases, even less computation time. In difficult cases, the SO-SCI method not only speeds up convergence but also avoids convergence to saddle-points. Furthermore, it helps to find spin-symmetry broken solutions in the cases of UHF or UKS. In the case of CAHF, convergence can also be significantly improved as compared to a previous SCF implementation. This is particularly important for multi-center cases with two or more equal heavy atoms. The performance is demonstrated for various two-center complexes with different lanthanide atoms.
Photocurrent detection of radially polarized optical vortex with hot electrons in Au/GaN
Authors: Hou Yaonan , Kappers Menno , Jin Chaoyuan , Oliver Rachel
Published: May 2022

We report a GaN based metal–semiconductor–metal (MSM) infrared photodetector enabled with azimuthally distributed sub-wavelength gratings fabricated on one of the working electrodes. Under illumination, hot electron transfer is introduced by the plasmonic resonance in the infrared waveband formed at the interface of Au/GaN. Without the help of using any external optical polarizers, the device is able to detect radial polarization vortices in the form of photocurrents with a prescribed response spectrum. The detector exhibits a 10%–90% rise and fall time of 0.9 ms under modulated light, much faster than that of conventional ultraviolet GaN MSM photodetectors based on the band edge absorption. This work provides a viable way to measure spatially variant polarization beams with a compact plasmonic photodetectors fabricated from wide bandgap semiconductors.
Ray-tracking methods for characterizing the dynamics of curved detonation
Authors: Xiao Qiang , Mével Rémy , Gallier Stany , Radulescu Matei I.
Published: May 2022

Current analyses of curved detonations are mostly limited to the dynamics along the wall or the symmetry axis due to the lack of efficient approaches for reliably tracking stream tubes with curved shock fronts. To address this lack, the present work proposes a novel curved ray-tracking algorithm with two implementation methods. The curved ray is characterized by a specific arc of constant curvature perpendicularly intersecting both successive fronts. The methods were validated against Whitham's exact geometrical shock dynamics solutions of the self-similar shock diffraction problem. As compared to the typical forward straight-ray method, which is of the first order, the proposed methods demonstrate convergence rates greater by more than one order of magnitude and tend to be of the second order. The convergence analysis enabled to determine the range of time resolution required for the proposed methods to provide reliable results. This range is comparable to the acquisition rate of a modern high-speed camera that is commonly used in detonation visualization experiments. Differences between the proposed curved ray-tracking methods and the typical forward straight-ray method have been further examined by analyzing the ray dynamics during the weakly unstable hydrogen–oxygen–argon detonation diffraction. The ray-tube-based velocity-curvature relationship showed satisfactory agreement with those already well-established in quasi-steady experiments and predicted by the generalized Zeldovich–von Neumann–Doering model. This suggests the limited role of unsteadiness and cellular structure in the macro-scale dynamics of weakly unstable detonations.
Ultrafast bandgap narrowing and cohesion loss of photoexcited fused silica
Authors: Tsaturyan Arshak , Kachan Elena , Stoian Razvan , Colombier Jean-Philippe
Published: May 2022

Coupling and spatial localization of energy on ultrafast timescales and particularly on the timescale of the excitation pulse in ultrashort laser irradiated dielectric materials are key elements for enabling processing precision beyond the optical limit. Transforming matter on mesoscopic scales facilitates the definition of nanoscale photonic functions in optical glasses. On these timescales, quantum interactions induced by charge non-equilibrium become the main channel for energy uptake and transfer as well as for the material structural change. We apply a first-principles model to determine dynamic distortions of energy bands following the rapid increase in the free-carrier population in an amorphous dielectric excited by an ultrashort laser pulse. Fused silica glass is reproduced using a system of (SiO4)4− tetrahedra, where density functional theory extended to finite-temperature fractional occupation reproduces ground and photoexcited states. Triggered by electronic charge redistribution, a bandgap narrowing of more than 2 eV is shown to occur in fused silica under geometry relaxation. Calculations reveal that the bandgap decrease results from the rearrangement of atoms altering the bonding strength. Despite an atomic movement impacting strongly the structural stability, the observed change of geometry remains limited to 7% of the interatomic distance and occurs on the femtosecond timescale. This structural relaxation is thus expected to take place quasi-instantly following the photon energy flux. Moreover, under intense laser pulse excitation, fused silica loses its stability when an electron temperature of around 2.8 eV is reached. A further increase in the excitation energy leads to the collapse of both the structure and bandgap.
Quantitative imaging and modeling of colloidal gelation in the coagulant dipping process
Authors: Williams Ian , Naderizadeh Sara , Sear Richard P. , Keddie Joseph L.
Published: May 2022

Many common elastomeric products, including nitrile gloves, are manufactured by coagulant dipping. This process involves the destabilization and gelation of a latex dispersion by an ionic coagulant. Despite widespread application, the physical chemistry governing coagulant dipping is poorly understood. It is unclear which properties of an electrolyte determine its efficacy as a coagulant and which phenomena control the growth of the gel. Here, a novel experimental protocol is developed to directly observe coagulant gelation by light microscopy. Gel growth is imaged and quantified for a variety of coagulants and compared to macroscopic dipping experiments mimicking the industrial process. When the coagulant is abundant, gels grow with a t1/2 time dependence, suggesting that this phenomenon is diffusion-dominated. When there is a finite amount of coagulant, gels grow to a limiting thickness. Both these situations are modeled as one-dimensional diffusion problems, reproducing the qualitative features of the experiments including which electrolytes cause rapid growth of thick gels. We propose that the gel thickness is limited by the amount of coagulant available, and the growth is, therefore, unbounded when the coagulant is abundant. The rate of the gel growth is controlled by a combination of a diffusion coefficient and the ratio of the critical coagulation concentration to the amount of coagulant present, which in many situations is set by the coagulant solubility. Other phenomena, including diffusiophoresis, may make a more minor contribution to the rate of gel growth.
The WKRY transcription factor MdWRKY75 regulates anthocyanins accumulation in apples (
Authors: Su Mengyu , Zuo Weifang , Wang Yicheng , Liu Wenjun , Zhang Zongying , Wang Nan , Chen Xuesen
Published: May 2022

Anthocyanins play important roles in plant secondary metabolism. Although previous studies have identified many transcription factors (TFs) that participate in the synthetic pathway of anthocyanins, the regulation mechanism of the pathway remain poorly understood. In this study, we identified a WRKY Group IIc TF, MdWRKY75, which contained a typical WRKYGQK heptapeptide sequence and a C2H2-zinc finger structure. Subcellular localisation assays found that MdWRKY75 was located in the nucleus. Overexpression of MdWRKY75 promoted the accumulation of anthocyanins in apple (Malus domestica L.) ‘Orin’ calli. MdWRKY75 mainly stimulated the accumulation of anthocyanins by binding to the promoter of MYB transcription factor, MdMYB1. Our research could provide new insights into how WRKY TFs regulate the accumulation of anthocyanins in apples.
A male pheromone that improves the quality of the oogenic germline
Authors: Aprison Erin Z. , Dzitoyeva Svetlana , Angeles-Albores David , Ruvinsky Ilya
Published: May 2022

Significance

Aging animals, particularly females, suffer from diminished reproductive ability, likely due to high costs of germline maintenance. Potential remedies may be found in signals exchanged by members of opposite sexes to promote reproductive success. We show that in the nematodeCaenorhabditis elegans, male pheromone facilitates healthy oocyte aging. This pheromone increases germline proliferation and physiological cell death, which is required to maintain oocyte quality. We show that young adults that have not yet commenced reproduction are particularly sensitive to signals from mates and nutrients, likely because during this narrow time window, they set an environment-appropriate balance between germline and soma investment. We advocate the study of social signals as a productive avenue for identifying regulators of physiology and aging.
Existence of twisting in dislocation-free protein single crystals
Authors: Abe Marina , Suzuki Ryo , Hirano Keiichi , Koizumi Haruhiko , Kojima Kenichi , Tachibana Masaru
Published: May 2022

Significance

Growing high-quality protein crystals is a prerequisite for the structure analysis of proteins by X-ray diffraction. However, dislocation-free perfect protein crystals such as silicon and diamond are limited to two kinds of protein crystals. We wonder whether other high-quality or dislocation-free protein crystals still exhibit some imperfection. Here, we explore the existence of twisting as a cause of imperfection in high-quality protein crystals by X-ray topography with synchrotron radiation. The magnitude of twisting is quite small and cannot be detected by conventional techniques as optical and electron microscopy. The formation of twisting may be related to the geometric frustration mechanism proposed as a primary mechanism of twisting. This finding provides insights on high-quality protein crystals with the ubiquity of twisting.
DPYSL2 interacts with JAK1 to mediate breast cancer cell migration
Authors: Abu Rmaileh Areej , Solaimuthu Balakrishnan , Khatib Anees , Lavi Shirel , Tanna Mayur , Hayashi Arata , Ben Yosef Michal , Lichtenstein Michal , Pillar Nir , Shaul Yoav D.
Published: May 2022

The intricate neuronal wiring during development requires cytoskeletal reorganization orchestrated by signaling cues. Because cytoskeletal remodeling is a hallmark of cell migration, we investigated whether metastatic cancer cells exploit axon guidance proteins to migrate. Indeed, in breast cancer patients, we found a significant correlation between mesenchymal markers and the expression of dihydropyrimidinase-like 2 (DPYSL2), a regulator of cytoskeletal dynamics in growing axons. Strikingly, DPYSL2 knockout in mesenchymal-like breast cancer cells profoundly inhibited cell migration, invasion, stemness features, tumor growth rate, and metastasis. Next, we decoded the molecular mechanism underlying this phenomenon and revealed an interaction between DPYSL2 and Janus kinase 1 (JAK1). This binding is crucial for activating signal transducer and activator of transcription 3 (STAT3) and the subsequent expression of vimentin, the promigratory intermediate filament. These findings identify DPYSL2 as a molecular link between oncogenic signaling pathways and cytoskeletal reorganization in migrating breast cancer cells.
One-sided multidimensional statistical significance testing: a new method of calculating the statistical significance of spectra used to demonstrate magnetic nanoparticle sensitivity*
Authors: Weaver John B , Weaver Claire V , Ness Dylan B , Gordon-Wylie Scott W , Demidenko Eugene
Published: May 2022

Estimating statistical significance of the difference between two spectra or series is a fundamental statistical problem. Multivariate significance tests exist but the limitations preclude their use in many common cases; e.g. one-sided testing, unequal variance and when few repetitions are acquired all of which are required in magnetic spectroscopy of nanoparticle Brownian motion (MSB). We introduce a test, termed the T-S test, that is powerful and exact (exact type I error). It is flexible enough to be one- or two-sided and the one-sided version can specify arbitrary regions where each spectrum should be larger. The T-S test takes the-one or two-sided p-value at each frequency and combines them using Stouffer’s method. We evaluated it using simulated spectra and measured MSB spectra. For the single-sided version, mean of the spectrum, A-T, was used as a reference; the T-S test is as powerful when the variance at each frequency is uniform and outperforms when the noise power is not uniform. For the two-sided version, the Hotelling T2 two-sided multivariate test was used as a reference; the two-sided T-S test is only slightly less powerful for large numbers of repetitions and outperforms rather dramatically for small numbers of repetitions. The T-S test was used to estimate the sensitivity of our current MSB spectrometer showing 1 ng sensitivity. Using eight repetitions the T-S test allowed 15 pM concentrations of mouse IL-6 to be identified while the mean of the spectra only identified 76 pM.