bluuebunny/crossref_metadata_2025 huggingface dataset:
Coherent state superpositions, entanglement, and gauge/gravity correspondence
Authors: Lin Hai , Zhu Yuwei
Published: May 2021

We focus on two types of coherent states, the coherent states of multi-graviton states and the coherent states of giant graviton states, in the context of gauge/gravity correspondence. We conveniently use a phase shift operator and its actions on the superpositions of these coherent states. We find N-state Schrödinger cat states, which approach the one-row Young tableau states, with fidelity between them asymptotically reaching 1 at large N. The quantum Fisher information of these states is proportional to the variance of the excitation energy of the underlying states and characterizes the localizability of the states in the angular direction in the phase space. We analyze the correlation and entanglement between gravitational degrees of freedom using different regions of the phase space plane in bubbling AdS. The correlation between two entangled rings in the phase space plane is related to the area of the annulus between the two rings. We also analyze two types of noisy coherent states, which can be viewed as interpolated states that interpolate between a pure coherent state in the noiseless limit and a maximally mixed state in the large noise limit.
Investigation of damage traces on the SWS of the RBWO with a low guiding magnetic field
Authors: Yang Dewen , Chen Changhua , Teng Yan , Li Shuang , Li Xiaoze , Tan Weibing , Zhu Xiaoxin , Zhang Ligang , Sun Jun , Su Jiancang
Published: May 2021

For the high power microwave (HPM) generator, damage on an RF structure surface is harmful for a long time operation. In this paper, we investigate damage traces on slow-wave structure (SWS) of the relativistic backward-wave oscillator (RBWO) with a low guiding magnetic field. By theoretical and experimental analysis, we find that damage traces on SWS surface are mainly caused by the bombardment of beam electrons pulled back. Moreover, it is suggested that damage traces are not caused by RF breakdown, the bombardment of secondary electrons, and the bombardment of particles from collector plasma. Importantly, to decrease damages and prolong the working life of the RBWO with a low guiding magnetic field, the electric field which pulls electrons to the RF structure surface (saying Ez and −Er) should be decreased by special design for the RF structure, such as blending and parameters adjustment. Those results may offer benefit guides for study of the RBWO with a low guiding magnetic field.
Toroidal soft x-ray array on the EXL-50 spherical tokamak
Authors: Huang X. L. , Zhang Y. P. , Zhu Y. B. , Li X. , He L. , Li Y. X. , Zhou J. , Cheng S. K. , Yang Y. M. , Bai R. H. , Zhao X. , Tao R. Y. , Chen B. , Dai L. L. , Zeng G. Q. , Liu Y. , Liu M. S.
Published: May 2021

A toroidal soft x-ray array system for spectrum and intensity measurements on the EXL-50 spherical tokamak is described. Silicon drift detectors and digital multichannel analyzers are adopted for all 21 channels of the array, and an average energy resolution of 147 eV at 5.89 keV has been achieved at count rates over 500 kcps. In total, 20 channels of the array are symmetrically observed in both co- and counter-current directions on the EXL-50 mid-plane with a spatial resolution of around 10 cm, and the remaining one serves as a background reference channel. Tungsten emissions from tungsten coating of the limiters on the central post are observed. The influence of hard x rays on measured soft x-ray spectra and system operation is discussed.
A flexible nitrogen-vacancy center probe for scanning magnetometry
Authors: Guo Maosen , Wang Mengqi , Wang Pengfei , Wu Diguang , Ye Xiangyu , Yu Pei , Huang You , Shi Fazhan , Wang Ya , Du Jiangfeng
Published: May 2021

The key component of the scanning magnetometry based on nitrogen-vacancy centers is the diamond probe. Here, we designed and fabricated a new type of probe with an array of pillars on a (100 µm)2 × 50 µm diamond chip. The probe features high yield, convertibility to be a single pillar, and expedient reusability. Our fabrication is dramatically simplified by using ultraviolet laser cutting to shape the chip from a diamond substrate instead of additional lithography and time-consuming reactive ion etching. As an example, we demonstrate the imaging of a single magnetic skyrmion with nanoscale resolution. In the future, this flexible probe will be particularly well-suited for commercial applications.
First-principles study of the composition, cation arrangement, and local structure in high-performance Bi(Me3+)O3–PbTiO3 (Me3+ = Ga, Sc, In) ferroelectric solid solutions
Authors: Yadav Suhas , Grinberg Ilya
Published: May 2021

Ferroelectric perovskite solid solutions are of interest due to their extensive use in modern electronic devices. Cation off-centering is the dominant mechanism of ferroelectricity in perovskite oxides, and it was shown that the average off-centering of these cations can be used to predict some of the essential properties of solid solutions. In this work, we use first-principles density functional theory to investigate the dependence of the cation displacements on the ionic size, amount of substitution, O6 tilt, and locations of the Bi and Me3+ cations in xBiMe3+O3–(1 − x)PbTiO3 (Me3+ = Ga, Sc, In) solid solutions. We carry out our calculations for the x = 0.125 and x = 0.25 BiMe3+O3 substitution concentrations and the ⟨100⟩, ⟨110⟩, ⟨111⟩, ⟨011⟩, and ⟨001⟩ arrangements of the BiMe3+O3 substituent units. We demonstrate that the substitution of larger ions leads to greater variation in the energy and cation displacement magnitudes of the different cation arrangements. Our study reveals that cation displacements are governed by the interplay of the volume expansion effect that favors higher displacements and the cooperative O6 tilt effect that decreases the displacements. Both of these effects increase with greater ionic radius and their relative strengths depend on the cation arrangement. We also illustrate how negative pressure can be achieved experimentally by the doping of large In cations in these solid solutions. Understanding the dependence of the different directional arrangements, O6 tilting, and the effect of ionic size is important for precise prediction of ferroelectric materials properties and enables rational design of new piezoelectric materials.
Automated signal classification in the C-2W fusion experiment
Authors: Bolte Nathan , Allfrey Ian , Mendoza Roberto ,   TAE Team
Published: May 2021

In TAE Technologies’ current experimental fusion device, C-2W (also called “Norman”), record breaking, advanced beam-driven field-reversed configuration plasmas are produced and sustained in steady state utilizing variable-energy neutral beams, expander divertors, end-bias electrodes, and an active plasma control system. With a rapid shot-pace and an extensive number of data channels, the amount of data generated necessitates automated signal processing. To this end, a machine learning algorithm consisting of a multi-layered neural network as well as other data processing software has been designed for signal feature identification, allowing for accurate and fast signal classification, anomalous condition detection, and providing for signal pre-processing. With a small set of training data, the neural network can be “bootstrapped” to provide a robust classification system while minimizing human oversight. An example using data from the theta pinch plasma formation pulsed power system is presented. With an overall accuracy of ∼97%—having classified more than 5 × 106 pulsed power signals—the classification scheme is more than sufficient to fine-tune machine set points. However, this technique can be used for near-real-time preprocessing of any plasma physics signal and has wide ranging application in fusion experiments for the varied data produced by plasma diagnostics.
Dehydration induced dynamical heterogeneity and ordering mechanism of lipid bilayers
Authors: Malik Sheeba , Debnath Ananya
Published: May 2021

Understanding the influence of dehydration on the membrane structure is crucial to control membrane functionality related to domain formation and cell fusion under anhydrobiosis conditions. To this end, we perform all-atom molecular dynamic simulations of 1,2-dimyristoyl-sn-glycero-3-phosphocholine dimyristoylphosphatidylcholine lipid membranes at different hydration levels at 308 K. As dehydration increases, the lipid area per head group decreases with an increase in bilayer thickness and lipid order parameters indicating bilayer ordering. Concurrently, translational and rotational dynamics of interfacial water (IW) molecules near membranes slow down. On the onset of bilayer ordering, the IW molecules exhibit prominent features of dynamical heterogeneity evident from non-Gaussian parameters and one-dimensional van Hove correlation functions. At a fully hydrated state, diffusion constants (D) of the IW follow a scaling relation, D∼τα−1, where the α relaxation time (τα) is obtained from self-intermediate scattering functions. However, upon dehydration, the relation breaks and the D of the IW follows a power law behavior as D∼τα−0.57, showing the signature of glass dynamics. τα and hydrogen bond lifetime calculated from intermittent hydrogen bond auto-correlation functions undergo a similar crossover in association with bilayer ordering on dehydration. The bilayer ordering is accompanied with an increase in fraction of caged lipids spanned over the bilayer surface and a decrease in fraction of mobile lipids due to the non-diffusive dynamics. Our analyses reveal that the microscopic mechanism of lipid ordering by dehydration is governed by dynamical heterogeneity. The fundamental understanding from this study can be applied to complex bio-membranes to trap functionally relevant gel-like domains at room temperature.
Effects of temperature and ion channel blocks on propagation of action potential in myelinated axons
Authors: Ding Qianming , Jia Ya
Published: May 2021

Potassium ion and sodium ion channels play important roles in the propagation of action potentials along a myelinated axon. The random opening and closing of ion channels can cause the fluctuation of action potentials. In this paper, an improved Hodgkin–Huxley chain network model is proposed to study the effects of ion channel blocks, temperature, and ion channel noise on the propagation of action potentials along the myelinated axon. It is found that the chain network has minimum coupling intensity threshold and maximum tolerance temperature threshold that allow the action potentials to pass along the whole axon, and the blockage of ion channels can change these two thresholds. A striking result is that the simulated value of the optimum membrane size (inversely proportional to noise intensity) coincides with the area range of feline thalamocortical relay cells in biological experiments.
Gyrokinetic theory of low-frequency electromagnetic waves in finite-β anisotropic plasmas
Authors: Chen Haotian , Chen Liu
Published: May 2021

We present a gyrokinetic theory for the electromagnetic waves and instabilities with frequencies much lower than the ion cyclotron frequency in finite-β anisotropic uniform plasmas. Here, β is the ratio between plasma and magnetic pressures. Kinetic effects due to both the finite Larmor radii and wave-particle resonances are fully kept in the analysis. Corresponding linear dispersion relation and wave polarizations, valid for general β value and perpendicular wavelength, are then specifically derived for a bi-Maxwellian plasma. Analytic expressions for the criteria of kinetic firehose and mirror instabilities are also given. The mode frequency, stability, and wave polarization of a broad spectrum of normal modes are then investigated numerically in a systematic study over a set of parameters. Our study clearly demonstrates that, due to the finite ion Larmor radius effect, the ion-sound wave, mirror mode, and shear Alfvén wave are intrinsically coupled.
Liquid crystal elastomer shells with topological defect-defined actuation: Complex shape morphing, opening/closing, and unidirectional rotation
Authors: Sharma A. , Stoffel A. M. , Lagerwall J. P. F.
Published: May 2021

We produce hollow sphere liquid crystal elastomer (LCE) actuators from a nematic precursor mixture, brought into the shape of a self-closing shell with tangential anchoring of the director field n(r), using a solvent-assisted microfluidic technique. By separating the shell production from the polymerization and cross-linking, the precursor is allowed to approach its equilibrium n(r) configuration in the shell, spontaneously forming topological defects of total strength +2. However, the photopolymerization into an LCE induces a brief but strong distortion of the overall n(r) and the defect configuration, even changing the ground state shape in the case of thick shells. The resulting LCE shells show a rich capacity for reversible shape morphing upon heating and cooling, the exact actuation mode defined by n(r), and the final defect configuration stabilized at the end of polymerization. In regions with a single +1 defect, a reversal of curvature from concave to convex is found, punctured shells exhibit a strong shape change between a nearly closed sphere at low temperature and an open-ended spherocylinder at high temperature, and all shells rotate upon actuation when suspended in a fluid. As the rotation is stronger during relaxation than during actuation, thus breaking the symmetry, the net rotation is unidirectional.
Characterizing polymer structure with small-angle neutron scattering: A Tutorial
Authors: Wei Yuan , Hore Michael J. A.
Published: May 2021

Small-angle neutron scattering (SANS) is a powerful technique that has been widely used to study polymer materials. In particular, it can provide information on the size, shape, and structure of polymers as well as associated thermodynamic quantities. However, to properly design SANS experiments and correctly interpret the results, it is necessary to understand the unique advantages inherent to neutron scattering measurements of soft materials and the underlying principles of the technique. In addition, it may be necessary to construct new scattering models. In this Tutorial, we provide an overview of SANS and a guide to interpreting SANS measurements of polymers that is aimed at new and prospective users—focusing on standard plots, models, and simple methods by which new models can be quickly constructed.
Effect of time delay in a bistable synthetic gene network
Authors: Cheng Guanghui , Zheng Shutao , Dong Jiahao , Xu Zhenqin , Gui Rong
Published: May 2021

The essence of logical stochastic resonance is the dynamic manipulation of potential wells. The effect of time delay on the depth of potential wells and the width of a bistable region can be inferred by logic operations in the bistable system with time delay. In a time-delayed synthetic gene network, time delay in the synthesis process can increase the depth of the potential wells, while that in the degradation process, it can reduce the depth of the potential wells, which will result in a decrease in the width of the bistable region (the reason for time delay to induce logic operations without external driving force) and the instability of the system (oscillation). These two opposite effects imply stretching and folding, leading to complex dynamical behaviors of the system, including period, chaos, bubble, chaotic bubble, forward and reverse period doubling bifurcation, intermittency, and coexisting attractors.
Topological constraints in the reconnection of vortex braids
Authors: Candelaresi S. , Hornig G. , Podger B. , Pontin D. I.
Published: May 2021

We study the relaxation of a topologically nontrivial vortex braid with zero net helicity in a barotropic fluid. The aim is to investigate the extent to which the topology of the vorticity field—characterized by braided vorticity field lines—determines the dynamics, particularly the asymptotic behavior under vortex reconnection in evolution at high Reynolds numbers (25 000). Analogous to the evolution of braided magnetic fields in plasma, we find that the relaxation of our vortex braid leads to a simplification of the topology into large-scale regions of opposite swirl, consistent with an inverse cascade of the helicity. The change of topology is facilitated by a cascade of vortex reconnection events. During this process, the existence of regions of positive and negative kinetic helicities imposes a lower bound for the kinetic energy. For the enstrophy, we derive analytically a lower bound given by the presence of unsigned kinetic helicity, which we confirm in our numerical experiments.
Pt enhanced capacitive performance of Cr2N electrode toward flexible asymmetric supercapacitor
Authors: Adalati Ravikant , Kumar Ashwani , Sharma Meenakshi , Chandra Ramesh
Published: May 2021

In the present work, the Pt-Cr2N composite and carbon thin film electrodes were directly deposited on a flexible 304 stainless steel current collector by the one-step sputtering technique. The inclusion of platinum (Pt) in chromium nitride (Cr2N) provides a significant enhancement in the electrochemical properties of Cr2N. The prepared Pt-Cr2N composite-based electrode demonstrates a high specific capacitance and cyclic life compared to the pristine Cr2N electrode. The designed Pt-Cr2N//carbon flexible asymmetric supercapacitor (FASC) has been examined for practical applications. The FASC (at 80° bend state) shows excellent capacitance retention of 82.6% for 30 000 charging/discharging cycles with a high specific capacitance of 106 Fg−1 and a specific energy of 48 Wh kg−1. The remarkable capacitive performance of this designed FASC makes it a potential candidate for energy storage applications, long life span, and flexible electronic devices.
Strain-controlled oxygen content and the cationic electronegativity in LaBaCo2O5.5+δ thin films
Authors: Xu X. M. , Shi L. , Pan S. Y. , Zhao J. Y. , Tong R. X.
Published: May 2021

LaBaCo2O5.5+δ (LBCO) films were grown on (001)-oriented SrTiO3 (STO), (LaAlO3)0.3(SrAlTaO6)0.7 (LSAT), and LaAlO3 (LAO) substrates by a polymer assisted deposition method. The effects of strain induced by lattice mismatch on magnetic and electrical properties of LBCO films were studied. It is found that both the conductivity and ferromagnetic (FM) transition temperature of LBCO films show an abnormally ascending order of STO < LAO < LSAT. It is suggested that there are three main factors essentially to affect the physical properties of LBCO films, i.e., the oxygen content, cationic ordering, and cationic electronegativity. The tensile strain induced-decrease of oxygen content and lowest nanoscale ordering of cations will result in the decrease of FM interactions and conductivity and the increase of antiferromagnetic interactions. Besides, the difference of the cationic electronegativities can lead to the different shrinkages of Co3+–O and Co4+–O bonds when strain is applied, especially under compressive strain, resulting in the changes in the cobalt spin states and a charge transfer between Co3+ and Co4+ ions, altering the physical properties of LBCO films. The combination and competition of the functions of the oxygen content, cationic ordering, and the cationic electronegativity lead to an abnormal change of the conductivity and magnetization for LBCO films with substrates. This provides a new way to understand the function of electronegativity in the strain-controlled physical properties of the films.
Bursting the bubble: A molecular understanding of surfactant-water interfaces
Authors: Baryiames Christopher P. , Garrett Paul , Baiz Carlos R.
Published: May 2021

Surfactant science has historically emphasized bulk, thermodynamic measurements to understand the microemulsion properties of greatest industrial significance, such as interfacial tensions, phase behavior, and thermal stability. Recently, interest in the molecular properties of surfactants has grown among the physical chemistry community. This has led to the application of cutting-edge spectroscopic methods and advanced simulations to understand the specific interactions that give rise to the previously studied bulk characteristics. In this Perspective, we catalog key findings that describe the surfactant–oil and surfactant–water interfaces in molecular detail. We emphasize the role of ultrafast spectroscopic methods, including two-dimensional infrared spectroscopy and sum-frequency-generation spectroscopy, in conjunction with molecular dynamics simulations, and the role these techniques have played in advancing our understanding of interfacial properties in surfactant microemulsions.
Intrinsic fractional noise in nanopores: The effect of reservoirs
Authors: Marbach S.
Published: May 2021

Fluctuations affect nanoporous transport in complex and intricate ways, making optimization of the signal-to-noise ratio in artificial designs challenging. Here, we focus on the simplest nanopore system, where non-interacting particles diffuse through a pore separating reservoirs. We find that the concentration difference between both sides (akin to the osmotic pressure drop) exhibits fractional noise in time t with mean square average that grows as t1/2. This originates from the diffusive exchange of particles from one region to another. We fully rationalize this effect, with particle simulations and analytic solutions. We further infer the parameters (pore radius and pore thickness) that control this exotic behavior. As a consequence, we show that the number of particles within the pore also exhibits fractional noise. Such fractional noise is responsible for noise spectral density scaling as 1/f3/2 with frequency f, and we quantify its amplitude. Our theoretical approach is applicable to more complex nanoporous systems (for example, with adsorption within the pore) and drastically simplifies both particle simulations and analytic calculus.
Many-particle based evaluations for maximum current output from bimodal electron emitter arrays
Authors: Guo D. , Milestone W. , Joshi R. P.
Published: May 2021

Evaluations of the current output from emitter arrays have been carried out based on time-dependent kinetic simulations that include many-body Coulombic contributions from the electron swarm, geometric field enhancements with shielding based on a line charge model, and dynamic screening due to the evolution of the swarm in the position and velocity space. Numerical evaluations are applied to different multi-emitter array arrangements having a hexagonal lattice, with a focus on bimodal distributions. Our results show the expected role of field screening with reductions in emitter separation and positional dependence within the array based on connectivity. Different patterns were examined within a hexagonal lattice structure. For a bimodal distribution, output current optimization is shown for alternating arrangements with three or more successive emitters of the same length along primitive axes predicted to have an advantage.
Current-limiting amplifier for high speed measurement of resistive switching data
Authors: Hennen T. , Wichmann E. , Elias A. , Lille J. , Mosendz O. , Waser R. , Wouters D. J. , Bedau D.
Published: May 2021

Resistive switching devices, important for emerging memory and neuromorphic applications, face significant challenges related to the control of delicate filamentary states in the oxide material. As a device switches, its rapid conductivity change is involved in a positive feedback process that would lead to runaway destruction of the cell without current, voltage, or energy limitation. Typically, cells are directly patterned on MOS transistors to limit the current, but this approach is very restrictive as the necessary integration limits the materials available as well as the fabrication cycle time. In this article, we propose an external circuit to cycle resistive memory cells, capturing the full transfer curves while driving the cells in a way that suppresses runaway transitions. Using this circuit, we demonstrate the acquisition of 105 I, V loops per second without using on-wafer current limiting transistors. This setup brings voltage sweeping measurements to a relevant timescale for applications and enables many new experimental possibilities for device evaluation in a statistical context.
Design and operation of a transportable 87Rb atomic fountain clock
Authors: Cheng He-nan , Zhang Zhen , Deng Siminda , Ji Jing-wei , Ren Wei , Xiang Jing-feng , Zhao Jian-bo , Zhao Xin , Ye Mei-feng , Li Lin , Li Tang , Qu Qiu-zhi , Chen Weiliang , Liu Kun , Dai Shaoyang , Fang Fang , Li Tianchu , Liu Liang , Lü De-sheng
Published: May 2021

A transportable fountain clock with high reliability is important for high-precision time-frequency measurements. Because of its relatively small cold atoms’ collision frequency shift and ease of attaining high quantum state preparation efficiency, the rubidium atomic fountain clock has an indicated higher stability and reliability. This paper reports the design and operation of a transportable rubidium atomic fountain clock developed by the Shanghai Institute of Optical and Fine Mechanics, Chinese Academy of Science. After being transported more than 1000 km from Shanghai to the Changping Campus of the National Institute of Metrology, China, the optical platform and other hardware of the fountain clock did not need to be adjusted. The rubidium fountain clock maintained a stability of 4.0 × 10−13τ1/2, reaching 5.0 × 10−16 at 300 000 s. After transportation, the rubidium fountain clock and a cesium fountain clock (NIM5) were operated together against the reference frequency of a hydrogen maser. In three separate operating periods, over a total of nearly three months, the average frequency repeatability of the rubidium fountain was less than 3.8 × 10−15.
Toward alcohol synthesis from CO hydrogenation on Cu(111)-supported MoS2 – predictions from DFT+KMC
Authors: Rawal Takat B. , Le Duy , Hooshmand Zahra , Rahman Talat S.
Published: May 2021

In the quest for cheap and efficient catalysts for alcohol synthesis from syngas, a material of interest is single-layer MoS2 owing to its low cost, abundancy, and flexible structure. Because of the inertness of its basal plane, however, it is essential to find ways that make it catalytically active. Herein, by means of density functional theory based calculations of reaction pathways and activation energy barriers and accompanying kinetic Monte Carlo simulations, we show that while S vacancy row structures activate the MoS2 basal plane, further enhancement of chemical activity and selectivity can be achieved by interfacing the MoS2 layer with a metallic support. When defect-laden MoS2 is grown on Cu(111), there is not only an increase in the active region (surface area of active sites) but also charge transfer from Cu to MoS2, resulting in a shift of the Fermi level such that the frontier states (d orbitals of the exposed Mo atoms) appear close to it, making the MoS2/Cu(111) system ready for catalytic activity. Our calculated thermodynamics of reaction pathways lead to the conclusion that the Cu(111) substrate promotes both methanol and ethanol as the products, while kinetic Monte Carlo simulations suggest a high selectivity toward the formation of ethanol.
Perturbation theory made efficient and effective for predictions of ionization potential and electron affinity
Authors: Su Neil Qiang , Xu Xin
Published: May 2021

Ionization potential and electron affinity are essential molecular properties. The most straightforward method is to calculate them by taking the total energy differences of the initial and final states according to the definition. However, it often suffers from a serious convergence problem due to the requirement of the self-consistent field (SCF) calculations for the ionic states with non-Aufbau choices of occupations. In the present work, we have constructed a theoretical framework in view of perturbation theory to bypass the SCF calculations of the ionic states. To address the imbalance issue that arises from the precisely treated neutral ground state followed by the truncated perturbative treatment of the ionic states, an accurate yet effective method has been developed here, which adds back some terms from the higher order perturbations into the lower order to cancel out the most computationally cost terms in the truncated expansion, thus reaching a better convergence with less computation. The validity of the present methodology has been tested out by applying it to the Hartree–Fock (HF) method in combination with the correlation effect described at the second-order Møller–Plesset level in a frozen-orbital approximation. All the derivations in this work are given in a general framework, which are applicable not only to HF but also to a wide range of density functional theory methods from semi-local functionals to hybrid and doubly hybrid functionals.
Velocity and density measurements in forced fountains with negative buoyancy
Authors: Addona Fabio , Chiapponi Luca , Archetti Renata
Published: May 2021

In fluid mechanics, fountains take place when a source fluid is driven by its own momentum into a surrounding ambient fluid, and it is counterbalanced by buoyancy. These phenomena are largely encountered in nature and human activities. Despite the numerous studies on the subject, few experimental data are available about the internal structure of turbulent fountains. Here, we present a set of laboratory experiments with the aim to (i) get direct velocity and density measurements of fountains in a controlled environment and (ii) obtain insights about the basic physics of the phenomenon. The results concern the characteristics of the mean and turbulent flow: we report the analysis of the turbulent kinetic energy, the velocity skewness, and the Reynolds stresses, including a quadrant analysis of the fluctuating velocities. For some tests, the correlation between density and vertical velocity is investigated for both mean and fluctuating values. We have quantified the momentum transport, which is mainly out-downward at the nozzle axis with peaks at the mean rise height, where also maximum levels of the buoyancy and mass fluxes are present. The ability of acoustic Doppler current profilers to identify the rise height of the fountain and to measure the velocity field is also discussed.
Strain modulated quantum spin Hall effect in monolayer NiB
Authors: Yu Qiaolin , Fang Yimei , Cao Xinrui , Wu Shunqing , Zhu Zi-zhong
Published: May 2021

Since boron has diverse coordination chemistry, it is capable of bonding with transition metals to form a new family of two-dimensional (2D) transition metal borides (MBenes) that exhibit rich electronic properties. Here, we propose a 2D planar monolayer NiB with topologically nontrivial electronic structures as the new member of the MBenes family. The NiB monolayer exhibits metallic behavior with two Dirac cones residing slightly below the Fermi level in the absence of spin–orbit coupling (SOC). When a tensile strain of 11% is applied, the NiB monolayer transforms into a semimetal. A gap opening of 18 meV is observed at the Dirac points when SOC is considered. Based on the results of Z2 invariant (Z2=1) and the helical edge states, we identify the pristine NiB as a topological metal, while the stretched monolayer under 11% strain as a quantum spin Hall (QSH) insulator. In addition, the NiB monolayer undergoes a phase transition from topological metal to QSH insulator and then to topological metal with the increase in strain from 0% to 14%. Our findings demonstrate that the electronic properties of NiB, the new member of the MBene family, can be modulated by strain.
Detector thickness effects on nanosecond-gated imager response
Authors: Looker Quinn , Colombo Anthony P. , Porter John L.
Published: May 2021

Hybrid CMOS multi-frame imagers with exposure times down to ∼2 ns have made significant impacts in high energy density physics and inertial confinement fusion research. The detector thickness is a key parameter in both detector quantum efficiency and temporal response. The Icarus hybrid CMOS imager has been fabricated with Si detector thicknesses of 8, 25, and 100 µm. The temporal response of imaging sensors with exposure time down to 2 ns has been examined and compared to directly measured photodiode current. The 100-μm thick variant displays extended features related to charge carrier collection and is more susceptible to field collapse. We also demonstrate charge collection time effects on spatial response.
Reversed role of liquid viscosity on drop splash
Authors: Zhang Haixiang , Zhang Xiwen , Yi Xian , He Feng , Niu Fenglei , Hao Pengfei
Published: May 2021

The influence of liquid viscosity on the splashing behavior of a drop impacting a smooth surface is investigated. It is found that the liquid viscosity plays a reversed role on the drop splash, and the liquid viscosity promotes the drop splash in the low-viscosity cases but suppresses the drop splash in the high-viscosity cases. Here, we focus on the dynamics of the lifting lamella during the splashing behavior and demonstrate that the increase in liquid viscosity could contribute to the lower splashing angle αs. Furthermore, an empirical relationship of the splashing angle is obtained according to the experimental results. The reversed role of liquid viscosity is reflected in the positive effect both on the aerodynamic force and viscous force. For low-Oh cases, the increase in aerodynamic force predominates and promotes the drop splash. For high-Oh cases, the increase in viscous force predominates and suppresses the drop splash. We eventually put forward a splash criterion on smooth surfaces, which could successfully characterize the splashing behavior in this work and previous studies, and indicate the reversed role of liquid viscosity on drop splash.
Air filament contraction
Authors: Deng Peng , Jian Zhen , Thoraval Marie-Jean
Published: May 2021

We investigate numerically the contraction dynamics of a long air filament surrounded by liquid for a range of Ohnesorge numbers Oh. The contraction velocity rises to a maximum value Umax and then decreases due to the hydrodynamic drag force from the liquid medium. Umax follows a capillary-inertial scaling for low Oh while it shifts to a capillary-viscous scaling with increasing Oh. Our simulations reveal that contracting air filaments always first rupture via end-pinching mechanism before the Rayleigh–Plateau instability can develop.
A high-fidelity numerical study on the propulsive performance of pitching flexible plates
Authors: Li Guojun , Kemp Gaël , Jaiman Rajeev Kumar , Khoo Boo Cheong
Published: May 2021

In this paper, we numerically investigate the propulsive performance of three-dimensional pitching flexible plates with varying flexibility and trailing edge shapes. We employ our recently developed body-conforming fluid-structure interaction solver for our high-fidelity numerical study. To eliminate the effect of other geometric parameters, only the trailing edge angle is varied from 45° (concave plate), 90° (rectangular plate) to 135° (convex plate) while maintaining the constant area of the flexible plate. For a wide range of flexibility, three distinctive flapping motion regimes are classified based on the variation of the flapping dynamics: (i) low bending stiffness KBlow, (ii) moderate bending stiffness KBmoderate near resonance, and (iii) high bending stiffness KBhigh. We examine the impact of the frequency ratio f* defined as the ratio of the natural frequency of the flexible plate to the actuated pitching frequency. Through our numerical simulations, we find that the global maximum mean thrust occurs near f*≈1 corresponding to the resonance condition. However, the optimal propulsive efficiency is achieved around f* = 1.54 instead of the resonance condition. While the convex plate with low and high bending stiffness values shows the best performance, the rectangular plate with moderate KBmoderate is the most efficient propulsion configuration. To examine the flow features and the correlated structural motions, we employ the sparsity-promoting dynamic mode decomposition. We find that the passive deformation induced by the flexibility effect can help in redistributing the pressure gradient, thus, improving the efficiency and the thrust production. A momentum-based thrust evaluation approach is adopted to link the temporal and spatial evolution of the vortical structures with the time-dependent thrust. When the vortices detach from the trailing edge, the instantaneous thrust shows the largest values due to the strong momentum change and convection process. Moderate flexibility and convex shape help to transfer momentum to the fluid, thereby improving the thrust generation and promoting the transition from drag to thrust. The increase in the trailing edge angle can broaden the range of flexibility that produces positive mean thrust. The role of added mass effect on the thrust generation is quantified for different pitching plates and the bending stiffness. These findings are of great significance to the optimal design of propulsion systems with flexible wings.
Modeling cyclic voltammetry during solid electrolyte interphase formation: Baseline scenario of a dynamically evolving tunneling barrier resulting from a homogeneous single-phase insulating film
Authors: Steinrück Hans-Georg
Published: May 2021

The solid electrolyte interphase (SEI) is an insulating film on anode surfaces in Li-ion batteries, which forms via the reaction of Li ions with reduced electrolyte species. The SEI leads to a reduction in the electrochemical current in heterogeneous electrochemical redox reactions at the electrode/electrolyte interface. Hence, the growth of the SEI is, in principle, self-limited. Toward our ultimate goal of an improved understanding of SEI formation, we develop a baseline quantitative model within Butler–Volmer electrode kinetics, which describes the cyclic voltammetry (CV) of a flat macroelectrode during SEI growth. Here, the SEI building up electrochemically during CV forms a homogeneous single-phase electronically insulating thin film due to the corresponding current. The model is based on a dynamically evolving electron tunneling barrier with increasing film thickness. Our objective is to provide a framework, which allows for both the qualitative, intuitive interpretation of characteristic features of CV measurements and the quantitative extraction of physicochemical parameters via model fitting. We also discuss the limitations of the baseline model and give a brief outlook for improvements. Finally, comparisons to exemplary CVs from the literature relevant to Li-ion battery science are presented.
Resetting transition is governed by an interplay between thermal and potential energy
Authors: Ray Somrita , Reuveni Shlomi
Published: May 2021

A dynamical process that takes a random time to complete, e.g., a chemical reaction, may either be accelerated or hindered due to resetting. Tuning system parameters, such as temperature, viscosity, or concentration, can invert the effect of resetting on the mean completion time of the process, which leads to a resetting transition. Although the resetting transition has been recently studied for diffusion in a handful of model potentials, it is yet unknown whether the results follow any universality in terms of well-defined physical parameters. To bridge this gap, we propose a general framework that reveals that the resetting transition is governed by an interplay between the thermal and potential energy. This result is illustrated for different classes of potentials that are used to model a wide variety of stochastic processes with numerous applications.
Scaling patch analysis of turbulent planar plume
Authors: Wei Tie , Livescu Daniel
Published: May 2021

Proper scaling in turbulent planar plumes is investigated here using a scaling patch approach. Based on the scaled boundary conditions, a proper velocity scale for the mean axial flow is the plume centerline velocity Uref=Uctr, and a proper temperature scale for the temperature excess is Θref=Tctr−T∞, where Tctr is the plume centerline temperature and T∞ is the ambient fluid temperature. By seeking an admissible scaling, a key concept in the scaling patch approach, for the mean continuity, mean momentum, and mean energy equations, respectively, the following is found: (1) a proper scale for the mean transverse flow is Vref=(dδ/dx)Uctr, where dδ/dx is the growth rate of the plume width. (2) A proper scale for the Reynolds shear stress is Rvu,ref=UctrVref=(dδ/dx)Uctr2, a mix of the scales for the mean axial and transverse flows. (3) A proper scale for the turbulent heat flux is Rvθ,ref=VrefΘctr, a mix of the scales for the mean transverse flow and mean temperature excess. The mean transverse flow thus plays a critical role in the scaling of turbulent planar plumes. Approximate functions are developed for the scaled mean transverse flow, Reynolds shear stress, and turbulent temperature flux, and are found to agree favorably with experimental and numerical simulation data. The integral analysis of the mean momentum equation yields a Richardson number Ri, which remains invariant in the axial direction. The Richardson number is defined as Ri=defgβΘctrδt/(UctrVref)≈1/2, where g is the gravitational acceleration, β is the thermal expansion coefficient, and δt is the plume half-width based on the mean temperature profile. This Richardson number arises directly from the scaling patch analysis of the mean momentum equation, including both the streamwise and transverse velocity scales.
Exceeding 19% efficiency for inverted perovskite solar cells used conventional organic small molecule TPD as hole transport layer
Authors: Wang Zijun , Zhang Dayong , Yang Genjie , Yu Junsheng
Published: May 2021

In the fabrication of inverted perovskite solar cells (PeSCs), it is necessary to select an appropriate p-type semiconductive material as hole transport layer (HTL), which will determine the crystallization quality of the subsequent perovskite films and hole charge extraction at the perovskite/HTL interface. Herein, a low-cost, low-temperature processed, and hydrophobic organic small molecule, N,N-bis(3-methylphenyl)-N,N-bis(phenyl) benzidine (TPD), is utilized as HTL in fabricating inverted PeSCs. It achieves a peak power conversion efficiency of 19.77% by optimizing the thickness, which is about 1.4 times higher than the PeSCs employing poly(3,4-ethylenedioxythiophene)-poly (styrenesulfonate) (PEDOT:PSS) as HTL. Compared with PEDOT:PSS-based PeSCs, the outstanding performance of PeSCs-based TPD derives from that of the employment of TPD as the HTL produced perovskite films with larger grain size and higher crystallinity. Owing to the hydrophobicity of TPD, TPD-based PeSCs exhibited longer stability. After storage of 700 h, the PeCE of TPD-based PeSCs retains 84.1%.
Force field nonlinear coupling and force/energy optimization in a field-induced system
Authors: Tang Xingwei , Wu Xiaoxiao , Wen Weijia
Published: May 2021

In a simple harmonic vibration experiment, the amplitude and energy of the vibrating object rely on the excitation field strength that determine the evolution of the vibration system. For some specific applications, such as an audio loudspeaker, in order to improve its efficiency, how to generate optimal output by applying a small exciting field to the vibration diaphragm is a big challenge for researchers. To address the difficulties, a hybrid coupling field system that consists of a coupling between static and dynamic magnetic fields is proposed in this report. In our experiment, a flexible magnetic diaphragm fabricated with the magnetic particles and polydimethylsiloxane composite is used for demonstration, where the diaphragm sandwiched between two coils generates the harmonic vibration once an external audio signal is applied, and a great enhancement of vibration can be observed when an additional magnet array is placed close to the coils. We find that the amplification of output energy is attributed to the nonlinear coupling between the static and dynamic magnetic fields excited by the magnets and currents in coils, respectively. Another interesting phenomenon resulting from the coupling is that the magnets are able to improve the audio quality, leading to a much better frequency response, which may explore some potential applications for spectrum management and acoustic metamaterials.
The microbiomes on the roots of wheat (
Authors: Kawasaki Akitomo , Dennis Paul G. , Forstner Christian , Raghavendra Anil K. H. , Richardson Alan E. , Watt Michelle , Mathesius Ulrike , Gilliham Matthew , Ryan Peter R.
Published: May 2021

There is increasing interest in understanding how the microbial communities on roots can be manipulated to improve plant productivity. Root systems are not homogeneous organs but are comprised of different root types of various ages and anatomies that perform different functions. Relatively little is known about how this variation influences the distribution and abundance of microorganisms on roots and in the rhizosphere. Such information is important for understanding how root–microbe interactions might affect root function and prevent diseases. This study tested specific hypotheses related to the spatial variation of bacterial and fungal communities on wheat (Triticum aestivum L.) and rice (Oryza sativa L.) roots grown in contrasting soils. We demonstrate that microbial communities differed significantly between soil type, between host species, between root types, and with position along the root axes. The magnitude of variation between different root types and along individual roots was comparable with the variation detected between different plant species. We discuss the general patterns that emerged in this variation and identify bacterial and fungal taxa that were consistently more abundant on specific regions of the root system. We argue that these patterns should be measured more routinely so that localised root–microbe interactions can be better linked with root system design, plant health and performance.
Belief polarization in a complex world: A learning theory perspective
Authors: Haghtalab Nika , Jackson Matthew O. , Procaccia Ariel D.
Published: May 2021

Significance

Differences in beliefs within a society are a prevalent human phenomenon. A standard explanation for polarized beliefs relies on “echo chambers” that expose people to different sources of information. However, there is ample evidence that people sustain different beliefs even when faced with the same information, and they interpret that information differently—facts often attributed to a confirmatory bias. We suggest models of how humans form beliefs based on machine learning theory. These models show how stark differences in beliefs can arise and endure due to human limitations in interpreting complex information. Our framework illuminates inherent challenges and potential ways of overcoming polarization.
The N terminus of Orai1 couples to the AKAP79 signaling complex to drive NFAT1 activation by local Ca
2+
entry
Authors: Kar Pulak , Lin Yu-Ping , Bhardwaj Rajesh , Tucker Charles J. , Bird Gary S. , Hediger Matthias A. , Monico Carina , Amin Nader , Parekh Anant B.
Published: May 2021

Significance

Store-operated Orai1 Ca
2+
channels are a major route for trigger Ca
2+
in immune cells. Local Ca
2+
entry through the channels activates NFAT transcription factors, which in turn increase expression of chemokines and cytokines that orchestrate inflammatory responses. We identify a region on the N terminus of Orai1 that is indispensable for activating NFAT, through interaction with the scaffolding protein AKAP79. We show that a peptide that uncouples Orai1 from AKAP79 suppresses cytokine production, leaving other functional consequences of the channel intact. Our results identify an approach for developing immunosuppressant drugs.