bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantum double aspects of surface code models
Authors: Cowtan Alexander , Majid Shahn
Published: April 2022

We revisit the Kitaev model for fault tolerant quantum computing on a square lattice with underlying quantum double D( G) symmetry, where G is a finite group. We provide projection operators for its quasiparticles content as irreducible representations of D( G) and combine this with D( G)-bimodule properties of open ribbon excitation spaces [Formula: see text] to show how open ribbons can be used to teleport information between their endpoints s0, s1. We give a self-contained account that builds on earlier work but emphasizes applications to quantum computing as surface code theory, including gates on D( S3). We show how the theory reduces to a simpler theory for toric codes in the case of [Formula: see text], including toric ribbon operators and their braiding. In the other direction, we show how our constructions generalize to D( H) models based on a finite-dimensional Hopf algebra H, including site actions of D( H) and partial results on ribbon equivariance even when the Hopf algebra is not semisimple.
Phase and frequency linear response theory for hyperbolic chaotic oscillators
Authors: Tönjes Ralf , Kori Hiroshi
Published: April 2022

We formulate a linear phase and frequency response theory for hyperbolic flows, which generalizes phase response theory for autonomous limit cycle oscillators to hyperbolic chaotic dynamics. The theory is based on a shadowing conjecture, stating the existence of a perturbed trajectory shadowing every unperturbed trajectory on the system attractor for any small enough perturbation of arbitrary duration and a corresponding unique time isomorphism, which we identify as phase such that phase shifts between the unperturbed trajectory and its perturbed shadow are well defined. The phase sensitivity function is the solution of an adjoint linear equation and can be used to estimate the average change of phase velocity to small time dependent or independent perturbations. These changes in frequency are experimentally accessible, giving a convenient way to define and measure phase response curves for chaotic oscillators. The shadowing trajectory and the phase can be constructed explicitly in the tangent space of an unperturbed trajectory using co-variant Lyapunov vectors. It can also be used to identify the limits of the regime of linear response.
IWAVE—An adaptive filter approach to phase lock and the dynamic characterization of pseudo-harmonic waves
Authors: Daw E. J. , Hollows I. J. , Jones E. L. , Kennedy R. , Mistry T. , Edo T. B. , Fays M. , Sun L.
Published: April 2022

We present a novel adaptive filtering approach to the dynamic characterization of waves of varying frequencies and amplitudes embedded in arbitrary noise backgrounds. This method, known as IWAVE (Iterative Wave Action angle Variable Estimator), possesses critical advantages over conventional techniques, making it a useful new tool in the dynamic characterization of a wide range of data containing embedded oscillating signals. After a review of existing techniques, we present the IWAVE algorithm, derive its key characteristics, and provide tests of its performance using simulated and real world data.
Toward a modular, integrated, miniaturized, and portable microfluidic flow control architecture for organs-on-chips applications
Authors: Özkayar Gürhan , Lötters Joost C. , Tichem Marcel , Ghatkesar Murali K.
Published: April 2022

Microfluidic organs-on-chips (OoCs) technology has emerged as the trend for in vitro functional modeling of organs in recent years. Simplifying the complexities of the human organs under controlled perfusion of required fluids paves the way for accurate prediction of human organ functionalities and their response to interventions like exposure to drugs. However, in the state-of-the-art OoC, the existing methods to control fluids use external bulky peripheral components and systems much larger than the chips used in experiments. A new generation of compact microfluidic flow control systems is needed to overcome this challenge. This study first presents a structured classification of OoC devices according to their types and microfluidic complexities. Next, we suggest three fundamental fluid flow control mechanisms and define component configurations for different levels of OoC complexity for each respective mechanism. Finally, we propose an architecture integrating modular microfluidic flow control components and OoC devices on a single platform. We emphasize the need for miniaturization of flow control components to achieve portability, minimize sample usage, minimize dead volume, improve the flowing time of fluids to the OoC cell chamber, and enable long-duration experiments.
Stability of a parametrically driven, coupled oscillator system: An auxiliary function method approach
Authors: McMillan Andrew N. , Young Yin Lu
Published: April 2022

Coupled, parametric oscillators are often studied in applied biology, physics, fluids, and many other disciplines. In this paper, we study a parametrically driven, coupled oscillator system where the individual oscillators are subjected to varying frequency and phase with a focus on the influence of the damping and coupling parameters away from parametric resonance frequencies. In particular, we study the long-term statistics of the oscillator system’s trajectories and stability. We present a novel, robust, and computationally efficient method, which has come to be known as an auxiliary function method for long-time averages, and we pair this method with classical, perturbative-asymptotic analysis to corroborate the results of this auxiliary function method. These paired methods are then used to compute the regions of stability for a coupled oscillator system. The objective is to explore the influence of higher order, coupling effects on the stability region across a broad range of modulation frequencies, including frequencies away from parametric resonances. We show that both simplified and more general asymptotic methods can be dangerously un-conservative in predicting the true regions of stability due to high order effects caused by coupling parameters. The differences between the true stability region and the approximate stability region can occur at physically relevant parameter values in regions away from parametric resonance. As an alternative to asymptotic methods, we show that the auxiliary function method for long-time averages is an efficient and robust means of computing true regions of stability across all possible initial conditions.
Effect of proton irradiation temperature on persistent photoconductivity in zinc oxide metal-semiconductor-metal ultraviolet photodetectors
Authors: Heuser Thomas A. , Chapin Caitlin A. , Holliday Max A. , Wang Yongqiang , Senesky Debbie G.
Published: April 2022

The electrical and structural characteristics of 50-nm-thick zinc oxide (ZnO) metal-semiconductor-metal ultraviolet (UV) photodetectors subjected to proton irradiation at different temperatures are reported and compared. The devices were irradiated with 200 keV protons to a fluence of 1016 cm−2. Examination of the x-ray diffraction (XRD) rocking curves indicates a preferred (100) orientation prior to irradiation, with decrease in crystal quality afterward. Additionally, peak shifts in XRD and Raman spectra of the control sample relative to well-known theoretical positions are indicative of tensile strain in the as-deposited ZnO films. Shifts toward theoretical unstrained positions are observed in the irradiated films, which indicates partial relaxation. Raman spectra also indicate increase in oxygen vacancies (VO) and zinc interstitial defects (Zni) compared to the control sample. Additionally, transient photocurrent measurements performed on each sample at different temperatures showed up to 2× increase in photocurrent decay time constants for irradiated samples vs the control. This persistent photoconductive behavior is linked to the activation of electron and hole traps near the surface, and to the desorption and reabsorption of O2 molecules on the ZnO surface under the influence of UV light. Using an Arrhenius model, trap activation energies were extracted and, by comparing with known energies from the literature, the dominant defects contributing to persistent photoconductivity for each irradiation condition were identified. The persistence of differences in photocurrent transients between different samples months after irradiation indicates that the defects introduced by the suppression of thermally activated dynamic annealing processes have a long-term deleterious effect on device performance.
Bioinspired materials: Physical properties governed by biological refolding
Authors: Rosenman G. , Apter B.
Published: April 2022

Peptide and protein biomolecules folded into two fundamentally different conformations, either α-helical or β-sheet, carry out dissimilar biological functions. In living organisms, an α-helical secondary structure is adopted by different types of proteins such as myoglobin, keratin, collagen, and more. They can be found in diverse biological tissues of muscle, bone, cartilage, etc.. Biological functions of β-sheet peptide/protein structures are different and associated with a wide range of human mental amyloid diseases such as Alzheimer and Parkinson. The fundamental basis of these diseases is misfolding or refolding of natively soluble α-helical amyloid proteins into solid-state β-sheet fibrillary structures. Bioinspired chemically synthesized biomolecules mimic their biological counterparts. Although these artificial and biological peptides/proteins molecules are completely dissimilar in origin and environment, they demonstrate the common properties of folding and refolding into identical secondary architectures. In this review, we show that these two structural conformations, native (helix-like) and β-sheet, exhibit exclusive and different sets of fold-sensitive physical properties that are surprisingly similar in both biological and bioinspired materials. A native (helix-like) self-assembled fold having asymmetric structure demonstrates ferroelectric-like pyroelectric, piezoelectric, nonlinear optical, and electro-optical effects. β-sheet peptide/protein structures acquire unique visible fluorescence (FL) and reveal a new property of lossless FL photonic transport followed by a long-range FL waveguiding in amyloidogenic fibers. An applied thermally mediated refolding native-to-β-sheet allows us to observe adoption, disappearance, and switching of the revealed physical properties in detail in each fold and study dynamics of all critical stages of refolding from the metastable (native) helix-like conformation via intermediate disordered state to stable β-sheet fibrillary ordering. In the intermediate state, the appearance of the visible FL provides imaging, monitoring, and direct observation of the early stages of seeding and nucleation of β-sheet fibrils. The diverse fold-sensitive physical properties found, give a new insight into biological refolding processes and pave the way for the development of advanced physical methods of fold recognition, bioimaging, light theranostics at nanoscale, and peptide/protein nanophotonics from new visible FL bionanodots to bioinspired multifunctional peptide photonic chips.
Practical guide to replica exchange transition interface sampling and forward flux sampling
Authors: Hall Steven W. , Díaz Leines Grisell , Sarupria Sapna , Rogal Jutta
Published: April 2022

Path sampling approaches have become invaluable tools to explore the mechanisms and dynamics of the so-called rare events that are characterized by transitions between metastable states separated by sizable free energy barriers. Their practical application, in particular to ever more complex molecular systems, is, however, not entirely trivial. Focusing on replica exchange transition interface sampling (RETIS) and forward flux sampling (FFS), we discuss a range of analysis tools that can be used to assess the quality and convergence of such simulations, which is crucial to obtain reliable results. The basic ideas of a step-wise evaluation are exemplified for the study of nucleation in several systems with different complexities, providing a general guide for the critical assessment of RETIS and FFS simulations.
Information dynamics of price and liquidity around the 2017 Bitcoin markets crash
Authors: Vasiliauskaite Vaiva , Lillo Fabrizio , Antulov-Fantulin Nino
Published: April 2022

We study information dynamics between the largest Bitcoin exchange markets during the bubble in 2017–2018. By analyzing high-frequency market microstructure observables with different information-theoretic measures for dynamical systems, we find temporal changes in information sharing across markets. In particular, we study time-varying components of predictability, memory, and (a)synchronous coupling, measured by transfer entropy, active information storage, and multi-information. By comparing these empirical findings with several models, we argue that some results could relate to intra-market and inter-market regime shifts and changes in the direction of information flow between different market observables.
Fringing field induced current coupling in concentric metal–insulator–semiconductor (MIS) tunnel diodes with ultra-thin oxide
Authors: Chen Jen-Hao , Chen Kung-Chu , Hwu Jenn-Gwo
Published: April 2022

Coupling phenomenon between two Al/SiO2/Si(p) metal–insulator–semiconductor (MIS) tunneling diodes (TD) with various thin oxide thicknesses was studied in detail. When the bias voltage at one MIS TD is positive enough, the saturation currents of the two neighboring MIS TDs with concentric gate structures would be approximately the same due to saturation current coupling effect though the areas of these two devices are different. With thinner oxide, the saturation current coupling effect occurs earlier. This result indicates an enhancement of coupling sensitivity between two neighboring MIS TDs with thinner oxide. A physical mechanism of lateral minority carrier flow attracted by the fringing field was given to explain this phenomenon. Moreover, this oxide thickness dependent phenomenon of coupling effect was confirmed by capacitance–voltage (C–V) characteristics, and the fringing field extension and strengthening were clarified by 2D TCAD simulation.
Two-dimensional monitoring of a laser–solid x-ray source spot via penumbral coded aperture imaging technique
Authors: Bai Xue-Jie , Yan Yi-Hong , Lei Hong-Yi , Sun Fang-Zheng , Wang Tian-Ze , Zhu Chang-Qing , Tan Jun-Hao , Hu Guang , Li Yan-Fei , Ma Jing-Long , Liao Guo-Qian , Zhang Zhe , Hu Hua-Si , Li Yu-Tong
Published: April 2022

The uncertainties of spot size and position need to be clarified for x-ray sources as they can affect the detecting precision of the x-ray probe beam in applications such as radiography. In particular, for laser-driven x-ray sources, they would be more significant as they influence the inevitable fluctuation of the driving laser pulses. Here, we have employed the penumberal coded aperture imaging technique to diagnose the two-dimensional spatial distribution of an x-ray emission source spot generated from a Cu solid target irradiated by an intense laser pulse. Taking advantage of the high detection efficiency and high spatial resolution of this technique, the x-ray source spot is characterized with a relative error of ∼5% in the full width at half maximum of the intensity profile in a single-shot mode for general laser parameters, which makes it possible to reveal the information of the unfixed spot size and position precisely. Our results show the necessity and feasibility of monitoring the spot of these novel laser-driven x-ray sources via the penumbral coded aperture imaging technique.
Switching pathway-dependent strain-effects on the ferroelectric properties and structural deformations in orthorhombic HfO2
Authors: Wei Wei , Zhao Guoqing , Zhan XuePeng , Zhang Weiqiang , Sang Pengpeng , Wang Qianwen , Tai Lu , Luo Qing , Li Yuan , Li Can , Chen Jiezhi
Published: April 2022

The polarization switching pathway plays a key role in deciding the magnitudes of the spontaneous polarization and the coercive electric field, which can be used to realize controllable ferroelectric properties. In this paper, by first-principles calculations, we reveal how the spontaneous polarization (Ps) and the switching barrier (Eb) of orthorhombic HfO2 (o-HfO2) respond to various lattice strains depending on two kinds of switching pathways, i.e., the shift-across (SA) pathway and the shift-inside pathway. It is revealed that the existence of the two pathways is most likely dependent on the interface termination of o-HfO2, and the SA pathway exhibits higher critical values of both Ps and Eb. By applying lattice strains on o-HfO2 (001) and (010) planes, a ferroelectric–paraelectric phase transition from the polar Pca21 to the nonpolar Pbcn can be observed. Importantly, the variation trends of Ps and Eb under the same lattice strains are found to be highly different depending on the switching pathways. However, by carefully designing the interfacial tail atoms, strain engineering can efficiently improve Eb and Ps for both pathways in o-HfO2 films. Our work uncovers the mechanisms of the switching pathways and opens a new avenue for preparing high-performance ferroelectric devices using strain engineering.
Logarithmic trapping and detrapping in
β
-Ga2O3 MOSFETs: Experimental analysis and modeling
Authors: Fregolent Manuel , Brusaterra Enrico , De Santi Carlo , Tetzner Kornelius , Würfl Joachim , Meneghesso Gaudenzio , Zanoni Enrico , Meneghini Matteo
Published: April 2022

In this paper, we extensively characterize and model the threshold voltage instability in lateral β-Ga2O3 MOSFETs with Al2O3 gate dielectric. Specifically, (i) the results indicate that the threshold voltage instability originates from electron trapping at gate dielectric border traps close to the Al2O3/β-Ga2O3 interface. (ii) Logarithmic kinetics were detected for both stress and recovery by means of a innovative fast-capacitance experimental setup, over more than seven decades of time; (iii) a generalized model, which is capable of accurately reproducing the experimental results, was proposed to explain this trend.
Detailed balance for particle models of reversible reactions in bounded domains
Authors: Zhang Ying , Isaacson Samuel A.
Published: April 2022

In particle-based stochastic reaction–diffusion models, reaction rates and placement kernels are used to decide the probability per time a reaction can occur between reactant particles and to decide where product particles should be placed. When choosing kernels to use in reversible reactions, a key constraint is to ensure that detailed balance of spatial reaction fluxes holds at all points at equilibrium. In this work, we formulate a general partial-integral differential equation model that encompasses several of the commonly used contact reactivity (e.g., Smoluchowski-Collins-Kimball) and volume reactivity (e.g., Doi) particle models. From these equations, we derive a detailed balance condition for the reversible A + B ⇆ C reaction. In bounded domains with no-flux boundary conditions, when choosing unbinding kernels consistent with several commonly used binding kernels, we show that preserving detailed balance of spatial reaction fluxes at all points requires spatially varying unbinding rate functions near the domain boundary. Brownian dynamics simulation algorithms can realize such varying rates through ignoring domain boundaries during unbinding and rejecting unbinding events that result in product particles being placed outside the domain.
The effects of match circuit on the breakdown process of capacitively coupled plasma driven by radio frequency
Authors: Wu Hao , Chen Zhaoyu , Yu Shimin , Wang Qixuan , Li Xiandi , Jiang Wei , Zhang Ya
Published: April 2022

The breakdown process of capacitively coupled plasma (CCP) in the presence of a matching network is rarely studied, even though it is the indispensable part of the most laboratory and industrial devices of CCP. Based on the method of Verboncoeur, the solution method of the general “L”-type match circuit coupled with a particle-in-cell/Monte Carlo code is deduced self-consistently. Based on this method, the electrical breakdown process of CCP is studied. Both the plasma parameters and the electric parameters of the matching network during the breakdown are given and analyzed. In the pre-breakdown phase, the entire circuit can be considered as a linear system. However, the formation of the sheath during breakdown significantly enhanced the capacitance of the discharge chamber, which changed the electric signal amplitude of the external circuit. With the stabilization of plasma, the equivalent capacitance of CCP increases, which continues to change the electrical signal until the steady-state is reached. Accompanied by plasma stabilization is the appearance of high-order harmonics of discharge current caused by the gradually oscillating CCP capacitance. The breakdown characteristics can be obviously affected by the capacitance of the matching network. In the case of a breakdown zone, some breakdowns with special characteristics can be obtained by choosing the different capacitors. These works might be a reference for understanding the interaction between the plasma and the external circuit during the breakdown process and how to modulate the gas breakdown by controlling the external circuit.
On Oreology, the fracture and flow of “milk's favorite cookie®”
Authors: Owens Crystal E. , Fan Max R. , Hart A. John , McKinley Gareth H.
Published: April 2022

The mechanical experience of consumption (i.e., feel, softness, and texture) of many foods is intrinsic to their enjoyable consumption, one example being the habit of twisting a sandwich cookie to reveal the cream. Scientifically, sandwich cookies present a paradigmatic model of parallel plate rheometry in which a fluid sample, the cream, is held between two parallel plates, the wafers. When the wafers are counter-rotated, the cream deforms, flows, and ultimately fractures, leading to separation of the cookie into two pieces. We introduce Oreology (/ɔriːˈɒlədʒi/), from the Nabisco Oreo for “cookie” and the Greek rheo logia for “flow study,” as the study of the flow and fracture of sandwich cookies. Using a laboratory rheometer, we measure failure mechanics of the eponymous Oreo's “creme” and probe the influence of rotation rate, amount of creme, and flavor on the stress–strain curve and postmortem creme distribution. The results typically show adhesive failure, in which nearly all (95%) creme remains on one wafer after failure, and we ascribe this to the production process, as we confirm that the creme-heavy side is uniformly oriented within most of the boxes of Oreos. However, cookies in boxes stored under potentially adverse conditions (higher temperature and humidity) show cohesive failure resulting in the creme dividing between wafer halves after failure. Failure mechanics further classify the creme texture as “mushy.” Finally, we introduce and validate the design of an open-source, three-dimensionally printed Oreometer powered by rubber bands and coins for encouraging higher precision home studies to contribute new discoveries to this incipient field of study.
Engineering the stoichiometry of a TiO2-rich SrTiO3(001) surface
Authors: Smink Sander , Lin Wilson , Mannhart Jochen , Braun Wolfgang
Published: April 2022

We investigate the stoichiometry of a TiO2-rich SrTiO3(001) surface by depositing less than one monolayer of SrO under typical epitaxy conditions. We find that this deposition yields atomically flat islands on the step-and-terrace surface. All these islands have a height of exactly one full SrTiO3 unit cell, instead of the expected half unit cell. Reflection high-energy electron diffraction indicates that a reconstruction occurs on the bare surface, which disappears with SrO deposition. To explain these results, we propose a simple model with two key elements: (i) a TiO2 double layer must intrinsically be present on the as-prepared SrTiO3(001) surface, and (ii) with deposited SrO, this top layer rearranges itself to form islands with a height of one unit cell.
A modularized high-power ultra-wideband radiation system based on the space-synthesis method
Authors: Qiu Yang-xin , Xie Yan-zhao , Wang Shao-fei , Zhang Pu-qing , Zhou Tong , Zhang Lan-qi , Yang Yu , Gao Ming-xiang , Zhang Hong-ye
Published: April 2022

In this paper, a high-power ultra-wideband radiation system, composed of multiply radiation modules, is developed based on the space-synthesis method. The radiation module mainly consists of a transistorized pulser, a 2 × 2 combined antenna array, and a power divider. To improve the out parameters [the amplitude, the pulse repetition frequency (PRF), and the rise time] of the transistorized pulser based on the Marx circuit, the influence of the traveling wave process on the output pulse must be concerned. Based on the theoretical analysis, the printed circuit board circuit parameters and the circuit structure of the pulser are optimized. To improve the power synthesis efficiency, the pulse jitter characteristic of the pulser is improved by replacing the conventional base triggering mode with the collector voltage ramp triggering mode for the first-stage avalanche transistor in the pulser. The previous optimized antenna array is utilized in this radiation system, which has a better radiation performance in the prescribed aperture area. In addition, based on the gradient microstrip structure, the power divider integrated with the pulser is designed, which has the advantages of wide bandwidth, low loss, and light weight. Experimental results show that the peak effective potential rEp of the radiation system of 20 radiation modules is 221.8 kV, the maximum PRF could reach 10 kHz, and the half-power radiation angles of its radiation field are about 5° in both the E plane and the H plane. More radiation modules could be integrated into the system to achieve a higher electric field in the future.
The effect of dielectric environment on the brightening of neutral and charged dark excitons in WSe2 monolayer
Authors: Zinkiewicz Małgorzata , Grzeszczyk Magdalena , Kipczak Łucja , Kazimierczuk Tomasz , Watanabe Kenji , Taniguchi Takashi , Kossacki Piotr , Babiński Adam , Molas Maciej R.
Published: April 2022

The dielectric environment of atomically thin monolayer (ML) of semiconducting transition metal dichalcogenides affects both the electronic bandgap and the excitonic binding energy in the ML. We investigate the effect of the environment on the in-plane magnetic field brightening of neutral and charged dark exciton emissions in the WSe2 ML. The monolayers placed in three dielectric environments are studied, in particular, the ML encapsulated in hexagonal BN (hBN) flakes, the ML deposited on a hBN layer, and the ML embedded between the hBN flake and SiO2/Si substrate. We observe that the brightening rates of the neutral and charged dark excitons depend on the dielectric environment, which may be related to the variation of the level of carrier concentration in the ML. Moreover, the surrounding media, characterized by different dielectric constants, weakly influence the relative energies of the neutral and charged dark excitons in reference to the bright ones.
Loss mechanisms in TiN high impedance superconducting microwave circuits
Authors: Amin Kazi Rafsanjani , Ladner Carine , Jourdan Guillaume , Hentz Sébastien , Roch Nicolas , Renard Julien
Published: April 2022

Aluminum-based platforms have allowed to reach major milestones for superconducting quantum circuits. For the next generation of devices, materials that are able to maintain low microwave losses while providing new functionalities, such as large kinetic inductance or compatibility with CMOS platform, are needed. Here, we report on a combined direct current and microwave investigation of titanium nitride films of different thicknesses grown using CMOS compatible methods. For microwave resonators made of 3 nm thick TiN, we measured large kinetic inductance LK ∼240 pH/sq, high mode impedance of ∼4.2 kΩ while maintaining microwave quality factor ∼105 in the single photon limit. We present an in-depth study of the microwave loss mechanisms in these devices that indicates the importance of quasiparticles and provide insight for further improvement.
Enhancement of voltage controlled magnetic anisotropy (VCMA) through electron depletion
Authors: Peterson Thomas J. , Hurben Anthony , Jiang Wei , Zhang Delin , Zink Brandon , Chen Yu-Chia , Fan Yihong , Low Tony , Wang Jian-Ping
Published: April 2022

Recent advancement in the switching of perpendicular magnetic tunnel junctions with an electric field has been a milestone for realizing ultra-low energy memory and computing devices. To integrate with current spin-transfer torque-magnetic tunnel junction and spin–orbit torque-magnetic tunnel junction devices, the typical linear fJ/V m range voltage controlled magnetic anisotropy (VCMA) needs to be significantly enhanced with approaches that include new materials or stack engineering. A possible bidirectional and 1.1 pJ/V m VCMA effect has been predicted by using heavily electron-depleted Fe/MgO interfaces. To improve upon existing VCMA technology, we have proposed inserting high work function materials underneath the magnetic layer. This will deplete electrons from the magnetic layer biasing the gating window into the electron-depleted regime, where the pJ/V m and bidirectional VCMA effect was predicted. We have demonstrated tunable control of the Ta/Pd(x)/Ta underlayer's work function. By varying the Pd thickness (x) from 0 to 10 nm, we have observed a tunable change in the Ta layer's work function from 4.32 to 4.90 eV. To investigate the extent of the electron depletion as a function of the Pd thickness in the underlayer, we have performed DFT calculations on supercells of Ta/Pd(x)/Ta/CoFe/MgO, which demonstrate that electron depletion will not be fully screened at the CoFe/MgO interface. Gated pillar devices with Hall cross geometries were fabricated and tested to extract the anisotropy change as a function of applied gate voltage for samples with various Pd thicknesses. The electron-depleted Pd samples show three to six times VCMA improvement compared to the electron accumulated Ta control sample.
Dynamic Monte Carlo calculation generating particle trajectories that satisfy the diffusion equation for heterogeneous systems with a position-dependent diffusion coefficient and free energy
Authors: Nagai Tetsuro , Yoshimori Akira , Okazaki Susumu
Published: April 2022

A series of new Monte Carlo (MC) transition probabilities was investigated that could produce molecular trajectories statistically satisfying the diffusion equation with a position-dependent diffusion coefficient and potential energy. The MC trajectories were compared with the numerical solution of the diffusion equation by calculating the time evolution of the probability distribution and the mean first passage time, which exhibited excellent agreement. The method is powerful when investigating, for example, the long-distance and long-time global transportation of a molecule in heterogeneous systems by coarse-graining them into one-particle diffusive molecular motion with a position-dependent diffusion coefficient and free energy. The method can also be applied to many-particle dynamics.
Ground state energy of a Bose gas in the Gross–Pitaevskii regime
Authors: Basti Giulia , Cenatiempo Serena , Olgiati Alessandro , Pasqualetti Giulio , Schlein Benjamin
Published: April 2022

We review some rigorous estimates for the ground state energy of dilute Bose gases. We start with Dyson’s upper bound, which provides the correct leading order asymptotics for hard spheres. Afterward, we discuss a rigorous version of Bogoliubov theory, which recently led to an estimate for the ground state energy in the Gross–Pitaevskii regime, valid up to second order, for particles interacting through integrable potentials. Finally, we explain how these ideas can be combined to establish a new upper bound, valid to second order, for the energy of hard spheres in the Gross–Pitaevskii limit. Here, we only sketch the main ideas; details will appear elsewhere.
Evidences of accumulation points: Effect of high voltage DC conditioning on concave electrodes insulated by large vacuum gaps
Authors: Pilan Nicola , Agostini Matteo , Bernardi Marco , Cavenago Marco , Fincato Michele , Fontana Cristiano , Gobbo Renato , Lotto Luca , McCormack Oisin , Pasqualotto Roberto , Pesavento Giancarlo , Patton Tommaso , Pino Felix , Spada Emanuele , Spagnolo Silvia , De Lorenzi Antonio
Published: April 2022

Counterintuitive experimental evidences have been observed during High Voltage Direct Current (HVDC) tests of two concave, axial-symmetric, electrodes insulated by large vacuum gaps of 3 and 7 cm with voltages from 150 to 370 kVdc. The dissipation of microdischarge power during the conditioning procedure occurs mostly on the anodic side in a region close to the axis of the system where the electric field is at a minimum, far from the positions where the breakdowns have been observed. The analyses of the phenomena are carried out by comparing the temporal evolution of voltages, currents, pressure, measurements of x-ray energy spectra, and images from infrared and visible light cameras. Numerical simulations, based on ray-tracing algorithm, correctly identify the positions where the power dissipation of microdischarges occurs. A mutual exchange of charged particles in the electrostatic field between electrodes seems a reasonable physical mechanism to interpret the observations. These findings suggest a new perspective to review the current literature and interpret new results considering geometric details which were so far omitted: the areas with the most intense electric field, typically located on the surfaces of the electrodes under test, are not necessarily the sole surfaces involved in the HVDC conditioning in high vacuum.
Spontaneous generation of magnetic fields in thin layers of stratified plasma
Authors: Kopp M. I. , Tur A. V. , Yanovsky V. V.
Published: April 2022

In this work, the processes of spontaneous generation of magnetic fields by Rayleigh–Benard convection in a thin layer of plasma in a constant gravitational field are investigated. The values of the critical Rayleigh number for stationary convection are obtained, and the criteria for the occurrence of instability leading to the generation of magnetic fields are determined within the framework of electron magnetic hydrodynamics (EMHD). The weakly nonlinear regime of magnetic fields generation is studied using the method of perturbation theory with respect to the small supercriticality parameter ε=(Ra−Rac)/Rac of the stationary Rayleigh number Rac. A nonlinear equation of the Ginzburg–Landau type is obtained, which describes the evolution of the stationary level of excited magnetic fields.
Slip and stress from low shear rate nonequilibrium molecular dynamics: The transient-time correlation function technique
Authors: Maffioli Luca , Smith Edward R. , Ewen James P. , Daivis Peter J. , Dini Daniele , Todd B. D.
Published: April 2022

We derive the transient-time correlation function (TTCF) expression for the computation of phase variables of inhomogenous confined atomistic fluids undergoing boundary-driven planar shear (Couette) flow at constant pressure. Using nonequilibrium molecular dynamics simulations, we then apply the TTCF formalism to the computation of the shear stress and the slip velocity for atomistic fluids at realistic low shear rates, in systems under constant pressure and constant volume. We show that, compared to direct averaging of multiple trajectories, the TTCF method dramatically improves the accuracy of the results at low shear rates and that it is suitable to investigate the tribology and rheology of atomistically detailed confined fluids at realistic flow rates.
Waves on the equatorial β-plane in the presence of a uniform zonal flow: Beyond the Doppler shift
Authors: De-Leon Yair , Garfinkel Chaim I. , Paldor Nathan
Published: April 2022

Analytical and numerical solutions of the eigenvalue equation associated with zonally propagating waves of the linearized rotating shallow water equations are derived in a channel on the equatorial β-plane in the presence of a uniform mean zonal flow. The meridionally varying mean height field is in geostrophic balance with the prescribed mean zonal flow. In addition to the trivial Doppler shift of the free waves' phase speeds, the mean state causes the dispersion curves of each of the free Rossby and Poincaré waves to nearly coalesce in pairs of modes when the zonal wavenumber increases. For large zonal wavenumber or large mean flow, the latitudinal variation of the waves' amplitudes differs from that of free waves, i.e., Hermite functions (in wide channels) and harmonic functions (in narrow channels) do not describe the amplitude structure. For large mean speed and for large zonal wavenumber, the eigenvalue problem loses its Sturm–Liouville structure and the eigenfunctions have multiple extrema between successive zeros of the function itself. In contrast to free Kelvin waves, in the presence of a mean flow the meridional velocity component of these waves does not vanish identically. For zonal winds of order 20 m s−1 and for gravity wave speed of order 25 m s−1, conditions relevant to Earth's stratosphere, the phase speed with mean wind can be twice that of the classical theory with no mean zonal wind.
Molecular insight of the interface evolution of silicon carbide under hyperthermal atomic oxygen impact
Authors: Cui Zhiliang , Zhao Jin , Yao Guice , Li Zhihui , Wen Dongsheng
Published: April 2022

One of the key challenges faced by hypersonic flying is the complex thermal–mechanical–chemical coupling effect between thermal protection materials and non-equilibrium flow environment. Silicon carbide (SiC) has drawn much attention due to its superior physical and chemical characteristics, and its performance under hyperthermal atomic oxygen (AO) impact, however, is still little known. This work investigates the effects of various SiC crystalline polytypes, surface temperature, and crystal orientations on the SiC interface evolution by hyperthermal AO collisions via the reactive molecular dynamics method. The results showed that SiC surface erosion is highly dependent on the temperature and the presence of different interfacial structures. In the range of 500–2000 K, the proceeding of the passive oxidation advances the amorphous SiO2/SiC interface and the formation of SixOy phase weakens the surface catalytic characteristics and mechanical properties. The presence of defects, such as dangling bonds at the gas–solid interface, caused by different surface orientations affects the anti-erosion capabilities of SiC significantly, which may limit its further wide applications.
Strong increase of correlations in liquid glycerol observed by nonlinear dielectric techniques
Authors: Thoms Erik , Matyushov Dmitry V. , Richert Ranko
Published: April 2022

Nonlinear dielectric measurements are an important tool to access material properties and dynamics concealed in their linear counterparts, but the available data are often intermittent and, on occasion, even contradictory. Employing and refining a recently developed technique for high ac field dielectric measurements in the static limit, we ascertain nonlinear effects in glycerol over a wide temperature range from 230 to 320 K. We find that the temperature dependence of the Piekara factor a, which quantifies the saturation effect, changes drastically around 290 K, from ∂a/∂T = +1.4 to −130 in units of 10−18 V2 m−2 K−1. These high values of |a| quantify not only elevated dielectric saturation effects but also indicate a temperature driven increase in higher-order orientational correlations and considerable correction terms with respect to the central limit theorem. No signature of this feature can be found in the corresponding low field data.
Review of Scientific Instruments New Products
Authors: Mandelis Andreas
Published: April 2022

In order to supplement manufacturers’ information, this department will welcome the submission by our readers of brief communications, reporting measurements on the physical properties of materials, which supersede earlier data or suggest new research applications.
An epilepsy-associated K
V
1.2 charge-transfer-center mutation impairs K
V
1.2 and K
V
1.4 trafficking
Authors: Nilsson Michelle , Lindström Sarah H. , Kaneko Maki , Wang Kaiqian , Minguez-Viñas Teresa , Angelini Marina , Steccanella Federica , Holder Deborah , Ottolia Michela , Olcese Riccardo , Pantazis Antonios
Published: April 2022

Significance

A child with epilepsy has a previously unreported, heterozygous mutation in
KCNA2
, the gene encoding K
V
1.2 proteins. Four K
V
1.2 assemble into a potassium-selective channel, a protein complex at the neuronal cell surface regulating electrical signaling. K
V
1.2 subunits assemble with other K
V
1-family members to form heterotetrameric channels, contributing to neuronal potassium-channel diversity. The most striking consequence of this mutation is preventing K
V
1.2-subunit trafficking, i.e., their ability to reach the cell surface. Moreover, the mutation is dominant negative, as mutant subunits can assemble with wild-type K
V
1.2 and K
V
1.4, trapping them into nontrafficking heterotetramers and decreasing their functional expression. Thus, K
V
1-family genes’ ability to form heterotetrameric channels is a double-edged sword, rendering K
V
1-family members vulnerable to dominant-negative mutations in a single member gene.
Crystalline C
3
N
3
H
3
tube (3,0) nanothreads
Authors: Gao Dexiang , Tang Xingyu , Xu Jingqin , Yang Xin , Zhang Peijie , Che Guangwei , Wang Yajie , Chen Yongjin , Gao Xiang , Dong Xiao , Zheng Haiyan , Li Kuo , Mao Ho-kwang
Published: April 2022

Significance

The diamond nanothread is predicted to have comparable or larger strength and stiffness than the carbon nanotube but severely suffers from intrathread bonding disorder in practice. Here, we synthesized a bulk crystalline diamond nanothread material C
3
N
3
H
3
with a C/N-ordered tube (3,0) structure via high-pressure topochemical polymerization of
s
-triazine. The π-stacked
s
-triazine experienced a selective concerted bonding of three neighbored C···N pairs, completely different from the classical Diels–Alder reactions of aromatics under high pressure. This study obtained the structure-specific diamond nanothread with an unambiguous elemental reaction, which is the basis to realize the expected excellent properties of diamond nanothreads. Following the identified reaction selectivity under high pressure, more structure-specific carbon materials can be designed.
An empirical study of Chinese university student advisors’ dynamic identity construction in the context of individual consultation
Authors: Chen Jing , Zhao Xin
Published: April 2022

While extensive research has been done on pragmatic identity construction in various contexts by various social groups, little is known about how and why university student advisors may dynamically construct their pragmatic identity in their interaction with their students. Based on the analysis of naturally-occurring data about 5 student advisors’ consultation, this article explores the various pragmatic identities constructed by Chinese university student advisors as well as their underlying motivations. It finds that the identities constructed by the student advisors can be non-professional (such as a student, an individual, a friend, and a family member) and professional (such as an administrator, a tutor and a teacher). It suggests that their pragmatic identity construction may signify their effort to balance their various communicative needs in the educational contexts. Such balance may serve to meet their goal of constructing a new type of Chinese advisor-student relation characterized by equality, democracy, and harmony.
A Medical Student-Led Model for Telephone-Based Opioid Overdose Education and Naloxone Distribution during the COVID-19 Pandemic
Authors: Hughes Terence M. , Kalicki Alexander , Huxley-Reicher Zina , Toribio Wilma , Samuels Don L. , Weiss Jeffrey J. , Herscher Michael , Wang Linda
Published: April 2022

Background: The co-occurrence of the COVID-19 pandemic and opioid epidemic has increased the risk of overdose and death for patients with opioid use disorder (OUD). COVID-19 has also exacerbated already limited access to opioid overdose education and naloxone distribution (OEND). In this context, we aim to increase access to OEND for patients at risk for opioid overdose. Methods: Medical student volunteers were trained to conduct telephone-based OEND, and subsequently contacted all patients at a NYC primary care clinic for people who use drugs as well as those presenting to the hospital with OUD or a history of opioid overdose. Interested patients who completed the training received naloxone kits via mail or at hospital discharge. Results: OEND provision was converted to a remote-only model from May to June 2020. During this time, eight pre-clinical medical students called a total of 503 high-risk patients. Of these patients, 165 were reached, with 90 (55%) accepting telephone-based OEND. Comparing across populations, 51% of primary care patients versus 76% of ED/hospitalized patients accepted opioid overdose education. Eighty-four total patients received naloxone. Conclusions: We have outlined a scalable, adaptable model by which clinics and hospitals with affiliated medical schools can provide OEND by telephone. Medical student-driven, telephone-based OEND efforts can effectively reach at-risk patients and increase naloxone access.
Familial Support in Integrated Treatment with Antiretroviral Therapy and Medications for Opioid use Disorder in Vietnam: A Qualitative Study
Authors: Brown Patrick C. M. , Dinh Thị Thanh Thuy , Edsall Andrew , Nguyen Thu Hang , Mai Pham Phuong , Hoffman Kim , Bart Gavin , Korthuis P. Todd , Le Minh Giang
Published: April 2022

Background: Patients report that familial support can facilitate initiation and maintenance of antiretroviral therapy (ART) and medications for opioid use disorder (MOUD). However, providing such support can create pressure and additional burdens for families of people with opioid use disorder (OUD) and HIV. We examined perspectives of people with HIV receiving treatment for OUD in Vietnam and their family members. Methods: Between 2015 and 2018, we conducted face-to-face qualitative interviews with 44 patients and 30 of their family members in Hanoi, Vietnam. Participants were people living with HIV and OUD enrolled in the BRAVO study comparing HIV clinic-based buprenorphine with referral to methadone treatment at 4 HIV clinics and their immediate family members (spouses or parents). Interviews were professionally transcribed, coded in Vietnamese, and analyzed using a semantic, inductive approach to qualitative thematic analysis. Results: Family members of people with OUD and HIV in Vietnam reported financially and emotionally supporting MOUD initiation and maintenance as well as actively participating in treatment. Family members described the burdens of supporting patients during opioid use, including financial costs and secondary stigma. Conclusions: Describing the role of family support in the lives of people living with OUD and HIV in the context of Vietnam enriches our understanding of their experiences and will support future treatment efforts targeting the family unit.