bluuebunny/crossref_metadata_2025 huggingface dataset:
The superconducting transition temperatures of C–S–H based on inter-sublattice S−H4-tetrahedron electronic interactions
Authors: Harshman Dale R. , Fiory Anthony T.
Published: January 2022

Significant characteristics of the superconducting transitions reported for carbonaceous sulfur hydride [Snider et al., Nature 585, 373 (2020)] are the exceptionally abrupt onset temperatures and their marked increase toward room temperature at high pressures. Theoretical and experimental studies addressing the superconducting composition and structure have thus far returned mixed results. One possibility, consistent with the experimentally suggested stoichiometry of CSHx, is the theoretically discovered compressed I4¯3m CSH7 structure [Sun et al., Phys. Rev. B 101, 174102 (2020)], which comprises a sublattice similar to Im3¯m H3S with CH4 intercalates. Positing an electronic genesis of the superconductivity, a model is presented in analogy with earlier work on superconductivity in Im3¯m H3S, in which pairing is induced via purely electronic Coulomb interactions across the mean distance ζ between the S and H4-tetrahedra enclosing C. Theoretical superconducting transition temperatures for I4¯3m CSH7 are derived as TC0 = (2/3)1/2σ1/2β/aζ, where β = 1247.4 Å2 K is a universal constant, σ is the participating charge fraction, and a is the lattice parameter. Analysis suggests persistent bulk superconductivity with a pressure-dependent σ, increasing from σ = 3.5, determined previously for Im3¯m H3S, to σ = 7.5 at high pressure owing to additionally participating C–H bond electrons. With a and ζ determined by theoretical structure, TC0 = 283.6 ± 3.5 K is predicted at 267 ± 10 GPa, in excellent agreement (within uncertainty) with the corresponding experimental TC = 287.7 ± 1.2 K. Pressure-induced variations in σ combined with experimental uncertainties in pressure yield overall average (TC − TC0) = (−0.8 ± 3.5) K.
Effect of triangularity on ion-temperature-gradient-driven turbulence
Authors: Duff J. M. , Faber B. J. , Hegna C. C. , Pueschel M. J. , Terry P. W.
Published: January 2022

The linear and nonlinear properties of ion-temperature-gradient-driven turbulence with adiabatic electrons are modeled for axisymmetric configurations for a broad range of triangularities δ, both negative and positive. Peak linear growth rates decrease with negative δ but increase and shift toward a finite radial wavenumber kx with positive δ. The growth-rate spectrum broadens as a function of kx with negative δ and significantly narrows with positive δ. The effect of triangularity on linear instability properties can be explained through its impact on magnetic polarization and curvature. Nonlinear heat flux is weakly dependent on triangularity for |δ|≤0.5, decreasing significantly with extreme δ, regardless of sign. Zonal modes play an important role in nonlinear saturation in the configurations studied, and artificially suppressing zonal modes increased nonlinear heat flux by a factor of about four for negative δ, increasing with positive δ by almost a factor of 20. Proxies for zonal-flow damping and drive suggest that zonal flows are enhanced with increasing positive δ.
Plasma technology in antimicrobial surface engineering
Authors: Nikiforov Anton , Ma Chuanlong , Choukourov Andrei , Palumbo Fabio
Published: January 2022

The design of advanced materials with superb anti-bacterial efficiency by engineering appropriate surface properties has now become a consolidated strategy to improve the functional properties of polymers, metals, and a variety of biomedical materials. Antimicrobial coatings can create a healthier living and working environment and offer holistic solutions to people with health problems. This Tutorial will serve as a reference point for scientists pursuing sustainable antimicrobial coatings development, by providing a design framework and a toolbox for enabling plasma-based technologies in additive engineering of new materials. A succinct description of how novel, efficient methods based on non-equilibrium reactive plasma chemistries can be applied to produce sophisticated, high-value advanced coatings with the anti-bacterial or antifungal function will be used to illustrate the utility of plasma methods. Described plasma-based methods can minimize the process steps and dramatically reduce the use of expensive and hazardous reagents, which is a point of high interest in the development of novel sustainable and green manufacturing processes. The Tutorial aims to provide an overview of the principle and state-of-the-art in plasma technology, which is useful for researchers and broad auditoria of students working in antimicrobial materials development and additive engineering.
Ultrafast time- and angle-resolved photoemission spectroscopy with widely tunable probe photon energy of 5.3–7.0 eV for investigating dynamics of three-dimensional materials
Authors: Bao Changhua , Zhong Haoyuan , Zhou Shaohua , Feng Runfa , Wang Yuan , Zhou Shuyun
Published: January 2022

Time- and angle-resolved photoemission spectroscopy (TrARPES) is a powerful technique for capturing the ultrafast dynamics of charge carriers and revealing photo-induced phase transitions in quantum materials. However, the lack of widely tunable probe photon energy, which is critical for accessing the dispersions at different out-of-plane momentum kz in TrARPES measurements, has hindered the ultrafast dynamics investigation of 3D quantum materials, such as Dirac or Weyl semimetals. Here, we report the development of a TrARPES system with a highly tunable probe photon energy from 5.3 to 7.0 eV. The tunable probe photon energy is generated by the fourth harmonic generation of a tunable wavelength femtosecond laser source by combining a β-BaB2O4 crystal and a KBe2BO3F2 crystal. A high energy resolution of 29–48 meV and time resolution of 280–320 fs are demonstrated on 3D topological materials ZrTe5 and Sb2Te3. Our work opens up new opportunities for exploring ultrafast dynamics in 3D quantum materials.
Limitations of field-theory simulation for exploring phase separation: The role of repulsion in a lattice protein model
Authors: Nilsson Daniel , Bozorg Behruz , Mohanty Sandipan , Söderberg Bo , Irbäck Anders
Published: January 2022

Field-theory simulation by the complex Langevin method offers an alternative to conventional sampling techniques for exploring the forces driving biomolecular liquid–liquid phase separation. Such simulations have recently been used to study several polyampholyte systems. Here, we formulate a field theory corresponding to the hydrophobic/polar (HP) lattice protein model, with finite same-site repulsion and nearest-neighbor attraction between HH bead pairs. By direct comparison with particle-based Monte Carlo simulations, we show that complex Langevin sampling of the field theory reproduces the thermodynamic properties of the HP model only if the same-site repulsion is not too strong. Unfortunately, the repulsion has to be taken weaker than what is needed to prevent condensed droplets from assuming an artificially compact shape. Analysis of a minimal and analytically solvable toy model hints that the sampling problems caused by repulsive interaction may stem from loss of ergodicity.
Turbulence-driven magnetic reconnection and the magnetic correlation length: Observations from Magnetospheric Multiscale in Earth's magnetosheath
Authors: Stawarz J. E. , Eastwood J. P. , Phan T. D. , Gingell I. L. , Pyakurel P. S. , Shay M. A. , Robertson S. L. , Russell C. T. , Le Contel O.
Published: January 2022

Turbulent plasmas generate a multitude of thin current structures that can be sites for magnetic reconnection. The Magnetospheric Multiscale (MMS) mission has recently enabled the detailed examination of such turbulent current structures in Earth's magnetosheath and revealed that a novel type of reconnection, known as electron-only reconnection, can occur. In electron-only reconnection, ions do not have enough space to couple to the newly reconnected magnetic fields, suppressing ion jet formation and resulting in thinner sub-proton-scale current structures with faster super-Alfvénic electron jets. In this study, MMS observations are used to examine how the magnetic correlation length (λC) of the turbulence, which characterizes the size of the large-scale magnetic structures and constrains the length of the current sheets formed, influences the nature of turbulence-driven reconnection. We systematically identify 256 reconnection events across 60 intervals of magnetosheath turbulence. Most events do not appear to have ion jets; however, 18 events are identified with ion jets that are at least partially coupled to the reconnected magnetic field. The current sheet thickness and electron jet speed have a weak anti-correlation, with faster electron jets at thinner current sheets. When λC≲20 ion inertial lengths, as is typical near the sub-solar magnetosheath, a tendency for thinner current sheets and potentially faster electron jets is present. The results are consistent with electron-only reconnection being more prevalent for turbulent plasmas with relatively short λC and may be relevant to the nonlinear dynamics and energy dissipation in turbulent plasmas.
Multi-scale modeling of ionic electrospray emission
Authors: Asher Jeffrey , Huang Ziyu , Cui Chen , Wang Joseph
Published: January 2022

The physics of ionic electrospray propulsion spans multiple length scales. This paper combines a molecular dynamics model, a particle–particle model, and a particle-in-cell model to investigate the physics of ionic electrospray propulsion over 9 orders of magnitude in length scale. The combined models are applied to simulate beam emission for an ionic electrospray propulsion system with porous emitter tips and 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid propellant from the emission site to the downstream plume. Additionally, the impact of multiple emission sites from a single emitter tip is analyzed with regard to extractor grid interception and overall beam neutralization for bipolar thruster pairs. Results show that beams consisting of species of different masses (i.e., monomer and dimer species) are affected by particle–particle forces during acceleration and should not be treated as a superposition of independently accelerated species in macro-scale plume models. The activation of multiple emission sites also causes a noticeable increase in the beam’s spread, leading to increased intercepted current but relatively little adverse effects in the downstream plume region.
Radiation direction mutation in a spherical plasma filled multilayered core–shell particle
Authors: Yang Tianbo , Fu Tao , An Yinbing
Published: January 2022

An actively tunable Fano resonance and the radiation direction mutation are supported in a multilayered core–shell particle composed of a spherical plasma-core and three-layered dielectric shells through varying plasma frequency. The simulated and theoretical results reveal that the Fano resonance relies on the interference between a narrow band electric dipole resonance and a broad band magnetic dipole resonance. The electric and magnetic dipole resonances can be controlled independently. The radiation direction mutates between forward and backward scatterings at Fano resonance frequency with lower plasma frequency, but there is a “delay” of the mutation in frequency with higher plasma frequency. The reasons for generating the mutation and delay are explained by using scattering amplitudes. The research results can be applied to antenna, directional emission control, and sensor areas.
Numerical analysis of energy harvesting system including an inclined inverted flag
Authors: Lim Se Hwan , Park Sung Goon
Published: January 2022

An inverted flag with the free leading edge and fixed trailing edge has been widely adopted in an energy harvesting system due to its highly unstable characteristics in a flow. In the present study, the non-zero inclination angle is set on the fixed trailing edge of the inverted flag to increase its instability and improve the energy harvesting performance. The effects of the bending rigidity and the inclination angle on the energy harvesting efficiency are numerically analyzed where the interaction between the flag and the surrounding fluid is considered by using an immersed boundary method. The inverted flag shows five flapping motions depending on the bending rigidity and the inclination angle: straight, symmetric, asymmetric, biased, and the over flapping modes. The mode change is observed from the straight mode to the flapping mode by increasing the inclination angle from the zero to non-zero degree, which is favorable in terms of the energy harvesting performance. The optimal efficiency is obtained by the inverted flag at the inclination angle of around 40°–45° corresponding to the biased flapping mode. In the biased flapping mode, the strain energy is continuously produced without a period where energy production drops to zero. The strain energy is quantitatively scaled based on a vortex formation that consists of factors associated with the kinematics of the inverted flag.
Strength of tantalum to 276 GPa determined by two x-ray diffraction techniques using diamond anvil cells
Authors: Perreault Christopher , Huston Larissa Q. , Burrage Kaleb , Couper Samantha C. , Miyagi Lowell , Moss Eric K. , Pigott Jeffrey S. , Smith Jesse S. , Velisavljevic Nenad , Vohra Yogesh , Sturtevant Blake T.
Published: January 2022

Tantalum (Ta) is a metal that has useful properties that make it useful in extreme environments. It is, therefore, important to understand how Ta performs in such extreme conditions by accurately measuring its properties. In this work, the yield strength of tantalum has been measured at pressures up to 276 GPa using axial and radial x-ray diffraction (XRD) methods in diamond anvil cells (DACs). We measured strength using XRD in a radial DAC to 50 GPa, in an axial DAC to 60 GPa using diamonds with standard flat culets, and in a final experiment to 276 GPa using toroidal diamond anvils. The radial XRD data were refined using the Material Analysis Using Diffraction Rietveld software package to extract lattice strain and the yield strength. The axial data were refined using the General Structure Analysis System II and a linewidth method was used to calculate the yield strength. The yield strength measured near ambient pressure was found to be 0.5 GPa and increased with a pressure of up to 50 GPa, where the yield strength plateaued at a value of 2.4 GPa. At pressures above 60 GPa, the strength increased again to a maximum value of 9 GPa at the highest pressure of 276 GPa. The data from the three experiments show good agreement between the methods and previously reported experimental data. This agreement illustrates the value of axial diffraction data for material strength determination and allows for measurements at multi-hundreds of GPa using toroidal DACs.
Mechanical unfeelability concentrator through topology optimization
Authors: Ota Motoaki , Fujii Garuda
Published: January 2022

Mechanical cloaks made from elastic metamaterials that make objects unfeelable have been developed, but usually each cloaking device performs only a single function. In this Letter, we present our computational attempts at instilling two different functionalities, cloaking and stress concentration, in a metastructure designed through topology optimizing a mechanical cloak-concentrator for linear elasticity. Solving this optimization problem involved improving two different objective functions, one for cloaking and the other for stress concentration. As an optimizer, the covariance matrix adaptation evolution strategy was adopted to find the optimal level set functions, which express the design configurations with clearly delineated boundaries. Optimized cloak-concentrators reproduce outer displacements as if nothing is present despite the presence of a system concentrating stress on an interior domain. We also present demonstrations of topology optimized configurations for mechanical unfeelability concentrators that perform robustly under loads at any location around the system and under the cloaked region of arbitrary Young's modulus. Our design scheme paves the way for designing metastructures that accommodate various multiple functions via the means of elastostatics.
Spectrally filtered ps–ns emission dynamics of atmospheric-pressure nanosecond pulsed plasmas
Authors: Patel Karna , Saha Anup , Zhou Tanbo , Meyer Terrence R. , Bane Sally , Satija Aman
Published: January 2022

The temporal dynamics of atmospheric-pressure nanosecond pulsed plasma discharges in a pin-to-pin electrode configuration are studied using streak-camera line imaging of the interelectrode gap with a time resolution as short as ∼25 ps. Discharge emission initiates homogeneously throughout the interelectrode gap with no detectable streamer propagation and then temporally decays in two distinct phases. Plasma emission bands attributed to various electronic transitions are tracked for single discharges in air and N2. Spectral filtering of the excited molecular states reveals that the N2(C–B) and N2(B–A) emission bands evolve in distinct early and late phases, respectively, with a time separation of ∼15–20 ns. Furthermore, significant differences in the temporal dynamics of plasma discharges in air and N2 are observed. High levels of excited-state atomic oxygen and NO appear after the initial decay of the N2(C) state and coincide primarily with the latter phases of plasma evolution in air environments. From temporal traces of discharge emission, the formation and relaxation timescales of the electronically excited states of N2 are quantified in pure N2 and air environments with sub-nanosecond resolution. The streak-OES (optical emission spectroscopy) technique enables quantitative time-resolved studies of key chemical species for model validation in ultra-short-pulsed plasmas.
Diagnostic techniques of minimum-B ECR ion source plasma instabilities
Authors: Toivanen V. , Bhaskar B. S. , Izotov I. V. , Koivisto H. , Tarvainen O.
Published: January 2022

The performance of a minimum-B Electron Cyclotron Resonance Ion Source (ECRIS) is traditionally quantified by measuring the beam current and quality of the extracted ion beams of different charge state ions. The stability of the extracted ion beam currents has drawn more attention recently as the technology is pushing its limits toward higher ion charge states and beam intensities. The stability of the extracted beam is often compromised by plasma instabilities manifesting themselves as rapid oscillations of the beam currents in millisecond scale. This paper focuses on practical aspects of diagnostics techniques of the instabilities, showcases examples of instability-related diagnostics signals, and links them to the plasma physics of ECR ion sources. The reviewed techniques include time-resolved microwave emission diagnostics, bremsstrahlung measurements, direct measurement of electron and ion fluxes, measurement of the ion beam energy spread, and optical emission diagnostics. We list the advantages and disadvantages of each technique and outline the development needs of further diagnostics. Finally, we discuss the implications of the instabilities in both historical and forward-looking context of ECRIS development.
Flow-induced birefringence study of secondary flow in entrance region of rectangular slit channel for long-chain-branched polyethylene melt
Authors: Musil Jan , Zatloukal Martin
Published: January 2022

This work presents an analysis of the inner boundary of the secondary flow (i.e., corner vortex flow) in the entrance region of a rectangular slit channel for long-chain-branched polyethylene melt evaluated using particle tracking and stress-induced birefringence measurements. Further, the flow-induced birefringence technique was used to investigate the effects of temperature and shear rate on the size of the secondary entry flow. Obtained results and trends were compared with the laser-Doppler velocimetry data taken from the open literature for the same polymer melt and comparable flow conditions. Interestingly, the results of both methods were very similar. This suggests that the stress-induced birefringence measurements may be a useful tool for investigating secondary entry flows of polymer melts.
Learning continuous chaotic attractors with a reservoir computer
Authors: Smith Lindsay M. , Kim Jason Z. , Lu Zhixin , Bassett Dani S.
Published: January 2022

Neural systems are well known for their ability to learn and store information as memories. Even more impressive is their ability to abstract these memories to create complex internal representations, enabling advanced functions such as the spatial manipulation of mental representations. While recurrent neural networks (RNNs) are capable of representing complex information, the exact mechanisms of how dynamical neural systems perform abstraction are still not well-understood, thereby hindering the development of more advanced functions. Here, we train a 1000-neuron RNN—a reservoir computer (RC)—to abstract a continuous dynamical attractor memory from isolated examples of dynamical attractor memories. Furthermore, we explain the abstraction mechanism with a new theory. By training the RC on isolated and shifted examples of either stable limit cycles or chaotic Lorenz attractors, the RC learns a continuum of attractors as quantified by an extra Lyapunov exponent equal to zero. We propose a theoretical mechanism of this abstraction by combining ideas from differentiable generalized synchronization and feedback dynamics. Our results quantify abstraction in simple neural systems, enabling us to design artificial RNNs for abstraction and leading us toward a neural basis of abstraction.
Study of similarity rules for electromagnetic process in partially ionized plasmas
Authors: Yao Jiansheng , Zhao Yingkui , Zhang Hantian , Ye Difa , Ouyang Biyao
Published: January 2022

As proved by a previous study, the similarity of electromagnetic processes in plasmas will be violated by Coulomb collisions between electron and ions. Therefore, there is no similarity in highly ionized collisional plasma. However, the situation will be completely different for collisional plasmas with a low ionization degree. The main collision type will change from electron–ion Coulomb collision to electron–molecule collision, and a new variable (the number density of neutral molecules) will be introduced into the similarity constraint, which can increase the degree of freedom. Thus, in this condition, the similarity restriction caused by the collision process does not conflict with the other restrictions. Therefore, the similarity for the electromagnetic process in collisional plasmas can be valid for partially ionized plasmas. In this paper, we propose the similarity in partially ionized plasmas and prove it via particle in cell/Monte Carlo simulation. Our research has a wide range of engineering applications.
Femtosecond laser comb driven perpendicular standing spin waves
Authors: Awad A. A. , Muralidhar S. , Alemán A. , Khymyn R. , Hanstorp D. , Åkerman J.
Published: January 2022

We study femtosecond laser comb driven sustained and coherent spin wave (SW) generation in Permalloy films over a thickness range of d = 40–100 nm. A simple rapid demagnetization model describes the dependence of the observed SW intensity on laser power for all film thicknesses. In the thicker films, we observe laser comb excited perpendicular standing spin waves up to the third order and to 18 multiples of the 1 GHz laser repetition rate. Our results demonstrate the versatility of femtosecond combs as contact-less SW point sources over a wide range of film thickness and type of SW modes.
Microbubble dynamics in a viscous compressible liquid subject to ultrasound
Authors: Wang Qianxi , Liu Wenke , Corbett Callan , Smith Warren R.
Published: January 2022

When a microbubble is subject to ultrasound, non-spherical oscillation or surface modes can be generated after many acoustic cycles. This phenomenon has wide applications, including ultrasonic cleaning, sonochemistry, and biomedical ultrasonics. Yet, the nonlinear development of the bubble shape modes over dozens of cycles is not well understood. Here, we describe a grid-free and robust model to simulate the phenomenon. A viscous pressure correction is introduced to compensate the non-zero tangential stress at the free surface in the potential flow model, based on conservation of energy. Consequently, the phenomenon is modeled using the boundary integral method, in which the compressible and viscous effects are incorporated into the model through the boundary conditions. The computations have been carried out for axisymmetric cases; however, the numerical model can be extended for three-dimensional cases in a straightforward manner. The numerical results are shown to be in good agreement for many cycles with some independent viscous and compressible theories for axisymmetric bubbles and experiments for microbubbles undergoing shape oscillation subject to ultrasound. The development of the shape oscillation of a bubble after a dozen cycles, the formation of a reentry jet and its penetration through the bubble, and the topological transformation of the bubble are simulated and analyzed in terms of the amplitude and frequency of the ultrasound. The computations and physical analysis are carried out for the development of shape modes due to a resonant volume oscillation, strong pressure wave, or the matching of the acoustic wave frequency with the shape mode frequency.
High-resolution infrared spectroscopy of supersonically cooled singlet carbenes: Bromomethylene (HCBr) in the CH stretch region
Authors: Chan Ya-Chu , Kortyna Andrew , Nesbitt David J.
Published: January 2022

First high-resolution spectra of cold (∼35 K) singlet bromomethylene HCBr in the CH stretching (v1) region from 2770 to 2850 cm−1 are reported using near quantum shot-noise limited laser absorption methods in a slit jet supersonic discharge expansion source. Three rovibrational bands are identified at high S/N (20:1–40:1) and rotationally assigned to (i) the CH stretch fundamental (v1) band X̃1,0,0←X̃0,0,0 and (ii) vibrational hot bands [X̃(1,1,0)←X̃(0,1,0) and X̃(1,0,1)←X̃(0,0,1)] arising from vibrationally excited HCBr populated in the discharge with single quanta in either the H–C–Br bend (v2) or C–Br stretch (v3) modes. Precision rotational constants are reported for a total of six states, with an experimentally determined CH stretch vibrational frequency (2799.38 cm−1) in good agreement with previous low-resolution fluorescence studies [M. Deselnicu et al., J. Chem. Phys. 124(13), 134302 (2006)]. Detailed analysis of the fundamental v1 band highlights the presence of perturbations in the X̃1,0,0 level, which we tentatively attribute to arise from the nearby triplet state ã(0,0,1) through spin–orbit interaction or the multiple quanta X̃0,2,1 singlet state via c-type Coriolis coupling. Reduced-Doppler resolution (60 MHz) in the slit-jet IR spectrometer permits for clear observation of a nuclear spin hyperfine structure, with experimental line shapes well reproduced by nuclear quadrupole/spin-rotation coupling constants from microwave studies [C. Duan et al., J. Mol. Spectrosc. 220(1), 113–121 (2003)]. Finally, the a-type to b-type transition intensity ratio for the fundamental CH stretch band is notably larger than that predicted by using a bond-dipole model, which from high level ab initio quantum calculations [CCSD(T)/PVQZ] can be attributed to vibrationally induced “charge-sloshing” of electron density along the polar C–Br bond.
Atomic-level study of AuSn–Au5Sn eutectic interfaces
Authors: Sun Yingjie , He Junjie , Ma Houyu , Xiong Kai , Liu Yue , Mao Yong , Wang Jian
Published: January 2022

Au-20Sn solder is obtained through severe plastic deformation and subsequent spheroidization of Au-20Sn eutectic alloys, which are composed of alternating intermetallic compounds δ-AuSn and ξ′-Au5Sn. Understanding AuSn–Au5Sn eutectic interfaces is essential for processing the Au-20Sn solder. Here, we studied the δ-AuSn/ξ′-Au5Sn eutectic interfaces at different deformation sates by electron backscattered diffraction analysis, high resolution transmission electron microscope, and first-principles density-function theory (DFT) calculations. We observed three orientation relationships and corresponding interfaces. One is thermally preferred during casting, and the other two are formed during the hot rolling process. Crystallographic analysis and DFT calculations suggest that the dominant orientation relationship is attributed to the small lattice mismatch and the low interface formation energy. These results provide insights for understanding the interface effect on microstructure evolution of ingot Au-20Sn alloys during severe plastic deformation.
Vortex stretching and enstrophy production in stationary homogeneous isotropic turbulence
Authors: Okamura Makoto
Published: January 2022

On average, the length of a material line element at any given time is longer than that at the initial time. Because a vortex line is frozen into the fluid at an infinite Reynolds number, it seems that the relation between the mean enstrophies (half the squared vorticity) at two time instances can be easily derived using a method similar to that for a material line element. However, this relation has not been analytically derived because a vortex line depends on the velocity even at the initial time. In this paper, we analytically show, using the conditional average, that the mean enstrophy normalized by the initial enstrophy at any given time is larger than one. We also analytically show that the mean enstrophy production is positive in stationary homogeneous isotropic turbulence for high Reynolds numbers.
Efficient asymptotics of solutions to the Cauchy problem with localized initial data for linear systems of differential and pseudodifferential equations
Authors: Dobrokhotov S. Yu. , Nazaikinskii V. E. , Shafarevich A. I.
Published: January 2022

We say that the initial data in the Cauchy problem are localized if they are given by functions concentrated in a neighbourhood of a submanifold of positive codimension, and the size of this neighbourhood depends on a small parameter and tends to zero together with the parameter. Although the solutions of linear differential and pseudodifferential equations with localized initial data constitute a relatively narrow subclass of the set of all solutions, they are very important from the point of view of physical applications. Such solutions, which arise in many branches of mathematical physics, describe the propagation of perturbations of various natural phenomena (tsunami waves caused by an underwater earthquake, electromagnetic waves emitted by antennas, etc.), and there is extensive literature devoted to such solutions (including the study of their asymptotic behaviour). It is natural to say that an asymptotics is efficient when it makes it possible to examine the problem quickly enough with relatively few computations. The notion of efficiency depends on the available computational tools and has changed significantly with the advent of Wolfram Mathematica, Matlab, and similar computing systems, which provide fundamentally new possibilities for the operational implementation and visualization of mathematical constructions, but which also impose new requirements on the construction of the asymptotics. We give an overview of modern methods for constructing efficient asymptotics in problems with localized initial data. The class of equations and systems under consideration includes the Schrödinger and Dirac equations, the Maxwell equations, the linearized gasdynamic and hydrodynamic equations, the equations of the linear theory of surface water waves, the equations of the theory of elasticity, the acoustic equations, and so on.

Bibliography: 109 titles.
Pooled testing efficiency increases with test frequency
Authors: Augenblick Ned , Kolstad Jonathan , Obermeyer Ziad , Wang Ao
Published: January 2022

Significance

Frequent mass testing can slow a rapidly spreading infectious disease by quickly identifying and isolating infected individuals from the population. One proposed method to reduce the extremely high costs of this testing strategy is to employ pooled testing, in which samples are combined and tested together using one test, and the entire pool is cleared given a negative test result. This paper demonstrates that frequent pooled testing of individuals with correlated risk—even given large uncertainty about infection rates—is particularly efficient. We conclude that frequent pooled testing using natural groupings is a cost-effective way to suppress infection risk in a pandemic.
“Late-stage” deforestation enhances storm trends in coastal West Africa
Authors: Taylor Christopher M. , Klein Cornelia , Parker Douglas J. , Gerard France , Semeena Valiyaveetil Shamsudheen , Barton Emma J. , Harris Bethan L.
Published: January 2022

Significance

Tropical deforestation tends to increase regional air temperatures, but its impacts on rainfall are more complex. The conventional picture, based largely on studies over Amazonia, is that storm frequency can increase over small, deforested areas but is reduced when the landscape is predominantly deforested. This study examines Southern West Africa, a coastal region that has little remaining intact forest. Here, the ongoing patchy deforestation increases the frequency of afternoon storms locally. Deforestation appears especially effective at triggering storms near the coast, where temperature-sensitive sea breezes dominate, and rapidly urbanizing populations are vulnerable to flood risk. Our results emphasize dynamical processes over moisture limitation and are highly relevant for many tropical deforestation hotspots, which, unlike Amazonia, are located near the coastline.
Symmetric tangled Platonic polyhedra
Authors: Hyde Stephen T. , Evans Myfanwy E.
Published: January 2022

Significance

Tangled tetrahedra, octahedra, cubes, icosahedra, and dodecahedra are generalizations of classical—untangled—Platonic polyhedra. Like the Platonic polyhedra, all vertices, edges, and faces are symmetrically equivalent. However, the edges of tangled polyhedra are curvilinear, or kinked, to allow entanglement, much like warps and wefts in woven fabrics. We construct the most symmetric entanglements of these polyhedra via assemblies of multistrand helices wound around edges of the conventional polyhedra; they are all necessarily chiral. The construction gives self-entangled chiral polyhedra and compound polyhedra containing catenated multiple tetrahedra or “generalized
θ
-polyhedra.” An unlimited variety of tangling is possible for any given topology. Related structures have been observed in synthetic materials and clathrin assemblies within cells.
Observing the loss and revival of long-range phase coherence through disorder quenches
Authors: Nagler Benjamin , Barbosa Sian , Koch Jennifer , Orso Giuliano , Widera Artur
Published: January 2022

Significance

Understanding the combined effects of disorder and interactions in quantum many-body systems is a key topic of condensed matter physics. While most studies have considered a static disorder, here we investigate the relaxation dynamics of a three-dimensional Bose–Einstein condensate after switching on or off an optical disorder potential. We study, experimentally and numerically, the transient and steady-state atomic density distribution and the ability of the gas to hydrodynamically expand, directly reflecting long-range phase coherence. We find that, when the gas is exposed to disorder, long-range phase coherence breaks down one order of magnitude faster than the density distribution responds. In the opposite case, surprisingly, long-range coherence takes two orders of magnitude longer times to revive than the density relaxation.
Structural insights into how vacuolar sorting receptors recognize the sorting determinants of seed storage proteins
Authors: Tsao Hsi-En , Lui Shu Nga , Lo Anthony Hiu-Fung , Chen Shuai , Wong Hiu Yan , Wong Chi-Kin , Jiang Liwen , Wong Kam-Bo
Published: January 2022

Significance

Seeds such as rice and soybean are major food staples in the human diet. During seed development, storage proteins are deposited in a specialized organelle called the protein storage vacuole and are mobilized to provide nutrients during germination. Storage proteins are transported as cargoes via specific protein–protein interactions with the vacuolar sorting receptors. Supported by structural and mutagenesis studies, our work provides insights into how the sequence-specific information, or the vacuolar sorting determinant, on the storage proteins is recognized by the vacuolar sorting receptors for their targeting to the vacuoles. Insights gained into the rules of receptor–cargo recognition will be useful in engineering recombinant proteins for biotechnological applications of the protein storage vacuoles in seeds.
Convergent evolution of venom gland transcriptomes across Metazoa
Authors: Zancolli Giulia , Reijnders Maarten , Waterhouse Robert M. , Robinson-Rechavi Marc
Published: January 2022

Significance

On more than 100 occasions, animals have independently evolved the ability to produce and deliver potent secretions to subdue prey or predators—venom. This prompts the following question: Have animals repeatedly adopted the same genetic toolkit for venom production? In this study, we found, surprisingly, that the venom glands of different animal lineages had similar global gene expression patterns. Notably, groups of genes involved in protein secretion, and especially stress response pathways, had similar expression levels, revealing that many animals have come up with the same solution independently. On the other hand, signaling and regulatory networks had lineage-specific patterns, suggesting that the way in which cells are regulated and communicate might reflect the diverse developmental origins of venom systems.
Intersectional inequalities in science
Authors: Kozlowski Diego , Larivière Vincent , Sugimoto Cassidy R. , Monroe-White Thema
Published: January 2022

Significance

The US scientific workforce is not representative of the population. Barriers to entry and participation have been well-studied; however, few have examined the effect of these disparities on the advancement of science. Furthermore, most studies have looked at either race or gender, failing to account for the intersection of these variables. Our analysis utilizes millions of scientific papers to study the relationship between scientists and the science they produce. We find a strong relationship between the characteristics of scientists and their research topics, suggesting that diversity changes the scientific portfolio with consequences for career advancement for minoritized individuals. Science policies should consider this relationship to increase equitable participation in the scientific workforce and thereby improve the robustness of science.
Strategic protection of landslide vulnerable mountains for biodiversity conservation under land-cover and climate change impacts
Authors: Li Binbin V. , Jenkins Clinton N. , Xu Weihua
Published: January 2022

Significance

Landslides are triggered more often by human-induced changes, such as deforestation, infrastructure building, and increasing precipitation extremes, because of climate change. The huge economic and societal loss calls for a more cost-effective way to reduce risks and ensure sustainable development. Land-cover and land-use changes not only increase landslide susceptibility but also drive habitat loss and species extinctions. The high spatial overlap between landslide susceptibility and biodiversity in mountains provides an opportunity to achieve co-benefits in conservation and development. The identification of vulnerable mountains with both high biodiversity and landslide susceptibility prioritizes the regions for expansion of protected areas, forest conservation, and restoration, providing a nature-based solution to mitigate landslide risks through the protection of natural habitat.
Evolution of cooperation with asymmetric social interactions
Authors: Su Qi , Allen Benjamin , Plotkin Joshua B.
Published: January 2022

Significance

Humans have a remarkable, but not ubiquitous, tendency toward altruism. This behavior reflects a classic enigma in evolutionary theory: When and why would individuals forgo selfish interests to help strangers? Population structure is known to catalyze cooperation because it enables local reciprocity—I help you, and you help me. But this explanation assumes bidirectional social interactions, whereas human interactions are often unidirectional: One individual has the opportunity to contribute altruistically to another, but not conversely. Here we uncover a surprising result, that directionality can actually facilitate cooperation. We study this effect theoretically and also in empirical social networks. We suggest several practical implications, including how to modify the directions of social interactions to promote cooperation.
Direct measurement of the viscoelectric effect in water
Authors: Jin Di , Hwang Yongyun , Chai Liraz , Kampf Nir , Klein Jacob
Published: January 2022

Significance

The viscosity of polar liquids increases in an electric field because of its interaction with the dipolar molecules. This viscoelectric effect was measured for organic liquids, but for water, the most important polar liquid, where it is crucial in areas from surface potential determination to nanofluidic applications, this is very challenging, and no direct measurements have been carried out to date. Consequently, estimates of its magnitude in water vary by more than a thousandfold. Here, we use a surface force balance to measure the dynamic approach of two molecularly smooth surfaces with a uniform, controlled electric field between them across water; this is modulated by the water viscosity and hence the viscoelectric effect, enabling its magnitude to be directly determined.
Temporal–spectral signaling of sensory information and expectations in the cerebral processing of pain
Authors: Nickel Moritz M. , Tiemann Laura , Hohn Vanessa D. , May Elisabeth S. , Gil Ávila Cristina , Eippert Falk , Ploner Markus
Published: January 2022

Significance

Pain is not only shaped by sensory information but also by an individual’s expectations. Here, we investigated how commonly analyzed electroencephalography (EEG) responses to pain signal sensory information, expectations, and discrepancies thereof (prediction errors) in the processing of pain. Bayesian analysis confirmed that pain perception was shaped by objective sensory information and expectations. In contrast, EEG responses at different latencies (including the N1, N2, and P2 components) and frequencies (including alpha, beta, and gamma oscillations) were shaped by sensory information but not by expectations. Thus, EEG responses to pain are more involved in signaling sensory information than in signaling expectations or prediction errors. Expectation effects are obviously mediated by other brain mechanisms than the effects of sensory information on pain.
An asymmetric grating refractive index sensor generating quasi-bound states in the continuum with high figure of merit and temperature self-compensation
Authors: Wang Qi , Jiang Ju-Xin , Wang Lei , Yin Xiang-Yu , Yan Xin , Zhu Aisong , Qiu Fengmei , Zhang Ke-Ke
Published: January 2022

A subwavelength asymmetric grating refractive index (RI) sensor based on quasi-bound states in the continuum (q-BIC) with temperature self-compensation was proposed. The sensor structure consisted of a prism/asymmetric grating/analytes, where the grating layers were periodically arranged asymmetric silicon (Si) and polydimethylsiloxane. The asymmetry of the structure led to the fact that the tangential field component and the radiative field component in the grating layer were no longer in a fully decoupled state at the resonance position, creating two extremely narrow q-BIC resonance peaks, which gave the sensor a high figure of merit (FOM) and a low detection limit (DL). In addition, the thermo-optical coefficient of the materials made one of the resonance peaks more sensitive to temperature changes, realizing the temperature self-compensation of RI detection and thus improving the detection accuracy. From the results, reducing the asymmetry of the structure by modifying the parameters could theoretically make FOM > 5.1 × 106 RIU−1 and DL < 9.8 × 10−9 RIU. For the RI sensor with temperature self-compensation, FOM = 3057.85 RIU−1 and DL = 1.64 × 10−5 RIU for the RI, FOM = 0.88 °C−1 and DL = 0.057 °C for the temperature. These findings could effectively improve the temperature interference resistance of the sensor and thus the accuracy of trace substance detection.
Comparison of form measurement results for optical aspheres and freeform surfaces
Authors: Fortmeier Ines , Schulz Michael
Published: January 2022

Comparing form measurement data for aspheres and freeform surfaces is an important tool for ensuring the quality and functionality of the devices used to take such measurements and may also allow the underlying measurement methods to be evaluated. However, comparing the highly accurate form measurements of such complex surfaces is a demanding task. It is difficult to analyze measurement results whose accuracies are in the range of several tens of nanometers root-mean-square, especially when comparing data with different, and anisotropic distributions of the 3D measurement points on the surface under test. In this paper, we investigate eight different 3D measurement point distributions that are typical of highly accurate measurement systems currently in use and demonstrate the effects of these distributions on the comparison results by using virtually generated data and applying different evaluation strategies. The results show that, for the examples investigated, the different 3D measurement point distributions can yield different levels of accuracy for the comparison. Furthermore, an improved evaluation procedure is proposed and recommendations on how to significantly reduce the influence of the different 3D measurement point distributions on the comparison result are given. A method of employing virtually generated test data is presented that may be generalized in order to further improve and validate future comparison methods.
Development of a metrological reference system for the form measurement of aspheres and freeform surfaces based on a tilted-wave interferometer
Authors: Fortmeier Ines , Stavridis Manuel , Schulz Michael , Elster Clemens
Published: January 2022

Aspheres and freeform surfaces play an important role in today’s optics industry. However, the measurement of such complex surfaces is still challenging even with state-of-the-art manufacturing technology, and there is an urgent need in industry for a non-contact, highly accurate reference measurement technique. To meet this demand, at Physikalisch-Technische Bundesanstalt (PTB), a metrological reference system for the contact-free form measurement of aspheres and freeform surfaces is under development. The measurement system is based on a tilted-wave interferometer. Advances in computational capabilities have made it possible to solve the complex inverse problems associated with this measurement system and to develop sophisticated analysis procedures for reconstructing the surface under test from the measured interferogram data. In this paper, we will present the status of the tilted-wave interferometer-based measurement system at PTB, describe the analysis procedures we have designed and show initial measurement results. The benefit of the implementation presented here is that it allows insight to be gained into the performance of the measurement system and enables traceable measurements to be established with low uncertainty.