bluuebunny/crossref_metadata_2025 huggingface dataset:
Error field feedback control system in the Keda Torus eXperiment and open loop control experiment
Authors: Wu Yanqi , Li Hong , Adil Yolbarsop , Zhang Yuan , Yan Wentan , Chen Zheng , Rao Xianhao , Song Kezhu , Xie Jinlin , Lan Tao , Liu Adi , Mao Wenzhe , Zhou Chu , Liu Zixi , Xiao Chijin , Ding Weixing , Zhuang Ge , Liu Wandong
Published: May 2020

A feedback control system has been designed for the Keda Torus eXperiment device to achieve the following goals: (a) suppression of the error field at the poloidal gap, (b) three-dimensional plasma stability control, and (c) improvement of plasma discharge quality. The system consists of a boundary electromagnetic probe array, a field-programmable gate array, a linear power amplifier, and an active control coil array. The system adopts a compound control method that includes both active and passive control methods. To control the plasma, an active control coil array is used to generate a localized radial magnetic field as needed at two poloidal gaps of the device. In the open-loop control experiment, the active control coils near the poloidal gaps reduced the original error field and thus increased the plasma discharge current amplitude by 50% and effectively extended the plasma discharge duration.
Electrocaloric and pyroelectric properties of barium zirconate titanate
Authors: Co K. , Khassaf H. , Alpay S. P.
Published: May 2020

The electrocaloric response of bulk monodomain BaZrxTi(1−x)O3 (BZT) under modest electrical fields at room temperature has been evaluated using a Landau theory thermodynamic model as a function of the zirconium content x. The computations show that increasing x changes the nature of the ferroelectric phase transitions of BZT. There are potentially three ferroelectric phases in BZT for zirconium contents 0 < x < 0.30. For 0 < x < 0.15, the cubic paraelectric phase transitions successively into the tetragonal, orthorhombic, and rhombohedral phases with decreasing temperature. For x > 0.15, the rhombohedral phase becomes the sole ferroelectric phase upon cooling from the cubic paraelectric state. The magnitude of the polarization discontinuity at the phase transition decreases with increasing x as it approaches a continuous, second order transition. We show here that these phase changes have a significant effect on electrocaloric and pyroelectric properties of BZT. The room temperature adiabatic temperature change was calculated for compositions of BZT with 0 < x < 0.30, revealing a maximum temperature change of ΔTad = 1.25 °C for an electric field difference of 100 kV/cm for x = 0.20 near room temperature.
Role of magnetic and temperature cycling on martensite formation in Ni2.19Mn0.81Ga single crystals of a Heusler alloy
Authors: Dilmieva Elvina T. , Koshkid’ko Yurii S. , Koledov Victor V. , Khovaylo Vladimir V. , Cwik Jacek , Shavrov Vladimir G. , Sampath V.
Published: May 2020

The results of in situ studies of the magnetostructural transition occurring in single crystals of an Ni2.19Mn0.81Ga Heusler alloy are presented in this paper. The formation of martensitic twins on exposure to high magnetic fields up to 10 T in the magnetostructural transition regime was observed using an indigenously developed optical microscope. Experiments on magnetization were performed on single crystals of Ni2.19Mn0.81Ga in high magnetic fields, a phase diagram between magnetic field and temperature was constructed, and the isothermal entropy change was estimated. Based on the experimental data and the results from optical microscopic examination, the influence of magnetic field and thermal cycling on martensitic twins and, in turn, on the magnetocaloric effect, is discussed.
Effect of viscosity ratio on the dynamic response of droplet deformation under a steady electric field
Authors: Jiang Zhengwei , Gan Yunhua , Luo Yanlai
Published: May 2020

The effect of the fluid viscosity ratio on the transient deformation of a droplet is investigated. A numerical model is developed by employing the phase field method to capture the interface. The model is validated in both steady and transient cases with literature data with good agreement. In the creeping flow regime, the droplet always undergoes monotonic deformation. When the viscosity of the suspending fluid dominates, the transient process of the droplet deformation is nearly independent of the viscosity ratio. When the viscosities of the droplet and suspending fluid are comparable, the damping effect of the droplet viscosity on the deformation is magnified and the time to reach the steady-state deformation increases with viscosity. When the effect of suspending fluid inertia prevails, the droplet will deform to the steady state either in a monotonic way or in an oscillating way depending on the viscosity ratio. A quasi-steady mode, which can be considered as an intermediate mode between the oscillating and the steady mode, is identified for the first time. When the droplet is in the quasi-steady mode, the increase in the electric capillary number can turn it into the steady mode. The flow field evolution is analyzed and it shows that the vortices inside the droplet play an important role in the transient deformation. The deformation process can be determined by the competition between the inner and outer vortices. It is found that the minimum deformation time can be obtained for the quasi-steady mode when the viscosity of the suspending fluid is low.
A cryogenic ice setup to simulate carbon atom reactions in interstellar ices
Authors: Qasim D. , Witlox M. J. A. , Fedoseev G. , Chuang K.-J. , Banu T. , Krasnokutski S. A. , Ioppolo S. , Kästner J. , van Dishoeck E. F. , Linnartz H.
Published: May 2020

The design, implementation, and performance of a customized carbon atom beam source for the purpose of investigating solid-state reaction routes in interstellar ices in molecular clouds are discussed. The source is integrated into an existing ultrahigh vacuum setup, SURFace REaction SImulation DEvice (SURFRESIDE2), which extends this double atom (H/D, O, and N) beamline apparatus with a third atom (C) beamline to a unique system that is fully suited to explore complex organic molecule solid-state formation under representative interstellar cloud conditions. The parameter space for this system is discussed, which includes the flux of the carbon atoms hitting the ice sample, their temperature, and the potential impact of temperature on ice reactions. Much effort has been put into constraining the beam size to within the limits of the sample size with the aim of reducing carbon pollution inside the setup. How the C-atom beam performs is quantitatively studied through the example experiment, C + 18O2, and supported by computationally derived activation barriers. The potential for this source to study the solid-state formation of interstellar complex organic molecules through C-atom reactions is discussed.
Classification strategies in machine learning techniques predicting regime changes and durations in the Lorenz system
Authors: Brugnago Eduardo L. , Hild Tony A. , Weingärtner Daniel , Beims Marcus W.
Published: May 2020

In this paper, we use machine learning strategies aiming to predict chaotic time series obtained from the Lorenz system. Such strategies prove to be successful in predicting the evolution of dynamical variables over a short period of time. Transitions between the regimes and their duration can be predicted with great accuracy by means of counting and classification strategies, for which we train multi-layer perceptron ensembles. Even for the longest regimes the occurrences and duration can be predicted. We also show the use of an echo state network to generate data of the time series with an accuracy of up to a few hundreds time steps. The ability of the classification technique to predict the regime duration of more than 11 oscillations corresponds to around 10 Lyapunov times.
Numerical investigation of lift enhancement in flapping hover flight
Authors: Bharadwaj Anand Sundaresan , Ghosh Santanu
Published: May 2020

The focus of this work is the study of lift enhancement in flapping hover flight using numerical simulations. An idealized set of kinematics for a NACA0012 airfoil consisting of sequential translations and rotations is considered for this purpose, such that the Cl response can be demarcated into translational and rotational parts, which facilitates comparison of forces attributed to translation and rotation. Additionally, comparisons with pure translation and pure rotation are done to isolate the effect of wing–wake interactions. The investigation reveals that the majority of lift is produced in the translational phase. The wing–wake interactions affect the translational phase of the response more than the rotational phase. However, the rotation rate determines the extent of influence of wing–wake interactions on the translational lift response. The effect of different durations of overlap between the translational and rotational motions is also assessed based on the Cl time histories and mean Cl, and the study reveals that an optimum duration of overlap can maximize the lift. An immersed-boundary method with integrated surface-load reconstruction capabilities is used for the computations presented here. The reconstruction of the surface stresses and their integration are carried out with the framework of a parallel solver. The method is validated for a flow past a NACA0012 airfoil executing a non-periodic plunge motion and a non-periodic pitch/plunge motion and a flow around an elliptic airfoil executing a flapping motion.
Persistence in Brownian motion of an ellipsoidal particle in two dimensions
Authors: Ghosh Anirban , Chakraborty Dipanjan
Published: May 2020

We investigate the persistence probability p(t) of the position of a Brownian particle with shape asymmetry in two dimensions. The persistence probability is defined as the probability that a stochastic variable has not changed its sign in the given time interval. We explicitly consider two cases—diffusion of a free particle and that of a harmonically trapped particle. The latter is particularly relevant in experiments that use trapping and tracking techniques to measure the displacements. We provide analytical expressions of p(t) for both the scenarios and show that in the absence of the shape asymmetry, the results reduce to the case of an isotropic particle. The analytical expressions of p(t) are further validated against numerical simulation of the underlying overdamped dynamics. We also illustrate that p(t) can be a measure to determine the shape asymmetry of a colloid and the translational and rotational diffusivities can be estimated from the measured persistence probability. The advantage of this method is that it does not require the tracking of the orientation of the particle.
Suppression of thermally excited electron-spin relaxation in InGaAs quantum dots using p-doped capping layers toward enhanced room-temperature spin polarization
Authors: Sato Shino , Hiura Satoshi , Takayama Junichi , Murayama Akihiro
Published: May 2020

The suppression of a thermally excited electron-spin relaxation in InGaAs quantum dots (QDs) using p-doped capping layers toward enhanced room-temperature (RT) spin polarization has been demonstrated, in which the electron-spin polarization in QD excited states (ESs) was measured through time-resolved spin-dependent photoluminescence. We revealed that the p-doping of QDs can enhance the emission intensity of QD-ES by approximately twofold to threefold over a wide temperature range. An electron-spin relaxation time of 106 ps was observed at 293 K for p-doped QDs, which is approximately three times longer than the radiative lifetime of 36 ps, relative to the shorter electron-spin relaxation time of 71 ps for undoped QDs. The increased electron-spin lifetime was mainly attributed to the suppressed relaxation of the electron spin reinjected from the p-doped capping barrier after thermal escape from an ES, where the D'yakonov-Perel' spin relaxation in the barrier was potentially weakened through impurity scattering. These results suggest that InGaAs QDs with p-doped capping layers have a significant advantage for use in spin-functional optical active layers with a higher spin polarization toward RT.
Uncovering episodic influence of oceans on extreme drought events in Northeast Brazil by ordinal partition network approaches
Authors: Wu Huanyu , Zou Yong , Alves Lincoln M. , Macau Elbert E. N. , Sampaio Gilvan , Marengo Jose A.
Published: May 2020

Since 2012, the semiarid region of Northeast Brazil (NEB) has been experiencing a continuous dry condition imposing significant social impacts and economic losses. Characterizing the recent extreme drought events and uncovering the influence from the surrounding oceans remain to be big challenges. The physical mechanisms of extreme drought events in the NEB are due to varying interacting time scales from the surrounding tropical oceans (Pacific and Atlantic). From time series observations, we propose a three-step strategy to establish the episodic coupling directions on intraseasonal time scales from the ocean to the precipitation patterns in the NEB, focusing on the distinctive roles of the oceans during the recent extreme drought events of 2012–2013 and 2015–2016. Our algorithm involves the following: (i) computing drought period length from daily precipitation anomalies to capture extreme drought events; (ii) characterizing the episodic coupling delays from the surrounding oceans to the precipitation by applying the Kullback–Leibler divergence (KLD) of complexity measure, which is based on ordinal partition transition network representation of time series; and (iii) calculating the ratio of high temperature in the ocean during the extreme drought events with proper time lags that are identified by KLD measures. From the viewpoint of climatology, our analysis provides data-based evidence of showing significant influence from the North Atlantic in 2012–2013 to the NEB, but in 2015–2016, the Pacific played a dominant role than that of the Atlantic. The episodic intraseasonal time scale properties are potential for monitoring and forecasting droughts in the NEB in order to propose strategies for drought impacts reduction.
Tunable interaction potentials and morphology of polymer–nanoparticle blends
Authors: Pasquini Marta , Raos Guido
Published: May 2020

We present the results of molecular dynamics simulations of a family of polymer nanocomposite systems. The polymer is described by a generic bead-and-spring model, while the polymer chains and the nanoparticles (NPs) interact by Hamaker-style potentials. The potential describing NP–NP interactions is modified by a tuning parameter f, which can be changed continuously between f = 0 (for fully developed van der Waals attractions between the NPs) and f = 1 (for completely repulsive interparticle interactions). We explore systematically the effect of the f parameter on the blend morphologies, for two representative NP sizes. When the polymer–NP attractions are decreased, the systems undergo a transition from dispersed to aggregated morphologies. The sharpness of the transition gradually increases with the interparticle attractions (i.e., decreasing f).
Role of charge doping and distortions on the structural, electrical, and magnetic properties of modified CuFeO2 compounds
Authors: Barot Nishant , Mehta Prashant K. , Rao Ashok , Thomas Riya , Kuo Yung-Kang , Mishra S. K.
Published: May 2020

Single phase CuFeO2, CuFe0.96M0.03V0.01O2 (M = Ti, Mn, and Ga), and CuFe0.96V0.04O2 compounds with space group R3¯m were prepared through a newly developed solid-state technique using annealing under high vacuum. Raman studies demonstrate, for the first time, a minor shift in Ti and Mn-doped samples as well as the Jahn–Teller effect induced distortions around 500 cm−1 along with well-documented peaks of Eg and A1g modes. Mössbauer studies confirm the presence of iron in high spin Fe3+ and quadruple splitting values endorsing the presence of octahedron distortions. An increase in the electrical conductivity at low temperatures is observed due to the enhanced charge doping with minor variations related to local distortions. Low-temperature magnetic studies of pristine and Ti-doped samples demonstrate paramagnetic nature up to 25 K. However, on one hand, the pristine sample shows a sharp rise in magnetization values at low applied fields and on the other side, Ti-doped samples exhibit nearly linear behavior. Dielectric measurements confirm weakening of electrical ordering near the magnetic transition in distorted Ti-doped samples, compared to pure CuFeO2 sample. Level of charges along with its local distortions affected mobility has significant effects on transport and multiferroic nature of these samples.
Theoretical analysis on the atomization characteristics of liquid nitrogen jets
Authors: Gao Xinxin , Bao Songling , Shao Shuangquan , Hu Haitao , Zhou Suming , Chen Jianye , Xie Junlong
Published: May 2020

Atomization with cryogenic fluids is complicated due to the combined effects of both the mechanical breakup and thermodynamic flashing. However, the weight of the two effects on the atomization has not been determined yet. This paper proposes a hybrid mathematical model to evaluate the weight of the thermodynamic effect and aerodynamic effect. The entire process of jet spray breakup, including the primary breakup and secondary atomization, is described in the model. A linear stability analysis is carried out using the dispersion equations for the primary breakup. In the secondary atomization, the Taylor analogy breakup and bubble micro-explosion models are employed to study aerodynamic and thermodynamic effects on the atomization, respectively. The homogeneous nucleation is implemented in the bubble micro-explosion models. A criterion is obtained which can be evaluated to predict the dominant effect. Accordingly, the influence of factors such as ambient pressure and other physical parameters on the atomization process is analyzed. The results reveal that, under low ambient pressure, thermodynamic flashing is stronger. Besides, the mechanical action is restrained when the surface tension is increased.
Delay of subsonic choking in slip regime by structured roughness in microchannel
Authors: Garg Richie , Agrawal Amit
Published: May 2020

Roughness is an intrinsic property of a surface. Its presence is recognized at the micro-scale due to the high surface area to volume ratio. In the present experimental work, three-dimensional microchannels with structured roughness in the form of cuboidal protrusions called micro-ridges are fabricated. Ridge fraction (δ) is the ratio of the length of the ridge (s) to the distance between the ridges (L). δ is varied as 0.75, 0.50, 0.25, and 0 to check the occurrence of the choking phenomenon and its impact on the frictional resistance in gaseous slip flow. To this end, mass flow controllers, pressure sensors, and thermocouples are employed to explore the dependence of Poiseuille number (fRe) on Mach number (Ma) in the microchannel. It is demonstrated that the smooth microchannel (δ = 0) and the ridge with the shortest length (δ = 0.25) gets choked subsonically, but the longer ridges (δ = 0.50, 0.75) do not choke under the investigated conditions. Interestingly, fRe (δ = 0.50) > fRe (δ = 0.25) > fRe (δ = 0.75) ≈ fRe (δ = 0). Since choking limits the maximum amount of mass flow rate through a microchannel, its occurrence could be counter-productive or could even be beneficially employed, depending on the specific application.
A new Bi0.7Fe1.3O1.5F1.7 phase: Crystal structure, magnetic properties, and cathode performance in fluoride-ion batteries
Authors: Takami Tsuyoshi , Saito Takashi , Kamiyama Takashi , Kawahara Katsumi , Fukunaga Toshiharu , Abe Takeshi
Published: May 2020

We synthesize a Bi0.7Fe1.3O1.5F1.7 (BFOF) phase via a non-topochemical reaction with a fluorination agent. The crystal structure is refined by Rietveld refinement on the neutron diffraction patterns as a hexagonal lattice in the R3¯ space group, along with the defect structure. The sudden decrease in magnetic susceptibility below 250 K and the linear relationship between the magnetization and the magnetic field indicate that BFOF is an antiferromagnetic material. When BFOF is used as a cathode in fluoride-ion batteries (FIBs), a discharge (charge) capacity of 360 (225) mAh/g is achieved at 140 °C. Magnetization and x-ray diffraction measurements confirm that the F ions are transferred from the cathode to the Pb counter electrode during discharge and in the opposite direction during charge, in a manner analogous to the transfer of lithium (Li) ions in Li-ion batteries. These findings contribute to the development of quaternary oxyfluorides serving as FIB cathodes.
Baroclinic toroidal quasi-geostrophic vortices
Authors: Reinaud Jean N.
Published: May 2020

We investigate the stability and nonlinear evolution of two tori of opposite-signed uniform potential vorticity, located one above the other, in a three-dimensional, continuously stratified, quasi-geostrophic flow. We focus on the formation of hetons as a result of the destabilization of the tori of potential vorticity. Hetons are pairs of vortices of opposite signs lying at different depths capable of transporting heat, momentum, and mass over large distances. Particular attention is paid to the condition under which the hetons move away from their region of formation. We show that their formation and evolution depend on the aspect ratio of the tori, as well as the vertical gap separating them. The aspect ratio of a torus is the ratio of its major (center line) radius to its minor (cross-sectional) radius. Pairs of thin opposite-signed potential vorticity tori self-organize into a large number of hetons. On the other hand, increasing the vertical gap between the tori decreases the coupling between the opposite-signed vortices forming the hetons. This results in a more convoluted dynamics where the vortices remain near the center of the domain.
Exchange-correlation corrections for electronic properties of half-metallic Co2FeSi and nonmagnetic semiconductor CoFeTiAl
Authors: Miroshkina Olga N. , Baigutlin Danil R. , Sokolovskiy Vladimir V. , Zagrebin Mikhail A. , Pulkkinen Aki , Barbiellini Bernardo , Lähderanta Erkki , Buchelnikov Vasiliy D.
Published: May 2020

We consider two cobalt-based full-Heusler compounds, CoFeTiAl and Co2FeSi, for which Coulomb correlation effects play an important role. Since the standard GGA scheme does not provide a precise description of the electronic properties near the Fermi level, we use a meta-GGA functional capable to improve the description of the electronic properties of CoFeTiAl and Co2FeSi. In particular, we find a better agreement with the experiment for the magnetic moment and the energy bandgap. Moreover, our calculations show that pressure enhances the insulating properties of Co2FeSi and CoTiFeAl.
Strong polaronic effect in a superatomic two-dimensional semiconductor
Authors: Li Qiuyang , Liu Fang , Russell Jake C. , Roy Xavier , Zhu Xiaoyang
Published: May 2020

Crystalline solids assembled from superatomic building blocks are attractive functional materials due to their hierarchical structure, multifunctionality, and tunability. An interesting example is Re6Se8Cl2, in which the Re6Se8 building blocks are covalently linked into two-dimensional (2D) sheets that are stacked into a layered van der Waals solid. It is an indirect gap semiconductor that, when heavily doped, becomes a superconductor at low temperatures. Given the finite electronic bandwidths (300–400 meV), carrier properties in this material are expected to be strongly influenced by coupling to phonons. Here, we apply angle-resolved photoemission spectroscopy to probe the valence band edge (VBE) of Re6Se8Cl2. We find that dispersion of the VBE is a strong function of temperature. The bandwidth is W = 120 ± 30 meV at 70 K and decreases by one order of magnitude to W ∼ 10 ± 20 meV as temperature is increased to 300 K. This observation reveals the dominant polaronic effects in Re6Se8Cl2, consistent with the Holstein polaron model commonly used to describe molecular solids.
Predicting the quantum texture from transmission probabilities
Authors: Valagiannopoulos Constantinos
Published: May 2020

Inverse formulas for the energy potential level and the effective electron mass within an unknown quantum material are obtained, solely based on the transmission probabilities of obliquely incident beams through a thin lamellar sample. The estimator is robust-to-noise and does not require phase unwrapping of the wave functions; importantly, it is very reliable for low-contrast samples and high impinging energies. Even when the proposed method fails to deliver an accurate prediction, it can serve well the purpose of disclosing the identity of the medium in the case it has been picked from a well-known list. The introduced scheme may constitute the first step toward flawless generic estimation of quantum texture if implemented multiple times for various energies or incidence angles, and the collected data are post-processed by suitable algorithmic routines.
Electromechanical analysis and simplified modeling of dielectric elastomer multilayer bending actuator
Authors: Zhou Fanghao , Yang Xuxu , Xiao Youhua , Zhu Ziqi , Li Tiefeng , Xu Zhongbin
Published: May 2020

Dielectric elastomers can generate large voltage-induced deformation and have been widely used as soft actuators. Dielectric elastomer multilayer structures function as bending-type actuators, enhancing their stiffness and ability to resist external loads. Modeling a dielectric elastomer multilayer bending actuator allows analyzing its bending performance, and obtaining the stress and strain distributions in each layer of the actuator. It is of practical importance to develop a simple, yet accurate model. This work develops a model to analyze the electromechanical behavior of the dielectric elastomer multilayer bending actuator with various pre-stretch, material, and structural parameters. We also propose a simplified model for a bilayer slender beam, which is a typical multilayer structure. The simplified model describes the relation between the beam bending curvature and the applied voltage, achieving fast calculation with little accuracy sacrificed. Both the model for the dielectric elastomer multilayer and the simplified model for the bilayer beam agree well with the experiment results, validating the models for practical applications in soft robots, flexible sensors, and smart structures.
Depth dependence of spin-specific magnetization hysteresis loops measured by magnetic Compton scattering
Authors: Tsuji Naruki , Sakurai Hiroshi , Sakurai Yoshiharu
Published: May 2020

An application of magnetic Compton scattering to measure the depth dependence of spin-specific magnetization hysteresis (SSMH) loops in a Nd–Fe–B sintered magnet is presented herein. The depth dependence of SSMH was obtained by changing the position of x-rays with a vertical beam size of 10 μm. The results show that the surface deterioration area has a depth of 120 μm, where the magnetization begins to decrease gradually. In the internal region, we also observed decreased coercivity, which might be caused by the demagnetizing field.
A flexion-based approach for the simulation of turbulent flows
Authors: Nwogu Okey G.
Published: May 2020

Turbulent flows at high Reynolds numbers are dominated by vortex filaments and/or sheets with sharp gradients in the vorticity field near the boundaries of the vortical structures. Numerical simulations of high Reynolds number flows are computationally demanding due to the fine grid required to accurately resolve these sharp gradient regions. In this paper, an alternative approach is proposed to improve the computational efficiency of Navier–Stokes solvers by reformulating the momentum equations as a set of equations for the time-dependent evolution of the flexion field. The flexion vector represents the curl of the vorticity field and is better able to resolve nonlinear effects in regions with large vorticity gradients. The improved resolution capabilities of the flexion-based approach are illustrated through the pseudospectral computations of the rollup of a perturbed 2D shear layer and the transition to a turbulence/viscous decay of the three-dimensional (3D) Taylor–Green vortex. The flexion-based formulation also provides further insight into the dynamics of turbulence through the evolution of the mean-square flexion or palinstrophy. Analysis of data from the Taylor–Green vortex simulations shows that the observed rapid growth of small-scale features and palinstrophy in 3D turbulent flows is primarily associated with flexion amplification by the curl of the vortex stretching vector. Consequently, we hypothesize that the primary physical mechanism responsible for energy cascade from large to small scales is the curl of the vortex stretching vector of interacting vortex tubes, as opposed to the stretching of individual vortex tubes.
Influence of glow discharge on evolution of disturbance in a hypersonic boundary layer: The effect of first mode
Authors: Li Chi , Zhang Yunchi , Lee Cunbiao
Published: May 2020

The evolution of the first- and second-mode instabilities in a hypersonic flat plate boundary layer is investigated. Experiments are conducted in a Mach 6.5 quiet wind tunnel using particle image velocimetry, Rayleigh-scattering flow visualization, and schlieren methods. Glow discharge is introduced as an artificial disturbance. The results show that an artificially introduced disturbance in the first-mode frequency range can excite a specific second-mode wave that is one of the high-order harmonics of the added disturbance. For the first time, we find a clear harmonic relationship between the first- and second-mode waves, as well as the phase lock phenomenon between them.
The role of timescale separation in oscillatory ensembles with competitive coupling
Authors: Kirillov S. Yu. , Klinshov V. V. , Nekorkin V. I.
Published: May 2020

We study a heterogeneous population consisting of two groups of oscillatory elements, one with attractive and one with repulsive coupling. Moreover, we set different internal timescales for the oscillators of the two groups and concentrate on the role of this timescale separation in the collective behavior. Our results demonstrate that it may significantly modify synchronization properties of the system, and the implications are fundamentally different depending on the ratio between the group timescales. For the slower attractive group, synchronization properties are similar to the case of equal timescales. However, when the attractive group is faster, these properties significantly change and bistability appears. The other collective regimes such as frozen states and solitary states are also shown to be crucially influenced by timescale separation.
Genetic diversity within and across gametophytic ploidy levels in a Sphagnum cryptic species complex
Authors: Karlin Eric F. , Robinson Sean C. , Smouse Peter E.
Published: May 2020

We deploy Shannon analysis of five ancestrally (ANCE) diagnostic microsatellite loci to explore the patterns of ‘deep’ allelic genetic diversity within the peat moss Sphagnum ×australe Mitt. s.l. cryptic species complex across its Australasian distribution. There is both notable divergence among and considerable allelic overlap within the three allopolyploid lineages of this complex, two gametophytically allodiploid (R1S1 and R2S2) and one gametophytically allotriploid (FR1*S1*). Detailed biogeographic patterns reflect historical differences in genetic isolation and interbreeding. Lineage I (R1S1) occurs in both Australia and New Zealand, while Lineage II (R2S2) and Lineage III (FR1*S1*) are endemic to New Zealand, where Lineage III predominates. Available data suggest that Lineage I arose in Australia, whereas both Lineage II and Lineage III originated in New Zealand. ‘Deep’ allelic diversity provides a pronounced signal of evolutionary radiation within and among the three lineages. We develop a methodology to explore allelic diversity across ploidy levels and elaborate another for scaling additive allele-metric diversity values [0,1], relative to attainable minimal and maximal values, given the sampling frame. We suggest the following taxonomic disposition: gametophytically allodiploid Lineages I and II → S. ×australe; gametophytically allotriploid Lineage III → S. ×antarcticum. Epitypes are designated for both species.
Exogenous application of 24-epibrassinosteroid mitigates NaCl toxicity in flax by modifying free amino acids profile and antioxidant defence system
Authors: Amraee Leila , Rahmani Fatemeh , Abdollahi Mandoulakani Babak
Published: May 2020

In the present study, we investigated the ameliorative effects of 24-epibrassinosteroid (24-epiBL) on antioxidant response and ion homeostasis in two NaCl-stressed Linum usitatissimum L. (flax) cultivars differing in salt tolerance. The content and profile of amino acids were also studied in the tolerant cultivar. Salt stress differently altered the activity of antioxidant enzymes, phenol and flavonoid contents, total antioxidant capacity and ion homeostasis in both cultivars, whereas H2O2 and malondialdehyde (MDA) contents were induced only in the TN-97-95 cultivar. Free amino acid concentrations showed variable patterns under salinity conditions compared with the control plants. 24-epiBL decreased the soluble protein content in NaCl-treated plants and also decreased stimulatory effects of salinity on the production and accumulation of phenol and flavonoid contents and antioxidant capacity with altered ion (Na+, K+, and Cl–) contents. The 24-epiBL reduced the chlorophylls (a, b) and carotenoid contents in salt-treated TN-97-95 cultivar while enhanced the activity of antioxidant enzymes and declined the H2O2 content and lipid peroxidation in both NaCl-stressed cultivars. The profile and content of amino acids were significantly changed by 24-epiBL application under salinity treatment. In summary, our findings demonstrate that 24-epiBL seed priming mitigates the deleterious effects of salt stress in flax plants.
PAC Learning and Occam’s Razor: Probably Approximately Incorrect
Authors: Herrmann Daniel A.
Published: May 2020

Computer scientists have provided a distinct justification of Occam’s Razor. Using the probably approximately correct framework, they provide a theorem that they claim demonstrates that we should favor simpler hypotheses. The argument relies on a philosophical interpretation of the theorem. I argue that the standard interpretation of the result in the literature is misguided and that a better reading does not, in fact, support Occam’s Razor at all. To this end, I state and prove a very similar theorem that, if interpreted the same way, would justify the contradictory Anti-Occam’s Razor—the principle that we should favor more complex hypotheses.
Discriminating High-Pressure Water Phases Using Rare-Event Determined Ionic Dynamical Properties*
Authors: Zhuang Lin , Ye Qijun , Pan Ding , Li Xin-Zheng
Published: May 2020

Recent discoveries of dynamic ice VII and superionic ice highlight the importance of ionic diffusions in discriminating high-pressure (P) water phases. The rare event nature and the chemical bond breaking associated with these diffusions, however, make extensive simulations of these processes unpractical to ab initio and inappropriate for force field based methods. Using a first-principles neural network potential, we performed a theoretical study of water at 5–70 GPa and 300–3000 K. Long-time dynamics of protons and oxygens were found indispensable in discriminating several subtle states of water, characterized by proton’s and oxygen ion’s diffusion coefficients and the distribution of proton’s displacements. Within dynamic ice VII, two types of proton transfer mechanisms, i.e., translational and rotational transfers, were identified to discriminate this region further into dynamic ice VII T and dynamic ice VII R. The triple point between ice VII, superionic ice (SI), and liquid exists because the loosening of the bcc oxygen skeleton is prevented by the decrease of interatomic distances at high P’s. The melting of ice VII above ∼40 GPa can be understood as a process of two individual steps: the melting of protons and the retarded melting of oxygens, responsible for the forming of SI. The boundary of the dynamic ice VII and SI lies on the continuation line ice VII’s melting curve at low P’s. Based on these, a detailed phase diagram is given, which may shed light on studies of water under P’s in a wide range of interdisciplinary sciences.
Pulsed nanosecond air discharge in contact with water: influence of voltage polarity, amplitude, pulse width, and gap distance
Authors: Hamdan Ahmad , Ridani Daniel A , Diamond James , Daghrir Rimeh
Published: May 2020

Plasma technology is a highly promising and advantageous technology for liquid processing. In air in-contact with water, plasma produces highly reactive species (ions, electrons, radicals, photons, etc) that diffuse into the water volume and initiate physical and chemical phenomena of interest, e.g. organic and inorganic pollutant degradation. In this study, we investigate the influence of basic parameters, such as voltage polarity, voltage amplitude, plasma lifetime, and air-gap distance, on the properties of a discharge in air in-contact with deionized water. Specifically, we analyze the electrical characteristics, the plasma behaviour at the water surface, water acidity and conductivity, and the decoloration rate of a standard organic dye (methylene blue). The concentration of the main reactive oxygen and nitrogen species produced in water is also reported. Compared to positive polarity conditions, the negative polarity voltages enhance the decolaration rate of methylene blue. For instance, under negative polarity voltages and while applying 4 and 6 kV, the decoloration rate is relatively low (<30%) and reaches 100% after 25 min of processing at −10 kV. The decoloration rate of MB is also strongly influenced by air-gap distance. Under positive polarity conditions, the decoloration rate decreases from ∼80 to ∼0% as the air-gap distance increases from 0.5 to 7.5 mm, whereas, under negative polarity conditions, the decoloration rate is ∼100%, irrespective of the air-gap distance (0.5 and 4.5 mm).
A dual-domain deep learning-based reconstruction method for fully 3D sparse data helical CT
Authors: Zheng Ao , Gao Hewei , Zhang Li , Xing Yuxiang
Published: May 2020

Helical CT has been widely used in clinical diagnosis. In this work, we focus on a new prototype of helical CT, equipped with sparsely spaced multidetector and multi-slit collimator (MSC) in the axis direction. This type of system can not only lower radiation dose, and suppress scattering by MSC, but also cuts down the manufacturing cost of the detector. The major problem to overcome with such a system, however, is that of insufficient data for reconstruction. Hence, we propose a deep learning-based function optimization method for this ill-posed inverse problem. By incorporating a Radon inverse operator, and disentangling each slice, we significantly simplify the complexity of our network for 3D reconstruction. The network is composed of three subnetworks. Firstly, a convolutional neural network (CNN) in the projection domain is constructed to estimate missing projection data, and to convert helical projection data to 2D fan-beam projection data. This is follwed by the deployment of an analytical linear operator to transfer the data from the projection domain to the image domain. Finally, an additional CNN in the image domain is added for further image refinement. These three steps work collectively, and can be trained end to end. The overall network is trained on a simulated CT dataset based on eight patients from the American Association of Physicists in Medicine (AAPM) Low Dose CT Grand Challenge. We evaluate the trained network on both simulated datasets and clinical datasets. Extensive experimental studies have yielded very encouraging results, based on both visual examination and quantitative evaluation. These results demonstrate the effectiveness of our method and its potential for clinical usage. The proposed method provides us with a new solution for a fully 3D ill-posed problem.
Kappaphobia is the elephant in the fret room
Authors: VanDerMeer B Wieb
Published: May 2020

FRET is both a phenomenon and a spectroscopic technique, capable of measuring one geometric quantity: kappa-squared divided by the sixth power of the donor-acceptor distance. Kappa-squared is often replaced by a constant even though such a replacement may lead to serious errors. Kappaphobia, the fear of kappa or the reluctance to deal with kappa-squared adequately, is a looming presence in the FRET community. Unfortunately, this reluctance, or fear, is often tolerated, and sometimes encouraged. A decrease in kappaphobia will lead to an increase in the impact and success of FRET.
Poetics
Authors: Culler Jonathan
Published: May 2020

The term poetics designates both a field of study and the practice of a particular author or group of authors. Aristotle’s Poetics, the most important work of literary theory in the Western tradition, undertakes to describe in systematic fashion the major forms of literature, the components of each, and how these elements contribute to the effects desired. Aristotle proceeds on the assumption that there is a comprehensive structure of knowledge attainable about poetry, which is not the experience of poetry, but poetics. Such a poetics treats literature as an autonomous object of knowledge, whose major genres or forms it seeks to analyze. This is an explicit poetics; but we also speak of the poetics implicit in the work of an individual writer, or of a group of writers, or of the literature of an era, as in The Poetics of Dante’s Paradiso, or even The Poetics of Postmodernism, which focus on the characteristic techniques, compositional habits, and ways of treating subjects in the literary practice under consideration. As the latter title indicates, the term poetics is used even when the literature treated does not include much poetry. Poetics can be distinguished from literary history, in that it focuses on literature as a system of possibilities rather than as a historical sequence or a practice in history, although categories from poetics will be important for any study of the evolution of literature. In literary theory, poetics is set apart for concentrating on intrinsic characteristics of literature as a system, as opposed to treating it as a phenomenon to be explained in social, historical, economic, or psychological terms. Poetics is particularly distinguished from hermeneutics or interpretation, in that it does not attempt to determine the meaning of literary works but asks how they function: What are characteristics of different literary genres and their constituents? How do their various elements work together to produce the effects they do for readers? Many contributions to the theory of literature can be seen as contributions to poetics, insofar as they try to explain the nature of literature and describe some of its major forms, even if they are presented as arguments about the literary practice of a particular period or literary mode. Western poetics begins with Aristotle, whose poetics is based on drama: literature is defined an imitation of action, in which plot is central. In Chinese and Japanese cultures, by contrast, foundational poetics have been drawn from lyric poetry and have focused on affect and expression rather than on representation. In the history of Western poetics mimesis has remained fundamental, despite changes that, from time to time, treat literature as the expression of the experience of the author or the attempt to create certain experiences for the reader.
Literary Translation
Authors: Pym Anthony
Published: May 2020

Literary translation has progressively been dominated by a Western translation form that imposes basic binarisms, assuming separate (national) languages, a foundational opposition between domesticating and foreignizing translation strategies, and separate voices for author and translator, with the latter in a subordinate position. This binary, individualist, and nationalist conceptualization furnishes a way of talking about translations that often has little to do with the vitality and pragmatism of the literary translator’s craft, where there are mostly more than two options in play. When coupled to notions of literariness that privilege means of expression, the form also produces strong concepts of untranslatability, usually based on the banal observation that different languages offer different means of expression. A strong answer to the alleged impossibility of translation is the idea, found in Walter Benjamin and Andrey Fedorov, that literary translations do not replace their “source” or “start texts” but are instead an interpretative extension of them, and should be read as such. The Western translation form also overlooks the variety of translative activities that existed prior to its rise in the early modern period. With its emphasis on separation and accuracy, it traveled out with the railway lines and steam printing presses of modernity, supplanting most of the non-Western translation forms as literary practices. Western translation studies, as an academic discipline, has followed the same paths several generations later, imposing its binary metalanguage in the process. In this, it has become part and parcel of a world configuration of networks where a few central languages, with English as a super-central language, have enormous numbers of translations being done from them, while they themselves appear to have relatively few translations in them. This has been called the “three-percent problem,” so named because only 3 to 4 percent of texts in English are translations. The low percentage is nevertheless a function of the huge number of titles published in English, which means that English regularly has more translations than do French or Italian, for example. There are nevertheless hegemonic relations in the way that international literary events are created in central languages and then translated outward, such that a disproportionate degree of fame tends to accrue to those who write in the central languages. Can this configuration be changed? If the foundational binarisms of the Western translation form were based on the fixity of the printing press, which separated languages and objectified stable texts, then new translation forms should be sought in the global accessibility and fluidity of digital technologies, which offer translators unexplored possibilities.