bluuebunny/crossref_metadata_2025 huggingface dataset:
A non-syndromic case of maxillo-mandibular keratocysts
Authors: Brechard P.M. , Hervé G. , Descroix V. , Lescaille G. , Guyon A.
Published: February 2020

Introduction: Odontogenic keratocysts (OKCs) are frequent, aggressive lesions with a strong tendency to recur, particularly in their para-keratinized majority form. Although they are mainly non-syndromic, these lesions are found in a large majority of patients with Gorlin syndrome. Thus, multiple forms are almost always associated with this syndrome and require investigation to prevent the risk of various cancers. Non-syndromic multiple forms are exceptional. Observation: A 20-year-old patient presented with dual localization of maxillary and left mandibular OKC at consultation. Under general anesthesia, excision of the lesions and extraction of the impacted wisdom teeth 28 and 38 were performed. The patient showed no clinical sign of Gorlin syndrome. Discussion: The OKC or epidermoid cyst is derived from the dental lamina or its remnants and from the basal part of the oral epithelium and represents between 10 and 20% of all cystic lesions in the maxillae. Its peak of incidence is between the second and fourth decade (or earlier in case of association with basal cell necrosis). OKC occurs mainly in the mandible and preferentially at the Ramus, where its frequency can reach 70% depending on the series. Conclusion: The management of OKC by oral surgeons must be conducted in a multidisciplinary setting in close collaboration with dermatologists, geneticists, and anatomic pathologists. Due to the strong recidivating character of OKCs, patient monitoring is essential.
N-Heterocyclic Carbene-Organocatalyzed Arene Formation: Application in Atroposelective Synthesis of Polysubstituted Benzenes
Authors: Zhu Tingshun , Xu Ke , Wang Ziyuan
Published: February 2020

In recent decades, organocatalysis by N-heterocyclic carbenes (NHCs) has emerged as a versatile and powerful method in organic synthesis. As a result of the power of NHC organocatalysis to produce cyclic compounds, polysubstituted benzenes, which are among the most important cyclic compounds in organic chemistry, can be synthesized efficiently and selectively. This article briefly summarizes the history of NHC organocatalysis, including recent developments in benzene-formation methods, and highlights our recent work in atroposelective arene formation by carbene-catalyzed formal [4+2] cyclo­additions. We expect that more NHC-catalyzed methods for the synthesis of asymmetric arenes will be developed in the near future, providing shortcuts to syntheses of sophisticated chiral functional molecules with polysubstituted benzene nuclei.
Difluorocarbene-Based Cyanation of Aryl Iodides
Authors: Zhang Yin-Xiang , Xiao Xuan , Fu Zhi-Hong , Lin Jin-Hong , Guo Yu , Yao Xu , Cao Yu-Cai , Du Ruo-Bing , Zheng Xing , Xiao Ji-Chang
Published: February 2020

A large number of efficient cyanation methods have been developed because of the wide range of applications of nitriles, but conventional methods usually suffer from the need for a toxic cyanation reagent. Although difluorocarbene chemistry has received increasing attention, the use of difluorocarbene as a sources of the nitrile carbon for nitrile groups remains largely unexplored. We describe a difluorocarbene-based cyanation of aryl iodides promoted by a cheap copper source, Cu(NO3)2·2.5H2O, under an air atmosphere. Ph3P+CF2CO2
–, an easily available and shelf-stable difluorocarbene reagent, and NaNH2 are used as the carbon source and the nitrogen source for the nitrile group, respectively. The cyanation protocol is attractive because no toxic reagent is used and performing the reactions under an air atmosphere is operationally convenient.
Ultra slow electron holes in collisionless plasmas: Stability at high ion temperature
Authors: Mandal Debraj , Sharma Devendra , Schamel Hans
Published: February 2020

Numerical simulations recover ultraslow solitary electron holes (SEH) of electron-acoustic genre propagating stably well below the ion acoustic speed Cs, where no pure electron perturbation is known to exist yet, as they are disallowed by the ion response. Recovered at high ion temperature (Ti > Te), the reason for this stability (unaccelerated propagation, unseen before in existing literature) of SEH is traced to the loss of neutralizing cold ion response. In the opposite case of a background of sufficiently cold ions, Te>3.5Ti, SEHs are accompanied by an ion compression that yields phase velocities above Cs (ion acoustic genre) and accelerates them, forcing a jump over a forbidden velocity gap, and settle on the high velocity tail of the electron distribution fe. In the observed ultraslow structures having Ti > Te, however, the warm ions begin to supplement the electron response and show Boltzmannlike behavior, transforming the ion compression to decompression (rarefaction) at the hole location. SEHs, hence, belong to the continuous spectrum of slow electron acousticlike modes being triggered by the electron trapping nonlinearity. The results also suggest a scope of generalization of the basic EH theory.
A stable quantum Darmois-Skitovich theorem
Authors: Cuesta Javier
Published: February 2020

The Darmois-Skitovich theorem is a simple characterization of the normal distribution in terms of the independence of linear forms. We present here a non-commutative version of this theorem in the context of Gaussian bosonic states and show that this theorem is strongly stable under small errors in its underlying conditions. An explicit estimate of the stability constants which depend on the physical parameters of the problem is given.
Investigation of room temperature multiferroic properties in sol-gel derived gadolinium, cobalt doped BiFeO3 nanoceramics
Authors: Das Sananda , Sahoo R. C. , Nath T. K.
Published: February 2020

Detailed studies of structural, dielectric, magnetic, ferroelectric, and optical properties of a chemically sol-gel synthesized series of Bi1 − xGdxFe1 − yCoyO3 (x = 0, 0.1 and y= 0, 0.1) nanoceramics are presented. These nanoceramics attract attention as promising candidates for application as room temperature multiferroics in spintronics devices, exhibiting an optimistic set of properties. The average particle sizes of all the samples are calculated, and it was found to be ∼45 nm from the Scanning Electron Microscopy image. The dielectric behavior of the prepared nanoceramics was investigated over a wide frequency (100 Hz–103 kHz) and a temperature (35–350 °C) range. Interestingly, a low temperature dielectric anomaly is observed at around 170 °C for Bi0.9Gd0.1Fe0.9Co0.1O3 due to the magnetoelectric coupling. A noticeably large value of dielectric constant (∼990) and a low tan δ loss have also been observed for this nanoceramic at room temperature. The complex impedance spectroscopic analysis was also performed by plotting Nyquist plots, and the corresponding activation energies are evaluated from the Arrhenius fittings. Magnetization measurements of the samples reveal the presence of weak ferromagnetism due to surface spins as well as a noticeable improvement in the magnetic properties with Gd and Co doping. Ferroelectric properties have also been observed to be slightly improved because of doping, though it becomes somewhat lossy for Gd and Co doped samples. All the promising improved properties directly depend on the subsequent increase in the bandgap from 2.29 eV to 2.45 eV, with doping in the parent BiFeO3 compound confirmed from UV–Vis spectroscopy.
Machine learning control for disruption and tearing mode avoidance
Authors: Fu Yichen , Eldon David , Erickson Keith , Kleijwegt Kornee , Lupin-Jimenez Leonard , Boyer Mark D. , Eidietis Nick , Barbour Nathaniel , Izacard Olivier , Kolemen Egemen
Published: February 2020

Real-time feedback control based on machine learning algorithms (MLA) was successfully developed and tested on DIII-D plasmas to avoid tearing modes and disruptions while maximizing the plasma performance, which is measured by normalized plasma beta. The control uses MLAs that were trained with ensemble learning methods using only the data available to the real-time Plasma Control System (PCS) from several thousand DIII-D discharges. A “tearability” metric that quantifies the likelihood of the onset of 2/1 tearing modes in a given time window, and a “disruptivity” metric that quantifies the likelihood of the onset of plasma disruptions were first tested off-line and then implemented on the PCS. A real-time control system based on these MLAs was successfully tested on DIII-D discharges, using feedback algorithms to maximize βN while avoiding tearing modes and to dynamically adjust ramp down to avoid high-current disruptions in ramp down.
High Seebeck coefficient in thermally evaporated Sb-In co-alloyed bismuth telluride thin film
Authors: Singh Sukhdeep , Jindal Silky , Tripathi S. K.
Published: February 2020

In the present work, we have obtained high magnitudes of the Seebeck coefficient in Sb and In coalloyed bismuth telluride thin film that has been deposited by a simple and cost-efficient thermal evaporation procedure. The films display an exceptional peak Seebeck coefficient of −310 μV/K at the working temperature of 90 °C. In addition to this, a high value of −191.6 μV/K is obtained at room temperature along with appreciable conductivity (6.2 × 103 S/m). The x-ray diffraction (XRD) pattern of the film has been analyzed for probing the crystal profile that depicts a polycrystalline and nanoscale structure. Films’ surface and cross-sectional morphologies are investigated using Field Emission Scanning Electron Microscope (FESEM), where a nanocrystalline morphology of thickness 150 nm is observed. Raman analysis supports the results obtained from XRD and FESEM for nanomorphology and indicates the presence of Te segregates. Atomic composition of the film produced is probed using Energy Dispersive x-ray spectroscopy, which also indicates the presence of excess Te. The Seebeck coefficient of the films shows an enormous enhancement as compared to previously reported work for undoped samples (BST-100S). The magnitudes of the Seebeck coefficient obtained in the present work are among the highest values reported for a bismuth antimony telluride material. These enhancements are attributed to the combined effect of coalloying, the presence of highly mobile (00l) orientations, and confinement effects of a nanocrystalline profile.
Optimization analysis of piezoelectric actuator based on energy transfer
Authors: Fan Pingqing , Liu Jianyu
Published: February 2020

Based on energy transfer theory, the power flow method is used to optimize the piezoelectric actuator to improve its output performance. First, the mode analysis of the piezoelectric actuator is performed, and the actuator is discretized according to the mode nodes of the operational mode. On the basis of the Norton’s equivalent circuit, the equivalent mechanical network of the actuator is established, and the expression of power flow is imported to the mass block of driving foot. Second, on the basis of the actuator power flow expression, simulation analysis is conducted to obtain the influence of actuator parameters on the power flow amplitude for optimizing the driver parameters. Finally, a test platform is built to compare the improved piezoelectric actuator with the original one. Results show that the output force and power of the improved piezoelectric actuator have increased by 8.3% and 22%, respectively, to verify the effectiveness of the optimization method.
Apparatus design for measuring of the strain dependence of the Seebeck coefficient of single crystals
Authors: Qian Tiema , Mutch Joshua , Wu Lihua , Went Preston , Jiang Qianni , Malinowski Paul , Yang Jihui , Chu Jiun-Haw
Published: February 2020

We present the design and construction of an apparatus that measures the Seebeck coefficient of single crystals under in situ tunable strain at cryogenic temperatures. A home-built three piezostack apparatus applies uni-axial stress to a single crystalline sample and modulates anisotropic strain up to 0.7%. An alternating heater system and cernox sensor thermometry measure the Seebeck coefficient along the uniaxial stress direction. To demonstrate the efficacy of this apparatus, we applied uniaxial stress to detwin single crystals of BaFe2As2 in the orthorhombic phase. The obtained Seebeck coefficient anisotropy is in good agreement with previous measurements using a mechanical clamp.
Photon waiting-time distributions: A keyhole into dissipative quantum chaos
Authors: Yusipov I. I. , Vershinina O. S. , Denisov S. V. , Ivanchenko M. V.
Published: February 2020

Open quantum systems can exhibit complex states, for which classification and quantification are still not well resolved. The Kerr-nonlinear cavity, periodically modulated in time by coherent pumping of the intracavity photonic mode, is one of the examples. Unraveling the corresponding Markovian master equation into an ensemble of quantum trajectories and employing the recently proposed calculation of quantum Lyapunov exponents [I. I. Yusipov et al., Chaos 29, 063130 (2019)], we identify “chaotic” and “regular” regimes there. In particular, we show that chaotic regimes manifest an intermediate power-law asymptotics in the distribution of photon waiting times. This distribution can be retrieved by monitoring photon emission with a single-photon detector so that chaotic and regular states can be discriminated without disturbing the intracavity dynamics.
Spatio-temporal dynamics and formation mechanism of the square super-lattice pattern with saturn-like white-eye in dielectric barrier discharge
Authors: Dong Lifang , Mi Yanlin , Pan Yuyang
Published: February 2020

We report a square superlattice pattern with two types of white-eyes in dielectric barrier discharge, one of which has an obvious black area around the center spot and is named “saturnlike white-eye.” By using an intensified charge-coupled device, it is found that the pattern has five spatiotemporal sublattices, which should be the most complex pattern in dielectric barrier discharge to date. The results measured by the spectrograph and photomultiplier tubes show that the center spots of two types of white-eyes approximately have the same plasma parameters, while the current intensity of the center spot of saturnlike white-eye is about 1/3 of that of ordinary white-eye. Based on the above results, it can be estimated that the velocity of electrons in discharge of the center spot of saturnlike white-eye is much slower than that of ordinary white-eye, resulting in exhaustion of wall charges at the falling edge of voltage (d∣Uapp∣∕dt < 0) and occurrence of discharge at the next rising edge of voltage (d∣Uapp∣∕dt > 0). It inhibits discharge around the center spot and then the black area is formed. The differences of formation processes between two types of white-eyes are discussed. We believe that the research will contribute to advancement of pattern dynamics in dielectric barrier discharge.
Control system for the new RIKEN 28-GHz superconducting electron cyclotron resonance ion source for SRILAC
Authors: Uchiyama A. , Nagatomo T. , Higurashi Y. , Ohnishi J. , Komiyama M. , Kumagai K. , Fujimaki M. , Yamauchi H. , Tamura M. , Kaneko K. , Fukunishi N. , Nakagawa T.
Published: February 2020

A new RIKEN 28-GHz superconducting electron cyclotron resonance ion source (SC-ECRIS) has been installed for the superconducting RIKEN linear accelerator (SRILAC). The new SC-ECRIS control system mainly consists of programmable logic controllers (PLCs) embedded with the Experimental Physics and Industrial Control System. To improve the reliability as compared with previous control systems, two types of PLC central processing units, sequential and Linux, have been installed in the same unit. Past experience has shown that new types of designs that can rapidly respond to system scalability are key. By connecting PLC stations using star-topology field buses, their rapid and cost-effective response to system changes is realized for the new devices. Furthermore, a unique data acquisition system employing a 920-MHz-band radio was developed to measure analog data such as the temperature at the high-voltage stage.
Different responses of the Rayleigh–Taylor type and resistive drift wave instabilities to the velocity shear
Authors: Zhang Y. , Krasheninnikov S. I. , Smolyakov A. I.
Published: February 2020

The effects of velocity shear on the unstable modes driven by the effective gravity (Rayleigh–Taylor and interchange) and resistive drift wave instabilities for inhomogeneous equilibrium fluid/plasma density are analyzed for the localized eigenmode problems. It is shown that the effect of the velocity shear drastically depends on the type of instability. Whereas the velocity shear can significantly suppress both Rayleigh–Taylor and interchange instabilities, it has only a weak impact on the growth rate of the resistive drift wave. This is directly related to the physical nature of these instabilities. For the Rayleigh–Taylor and interchange instabilities, the shear flow tilts the eddies of the stream functions, while for the resistive drift wave instability the shear flow simply shifts the eddies in the radial direction with no tilting. However, for a large velocity shear, the eigenmode solutions for resistive drift waves cease to exist.
Expanding the strong absorption band by impedance matched mosquito-coil-like acoustic metamaterials
Authors: Hou Mingming , Wu Junxiang , Yang Shaokun , Wu Jiu Hui , Ma Fuyin
Published: February 2020

A mosquito-coil-like acoustic artificial structure consisting of a spiral channel and a perforated plate with excellent impedance matching is proposed, which can realize strong sound absorption within a certain frequency range. Due to the difficulty in matching the impedance of the single-hole structure with that of the sound propagation medium, the sound absorption should be poor. To overcome this shortcoming caused by the mismatched impedance, some multi-hole microstructures are designed. Moreover, since single-chamber labyrinth can only achieve single-frequency perfect sound absorption, a labyrinthine channel is divided into several chambers with each length distributing by an arithmetic progression gradient. The sound absorption bandwidth can be extended by synergetic coupling resonance among multiple chambers. By selecting different structural parameters including the number of holes, the width of the labyrinthine channel, and the depth of labyrinthine channel, sound absorption of these mosquito-coil-like structures is investigated. The results suggest that the multi-hole structures are helpful in improving the impedance matching, while the synergetic coupling resonance among multiple chambers ensures that the sound absorption coefficient of the structure can be maintained at a high level within a certain frequency range. In addition, some mosquito-coil-like sound absorption structures are fabricated by 3D printing, then the sound absorptions under vertical sound incident conditions are measured, and the strong sound absorption ability in a wide band is experimentally demonstrated. Finally, a method is proposed for adjusting the sound absorptions by proportionally zooming in or out the structure, by which the sound absorptions of the acoustic structure can be effectively shifted to lower or higher frequencies.
Nanoscale quantification of longitudinal and transverse mechanics of bacterial bodies
Authors: Lee Briana , Castaneda Nicholas , Doomra Mitsushita , Modha Nirav , Santra Swadeshmukul , Thornton John , Zhang Taiye , Kang Ellen Hyeran , Tetard Laurene
Published: February 2020

Mechanical studies focused on flagella and pili of bacteria, typically estimated by evaluating bending persistence length measurements or Young's modulus, fail to consider the behavior of the whole bacterial body, which can undergo significant changes during antimicrobial resistance. In this Letter, we investigate the biophysical properties of an important plant bacterial pathogen, Xanthomonas perforans, the causal agent for bacterial spot disease of tomato and pepper. The emergence of copper-tolerant strains of X. perforans is predicted to have a devastating impact on industrial scale productions, making it essential to advance approaches to distinguish copper-tolerant from the copper-sensitive X. perforans strains. After introducing a means to measure the bending stiffness of bacteria using atomic force microscopy (AFM), we propose a comparison of the longitudinal and transverse mechanical properties by acquiring high resolution images and force curves of the bacteria. A quantification of the longitudinal and transverse Young's modulus of bacteria reveals significant differences between copper-sensitive and copper-tolerant strains of X. perforans. The present approach is expected to significantly advance the fundamental understanding of bacterial phenomena, such as by monitoring the therapeutic efficacy of newly developed materials on individual X. perforans in situ to relate them to the behavior of their colonies or biofilms.
Linear and weakly nonlinear stability analysis on a rotating anisotropic ferrofluid layer
Authors: Mahajan Amit , Parashar Hemant
Published: February 2020

In this article, the linear and weakly nonlinear instability in a rotating anisotropic magnetic fluid layer when the layer is internally heated and the solid matrix and fluid are not in local thermal equilibrium is studied. The Darcy model for the permeable medium and Coriolis force term for rotation are considered in the momentum equation. For the linear stability analysis, normal mode has been performed while weakly nonlinear analysis is carried out with a truncated Fourier series. The Runge–Kutta–Gill numerical method is used for solving the finite-amplitude equation to study the transient behavior of the Nusselt number at the lower boundary. Effects of parameters on the Rayleigh number have been studied in gravitational as well as microgravity conditions. It was found that Taylor number Ta and thermal anisotropy parameter ηf had a stabilizing effect on the convection. Heat transport is decreased with the increase in Taylor number Ta and thermal anisotropy parameter ηf. When internal heat is less (ξ = 1.5), the heat transport rate is high, and when internal heat is sufficient (ξ = 0.3), the heat transfer rate is low.
Sequence-to-sequence prediction of spatiotemporal systems
Authors: Shen Guorui , Kurths Jürgen , Yuan Ye
Published: February 2020

We propose a novel type of neural networks known as “attention-based sequence-to-sequence architecture” for a model-free prediction of spatiotemporal systems. This architecture is composed of an encoder and a decoder in which the encoder acts upon a given input sequence and then the decoder yields another output sequence to make a multistep prediction at a time. In order to demonstrate the potential of this approach, we train the neural network using data numerically sampled from the Korteweg–de Vries equation—which describes the interaction between solitary waves—and then predict its future evolution. Furthermore, we validate the applicability of the approach on datasets sampled from the chaotic Lorenz system and three other partial differential equations. The results show that the proposed method can achieve good performance in predicting the evolutionary behavior of studied spatiotemporal dynamics. To the best of our knowledge, this work is the first attempt at applying attention-based sequence-to-sequence architecture to the prediction task of solitary waves.
Effect of parametric excitation on a bifractional-order damped system with a fractional-power nonlinearity
Authors: Yan Zhi , Liu Xianbin
Published: February 2020

Investigation on linear/nonlinear resonance phenomena and supercritical/subcritical pitchfork bifurcation mechanism is reported in a complex bifractional-order damped system which endures a high-frequency parametric excitation and contains fractional-power nonlinearity. The approximate theoretical expression of the linear response amplitude at the primary frequency and the superharmonic response amplitude at the second and third harmonic frequencies are obtained by utilizing an analytical method and an iterative formula. A numerical approximation scheme based on the Caputo derivative for the simulation of the system is introduced, showing sufficient precision. Due to the parametric excitation, analytical approximation expressions of the stable equilibrium points are given explicitly when the exponent is not an integer so that the pitchfork bifurcation, nonlinear resonance can be studied in an analytical way, exhibiting much more operability than the external excitation case. It is found that the fractional-order derivative may bring new multibifurcation and new multiresonance phenomena, which have not yet been reported before. With the variation of different control parameters of the system, the equivalent slow-varying system can be converted from bistability to monostability and finally to bistability. Unlike the cases of the system excited by bifrequency external excitation, the optimum response amplitude of the parametric excited system is not monotonous with respect to the values of the exponent. For a range of parameters of the system, it is also found that the superharmonic resonance at the second and third harmonic frequencies is affected deeply by the parametric excitation.
Synthesis, structure, and transport properties of Ba8Cu16 – xAuxP30 clathrate solid solution
Authors: Wang Jian , Voyles Jackson , Grzybowski Scott , Kovnir Kirill
Published: February 2020

A new clathrate solid solution Ba8Cu16 − xAuxP30 (x = 4, 8, 12) was synthesized by a high-temperature solid-state annealing method. The crystal structures of Ba8Cu16 − xAuxP30 were determined by single crystal x-ray diffraction. This clathrate solid solution crystallizes in the orthorhombic superstructure of clathrate-I type with 23 crystallographically independent framework sites, eight of them are occupied by Au/Cu and 15 are exclusively occupied by P atoms. The distribution of Au and Cu atoms over these eight framework sites is not random with a clear preference for Au to occupy the largest (Au/Cu)P4 tetrahedra in the framework. The thermal stability and thermoelectric properties of the Ba8Cu16 − xAuxP30 solid solution were evaluated. Low thermal conductivity was achieved for Ba8Cu16 − xAuxP30 due to the combination of the host–guest crystal structure with rattling Ba atoms with the presence of heavy Au atoms and substitutional Cu/Au disorder in the clathrate framework.
Spatially focused microwave ignition of metallized energetic materials
Authors: Kline Dylan J. , Rehwoldt Miles C. , Turner Charles J. , Biswas Prithwish , Mulholland George W. , McDonnell Shannon M. , Zachariah Michael R.
Published: February 2020

This study investigates the ability to locally ignite metallized propellants via microwave absorption. Metallized energetic composite films incorporating high mass loadings of aluminum and titanium nanoparticle fuels within a polyvinylidene fluoride (PVDF) polymer matrix were constructed by direct-write additive manufacturing (3D printing). Simulations of power absorption for both Ti and Al nanoparticles reveal that the passivating shell composition likely plays a significant role in the observed ignition phenomenon. Various architectures of interest were constructed for predictable microwave ignition and propellant propagation. It was found that, although aluminum nanoparticles and composites do not ignite via exposure to microwaves, titanium nanoparticles can be used as efficient reactive microwave susceptors enabling a localized ignition source. This approach enables various architectures of previously studied high energy Al/PVDF systems to be fabricated and outfitted with a microwave-sensitive titanium composite in strategic locations as a means of remote ignition for aluminum systems.
Three-dimensional viscoelastic instabilities in a four-roll mill geometry at the Stokes limit
Authors: Gutierrez-Castillo Paloma , Kagel Adam , Thomases Becca
Published: February 2020

Three-dimensional numerical simulations of viscoelastic fluids in the Stokes limit with a four-roll mill background force (extended to the third dimension) were performed. Both the Oldroyd-B model and FENE-P model of viscoelastic fluids were used. Different temporal behaviors were observed depending on the Weissenberg number (non-dimensional relaxation time), model, and initial conditions. Temporal dynamics evolve on long time scales, and simulations were accelerated by using a Graphics Processing Unit (GPU). Previously, parameter explorations and long-time simulations in 3D were prohibitively expensive. For a small Weissenberg number, all the solutions are constant in the third dimension, displaying strictly two-dimensional temporal evolutions. However, for a sufficiently large Weissenberg number, three-dimensional instabilities were observed, creating complex temporal behaviors. For certain Weissenberg values and models, the instability that first emerges is two-dimensional (in the x, y plane), and then the solution develops an instability in the z-direction, whereas for others the z instability comes first. Using a linear perturbation from a steady two-dimensional background solution, extended to three dimensions as constant in the third dimension, it is demonstrated that there is a linear instability for a sufficiently large Weissenberg number, and possible mechanisms for this instability are discussed.
Totally asymmetric simple exclusion process on multiplex networks
Authors: Shen Guojiang , Fan Xinye , Ruan Zhongyuan
Published: February 2020

We study the totally asymmetric simple exclusion process on multiplex networks, which consist of a fixed set of vertices (junctions) connected by different types of links (segments). In particular, we assume that there are two types of segments corresponding to two different values of hopping rate of particles (larger hopping rate indicates particles move with higher speed on the segments). By simple mean-field analysis and extensive simulations, we find that, at the intermediate values of particle density, the global current (a quantity that is related to the number of hops per unit time) drops and then rises slightly as the fraction of low-speed segments increases. The rise in the global current is a counterintuitive phenomenon that cannot be observed in high or low particle density regions. The reason lies in the bimodal distribution of segment densities, which is caused by the high-speed segments.
Modeling of particle cloud dispersion in compressible gas flows with shock waves
Authors: Gai Guodong , Thomine Olivier , Hadjadj Abdellah , Kudriakov Sergey
Published: February 2020

The effect of shock waves on the dispersion characteristics of a particle cloud is investigated both numerically and analytically. A one-dimensional analytical model is developed for the estimation of the cloud topology in the wake of a shock wave, as a function of time, space, and characteristic response time τp of the cloud based on the one-way formalism. The model is compared with the results obtained with numerical simulations over a wide range of incident Mach numbers Ms and particle volume fraction τv,0. An extension of the one-way formalism to the two-way is proposed by taking into account the post-shock gas deceleration due to the presence of particles. A significant increase in the cloud density is noticed. The effects of different parameters affecting the shock–spray interaction are elucidated and discussed. The two-way formalism is seen to better describe the effects of the particles on the propagation of the shock wave.
Engineering of defects in resistive random access memory devices
Authors: Banerjee Writam , Liu Qi , Hwang Hyunsang
Published: February 2020

Defects are essential to switch the resistance states in resistive random-access memory (RRAM) devices. Controlled defects in such devices can lead to the stabilization of the switching performance, which is useful for high-density memory and neuromorphic computing applications. In contrast, uncontrolled defects in RRAM can generate randomness and increase intrinsic entropy, which are useful for security applications. In this tutorial, we explain how to engineer defects in RRAM devices. More specifically, we focus on defect engineering of the oxide layer and how the defects can affect the switching mechanism. Defect engineering processes include the doping effect, nanocrystal-based switching layer design, embedded metals in switching oxide, defective electrode design, etc. We explain how defects can improve the electrical performance of RRAM devices and the recent development of applications using defect-based RRAM devices.
Sulfur hexafluoride bubble evolution in shock accelerated flow with a transverse density gradient
Authors: Zhu Yuejin , Gao Longkun , Yang Zhiwei
Published: February 2020

Sulfur hexafluoride (SF6) is a colorless, odorless, non-toxic, non-flammable stable gas, which has been widely adopted as the heavy gas in the Richtmyer–Meshkov instability study. In this paper, a computational analysis of SF6 bubble evolution in shock-accelerated flow with a transverse density gradient is presented. The influences of different incident shock Mach numbers on various interactions were clarified using high-resolution computation schemes. The results showed that the incident shock wave becomes curved during propagation because of the transverse density gradient. Based on this, two separate shock-focusing processes were identified when Ma = 1.21 and three separate shock-focusing processes were identified when Ma = 2.0. However, the shock-focusing intensity was weaker than previously observed in a flow field with a uniform density distribution. High- and relevant-pressure impingement played vital roles in the formation of three jets near the downstream pole of the SF6 bubble in both cases. In addition, impingement by incident and reflected shocks could induce additional vorticities in the bubble region and promote increased bubble volumes, but these increased bubble volumes could weaken the average vorticity. Upon increasing the incident shock Mach number, the effective bubble volume decreased with the enhanced shock intensity, but the vorticities were strengthened. Furthermore, analyzing the factors that affected vorticity evolution allowed us to find that the compression term had a stronger influence on vorticity evolution than the baroclinic term or the viscosity term. All of these studies complement the Richtmyer–Meshkov instability study.
A density functional theory study on reduction-induced structural transformation of copper-oxide-based oxygen carrier
Authors: Li Liwen , Wang Hua , Han Jinyu , Zhu Xinli , Ge Qingfeng
Published: February 2020

A clear understanding of the structural transformation of copper-oxide-based oxygen carriers accompanying their reduction by fuels helps to design more efficient oxygen carriers for chemical looping combustion. Herein, density functional theory calculations have been performed on the bulk CuO, CuO(111) surface, and (CuO)32 cluster models with the same number of CuO molecular units to investigate structural transformation accompanying the reduction. The results showed that the averaged reaction energies of desorbing an oxygen molecule from the bulk and surface models are roughly the same [246.2 kJ/(mol O2) and 245.9 kJ/(mol O2), respectively]. The slab model does not significantly lower the overall reaction energy compared to the bulk model. In contrast, the averaged reaction energy using the cluster model is significantly lower [127.5 kJ/(mol O2)] than that of bulk and slab models. The key structural difference is the obvious Cu–Cu bond formation in the cluster model, which would result in nucleation of a metallic Cu phase. The results also showed that different states can be reached by desorbing different number oxygen atoms in a single step, corresponding to different reaction rates, when the system reaches the same level of reduction. These results demonstrate the complexity of reactions involving solid state materials and are consistent with the structural diversity observed experimentally. This study illustrates the importance of particle sizes and reaction conditions in the formation of suboxides during CuO reduction.
Model of graphene nanobubble: Combining classical density functional and elasticity theories
Authors: Aslyamov T. F. , Iakovlev E. S. , Akhatov I. Sh. , Zhilyaev P. A.
Published: February 2020

A graphene nanobubble consists of a graphene sheet, an atomically flat substrate, and a substance enclosed between them. Unlike conventional confinement with rigid walls and a fixed volume, the graphene nanobubble has one stretchable wall, which is the graphene sheet, and its volume can be adjusted by changing the shape. In this study, we developed a model of a graphene nanobubble based on classical density functional theory and the elastic theory of membranes. The proposed model takes into account the inhomogeneity of the enclosed substance, the nonrigidity of the wall, and the alternating volume. As an example application, we utilize the developed model to investigate fluid argon inside graphene nanobubbles at room temperature. We observed a constant height-to-radius ratio over the whole range of radii considered, which is in agreement with the results from experiments and molecular dynamics simulations. The developed model provides a theoretical tool to study both the inner structure of the confined substance and the shape of the graphene nanobubble. The model can be easily extended to other types of nonrigid confinement.
Growth and structural studies of In/Au(111) alloys and InOx/Au(111) inverse oxide/metal model catalysts
Authors: Kang Jindong , Mahapatra Mausumi , Rui Ning , Orozco Ivan , Shi Rui , Senanayake Sanjaya D. , Rodriguez José A.
Published: February 2020

Indium oxide has received attention as an exciting candidate for catalyzing the CO2 hydrogenation to methanol due to its high selectivity (>80%). Compared to the extent of research on the activity of indium oxide-based powder catalysts, very little is known about the phenomena associated with the formation of surface alloys involving indium or the growth mechanism for indium oxide nanoparticles. In this report, scanning tunneling microscopy and X-ray photoelectron spectroscopy (XPS) were employed to elucidate the growth mode, structure, and chemical state of In/Au(111) alloys and InOx/Au(111) inverse model catalysts. Our study reveals distinct morphological differences between In/Au(111) and InOx/Au(111), and the InOx structure also depends strongly on the preparation conditions. In/Au surface alloy systems with extremely low coverage (0.02 ML) form islands preferentially on the elbow sites of reconstructed Au(111) herringbone, regardless of hexagonally closed packed and face centered cubic stacking. At higher coverage (0.1 ML), the In islands expand over the herringbone in the ⟨110⟩ direction and create two dimensional domain structures over the entire surfaces. Moreover, this 2D domain structure is disturbed by temperature with high dispersion of indium atoms observed during the annealing process. Oxidation of the In/Au(111) surface alloys with O2 at 550 K produces InOx/Au(111) systems which contain various sizes of InOx aggregates (from 0.7 nm to 10 nm). On the other hand, InOx/Au(111) surfaces prepared by vapor deposition of In at 550 K in an O2 background exhibit highly dispersed and uniformly small InOx particles (∼1 nm). Both InOx systems were confirmed to be partially oxidized by XPS.
Mechanical modeling of bending stiffness degradation for soft-honeycomb sandwich structure under CW laser heating
Authors: Wang Jiawei , Li Bin , Zhu Yongxiang , Liu Weiping , Wu Lixiong , Lv Yuwei
Published: February 2020

Based on the theory of Reissner’s sandwich structure bending, a mechanical model of bending stiffness degradation for a soft-honeycomb sandwich structure under continuous wave (CW) laser heating was established by introducing the equivalent debonding coefficient of adhesive and elastic modulus temperature dependence of panels. To verify the rationality of the mechanical model, a real-time bending stiffness measurement system for a soft-honeycomb sandwich structure under CW laser heating was proposed using the overhanging beam three-point bending method. The results show that the mechanical model works good to describe the decreasing trend of the soft-honeycomb sandwich structure under CW laser heating and to predict the residual bending stiffness after CW laser heating, despite the fact that in the early stage of CW laser heating, the bending stiffness of some kind of soft-honeycomb sandwich structure may increase for a short time due to the pyrolysis gas production. However, with the overflowing of pyrolysis gas and the elastic modulus of panel degradation at a high temperature, the bending stiffness of soft-honeycomb sandwich structure declines rapidly and soon fails to withstand any bending load. The research shows that special attention should be paid to the effect of laser heating on the mechanical properties of the soft-honeycomb sandwich structure. It also enlightens the study of mechanical properties and temperature dependence of the honeycomb sandwich structure at a high heating rate.
Linear instability in two-layer channel flow due to double-diffusive phenomenon
Authors: Sahu Kirti Chandra
Published: February 2020

The linear stability characteristics of a pressure-driven channel flow of two miscible fluids flowing in a layered manner are investigated in the presence of two scalar components diffusing at different rates [double-diffusive (DD) phenomenon]. The fluids are assumed to have the same density but different viscosities. The parameters varied are the Reynolds number, Schmidt number, and thickness of the bottom layer. It is observed that the linear stability behavior in the presence of the DD effect is strikingly different from that observed in the single-component (SC) system. While the SC two-layer configuration is stable, the DD two-layer flow becomes unstable at low and moderate Reynolds numbers. It is found that increasing the diffusivity ratio of the faster to the slower diffusing scalar destabilizes the system. A region of instability distinct from that of the Tollmien–Schlichting (TS) mode appears for some combinations of the log-mobility ratios of the slower and faster diffusing scalars. This unstable region grows as the diffusivity ratio increases and the thickness of the bottom layer decreases. For a constant diffusivity ratio, decreasing the Schmidt number of the slower diffusing scalar also increases the region of instability. An energy budget analysis is conducted to understand the underlying mechanism of this instability. Two mechanisms, namely, (i) the rate of energy transfer from the basic flow to the disturbance and (ii) the disturbance energy due to mean viscosity gradient, are found to be the significant contributors to the increase in the rate of change of the disturbance kinetic energy.
Thermal boundary conductance between high thermal conductivity boron arsenide and silicon
Authors: Wei Zhiyong , Yang Ze , Liu Ming , Wu Honglei , Chen Yunfei , Yang Fan
Published: February 2020

Thermal boundary conductance (TBC) is important for heat dissipation in light-emitting diodes (LEDs). In this study, we predicted the TBC between the high thermal conductivity boron arsenide (BAs) and silicon (Si) by nonequilibrium molecular dynamics (MD) simulations. From the thermal conductivity accumulation function with respect to phonon frequency, the dominant phonon frequencies for heat conduction in BAs are extremely different from those in Si. However, our nonequilibrium MD simulations indicated that the TBC of the BAs/Si interface was still high compared to most other interfaces, even though there was a major frequency mismatch in the thermal conductivity accumulation function between BAs and Si. The primary reason for the high TBC is the overlap of phonon density of states between BAs and Si in the frequency range of 5–8 THz. The range of predicted TBC of the BAs/Si interface was between 200 and 300 MW/m2 K in the temperature range of 300–700 K, and the values of the TBC were not sensitive to the temperature. We also found that the TBCs in Si/BAs and Si/Ge interfaces were close to each other considering the simulation uncertainty. This work indicates BAs as an excellent material for heat dissipation across the interfaces.
Stability of a vertical Couette flow in the presence of settling particles
Authors: Boronin S. A. , Osiptsov A. N.
Published: February 2020

We consider the linear stability of a particle-laden vertical Couette flow between two flat plates. The flow is described in the framework of a two-fluid approach with a negligibly small volume fraction of the dispersed phase (the “dusty-gas model”). The carrier-fluid velocity profile in the main flow is modified by the presence of settling particles distributed non-uniformly between the plates. Two types of particle number density distributions are considered, namely, a single layer with a maximum at the flow center line and two symmetric layers located between the center line and the walls. Linearized governing equations are reduced to a modified Orr–Sommerfeld equation for the amplitude of a disturbance in the form of a normal mode. On the basis of a parametric study of the eigenvalues, it is shown that, in contrast to the case of two-phase Couette flow with zero particle velocity slip, the vertical disperse flow is unstable over a wide range of governing parameters, including small Reynolds numbers. In flows with both kinds of particle concentration profiles considered, there are two types of growing modes. A gravitational mode is triggered at low Reynolds numbers and typically small wavenumbers, while a shear mode with the wavelength of the order of the channel width and larger time-amplification rates is triggered at large Reynolds numbers. It is found that both modes are amplified with an increase in the particle mass loading or the ratio of the Reynolds number to squared Froude number, determining the carrier-fluid velocity profile. The results of the study can be used to control the stability of various technological processes involving particle-laden flows.
Eulerian modeling of charge transport in bi-disperse particulate flows due to triboelectrification
Authors: Ray M. , Chowdhury F. , Sowinski A. , Mehrani P. , Passalacqua A.
Published: February 2020

An Eulerian model to describe the behavior of electrically charged particles, which considers charge separation and transfer between particles of two separate species, is developed using the kinetic theory of granular flows. A transport equation for the charge of each particle species is obtained, incorporating the effect of the charge–velocity correlation. Closures for the collisional diffusion of charge and for the charge-velocity covariance are obtained. The developed model is applied to steady-state simulations in a one-dimensional domain with no advection, neglecting momentum transport and assuming a constant granular temperature for the solid species. While this is only a preliminary test of the model, which will require further validation, the results show the prediction of bipolar charging when the particles have different sizes, even though they are made of the same material. This phenomenon is analyzed and is shown to be driven by the electric field produced by the charge accumulated on the particles.