bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal properties of cubic GaN/GaAs heterostructures grown by molecular beam epitaxy
Authors: Macias Marcos , Casallas-Moreno Yenny Lucero , Camacho-Reynoso Marlene , Zambrano-Serrano Mario Alberto , Pérez-Hernández Briseida Guadalupe , Yee-Rendón C. M. , Gurevich Yuri G. , López-López Máximo , Cruz-Orea Alfredo
Published: October 2020

Cubic GaN/GaAs (001) heterostructures were grown by RF-plasma assisted molecular beam epitaxy with different GaN nucleation temperatures. The heterostructures were studied by an open cell configuration of a photoacoustic experiment to obtain the effective thermal diffusivity (α) of the composite, which presented values varying from 14 to 28mm2/s. Also, a two-layer model was used in order to obtain the interfacial thermal conductivity (η), revealing values from 5 to 35W/cm2 K. Both α and η presented higher values for cubic GaN films grown with higher nucleation temperatures. The crystalline quality of the samples, studied with high resolution x-ray diffraction and photoluminescence measurements, showed that the increase in the nucleation temperature produced films with fewer defects, implying a dependence between the interfacial thermal properties and the bulk crystalline quality. This variation of η can be associated with phonon scattering due to disorder at the interface region. The results provide an important understanding of how the growth temperature of the nucleation layer can affect the quality and the properties of the cubic GaN.
Density ratio effects on the topology of coherent turbulent structures in two-way coupled particle-laden channel flows
Authors: Mortimer L. F. , Fairweather M.
Published: October 2020

This investigation considers the effect of density ratio on the modification of coherent turbulent structures in particle-laden channel flows at a shear Reynolds number of Reτ = 180. Direct numerical simulation and Lagrangian particle tracking are used to accurately predict the motion of particles dispersed within the flow at three Stokes numbers, St+ = 0.1, 50, and 92. Particle–fluid coupling is achieved through a local element-based force feedback field in the Navier–Stokes equations, which are solved using a seventh-order accurate spectral element method. After an initial transitory period wherein the effects of particle–fluid interaction are emphasized, the low density ratio particles are found to enhance the turbulence field, increasing the frequency of Q-criterion satisfying regions, while the inertial particles suppress the turbulence, reducing the number of quasistreamwise vortices. Results indicate that the topology of the quasistreamwise vortices is altered by the presence of the particles in the viscous sublayer, the buffer layer, and the log-law region such that the distribution of the third invariant of the deviatoric tensor, R, is widened by the presence of tracer-like particles and made thinner by the inertial particles. This effect reduces the amount of unstable focus/compressing regions and stable focus/stretching regions, which account for the streamwise vortical structures observed in these types of flow. Investigating the instantaneous coupling force field surrounding turbulent structures and low speed streaks shows that particles exert their greatest influence on the fluid in the regions noted, and mechanisms by which the particulate phase interacts with turbulent vortices are analyzed.
Finger instability of oscillating liquid–liquid interface in radial Hele-Shaw cell
Authors: Kozlov Viktor , Karpunin Ivan , Kozlov Nikolai
Published: October 2020

The dynamics of the interface between two immiscible liquids with a high viscosity contrast is studied experimentally when the liquids are pumped through a radial Hele-Shaw cell. Two cases are considered: a monotonous radial displacement of the viscous fluid, when the classical Saffman–Taylor instability develops, and an oscillatory interface motion due to harmonic flowrate modulation in the absence of the average displacement flow. At small amplitudes of flowrate modulation, the interface performs axisymmetric radial oscillations, maintaining the ring shape during the entire period, while with an increase in the amplitude, it loses stability in a threshold manner. In the phase of fluid displacement, finger instability develops at the interface in the form of an azimuthally periodic structure during a fraction of the period. Fingers reach the greatest length in the phase of maximum fluid displacement, while in the contraction phase (maximum displacement toward the cell center), the interface restores its concentric shape. The threshold for the occurrence of finger instability is determined by the relative amplitude of interface oscillations and under conditions of high contrast of viscosities (one liquid oscillates following the “viscous” law and the other obeys the “inviscid” law) coincides at different oscillation frequencies and different average radii of the interface. The discovered type of instability is new and is studied for the first time. A comparison of the wavelengths of the pulsating fingers with the well-known case of continuous displacement of a viscous fluid in a Hele-Shaw cell indicates that the Saffman–Taylor instability mechanism underlies the observed phenomenon.
Hard x-ray single-shot spectrometer at the European X-ray Free-Electron Laser
Authors: Kujala Naresh , Freund Wolfgang , Liu Jia , Koch Andreas , Falk Torben , Planas Marc , Dietrich Florian , Laksman Joakim , Maltezopoulos Theophilos , Risch Johannes , Dall’Antonia Fabio , Grünert Jan
Published: October 2020

The European X-ray Free-Electron Laser Facility in Germany delivers x-ray pulses with femtosecond pulse duration at a repetition rate of up to 4.5 MHz. The free-electron laser radiation is created by the self-amplified spontaneous emission (SASE) process, whose stochastic nature gives rise to shot-to-shot fluctuations in most beam properties, including spectrum, pulse energy, spatial profile, wavefront, and temporal profile. Each spectrum consisting of many spikes varies in width and amplitude that appear differently within the envelope of the SASE spectrum. In order to measure and study the SASE spectrum, the HIgh REsolution hard X-ray single-shot (HIREX) spectrometer was installed in the photon tunnel of the SASE1 undulator beamline. It is based on diamond gratings, bent crystals as a dispersive element, and a MHz-repetition-rate strip detector. It covers a photon energy range of 3 keV–25 keV and a bandwidth of 0.5% of the SASE beam. The SASE spikes are resolved with 0.15 eV separation using the Si 440 reflection, providing a resolving power of 60 000 at a photon energy of 9.3 keV. The measured SASE bandwidth is 25 eV. In this paper, we discuss the design specifications, installation, and commissioning of the HIREX spectrometer. The spectral results using Si (110), Si (111), and C (110) crystals are presented.
Deep neural networks for nonlinear model order reduction of unsteady flows
Authors: Eivazi Hamidreza , Veisi Hadi , Naderi Mohammad Hossein , Esfahanian Vahid
Published: October 2020

Unsteady fluid systems are nonlinear high-dimensional dynamical systems that may exhibit multiple complex phenomena in both time and space. Reduced Order Modeling (ROM) of fluid flows has been an active research topic in the recent decade with the primary goal to decompose complex flows into a set of features most important for future state prediction and control, typically using a dimensionality reduction technique. In this work, a novel data-driven technique based on the power of deep neural networks for ROM of the unsteady fluid flows is introduced. An autoencoder network is used for nonlinear dimension reduction and feature extraction as an alternative for singular value decomposition (SVD). Then, the extracted features are used as an input for a long short-term memory (LSTM) network to predict the velocity field at future time instances. The proposed autoencoder-LSTM method is compared with non-intrusive reduced order models based on dynamic mode decomposition (DMD) and proper orthogonal decomposition. Moreover, an autoencoder-DMD algorithm is introduced for ROM, which uses the autoencoder network for dimensionality reduction rather than SVD rank truncation. The results show that the autoencoder-LSTM method is considerably capable of predicting fluid flow evolution, where higher values for the coefficient of determination R2 are obtained using autoencoder-LSTM compared to other models.
Liquid–liquid transition and polyamorphism
Authors: Tanaka Hajime
Published: October 2020

Two or more liquid states may exist even for single-component substances, which is known as liquid polymorphism, and the transition between them is called liquid–liquid transition (LLT). On the other hand, the existence of two or more amorphous states is called polyamorphism, and the transition between them is called amorphous–amorphous transition (AAT). Recently, we have accumulated a lot of experimental and numerical evidence for LLT and AAT. These intriguing phenomena provide crucial information on the fundamental nature of liquid and amorphous states. Here, we review the recent progress in this field and discuss how we can physically rationalize the existence of two or more liquids (glasses) for a single-component substance. We also discuss the relationship between liquid-, amorphous-, and crystal-polymorphisms, putting a particular focus on the roles of thermodynamics, mechanics, and kinetics.
Numerical simulation of the swirling flow of a finitely extensible non-linear elastic Peterlin fluid
Authors: Khambhampati Krishna T. , Handler Robert A.
Published: October 2020

Viscoelastic fluids have been shown to undergo instabilities even at very low Reynolds numbers, and these instabilities can give rise to a phenomenon called elastic turbulence. This phenomenon, observed experimentally in viscoelastic polymer solutions, is driven by the strong coupling between the fluid velocity and the elasticity of the flow. To explore the emergence of these instabilities in a viscoelastic flow, we have chosen to explore, by means of direct numerical simulations, a particular case called von Kármán swirling flow. The simulations employ the finitely extensible nonlinear Peterlin model to represent the dynamics of a dilute polymer solution. Notably, a log-conformation technique is used to solve the governing equations. This method is useful in overcoming the high Weissenberg number problem. The results obtained from the simulations were generally in good agreement with experiments. The torque on the top plate was decomposed into Newtonian and polymeric components, and it was found that the polymeric component was dominant. In addition, flow visualizations revealed that a toroidal vortex was strongly correlated with the distribution of the stresses on the rotating plate.
Shape evolution and scaling analysis of soluble cylinders in dissolutive flow
Authors: Miao Qing , Yuan Quanzi , Zhao Ya-Pu
Published: October 2020

The evolution of solid shapes in dissolutive flows is studied using molecular dynamics simulations. The final self-similar structures of the solid are distinct under the convection- and diffusion-dominated conditions. Introducing a dimensionless number, Ds, allows characterizing the relative influence of convection and diffusion on the final structure. When convection dominates, the convergent shape of the solid is approximately triangular, while the solid is more likely to be sculptured into a cylinder when diffusion dominates. There is a critical value of Ds that controls the transition between convection- and diffusion-dominated cases. However, the convergent shapes are insensitive to their initial states due to the solid assembly at the nanoscale. Furthermore, we discuss the influences of solid dissolution and assembly on the liquid density along different directions and provide fitting curves for the theoretical density distribution as explained from the Smoluchowski equation. Finally, the scaling laws are constructed to quantify the solid evolution, which can analytically forecast the shape evolution under different dominant factors. We believe that these findings provide theoretical support for structure optimization and industrial applications.
Refined mean field model of heat and momentum transfer in magnetoconvection
Authors: Zürner Till
Published: October 2020

In this article, the theoretical model on heat and momentum transfer for Rayleigh–Bénard convection in a vertical magnetic field by Zürner et al. [“Heat and momentum transfer for magnetoconvection in a vertical external magnetic field,” Phys. Rev. E 94, 043108 (2016)] is revisited. Using new data from recent experimental and numerical studies, the model is simplified and extended to the full range of Hartmann numbers, reproducing the results of the Grossmann–Lohse theory in the limit of vanishing magnetic fields. The revised model is compared to experimental results in liquid metal magnetoconvection and shows that the heat transport is described satisfactorily. The momentum transport, represented by the Reynolds number, agrees less well, which reveals some shortcomings in the theoretical treatment of magnetoconvection.
The Gibbs free energy of cavity formation in a diverse set of solvents
Authors: Sedov Igor , Magsumov Timur
Published: October 2020

The concept of the formation of a solute-sized cavity in a solvent is widely used in the theories of solvation processes; however, most of the studies of cavity formation using atomistic simulations were limited to water and hydrocarbon models. We calculated the Gibbs free energy of cavity formation ΔcavG for a structurally diverse set of 23 common organic solvents. For the calculation, molecular dynamics simulations of solvent boxes were conducted, and the Widom particle insertion method was applied. The results obtained with two different force fields for the same solvent were in good agreement with each other in most cases. The obtained cavity size dependences of ΔcavG allowed ranking the solvents by the free energy cost of creation of a cavity with a certain size. Surprisingly, this cost was somewhat higher in glycerol, formamide, and ethylene glycol than in water. In general, higher values of ΔcavG are observed for the solvents with a branched network of intermolecular hydrogen bonds and strongly polar aprotic solvents. The numerical results can be used to improve the accuracy of the calculation of the cavity term in non-aqueous continuum solvation models.
Elasto-hydrodynamic interaction of two swimming spermatozoa
Authors: Taketoshi Nanami , Omori Toshihiro , Ishikawa Takuji
Published: October 2020

Due to its biological importance in the fertilization process, the swimming of a solitary spermatozoon has been investigated intensively. However, the elasto-hydrodynamic interactions between spermatozoa remain unclear, and the collective swimming of cells has not been fully clarified. In this study, we numerically investigated pairwise interactions of sperm cells in terms of fluid and solid mechanics. To describe fluid–structure interactions between sperm cells, we developed a boundary element–finite element coupling method. When two sperm cells swim side-by-side, their swimming speed may increase compared to solitary swimming. On the other hand, when two sperm cells swim in line, the front sperm swims faster, while the rear sperm swims slower. To reproduce the experimentally observed flagellar synchronization, we employed a geometric clutch hypothesis and proposed a curvature-associated wave-propagation model. The elasto-hydrodynamic synchronization of flagella resulted in an increase in the swimming speeds of side-by-side sperm cells of up to 16%, indicating that elasto-hydrodynamic synchronization is beneficial for cells in terms of swimming speed. The results clarify the fluid–structure interactions of flagellar mechanics and are important in understanding the collective swimming of spermatozoa.
Experimental and numerical study of an electrohydrodynamic pump operating due to the field-enhanced dissociation near a dielectric barrier
Authors: Vasilkov S. A. , Poluektova K. D. , Stishkov Yu. K.
Published: October 2020

So far, electrohydrodynamic (EHD) pumps based on the injection or the field-enhanced dissociation (the Wien effect) at the surface of metal electrodes have been studied. This paper proposes and studies both numerically and experimentally a fundamentally new pump scheme, namely, the EHD pump operating due to the Wien effect in a conical hole located in the solid insulation barrier. An experimental setup of the pump has been created, and performance (pressure vs flow rate) characteristics have been measured that satisfactorily agree with the results of computer simulation. With the size of the hole being a fraction of a millimeter, the proposed system performance is comparable to that of the previously studied EHD pumps.
A theoretical model on vortex ring formation based on the roll-up of a vortex sheet with finite thickness
Authors: Fang Ting-Ting , Yang Li-Jun , Qin Li-Zi
Published: October 2020

The formation process of a vortex ring can be delineated with the roll-up of a vortex sheet, and the latter idealizes the vortex layer into a sheet with zero-thickness in inviscid fluids. In view of the mass transport from the nozzle into the rolling spiral in vortex ring generation experiments, the effects of the finite thickness of the detaching shear layer on the formation model of vortex rings are investigated in the present study. In this paper, we introduced a theoretical model termed a vortex-source sheet, which is able to describe the induced motion of a vortex sheet with nonzero-thickness. A relationship between the flow and the circulation of a fluid element is developed in two-dimensional, inviscid, conservative flows, making the motion equation of the vortex-source sheet discretized into a closed equation set. The numerical solutions show that the predictions of the vortex-source sheet model on the geometric structure of the vortex ring are much closer to the experimental results than the conventional similarity theory. The reasons for this result are also discussed. Moreover, the consideration of the mass transport also gives a deeper insight into the picture of vortex ring generation. However, there still exists a discrepancy between the theoretical prediction and the experimental result on the circulation of the formed vortex rings. We speculate that it may be attributed to the convective entrainment of the environmental fluids during the formation of vortex rings, and this assumption needs to be studied further.
Locomotion of a rotating cylinder pair with periodic gaits at low Reynolds numbers
Authors: Ji Lingbo , van Rees Wim M.
Published: October 2020

We consider the periodic gaits of a microswimmer formed by two rotating cylinders, placed apart at a fixed width. Through a combination of theoretical arguments and numerical simulations, we derive semi-analytic expressions for the system’s instantaneous translational and rotational velocities, as a function of the rotational speeds of each cylinder. We can then integrate these relations in time to find the speed and efficiency of the swimmer for any imposed gait. Here, we focus particularly on identifying the periodic gaits that lead to the highest efficiency. To do so, we consider three stroke parameterizations in detail: alternating strokes, where only one cylinder rotates at a time; tilted rectangle strokes, which combine co- and counter-rotation phases; and smooth strokes represented through a set of Fourier series coefficients. For each parameterization, we compute maximum efficiency solutions using a numerical optimization approach. We find that the parameters of the global optimum, and the associated efficiency value, depend on the average mechanical input power. The globally optimal efficiency asymptotes toward that of a steadily counter-rotating cylinder pair as the input power increases. Finally, we address a possible three-dimensional (3D) extension of this system by evaluating the efficiency of a counter-rotating 3D cylinder pair with spherical end caps. We conclude that the counter-rotating cylinder pair combines competitive efficiency values and high versatility with simplicity of geometry and actuation, and thus forms a promising basis for engineered microswimmers.
α
-(AlxGa1−x)2O3 single-layer and heterostructure buffers for the growth of conductive Sn-doped α-Ga2O3 thin films via mist chemical vapor deposition
Authors: Dang Giang T. , Sato Shota , Tagashira Yuki , Yasuoka Tatsuya , Liu Li , Kawaharamura Toshiyuki
Published: October 2020

A third generation mist chemical vapor deposition (3rd G mist CVD) system was used to grow six single-layer and two heterostructure α-(AlxGa1−x)2O3 buffers on c-plane sapphire substrates for the subsequent deposition of conductive Sn-doped α-Ga2O3 (Sn:α-Ga2O3) thin films. In the six single-layer buffers, the Al contents x increased from 0 to 0.66. The two heterostructure buffers consisted of six ∼20-nm- and ∼100-nm-thick layers laying on top of each other. The 3rd G mist CVD system enabled the growth of these complicated multi-layer heterostructures in a single run, while mono-crystallinity was still maintained in all grown layers. Strain was observed in the 20-nm heterostructure, while the layers in the 100-nm heterostructure almost fully relaxed and the Vegard’s law was followed even when the α-(AlxGa1−x)2O3 layers were stacked on each other. Transmission electron microscopy analyses show that the dislocation densities remained high in the order of 1010 cm−2 despite the employment of the buffers. PtOx and AgOx Schottky diodes (SDs) were fabricated on the Sn:α-Ga2O3 films. The barrier height vs ideality factor plots could be fitted by linear dependences, indicating that the large ideality factors observed in α-Ga2O3 SDs could be explained by the inhomogeneity of the SDs. The extrapolation of the dependences for the PtOx and AgOx SDs yielded homogeneous Schottky barrier heights of ∼1.60 eV and 1.62 eV, respectively, suggesting that the Fermi level was pinned at the Ec − 1.6 eV level. The Sn:α-Ga2O3 film grown on the strained 20-nm heterostructure buffer showed best characteristics overall.
First principles calculations of the vibrational properties of single and dimer F-type centers in corundum crystals
Authors: Platonenko Alexander , Gryaznov Denis , Popov Anatoly I. , Dovesi Roberto , Kotomin Eugene A.
Published: October 2020

The present paper investigates the F-type centers in α-Al2O3 through their electronic and vibrational properties from first principle calculations using a periodic supercell approach, a hybrid functional, and all-electron Gaussian basis sets as implemented in the CRYSTAL17 code. Single F-type and dimer F2-type centers related to oxygen vacancies in various charge states were considered. The defect-induced vibrational modes were identified and found to appear mainly in the low (up to 300 cm−1) and high (above 700 cm−1) frequency regions, depending on the defect charge. The perturbation introduced by the defects to the thermal nuclear motion in the crystal lattice is discussed in terms of atomic anisotropic displacement parameters. The calculated Raman spectra are discussed for the first time for such defects in α-Al2O3, suggesting important information for future experimental and theoretical studies and revealing deeper insight into their behavior.
The dark side of energy transport along excitonic wires: On-site energy barriers facilitate efficient, vibrationally mediated transport through optically dark subspaces
Authors: Davidson Scott , Fruchtman Amir , Pollock Felix A. , Gauger Erik M.
Published: October 2020

We present a novel, counter-intuitive method, based on dark-state protection, for significantly improving exciton transport efficiency through “wires” comprising a chain of molecular sites with an intrinsic energy gradient. Specifically, by introducing “barriers” to the energy landscape at regular intervals along the transport path, we find that undesirable radiative recombination processes are suppressed due to a clear separation of sub-radiant and super-radiant eigenstates in the system. This, in turn, can lead to an improvement in transmitted power by many orders of magnitude, even for very long chains. From there, we analyze the robustness of this phenomenon to changes in both system and environment properties to show that this effect can be beneficial over a range of different thermal and optical environment regimes. Finally, we show that the novel energy landscape presented here may provide a useful foundation for overcoming the short length scales over which exciton diffusion typically occurs in organic photo-voltaics and other nanoscale transport scenarios, thus leading to considerable potential improvements in the efficiency of such devices.
Solvent influence on non-adiabatic interfacial electron transfer at conductive oxide electrolyte interfaces
Authors: Aramburu-Trošelj Bruno M. , Bangle Rachel E. , Meyer Gerald J.
Published: October 2020

The kinetics for interfacial electron transfer (ET) from a transparent conductive oxide (tin-doped indium oxide, ITO, Sn:In2O3) to molecular acceptors 4-[N,N-di(p-tolyl)amino]benzylphosphonic acid, TPA, and [RuII(bpy)2(4,4′-(PO3H2)2-bpy)]2+, RuP, positioned at variable distances within and beyond the electric double layer (EDL), were quantified in benzonitrile and methanol by nanosecond absorption spectroscopy as a function of the thermodynamic driving force, −ΔG°. Relevant ET parameters such as the rate constant, ket, reorganization energy, λ, and electronic coupling, Hab, were extracted from the kinetic data. Overall, ket increased as the distance between the molecular acceptor and the conductor decreased. For redox active molecules within the Helmholtz planes of the EDL, ket was nearly independent of −ΔG°, consistent with a negligibly small λ value. Rips–Jortner analysis revealed a non-adiabatic electron transfer mechanism consistent with Hab < 1 cm−1. The data indicate that the barrier for electron transfer is greatly diminished at the conductor–electrolyte interface.
Electronic-ionic coupling in perovskite based solar cells: Implications for device stability
Authors: Bitton Sapir , Tessler Nir
Published: October 2020

Ion migration into blocking layers toward the metallic electrodes is studied within a semiconductor device model framework. We find that ion leakage into the blocking layers and their accumulation at the electrode interface are significantly affected by the electronic injection barrier at the contact. Specifically, we find that if the device structure promotes, under light, hole (electron) accumulation within the perovskite layer, these excess holes (electrons) would release an almost equivalent number of cations (anions) into the transport layers toward the contacts. Our analysis suggests that it would be beneficial to include intentional doping of the blocking layers and that it should follow the “just enough” strategy.
Mixed bulky cations for efficient and stable Ruddlesden−Popper perovskite solar cells
Authors: Shi Jishan , Jin Xing , Wu Youzhi , Shao Ming
Published: October 2020

2D Ruddlesden–Popper perovskite solar cells (PSCs) with structure formulated as R2MAn−1PbnI3n+1 (R is the organic bulky cation) exhibit superior environmental stability, but their efficiency still lags behind that of their 3D counterpart, which is mainly limited by the insufficient light absorption and carrier transportation. Herein, we incorporated guanidinium (GA+) into the PEA at the “R” site to form mixed bulky cations and investigated the doping effect of GA+ on the photovoltaic performance of layered 2D perovskites. Our results show that incorporating GA+ into the “R” site of 2D PSCs exhibits a stronger and wider light absorption, faster charge carrier mobility, and better quality perovskite films. Consequently, both the short circuit current density (Jsc) and fill factor (FF) of the 2D PSCs were significantly improved. As a result, the energy conversion efficiency (PCE) of the (PEA, GA)2MA4Pb5I16 champion device achieved 15.27%, which is much higher than the 11.58% PCE of the single cation 2D PSCs. Also, the 2D PSCs with the mixed (PEA, GA) cations exhibit improved environmental stability. Our work provides important guidance to obtain efficient and stable 2D PSCs through bulky cation engineering and modulating the interlayer interaction in 2D perovskite.
Isomorph theory beyond thermal equilibrium
Authors: Dyre Jeppe C.
Published: October 2020

This paper generalizes isomorph theory to systems that are not in thermal equilibrium. The systems are assumed to be R-simple, i.e., to have a potential energy that as a function of all particle coordinates R obeys the hidden-scale-invariance condition U(Ra) < U(Rb) ⇒ U(λRa) < U(λRb). “Systemic isomorphs” are introduced as lines of constant excess entropy in the phase diagram defined by density and systemic temperature, which is the temperature of the equilibrium state point with the average potential energy equal to U(R). The dynamics is invariant along a systemic isomorph if there is a constant ratio between the systemic and the bath temperature. In thermal equilibrium, the systemic temperature is equal to the bath temperature and the original isomorph formalism is recovered. The new approach rationalizes within a consistent framework previously published observations of isomorph invariance in simulations involving nonlinear steady-state shear flows, zero-temperature plastic flows, and glass-state isomorphs. This paper relates briefly to granular media, physical aging, and active matter. Finally, we discuss the possibility that the energy unit defining the reduced quantities should be based on the systemic rather than the bath temperature.
One photon’s transmission usefully controls another
Authors: Lopatka Alex
Published: October 2020

To preserve the quantum correlations between two particles of light, researchers mapped the scattering that a photon experienced onto the entangled state.
Tropical soils could be accelerating global warming
Authors: Berkowitz Rachel
Published: October 2020

A field study challenges climate simulations by showing increased carbon loss from warmed low-latitude soils.
High-fat diet leads to elevated lipid accumulation and endoplasmic reticulum stress in oocytes, causing poor embryo development
Authors: Rao Arpitha , Satheesh Aparna , Nayak Guruprasad , Poojary Pooja Suresh , Kumari Sandhya , Kalthur Sneha Guruprasad , Mutalik Srinivas , Adiga Satish Kumar , Kalthur Guruprasad
Published: October 2020

The present study was designed to investigate the effect of diet-induced obesity on endoplasmic reticulum (ER) stress in oocytes. Swiss albino mice (3 weeks old) were fed with a high-fat diet (HFD) for 8 weeks. Oocytes were assessed for lipid droplet accumulation, oxidative stress, ER stress and their developmental potential invitro. High lipid accumulation (P<0.01) and elevated intracellular levels of reactive oxygen species were observed in both germinal vesicle and MII oocytes of HFD-fed mice (P<0.05 and P<0.01 respectively compared with control). Further, expression of the ER stress markers X-box binding protein 1 (XBP1), glucose-regulated protein 78 (GRP78), activating transcription factor 4 (ATF4) and activating transcription factor 6 (ATF6) was significantly (P<0.001) higher in oocytes of the HFD than control group. Oocytes from HFD-fed mice exhibited poor fertilisation and blastocyst rates, a decrease in total cell number and high levels of DNA damage (P<0.01) compared with controls. In conclusion, diet-induced obesity resulted in elevated lipid levels and higher oxidative and ER stress in oocytes, which contributed to the compromised developmental potential of embryos.
Hepatitis B virus surface protein induces oxidative stress by increasing peroxides and inhibiting antioxidant defences in human spermatozoa
Authors: Cheng Lin , Sun Pingnan , Xie Xiaoling , Sun Dongmei , Zhou Qi , Yang Shaozhe , Xie Qingdong , Zhou Xiaoling
Published: October 2020

Hepatitis B virus (HBV) infection may affect sperm motility in patients with HBV. HBV surface protein (HBs) decreases mitochondrial membrane potential, impairs motility and induces apoptotic-like changes in human spermatozoa. However, little is known about how human spermatozoa respond to reactive oxygen species (ROS; mainly peroxides) induced by HBs. In this study, HBs induced supraphysiological ROS levels in human spermatozoa and reduced the formation of 2-cell embryos (obtained from hamster oocytes and human spermatozoa). HBs induced a pre-apoptotic status in human spermatozoa, as well as antioxidant defences by increasing glutathione peroxidase 4 (GPX4) and peroxiredoxin 5 (PRDX5) levels. These results highlight the molecular mechanism responsible for the oxidative stress in human spermatozoa exposed to HBV and the antioxidant defence response involving GPX4 and PRDX5.
Asbestos induces mesothelial cell transformation via HMGB1-driven autophagy
Authors: Xue Jiaming , Patergnani Simone , Giorgi Carlotta , Suarez Joelle , Goto Keisuke , Bononi Angela , Tanji Mika , Novelli Flavia , Pastorino Sandra , Xu Ronghui , Caroccia Natascia , Dogan A. Umran , Pass Harvey I. , Tognon Mauro , Pinton Paolo , Gaudino Giovanni , Mak Tak W. , Carbone Michele , Yang Haining
Published: October 2020

Significance

Millions of people have been exposed to asbestos and are at increased risk of developing mesothelioma, an aggressive malignancy resistant to current therapies. Here, we elucidate critical steps in asbestos carcinogenesis: asbestos induces the release of high mobility group box 1 that triggers autophagy. Autophagy activation constitutes a key biological process that allows some mesothelial cells to survive asbestos cytotoxicity and consequently increases the fraction of DNA-damaged human mesothelial cells susceptible to malignant transformation. We found that the inhibition of autophagy using either chloroquine or the antidepressant drug desmethylclomipramine increased asbestos-induced cell death and reduced asbestos-mediated cell transformation. Our data suggest that these Food and Drug Administration-approved drugs might be repurposed to protect high-risk asbestos-exposed individuals from developing mesothelioma.
Inter-rater reliability in Learner Corpus Research
Authors: Larsson Tove , Paquot Magali , Plonsky Luke
Published: October 2020

In Learner Corpus Research (LCR), a common source of errors stems from manual coding and annotation of linguistic
features. To estimate the amount of error present in a coded dataset, coefficients of inter-rater reliability are used. However, despite
the importance of reliability and internal consistency for validity and, by extension, study quality, interpretability and generalizability,
it is surprisingly uncommon for studies in the field of LCR to report on such reliability coefficients. In this Methods Report, we use a
recent collaborative research project to illustrate the pertinence of considering inter-rater reliability. In doing so, we hope to initiate
methodological discussion on instrument design, piloting and evaluation. We also suggest some ways forward to encourage increased
transparency in reporting practices.
What is a word?
Authors: Böhm Manuela , Mehlem Ulrich
Published: October 2020

Practices of word segmentation in French and Moroccan Arabic by beginning and advanced bilingual writers in two historically and linguistically divergent settings are analysed in a threefold perspective: (1) In the different sociocultural contexts of linguistically heterogeneous France in the 1870’s and a town with remarkable immigration from Morocco in Germany in 2000, dictations constitute monolingual settings of language policy and normativity; (2) structurally, open and closed spellings of (clitic) function and content words indicate constraints of different orthographies, focussing either phonology or morphosyntax; (3) in the framework of contact linguistics, bilingual students write in one of their languages (French, Moroccan Arabic) with resources of other languages (like Breton, German, Classical Arabic).

The results show that the students’ writings are influenced by graphematic structures not directly related to the language dictated. In French Brittany, a great importance of closed spellings may be supported by the agglutinative feature of the Breton language, while the apostrophe as a striking feature of French orthography is used primarily, but often only emblematically, by the students in Gascony. Moroccan Arabic writers in Germany are influenced indirectly by their first school language, German, in the way they mark word boundaries in prepositional phrases (PP) and imperfective verb forms. Classical Arabic, however, remains of marginal influence although both varieties are historically and structurally closely related.
The advanced acquisition of orthography in heritage Turkish in Germany
Authors: Schroeder Christoph
Published: October 2020

The paper investigates Turkish texts from heritage speakers of Turkish in Germany in a pseudo-longitudinal setting, looking at pupils’ texts from the 5th, 7th, 10th and 12th grades. Two types of dynamics are identified in the advanced acquisition1of Turkish orthography in the heritage context. One is the dynamic of language contact, where in certain areas of the orthography, we find a re-interpretation of Turkish principles according to the German model. However, this changes as the pupils grow up. The second dynamic is the heritage situation. The heritage situation on one side leads to the establishment of new practices, and it also leads to a higher degree of variability of spelling solutions in those areas, where the orthographic system of Turkish poses challenges to every writer, whether monolingual and growing up in Turkey or heritage speaker.2
V
OC variation with different molecular weight fractions in highly efficient organic photovoltaic bulk heterojunctions
Authors: Zhen-Chuan Wen , Niu Meng-Si , Wang Tong , Chen Zhi-Hao , Guo Jia-Jia , Qin Chao-Chao , Feng Lin , Yin Hang , Hao Xiao-Tao
Published: October 2020

Tuning molecular weight fractions is one of the most important strategies for optimizing the morphology of bulk heterojunctions (BHJs) to obtain high-performance organic solar cells. Here, we investigate the effects of molecular weight fractions on the performance of state-of-the-art PM6:Y6 BHJ solar cells. A remarkable blueshift in the photoluminescence spectra can be observed with the introduction of the PM6 component. The electroluminescent and morphological analyses indicate that this observation can be attributed to increased charge-transfer state energy and an intermolecular interaction between donor and acceptor, leading to open circuit voltage (V
OC) variations in the photovoltaic device. The transient absorption spectra confirm that the optimized donor:acceptor (D:A) ratio can suppress the generation of polarons and achieve high efficiency exciton dissociation. The results of atomic force microscopy and neutron reflectometry reveal that higher acceptor contents promote the formation of a desirable interpenetrating network and enable high fill factors and short-circuit currents to be obtained.
Graphene-supported single-atom catalysts and applications in electrocatalysis
Authors: Zhang Qin , Zhang Xiaoxiang , Wang Junzhong , Wang Congwei
Published: October 2020

Supported metal nanostructures are the most extensively studied heterogeneous catalysts, benefiting from easy separation, regeneration and affordable cost. The size of the supported metal species is one of the decisive factors in determining the activity of heterogeneous catalysts. Particularly, the unsaturated coordination environment of metal atoms preferably act as the active centers, minimizing these metal species can significantly boost the specific activity of every single metal atom. Single-atom catalysts/catalysis (SACs), containing isolated metals atomically dispersed on or coordinated with the surface of a support material, represent the ultimate utilization of supported metals and maximize metal usage efficiency. Graphene, a two-dimensional star material, exhibiting extraordinary physical and chemical properties, has been approved as an excellent platform for constructing SACs. When atomically dispersed metal atoms are strongly anchored on the graphene surface, featuring ultra-high surface area and excellent electronic properties, SACs offer a great potential to significantly innovate the conventional heterogeneous catalysis, especially in the field of electrocatalysis. In this review, a detailed discussion of graphene-supported SACs, including preparation approaches, characterization techniques and applications on typical electrocatalytic reactions is provided. The advantages and unique features of graphene-supported SACs as efficient electrocatalysts and the upcoming challenges for improving their performance and further practical applications are also highlighted.
Addendum: Cosmological dependence of non-resonantly produced sterile
neutrinos
Authors: Graciela B. Gelmini  , Philip Lu  , Volodymyr Takhistov
Published: October 2020

In this addendum to the article JCAP 12 (2019) 047 on the
cosmological dependence of non-resonantly produced sterile neutrinos we discuss,
using an analytic treatment, the parameter regions of large active-sterile
neutrino mixing angles where sterile neutrinos can approach thermalization. We
show that these additional considerations affect only large active-sterile
neutrino mixing already rejected by different limits. Hence, the allowed sterile
neutrino parameter regions are unaffected.
Review of semi-dry electrodes for EEG recording
Authors: Li Guang-Li , Wu Jing-Tao , Xia Yong-Hui , He Quan-Guo , Jin Hong-Guang
Published: October 2020

Developing reliable and user-friendly electroencephalography (EEG) electrodes remains a challenge for emerging real-world EEG applications. Classic wet electrodes are the gold standard for recording EEG; however, they are difficult to implement and make users uncomfortable, thus severely restricting their widespread application in real-life scenarios. An alternative is dry electrodes, which do not require conductive gels or skin preparation. Despite their quick setup and improved user-friendliness, dry electrodes still have some inherent problems (invasive, relatively poor signal quality, or sensitivity to motion artifacts), which limit their practical utilization. In recent years, semi-dry electrodes, which require only a small amount of electrolyte fluid, have been successfully developed, combining the advantages of both wet and dry electrodes while addressing their respective drawbacks. Semi-dry electrodes can collect reliable EEG signals comparable to wet electrodes. Moreover, their setup is as fast and convenient similar to that of dry electrodes. Hence, semi-dry electrodes have shown tremendous application prospects for real-world EEG acquisition. Herein, we systematically summarize the development, evaluation methods, and practical design considerations of semi-dry electrodes. Some feasible suggestions and new ideas for the development of semi-dry electrodes have been presented. This review provides valuable technical support for the development of semi-dry electrodes toward emerging practical applications.
Total Solar Eclipse Observations: A Treasure Trove from the Source and Acceleration Regions of the Solar Wind
Authors: Rifai Habbal Shadia
Published: October 2020

A comprehensive exploration of the inner corona, namely the spatial span starting from the solar surface out to a few solar radii, is essential for investigating the physical processes responsible for its quiescent and dynamic state. Such an exploration encompasses the source regions of the solar wind, and is thus essential for reliably establishing their link to in-situ measurements, including those from the more recent Parker Solar Probe mission. Total solar eclipses are the only platform available at present to fulfill these requirements, as they offer a spatially uninterrupted diagnosis of the inner corona through multi-wavelength imaging and spectroscopy. This review highlights results from almost two decades of eclipse observations. Particular emphasis is placed on the discovery of the complexity of coronal structures, in particular at the source regions of the solar wind, directly connected to prominences. Complex structures include different manifestations of waves and plasma instabilities. Imaging in coronal emission lines yields the only diagnostic tool, known to date, for the empirical inference of the freeze-in distance of heavy ions. Imaging also enables the mapping of the electron temperature in the inner corona, and its changes in response to the passage of a coronal mass ejection (CME). Furthermore, spectroscopic observations reveal that cool prominence material associated with a CME, travels in tandem, unscathed, into interplanetary space. Multi-wavelength imaging and spectroscopy during total solar eclipses thus yield a treasure trove from the sources and acceleration regions of the solar wind, which beg continued exploitation in search of signatures of coronal heating and solar wind acceleration processes.
Estimating Effective Collision Frequency and Kinetic Entropy Uncertainty in Particle-in-Cell Simulations
Authors: Liang Haoming , Cassak P. A. , Swisdak M. , Servidio Sergio
Published: October 2020

A kinetic entropy diagnostic was systematically developed for fully kinetic collisionless particle-in-cell (PIC) simulations in Liang et al., Phys. Plasmas 26, 082903 (2019). Here, we first show that kinetic entropy can be used to quantitatively evaluate numerical dissipation in the PIC simulation. Assuming numerical effects can be treated using a relaxation time approximation collision operator, the rate of increase of the kinetic entropy is related to the kinetic entropy. The effective collision frequency due to numerical effects is then easy to evaluate in a collisionless PIC simulation. We find an effective collision frequency of approximately a tenth of the ion cyclotron frequency. This could have important implications for collisionless PIC simulation studies of magnetic reconnection, plasma turbulence, and collisionless shocks. Then, we analyze the uncertainty of the local kinetic entropy density at different locations as a function of the chosen velocity space grid. We find that although the numerically obtained kinetic entropy density varies significantly for small or large velocity space grids, there is a range for which the kinetic entropy density is only weakly sensitive to the velocity space grid. Our analysis of the uncertainty suggests a velocity space grid close to the thermal velocity is optimal, and the uncertainty introduced is significantly less than the physical change in kinetic entropy density.
A data-driven MHD model of the weakly-ionized chromosphere
Authors: Sarp Yalim Mehmet , Prasad Avijeet , Pogorelov Nikolai , Zank Gary , Hu Qiang
Published: October 2020

The physics of the solar chromosphere is complex from both theoretical and modeling perspectives. The plasma temperature from the photosphere to corona increases from ∼5, 000 K to ∼1 million K over a distance of only ∼10, 000 km from the chromosphere and the transition region. Certain regions of the solar atmosphere have sufficiently low temperature and ionization rates to be considered as weakly-ionized. In particular, this is true at the lower chromosphere. In this paper, we present an overview of our data-driven magnetohydrodynamics model for the weakly-ionized chromosphere and show a benchmark result. It utilizes the Cowling resistivity which is orders of magnitude greater than the Coulomb resistivity. Ohm’s law therefore includes anisotropic dissipation. We investigate the effects of the Cowling resistivity on heating and magnetic reconnection in the chromosphere as the flare-producing active region (AR) 11166 evolves. In particular, we analyze a C2.0 flare emerging from AR11166 and find a normalized reconnection rate of 0.12.