bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiplet structure for perovskite-type Ba0.9Ca0.1Ti0.9Zr0.1O3 by core–hole spectroscopies
Authors: Herrera-Pérez G. , Solis-Canto O. , Silva-Vidaurri G. , Pérez-García S. , Borja-Urby R. , Paraguay-Delgado F. , Rojas-George G. , Reyes-Rojas A. , Fuentes-Cobas L.
Published: August 2020

Core–hole spectroscopies such as x-ray photoelectron spectroscopy (XPS) and high-resolution electron energy loss spectroscopy (HR-EELS) in combination with multiplet calculation are important tools to elucidate the electronic structure of transition metal compounds. This work presents a comparison between the electronic structure obtained by XPS and HR-EELS for polycrystalline perovskite-type Ba0.9Ca0.1Ti0.9Zr0.1O3. Raman analysis suggests that Ca2+ cations could partly occupy the Ti4+ cations in the B-site of a perovskite structure with the tetragonal phase. A multiplet structure was determined by XPS for Ti 2p and by HR-EELS for Ca L2,3 and Ti L2,3 edges. Octahedral (Oh) symmetry in the crystal field (CF) effects reproduces the local distortion of TiO6 octahedra. The charge transfer (CT) effects were also considered to reproduce L3-edge EELS shoulders and the satellite in the Ti 2p XPS region. CF and CT parameters, 10 Dq, (charge transfer energy) Δ, and (Coulomb repulsion energy) Udd, are reported for future reference. The broadening of the Ti L2-edge suggests the presence of the Coster–Kronig electron decay process. Multiplet calculation in Oh symmetry for the Ca L2,3-edge could support the Raman interpretation.
Two-dimensional BP/
β
-AsP van der Waals heterostructures as promising photocatalyst for water splitting
Authors: Liu Yu-Liang , Shi Ying , Yin Hang , Yang Chuan-Lu
Published: August 2020

Constructing two-dimensional (2D) van der Waals (vdW) heterostructures is becoming a promising way for photocatalytic water splitting to produce hydrogen. In this Letter, we perform a 2D vdW blue phosphorous/β-AsP (BP/β-AsP) heterostructure based on density functional theory calculations. The type II band alignment in the BP/β-AsP vdW heterostructure is beneficial for separating the photogenerated electrons and holes and suppressing their recombination. The BP/β-AsP heterostructure not only keeps a suitable band edge position for the water splitting reaction but also significantly improves the optical absorption in the visible and ultraviolet light region. Appropriate uniaxial strain can change the indirect bandgap of the BP/β-AsP heterostructure into a direct one. The present findings indicate that the BP/β-AsP heterostructure is a promising candidate for applications in photovoltaic devices and photocatalysis.
Numerical investigation of a minority heating scenario in three-ion components plasma on EAST
Authors: Yin Lan , Yang Cheng , Zhang Xinjun , Zheng Pingwei , Liu Haiqing , Li Guoqiang , Wang Yifeng , Li Yingying , Lyu Bo , Zang Qing , Zheng Zhen , Men Zongzheng , Song Chengyi , Huang Qianhong , Chen You , Gong Xueyu
Published: August 2020

Heating with the wave in the ion cyclotron range of frequencies (ICRF) has been used in the development of high-performance H-mode operations in EAST. A different ion cyclotron resonance heating scenario in three-ion component plasma with real experimental parameters on EAST was investigated using a numerical tool. Excellent radio frequency wave absorption was found with an extremely low 3He concentration (0.1%–0.4%) in D-H-(3He) plasma, by adjusting the plasma composition appropriately in our simulation. In this case, the 3He fundamental resonance layer is located between the two ion–ion hybrid resonance-cutoff pairs in close proximity, and therefore E+ of the wave was considerably enhanced near the 3He fundamental resonance layer. The minority 3He tail was estimated to be superenergetic (∼1 MeV) because of the high power carried by each resonant 3He ion. The potential of the three-ion ICRF heating means on EAST was shown, and the scenarios investigated are particularly promising for fast particle generation schemes.
Dynamic manipulation of piezotronic behaviors of composite multiferroic semiconductors through time-dependent magnetic field
Authors: Kong Dejuan , Cheng Ruoran , Zhang Chunli , Zhang Chuanzeng
Published: August 2020

A dynamic non-contact approach to tuning the semiconducting (SM) properties of multiferroic composite semiconductor (MCS) fibers by applying a time-dependent magnetic field is proposed and theoretically demonstrated in this paper. The considered fiber is symmetric with respect to its geometrical middle plane and made from two outer piezomagnetic (PM) layers, two piezoelectric (PE) layers, and a SM core. Through the interface strain or deformation transfer, the MCS fiber exhibits not only the conventional magnetoelectric (ME) coupling effect but also the comprehensive magneto-electro-semiconductive (MES) coupling effect. Based on a one-dimensional model for the MCS fibers, we present the analytical solutions for the physical fields of the MCS fiber with a pure longitudinal deformation under a time-dependent magnetic field. The electrons redistribute themselves in the MCS fiber under the driving of the induced piezoelectric field due to the MES coupling effect. Near the natural frequencies, the magnetic field has a remarkable tuning effect. The ME and MES coefficients achieve their local peak values at the natural frequencies. There is an optimal range for the volume fraction of the PM or PE layer for the MES coupling effects. We can manipulate the electrons to assemble in multiple local regions in the MCS fiber by setting the exciting frequency to a specific higher natural frequency. This provides a new way to explore multi-tunnel electronic devices through the dynamic contactless magnetic control approach.
Two-dimensional hybrid organic–inorganic perovskites as emergent ferroelectric materials
Authors: Hou Yuchen , Wu Congcong , Yang Dong , Ye Tao , Honavar Vasant G. , van Duin Adri C. T. , Wang Kai , Priya Shashank
Published: August 2020

Hybrid organic–inorganic perovskite (HOIP) materials have attracted significant attention in photovoltaics, light emission, photodetection, etc. Based on the prototype metal halide perovskite crystal, there is a huge space for tuning the composition and crystal structure of this material, which would provide great potential to render multiple physical properties beyond the ongoing emphasis on the optoelectronic property. Recently, the two-dimensional (2D) HOIPs have emerged as a potential candidate for a new class of ferroelectrics with high Curie temperature and spontaneous polarization. Room-temperature solution-processability further makes HOIP a promising alternative to traditional oxide ferroelectrics such as BaTiO3 and PbTiO3. In this perspective, we focus on the molecular aspects of 2D HOIPs, their correlation with macroscopic properties, as well as the material design rules assisted by advanced simulation tools (e.g., machine learning and atomistic modeling techniques). The perspective provides a comprehensive discussion on the structural origin of ferroelectricity, current progress in the design of new materials, and potential opportunities and challenges with emerging materials. We expect that this perspective will provide inspiration for innovation in 2D HOIP ferroelectrics.
Enhanced stability of free viscous films due to surface viscosity
Authors: Choudhury Anjishnu , Paidi Venkatesh Kumar , Kalpathy Sreeram K. , Dixit Harish N.
Published: August 2020

The stability of a thin liquid film bounded by two free surfaces is examined in the presence of insoluble surface-active agents. This study is broadly aimed at understanding enhanced stability of emulsions with the increasing surface concentration of surface-active agents. Surface-active agents not only cause gradients in surface tension but could also render surface viscosity to be significant, which could vary with surface concentration. We employ two phenomenological models for surface viscosity, a linear viscosity model and a nonlinear viscosity model. In the latter, surface viscosity diverges at a critical concentration, which is termed the “jamming” limit. We show that rupture can be significantly delayed with high surface viscosity. An analysis of the “jamming” limit reveals that Γi(nl)>3D/M provides a simple criterion for enhanced stability, where Γi(nl), D, and M are the normalized initial surfactant concentration, disjoining pressure number, and Marangoni number, respectively. Nonlinear simulations suggest that high surface viscosity renders free films remarkably stable in the jamming limit, and their free surfaces behave like immobile interfaces consistent with experimental observations. Furthermore, it is shown that rupture times can be arbitrarily increased by tuning the initial surfactant concentration, offering a fluid dynamical route to stabilization of thin films.
Energy budget of a viscoelastic planar liquid sheet in the presence of gas velocity oscillations
Authors: Jia Bo-qi , Xie Luo , Yang Li-jun , Fu Qing-fei , Cui Xiao
Published: August 2020

This study investigates the energy budget of a viscoelastic planar liquid sheet in the presence of gas velocity oscillations. The energy budget is studied in different unstable regions, and the results are very different from those obtained for steady basic flow. The work done by surface tension and aerodynamic forces is periodic, leading to the growth of standing waves on liquid sheets. The positive work done by aerodynamic forces is the main cause of the instability, as for steady basic flow. However, treating the negative work of the surface tension as an increment in the surface energy is an effective means of determining the instability mechanisms. The unsteady basic flow causes the rate of change in the work done by viscosity and elasticity to vary periodically. An increase in elasticity and a decrease in deformation retardation promote the instability by increasing the work done by the gas medium, with reduced dissipation only as a secondary factor. This effect is more significant in parametric unstable regions than in the Kelvin–Helmholtz unstable region.
A structural impedance measurement method by using polyvinylidene fluoride as actuator and sensor
Authors: Zhang Xin , Xu Jiawen , Yan Ruqiang
Published: August 2020

Polyvinylidene fluoride (PVDF) patches have extremely small Young’s modulus and piezoelectric coefficients. They are usually chosen as sensors in the structural impedance measurement for health monitoring. In this paper, a novel method is demonstrated for structural impedance measurement using PVDF patches as actuators and sensors. The impedance of the host structure is decoupled from the capacitance impedance of the piezoelectric transducer by using one of the patches as the actuator and the other as the sensor. Phase sensitive detection is then adopted to recover weak impedance signals in the experimental studies. This technique enables measurement of the resonant frequencies and further identification of the health condition of the host structure. The superiority of this method is illustrated theoretically comparing to the conventional impedance-base method. A prototype consisting of a metal cantilever with two PVDF patches is fabricated and tested. Experimental results demonstrate the effectiveness of the proposed method in the detection of the resonance of the substrate precisely with respect to FEM simulation and the results under base-movement excitations. Moreover, mass change induced impedance shifting can be obtained.
Magnon-drag thermoelectric transport with skyrmion structure
Authors: Hoshi Koujiro , Yamaguchi Terufumi , Takeuchi Akihito , Kohno Hiroshi , Ohe Jun-ichiro
Published: August 2020

Thermoelectric effects driven by magnetization dynamics under a temperature gradient are studied for ferromagnets with and without a skyrmion structure. We calculate charge currents in a four-terminal geometry using the adiabatic pumping formula with full account of magnetization dynamics based on the stochastic Landau–Lifshitz–Gilbert equation. The longitudinal current (Seebeck effect) is induced from the thermally driven spin waves via the spin-transfer and momentum-transfer processes, and these two processes contribute constructively (destructively) in ferromagnets having a negative (positive) s-d exchange interaction. The transverse currents (anomalous Nernst effect) arise in proportion to the number of skyrmions, whose mechanism is identified as the thermal topological Hall effect of magnons followed by the momentum-transfer drag process.
Investigation on explosive emission and attenuation processes of an intense current electron beam diode with annular graphite cathode via 24 framing camera
Authors: Wang Tengfang , Huang Hua , Liu Zhenbang , Li Shifeng , Zhao Guangyi , Jin Xiao , Peng Shuming
Published: August 2020

An experimental study of an intense current electron beam diode with a foil-free annular graphite cathode is carried out. The explosive emission images of a graphite cathode at discharging voltages of 240 kV and 780 kV and the attenuation images of cathode carbon ions at different magnetic fields are recorded using a 24-framing camera for the first time. The experimental results show that when the discharging voltage is 240 kV, the light spots of the plasma generated by the explosive emission process are randomly distributed over the annular cathode and the size and brightness of the light spots of the plasma are also randomly distributed; when the discharging voltage is 780 kV, if the background light generated by Čerenkov radiation is not taken into account, the light spots of the plasma generated by the explosion emission is more uniform than that when the discharging voltage is 280 kV and the brightness of the light spots of the plasma is higher, too. Meanwhile, when the axial magnetic field strength is less than 0.77 T, the plasma spots appear in the gap between the cathode and the anode. The smaller the axial magnetic field strength is, the higher the brightness of the plasma spots will be. In addition, when the discharging voltage is 780 kV/200 ns and the axial magnetic field strength is 0.77 T, a rough calculation indicates that the axial diffusion velocity of the cathode carbon ions ranges from 1.77 cm/μs to 2.1 cm/μs.
Frequency conversion through nonlinear mixing in acoustic waves
Authors: Schneider Joseph D. , Lu Ting , Tiwari Sidhant , Zou Xiating , Mal Ajit , Candler Robert N. , Wang Yuanxun Ethan , Carman Gregory P.
Published: August 2020

Frequency conversion is an essential tool in modern communication devices. Traditionally, frequency conversion is achieved through parametric coupling via nonlinear inductors or capacitors whose reactance is modulated by a carrier wave. In this study, nonlinear acoustic Lamb wave devices are explored for simultaneous signal filtering and frequency conversion. Three sets of interdigitated transducers are fabricated on a piezoelectric aluminum nitride (AlN) thin film to provide a carrier wave, a low-power signal wave, and to receive a frequency converted mixed wave. Two devices are fabricated and tested to demonstrate frequency upconversion and downconversion by utilizing mechanical nonlinearity of AlN, and the results are compared to a nonlinear circuit model. The nonlinear circuit model is used to link experimentally observed phenomenon to the acoustic material's intrinsic nonlinearity. The nonlinearity of AlN reaches a maximum of 2.8% with a carrier wave power at 28 dBm. An analytical model is used to predict device performance along with physical dimensions. These analytical results show that nonlinear acoustic mixers and filters can approach sub-millimeter sizes, which is orders-of-magnitude smaller than conventional structures using nonlinear inductors and capacitors.
Full-dimensional MRCI-F12 potential energy surface and dynamics of the F(2P3/2) + C2H6 → HF + C2H5 reaction
Authors: Papp Dóra , Czakó Gábor
Published: August 2020

We report a detailed quasi-classical dynamics study on a new full-dimensional multireference spin–orbit-corrected potential energy surface (PES) for the F(2P3/2) + C2H6 → HF + C2H5 reaction. For the PES development, the Robosurfer program package is applied and the MRCI-F12+Q(5,3)/aug-cc-pVDZ energy points are fitted using the monomial symmetrization approach of the permutationally invariant polynomial method. Our simulations provide substantial reaction probabilities and sharply increasing cross sections with an increase in collision energy for this early- and negative-barrier reaction. A direct rebound/stripping mechanism is preferred at low/high collision energies, and the initial translational energy turns out to convert mostly into product recoil, whereas the reaction energy excites the HF vibration. Vibrational and vibrationally resolved rotational state distributions of the HF product obtained from our computations agree well with the single-collision experimental data for the vHF = 1, 2, and 3 states.
Well-posedness of a higher dispersion KdV equation on the half-line
Authors: Yan Fangchi
Published: August 2020

The initial-boundary value problem (ibvp) for the mth order Korteweg–de Vries (KdVm) equation on the half-line is studied by extending a novel approach recently developed for the well-posedness of KdV on the half-line, which is based on the solution formula produced via the Fokas unified transform method for the associated forced linear ibvp. Replacing in this formula the forcing by the nonlinearity and using data in Sobolev spaces suggested by the space–time regularity of the Cauchy problem of the linear KdVm equation give an iteration map for the ibvp, which is shown to be a contraction in an appropriately chosen solution space. The proof relies on key linear estimates and a bilinear estimate similar to the one used for the KdV equation on the line by Kenig, Ponce, and Vega [J. Am. Math. Soc. 4, 323–347 (1991)].
Hybrid metamaterials enable multifunctional manipulation of mechanical waves on solid-fluid interfaces
Authors: Wang Xiaole , Luo Xudong , Huang Zhenyu
Published: August 2020

Mechanical waves exhibit complex propagations and waveform transitions on the interfaces of different media. By attaching an ultra-thin layer including local resonators on a solid panel, we demonstrate that this ultra-thin layer contains two control paths for solid and air, manipulating elastic and sound waves on the solid–air interface, respectively. Owing to simultaneously breaking the spatial symmetry of the solid panel and adjusting the boundary impedance of the solid–air interface, the proposed ultra-thin layer combines three operating states that are unique to each of the existing mechanical wave metamaterials. Specifically, we observe the “sound state” for intensely reflecting sound waves at the local anti-resonance, the “elastic state” for completely preventing elastic waves at the local resonance, and the “transition state” for totally converting elastic waves into sound waves at the entire monopole-type resonance. Hence, we denote such an ultra-thin layer as the “hybrid metamaterial.” Our work may broaden the way of designing multifunctional materials and devices for manipulating mechanical waves.
Bubble dynamics of Rayleigh–Taylor flow
Authors: Ni Weidan , Zhang Yousheng , Zeng Qinghong , Tian Baolin
Published: August 2020

A flow of semi-bounded Rayleigh–Taylor instability (SB-RTI) is constructed and simulated to understand the bubble dynamics of the multi-mode Rayleigh–Taylor mixing (MM-RTM). SB-RTI is similar to the well-known single-mode Rayleigh–Taylor instability (SM-RTI), and it acts as a bridge from SM-RTI to MM-RTM. This idea is inspired by Meshkov’s recent experimental observation on the structure of the mixing zone of MM-RTM [E. E. Meshkov, J. Exp. Theor. Phys. 126, 126–131 (2018)]. We suppose that the bubble mixing zone consists of two parts, namely, the turbulent mixing zone at the center and the laminar-like mixing zone nearby the edge. For the latter, the bubble fronts are situated in an environment similar to that of SM-RTI bubbles in the potential flow stage, but with a much looser environment between neighboring bubbles. Therefore, a semi-bounded initial perturbation is designed to produce a bubble environment similar to that in MM-RTM. A non-dimensional potential speed of FrpSB≈0.63 is obtained in SB-RTI, which is larger than that of FrpSM=0.56 in SM-RTI. Combining this knowledge and the widely reported quadratic growth coefficient of αb ≈ 0.025 in the short-wavelength MM-RTM, we derive β ≡ D(t)/hb(t) ≈ (1 + A)/4. This relation is consistent with the MM-RTM simulations from Dimonte et al. [Phys. Fluids 16, 1668–1693 (2004)]. The current three-dimensional and previous two-dimensional results [Zhou et al., Phys. Rev. E 97, 033108 (2018)] support a united mechanism of bubble dynamics in short-wavelength MM-RTM.
Influence of seed priming techniques on grain yield and economic returns of bread wheat planted at different spacings
Authors: Farooq Muhammad , Hussain Mubshar , Habib Muhammad Mazhar , Khan Muhammad Shoaib , Ahmad Imran , Farooq Shahid , Siddique Kadambot H. M.
Published: August 2020

A 3-year study evaluated the effect of different seed-priming techniques on the performance of two bread wheat (Triticum aestivum L.) cultivars, Seher-2006 and Shafaq-2006, planted in rows spaced at 22.5 or 30 cm. Three seed priming techniques—on-farm priming, hydropriming, and osmopriming (using CaCl2)—and an untreated control (dry seeds) were included in the study. Seed priming resulted in earlier and more uniform crop emergence and improved allometric and yield-related traits compared with untreated seeds. Hydropriming and osmopriming significantly improved the allometric traits of Seher-2006 planted at 22.5-cm row spacing and Shafaq-2006 planted at 30-cm row spacing each year. The combination of osmopriming and 30-cm row spacing produced the highest number of productive tillers, number of grains per spike and 1000-grain weight across all experimental years. The highest grain yield and harvest index were recorded for osmopriming and 22.5-cm row spacing each year. Shafaq-2006 produced higher biological yield, whereas Seher-2006 produced the higher grain yield and harvest index. Osmoprimed seeds planted at 22.5-cm row spacing recorded the highest economic returns and benefit:cost ratios in both cultivars. In conclusion, planting osmoprimed seeds of wheat in 22.5-cm spaced rows could be effectively used to increase productivity and economic returns.
The effect of low-intensity prescribed burns in two seasons on litterfall biomass and nutrient content
Authors: Espinosa J. , Madrigal J. , Pando V. , de la Cruz A. C. , Guijarro M. , Hernando C.
Published: August 2020

Litterfall production and composition, fall pattern and nutrient content were studied in a mixed stand of Pinus nigra and Pinus pinaster (El Pozuelo), as well as in a pure stand of Pinus nigra (Beteta) in the Cuenca Mountains in order to determine the effect of two-season prescribed burning treatments. Needles were the most abundant fraction. Pinecone fraction decreased after burning in the mixed stand and the opposite occurred in the pure stand. The inflorescence fraction showed a decrease in the spring-burned plots at El Pozuelo and Beteta. Bark, branch and miscellaneous fractions were affected mainly by meteorological events. Low-intensity prescribed burning was not found to cause significant perturbations. The perturbation was mitigated over the years. An immediate effect of prescribed burning in spring was seen at El Pozuelo and Beteta, although it was more significant for the pure stand. The effect of prescribed burning in autumn at Beteta had a delayed response. As regards nutrient contents, no differences in carbon concentrations were detected. Overall, an increasing trend in N, P, K concentrations in needles after the burning treatment was found. Calcium was not a limiting factor. Magnesium content exhibited no clear trend.
Alpha-lipoic acid ameliorates H2O2-induced human vein endothelial cells injury via suppression of inflammation and oxidative stress
Authors: Wang Wei , An Li-Ping , Li Yun-Feng , An Ran , Bian Zhe , Liu Wei-Zhe , Song Qiu-Hang , Li Ai-Ying
Published: August 2020

The study was aimed to investigate the effect of alpha-lipoic acid (ALA) on human umbilical vein endothelial cells (HUVECs) injury induced by hydrogen peroxide (H2O2) and to explore its possible mechanisms. We established the H2O2-induced HUVECs injury model and the ALA treatment groups in which HUVECs were co-incubated with H2O2 (250 μmol/L) and different final concentrations of ALA (100,200,400 μmol/L) for 48 h. Cell survival rate assay and LDH activity assay were carried out. The levels of related proteins were performed by Western Blot. We observed that H2O2 administration resulted in an increase in the LDH activity and a decrease in cell survival rate. The expression levels of Nox4, Bax, NF-κB p65, Caspase-9, Caspase-3, iNOS, VCAM-1 and ICAM-1 were up-regulated, while the expression level of Bcl-2 was down-regulated. All these factors were significantly improved by ALA treatment. In brief, ALA treatment ameliorates H2O2-induced HUVECs damage by inhibiting inflammation and oxidative stress.
A time domain factorization method for obstacles with impedance boundary conditions
Authors: Haddar Houssem , Liu Xiaoli
Published: August 2020

We consider the inverse acoustic time domain scattering problem for absorbing scatterers modeled by impedance boundary conditions. We present and analyze a factorization method for reconstructing the obstacle boundary from far field measurements. The analysis is based on using the Laplace transform and proving the coercivity of the solution operator in suitable weighted spaces in time. This leads us to consider a modified far field operator parameterized by the imaginary part of Laplace variable which is different but can be arbitrarily close to the original far field operator. As a proof of concept we also provide some preliminary numerical examples to test and discuss the effectiveness of the resulting inversion method when applied to the original far field operator.
Auto-oscillations for the coupling between breathing mode and chiral switching in magnetic skyrmions
Authors: Hu Chenglong , Ji Lianze , Zhao Rongzhi , Chen Wenchao , Zhang Xuefeng
Published: August 2020

Magnetic skyrmions are topological protected nanometric swirling spin structures, and usually possess a fixed chiral feature. Herein, we theoretically demonstrate a dynamic switching for the chirality in magnetic skyrmions by optimizing the spin-transfer torque (STT). Such a switching process is coupled with the breathing mode, presented as an auto-oscillation phenomenon. In this case, the STT plays a role as the compensation of the intrinsic magnetic damping over a period of oscillation. The oscillation frequency could be tuned by the applied current density and type, and the material parameters such as the anisotropy constant and ferromagnetic exchange coefficient. Our results would be significant for designing nanoscale spin-transfer nano-oscillators.
Evaluation of the impact of faulty scanning trajectories in robot-based x-ray computed tomography
Authors: Hiller Jochen , Landstorfer Peter , Marx Philipp , Herbst Matthias
Published: August 2020

X-ray computed tomography (CT) imaging for industrial applications is limited to certain physical conditions to be fulfilled. The size of the measuring object and the accumulated wall thickness are two fundamental conditions. An omission of these conditions by not capturing object attenuation information by the x-ray detector leads to missing data in the 3D reconstruction process and results as a consequence in image degradation and artifacts. Conventional industrial x-ray CT is based on cone-beam projections and circular or helical scanning trajectories using linear axis and a rotary (lift) table. For many inspection tasks on big-sized or unusually shaped objects the physical limits for obtaining a sufficient high image quality are reached very quickly when using conventional CT systems. Industrial six-axis robots offer much more flexibility with respect to the conditions mentioned earlier and can overcome the limitations of conventional scanners. In the present work we characterized an industrial six-axis robot in its working space following ISO 9283 in terms of pose accuracy and pose repeatability. These results are then used to simulate faulty scanning trajectories in terms of pose deviations where a single robot is used as an object manipulator to rotate virtual specimens on a circular trajectory resulting in different (faulty) reconstruction datasets. These datasets are evaluated visually and by using performance parameters and geometrical features in order to determine the reproduction fidelity (performance) of a one arm robot-based CT system depending on different pose errors. With the results obtained it was shown that a robot-based CT system of type B (in our classification scheme) using one robot as object manipulator should be able to reach a spatial resolution power in the range of the voxel size (in our case 200 µm) and smaller (neglecting effects from focal spot size, detector unsharpness from x-ray to light conversation and scatter radiation) if systematic pose errors are compensated using appropriate calibration methods.
Melting of tungsten under uniaxial and shear stresses: molecular dynamics simulation
Authors: Akzhigitov Dulat , Srymbetov Tamerlan , Golman Boris , Spitas Christos , Utegulov Zhandos N
Published: August 2020

Understanding melting processes in refractory materials under external stresses is important and can be of particular interest in harsh environment applications ranging from aerospace to nuclear and fusion energy where these materials have to simultaneously withstand the effect of high temperatures and complex stress states in such ways, that a melting process might be initiated in extreme conditions. However, most if not all of the prior research was focused on melting phenomena in the presence of hydrostatic compression. In our work, we investigate melting phenomena in pure tungsten under uniaxial tension, uniaxial compression, hydrostatic tension, and shear stress states. We explore these relationships numerically by molecular dynamics simulations employing extended Finnis–Sinclair (EFS) potential and two-phase method and compare our results with theoretical and experimental findings reported in the literature. The melting behaviour was investigated for all the studied stress states and compared both quantitatively and qualitatively on the basis of equivalent strain, Cauchy stress tensor invariants, and maximum shear stress. For uniaxial tension, hydrostatic tension, and shear stress an abrupt decline of stress-induced melting point values was detected after certain critical stress values. New high-temperature thermo-mechanical results are correlated with intricate structural changes taking place on the atomic scale during metal-melt phase transition.
Simulation using Excel: reservoirs exchanging heat through a conducting rod
Authors: Ladino L A
Published: August 2020

In this work we discuss the intricacies of a simulation using the MS Excel spreadsheet that allows to study in detail the process of heat transfer between two reservoirs at different temperatures through a conducting rod when heat losses are neglected. The proposed physical model computes the time dependence of the reservoir temperatures and delivers reasonable results. This simulation can be used in a first year course in general physics.
A two-dimensional version of Newton’s cradle
Authors: Cross Rod
Published: August 2020

Three billiard balls arranged in a triangle were impacted head-on by another
billiard ball. Since there were more unknown velocities after the collision than
the two conservation equations, several guesses of possible outcomes were
explored. The same problem arises even if the three balls are arranged in a
straight line, as they are in Newton’s cradle. One guess was found to be
consistent with experimental results.
Punching holes in light: recent progress in single-shot coded-aperture optical imaging
Authors: Liang Jinyang
Published: August 2020

Single-shot coded-aperture optical imaging physically captures a code-aperture-modulated optical signal in one exposure and then recovers the scene via computational image reconstruction. Recent years have witnessed dazzling advances in various modalities in this hybrid imaging scheme in concomitant technical improvement and widespread applications in physical, chemical and biological sciences. This review comprehensively surveys state-of-the-art single-shot coded-aperture optical imaging. Based on the detected photon tags, this field is divided into six categories: planar imaging, depth imaging, light-field imaging, temporal imaging, spectral imaging, and polarization imaging. In each category, we start with a general description of the available techniques and design principles, then provide two representative examples of active-encoding and passive-encoding approaches, with a particular emphasis on their methodology and applications as well as their advantages and challenges. Finally, we envision prospects for further technical advancement in this field.
Dynamical network size estimation from local observations
Authors: Tang Xiuchuan , Huo Wei , Yuan Ye , Li Xiuting , Shi Ling , Ding Han , Kurths Jürgen
Published: August 2020

Here we present a method to estimate the total number of nodes of a network using locally observed response dynamics. The algorithm has the following advantages: (a) it is data-driven. Therefore it does not require any prior knowledge about the model; (b) it does not need to collect measurements from multiple stimulus; and (c) it is distributed as it uses local information only, without any prior information about the global network. Even if only a single node is measured, the exact network size can be correctly estimated using a single trajectory. The proposed algorithm has been applied to both linear and nonlinear networks in simulation, illustrating the applicability to real-world physical networks.
Non-equilibrium atomic simulation for Frenkel–Kontorova model with moving dislocation at finite temperature*
Authors: Liu Baiyili , Tang Shaoqiang
Published: August 2020

We apply the heat jet approach to realize atomic simulations at finite temperature for a Frenkel–Kontorova chain with moving dislocation. This approach accurately and efficiently controls the system temperature by injecting thermal fluctuations into the system from its boundaries, without modifying the governing equations for the interior domain. This guarantees the dislocation propagating in the atomic chain without nonphysical damping or deformation. In contrast to the non-equilibrium Nosé–Hoover heat bath, the heat jet approach efficiently suppresses boundary reflections while the moving dislocation and interior waves pass across the boundary. The system automatically returns back to the equilibrium state after all non-thermal motions pass away. We further apply this approach to study the impact of periodic potential and temperature field on the velocity of moving dislocation.
Application of topological soliton in modeling protein folding: Recent progress and perspective
Authors: Peng Xu-Biao , Liu Jiao-Jiao , Dai Jin , Niemi Antti J , He Jian-Feng
Published: August 2020

Proteins are important biological molecules whose structures are closely related to their specific functions. Understanding how the protein folds under physical principles, known as the protein folding problem, is one of the main tasks in modern biophysics. Coarse-grained methods play an increasingly important role in the simulation of protein folding, especially for large proteins. In recent years, we proposed a novel coarse-grained method derived from the topological soliton model, in terms of the backbone C
α
chain. In this review, we will first systematically address the theoretical method of topological soliton. Then some successful applications will be displayed, including the thermodynamics simulation of protein folding, the property analysis of dynamic conformations, and the multi-scale simulation scheme. Finally, we will give a perspective on the development and application of topological soliton.
The effects of Er3+ ion concentration on 2.0-μm emission performance in Ho3+/Tm3+ co-doped Na5Y9F32 single crystal under 800-nm excitation*
Authors: Ding Benli , Zhou Xiong , Zhang Jianli , Xia Haiping , Song Hongwei , Chen Baojiu
Published: August 2020

Na5Y9F32 single crystals doped with ∼ 0.8-mol% Ho3+, ∼ 1-mol% Tm3+, and various Er3+ ion concentrations were prepared by a modified Bridgman method. The effects of Er3+ ion concentration on 2.0-μm emission excited by an 800-nm laser diode were investigated with the help of their spectroscopic properties. The intensity of 2.0-μm emission reached to maximum when the Er3+ ion concentration was ∼ 1 mol%. The energy transfer mechanisms between Er3+, Ho3+, and Tm3+ ions were identified from the change of the absorption spectra, the emission spectra, and the measured decay curves. The maximum 2.0-μm emission cross section of the Er3+/Ho3+/Tm3+ tri-doped Na5Y9F32 single crystal reached 5.26 × 10−21 cm2. The gain cross section spectra were calculated according to the absorption and emission cross section spectra. The cross section for ∼ 2.0-μm emission became a positive gain once the inversion level of population was reached 30%. The energy transfer efficiency was further increased by 11.81% through the incorporation of Er3+ ion into Ho3+/Tm3+ system estimated from the measured lifetimes of Ho3+/Tm3+- and Er3+/Ho3+/Tm3+-doped Na5Y9F32 single crystals. The present results illustrated that the Er3+/Ho3+/Tm3+ tri-doped Na5Y9F32 single crystals can be used as promising candidate for 2.0-μm laser.
Tunable dual-band terahertz graphene absorber with guided mode resonances*
Authors: Wu Jun , Liu Xia-Yin , Huang Zhe
Published: August 2020

A tunable dual-band terahertz absorber is designed and investigated. The unit cell of the proposed absorber consists of a graphene monolayer on a guided-mode resonant filter. The graphene absorber presents >40% absorption at two resonance frequencies, which is attributed to the guided mode resonances with different mode numbers. The electric field intensity distribution is analyzed to disclose the physical mechanism of such a dual-band absorption effect. Furthermore, the influence of optical properties of graphene, including Fermi level and relaxation time, on the absorption spectra are investigated. Finally, the influence of geometric parameters on the absorption spectrum is studied, which will provide useful guidance for the fabrication of this absorber. We believe that the results may be useful for developing the next-generation graphene-based optoelectronic devices.
Effect of source temperature on phase and metal–insulator transition temperature of vanadium oxide films grown by atomic layer deposition*
Authors: Meng Bingheng , Wang Dengkui , Guo Deshuang , Liu Juncheng , Fang Xuan , Tang Jilong , Lin Fengyuan , Wang Xinwei , Fang Dan , Wei Zhipeng
Published: August 2020

Vanadium oxide films were grown by atomic layer deposition using the tetrakis[ethylmethylamino] vanadium as the vanadium precursor and H2O as the oxide source. The effect of the source temperature on the quality of vanadium oxide films and valence state was investigated. The crystallinity, surface morphology, film thickness, and photoelectric properties of the films were characterized by x-ray diffraction, atomic force microscope, scanning electron microscope, I–V characteristics curves, and UV–visible spectrophotometer. By varying the source temperature, the content of V6O11, VO2, and V6O13 in the vanadium oxide film increased, that is, as the temperature increased, the average oxidation state generally decreased to a lower value, which is attributed to the rising of the vapor pressure and the change of the ionization degree for organometallics. Meanwhile, the root-mean-square roughness decreased and the metal–insulator transition temperature reduced. Our study is great significance for the fabrication of vanadium oxide films by atomic layer deposition.
Improving the colonization and functions of Wharton’s Jelly-derived mesenchymal stem cells by a synergetic combination of porous polyurethane scaffold with an albumin-derived hydrogel
Authors: Lutzweiler G , Barthes J , Charles A L , Ball V , Louis B , Geny B , Vrana N E
Published: August 2020

The development of neo-tissues assisted by artificial scaffolds is continually progressing, but the reproduction of the extracellular environment surrounding cells is quite complex. While synthetic scaffolds can support cell growth, they lack biochemical cues that can prompt cell proliferation or differentiation. In this study, Wharton’s Jelly-derived mesenchymal stem cells are seeded on a polyurethane (PU) scaffold combined with a hydrogel based on bovine serum albumin (BSA). BSA hydrogel is obtained through thermal treatment. While such treatment leads to partial unfolding of the protein, we show that the extent of denaturation is small enough to maintain its bioactivity, such as protein binding. Therefore, BSA provides a suitable playground for cells inside the scaffold, allowing higher spreading, proliferation and matrix secretions. Furthermore, the poor mechanical properties of the hydrogel are compensated for by the porous PU scaffold, whose architecture is well controlled. We show that even though PU by itself can allow cell adhesion and protein secretion, cell proliferation is 3.5 times higher in the PU + BSA scaffolds as compared to pure PU after 21 d, along with the non-collagenous protein secretions (389 versus 134 μmmg
−1). Conversely, the secretion of sulphated glycosaminoglycans is 12.3-fold higher in the scaffold made solely of PU. Thereby, we propose a simple approach to generating a hybrid material composed of a combination of PU and BSA hydrogel as a promising scaffold for tissue regeneration.
On the problem of formation the cultures of the Early Iron Age and the Middle Ages of the taiga and tundra zones in the extreme North-East of Europe
Authors: Murygin A
Published: August 2020

The article summarizes the results of the excavations of the settlement of reindeer hunters (Rangifer tarandus) in the settlement More-Yu II (Bolshezemelskaya tundra). The settlement by 14C is dated back to the Early Iron Age. The materials of the site document the Arctic component associated with the West-Siberian ethno-cultural area. It became a part of the Northern Glyadenovo collectives and by the middle of the Ist millennium A.D. radically changed the traditional appearance of the material culture of the taiga (Finnish-Permian) population of the Pechora Pre-Urals.
Formation of the region’s subjectivity in the Russian Arctic (To the problem of periodization of the process of forming the administrative-territorial borders of the Kola Peninsula)
Authors: Voronin A , Gaynutdinov R
Published: August 2020

The article is devoted to the main stages and results of the process of forming administrative and territorial boundaries on the Kola Peninsula located in the Russian Arctic zone from the 12th to the 20th centuries, during which it became a completely independent entity, with significant natural and human resources, organically integrated into the russian-wide strategic, economic and socio-cultural space. The authors highlight 4 main stagesand the administrative-territorial developmentof the region: the 1st (12th - 15th centuries) - «cross-border», meaning that there are no clear boundaries, both external and internal; the 2nd (16th to 17th centuries) - «border» during which the external (state) border was formed; The 3rd (XVIII to early 20th centuries) is a «state» defined as a stage of existence in the form of a region with low administrative status; 4th (1920th to 1930th) «subjective», that finally defined the external and internal borders and the place of the region within Russia.
Soviet transarctic flights in the late 1920s and their role in the geographical development of the Arctic regions of Siberia
Authors: Ulyanova S B , Anosova N E , Fisheva A A
Published: August 2020

The role of aviation in the development of the Arctic became evident in the late 1930s. The long-distance flights of V. Chkalov, V. Molokov, M. Gromov and other pilots not only symbolized Soviet heroism, but also contributed to the exploration and development of Arctic spaces by the Soviet Union. However, the achievements of those who made the way to the North for our aviators in 1920s are in the shadow of their successes.This article analyzes the materials of first transarctic flights - their routes, organization, technical and financial support, and the work of flight crews, both in terms of the achieved results and in the political aspect. The analysis of the goals and achievements of the USSR Osoaviahim Northern Air Expedition in 1927 and the Transarctic Expedition in 1928 is based on the materials of St. Petersburg Central State Archive of Scientific and Technical Documentation and other materials. The authors highlight the contribution made by these expeditions into the exploration of Eastern Siberia and the Arctic Ocean and into the development of the regional transport infrastructure. The authors dwell on the work of various departments and the researchers in the field of the national aeronautics in the organization of the expedition. The conclusion is drawn on the importance of scientific and commercial interest in the development of polar aviation in the 1920s and early 1930s.
Arctic military security: geopolitical interaction in “the United States-Russia-Norway” triangle
Authors: Trebukh A D , Dzis Yu I , Filonchik S E , Startseva A A , Yu Krasnoyarov A
Published: August 2020

It is common knowledge that during the Cold War the Arctic was a region for the global confrontation between the USSR and the U.S. Over the past decades the situation has changed dramatically. Nowadays there are no serious hard security threats to the Arctic states in the region and the soft security agenda is much more important. The article examines an emerging military security system in the Arctic. Special attention is paid to the analysis of threat perceptions, security policies and regional military strategies of the U.S., Russia and Norway as well as to the peculiarities of their geopolitical interaction in the region. The research is based on a number of methods, the most important of which are document analysis and expert opinion methods. Summarizing everything the authors stress that it is crucial to calm tensions between the U.S., Russia and Norway so the animosity does not lead to dangerous military incidents in the Arctic as it may threaten global security in general. Thus, it is clear that in order to stabilize the system of the military security in the Arctic, the US, Russia and Norway should establish a tripartite dialogue based on trust and pragmatic interest.
Features of the organization of fuel supplies to the Arctic regions of Russia: assessment of transport conditions
Authors: Biev A A , Serova N A
Published: August 2020

Maintaining the stability of territorial fuel and energy supply systems is an important task for state authorities. The problem of fuel supply in the Arctic zone of Russia is caused by the factor of its insufficient transport and infrastructure development. There are no large facilities of petrochemical industry, as well as a network of transport and energy communications, which leads to high logistics costs associated with the need for seasonal delivery, storage and distribution of fuel resources. To the foregoing, the subject of research in this work is the sphere of material and technical supply of consumers of the Arctic territories of Russia. The object is the process of formation of regional subsystems of fuel supply. The purpose is to investigate the organizational processes of the formation of the fuel supply system in the Arctic zone of the Russian Federation and also to determine possible ways to solve the problems of its modernization. As basic methods of research a systems analysis and some elements of the methodology of the territorial approach are used. As a result of the work were recommendations on promising ways to modernize regional fuel and energy subsystems.