bluuebunny/crossref_metadata_2025 huggingface dataset:
Two-atomic-layered optoelectronic device enabled by charge separation on graphene/semiconductor interface
Authors: Yang Qirong , Guan Jianxin , Deng Jingwen , Xu Zihan , Yu Zhihao , Zheng Junrong
Published: January 2022

The Fermi level of graphene on different substrates usually changes significantly due to the interface difference between graphene and two-dimensional semiconductors. This feature opens many possibilities of manipulating optoelectronic devices by constructing graphene heterostructures through interface modification. Herein, we report the fabrication and optoelectronic response of an unconventional heterojunction device based on a graphene–MoSe2 hybrid interface. Different from the traditional three or more layered structure where the semiconductor is sandwiched between two electrodes, this device contains only two atomic layers: the MoSe2 layer serving as the photon absorber and the graphene layer functioning as the charge acceptor and both electrodes. This structure looks like short-circuited but shows an obvious photoelectric response, which is aided by electron transfers from MoSe2 to graphene. The photocurrent generation is explored quantitatively with electronic dynamics of graphene aided with ultrafast measurements. The two-layered architecture simplifies the fabrication of atomic-thick optoelectronic devices, allowing the as-grown semiconductors to be directly used and eliminating the damage-prone transfer process.
The two dimensional gas expansion problem of the Euler equations for a class of pressure laws
Authors: Xiao Wei , Li WeiLi
Published: January 2022

We consider the expansion problem of a wedge of gas into vacuum in the two-dimensional isentropic Euler equation for a class of pressure laws. We prove the global existence of the smooth solution in the case 0<θ<2θ̄(ρ0), where θ is the half-angle of the wedge, and simplify this problem to a two-dimensional self-similar Euler system with a Goursat problem. By using a special symmetric structure of the characteristic form as well as characteristic decompositions, a prior C1 estimate of the solution of the Goursat problem can be obtained.
Extensions of a classical mechanics “piston-model” for understanding the impact of asymmetry on ICF implosions: The cases of mode 2, mode 2/1 coupling, time-dependent asymmetry, and the relationship to coast-time
Authors: Hurricane O. A. , Casey D. T. , Landen O. , Callahan D. A. , Bionta R. , Haan S. , Kritcher A. L. , Nora R. , Patel P. K. , Springer P. T. , Zylstra A.
Published: January 2022

As long suspected, low mode asymmetry in inertially confined fusion (ICF) implosions has been implicated as a performance limiting factor [Casey et al., “Evidence of three-dimensional asymmetries seeded by high-density carbon-ablator nonuniformity in experiments at the national ignition facility,” Phys. Rev. Lett. 126, 025002 (2021)]. Recently a non-linear, but solvable, theory [Hurricane et al., “An analytic asymmetric-piston model for the impact of mode-1 shell asymmetry on ICF implosions,” Phys. Plasmas 27, 062704 (2020)] based upon the simple picture of a pair of asymmetric pistons has generated new insights and provided some practical formulas for estimating the degradation of an implosion due to mode-1 asymmetry and demonstrated a previously unrecognized connection between measured hot-spot drift velocity, nuclear down-scatter ratio asymmetry, and the concept of residual kinetic energy (RKE). Asymmetry of the implosion “shell,” as opposed to asymmetry of the hot-spot, was key to the classical mechanics model because the majority of the kinetic energy in an implosion is carried by the shell. Herein, the two-piston model is extended to a six-piston model in order to capture mode-2 asymmetry and coupling between mode-1 and mode-2. A key result of this new six-piston model is that the weighted harmonic mean of shell areal density is the fundamental quantity that determines the RKE and performance degradations for a three-dimensional implosion. Agreement is found between the scalings coming from the theory and ICF implosion data from the National Ignition Facility and to large ensembles of detailed simulations. The connection between the piston model's dependence upon the radius of peak velocity and coast-time is also highlighted in this paper. Finally, by extending the two-piston model to include time-dependent “swing,” it is shown in the Appendix that the shell asymmetry at the time of stagnation dominates the solution for RKE.
Intermingled attractors in an asymmetrically driven modified Chua oscillator
Authors: Tanze Wontchui Thierry , Ekonde Sone Michael , Ujjwal Sangeeta Rani , Effa Joseph Yves , Ekobena Fouda Henri Paul , Ramaswamy Ram
Published: January 2022

Understanding the asymptotic behavior of a dynamical system when system parameters are varied remains a key challenge in nonlinear dynamics. We explore the dynamics of a multistable dynamical system (the response) coupled unidirectionally to a chaotic drive. In the absence of coupling, the dynamics of the response system consists of simple attractors, namely, fixed points and periodic orbits, and there could be chaotic motion depending on system parameters. Importantly, the boundaries of the basins of attraction for these attractors are all smooth. When the drive is coupled to the response, the entire dynamics becomes chaotic: distinct multistable chaos and bistable chaos are observed. In both cases, we observe a mixture of synchronous and desynchronous states and a mixture of synchronous states only. The response system displays a much richer, complex dynamics. We describe and analyze the corresponding basins of attraction using the required criteria. Riddled and intermingled structures are revealed.
Biaxial compression mechanical properties of HTPB propellant under dynamic loading
Authors: Geng Tingjing , Qiang Hongfu , Wang Zhejun , Wang Xueren , Yue Chunguo
Published: January 2022

To study the biaxial compression mechanical properties of hydroxyl-terminated polybutadiene (HTPB) solid propellants under dynamic loading, biaxial compression tests were carried out at room temperature (25 °C) with the strain rate ranging from 1 to 85 s−1 using an INSTRON testing machine with a new fixture, and microcomputed tomography (micro-CT) was used to observe the meso-damage of the loaded specimens. At the same time, a comparison test with a strain rate of 0.01 s−1 was carried out using a universal material testing machine. The experimental results indicate that the biaxial compression mechanical curves show strong nonlinear characteristics under all test conditions. Moreover, the mechanical properties of the HTPB propellant in biaxial compression are significantly affected by the strain rate, and the strain rate correlation of the HTPB propellant is controlled by different mechanisms with a strain rate of 18 s−1 as the demarcation point. Finally, from the analysis of microscopic theory combined with micro-CT reconstruction results, it is clarified that the strain rate correlation of the HTPB propellant is controlled by two different ways from the mechanism and that the effect of the strain rate on the mechanical properties of the HTPB propellant is closely related to its damage mechanism.
Continuously tunable acoustic Fano resonance in side-coupled Helmholtz resonator array assisted by a surface phononic crystal
Authors: Biçer Ahmet , Günay Mehmet , Korozlu Nurettin , Cicek Ahmet
Published: January 2022

Fano-like asymmetric line shape in a side-coupled series Helmholtz resonator array-waveguide system is continuously tuned by means of a one-dimensional surface phononic crystal, whose dispersion is exploited to adjust the phase factor appearing in indirectly coupled resonators. Finite-element method simulations reveal that the quality factor of the transmission spectrum can reach values on the order of 107, which can be finetuned by varying either waveguide width or phononic crystal groove depth. The Fano line shape dip, which appears around 25 kHz, red-shifts linearly with respect to the waveguide width at a rate of 308 Hz/mm. The quality factor exhibits a two order of magnitude drop for 0.01 mm waveguide width detuning from the optimal value. In comparison, three orders of magnitude decrease are observed for the same variation from the optimal value of the surface phononic crystal groove depth. Fano-like line shape is preserved when thermo-viscous losses are taken into account, where tunability with geometrical factors is still possible. Fine-tuning of either the dip frequency or quality factor can be utilized in demanding applications such as measurement of distance and concentrations of fluid mixtures with ultra high sensitivity.
Abnormal radiation resistance via direct-amorphization-induced defect recovery in HgTe
Authors: Gao Fei , Peng Qing , Huang Danhong
Published: January 2022

Understanding and mitigating effects of radiation are central to ensure reliable, long-term operation in space and strategic environments for compound semiconductor based electronics. A multiscale modeling approach has been employed to reveal the damage process and explore radiation resistance mechanisms in HgTe. Contrary to general belief, direct-amorphization and fast migration of interstitials within amorphous pockets provide a dominant driving force for rapid defect recovery, thus significantly enhancing radiation resistance. This study provides a precursor for developing predictive capabilities in designing and enabling radiation resistance with confidence for robust semiconductors.
Excitation dynamics in polyacene molecules on rare-gas clusters
Authors: Bohlen Matthias , Michiels Rupert , Michelbach Moritz , Ferchane Selmane , Walter Michael , Eisfeld Alexander , Stienkemeier Frank
Published: January 2022

Laser-induced fluorescence spectra and excitation lifetimes of anthracene, tetracene, and pentacene molecules attached to the surface of solid argon clusters have been measured with respect to cluster size, density of molecules, and excitation density. Results are compared to previous studies on the same sample molecules attached to neon clusters. A contrasting lifetime behavior of anthracene on neon and argon clusters is discussed, and mechanisms are suggested to interpret the results. Although both neon and argon clusters are considered to be weakly interacting environments, we find that the excitation decay dynamics of the studied acenes depends significantly on the cluster material. Moreover, we find even qualitative differences regarding the dependence on the dopant density. Based on these observations, previous assignments of collective radiative and non-radiative decay mechanisms are discussed in the context of the new experimental findings.
Active stabilization of terrestrial magnetic field with potassium atomic magnetometer
Authors: Ding Yudong , Zhang Rui , Zheng Junhe , Chen Jingbiao , Peng Xiang , Wu Teng , Guo Hong
Published: January 2022

This paper introduces a magnetically quiet environment where the magnetic-field noise is actively suppressed using an optically pumped potassium magnetometer. In a large dynamic range of Earth’s magnetic fields, the magnetic-resonance signals of potassium are completely separated in frequency, and we experimentally demonstrate that one of them could be used to measure and compensate magnetic-field noise. The magnetic-field noise floor after stabilization is ∼100 fT/Hz under a bias field ranging from 20 to 100 μT. This method could be useful for fundamental-physics experiments and biomedical sciences where a large dynamic range of quiet magnetic fields is needed.
Measurement method of natural frequencies and tension forces for cables based on elasto-magnetic sensors calibrated by frequencies
Authors: Liu Xiaofeng , Chen Yuehua , Hu Haigang , Feng Shaoyu , Feng Zhimin
Published: January 2022

Vibration-based (VB) method and elasto-magnetic (EM) method are usually used to measure cable forces of cable-supported bridges. For the VB method, it is difficult to accurately identify each order natural frequency of the cable disturbed by random excitations, and there are also no precise selection criteria between the taut string model and the hinged beam model. For the EM method, it is not convenient to calibrate EM sensors on bridges in service due to unknown cable forces. To address these issues, a vibration-based elasto-magnetic (VBEM) method is proposed. In this method, a numerical model describing the tie between each order natural frequency and induced voltage was constructed first, and then, a new cable force formula with nominal flexural stiffness was derived. To verify the VBEM method, a steel strand experimental platform was built and the load applied to the steel strand was achieved by a jack. At 18 °C, the first three order natural frequencies of the steel strand and corresponding induced voltage were recorded for each load. According to the obtained experimental data, the VBEM method is tested and analyzed. The results show that the VBEM method exhibits the ability to identify each order natural frequency of the steel strand with high precision; the introduction of nominal flexural stiffness makes the hinged beam model cover the taut string model, resulting in tension force measurement with satisfactory accuracy; the constructed models do not contain tension forces, and this will make it very beneficial to calibration of EM sensors on bridges in service.
The effect of hardness on polymer-bonded pentaerythritol tetranitrate (PETN) explosive impact sensitivity
Authors: Burch Alexandra C. , Kay Lisa M. , Yeager John D. , Brown Geoff W. , Tappan Bryce C. , Cawkwell Marc J. , Manner Virginia W.
Published: January 2022

Handling sensitivity is an important property to assess when working with explosive samples and can be measured using a variety of tests, including drop-weight impact sensitivity. There exists a longstanding interest in the explosives community on the importance of measurable chemical, physical, and mechanical properties of explosives in impact sensitivity. However, most recent work in this area has explored chemical attributes rather than physical and mechanical properties of explosives. In this study, we measure hardness of explosive samples of pentaerythritol tetranitrate and Sylgard binder (XTX) during the curing process. The samples have been characterized for particle morphology through scanning electron microscopy and handling sensitivity through drop-weight impact testing. The relative importance of states of cure, methods of curing, morphology, and age of material are discussed. The data indicate that although there is a notable difference in morphology and mechanical properties for the samples as the polymer-bonded mixtures cure, the resulting changes to mechanical properties have a minimal effect on the sensitivity of the XTX.
Micrometer-sized droplets from liquid helium jets at low stagnation pressures
Authors: Kolatzki Katharina , Schubert Marie Louise , Ulmer Anatoli , Möller Thomas , Rupp Daniela , Tanyag Rico Mayro P.
Published: January 2022

Droplets and droplet beams produced from the breakup of micrometer-sized liquid helium jets in vacuum were studied in this work, advancing into previously unexplored regimes of low stagnation pressures. Using a 5 μm orifice, the droplet beam shows surprisingly diverse characteristics at increasing nozzle pressures from 0.6 to 100 bar: a well-collimated beam at low stagnation pressures, a spray at some intermediate values, and a less-collimated beam at high pressures. Focusing on a nozzle stagnation of 0.6 bar and 2.7 K, we highlight the spectrum of jet disturbances, resulting in different droplet beam behaviors. On some occasions, we observed uniformly sized and equidistant droplets with diameters ranging from 11 up to more than 25 μm and separations from 15 to 100 μm. From simple estimates using the ratio between the droplet separations and diameters, we determined the disturbance frequencies benchmarking the production of repeatable targets for future experiments with superfluid helium droplets. Further analysis of the droplet beam behavior at farther distances from the nozzle revealed that the droplet diameter grew downstream up to 22 μm from an initial value of 13 μm, while their aspect ratio decreased from 1.33 to 1.16. These results indicate that droplet coagulation and superfluidity both influence the droplet beam up to several hundreds of millimeters after the nozzle exit.
Electronic properties and ion migration of “in vacuo” lithiated nanoporous WO3:Mo thin films
Authors: Fleury Jeremy , Burnier Luc , Schüler Andreas
Published: January 2022

Electrochromic (EC) glazing helps manage daylight and solar heat gains in building, thereby allowing a reduction in energy consumption caused by heating, cooling, and artificial lighting. This study relates the optical and electronic properties of nanoporous amorphous molybdenum-doped tungsten trioxide thin films (WO3:Mo) in the pristine state and upon lithiation. When such a film is used as a cathode in EC devices, the color neutrality can be improved with respect to pure WO3, and electrochromic transmission control can be achieved in the full spectral range of solar radiation. In situ x-ray photoelectron spectroscopy reveals that the coloration mechanism is related to the reduction of W6+ to W5+ and Mo6+ to Mo5+. In the initial stages of lithiation, Mo is preferably reduced followed by the reduction of W. Ultraviolet photoelectron spectroscopy highlights systematic trends in the position of the valence band edge and in work function. The occurrence of peaks at 2.2 and 0.8 eV is observed and is related to the formation of partially delocalized Mo5+ and W5+ midgap states. Visible/near-infrared spectrophotometry shows initial absorption mainly in the visible spectral range, followed by absorption in the near infrared. Both absorption bands can be associated with the midgap states due to the occurrence of Mo5+ and W5+, respectively. Lithiation of bilayers composed of WO3:Mo and WO3 shows that the Mo5+ states, which are energetically lower, trap preferentially the transferred charges. Furthermore, our results suggest that lithium ions diffuse rather freely in the direction perpendicular to the substrate. These findings pave the way to next-generation EC devices with color neutral and broadband modulation of spectral transmission and in principle also with dual-band modulation of visible and near-infrared light.
Dynamic modeling and simulation of variable-length hose–drogue aerial refueling systems
Authors: Cheng Jiangfeng , Ji Kang
Published: January 2022

This paper describes an improved modeling and simulation analysis of a variable-length reel take-up system for hose retrieval/deployment during aerial refueling. Based on a previously developed finite segment model, full reel acceleration is applied to the first rigid link connected to the towing point. The variation in the length of the hose and its rate of change are distributed evenly across all of the hose segments through a re-discretization technique, and the dynamics of the hose’s motion are regarded as a series of quasi-static processes. First, numerical simulations of the steady-state trailing hose are compared with previous results and flight data. The non-linear dynamics of a variable-length hose–drogue system during aerial refueling are then analyzed under various retrieval/deployment conditions. The results indicate that the finite segment model is prone to inducing chain-link oscillations in the hose dynamics, which are not appropriate for such a flexible body. In two application cases, the non-physical oscillations were well filtered using the proposed method, achieving a simultaneous combination of accuracy, stability, and robustness. Several advantages of the simulated hose dynamics provide a theoretical basis and platform for subsequent research into control strategies for suppressing the hose whipping phenomenon during hook-up.
Macro strain-stress determination in a high pressure rotational anvil apparatus
Authors: Lin Lin , Ji Cheng , Ma Yanzhang
Published: January 2022

With the increasing development of techniques that utilize high-pressure shear in multiple fields, constructing a proper interpretation of strain and stress in rotational anvil apparatuses is becoming more and more urgent. A macro strain analysis in a rotational anvil apparatus that generates high pressure and shear was performed based on a polycrystal strain spatial distribution. Based on the strain, macro stress components were retrieved. Three analytical methods suitable for various application purposes are presented that can be used to conduct stress/strain analysis of a sample under pressure and shear: a sample center fitting method that obtains macro strain components from the refinement of d-spacing azimuth angle distribution, a six-point graphical method that calculates macro strain components from graphical strain distribution, and a four-point graphical method that determines the components directly from a diffraction image. This study also discusses and verifies the validity of and comparison between the methods through experimental data. The present work is expected to provide a foundation for further experimental studies of shear at pressures and expand the field of high-pressure sciences.
Shock wave propagation in a non-ideal rotating medium with azimuthal magnetic field effect using Lie group technique
Authors: Chauhan Astha
Published: January 2022

The present article demonstrates the propagation of a strong cylindrical shock wave in a rotating adiabatic flow of a van der Waals gas in the presence of an azimuthal magnetic field. Using the Lie group technique, self-similar solutions are obtained with an assumption of uniform density in the undisturbed medium. In contrast, the azimuthal component of the fluid velocity and the magnetic field are supposed to vary. The profiles of the flow variables are depicted graphically, followed by a brief discussion on the behavior of the solutions obtained through the graph. The effects of variation in the values of the adiabatic index, Alfvén Mach Number, non-idealness parameter, and the ambient azimuthal velocity exponent on the flow variables are discussed in detail. The computational work is performed by using Mathematica (a software package).
Demonstration of device-quality 60% relaxed In0.2Ga0.8N on porous GaN pseudo-substrates grown by PAMBE
Authors: Wurm Christian , Collins Henry , Hatui Nirupam , Li Weiyi , Pasayat Shubhra , Hamwey Robert , Sun Kai , Sayed Islam , Khan Kamruzzaman , Ahmadi Elaheh , Keller Stacia , Mishra Umesh
Published: January 2022

Achieving high-quality, relaxed InGaN substrates for longer-wavelength light emitting diodes (LEDs) is of great interest for the development of micro-LED based display technology. This work demonstrates molecular beam epitaxy (MBE)-grown In0.2Ga0.8N with a strain relaxation of 60% corresponding to an equivalently fully relaxed In composition of 12%. This was done by growing on a GaN-on-porous GaN pseudo-substrate (PS). The surface morphology of this film was found to be free of V-defects on the surface and with a threading dislocation density comparable to that of the GaN layers beneath. While InGaN grown on planar GaN-on-sapphire substrates remained nearly strained to the GaN underlayer, InGaN grown under identical conditions on PS displayed elastic-like relaxation. Furthermore, an increase in indium (In) composition was observed for the InGaN grown on PS. Where past work of InGaN grown on porous GaN PS by metalorganic chemical vapor deposition also resulted in relaxed InGaN templates suitable for device application, the surfaces of these relaxed films exhibited V-defects for thicker layers. Employing MBE, thicker films with higher In composition can be achieved with smooth surface morphology, thus enabling pseudo-substrates with a wide range of lattice constants. These pseudo-substrates of varying in-plane lattice constant are attractive for III-nitride based optoelectronics, particularly for green, amber, and red micro-LEDs.
Initial state-selected scattering for the reactions H + CH4/CHD3 and F + CHD3 employing ring polymer molecular dynamics
Authors: Marjollet A. , Inhester L. , Welsch R.
Published: January 2022

The inclusion of nuclear quantum effects (NQEs) in molecular dynamics simulations is one of the major obstacles for an accurate modeling of molecular scattering processes involving more than a couple of atoms. An efficient method to incorporate these effects is ring polymer molecular dynamics (RPMD). Here, we extend the scope of our recently developed method based on non-equilibrium RPMD (NE-RPMD) from triatomic chemical reactions to reactions involving more atoms. We test the robustness and accuracy of the method by computing the integral cross sections for the H/F + CH4/CHD3 reactions where the methane molecule is either initially in its vibrational ground or excited state (C–H stretch). Furthermore, we analyze the extent to which NQEs are described by NE-RPMD. The method shows significant improvement over the quasiclassical trajectory approach while remaining computationally efficient.
Control of the chirality of a vortex in a ferroelectric nanodot by uniform electric fields mediated by inhomogeneous surface screening
Authors: Xiong P. C. , Ma W. B. , Yuan S. , Liu Y. L. , Wang B.
Published: January 2022

The manipulation of a ferroelectric vortex under the boundary condition of inhomogeneous screening is simulated by phase-field calculations. It is revealed that the vortex chirality can be tuned by utilizing uniform electric fields under inhomogeneous screening boundary conditions in which the switching mechanism is distinct from that under boundary conditions of asymmetric screening previously reported. The influence of the screening inhomogeneity and the ambient temperature on the vortex switching is further studied. The results indicate that inhomogeneous screening conditions are of vital importance to the switching behaviors of vortex chirality in a ferroelectric nanodot under the influence of a uniform electric field. Furthermore, the critical electric field is inextricably linked to the screening inhomogeneity and the ambient temperature.
Dynamics of a gas bubble penetrating through porous media
Authors: Yi Tianhao , Yang Guang , Wang Bin , Zhuan Rui , Huang Yonghua , Wu Jingyi
Published: January 2022

Porous media have been widely used for liquid-gas separation, benefiting from the strong capillary force generated from the micro/nanoscale pores. Understanding the flow characteristics in pore scale is significant for the design of porous structure. In this study, a numerical model was established to investigate the dynamics of a bubble penetrating through porous media at the pore scale. The two-phase interface was captured using the diffuse interface method. The influence of pore shape, width, and height on the bubble deformation, velocity, and critical pressure was investigated. For the same pore size, the largest bubble centroid velocity and the highest critical pressure exist in the quadrilateral pores compared rather than in the circular or triangular pores. As the pore width decreases, both the average velocity of the bubble centroid and the critical pressure increase. However, the critical pressure is independent of the pore height. As the pore height increases, the average velocity of the bubble centroid increases. A new correlation of the critical pressure for bubble penetration has been proposed, which is a function of the shape factor, the pore width, and the bubble diameter. The findings of this work can contribute to improving the design of porous media for two-phase separation.
Singularity-free internal conversion golden-rule rate with application to correlated triplet pair recombination in bipentacenes
Authors: Miyazaki Ken , Ananth Nandini
Published: January 2022

We introduce a singularity-free golden-rule rate expression for internal conversion (IC), a spin-conserved radiationless relaxation process, expressed as the product of a nonadiabatic coupling term and the time integral of a vibration correlation function. For a set of small polyatomic molecules (acenes and azulene), we show that our calculated rates are in near quantitative agreement with the rates derived from experiments. Interestingly, we find that our rates do not agree with previous golden-rule-based theoretical efforts; detailed analysis shows that while the level of electronic structure theory can play a role, the more significant error is from not fully converging the numerical time integral over the oscillatory vibration correlation function. We then use our singularity-free IC rate expression to compute the rate of recombination of the correlated triplet pair state generated by intramolecular singlet fission in a trio of bipentacenes. We show that the recombination rates are in good agreement with experimentally observed trends—specifically, the rates are robust to temperature changes and decrease rapidly with increasing inter-monomer dihedral angle. Finally, we use a pair-wise breakdown of normal mode contributions to the rate to identify the key vibrational modes that drive recombination in bipentacenes.
A non-decomposable approximation on the complete density function space for the non-additive kinetic potential
Authors: Polak Elias , González-Espinoza Cristina E. , Gander Martin J. , Wesolowski Tomasz A.
Published: January 2022

A new non-decomposable approximation of the non-additive kinetic energy potential is constructed starting from the same exact property in the limit (ρA → 0 and ∫ρB = 2), as introduced in the work of Lastra et al. [J. Chem. Phys. 129, 074107 (2008)]. In order to cover the complete function space for exponentially decaying densities, the kernel of a differential operator Dγ[ρ] is introduced and analyzed in dependence of γ. The conclusive choice of γ = 1 assures that the solution functions span the complete space of molecular electron densities. As a result, the new approximant preserves the desired feature of the older approximation, which is the reciprocal singularity if the electron density decays exponentially, and eliminates artificial shallow wells (holes), which are responsible for an artificial “charge leak.” Numerical considerations using the standard validation procedure introduced by Wesolowski and Weber [Chem. Phys. Lett. 248, 71–76 (1996)] demonstrate the numerical performance of the developed approximation, which increases the range of applicability of semilocal functionals.
Pitch angle scattering of fast particles by low frequency magnetic fluctuations
Authors: Xu Yi , Egedal Jan
Published: January 2022

The adiabatic invariance of the magnetic moment during particle motion is of fundamental importance to the dynamics of magnetized plasma. The related rate of pitch angle scattering is investigated here for fast particles that thermally stream through static magnetic perturbations. For a uniform magnetic field with a localized perturbation, it is found that the curvature parameter κ2=min(Rc/ρL) does not predict the level of pitch angle scattering. Instead, based on numerical integration of particle orbits in prescribed magnetic fields, we derive predictions for the particle scattering rates, which can be characterized by the relative perturbation amplitude A≃δB/B, and the particle Larmor radius normalized by the field-aligned wavelength of the perturbations, ρL/λ||. Particles with ρL/λ||≃1 are subject to strong pitch angle scattering, while the level of scattering vanishes for both the limits of ρL/λ||≪1 and ρL/λ||≫1. The results are summarized in terms of a scattering operator, suitable for including the described scattering in basic kinetic models.
A pH-based bio-rheostat: A proof-of-concept
Authors: Alfinito E. , Cataldo R. , Reggiani L.
Published: January 2022

Biological matter is attracting increasing attention because it shows innovative features that have found several applications in technology, from highly sensitive sensors for medical treatments to devices for energy harvesting. Furthermore, most of its phenomenology remains unclear, thus giving hints for speculative investigations. In this Letter, we explore the possibility to use a well-known photosensitive protein, the Reaction Center of Rhodobacter sphaeroides, to build up an electrical pH sensor, i.e., a device able to change its resistance depending on the pH of the solution in which it crystalizes. By using a microscopic model previously tested on analog proteins, we investigate the electrical response of the reaction center single protein under different conditions of applied bias, showing the feasibility of the bio-rheostat hypothesis. As a matter of fact, the calculated resistance of this protein grows about 100% when going from a pH = 10 to a pH = 6.5. Moreover, calculations of the current voltage characteristics well agree with available experiments performed with current atomic force microscopy under neutral conditions. All findings are in qualitative agreement with the known role of pH in biochemical activities of reaction center and similar proteins, therefore supporting a proof-of-concept for the development of innovative electron devices based on biomaterials.
Solar-blind UV detection by ultra-wide-bandgap 4HCB organic single crystal semiconductor
Authors: Zhao Dou , Ma Donghao , Xu Meng , Liu Linyue , Li Yang , Li Fangpei , Zhang BinBin , Zhu Menghua , Xu Yadong , Jie Wanqi
Published: January 2022

In this work, the solar-blind ultraviolet (UV) detection performance of organic single crystals 4-hydroxycyanobenzene (4HCB) is demonstrated. The ultra-wide bandgap and low dark current make 4HCB an important candidate for this application. Detectors with two electrode configurations, i.e., sandwiched electrode (SWE) and interdigital electrode (IDE), are fabricated based on 4HCB single crystals and measured under the illumination of 254 nm-UV light. Apparently, the IDE detector exhibits a responsivity R of 14 000 μA W−1 at a bias voltage of 1000 V, which is 2000 times higher than that of the SWE detector, due to its enhanced photoconductive gain by the surface layer edge states. To explore the possibility for the space UV detection applications in the radiation environment, the effect of neutron radiation on 4HCB detector performance is revealed. The point defects introduced by fast neutrons, mainly H vacancies, dominate the variation of the Fermi energy level and electric properties; however, this effect on photodetection is limited when the neutron flux is below 1013 n cm−2.
A reentrant phase transition and a novel polymorph revealed in high-pressure investigations of CF4 up to 46.5 GPa
Authors: Laniel Dominique , Fedotenko Timofey , Winkler Bjoern , Aslandukova Alena , Aslandukov Andrey , Aprilis Georgios , Chariton Stella , Milman Victor , Prakapenka Vitali , Dubrovinsky Leonid , Dubrovinskaia Natalia
Published: January 2022

The high-pressure behavior of simple molecular systems, devoid of strong intermolecular interactions, provides a unique avenue toward a fundamental understanding of matter. Tetrahalides of the carbon group elements (group 14), lacking all intermolecular interactions but van der Waals, are among the most elementary of molecular compounds. Here, we report the investigation of CF4 up to 46.5 GPa—the highest pressure up to which any tetrahalides of group 14 elements have been studied so far—by a combination of single-crystal x-ray diffraction (SC-XRDp), Raman spectroscopy, and ab initio calculations. These measurements reveal a pressure-induced reentrant phase transition (phase II →2.8GPa phase III →∼20GPa phase IIR) at room temperature and the formation of a previously unknown CF4 cubic polymorph, named phase IV, after the laser heating of CF4 at 46.5 GPa. In this work, the structures of phases IIR, III, and IV were solved and the atomic coordinates were refined on the basis of SC-XRDp. A comparison of tetrahalides of group 14 elements underlines that reducing the intermolecular halogen–halogen distances leads to a structural rearrangement from close packing of the tetrahedral molecules to close packing of the halogen atoms.
A micro-thin-film getter–heater unit for high vacuum capsulation of MEMS devices
Authors: Ji Yucheng , Feng Liuhaodong , Guo Song , Peng Xinlin , Chen Shuo , Li Wenbing , Wang Shinan
Published: January 2022

In this paper, we proposed a micro-getter unit with a square thin-film getter formed atop a thin-film heater for vacuum packaging of a Micro-Electro-Mechanical System (MEMS) device. This innovation through an integrated module unit can be fabricated by MEMS compatible processes and can be sealed together with a MEMS device by wafer level package technology sequentially. It has the advantage of locally and repeatedly activating the getter by supplying a DC power to the micro-thin-film heater. Two models have been studied comparatively in this work, in which a conventional solid structure (SS) model with a micro-heater directly above a silica glass substrate was used as a reference model for comparison with the newly designed innovative floating structure (FS) model with a micro-heater floating over a cavity in a silicon substrate. According to a finite element method simulation based on Fourier’s law of heat conduction, the FS model showed better thermal efficiency than the SS model during the activation process. For a square micron thin-film getter with a size as 1000 × 1000 × 5 µm3, a rather low input voltage as 2 V can raise the temperature of the getter up to 300 °C calculated by the FS Model, while the SS model requires a much higher input voltage as 18 V to reach the same temperature.
“Sitting in the back of the class”
Authors: Steadman Angel N.
Published: January 2022

This study examines how teacher candidates’ positions in a fully
online MA TESOL program accumulate into more stable positional identities
over the span of a 7.5-week course. Overreliance on asynchronous, text-based
posts mired teacher candidates in static positions that hindered their
learning. One participant, positioned as a good teacher,
did not receive the constructive criticism he wanted, while the other
participant, positioned as inexperienced and
deficient, resorted to participatory patterns that
isolated her from the group. These findings illustrate the effects that
course design may have on identity construction in online settings in which
outside peer-to-peer interaction may be limited.
Sharing stories around the digital campfire
Authors: Green-Eneix Curtis , De Costa Peter I.
Published: January 2022

As the educational landscape evolves to address emerging
international demands (De Costa,
Green-Eneix & Li, 2020), teacher educators and researchers
have begun to reevaluate what it means to be a ‘good’ teacher within digital
classrooms. An area that has not been fully explored is how language teacher cognition
(LTC) and language
teacher emotions (LTE) dialectically occur through the stories
and conversations in asynchronous online language teaching classrooms. This
semester-long netnographic case study (Kozinets, 2010) sets out to understand how a fully asynchronous
class helps novice in-service language teachers better understand their LTC
and LTE concerning their respective teaching contexts. We found a digital
space for in-service teachers to develop professionally both in the
classroom and their respective contexts.
Gender assignment in mixed noun phrases
Authors: Bellamy Kate , Parafita Couto M. Carmen
Published: January 2022

Noun phrases (NPs) constitute one of the most frequent sites where bilingual speakers code-switch.
In this chapter we aim to provide a comprehensive overview of research into grammatical gender assignment in mixed
NPs, namely NPs containing a noun from one language and a gender-agreeing element from another. We outline the three
main gender assignment strategies observed in mixed NPs: (i) translation equivalent, (ii) shape-based, and (iii)
default, and in which language pairs, using which tasks, they have been observed. We discuss how the order of
acquisition of the gendered and non-gendered language, language dominance, task type, and community norms combine with
linguistic properties to modulate gender assignment patterns. Findings suggest that bilinguals who learned a gendered
language first seem to prefer the translation equivalent strategy. Since insufficient data from a wide variety of
language dyads is currently available, we are cautious about offering further generalisations. Nonetheless, we
highlight findings suggesting that more habitual code-switchers prefer the masculine default strategy. In order to
progress beyond the current state of the art, we suggest that the field needs to expand into more language dyads, as
well as extend existing research on individual language dyads, using multiple methodologies and in communities
differing in their code-switching frequency.
Constructional variation and change in N-is focaliser constructions
Authors: Hundt Marianne
Published: January 2022

This paper revisits the emergence of N-is focaliser constructions. It is the first to systematically use qualitative evidence from the Oxford English Dictionary (OED) and Early English Books Online (EEBO) to establish the chronology of developments from a full clause to a parenthetical. In a second step, diachronic evidence from the Late Modern English Corpus of Historical American English (COHA) is used for a quantitative, variationist study of constructional change in the Late Modern period. The relevant stages for this are determined in a bottom-up fashion, using Variability-based Neighbour Clustering (VNC). Multivariate statistical modelling is then applied to model the relative importance of predictor variables for the degree of syntactic integration. The chronological data from the OED and EEBO provide evidence of lexical diffusion from truth is and various other shell nouns to problem is. COHA data further show N-is focalisers to be spreading in discourse frequency. The variationist evidence shows that punctuation is not the most important predictor variable throughout and that it interacts in interesting ways with other predictors. Finally, relatively minor (i.e. numerically infrequent) but conceptually salient changes (such as article omission) are taken to contribute to further constructionalisation.
Principles of integrated language policy
Authors: Grin François
Published: January 2022

This chapter proposes a novel perspective on language policy as a form of public policy, highlighting some of the epistemological implications of this approach and discussing its linkages with more standard approaches originating in applied linguistics. After introducing the relevance of interdisciplinarity and complexity as defining features of this enterprise, it focuses on the connections between principles of public policy on the one hand, and the specificities of language policy on the other hand. To this end, this chapter develops an entirely novel typology of the main dimensions of language policy (type, domain, sphere, tier, welfare, target, causation and instrument), with which the latter may be extensively described and characterised. These dimensions bring to the fore the importance of jointly considering the micro, meso and macro levels at which language policies necessarily unfold. Given the extreme complexity of practically any language policy, and the associated difficulty of establishing the full range of effects (including both advantages and drawbacks) of alternative policy choices, analysts often need to fall back on pragmatic solutions in the selection and design process. Accordingly, this chapter emphasizes the role of plausibility as a valid criterion for evaluating such effects.
How to upgrade the status of migrant languages in the European Union
Authors: Houtkamp Christopher , Marácz László
Published: January 2022

In this chapter, we will compare the status of traditional minority and migrant languages in the European context and its practical implications for the trade-off between mobility and inclusion. It has been observed that traditional minority languages in Central and Eastern European (CEE) states have fewer rights compared to official languages and that their status and position is best described by language hierarchies, asymmetries, subordination, and threshold restrictions. This against the background of international treaties, such as article 22 of the Charter of Fundamental Rights of the European Union (CFREU) stating that the European Union (EU) respects cultural, religious, and linguistic diversity and the charters of the Council of Europe (CoE). Although linguistic inequality is an unwanted state of affairs violating international treaties and obligations of member states, these traditional minority language cases might refer to the assignment of linguistic rights to languages of migrants. Both categories belong to the domain of the non-official, majority languages and are expected to be assigned less rights than ‘national languages’, although traditional minority languages have been assigned limited rights in terms of the personality principle next to the territoriality principle applied to the national languages. Note that the language rights of migrants in the EU are also restricted by the mobility-and-inclusion trade-off, which is detrimental to migrant languages in the national context. A solution to this inequality is provided by the fact that the personality principle is a common denominator in the assignment of linguistic rights to minority-language speakers and has already been introduced into transnational European spaces. Hence, the rights of migrant languages can be accounted for by applying the personality principle in these spaces as well. This results in a Union-wide supranational language policy for migrant languages which supports the upgrading of migrant languages in accordance with the personality principle.
Multilingualism and security
Authors: Ozoliņa Žaneta , Bambals Rihards
Published: January 2022

The 20th century left permanent marks on the European geographical, socio-political and linguistic maps. No EU member states other than Estonia and Latvia have five percent or more native Russian-speakers in their population, which makes the case of the Baltic States unique in the wider pan-European context. Russia, the EU’s largest neighbour, has struggled to cope with the political reality of tens of millions of Russian-speakers being left outside of its borders. The mix of ethno-linguistic borders that do not coincide with politico-geographic ones raises several security-related questions; one of them is whether language can be used as a tool of manipulation, propaganda and source of unrest in society. Russia has securitised the protection of Russian-speakers abroad as analysis of its strategic foreign, security and military policy documents proved. In countries not included in NATO and the EU, such as Georgia and Ukraine, the Russian authorities have used the protection of ethnic Russians and Russian-speakers as a legitimate reason to violate the sovereignty and indivisibility of independent nations. Any country with a substantial Russian-speaking diaspora, especially in the former Soviet territories with less power and resources than Russia, may find its national security and societal resilience put to the test. The aim of the article is to analyse potential security implications stemming from different linguistic groups from the perspective of societal security, national security, risk to state sovereignty, and security at the wider EU level, as well as to identify challenges that may arise when conflicts of international actors spill over into state domains, and cause dissent within the local population.