bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of current challenges, risks and uncertainties in the field of natural resource management
Authors: Grevtsev N.V. , Lebedeva T.A. , Belov V.V. , Ivanova N.S.
Published: July 2020

Modern challenges, environmental risks and economic uncertainties in the field of natural resource management in the Urals and Western Siberia are considered. Information relating to the regional changes in the soil surface (air) temperature, the state of the cryolitic zone of the forest and swamp ecosystems, and extreme uncertainties is presented.
In the race for knowledge, is human capital the most essential element?
Authors: Sinay Laura , Carter Rodney William , de Sinay Maria Cristina Fogliatti
Published: July 2020

Clarivate Analytics, managers of Web of Science, publishes an annual listing of highly cited researchers. The opening sentence of the 2019 report asks “Who would contest that in the race for knowledge, is human capital that is most essential?”. They go on to state that “talent—including intelligence, creativity, ambition, and social competence (where needed)—outpaces other capacities such as access to funding and facilities”. These contradict previous findings, according to which other factors are possibly more influential than human capital. Using Clarivate Analytics’ database for 2018, we investigated which factors are most relevant in development of scientific knowledge. Rather than human capital alone, we found that language, gender, funding, and facilities introduce bias to assessments and possibly prevent talent and discoveries from emerging. We also found that the profile of the highly cited scholars, as established by Clarivate Analytics, is so narrow that it may compromise the validity of scientific knowledge, because it is biased towards the perception and interests of male scholars affiliated with very-highly developed countries where English is commonly spoken and of their sponsors. This highly cited scholars accounted for 76% of the random sample analyzed, absent were women from Latin-America, Africa, Asia, and Oceania, and scholars affiliated with institutions in low-human-developed countries. Also, 98% of the published research came from institutions located in very-highly developed countries. These findings provide evidence that challenges the view that ‘talent is the primary driver of scientific advancement’. This is important because search engines, such as Web of Science, can modify their algorithms to ensure the work of scholars that does not fit the currently dominant profile can have their importance increased so that their findings can more equitably contribute to knowledge development. This, in turn, will increase the validity of scientific inquiry.
Sentiments and emotions evoked by news headlines of coronavirus disease (COVID-19) outbreak
Authors: Aslam Faheem , Awan Tahir Mumtaz , Syed Jabir Hussain , Kashif Aisha , Parveen Mahwish
Published: July 2020

The chronic nature of coronavirus disease (COVID-19) outbreak and lack of success in treatment and cure is creating an environment that is crucial for mental wellbeing. Presently, we extracted and classified sentiments and emotions from 141,208 headlines of global English news sources regarding the coronavirus disease (COVID-19). The headlines considered were those carrying keyword coronavirus between the time frame 15 Janaury, 2020 to 3 June, 2020 from top rated 25 English news sources. The headlines were classified into positive, negative and neutral sentiments after the calculation of text unbounded polarity at the sentence level score and incorporating the valence shifters. In addition, the National Research Council Canada (NRC) Word-Emotion Lexicon was used to calculate the presence of eight emotions at their emotional weight. The results reveal that the news headlines had high emotional scores with a negative polarity. More precisely, around 52% of the news headlines evoked negative sentiments and only 30% evoked positive sentiments while 18% were neutral. Fear, trust, anticipation, sadness, and anger were the main emotions evoked by the news headlines. Overall, the findings of this study can be weaved together into important implications for emotional wellbeing and economic perspective.
Spoof plasmonic Brewster angle transmission for broadband electromagnetic energy squeezing in the microwave regime
Authors: Pederson Dylan M. , Kim Yunho , Raja Laxminarayan L.
Published: July 2020

We demonstrate through numerical experiments and analytical calculations that extreme subwavelength gaps between two corrugated surfaces support high effective refractive index guided modes. The corrugated gap mode is of low loss because it does not rely on plasmonic currents induced inside a metal. This enables guided modes with a much higher effective refractive index than is possible in natural plasmonic materials. These high-index guided modes are incorporated as periodic slots in an opaque screen, which is then shown to support broadband highly transmitting modes at a certain oblique incidence angle in addition to the usual Fabry–Pérot resonances. This anomalously high transmission is the extension of the plasmonic Brewster angle to arbitrarily low frequency, controlled by the geometry of the corrugated slots. We demonstrate the preservation of the shape of a broadband low-frequency pulse transmitted through the slotted screen, opening up the possibility to use the structure for broadband energy squeezing applications in the GHz to THz regime.
An entanglement-based quantum network based on symmetric dispersive optics quantum key distribution
Authors: Liu Xu , Yao Xin , Xue Rong , Wang Heqing , Li Hao , Wang Zhen , You Lixing , Feng Xue , Liu Fang , Cui Kaiyu , Huang Yidong , Zhang Wei
Published: July 2020

Quantum key distribution (QKD) is a crucial technology for information security in the future. Developing simple and efficient ways to establish QKD among multiple users is important to extend the applications of QKD in communication networks. Herein, we proposed a scheme of symmetric dispersive optics QKD and demonstrated an entanglement-based quantum network based on it. In the experiment, a broadband entangled photon pair source was shared by end users via wavelength and space division multiplexing. The wide spectrum of generated entangled photon pairs was divided into 16 combinations of frequency-conjugate channels. Photon pairs in each channel combination supported a fully connected subnet with eight users by a passive beam splitter. Eventually, it showed that an entanglement-based QKD network over 100 users could be supported by one entangled photon pair source in this architecture. It has great potential on applications of local quantum networks with large user number.
Solvent reaction coordinate for an SN2 reaction
Authors: Leitold Christian , Mundy Christopher J. , Baer Marcel D. , Schenter Gregory K. , Peters Baron
Published: July 2020

We study the prototypical SN2 reaction Cl− + CH3Cl → CH3Cl + Cl− in water using quantum mechanics/molecular mechanics (QM/MM) computer simulations with transition path sampling and inertial likelihood maximization. We have identified a new solvent coordinate to complement the original atom-exchange coordinate used in the classic analysis by Chandrasekhar, Smith, and Jorgensen [J. Am. Chem. Soc. 107, 154 (1985)]. The new solvent coordinate quantifies instantaneous solvent-induced polarization relative to the equilibrium average charge density at each point along the reaction pathway. On the basis of likelihood scores and committor distributions, the new solvent coordinate improves upon the description of solvent dynamical effects relative to previously proposed solvent coordinates. However, it does not increase the transmission coefficient or the accuracy of a transition state theory rate calculation.
A quick measuring method for yield temperatures of materials under constant prestress at ultra-high temperatures
Authors: Yue Xing , Wei Zhen , Peng Xianghe , Xue Yucong , Chen Xiang , Fu Tao
Published: July 2020

A new method for the rapid measurement of the yield temperatures of the material subjected to constant prestress at ultra-high temperatures was proposed, combining electric heating with non-contact image measurement technology. In this method, the yield temperature could be determined with a small number of thermal cycles in which the peak temperature increases with an increase in the number of thermal cycles, and in each cycle, the material is heated to a prescribed peak temperature and then cooled. There are two pairs of tiny sharp protrusions in the central part of the specimen. During the test, the surface optical image is recorded and analyzed with code Halcon to determine the temperature and elongation of the specimen. The time of each test is less than 20 min, so the influence of over-heating on the properties and microstructure of the material can be avoided. It is worth noting that the developed method can effectively reduce the test time and cost without breaking the specimen, and should have great potential in testing for the mechanical properties of materials at ultra-high temperatures.
Interface engineering for graphene nanowalls/silicon Schottky solar cells prepared by polymer-free transfer method
Authors: Zhang Ling , Huang Feifei , Li Shuai , He Song , Yu Meng , Fu Junchi , Yang Qinru , Huang Ruiming , Cheng Qijin
Published: July 2020

To date, almost all reported graphene nanowalls (GNWs)/Si solar cells are fabricated through the direct deposition of GNWs on the silicon wafer. In this work, we report a polymer-free transfer method of GNWs grown on the copper foil for the fabrication of GNWs/Si solar cells. This allows us to further improve the photovoltaic performance of the solar cells by means of interface engineering. An optimized photovoltaic conversion efficiency (PCE) of the as-fabricated GNWs/Si solar cell can reach up to 4.99%. Furthermore, the PCE of the device is further improved by introducing the spiro-OMeTAD thin film as an interface layer, which serves as an electron-blocking and hole-transporting layer through tuning the band structure of the solar cells. Without any chemical doping and anti-reflecting coating, the maximum PCE of 8.27% has been achieved for the GNWs/spiro-OMeTAD/Si solar cell through optimizing the dopant content and the thickness of the spiro-OMeTAD thin film. We believe that our study indicates a new route for the fabrication of high-efficiency, low-cost GNWs/Si Schottky heterojunction solar cells without the need for chemical doping of the GNWs.
A simple model to scope out parameter space for indirect drive designs on NIF
Authors: Callahan D. A. , Hurricane O. A. , Kritcher A. L. , Casey D. T. , Hinkel D. E. , Opachich Y. P. , Robey H. F. , Rosen M. D. , Ross J. S. , Rubery M. S. , Young C. V. , Zylstra A. B.
Published: July 2020

We present a simple model to scope out parameter space for indirect-drive, inertial confinement fusion designs for the National Ignition Facility laser. Because the parameter space is large, simple models can be used to identify regions of parameter space for further study with more sophisticated models and experiments. We include a model for Hohlraum radiation drive and symmetry—both based on empirical scalings from the data. The model for radiation drive is based on assuming that the high atomic number (Z) Hohlraum wall dominates the energy balance during the high power, peak of the pulse (≳300 TW). We find that the time-dependent radiation drive flux can be described by the running integral of the laser energy divided by the Hohlraum area multiplied by constant slopes in two distinct time periods. The first period is when the laser power rises rapidly, so the radiation temperature increases due to changes in laser power and wall albedo. The second period is during peak power—here, the laser power is typically held constant—so, the radiation temperature increases only due to changes in the wall albedo. This model is applied to several NIF designs with different Hohlraum sizes, laser pulse length durations, and peak powers and energies. Drive and symmetry models can be combined to find regions of parameter space that have high capsule absorbed energy while maintaining a symmetric implosion. We propose a new metric for evaluating designs based on minimizing the radius at which the maximum implosion kinetic energy is achieved.
Molecular dynamics simulations of key physical properties of nanodielectrics manufactured with epoxy resin doped with C60, C70, and C60 derivatives
Authors: Wang Tianyu , Zhang Guixin , Li Dayu , Hou Yicen
Published: July 2020

With the rapid development of high-voltage direct current transmission systems and trends of miniaturization and integration of power and electronic equipment, higher requirements have been imposed on the key physical properties of insulating materials, such as their electrical insulation and thermal and mechanical properties. This has made research on the modification of epoxy resin by doping with nanoparticles a timely topic. In this paper, molecular dynamics simulations are used to study changes in various key physical properties of composites after doping epoxy resin with C60, C70, or the C60 derivatives phenyl-C61-butyric acid methyl ester ([60]PCBM) and bis-phenyl-C61-butyric acid methyl ester (Bis[60]PCBM). All doping treatments effectively reduced the thermal expansion coefficient, the free volume ratio, and relative permittivity; inhibited molecular chain segment motion; and increased thermal conductivity as well as Young's modulus, bulk modulus, and shear modulus. The effects on glass transition temperature were not significant. Furthermore, the analysis indicated that Bis[60]PCBM had the most prominent effects. Therefore, doping epoxy resin with Bis[60]PCBM may be an effective material modification solution for improving dielectric properties in the future.
Nanoexplosion initiated by short-wavelength radiation: Optical breakdown in soft matter revisited
Authors: Janulewicz K. A. , Jach K. , Świerczyński R. , Bartnik A. , Kostecki J. , Wachulak P. , Fiedorowicz H. , Kim C. M.
Published: July 2020

The term “laser microexplosion” has been introduced to stress the violent character of the optical breakdown by laser radiation under conditions of tight focusing. Generally, the starting phase of the breakdown has been neglected by the assumption of absorption triggered by the presence of damage precursors. The application of the plasticity–elasticity theory in the analysis of the dynamics of this phenomenon has not been extensively examined to date. This paper formulates a phenomenological model attempting to explain the creation of nanovoids in a soft matter under irradiation by a flux of extreme ultraviolet (XUV)/soft x-ray photons. The combined action of plastic deformation and dissociation waves on soft matter is found to be responsible for the material modifications. It is suggested that localized (volume≃λ3) abundance of energy, coming most likely from photon bunching, constitutes the real onset of the photo-ablative decomposition. It is shown that the coincidental presence of some small number of energy carriers (2–3 XUV photons in the considered case) in such a small volume triggers processes denoted from now on as a laser nanoexplosion. The effect is considered to be the first step in the optical breakdown followed by an intense material removal resembling, to some extent, a phase explosion.
Neutron fluence distribution in experiments with 3 MA deuterium gas-puff z-pinch
Authors: Cikhardt J. , Klir D. , Shishlov A. V. , Kokshenev V. A. , Rezac K. , Cherdizov R. K. , Dudkin G. N. , Fursov F. I. , Kravarik J. , Kubes P. , Kurmaev N. E. , Munzar V. , Novotny J. , Ratakhin N. A. , Turek K. , Varlachev V. A.
Published: July 2020

Deuterium gas-puff z-pinches are very efficient laboratory sources of neutron pulses. Using a novel hybrid gas-puff load on the GIT-12 generator, a significant increase in the neutron yields up to 5.6×1012 is reached. At the same time, a very broad neutron energy spectrum up to energies on the order of tens of MeV is observed. In these experiments, the neutrons are produced not only by the D(d,n)3He (DD) nuclear reaction but also by reactions of multi-MeV deuterons with the experimental hardware. The angular distribution of the neutron fluence and dependence of the fluence on the distance from the z-pinch are measured using neutron activation diagnostics. By this method, a number of produced non-DD neutrons and anisotropy of DD neutron emission are evaluated.
Detecting band profiles of devices with conductive atomic force microscopy
Authors: Li Ranran , Taniguchi Takashi , Watanabe Kenji , Xue Jiamin
Published: July 2020

Band profiles of electronic devices are of fundamental importance in determining their properties. A technique that can map the band profile of both the interior and edges of a device at the nanometer scale is highly demanded. Conventional scanning tunneling spectroscopy (STS) can map band structure at the atomic scale but is limited to the interior of large and conductive samples. Here, we develop contact-mode STS based on a conductive atomic force microscope that can remove these constraints. With this technique, we map the band profile of MoS2 transistors with nanometer resolution at room temperature. A band bending of 0.6 eV within 18 nm of the edges of MoS2 on an insulating substrate is discovered. This technique will be of great use for both fundamental and applied studies of various electronic devices.
Charge influence on point defect interactions with xenon bubbles in uranium dioxide
Authors: Yang L. , Wirth B. D.
Published: July 2020

The interaction of xenon (Xe) bubbles with small self-defects in uranium dioxide (UO2) has been studied using molecular statics simulations. The results show that the pressure and size of bubbles have a minimal impact on the heterogeneity of the interaction between a charge neutral Xe bubble and charged point defects, while the local charge distribution around the bubble overwhelmingly determines the interaction strength and critical interaction distance. The charge effect on the interactions between Xe bubbles and defects was further confirmed by assessing the point defect interaction energies with negatively or positively charged Xe bubbles. The Xe density, or pressure, has a much smaller effect on the interaction energy between charged bubbles and small defects at least for low and medium pressure bubbles. The interactions between charged Xe bubbles and point defects basically follow the Coulomb electrostatic interaction law, which is independent of the empirical potentials employed for the Xe–UO2 system in this work.
WRe26–In2O3 probe-type thin film thermocouples applied to high temperature measurement
Authors: Tian Bian , Liu Yan , Zhang Zhongkai , Zhao Libo , Liu Zhaojun , Shi Peng , Lin Qijing , Mao Qi , Lu Dejiang , Jiang Zhuangde
Published: July 2020

A novel probe-type thin film thermocouple has been fabricated successfully for high temperature measurement applications. WRe26 (tungsten–26% rhenium)–In2O3 thermoelectric materials were used in the thermocouples to achieve high thermoelectric output and high temperature resistance. The films were deposited on a cylindrical substrate by magnetron sputtering technology. The annealing process of the thermocouples was studied to achieve optimal performance. The calibration results showed the thermoelectric output of WRe26–In2O3 thin film thermocouples reached 93.7 mv at 700 °C, and its sensitivity was 165.5 µV/°C under the temperature of the cold junction, which was 133.8 °C. The thermocouples developed in this work have great potential for practical applications.
Atomistic simulation for the interaction between dislocation and solute atoms, clusters, and associated physical insights
Authors: Wang Peng , Song Zhicheng , Li Qianqian , Wang Hongtao
Published: July 2020

Solid-solution hardening (SSH), originated mainly from the point obstacles with prescribed resistance (short-range) or spherical inclusions with purely dilatational eigenstrain (long-range), is critical to materials science and technological applications. Dislocation gliding in solid-solution hardening alloys generally undergoes both short-range and long-range interactions. However, the respective contribution of each aspect remains unclear. Here, we successfully decouple the short-range lattice distortion and long-range size misfit of the solid-solution hardening effect by introducing two scaling factors (s1 and s3) and analyzing the contributions of each aspect on the solute/dislocation interaction, respectively. For scaling factor s1, the interaction energy is localized, resembling the short-range interactions without volume change. The scaling factor s3 is equivalent to a dilatation/constriction center with volume change. The interaction energy is a long-range parameter and well predicted from the pure continuum elasticity perspective. Large-scale molecular dynamics (MD) simulations reveal the unique impacts of two strengthening mechanisms on dislocations with different scaling factors. It is found that the energy landscape and size misfit effect of the solute atoms play important roles in the SSH effect. With deeply understanding the SSH effects and the rapidly increasing computational power, it may pave a practical way to apply MD simulations on complex strengthening mechanism studies.
Exactly solvable model for transmission line with artificial dispersion
Authors: Shvartsburg A. B. , Artekha S. N. , Artekha N. S.
Published: July 2020

The problem of the emergence of wave dispersion due to the heterogeneity of a transmission line is considered. An exactly solvable model helps us to better understand the physical process of a signal passing through a non-uniform section of the line and to compare the exact solution and solutions obtained using various approximate methods. Based on the transition to new variables, the developed approach made it possible to construct exact analytical solutions of telegraph equations with a continuous distribution of parameters, which depend on the coordinates. The flexibility of the discussed model is due to the presence of a number of free parameters, including two geometric factors characterizing the lengths of inhomogeneities in values of the inductance L and of the capacitance C. In the new variables, the spatiotemporal structure of the solutions is described using sine waves and elementary functions, and the dispersion is determined by the formulas of the waveguide type. The dispersive waveguide-like structure is characterized by the refractive index N and the cutoff frequency Ω. The exact expressions for the complex reflection and transmission coefficients are derived. These expressions describe phase shifts for reflected and transmitted waves. The following interesting cases are analyzed: the passage of waves without phase change, the reflectionless passage of waves, and the passage of signals through a sequence of non-uniform sections. The developed mathematical formalism can be useful for the analysis of a wider range of problems.
The role of two-stage phase formation for the solid-state runaway reaction in Al/Ni reactive multilayers
Authors: Neuhauser T. , Tinti G. , Leiste H. , Casati N. , Ulrich S. , Stüber M. , Woll K.
Published: July 2020

While extensively studied for heating rates below 1.7 K/s and above 1000 K/s, the solid-state phase transformations in Al/Ni reactive multilayers have not been examined at intermediate heating rates between 100 K/s and 1000 K/s. Combined nanocalorimetry and time-resolved synchrotron x-ray diffraction studies are utilized to address this range of heating rates for multilayers with an overall composition of 10 at. % Ni and a bilayer thickness of 220 nm. It was found that a two-stage phase formation of Al3Ni proceeds up to a heating rate of 1000 K/s. The two growth stages occur in the solid-state and are kinetically separated. The activation energy of the first growth stage is determined to be 137 kJ/mol, which agrees well with the literature data at low heating rates. At 1000 K/s, a transition to a runaway reaction is observed. Unusual for metallic multilayers, the reaction proceeds completely in the solid-state which is also known as “solid flame.” Using nanocalorimetry, a critical input power density for ignition of 5.8 × 104 W/cm3 was determined. The rapid succession of the two Al3Ni formation stages was identified as the underlying mechanism for the self-sustaining reaction.
Effects of natural frequency ratio on vortex-induced vibration of a circular cylinder in steady flow
Authors: Zhao Ming
Published: July 2020

This paper investigates the effects of the natural frequency ratio on the vibration response of an elastically mounted circular cylinder in fluid flows at a low Reynolds number of 200 and a mass ratio of 2. The natural frequency ratio (RF) is defined as the ratio of natural frequency in the in-line direction to that in the cross-flow direction. Compared with previous studies, this paper extended the range of natural frequency ratios from 1–2 to 1–4 and found the most complex vibration and wake flow occur at natural frequency ratios of 2.5 and 3. Modes 2S (two single vortices), 2P (two pairs of vortices), and P+S (one pair and a single vortex) are defined as flow modes where two single vortices, two pairs of vortices, and one pair plus and one single vortices are shed from the cylinder in one period of vibration, respectively. The new findings for RF = 2.5 and 3 include a new 2P mode that only exists when RF = 2.5 and 3, a bi-stable wake mode where the wake flow could be either the 2P or the P+S mode, depending upon the initial condition, and, most interestingly, a tri-stable wake mode where the wake flow could be the 2P, P+S, or non-lock-in mode. In bi-stable and tri-stable regimes, once one wake flow mode is set, it does not change to other modes. In addition, the vibrations for a specific flow velocity but different modes may have different amplitudes, but their vibration frequencies are the same. The mode T wake flow is a flow mode where the flow switches between two modes alternately and the vibration has a beating feature. Three types of flow switching in mode T are found: 2S–1S switch, 2S–P+S switch, and 2S–2P switch. Mode 1S is a mode where two single vortices are shed in two vibration periods. It cannot exist itself and must co-exist with mode 2S. A 270°–360° phase between the displacements in the in-line and cross-flow directions suppresses the formation of the mode 2P wake, and a 0°–45° phase stimulates the mode 2P wake.
Effective basis set extrapolations for CCSDT, CCSDT(Q), and CCSDTQ correlation energies
Authors: Karton Amir
Published: July 2020

It is well established that extrapolating the coupled-cluster single double triple [CCSD and (T)] correlation energies using empirically motivated extrapolation exponents can accelerate the basis set convergence. Here, we consider the extrapolation of coupled-cluster expansion terms beyond the CCSD(T) level to the complete basis set (CBS) limit. We obtain reference CCSDT–CCSD(T) [T3–(T)], CCSDT(Q)–CCSDT [(Q)], and CCSDTQ–CCSDT(Q) [T4–(Q)] contributions from cc-pV{5,6}Z extrapolations for a diverse set of 16 first- and second-row systems. We use these basis-set limit results to fit extrapolation exponents in conjunction with the cc-pV{D,T}Z, cc-pV{T,Q}Z, and cc-pV{Q,5}Z basis set pairs. The optimal extrapolation exponents result in noticeable improvements in performance (relative to α = 3.0) in conjunction with the cc-pV{T,Q}Z basis set pair; however, smaller improvements are obtained for the other basis sets. These results confirm that the basis sets and basis set extrapolations used for obtaining post-CCSD(T) components in composite thermochemical theories such as Weizmann-4 and HEAT are sufficiently close to the CBS limit for attaining sub-kJ/mole accuracy. The fitted extrapolation exponents demonstrate that the T3–(T) correlation component converges more slowly to the CBS limit than the (Q) and T4 terms. A systematic investigation of the effect of diffuse functions shows that it diminishes (i) in the order T3–(T) > (Q) > T4–(Q) and (ii) with the size of the basis set. Importantly, we find that diffuse functions tend to systematically reduce the T3–(T) contribution but systematically increases the (Q) contribution. Thus, the use of the cc-pVnZ basis sets benefits from a certain degree of error cancellation between these two components.
Permutationally invariant polynomial potential energy surfaces for tropolone and H and D atom tunneling dynamics
Authors: Houston Paul , Conte Riccardo , Qu Chen , Bowman Joel M.
Published: July 2020

We report permutationally invariant polynomial (PIP) fits to energies and gradients for 15-atom tropolone. These include standard, augmented, and fragmented PIP bases. Approximately, 6600 energies and their associated gradients are obtained from direct-dynamics calculations using DFT/B3LYP/6-31+G(d) supplemented by grid calculations spanning an energy range up to roughly 35 000 cm−1. Three fragmentation schemes are investigated with respect to efficiency and fit precision. In addition, several fits are done with reduced weight for gradient data relative to energies. These do result in more precision for the H-transfer barrier height. The properties of the fits such as stationary points, harmonic frequencies, and the barrier to H-atom transfer are reported and compared to direct calculations. A previous 1D model is used to obtain the tunneling splitting for the ground vibrational state and qualitative predictions for excited vibrational states. This model is applied to numerous fits with different barrier heights and then used to extrapolate the H and D atom tunneling splittings to values at the CCSD(T)-F12 barrier. The extrapolated values are 2.3 and 0.14 cm−1, respectively for H and D. These are about a factor of two larger than experiment, but within the expected level of agreement with experiment for the 1D method used and the level of the electronic structure theory.
Low-frequency Raman scattering in WSe2−MoSe2 heterobilayers: Evidence for atomic reconstruction
Authors: Holler Johannes , Meier Sebastian , Kempf Michael , Nagler Philipp , Watanabe Kenji , Taniguchi Takashi , Korn Tobias , Schüller Christian
Published: July 2020

We investigate WSe2–MoSe2 heterobilayers with different twist angles θ±δ between the two layers by low-frequency Raman scattering. In sufficiently aligned samples with θ=0° or θ=60° and δ≲3°, we observe an interlayer shear mode (ISM), which is a clear sign of a commensurate bilayer structure, i.e., the layers must undergo an atomic reconstruction to form R-type or H-type stacking orders. We find slightly different ISM energies of about 18 cm–1 and 17 cm–1 for H-type and R-type reconstructions, respectively, independent of the exact value of θ±δ. Our findings are corroborated by the fact that the ISM is not observed in samples with twist angles, which deviate by δ>3° from 0° or 60°. This is expected since, in such incommensurate structures, with the possibility of Moiré-lattice formation, there is no restoring force for an ISM. Furthermore, we observe the ISM even in sufficiently aligned heterobilayers, which are encapsulated in hexagonal Boron nitride. This is particularly relevant for the characterization of high-quality heterostructure devices.
Role of various scale-similarity models in stabilized mixed subgrid-scale model
Authors: Inagaki Kazuhiro , Kobayashi Hiromichi
Published: July 2020

We investigate the physical role of various scale-similarity models in the stabilized mixed model [K. Abe, “An improved anisotropy-resolving subgrid-scale model with the aid of a scale-similarity modeling concept,” Int. J. Heat Fluid Flow 39, 42 (2013); M. Inagaki and K. Abe, “An improved anisotropy-resolving subgrid-scale model for flows in laminar–turbulent transition region,” Int. J. Heat Fluid Flow 64, 137 (2017)] and evaluate their performance in turbulent channel flows. Among various models in the present study, the original model combined with the scale-similarity model for the subgrid-scale (SGS)-Reynolds term yields the best prediction for the anisotropy of the grid-scale (GS) velocity fluctuations and the SGS stress, even in coarse grid resolutions. Moreover, it successfully predicts large intensities of the spectra close to the cut-off scale in accordance with the filtered direct numerical simulation, whereas other models predict a rapid decay of the spectra in the low-wavelength region. To investigate the behavior of the models close to the cut-off scale, we analyze the budget equation for the GS Reynolds stress spectrum. The result shows that the scale-similarity model for the SGS-Reynolds term plays a role in the enhancement of the wall-normal velocity fluctuation close to the cut-off scale. Thereby, it activates turbulence close to the cut-off scale, leading to a reproduction of the proper streak structures observed in wall-bounded turbulent flows. The reproduction of velocity fluctuations close to the cut-off scale and turbulent structures is a key element for further development of SGS models.
Interparticle acoustic radiation force between a pair of spherical particles in a liquid exposed to a standing bulk acoustic wave
Authors: Hoque S. Z. , Sen A. K.
Published: July 2020

We elucidate the interparticle force between a pair of particles suspended in a liquid exposed to a standing bulk acoustic wave. A three-dimensional model based on the perturbation technique and tensor integral method is employed to predict the interparticle force by subtracting the time-averaged primary radiation force due to the scattering effect from the time-averaged total radiation force due to combined scattering and re-scattering effects. The results show that irrespective of the sizes of particles at the nodal plane, interparticle force Fs* is attractive and symmetric and scales with the product of wavenumber (k) and interdistance (δx) as Fs*∼kδx−4. By studying the interparticle force between a pair of particles located out of the nodal plane, we unravel that the interparticle force is independent of their positions and depends on the horizontal (parallel to the nodal plane) and vertical interdistances. Our results reveal interparticle force changes from attractive to repulsive at a critical interdistance, attributed to the competition between time-averaged second-order pressure and velocity terms. We found that for a pair of particles parallel to the nodal plane, the interparticle force is independent of their distance from the nodal plane. Considering the total radiation force as the sum of the interparticle force, axial primary force, and drag force, we demonstrate a methodology for experimental quantification of the interparticle force. The interparticle force predicted from the model shows good agreement with experimental data (within 5%). Our study sheds light on interparticle forces that will facilitate more accurate estimation of forces on particles in an acoustic field.
Thermal convection-diffusion crystal for prohibition and modulation of wave-like temperature profiles
Authors: Xu Liujun , Huang Jiping
Published: July 2020

Periodic structures have various applications in wave systems, such as atomic crystals, photonic crystals, and phononic crystals. Here, we extend the related physics from wave systems to convection-diffusion systems and propose the concept of thermal convection-diffusion crystals, referring to a periodic porous medium with moving fluid. Phenomenally speaking, only the temperature profiles with allowed frequencies can propagate stably in a thermal convection-diffusion crystal, and those with forbidden frequencies try to change their frequencies for stable propagation. As an application of thermal convection-diffusion crystals, we further design a thermal frequency modulator to manipulate wave-like temperature profiles. These results broaden the application scope of periodic structures in convection-diffusion systems and enlighten further development of thermal management and thermal metamaterials with thermal convection-diffusion crystals.
On-the-fly ab initio semiclassical evaluation of vibronic spectra at finite temperature
Authors: Begušić Tomislav , Vaníček Jiří
Published: July 2020

To compute and analyze vibrationally resolved electronic spectra at zero temperature, we have recently implemented the on-the-fly ab initio extended thawed Gaussian approximation [A. Patoz et al., J. Phys. Chem. Lett. 9, 2367 (2018)], which accounts for anharmonicity, mode–mode coupling, and Herzberg–Teller effects. Here, we generalize this method in order to evaluate spectra at non-zero temperature. In line with thermo-field dynamics, we transform the von Neumann evolution of the coherence component of the density matrix to the Schrödinger evolution of a wavefunction in an augmented space with twice as many degrees of freedom. Due to the efficiency of the extended thawed Gaussian approximation, this increase in the number of coordinates results in nearly no additional computational cost. More specifically, compared to the original, zero-temperature approach, the finite-temperature method requires no additional ab initio electronic structure calculations. At the same time, the new approach allows for a clear distinction among finite-temperature, anharmonicity, and Herzberg–Teller effects on spectra. We show, on a model Morse system, the advantages of the finite-temperature thawed Gaussian approximation over the commonly used global harmonic methods and apply it to evaluate the symmetry-forbidden absorption spectrum of benzene, where all of the aforementioned effects contribute.
The effect of Te dopant on the optical and electrical properties of high-resistivity AlSb crystals
Authors: Yin Ziang , Jie Wanqi , Zhang Xianggang , Wang Tao
Published: July 2020

Aluminum antimonide (AlSb) has a great potential application in electronic devices used at high temperatures. However, the properties of available AlSb crystals were still far away from the theoretical ones due to the high density of variant defects, especially point defects. Here, an improvement in optical transmittance and resistivity of AlSb was achieved by doping the as-grown AlSb with appropriate content of Te, through which the absorption of a spin split-off-heavy-hole band transition near 1.65 μm disappeared and the resistivity was increased from 102 to 106 Ω cm. It was suggested that the residual acceptors with the binding energy EA of 37.4 meV were compensated by a Te donor with ED = 71 meV in the AlSb:Te crystal, according to the evaluation of the competing recombination (e, A0) and (Te0, A0). An energy band model was proposed to describe the recombination process and the underlying mechanism. The photo-response of the high resistance AlSb:Te crystal, illuminated by a pulsed LED light in the visible light range, revealed that the ratio of photocurrent to dark current was 128, indicating a great potential application for room-temperature photo-detection.
Electrical control of antiferromagnets for the next generation of computing technology
Authors: Amin O. J. , Edmonds K. W. , Wadley P.
Published: July 2020

Antiferromagnets are a class of magnetically ordered material with zero net magnetization. A swathe of recent experimental studies have shown that electrical control of antiferromagnetic order is possible by two distinct mechanisms: field-like and damping-like torques. This could be revolutionary for the next generation of computing technologies, as the properties of antiferromagnets are advantageous for high speed, high density memory applications. Here, we review the electrical control of antiferromagnets via field-like and damping-like torques as well as distinguishing from pervasive non-magnetic effects that have raised questions about the origins of electrically measured switching signals.
Time-resolved reconstruction of turbulent flows using linear stochastic estimation and sequential data assimilation
Authors: He Chuangxin , Liu Yingzheng
Published: July 2020

The present work concentrates on the reconstruction of the time-resolved turbulent flows from probe signals and low sampling rate flow fields using linear stochastic estimation (LSE) and sequential data assimilation (DA). The separated and reattached flow over a blunt plate is used as the benchmark configuration. Experimental data are acquired with a microphone array (34 probes) installed on the plate surface to capture the pressure fluctuation at a sampling rate 1000 Hz, and with planar particle image velocimetry (PIV) measuring the two-dimensional two-component (2D2C) velocity fields synchronized with the microphones at 1 Hz. LSE is conducted first to estimate the raw temporal sequence of the flow field from PIV and microphone data. This temporal sequence then serves as the observations for the DA process based on continuous adjoint formulation for the flow field correction and pressure determination. The LSE results show that an appropriate size of proper orthogonal decomposition (POD) database should be evaluated considering the combined error induced by the truncation of the mapping function M, the size of the POD database, and the scaling of the model coefficient for the compensation of M truncation. Subsequently, the LSE reconstructions using the POD database of size Nt = 100 are employed as the observations in the DA process. The mean flow field is recovered quite well, while the normal Reynolds stress also has a significant improvement compared to large-eddy simulation. The temporal variation of the LSE reconstruction is significantly improved, and the resultant fluctuating pressure coefficient distribution agrees reasonably well with the microphone measurement.
Global convergence in the balance between leaf water supply and demand across vascular land plants
Authors: Wen Yin , Zhao Wan-li , Cao Kun-fang
Published: July 2020

Coordination between the density of veins (water supply) and stomata (demand for water) has been found in the leaves of modern angiosperms and also in ferns. This suggests that this coordinated development is not a unique adaptation of derived angiosperms that enables their high productivity. To test this, we compiled leaf vein and stomatal density data from 520 land vascular plant species including derived angiosperms, basal angiosperms, gymnosperms and ferns. We found global coordination across vascular land plants, although the relationships were not significant in gymnosperms and vessel-less angiosperms. By comparing the evolution of xylem conduit elements with variation in the density of veins and stomata and theoretical stomatal conductance among plant lineages, we found that the physiological advantage of modern angiosperms is associated with the emergence of xylem with low intraconduit resistance and leaves with high vein and stomata densities. Thus our results indicate two major events associated with surges in xylem hydraulic capacity in angiosperms: (1) the origin of vessels and (2) the emergence of vessels with simple perforation plates, which diminished physical limitations on stomatal conductance. These evolutionary innovations may have enabled derived angiosperms to be more productive and adaptive to the changing climate.
Sensorimotor adaptation and aftereffect to frequency-altered feedback in Mandarin-speaking vocalists and non-vocalists
Authors: Ning Li-Hsin
Published: July 2020

This research examined sensorimotor adaptation and aftereffect in trained vocalists and non-vocalists whose native
language is Mandarin. The adaptive frequency-altered feedback paradigm involving a baseline of normal auditory feedback, a
training phase of incrementally or decrementally changed feedback, and a test phase of normal auditory feedback was administered.
The participants were asked to produce the sustained vowel /a/, Mandarin /ma1/ (“mother”), and Mandarin /ma2/ (“hemp”). The
results show that the vocalists compensated less than the non-vocalists, suggesting that the vocalists’ audio-motor
representations for pitch could be more entrenched than the non-vocalists’. All the participants displayed sensorimotor
adaptation, indicating that online recalibration is an innate and automatic process. The presence of the aftereffect, however,
depended on the stimulus type and vocal training experience. It appeared in all speakers’ responses to downward shift of /ma1/ and
/ma2/, but only in the non-vocalists’ responses to /a/.
The role of duration in speech plans uncovered by startling auditory stimulus
Authors: Chiu Chenhao
Published: July 2020

This study investigated how speech targets of different durations may be specified in speech plans and the release in response to startling auditory stimulus (SAS) triggering. In particular, we examined whether differentiated musical training background affects responses in terms of the preservation of duration. The results show that facilitated reaction time (RT) is only observed in SAS-induced responses shorter than 500 ms, suggesting that targets longer than 500 ms may not be as susceptible to SAS-induced rapid release. While both musically trained and untrained participants lacked accuracy in producing targets with fixed durations, they were able to differentiate syllable lengths, even though duration does not denote phonemic contrasts in Mandarin. The results also show a degree of compensation to elevated pitch level from musically trained participants, suggesting that they may have a higher sensitivity to pitch level even within a limited duration window.
A systematic review of occupational radiation individual dose monitoring among healthcare workers exposed in Africa
Authors: Gbetchedji Arnaud A , Houndetoungan Gilles D , Hounsossou Hubert C , Journy Neige , Haddy Nadia , Rubino Carole , Biaou Olivier , Medenou Daton , Amoussou-Guenou Kuassi M , de Vathaire Florent , Allodji Rodrigue S
Published: July 2020

Dosimetric monitoring is useful to limit exposures to ionising radiation in medical occupational settings, and reduce subsequent health risks. Scientific literatures, such as the UNSCEAR report 2017 and International Atomic Energy Agency Report 2014b, updated information on this subject; however, few African works have been found. This is the reason why we undertook this study, which summarises existing information on monitoring external radiation exposure doses for the whole body, using data from medical workers on this continent. Using standard terms and combining different keyword searches for radiation dose monitoring among radiology healthcare workers in Africa, from the titles, abstracts, and full texts, we found 3139 articles in the PubMed/MEDLINE, Google Scholar and INIS databases. Two reviewers screened the retrieved publications based on predefined eligibility criteria to identify relevant studies, extract key information from each, and summarise the data in table form. A total of 20 potentially relevant articles were identified. Among these 20 articles, 15 reported the overall average annual effective dose. Studies included in this systematic review represent an inventory of the radiation protection of medical workers in various African countries, with a focus on the monitoring of occupational radiation exposure. The size of studied populations ranged between 81 and 5152 occupational exposed workers. The mean annual effective doses ranged from 0.44 to 8.20 mSv in all specialities of medical sectors, while diagnostic radiology ranged from 0.07 to 4.37 mSv. For the nuclear medicine and radiotherapy from medical groups, the mean annual effective dose varied between 0.56 and 6.30 mSv. Industrial and research/teaching sectors data varied between 0.38 to 19.40 mSv. In conclusion, more studies implemented on dosimetric monitoring in Africa are needed to get a real picture of occupational exposure in the continent.