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Understanding vacuum ultraviolet photodissociation dynamics of Carbonyl sulfide (OCS) is of considerable importance in the study of atmospheric chemistry. Yet, photodissociation dynamics of the CS(X1Σ+) + O(3Pj=2,1,0) channels following excitation to the 21Σ+(ν1′,1,0) state has not been clearly understood so far. Here, we investigate the O(3Pj=2,1,0) elimination dissociation processes in the resonance-state selective photodissociation of OCS between 147.24 and 156.48 nm by using the time-sliced velocity-mapped ion imaging technique. The total kinetic energy release spectra are found to exhibit highly structured profiles, indicative of the formation of a broad range of vibrational states of CS(1Σ+). The fitted CS(1Σ+) vibrational state distributions differ for the three 3Pj spin–orbit states, but a general trend of the inverted characteristics is observed. Additionally, the wavelength-dependent behaviors are also observed in the vibrational populations for CS(1Σ+, v). The CS(X1Σ+, v = 0) has a significantly strong population at several shorter wavelengths, and the most populated CS(X1Σ+, v) is gradually transferred to a higher vibrational state with the decrease in the photolysis wavelength. The measured overall β-values for the three 3Pj spin–orbit channels slightly increase and then abruptly decrease as the photolysis wavelength increases, while the vibrational dependences of β-values show an irregularly decreasing trend with increasing CS(1Σ+) vibrational excitation at all studied photolysis wavelengths. The comparison of the experimental observations for this titled channel and the S(3Pj) channel reveals that two different intersystem crossing mechanisms may be involved in the formation of the CS(X1Σ+) + O(3Pj=2,1,0) photoproducts via the 21Σ+ state. [ABSTRACT FROM AUTHOR]

The spin-forbidden O(3P2) + CO(X1Σ+, v) channel formed from the photodissociation of CO2 in the low energy band centered at 148 nm is investigated by using the time-sliced velocity-mapped ion imaging technique. The vibrational-resolved images of the O(3P2) photoproducts measured in the photolysis wavelength range of 144.62–150.45 nm are analyzed to give the total kinetic energy releases (TKER) spectra, CO(X1Σ+) vibrational state distributions, and anisotropy parameters (β). The TKER spectra reveal the formation of correlated CO(X1Σ+) with well resolved v = 0–10 (or 11) vibrational bands. Several high vibrational bands that were observed in the low TKER region for each studied photolysis wavelength exhibit a bimodal structure. The CO(X1Σ+, v) vibrational distributions all present inverted characteristics, and the most populated vibrational state changes from a low vibrational state to a relatively higher vibrational state with a change in the photolysis wavelength from 150.45 to 144.62 nm. However, the vibrational-state specific β-values for different photolysis wavelengths present a similar variation trend. The measured β-values show a significant bulge at the higher vibrational levels, in addition to the overall slow decreasing trend. The observed bimodal structures with mutational β-values for the high vibrational excited state CO(1Σ+) photoproducts suggest the existence of more than one nonadiabatic pathway with different anisotropies in the formation of O(3P2) + CO(X1Σ+, v) photoproducts across the low energy band. [ABSTRACT FROM AUTHOR]

This letter focuses on the non-contact generation of surface acoustic waves by using a continuous wave laser moving along the sample surface. The desired large-amplitude surface acoustic waves can be generated efficiently if the laser moving speed matches the Rayleigh value, which is a typical characteristic of the continuous laser moving excitation method. The different amplitudes of surface acoustic waves were generated at different laser moving speeds, and the largest amplitude occurred when the laser moving speed approached the surface acoustic wave velocity of the material. Subsequently, the influence of laser moving distance on the wave's amplitude under Rayleigh resonance conditions was investigated. The surface acoustic waves' amplitude grew linearly with the laser's moving distance in the elastic range. In brief, this paper provides a novel method to excite large amplitude surface acoustic waves by simply changing the moving speed and moving distance of the light. [ABSTRACT FROM AUTHOR]

Gas dissolution or accumulation regulating in an aqueous environment is important but difficult in various fields. Here, we performed all-atom molecular dynamics simulations to study the dissolution/accumulation of gas molecules in aqueous solutions. It was found that the distribution of gas molecules at the solid–water interface is regulated by the direction of the external electric field. Gas molecules attach and accumulate to the interface with an electric field parallel to the interface, while the gas molecules depart and dissolve into the aqueous solutions with a vertical electric field. The above phenomena can be attributed to the redistribution of water molecules as a result of the change of hydrogen bonds of water molecules at the interface as affected by the electric field. This finding reveals a new mechanism of regulating gas accumulation and dissolution in aqueous solutions and can have tremendous applications in the synthesis of drugs, the design of microfluidic device, and the extraction of natural gas. [ABSTRACT FROM AUTHOR]

The carrier transport associated with interband tunneling in semiconductors has been investigated extensively both experimentally and theoretically. However, the associated heat exchange from interband tunneling is not discussed in depth. Due to the nanoscale nature of the tunneling phenomenon, people tend to use a "resistor model" to compute the heat generated. We present our analysis of heat exchange in tunneling junctions based on an extended Kane's model. We observe that the heat exchange is distinct when we apply forward bias, small reverse bias, and large reverse bias. In each of these bias regimes, we demonstrate that the internal temperature distribution of a tunneling junction can deviate from the simplified "resistor model" significantly. [ABSTRACT FROM AUTHOR]

The sliding dielectric barrier discharge (SL-DBD) has attracted attention due to its ability to suppress flow separation. This paper investigated the effect of SL-DBD on the flow field in the flat plate boundary layer by time-resolved particle image velocimetry. We obtained the finite-time Lyapunov exponent field and the Lagrangian coherent structures of the flow field through the velocity field. The results show the effect of SL-DBD has spatial differences, and SL-DBD will produce a "strong–weak–strong" spatial effect on the flow field. The directionality of the flow structure induced by SL-DBD is the main reason for the difference. SL-DBD will induce a large number of vortex structures in the local downstream area of the electrode. The vortex structure enhances the mixing and squeezing effects between the upper and lower flow fields. The upper flow field moves the lower flow field downward by about 0.1 mm through the squeezing effect. In addition, at the downstream region adjacent to the electrode, the oblique momentum injection of the SL-DBD is the dominant effect. At one electrode distance from the electrode, the SL-DBD induces a large number of vortex structures. However, when the distance from the electrode is twice the electrode spacing, the number of vortex structures decreases, and the structure becomes larger. The results show spatial differences in the perturbation of the flow field by SL-DBD, which cannot be ignored when SL-DBD is used to suppress flow separation. [ABSTRACT FROM AUTHOR]

Achieving broadband sound absorption in two-port open ducts is of fundamental importance in the acoustics, with wide applications ranging from noise control to duct sound mitigation. Yet the existing metamaterial designs are usually based on the use of Helmholtz-type cavities, posing limitations on the resulting absorption performance. Here, we propose and experimentally demonstrate a mechanism that uses coupling modulation of the resonance energy leakage and loss in ventilated metamaterials to realize optimal sound absorption. We design a slit-type unit cell as a practical implementation of the proposed mechanism and analytically prove its potential to obtain the desired leakage and loss factors simultaneously by properly adjusting the structural parameters. We benchmark our designed metamaterial with a conventional Helmholtz resonator-based design to demonstrate its advantage of sound absorption. Good agreement is observed between the theoretical predictions and experimental measurements. Our strategy represents a paradigm extending beyond classical models and opens up possibility for the design of high-efficiency acoustic absorbing devices and their applications in diverse scenarios especially broadband duct noise muffling. [ABSTRACT FROM AUTHOR]

The multidimensional motion ultrasonic motor with a single spherical stator is studied in this paper. It has the characteristics of miniaturization and can be used in precision motion applications. By bonding six identical pieces of piezoelectric ceramic onto the stator and applying the voltage signal of high frequency, the deformation of the inverse piezoelectric effect is used to excite the stator yaw vibration mode. The orthogonal superposition of the modes of the spherical stator on the driving foot produces elliptical trajectory around X, Y, and Z directions by different excitation methods. According to the yaw vibration mode of the spherical stator, 12 driving feet are designed to drive the rotation of the spherical rotor. The structure and mechanical characteristics of the motor are simulated by using simulation software, and the transient response of the stator driving foot was obtained, which proved its feasibility. Finally, the output performance of the motor in actual operation is given through experiments, which provides a new reference scheme in the field of precise multi-degree-of-freedom motion. At a voltage of 100 V and a frequency of 26.7 kHz, the prototype has a no-load speed of 73, 70, and 114 rpm around X, Y, and Z axes, respectively. [ABSTRACT FROM AUTHOR]

For a surface-piercing hydrofoil traveling at high speed, a turbulent hydraulic jump may arise at the intersection of the body with the free surface. This hydrodynamic phenomenon involves violent wave breaking, bringing great challenges for experimental analysis. In this work, a high-fidelity large eddy simulation is performed to study the turbulent air-entraining flow near foil. One advantage of the present simulation is that a quantitative analysis can be implemented even in the turbulent two-phase mixing region containing a large amount of entrained air, which is difficult for traditional experimental and theoretical approaches. We employ a conservative coupled level set/volume-of-fluid scheme to capture the free surface. A highly robust scheme is introduced to guarantee stability in simulating large density ratio two-phase flows. The present method is implemented based on a block-structured adaptive mesh, by which the efficiency of the high-fidelity simulation can be improved. The main flow features of the wedge-shaped hydraulic jump, including the wave patterns, free surface elevation, and frequency spectra, are compared with experimental data. We find that the flow structures show clear differences from those found in the canonical hydraulic jump, owing to the presence of the foil surface. Shoulder wave breaking starts at the trough of the mid-body, develops in a wedge shape, depends strongly on Froude number, and is responsible for most of the large-scale air entrainment. The properties of the turbulent hydraulic jump and some of the key quantities characterizing the air-entraining flow, including the spatial distribution of the bubble cloud, the void fraction, and the bubble/droplet size spectrum, are fully investigated for typical Froude numbers. [ABSTRACT FROM AUTHOR]

The present study investigates the discharge and flow characteristics of a sliding discharge (SD) driven by alternating current (AC) and negative direct current (DC) high voltage in continuous operation and burst-mode actuation in quiescent air. The burst frequency f is set at 20, 40, 50, and 100 Hz with a duty cycle τ fixed at 50%. Different actuation cases exhibit similar discharge morphologies and electrical properties. The results indicate that the flow induced by the horizontal body force generated by the SD undergoes the following stages: formation, intensification, accumulation, and stabilization. Based on the effects of the body force, the evolution of the induced flow field can be divided into three stages: the initial stage (starting-vortex stage), the transition stage, and the final stage. In continuous operation, the transition stage is marked by a complex flow structure, while the final stage is distinguished by a deflecting jet. When the burst frequency f ≤ 50 Hz, the duration of the transition stage increases with the burst frequency, and it becomes transient at f = 100 Hz due to the short voltage input time. Phase-averaged particle image velocimetry results indicate that the final stage of the burst-mode actuation can be categorized into three types mostly based on the interaction of the vortices from the AC and DC electrodes. Compared to the continuous operation, the application of the burst-mode actuation in this study has a shorter transition stage duration, resulting in a more rapid realization of flow control. [ABSTRACT FROM AUTHOR]

In this paper, a piezoelectric actuator with three symmetrical distributions is designed. Piezoelectric ceramics are polarized in a set manner. The excitation voltage signals of the same amplitude and different phases are applied to the actuator, and an elliptical trajectory is generated on the driving foot to drive the slide rail to move. Its driving principle is different from that of previous drivers of this type. For example, when moving in a certain direction, the horizontal displacement is formed by a mixture of the longitudinal vibration of one sub-actuator and the bending vibration of two sub-actuators, while the vertical displacement is generated by the bending vibration of the actuator. Through the close cooperation of the three sub-actuators, the output efficiency is greatly improved. The actuator is suitable for small high-precision control. First, the overall structure and working principle of the piezoelectric actuator are briefly introduced. Then, through the finite element analysis, the working mode with output performance and the motion track on the driving foot are analyzed. Finally, the output performance of the actuator is analyzed. When the voltage frequency is 200 Hz and the amplitude is 200 V, the maximum output speed is 5.1 mm/s and the maximum load of about 1.2 kg can be applied, which verifies that the actuator has good driving ability. [ABSTRACT FROM AUTHOR]

Metalized film capacitors in a.c. applications suffer high frequency and high voltage, which will induce electrode corrosion, leading to capacitance degradation. The intrinsic mechanism of the corrosion is oxidation caused by ionic migration in the oxide film formed on the electrode surface. In this work, a D–M–O illustration structure for the nanoelectrode corrosion process is established, and thereby, an analytical model is derived to study the influences of frequency and electric stress on corrosion speed in a quantitative approach. The analytical results well conform to the experimental facts. It is found the corrosion rate rises with frequency and finally tends to reach a saturation value. The electric field in oxide has an exponential-like contribution to the corrosion rate. In the case of aluminum metalized films, the saturation frequency and minimum field required for corrosion initiation are, respectively, 3434 Hz and 0.35 V/nm calculated by the proposed equations. [ABSTRACT FROM AUTHOR]

A one-dimensional (1D) unsteady and viscous flow model that is derived from the momentum and mass conservation equations is described, and to enhance this physics-based model, a machine learning approach is used to determine the unknown modeling parameters. Specifically, an idealized larynx model is constructed and ten cases of three-dimensional (3D) fluid–structure interaction (FSI) simulations are performed. The flow data are then extracted to train the 1D flow model using a sparse identification approach for nonlinear dynamical systems. As a result of training, we obtain the analytical expressions for the entrance effect and pressure loss in the glottis, which are then incorporated in the flow model to conveniently handle different glottal shapes due to vocal fold vibration. We apply the enhanced 1D flow model in the FSI simulation of both idealized vocal fold geometries and subject-specific anatomical geometries reconstructed from the magnetic resonance imaging images of rabbits' larynges. The 1D flow model is evaluated in both of these setups and shown to have robust performance. Therefore, it provides a fast simulation tool that is superior to the previous 1D models. [ABSTRACT FROM AUTHOR]

A novel spherical multi-degree-of-freedom ultrasonic motor is designed, which can achieve three-degree-of-freedom motion through the cooperative drive of three built-in traveling wave stators. The novel ultrasonic motor has the characteristics of compact structure and high power density. Additionally, in order to solve the problem of impedance mismatch between the ultrasonic motor and the driving power supply, a semi-analytical method of impedance matching based on parallel resonance is proposed according to the impedance characteristics of ultrasonic motor. Through the combination of theoretical derivation and finite element simulation, the ultrasonic motor impedance matching on the impedance circle is analyzed. By this method, the optimum matching inductor of the motor is determined. After matching, the motor obtains a larger vibration amplitude and higher transmission efficiency. Finally, the reliability of the method is verified by simulation and experiment, which provides a reference for further improving the motor performance. [ABSTRACT FROM AUTHOR]

Multiferroics that simultaneously exhibit ferroelectricity and ferromagnetism have recently attracted great attention due to their potential application in next generation electronic devices. However, only a few single-phase multiferroic materials exhibit ferroelectric and ferromagnetic orders at room temperature. Recently, some bismuth layer-structured Aurivillius compounds were reported as multiferroics at room temperature, but the origin of their magnetic property is still under debate because the net magnetization may originate from the presence of secondary phases that are not easily detected by laboratory XRD diffractometers. Here, textured Aurivillius phase Bi5.25La0.75FeCoTi3O18 ceramics were prepared by Spark Plasma Sintering. The ferromagnetic character of the ceramics was indicated by the magnetic field-induced reversible intensity changes of a certain set of crystalline planes belonging to the Aurivillius phase, as measured by in situ neutron diffraction under the applied magnetic field. The first principles calculations indicate that the ferromagnetism originates from double exchange interactions Fe3+–O–Fe3+, Co3+–O–Co3+, and Fe3+–O–Co3+ in the ferro-toroidal main phase. The magnetic-controlled ferroelectric domain switching was observed by piezoelectric force microscopy at room temperature. The prepared Aurivillius phase ceramics, with Co/Fe contributing to magnetization and polarization at the same time, can be considered an intrinsic room-temperature multiferroic. [ABSTRACT FROM AUTHOR]

In this article, we describe the use of a continuous-wave laser scanning method to generate non-dispersive surface acoustic wavepackets, which propagate along the sample surface without any waveform change. To achieve this goal, a coated linear elastic film on a non-linear substrate allows for careful balancing of dispersion and non-linearity effects. The scanning speed of the laser source and the thickness of the coated film were parametrically investigated to determine the optimal scanning speed for the generation of ultrasound for a given thickness of the coated film. In the first step, four different combinations of scanning speeds and the thickness of the coated film are presented to illustrate the generation of the narrowband ultrasound. The purpose of the scanning laser source is to effectively generate large amplitude ultrasound that takes the material into the nonlinear range. Further optimization through a careful matching combination of the scanning speed and the thickness of the coated film, whereby the dispersion effect was compensated entirely by the non-linearity effect, was used to generate non-dispersive ultrasonic wavepackets, which subsequently propagate with little distortion. The main findings of the simulations indicate that non-dispersive surface acoustic wavepackets for coated systems can be generated via the scanning laser source approach for specific values of scanning speed and thickness of the coated film. [ABSTRACT FROM AUTHOR]

Supersonic expansions to vacuum produce clusters of sufficiently small size that properties such as heat capacities and latent heat of evaporation cannot be described by bulk vapor thermodynamic values. In this work the Monte-Carlo Canonical-Ensemble (MCCE) method was used to provide potential energies and constant-volume heat capacities for small water clusters. The cluster structures obtained using the well-known simple point charge model were found to agree well with earlier simulations using more rigorous potentials. The MCCE results were used as the starting point for molecular dynamics simulations of the evaporation rate as a function of cluster temperature and size which were found to agree with unimolecular dissociation theory and classical nucleation theory. The heat capacities and latent heat obtained from the MCCE simulations were used in direct-simulation Monte-Carlo of two experiments that measured Rayleigh scattering and terminal dimer mole fraction of supersonic water-jet expansions. Water-cluster temperature and size were found to be influenced by the use of kinetic rather than thermodynamic heat-capacity and latent-heat values as well as the nucleation model. [ABSTRACT FROM AUTHOR]

The traditional stick-slip piezoelectric actuator uses a single flexible hinge structure, and the output force of the piezoelectric stack is greater than the clamping force between the driving foot and the slider, resulting in a small working stroke, slow speed, and poor load capacity. A new piezoelectric actuator based on a two-stage flexible hinge structure is proposed. The piezoelectric actuator uses a combination of a lever flexible hinge and a triangular flexible hinge. The working stroke and speed of the actuator are enlarged by the lever flexible hinge, and the output force of the piezoelectric stack is perpendicular to and greater than the clamping force between the driving foot and the slider through the triangular flexible hinge, which enhances the load capacity of the actuator. First, the structure and working principle of the piezoelectric actuator are presented. The lateral output displacement of the piezoelectric ceramic stack is amplified by the lever amplification structure so that the triangular flexible hinge structure is then used to convert the lateral displacement into a coupled motion composed of longitudinal and lateral displacement to drive the slide rail to generate total displacement. Then, the superiority of the piezoelectric actuator was verified through the analysis of displacement amplification and clamping force and finite element analysis. Finally, the performance of the piezoelectric actuator is studied. It can produce an output speed of 354.55 mm/s under a driving voltage of 4.7 kHz and 150 V, and the maximum load can reach 3 kg. This article provides a new design idea for stick-slip piezoelectric actuators. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations have been performed to investigate the behavior of the EMIM- BF4 ionic liquid for conditions similar to those of electrospray thrusters. To study the physics of ion extrusion a large system composed of approximately 2160 ion pairs was placed inside a platinum capillary and equilibrated. Diffusion coefficients and electrical conductivity were calculated and compared with literature values, showing good agreement and validating the use of a constrained dynamics model with a coarse-grained potential. An electric field was applied to the system in the longitudinal direction and the fraction of solvated and non-solvated emitted ions was analyzed. The threshold electric field for particle emission was found to be 1.2 V/nm, consistent with other reported work. [ABSTRACT FROM AUTHOR]

The converse magnetoelectric (ME) effect was investigated in bi-layered Ni/Pb(Zr0.52Ti0.48)O3 (PZT) thin films grown on Si substrates, with different thicknesses of Ni thin layers. By using an AC-mode magneto-optical Kerr effect method, it was revealed that the electric-voltage induced magnetization variation was dependent on the thickness of the Ni thin layer. The results showed that the Ni/PZT bilayered films with thick (about 40 nm) Ni films presented a dominative strain mediated ME coupling, whereas an interface-charge and strain co-mediated ME coupling might coexist in the Ni/PZT bilayered films with decreasing thickness (e.g., about 10 nm) of Ni films. [ABSTRACT FROM AUTHOR]

Using molecular dynamics (MD), we have studied the mechanism of heat accommodation between carbon dioxide clusters and monomers for temperatures and cluster size conditions that exist in homogeneous condensing supersonic expansion plumes. The work was motivated by our meso-scale direct simulation Monte Carlo and Bhatnagar-Gross-Krook based condensation simulations where we found that the heat accommodation model plays a key role in the near-field of the nozzle expansion particularly as the degree of condensation increases [R. Kumar, Z. Li, and D. Levin, Phys. Fluids 23, 052001 (2011)]. The heat released by nucleation and condensation and the heat removed by cluster evaporation can be transferred or removed from either the kinetic or translational modes of the carbon dioxide monomers. The molecular dynamics results show that the time required for gas-cluster interactions to establish an equilibrium from an initial state of non-equilibrium is less than the time step used in meso-scale analyses [R. Kumar, Z. Li, and D. Levin, Phys. Fluids 23, 052001 (2011)]. Therefore, the good agreement obtained between the measured cluster and gas number density and gas temperature profiles with the meso-scale modeling using the second energy exchange mechanism is not fortuitous but is physically based. Our MD simulations also showed that a dynamic equilibrium is established by the gas-cluster interactions in which condensation and evaporation processes take place constantly to and from a cluster. [ABSTRACT FROM AUTHOR]

Quantum and quasiclassical state-to-state dynamics for the NH + H′ reaction at high collision energies up to 1.6 eV was studied on an accurate ab initio potential energy surface. Both of the endothermic abstraction (NH + H′ → N + HH′) and thermoneutral exchange (NH + H′ → H + NH′) channels were investigated from the same set of wave packets using an efficient coordinate transformation method. It is found that the abstraction represents a minor reaction channel in the energy range studied, primarily due to endothermicity. The cross section for the abstraction reaction increases monotonically with the collision energy, while that for the exchange reaction is relatively energy insensitive. As a result, the thermal rate constant for the abstraction reaction follows the Arrhenius law, where that for the exchange reaction is nearly temperature independent. Finally, it is shown that the quantum mechanical results can be reasonably reproduced by the Gaussian-binning quasiclassical trajectory method and to a lesser extent by a quantum statistical model. [ABSTRACT FROM AUTHOR]

A coalescence model for homogeneous condensation of ammonia in supersonic expansions to vacuum has been developed using molecular dynamics trajectory calculations. The MD calculations show that the sticking probability increases as the ammonia cluster size increases or the cluster temperature decreases. In addition, the sensitivity of the sticking probability to cluster size decreases as the temperature decreases. Comparison of the Ashgriz-Poo semiempirical coalescence model with MD simulations show that for cluster sizes larger than 100 the former model may be used. To model homogeneous nucleation in an ammonia jet, direct simulation Monte Carlo (DSMC) simulations were performed for different stagnation pressure conditions using the MD simulation outcomes for smaller cluster-cluster collisions and the Ashgriz-Poo model for cluster sizes larger than 100. We found that, by including the combined coalescence model, the average cluster sizes and size distributions predicted by DSMC agree reasonably well with experiment. [ABSTRACT FROM AUTHOR]

BiFeO3 films with different thicknesses and crystallographic orientations were grown on LaNiO3-buffered Si substrates via a modified chemical route. Remarkable size effect in ferroelectric behavior was observed with thicker films exhibiting a larger polarization value, due to combined depolarization effect and microstructure of the BiFeO3 films. High resolution transmission electron micrograph revealed a complex strain state in the BiFeO3 films, and the net magnetic moment induced by the canting of the antiparallel spins was arranged in disorder in thicker films, presenting a spin-glass state; while in the thinner BiFeO3 films, the disorder spins turned to be orderly arranged to induce a ferromagnetic behavior. Thus there exists a competition between ferroelectric and magnetic behaviors as film thickness changes. Furthermore, magnetoelectric coupling was observed in the BiFeO3 films with a magnetic-field-induced electrical voltage of around 3.5 μV/Oe. [ABSTRACT FROM AUTHOR]

We present a finite temperature quantum mechanical study of the dynamical and structural properties of small 4HeN–CO2 clusters (N≤=17) using a path integral Monte Carlo (PIMC) method. The simulations were based on a He–CO2 interaction potential with explicit dependence on the asymmetric stretch of the CO2 molecule obtained at the CCSD(T) level. The shift of the CO2 antisymmetric stretching (ν3) band origin and effective rotational constant were calculated as a function of the cluster size. In excellent agreement with experimental observations, the CO2 vibrational band origin shifts and rotational constant show a turnaround near N=5, corresponding to a donut structure with the He atoms in equatorial positions of the linear dopant molecule [ABSTRACT FROM AUTHOR]

We propose a quantum tomography (QT) approach to retrieve the temporally evolving reduced density matrix in electronic state basis, where the populations and coherence between the ground state and excited state are reconstructed from the ultrafast electron diffraction signal. In order to showcase the capability of the proposed QT approach, we simulate the nuclear wavepacket dynamics and ultrafast electron diffraction of photoexcited pyrrole molecules using the ab initio quantum chemical CASSCF method. From the simulated time-resolved diffraction data, we retrieve the evolving density matrix in a crude diabatic representation basis and reveal the symmetry of the excited pyrrole wavepacket. Our QT approach opens the route to make a quantum version of "molecular movie" that covers the electronic degree of freedom and equips ultrafast electron diffraction with the power to reveal the coherence between electronic states, relaxation, and dynamics of population transfer. [ABSTRACT FROM AUTHOR]

Double-zero-index properties of electromagnetic and acoustic waveguides have been recently realized based on Dirac/Dirac-like cones at the Brillouin zone (BZ) center. However, very limited research has been devoted to double-zero-index structural systems of elastic waveguides, and almost no lattice system has been able to achieve multiple separated Dirac cones generated around different frequencies at the BZ center. Here, we report two separated elastic-wave Dirac-like cones, which are simultaneously achieved around different Dirac points at the BZ center, due to the accidental degeneracy and frequency repulsion effect in a Lieb-like lattice metamaterial. Using the proposed elastic medium, the double-zero-index properties of various elastic wave modes are theoretically analyzed, numerically computed, and experimentally observed at the neighborhood of both Dirac-like points. The performance of near total transmission without the phase change and the ability of wave-front shaping are unambiguously verified by numerical simulation and experimental measurements. [ABSTRACT FROM AUTHOR]

Convective heat transfer plays an important role in both the fundamental research and the development of high-performance heat exchangers. Inspired by blades of grass vibrating in the wind, we developed a self-agitator for convective heat transfer enhancement. Because of fluid-structure interactions, the agitator, with self-sustained vibration, can generate strong vortices to significantly break the thermal boundary layer and improve fluid mixing for enhanced convective heat transfer. In particular, we establish a methodology to link the vorticity field at a preferred frequency to the optimal improvement in the convective heat transfer. To identify the self-agitator preferred frequency, mode analysis is performed with simulation results using dynamic mode decomposition. Experimental results are also obtained to further validate the proposed approach. These results show that the proposed self-agitator design can improve the convective heat transfer by 120% in a conventional heat exchanger without additional pumping power requirements and can achieve a Nusselt number of up to 30 within the laminar flow region, which is improved by 200% with the same Reynolds number compared to the clean channel. [ABSTRACT FROM AUTHOR]

Presents a study which described the fabrication and performance of a type of solid-state hydrogen detector. Method of the study; Results and discussion; Conclusion.

A novel characterization method is presented to directly observe the pure converse magnetoelectric (ME) effect, i.e., the electric-field modification of magnetization, in composite magnetic/ferroelectric (FE) layered thin films. A low-frequency AC electric-voltage, rather than DC voltage bias, is applied to the FE thin films to minimize the leakage current, whereby the possible side effect of heating can be avoided. In particular, by synchronizing the frequency of the Kerr signal detector to the AC actuation voltage bias, the voltage-induced change of the magnetization in the magnetic films can be in situ recorded even under zero external magnetic fields. For illustration, this method is applied to two similar magnetic/FE composite thin films, with significant strain-mediated converse ME coupling being demonstrated in both cases. [ABSTRACT FROM AUTHOR]

Since the 3D-Open-Shell-Electrode Detector (3DOSED) is proposed and the structure is optimized, it is important to study 3DOSED’s electrical properties to determine the detector’s working performance, especially in the heavy radiation environments, like the Large Hadron Collider (LHC) and it’s upgrade, the High Luminosity (HL-LHC) at CERN. In this work, full 3D technology computer-aided design (TCAD) simulations have been done on this novel silicon detector structure. Simulated detector properties include the electric field distribution, the electric potential distribution, current-voltage (I-V) characteristics, capacitance-voltage (C-V) characteristics, charge collection property, and full depletion voltage. Through the analysis of calculations and simulation results, we find that the 3DOSED’s electric field and potential distributions are very uniform, even in the tiny region near the shell openings with little perturbations. The novel detector fits the designing purpose of collecting charges generated by particle/light in a good fashion with a well defined funnel shape of electric potential distribution that makes these charges drifting towards the center collection electrode. Furthermore, by analyzing the I-V, C-V, charge collection property and full depletion voltage, we can expect that the novel detector will perform well, even in the heavy radiation environments. [ABSTRACT FROM AUTHOR]

The behavior of a nanosecond pulsed sliding discharge plasma actuator with the ambient pressure from 27 to 101 kPa is experimentally investigated. The electric characteristics, discharge morphologies, and surface temperature distribution of the actuator supplied by constant voltages are studied under different pressure conditions. The threshold pressure for sliding discharge establishment is 54–75 kPa in this paper. The results show that the positive peak value of the current tends to increase as the pressure decreases. Time-integrated discharge images indicate that plasma luminosity and uniformity are enhanced under low-pressure conditions. The discharge morphology of the actuator at 27 kPa displays an alternating distribution of bright and dark stripes. The infrared thermal results demonstrate that decreasing the pressure increases the actuator's surface temperature, intensifies the intensity of spanwise temperature oscillations, and improves the homogeneity in the streamwise direction. [ABSTRACT FROM AUTHOR]

The quantum state-to-state rotationally inelastic quenching of N2O by colliding with a He atom is studied on an ab initio potential energy surface with N2O lying on its vibrational ground state. The cross sections for collision energies from 10−6–100 cm−1 and rate constants from 10−5–10 K are calculated employing the fully converged quantum close-coupling method for the quenching of the j = 1–6 rotational states of N2O. Numerous van der Waals shapes or Feshbach resonances are observed; the cross sections of different channels are found to follow the Wigner scaling law in the cold threshold regime and may intersect with each other. In order to interpret the mechanism and estimate the cross sections of the rotational energy transfer, we propose a minimal classical model of collision between an asymmetric double-shell ellipsoid and a point particle. The classical model reproduces the quantum scattering results and points out the attractive interactions and the potential asymmetry can affect the collision process. The resulting insights are expected to expand our interpretations of inelastic scattering and energy transfer in molecular collisions. [ABSTRACT FROM AUTHOR]

Al2O3 films are deposited directly onto graphene by H2O-based atomic layer deposition (ALD), and the films are pinhole-free and continuously cover the graphene surface. The growth process of Al2O3 films does not introduce any detective defects in graphene, suppresses the hysteresis effect and tunes the graphene doping to n-type. The self-cleaning of ALD growth process, together with the physically absorbed H2O and oxygen-deficient ALD environment consumes OH- bonds, suppresses the p-doping of graphene, shifts Dirac point to negative gate bias and enhances the electron mobility. [ABSTRACT FROM AUTHOR]

Thermoelectric materials have been considered as an alternative clean energy technology that can realize direct conversion between heat and electricity. However, few studies have focused on the underlying relationship between the bonding orbitals and physical properties, which has severely impeded the development of new thermoelectric materials with outstanding electrical properties. α-BaCu4S3 is a thermoelectric material that has a high density of states at the upper end of the valence band due to triply-degenerate Cu 3d orbitals in the CuS4 tetrahedral structure. Thus, it has a high Seebeck coefficient at the same carrier density among thermoelectric materials. α-BaCu4S3 shows a zT value of 0.22 at 750 K. A higher zT of 0.32 at 750 K was realized in BaCu3.96S3 by introducing copper vacancies. The current study provides a strategy to identify high-performance thermoelectric materials through high degeneracy of orbitals that comprise the electronic bands. [ABSTRACT FROM AUTHOR]

A new scenario to realize superfocusing of terahertz waves based on a gradient index (GRIN) metasurface is proposed. To design the GRIN material, a robust algorithm is presented and numerically demonstrated to retrieve the constitutive effective parameters (permittivity and permeability) of the metasurface from the measurement of S parameters. In addition, a new kind of unit cell with a simple structure is designed to verify the theory of effective parameters. By computing the effective refractive index of the unit cell using the algorithm, we design a plate with a thickness of approximately 0.11λ0 (free-space wavelength) at 0.967 THz to superfocus terahertz waves in one dimension. We also revise the theory of superfocusing to make full use of the coupling effect among the cells in the plate and are able to demonstrate it. Comprehensive simulations of focusing are provided, and the full width at half-maximum beam width reaches up to 0.167λ0 at a distance of 0.2λ0. The focusing depth can be further enhanced by decreasing the cell size of the metasurface. This work is beneficial for metasurface design, super-resolution imaging, and other applications in the near field. [ABSTRACT FROM AUTHOR]

Pulsed surface arc discharge (PSAD) is one of the essential techniques in flow control. In this paper, the effects of electrode configuration on heat transfer characteristics of PSAD and disturbance characteristics of PSAD on the flow field were investigated by thermal imaging technology and high-speed photography technology. By defining the curvature of curve (COC) of the electrode, we investigated the physical mechanism of the electrode configuration, affecting the PSAD disturbed flow field. The results show that the COC has the optimal solution COCopt. When COC ≤ COCopt, the smaller the COC, the more concentrated the PSAD disturbances to the flow field. When COC > COCopt, the electrode configuration will have an end point effect, resulting in a deviation between the theoretical COC and the real COC. The larger the COC, the stronger the end point effect, and the more concentrated the PSAD disturbances to the flow field. The COC affects the disturbance degree of PSAD to the flow field by distorting the electric field intensity distribution. The change in the electric field intensity causes the fluctuation frequency of the flow field to be inconsistent with the discharge frequency of the PSAD. The stronger the distortion degree of the electric field intensity, the stronger the high-frequency characteristics of the fluctuating frequency of the flow field, and the stronger the high-frequency characteristics of the flow mode of the flow field. In addition, we obtained the value range of COCopt within 0.5–0.7 through theoretical derivation and established a mathematical model of electrode structure's effect on the flow field's flow structure. [ABSTRACT FROM AUTHOR]

The complete flow structure and the composition of the flow structure generated by Pulsed Surface Arc Discharge in a Magnetic Field (M-PSAD) are the keys to explaining the plasma application mechanism. The experimental results show that the M-PSAD can produce plasma clusters and detonation waves. The thermal motion of charged particles in the plasma cluster is the main reason for the thermal effect of arc discharge. The detonation wave consists of the shock wave, Taylor expansion wave, and two different thickness zones of charged particles. The experimental results provide a profound physical mechanism for applying plasma. [ABSTRACT FROM AUTHOR]

A better understanding of the mechanism of flow separation suppression by a dielectric barrier discharge is essential for flow control. This paper investigates the mechanism of improving the aerodynamic performance of the airfoil by dielectric barrier discharge when the Reynolds number is in the range of 6 × 104–4 × 105. The results show that the disturbance of the gas discharge to the flow field will form a new flow structure. The fluctuating frequency of the new flow structure determines the ability of the plasma actuator to suppress flow separation. This investigation improves and develops the mechanism of plasma flow control. [ABSTRACT FROM AUTHOR]

This paper presents an ultrathin screen with magnetic substrate for broadband microwave reflectivity reduction. The magnetic substrate was fabricated by mixing a MnTi substituted M-type barium ferrite and a Co substituted W-type barium ferrite. The screen with the magnetic substrate thickness of 1.1 mm (λ0/25) can achieve the fractional bandwidth (Δf/f0) of 46% at X band, which almost increases by 150%, as compared to the corresponding screen with dielectric substrate. [ABSTRACT FROM AUTHOR]

Utilizing the anti-Zeno effect, we demonstrate that the resonances of ultracold molecular interactions can be selectively controlled by modulating the energy levels of molecules with a dynamic magnetic field. We show numerically that the inelastic scattering cross section of the selected isotopic molecules in the mixed isotopic molecular gas can be boosted for 2–3 orders of magnitude by modulation of Zeeman splittings. The mechanism of the resonant anti-Zeno effect in the ultracold scattering is based on matching the spectral modulation function of the magnetic field with the Floquet-engineered resonance of the molecular collision. The resulting insight provides a recipe to implement resonant anti-Zeno effect in control of molecular interactions, such as the selection of reaction channels between molecules involving shape and Feshbach resonances, and external field-assisted separation of isotopes. [ABSTRACT FROM AUTHOR]

The voltage-modulated magnetic behavior in multiferroic Ni/BaTiO3 heterostructures grown on SrTiO3 single crystal substrate was observed by the magneto-optical Kerr effect measurement in an AC modulation technique with synchronizing the frequency of the Kerr signal detector to the low-frequency AC actuation voltage. The results showed coexistence at room-temperature of two magnetoelectric (ME) mechanisms, i.e., strain- and interface charge-mediated couplings. The interaction between the different ME couplings leads to a remarkable thickness-dependent voltage modulation of the magnetic behavior. [ABSTRACT FROM AUTHOR]