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Electron–phonon coupling is an important energy transfer mechanism in solids after ultrafast laser excitation. In this study, we present an extreme ultraviolet (EUV) and infrared (IR) pump-probe photoemission experiment to investigate the electron–phonon coupling in nonequilibrium gold. The energy of IR-laser-emitted photoelectrons is shifted due to the EUV photoemission and oscillates with a ∼ 4 T H z frequency. Such oscillation is considered as the effective excitation of the longitudinal acoustic phonon mode in gold through the spectral-dependent electron–phonon coupling. Our study showcases the capability of time-resolved photoemission electron microscopy to monitor the non-equilibrium lattice vibrations with ultrahigh spatial and temporal resolution. [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]

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]

The binary nitride coatings corresponding to Ti, Zr, Nb, Mo, and Ta have good thermal stability, hardening wear resistance, and high-temperature oxidation resistance. Therefore, the high-entropy alloy nitride coating composed of these five elements is expected to show excellent mechanical properties, and it is suitable for extending tool life in dry-cutting environments. In this paper, (TiZrNbMoTa)Nx high-entropy nitride films were synthesized using a multitarget nonequilibrium magnetron sputtering technique. The paper aimed at investigating the effects of different nitrogen flow rates (FN) on the microstructure and mechanical properties of the films. The results show that, with the increase in FN, the deposition rate gradually decreased, the films exhibited a face-centered cubic structure, and the grain gradually changed from coarse columnar crystals to ultrafine grain structures. The hardness, elastic modulus, and binding force all showed a tendency to increase and then decreased with increasing FN. The hardness and elastic modulus reached their maximum values of 34.39 and 400.97 GPa, respectively, at an FN of 60 SCCM, and the formation of covalent bonds and grain refinement promoted the increase in hardness. This research provided a theoretical foundation for designing and preparing high-entropy ceramic coatings with high performance. [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]

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]

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]

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]

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]

High-mobility spin-polarized two-dimensional electron gas (2DEG) at the interfaces of complex oxide heterostructures provide great potential for spintronic device applications. Unfortunately, the interfacial ferromagnetism and its associated spin polarization of mobile electrons and negative magnetoresistance (MR) are too weak. As of now, obtaining enhanced interfacial ferromagnetism and MR and strong spin-polarized 2DEG is still a great challenge. In this paper, we report on the realization of strong spin-polarized 2DEG at the interface of EuTiO3/SrTiO3 (110) heterostructures, which were prepared by directly depositing 39-nm EuTiO3 films onto as-received SrTiO3 (110) substrates. Hall and Kondo effects, low-field MR, Shubnikov–de Haas (SdH) oscillation, and magnetic hysteresis loop measurements demonstrate that high mobility electrons (1.4 × 104 cm2 V−1 s−1) accumulate at the interface of the heterostructures, which are not only highly conducting and show SdH oscillations with a non-zero Berry phase but also show a large out-of-plane and in-plane butterfly-like negative low-field MR whose magnitude is unprecedentedly large (46%–59% at 500 Oe and 1.8 K), approximately one to two orders higher than those of previously reported spin-polarized 2DEG systems. The strong spin polarization of the interfacial 2DEG is attributed to the presence of interfacial Eu2+ 4f (3.6–4 μB/f.u.) and Ti3+ 3d moments. Our results may provide guidance for exploring strong spin-polarized 2DEG at the interface of rare-earth titanate–strontium titanate heterostructures. [ABSTRACT FROM AUTHOR]

A novel floating-electrode silicon pixel detector has been proposed. The novel configuration of the floating electrode in the silicon pixel detector reduces the size of the collecting cathode and decreases both the capacitance and leakage current of the detector compared to the conventional silicon pixel detector. For the design, we used a 200 × 200 µm2 detector as the model to analyze the impact of varying numbers of floating rings on the electrical performance [Wu et al., AIP Adv. 11(2), 025315 (2021)]. We used Technology Computer Aided Design simulation to compare and analyze the simulated electric field, potential, capacitance, and breakdown voltage of the detector. The results show that decreasing the gap-to-width ratio of the floating electrode, as well as increasing the quantity of floating rings, enhances the detector's performance. [ABSTRACT FROM AUTHOR]

An extremely thin metasurface is proposed for manipulating underwater reflected waves. Each metasurface unit is only 1/61.7 of the target wavelength in thickness and comprises an air cavity capped with a thin vibration plate held in place by rubber spacers on steel supports. The unit-cell design is thin, simple, and can be adjusted to obtain a full 2π phase shift in water waves that are reflected from the metasurface. It also provides this phase shift for a broad frequency range of 20–800 Hz for incident waves. The effectiveness of the design and the resolution of the expected effect is demonstrated for sharp focusing, self-bending, and directional carpet cloaking, which are applications with great potential in energy harvesting, underwater communication, and submarine stealth and antidetection. [ABSTRACT FROM AUTHOR]

We realize single-mode, waveguide-coupled, electrically driven silicon light emitting diodes in commercial, unmodified silicon photonics foundry processes and develop a model of both the electrical and optical behavior to understand the performance limitations. We measure a center wavelength of 1130 nm, a 90 nm 3 dB optical bandwidth, and 200 pW of optical power propagating in each direction. We show on-chip modulation and detection of the generated light using native resonant photodetectors integrated in the same chip. Our work unveils a new native light source available in silicon photonics processes, which can find applications ranging from device screening and fabrication quality assessment to imaging, refractive index sensing, or intra-chip communication. [ABSTRACT FROM AUTHOR]

We demonstrate photon-counting single-pixel imaging in the ultraviolet region. Toward this target, we develop a high-performance compact single-photon detector based on a 4H-SiC single-photon avalanche diode (SPAD), where a tailored readout circuit with active hold-off time is designed to restrain detector noise and operate the SPAD in the free-running mode. We use structured illumination to reconstruct 192 × 192 compressed images at a 4 fps frame rate. To show the superior capability of ultraviolet characteristics, we use our single-pixel imaging system to identify and distinguish different transparent objects under low-intensity irradiation and image ultraviolet light sources. The results provide a practical solution for general ultraviolet imaging applications. [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]

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]

Adding a small amount of polymers can achieve significant drag reduction effects. However, for external flows, the common homogeneous mixing and diffusing injection methods are not feasible. As an alternative, the present work developed a novel water-soluble polymer composite coating. The coating made use of the film-forming property of polyvinyl alcohol with polyethyleneoxide (PEO, a well-known drag reduction polymer) incorporated into it. When the coating dissolved, PEO continuously dispersed into the external flow. The surface characteristics of the water-soluble polymer coating were characterized. Drag reduction tests were conducted using a gravity circulation system. The coating exhibited a maximum drag reduction rate (DR) of 7% in the coating section and 27% in the downstream section. The larger percentage and the greater molecular weight of PEO not only promoted polymer drag reduction but also increased the surface roughness. Competition between effects of drag reduction and surface roughness led to complex effects in the coating section. It was also found that partial coating could induce significant drag reduction effects. The optimal length ratio of coated to total surface was related to the polymer characteristics and the speed of the main flow. The 1/4 and 1/2 coating resulted in a maximum DR of approximately 7% (Re = 27 523) in the test plate section for coatings with 10 000 wppm PEO, while the 1/4 coating had a maximum DR of approximately 9% (Re = 11 468) for coatings with 20 000 wppm PEO. These results indicated that such drag-reducing composite polymer coatings have great potential to be applied in underwater equipment. [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]

A novel resonator-based metasurface is devised to control reflected underwater waves. Each metasurface unit is constructed with an aluminum plate attached to a lead mass. By tailoring the thickness of the plate, full 2π phase shift of the reflected wave can be achieved. Examples of redirection, focusing, and directional carpet cloaking are demonstrated as applications. The target frequency can be as low as 500 Hz and it can operate in a broadband range. Slight modifications allow the design to perform excellently from tens to thousands of hertz. This metasurface provides a new design paradigm when there is a need to manipulate low frequency underwater waves, such as in submarines for stealth operation or detection-signal manipulation to provide deceptive information. [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]

Guided wave-based nondestructive testing and structural health monitoring methods have been developed to exhibit attractive potentials and best prospects for rapid and sensitive detection of defects or damage in engineering structures. Different modes of guided waves can provide different sensitivities of damage detection. However, the multimode and mode conversion nature of guided waves poses significant challenges to mode purification of received signals. This study aims to design a metamaterial-based smart transducer for mode purification of Lamb waves in a plate, which can filter out an undesired mode of the Lamb wave to enhance sensing and actuating signals of a dominated mode. The smart transducer consists of a periodic array of shunted piezoelectric unimorphs with staggered polarization directions and is bonded on the surface of a host plate. Numerical and experimental results show that a local resonance bandgap for an anti-symmetric Lamb wave, rather than a symmetric Lamb wave, can be obtained and tuned through the shunting inductance circuit. Within such mode bandgap, the wave control for propagating a specific mode of the Lamb wave can be further realized, i.e., the mode of the Lamb wave is purified. The design presented herein offers enhanced capabilities in controlling guided wave propagation for engineering applications and nondestructive testing techniques. [ABSTRACT FROM AUTHOR]

We follow the assumption that the dilatational response of glassy polymers can be characterized by a back-stress type analog that includes a thermal expansion for each elastic component and with a viscosity that is dependent on the expansion of the elastic back-stress component. To this, we add the assumption of an unloaded equilibrium temperature that correlates to the past processing through the viscous flow. After setting this in a thermodynamically consistent structure, elastic, elastic back-stress, thermal expansion, back-stress thermal expansion, heat capacity, and viscous damping are evaluated using existing experiments for the response of polycarbonate over the glassy and rubbery ranges. For the demonstration, this is done entirely using a WLF shift factor that is augmented to include, in addition, back strain superposition. We then examine the resulting model under different thermal and mechanical loadings that have the material passing through the glass transition. [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]

Vacuum ultraviolet photodissociation dynamics of N 2 O + h v → N 2 (X 1 Σ g +) + O(1 S 0) in the short wavelength tail of D1Σ+ band has been investigated using the time-sliced velocity-mapped ion imaging technique by probing the images of the O(1S0) photoproducts at a set of photolysis wavelengths including 121.47 nm, 122.17 nm, 123.25 nm and 123.95 nm. The product total kinetic energy release distributions, vibrational state distributions of the N 2 (X 1 Σ g +) photofragments and angular anisotropy parameters have been obtained by analyzing the raw O(1S0) images. It is noted that additional vibrationally excited photoproducts (3≤v≤8) with a Boltzmann-like feature start to appear except the non-statistical component as the photolysis wavelength decreases to 123.25 nm, and the corresponding populations become more pronounced with decreasing of the photolysis wave-length. Furthermore, the vibrational state specific anisotropy parameter β at each photolysis wavelength exhibits a drastic fluctuation near β=1.75 at v<8, and decreases to a minimum as the vibrational quantum number further increases. While the overall anisotropy parameter β for the N 2 (X 1 Σ g +) + O(1 S 0) channel presents a roughly monotonical increase from 1.63 at 121.47 nm to 1.95 at 123.95 nm. The experimental observations suggest that there is at least one fast nonadiabatic pathway from initially prepared D1Σ+ state to the dissociative state with bent geometry dominating to generate the additional vibrational structures at high photoexcitation energies. [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]

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]

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]

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]

Jet flow-control technology is a promising area of fluid research. In this work, the flow-control effect of a curved-surface jet in an incoming flow of Mach = 5 and its underlying control mechanism are experimentally studied using high-speed photography and dynamic force measurement. From the establishment of complete stability of the flow field, the evolutionary process can be roughly divided into five stages: two equilibrium stages (short and long term), jet acceleration stage, bow shock formation stage, interference removal stage, and stable state. By defining the pressure ratio (PR) as an independent variable, it is found that the flow control of the jet occurs through different wave-system structures. The interaction between the jet and the incoming flow produces an oblique shockwave and expansion waves. The shockwave generates thrust and forms a virtual rudder surface; the expansion waves interact with the backflow region and the separated shear layer to generate lift. Moreover, PR has an optimal solution of PRopt. When PR < PRopt, the effect of flow control is related to α, Ve, and ρe, and the greater the PR, the stronger the flow-control effect. When PR > PRopt, the flow-control effect is related to α and ρe, and the larger the PR, the weaker the effect of the shockwave and the stronger the effect of the expansion waves but the slower the growth. In experiments, the thrust, pitching moment, and lift increased by 17.43%, 17.75%, and 9.45%, respectively, because of the appearance of wave-system structure when PRopt = 201.32. [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]

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]

The actuations generated by the plasma synthetic jet actuator (PSJA) may become weak under multiple pulses when the discharge frequency increases. In order to further study the frequency characteristics of the actuations, the high-speed Schlieren method is adopted for the experimental study on a nanosecond plasma synthetic jet actuator (NS-PSJA) made of the machinable ceramic. Three typical working states are captured by the numbers of Schlieren measurements, which are continuous, critical, and discontinuous states. For a deep understanding, the relationship between the discharge frequency and the working states of the NS-PSJA is discussed in two aspects: heat and electric charge. The critical and the saturated discharge frequencies are defined, respectively. In addition, the effects of the geometry on the frequency characteristics of the NS-PSJA are also studied such as the shape of the orifice, the electrode spacing, the depth of the cavity, and the height of the electrode. The results suggest that those geometric parameters affect the accumulation of the heat and electric charge, causing the changes of both the critical and the saturated discharge frequencies. [ABSTRACT FROM AUTHOR]

Traditional pixel detectors are neatly arranged rectangular or square electrodes that cover almost the entire surface. Large electrode areas lead to high capacitance, and capacitance is the primary factor affecting detector noise. A large noise signal will reduce detector detection performance and the system S/N ratio. We have designed a spiral ring electrode silicon detector cell with n-type silicon bulk and systematically studied its electrical properties, including electric potential distribution, electric field distribution, electron concentration distribution, leakage current, full depletion voltage, and detector capacitance. It has been verified that the spiral ring electrode silicon detector has a smaller capacitance than the traditional detector and a smaller depletion voltage compared with the previously designed structures such as the inner circle broom-shaped structure. At the same time, high position resolution pixel detectors can be made by the array of these detector cells. [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]

Understanding the thermal conductivity of highly disordered materials has received growing interest. However, conventional thermal conductivity models fail in these materials due to the breakdown of the "phonon" image caused by the disorder of interatomic force constant. In this work, a quantitative thermal conductivity model is proposed based on "propagon" and "diffuson," which can better describe the lattice vibrational modes in disordered materials. Lattice dynamics analysis is performed to investigate the vibrational modes in the disordered solid solution Y1−xNbxO1.5+x. The contribution to thermal conductivity from the propagons, which exhibit phonon-like high eigenvector periodicity, is calculated by the Debye–Klemens–Callaway equation. The contribution from diffusons, which exhibit low eigenvector periodicity, is calculated by Cahill's equation. The proposed thermal conductivity model produces an accurate temperature dependence for the Y1−xNbxO1.5+x that cannot be attained in the conventional models. Both the lattice dynamics analysis and thermal conductivity fitting suggest a decreasing trend with the Nb content for the propagon modes in Y1−xNbxO1.5+x. [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]

In order to reduce the noise of traditional silicon pixel detectors, a new type of low-capacitance silicon pixel detector with three floating electrodes is proposed in this paper, which reduces the cathode area while keeping the volume unchanged. A TCAD simulator is used to simulate the electrical performance of the detector and obtain electrical characteristics including depletion voltage, capacitance, and leakage current. According to the results of simulation and calculation, compared with the traditional silicon pixel detector with the same volume, the capacitance of the detector without floating electrodes was reduced by 68%, the capacitance of the detector with three floating electrodes was reduced by 68%, and the leakage current was reduced by two orders of magnitude. [ABSTRACT FROM AUTHOR]

Voltage-modified Kerr magnetometer has been widely used to measure the voltage-modulated magnetic properties in multiferroic magnetic/ferroelectric heterostructures, where the Kerr signal change is considered to be in proportion to magnetization change, i.e., the magneto-optical Kerr effect. However, the total Kerr signal changes might also incorporate contribution from the electro-optical effect of the ferroelectric layer in the multiferroic heterostructure. Here, we evaluate quantitatively, by combining analytical calculations with experimental observations, such electro-optical contribution in the total voltage-induced Kerr signal changes with comparison to those from Kerr effect via converse magnetoelectric coupling. Influences of several parameters, including the magnetic film thickness on the Kerr signal changes, are also investigated. [ABSTRACT FROM AUTHOR]

Enabling the traditional concentric silicon drift detector (CSDD) does not need an external voltage divider in the application; hence, a novel CSDD structure is proposed in this paper, in which resistor chains of equal width are deposited equally between the cathode rings and come in contact with the cathode rings. The new CSDD can achieve voltage division automatically and only needs to bias the voltage on the cathodes of the innermost ring and the outermost ring. In addition, floating cathodes were designed between the cathodes to obtain a nearly straight line drift channel and to reduce the low electric field area near the surface. The electrical properties of three types of floating cathodes (called floating cathodes of a single-ring, floating cathodes of a double-ring, and floating cathodes of a four-ring) were simulated and compared using the technology computer aided design tool. Under the field effect between the floating cathodes and the bulk, the electric field near the surface increased substantially. Moreover, the electric field near the surface of the CSDD with the floating cathodes of a double-ring changes the most uniformly so that the drift path is the straightest. [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]

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]

Previous experimental studies on electrostatic ion-cyclotron waves (EICWs) and their instability were often performed in a narrow plasma column in Q-machines, in which the wave was conventionally generated via the instability driven by an electron current parallel to a magnetic field. The propagation characteristics of wave patterns have seldom been studied, especially the different characteristics in pulse and continuous wave patterns. In this paper, we present the experimental launching of the EICW via a grid applied with either a pulsed or a sinusoidal external excitation voltage in a magnetized plasma device. Either pulsed or continuous EICWs were excited, and the wave pattern trajectories were observed. Using the time-of-flight method, both phase and pulse (group) velocities of the wave signals were directly measured. It was shown that for the continuous EICW excitation, the measured dispersion relation is in agreement with the result from the kinetic theory in some range of parameters in the fundamental and harmonic frequency bands. The dependence of the measured pulse and phase velocities on the magnetic field shows agreement with the fluid theory only in the low field strength case but is closer to the result from the kinetic theory in the high field strength case. [ABSTRACT FROM AUTHOR]

In this study, a novel three-dimensional trench detector structure was proposed. The detector structure includes trench electrodes and columnar electrodes. The columnar electrodes are distributed in the middle, the middle of the sides, and the four corners of the cross section of the substrate. A cross-shaped electrode is etched from top to bottom, and a polygonal trench electrode is etched from bottom to top; the bottom of the cross-shaped electrode abuts the top of the polygonal electrode. Electrical characteristics of the novel detector are simulated by Technology Computer Aided Design simulation, and we can obtain that this design reduces the area of the bottom low electric field, optimizes the electric field, and reduces the mutual interference between the cells. [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]

Semiconducting molybdenum disulfide (MoS2) has drawn a lot of attention for its exceptional electronic and optoelectronic properties. Despite the potential advantages, the large contact resistance at the metal–MoS2 interfaces has been one of the biggest obstacles for the realization of ideal MoS2 transistors. One solution to improve the metal–MoS2 interfaces is to use the graphene electrodes. Here, we provide a selective etching method for fabricating graphene-contacted MoS2 transistors. It has been proved that the graphene could be totally etched with Ar+ plasma treatment, and the multilayer MoS2 flake can also be reduced layer by layer with Ar+ plasma treatment. By etching graphene selectively in graphene–MoS2 heterostructures, one can obtain graphene-contacted MoS2 transistors successfully. The transistor reported in this paper shows an on–off ratio about 106 and a carrier mobility about 42 cm2 V−1 s−1. This selective etching method would be beneficial for some other graphene-contacted electronic devices. [ABSTRACT FROM AUTHOR]

Interactions between neighboring cells often occur in a semiconductor silicon detector array. That is, there are high-energy particles incident on one cell of the detector that generate an electric signal for the cell, while weak signals are also generated in other neighboring cells. Therefore, isolation of the detector cells is an important factor in the performance of the detector, particularly for its energy resolution. To eliminate the dead space in the 3D-trench-electrode detector proposed by Brookhaven National Laboratory, a novel three-dimensional (3D) detector, the 3D-Open-Shell-Electrode Detector (3DOSED), was proposed in 2018, in which good isolation between cells was achieved. To verify this and determine the optimal structure design, a Silvaco technology computer-aided design simulation tool was used to simulate the electrical characteristics of the detector in 3D. The distributions of the electric field and the weighting field of 3DOSEDs were obtained with different opening gap angles. A single minimum ionizing particle was used that was incident vertically on the middle of the central collection electrode and peripheral trench electrode of the detector cell, according to the Ramo theorem of the principle of induced-current generation, and the mathematical software matlab was employed to calculate the induced current and carrier drift time. The interference current between the neighboring cells of a 3DOSED was obtained. Good isolation was found between neighboring cells in the 3DOSED. [ABSTRACT FROM AUTHOR]