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Fast electron beams (FEBs) are one of the main products of various active events and are ubiquitous in solar, space and cosmic plasmas. They reveal themselves in hard X-ray and radio emissions. The observed characteristics of X-ray and radio emissions sensitively depend on the energy distribution of FEBs, which usually have a power-law energy spectrum. As FEBs travel in the solar atmosphere, their energy distribution can considerably vary due to the interaction with ambient plasmas. Tang et al. investigated the evolution of the energy spectrum of the FEBs traveling along a flare loop and discussed the possible effects on associated hard X-ray (HXR) and radio emissions. Considering the ubiquitous coronal loops in active regions, in the present paper, we investigate the parametric evolution of the energy spectra of FEBs when propagating along coronal loops. Here, we take the sunpot atmospheric model as an approximate coronal loop atmosphere model. The results show that the energy loss has an important impact on the cutoff behavior and energy spectra of FEBs when precipitating in a coronal loop with density ratio n b /n e = 0.01. The initially single power-law spectrum with a steepness cutoff can evolve into a more complex double power-law spectrum or two “knees” power-law spectrum with a flattened steepness cutoff behavior or saturation cutoff behavior. Our calculations also demonstrate that the energy spectrum evolution is not obvious if n b /n 0 = 0.001 as Tang et al. asserted. The present results are helpful for a more comprehensive understanding of the dynamic spectra of HXR and radio emissions from FEBs.

Chemical oxygen demand (COD) reflects the degree of water damage by organic pollutants, and is an important indicator for water environment protection and marine hydrological monitoring, so it is very important to accurately measure COD. However, changes in ambient temperature and atmospheric noise cause huge deviations in the precise measurement of COD by optical-based water quality detectors. The purpose of this research is to realize the accurate measurement of COD of the optical water quality detector by compensating the environmental parameters of the water quality detector. The compensation model established in this paper is a particle swarm optimization (PSO) back-propagation neural network (BPNN), which can compensate for temperature and filter out atmospheric noise, named back-propagation neural network of particle swarm optimization of filter out atmospheric noise (FAN-PSO-BPNN). FAN-PSO-BPNN reduced the maximum relative error by 92.51%, root mean square error by 91.64%, coefficient of variation by 91.74%, and the distance between the maximum and minimum prediction errors by 92.94% compared with BPNN in filtering out atmospheric noise interference and temperature compensation. The optimization scheme proposed in this paper for BPNN is crucial and effective, and the FAN-PSO-BPNN compensation model improves the anti-interference ability of the water quality detector, guarantees the accurate measurement of COD in seawater, and helps the water quality detector to monitor in seawater for a long time.

The yttria-stabilized zirconia (YSZ) is a famous thermal barrier coating material to protect hot-end components of an engine. As a characteristic feature of the YSZ, the surface roughness shall play an important role in the interface thermal conductance between the YSZ and gas, considering that the gas is typically at an extremely high temperature. We investigate the effect of the surface roughness on the thermal conductance of the YSZ–gas interface with surface roughness described by nanoscale pores on the surface of the YSZ. We reveal two competitive mechanisms related to the microstructure of the pore, i.e., the actual contact area effect and the confinement effect. The increase of the pore depth will enlarge the actual contact area between the YSZ and gas, leading to enhancement of the solid–gas interface thermal conductance. In contrast to the positive actual contact area effect, the geometry-induced confinement effect greatly reduces the interface thermal conductance. These findings shall offer some fundamental understandings for the microscopic mechanisms of the YSZ–gas interface thermal conductance.

The gas permeation through nanoscale membranes like graphene has been extensively studied by experiments and empirical models. In contrast to planar membranes, the single-walled carbon nanotube has a natural confined hollow structure, which shall affect the gas permeation process. We perform molecular dynamics simulations to investigate the effect of the nanotube diameter on the gas permeation process. It is found that the permeance constant increases with the increase of the nanotube diameter, which can not be explained by existing empirical models. We generalize the three-state model to describe the diameter dependence for the permeance constant, which discloses a distinctive confinement-induced adsorption phenomenon for the gas molecule on the nanotube’s inner surface. This adsorption phenomenon effectively reduces the pressure of the bulk gas, leading to the decrease of the permeance constant. These results illustrate the importance of the adsorption within the confined space on the gas permeation process.

This paper presents a high-speed integrated circuit for narrow-gated single-photon detection. Due to the parasitic capacitor that exists in the avalanche photo-diode (APD), the avalanche signal pulse triggered by the received photon is easily mixed with unavoidable spike noise arising from the gated clock. The traditional double-ended architecture extracts avalanche signals by suppressing common-mode noise. In order to overcome the shortcomings of high cost and mismatch in the traditional architecture, this paper adopts a single-ended detection architecture and deals with the problem of spike noise from the perspective of the frequency domain. According to the difference between the frequency characteristics of the spike noise and the avalanche signal, the effective separation of the two signals can be realized in the frequency domain by a low-pass filter with a specific cut-off frequency. The signal-to-noise ratio of the detection system is improved by using the subsequent amplification and discrimination circuit, so as to realize sensitive detection of the avalanche signals. The proposed circuit is implemented in 180 nm complementary metal oxide semiconductor technology and occupies an effective area of 2.6 mm2. The test results show that the single-ended detection system can sensitively discriminate photon signals with an emission frequency below 20 MHz when the whole circuit, including the APD, is operated at room temperature, where the minimum voltage amplitude converted from the avalanche current of the APD is around 20 mV, and the stopband attenuation of the filter at 1 GHz frequency is −58.8 dB.

Few-layer graphene has been widely regarded as an efficient filter for gas separation, but the effect of the layer number on the gas permeation process is still unclear. To explore the layer number effect, we perform molecular dynamics simulations to investigate the gas permeation through a nanopore within the few-layer graphene. Our numerical simulations show that the permeation constant decreases with increasing layer number, which is analyzed based on the macroscopic Kennard empirical model. The macroscopic model is in good agreement with the numerical result in the limit of large layer number, but there are obvious deviations for the medium layer number. We generalize the macroscopic model by considering the nanoscale effect from the surface morphology of the nanoscale pore, which can well describe the layer number dependence for the gas permeation constant in the full range. These results provide valuable information for the application of few-layer graphene in the gas permeation field.

It is proposed that ratios of the sixth order to the second order cumulant ( \begin{document}$C_6/C_2$\end{document} ) of conserved quantities are sensitive to the chiral crossover transition. Recently, the negative \begin{document}$C_6/C_2$\end{document} was obtained in both theoretical Lattice QCD and experiments at \begin{document}$\sqrt{s_{NN}}$\end{document} = 200 GeV. In this study, we investigate the behavior of net-proton \begin{document}$C_6/C_2$\end{document} in statistical Binomial distribution (BD) at \begin{document}$\sqrt{s_{NN}}$\end{document} = 200 GeV in Au + Au collisions. With the BD parameters extracted from RHIC/STAR, it is found that \begin{document}$C_6/C_2$\end{document} can be negative. Furthermore, the obtained \begin{document}$C_6/C_2$\end{document} becomes smaller when applying the same magnitude of experimental statistics and calculation method to simulations. In 0-10% centrality, there is a significant difference between the simulated result and theoretical expectation. Based on the extracted parameters and experimentally collected statistics, the baseline of net-proton \begin{document}$C_6/C_2$\end{document} in BD is presented.

Van der Waals heterostructures inherit many novel electronic and optical properties from their constituent atomic layers. Mechanical stability is key for realizing high-performance nanodevices based on van der Waals heterostructures. However, buckling instability is a critical mechanical issue for heterostructures associated with its two-dimensional nature. Using molecular dynamics simulations of graphene/MoS2heterostructures, we demonstrate the relationship between buckling instability and the misfit strain that arises inevitably in such heterostructures. The impact of misfit strain on buckling depends on its magnitude: (1) A negative misfit strain causes a pre-compression of the graphene layer, which in turn initiates and accelerates buckling in this layer and reduces the buckling stability in the heterostructure as a whole. (2) A small positive misfit strain enhances the buckling stability of the graphene/MoS2heterostructure by pre-stretching and hence decelerating the buckling of the graphene layer (where heterostructure buckling is initiated). (3) In the case of a large positive misfit strain, the graphene layer is pre-stretched while the MoS2layer is significantly pre-compressed, so that heterostructure buckling is initiated by the MoS2layer. Consequently, the buckling stability of the graphene/MoS2heterostructure is reduced by increasing the large positive misfit strain. These findings are valuable for understanding the mechanical properties of van der Waals heterostructures.

When breaking low current, DC fuse is prone to voltage drop. It is caused by uneven arc burning between parallel necks. The problem of uneven arc burning in parallel slows down the breaking speed of the fuse, and in severe cases causes the fuse to overheat and arc spray. To solve this problem, this paper establishes a mathematical model of fuse arc, a commutation model between parallel necks and a pre-arc time model of necks. Based on Matlab, the current of each branch is calculated as well as temperature of necks. Then this paper explains the cause of uneven parallel arcing and analyzes the influence of the machining error and current on the phenomenon. Finally this paper calculates the minimum current density that fuse can arc evenly in parallel under different machining errors, and the conclusion can be used to guide the design of DC fuse.

The compression molding process of CFRP(Carbon Fiber Reinforced Polymer) is a multi-parameter coupled system, and its molding mechanism is very complex. Based on the Gel point and the glass transition temperature of the matrix material, the compression molding process of CFRP is divided into three sub-processes: thermal-chemical process, flow-compaction process and residual stress-deformation process, and the mathematical constitutive model of each sub-process is established. On the basis, the interaction and calling relationship of each sub-process are determined, which lays a foundation for the molding process simulation of CFRP and further analysis of its multi-parameter coupling effect mechanism.

Studying and controlling the risk factors of shield tunnel crossing underneath the adjacent existing subway tunnel will be of great significance for guaranteeing the safety of tunnel structure. Under the background of subway undercrossing engineering in Shenzhen, 3D finite element models under different working conditions were established using the theory of orthogonal experimental design. The disturbing impacts generated by newly built tunnel shield crossing beneath the existing tunnel to the existing tunnel were explored in consideration of different factors. Based on the impact degrees of different experimental indexes, the priority and weight of each index were determined via the analyses of range and variance in the orthogonal experiment. The results show that the clear distance and spatial angle between new and old tunnels, and soil chamber pressure exert highly significant impacts on the settlement of the existing tunnel structure; the maximum tensile stress of the existing tunnel structure is significantly impacted by the clear distance, spacing, thickness of overburden layer, and angle; the settlement value of the existing tunnel is extremely sensitive to the soil chamber pressure, with the impact weight reaching 24.9%, and the maximum tensile stress of the existing tunnel is sensitive to the change in the thickness of overburden layer: With the increase in the thickness of overburden layer, the maximum tensile stress presents a significant trend of progressive increase, and the impact weight reaches 19.25%. The study results will be of reference significance to the safety construction of shield tunnel crossing beneath the adjacent existing subway tunnel.

Spectroscopic data, such as precise γ-ray branching and E2/M1 multipole-mixing ratios, provide vital constraints when performing multi-dimensional Coulomb-excitation analyses. Consequently, as part of our new Coulomb-excitation campaign aimed at investigating the role of exotic non-axial (triaxial) deformations in the unstable refractory Ru-Mo isotopes, additional beta-decay data was obtained. These measurements make use of ANL’s CARIBU facility, which provides intense beams of radioactive refractory isotopes along with the excellent efficiency and angular resolution of the GRETINA γ-ray tracking array. In this article, we report on the analysis of the A = 110 decay chain, focussing on the identification of previously unreported states in 110Ru following the decay of 110Tc.

We report on the growth of high-quality stoichiometric layered Cr2Se3 single crystals with metallic and noncollinear antiferromagnetic ground state using the chemical vapor transport (CVT) method. The crystals show weak ferromagnetism in the in-plane and out-of-plane directions below the Neel temperature (T N), however, the field-cooled out-of-plane magnetization at 500 Oe and 10 K (∼0.24 μ B/f.u.) is approximately 15 times larger than that of the in-plane one, indicating strong c-axis easy uniaxial magnetic anisotropy, which is further supported by the in-plane and out-of-plane isothermal anisotropic magnetic hysteresis loops and the angular dependent magnetoresistance (MR). The latter also reveals a decrease of the coercive field of the crystal upon the tilting of the weak ferromagnetic easy axis away from the direction of the magnetic field. Further, the out-of-plane isothermal MR are negative below T N and show butterfly shapes for T < 10 K and couple with the magnetic hysteresis M(H) loop. These results may help researchers better understand the interplay between the weak ferromagnetism and the magnetotransport properties of 2D itinerant noncollinear antiferromagnetic systems.

To researching the damage characteristics of typical logical chip modules in spacecraft due to plasma generated by hypervelocity impacts, we have established a triple Langmuir probe diagnostic system and a logical chips measurement system, which were used to diagnose plasma characteristic parameters and the logical chip module's logical state changes due to the plasma created by a 7075 aluminum projectile hypervelocity impact on the 2A12 aluminum target. Three sets of experiments were performed with the collision speeds of 2.85 km/s, 3.1 km/s and 2.20 km/s, at the same incident angles of 30 degrees and logical chip module's positions by using a two-stage light gas gun loading system, a plasma characteristic parameters diagnostic system and a logical chip module's logical state measurement system, respectively. Electron temperature and density were measured at given position and azimuth, and damage estimation was performed for the logical chip module by using the data acquisition system. Experimental results showed that temporary damage could be induced on logical chip modules in spacecraft by plasma generated by hypervelocity impacts under the given experimental conditions and the sensors' position and azimuth.

The thermal expansion effect plays an important role in governing the thermal stability or the stable configuration of quasi-two-dimensional atomic layers, where the difference between the thermal expansion coefficient of different kinds of atomic layer in lateral heterostructure may cause strong thermal rippling of the atomic layer. We investigate the thermal expansion phenomenon in the WSe2-MoS2 lateral heterostructure. We find that the thermal expansion coefficient can be enhanced by more than a factor of two via varying the ratio between the WSe2 and MoS2 components in the heterostructure. The underlying mechanism is disclosed to be the buckling of the WSe2 region that is induced by the misfit strain at the coherent interface between WSe2 and MoS2. These findings shall be helpful in handling the thermal stability of functional devices based on the transition-metal dichalcogenide lateral heterostructures and other similar quasi-two-dimensional lateral heterostructures.

Single-walled carbon nanotubes (SWCNTs) are usually synthesized by the chemical vapor deposition method, in which the resultant SWCNT's chirality and diameter are sensitive to the catalyst and the experimental conditions. To gain effective control over the geometry of SWCNTs, we propose to grow SWCNTs by stacking carbon rings in a layer-by-layer mode, taking advantage of the high reactivity of carbon rings revealed in the very recent experiment (Kaiser et al 2019 Science 365, 1299–1301). More specifically, we examine possible structures for the stacking of carbon rings along the out-of-plane direction or the linking of carbon rings within the in-plane direction based on the cohesive energy calculation. We illustrate that carbon rings can be used as building blocks to construct SWCNTs of well defined zigzag chirality and with precise diameters predetermined by the size of the carbon ring. By linking carbon rings into the chain configuration, we also find a particular type of chain that can sustain a superhigh tensile strain of 0.68 benefiting from its specific inter-ring configuration. The present work brings a fresh way to grow SWCNTs of well defined geometry and demonstrates possible applications of the recently synthesized carbon rings.

A cable-driven continuum throat surgery robot is designed in this paper, which is a new type of bionic robot with softness and flexibility. Throat surgery robot in the market has the disadvantage of large-scale wound and discomfort, robot in this can solve these problem. Firstly, the joint of the robot is modularized by simulating the skeleton of the snake, and the modules are connected by spherical joints to simulate the high flexibility of the snake. Secondly, each part of the robot is controlled by three cables to control the bending motion in the pitch and yaw directions. Lastly, the kinematics analysis is carried out by the D-H method, including the mapping of the driving space, joint space and operation space of the joint module. According to the entity we make, it is approved that the robot has the advantages of small structural size, high positioning accuracy, and strong space flexibility for that the structure of the snake robot is integrated with the drive of the continuous robot. It is ideal for transoral throat surgery, and the operation is performed through the natural cavity to ensure the accuracy and safety of the operation, and the postoperative recovery is also faster.

The cross-sectional shape of the nanotube is a key factor governing fundamental mechanical properties of the nanotube and the nanotube forest. In contrast to most circular nanotubes, in the present work, we demonstrate that the holey phenine nanotubes have polygonal cross sections with diameter-dependent number of sides. The non-circular cross section is attributed to the high twistability of the continuous C-C chains in the phenine nanotube. Consequently, the phenine nanotube forest has a square lattice structure rather than the regular hexagonal lattice of the carbon nanotube forest, resulting in a smooth buckling process under biaxial compression. The buckling pattern of the phenine nanotube forest is highly ordered with the orientation determined by the initial dislocation that frequently appears in the phenine nanotube forest.

Alkaline phosphatase (ALP) plays an integral role in the metabolism of liver and development of the skeleton in humans. To date, the interactions between different-duration terahertz (THz) radiation and ALP activities, as well as the influence mechanism are still unclear. In this study, by using the para-nitro-phenyl-phosphate (pNPP) method, we detected changes in ALP activities during 40-minute THz radiation (0.1 THz, 13 mW/cm2). We found that the activity of ALP decreased in the first 25 minutes, and subsequently increased in the later 15 minutes. Compared with the activity of ALP being heated, the results suggested that short-term terahertz radiation induced a decrease in enzyme activity through the non-thermal mechanism. In order to explore the non-thermal effects of THz radiation on ALP, we focused on the impacts of 0.1 THz radiation for 20 minutes on the activity of ALP in different concentrations. The results revealed that the activity of ALP decreased significantly after exposure to THz radiation. In addition, it could be deduced from fluorescence, ultraviolet-visible (UV-vis), and THz spectra results that THz radiation has induced changes in ALP structures. In conclusion, our studies unlocked non-thermal interactions between THz radiation and ALP, as well as suggested that THz spectroscopy was a promising technique to distinguish ALP structures.

In order to obtain the elemental compositions of the projectile and target materials during 2A12 aluminum projectile shot on a natural dolomite plate, three kinds of experiments have been conducted using a spectral acquirement system established on a two-stage light gas gun for impact velocities ranging from 2.20 km/s to 4.20 km/s, at the same projectile incidence angle of 30°. Experimental results show that the elemental compositions of the projectile and target materials in the strong shock experiments have a good agreement with the original elemental compositions of the projectile and target. In addition, the relations between spectral radiant intensity and elemental compositions of the projectile and target materials have been obtained for different impact velocities, in which the spectral radiant intensity of the main elements in the material increases with increasing impact velocity, and more elements appear with increasing impact velocity since more energy would result from a higher velocity impact.

Centrifugal cold compressors, now being developed at Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, are used to pump gaseous helium from saturated liquid helium tank to obtain super-fluid helium in cryogenic refrigeration systems. Active magnetic bearings (AMB) are replacing traditional oil-fed bearings as the optimal supporting assembly for cold compressors because of their many advantages. In this paper, five degrees of freedom AMBs are developed for the centrifugal cold compressor application. Considering the rotational speed is high, causing the nominal plant model to deviate materially from the precise mathematical model, robust H∞ control methods are proposed to control AMB systems. Experimental results show that H∞ controllers guarantee good dynamic and steady state performance in the closed-loop system at the rotation speed of 50 000 rpm.