Self-absorption effects of laser-induced breakdown spectroscopy under different gases and gas pressures

The self-absorption effect is one of the main factors affecting the quantitative analysis accuracy of laser-induced breakdown spectroscopy.In this paper,the self-absorption effects of laserinduced 7050 Al alloy plasma under different pressures in air,Ar,and N2have been studied.Compared with air and N2,Ar significantly enhances the spectral signal.Furthermore,the spectral self-absorption coefficient is calculated to quantify the degree of self-absorption,and the influences of gas species and gas pressure on self-absorption are analyzed.In addition,it is found that the spectral intensity fluctuates with the change of pressure of three gases.It can also be seen that the fluctuation of spectral intensity with pressure is eliminated after correcting,which indicates that the self-absorption leads to the fluctuation of spectral intensity under different pressures.The analysis shows that the evolution of optical thin spectral lines with pressure in different gases is mainly determined by the gas properties and the competition between plasma confinement and Rayleigh–Taylor instability.

Quantitative analysis and time-resolved characterization of simulated tokamak exhaust gas by laser-induced breakdown spectroscopy

Tokamak exhaust is an important part of the deuterium-tritium fuel cycle system in fusion reactions.In this work,we present a laser-induced breakdown spectroscopy(LIBS)-based method to monitor the gas compositions from the exhaust system in the tokamak device.Helium(He),a main impurity in the exhaust gas,was mixed with hydrogen(H_(2))in different ratios through a self-designed gas distribution system,and sealed into a measurement chamber as a standard specimen.A 532 nm wavelength laser pulse with an output power of 100 mJ was used for plasma excitation.The time-resolved LIBS is used to study the time evolution characteristics of the signal strength,signal-to-background ratio(SBR),signal-to-noise ratio(SNR)and relative standard deviation(RSD)of the helium and hydrogen characteristic lines.The Boltzmann twoline method was employed to estimate the plasma temperature of laser-induced plasma(LIP).The Stark-broadened profile of He I 587.56 nm was exploited to measure the electron density.From these studies,an appropriate time was determined in which the low RSD%was consistent with the high signal-to-noise ratio.The He I 587.56 nm and Hαemission lines with good signalto-noise ratio were extracted from the spectrum and used in the external standard method and internal standard method for quantitative analysis.The test results for mixed gas showed that the average relative error of prediction was less than 11.15%,demonstrating the great potential of LIBS in detecting impurities in plasma exhaust gas.

Calcium-Doped Boron Nitride Aerogel Enables Infrared Stealth at High Temperature Up to 1300℃

Boron nitride(BN)aerogels,composed of nanoscale BN building units together with plenty of air in between these nanoscale building units,are ultralight ceramic materials with excellent thermal/electrical insulation,great chemical stability and high-temperature oxidation resistance,which offer considerable advantages for various applications under extreme conditions.However,previous BN aerogels cannot resist high temperature above 900℃ in air atmosphere,and hightemperature oxidation resistance enhancement for BN aerogels is still a great challenge.Herein,a calcium-doped BN(Ca-BN)aerogel with enhanced high-temperature stability(up to~1300℃ in air)was synthesized by introducing Ca atoms into crystal structure of BN building blocks via high-temperature reaction between calcium phosphate and melamine diborate architecture.Such Ca-BN aerogels could resist the burning of butane flame(~1300℃)and keep their megashape and microstructure very well.Furthermore,Ca-BN aerogel serves as thermal insulation layer,together with Al foil serving as both low-infrared-emission layer and high-infrared-reflection layer,forming a combination structure that can effectively hide high-temperature target(heated by butane flame).Such successful chemical doping of metal element into crystal structure of BN may be helpful in the future design and fabrication of advanced BN aerogel materials,and further extending their possible applications to extremely high-temperature environments.

Quench-tailored Al-doped V_(2)O_(5) nanomaterials for efficient aqueous zinc-ion batteries

Rechargeable aqueous zinc-ion batteries(ZIBs)are regarded as a promising competition to lithium-ion batteries as energy storage devices,owing to their high safety and low cost.However,the development of high-performance ZIBs is largely hindered by the shortage of ideal cathode materials with high-rate capability and long-cycle stability.Herein,we address this bottleneck issue by the quenching-tailored surface chemistry of V_(2)O_(5) cathode nanomaterial.By rapid quenching from high temperatures,Al ions are doped into V_(2)O_(5) lattice(Al-V_(2)O_(5))and abundant oxygen vacancies are formed on the surface/nearsurface,which facilitate the desired rapid electron transfers.Our density functional theory(DFT)simulations elucidate that the doping of Al ions into V_(2)O_(5) remarkably reduces the Zn^(2+)-diffusion barriers and improves the electrical conductivity of V_(2)O_(5).As a proof-of-concept application,the thus-optimized AlV_(2)O_(5) cathode delivers a superior specific capacity of 532 m Ah g^(-1) at 0.1 A g^(-1) and a long-cycling life with76%capacity retention after 5000 cycles,as well as a good rate performance.This work provides not only a novel strategy for tuning the surface chemistry of V_(2)O_(5) to boost the Zn^(2+)storage but also a general pathway of modifying metal oxides with improved electrochemical performance.

Singular integrals in axisymmetric problems of elastostatics

Singular integral equations arisen in axisymmetric problems of elastostatics are under consideration in this paper.These equations are received after applying the integral transformation and Gauss-Ostrogradsky’s theorem to the Green tensor for equilibrium equations of the infinite isotropic medium.Initially,three-dimensional problems expressed in Cartesian coordinates are transformed to cylindrical ones and integrated with respect to the circumference coordinate.So,the three-dimensional axisymmetric problems are reduced to systems of one-dimensional singular integral equations requiring the evaluation of linear integrals only.The thorough analysis of both displacement and traction kernels is accomplished,and similarity in behavior of both kernels is established.The kernels are expressed in terms of complete elliptic integrals of first and second kinds.The second kind elliptic integrals are nonsingular,and standard Gaussian quadratures are applied for their numerical evaluation.Analysis of external integrals proved the existence of logarithmic and Cauchy’s singularities.The numerical treatment of these integrals takes into account the presence of this integrable singularity.The numerical examples are provided to testify accuracy and efficiency of the proposed method including integrals with logarithmic singularity,Catalan’s constant,the Gaussian surface integral.The comparison between analytical and numerical data has proved high precision and availability of the proposed method.

用于无线传输和神经网络计算的碳化硅纳米线多功能高效视觉突触器件

随着大数据和物联网的快速发展,基于传统冯·诺依曼架构的计算机存在吞吐量有限和能源利用效率低下的问题.基于忆阻器的人工神经网络计算系统被认为是克服这一瓶颈的候选之一.本研究成功研制了基于碳化硅纳米线薄膜的光电忆阻器,不仅可以很好地实现生物视觉突触的基本功能,还可以实现更为复杂的树突神经元和巴甫洛夫学习等类脑学习特性.在视觉功能的基础上,实现了集成在SiC忆阻器中的感知、存储和计算的功能.更重要的是,得益于SiC纳米线视觉突触优异的计算能力构建的脉冲神经网络能够实现早期肺癌病灶的识别.该方法迭代次数少,检测准确率可达90%以上,在医疗领域具有良好的应用前景.本研究为神经形态计算技术中基于SiC的感知-存储-计算一体化人工智能设备的开发和推广提供了一条有前景的途径.

Fluctuation relations for heat exchange in the generalized Gibbs ensemble

In this work, we investigate the heat exchange between two quantum systems whose initial equilibrium states are described by the generalized Gibbs ensemble. First, we generalize the fluctuation relations for heat exchange discovered by Jarzynski and Wojcik to quantum systems prepared in the equilibrium states described by the generalized Gibbs ensemble at various generalized temperatures. Secondly, we extend the connections between heat exchange and the Renyi divergences to quantum systems under generic initial conditions. These relations are applicable for quantum systems with conserved quantities and universally valid for quantum systems in the integrable and chaotic regimes.