一种高温SHPB实验技术中的温度场分析

近年来发展了一种单独对试件加温的高温SHPB技术,即首先对试件单独加热,然后在短时内完成导杆和试件的组装,随即进行实验.本文针对使用这一实验技术的ψ5mm、ψ22mm的SHPB试验系统,对室温的导杆和高温的试件间的短时界面热传导进行了数值模拟,得到了实验过程中导杆和试件的温度场变化.综合导杆中的温升以及试件中的温差两方面的原因,本文分析认为,在研究材料高温动态力学性能方面,小杆更具优势.     

CONTROLLABILITY OF A CLASS OF HYBRID DYNAMIC SYSTEMS (Ⅱ)—SINGLE TIME_DELAY CASE

IntroductionConsideraswitchedlinearsystemwithsingletime_delayinthecontrolfunctiongivenby x(t) =Ar(t) x(t) +Br(t) u(t) +Dr(t) u(t -τ) ,(1)wherex(t) ∈Rnisthestate,u(t) ∈R mtheinput,thepiecewiseconstantscalarfunctionr(t) :R+ → 1,2 ,… ,Nistheswitchingpath ,(Ai,Bi,Di) ｜i =1,… ,Nisafinitefamilyofsystemrealizations.Moreover,r(t) =iimpliesthat(Ai,Bi,Di)ischosenasthesystemrealizationattimet.τ >0isthefixedtimedelayincontrol.Inthispaper ,wewillstudythecontrollabilityofsystem (1) .Theone_per…     

CONTROLLABILITY OF A CLASS OF HYBRID DYNAMIC SYSTEMS (Ⅲ)—MULTIPLE TIME_DELAY CASE

IntroductionConsidertheswitchedlinearsystemwithmultipletime_delaysincontrolfunctiongivenby x(t) =Ar(t) x(t) +Br(t) u(t) + Kk=1Dr(t) ,ku(t -τk) ,(1)wherex(t) ,u(t)andr(t)isdefinedasbefore ,(Ai,Bi,Di,1,… ,Di,K)｜i=1,… ,Nisafinitefamilyofsystemrealizations.Moreover,r(t) =iimplies (Ai,Bi,Di,1,… ,Di,K)ischosenasthesystemrealizationattimet.K <∞isthenumberoftime_delaysinthesystem .0<τ1<… <τKareKfixedtime_delays .Remark 1　Similarly ,wecandescribeswitchingpathbyintroducingswitchingsequ…     

饱和砂土振动扎隙水压力理论与应用研究进展

本文简要回顾了地震、波浪等引起的往返载荷作用下饱和砂土孔隙水压力理论与应用的研究历史和实践背景,并从影响因素、计算理论与应用等较广泛的范围,就目前国内外对饱和砂土振动孔隙水压力问题的研究现状作了较系统的评述,最后讨论了有待进一步研究的问题。     

负载型BINAP-M类催化剂

1,1'-联萘-2,2'-双二苯膦与金属配位化合物(BINAP-M)作为最重要和著名的手性催化剂之一,过去的几十年中在工业和基础理论研究中受到广泛关注。虽然BINAP-M作为均相手性催化剂具有活性高和选择性好的特点,但存在价格昂贵、应用成本较高和难以回收利用等局限性,特别是催化剂残留在合成产物中,如药品中,限制了其在工业上的大规模应用。因此,寻求既能保持高催化活性,又能方便回收和循环应用的BINAP-M类催化剂成为重要研究课题。本文总结了近年来可回收BINAP-M催化剂研究进展,重点介绍了吸附负载型与共价负载型BINAP-M催化剂在可回收领域的研究成果,分析讨论了不同类型可回收的负载型BINAP-M催化剂的优缺点。在此基础上,本文还介绍了一种具有“柔性桥链”结构的共价负载BINAP-M催化剂,并分析了其在“拟均相”催化反应中的应用前景,为负载型催化剂的设计与制备提供了新的研究思路。     

CuInS2/CdS基掺杂纳米晶的晶体结构、光谱性质及性能调控研究

多功能纳米晶的制备、性能及其应用是材料、化学、能源、生物医学等领域十分关注的课题之一。基于掺杂调控纳米晶生长和性能的思想,发展了纳米晶修饰和复合的概念和技术,使用绿色安全的化学溶液法结合外延生长技术合成了巯基丙酸(MPA)包覆的掺杂CuInS₂/CdS基纳米晶材料。通过适当调整掺杂异价离子的种类,实现了对CuInS₂/CdS基纳米晶显微结构和性能的调控,获得了具有特定相结构、组分、尺度和光学性能(吸收性质、光学带隙、发光强度)的纳米晶。存在于基质晶体中不同金属掺杂离子,会造成半导体的禁带中间产生掺杂能级,导致二次跃迁,进而产物体现出不同的禁带宽度。掺杂Co ²⁺、Fe ²⁺、Er ³⁺离子的CuInS₂/CdS纳米晶光致发光(PL)峰强度降低明显,这是由于Co ²⁺、Fe ²⁺、Er ³⁺离子掺杂有效地抑制了空穴-电子对的复合,降低了纳米晶的光生电子-空穴复合几率,使得其光催化活性得到增强。这些半导体纳米材料在光催化、能量转换与储存方面具有良好的应用潜力。     

Enhancement of electron-positron pairs in combined potential wells with linear chirp frequency

Effect of linear chirp frequency on the process of electron-positron pairs production from vacuum is investigated by the computational quantum field theory. With appropriate chirp parameters, the number of electrons created under combined potential wells can be increased by two or three times. In the low frequency region, frequency modulation excites interference effect and multiphoton processes, which promotes the generation of electron-positron pairs. In the high frequency region, high frequency suppression inhibits the generation of electron-positron pairs. In addition, for a single potential well, the number of created electron-positron pairs can be enhanced by several orders of magnitude in the low frequency region.     

THE NONLINEAR BOUNDARY VALUE PROBLEM FOR k HOLOMORPHIC FUNCTIONS IN C2

k holomorphic functions are a type of generation of holomorphic functions. In this paper, a nonlinear boundary value problem for k holomorphic functions is primarily discussed on generalized polycylinders in C². The existence of the solution for the problem is studied in detail with the help of the boundary properties of Cauchy type singular integral operators with a k holomorphic kernel. Furthermore, the integral representation for the solution is obtained.     

具有时变时滞的离散时间切换奇异正系统的l_(1)滤波北大核心CSCD

该文主要研究了一类具有时变时滞的离散时间切换奇异系统在正性约束下的l_(1)滤波器的设计问题.通过构造合适的共正Lyapunov函数并且利用平均驻留时间的方法,以线性规划的形式给出使得相应的滤波误差系统是正的、正则的、因果的、指数稳定的充分条件.另外,外部扰动输入对系统性能的影响也被加以分析和讨论,并在稳定性的基础上进一步给出滤波误差系统具有给定l_(1)增益性能的充分条件和相应滤波器的设计方法.最后,通过数值算例来验证所给方法的有效性和可行性.     

Ultrabright γ-ray emission from the interaction of an intense laser pulse with a near-critical-density plasma

An efficient scheme for generating ultrabright γ-rays from the interaction of an intense laser pulse with a near-critical-density plasma is studied by using the two-dimensional particle-in-cell simulation including quantum electrodynamic effects. We investigate the effects of target shape on γ-ray generation efficiency using three configurations of the solid foils attached behind the near-critical-density plasma: a flat foil without a channel (target 1), a flat foil with a channel (target 2), and a convex foil with a channel (target 3). When an intense laser propagates in a near-critical-density plasma, a large number of electrons are trapped and accelerated to GeV energy, and emit γ-rays via nonlinear betatron oscillation in the first stage. In the second stage, the accelerated electrons collide with the laser pulse reflected from the foil and emit high-energy, high-density γ-rays via nonlinear Compton scattering. The simulation results show that compared with the other two targets, target 3 affords better focusing of the laser field and electrons, which decreases the divergence angle of γ-photons. Consequently, denser and brighter γ-rays are emitted when target 3 is used. Specifically, a dense γ-ray pulse with a peak brightness of 4.6×10²⁶ photons/s/mm²/mrad²/0.1%BW (at 100 MeV) and 1.8×10²³ photons/s/mm²/mrad²/0.1%BW (at 2 GeV) are obtained at a laser intensity of 8.5×10²² W/cm² when the plasma density is equal to the critical plasma density n_c. In addition, for target 3, the effects of plasma channel length, foil curvature radius, laser polarization, and laser intensity on the γ-ray emission are discussed, and optimal values based on a series of simulations are proposed.