Nonlinear averaging theorems, and the determination of parameter convergence rates in adaptive control

The paper presents nonlinear averaging theorems for two-time scale systems, where the dynamics of the fast system are allowed to vary with the slow system. The results are applied to the Narendra-Valavani adaptive control algorithm, and estimates of the parameter convergence rates are obtained which do not rely on a linearization of the system around the equilibrium, and therefore are valid in a larger region in the parameter space.     

基于蒙特卡罗方法的复合材料辐射屏蔽设计北大核心CSCD

在乏燃料后处理厂的工作环境中可能存在着低能中子-γ射线混合辐射,严重威胁工作人员的人身安全。本文针对上述混合辐射环境,利用蒙特卡罗程序Geant4模拟计算了一种钨/硼纤维增强含硼/铋聚合物复合材料中不同材料参数对低能中子和γ射线综合防护效果的影响。结果显示,此种钨/硼纤维复合材料对低能中子和γ射线均具有良好的屏蔽效果。文章证实了纤维垂直排布方式具有比平行排布方式更优的屏蔽效果,且垂直排布方式下透过粒子束的强度分布更加均匀。此外,在聚合物基体中掺杂一定质量分数的硼/铋可以进一步增强复合材料的辐射屏蔽效果。依据这些结果我们认为此种复合材料可以为后处理厂等辐射环境中的防护服及相关防护用具提供参考。     

基于多体动力学的汽轮机振动声辐射机理及传递路径

采用多体动力学方法进行汽轮机机械振动激励源精确分析,在激励源分析结果的基础上研究低频激励下的机组振动响应,并采用声传递向量（Acoustic Transfer Vector,ATV）方法研究汽轮机组表面与外场辐射的声压传递贡献量,从多体动力学的角度并结合流固耦合的方法综合分析汽轮机组振动噪声产生机理并研究噪声典型传递路径。研究结果表明,旋转激励源为汽轮机组的主要振动激励源,在低频段汽轮机组辐射模式为单极子,在中高频段汽轮机组辐射模式为偶极子。由噪声辐射的指向性极坐标图可知,在不同高度处噪声指向性相似,并都在长度方向上取得噪声声压级较大值,具有较强的指向性。计算方法对汽轮机组减振降噪研究具有一定的指导意义。     

对象随型粗糙面近红外单目视觉测量与基准图像自愈

针对复杂应用环境中近红外单目视觉位姿测量系统偏离预置合作目标对象后,无法完成位姿测量的特殊情况,提出一种以合作目标周边随型粗糙面图像为测量对象的单目视觉测量方法,以及图像受损后的动态自愈方法。通过将实时获取的随型粗糙面图像特征与预存基准图像特征进行匹配计算,完成特殊情况下的应急测量。同时,为减少随型粗糙面图像污染或受损后对位姿测量精度的影响,实时计算污染或受损程度并动态自愈基准图像特征。实验结果表明,以随型粗糙面为对象的位姿测量精度稍低于合作目标对象,但能够满足特殊情况下的应急使用需求,提高了测量系统的鲁棒性;当随型粗糙面图像污染或受损达到70%时,采用自愈处理与未做自愈处理相比,方位角测量误差减少72%以上,验证了基准图像自愈方法的有效性。     

透视/遮阳/控温/红外隐身多功能集成序构薄膜研究

为了解决光学材料多功能耦合与集成的光谱诉求及其材料设计冲突难题,本文提出一种基于［TiAlN/Ag］²/TiAlN序构复合薄膜开展可见光透射诱导与红外辐射抑制的协同设计方法,诠释序构薄膜材料多功能耦合的新原理与新机制,并对其光学兼容性能测试表征。研究表明,构筑的［TiAlN（厚度30 nm）/Ag（厚度15 nm）］²/TiAlN（厚度30 nm）序构复合薄膜具备带通状选择性透射与中远红外低辐射的光学特性,可较好实现透视、遮阳、低辐射控温与红外隐身多功能兼容效果,在军用车辆、绿色建筑等特种玻璃的辐射控温与红外隐身领域有应用潜力。     

Operational experience and relation to deposition process for NEG-coated chambers installed on the ESRF electron storage ring

A majority of the ESRF insertion device sections have been equipped with NEG-coated low gap vacuum chambers made of extruded aluminium and PVD coated with a low-temperature non-evaporable getter coating at ESRF. The low initial outgassing and quick conditioning allowed some modifications for chamber installation and accelerator restart procedures. The operational behaviour of those chambers has been studied not only by means of vacuum gauges but also with ionisation chambers measuring the bremsstrahlung sent to the connected synchrotron beamlines. The NEG-coating film thickness was optimised taking into account vacuum performance and also coating process parameters and duration. The 2nd more flexible and powerful NEG-coating device is under commissioning in the NEG-coating facility at ESRF.     

硅离子注入引入纳米晶对SIMOX材料进行总剂量辐射加固

本研究工作采用硅离子注入和高温退火工艺对SIMOX材料的BOX层进行总剂量辐射加固.辐射实验结果证明了该加固方法的有效性.PL谱和HRTEM图像显示了硅离子注入及退火工艺在材料的BOX层中引入了Si纳米晶,形成电子陷阱能级,有效俘获电子,从而提高了材料BOX层的抗总剂量辐射能力.     

New Beta-lactamases in Candidate Phyla Radiation: Owning Pleiotropic Enzymes Is a Smart Paradigm for Microorganisms with a Reduced Genome

The increased exploitation of microbial sequencing methods has shed light on the high diversity of new microorganisms named Candidate Phyla Radiation (CPR). CPR are mainly detected via 16S rRNA/metabarcoding analyses or metagenomics and are found to be abundant in all environments and present in different human microbiomes. These microbes, characterized by their symbiotic/epiparasitic lifestyle with bacteria, are directly exposed to competition with other microorganisms sharing the same ecological niche. Recently, a rich repertoire of enzymes with antibiotic resistance activity has been found in CPR genomes by using an in silico adapted screening strategy. This reservoir has shown a high prevalence of putative beta-lactamase-encoding genes. We expressed and purified five putative beta-lactamase sequences having the essential domains and functional motifs from class A and class B beta-lactamase. Their enzymatic activities were tested against various beta-lactam substrates using liquid chromatography-mass spectrometry (LC-MS) and showed some beta-lactamase activity even in the presence of a beta-lactamase inhibitor. In addition, ribonuclease activity was demonstrated against RNA that was not inhibited by sulbactam and EDTA. None of these proteins could degrade single- and double-stranded-DNA. This study is the first to express and test putative CPR beta-lactamase protein sequences in vitro. Our findings highlight that the reduced genomes of CPR members harbor sequences encoding for beta-lactamases known to be multifunction hydrolase enzymes.     

Recombination luminescence from defects in boron-ion implantation-doped diamond using low fluences

 Two identical, high purity, natural type IIa diamonds, which displayed the ubiquitous blue cathodoluminescence (CL) band at ≈ 2.9 eV, as well as an indication of the corresponding green band at ≈ 2.4 eV, have been equivalently doped by using extremely low dose B⁺- and C⁺-ion CIRA-implantations respectively. Comparative CL measurements showed changes in the intensities of the 2.9 and 2.4 eV bands and the generation of bands at ≈ 4 eV, as well as at ≈ 3.5 and ≈ 4.6 eV (the latter two in the B⁺-CIRA diamond). The results are commensurate with the model (proposed previously) in which the 2.9 and 4 eV bands are generated respectively by electron-hole recombinations at negatively charged acceptor- and positively charged donor-like, intrinsic defects. The present results indicate that Coulomb interactions between the latter defects and (at least partially) compensated, negatively charged, boron acceptors, generate the 3.5 and 4.6 eV bands, which may be considered as higher energy (≈ 0.6 eV) replicas of the 2.9 and 4 eV bands. In both cases, two electrons and a hole interact just before the hole combines with an electron. Such a configuration of charges seems related to, and could possibly be described as, a type of ”ionised exciton molecule”, where the ”bonding” of two negative ”nuclei” is facilitated by the presence of the hole. The CL measurements further indicate that the 2.4 eV band forms when a high enough density of, in this case, neutral acceptors are present. These neutral acceptors compete with the valence band to supply holes for recombination at the negatively charged, acceptor-type, intrinsic defects which are, in the absence of the boron, responsible for the generation of the blue, 2.9 eV band. Received: 5 December 1997 / Accepted: 13 December 1997     

声学-结构设计灵敏度分析

声学 -结构设计灵敏度分析揭示了结构振动引起的辐射声压与结构设计变量之间的关系。分别用有限元法和边界元法计算结构设计灵敏度和声学灵敏度。将两个灵敏度结合得到最终的声学 -结构设计灵敏度。在边界元计算中 ,采用退化元处理奇异积分问题 ,对特征频率不唯一问题采用CHIEF方法处理。以脉动球和箱体为例 ,验证了算法的可行性和精确性。