双角度光学粒子计数器标定研究

针对光学粒子计数器的标定对其测量精度的重要性,根据球形粒子的Mie散射理论对双角度光学粒子计数器的标定进行了研究,对标定过程中的一些现象进行了理论分析。通过对它们的研究以及对标定的分析可以对双角度光学粒子计数器测量数据的合理性进行判断,这对光学粒子计数器的研制和标定是很有意义的。     

利用Gordon-Kim模型对NaCl物态方程的研究

 本文对孤立离子Hartree-Fock波函数的数值解出发，直接计算了NaCl晶体中各种离子对的相互作用势。结果表明，对不同的离子对，其短程作用势性质不同。对Na⁺-Cl^-离子对，其短程作用势为正，而对Cl^--Cl^-离子对和Na⁺-Na⁺离子对，对物理上感兴趣的大部分距离范围内，其短程作用势为负。在对以上的离子对势进行了解析拟合后，通过晶格动力学的方法计算了晶体的Grüneisen参数和物态方程，其结果与实验符合程度是令人满意的。     

非对易相空间中阻尼系统的Wigner函数

用量子力学来处理经典的阻尼系统,考虑到空间变量对易关系中包含的坐标-坐标和动量-动量的非对易性,利用Wigner函数在非对易相空间的基本性质,得到了阻尼谐振子在非对易相空间中的Wigner函数与对易空间及非对易空间的形式一致.     

能量密度泛函中不同对关联处理方式对原子核形变描述影响的探讨

在Skyrme能量密度泛函理论的框架下,研究了不同对关联处理近似,如Hartree-Fock-Bogoliubov(HFB)、Hartree-Fock-Bogoliubov Lipkin-Nogami (HFBLN)及在HFBLN基础上考虑粒子数投影,对于原子核势能曲面计算及基态结合能的影响。同时,也研究了不同对力,如体积对力、表面对力及混合对力对结果的影响。研究的对象为典型的双幻核16O,40Ca,100Sn和208Pb,它们的基态为球形;还有典型的形变核48Cr,也研究了相应的Cr和Fe同位素链的结合能,最后讨论了对超重核298Fl的势能面计算。研究发现,对关联基本不改变形变极小点,但是由于对关联能的引入,对结合能会带来几个MeV的修正能量,HFB、HFBLN及投影计算的修正能量逐渐递增。对关联可以改变位能面最小点附近曲线的软度,使得形变较小点变浅,而在HFBLN基础上考虑粒子数投影,又可以让形变极小点变得更加明显。对关联也降低了位垒高度。在相同对关联处理近似下,混合对力与体积对力计算的势能面结果相接近,表面对力带来了更多的对关联能,对关联的效果更加显著。     

从亮点工作看三代北京谱仪上粲强子物理研究的发展

 “天地玄黄，宇宙洪荒。”有史以来，人类便没有停止过对自身所处大千世界的探索。这种探索并不局限于谋求更好的物质条件，也包含对天空的观察、对生命的探究和对未知的渴求，追根溯源来自于我们内心在精神层面对未知事物的好奇和对真理的追求。     

两库柏对相互作用问题的研究

在文中给出了库柏对的两种不同表达形式。发现用由对算符组成的哈密顿量来计算更方便,用这些对算符对易性质,而不是把它们看成费米子算符的组合产物。这样一来,研究的库柏对相互作用问题也把库柏对看成对算符。文中解决了两个库柏对相互作用问题,并讨论了推广到多库柏系统的情况。     

不同分离距离的涡对融合

为研究涡对融合过程的非线性现象,将模型简化,用数值模拟方法,通过求解LES的N-S方程,得出不同分离距离的涡对融合过程.根据不同截面位置的流线变化,通过流场的拓扑结构,分析相互耦合涡对融合的机理及分离距离对融合过程的影响,及不同强度比例的涡对融合过程对漩涡位置的控制作用.结果表明,融合距离随分离距离增大呈非线性增加趋势,涡对分离距离的增加使其对漩涡位置的控制作用减弱.     

非对易相空间中的狄拉克振子的能级和Wigner函数

非对易几何、弦论和圈量子引力理论的发展,使非对易空间受到越来越多的关注.非对易量子理论不同于平常的量子理论,它是弦尺度下的特殊的物理效应,处理非对易量子力学问题需要特殊方法.本文首先介绍了Moyal方程与Wigner函数,利用Moyal-Weyl乘法与Bopp变换将H(x,p)变换成^H(^x,^p),考虑坐标—坐标、动量—动量的非对易性,实现对非对易相空间中星乘本征方程的求解.并利用非对易相空间量子力学的代数关系,讨论了非对易相空间中狄拉克振子的Wigner函数和能级,研究结果发现非对易相空间中狄拉克振子的能级明显依赖于非对易参数.     

爆轰波对碰驱动下加环紫铜圆管对碰区的变形特性

爆轰波对碰驱动下金属圆管对碰区易出现过早断裂现象，为了推迟圆管对碰区的断裂时间，文中在紫铜圆管对碰部位设计了铝保护环结构，以研究加环后紫铜圆管对碰区的膨胀变形特性及其对圆管对碰部位破裂时间的影响。采用高速分幅摄影、脉冲x光照相两种观测技术，对加环紫铜圆管在爆轰波对碰驱动下的膨胀变形及破坏过程进行了观测。实验装置示意图及高速分幅摄影实验结果见图I。     

压印光刻中的两步对正技术

压印光刻中套刻需要粗、精两级对正.实验采用一对斜纹结构光栅作为对正标记.利用物镜组观察光栅标记图像的边界特征进行粗对正,其准确度在精对正信号的捕捉范围内;利用光电接收器件阵列组合接收光栅莫尔信号,在莫尔信号的线区进行精对正.由于线性区的斜率大, 精对正过程中得到相应x,y方向的对正误差信号灵敏度高,利用高灵敏度对正误差信号作为控制系统的驱动信号,对承片台进行驱动定位,实现精对正.最终使X,Y方向上的重复对正准确度分别达到了± 21 nm(± 3σ)和±24 nm(± 3σ).     

Effect of ausforming temperature and strain on the bainitic transformation kinetics of a low carbon boron steel

The effect of ausforming temperature and strain on the bainitic transformation kinetics was investigated in a low carbon boron steel. A new mechanism, which is based on the competition between the increase in nucleation rate and the decrease in average volume of bainite sheaf after deformation, is proposed. The increase in nucleation rate is due to the decrease in boron concentration at the grain boundaries after small deformation and the formation of sub-grain boundaries at the grain interior after large deformation. The decrease in average volume of bainite sheaf is ascribed to the frequent impingement of bainite sub-units after deformation. The increase in nucleation rate after deformation results in the decrease in incubation time, which is confirmed from the experiment. The increase in nucleation rate overcomes the decrease in average volume of bainite sheaf, resulting in the increase in transformation velocity and volume fraction after small deformation. On the contrary, the decrease in the average volume of bainite sheaf overcomes the increase in nucleation rate after large deformation, leading to the decrease in transformation velocity and volume fraction of bainite.     

Changes in ADC caused by tensile loading of rabbit achilles tendon: evidence for water transport

Water diffusion measurements were performed on rabbit Achilles tendons during static tensile loading and tendons in an unloaded state. The apparent diffusion coefficient (ADC) was measured along two directions: parallel and perpendicular to the long axis of the tendon. Tendons were studied after being prepared in two ways: (a) after being stored frozen in phosphate-buffered saline (PBS) and (b) freshly isolated. Statistically significant directional anisotropy was observed in the ADC in all tendons. The ADC was significantly greater in the direction parallel to the long axis of the tendon than in the perpendicular direction. The anisotropy is attributed to the greater restrictions seen by the water molecules in the perpendicular direction and is consistent with the known geometry of the tendon. Storage in PBS caused tendons to swell. This increased the ADC measured along both directions and reduced the anisotropy. The existence of anisotropy in the ADC was not related to the orientation of the specimen in the magnet. The ADC increased along both directions following the application of a 5-N tensile load; the increase was greatest along the perpendicular axis of the tendon. In order to determine whether load-related changes in the ADC reflected changes in interfibrilar spacing, we used electron microscopy to measure load-related changes in fibril spacing. Load-related changes in fiber spacing could not account for the observed changes in the ADC. The increase in ADC caused by loading was attributed to the extrusion of tendon water into a bulk phase along the outside surface of the tendon. In PBS-stored samples, enough fluid was extruded that it could be visualized. The transient response of the ADC to a 5-N tensile load was also studied. The absolute ADC in both directions increased with loading and recovered to baseline upon unloading. The transient changes in ADC, for both loading and unloading, had a mean time constant of approximately 15 min. The magnitude of the load-induced transient ADC changes was comparable to that seen in the static-loading experiments.     

Thermodynamically equilibrium roton states of nanoparticles in molten and vapour phases

We show a possibility for a thermodynamically equilibrium nanocrystalline structure consisting of nanosized solid inclusions to appear in a melt just beyond the melting curve. Thermodynamic stability of the nanocrystalline structure in the melt results from the free energy lowering due to rotational motion of nanoparticles. The main contribution to the reduction of the free energy of the system is due to an increase in the rotational entropy and change in formation energy of nanocrystals, i.e. the nanocrystalline structure in the melt, like vacancies in a crystal, is an equilibrium defect structure of the melt. It is demonstrated that similar nanocrystalline structures can also appear in the vapour phase in the form of liquid nanodrops and in liquid solutions, e.g. in He II.     

水溶液中微量Cu元素的激光诱导光谱检测

采用普通打印纸作为基底置于含有痕量重金属离子的水溶液中,用于富集溶液中的重金属Cu元素,烘干后用激光诱导击穿光谱进行定量分析。该方法克服了用激光诱导击穿光谱方法直接分析液相样品中重金属含量时存在水的溅射和灵敏度低等不足。实验中选用324.7 nm的光谱线作为分析线,研究了光谱强度与富集时间的关系,建立了用于溶液中Cu元素定量测量的校正曲线,检测限达到0.023 mg·L-1。为水体中重金属检测提供了一个可行的具有良好灵敏度分析技术。     

降雨对无线激光通信的影响

通过激光信号在雨介质中传输的实验发现,在大雨环境下,激光信号透射率要比在小雨或微雨的情况下大。这说明光信号在小雨时衰减较大,在大雨时衰减较小。这一现象与人们通常所认为的有所不同。针对降雨对激光信号的影响,根据Mie散射理论和Weibull雨滴尺寸分布模型,分析了不同尺寸的粒子对光的散射作用以及对衰减效率因子的影响,推导出单球粒子对光波的衰减公式,得到了衰减与降雨率的确定关系。通过数值计算发现,与小粒子相比大粒子的前向散射光强更大且更加集中;激光信号在雨介质中传输时,衰减系数在小雨时较大,中雨、大雨时较小,暴雨时不断增大。这一结果与实际情况较吻合,为激光在通信系统中的应用提供了一定的理论依据。     

XPS and SIMS investigation on the role of nitrogen in Si nanocrystals formation

Since the demonstration of optical gain in silicon nanocrystals, in the last few years several papers appeared in the literature reporting gain measurements in silicon nanocrystals embedded in a silica matrix produced by different techniques. However, it is still unclear which are the structural, physical and chemical factors that contribute to enhance photoluminescence and gain in this type of samples. In particular, the presence and the role of nitrogen in the SiO₂ matrix are in fact supposed to be essential factors in understanding the gain mechanism.In fact it is possible to obtain similar samples with very different nitrogen content in the silica matrix changing one of the precursor gases used in the deposition process, thus evidencing the structural and chemical differences introduced by the presence of nitrogen. In this paper SIMS and XPS analysis of two series of similar samples, but with a very different nitrogen content, will be presented and compared. The data collected at different annealing temperatures, together with ellipsometric measurements, give important information on the role played by the nitrogen present in the matrix in the process of silicon nanocrystal formation. Moreover, we demonstrate that the annealing process causes always some oxidation of the sample surface and that nitrogen is incorporated in the material from the annealing atmosphere in nitrogen free samples.     

‘Phase transitions’ in bacteria – From structural transitions in free living bacteria to phenotypic transitions in bacteria within biofilms

Phase transitions are common in inanimate systems and have been studied extensively in natural sciences. Less explored are the rich transitions that take place at the micro- and nano-scales in biological systems. In conventional phase transitions, large-scale properties of the media change discontinuously in response to continuous changes in external conditions. Such changes play a significant role in the dynamic behaviours of organisms. In this review, we focus on some transitions in both free-living and biofilms of bacteria. Particular attention is paid to the transitions in the flagellar motors and filaments of free-living bacteria, in cellular gene expression during the biofilm growth, in the biofilm morphology transitions during biofilm expansion, and in the cell motion pattern transitions during the biofilm formation. We analyse the dynamic characteristics and biophysical mechanisms of these phase transition phenomena and point out the parallels between these transitions and conventional phase transitions. We also discuss the applications of some theoretical and numerical methods, established for conventional phase transitions in inanimate systems, in bacterial biofilms.     

CPL技术在空间飞行器上的应用

本文对ＣＰＬ技术进行了简要概述,介绍了其工作原理与工作特性,并讨论了ＣＰＬ技术在空间飞行器上的可能应用方式。其中,对ＣＰＬ技术应用于空间设备的散热进行了全面阐述,并给予理论分析;此外,对ＣＰＬ技术应用于空间设备的主动热控制,也作了简要介绍;对ＣＰＬ技术未来有发展前景的应用方式进行了展望。     

污染土壤对脐橙叶片镉含量影响的光谱预测

近年来可见-近红外光谱技术在农业污染监测中应用越来越广泛,但在果树的重金属污染研究中应用较少。本文以纽荷尔脐橙(Citrus sinensis[L.]Osbeck cv. Newhall)为研究对象,采用盆栽方法,通过添加镉（Cd）形成不同污染程度的土壤,然后定期监测叶片中Cd含量及其光谱,分别建立了基于光谱指数的线性回归预测模型,以及基于偏最小二乘回归（PLSR）的Cd含量高光谱预测模型。结果表明：Cd更容易向新叶迁移和聚集,在高Cd污染的土壤中这种现象更加明显;新叶光谱在700～730 nm之间反射率升高,发生红边蓝移现象,老叶光谱没有显著变化;基于光谱指数建立的线性回归模型的R2达到0.8左右,而利用PLSR方法建立的预测模型精度普遍高于线性回归模型,其R2达到0.9左右,并且标准归一化（SNV）的光谱预处理方法可以显著提高PLSR模型的预测精度。研究显示,可见-近红外光谱技术在脐橙重金属污染监测上有很好的潜力。     

Raman and fluorescence investigations on retrieved Biolox® delta femoral heads

Since the introduction of ceramic‐on‐ceramic couplings in total hip arthroplasty, continuous efforts have been performed to improve the performance of the prosthetic components. To expand the applications of ceramics, in 2000 an innovative alumina–zirconia composite was introduced in the market. The present study represents the first investigation aimed at characterising at the molecular level Biolox® delta retrievals implanted between 1999 and 2009. Fluorescence and Raman results showed that a progressive improvement of the material properties has occurred in the period between 1999 and 2009. Raman spectroscopy showed that wear was the main cause of the in vivo tetragonal‐to‐monoclinic zirconia transformation. Our findings validated the in vitro accelerated ageing protocols proposed in the literature to simulate the effects of the in vivo wear, because the mechanism operating in vivo was found to be the same active in vitro. The in vitro fracture of a new femoral head appeared to be an extreme wear condition that determined the most significant changes in the residual stress state and monoclinic content both in the section of the fragments and on their surface. The micro‐Raman mapping of the fractured articulating surface showed that the tetragonal‐to‐monoclinic transformation involved a region much more extended than as reported in the literature. Copyright © 2012 John Wiley & Sons, Ltd.