作为宇宙信使的X射线

60年前,里卡多·贾科尼团队用探空火箭首次探测到了来自太阳系以外的X射线辐射,从此打开了人类探索宇宙的一个全新的窗口。与我们所熟悉的可见光天空不同,在“看不见”的X射线宇宙,明亮的发光天体涵盖了黑洞、中子星、白矮星等致密天体,星系团和星系中弥漫的大量不可见的高温气体,以及各种剧烈的灾变事件。它们代表着宇宙中最为奇特的天体和极端的物理条件,如极强引力场、极强磁场和极高温。文章重点介绍最有代表性的X射线源,包括中子星和黑洞X射线双星、超大质量黑洞和活动星系核、星系团,以及伽马暴、超新星和潮汐瓦解恒星事件等爆发天体。     

Exact solution of finite size Mean Field Percolation and application to nuclear fragmentation

Random Graphs and Mean Field Percolation are two names given to the most general mathematical model of systems composed of a set of connected entities. It has many applications in the study of real life networks as well as physical systems. The model shows a precisely described phase transition, but its solution for finite systems was yet unresolved. However, atomic nuclei, as well as other mesoscopic objects (e.g. molecules, nano-structures), cannot be considered as infinite and their fragmentation does not necessarily occur close to the transition point. Here, we derive for the first time the exact solution of Mean Field Percolation for systems of any size, as well as provide important information on the internal structure of Random Graphs. We show how these equations can be used as a basis to select non-trivial correlations in systems and thus to provide evidence for physical phenomena.     

液体-液体相变与反常特性

绝大多数物质的液态密度随温度降低而增大,即常见的热胀冷缩现象.但存在一类物质,如水及第四主族的硅、锗等,其液态密度在一定温度范围内随温度的升高而增大,即密度反常现象.此外,该类物质还存在动力学反常(密度越大粒子运动越快)、热力学反常(热力学量的涨落随温度降低而升高)等其他反常特性.这类材料的化学性质千差万别,但却具有相似的物理反常特性.进一步的理论研究发现部分材料具有两种液态,即高密度液态和低密度液态,两者之间存在一级相变.因此,反常特性与液体-液体相变是否有直接关联是一个值得深入研究的课题.本文主要介绍了具有液体-液体相变的一类材料及其反常特性,包括高温高压下氢的液体-液体相变及其超临界现象,镓的反常特性及其与液体-液体相变的关联等.     

High-loading polyglycerol supported reagents for Mitsunobu- and acylation-reactions and other useful polyglycerol derivatives

Summary In this paper we present soluble dendritic polyglycerol (PG) supported reagents PG-DEAD, PG-PPh₃, and PG-DCC as well as scavengers PG-carbonate, PG-carbazate, and PG-amine, which all have been synthesized in high overall conversions and yields using simple purification techniques. The supported reagents have been used simultaneously in Mitsunobu and acylation reactions. All polymeric reagents and scavengers can be removed by simple precipitation/filtration protocols to give chromatography-free products of high purity. In the course of the syntheses of the polymeric reagents three intermediates turned out to be precious polyglycerol derivatives: a mixed carbonate as an electrophilic derivative, polyglyceryl carbazate as a scavenger for carbonyl compounds, as well as polyglycerylamines as amino analogues of polyglycerol.     

分光光度法同时测定铝(Ⅲ)和铁(Ⅱ)

以甲基百里酚蓝(MTB)为显色剂、CTMAB为增溶增敏剂,利用系数补偿和双峰双波长的两次分光光度法同时测定铝(Ⅲ)和铁(Ⅱ)的结果令人满意.     

Thermal modelling of laser welding and related processes: a literature review

The main emphasis of this review is on thermal modelling and prediction of laser welding in metals. However as similar techniques are employed to model conventional welding processes such as arc, resistance and friction, as well as related processes such as alloying, cladding and surface hardening, part of this review is given over to the modelling of these processes where appropriate. The time frame of the review is up to the year 2002.     

500 kV全固态Marx发生器

500 kV全固态Marx发生器采用Z型电路结构,以28个最大工作电压达22 kV、满载最高连续重复运行频率达200 Hz的绝缘栅双极型晶体管组件作为脉冲控制开关,采用以金属化膜电容器和线绕电感构成的梯形脉冲形成网络作为储能和脉冲形成器件。目前已实现500 kV脉冲输出,在50 Hz的重复频率下实现数十个脉冲的猝发输出。该发生器的输出脉冲电压峰值与已有文献报道的最高功率固态Marx发生器技术指标相近,输出脉冲电流峰值提高1倍,达到1000 A,发生器输出脉冲功率峰值达到500 MW。在采用电容器作为储能元件时,此Marx发生器输出脉冲宽度可在3～10 s范围内连续调整。     

500 kV全固态Marx发生器

500 kV全固态Marx发生器采用Z型电路结构,以28个最大工作电压达22 kV、满载最高连续重复运行频率达200 Hz的绝缘栅双极型晶体管组件作为脉冲控制开关,采用以金属化膜电容器和线绕电感构成的梯形脉冲形成网络作为储能和脉冲形成器件。目前已实现500 kV脉冲输出,在50 Hz的重复频率下实现数十个脉冲的猝发输出。该发生器的输出脉冲电压峰值与已有文献报道的最高功率固态Marx发生器技术指标相近,输出脉冲电流峰值提高1倍,达到1000 A,发生器输出脉冲功率峰值达到500 MW。在采用电容器作为储能元件时,此Marx发生器输出脉冲宽度可在3～10 s范围内连续调整。     

空间声的研究与应用——历史、发展与现状

空间声的目的是通过电声的手段重放声音空间信息,给聆听者再现特定的空间听觉感知。它在文化生活、通信、多媒体和虚拟现实等方面以及航空、航天等领域都有重要的应用。国内对空间声的研究起步于1958年,五十多年来进行了大量的基础研究工作,是和国际上的发展前沿相接轨的。本文在回顾空间声的基本原理与分类、国际上空间声发展历史的基础上,侧重评述了国内空间声研究和应用的历史、发展与现状,并展望了今后的发展前景。     

Electronic density of states in sequence dependent DNA molecules

We report in this work a numerical study of the electronic density of states (DOS) in π-stacked arrays of DNA single-strand segments made up from the nucleotides guanine G, adenine A, cytosine C and thymine T, forming a Rudin-Shapiro (RS) as well as a Fibonacci (FB) polyGC quasiperiodic sequences. Both structures are constructed starting from a G nucleotide as seed and following their respective inflation rules. Our theoretical method uses Dyson’s equation together with a transfer-matrix treatment, within an electronic tight-binding Hamiltonian model, suitable to describe the DNA segments modelled by the quasiperiodic chains. We compared the DOS spectra found for the quasiperiodic structure to those using a sequence of natural DNA, as part of the human chromosome Ch22, with a remarkable concordance, as far as the RS structure is concerned. The electronic spectrum shows several peaks, corresponding to localized states, as well as a striking self-similar aspect.     

Cooperation between scientists and the government in the US: benefits and problems

This paper discusses the importance of maintaining close working relations between scientists and their government. Several examples of this cooperation in the U.S. are presented to illustrate the benefits, as well as problems, that result from such cooperation, or lack thereof. These examples include government support of scientific research, as well as contributions by science to help governments understand both the possibilities and the limitations of science as they formulate national policy.     

生物质气为燃料的燃料电池理论电动势计算

在以生物质气体为燃料的固体氧化物燃料电池体系中,通过热力学平衡分析编程计算出700-1200 K时气体中各物种例如H2、CO、CO2和CH4的平衡组成,从而得到以氧化钇稳定氧化锆(YSZ)为电解质的电池理论电动势．碳沉积对电动势有显著影响．通过计算可以推测比较适宜的操作温度和增湿条件．还计算了以掺杂氧化铈为电解质的电池电动势,相比氢气为燃料时,使用生物质气体导致的电动势的下降比使用YSZ为电解质的电池要小的多．     

Organic- and molecule-based magnets

The discovery of organic- and molecule-based magnets has led to design and synthesis of several families with magnetic ordering temperatures as high as ∼125°C. Examples of soft and hard magnets with coercivities as high as 27 kOe have also been reported. Examples from our laboratory of organic-based magnets using the tetracyanoethylene radical anion, [TCNE]^•−, are discussed. In addition, several molecule-based magnets based on Prussian Blue structured materials as well as dicyanamide are discussed.     

Read and write processes, and head technology for perpendicular recording

In this paper, we present a review of the write and read processes in perpendicular magnetic recording. We also discuss their impact, based on recording physics aspects, on design considerations for writers and readers. For the write process, we discuss fundamental write-ability limitations as well as possible paths to ultra-high areal density perpendicular recording. The impacts of different medium designs, geometrical scaling, and the breakdown of scaling, both in terms of write-ability and transition curvature, are shown based on different modeling techniques, including analytical formulas, finite element modeling (FEM), and micromagnetic simulations. Basic design rules as well as alternative designs that enable high areal density are briefly explained. For the read-back process, the relation between reader signal to noise ratio (SNR) and resistance, as well as reader resistance shunt and spacing loss, are discussed. Finally, we use a simple example to illustrate, both from a write as well as a read-back perspective, the complicated nature of perpendicular recording systems, and how different medium designs impact recording head technology for ultra high density perpendicular recording.     

Spectrometric-based techniques for metal-binding protein assessment in clinical,environmental, and food samples

Metalloproteins and metal–protein complexes play key roles in all organisms. For example, certain metalloproteins are involved in metal homeostasis and detoxification, or oxidative stress protection; whereas, metals serve as essential cofactors in a large number of metal–protein complexes. Advances in analytical instrumentation as well as informatics have allowed a complete characterization/assessment of both metalloproteins and metal–protein complexes. In some cases, the identification of the protein is a key factor for understanding its physiological function, such as when assessing protein corona in nanoparticles–protein assemblies. On other occasions, the identification of the binding sites in the peptide chain and conformational changes as a consequence of the metal–protein interaction, as well as the lability of this interaction, can explain the role of these metal-based biomolecules in living organisms. This article attempts to critically review the current state-of-the-art of the available analytical techniques for characterizing metalloproteins and metal–protein complexes. Methods for assessing the structure, characterization of the metal-binding sites, as well as the class of proteins involved in some metal (metallic nanoparticle)-binding proteins are discussed. Recent developments when assessing metalloproteins and metal–protein complexes in the clinical, environmental, and food fields, and pioneering research regarding nanoparticle–protein characterization, are also reviewed.     

一维快装置中心反应率模拟计算的灵敏度和不确定度分析

采用广义微扰理论和离散纵标输运计算方法,推导了中心反应率比值对重要核反应参数的灵敏度的计算公式。以一维快基准装置Jezebel-Pu239为例,计算了其中心反应率比值对关键核数据的灵敏度,并结合多群协方差数据,分析了其中心反应率比值计算中由于核数据的不确定度所引入的不确定度及其来源。根据计算结果以及评价数据的协方差信息,建议对Pu-239的非弹截面数据进行更精细的评价,以期降低反应率比的模拟计算不确定度。On the base of the generalized perturbation theory and SN method, the theoretical model for calculating the sensitivity and uncertainty of reaction rates ratio (RRR) versus nuclear data is developed. Taking Jezebel-Pu239 critical benchmarking facility as an example, the sensitivity of F49/F25 ratio versus important nuclear data is calculated, as well as the uncertainty arising from the nuclear data. Basing on the sensitivity and uncertainty analysis as well as the covariance information of input evaluated data, refined evaluation of the inelastic data of Pu-239 is considered as a feasible measure to reduce the uncertainty of reaction rates ratios.     

Laser performance of monolithic Cr,Nd:YAG self-Q-switched laser

The self-Q-switched laser performance of monolithic Cr⁴⁺,Nd³⁺:YAG concave-planar resonator with 5-mm length was studied experimentally and theoretically. The slope efficiency is as high as 24% and pump threshold is as low as 64 mW. The pulse width, the single pulse energy and the pulse repetition rate of monolithic Cr,Nd:YAG self-Q-switched laser were measured as a function of absorbed pump power. With the increase of pump power, the pulse width decreases and the pulse energy and the pulse repetition rate increase. The average output power of 91 mW with pulse width of 7 ns at repletion rate of 35.5 kHz was obtained at the maximum absorbed pump power of 440 mW, the peak power is as high as 370 W. The theoretical prediction of pulse energy, pulse width and pulse repetition rate as a function of absorbed pump power based on rate equations is in a good agreement with our experimental data. This can lead to develop the diode laser-pumped monolithic self-Q-switched solid-state microchip lasers.     

喷水对半闭环燃气轮机循环的影响

本文对燃气轮机的简单循环、开环和半闭环系统,分别以空气和CO2作为工质、纯氧为氧化物、天然气为燃料时的热力循环过程,在喷水及不喷水条件下,利用自行设计的分析软件进行了较为系统的数值分析和性能评估,详尽分析了喷水量对使用空气或CO2作为工质的半闭环燃气轮机循环的影响,揭示了适量喷水有助于提高循环效率和输出功率的客观规律,为研制CO2零排放的高效燃气轮机装置奠定了坚实的理论基础.     

光谱线型函数的四种形式及其变换关系

从理论上研究了光谱线型函数的四种形式及其关系,以多普勒展宽导致的线型函数为例,分析了光子数、能量按频率及波长分布函数的最大值和半高全宽。结果表明,光子数、能量按频率的分布函数近似相等,光子数、能量按波长的分布函数也近似相等。通过对多普勒线型函数的分析,建立了根据两条光谱线的线型函数的最大值比值求得光子数比值的方法。