低温低噪声放大器的发展概况及其结构设计综述

介绍了低温低噪声放大器的研制历史、现状及应用情况 ,举例分析了在该类放大器的结构设计中需要解决的关键技术 ,对军事和民用装备的有关领域有参考作用。     

面向微穿孔板吸声结构和吸声特性混合设计的软件平台

微穿孔板吸声结构是由微穿孔板与板后空腔组成的共振吸声结构,被认为是继多孔吸声材料之后发展起来的最有吸引力的吸声结构,其吸声特性与结构参数孔径d、板厚t、孔距b及空腔深度D有关,如何按需设计一个有效的微穿孔板吸声结构已成为目前研究的热点。本文从微穿孔板吸声结构和吸声特性混合设计的角度出发,使用面向对象的编程语言C++开发了微穿孔板吸声结构设计平台。与以往设计方法不同,本文开发的软件平台综合考虑了结构参数和吸声特性参数两方面的限制,根据实际应用要求平衡微穿孔板吸声结构的最大吸声系数与吸声带宽之间的制约关系,并以饱满的吸声曲线为目标,提供满足混合设计要求的优化结构参数。     

Anomalous heat evolution of deuteron implanted al upon electron bombardment III - try to observe the nuclear d-d reaction

In previous papers, one of the authors (K. K.) has observed the anomalous melting of the surface layer of deuteron implanted Al, containing so-called "tunnel structures", on the electron bombardment in transmission electron microscope. In the present paper, we intended to observe the evidence of the d-d nuclear reaction, expecting neutron emission, associated with the melting phenomenon. However, the result was rather unexpected. The melting phenomenon was certainly observed under the same experimental conditions as before. But, in spite of the melting, neutron emission associated with the nuclear reaction was not observed. And, more unexpectedly, X-ray emission of energy less than roughly 400 v keV was observed when specimens with a bubble structure, which never showed melting, were bombarded with electron beams. Several conceivable mechanisms are discussed which, however, are all not convincing to explain the melting. The melting is attributed to some excess energy generation. The error estimation of the radiation measurements was undertaken.     

CONFORMATIONAL ANALYSIS AND MOLECULAR MODELING OF CHOLESTERIC LIQUID CRYSTAL POLYESTERS BASED ON XRD,RAMAN, AND TRANSITION THERMAL ANALYSIS

Molecular modeling of the cholesteric liquid crystal polyester poly[oxy(1,2 - dodecane)oxycarbonyl-1,4-phenyleneoxycarbonyl-1,4-phenylenecarbonyloxy-1,4-phenylenecarbonyl] (PTOBDME), [C₃₄H₃₆O₈] _n , synthesized in our laboratory and thermally characterized by differential scanning calorimetry (DSC), was performed to explain both its cholesteric mesophase and 3D crystalline structure. Conformational analysis (CA) was run for the monomer both by systematic search and with molecular dynamics (MD) simulations. Minima energy conformers were “polymerized” with Cerius² and helical, cholesteric molecules were obtained in all cases. Our models agree with the chiral behavior observed by X-ray diffraction (XRD), thermooptical analysis (TOA) and circular dichroism (CD) experiments. Crystal packing of the polymer molecules were simulated in cells with parameters a and b obtained from experimental powder X-ray diffraction patterns and c calculated from the translational repetitive unit during the theoretical polymerization. Recalculated X-ray powder diffraction patterns of our models matched the observed ones. Morphology simulation from those crystal models is in good agreement with the crystals observed by optical microscopy. We have also modeled the self-associating nature of those polyesters when dispersed in aqueous media. Simulation of our models surrounded by different solvents, such as water and chloroform, were performed by calculating their interaction energies, coordination numbers, and mixing energies, applying Monte Carlo simulation techniques based on the Flory-Huggins theory. These results were compared with their experimental vibrational Fourier transform (FT)–Raman spectra in the regions in which structural marker bands of the polymer appear.     

Effects of Modifier Concentration on Structure and Viscoelastic Properties of Copolyester/Clay Nanocomposites

Abstract

Poly(ethylene glycol‐co‐cyclohexane‐1,4‐dimethanol terephthalate)(PETG)/clay nanocomposites were prepared via melt intercalation technique. The effects of concentration of the organic modifier in the clay on the properties of the nanocomposites were studied. Three clays modified using the same alkyl ammonium modifier, but differing in modifier concentration, are used for this purpose. The nanocomposites are characterized using wide‐angle x‐ray diffraction for their structure. Dynamic mechanical analysis of these nanocomposites is also studied to investigate their viscoelastic behaviors. The x‐ray diffraction study shows an increase in the interlayer spacing of organically modified clays as compared to that of Na⁺ clay. The extent of increase in the interlayer spacing is dependent on the concentration of organic modifier used to modify the montmorillonite. The presence of well‐defined diffraction peaks and the observed increase in the interlayer spacing in the nanocomposites imply the formation of an intercalated hybrid. Dynamic mechanical properties show an increase in the storage modulus of the nanocomposite over the entire temperature range studied, as compared to the pristine polymer. Investigation of the rubbery plateau modulus confirms the reinforcing effect of organically modified clay. The observed enhancement in the modulus was greater for the clay with the lowest content of the organic modifier. These results indicate that in nanocomposites, apart from the compatibility of the organic modifier with the polymer, its concentration in the interlayer also plays a critical role in the structure development and thus in the enhancement of the properties. The nanocomposites showed reduced damping, which was governed by the modifier concentration in the clay.     

第一性原理对SinMg(n=1-12)团簇结构、稳定性与电子性质的研究

运用密度泛函理论(DFT)的杂化密度泛函B3LYP方法,在6-311G基组水平上对 团簇进行了构型优化、频率分析与电子性质计算.同时讨论了团簇的平均结合能、能级间隙、二阶能量差分、自然电子布居、极化率.研究结果表明： 团簇的基态绝大多数为立体结构. 时,体系的基态为自旋三重度, 时,则为单重态.镁原子的掺入使得主团簇的电子性质发生了明显的变化,掺杂使体系的平均结合能降低,能隙减小,化学硬度减小,电子亲和能增大.电子总是从 原子向 原子转移.团簇中原子之间的成键相互作用随n的增大 而增强,团簇的电子结构随n的增大而趋于紧凑.     

大电流两电极气体开关研究

 由于引燃管难以满足现在能源系统对放电开关承受大电流的要求,因此研制了大电荷转移量两电极气体开关。这种新型气体开关电极间距可调,无触发极,采用同轴结构,并将主电极置于金属腔体内,减少了放电对绝缘支撑的污染。主电极为铜钨合金材料,设计为平顶圆柱状,以提高烧蚀均匀度和热传导效率,减少电极材料喷溅,延长其寿命。绝缘支撑采用碗状结构,提高了机械强度,增加了沿面击穿距离。该开关工作电压达25 kV,放电电流超过100 kA（脉冲宽度600 μs）,单次脉冲电荷转移量达50 C。实验结果显示该气体开关触发性能稳定,电极表面烧蚀均匀,多次大电流实验后电极表面保持完好,可应用于强激光能源系统。     

Monte Carlo simulations of star-branched polyelectrolyte micelles

The concentration profiles of monomers and counterions in star-branched polyelectrolyte micelles are calculated through Monte Carlo simulations, using the freely jointed chain model. We have investigated the onset of different regimes corresponding to the spherical and Manning condensation of counterions as a function of the strength of the Coulomb coupling. The Monte Carlo results are in fair agreement with the predictions of Self-Consistent-Field analytical models. We have simulated a real system of diblock copolymer micelles of (sodium-polystyrene-sulfonate)(NaPSS)-(polyethylene-propylene)(PEP) with f = 54 hydrophilic branches of N = 251 monomers at room temperature in salt-free solution. The calculated form factor compares nicely with our neutron scattering data. Received 18 July 2002 and Received in final form 11 October 2002 RID="a" ID="a"e-mail: roger@drecam.saclay.cea.fr     

β-环糊精与环氧氯丙烷共聚物的13C-NMR研究

¹³C NMR测定了一个系列的环氧氧丙烷与β-环糊精的共聚物,进行了谱峰归属和DEPT谱验证,实验测得2,3-丙二醇基在β-环糊精C(2)-O-位、C(3)-O-位和C(6)-O-位取代的¹³C NMR化学位移α-取代效应参数,描述了该共聚物分子链的组成和链化学结构特征.