A simple correlation for predicting heats of fusion of nitroaromatic carbocyclic energetic compounds

In this paper, it is shown that heats of fusion of nitroaromatic carbocyclic energetic compounds can be predicted by using some structural parameters. Elemental composition and the contribution of some specific polar functional groups would be needed in the new method. Predicted heats of fusion using the method described herein for 41 nitroaromatic carbocyclic compounds are compared with experimental data. Calculated heats of fusion have a root mean square (rms) deviation of 3.01 kJ/mol and average deviation of 2.35 kJ/mol for these energetic compounds.     

A detailed model for the decomposition of nitramines: RDX and HMX

A unified decomposition scheme for two very important cyclic nitramines used as primary explosives – RDX and HMX – has been constructed using ab initio Density Functional Theory (DFT) calculations. Molecular parameters such as vibrational frequencies and moments of inertia corresponding to the computed potential energy profile of unimolecular decomposition of these nitramines were then used to obtain the thermochemistry of all identified species and reaction rate constants of each individual channel. These primary decomposition reactions were then combined with: (i) important secondary reactions of the key reactive radical intermediates, such as CH₂NNO₂ (Methylene Nitramine MN), CH₂N, NO, NO₂, OH, etc.; (ii) existing nitramie reaction networks [33]. We have developed an improved mechanism for the detailed chemistry of nitramines which can be applied to combustion and detonation phenomena of this class of energetic materials. This revised version was published online in June 2006 with corrections to the Cover Date.     

Theoretical prediction of condensed phase heat of formation of nitramines, nitrate esters, nitroaliphatics and related energetic compounds

An empirical approach is presented for calculation heats of formation of nitramines, nitrate esters, nitroaliphatics and related energetic compounds which contain at least one of the functional groups including N-NO(2), C-ONO(2) or nonaromatic C-NO(2). This approach is based on elemental composition and various structural and functional group parameters of C(a)H(b)N(c)O(d) energetic compounds. Heat of formation for 78 nitrocompounds including nitramines, nitrate esters, nitroaliphatics and the data obtained is compared with experimental data. Root mean square (rms) of deviation for 19 well known of mentioned energetic compounds are also compared with complex quantum mechanical computations which show 23.8 and 21.3 kJ/mol for new and quantum mechanical methods, respectively. Predicted condensed phase heats of formation for remainder 59 energetic molecules with complex molecular structures have a rms deviation from experiment of 42.3 kJ/mol.     

Approximate prediction of melting point of nitramines, nitrate esters, nitrate salts and nitroaliphatics energetic compounds

A simple new procedure is introduced to predict melting point of selected class of energetic compounds containing nitramines, nitrate esters, nitrate salts and nitroaliphatics energetic compounds. The number of nitrogen and oxygen as well as the number of nitramine group and the contribution of some specific functional groups would be needed in the new method. Energetic compounds should contain at least one of the functional groups including N-NO(2), C-ONO(2) or nonaromatic C-NO(2). Calculated melting point for 33 nitramines, nitrate esters, nitrate salt and nitroaliphatics are compared with experimental data. Predicted melting points have average deviation of 5.4% for these energetic compounds.     

A simple experimental arrangement for measuring the vapour pressures and sublimation enthalpies by the Knudsen effusion method: Application to DNA and RNA bases

We measured the vapour pressure of several DNA and RNA bases—uracil, adenine, guanine, thymine and cytosine—in the 300–450 K range. In each case the sample mass loss rate was measured as function of temperature with a simple setup consisting of a commercial film deposition system and a homemade oven. Afterwards vapour pressure values were extracted from these data using the Knudsen effusion method. Sublimation enthalpy values, obtained from vapour pressure data by applying the Clausius–Clapeyron equation, are in very good agreement with literature values. The results suggest that crystal-based film thickness monitors may be useful in on-line cross-section measurements, monitoring the gas target thickness. They also show the viability of using this oven for producing a biomolecular gas target.     

基于露点法判断冻干过程的一次升华结束点

本文根据冻干过程干燥室内的露点值和物料的水分含量有关提出一种新的方法--露点法来监控冻干过程物料的水分迁移情况.以浓度为2%(W/V)的甘露醇(冻干保护剂)为研究对象,分别取80个,160个,20个小瓶,通过不同的过充小瓶数(1个,2个),不同的溶液高度(溶液高度6.5 mm,0.32 mm)来检验露点法在监测整批样品冻干过程的灵敏性.与称重法对照,称重法即在冻干过程不同的时刻取出样品测量整批样品质量.实验结果表明露点法即使当过充小瓶率为0.625%,或者溶液高度为0.32mm时仍有足够的灵敏度,露点法得到的一次升华结束点与称重法结果一致.这说明非接触法露点法是一种可靠,便利的监测一次升华结束点的方法,将其应用于控制成批冻干样品大有可为.     

Detonation temperature of high explosives from structural parameters

A new scheme is introduced for calculating detonation temperature of different classes of high explosives. The ratio of oxygen to carbon and hydrogen to oxygen as well as specific structural parameters are the fundamental factors in the new method. An empirical new correlation is used to calculate detonation temperature of energetic compounds without considering heat contents of explosives and detonation products. Calculated detonation temperatures for both pure and explosive formulations show good agreement with respect to measured detonation temperatures and complicated computer code using BKWR and BKWS equations of state. Predicted detonation temperatures have root-mean-square (rms) percent deviation of 4.6, 14.2 and 4.6 from measured values for new method, BKWR and BKWS equations of state, respectively.     

控制降温对近空间升华法沉积CdZnTe薄膜形貌与结构的影响

采用场发射扫描电镜和X射线衍射技术研究了生长结束后的降温过程对以近空间升华法生长的CdZnTe薄膜形貌与结构的影响。分析了快速(炉冷,673K以上-8K/min)和慢速(-2K/min)两种降温速率下获得的CdZnTe薄膜的结构与形貌,并考察了降温中是否阻断生长源向薄膜的传质的影响。结果表明,所得到的薄膜均为闪锌矿结构,降温时薄膜的持续生长将抑制晶粒在平面内铺展而使其棱角钝化的趋势,以较慢的速率降温和降温时阻断传质均有利于提高薄膜的致密度,降低粗糙度及薄膜的织构强度。     

基于多体力学的汽车空气弹簧悬架优化

基于ADAMS/View软件对湖南大学自主研发的某一车型,以提高整车行驶平顺性为目的,综合考虑阻尼系数、悬架刚度和非簧载质量各因素对平顺性的影响,建立了空气弹簧悬架及整车仿真分析模型,构造了仿真分析所需路谱的高程样本,对其影响汽车安全性、平稳性、舒适性的参数进行敏感性分析,并在此基础上对空气弹簧悬架系统参数进行优化设计.通过实车道路试验和仿真结果的对比,验证了仿真的可信度及可行性.     

CdZnTe薄膜的CdCl2退火及性能表征

采用近空间升华法制备了CdZnTe薄膜,并对其进行CdCl2退火,采用扫描电镜(SEM)、能谱仪(EDS)、X射线衍射仪(XRD)、紫外光谱仪、I-V测试仪等研究了退火对薄膜表面形貌、成分、结构以及光电性能的影响。结果表明,经过CdCl2退火后薄膜的晶粒尺寸明显增大,晶粒分布更加均匀;XRD分析结果显示,退火后薄膜的最强峰(111)峰的半峰宽变窄,薄膜沿(111)方向的择优取向明显增强;退火后薄膜的光学透过率降低,截止边红移,光学禁带宽度减小;薄膜的电阻率在退火后下降了两个数量级。     

A combined template and closed space sublimation approach to the synthesis of single-crystalline CdS nanowires and their optical properties

High-quality single-crystalline CdS nanowires about 40 nm in diameter have been successfully synthesized without any catalyst at ambient pressure by combining the closed space sublimation (CSS) technique with porous anodic alumina membrane (AAM) template method. Extensive characterizations of the nanowires have been carried out using scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy and UV-Visible absorption spectroscopy. A band gap of 2.38 eV is determined from the UV-Vis absorption spectrum obtained from the nanowire sample. Our facile technique may in principle also be used for synthesizing other one-dimensional (1D) materials with high vapor pressure and axial nanowire heterostructures.     

CSS法制备CdZnTe薄膜时衬底温度的影响规律

采用近空间升华法(close-spaced sublimation,CSS),以CdZnTe化合物粉料为原料制备了CdZnTe薄膜,采用XRD、SEM、紫外光谱仪等对其进行了性能表征,并研究了不同生长温度对薄膜生长速率、结构、Zn含量和光学特性的影响规律.研究结果表明,薄膜的生长速率随着生长温度的升高而增大,且温度>5...     

基于最优复Morlet小波的结构密集模态参数识别

针对结构密集模态参数识别精度不高的问题,提出了一种小波Shannon熵与最小标准差相结合来优化复Morlet小波参数的方法。首先理论推导了中心频率与带宽参数的取值范围,其次采用两个最小原则对中心频率与带宽参数同时进行优化,通过仿真算例和模型实验的参数识别,验证了参数优化后的Morlet小波可准确地识别结构的密集模态参数,并且具有一定的抗噪性能。     

Sublimation of Cobalt in the Neighborhood of the Curie Point

The results of experiments in sublimation of cobalt in the neighborhood of the Curie point are analyzed. The kinetics of sublimation are described under conditions of permanent evacuation of the gas phase of cobalt. A magnetic model is suggested, which makes it possible to derive a quantitatively correct correlation between the Curie point and exchange splitting for Ni and Co. The contribution of magnetic interactions to the energy of sublimation of monatomic magnetic is calculated.     

PAN基炭纤维中sp2杂化的C-C原子键距与结构参数之间关系

利用Raman散射及X射线衍射方法，对不同炭化温度下制备的PAN基炭纤维样品进行了测试。根据Raman散射的测试结果，从Fitzer碳键键距出发，给出了PAN基炭纤维中sp^2杂化的C—C原子键距a0随炭化温度的变化规律。由各样品的X射线衍射测试结果，得到了各样品的结构参数（La、Lc、d002）。分析了sp^杂化的C—C原子键距a0随结构参数（La、Lc、d002）变化的原因。结果表明，C—C原子键距a0与石墨化程度有关，且随La、lc的增大及d002的减小C—C原子键距增大。     

Conceptual stabilizer selection for nanomilling based on dispersibility parameters

The choice of stabilizers to prevent particle agglomeration during nanomilling is an elaborate process which is often based on empirical rules and experience. Usually, extensive screening studies are required to find an appropriate stabilizing additive. The present study shows how the selection of polymeric stabilizers can be narrowed down to a couple of additives based on Hansen solubility parameters. The stabilizing capability was found to be a function of the difference between solubility parameters of additive and particulate species. Solubility parameters of different additives and two particle species were determined by inverse gas chromatography and the stabilization performance was evaluated by nanomilling experiments conducted with a stirred media mill. It is shown that a certain difference of solubility parameters between particle and additive is necessary in order to provide colloidal stability of small particles after milling. On the one hand, the additive needs a certain affinity to the particle surface, while on the other hand it also has to be compatible with the solvent. Based on experimental data, a solubility parameter difference in the range of 7.5–10 MPa^0.5 was identified as a good measure for a proper stabilizer selection. The approach was proved for two organic particle species and represents a promising tool for a more efficient formulation development of drug nanosuspensions.     

基于盲源分离的结构模态参数识别

提出一种结构模态参数识别的新方法。该方法以盲源分离理论中基于二阶统计量的AMUSE算法为基础,通过对测试数据Hilbert变换构建分析数据矩阵,通过求解不同时滞下数据协方差矩阵的广义特征值问题实现对结构模态参数的识别。数值算例结果表明,该方法不仅适用于实模态情况,同时适用于复模态情况,且计算简单,识别精度高,对测量白噪声有很好的鲁棒性。     

双目视觉飞行目标落地参数测量

采用放置在落弹点区域附近的凝视等待式双目视觉摄像机,高速摄影交汇测量飞行目标的落地参数.根据不同时刻质心的空间三维坐标,用最小二乘法对目标航迹进行拟合,建立了目标三维空间轨迹的多项式函数,对多项式函数求导得到目标的飞行速度.针对回转体类飞行目标的特点,根据其在摄像机像面成像的大小,将目标分为三类,对不同目标采用了不同的姿态测量方案,并对测量的误差来源进行了分析,提出了减小测量误差的方法.实验与理论分析表明,本文采用的速度与姿态测量方法具有精确、稳定等优点.     

基于小波变换和反向传播网络的模态参数辨识

为了减小连续小波变换带来的边界效应对模态参数识别的影响,提出利用人工神经网络对自由衰减响应信号进行双向延拓。设计了多输入单输出的反向传播网络,网络根据当前有限多个离散采样点数据预测下一时刻信号的幅值,训练网络的样本来自于对原始信号的简单分组。使用数值仿真和实验检验了提出方法的实用性。实验装置是用于微创外科手术机器人的力传感器。结果表明提出的方法能够准确地从短信号中辨识出阻尼比和无阻尼自振频率。     

超声导波频散曲线反演皮质骨参数的研究

皮质骨参数的变化可以反映骨质的健康状况,因此文章提出了一种频散能量匹配算法来反演皮质骨参数。首先,通过频散特性方程计算出预定义参数下的频散曲线数据库;其次,利用时域有限差分算法建立皮质骨声场模型,将仿真的时域信号通过功率谱估计得到频散能量信息,并与数据库进行匹配,通过分析匹配结果的能量从而得到皮质骨的厚度、纵波速度和横波速度。仿真结果显示：与理论值相比,厚度的平均相对误差为3.8%,纵波速度与横波速度的平均相对误差分别为0.6%、0.9%。对三组离体牛胫骨皮质骨进行反演,离体实验结果显示：与真实值相比,厚度相对误差为4.9%,且实验频散曲线与反演得到的理论频散曲线吻合。因此文中所提出的反演算法可以有效获取皮质骨的厚度,横波速度和纵波速度,从而为评价骨质的健康状况提供可靠的依据。