色谱柱分离过程的驰豫理论基本模型的建立

根据样品分子在色谱柱分离过程中的输运特征,认为样品在系统中以跃迁的方式完成迁移,建立了色谱柱分离过程驰豫理论的基本模型。假设溶质在两相间平衡,用母函数方法研究非连续递推形式的驰豫理论输运动力学微分方程组,得到了描述组分在柱后浓度分布规律的基本流出曲线方程,并通过数值解方法模拟谱图对各输运参量与流出曲线特征的关系加以讨论。     

电子电气产品中19种元素的无损测定、分布研究及风险评估

采用X射线荧光光谱法快速无损扫描测定电子电气产品中19种元素,考察了特征X射线以及计数时间的选择,并通过自制标准块绘制标准曲线。同时利用MAPPING功能进行微区原位扫描,掌握19种元素的分布情况及分布特征。并利用换算因子计算REACH高关注物质的含量,对19种元素进行风险性评价。     

脉冲激光引发自由基聚合的动力学研究

处理了无链转移时脉冲激光引发自由基聚合中的动力学问题:推导出聚合产物数均和重均分子量的严格数学表达式,给出了链自由基、死聚物及总的聚合产物的归一化的分子量分布函数,计算结果表明:随着单体转化率的上升,各种分子参数,例如数均和重均分子量,以及多分散指数的数值周期性地振荡,且振幅逐渐下降,分子量分布曲线则包含一些特征峰,且随着每次脉冲激光产生的初级自由基浓度的降低,分布曲线峰的数目增加,另外,与歧化终止相比,偶合终止使产物的分子量分布略为变窄.     

酸碱滴定曲线的数学分析及其化学意义的探讨

酸碱滴定是化学专业教师及学生最为熟悉的基本实验，滴定曲线反映了整个中和反应的过程，对理解和掌握酸碱滴定十分重要。本文从三个基本假设出发，基于化学平衡思想，应用滴定过程中的电荷守恒与物料守恒关系，在一个参数不变与两个参数变动的初始条件下分别建立了电离度和pH与滴定分数之间的函数关系。通过对函数本身及其导函数进行数学分析，还原了酸碱滴定曲线；尝试利用两个初始条件在数学表达式中的位置及对函数的影响，定量验证了现有教材中对不同数量级初始浓度与不同强度的酸在滴定过程中所表现出差异的定性解释，进而对滴定曲线进行延拓，提出了一种滴定弱酸的可能方式。     

沉降分析实验的一种数据处理方法

介绍了沉降分析实验的一种数据处理方法——解析法。该方法克服了传统图解法的一些缺点,采用一个包含有两个参数的函数拟合沉降曲线,并由该函数直接求得粒子分布函数的数学表达式。所用的函数能较好地归纳大量的实验数据。从解析法求出的粒子大小分布曲线及粒子的最可几半径与图解法得出的结果基本吻合。     

尼龙6/碳纤维微复合材料的界面微观力学

选用微球脱黏实验,在其基础上改进了制样方法,并分析了界面参数对界面微观力学性能的影响.结果显示,树脂微球脱黏时的力值Fmax随着纤维在树脂基体中的包埋长度le增大而以斜率k的趋势线性增大,截距为b;界面剪切强度τIF与le呈双曲线函数关系,随着le增大而增大,并最终趋向于一个极限值k′.此外,还讨论了不同的界面参数,如函数Fmax(le)的斜率k,截距b值,对函数Fmax(le)和τIF(le)的曲线分布的影响,以及试样形貌对实验数据分散性的影响。     

定量解析差热分析曲线的计算方法

对于有特征热效应发生的化学反应,本文根据合理的动力学模型提出了二元线性回归解析DTA曲线,求取动力学参数的方法。该法的特点在于仅通过一次DTA实验及一次回归即得到多个动力学参数。结合实例详细说明了截取DTA数据的三次样条插值函数法及D-M分布函数法,并指出这两种计算方式求出的基本数据按二元线性回归法得到结果的一致性,可做为所求动力学参数正确与否的判据。     

多相聚合物体系熔体动态过程中相形成与发展——PS/PcBR非相容体系的扫描电子显微镜图样分析

以连续共混过程间歇出料法研究了PS/PcBR非相容体系共混过程中的扫描电子显微镜图样演化过程 ,从平均粒径、特征长度Λ和平均特征长度Λm 多个方面讨论了非相容体系的共混过程 ,并以标度函数P(Λ/Λm)证明非相容体系共混过程在一定时间和空间范围内具有自相似性 ,且分形维数D可以作为一个参数描述熔体动态过程     

1-辛烯Ziegler-Natta聚合的活性中心多分散性——分子量分布及动力学的研究

本文通过对TiCl_3-Al(C_2H_5)_3聚合1-辛烯产物的双峰型分子量分布曲线用Schulz函数进行拟合、分峰处理,发现这种双峰型分布中的高分子量峰部分由一种活性中心生成,低分子量峰部分则由至少两种活性中心生成.将不同转化率时聚辛烯的分子量分布分峰拟合数据与聚合速率、活性中心数等测定数据相结合,得到了高分子量和低分子量两部分产物相应的活性中心上各自的动力学参数(增长速率常数、活性中心数、链转移常数等)及各自的聚合速率曲线,从而证实了多种活性中心的存在、它们催化特性的差异及与聚合物分子量分布增宽的关系.     

用隐函数方法处理不断引发,链增长自由基聚合反应

利用图形分析方法给出了不断引发、链增长自由基聚合反应的分子量分布函数，结合反应转化率曲线，利用隐函数方法和数学随机模拟法，得到了分子量分布曲线，利用计算结果计算结果讨论了不同终止形式及反应速率对聚合物分子量分布的影响，考虑反应体的扩散控制。给出了苯乙烯本体聚合的分子量分布，得到与实验事实相一致的结论。     

青山烟煤中痕量元素的分布特性

青山烟煤中痕量元素的分布特性晏蓉，欧阳中华，曾汉才，吴育松，王秋华，陆晓华，徐涛（华中理工大学煤燃烧国家重点实验室，武汉４３００７４）（华中理工大学化学系，武汉４３００７４）关键词烟煤，痕量元素，分布特征煤中矿物质的存在对煤的使用有很大影响，最大影响...     

Elemental composition of dust in an iron foundry as determined by instrumental neutron activation analysis

In the workplace of an iron foundry total and respirable suspended particulate matter was daily collected with a network of stationary filtration systems, with Andersen cascade impactors and with personal samplers. The performances of the different sampling systems are evaluated. All samples were analysed by instrumental neutron activation analysis. More than 30 elements were determined. The composition of the particulate samples is compared to that of the major emission sources. For visualising and interpretation of the data computer programs for contour plotting, classification and clustering of the elements and the samples are applied. On the basis of their distribution and particle size the elements can be divided in a number of groups, for which easily determined elements are proposed as indicator elements. The results allow an estimate of the impact of the major emission sources on the air quality in the entire workroom. Suggestions for representative sampling techniques and locations are made.     

Chemical bonding in cesium uranyl chloride based on the experimental electron density distribution

Details of the electron density distribution in Cs(2)UO(2)Cl(4) have been obtained from an accurate X-ray diffraction experiment at 20 K. The electron density was described with the Hansen-Coppens multipole model. Topological analysis of the electron density confirms that the U-O bond is probably a triple bond, the U-Cl bonds are incipient covalent interactions, and the Cs-Cl and Cs-O interactions are of the closed-shell type. The results obtained serve as a proof of principle that electron density features related to chemical bonding may be obtained from X-ray data for even the heaviest elements.     

Evaluation of minor element concentrations in potatoes using laser-induced breakdown spectroscopy

We have performed spectroscopic analysis of the plasma generated by Nd:YAG laser irradiation of flesh and skin of fresh potatoes. From the spectra recorded with an Echelle spectrometer 11 minor elements have been identified. Their relative concentrations were estimated by comparing the measured spectra to the spectral radiance computed for a plasma in local thermal equilibrium. According the moderate plasma temperature of about 6500 K at the time of spectroscopic observation, the electrons are essentially generated by the ionization of the minor metal atoms, making plasma modeling possible although the organic elements may be out of equilibrium. Among the spectral lines selected for the analysis, the Na I 588.99 and 589.59 nm doublet was found to be partially self-absorbed allowing us to estimate the number density of sodium atoms. The value was found to agree with the number density predicted by the plasma model. As a result, the relative concentrations of the detected minor elements have been estimated for both the flesh and skin of the potatoes. Among these, aluminum and silicon were found to have relatively large mass fractions in the potato skin whereas their presence was not detected in the flesh. The present study shows that laser-induced breakdown spectroscopy is a promising tool to measure the elemental composition of fresh vegetables without any sample preparation.     

Peculiarities of metal—ligand bonding in europium trinitrate complexes: a viewpoint of comparative charge density analysis in crystals

The results of high-resolution X-ray diffraction studies of the charge density distribution in crystals of three europium trinitrate complexes, including those with N-donor "antenna"-ligands are summarized. It is shown that the charge transfer between lanthanide ion and "antenna" correlates with the energy of interaction between the metal and nitrate anion, and the total stabilization energy of the metal polyhedron depends weakly on the coordination number of the metal and the nature of the ligands. The statistical treatment of the crystal structural data for similar complexes and the energies of the corresponding metal—ligand interactions allowed us to suggest the stability of mer-arrangement of the coordinated nitrate anions and to propose a semiempirical relationship to estimate the energy of Eu—O interactions. The influence of vibration processes on the electron density distribution in the EuO₂NO fragment was additionally considered, and a feasibility to estimate the energy of interaction between the ligand and lanthanide ion at non-stationary points on the potential energy surface was validated.     

Estimation of dissociation energy in donor-acceptor complex AuCl x PPh3 via topological analysis of the experimental electron density distribution function

The high-resolution X-ray diffraction analysis and plane-wave density functional theory were applied to the investigation of charge density distribution in the donor-acceptor complex of AuCl with PPh3. The approach allows us to estimate the atomic charges, the charge transfer, the energy of weak interactions (Au...H, Au...C, H...Cl, etc.), and Au-P bond energy directly from the experimental data.     

Estimation of the barrier to rotation of benzene in the (eta 6-C6H6)2Cr crystal via topological analysis of the electron density distribution function

The high-resolution X-ray diffraction analysis of the electron density distribution and plane-wave density functional theory has been applied to estimate the lattice energy and barrier to rotation of a benzene ring in the crystal of (eta(6)-C(6)H(6))(2)Cr. Experimental data made it possible to perform analysis of the metal-(pi-ligand) bond and estimate the nature and energy of weak H...H and H...C intermolecular interactions in the crystal. Summation of the intermolecular H...H and H...C interaction energies makes it possible to reproduce the experimental sublimation enthalpy value with high accuracy.     

Estimating statistical distributions using an integral identity

We present an identity for an unbiased estimate of a general statistical distribution. The identity computes the distribution density from dividing a histogram sum over a local window by a correction factor from a mean-force integral, and the mean force can be evaluated as a configuration average. We show that the optimal window size is roughly the inverse of the local mean-force fluctuation. The new identity offers a more robust and precise estimate than a previous one by Adib and Jarzynski [J. Chem. Phys. 122, 014114 (2005)]. It also allows a straightforward generalization to an arbitrary ensemble and a joint distribution of multiple variables. Particularly we derive a mean-force enhanced version of the weighted histogram analysis method. The method can be used to improve distributions computed from molecular simulations. We illustrate the use in computing a potential energy distribution, a volume distribution in a constant-pressure ensemble, a radial distribution function, and a joint distribution of amino acid backbone dihedral angles.     

Enthalpies of formation from B3LYP calculations

We have calculated the geometries, energies, and normal vibrations of 845 compounds containing the elements H, C, N, O, F, Al, Si, P, S, and Cl using hybrid density functional theory in order to investigate the accuracy of atom-additive schemes for predicting enthalpies of formation at 298 K. The results give a more realistic estimate of the accuracy of density functional calculations than some overoptimistic earlier correlations. We have also calculated atom-additive schemes for the zero-point energies and enthalpic corrections to the energies. Remarkably, it is not important to include the vibrational or rotational contributions, which can be estimated well within a purely Born-Oppenheimer regression model.