On the Computation of Eigenvalues of the Anharmonic Coulombic Potential

In this work, we propose a method combining the Sinc collocation method with the double exponential transformation for computing the eigenvalues of the anharmonic Coulombic potential. We introduce a scaling factor that improves the convergence speed and the stability of the method. Further, we apply this method to Coulombic potentials leading to a highly efficient and accurate computation of the eigenvalues.     

Effect of gas supply method on the performance of the single-chamber SOFC micro-stack and the single cells

The effect of gas supply method on the performance of a single-chamber solid oxide fuel cell micro-stack and single cells was studied, and a novel gas supply method with separated gas vents in the gas tube was proposed. The traditional gas supply method was also investigated for comparison. Results showed that the single cells could obtain a uniform open-circuit voltage and power output by using the separated gas supply method. For the traditional gas supply method, the cell at the outlet position yielded inferior performance compared to that of the inlet cell. The gas flow rate showed a significant effect on the performance of the cells. Finally, the stack operated with the separated gas supply method produced a higher power output than that operated with the traditional gas supply method.     

胶囊中铬的测定方法研究

通过对比不同的前处理措施,建立准确、快速测定胶囊中铬（Cr）的方法。分别采用微波消解和电热恒温自动消解法进行前处理,石墨炉原子吸收法进行测定。试验表明：该方法在0~40.0μg/L范围内呈线性相关,相关系数为0.997 7,检出限为0.017 mg/kg,样品的加标回收率在90%~110%之间。对标准物质圆白菜中铬的测定在所要求的准确度范围之内。同时作了原子吸收光谱仪和电感耦合等离子体（ICP）发射光谱仪两种仪器的对照试验,方法的稳定性良好。采用微波消解或电热恒温消解作为胶囊的前处理,通过原子吸收法或ICP法均能准确测定胶囊中的铬。     

Analysis of the relative strength of the singular values obtained from the non-parametric kinetic method

The non-parametric kinetic method (NPK) is a method for the processing of thermoanalytical data, which does not make any assumption about the functionality of the reaction rate with the degree of conversion or with the temperature. This method has not been widely used due to its mathematical sophistication and difficulty of automation. The original NPK method uses only the first (maximum) singular value whereas additional information could be drawn from the remaining singular values. A hypothetical application of the NPK, which uses all the significant singular values (modified version of the NPK), is the separation of two or more steps of a complex decomposition reaction. Using simulated data, we have demonstrated that the modified version of the NPK is not useful to discriminate among the decomposition steps of a consecutive complex decomposition reaction scheme. Nevertheless, the analysis of the relative strength of the singular values is useful to assess the degree of separability of the temperature and conversion functions, which are the outcome of the NPK. Taking into account the relative magnitude of the first singular value with regard to the remaining singular values, we have proposed an automated two-scan version of the NPK method which guarantees two separable functions. As the separability of both temperature and conversion functions is the imperative assumption of the single-step kinetics approximation, the two-scan NPK method can be used as a testing method for those methods based on this approximation, the model-free and model-fitting methods.     

The correlations of the enthalpy of vaporization and the surface tension of molecular liquids

Correlation relations based on Stefan's rule, which defined dependence between the enthalpy of vaporization, the surface tension, the molar volume and the molar mass of a substance, were obtained. For development of the correlation equations two computational procedures were used: a method of the least squares and a method of artificial neural networks. The method of artificial neural networks was shown to give somewhat better results than the linear least-squares procedure. The average deviation of the calculated values from the experimental ones did not exceed 6% for training set of substances and 10% for control set (the method of the least squares). For the method of artificial neural networks it is 3% and 8%, respectively.     

Variation of the vector potential in the method of superposing singly excited configurations

A method for calculating the second correction to the energy of many-electron systems with a closed shell in an external magnetic field, which is a combination of the method of superposing singly excited configurations and the method of varying the vector potential has been proposed. The method is based on the simultaneous variation of the vector potential and the coefficients determining the contributions of different singly excited configurations to the correction wave function. Such an approach makes it possible to reduce the errors of the method of superposing singly excited configurations associated with the use of a restricted basis in the construction of the correction function and to eliminate the difficulties in the method of varying the vector potential associated with the need to include singular terms in the test gradient-transformation function for the vector potential.Translated from Teoreticheskaya i Éskperimental'naya Khimiya, Vol. 22, No. 3, pp. 337–341, May–June, 1986.     

钛粉质量鉴定新方法试验研究

钛粉质量鉴定一直是用化学分析测定全钛含量，而不能确定单质态的钛含量，实验表明用Ｘ射线衍射分析鉴定钛粉质量效果较好，避名了化学分析的缺点，是一种值得推广的鉴定方法。     

Densitometry Evaluation of the Arsenic Content of Biological Materials Using the method of Gutzeit

Abstract

By using densitometry the method of Gutzeit, previously considered to be a semiquantitative method, attains a quantitative character. The entire method, digestion of the biological materials included, is characterised by a coefficient of variation of 14%. This procedure appears to be well suited for the determination of normal values of arsenic in urine.     

分子探针法研究NiO-Cr2O3-SiO2和NiO-SiO2体系催化剂的表面结构

本文用分子探针法测定、研究了NiO-Cr₂O₃-SiO₂和NiO-SiO₂催化剂的表面吸附中心结构,且通过逐步溶解分析、X-衍射法、TPD、磁分析等测试方法证实用该法所得结论的正确。表明这是一种研究催化剂表面吸附中心结构的新的有效方法。其特点是能在接近实际的反应条件下,快速、方便地获得催化剂表面吸附中心的结构信息。     

Application of the accelerated molecular dynamics simulations to the folding of a small protein

In this paper, we further explore the applicability of the accelerated molecular dynamics simulation method using a bias potential. The method is applied to both simple model systems and real multidimensional systems. The method is also compared to replica exchange simulations in folding a small protein, Trp cage, using an all atom potential for the protein and an implicit model for the solvent. We show that the bias potential method allows quick searches of folding pathways. We also show that the choice of the bias potential has significant influence on the efficiency of the bias potential method.     

Mathematical optimization in the determination of the dissociation constants of a tribasic organic acid by 13C NMR spectroscopy

The calculation of dissociation constants from the chemical shifts of (13)C NMR spectra leads to a complicated non-linear equation. Two different mathematical methods for solution of this equation have been chosen--an iterative step method and a matrix pseudo-inversion method. When the iteration method is used the initial guesses for the parameters, the initial value of the step size and the escalation of the iteration must be optimized. For comparison the matrix pseudo-inversion method was used because it gives a unique result. With the optimized step method the results were as accurate or even better than those obtained with the matrix method. Although it takes time to optimize the system, the step method is the more suitable method of solving the problem. The matrix inversion can be done only with a computer with 13 significant digits and exponent capacity larger than +/- 38.     

A recipe for the computation of the free energy barrier and the lowest free energy path of concerted reactions

The recently introduced hills method (Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 12562) is a powerful tool to compute the multidimensional free energy surface of intrinsically concerted reactions. We have extended this method by focusing our attention on localizing the lowest free energy path that connects the stable reactant and product states. This path represents the most probable reaction mechanism, similar to the zero temperature intrinsic reaction coordinate, but also includes finite temperature effects. The transformation of the multidimensional problem to a one-dimensional reaction coordinate allows for accurate convergence of the free energy profile along the lowest free energy path using standard free energy methods. Here we apply the hills method, our lowest free energy path search algorithm, and umbrella sampling to the prototype S(N)2 reaction. The hills method replaces the in many cases difficult problem of finding a good reaction coordinate with choosing relatively simple collective variables, such as the bond lengths of the broken and formed chemical bonds. The second part of the paper presents a guide to using the hills method, in which we test and fine-tune the method for optimal accuracy and efficiency using the umbrella sampling results as a reference.     

Use of the o-phenylenediamine fluorescence system in the enzymatic assay of serum uric acid.

A manual enzymatic method is described for sensitive fluorometric determination of uric acid in human serum. This method is based on an enzymatic reaction with uricase to form hydrogen peroxide from uric acid and the following oxidation of o-phenylenediamine with peroxidase and hydrogen peroxide for the production of a fluorescence compound. The specificity and the selectivity in the method are due to the uricase reaction and the fluorometry, respectively. The formed fluorescence in the reaction mixture is measured at 410 nm (an excitation) and 550 nm (an emission). This enzymatic method can determine uric acid at 30-1000 microM, with a between-assay relative standard deviation of 4.35% or less. A good correlation is obtained between the present method and the colorimetric kit method.     

蔗糖酯的合成研究进展

综述了蔗糖酯的合成方法及工艺的研究进展,并对其反应机理进行了阐述.蔗糖酯的合成方法主要有四种:溶剂法、微乳化法、无溶剂法以及酶催化法.溶剂法采用DMF或DMSO为溶剂,但是这两种溶剂均有毒,限制了蔗糖酯在食品等行业的应用.微乳化法采用丙二醇或水代替溶剂法所使用的有毒溶剂,并加入乳化剂,使反应体系近似为均相体系.无溶剂法则是通过在反应体系中加入乳化剂或表面活性剂等使熔融相成均一相,反应平稳.但是一般无溶剂法反应温度较高,反应不易进行,产率低,且产品质量得不到保证.酶催化合成法是一种新的生物合成方法,采用生物酶代替传统的催化剂合成蔗糖酯,该法催化活性高、反应条件温和、选择性强、产物易分离等优点.文中还对蔗糖酯粗品的纯化工艺进行了介绍.     

一种通过剪断最短桥确定复杂桥环化合物主环的方法介绍

确定主环是命名复杂桥环化合物的难点所在。我们介绍一种"剪断最短桥,显露最大环"的方法,可以帮助学生快速准确地确定最大环的位置,从而对复杂桥环化合物命名。     

Relation between the refractive index increment and the density increment of binary mixtures: Application to the determination of partial specific volumes of polymers in solution

Starting from the Lorentz-Lorenz equation, Heller, a few years ago, advanced a method for calculating the partial specific volume of a substance in a dilute solution from the refractive index increment of the solution and the specific refraction of the solute. It is shown that this method, based on graphical extrapolation, can be considerably simplified. Further, a method is indicated by which the partial specific volume of a substance over the whole range of concentrations can be calculated in an analogous manner. The method is checked and elucidated with reference to some experimental examples.     

Improving the efficiency of the NEB reaction path finding algorithm

The nudged elastic band (NEB) method is a successful optimization method for obtaining minimum energy reaction paths if only the initial and final structures are known. However, the original implementation of the method had some limitations, which has meant that there has been considerable interest in proposing alternative NEB formulations, which show improved convergence behavior. In this work, we present two modifications to the standard NEB procedure. The first involves the use of a second-order quasi-Newton optimization technique applied separately to each of the images that form the path. The second consists of the use of an interpolating spline to represent the path. This ensures that the images along the path are evenly spaced and means that the arbitrary spring forces employed in the standard NEB method are no longer necessary. We tested these modifications on a set of small, but relatively complex, chemical systems and found that the computation time was reduced by as much as 90% compared with the standard method.     

On the separation of motions in the theory of polyatomic molecular spectra

A method has been suggested for the separation of rotational and vibrational motions of nuclei in polyatomic molecules. The method is based on the introduction of the angular velocity vector associated with the kinetic moment and provides the complete separation of motions in the case of arbitrary molecule deformations. The method requires no a priori assumptions on vibrational amplitudes.     

Continuous flow system for the evaluation of the extrinsic coagulation pathway

A simple and reliable method for the evaluation of the extrinsic coagulation pathway is presented. The method is based on the monitoring of the last step of the coagulation pathway in which the human plasma is clotted by the presence of the coagulations factors (prothrombin, factor V, factor X, calcium and phospholipids) in an excess of thromboplastin. It has been developed using a flow injection system involving the merging-zones and stopped-flow modes. The clotting reaction rate is monitored photometrically at 340 nm. The linear range expressed as a percentage of total clottable activity was found to be between 10 and 100%, with a relative standard deviation between 0.9 and 2.8%). The usefulness of the method was tested by determining the fibrin clotting capacity in human plasma from healthy and sick individuals with excellent agreement with the conventional clotting method (automated coagulation laboratory-nephelometric method).     

Estimation of the zeta potential and the dielectric constant using velocity measurements in the electroosmotic flows

In this paper we develop a method for the determination of the zeta potential zeta and the dielectric constant epsilon by exploiting velocity measurements of the electroosmotic flow in microchannels. The inverse problem is solved through the minimization of a performance function utilizing the conjugate gradient method. The present method is found to estimate zeta and epsilon with reasonable accuracy even with noisy velocity measurements.