Characteristic Galerkin method for convection-diffusion equations and implicit algorithm using precise integration

This paper presents a finite element procedure for solving transient, multidimensional convection-diffusion equations. The procedure is based on the characteristic Galerkin method with an implicit algorithm using precise integration method. With the operator splitting procedure, the precise integration method is introduced to determine the material derivative in the convection-diffusion equation, consequently, the physical quantities of material points. An implicit algorithm with a combination of both the precise and the traditional numerical integration procedures in time domain in the Lagrange coordinates for the characteristic Galerkin method is formulated. The stability analysis of the algorithm shows that the unconditional stability of present implicit algorithm is enhanced as compared with that of the traditional implicit numerical integration procedure. The numerical results validate the presented method in solving convection-diffusion equations. As compared with SUPG method and explicit characteristic Galerkin method, the present method gives the results with higher accuracy and better stability. The project sponsored by the State Scientific and Technological Commission of China through “China State Key Project: the Theory and Methodology for Scientific and Engineering Computations with Large Scale”, the National Natural Science Foundation of China and the European Commission Research Project CI1^*CT94-0014.     

不同操作模式下多环芳烃气相色谱特性的研究

在气相色谱分析萘、联苯、苊、芴、菲、蒽、荧蒽、芘、苯并（ａ）蒽、屈艹、苯并（ａ）芘和匹艹的研究过程中,以有效塔板数（ｎｅｆｆ）作为考察指标对新型色谱操作模式——程序升温升压操作条件进行了优化。通过对Ｋｏｖａｔｓ保留指数体系和Ｌｅｅ 保留指数体系在不同操作模式下的对比实验表明,在脉冲进样和程序升压等新型色谱操作条件下,Ｌｅｅ 保留指数体系仍能够满足对多环芳烃定性分析的要求, 前者则不能。     

Molecular chain properties of poly (N-isopropyl acrylamide)

A series of poly( N-isopropyl acrylamide) (PNIPAM) samples with molecular weight ranging from 2.23×10~4 to 130×10~4 and molecular weight distribution M_w/M_n≤1.28 were obtained by free radical polymerization and repeat precipitation fractionation. The molecular weight M_w, second virial coefficient A_2 as well as the mean-square-root radius of gyration 〈S~2〉 for PNIPAM samples in tetrahydrofuran (THF) were determined by light scattering, and the relations were estimated at A_2 ∞ M_w~0.25) and 〈S~2〉~(1/2)=1.56×10~(-9) M_w~(0.56). The intrinsic viscosity for THF solution and methanol solution of PNIPAM samples was measured and the Mark-Houwink equations were obtained as [η]=6.90×10~(-5) M~(0/73) (THF solution) and [η]=1.07×10~(-4) M~(0.71) (methanol solution). The above results indicate that both THF and methanol are good solvents for PNIPAM. The limit characteristic ratio C_∞ for PNIPAM in the two solutions was determined to be 10.6 by using Kurata-Stockmayer equation, indicating that the f     

静电离子色谱用于硼酸溶液中硼不同形态组分分离的研究

改进了把胆汁酸诱导体胶束(CHAPSO)涂覆在ODS载体上制备静电离子色谱固定相的方法.以纯水为流动相,采用示差折光检测器,研究了硼酸溶液中硼的形态、分离条件,并对色谱峰进行了解析.此外,还对硼酸溶液中硼离子、硼分子的色谱保留行为进行了探讨.     

三轴转台执行机构起动摩擦特性的测试与研究

本文以液压马达作为研究对象,对其起动摩擦特性进行了测试与分析。实时获得了驱动扭矩、被测马达转角的变化过程。通过建模分析,准确估计出了起动时动、静摩擦特性的变化规律。得出了液压马达在起动的瞬间不存在摩擦力瞬态突变的结论,并据此对摩擦振动的产生机理加以分析,推导了产生爬行的各种临界条件。     

煤燃烧过程矿物质行为研究

１前言煤中矿物质行为直接影响到煤灰熔融特性,影响到燃烧锅炉的结渣程度。以前曾对单种煤煤灰加热过程中矿物质行为特征［１,２］,以及混煤煤灰熔融行为与矿物形态间的关系［３,４］进行过研究。但这些研究均是以煤灰做为试样,静态加热处理并分析的基础性研究,而未考虑到燃烧锅炉内煤灰颗粒的加热燃烧速度、空间分布情况以及炉内温度分布。本研究将在四角燃烧炉内,煤燃烧过程中不同位置取出友样进行矿物质形态分析,并与煤灰静态加热过程矿物质组成及含量变化进行比较分析。２实验方法试样采用株州煤。制成８００”Ｃ灰样,株州煤的…     

Tuning characteristics of asymmetric inhomogeneously pumped quantum-well lasers

An analysis of the power-current and tuning characteristics of asymmetric multiple-layer inhomogeneously pumped quantum-well lasers with mode selection in the external resonator was performed. It is shown that the choice of the parameters of the barrier and active layers of the laser heterostructure and optimization of the dispersion characteristics of the selective element of the external resonator make it possible to realize continuous tuning of the lasing wavelength in a wide spectral range at a practically constant output radiation power. Reported at the Second International Scientific and Technical Conference on Quantum Electronics, Minsk, November 23–25, 1998. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 5, pp. 687–692, September–October, 1999.     

The Lagrange–Galerkin method for the two‐dimensional shallow water equations on adaptive grids

The weak Lagrange–Galerkin finite element method for the two‐dimensional shallow water equations on adaptive unstructured grids is presented. The equations are written in conservation form and the domains are discretized using triangular elements. Lagrangian methods integrate the governing equations along the characteristic curves, thus being well suited for resolving the non‐linearities introduced by the advection operator of the fluid dynamics equations. An additional fortuitous consequence of using Lagrangian methods is that the resulting spatial operator is self‐adjoint, thereby justifying the use of a Galerkin formulation; this formulation has been proven to be optimal for such differential operators. The weak Lagrange–Galerkin method automatically takes into account the dilation of the control volume, thereby resulting in a conservative scheme. The use of linear triangular elements permits the construction of accurate (by virtue of the second‐order spatial and temporal accuracies of the scheme) and efficient (by virtue of the less stringent Courant–Friedrich–Lewy (CFL) condition of Lagrangian methods) schemes on adaptive unstructured triangular grids. Lagrangian methods are natural candidates for use with adaptive unstructured grids because the resolution of the grid can be increased without having to decrease the time step in order to satisfy stability. An advancing front adaptive unstructured triangular mesh generator is presented. The highlight of this algorithm is that the weak Lagrange–Galerkin method is used to project the conservation variables from the old mesh onto the newly adapted mesh. In addition, two new schemes for computing the characteristic curves are presented: a composite mid‐point rule and a general family of Runge–Kutta schemes. Results for the two‐dimensional advection equation with and without time‐dependent velocity fields are illustrated to confirm the accuracy of the particle trajectories. Results for the two‐dimensional shallow water equations on a non‐linear soliton wave are presented to illustrate the power and flexibility of this strategy. Copyright © 2000 John Wiley & Sons, Ltd.     

Relationships between Retention Factors and Analyte Hydrophobicity on Cyanopropyl and n‐Octadecyl Bonded Silicas,Cross‐Linked Polymers and Porous Graphitic Carbon Stationary Phases. Consequences for the Trace Analysis of Highly Polar Organic Compounds

LC retention data have been measured using various stationary phases with an emphasis on highly polar to moderately polar neutral organic compounds having octanol‐water partition coefficients (K_ow) in log units between 0 and 3. The relationships between the retention factor measured in water and the octanol‐water partition coefficient are linear but with different slopes for octadecyl (C₁₈) silicas, and two polystyrene divinylbenzene (PS‐DVB) phases with low and high surface areas. These relationships confirm that highly cross‐linked polymers can provide more than 1000‐times higher retention values than C₁₈ silicas for moderately polar analytes but close values for highly polar ones. They also explain why C₁₈ silicas and polymers are equivalent for the separation of very polar analytes. In contrast, due to a different retention mechanism, no relation exists between the retention shown by porous graphitic carbons (PGC) and analyte hydrophobicity, but highly polar analytes are in general much more strongly retained than by any other sorbent. The potential of PGC for both the extraction and the separation of analytes is shown. Due to the difference in separation mechanism, PGC is the analytical phase that should be used for confirmation of the identity of analytes instead of a cyanopropylsilica column as recommended in some environmental procedures. Applications are presented for the trace‐determination of triazines and polar degradation products in ground and surface water with detection limits below the 0.1 μg/L level.     

Effects of multi-frequency ultrasound on physicochemical properties,structural characteristics of gluten protein and the quality of noodle

In this study, the influence of multi-frequency ultrasound irradiation on the functional properties and structural characteristics of gluten, as well as the textural and cooking characteristics of the noodles were investigated. Results showed that the textural and cooking characteristics of noodles that contain less gluten pretreated by multi-frequency ultrasonic were ultrasonic frequency dependent. Moreover, the noodles that contain a smaller amount of sonicated gluten could achieve the textural and cooking quality of commercial noodles. There was no significant difference in the cooking and texture characteristics between commercial noodles and noodles with 12%, 11%, and 10% gluten pretreated by single-frequency (40 kHz), dual-frequency (28/40 kHz), and triple-frequency sonication (28/40/80 kHz), respectively. Furthermore, the cavitation efficiency of triple-frequency ultrasound was greater than that of dual-frequency and single-frequency. As the number of ultrasonic frequencies increased, the solubility, water holding capacity and oil holding capacity of gluten increased significantly (p < 0.05), and the particle size was reduced from 197.93 ± 5.28 nm to 110.15 ± 2.61 nm. Furthermore, compared to the control group (untreated), the UV absorption and fluorescence intensity of the gluten treated by multi-frequency ultrasonication increased. The surface hydrophobicity of gluten increased from 8159.1 ± 195.87 (untreated) to 11621.5 ± 379.72 (28/40/80 kHz). Raman spectroscopy showed that the α-helix content of all sonicated gluten protein samples decreased after sonication, while the β-sheet and β-turn content increased, and tryptophan and tyrosine residues were exposed. Through scanning electron microscope (SEM) analysis, the gluten protein network structure after ultrasonic treatment was loose, and the pore size of the gluten protein network increased from about 10 μm (untreated) to about 26 μm (28/40/80 kHz). This work elucidated the effect of ultrasonic frequency on the performance of gluten, indicating that with increasing frequency combination increases, the ultrasound effect became more pronounced and protein unfolding increased, thereby impacting the functional properties and the quality of the final product. This study provided a theoretical basis for the application of multi-frequency ultrasound technology in the modification of gluten protein and noodle processing.