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91.
This article presents the study of singularly perturbed parabolic reaction–diffusion problems with boundary layers. To solve these problems, we use a modified backward Euler finite difference scheme on layer adapted nonuniform meshes at each time level. The nonuniform meshes are obtained by equidistribution of a positive monitor function, which involves the second-order spatial derivative of the singular component of the solution. The equidistributing monitor function at each time level allows us to use this technique to non-linear parabolic problems. The truncation error and the stability analysis are obtained. Parameter–uniform error estimates are derived for the numerical solution. To support the theoretical results, numerical experiments are carried out. 相似文献
92.
93.
In this article we discuss the finite element discretization of the two-dimensional, incompressible, and turbulent boundary layers. The formulation of the momentum equation is essentially due to Baker and Soliman [1] with some modifications.The versatility and the accuracy of the method is established by considering several test cases. The predictions are satisfactory and compare favorably with alternative numerical techniques. 相似文献
94.
Glow discharge spectroscopy (GDOS) will be shown to be a quick, informative and simple method for quantitative depth profile analysis of elements of nitrided layers well suited for their quality control. By systematic variation of all glow discharge determining parameters it is possible to get an excellent depth resolution in the order of sub-m corresponding to a comparatively large analytical activated area (50 mm2). In this paper the behaviour of a number of important parameters related to sputtering of the activated area will be discussed. Some quantitative GDOS depth profiles of carbon and nitrogen of pure iron samples nitrided by different procedures will be shown as examples for application. 相似文献
95.
The evolution of 2-D disturbances in hypersonic boundary layer with Mach number 6,8, and 10 was investigated numerically by
three different numerical schemes. At the entrance, second mode T-S waves with different amplitudes were introduced, and the
relation between the Mach number and the amplitude of the disturbance when shocklets started to appear was investigated. By
comparing the disturbance velocity profiles with those provided by linear stability theory, the effects of shocklets on flow
structures were also investigated. 相似文献
96.
以XLPE高压电力电缆内外侧绝缘中的电树枝特性为研究对象,通过分析电树枝引发与生长的统计实验规律和采用扫描电子显微镜分析发现,由于不同结晶状态的影响,电缆绝缘内外侧的电树枝特性存在很大的差异.引发于绝缘内侧电树枝引发时间短、生长速度快、电树枝形状具有多样性;起始于绝缘外侧的电树枝不仅引发时间长、生长速度极慢,而且电树枝形状(结构)比较单一.并对这两个位置电树枝的引发和生长机理进行了探讨.
关键词:
电树枝
结晶状态
统计规律
内侧和外侧绝缘层 相似文献
97.
The present study evaluates the growth kinetics of the boride layer Fe2B in AISI 1045 steel, by means of neural networks and the least square techniques. The Fe2B phase was formed at the material surface using the paste boriding process. The surface boron potential was modified considering different boron paste thicknesses, with exposure times of 2, 4 and 6 h, and treatment temperatures of 1193, 1223 and 1273 K. The neural network and the least square models were set by the layer thickness of Fe2B phase, and assuming that the growth of the boride layer follows a parabolic law. The reliability of the techniques used is compared with a set of experiments at a temperature of 1223 K with 5 h of treatment time and boron potentials of 2, 3, 4 and 5 mm. The results of the Fe2B layer thicknesses show a mean error of 5.31% for the neural network and 3.42% for the least square method. 相似文献
98.
F. Pippig 《Applied Surface Science》2007,253(16):6817-6823
Some surface bonded and fluram labeled primary amines show a new red-shifted emission in their fluorescence spectrum. We compared the fluorescence of fluram bonded to various amine functionalized surfaces including tetraethylene pentamine (TEPA), 1,2-ethylene diamine (EDA), 3-aminopropyltriethoxy silane (APTES) and trimetylol-propanetris-(beta-aziridino)-propionate (ATA). All reactions were also monitored using XPS. It was found that the new spectral features seem to be related to the local density of amino groups on the surface. In order to verify this hypothesis we synthesized a surface bonded dendrimer with a step-wise increasing NH2 density. Using molecules with different lengths as branches in the dendrimer, the amine density can be varied. Only in the case of the highest density, the new fluorescence emission was detected. Consequently, the fluorescence of fluram coupled to amines at a surface can be used to quantify the concentration of these amines and the appearance of the red-shifted emission indicates a high local density of the amino groups. 相似文献
99.
A device of multiple nano-TiO2 layers was proposed and fabricated to prevent a dye/nano-TiO2 region from serious photo-degradation. In this device, the top of the dye/TiO2 region was designed to be coated using sol-gel nano-TiO2 thin films to shield UV irradiation from the photo-degradation effect. The sol-gel TiO2 was prepared in a low temperature (75 °C) and verified as nano-sized particles and an anatase crystalline structure. Different devices of the multi-layer samples fabricated using different compositions of nano-TiO2 were produced and exposed for UV irradiation tests. Results show that the presence of the sol-gel TiO2 films coated on top of the dye/TiO2 region can significantly alleviate the dye photo-degradation under UV irradiation. This multi-layer device can effectively improve the photo-stability of the dye/TiO2 region in a UV-exposure environment. 相似文献
100.
Wen Zhang Jing Jiang Chunhua Qin Lisa M. Pérez Alan R. Parrish Stephen H. Safe 《Supramolecular chemistry》2013,25(7-8):607-616
Three criteria are evaluated to assess the potential of a dendrimer based on triazines, 1, for use as a vehicle for drug delivery. These criteria are: (1) its ability to solubilize small hydrophobic guests as measured spectrophotometrically; (2) its ability to deliver a drug in vitro as evaluated using a gene reporter assay; and (3) its in vivo toxicity in mice as determined by autopsy and screens of liver and kidney function. Vehicle 1 solubilizes pyrene to a similar extent to dendrimers based on poly(arylether)s, 4, encapsulating approximately 0.2 molecules of pyrene per dendrimer. This activity is approximately 10-fold greater than that of the more polar poly(propyleneimine) and poly(amidoamine) dendrimers, 2 and 3. Gas-phase computational models reveal that both 1 and 4 have cores that are accessible to solvent, suggesting that these dendrimers can occupy much greater volumes than 2 and 3 whose cores are confined toward the interior of the structure. Electrostatic potential maps can be used to rationalize differences in solubilization between 1 and 4. Precipitation results from mixing cationic 1 with the anionic indomethacin, but not with methotrexate, suggesting that the composition of the drug may dictate the scope of delivery applications. Dendrimer 1 solubilizes 10-hydroxycamptothecin and a novel bisindolemethane; approximately four and five molecules of drug per dendrimer are solubilized, respectively. In cell-culture experiments using a luciferase reporter gene assay, the dendrimer:bisindolemethane conjugate shows comparable activity to the bisindolemethane delivered in aqueous DMSO, suggesting that the dendrimer does not preclude delivery of the molecule to an intracellular target. Preliminary toxicology studies of 1 in mice show that this molecule has no adverse toxicity to the kidneys or the liver in single doses delivered intraperitoneally up to 10?mg/kg. 相似文献