涡轮增压柴油机模拟计算等压法的探讨

针对有些模拟计算可以忽略排气压力波的影响，提出了等压法计算的设想，这是一种每一工作循环缸外热力过程只计算一次的简化方法。分析结果表明，这种计算可以满足零维模型必须满足的所有制约方程，能真实地模拟涡轮增压柴油机的实际工作过程，适用于各种增压系统，但仍有待于进一步的研究与改进。根据等压法，建立了一种适用于定压涡轮系统的计算模型--“定压涡轮”模型，用于MPC增压系统的计算，计算结果与试验结果基本吻合，与容积法计算结果趋于一致，从而验证了模型的正确性，同时也表明这种缸外计算法是有效的。     

Determination of the total concentration and speciation of Al(III) in tea infusions

The aluminium species in different tea infusions were investigated, by determining their stability constants and concentration. This was done for some particular samples using a simple experimental method based on the sorption of aluminium on the strongly sorbing resin Chelex 100, by a batch procedure. From the thermodynamic information obtained it is possible to calculate the concentration of the different species, and in particular that of the free metal ion, which is very important for evaluating the adsorption of aluminium on biological membranes. It was found that aluminium in the tea infusions here considered is present at high total concentration, approximately 0.1 mM, but mainly linked to strong complexes, for instance with side reaction coefficient higher than 10(5.11) at pH 3.95 in one case (tea 1). This could be the reason for the low toxicity of aluminium in tea. These strong complexes were not dissociated even in the presence of Chelex 100. In this case only a limiting value of the reaction coefficient could be evaluated. The presence of the very strong complexes was found in all the tea sample here considered. In two of the considered samples (one black and one green tea) a part of Al(III) was linked to less strong complexes, for example with a reaction coefficient 10(4.14) (tea 2, pH 4.20). The presence in the considered tea infusions of other substances able to complex aluminium was also detected, by the well known ligand titration procedure, at concentration ranging from 0.65 to 3.37 mM in three tea infusions, and at somewhat higher concentration in the case of the ready drink, which was also considered for comparison.     

Self-controlled case series analyses: Small-sample performance

Second-order expressions for the asymptotic bias and variance of the log relative incidence estimator are derived for the self-controlled case series model in a simplified scenario. The dependence of the bias and variance on factors such as the relative incidence and ratio of risk to observation period are studied. Small-sample performance of the estimator in realistic scenarios is investigated using simulations. It is found that, in scenarios likely to arise in practice, asymptotic methods are valid for numbers of cases in excess of 20-50 depending on the ratio of the risk period to the observation period and on the relative incidence. The application of Monte Carlo methods to self-controlled case series analyses is also discussed.     

Issues in modelling of advanced heterogeneous ceramics

Summary The conceptual and computational issues regarding the development of models to predict microstructure/mechanical-property relationships in advanced ceramics are discussed. Advanced ceramics provide a particular challenge because their higher toughness or reliability, relative to monolithic ceramics, is a result of stable, distributed damage evolution. Capturing the details of distributed damage at atomistic and microstructural length scales is computationally prohibitive, but only in certain systems does it appear plausible to neglect atomistic and crack-tip details in favor of larger-scale damage propagation and interaction. Examples, mainly from the author's own work, are briefly presented to indicate the range of problems that have been addressed and the relative successes and failures.     

北京核电站模拟器硬件的功能和特点

本文介绍北京核电站模拟器硬件构成并分析其功能和特点。     

Simulation of a PCB assembly line: A modified JIT approach

In this paper, a simulation model of an existing printed circuit board (PCB) assembly line is developed in an attempt to identify strategies which tend to improve the system performance. The model is based on the concept of the JIT (Just-In-Time) production approach. Parameters investigated includes sequencing rules, lot sizes, number of Kanbans used, and number of PCB types.     

Automatically modeling, simulating and explaining physical systems

This paper presents an interactive framework for constructing models from high-level specifications of real physical systems, deriving low-level simulations from the constructed models and then generating explanations of the simulated behavior to help engineers interpret and control the real physical systems. To demonstrate our method, we show an example of modeling river networks, which are eco-environmental engineering systems, to provide a computer-based solution to problems of simulating and controlling concentrations of water quality constituents in river networks[1].     

Simulation of nitrogen dynamics and biomass production in winter wheat using the Danish simulation model DAISY

A dynamic simulation model for the soil plant system is described. The model includes a number of main modules, viz., a hydrological model including a submodel for soil water dynamics, a soil temperature model, a soil nitrogen model including a submodel for soil organic matter dynamics, and a crop model including a submodel for nitrogen uptake. The soil part of the model has a one-dimensional vertical structure. The soil profile is divided into layers on the basis of physical and chemical soil characteristics. The simulation model was used to simulate soil nitrogen dynamics and biomass production in winter wheat grown at two locations at various levels of nitrogen fertilization. The simulated results were compared to experimental data including concentration of inorganic nitrogen in soil, crop yield, and nitrogen accumulated in the aboveground part of the crop. Based on this validation it is concluded that the overall performance of the model is satisfactory although some minor adjustments of the model may prove to be necessary.     

多元复杂精馏过程模拟和优化

采用非平衡级METSH方程组，对丙烯精馏过程进行了模拟计算和优化，提出了一种全新的、实用的塔板组成的圆整归一方法，摸索出了一套行之有效的计算程式，大大提高了模型方程组迭代计算的收敛性，求解更加稳定。本文还以精馏塔利润为目标，建立了优化目标函数，进行了优化计算，计算结果对丙烯塔生产具有一定意义。     

Packed-microtubes model for flowthrough chromatography of protein

A mathematical model for flowthrough (perfusion) chromatography, namely packed-microtubes (PMT) model, has been proposed for a column packed with biporous (BiP) anion exchanger in which the mesopores and flowthrough pores are created with liquid and solid porogens, respectively. The model is established based on the assumption that the BiP particle is made up of packed microtubes. Bovine serum albumin (BSA) is used as a model protein and three kinds of anion exchangers (i.e., mesoporous, macroporous and BiP resins) are used as adsorbents to determine the model parameters and to evaluate the model. Adsorption equilibrium and finite bath experiments are performed to determine the adsorption isotherms and kinetics parameters. Both the bound amounts of the protein on the surface of the mesopores and macropores are experimentally determined and taken into account in the mathematical model. With all the model parameters determined by independent experiments or calculated from available correlations, model simulations are performed and compared with the experimentally determined breakthrough profiles of the BiP column. It is found that the model predictions agree reasonably well with the experimental data obtained under various conditions and the PMT model fit experimental data better than the modified double linear driving force (LLDF) model proposed by Leitão and Rodriogues (1999. Biochemical Engineering Journal 3, 131) in which the adsorbent particle is considered to be made up of packed microparticles. The results indicate that the PMT model is more reasonable for this kind of BiP adsorbent.