带法兰盘的阶梯轴冷镦挤成形工艺研究

为了研究法兰盘阶梯轴零件成形过程,确定其合理的工艺方案,课题组运用Deform 3D软件对带法兰盘阶梯轴零件镦挤过程进行数值模拟。通过模拟结果对初定工艺方案进行分析,确定了3步成形工艺,并对该工艺进行改进。基于正交试验对改进工艺进行优化,综合模具载荷、折叠角大小和分布及应力分布等因素,确定了最佳的工艺方案。结果表明：采用3步成形工艺时,对法兰盘进行2步镦粗成形,即采用挤压法兰盘1次镦粗 法兰盘2次镦粗成形工艺,该工艺可有效降低模具载荷、折叠角的角度和面积及零件应力;且当压力机工作速度为5 mm/s,法兰盘拐角处模具圆角半径为5 mm,摩擦因数为0.05时,工件成形质量较优。通过实际生产获得了表面质量良好的法兰盘阶梯轴零件。     

异形热成型包装件仿形裁切机构研究

为实现异形热成型包装件的准确分切,研究异形新型裁切工艺过程与仿形裁切机构。通过分析异形包装件的外形轮廓和裁切要求,确定了裁切的工艺过程和裁切刀的运动轨迹。选定相应的执行机构,并对仿形裁切机构进行参数化设计。采用可实现运动轨迹的凸轮 连杆机构带动裁切刀进行仿形裁切;采用解析法对执行机构进行参数化分析计算,找到固定凸轮与连杆的几何关系,最终确定执行机构关键部件固定凸轮的外形轮廓。采用仿形裁切方法可以实现异形热成型包装件的有效分切,本研究可为异形件裁切系统的设计提供参考。     

UML和WebML在电子商务信息流系统建模中的应用

采用面向对象的方法，对电子商务系统信息流的建模进行研究，提出在电子商务信息流建模过程中采用UML和WebML相结合的方法，可以加速系统建模过程，提高效率。     

Remedial Policies in Radiologically-Contaminated Forests: Environmental Consequences and Risk Assessment

As a result of the Chernobyl nuclear power plant accident in 1986, large forested areas in Europe were contaminated by radionuclides. Extensive societal pressure has been exerted to decrease the radiation dose to the population and to the environment. Thus, in making abatement and remediation policy decisions not only economic costs, but also human and environmental risk assessment are desired. Forest remediation by organic layer removal, one of the most promising cleanup policies, is considered in this paper. Ecological risk assessment requires evaluation of the radionuclide distribution in forests. The FORESTPATH model^(1,2) is used for predicting the radionuclide fate in forest compartments after deposition as well as for evaluating the application of the remedial policy. Time of intervention and radionuclide deposition profile was predicted as being crucial for the remediation efficiency. Risk assessment conducted for a critical group of forest users in Belarus shows that consumption of forest products (berries and mushrooms) leads to about 0.004% risk of a fatal cancer. Cost-benefit analysis for forest cleanup suggests that complete removal of organic layer is too expensive for application in Belarus.     

Estimating the Ozone Depletion Potential of Methyl Bromide

Ozone depletion potential (ODP) represents the cumulative ozone depletion induced by a particular halocarbon relative to a reference gas (usually trichlorofluoromethane, CFC-11). We focus on ODP estimation for methyl bromide. Previous attempts at its estimation have assumed that components of the ODP equation are lognormally distributed. By considering a wide range of modeling scenarios, we show that this restriction (which is based on computational convenience rather than experimental evidence) has obscured the true uncertainty in the ODP value. Moreover, when publishing point estimates for the ODP value, previous authors have given either mean or median values. We submit that a more appropriate choice for a point estimate is the mode since the distribution of ODP is skewed and since the mode is by definition, the most likely value. For each modeling scenario considered, modal values are given. In general, we find these ODP point estimates are considerably lower than those published elsewhere.     

钢琴曲《艾斯特山庄的喷泉》与《水的嬉戏》结构之比较

李斯特的《艾斯特山庄的喷泉》与拉威尔的《水的嬉戏》是两首以水为题材的作品。从音乐本体出发对这两部作品的结构进行细致的对比分析,有助于我们更好地理解和演奏李斯特、拉威尔的钢琴作品,提高对钢琴音响色彩及钢琴的表现力方面的鉴赏水平,有助于我们更全面地掌握李斯特和拉威尔创作的总体风格。     

论大学综合英语课的教学

文章就综合英语教学的理论背景和实际教学意义做了阐述,并对综合英语教学的不同实施方法以及目前教学中反映的问题进行了分析,重点对综合英语教学中教材的选择和应用,课堂教学中的语言信息输入和组织课堂活动等方面进行了探讨,并提出一些教学启示.     

Effects of the Mechanism of Receptor-Mediated Gene Expression on the Shape of the Dose-Response Curve

A mathematical model of receptor-mediated gene expression that includes receptor binding of natural and xenobiotic ligands, protein synthesis and degradation, and metabolism of the xenobiotic ligand was created to identify the determinants of the shape of the dose-response profile. Values of the model's parameters were varied to reflect alternative mechanisms of expression of the protein. These assumptions had dramatic effects on the computed response to a bolus dose of the xenobiotic ligand. If all processes in the model exhibit hyperbolic kinetics, the dose-response curves can appear sigmoidal but actually be linear with a positive slope at low doses. The slope of the curve only approached zero at low dose, indicative of a threshold for response, if binding of the xenobiotic ligand to the receptor exhibited positive cooperativity (ligand binding at one site increases the affinity for ligand at another binding site on the receptor). Positive cooperativity in the rate-limiting step of protein synthesis produced dose-response curves which were "U-shaped" at low doses, also indicative of a threshold. Positive cooperativity in the metabolism of the xenobiotic ligand produced dose-response curves that increased more rapidly than linearly with increasing dose. The model illustrates the fact that response cannot be predicted from qualitative mechanistic arguments alone; any assessment of risk to health from xenobiotic chemicals must be based on a detailed quantitative examination of the kinetic behavior of each chemical species individually.     

Uncertainties in Pharmacokinetic Modeling for Perchloroethylene: II. Comparison of Model Predictions with Data for a Variety of Different Parameters

In this paper we compare expectations derived from 10 different human physiologically based pharmacokinetic models for perchloroethylene with data on absorption via inhalation, and concentrations in alveolar air and venous blood. Our most interesting finding is that essentially all of the models show a time pattern of departures of predictions of air and blood levels relative to experimental data that might be corrected by more sophisticated model structures incorporating either (a) heterogeneity of the fat compartment (with respect to either perfusion or partition coefficients or both) or (b) intertissue diffusion of perchloroethylene between the fat and muscle/VRG groups. Similar types of corrections have recently been proposed to reduce analogous anomalies in the fits of pharmacokinetic models to the data for several volatile anesthetics.^(17-20) A second finding is that models incorporating resting values for alveolar ventilation in the region of 5.4 L/min seemed to be most compatible with the most reliable set of perchloroethylene uptake data.     

高等数学教学改革的探讨

文章认为现行高等数学教学中存在一些突出问题:课程基本目标与实际教学之间的矛盾;课时减少带来的矛盾;教育目标与应试式教学之间的矛盾;理论知识与应用之间的矛盾;现代化教学手段与部分教师惰性之间的矛盾等。同时针对上述问题提出了改革措施。