浅析电火花线切割加工和电火花成型加工的特点

本文通过电火花线切割加工和电火花成型加工的三要素,电火花加工和铣削加工的比较,电火花线切割加工和电火花成型加工的共同特点和不同特点的阐述,从不同角度分析了两种不同的电火花加工方法的特点,对实际加工方法的选择和应用起到了指导作用。     

浅析电火花线切割加工和电火花成型加工的特点

本文通过电火花线切割加工和电火花成型加工的三要素,电火花加工和铣削加工的比较,电火花线切割加工和电火花成型加工的共同特点和不同特点的阐述,从不同角度分析了两种不同的电火花加工方法的特点,对实际加工方法的选择和应用起到了指导作用。     

钻铣复合机床的研究与开发

介绍了一种可进行铣削加工和单管钻超深孔加工的复合机床,根据加工需求,机床设备可在深孔加工和铣削加工之间切换,避免了多次装夹造成的定位不精确等问题,实现了深孔加工和铣削加工在一台机床上完成,省时省力,大大提高了加工效率与精度。     

面向板腔类零件机加工艺的加工特征识别方法EI北大核心CSCD

为了实现板腔类零件加工特征智能识别,加快三维机加工艺的设计速度,研究了面向板腔类零件机加工艺的加工特征识别方法。综合考虑加工特征的通透性和开放性,将加工特征分为完全开放加工特征、半开放加工特征、封闭盲加工特征、半开放通加工特征和封闭通加工特征5种类型;介绍了加工特征识别过程的原则,提出了基于主加工面自底向上的特征识别策略;详细阐述了加工特征的识别过程,主要包括特征类型的判别、加工特征的多义性处理和加工特征体的提取等关键步骤。建立了面向腔板类零件的三维CAD/CAPP集成系统的原型系统,实现了加工特征识别模块,并通过实例零件验证了所提方法的有效性和正确性。     

基于轴承座的数控加工工艺设计与处理

作为支承火车车轮轮轴的轴承座,加工内容复杂,有深孔加工和大孔加工,而且体形大,加工精度高,难以加工;对轴承座零件的特点进行了分析,针对性地进行了数控加工工艺设计,确定了加工机床、加工方案和加工顺序;对于深孔,采用正反两面、两次定位装夹进行深孔加工;对于轴承座大孔,以铣代镗、正反两次粗加工,然后再进行精加工;并提出了零件加工时的注意事项,成功解决了轴承座零件的加工问题,提高了加工精度,保证了加工质量.     

椭圆凸台的数控仿真加工

对椭圆凸台的数控仿真加工进行了分析和研究,选用了刀具和加工的方法,编制了零件的加工程序,采用UG绘图自动编程,优化了加工程序,加工中可以节省加工时间,提高生产效率。     

薄板类零件加工精度可靠性分析及工艺参数优化

针对薄板类零件加工过程中加工变形导致加工精度低的问题,利用有限元法和高斯过程回归算法建立了加工变形预测模型,综合考虑机床运动误差与工件加工变形,对薄板件加工精度可靠性进行分析,建立了以加工效率和平均加工变形为目标、加工精度可靠度为约束的铣削加工工艺参数优化设计模型,并利用多目标优化算法进行求解,确定了协调加工效率和加工变形最优的工艺参数组合。案例研究结果表明,经优化设计后最低加工精度可靠度达到98.21%,平均加工变形减小21.14%,加工效率提高了4.18%,为薄板类零件铣削加工工艺参数选择提供了一种可行的方法。     

模具制造中的电火花加工和高速切削加工

模具先进制造技术种类繁多,电火花加工和高速切削是模具加工的两大主力军。本文简述了电火花加工和高速切削加工在模具加工方面的应用,并对两种加工方法进行了比较,指出电火花加工和高速切削加工是互补的,又形成一种竞争。     

某型飞机超薄腹板类零件的加工

对某型机超薄腹板类零件的加工方案进行了研究,列举了传统的加工方案和多种新式加工方案,并对各种加工方案进行了对比,分析了各自优势和不足,凸显出新式加工方案在此类零件加工中的优势。     

基于UG8.0软件在高速数控加工中的应用

介绍了应用UG8.0软件对模具进行工艺分析、数控编程、仿真加工和后处理加工。同时分析了数控编程过程中对加工参数的设置和加工策略的选择,解决了模具细小部位的加工,减少了放电加工,大大提高了模具的生产效率和尺寸精度。     

Histochemical and ultrahistochemical localization of heavy metals in calf organs

Cadmium, zinc, selenium, and copper were administered, singly or in combination, orally or subcutaneously. Experiment I included 32 calves of both sexes; six received Cd (two groups), Zn, Cd, and Zn, and Cd and Se (two groups) and one group was a control. In Experiment II (21 bulls), three were given Cd, Cd, and Cu, and Cd and Zn, respectively, and one group was a control. For light microscopy, in Experiment I the highest amounts of silver granules were present in the samples of liver, small intestine, and vesicular gland of all the exposed groups; in Experiment II the most affected organs were liver, kidney, and small intestine. For electron microscopy, in Experiment I, after administration of Cd and Zn, the highest amounts of granules were seen in the cytoplasm of hepatocytes and cells of the proximal and distal renal tubules and the lowest amounts were found in glandular cells of the pancreas. Administration of Cd and Se resulted in the presence of large numbers of granules in the nuclei and nucleoli of spermatogonies. In Experiment II, ingestion of Cd and Zn in feed led to the appearance of highest amounts of granules in the nucleoli, nuclei, and cytoplasm of cells in testes, kidneys, and pancreas. Following Cd intake, the highest accumulation of granules was observed in the nucleoli of hepatocytes and cells of the proximal and distal renal tubules. Combined Cd and Cu produced the highest number of granules in cells of the proximal and distal renal tubules and in the nucleoli and nuclei of germinal epithelium.     

Immunohistochemistry of neuronal nitric oxide synthase and protein nitration in the striatum of the aged rat

To ascertain the possible implications of the nitric oxide (NO*) producing system in striatal senescence, and by using immunohistochemistry and image-processing approaches, we describe the presence of the enzyme nitric oxide synthase (NOS), the NADPH-diaphorase (NADPH-d) histochemical marker, and nitrotyrosine-derived complexes (N-Tyr) in the striatum of adult and aged rats. The results showed neuronal NOS immunoreactive (nNOS-IR) aspiny medium-sized neurons and nervous fibres in both age groups, with no variation in the percentage of immunoreactive area but a significant decrease in the intensity and in the number of somata with age, which were not related to the observed increase with age of the striatal bundles of the white matter. In addition, NADPH-d activity was detected in neurons with morphology similar to that of the nNOS-IR cells; a decrease in the percentage of area per field and in the number of cells, but an increase in the intensity of staining for the NADPH-d histochemical marker, were detected with age. The number of neuronal NADPH-d somata was higher than for the nNOS-IR ones in both age groups. Moreover, N-Tyr-IR complexes were observed in cells (neurons and glia) and fibres, with a significant increase in the percentage of the area of immunoreaction, related to the increase of white matter, but a decrease in intensity for the aged group. On the other hand, we did not detect the inducible isoform (iNOS) either in adult or in aged rats. Taken together, these results support the contention that NADPH-d staining is not such an unambiguous marker for nNOS, and that increased protein nitration may participate in striatal aging.     

五自由度机器人的结构设计及其控制

介绍了串联五自由度机器人的机械结构和机器人控制系统的设计.文中设计的五自由度机器人既可以用于实际生产,也可以用于教学和科研.用于实际生产既可以执行点位控制下的操作,也可以执行连续轨迹控制下的操作;用于教学和科研时,该机器人可用于机器人结构分析、机构运动学分析及机器人控制系统的教学演示和实验操作.它具有结构简单、操控方便等特点,而且可以做进一步的研发.     

Immunolocalization of S100-like protein in the brain of an emerging model organism: Nothobranchius furzeri

The S100 protein in nervous tissue appears to play important roles in regulating neuronal differentiation, glial proliferation, plasticity, development, axonal growth, and in neurogenetic processes. In fish, the adult neurogenic activity is much higher than in mammals. In this study, the localization of S100 protein was investigated in the brain of annual teleost fish, Nothobranchius furzeri, which is an emerging model organism for aging research. By immunohistochemical techniques, S100 immunoreactivity (IR) was detected in glial cells, small neurons, and fibers throughout all regions of central nervous system (CNS) with different pattern of distribution. In the telencephalon, S100 IR was seen in the olfactory bulbs and in different areas of the telencephalic hemispheres. In the diencephalon, S100 positivity was observed in the habenular nuclei of the epithalamus, in the cortical thalamic nucleus, in the dorsal, ventral and caudal portions, the latter with the posterior recessus nucleus, and in the diffuse inferior lobe of the hypothalamus, along the diencephalic ventricle and in the dorsal optic tract. In the mesencephalon, S100 IR was observed in the longitudinal tori, in the optic tectum, and along the mesencephalic ventricle. In the rhombencephalon, S100 IR was shown in valvula and body of the cerebellum, and in some nuclei of the medulla oblongata. The results suggest that S100 may play a key role in the maintenance of the CNS and in neurogenesis processes in the adulthood.     

The compression and expansion waves of the forward and backward flows: an in-vitro arterial model

Although the propagation of arterial waves of forward flows has been studied before, that of backward flows has not been thoroughly investigated. The aim of this research is to investigate the propagation of the compression and expansion waves of backward flows in terms of wave speed and dissipation, in flexible tubes. The aim is also to compare the propagation of these waves with those of forward flows. A piston pump generated a flow waveform in the shape of approximately half-sinusoid, in flexible tubes (12 mm and 16 mm diameter). The pump produced flow in either the forward or the backward direction by moving the piston forward, in a 'pushing action' or backward, in a 'pulling action', using a graphite brushes d.c. motor. Pressure and flow were measured at intervals of 5 cm along each tube and wave speed was determined using the PU-loop method. The simultaneous measurements of diameter were also taken at the same position of the pressure and flow in the 16 mm tube. Wave intensity analysis was used to determine the magnitude of the pressure and velocity waveforms and wave intensity in the forward and backward directions. Under the same initial experimental conditions, wave speed was higher during the pulling action (backward flow) than during the pushing action (forward flow). The amplitudes of pressure and velocity in the pulling action were significantly higher than those in the pushing action. The tube diameter was approximately 20 per cent smaller in the pulling action than in the pushing action in the 16 mm tube. The compression and expansion waves resulting from the pushing and pulling actions dissipated exponentially along the travelling distance, and their dissipation was greater in the smaller than in the larger tubes. Local wave speed in flexible tubes is flow direction- and wave nature-dependent and is greater with expansion than with compression waves. Wave dissipation has an inverse relationship with the vessel diameter, and dissipation of the expansion wave of the pulling action was greater than that of the pushing action.     

Gender-related changes in the avian vasotocin system during ontogeny

The arginine vasotocin (AVT) system of the avian brain includes a sexually dimorphic part that extends from the caudal part of preoptic region through the medial part of the bed nucleus of stria terminalis (BSTm) to the lateral septum. It is composed of the parvocellular neurons located in the BSTm and the dense innervation of the medial preoptic region and lateral septum. In this part of the brain, AVT expression is stronger in males than in females in a few bird species investigated to date. This review focuses on the ontogeny of sexual differences in the vasotocinergic system of two gallinaceous species, domestic chicken and Japanese quail, and on the role of gonadal hormones in organizing during development and maintaining in adulthood these differences. Parvocellular AVT neurons become discernible in the BSTm of males and females during the second half of embryonic development. These cells undergo a profound and irreversible sexual differentiation during ontogenetic development. Recent findings demonstrate a dual role of estrogens in the organization and activation of sex differences in the AVT system. During the embryonic period of ontogeny, estrogens differentiate the AVT system in a sexually dimorphic manner in parallel with the differentiation of sexual behavior, while in adulthood estrogens, locally produced from testosterone in the male brain, activate AVT synthesis in the BSTm. The sexually dimorphic part of the AVT system is sensitive to a number of abiotic factors such as light, temperature, and water availability. It is suggested that sex dimorphic vasotocinergic systems could be implicated in processes of social recognition in various behavioral contexts.     

Study of the myenteric and submucous plexuses after BAC treatment in the intestine of rats.

A morphological and quantitative study in the ileal and colonic myenteric and submucous plexuses of rats after BAC denervation was performed. Four groups were employed: SI--ileum control; CBI--denervated ileum; SC--colon control; and CBC--denervated colon. We used the Myosin-V immunohistochemistry technique to study the myenteric and submucous plexuses. In the submucous plexus of the ileum and colon there was not a significant decrease in the number of neurons/mm2 and of ganglia/mm2. The denervation of the myenteric plexus in the group CBI was 44.7% and in the group CBC, 68.3%. In the myenteric plexus there was also a significant decrease in the number of ganglia/mm2 (13.8% in group CBI and 52.14% in group CBC) and in the number of neurons/ganglion (33.9% in group CBI and 39.6% in group CBC). The morphological analyses showed that there was an alteration in the shape of the ganglia of the ileal and colonic myenteric plexus. The area of the cell bodies had a significant increase both in the myenteric and the submucous plexus in groups CBI and CBC. These data demonstrate that the BAC treatment causes morphologic and quantitative changes in the myenteric plexus and quantitative changes in the cell body area of the submucous plexus.     

Distribution of sex steroid hormone receptors in the avian brain: functional implications for neural sex differences and sexual behaviors

Developmental and seasonal changes in the production of androgens, estrogens, and progestins seem to control sex-specific differentiation and seasonal changes in appetitive and consummatory sexual behaviors of birds. This results in profound sex differences in the quality (sex-specific) or quantity (sex-typical) of behaviors such as courtship, territoriality, or copulation. Steroids affect the brain by binding to intracellularly located receptors. The same brain areas express androgen, estrogen, and progesterone receptors in male and female brains. Sex differences in these genetically determined patterns occur in the size of neuron populations that intrinsically express sex steroid receptors. Further permanent sex differences are subsequent to degenerative fates of receptor expressing neuron populations during ontogeny. Transient sex differences in receptor expression appear to be due to area-specific up- and down-regulation of receptor levels, reflecting transient changes in the level of circulating steroids, changes in environmental conditions, or in the physiological status of the individuals. In particular, intrinsic sex differences in the expression pattern of sex steroid receptors and steroid-independent regulation of the expression level of these receptors in the brain are limiting mechanisms for gonad-dependent sexual development and activities.     

Extracellular breakdown of collagen by mice decidual cells. A cytochemical and ultrastructural study.

The interaction of antimesometrial decidual cells and collagen fibrils was studied by light microscopy and ultrastructural cytochemistry in fed and acutely fasted mice on days 9-11 of pregnancy. Fibrillar elements in the extracellular space consisted of collagen fibrils and filamentous aggregates (disintegrating collagen fibrils). Intracellular vacuoles exhibited typical collagen immersed in electron-translucent material (clear vacuoles) and faint cross-banded collagen immersed in electron-opaque material (dark vacuoles). Fibrillar elements showed extracellular acid phosphatase activity which was stronger in the region of mature decidua than in predecidual cells region in all animals; it was conspicuous in mature decidua of fasted animals. Intracellular acid phosphatase activity was observed in dark vacuoles and lysosomes, and was absent in clear vacuoles in all cells studied. Since acid phosphatase activity reflects the presence of lysosomal hydrolases in general, the results indicate that breakdown of extracellular collagen occurs by release of lysosomal enzymes by decidual cells and also by internalization of collagen for intracellular degradation in fed and fasted mice. Collagen breakdown may be part of the process of tissue remodeling in mature and predecidual regions, however, in mature decidua, collagen breakdown is enhanced and may therefore contribute to nutrition of the fetus, specially in acutely fasted mice.     

高校学业考试作弊现象的社会学探析

从学生、学校、社会以及文化传统四个层面探微,认为高校学业考试作弊是学校场域中处于弱势地位的学生以追求分数为表象,以追逐位置和争夺资本为目的的主动“求生”策略,他们用异常的方式表达了对教育教学公平的渴望。而唯分数论的教育评价体系及僵化的考试形式对学生“超越”和偏离学校规章制度负有责任,反映了高校在教育理念、教学质量观、人才观、学生观等方面的迷失。当然,学历社会、考试社会中考试功能的畸变以及文化传统中重视考试的教育价值取向也隐含了高校教育逐渐由知识到标签的异化之路。对其防治乃是一个系统性的工程和长期性的过程。