ATM局域网仿真系统的设计

介绍了ATM局域网仿真出现的背景,说明了ATM局域网基本工作原理及与传统局域网的区别。阐述了ATM局域网仿真的基本概念、系统结构及其工作原理,并对ATM局域网仿真系统进行简单地分析。     

如何解决局域网内盗用IP的问题

主要列举了当前局域网的使用当中在网内出现IP地址冲突 ,造成局域网管理混乱的几种主要现象 ,针对这几种现象 ,讨论、分析在局域网的使用中如何有效避免网内IP地址盗用 ,提高局域网使用效率的几种方法     

解决局域网IP地址冲突的策略与方法

随着信息网络的建设和发展,局域网的建立和应用也越来越广泛,企业、学校、小区、家庭都随处可见.但随着计算机数量的增加,IP地址分配的增多,局域网IP地址冲突或被盗用的现象就时有发生,已严重影响了局域网的正常运作.从管理策略和技术实战策略两方面的应用入手,提出了自己的建议和方法,解决局域网IP地址冲突、被盗用的问题,提高局域网管理和维护效率.     

初轧厂计算机局域网的建立与应用

本文论述了初轧厂计算机局域网的建立与应用情况，介绍了该局域网的系统结构，主要功能，特点，物理设计以及运行效果等，认为此种计算机局域网不失为一个提高企业两经管理水平的有力工具。     

企业局域网中的VLAN应用

随着企业网络规模的扩大，难以避免产生广播风暴，造成网络的阻塞，甚至导致整个网络瘫痪。虚拟局域网技术可将一个网络划分为多个虚拟网络，从而避免由广播风暴引发的网络灾难。本文简要介绍了虚拟局域网技术的特点和划分方法，并通过在企业局域网中的具体应用实例，说明了虚拟局域网的优越性。     

浅谈企业局域网建设方法

通过简单介绍莱钢热电厂局域网建设工程这样一个案例，阐述了企业内部局域网的建设方法。     

基于逻辑分层法对高校局域网故障排除的探究

对比开放系统互连基本参考模型,分析了高校局域网逻辑分层参考模型,提出了基于此模型的逻辑分层方法,给出了高校局域网故障排除流程图,进一步分层次提出了解决方法及应对策略.并就基于下一代互联网技术的高校局域网的故障排除挑战给出了参考性建议.     

利用路由器防护局域网ARP攻击的研究

本文针对局域网接入互联网环境下所面临的ARP攻击的威胁,探讨了通过局域网路由器进行ARP攻击防护的方法和效果.     

企业局域网的无线延伸

随着企业网络应用范围的不断扩大,通信网络技术的快速发展,特别是迅驰移动技术的笔记本电脑的广泛应用,企业网络面临着越来越多的无线接入局域网的需求.本文简要介绍了无线局域网技术以及安全接入企业局域网的部署及管理.并通过在企业中的应用实例,进行具体的说明.     

企业局域网数据安全分析及对策

企业局域网数据安全的问题主要来自两方面 :一方面是来自网络及操作系统自身的缺陷 ;另一方面是因为网络具有的开放性和网络病毒及黑客工具无意或有意地攻击带来的危害。本文对企业局域网数据安全从多角度进行了分析 ,并应用《计算机密码学》知识提出了保证企业局域网数据安全的对策     

The importance of the results of pretreatment pelvic lymphographies in the prognosis of carcinomas of the uterine cervix. A critical evaluation of the proposal to classify these tumors according to the TNM system (author's transl)

Between 1966 and 1969, 494 patients with carcinoma of the uterine cervix stages I a to IV were admitted in our hospital for primary treatment. In 420 of these patients with carcinoma of the cervix stage I b to IV, complete results of bilateral pretreatment pelvic lymphography are available. The correlation between the results of the lymphographies, the choice of the operative treatment and the cure rates in these 420 cases are reported. All the correlations between the results of the pretreatment lymphography and the prognosis are described. A positive lymphography was in our series of high prognostic value. A plea is therefore made to include the results of the pretreatment lymphography into the classification of carcinoma of the cervix. Classification of the carcinoma of the cervix into the TNM categories is desirable. Our series is reported in these TNM categories. The advantages of such classification are described. The morbid entity of carcinoma of the cervix becomes more transparent to the observer and the choice of operative therapy becomes easier. The prognosis is more clearly established. The proposals of the TNM committee of the UICC for the classification of carcinoma of the cervix according to the TNM categories and the staging according to these categories are discussed critically.     

An investigation of the effect of porosity and diluents on micropyretic synthesis

A numerical model of combustion/micropyretic synthesis of a composite system is developed. The new features of the model include the consideration of melting of each constituent of the reactants and products and the inclusion of considerations involving dilution and porosity. The effect of porosity is to change both the thermal conductivity and density. The model for the porosity which is considered in this article shows the significance of its effect on the velocity and the type of the combustion front. Different values of porosities are considered for the reactants and products. For an illustrative analysis, a systematic study of the variation of porosity of reactants and products is carried out for the combustion synthesis of TiB₂ and TiC. The numerical results indicate that as the reactant porosity values are decreased, the combustion velocity first increases because of an increase in the thermal conductivity. The combustion velocity, after reaching a maximum, decreases with a further decrease in the porosity. As the porosity is varied, there is a considerable effect on the nature of propagation of the combustion front, which may change from a steady state to an oscillatory mode. Results indicate that as the reactant porosity is decreased, the frequency of oscillations of the combustion front first increase and then decrease with a further decrease in the reactant porosity. The differences in the mechanism for the decrease in velocities at very low values of reactant porosities for the two systems TiC and TiB₂ are identified. The results of considering different values of porosities in the reactants and the product are also presented. For the study of the effect of diluents, the product itself is considered as the diluent. The effect of adding the diluent to the initial reactants is to decrease the combustion temperature and the combustion velocity. The diluent also changes the mode of combustion. An increase in the amount of the diluent results in the decrease of the frequency of oscillations.     

Sucking effect of diaphragm and its significance in drainage of abdominal cavity during hepatic surgery

Investigation of the value of the sucking effect of the diaphragm in 44 patients was carried out. The first group consisted of 28 patients who have not undergone hepatic resection. The second group included patients after hepatic resections of various volume in local pathology. The balloon method in modification of this clinic was used for measurement of the value of the sucking effect. In patients of the first group the value of sucking effect was almost two times more under the right cupula of the diaphragm (130.33 + 4.78 mm of water column) in comparison with the left infradiaphragmatic space. It is responsible for presence of the slot between the right half of the liver and the diaphragm, which aggravates the sucking effect. In the second group of patients the value of the sucking effect under the right diaphragmatic cupula was practically the same as in patients of the first group. After right-sided hemihepatectomy the value of the sucking effect under right cupula of the diaphragm has significantly diminished. After resection of the right lobe of the liver as well as after left-sided hemihepatectomy, or without them, the value of sucking effect under left cupula of the diaphragm did not significantly differ. The investigations showed that vacuum-aspiration with vacuum of not less than 150 mm water column should be used for effective drainage of infradiaphragmatic space.     

Rolling of metal balls

The rolling of balls (diameter 93 and 125 mm) of precise mass in helical grooves is simulated by means of QForm-3D and DEFORM-3D software. A model of a virtual rolling mill is created. Analysis of the stress state at characteristic points along the rolling axis focuses on the effective stress, the components of the stress tensor, and the mean normal stress. The mass of balls rolled on new and worn rollers is measured. The quality of internal metal layers is verified, and the hardness of rolled balls over the vertical and horizontal symmetry axes is measured. Modeling of ball rolling shows that the hot blank (a rod of hot-rolled steel) is satisfactorily captured by the rollers. Rolling is stable, without slipping. The blank completely fills the grooves; no gaps are observed between the metal and the walls. The crosslinks between the balls are completely eliminated within the rollers. The crosslinks are cut by the rim of the rollers and pressed into the body of the ball. The individual balls continue to roll along the finishing section of the groove; the stubs of the crosslinks are smoothed; and a completely shaped ball with a smooth surface emerges from the rollers. In modeling the stress–strain state, all the components of the stress tensor are negative. In other words, all the components of the stress tensor are compressive in rolling of the balls. Statistical analysis of the data from weighing of the rolled balls (diameter 93 and 125 mm) shows that the mass deviates from the required value by no more than 1%. Measurement of the hardness over the diametric cross section of the balls shows that there is no decline in hardness in the internal layers. That indicates high quality of the ball core.     

连铸方坯中心线凝固行为波动现象及变化规律

连铸坯中心线区域钢液的凝固行为与中心偏析缺陷的形成及控制密切相关。基于中碳钢连铸方坯纵断面的实际凝固组织,以中心偏析点内部二次枝晶间距计算局部冷却速率,揭示了铸坯中心线局部冷却速率的波动特征。结合连铸三维凝固模型,研究了铸坯中心线固相率波动引起局部冷却速率波动并最终影响铸坯中心组织和性能的均匀性的机理;对不同工况铸坯中心线固相率和局部冷却速率波动的周期性进行了分析对比,提出了连铸坯凝固终点位置的周期性波动机理并得到了不同拉速下凝固终点波动距离的判断方程,对于所选连铸方坯,凝固终点波动距离为25.0～27.5 mm;在此基础之上,研究了拉速对中心线固相率波动程度的影响规律,并分析了凝固终点波动距离变化对末端电磁搅拌(final electromagnetic stirring, F-EMS)和轻压下(mechanical soft reduction, MSR)作用均匀性的影响。结果表明,拉速由1.8 m/min提高至2.4 m/min后,虽然液相穴长度增加可能增加整体偏析程度,但铸坯中心线固相率波动程度降低了20%,这有利于减轻中心线偏析沿拉坯方向的波动性,提高铸坯中心质量的均匀性。并...     

Reliability-Based Optimal Design of Truss Structures Using Particle Swarm Optimization

In this work, the particle swarm optimization method is employed for the reliability-based optimal design of statically determinate truss structures. Particle swarm optimization is inspired by the social behavior of flocks (swarms) of birds and insects (particles). Every particle’s position represents a specific design. The algorithm searches the design space by adjusting the trajectories of the particles that comprise the swarm. These particles are attracted toward the positions of both their personal best solution and the best solution of the swarm in a stochastic manner. In typical structural optimization problems, safety is dealt with in a yes/no manner fulfilling the set of requirements imposed by codes of practice. Considering uncertainty for the problem parameters offers a measure to quantify safety. This measure provides a rational basis for the estimation of the reliability of the components and of the entire system. Incorporating the reliability into the structural optimization framework one can seek a reliability-based optimal design. For the problems examined herein, the reliability indexes of the structural elements are obtained from analytical expressions. The structure is subsequently analyzed as a series system of correlated elements and the Ditlevsen bounds are used for the calculation of its reliability index. The uncertain-random parameters considered in this work are the load, the yield-critical stress; and the cross sections of the elements. The considered design variables of the optimization problem are the cross-sectional areas of the groups, which control the size of the truss, and the heights and lengths that control the shape of the truss. The results of the optimization are presented for a 25-bar truss and a 30-bar arch and the robustness of the optimization scheme is discussed.     

In vitro expression of n-cadherin adhesion molecule during early cardiac morphogenesis

The aim of the present study was to investigate, "in vitro", the degree of organogenetic potentiality of the cells of the cardiogenic area during the early developmental stages of the chick embryo. Embryos from between the end of the presomitic stage to the 8 somite stage were studied. The subcephalic fold was cultured in liquid medium for up to 7 days. After 24 hs of culturing, an extended migration ring was observed. In the explants, from 3 somite stage, onwards, beating masses were noted, the shape and size of which suggested a vascular-like structure. Sections of the cultures were processed for the detection of the N-Cadherin adhesion molecule. The observations stated that the diffusion and intensity of expression of this receptor is related to the stage od development of the embryo. Cultures from the presomitic stage to 3 somite stage did not express the molecule. Instead, expression took place in those cultures of embryos at the 3 somite stage, onwards. In the cultures to which the antiserum against N-Cadherin had been to the medium, the formation of vascular-like structures was affected. The changes depended on the age of the embryos. These observations suggest that the expression of the N-Cadherin is related to the potentiality of the presumptive myocardic cells to organize themselves, at least "in vitro", to form a well-defined tridimensional structure. The expression of the adhesion molecule and the potentiality of the cells to build tubular structures were transient features, "in vitro" in our cultures. This suggests that "in vivo" the expression of the N-Cadherin must be aided by factors which, at present, are unidentified.     

Ecology of flea groups of the species conformis (Siphonaptera: Pulicidae: Xenopsylla) of the fauna of Russia and adjacent countries (review)

Within the boundaries of the former USSR, the northern part of the conformis group distribution is located. It spreads over the arid regions of the Trans-Cacucasus, Pricaspijckaja lowland, Kazakhstan and Middle Asia. In this area 10 species and subspecies occur. They are mainly parasites of gerbillins. Unlike many other Siphonaptera the conformis fleas, when in the host's home, do not concentrate in the nest but inhabit the passages of burrow and food chambers throughout the year. On this reason the preimaginal development and existence of the adults take place not at the temperature of the habitable nest, which is heated by the host body, but at the temperature of the soil at a depth of burrow. The temperature threshold for preimaginal development of conformis fleas is reported to be 10-12 degrees. Temperature below the threshold is fatal for all immature instars. On the contrary the imago can survive at freezing temperature. The annual cycle of the conformis fleas is characterized by the presence of adults throughout the year. They breed in the warmer season and overwinter in the state of reproductive diapause. In this state the fleas are able to attack the host and to feed but do not deposit eggs. In the north deserts the reproduction begins at the early April and terminates at the early September. Southern, the reproductive period is longer. Furthermore, the complete interruption of the reproduction in the autumn-winter time may be absent as it was observed in X. gerbilli gerbilli and X. hirtipes in the south of the Middle Asia. On the other hand it is noted that in southern deserts the rate of oviposition falls in the most hot time. The number of generation per year in the conformis fleas varies from 2-3 in north deserts to 6-7 in south ones. The flea populations peak in late autumn when the insects cease to bread. The high abundance is maintained until springtime. After the diapause is ceased and the fleas begin breeding their abundance declines. In the late spring and early summer the emergence of adults begins and the populations increase. In a mild of summer the second fall takes place and then the fall is replaced by the autumnal peak. On their main hosts the conformis fleas prevail over all other species of Siphonaptera especially for warmer time when their quota among other fleas does not descend as a rule below 90% but more oftently it approaches to 100%. The fleas of this group and especially species parasitizing Rhombomys opimus are remarkable for the high level of their abundance. In the northern deserts in the periods of the most high abundance (late autumn, winter and early spring) the number of fleas per burrow occupied by family of Rh. opimus exceeds usually 1000 specimens and sometimes it can reach several thousands. In the southern deserts the abundance of the fleas is lower but the period of their active parasitizing is longer. In the species parasitizing Rh. opimus it is shown that in a complex burrow only some part of fleas has the possibility to feed regularly. In the spring and summer the percentage of fleas daily attacking the host varied from 17 to 86% and from 10 to 150 ectoparasites feed daily on one animal depending on the quantity of fleas and of hosts in the burrow. The number of attacking fleas is regulated by behaviour of the hosts, which change the used parts of burrow when the fleas are crowded there.     

Efferent and afferent connections of the nucleus lateralis posterior thalami ("pulvinar") in the albino rats (author's transl)

The efferent and afferent connections of the lateral posterior nucleus (LP) of the albino rat were investigated light microscopically with the silver-degeneration-methods and the HRP-methods as well. The results are: 1. The main projection region of the LP is the area of 18a of the peristriate visual cortex. Most degenerating axons terminate in layer IV. A few fibers pass layers III and II and terminate in layer I. It is not sure if there are also terminating fibers in layer IV. We could not find a topistic relation between LP and area 18 a. 2. We observed a small number of degenerating fibers in area 17, too. 3. A part of the degenerating fibers runs to the temporal cortex end enters area 20. 4. There is no evidence for a projection of the LP to both the subcortical regions and to the superior colliculus. 5. The majority of the LP's afferent fibers originates - on the subcortical level - from the superior colliculus. Especially the lamina III (Str. opticum) of the ipsilateral and of the contralateral side is here the source of fibers terminating in the LP. 6. Other subcortical sources of fibers terminating in the LP are: the pretectal region, the ventral part of the LGN, the Zona incerta, the thalamic reticular formation, and the dorsal raphe nucleus. 7. There exists a fiber projection of the area 17 to the LP. The axons originate mainly from pyramidal cells in layer V. It is discussed whether the area-17-fibers terminating in the LP are collaterals of the fibers terminating in the superior colliculus. The projection of the area 18a to the LP is of greater importance. The axons of this area originate mainly from cells of the layer VI. It becomes obvious that the thalamic relay-station of the second visual pathway seems to project nearly exclusively to the neocortex. In contrast to the dorsal LGN, however, the LP is not only a simple relay-station for visual information as also non-visual information arrives here. The morphological basis for these inputs has not yet been clarified completely. We have to take into consideration as well as the connections with the superior colliculus and the pretectal region and the cortical connections. It is remarkable that there exists also a projection of LP-fibers to a region outside the classical visual cortex. In mammals of higher evolution that kind of projection extends increasingly. It is discussed if - under comparative-anatomical aspect - the morphological changes in the pulvinar region are an expression of the neocorticalization, whereas the morphological changes in the dorsal LGN reflect mainly the functional specialization of the visual system.