一种改进的随机早期检测算法

针对随机早期检测算法(RED)参数配置困难的问题，提出了一种自适应阈值RED(SATRED)主动队列管理算法．该算法根据网络拥塞状况，周期性地自动调整最大阈值和最小阈值，以便改善RED路由器的性能．在调整周期内，每到达一个数据包，将平均队列长度和阈值进行比较，在周期结束时根据比较结果对阈值进行调整．仿真结果表明，在路由器缓冲区有限的情况下，相对于简单的尾部丢弃(ttail-drop）和RED，该算法能为TCP连接提供更好的公平性．     

基于拥塞通知速率的主动队列算法及仿真

随机早期确定(random early detectim,RED)算法是网络拥塞控制策略中基于网络节点的一种主动管理队列技术.就该算法的缺点-滞后效应进行了研究和探讨,并提出了一种基于分组丢失和链路使用历史的解决办法,使得RED的滞后效应得到克服,最后并用NS进行了仿真研究.并就仿真方法进行了探讨.对RED和blue算法用NS就队列长度、平均队列长度、吞吐量等进行了对比分析.     

一种改进的显式拥塞指示算法

首先仿真分析了ECN(Explicit Congestion Notification)协议RFC 3168网关的性能.研究表明,该协议中建议的平均队列长度超过门限上界时丢弃包的策略将导致网络吞吐量过低.如果改为标记包策略则可以显著提高吞吐量,但因此造成的长队列会增加系统的平均延迟,而且当负载持续增加时还可能导致不能成功建立连接。为保证高吞吐量、低延迟和连通的鲁棒性,提出一种名为LQRD(Long Queue Random Drop)的改进算法,该算法当平均队列超过队列上限时随机的丢弃分组.丢弃概率综合考虑到平均队列、路由器的缓存大小、链路容量和系统平均延迟等因素的影响,仿真结果表明其具有良好的性能.最后,我们给出并分析了该算法的解析模型.     

一种改进RED的Web集群许可控制算法

利用网络许可控制的数学模型,提出了一种改进RED的Web集群许可控制算法。该算法综合了平均请求队列长度、瞬时请求队列长度、请求之间的关系以及负载情况等多方面的因素进行调整。通过MRED算法有效性测试实验,表明了MRED有效地实现了许可控制。     

基于路由器的RED和Droptail算法比较

弃尾(Droptail)和随机早期检测RED(Random Early Detection)算法是目前路由器中采用的两种重要的队列管理算法.为了在路由器中广泛应用RED算法取代Droptail算法提供依据,对两种算法的性能和实现条件进行了对比研究.使用网络仿真平台NS2(Network Simulation Version 2),首次在缓冲区大小相同的条件下,证明了RED算法在网络拥塞控制、提高网络性能及利用率等方面较Droptail算法有很大提高.仿真结果表明,RED算法与Droptail算法相比,平均队长缩短32%;传输延时减小50%以上;网络净吞吐量提高13%;丢包率降低13%;并能在一定程度上避免发生"全局同步".     

针对RED的LDoS攻击模型

针对随机早期检测(RED)算法的低速率拒绝服务攻击(LDoS)会导致路由器的缓冲队列长度出现严重震荡、使网络服务质量急剧下降的问题,分析了针对RED的LDoS攻击模型,并推理了高速率攻击脉冲使路由器缓冲队列迅速增加的过程,提出了攻击脉冲长度l和脉冲速率R的理论计算方法.对于一个示例场景,当采用大于瓶颈链路带宽的攻击脉冲时,400 ms左右的脉冲能够对网络性能造成很大影响.在NS2中的模拟实验证明了实验结果与理论预期的一致性,针对RED的LDoS攻击流能够使网络服务质量大幅度下降,并且攻击流具有较好的隐蔽性.     

一种基于平均负载的阈值控制AQM算法

提出一种新的AQM算法——基于平均负载的阈值控制算法TLED,并研究在低延时状况下的性能情况。使用指数加权平均(EWMA)方法计算网络的平均负载强度,根据平均负载对数据包进行随机丢弃,通过一种阈值控制算法,将缓存区队列长度与负载状况有机结合起来,取得了吞吐量-队列延时的良好折中,并有效改善了原有的基于负载的控制算法对网络流量变化的自适应性。     

ABLUE—一种新的自适应主动队列管理方法

针对主动队列管理方法 BLUE存在队列抖动偏大的问题,提出一种新的自适应主动队列管理方法 (ABLUE).该方法通过考虑缓冲区长度和平均队列长度定义了丢包策略和丢包概率,利用菌群优化算法对平均队列长度模型进行求解.利用OPNET对ABLUE方法进行仿真实验,深入研究有效传输数据包个数、瞬时平均队列长度方差和缓冲区长度等因素之间的关系.研究结果表明:相对于与BLUE方法、RED方法,ABLUE方法具有较好的适应性.     

基于Linux下防止IP欺骗的SYN攻击防火墙的设计与实现

设计是以redhat5.O为实验平台构建一个防御IP欺骗SYN攻击的包过滤防火墙.是以RED算法为基础,结合TCP数据包重传机制,检验SYN数据包的IP地址真实性.对TCP请求数据包利用RED算法判断TCP请求的平均队列长度和包丢弃概率.平均队列长度超过系统负载最大值时,直接按照随机分配的丢弃概率判断是否丢弃数据包.平均队列长度在系统负载之内时,如果当前的丢弃概率大于给定的阈值,则查找哈希表是否有相同的数据节点,找到则接受该数据包,没找到则保存数据包信息到哈希表,同时丢弃该包.经过分析研究和实验的验证,该防火墙具有较好的吞吐量,同时正常数据包的通过率较高.     

基于测量的主动队列管理算法

针对RED(Random Early Detection)队列管理算法不能实现业务流之间带宽公平共享,提出了基于测量的主动队列管理算法(MBAQM).这种算法采用基于测量和预测的方式估计不同业务流的输入速率,并根据队列大小计算出新到来包的丢弃概率,在维持较少的流状态情况下,通过队列的丢弃机制,实现了不同速率输入业务流之间的链路公平共享.通过对参数的调整还可以实现优先带宽分配机制.该文从理论上说明了该算法能够保证各业务流近似公平地共享输出链路带宽,同时给出相应的仿真结果.     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

An Analysis of Catherine＇s Character——Wuthering Heights

Wuthering Heights, Emily Bronte＇s only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.     

Lower Paleozoic oil relationships within Williston Basin, Canada

The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Design and analysis of generic LBS application developing platform

Location based services is promising due to its novel working style and contents.A software platform is proposed to provide application programs of typical location based services and support new applications developing efficiently. The analysis shows that this scheme is easy implemented, low cost and adapt to all kinds of mobile nework system.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that