审计缓冲区的形式化模型及其验证

审计系统作为安全信息系统的一个重要组成部分,对于监督系统的正常运行、保障安全策略的正确实施、构造计算机入侵检测系统等都具有十分重要的意义。审计缓冲区的管理是审计系统的核心部分,本文利用时序Petri网对审计缓冲区管理的实现方案进行建模,进而对系统的安全性和活性进行了分析和验证。该方法利用时序逻辑扩充了Petri网缺乏描述系统事件之间时序关系的局限性,同时发挥了Petri网对系统并发和物理结构的有效描述及分析的优势,达到了系统验证的目的。     

一种新的基于BP神经网络的拥塞控制算法

针对计算机高速互联网中发送端速率调节的问题,在一般网络模型基础上,将BP（Back Propagation神经网络运用到计算机网络的拥塞控制中,提出了一种基于BP神经网络的动态资源管理机制以解决网络的拥塞问题,对所提出的拥塞控制方案,进行了仿真分析,仿真结果显示,控制方案有较好的可扩展性,有效性,并使网络性能表现良好。     

共享缓存分组交换系统中的最佳阈值Pushout策略

提出了一种用于共享缓存分组交换设备的最佳闽值Pushout的缓存管理策略（OTP）。在这个策略巾，缓存区采用共享的方式，而每个输出端口分组调度采用Pushout策略。OTP策略的主要思想是将输出端口按照其队列长度分为括跃和非活跃端口，根据队列长度与端口的话跃程度决定分组的接纳或丢弃。仿真结果表明，OTP策略在多个输出队列的情况下具有较好的公平性和鲁棒性，同时在丢包率方面，OTP策略的分组丢失率接近于SP（Selection Pushout）策略。     

基于流数据的大对象数据缓冲机制

通过对关系数据库管理系统Postgre SQL的大对象数据缓冲机制的分析,提出了基于流数据的大对象数据缓冲机制。该机制针对传统大对象数据缓冲所使用的页存储机制存在的性能缺陷,以流数据模型来取代一般的块页读取机制,并根据流数据的存储特点构建基于流数据管道的大对象数据缓冲器结构。该结构在内存中维护一个远小于大对象数据规模的可常驻内存的概要数据结构,从而可以迅速得到用户想要的数据,避免了冗余的磁盘I/O。     

防范入侵的静态分析技术比较

建立了一个具有常见漏洞的测试代码,然后通过扫描测试代码来比较3个典型应用静态分析技术来防范入侵的常用工具。比较结果揭示了检查漏洞库函数的工具漏报率较低,但误报率较高;基于约束分析的工具误报率较低,但漏报率较高;利用软件模型来检测漏洞的工具在检测违背指定安全规则的漏洞时漏报率较低,但在检测具有许多安全漏洞类型的程序时漏报率却非常低。     

The Compositing Buffer: A Flexible Method for Image Generation and Image Editing

In this paper, we describe a new buffer architecture called the Compositing Buffer. Although it is based on the A-buffer architecture described by Carpenter¹, the new architecture introduces two important ideas which make image generation more flexible. The first idea is the storing of bitmask index instead of the bitmask. This allows accurate images to be generated while at the same time, minimising memory usage. The second idea is the introduction of the concept of dynamic object. This allows images to be edited interactively. Applications of the two ideas will also be discussed in the paper.     

Two approaches for solving the buffer allocation problem in unreliable production lines

This paper presents an integrated approach to solve the buffer allocation problem in unreliable production lines so as to maximize the throughput rate of the line with minimum total buffer size. The proposed integrated approach has two control loops; the inner loop and the outer loop. While the inner loop control includes an adaptive tabu search algorithm proposed by Demir et al. [8], binary search and tabu search are proposed for the outer loop. These nested loops aim at minimizing the total buffer size to achieve the desired throughput level. To improve the efficiency of the proposed tabu search, alternative neighborhood generation mechanisms are developed. The performances of the proposed algorithms are evaluated by extensive computational experimentation, and the results are reported.     

Evaluation of buffer zone effectiveness in mitigating the risks associated with agricultural runoff in Prince Edward Island

To minimize the risk posed by runoff from row crops, Prince Edward Island introduced buffer legislation in 2000. The legislation mandates 10-m and 20-m buffers, respectively, for moderate sloped (i.e. < 5%) and steep sloped (i.e. > 5%) agricultural fields that border streams. Since 2001, Environment Canada has been evaluating the effectiveness of various buffer widths on operational farms in reducing toxicity and contaminant concentrations in runoff. Sample collectors, placed in 44 fields at the field edge (0 m), 10 m and at distances out to 30 m, collected overland flow following rainfall-induced runoff events. Samples were collected within 24 hours of an event and analysed for seven pesticides (endosulfan, chlorothalonil, carbofuran, linuron, metribuzin, metalaxyl, mancozeb), water quality parameters and Daphnia magna toxicity. The 10-m buffer required for moderate sloped fields was effective at reducing contaminant concentrations but not always to less than lethal concentrations to Daphnia magna. Limited data beyond 10 m for fields of both slope types precluded making recommendations on a suitable buffer width for shallow sloped fields and evaluating the effectiveness of 20-m buffers for steep sloped fields. When paired data were combined and statistically tested for all fields, the studied pesticides underwent a 52-98% and 68-100% reduction in aqueous and particulate concentrations within 10 m and 30 m, respectively. In addition, by 10 m, soluble phosphorus, nitrate-nitrogen and total suspended solids were reduced by 34%, 38% and 64%, respectively. Results suggest buffer zones on operational farms are capable of achieving contaminant reductions comparable to those reported for controlled experiments. Inconsistent siting of sample collectors beyond 10 m limited the evaluation of the effects of field slope and buffer width on buffer effectiveness on working farms. Future studies on buffer efficiency on operational farms should focus on building the data set beyond 10 m and evaluating load reductions.     

利用双缓冲技术实现宽幅测井曲线的显示与保存

由于测井曲线的幅度较大 ,如果应用程序直接向窗口的视区绘制曲线 ,则会使用大量的GDI调用 ,会引起视觉的明显闪烁 ,使得测井曲线保存为通用的图像格式难以实现。利用双缓冲技术 ,首先在内存中绘制整幅测井曲线 ,然后再实现图像显示、保存,能比较好地解决上面的问题     

A two-moment approximation for a buffer design problem requiring a small rejection probability

A useful model for buffer capacity design in communication systems is the single server queueing model with restricted accessibility where arriving customers are admitted only if their waiting plus service times do not exceed some fixed amount. A two-moment approximation for the buffer capacity in order to achieve a specific rejection probability is proposed for the case of Poisson arrivals and general service requirements. This approximation is a weighted combination of exact results for the special cases of deterministic and exponential service requirements where the weights use only the coefficient of variation of the general service requirement. Numerical experiments show an excellent performance of the approximation.