P-Start:一种分阶段TCP慢启动机制

针对现有TCP算法慢启动机制窗口指数增长导致一个窗口中出现多个包丢失现象，提出了一种分阶段的TCP慢启动机制－P-Start．该方法利用零界点（ssthresh／2）将慢启动分为两个阶段．窗口小于零界点，呈指数增长；窗口大于零界点，则以负指数方式增长，逐步迭代逼近门限值；使拥塞窗口增加幅度在连接启动时和过渡到拥塞避免阶段比较小，而在零界点附近窗口增加幅度大．从而有效避免了多个包丢失现象的发生，实现连接的平滑接入和过渡到拥塞避免阶段．考虑到慢启动传输效率低，改进算法通过参数配置，加快窗口的增加速度．减少慢启动的持续时间，提高其性能．仿真实验结果表明P-tart有效地提高了TCP协议的稳定性和网络的性能．     

UTP中一种分阶段求解算法

大学课程表问题UTP是一个应用广泛的、典型的组合优化和不确定性调度问题,并且已经被证明是NP完全问题。本文提出了一种分阶段解决大学课程表问题的算法,将课程表问题划分为时间安排和空间安排两个阶段,分别采用智能算法和最佳适应算法逐段求解,并最终求得全局较优解。通过设计实验对算法进行分析,结果表明这种分阶段决策算法在保证课表质量的同时能够有效减小遗传算法在求解UTP问题中的复杂度,提高程序的运行速度。     

Simulation of quasi-dimensional model for diesel engine working process

In order to satisfy the demand of validity and real time operating performance of diesel engine model used in hardware-in-the-loop simulation system, a simplified quasi-dimensional model for diesel engine working process was proposed, which was based on the phase-divided spray mixing model. The software MATLAB/Simulink was utilized to simulate diesel engine performance parameters. The comparisons between calculated results and experimental data show that the relative error of power and brake specific fuel consumption is less than 2.8%, and the relative error of nitric oxide and soot emissions is less than 9.1%. At the same time, the average computational time for simulation of one working process with the new model is 36 s, which presents good real time operating performance of the model. The simulation results also indicate that the nozzle flow coefficient has great influence on the prediction precision of performance parameters in diesel engine simulation model.