A novel adaptive HBCC technique for three-phase shunt APF

This paper proposes an important improvement of the hysteresis band current control (HBCC) technique for three-phase shunt active power filter (APF) to eliminate harmonics and to compensate the reactive power generated by three-phase rectifier. In this technique, a simple and quick prediction of the hysteresis band is added to a phase-locked-loop (PLL) control to ensure constant switching frequency and synchronization of modulation pulses independently on system parameters. This allows the advantages of quick response, good current tracking accuracy and minimal ripple in three-phase systems. This technique is robust and it is characterized by the simplicity, this aspect is very significant for a practice realization because it constitutes the factors which determine the cost and the reliability of industrial assembly. The proposed technique determines the switching signals of the three-phase shunt APF and the algorithm which is based on the dc bus capacitors voltage regulation using proportional-integral (PI) controller is used to determine the suitable current reference signals. The behavior of the proposed technique has been fully verified by digital simulation, where the obtained results show that the proposed technique can improve shunt APF performances noticeably.     

Simulation of atmospheric phenomena

This paper presents a physically based simulation of atmospheric phenomena. It takes into account the physics of non-homogeneous media in which the index of refraction varies continuously, creating curved light paths. As opposed to previous research on this area, we solve the physically based differential equation that describes the trajectory of light. We develop an accurate expression of the index of refraction in the atmosphere as a function of wavelength, based on real measured data. We also describe our atmosphere profile manager, which lets us mimic the initial conditions of real-world scenes for our simulations. The method is validated both visually (by comparing the images with the real pictures) and numerically (with the extensive literature from other areas of research such as optics or meteorology). The phenomena simulated include the inferior and superior mirages, the Fata Morgana, the Novaya–Zemlya, the Viking's end of the world, the distortions caused by heat waves and the green flash.     

Efficient location and allocation strategies for undesirable facilities considering their fundamental properties

The phrase “not in my backyard” (NIMBY) refers to the well-known social phenomena in which residents oppose the construction or location of undesirable facilities near their homes. Examples of such facilities include electric transmission lines, recycling centers and crematoria. Due to the opposition typically encountered in constructing an undesirable facility, the facility planner should understand the nature of the NIMBY phenomena and consider it as a key factor in determining facility location. We examine the characteristics of NIMBY phenomena and suggest two alternative mathematical optimization models with the objective of minimizing the total degree of NIMBY sentiments. Genetic algorithms are proposed to solve our linear and nonlinear integer programs. The results obtained via genetic algorithms for our linear integer programs are compared with those of CPLEX to evaluate their performance. The nonlinear programs are tested with various allocation policies. Sensitivity analysis is conducted about several system parameters.     

Universality in short-time critical gluodynamics with heat-bath-inspired algorithms

Short-time dynamics technique is used to study the relaxation process for the (2+1)-dimensional critical gluodynamics of the SU(2) lattice-gauge theory. A generalized class of heat-bath-inspired updating algorithms was employed during the short-time regime of the dynamic evolution for performance comparison. The static and dynamic critical exponents of the theory were measured, serving as a dynamic benchmark for algorithmic efficiency. Our results are in agreement with predictions from universality hypothesis and suggest that there is an underlying universal dynamics shared by the analyzed algorithms.     

异常网络流量中的相变理论研究

基于网络相变理论对网络异常流量的本质进行了研究,提出了基于Hurst参数反馈的动态拥塞缓解机制,理论分析和仿真结果验证了该方法的可行性和相对于传统方法的优越性,为异常流量的检测、控制研究做出了有益的探索。     

3DGIS环境下雨雪天气实时仿真

3D GIS最重要的特征之一就是虚拟现实表现,其本质是可视化技术与GIS数据库的整合,以满足各种应用如生态农业、灾害预测等方面的需求。以GIS数据库的环境数据和气象数据为基础,通过对雨雪的效果模拟,将GIS气象数据以实时的可视化形式逼真地表现出来。实验方法采用粒子系统,对单个点元赋予利用Photoshop制作的大面积纹理,这样采用的粒子数减少到普通粒子系统的十分之一,渲染速度为普通粒子系统的十倍以上,以较小的系统资源消耗达到了更加实时逼真的效果,对雪的动态堆积和雨水地面效果采用GPU加速3维渲染,原型系统同时能接受用户对实验环境如粒子纹理、雨雪量的设置。提出根据气象数据进行天气模拟的自适应策略,从而更加适应实际应用需要。     

基于有限元的挤压铸造压射机构卡擦分析

压射机构是挤压铸造设备中的核心零部件之一,卡擦现象是导致压射机构失效和压室寿命缩短的关键技术难题。利用有限元方法计算了压室与冲头的半径方向的变形值,并对压射机构卡擦现象进行了定性分析。结果表明:压射过程中压室和冲头之间的配合间隙变小是导致主要卡擦发生的主要原因。     

随机正则(k,r)-SAT问题的可满足临界

研究k-SAT问题实例中每个变元恰好出现r=2s次,且每个变元对应的正、负文字都出现s次的严格随机正则（k,r）-SAT问题.通过构造一个特殊的独立随机实验,结合一阶矩方法,给出了严格随机正则（k,r）-SAT问题可满足临界值的上界.由于严格正则情形与正则情形的可满足临界值近似相等,因此得到了随机正则（k,r）-SAT问题可满足临界值的新上界.该上界不仅小于当前已有的随机正则（k,r）-SAT问题的可满足临界值上界,而且还小于一般的随机k-SAT问题的可满足临界值.因此,这也从理论上解释了在相变点处的随机正则（k,r）-SAT问题实例通常比在相应相变点处同规模的随机k-SAT问题实例更难满足的原因.最后,数值分析结果验证了所给上界的正确性.