基于控制器切换的涡扇发动机转速调节及安全保护

本文通过多个控制器间的切换改善了航空发动机加速过程的动态性能,并在转速过高时加以保护。首先,根据航空发动机控制系统模型利用区域极点配置方法对于每个子系统设计一个H∞输出跟踪控制器,并且设计滞后切换规则,使发动机高压转子转速既能快速跟踪参考加速曲线又能保证较小超调,同时由于滞后切换规则的存在避免频繁切换造成的执行机构不必要的损耗;然后设计安全保护控制器及事件触发的切换机制,在高压转子转速过高时保护转速使其不超过最高转速边界,保证飞行安全;最后通过数例仿真验证了本文方法的有效性。     

可重构系统中基于空间邻接度的实时任务放置算法*

本文提出了一种基于三维空间邻接度的放置算法,该算法将硬件任务按照长、宽及调度时间构成一个三维资源模型,将每个硬件任务看成是一个空间块。首先对可重构资源进行编码,到达的任务总是通过某个顶点依附另一个任务的边界被放置,确定候选的放置顶点;然后以到达任务与已放置在三维空间的邻接度为代价函数,选择代价函数值最大的顶点放置任务,从而使得到达任务与已放置任务在三维空间接触的邻接面最大。可使任务安排得更紧凑,减小对系统资源的浪费,提高芯片利用率。     

多核机群下MPI程序优化技术的研究

多核处理器的新特性使多核机群的存储层次更加复杂,同时也给MPI程序带来了新的优化空间。国内外学 者提出了许多多核机群下MPI程序的优化方法和技术。测试了3个不同多核机群的通信性能,并分别在Intel与 AMD多核机群下实验评估了几种具有普遍意义的优化技术:混合MPI/OpcnMP、优化MPI运行时参数以及优化 MPI进程摆放,同时对实验结果和优化性能进行了分析。     

Virus coevolution partheno-genetic algorithms for optimal sensor placement

A virus coevolutionary partheno-genetic algorithm (VEPGA), which combined a partheno-genetic algorithm (PGA) with virus evolutionary theory, is proposed to place sensors optimally on a large space structure for the purpose of modal identification. The VEPGA is composed of a host population of candidate solutions and a virus population of substrings of host individuals. The traditional crossover and mutation operators in genetic algorithm are repealed and their functions are implemented by particular partheno-genetic operators which are suitable to combinatorial optimization problems. Three different optimal sensor placement performance index, one aim on the maximization of linear independence, one aim on the maximization of modal energy and the last is a combination of the front two indices, have been investigated. The algorithm is applied to two examples: sensor placement for a portal frame and a concrete arc dam. Results show that the proposed VEPGA outperforms the sequential reduction procedure (SRP) and PGA. The combined performance index makes an excellent compromise between the linear independence aimed index and the modal energy aimed index.     

Some results on the genericity of the pole placement problem

In this note, the pole placement problem for a linear MIMO systems with p outputs and m inputs is studied from the algebraic point of view. A formulation is proposed, that allows to analyze both theoretical and numerical aspects of the case min(m,p)=2 with more sharpness. Moreover, here it is shown that arbitrary pole placement by static output feedback of unitary rank is generically not possible even if m+p>n holds true.     

Sink placement on a 3D terrain for border surveillance in wireless sensor networks

With their distributed nature and redundant operation capability, wireless sensor networks are very suitable for border surveillance scenarios that track intruders trying to breach to a safe side. In such scenarios, keeping the operation going on for as long as possible is the most important aspect of the network. We propose that by placing sink at a carefully selected coordinate will results in a longer living network. We also place restrictions on the candidate locations so that the sensing quality of the network is above a useful predetermined value and the sink is placed in a relatively safe location to avoid destruction. In order to find the suitable coordinates we propose a modified lifetime metric which takes quality and safety measures into account. We also propose a genetic algorithm which uses a discrete event simulator-in-the-loop over a three dimensional terrain to find locations for the sink that fits the given quality and safety restrictions. Using a three dimensional underlying terrain makes the proposed approach more realistic. The results obtained for various sensor network scenarios indicate that the proposed algorithm can find locations that increase the lifetime by also considering the sensing quality and safety.     

Effects of display factors on Chinese proofreading performance and preferences

This experiment investigated the influence of four display factors, viz. typeface (Ming Liu and Jheng Hei), font size (10-point and 14-point), text direction (horizontal and vertical) and copy placement (left-right and top-bottom) on Chinese proofreading performance and subjective preferences. Proofreading performance was measured in terms of time and accuracy, and preferences were examined in terms of comfort, ease and fatigue. It was found that the horizontal text direction resulted in faster proofreading than the vertical one, but the other three factors were non significant. The faster proofreading using the horizontal text direction was valid for both the left-right and the top-bottom arrangements. There was an interaction between typeface and font size such that, for the smaller character size (10-point), the Ming Liu style produced a faster performance than the Jheng Hei style. However, for the larger character size (14-point), the Jheng Hei style produced a faster performance than the Ming Liu style. Regarding proofreading accuracy, the number of non-detected missing words and related false alarm in left-right copy placement setting was significantly larger than that in top-down setting. Greater accuracy was obtained in proofreading at the cost of a speed-accuracy trade-off – the higher the accuracy in the proofreading task, the longer the proofreading time. Font size and text direction had significant effects on proofreading preferences, but typeface and copy placement did not.

Practitioner Summary: This study examined four display factors on Chinese proofreading performance and subjective preferences. The findings of this experiment provide information and recommendations that should prove useful for the design of proofreading interfaces to improve proofreading time and accuracy, and to satisfy proofreaders' preference.     

Hand-hold location and trunk kinematics during box handling

Trunk kinematics variables have been shown to be related to low back injury risk during lifting tasks and it was hypothesised that changes in hand-hold positions could influence trunk kinematics and thereby risk. Fourteen subjects lifted a 5 or 10 kg box using four different hand placement locations (two symmetric and two asymmetric) while their trunk kinematics (position, velocity and acceleration in the sagittal, coronal and transverse planes) were captured using the lumbar motion monitor (LMM). These kinematics data were then used to calculate the probability of high risk group membership (PHRGM) as defined in the LMM risk assessment model. The results showed significant effects of hand placement on trunk kinematics, resulting in significant changes in the PHRGM variable ranging from a low of 20% in a the symmetric low load condition to a high of 38% under the asymmetric, 10 kg condition.

Statement of Relevance: Manual materials handlers use a variety of hand-hold positions on boxes during lifting. Where a lifter grabs the box can influence the trunk kinematics during the lifting task and these kinematics have been shown to provide some insight into risk of low back injury. This study documents the trunk postures and kinematics as a function of hand-hold position.     

多电子元件及芯片组布局的热分析

针对电子线路板上多电子元件及芯片组的不同布局所产生的热场分布问题,分析了分布元件的热产生、热传导、对流和辐射过程,采用有限元理论分析方法和ANSYS软件,对线路板上多芯片组件的热场分布进行仿真.结果表明:电子元件的不同布局将导致线路板热点的温度存在差别,在有限空间内合理布置元件可明显降低设备的热失效率.     

基于改进分组遗传算法的虚拟机放置研究

为了提高云计算的资源利用率以及减少能耗,采用改进的分组遗传算法来解决虚拟机放置的效率.通过对遗传算法的交配和突变等过程进行重新设计,提高遗传算法过程中优秀基因遗传给后代的几率,并提出了相应的算法,达到快速求解虚拟机放置问题的目的.实验结果表明,该算法可以快速采用最少的物理机来放置虚拟机,有效地提高了虚拟机放置问题的求解速度.