COMPARATIVE STUDY OF DISPATCHING RULES IN A REAL-LIFE JOB SHOP ENVIRONMENT

In this paper, we compare the performance of dispatching rules in a real-life job shop environment and provide guidance for schedulers to determine effective dispatching rules for this type of systems. We consider a total of 20 dispatching rules, that range from some previously developed rules to some recently developed sophisticated rules such as process time plus work in next queue plus negative slack (PT + WINQ + SL), multi factor rule, and bottleneck dynamics. The performance measures examined are average weighted tardiness and proportion of tardy jobs. Discrete event simulation model based on ARENA is developed to implement the rules. Results from this study are given in detail.     

Parallel implementation of molecular dynamics simulation for short-ranged interaction

A parallel molecular dynamics simulation method, designed for large-scale problems, employing dynamic spatial domain decomposition for short-ranged molecular interactions is proposed. In this parallel cellular molecular dynamics (PCMD) simulation method, the link-cell data structure is used to reduce the searching time required for forming the cut-off neighbor list as well as for domain decomposition, which utilizes the multi-level graph-partitioning technique. A simple threshold scheme (STS), in which workload imbalance is monitored and compared with some threshold value during the runtime, is proposed to decide the proper time for repartitioning the domain. The simulation code is implemented and tested on the memory-distributed parallel machine, e.g., PC-cluster system. Parallel performance is studied using approximately one million L-J atoms in the condensed, vaporized and supercritical states. Results show that fairly good parallel efficiency at 49 processors can be obtained for the condensed and supercritical states (∼60%), while it is comparably lower for the vaporized state (∼40%).     

A low-cost decision-aided channel estimation method for Alamouti OSTBC

In wireless communication systems, channel state information (CSI) acquisition is typically performed at the receiver side every time a new frame is received, without taking into account whether it is really necessary or not. Considering the special case of the 2 × 1 Alamouti orthogonal space-time block code, this work proposes to reduce computational complexity associated with the CSI acquisition by including a decision rule to automatically determine the time instants when CSI must be again updated. Otherwise, a previous channel estimate is reused. The decision criterion has a very low computational complexity since it consists in computing the cross-correlation between preambles sent by the two transmit antennas. This allows us to obtain a considerable reduction on the complexity demanded by both supervised and unsupervised (blind) channel estimation algorithms. Such preambles do not penalize the spectral efficiency in the sense they are mandatory for frame detection as well as for time and frequency synchronization in current wireless communication systems.     

面向同步规范的并行代码自动生成

随着对安全攸关实时系统功能与非功能要求的日益增加,使用多核技术将成为发展趋势.如何在多核平台条件下保证系统运行的可信任性及可靠性是学术上和应用上的关键问题.目前基于形式化方法的系统设计、验证以及自动代码生成已经在单核平台上形成很多研究成果,但在多核平台上的研究仍面临许多科学问题.同步语言SIGNAL是一种被广泛应用于安全攸关实时系统功能设计的形式化方法,适用于对系统确定性并发行为的描述.SIGNAL编译器也支持将同步规范SynchronousSpecification）生成仿真代码,以对其进行验证与分析.然而现有研究较少关注从SIGNAL同步规范到支持跨平台并行代码的生成方法.本文研究面向SIGNAL同步规范的并行自动代码生成方法.提出了方程依赖图EDG的概念,将SIGNAL规范转换为EDG以分析其全局数据依赖关系;研究了对EDG进行任务划分获取规范中可以并行执行部分的算法;最后,以跨平台并行编程API-OpenMP作为对象,结合程序中信号的时钟关系,将并行任务映射到OpenMP并行代码,并进行了实例验证.     

Molecular dynamics simulation of nanofluid’s flow behaviors in the near-wall model and main flow model

The flow behaviors of nanofluids were studied in this paper using molecular dynamics (MD) simulation. Two MD simulation systems that are the near-wall model and main flow model were built. The nanofluid model consisted of one copper nanoparticle and liquid argon as base liquid. For the near-wall model, the nanoparticle that was very close to the wall would not move with the main flowing due to the overlap between the solid-like layer near the wall and the adsorbed layer around the nanoparticle, but it still had rotational motion. When the nanoparticle is far away from the wall (d > 11 Å), the nanoparticle not only had rotational motion, but also had translation. In the main flow model, the nanoparticle would rotate and translate besides main flowing. There was slip velocity between nanoparticles and liquid argon in both of the two simulation models. The flow behaviors of nanofluids exhibited obviously characteristics of two-phase flow. Because of the irregular motions of nanoparticles and the slip velocity between the two phases, the velocity fluctuation in nanofluids was enhanced.     

Parallel computation of three-dimensional nonlinear magnetostatic problems

We describe a general-purpose parallel code for computing accurate solutions to large computationally demanding, 3D, nonlinear magnetostatic problems. The code, CORAL, is based on a volume integral equation formulation. Using an IBM SP parallel computer and iterative solution methods, we successfully solved the dense linear systems inherent in such formulations. A key component of our work was the use of the PETSc library, which provides parallel portability and access to the latest linear algebra solution technology. Copyright © 1999 John Wiley & Sons, Ltd.     

Thermally actuated buckling beam memory: a non-volatile memory configuration for extreme space exploration environments

A new nano-thermo-mechanical data storage memory is presented which combines two technologies of thermal actuation and buckling beam memory. The memory design is resistant in high radiation environments, making it a reliable memory for spacecraft computer systems. This memory has a data storage density, write/erase speed, and power consumption comparable with current memories. An integrated thermal–mechanical simulation of buckling in nano-mechanical memory is performed to optimize the design parameters. The preliminary system is a bridge with lengths of 20–40 μm, a width of 1 μm, and a thickness of 0.3 μm, in air with a pressure of 5 kPa. The simulation of high energy particle collisions shows radiation does not cause undesired buckling for silicon and silicon carbide bits, which makes the memory applicable for Jovian exploration. Optimization simulations are performed for silicon, silicon carbide, and kapton with various dimensions and actuation heating rates. The current work suggests the length of 20 μm for the bridge to balance the write time and the storage density. Among the beams with the fixed dimensions, kapton shows the fastest write time, with the lowest energy cost. However, high energy electron collision causes buckling in kapton, limiting its use in high radiation applications. The results show that silicon and silicon carbide based systems are viable for use in the extreme radiation environments that will be encountered in future space exploration missions.     

AN ANALYTICAL DEVELOPMENT OF A UNIVERSAL DISPLACEMENT MEASUREMENT SYSTEM FOR ULTRA-PRECISION METROLOGY

In recent years, precise metrology up to nanoscale has attracted substantial attention due to an increasing need for ultra-precision measurement systems for micro electro mechanical systems (MEMS) and nano electro mechanical systems (NEMS) calibration. In this paper, an analytical and numerical investigation for the proposed design of a 6-degree-of-freedom (6-dof) universal measurement system, using a relatively simple and inexpensive but highly sensitive set up, is presented. This system utilizes a convex mirror and two flat mirrors, one angled and one vertical, as targets to reflect laser beams onto photo detectors. These targets, placed on the object of interest for metrology applications, change the direction of the reflected beam when there is any movement in the object, which is detected by the photo detectors. The use of convex and angled mirrors greatly enhances the sensitivity of the system. Geometric relationships are established among all the optical components to predict the final intersection points of the laser beams reflected from the targets with the photo detector planes. These relationships are used to establish a Jacobian partial derivative matrix, which is further used to estimate the target pose when the photo detector outputs are given. Numerical simulation of the measurement process is performed using MATLAB®. Assuming the approximate distance from laser beam origin to target and the target to photo detector as 50 mm, and photo detector resolution as 0.1 µm, translations and rotations less than 50 nm and 2 arc sec, respectively, can be measured accurately. The highest amount of sensitivity in translation is obtained along the Z-axis with minimum a measurement of 3.4 nm; the highest amount of sensitivity in rotation is along the pitch-axis with a minimum measurement of 0.145 arc sec. The corresponding low sensitivity axes are X-axis and yaw-axis, with minimum measurements of 35 nm and 2 arc sec, respectively. The sensitivity and the resolution of the system can be increased many times further by increasing the curvature of the convex mirror or by increasing the distance between the target and the detectors. The analytical and simulation results of this work yield a scientific and engineering guideline for the development of meso, micro, as well as nanoscale metrology systems.     

槽流拟颗粒模型的并行算法

将流体处理为离散粒子,应用拟颗粒硬球模型来研究槽流中的流动现象,与分子动力学模拟的算法类似,是研究槽流机理的一种行之有效的方法。为了作大规模的模拟,本文采用区域分解算法和消息传递编程模型技术,将该模型串行程序并行化,应用一维划分、单相传递的方法简化了并行算法,采用轮换搜索法来避免硬球碰撞次序对结果的影响。在可扩展的机群系统上用实例计算,通过与串行程序的对比,验证了并行程序的正确性,表明本文设计的并行算法取得了较高的并行计算效率。     

A framework for efficient performance prediction of distributed applications in heterogeneous systems

Predicting distributed application performance is a constant challenge to researchers, with an increased difficulty when heterogeneous systems are involved. Research conducted so far is limited by application type, programming language, or targeted system. The employed models become too complex and prediction cost increases significantly. We propose dPerf, a new performance prediction tool. In dPerf, we extended existing methods from the frameworks Rose and SimGrid. New methods have also been proposed and implemented such that dPerf would perform (i) static code analysis and (ii) trace-based simulation. Based on these two phases, dPerf predicts the performance of C, C++ and Fortran applications communicating using MPI or P2PSAP. Neither one of the used frameworks was developed explicitly for performance prediction, making dPerf a novel tool. dPerf accuracy is validated by a sequential Laplace code and a parallel NAS benchmark. For a low prediction cost and a high gain, dPerf yields accurate results.     

Approaching parallel computing to simulating population dynamics in demography

Agent-based modelling and simulation is a promising methodology that can be applied in the study of population dynamics. The main advantage of this technique is that it allows representing the particularities of the individuals that are modeled along with the interactions that take place among them and their environment. Hence, classical numerical simulation approaches are less adequate for reproducing complex dynamics. Nowadays, there is a rise of interest on using distributed computing to perform large-scale simulation of social systems. However, the inherent complexity of this type of applications is challenging and requires the study of possible solutions from the parallel computing perspective (e.g., how to deal with fine grain or irregular workload). In this paper, we discuss the particularities of simulating populating dynamics by using parallel discrete event simulation methodologies. To illustrate our approach, we present a possible solution to make transparent the use of parallel simulation for modeling demographic systems: Yades tool. In Yades, modelers can easily define models that describe different demographic processes with a web user interface and transparently run them on any computer architecture environment thanks to its demographic simulation library and code generator. Therefore, transparency is provided by two means: the provision of a web user interface where modelers and policy makers can specify their agent-based models with the tools they are familiar with, and the automatic generation of the simulation code that can be executed in any platform (cluster or supercomputer). A study is conducted to evaluate the performance of our solution in a High Performance Computing environment. The main benefit of this outline is that our findings can be generalized to problems with similar characteristics to our demographic simulation model.     

Parallel implementation of the fluid particle model for simulating complex fluids in the mesoscale

Dissipative particle dynamics (DPD) and its generalization—the fluid particle model (FPM)—represent the ‘fluid particle’ approach for simulating fluid‐like behavior in the mesoscale. Unlike particles from the molecular dynamics (MD) method, the ‘fluid particle’ can be viewed as a ‘droplet’ consisting of liquid molecules. In the FPM, ‘fluid particles’ interact by both central and non‐central, short‐range forces with conservative, dissipative and Brownian character. In comparison to MD, the FPM method in three dimensions requires two to three times more memory load and a three times greater communication overhead. Computational load per step per particle is comparable to MD due to the shorter interaction range allowed between ‘fluid particles’ than between MD atoms. The classical linked‐cells technique and decomposing the computational box into strips allow for rapid modifications of the code and for implementing non‐cubic computational boxes. We show that the efficiency of the FPM code depends strongly on the number of particles simulated, the geometry of the box and the computer architecture. We give a few examples from long FPM simulations involving up to 8 million fluid particles and 32 processors. Results from FPM simulations in three dimensions of the phase separation in binary fluid and dispersion of the colloidal slab are presented. A scaling law for symmetric quench in phase separation has been properly reconstructed. We also show that the microstructure of dispersed fluid depends strongly on the contrast between the kinematic viscosities of this fluid phase and the bulk phase. This FPM code can be applied for simulating mesoscopic flow dynamics in capillary pipes or critical flow phenomena in narrow blood vessels. Copyright © 2002 John Wiley & Sons, Ltd.     

A new analytical model of single-stage microleverage mechanism in resonant accelerometer

Microleverage mechanism which is widely applied in microelectromechanical systems (MEMS) transfers and amplifies force or displacement from input to output. In this work, one-stage microleverage mechanism is integrated into a biaxial micro resonant accelerometer to improve sensitivity. Force amplification factor of the microleverage is analyzed and deduced by integral method. The results from theoretical model match well with the ones from finite element method (FEM) simulation, which proves that the proposed model is relatively accurate and the width of lever beam is a quite important parameter in design. The resonant accelerometer is successfully fabricated by MEMS technology. Preliminary experiments are conducted and demonstrate differential sensitivity of 71 Hz/g for the accelerometer with resonant frequency of 267.726 kHz.     

Parallel flow routing in SWMM 5

The hydrodynamic rainfall-runoff and urban drainage simulation model SWMM (Storm Water Management Model) is a state of the art software tool applied likewise in research and practice. In order to reduce the computational burden of long simulation runs and to use the extra power of modern multi-core computers, a parallel version of SWMM is presented herein. The challenge has been to modify the software in such minimal way that the resulting code enhancement may find its way into the commercial and non-commercial software tools that depend on SWMM for its calculation engine. A pragmatic approach to identify and enhance only the critical parts of the software in terms of run-time was chosen in order to keep the code changes as low as possible. The enhanced software was first tested for coherence against the original code and then benchmarked on four different input scenarios ranging from a very small village to a medium sized urban area. For the investigated sewer systems a speedup of six to ten times on a twelve core system was realized, thus decreasing the execution time to an acceptable level even for tedious system analysis.     

Parallel custom instruction identification for extensible processors

With the ability of customization for an application domain, extensible processors have been used more and more in embedded systems in recent years. Extensible processors customize an application domain by executing parts of application code in hardware instead of software. Determining parts of application code as custom instruction generally requires subgraph enumeration and subgraph selection. Both subgraph enumeration problem and subgraph selection problem are computationally difficult problems. Most of previous works focus on sequential algorithms for these two problems. In this paper, we present a parallel implementation of a latest subgraph enumeration algorithm based on a computer cluster. A standard ant colony optimization algorithm (ACO), a modified version of ACO with local optimum search and a parallel ACO algorithm are also proposed to solve the subgraph selection problem in this work. Experimental results show that the parallel algorithms outperform the sequential algorithms in terms of runtime or (and) quality of results. In addition, we have formally proved the upper bound on the number of feasible solutions in subgraph selection problem with or without the overlapping constraint.     

Code reordering using local random extraction and insertion (LREI) operator for GPGPU-based track-before-detect systems

Track-before-detect (TBD) algorithms are used for tracking systems, where the object’s signal is below the noise floor (low-SNR objects). A lot of computations and memory transfers for real-time signal processing are necessary. GPGPU in parallel processing devices for TBD algorithms is well suited. Finding optimal or suboptimal code, due to lack of documentation for low-level programming of GPGPUs is not possible. High-level code optimization is necessary and the evolutionary approach, based on the single parent and single child is considered, that is local search approach. Brute force search technique is not feasible, because there are N! code variants, where N is the number of motion vectors components. The proposed evolutionary operator—LREI (local random extraction and insertion) allows source code reordering for the reduction of computation time due to better organization of memory transfer and the texture cache content. The starting point, based on the sorting and the minimal execution time metric is proposed. The unbiased random and biased sorting techniques are compared using experimental approach. Tests shows significant improvements of the computation speed, about 8 % over the conventional code for CUDA code. The time period of optimization for the sample code is about 1 h (1,000 iterations) for the considered recursive spatio-temporal TBD algorithm.     

Tunable MEMS piezoelectric energy harvesting device

This work is focused on low frequency (<300 Hz) vibrations due to the fact that many industrial and commercial devices operate at those frequencies. The aim of the present work is to model by numerical simulation a Si cantilever beam with an AlN piezoelectric layer concept that tunes its resonant frequency post-processing, while reducing the separation of the first two modes of resonance in order to broaden its quality factor and, therefore, to harvest more environmental energy. This paper investigates by numerical simulation the influence of perforating sections of the Si beam has on the resonant frequencies of the cantilever. The authors have found that the distance between these modes is decreased by 30 % when 0.002 mm³ is extracted in a specific location of the initial structure. This difference between modes can be reduced above 80 % if a volume of 0.004 mm³ in a specific part of the initial design is subtracted. In these conditions, the first mode is decreased about 20 % the initial value and the second mode about 60 %.