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Cluster partitioning approaches to parallel Monte Carlo simulation on multiprocessors
We consider the parallelization of Monte Carlo algorithms for analyzing numerical models of charge transport used in semiconductor device physics. Parallel algorithms for the standard k-space Monte Carlo simulation of a three band model of bulk GaAs on hypercube multicomputers are first presented. This Monte Carlo model includes scattering due to polar-optical, intervalley, and acoustic phonons, as well as electron-electron scattering. The k-space Monte Carlo program, excluding electron-electron scattering, is then extended to simulate a semiconductor device by the addition of the real space position of each simulated particle and the assignment of particle charge, using a cloud in cell scheme, to solve the Poisson's equation with particle dynamics. Techniques for effectively partitioning this device so as to balance the computational load while minimizing the communication overhead are discussed. Approaches for improving the efficiency of the parallel algorithm, either by dynamically balancing of load or by employing the usual techniques for enhancing rare events in Monte Carlo simulations are also considered. The parallel algorithms were implemented on a 64-node NCUBE multiprocessor and test results were generated to validate the parallel k-space, as well as the device simulation programs. Timing measurements were also made to study the variation of speedups as both the problem size and number of processors are varied. The effective exploitation of the computational power of message passing multiprocessors requires the efficient mapping of parallel programs onto processors so as to balance the computational load while minimizing the communication overhead between processors. A lower bound for this communication volume when mapping arbitrary task graphs onto distributed processor systems is derived. For a K processor system this lower bound can be computed from the K (possibly) largest eigenvalues of the adjacency matrix of the task graph and the eigenvalues of the adjacency matrix of the processor graph. We also derive the eigenvalues of the adjacency matrix of the processor graph for a hypercube and give test results comparing the lower bound for the communication volume with the values given by a heuristic algorithm for a number of task graphs
Commodity Computing Clusters at Goddard Space Flight Center
The purpose of commodity cluster computing is to utilize large numbers of readily available computing components for parallel computing to obtaining the greatest amount of useful computations for the least cost. The issue of the cost of a computational resource is key to computational science and data processing at GSFC as it is at most other places, the difference being that the need at GSFC far exceeds any expectation of meeting that need. Therefore, Goddard scientists need as much computing resources that are available for the provided funds. This is exemplified in the following brief history of low-cost high-performance computing at GSFC
Beowulf: A Parallel Workstation For Scientific Computation
Network-of-Workstations technology is applied to the challenge of implementing very high performance workstations for Earth and space science applications. The Beowulf parallel workstation employs 16 PCbased processing modules integrated with multiple Ethernet networks. Large disk capacity and high disk to memory bandwidth is achieved through the use of a hard disk and controller for each processing module supporting up to 16 way concurrent accesses. The paper presents results from a series of experiments that measure the scaling characteristics of Beowulf in terms of communication bandwidth, file transfer rates, and processing performance. The evaluation includes a computational fluid dynamics code and an N-body gravitational simulation program. It is shown that the Beowulf architecture provides a new operating point in performance to cost for high performance workstations, especially for file transfers under favorable conditions. 1 INTRODUCTION Networks Of Workstations, or NOW [4] ..
Effects of MLC601 on early vascular events in patients after stroke: The CHIMES study
BACKGROUND AND PURPOSE - Early vascular events are an important cause of morbidity and mortality in the first 3 months after a stroke. We aimed to investigate the effects of MLC601 on the occurrence of early vascular events within 3 months of stroke onset. METHODS - Post hoc analysis was performed on data from subjects included in the CHInese Medicine Neuroaid Efficacy on Stroke recovery (CHIMES) study, a randomized, placebo-controlled, double-blinded trial that compared MLC601 with placebo in 1099 subjects with ischemic stroke of intermediate severity in the preceding 72 hours. Early vascular events were defined as a composite of recurrent stroke, acute coronary syndrome, and vascular death occurring within 3 months of stroke onset. RESULTS - The frequency of early vascular events during the 3-month follow-up was significantly less in the MLC601 group than in the placebo group (16 [2.9%] versus 31 events [5.6%]; risk difference=-2.7%; 95% confidence interval, -5.1% to -0.4%; P=0.025) without an increase in nonvascular deaths. Kaplan-Meier survival analysis showed a difference in the risk of vascular outcomes between the 2 groups as early as the first month after stroke (Log-rank P=0.024; hazard ratio, 0.51; 95% confidence interval, 0.28-0.93). CONCLUSIONS - Treatment with MLC601 was associated with reduced early vascular events among subjects in the CHIMES study. The mechanisms for this effect require further study. 漏 2013 American Heart Association, Inc.Link_to_subscribed_fulltex
Baseline characteristics and treatment response of patients from the Philippines in the CHIMES study
漏 2014 The Authors. Background: The CHIMES Study compared MLC601 with placebo in patients with ischemic stroke of intermediate severity in the preceding 72h. Sites from the Philippines randomized 504 of 1099 (46%) patients in the study. We aimed to define the patient characteristics and treatment responses in this subgroup to better plan future trials. Methods: The CHIMES dataset was used to compare the baseline characteristics, time from stroke onset to study treatment initiation, and treatment responses to MLC601 between patients recruited from Philippines and the rest of the cohort. Treatment effect was analyzed using end-points at month 3 as described in the primary publication, that is, modified Rankin Score, National Institutes of Health Stroke Scale, and Barthel Index. Results: The Philippine cohort was younger, had more women, worse baseline National Institutes of Health Stroke Scale, and longer time delay from stroke onset to study treatment compared with the rest of the cohort. Age (P=0路003), baseline National Institutes of Health Stroke Scale (P<0路001), and stroke onset to study treatment initiation (P=0路016) were predictors of modified Rankin Score at three-months. Primary analysis of modified Rankin Score shift was in favor of MLC601 (adjusted odds ratio 1路41, 95% confidence interval 1路01-1路96). Secondary analyses were likewise in favor of MLC601 for modified Rankin Score dichotomy 0-1, improvement in National Institutes of Health Stroke Scale (total and motor scores), and Barthel Index. Conclusions: The treatment effects in the Philippine cohort were in favor of MLC601. This may be due to inclusion of more patients with predictors of poorer outcome.Link_to_subscribed_fulltex