Tradeoffs in granularity and parallelization for a Monte Carlo shower simulation code

The EGS4 code, developed at Stanford Linear Accelerator Center, simulates electron-photon cascading phenomena. The original code is inherently sequential: processing one particle at a time. This paper reports on a series of experiments in parallelizing different versions of EGS4. Our parallel experiments were run on a 30-processor Sequent Balance B21 and a 6-processor Symmetry S27. We have considered the following approaches for parallel execution of this application code:

1. (1) Original sequential version modified for parallel processing: 1 processor;

2. (2) Version 1 run multiprocessed: 1 to 29 processors;

3. (3) Sequential version modified for large-grain parallel processing: 1 procssor;

4. (4) Version 3 run using the Sequent Microtasking Library: 1 to 29 processors.

For each approach, we discuss the relative advantages and disadvantages in the areas of coding effort, understandability and portability, as well as performance, and outline a new parallelization approach we are currently pursuing based on Large-Grain Data Flow techniques.     

Approximation of frequency responses based on Larsson's method

This paper discusses the new aspects of the formulation for structural model updates presented by Larsson and Sas at the 10th International Modal Analysis Conference held in San Diego, California in February 1991. First, a closed-form representation of the reduced impedance matrix is presented. It clarifies the issues associated with the range of the excitation frequencies used in model updates. Second, the applicable range of excitation frequencies is considered through an example where low frequency local modes are present. Third, the computational aspects of this algorithm are studied. It is shown that displacement sensitivity vectors corresponding to the virtual loads are critical in the computation of the reduced impedance matrix sensitivity. Finally, applicability of this algorithm for approximate frequency responses in structural optimization is studied. Numerical results are included to illustrate the essence of this formulation.[B1] Viscous damping matrix (N × N) - [B2] Structural damping matrix (N × N) - [E] Impedance matrix (N × N) [E] = [K+i(B ₁+B₂)–²M] - F Forcing vector used for analysis (N × 1) - G Measured force vector (N × 1) - [H] Receptance matrix (N × N) [H] = [E]^–1 - J Number of independent loading cases - [K] Stiffness matrix (N × N) - K Number of degrees of freedom where frequency responses are measured - KT Total number of responses for which measured data are available - L Number of excitation frequencies for each loading case - [M] Mass matrix (N × N) - M Number of parameters modified for system identification or design optimization - N Total number of structural system degrees of freedom in the analysis model - R Structural response - Q Number of vectors used in the modal analysis - U Frequency responses computed analytically - V Frequency responses measured in the shake tests - 0 Status prior to perturbation - model Quantities computed by an analysis model - red Indicates a reduced system obtained by isolating the measuredK degrees of freedom - test Quantities measured in the vibration tests - ~ Approximate quantity     

Polonium evaporation and adhesion experiments for the development of polonium filter in lead–bismuth cooled reactors

Fundamental experiments were performed to determine the adhesion characteristics of polonium to different metals and to develop a filter for polonium evaporated from neutron-irradiated LBE. The results of the first experiments suggested that adhesion characteristics are almost the same for stainless steel and nickel metal. The results of the preliminary experiments for a polonium filter suggested that stainless steel mesh with thin wires could effectively collect polonium evaporated from neutron-irradiated LBE. In the experiments, stainless steel wire mesh was used, but from the results of adhesion experiment, it is expected that the same effect can be obtained with wire mesh made of other kinds of metal.     

DC interruption characteristic of vacuum circuit breaker

A high‐speed vacuum circuit breaker (HSVCB) has been investigated. HSVCB makes high‐frequency current superimposed on a fault current so that the current is forced to be zero and is interrupted. Its interruption performance is considered to be dependent on the rate of change of the current (di/dt). As a fundamental research, we investigated the di/dt– dv/dt characteristics and the insulation recovery characteristic after interrupting the counter‐pulse current for various contact materials of AgWC, CuW, and CuCr. The results revealed that the case where the gap length is larger is better in a current interruption performance. Moreover, it was found that di/dt is not dependent on the insulation recovery characteristics, but the magnitude of interruption current is of great influence. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 161(1): 17– 25, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20362     

Removal of polonium from stainless steel surface contaminated by neutron irradiated lead-bismuth eutectic

Lead-bismuth eutectic (LBE) has good characteristics for the coolant and/or target of various nuclear systems, but it also has a problem of polonium contamination. In the study, baking experiment was performed to remove polonium contamination on type 316 stainless steel plate that was originated from neutron irradiated LBE. The contaminated type 316 stainless steel plate was baked in a vacuum condition at various temperatures from 200°C to 600°C. In the previous preliminary study, the effect of short time baking was investigated. In the study, the effect of long time baking was investigated. The detail of the experimental method was also described. The result of long time baking experiment showed that the baking method was effective for removal of polonium from stainless steel surface contaminated by neutron irradiated LBE, if the baking was performed at 500°C and higher in a vacuum condition. The obtained result was consistent to the previous preliminary study.     

Voluntary exercise influences behavioral development in rats exposed to alcohol during the neonatal brain growth spurt.

Children exposed to alcohol prenatally may suffer from severe brain damage, expressed as a variety of behavioral problems, including hyperactivity and learning deficits. There is a critical need to identify effective treatments for fetal alcohol effects. Physical exercise enhances cognitive ability and increases neurogenesis in the hippocampus, a brain area important for learning and memory. Thus, the present study examined whether physical exercise might reduce the severity of alcohol-induced behavioral alterations. Sprague-Dawley rats were intubated with 5.25 g/kg/day ethanol during the third trimester equivalent (postnatal days [PDs] 4-9). Intubated sham control and nontreated controls were included. From PD 21 to PD 51, half of the subjects were given access to running wheels. On PD 52, subjects were tested on the Morris water maze, and on PD 60, open field activity levels were measured. Morris maze performance was significantly impaired among ethanol-exposed subjects; exercise significantly improved performance of all groups. Similarly, ethanol-exposed subjects were overactive in the open field, an effect attenuated with exercise. In sum, these data suggest that exercise may increase neuronal plasticity not only in controls, but also in subjects exposed to alcohol during development. (PsycINFO Database Record (c) 2010 APA, all rights reserved)