2-D pseudo-spectral viscoacoustic modeling in a distributed-memory multi-processor computer

1993 ◽  
Vol 83 (5) ◽  
pp. 1345-1354
Author(s):  
Quingbo Liao ◽  
George A. McMechan
Keyword(s):  
Distributed Memory ◽  
Fourier Transforms ◽  
Relaxation Times ◽  
Empirical Method ◽  
Interprocessor Communication ◽  
Computing Environment ◽  
Absorbing Boundaries ◽  
Matrix Transposition ◽  
Pseudo Spectral ◽  
Frequency Curves

Abstract Two pseudo-spectral implementations of 2-D viscoacoustic modeling are developed in a distributed-memory multi-processor computing environment. The first involves simultaneous computation of the response of one model to many source locations and, as it requires no interprocessor communication, is perfectly parallel. The second involves computation of the response, to one source, of a large model that is distributed across all processors. In the latter, local rather than global, Fourier transforms are used to minimize interprocessor communication and to eliminate the need for matrix transposition. In both algorithms, absorbing boundaries are defined as zones of decreased Q as part of the model, and so require no extra computation. An empirical method of determining sets of relaxation times for a broad range of Q values eliminates the need for iterative fitting of Q-frequency curves.

IMPLEMENTING FAST FOURIER TRANSFORMS ON DISTRIBUTED-MEMORY MULTIPROCESSSORS USING DATA REDISTRIBUTIONS

1994 ◽  
Vol 04 (04) ◽  
pp. 477-488 ◽  
Author(s):  
S.K.S. GUPTA ◽  
C.-H. HUANG ◽  
P. SADAYAPPAN ◽  
R.W. JOHNSON
Keyword(s):  
Fourier Transform ◽  
Fast Fourier Transform ◽  
Distributed Memory ◽  
Fourier Transforms ◽  
Experimental Performance ◽  
Minimum Number ◽  
Data Redistribution ◽  
Using Data ◽  
Performance Results ◽  
Fft Algorithms

Implementations of various fast Fourier transform (FFT) algorithms are presented for distributed-memory multiprocessors. These algorithms use data redistribution to localize the computation. The goal is to optimize communication cost by using a minimum number of redistribution steps. Both analytical and experimental performance results on the Intel iPSC/860 system are presented.

ON MESSAGE PACKAGING IN TASK SCHEDULING FOR DISTRIBUTED MEMORY PARALLEL MACHINES

2001 ◽  
Vol 12 (03) ◽  
pp. 285-306 ◽  
Author(s):  
NORIYUKI FUJIMOTO ◽  
TOMOKI BABA ◽  
TAKASHI HASHIMOTO ◽  
KENICHI HAGIHARA
Keyword(s):  
Task Scheduling ◽  
High Performance ◽  
Distributed Memory ◽  
Parallel Machines ◽  
Scheduling Algorithm ◽  
Parallel Programs ◽  
Parallel Program ◽  
Interprocessor Communication ◽  
Task Scheduling Algorithm ◽  
Software Overhead

In this paper, we report a performance gap betweeen a schedule with small makespan on the task scheduling model and the corresponding parallel program on distributed memory parallel machines. The main reason of the gap is the software overhead in the interprocessor communication. Therefore, speedup ratios of schedules on the model do not approximate well to those of parallel programs on the machines. The purpose of the paper is to get a task scheduling algorithm that generates a schedule with good approximation to the corresponding parallel program and with small makespan. For this purpose, we propose algorithm BCSH that generates only bulk synchronous schedules. In those schedules, no-communication phases and communication phases appear alternately. All interprocessor communications are done only in the latter phases, and thus the corresponding parallel programs can make better use of the message packaging technique easily. It reduces many software overheads of messages form a source processor to the same destination processor to almost one software overhead, and improves the performance of a parallel program significantly. Finally, we show some experimental results of performance gaps on BCSH, Kruatrachue's algorithm DSH, and Ahmad et al's algorithm ECPFD. The schedules by DSH and ECPFD are famous for their small makespans, but message packaging can not be effectively applied to the corresponding program. The results show that a bulk synchronous schedule with small makespan has advantages that the gap is small and the corresponding program is a high performance parallel one.

Isometric contractile properties of diaphragm strips from alcoholic rats

1987 ◽  
Vol 63 (3) ◽  
pp. 1156-1164 ◽  
Author(s):  
M. B. Reid ◽  
H. A. Feldman ◽  
M. J. Miller
Keyword(s):  
Relaxation Times ◽  
Free Water ◽  
Force Transducer ◽  
Liquid Diet ◽  
Optimal Length ◽  
Left Hemidiaphragm ◽  
Chronic Ethanol Consumption ◽  
And Function ◽  
Frequency Curves

Chronic ethanol consumption alters the structure and function of human respiratory muscle. We have examined its effect on the active and passive mechanical properties of rat diaphragm strips in vitro. We conditioned eight rats using a liquid diet containing ethanol as 36% of calories. Eight control rats were pair-fed an isocaloric, ethanol-free liquid diet. Rats were killed after 23 wk. Two strips from the left hemidiaphragm were suspended in Krebs-Ringers solution at 25 degrees C, equilibrated with 5% CO2–95% O2. Isometric stresses were calculated from force transducer measurements. Strips were stimulated directly at supramaximal voltage. Twitch stress (Pt), measured at optimal length (Lo), was greater in ethanol-conditioned strips: 5.1 vs. 3.8 N/cm2. Times to peak Pt and twitch half-relaxation times were equal. Tetanic stress at Lo (Po) was also greater after ethanol conditioning: 17.2 vs. 12.8 N/cm2. Pt/Po ratios were equal. Expressed as %Po, tetanic stress-stimulation frequency curves and tetanic stress-length curves were identical. Ethanol-conditioned strips were marginally less compliant when passively stretched to lengths between Lo and 130% Lo. We postulate that ethanol may have increased active stress development by reducing intracellular free water.

Processing, rheology and structure of melt compounded PBTclay nanocomposites having different chemical composition.

e-Polymers ◽  
2006 ◽  
Vol 6 (1) ◽  
Author(s):  
Luigi Scatteia ◽  
Paola Scarfato ◽  
Domenico Acierno
Keyword(s):  
Flow Behavior ◽  
Relaxation Times ◽  
Empirical Method ◽  
Effect Of Temperature ◽  
Gradual Transition ◽  
Flow Properties ◽  
Butylene Terephthalate ◽  
Melt Compounding ◽  
The Matrix ◽  
Twin Screw

AbstractIn this study the melt flow behavior of poly(butylene terephthalate)-clay nanocomposites produced by melt compounding was investigated. Four commercial organo-modified montmorillonites, differing mainly by the organic treatment used in the modification, were employed as nanometric fillers and blended with the poly(butylene terephthalate) (PBT) at two weight percentages each (6 and 9wt%). The process was carried out using a laboratory-scale twin-screw extruder at two different extrusion rates, in order to evaluate the effect of the shear rate during the process on microstructure and flow properties. In this regard, the nanocomposite samples were submitted to morphological analyses and rheological measurements in the dynamic regime. The effect of temperature on the flow behavior of the hybrids with respect to the neat PBT matrix was also investigated. The obtained data were related to the hybrid compositions and then to the chemical affinity between polymer and clay type. All the reported results have shown a gradual transition from a pseudo-Newtonian trend towards a pseudo-solid-like flow behavior with the increase of the clay loading and the dispersion/exfoliation level of the clay particles, due to the corresponding increase of the polymer-silicate interactions that slow the relaxation times of the PBT chains. Moreover, it was also evident that for the fillers having the higher affinity towards the PBT the nano-scale dispersion benefit from higher residence times, and therefore slower extrusion rates; on the contrary, for the fillers having poor interaction with the polymer, higher shear stress, and therefore higher extrusion rates, are needed to disrupt the clay tactoids in smaller particles. In the last part of the work, in order to verify if a relationship between flow properties and degree of exfoliation does actually exist, the rheological data were also processed using a simple semi-quantitative empirical method proposed in literature. The method failed for our systems, thus underlining the insufficiency of the rheological response alone in quantifying the exfoliation degree of an organoclay in the matrix.

scholarly journals Modeling the dynamic properties of iii-nitrides in strong electric fields

2021 ◽  
Vol 1 (5 (109)) ◽  
pp. 37-52
Author(s):  
Kostyantyn Kulikov ◽  
Vladimir Moskaliuk ◽  
Vladimir Timofeyev
Keyword(s):  
Electric Fields ◽  
Fourier Transforms ◽  
Dynamic Properties ◽  
Relaxation Times ◽  
Dynamic Effect ◽  
Boltzmann Kinetic Equation ◽  
Significant Loss ◽  
System Of Equations ◽  
Relaxation Equation ◽  
Electronic Temperature

This paper proposes a method of modeling the dynamic properties of multi-valley semiconductors. The model is applied to the relevant materials GaN, AlN, and InN, which are now known by the general name of III-nitrides. The method is distinguished by economical use of computational resources without significant loss of accuracy and the possibility of application for both dynamic time-dependent tasks and the fields variable in space. The proposed approach is based on solving a system of differential equations, which are known as relaxation ones, and derived from the Boltzmann kinetic equation in the approximation of relaxation time by the function of distribution over k-space. Unlike the conventional system of equations for the concentration of carriers, their pulse and energy, we have used, instead of the energy relaxation equation, an equation of electronic temperature as a measure of the energy of the chaotic motion only. Relaxation times are defined not as integral values from the static characteristics of the material but the averaging of quantum-mechanic speeds for certain types of scattering is used. Averaging was carried out according to the Maxwellian distribution function in the approximation of electronic temperature, as a result of which various mechanisms of dispersion of carriers are taken into consideration through specific relaxation times. The system of equations includes equations in partial derivatives from time and coordinates, which makes it possible to investigate the pulse properties of the examined materials. In particular, the dynamic effect of the "overshoot" in drift velocity and a spatial "ballistic transport" of carriers. The use of Fourier transforms of pulse dependence of the drift carrier velocity to calculate maximum conductivity frequencies is considered. It has been shown that the limit frequencies are hundreds of gigahertz and, for aluminum nitride, exceed a thousand gigahertz

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