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951.
Numerical modeling of the propagation of an adiabatic shear band 总被引:1,自引:0,他引:1
The critical phenomena determining the propagation of an adiabatic shear band occur at its extremity. The stress and strain
distributions at the tip of a shear band are calculated as a function of applied shear strain using the finite element method
for an elasto-plastic material. Three assumptions simplify the calculations considerably: (a) the mechanical response of the
material follows an adiabatic stress-strain curve; (b) the material within the shear band has zero shear strength; (c) the
body is taken to be in equilibrium. The distribution of stresses and strains in the adiabatically-deformed material is compared
to that of a quasi-statically deformed material. While the stress-strain curve for an isothermally deformed material is monotonic
with continuous work-hardening, the adiabatic work-hardening curve reaches a plateau followed by work-softening (due to thermal
softening). The stress and strain fields for both cases are nearly identical, except in the region directly in front of the
shear band. In the adiabatically-deformed material a thin region (~5 μm) with large strains and lowered stresses is produced.
This region, in which accelerated deformation takes place as the applied shear deformation increases, is absent in the isothermally-deformed
material. The formation of this instability region, ahead of the shear band, is considered to be the mechanism for the propagation
of an adiabatic shear band. 相似文献
952.
Marc Hittinger Philippe Ravier Alain Bernard Jean Marc Fouet 《Nuclear Engineering and Design》1989,116(3)
Using large finite element analysis codes for heat transfer computations and for stresses and displacements under thermal loads computations is not always very simple because of the complexity of the problems and the number of domains involved. Often faulty results from computations are being used until an expert discovers that something was wrong in the simulation. As a result of recent advances in Artificial Intelligence techniques, solutions to these problems are now possible by making use of Knowledge Based Systems in which expertise in several domains can easily be introduced. In this paper, we present an application of knowledge based systems for a finite element analysis code in Heat Transfer. The system is fairly general, and we think that application to any well structured numerical code should be straightforward. 相似文献
953.
Assessed the degree to which the quality of the affective mother–child relationship is linked to the quality of interactions among siblings of preschool age. 44 intact families, with 2 children of which at least one was of preschool age, participated. Two evaluation methods were used: observation of relationships between siblings in semi-structured play situations at home, and a Q-sort questionnaire on the quality of the mother–child relationship. To a certain degree, there was a link between the quality of the relationship children had with their mothers and the quality of that they had with their siblings. Results indicate that the 2 kinds of intrafamilial relationships must be viewed differently for younger and older children and suggest that the relationship with the mother can contribute to the interior self- representation that could help children assert their position and play a role among siblings. (English abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
954.
Francois Doignon Nicolas Biteau Michel Aigle Marc Crouzet 《Yeast (Chichester, England)》1993,9(10):1131-1137
The DNA sequence of a 6794 bp fragment located at about 100 kb from the right telomere of chromosome II from Saccharomyces cerevisiae has been determined. Sequence analysis reveals five open reading frames. One is the ARO4 gene encoding the 3-deoxy-D -arabinoheptulosonate 7-phosphate synthase. Another presents strong homology with the S5 ribosomal protein from bacteria. The open reading frame YBR1705 shows significant homology with dUTPase, suggesting for the first time the existence of such an enzyme in S. cerevisiae. 相似文献
955.
956.
A computer tracking system was used to quantify the responses of infective second-stage juveniles of the plant-parasitic nematodeMeloidogyne incognita to carbon dioxide. A sudden increase in concentration caused an increase in the rate of locomotion and a decrease in the frequency of changes of direction. The threshold was about 0.01 % vol CO2/vol gas when the baseline concentration was very low and 0.05% CO2 when the baseline concentration was 1% CO2. The latter value represents a relative change of 5%. Concentrations above 10% CO2 caused a general decrease in movement. In a second type of experiment, a constant concentration gradient of CO2 was established, and the net movement of the nematodes along the gradient was determined. At low concentrations, the threshold was about 0.02% CO2/cm. At higher concentrations, the threshold gradient was below 0.01% CO2/cm or a relative gradient of less than 1% change/cm. At all concentrations to which nematodes responded they were attracted. The degree of orientation was estimated to be approximately 10% under most conditions. The rate of migration under the most favorable conditions was about 0.7 cm/hr. Three possible functions of the response are discussed: attraction to roots, movement toward optimal depth in soil, and as a collimating stimulus. 相似文献
957.
246 men and 191 women (aged 40–72 yrs) were monitored for medical care utilization in a health maintenance organization (HMO) over a 5-yr period. Rates of utilization were related to initially obtained indicators of life stress and social support and to interactions between life stress, social support, and age. Predictors of male and female HMO use are discussed. Multiple regression permitted a distinction between immediate and delayed effects of stresses on HMO visits. Implications regarding the buffering hypothesis for the mitigating effects of social support on the likelihood of health breakdown are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
958.
G. Paul Neitzel Marc K. Smith Michael J. Bolander 《International Journal of Heat and Mass Transfer》1994,37(18):2909-2915
Energy-stability theory is applied to the case of radiation heat transfer in an optically thin, quiescent fluid layer heated from below and bounded by rigid, black, perfectly conducting planes. The radiation term in the energy equation destroys the quadratic character of the energy identity. It is shown, however, that the right-hand side of the energy identity can be bounded by a suitable quadratic term for all physically allowable disturbances. The result is a conditional stability limit dependent upon disturbance amplitude. Results are computed for a variety of cases; these are compared to existing linear and energy stability results. 相似文献
959.
Marc Termote H. St. Seidenfus Ruth Shen Dale R. Schmeichel R. Keith Semple Lay James Gibson Ryszard Domanski Michael F. Sheehan Josephine Olu Abiodun A. M. Fuller Turgut Var Diane J. Martz Douglas M. Brown Peter Cowan James L. Mulvihill Tom Rijerkerk Konrad Dramowicz Roger F. Riefler C. J. Robertson Bernard Malamud Rudolf Andorka James L. LeBeau J. C. Stabler Wilbur R. Maki Jan S. Kowalski Nigel Thrift Richard W. Lichty Dr. Andre Simmons Raimund K. Herz Donald Jones Kurt Puchinger J. Barry Riddell R. Ross MacKay Noel D. Uri Peter Boothroyd John F. Jakubs Peter M. Schulze P. N. Mathur 《The Annals of Regional Science》1985,19(2):100-157
960.
Kalichman Seth C.; Roffman Roger A.; Picciano Joseph F.; Bolan Marc 《Canadian Metallurgical Quarterly》1997,28(4):355
The authors evaluated sexual practices, sexually tempting situations, and risk avoidance coping strategies among HIV-seropositive men who have sex with men and who were seeking HIV prevention services. HIV-seropositive men who practiced unprotected anal intercourse in the previous 4 weeks reported stronger temptations to engage in high-risk sex than men who were sexually safe. Being in a positive mood and being with desirable partners were particularly tempting risk situations for seropositive men, who also possessed less coping capacity to deal with risky situations than safer men. Prevention interventions must address the needs of men infected with HIV and must remove barriers to enrolling in prevention programs. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献