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A comment on the role of Frank–Read sources in plasticity of nanomaterials
Estrin, Y.,Kim, H.S.,Nabarro, F.R.N. Elsevier 2007 Acta materialia Vol.55 No.19
<P><B>Abstract</B></P><P>Dislocation generation by a Frank–Read source was considered for the case of nanocrystalline metallic materials. It was shown that thermally activated operation of this mechanism, which was proposed in the literature as an explanation for the observed grain size dependence of the strain rate sensitivity (SRS) of the flow stress, is only possible in a very limited range of the source lengths and stresses. By comparing the calculated SRS with the experimental data for copper, it was further demonstrated that the thermally activated Frank–Read mechanism can be discarded as a process underlying the observed strain rate sensitivity data.</P>
Wang Hanbiao,Yao Kung,Estrin Deborah The Korea Institute of Information and Commucation 2005 Journal of communications and networks Vol.7 No.4
In this paper, we describes the information-theoretic approaches to sensor selection and sensor placement in sensor networks for target localization and tracking. We have developed a sensor selection heuristic to activate the most informative candidate sensor for collaborative target localization and tracking. The fusion of the observation by the selected sensor with the prior target location distribution yields nearly the greatest reduction of the entropy of the expected posterior target location distribution. Our sensor selection heuristic is computationally less complex and thus more suitable to sensor networks with moderate computing power than the mutual information sensor selection criteria. We have also developed a method to compute the posterior target location distribution with the minimum entropy that could be achieved by the fusion of observations of the sensor network with a given deployment geometry. We have found that the covariance matrix of the posterior target location distribution with the minimum entropy is consistent with the Cramer-Rao lower bound (CRB) of the target location estimate. Using the minimum entropy of the posterior target location distribution, we have characterized the effect of the sensor placement geometry on the localization accuracy.
Strength and strain hardening of nanocrystalline materials
Kim, H.S.,Estrin, Y. Elsevier Sequoia 2008 Materials science & engineering. properties, micro Vol.483 No.-
In this paper, a phase mixture model was employed to simulate the strain hardening properties of metallic materials covering a wide grain size range from micrometer down to nanometer scale. In this model a polycrystalline nanomaterial is treated as a mixture of two phases: grain interior, whose plastic deformation is governed by a combination of the dislocation and diffusion mechanisms, and grain boundary 'phase', whose plastic flow is controlled by a boundary diffusion mechanism alone. The main focus of the paper is the effect of grain size on the flow stress and strain hardening. The model predictions of the grain size dependence of strain hardening are presented.