Videos for the Workshop ‘Barriers in Computational Complexity’

The videos for the workshop ‘Barriers in Computational Complexity’ (Aug 25-29) have been posted online.

You can access the videos from the workshop’s program page.

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Original source : http://intractability.princeton.edu/blog/2009/11/v...

Micromechanical viscoelasto-plastic models and finite element implementation for rate-independent and rate-dependent permanent deformation of stone-based materials

This paper presents parallel and serial viscoelasto-plastic models to simulate the rate-independent and the rate-dependent permanent deformation of stone-based materials, respectively. The generalized Maxwell viscoelastic and Chaboche's plastic models were employed to formulate the proposed parallel and serial viscoelasto-plastic constitutive laws. The finite element (FE) implementation of the parallel model used a displacement-based incremental formulation for the viscoelastic part and an elastic predictor - plastic corrector scheme for the elastoplastic component. The FE framework of the serial viscoelasto-plastic model employed a viscoelastic predictor - plastic corrector algorithm. The stone-based materials are consisted of irregular aggregates, matrix and air voids. This study used asphalt mixtures as an example. A digital sample was generated with imaging analysis from an optically scanned surface image of an asphalt mixture specimen. The modeling scheme employed continuum elements to mesh the effective matrix, and rigid bodies for aggregates. The ABAQUS user material subroutines defined with the proposed viscoelasto-plastic matrix models were employed.The micromechanical FE simulations were conducted on the digital mixture sample with the viscoelasto-plastic matrix models. The simulation results showed that the serial viscoelasto-plastic matrix model generated more permanent deformation than the parallel one by using the identical material parameters and displacement loadings. The effect of loading rates on the material viscoelastic and viscoelasto-plastic mixture behaviors was investigated. Permanent deformations under cyclic loadings were determined with FE simulations. The comparison studies showed that the simulation results correctly predicted the rate-independent and rate-dependent viscoelasto-plastic constitutive properties of the proposed matrix models. Overall, these studies indicated that the developed micromechanical FE models have the abilities to predict the global viscoelasto-plastic behaviors of the stone-based materials. Copyright © 2009 John Wiley & Sons, Ltd.

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Original source : http://dx.doi.org/10.1002%2Fnag.861...

Resolution of the finite Markov moment problem. (arXiv:0910.5791v1 [math.NA])

We expose in full detail a constructive procedure to invert the so--called
"finite Markov moment problem". The proofs rely on the general theory of
Toeplitz matrices together with the classical Newton's relations.

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Original source : http://arxiv.org/abs/0910.5791...