Stories of young dropouts: a social survey of success and failure

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Aperiodic quantum XXZ chains: Renormalization-group results

We report a comprehensive investigation of the low-energy properties of antiferromagnetic quantum XXZ spin chains with aperiodic couplings. We use an adaptation of the Ma-Dasgupta-Hu renormalization-group method to obtain analytical and numerical results for the low-temperature thermodynamics and the ground-state correlations of chains with couplings following several two-letter aperiodic sequences, including the quasiperiodic Fibonacci and other precious-mean sequences, as well as sequences inducing strong geometrical fluctuations. For a given aperiodic sequence, we argue that in the easy-plane anisotropy regime, intermediate between the XX and Heisenberg limits, the general scaling form of the thermodynamic properties is essentially given by the exactly-known XX behavior, providing a classification of the effects of aperiodicity on XXZ chains. We also discuss the nature of the ground-state structures, and their comparison with the random-singlet phase, characteristic of random-bond chains.Comment: Minor corrections; published versio

On the random neighbor Olami-Feder-Christensen slip-stick model

We reconsider the treatment of Lise and Jensen (Phys. Rev. Lett. 76, 2326 (1996)) on the random neighbor Olami-Feder-Christensen stik-slip model, and examine the strong dependence of the results on the approximations used for the distribution of states p(E).Comment: 6pages, 3 figures. To be published in PRE as a brief repor

Estudo das correntes oceânicas na região envolvente da Ilha Terceira no Arquipélago dos Açores

Este trabalho tem como principal objectivo o estudo das correntes oceânicas na região envolvente da Ilha Terceira no Arquipélago dos Açores. Pretende-se identificar os factores que mais influenciam as correntes na sua magnitude e direcção na região envolvente da ilha. Para tal, foram analisados trabalhos realizados anteriormente e foi desenvolvido um modelo hidrodinâmico para modelação das correntes. Os cenários simulados foram definidos, de forma a reproduzir situações próximas da realidade para a zona em estudo, fazendo variar nas fronteiras, a altura de maré, a velocidade da corrente e os ventos actuantes no domínio, considerando-se cenários quer em regime permanente, quer em regime variado

A mathematical framework for reducing the domain in the mechanical analysis of periodic structures

A theoretical framework is developped leading to a sound derivation of Periodic Boundary Conditions (PBCs) for the analysis of domains smaller then the Unit Cells (UCs), named reduced Unit Cells (rUCs), by exploiting non-orthogonal translations and symmetries. A particular type of UCs, Offset-reduced Unit Cells (OrUCs) are highlighted. These enable the reduction of the analysis domain of the traditionally defined UCs without any loading restriction. The relevance of the framework and its application to any periodic structure is illustrated through two practical examples: 3D woven and honeycomb.Comment: 18 page