A slip-based model for the size-dependent effective thermal conductivity of nanowires

The heat flux across a nanowire is computed based on the Guyer-Krumhansl equation. Slip conditions with a slip length depending on both temperature and nanowire radius are introduced at the outer boundary. An explicit expression for the effective thermal conductivity is derived and compared to existing models across a given temperature range, providing excellent agreement with experimental data for Si nanowires

Generality of shear thickening in suspensions

Suspensions are of wide interest and form the basis for many smart fluids. For most suspensions, the viscosity decreases with increasing shear rate, i.e. they shear thin. Few are reported to do the opposite, i.e. shear thicken, despite the longstanding expectation that shear thickening is a generic type of suspension behavior. Here we resolve this apparent contradiction. We demonstrate that shear thickening can be masked by a yield stress and can be recovered when the yield stress is decreased below a threshold. We show the generality of this argument and quantify the threshold in rheology experiments where we control yield stresses arising from a variety of sources, such as attractions from particle surface interactions, induced dipoles from applied electric and magnetic fields, as well as confinement of hard particles at high packing fractions. These findings open up possibilities for the design of smart suspensions that combine shear thickening with electro- or magnetorheological response.Comment: 11 pages, 9 figures, accepted for publication in Nature Material

Glassiness and constrained dynamics of a short-range non-disordered spin model

We study the low temperature dynamics of a two dimensional short-range spin system with uniform ferromagnetic interactions, which displays glassiness at low temperatures despite the absence of disorder or frustration. The model has a dual description in terms of free defects subject to dynamical constraints, and is an explicit realization of the ``hierarchically constrained dynamics'' scenario for glassy systems. We give a number of exact results for the statics of the model, and study in detail the dynamical behaviour of one-time and two-time quantities. We also consider the role played by the configurational entropy, which can be computed exactly, in the relation between fluctuations and response.Comment: 10 pages, 9 figures; minor changes, references adde

Testes neuropsicológicos de aplicação simples para o diagnóstico de demência

Os desempenhos em testes neuropsicológicos de trinta pacientes, com diagnóstico de demência leve ou moderada baseado nos critérios do DSM-III-R, com escore no Mini-exame do Estado Mental inferior a 24 pontos e escolaridade mínima de 4 anos, foram comparados aos de trinta voluntários normais equiparados quanto a idade, escolaridade e sexo. Foram calculadas as sensibilidades e especificidades dos testes na distinção entre doentes e controles normais Dentre os testes empregados, o que demonstrou maior acurácia nesta distinção, calculada através de curva ROC, foi o de informação-memória-concentração de Blessed, seguido em ordem decrescente de acurácia, pelos de construção (cópias de figuras simples), memória verbal tardia (após 5 minutos), reconhecimento de 10 figuras e fluencia verbal (animais). Seis testes de aplicação e interpretação simples (fluencia verbal, percepção visual, memória visual incidental, cálculo, desenho de um relógio e memória tardia após 5 minutos) permitiram definir função linear discriminante que revelou elevada capacidade de discriminação entre pacientes e controles, na amostra. Esta função deve ser submetida à comprovação em outra casuística. Em virtude da simplicidade e rapidez de aplicação, poderá ser associada ao MEM para identificar indivíduos com demência e indivíduos sadios em estudos epidemiológicos