Axisymmetric polydimethysiloxane microchannels for in vitro hemodynamic studies

The current microdevices used for biomedical research are often manufactured using microelectromechanical systems (MEMS) technology. Although it is possible to fabricate precise and reproducible rectangular microchannels using soft lithography techniques, this kind of geometry may not reflect the actual physiology of the microcirculation. Here, we present a simple method to fabricate circular polydimethysiloxane (PDMS) microchannels aiming to mimic an in vivo microvascular environment and suitable for state-of-the-art microscale flow visualization techniques, such as confocal µPIV/PTV. By using a confocal µPTV system individual red blood cells (RBCs) were successfully tracked trough a 75 µm circular PDMS microchannel. The results show that RBC lateral dispersion increases with the volume fraction of RBCs in the solution, i.e. with the hematocrit

On the nature of the spin-polarized hole states in a quasi-two-dimensional GaMnAs ferromagnetic layer

A self-consistent calculation of the density of states and the spectral density function is performed in a two-dimensional spin-polarized hole system based on a multiple-scattering approximation. Using parameters corresponding to GaMnAs thin layers, a wide range of Mn concentrations and hole densities have been explored to understand the nature, localized or extended, of the spin-polarized holes at the Fermi level for several values of the average magnetization of the Mn ystem. We show that, for a certain interval of Mn and hole densities, an increase on the magnetic order of the Mn ions come together with a change of the nature of the states at the Fermi level. This fact provides a delocalization of spin-polarized extended states anti-aligned to the average Mn magnetization, and a higher spin-polarization of the hole gas. These results are consistent with the occurrence of ferromagnetism with relatively high transition temperatures observed in some thin film samples and multilayered structures of this material.Comment: 3 page

DESENVOLVIMENTO E VALIDAÇÃO DA ESCALA DE AVALIAÇÃO DO RISCO DE VIOLÊNCIA PARA IDOSOS (EARVI)

o presente estudo teve por objetivo o desenvolvimento e a obtenção de evidências de validade e precisão da Escala de Avaliação do Risco de Violência para Idosos (EARVI). Método: Trata-se de um estudo metodológico, de corte transversal, no qual participaram 228 idosos com 65 ou mais anos, residentes de três regiões de Portugal. Resultado: Na análise fatorial, o instrumento apresentou evidências satisfatórias de validade e precisão, resultando na retenção de 21 itens que se agruparam em quatro fatores: confiança/segurança nas relações próximas, isolamento social, dependência funcional e segurança financeira. O alfa de Cronbach para a escala total foi de 0,74. A EARVI apresentou boa precisão, com índice de Youden de 0,77 e sensibilidade e especificidade de 88%. Conclusão: A EARVI poderá ser uma ferramenta útil na identificação de idosos em risco de violência, auxiliando na tomada de decisão por profissionais de saúde. No entanto, se faz necessário que o instrumento seja replicado em amostras mais amplas de idosos, incluindo outros contextos e localidades, de modo a comprovar a estrutura fatorial obtida na escala

An accurate formula for the period of a simple pendulum oscillating beyond the small-angle regime

A simple approximation formula is derived here for the dependence of the period of a simple pendulum on amplitude that only requires a pocket calculator and furnishes an error of less than 0.25% with respect to the exact period. It is shown that this formula describes the increase of the pendulum period with amplitude better than other simple formulas found in literature. A good agreement with experimental data for a low air-resistance pendulum is also verified and it suggests, together with the current availability/precision of timers and detectors, that the proposed formula is useful for extending the pendulum experiment beyond the usual small-angle oscillations.Comment: 15 pages and 4 figures. to appear in American Journal of Physic

An unusual case of intramural Meckel's diverticulum as a lead point for ileoileal intussusception - Laparoscopically assisted management

Intussusception is a frequent cause of intestinal obstruction in children. Ileoileal intussusception is rare and it is secondary to pathological or congenital lead points. We report an unusual case of an intramural Meckel's diverticulum as a lead point for ileoileal intussusception presenting with acute lower intestinal bleeding. Laparoscopically assisted resection of the involved ileum was successfully accomplished