Living bacteria rheology: population growth, aggregation patterns and cooperative behaviour under different shear flows

The activity of growing living bacteria was investigated using real-time and in situ rheology -- in stationary and oscillatory shear. Two different strains of the human pathogen Staphylococcus aureus -- strain COL and its isogenic cell wall autolysis mutant -- were considered in this work. For low bacteria density, strain COL forms small clusters, while the mutant, presenting deficient cell separation, forms irregular larger aggregates. In the early stages of growth, when subjected to a stationary shear, the viscosity of both strains increases with the population of cells. As the bacteria reach the exponential phase of growth, the viscosity of the two strains follow different and rich behaviours, with no counterpart in the optical density or in the population's colony forming units measurements. While the viscosity of strain COL keeps increasing during the exponential phase and returns close to its initial value for the late phase of growth, where the population stabilizes, the viscosity of the mutant strain decreases steeply, still in the exponential phase, remains constant for some time and increases again, reaching a constant plateau at a maximum value for the late phase of growth. These complex viscoelastic behaviours, which were observed to be shear stress dependent, are a consequence of two coupled effects: the cell density continuous increase and its changing interacting properties. The viscous and elastic moduli of strain COL, obtained with oscillatory shear, exhibit power-law behaviours whose exponent are dependent on the bacteria growth stage. The viscous and elastic moduli of the mutant have complex behaviours, emerging from the different relaxation times that are associated with the large molecules of the medium and the self-organized structures of bacteria. These behaviours reflect nevertheless the bacteria growth stage.Comment: 9 pages, 10 figure

Contributo para a validação do knee injury and osteoarthritis outcome score (Koos) em desportistas com lesão no joelho

OBJECTIVOS: Contribuir para a validação da versão portuguesa KOOS para uma população de desportistas com lesão do joelho, avaliando as suas propriedades psicométricas. RELEVÂNCIA: O KOOS é um questionário auto-administrado desenvolvido para pacientes mais jovens e/ou mais activos com lesão e/ou osteoartrose no joelho introduzindo as dimensões funcionalidade no desporto e lazer e qualidade de vida relacionada com o joelho. AMOSTRA: No estudo participaram 42 desportistas, (sexo: 10 mulheres, 32 homens; idade: 26,38±8,79 anos) que sofreram lesões no joelho e que se encontravam a receber cuidados de fisioterapia. METODOLOGIA: O KOOS foi administrado em três ocasiões separadas, com um intervalo de 48 horas e de 4 semanas. Na primeira e terceira ocasiões foram ainda administrados o Medical Outcome Study-36 item Short-Form Survey (MOS SF-36) e o Lysholm Knee Scale (LKS). ANÁLISE ESTATÍSTICA: O coeficiente alfa de Cronbach foi utilizado para testar a coerência interna. O coeficiente r de Pearson foi utilizado para testar a reprodutibilidade teste-reteste e a relação entre o KOOS e os MOS SF-36 e LKS (validade de critério). A percentagem de efeitos chão e tecto foi utilizada para testar a validade do conteúdo. O teste t de Student para amostras independentes foi utilizado para testar variáveis clínicas (validade de construção). O poder de resposta foi analisado através do teste de t student para amostras emparelhadas, pela dimensão estandardizada de resultados e pela média estandardizada de resposta. RESULTADOS/DISCUSSÃO: A coerência interna foi elevada alfa de Cronbach > 0,701), assim como a reprodutibilidade teste-reteste (r> 0,70 em 5 das 4 dimensões do KOOS). A quase totalidade das dimensões apresentou efeitos de chão e tecto não significativos. A validade de construção foi evidenciada com a obtenção de diferenças estatisticamente significativas, relativas às pontuações do KOOS, de acordo com o grau de incapacidade provocado pelo joelho, com o grau de desconforto a caminhar e com a utilização de auxiliar de marcha. A validade de critério foi demonstrada através da correlação de várias dimensões do KOOS com várias dimensões do MOS SF-36 e algumas do LKS. Em relação ao poder de resposta, obtiveram-se diferenças significativas, nas 5 dimensões do KOOS, relativamente ao início dos tratamentos com a situação após 4 semanas e valores de “effect size” bastante significativos, entre 0, 62 e 0,86. CONCLUSÃO: A versão portuguesa do KOOS, quando aplicada a desportistas com lesão no joelho, mostrou ser um instrumento de medida válido, fiável e com poder de resposta

Temperature effect on (2+1) experimental Kardar-Parisi-Zhang growth

We report on the effect of substrate temperature (T) on both local structure and long-wavelength fluctuations of polycrystalline CdTe thin films deposited on Si(001). A strong T-dependent mound evolution is observed and explained in terms of the energy barrier to inter-grain diffusion at grain boundaries, as corroborated by Monte Carlo simulations. This leads to transitions from uncorrelated growth to a crossover from random-to-correlated growth and transient anomalous scaling as T increases. Due to these finite-time effects, we were not able to determine the universality class of the system through the critical exponents. Nevertheless, we demonstrate that this can be circumvented by analyzing height, roughness and maximal height distributions, which allow us to prove that CdTe grows asymptotically according to the Kardar-Parisi-Zhang (KPZ) equation in a broad range of T. More important, one finds positive (negative) velocity excess in the growth at low (high) T, indicating that it is possible to control the KPZ non-linearity by adjusting the temperature.Comment: 6 pages, 5 figure

Graviton resonances on deformed branes

Plane wave solutions of Schrodinger-like equations obtained from the metric perturbations in 5D braneworld scenarios can present resonant modes. The search for those structures is important because they can provide us massive modes with not suppressed couplings with the membrane. We propose in this paper the study of graviton Kaluza-Klein spectrum in a special kind of membrane that possesses internal structure. The interest in study of these deformed defects is because they have a more rich internal structure that has implications in the matter-energy density along the extra dimensions an this produces a space-time background whose curvature has a splitting, if compared to the usual kink-like models. Such models arise from $(4,1)$-branes constructed with one scalar field coupled with gravity where we find two-kink solutions from deformations of a $\phi^4$ potential. The main objective of this work is to observe the effects of deformation process in the resonant modes as well as in the coupling between the graviton massive modes and the brane.Comment: 7 pages, 3 figures. To appear in Europhysics Letters. arXiv admin note: text overlap with arXiv:0912.402

Spin-glass behaviour on random lattices

The ground-state phase diagram of an Ising spin-glass model on a random graph with an arbitrary fraction $w$ of ferromagnetic interactions is analysed in the presence of an external field. Using the replica method, and performing an analysis of stability of the replica-symmetric solution, it is shown that $w=1/2$, correponding to an unbiased spin glass, is a singular point in the phase diagram, separating a region with a spin-glass phase ($w<1/2$) from a region with spin-glass, ferromagnetic, mixed, and paramagnetic phases ($w>1/2$)