Intracellular demography and the dynamics of Salmonella enterica infections.

An understanding of within-host dynamics of pathogen interactions with eukaryotic cells can shape the development of effective preventive measures and drug regimes. Such investigations have been hampered by the difficulty of identifying and observing directly, within live tissues, the multiple key variables that underlay infection processes. Fluorescence microscopy data on intracellular distributions of Salmonella enterica serovar Typhimurium (S. Typhimurium) show that, while the number of infected cells increases with time, the distribution of bacteria between cells is stationary (though highly skewed). Here, we report a simple model framework for the intensity of intracellular infection that links the quasi-stationary distribution of bacteria to bacterial and cellular demography. This enables us to reject the hypothesis that the skewed distribution is generated by intrinsic cellular heterogeneities, and to derive specific predictions on the within-cell dynamics of Salmonella division and host-cell lysis. For within-cell pathogens in general, we show that within-cell dynamics have implications across pathogen dynamics, evolution, and control, and we develop novel generic guidelines for the design of antibacterial combination therapies and the management of antibiotic resistance.

Computer generated hologram with geometric occlusion using GPU-accelerated depth buffer rasterization for three-dimensional display

We present a method of rapidly producing computer-generated holograms that exhibit geometric occlusion in the reconstructed image. Conceptually, a bundle of rays is shot from every hologram sample into the object volume.We use z buffering to find the nearest intersecting object point for every ray and add its complex field contribution to the corresponding hologram sample. Each hologram sample belongs to an independent operation, allowing us to exploit the parallel computing capability of modern programmable graphics processing units (GPUs). Unlike algorithms that use points or planar segments as the basis for constructing the hologram, our algorithm's complexity is dependent on fixed system parameters, such as the number of ray-casting operations, and can therefore handle complicated models more efficiently. The finite number of hologram pixels is, in effect, a windowing function, and from analyzing the Wigner distribution function of windowed free-space transfer function we find an upper limit on the cone angle of the ray bundle. Experimentally, we found that an angular sampling distance of 0:01' for a 2:66' cone angle produces acceptable reconstruction quality. © 2009 Optical Society of America.

Computer generated hologram from point cloud using graphics processor

Computer generated holography is an extremely demanding and complex task when it comes to providing realistic reconstructions with full parallax, occlusion, and shadowing. We present an algorithm designed for data-parallel computing on modern graphics processing units to alleviate the computational burden. We apply Gaussian interpolation to create a continuous surface representation from discrete input object points. The algorithm maintains a potential occluder list for each individual hologram plane sample to keep the number of visibility tests to a minimum.We experimented with two approximations that simplify and accelerate occlusion computation. It is observed that letting several neighboring hologramplane samples share visibility information on object points leads to significantly faster computation without causing noticeable artifacts in the reconstructed images. Computing a reduced sample set via nonuniform sampling is also found to be an effective acceleration technique. © 2009 Optical Society of America.

Spatial repeatability of dynamic tyre forces generated by heavy vehicles

Road damage due to heavy vehicles is thought to be dependent on the extent to which lorries in normal traffic apply peak forces to the same locations along the road. A validated vehicle simulation is used to simulate 37 leaf-sprung articulated vehicles with parametric variations typical of vehicles in one weight class in the highway vehicle fleet. The spatial distribution of tyre forces generated by each vehicle is compared with the distribution generated by a reference vehicle, and the conditions are established for which repeated heavy loading occurs at specific points along the road. It is estimated that approximately two-thirds of vehicles in this class (a large proportion of all heavy vehicles) may contribute to a repeated pattern of road loading. It is concluded that dynamic tyre forces are a significant factor influencing road damage, compared to other factors such as tyre configuration and axle spacing.

Laminar/Turbulent Plasma Jets Generated At Reduced Pressure

Laminar do plasma jets are attractive for precisely controlled plasma-material processing. The design of a novel non-transferred plasma torch enabled the switching between turbulent and laminar plasma flows by simply changing the plasma generation parameters. Images of the plasma flows generated at different conditions are presented.

Recuperar plásticos desechables a los fines de conformar elementos constructivos de una vivienda económica como respuesta social, analizada como un problema de ingeniería industrial

Resumen: El hecho de seleccionar a los plásticos dentro de nuestro proyecto es porque son en particular, partes abundantes y visibles en la composición de los residuos generados en nuestra sede UCA Campus Rosario. Razonamos que son varias las áreas que los producen en forma cotidiana o de modo transitorio (como es el caso de eventos), a las que podemos sumar un accionar ambientalmente responsable. Ello nos impone la responsabilidad de proponer algún modo de re-utilizarlos en el diseño de ciertos elemento que los integre como materia prima, material de aporte, insumo o material auxiliar, con un amplio campo de posibilidades como es en la construcción, a partir de una mirada desde la ingeniería ambiental. La metodología de trabajo que desarrollamos implica inspeccionar la materia prima con la cual se va a trabajar, a los fines de conocerla fehacientemente, así como internalizar la posible combinación entre los distintos tipos de plásticos de acuerdo a su composición y su respuesta en la integración con otros materiales de uso tradicional, de acuerdo a experiencias reconocidas Desde una mirada lineal la educación sola no alcanza, como tampoco la tecnología ni las medidas parciales son suficientes para aliviar este tremendo desequilibrio que venimos heredando. Ante estos hechos es perentorio comprender la complejidad, actuar desde allí descubriendo la conexión invisible entre el ser humano y el medio, y los seres humanos entre sí. Debido a ello entendemos que para restaurar el medio ambiente en principio hay que comenzar por restaurar los vínculos y los ciclos que los contienen, esto implica re-ciclar.

Statistical analysis of synthetic earthquake catalogs generated by models with various levels of fault zone disorder

The stress release model, a stochastic version of the elastic rebound theory, is applied to the large events from four synthetic earthquake catalogs generated by models with various levels of disorder in distribution of fault zone strength (Ben-Zion, 1996) They include models with uniform properties (U), a Parkfield-type asperity (A), fractal brittle properties (F), and multi-size-scale heterogeneities (M). The results show that the degree of regularity or predictability in the assumed fault properties, based on both the Akaike information criterion and simulations, follows the order U, F, A, and M, which is in good agreement with that obtained by pattern recognition techniques applied to the full set of synthetic data. Data simulated from the best fitting stress release models reproduce, both visually and in distributional terms, the main features of the original catalogs. The differences in character and the quality of prediction between the four cases are shown to be dependent on two main aspects: the parameter controlling the sensitivity to departures from the mean stress level and the frequency-magnitude distribution, which differs substantially between the four cases. In particular, it is shown that the predictability of the data is strongly affected by the form of frequency-magnitude distribution, being greatly reduced if a pure Gutenburg-Richter form is assumed to hold out to high magnitudes.

Sediment incipience in turbulence generated in a square tank by a vertically oscillating grid

The failure of hydraulic structures in many estuaries and coastal regions around the world has been attributed to sediment transport and local scour. The sediment incipience in homogenous turbulence generated by oscillating grid is studied in this paper. The turbulent flow is measured by particle tracer velocimetry (PTV) technique. The integral length scale and time scale of turbulence are obtained. The turbulent flow near the wall is measured by local optical magnification. The sediment incipience is described by static theory. The relationship of probability of sediment incipience and the turbulent kinetic energy were obtained experimentally and theoretically. The distribution of the turbulent kinetic energy near the wall is found to obey the power law and the turbulent energy is further identified as the dynamic mechanism of sediment incipience.