294 research outputs found
On the impact of controlled wall roughness shape on the flow of a soft-material
We explore the impact of geometrical corrugations on the near-wall flow
properties of a soft-material driven in a confined rough microchannel. By means
of numerical simulations, we perform a quantitative analysis of the relation
between the flow rate and the wall stress for a number of
setups, by changing both the roughness values as well as the roughness shape.
Roughness suppresses the flow, with the existence of a characteristic value of
at which flow sets in. Just above the onset of flow, we
quantitatively analyze the relation between and . While for
smooth walls a linear dependency is observed, steeper behaviours are found to
set in by increasing wall roughness. The variation of the steepness, in turn,
depends on the shape of the wall roughness, wherein gentle steepness changes
are promoted by a variable space localization of the roughness
Internal dynamics and activated processes in Soft-Glassy materials
Plastic rearrangements play a crucial role in the characterization of
soft-glassy materials, such as emulsions and foams. Based on numerical
simulations of soft-glassy systems, we study the dynamics of plastic
rearrangements at the hydrodynamic scales where thermal fluctuations can be
neglected. Plastic rearrangements require an energy input, which can be either
provided by external sources, or made available through time evolution in the
coarsening dynamics, in which the total interfacial area decreases as a
consequence of the slow evolution of the dispersed phase from smaller to large
droplets/bubbles. We first demonstrate that our hydrodynamic model can
quantitatively reproduce such coarsening dynamics. Then, considering
periodically oscillating strains, we characterize the number of plastic
rearrangements as a function of the external energy-supply, and show that they
can be regarded as activated processes induced by a suitable "noise" effect.
Here we use the word noise in a broad sense, referring to the internal
non-equilibrium dynamics triggered by spatial random heterogeneities and
coarsening. Finally, by exploring the interplay between the internal
characteristic time-scale of the coarsening dynamics and the external
time-scale associated with the imposed oscillating strain, we show that the
system exhibits the phenomenon of stochastic resonance, thereby providing
further credit to the mechanical activation scenario.Comment: 21 Pages, 9 figure
Inter-species variation in the oligomeric states of the higher plant Calvin cycle enzymes glyceraldehyde-3-phosphate dehydrogenase and phosphoribulokinase
In darkened leaves the Calvin cycle enzymes glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and phosphoribulokinase (PRK) form a regulatory multi-enzyme complex with the small chloroplast protein CP12. GAPDH also forms a high molecular weight regulatory mono-enzyme complex. Given that there are different reports as to the number and subunit composition of these complexes and that enzyme regulatory mechanisms are known to vary between species, it was reasoned that protein-protein interactions may also vary between species. Here, this variation is investigated. This study shows that two different tetramers of GAPDH (an A2B2 heterotetramer and an A4 homotetramer) have the capacity to form part of the PRK/GAPDH/CP12 complex. The role of the PRK/GAPDH/CP12 complex is not simply to regulate the 'non-regulatory' A4 GAPDH tetramer. This study also demonstrates that the abundance and nature of PRK/GAPDH/CP12 interactions are not equal in all species and that whilst NAD enhances complex formation in some species, this is not sufficient for complex formation in others. Furthermore, it is shown that the GAPDH mono-enzyme complex is more abundant as a 2(A2B2) complex, rather than the larger 4(A2B2) complex. This smaller complex is sensitive to cellular metabolites indicating that it is an important regulatory isoform of GAPDH. This comparative study has highlighted considerable heterogeneity in PRK and GAPDH protein interactions between closely related species and the possible underlying physiological basis for this is discussed. © 2011 The Author(s)
Turbulent pair dispersion of inertial particles
The relative dispersion of pairs of inertial particles in incompressible,
homogeneous, and isotropic turbulence is studied by means of direct numerical
simulations at two values of the Taylor-scale Reynolds number and 400. The evolution of both heavy and light particle pairs is
analysed at varying the particle Stokes number and the fluid-to-particle
density ratio. For heavy particles, it is found that turbulent dispersion is
schematically governed by two temporal regimes. The first is dominated by the
presence, at large Stokes numbers, of small-scale caustics in the particle
velocity statistics, and it lasts until heavy particle velocities have relaxed
towards the underlying flow velocities. At such large scales, a second regime
starts where heavy particles separate as tracers particles would do. As a
consequence, at increasing inertia, a larger transient stage is observed, and
the Richardson diffusion of simple tracers is recovered only at large times and
large scales. These features also arise from a statistical closure of the
equation of motion for heavy particle separation that is proposed, and which is
supported by the numerical results. In the case of light particles with high
density ratios, strong small-scale clustering leads to a considerable fraction
of pairs that do not separate at all, although the mean separation increases
with time. This effect strongly alters the shape of the probability density
function of light particle separations.Comment: 28 pages, 15 figure
Numerical simulations of compressible Rayleigh-Taylor turbulence in stratified fluids
We present results from numerical simulations of Rayleigh-Taylor turbulence,
performed using a recently proposed lattice Boltzmann method able to describe
consistently a thermal compressible flow subject to an external forcing. The
method allowed us to study the system both in the nearly-Boussinesq and
strongly compressible regimes. Moreover, we show that when the stratification
is important, the presence of the adiabatic gradient causes the arrest of the
mixing process.Comment: 15 pages, 11 figures. Proceedings of II Conference on Turbulent
Mixing and Beyond (TMB-2009
Bovine papillomavirus 1 gets out of the flock: Detection in an ovine wart in Sicily
A proliferative cauliflower lesion was excised from the udder of a sheep. Histological investigation confirmed the macroscopic classification of the lesion as a papilloma, without any fibroblastic proliferation. PCR revealed the presence of bovine papillomavirus (BPV), which was further confirmed by the identification of a Deltapapillomavirus 4 by Next Generation Sequencing analysis. This was subsequently classified as bovine papillomavirus type 1. Negative staining electron microscopy (EM) analyses produced negative test results for papillomavirus particles. RNA in situ hybridization (ISH) confirmed the presence of BPV-1. The results further confirm the ability of BPVs belonging to the Deltapapillomavirus genus to infect distantly related species and to cause lesions that are different from sarcoids
Severe cutaneous neoformations in animals caused by co-infection of orf virus and orthopoxvirus: A possible zoonosis?
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