757 research outputs found
On some singularities of the correlation functions that determine neutrino opacities
Certain perturbation graphs in the calculation of the effects of the medium
on neutrino scattering in supernova matter have a nonintegrable singularity in
a physical region. A number of papers have addressed the apparent pathology
through an ansatz that invokes higher order (rescattering) effects. Taking the
Gamow-Teller terms as an example, we display an expression for the spin-spin
correlation function that determines the cross-sections. It is clear from the
form that there are no pathologies in the order by order perturbation
expansion. Explicit formulae are given for a simple case, leading to an answer
that is very different from one given by other authors.Comment: 8 page
Femtosecond laser impact on calcium phosphate bioceramics assessed by micro-Raman spectroscopy and osteoblastic behaviour
The present work is an investigation of the biological response to the presence of grooves 3 µm deep, 15 µm wide and spaced by 100 µm, produced with femtosecond laser on ß-tricalcium phosphate (ß-TCP). The heat affected zone generated by the laser irradiation was investigated. Micro-Raman spectroscopy showed a transformation from ß-TCP phase into a-TCP phase, localised inside the grooves. The X Ray Diffraction analyses, correlated with micro-Raman data, confirmed that the use of femtosecond pulsed laser enables to limit the thermal impact. A selection of optimised process parameters allowed to obtain ß-TCP micro-patterned surfaces avoiding any phase transformation. The increase of the wettability with the micro-patterning, compared to smooth surfaces, was highlighted. An improvement of the osteoblastic proliferation was also demonstrated. Finally, the tendency of cell elongation along the grooves direction showed the ability of osteoblastic cells to adapt their morphology to the support topography on which they grow.The authors are grateful to the JECS Trust for funding the visit of Marie Lasgorceix to the Laboratory INEB (Contract N°2015106). Marie Lasgorceix also acknowledges the Walloon Region for financial support, within the “BEWARE” program (convention n°1510392) co-funded by Wallonia and European Union (FP7 – Marie Curie Actions) . The authors are grateful to Dr Sylvain Desprez (Materia Nova, Mons, Belgium) for micro-Raman analyses. This publication is based on the work of COST Action MP1301, funded by COST (European Cooperation in Science and Technology) www.cost.eu
The integrin αvβ8 mediates epithelial homeostasis through MT1-MMP–dependent activation of TGF-β1
Întegrins, matrix metalloproteases (MMPs), and the cytokine TGF-β have each been implicated in homeostatic cell behaviors such as cell growth and matrix remodeling. TGF-β exists mainly in a latent state, and a major point of homeostatic control is the activation of TGF-β. Because the latent domain of TGF-β1 possesses an integrin binding motif (RGD), integrins have the potential to sequester latent TGF-β (SLC) to the cell surface where TGF-β activation could be locally controlled. Here, we show that SLC binds to αvβ8, an integrin expressed by normal epithelial and neuronal cells in vivo. This binding results in the membrane type 1 (MT1)-MMP–dependent release of active TGF-β, which leads to autocrine and paracrine effects on cell growth and matrix production. These data elucidate a novel mechanism of cellular homeostasis achieved through the coordination of the activities of members of three major gene families involved in cell–matrix interactions
Percolation properties of the 2D Heisenberg model
We analyze the percolation properties of certain clusters defined on
configurations of the 2--dimensional Heisenberg model. We find that, given any
direction \vec{n} in O(3) space, the spins almost perpendicular to \vec{n} form
a percolating cluster. This result gives indications of how the model can avoid
a previously conjectured Kosterlitz-Thouless phase transition at finite
temperature T.Comment: 4 pages, 3 eps figures. Revised version (more clear abstract, some
new references
Second Order Thermal Corrections to Electron Wavefunction
Second order perturbative corrections to electron wavefunction are calculated
here at generalized temperature, for the first time. This calculation is
important to prove the renormalizeability of QED through order by order
cancellation of singularities at higher order. This renormalized wavefunction
could be used to calculate the particle processes in the extremely hot systems
such as the very early universe and the stellar cores. We have to re-write the
second order thermal correction to electron mass in a convenient way to be able
to calculate the wavefunction renormalization constant. A procedure for
integrations of hot loop momenta before the cold loop momenta integration is
maintained throughout to be able to remove hot singularities in an appropriate
way. Our results, not only includes the intermediate temperatures T m (where m
is the electron mass), the limits of high temperature T>>m and low temperature
T<<m are also retrievable. A comparison is also done with the existing results.Comment: 12 Pages and 1 figure; Submitted for publicatio
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