626 research outputs found
Dynamics of viscous dissipative gravitational collapse: A full causal approach
The Misner and Sharp approach to the study of gravitational collapse is
extended to the viscous dissipative case in, both, the streaming out and the
diffusion approximations. The dynamical equation is then coupled to causal
transport equations for the heat flux, the shear and the bulk viscosity, in the
context of Israel--Stewart theory, without excluding the thermodynamics
viscous/heat coupling coefficients. The result is compared with previous works
where these later coefficients were neglected and viscosity variables were not
assumed to satisfy causal transport equations. Prospective applications of this
result to some astrophysical scenarios are discussed.Comment: 22 pages Latex. To appear in Int. J. Mod. Phys. D. Typos correcte
Some analytical models of radiating collapsing spheres
We present some analytical solutions to the Einstein equations, describing
radiating collapsing spheres in the diffusion approximation. Solutions allow
for modeling physical reasonable situations. The temperature is calculated for
each solution, using a hyperbolic transport equation, which permits to exhibit
the influence of relaxational effects on the dynamics of the system.Comment: 17 pages Late
Pore-size dependence of the thermal conductivity of porous silicon : a phonon hydrodynamic approach
Phononhydrodynamics is used to analyze the influence of porosity and of pore size on reduction in thermal conductivity in porous silicon, with respect to crystalline silicon. The expressions predict that the thermal conductivity is lower for higher porosity and for smaller pore radius, as a consequence of phononballisticeffects. The theoretical results describe experimental data better than the assumption that they only depend on porosity
Modelling the transient processes produced under heavy particle irradiation
A new model for the thermal spike produced by the nuclear energy loss, as
source of transient processes, is derived analytically, for power law
dependences of the diffusivity on temperature, as solution of the heat
equation. The contribution of the ionizing energy loss to the spike is not
included. The range of validity of the model is analysed, and the results are
compared with numerical solutions obtained in the frame of the previous model
of the authors, which takes into account both nuclear and ionization energy
losses, as well as the coupling between the two subsystems in crystalline
semiconductors. Particular solutions are discussed and the errors induced by
these approximations are analysed.Comment: 13 page
Development of a polymeric piezoelectric C-block actuator using hybrid optimization technique
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76810/1/AIAA-13031-236.pd
Tissue-specific inducible expression of antimicrobial peptide genes in Drosophila surface epithelia
The production of antimicrobial peptides is an important aspect of host defense in multicellular organisms. In Drosophila, seven antimicrobial peptides with different spectra of activities are synthesized by the fat body during the immune response and secreted into the hemolymph. Using GFP reporter transgenes, we show here that all seven Drosophila antimicrobial peptides can be induced in surface epithelia in a tissue-specific manner. The imd gene plays a critical role in the activation of this local response to infection. In particular, drosomycin expression, which is regulated by the Toll pathway during the systemic response, is regulated by imd in the respiratory tract, thus demonstrating the existence of distinct regulatory mechanisms for local and systemic induction of antimicrobial peptide genes in Drosophila
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