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Monodisperse AuAg alloy NPs were synthesized by a one-pot approach with composition control. Oleylamine was used as the surfactant and was readily removed. The AuAg alloy NPs show the compositional dependent plasmonic absorptions and catalytic CO oxidation, indicating their great potentials as optical probes for bioimaging and as active catalyst for chemical reactions.

Monodisperse AuAg alloy nanoparticles (NPs) are made from core/shell Ag/Au NPs through Au and Ag diffusion in oleylamine. The composition of the alloy NPs is controlled by the Au shell thickness and the plasmonic absorptions can be tuned from 520 to 400 nm (see image). These alloy NPs have great potential as optical probes for biosensing and bioimaging, or as catalysts for CO oxidation.

Abstract.A model is proposed of a collapsing radiating star consisting of a shearing fluid with bulk viscosity undergoing radial heat flow with outgoing radiation. The pressure of the star, at the beginning of the collapse, is isotropic but due to the presence of the bulk viscosity the pressure becomes more and more anisotropic. The behavior of the density, pressure, mass, luminosity, the effective adiabatic index and the Kretschmann scalar is analyzed. Our work is compared to the case of a collapsing shearing fluid of a previous model, for a star with 6 M .

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A new model is proposed to a collapsing radiating star consisting of an isotropic fluid with shear viscosity undergoing radial heat flow with outgoing radiation. In a previous paper we have introduced a function time dependent into the g rr , besides the time dependent metric functions g θθ and g φφ . The aim of this work is to generalize this previous model by introducing shear viscosity and compare it to the non-viscous collapse. The behavior of the density, pressure, mass, luminosity and the effective adiabatic index is analyzed. Our work is compared to the case of a collapsing shearing fluid of a previous model, for a star with 6 M . The pressure of the star, at the beginning of the collapse, is isotropic but due to the presence of the shear the pressure becomes more and more anisotropic. The black hole is never formed because the apparent horizon formation condition is never satisfied. An observer at infinity sees a radial point source radiating exponentially until reaches the time of maximum luminosity and suddenly the star turns off. The effective adiabatic index has a very unusual behavior because we have a non-adiabatic regime in the fluid due to the heat flow.

A model is proposed of a collapsing radiating star consisting of an isotropic fluid with shear viscosity undergoing radial heat flow with outgoing radiation. The pressure of the star, at the beginning of the collapse, is isotropic but owing to the presence of the shear viscosity the pressure becomes more and more anisotropic. The behaviour of the density, pressure, mass, luminosity and the effective adiabatic index is analysed. Our work is compared to the case of a collapsing shearing fluid of a previous model, for a star with 6 M⊙.

Dynamical models of prototype gravastars are constructed and studied. The models are the Visser-Wiltshire three-layer gravastars, in which an infinitely thin spherical shell of a perfect fluid with the equation of state p = (1 − γ)σ divides the whole spacetime into two regions, where the internal region is de Sitter, and the external is Schwarzschild. When γ < 1 and Λ = 0, it is found that in some cases the models represent stable gravastars, and in some cases they represent "bounded excursion" stable gravastars, where the thin shell is oscillating between two finite radii, while in some other cases they collapse until the formation of black holes. However, when γ ≥ 1, even with Λ = 0, only black holes are found. In the phase space, the region for both stable gravastars and "bounded excursion" gravastars is very small in comparison to that of black holes, although it is not completely empty.