I revisit the question of the adiabaticity of initial conditions for cosmological perturbations in view of the 3–year WMAP data. I focus on the simplest alternative to pure adiabatic conditions, namely a superposition of the adiabatic mode and one of the 3 possible isocurvature modes, with the same spectral index as the adiabatic component. I discuss findings in terms of posterior bounds on the...

I revisit the question of the adiabaticity of initial conditions for cosmological perturbations in view of the 3-yr Wilkinson Microwave Anisotropy Probe (WMAP) data. I focus on the simplest alternative to purely adiabatic conditions, namely a superposition of the adiabatic mode and one of the three possible isocurvature modes, with the same spectral index as the adiabatic component. I discuss f...

A one-parameter family of time dependent adiabatic indices is introduced for any given type of cosmological fluid of constant adiabatic index by a mathematical method belonging to the class of Darboux transformations. The procedure works for zero cosmological constant at the price of introducing a new constant parameter related to the time dependence of the adiabatic index. I argue that these a...

Richtmyer–Meshkov Instability is an instability that develops at the interface between fluids of distinct acoustic impedance when impacted by a shock wave. Its applications include inertial confinement fusion, supernovae explosions, and evolution blast waves. We systematically study effect adiabatic index on dynamics strong-shock-driven flows, particularly amount energy available for interfacia...

We discuss the afterglow emission from a relativistic jet that is initially in the radiative regime in which the accelerated electrons are fast cooling. We note that such a “semiradiative” jet decelerates faster than an adiabatic jet does. We also take into account the effect of strong inverse-Compton scattering on the cooling frequency in the synchrotron component and therefore on the light cu...

A new, efficient adiabatic in-plane fiber-to-chip coupler design is proposed. In this design, the light from the fiber is coupled into a low-index waveguide with matching mode size. The mode is first adiabatically reduced in size with a rib taper, and then transferred into a high-index (e.g. silicon) waveguide with an inverse taper. The two-stage design allows to reduce the coupler length multi...

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A loss in smoothness of a switching process decreases the accuracy of an adiabatic invariant. Here we show that for classical Hamiltonian systems the degree of smoothness can be observed in the signal.