97,356 research outputs found
Comparison of differential gain in single quantum well and bulk double heterostructure lasers
The differential gain in single quantum well and bulk double heterostructure lasers is compared. In variance with previous predictions, no differential gain enhancement is found in single quantum well structure lasers at room temperature. Only at low temperatures do the quantum well lasers possess higher differential gain than bulk double heterostructure lasers. The results have important implications in the area of high speed phenomena for these devices
Refining MOND interpolating function and TeVeS Lagrangian
The phenomena customly called Dark Matter or Modified Newtonian Dynamics
(MOND) have been argued by Bekenstein (2004) to be the consequences of a
covariant scalar field, controlled by a free function (related to the MOND
interpolating function) in its Lagrangian density. In the context of this
relativistic MOND theory (TeVeS), we examine critically the interpolating
function in the transition zone between weak and strong gravity. Bekenstein's
toy model produces too gradually varying functions and fits rotation curves
less well than the standard MOND interpolating function. However, the latter
varies too sharply and implies an implausible external field effect (EFE).
These constraints on opposite sides have not yet excluded TeVeS, but made the
zone of acceptable interpolating functions narrower. An acceptable "toy"
Lagrangian density function with simple analytical properties is singled out
for future studies of TeVeS in galaxies. We also suggest how to extend the
model to solar system dynamics and cosmology, and compare with strong lensing
data (see also astro-ph/0509590).Comment: accepted for publication in ApJ Letter
A comparison of amplitude-phase coupling and linewidth enhancement in semiconductor quantum-well and bulk lasers
The amplitude-phase coupling factor α (linewidth enhancement factor) is compared for typical semiconductor quantum-well and bulk double heterostructure lasers. As a direct consequence of the reduction of the differential gain, there is no reduction of α in single-quantum-well lasers compared to bulk lasers. The number of quantum wells strongly affects the amplitude-phase coupling in quantum-well lasers. It is shown that the interband transition induced amplitude-phase coupling dominates that induced by the plasma effect of carriers in typical quantum-well lasers. By considering the spontaneous emission factor in the spectral linewidth, the authors show that there is an optimal number of quantum wells for achieving the narrowest spectral linewidth
Short-coherence length superconductivity in the Attractive Hubbard Model in three dimensions
We study the normal state and the superconducting transition in the
Attractive Hubbard Model in three dimensions, using self-consistent
diagrammatics. Our results for the self-consistent -matrix approximation are
consistent with 3D-XY power-law critical scaling and finite-size scaling. This
is in contrast to the exponential 2D-XY scaling the method was able to capture
in our previous 2D calculation. We find the 3D transition temperature at
quarter-filling and to be . The 3D critical regime is much
narrower than in 2D and the ratio of the mean-field transition to is
about 5 times smaller than in 2D. We also find that, for the parameters we
consider, the pseudogap regime in 3D (as in 2D) coincides with the critical
scaling regime.Comment: 4 pages, 5 figure
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