856,096 research outputs found
Decoherence at zero temperature
Most discussions of decoherence in the literature consider the
high-temperature regime but it is also known that, in the presence of
dissipation, decoherence can occur even at zero temperature. Whereas most
previous investigations all assumed initial decoupling of the quantum system
and bath, we consider that the system and environment are entangled at all
times. Here, we discuss decoherence for a free particle in an initial
Schr\"{o}dinger cat state. Memory effects are incorporated by use of the single
relaxation time model (since the oft-used Ohmic model does not give physically
correct results)
An in-medium full-folding model approach to quasielastic (p,n) charge-exchange reactions
A microscopic description of the quasielastic (p,n) charge-exchange reaction
(here, charge-exchange scattering between analogue states) is presented and
discussed. Emphasis is focused on the spin-isospin structure of the
projectile-target coupling. The model is a coupled-channel extension of the
full-folding optical model approach (OMP) developed for nucleon elastic
scattering, where emphasis is placed on retaining the genuine off-shell
behavior of realistic effective interactions in the nuclear medium. The
resulting non-local optical potentials are applied to the calculation of (p,n)
differential cross sections, with particular emphasis on small-angle Fermi
() cross-sections to isobaric analog states. These parameter-free
results provide a reasonable description of the C(p,n)-data at proton
energies above 100 MeV, but deteriorate for heavier targets. These
shortcomings are analyzed and possible ways to correct them are discussed.Comment: 20 pages plus 10 figures. Accepted for publication in Phys. Rev.
Mobile Bay turbidity study
The termination of studies carried on for almost three years in the Mobile Bay area and adjacent continental shelf are reported. The initial results concentrating on the shelf and lower bay were presented in the interim report. The continued scope of work was designed to attempt a refinement of the mathematical model, assess the effectiveness of optical measurement of suspended particulate material and disseminate the acquired information. The optical characteristics of particulate solutions are affected by density gradients within the medium, density of the suspended particles, particle size, particle shape, particle quality, albedo, and the angle of refracted light. Several of these are discussed in detail
Lorentz Transformation of Blackbody Radiation
We present a simple calculation of the Lorentz transformation of the spectral
distribution of blackbody radiation at temperature T. Here we emphasize that T
is the temperature in the blackbody rest frame and does not change. We thus
avoid the confused and confusing question of how temperature transforms. We
show by explicit calculation that at zero temperature the spectral distribution
is invariant. At finite temperature we find the well known result familiar in
discussions of the the 2.7! K cosmic radiation.Comment: 6 page
Note on the derivative of the hyperbolic cotangent
In a letter to Nature (Ford G W and O'Connell R F 1996 Nature 380 113) we
presented a formula for the derivative of the hyperbolic cotangent that differs
from the standard one in the literature by an additional term proportional to
the Dirac delta function. Since our letter was necessarily brief, shortly after
its appearance we prepared a more extensive unpublished note giving a detailed
explanation of our argument. Since this note has been referenced in a recent
article (Estrada R and Fulling S A 2002 J. Phys. A: Math. Gen. 35 3079) we
think it appropriate that it now appear in print. We have made no alteration to
the original note
Mission 73 - Summary and data catalog
Earth resources program geographic applications program summary, recommendations, and data catalog for remote sensor mission 7
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