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)

Flexible ring slosh damping baffle Patent

Flexible ring slosh damping baffle for spacecraft fuel tan

Additive for zinc electrodes

A zinc electrode for alkaline cells includes up to about ten percent by weight of Ba(OH)2.8H2O with about five percent being preferred. The zinc electrode may or may not be amalgamated with mercury

Magnetic spin excitations in diluted ferromagnetic systems: the case of Ga1−xMnxAsGa_{1-x}Mn_{x}As

We propose a theory which allow to calculate the magnetic excitation spectrum in diluted ferromagnetic systems. The approach is rather general and based on the Self-Consistent local Random Phase Approximation in which disorder (dilution) and thermal fluctuations are properly treated. To illustrate its reliability and accuracy we calculate the magnetic excitation in the diluted III-V magnetic semiconductor $Ga_{1-x}Mn_{x}As$. It is shown that dilution has a drastic effect on the excitation spectrum, indeed well defined magnon excitations exist only in a small region of the Brillouin zone centered around the $\Gamma$ point. We also calculate the spin stiffness in optimally annealed sample as a function of $Mn^{2+}$ concentration. A comparison to available measurements is done. We find a very good agreement for both the Curie temperature and the spin stiffness measured in well annealed samples and provide a plausible explanation for the very small values measured in as grown samples.Comment: The manuscript has been modified, 4 figures are included. Accepted for publication in Eur. Phys. Let

On the Form of the Spitzer Leavitt Law and its Dependence on Metallicity

The form and metallicity-dependence of Spitzer mid-infrared Cepheid relations are a source of debate. Consequently, Spitzer 3.6 and 4.5 um period-magnitude and period-color diagrams were re-examined via robust routines, thus providing the reader an alternative interpretation to consider. The relations (nearly mean-magnitude) appear non-linear over an extensive baseline (0.45< logPo <2.0), particularly the period-color trend, which to first-order follows constant (3.6-4.5) color for shorter-period Cepheids and may transition into a bluer convex trough at longer-periods. The period-magnitude functions can be described by polynomials (e.g., [3.6 um]=Ko-(3.071+-0.059) logPo-(0.120+-0.032)logPo^2), and Cepheid distances computed using 3.6 and 4.5 um relations agree and the latter provides a first-order consistency check (CO sampled at 4.5 um does not seriously compromise those distances). The period-magnitude relations appear relatively insensitive to metallicity variations ([Fe/H]~0 to -0.75), a conclusion inferred partly from comparing galaxy distances established from those relations and NED-D (n>700), yet a solid conclusion awaits comprehensive mid-infrared observations for metal-poor Cepheids in IC 1613 ([Fe/H] -1). The Cepheid-based distances were corrected for dust obscuration using a new ratio (i.e., A(3.6)/E(B-V)=0.18+-0.06) deduced from GLIMPSE (Spitzer) data.Comment: To appear in Ap

On approximating two distributions from a single complex-valued function

We consider the problem of approximating two, possibly unrelated probability distributions from a single complex-valued function $\psi$ and its Fourier transform. We show that this problem always has a solution within a specified degree of accuracy, provided the distributions satisfy the necessary regularity conditions. We describe the algorithm and construction of $\psi$ and provide examples of approximating several pairs of distributions using the algorithm.Comment: 9 pages, 4 figure

Fano-Feshbach resonances in two-channel scattering around exceptional points

It is well known that in open quantum systems resonances can coalesce at an exceptional point, where both the energies {\em and} the wave functions coincide. In contrast to the usual behaviour of the scattering amplitude at one resonance, the coalescence of two resonances invokes a pole of second order in the Green's function, in addition to the usual first order pole. We show that the interference due to the two pole terms of different order gives rise to patterns in the scattering cross section which closely resemble Fano-Feshbach resonances. We demonstrate this by extending previous work on the analogy of Fano-Feshbach resonances to classical resonances in a system of two driven coupled damped harmonic oscillators.Comment: 8 pages, 5 figures, submitted to J. Phys.