5,511 research outputs found
U.S. banks, competition, and the Mexican banking system: how much will NAFTA matter?
Bank competition ; North American Free Trade Agreement ; Mexico
Relative entropy as a measure of inhomogeneity in general relativity
We introduce the notion of relative volume entropy for two spacetimes with
preferred compact spacelike foliations. This is accomplished by applying the
notion of Kullback-Leibler divergence to the volume elements induced on
spacelike slices. The resulting quantity gives a lower bound on the number of
bits which are necessary to describe one metric given the other. For
illustration, we study some examples, in particular gravitational waves, and
conclude that the relative volume entropy is a suitable device for quantitative
comparison of the inhomogeneity of two spacetimes.Comment: 15 pages, 7 figure
Flux Compactifications: Stability and Implications for Cosmology
We study the dynamics of the size of an extra-dimensional manifold stabilised
by fluxes. Inspecting the potential for the 4D field associated with this size
(the radion), we obtain the conditions under which it can be stabilised and
show that stable compactifications on hyperbolic manifolds necessarily have a
negative four-dimensional cosmological constant, in contradiction with
experimental observations. Assuming compactification on a positively curved
(spherical) manifold we find that the radion has a mass of the order of the
compactification scale, M_c, and Planck suppressed couplings. We also show that
the model becomes unstable and the extra dimensions decompactify when the
four-dimensional curvature is higher than a maximum value. This in particular
sets an upper bound on the scale of inflation in these models: V_max \sim M_c^2
M_P^2, independently of whether the radion or other field is responsible for
inflation. We comment on other possible contributions to the radion potential
as well as finite temperature effects and their impact on the bounds obtained.Comment: 16 pages, 1 figure, LaTeX; v2: typos fixed and references adde
Macroscopic Quantum Phase Interference in Antiferromagnetic Particles
The tunnel splitting in biaxial antiferromagnetic particles is studied with a
magnetic field applied along the hard anisotropy axis. We observe the
oscillation of tunnel splitting as a function of the magnetic field due to the
quantum phase interference of two tunneling paths of opposite windings. The
oscillation is similar to the recent experimental result with Fe}\textrm{\
molecular clusters.}Comment: 8 pages, 2 postscript figures, to appear in J. Phys.: Condes. Matte
Nonadiabatic Landau Zener tunneling in Fe_8 molecular nanomagnets
The Landau Zener method allows to measure very small tunnel splittings \Delta
in molecular clusters Fe_8. The observed oscillations of \Delta as a function
of the magnetic field applied along the hard anisotropy axis are explained in
terms of topological quantum interference of two tunnel paths of opposite
windings. Studies of the temperature dependence of the Landau Zener transition
rate P gives access to the topological quantum interference between exited spin
levels. The influence of nuclear spins is demonstrated by comparing P of the
standard Fe_8 sample with two isotopically substituted samples. The need of a
generalized Landau Zener transition rate theory is shown.Comment: 5 pages, 6 figure
Low-Temperature Quantum Relaxation in a System of Magnetic Nanomolecules
We argue that to explain recent resonant tunneling experiments on crystals of
Mn and Fe, particularly in the low-T limit, one must invoke dynamic
nuclear spin and dipolar interactions. We show the low-, short-time
relaxation will then have a form, where depends on the
nuclear , on the tunneling matrix element between the two
lowest levels, and on the initial distribution of internal fields in the
sample, which depends very strongly on sample shape. The results are directly
applicable to the system. We also give some results for the long-time
relaxation.Comment: 4 pages, 3 PostScript figures, LaTe
Synthesis and investigation of the spectral-luminescence characteristics of powder based on zinc oxide
ZnO and ZnAlO composites were synthesized by thermal decomposition of a precursor salt, dried at 200 °C and annealed at 400 and 600 °C, respectively. It was shown that pH and temperature of synthesis has great influence on the spectral-luminescence properties of samples
- …