11,939 research outputs found
Speed of light on rotating platforms
It is often taken for granted that on board a rotating disk it is possible to
operate a \QTR{it}{global}3+1 splitting of space-time, such that both lengths
and time intervals are \QTR{it}{uniquely} defined in terms of measurements
performed by real rods and real clocks at rest on the platform. This paper
shows that this assumption, although widespread and apparently trivial, leads
to an anisotropy of the velocity of two light beams travelling in opposite
directions along the rim of the disk; which in turn implies some recently
pointed out paradoxical consequences undermining the self-consistency of the
Special Theory of Relativity (SRT). A correct application of the SRT solves the
problem and recovers complete internal consistency for the theory. As an
immediate consequence, it is shown that the Sagnac effect only depends on the
non homogeneity of time on the platform and has nothing to do with any
anisotropy of the speed of light along the rim of the disk, contrary to an
incorrect but widely supported idea.Comment: Latex, 2 figure
Density Matrix Renormalization Group for Dummies
We describe the Density Matrix Renormalization Group algorithms for time
dependent and time independent Hamiltonians. This paper is a brief but
comprehensive introduction to the subject for anyone willing to enter in the
field or write the program source code from scratch.Comment: 29 pages, 9 figures. Published version. An open source version of the
code can be found at http://qti.sns.it/dmrg/phome.htm
A continuous population of variable stars up to about 1.5 mag above the horizontal branch?
Increasing samples of pulsating variable stars populating the classical
instability strip from the horizontal branch to a few magnitudes brighter are
being found in several Local Group galaxies, irrespective of the galaxy
morphological type. We will review the observational scenario focusing in
particular on the Anomalous Cepheids and related objects.Comment: 5 pages, 2 figures, invited review in JENAM 2003, "Minisymposium:
Asteroseismology and Stellar Evolution", Communications in Asteroseismology,
in pres
Quantum Interference Effects in Spacetime of Slowly Rotating Compact Objects in Braneworld
The phase shift a neutron interferometer caused by the gravitational field
and the rotation of the earth is derived in a unified way from the standpoint
of general relativity. General relativistic quantum interference effects in the
slowly rotating braneworld as the Sagnac effect and phase shift effect of
interfering particle in neutron interferometer are considered. It was found
that in the case of the Sagnac effect the influence of brane parameter is
becoming important due to the fact that the angular velocity of the locally non
rotating observer must be larger than one in the Kerr space-time. In the case
of neutron interferometry it is found that due to the presence of the parameter
an additional term in the phase shift of interfering particle emerges
from the results of the recent experiments we have obtained upper limit for the
tidal charge as . Finally, as an example, we
apply the obtained results to the calculation of the (ultra-cold neutrons)
energy level modification in the braneworld.Comment: 12 pages, 2 figure
Kinetics of first-order phase transitions from microcanonical thermostatistics
More than a century has passed since van't Hoff and Arrhenius formulated
their celebrated rate theories, but there are still elusive aspects in the
temperature-dependent phase transition kinetics of molecular systems. Here I
present a theory based on microcanonical thermostatistics that establishes a
simple and direct temperature dependence for all rate constants, including the
forward and the reverse rate constants, the equilibrium constant, and the
nucleation rate. By considering a generic model that mimic the microcanonical
temperature of molecular systems in a region close to a first-order phase
transition, I obtain shape-free relations between kinetics and thermodynamics
physical quantities which are validated through stochastic simulations.
Additionally, the rate theory is applied to results obtained from protein
folding and ice nucleation experiments, demonstrating that the expressions
derived here can be used to describe the experimental data of a wide range of
molecular systems.Comment: 22 pages, 5 figure
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