10,965 research outputs found
Dirac versus Reduced Quantization of the Poincar\'{e} Symmetry in Scalar Electrodynamics
The generators of the Poincar\'{e} symmetry of scalar electrodynamics are
quantized in the functional Schr\"{o}dinger representation. We show that the
factor ordering which corresponds to (minimal) Dirac quantization preserves the
Poincar\'{e} algebra, but (minimal) reduced quantization does not. In the
latter, there is a van Hove anomaly in the boost-boost commutator, which we
evaluate explicitly to lowest order in a heat kernel expansion using zeta
function regularization. We illuminate the crucial role played by the gauge
orbit volume element in the analysis. Our results demonstrate that preservation
of extra symmetries at the quantum level is sometimes a useful criterion to
select between inequivalent, but nevertheless self-consistent, quantization
schemes.Comment: 24 page
Quasistationary binary inspiral. I. Einstein equations for the two Killing vector spacetime
The geometry of two infinitely long lines of mass moving in a fixed circular
orbit is considered as a toy model for the inspiral of a binary system of
compact objects due to gravitational radiation. The two Killing fields in the
toy model are used, according to a formalism introduced by Geroch, to describe
the geometry entirely in terms of a set of tensor fields on the two-manifold of
Killing vector orbits. Geroch's derivation of the Einstein equations in this
formalism is streamlined and generalized. The explicit Einstein equations for
the toy model spacetime are derived in terms of the degrees of freedom which
remain after a particular choice of gauge.Comment: 37 pages, REVTeX, one PostScript Figure included with epsfig; minor
formatting changes and copyright notice added for journal publicatio
TDP-43 regulates drosophila neuromuscular junctions growth by modulating futsch/MAP1B levels and synaptic microtubules organization
TDP-43 is an evolutionarily conserved RNA binding protein recently associated with the pathogenesis of different neurological diseases. At the moment, neither its physiological role in vivo nor the mechanisms that may lead to neurodegeneration are well known. Previously, we have shown that TDP-43 mutant flies presented locomotive alterations and structural defects at the neuromuscular junctions. We have now investigated the functional mechanism leading to these phenotypes by screening several factors known to be important for synaptic growth or bouton formation. As a result we found that alterations in the organization of synaptic microtubules correlate with reduced protein levels in the microtubule associated protein futsch/MAP1B. Moreover, we observed that TDP-43 physically interacts with futsch mRNA and that its RNA binding capacity is required to prevent futsch down regulation and synaptic defects. © 2011 Godena et al
Complete positivity and entangled degrees of freedom
We study how some recently proposed noncontextuality tests based on quantum
interferometry are affected if the test particles propagate as open systems in
presence of a gaussian stochastic background. We show that physical consistency
requires the resulting markovian dissipative time-evolution to be completely
positive.Comment: 23 pages, plain-TeX, no figure
Suzaku Observations of Four Heavily Absorbed HMXBs
We report on Suzaku observations of four unidentified sources from the
INTEGRAL and Swift BAT Galactic plane surveys. All the sources have a large
neutral hydrogen column density and are likely members of an emerging class of
heavily absorbed high mass X-ray binary (HMXB) first identified in INTEGRAL
observations. Two of the sources in our sample are approximately constant flux
sources, one source shows periodic variation and one source exhibited a short,
bright X-ray outburst. The periodicity is transient, suggesting it is produced
by a neutron star in an elliptical orbit around a stellar wind source. We
analyze the flaring source in several segments to look for spectral variation
and discuss the implications of the findings for the nature of the source. We
conclude that all four sources in our sample can be identified with the
emerging class of highly absorbed HMXBs, that one is a newly identified
transient X-ray pulsar and that at least one is a newly identified supergiant
fast X-ray transient (SFXT).Comment: 22 pages, 5 figures, submitted to Ap
Willingness to pay more for value-added pomegranate juice (Punica granatum L.): An open-ended contingent valuation.
The mass surface density in the local disk and the chemical evolution of the Galaxy
We have studied the effect of adopting different values of the total baryonic
mass surface density in the local disk at the present time in a model for the
chemical evolution of the Galaxy. We have compared our model results with the
G-dwarf metallicity distribution, the amounts of gas, stars, stellar remnants,
infall rate and SN rate in the solar vicinity, and with the radial abundance
gradients and gas distribution in the disk. This comparison strongly suggests
that the value of the total baryonic mass surface density in the local disk
which best fits the observational properties should lie in the range 50-75 Msun
pc-2, and that values outside this range should be ruled out.Comment: 6 pages, LaTeX, 3 figures, accepted for publication in the
Astrophysical Journal, uses emulateapj.st
Interaction anisotropy and random impurities effects on the critical behaviour of ferromagnets
The theory of phase transitions is based on the consideration of "idealized"
models, such as the Ising model: a system of magnetic moments living on a cubic
lattice and having only two accessible states. For simplicity the interaction
is supposed to be restricted to nearest--neighbour sites only. For these
models, statistical physics gives a detailed description of the behaviour of
various thermodynamic quantities in the vicinity of the transition temperature.
These findings are confirmed by the most precise experiments. On the other
hand, there exist other cases, where one must account for additional features,
such as anisotropy, defects, dilution or any effect that may affect the nature
and/or the range of the interaction. These features may have impact on the
order of the phase transition in the ideal model or smear it out. Here we
address two classes of models where the nature of the transition is altered by
the presence of anisotropy or dilution.Comment: 11 pages, 4 figures, To appear in Journal of Physics: Conference
Serie
- …