5,666 research outputs found
Medium effects in the pion pole mechanism (photon photon --> pion-zero --> neutrino-R antineutrino-L (neutrino-L antineutrino-R)) of neutron star cooling
Nuclear medium effects in the neutrino cooling of neutron stars through the
exotic reaction channel \gamma \gamma --> \pi^0--> \nu_R \bar{\nu_L} (\nu_L
\bar{\nu_R}) are incorporated. Throughout the paper we discuss different
possibilities of right-handed neutrinos, massive left-handed neutrinos and
standard massless left-handed neutrinos (reaction is then allowed only with
medium modified vertices). It is demonstrated that multi-particle effects
suppress the rate of this reaction channel by 6-7 orders of magnitude that does
not allow to decrease existing experimental upper limit on the corresponding
\pi^0\nu\bar{\nu} coupling. Other possibilities of the manifestation of the
given reaction channel in differente physical situations, e.g. in the quark
color superconducting cores of some neutron stars, are also discussed. We
demonstrate that in the color-flavor-locked superconducting phase for
temperatures T < (0.1-10) MeV (depending on the effective pion mass and the
decay width) the process is feasibly the most efficient neutrino cooling
process, although the absolute value of the reaction is rather small.Comment: Replaced with revised version. New appendix, many clarifying
comments, corrected figs 3 and
A genetic algorithm-assisted semi-adaptive MMSE multi-user detection for MC-CDMA mobile communication systems
In this work, a novel Minimum-Mean Squared-Error (MMSE) multi-user detector is proposed for MC-CDMA transmission systems working over mobile radio channels characterized by time-varying multipath fading. The proposed MUD algorithm is based on a Genetic Algorithm (GA)-assisted per-carrier MMSE criterion. The GA block works in two successive steps: a training-aided step aimed at computing the optimal receiver weights using a very short training sequence, and a decision-directed step aimed at dynamically updating the weights vector during a channel coherence period. Numerical results evidenced BER performances almost coincident with ones yielded by ideal MMSE-MUD based on the perfect knowledge of channel impulse response. The proposed GA-assisted MMSE-MUD clearly outperforms state-of-the-art adaptive MMSE receivers based on deterministic gradient algorithms, especially for high number of transmitting users
Expression of aldehyde dehydrogenase family 1, member A3 in glycogen trophoblast cells of the murine placenta
Introduction: Retinoic acid (RA) signaling is a well known regulator of trophoblast differentiation and placental development, and maternal decidual cells are recognized as the source of much of this RA. We explored possible trophoblast-derived sources of RA by examining the expression of RA synthesis enzymes in the developing mouse placenta, as well as addressed potential sites of RA action by examining the ontogeny of gene expression for other RA metabolizing and receptor genes. Furthermore, we investigated the effects of endogenous RA production on trophoblast differentiation
Theoretical fits of the \delta Cephei light, radius and radial velocity curves
We present a theoretical investigation of the light, radius and radial
velocity variations of the prototype Cephei. We find that the best fit
model accounts for luminosity and velocity amplitudes with an accuracy better
than , and for the radius amplitude with an accuracy of .
The chemical composition of this model suggests a decrease in both helium (0.26
vs 0.28) and metal (0.01 vs 0.02) content in the solar neighborhood. Moreover,
distance determinations based on the fit of light curves agree at the
level with the trigonometric parallax measured by the Hubble Space
Telescope (HST). On the other hand, distance determinations based on angular
diameter variations, that are independent of interstellar extinction and of the
-factor value, indicate an increase of the order of 5% in the HST parallax.Comment: accepted for publication on ApJ Letter
Non-perturbative fixed points and renormalization group improved effective potential
The stability conditions of a renormalization group improved effective
potential have been discussed in the case of scalar QED and QCD with a
colorless scalar. We calculate the same potential in these models assuming the
existence of non-perturbative fixed points associated to a conformal phase. In
the case of scalar QED the barrier of instability found previously is barely
displaced as we approach the fixed point, and in the case of QCD with a
colorless scalar not only the barrier is changed but the local minimum of the
potential is also changed.Comment: 6 pages, 8 figures, References added. Matching the journal versio
Scalar coupling evolution in a non-perturbative QCD resummation scheme
We compute the Standard Model scalar coupling () evolution in a
particular QCD resummation scheme, where the QCD coupling becomes infrared
finite due to the presence of a dynamically generated gluon mass, leading to
the existence of a non-perturbative infrared fixed point. We discuss how this
scheme can be fixed taking recourse to phenomenological considerations in the
infrared region. The QCD function associated to this non-perturbative
coupling when introduced into the SM renormalization group equations increases
the values at high energies.Comment: 4 pages, 1 figure, The manuscript has been rewritten and quite
shortened, one equation corrected, the title has been changed and the
conclusions remain the sam
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