18,679 research outputs found
Note on the helicity decomposition of spin and orbital optical currents
In the helicity representation, the Poynting vector (current) for a
monochromatic optical field, when calculated using either the electric or the
magnetic field, separates into right-handed and left-handed contributions, with
no cross-helicity contributions. Cross-helicity terms do appear in the orbital
and spin contributions to the current. But when the electric and magnetic
formulas are averaged ('electric-magnetic democracy'), these terms cancel,
restoring the separation into right-handed and left-handed currents for orbital
and spin separately.Comment: 10 pages, no figure
Monte Carlo simulation of events with Drell-Yan lepton pairs from antiproton-proton collisions: the fully polarized case
In this paper, we extend the study of Drell-Yan processes with antiproton
beams already presented in a previous work. We consider the fully polarized
process, because this is the
simplest scenario for extracting the transverse spin distribution of quarks, or
transversity, which is the missing piece to complete the knowledge of the
nucleon spin structure at leading twist. We perform Monte Carlo simulations for
transversely polarized antiproton and proton beams colliding at a
center-of-mass energy of interest for the future HESR at GSI. The goal is to
possibly establish feasibility conditions for an unambiguous extraction of the
transversity from data on double spin asymmetries.Comment: Produced in RevTeX 4, 10 figures in .eps forma
Compensation of anisotropy effects in the generation of two-photon light
We analyse a method to compensate for anisotropy effects in the spatial
distribution of parametric down-conversion (PDC) radiation in bulk crystals. In
this method, a single nonlinear crystal is replaced by two consecutive crystals
with opposite transverse walk-off directions. We implement a simple numerical
model to calculate the spatial distribution of intensity and correlations, as
well as the Schmidt mode structure, with an account for the anisotropy.
Experimental results are presented which prove the validity of both the model
and the method.Comment: 9 pages, 8 figure
Static and dynamic structure factors in three-dimensional randomly diluted Ising models
We consider the three-dimensional randomly diluted Ising model and study the
critical behavior of the static and dynamic spin-spin correlation functions
(static and dynamic structure factors) at the paramagnetic-ferromagnetic
transition in the high-temperature phase. We consider a purely relaxational
dynamics without conservation laws, the so-called model A. We present Monte
Carlo simulations and perturbative field-theoretical calculations. While the
critical behavior of the static structure factor is quite similar to that
occurring in pure Ising systems, the dynamic structure factor shows a
substantially different critical behavior. In particular, the dynamic
correlation function shows a large-time decay rate which is momentum
independent. This effect is not related to the presence of the Griffiths tail,
which is expected to be irrelevant in the critical limit, but rather to the
breaking of translational invariance, which occurs for any sample and which, at
the critical point, is not recovered even after the disorder average.Comment: 43 page
Neutrino current in a gravitational plane wave collision background
The behaviour of a massless Dirac field on a general spacetime background
representing two colliding gravitational plane waves is discussed in the
Newman-Penrose formalism. The geometrical properties of the neutrino current
are analysed and explicit results are given for the special Ferrari-Ibanez
solution.Comment: 17 pages, 6 Postscript figures, accepted by International Journal of
Modern Physics
Tadalafil modulates aromatase activity and androgen receptor expression in a human osteoblastic cell in vitro model
Purpose Phosphodiesterase type-5 inhibitor (PDE5i)
tadalafil administration in men with erectile dysfunction is
associated with increased testosterone/estradiol ratio, leading
to hypothesize a potential increased effect of androgen
action on target tissues. We aimed to characterize, in a cellular
model system in vitro, the potential modulation of
aromatase and sex steroid hormone receptors upon exposure
to tadalafil (TAD).
Methods Human osteoblast-like cells SAOS-2 were chosen
as an in vitro model system since osteoblasts are target
of steroid hormones. Cells were tested for viability upon
TAD exposure, which increased cell proliferation. Then,
cells were treated with/without TAD for several times to
evaluate potential modulation in PDE5, aromatase (ARO),
androgen (AR) and estrogen (ER) receptor expression.
Results Osteoblasts express significant levels of both PDE5
mRNA and protein. Exposure of cells to increasing concentrations
of TAD (10â8â10â7 M) decreased PDE5 mRNA and
protein expression. Also, TAD inhibited ARO mRNA and
protein expression leading to an increase in testosterone levels
in the supernatants. Interestingly, TAD increased total AR mRNA and protein expression and decreased ERα, with an
increased ratio of AR/ER, suggesting preferential androgenic
vs estrogenic pathway activation.
Conclusions Our results demonstrate for the first time
that TAD decreases ARO expression and increases AR
protein expression in human SAOS-2, strongly suggesting
a new control of steroid hormones pathway by PDE5i.
These findings might represent the first evidence of translational
actions of PDE5i on AR, which leads to hypothesize
a growing relevance of this molecule in men with
prostate cancer long-term treated with TAD for sexual
rehabilitation.
Keywords Tadalafil · Osteoblasts · Aromatase · Androgen
receptor · Estrogen recepto
Existence of the Stark-Wannier quantum resonances
In this paper we prove the existence of the Stark-Wannier quantum resonances
for one-dimensional Schrodinger operators with smooth periodic potential and
small external homogeneous electric field. Such a result extends the existence
result previously obtained in the case of periodic potentials with a finite
number of open gaps.Comment: 30 pages, 1 figur
- âŠ