21,235 research outputs found
Probing the gluon density of the proton in the exclusive photoproduction of vector mesons at the LHC: A phenomenological analysis
The current uncertainty on the gluon density extracted from the global parton
analysis is large in the kinematical range of small values of the Bjorken -
variable and low values of the hard scale . An alternative to reduces this
uncertainty is the analysis of the exclusive vector meson photoproduction in
photon - hadron and hadron - hadron collisions. This process offers a unique
opportunity to constrain the gluon density of the proton, since its cross
section is proportional to the gluon density squared. In this paper we consider
current parametrizations for the gluon distribution and estimate the exclusive
vector meson photoproduction cross section at HERA and LHC using the leading
logarithmic formalism. We perform a fit of the normalization of the
cross section and the value of the hard scale for the process and demonstrate
that the current LHCb experimental data are better described by models that
assume a slow increasing of the gluon distribution at small - and low
.Comment: 8 pages, 6 figures, 1 table. Version published in European Physical
Journal
Effects on the Non-Relativistic Dynamics of a Charged Particle Interacting with a Chern-Simons Potential
The hydrogen atom in two dimensions, described by a Schr\"odinger equation
with a Chern-Simons potential, is numerically solved. Both its wave functions
and eigenvalues were determined for small values of the principal quantum
number . The only possible states correspond to . How the result
depends on the topological mass of the photon is also discussed. In the case
, the energy of the fundamental state corresponding to different choice
for the photon mass scale are found to be comprehended in the interval , corresponding to a mean
radius of the electron in the range ~cm
~cm. In any case, the planar
atom is found to be very weekly bounded showing some features similar to the
Rydberg atoms in three dimensions with a Coulombian interaction.Comment: 6 pages, 5 figure
The Coester Line in Relativistic Mean Field Nuclear Matter
The Walecka model contains essentially two parameters that are associated
with the Lorentz scalar (S) and vector (V) interactions. These parameters are
related to a two-body interaction consisting of S and V, imposing the condition
that the two-body binding energy is fixed. We have obtained a set of different
values for the nuclear matter binding energies at equilibrium densities. We
investigated the existence of a linear correlation between and ,
claimed to be universal for nonrelativistic systems and usually known as the
Coester line, and found an approximate linear correlation only if remains
constant. It is shown that the relativistic content of the model, which is
related to the strength of , is responsible for the shift of the Coester
line to the empirical region of nuclear matter saturation.Comment: 7 pages, 5 figure
Polarized currents and spatial separation of Kondo state: NRG study of spin-orbital effect in a double QD
A double quantum dot device, connected to two channels that only see each
other through interdot Coulomb repulsion, is analyzed using the numerical
renormalization group technique. By using a two-impurity Anderson model, and
parameter values obtained from experiment [S. Amasha {\it et al.}, Phys. Rev.
Lett. {\bf 110}, 046604 (2013)], it is shown that, by applying a moderate
magnetic field, and adjusting the gate potential of each quantum dot, opposing
spin polarizations are created in each channel. Furthermore, through a well
defined change in the gate potentials, the polarizations can be reversed. This
polarization effect is clearly associated to a spin-orbital Kondo state having
a Kondo peak that originates from spatially separated parts of the device. This
fact opens the exciting possibility of experimentally probing the internal
structure of an SU(2) Kondo state.Comment: 4+ pages; 4 figures; supplemental material (1 page, 2 figures
Differential mesenteric fat deposition in bovines fed on silage or concentrate is independent of glycerol membrane permeability
© The Animal Consortium 2011In the meat industry, the manipulation of fat deposition in cattle is of pivotal importance to improve production efficiency, carcass composition and ultimately meat quality. There is an increasing interest in the identification of key factors and molecular mechanisms responsible for the development of specific fat depots. This study aimed at elucidating the influence of breed and diet on adipose tissue membrane permeability and fluidity and their interplay on fat deposition in bovines. Two Portuguese autochthonous breeds, Alentejana and Barrosã, recognized as late- and early-maturing breeds, respectively, were chosen to examine the effects of breed and diet on fat deposition and on adipose membrane composition and permeability. Twenty-four male bovines from these breeds were fed on silage-based or concentrate-based diets for 11 months. Animals were slaughtered to determine their live slaughter and hot carcass weights, as well as weights of subcutaneous and visceral adipose depots. Mesenteric fat depots were excised and used to isolate adipocyte membrane vesicles where cholesterol content, fatty acid profile as well as permeability and fluidity were determined. Total accumulation of neither subcutaneous nor visceral fat was influenced by breed. In contrast, mesenteric and omental fat depots weights were higher in concentrate-fed bulls relative to silage-fed animals. Membrane fluidity and permeability to water and glycerol in mesenteric adipose tissue were found to be independent of breed and diet. Moreover, the deposition of cholesterol and unsaturated fatty acids, which may influence membrane properties, were unchanged among experimental groups. Adipose membrane lipids from the mesenteric fat depot of ruminants were rich in saturated fatty acids, and unaffected by polyunsaturated fatty acids dietary levels. Our results provide evidence against the involvement of cellular membrane permeability to glycerol on fat accumulation in mesenteric fat tissue of concentrate-fed bovines, which is consistent with the unchanged membrane lipid profile found among experimental groups.This study was supported by Fundação para a Ciência e a Tecnologia (FCT) through grant PTDC/CVT/2006/66114 and individual fellowships to Ana P. Martins (SFRH/BD/2009/65046), Ana S. H. Costa (SFRH/BD/2009/61068) and Susana V. Martins (SFRH/BPD/2009/63019). Paula A. Lopes is a researcher from the program ‘‘Ciência 2008’’ from FC
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