1,460 research outputs found
Overconstrained dynamics in galaxy redshift surveys
The least-action principle (LAP) method is used on four galaxy redshift
surveys to measure the density parameter Omega_m and the matter and
galaxy-galaxy power spectra. The datasets are PSCz, ORS, Mark III and SFI. The
LAP method is applied on the surveys simultaneously, resulting in an
overconstrained dynamical system that describes the cosmic overdensities and
velocity flows. The system is solved by relaxing the constraint that each
survey imposes upon the cosmic fields. A least-squares optimization of the
errors that arise in the process yields the cosmic fields and the value of
Omega_m that is the best fit to the ensemble of datasets. The analysis has been
carried out with a high-resolution Gaussian smoothing of 500 km/s and over a
spherical selected volume of radius 9,000 km/s. We have assigned a weight to
each survey, depending on their density of sampling, and this parameter
determines their relative influence in limiting the domain of the overall
solution. The influence of each survey on the final value of Omega_m, the
cosmographical features of the cosmic fields and the power spectra largely
depends on the distribution function of the errors in the relaxation of the
constraints. We find that PSCz and Mark III are closer to the final solution
than ORS and SFI. The likelihood analysis yields Omega_m= 0.37\pm 0.01 to
1sigma level. PSCz and SFI are the closest to this value, whereas ORS and Mark
III predict a somewhat lower Omega_m. The model of bias employed is a
scale-dependent one, and we retain up to 42 bias coefficients b_{rl} in the
spherical harmonics formalism. The predicted power spectra are estimated in the
range of wavenumbers 0.02-0.49h Mpc^{-1}, and we compare these results with
measurements recently reported in the literature.Comment: 10 pages, no figure
Trasplante óseo
We describe the methodology of the Bone and Soft Tissue
Bank, from extraction and storage until use.
Since the year 1986, with the creation of the Bone Bank
in the University Clinic of Navarra, more than 3,000 grafts
have been used for very different types of surgery.
Bone grafts can be classified into cortical and
spongy; the former are principally used in surgery to save
tumour patients, in large post-traumatic reconstructions
and in replacement surgery where there are massive
bone defects and a structural support is required. The
spongy grafts are the most used due to their numerous
indications; they are especially useful in filling cavities
that require a significant quantity of graft when the autograft
is insufficient, or as a complement. They are also of
special help in treating fractures when there is bone loss
and in the treatment of delays in consolidation and
pseudoarthrosis in little vascularized and atrophic zones.
They are also used in prosthetic surgery against the presence
of cavity type defects.
Allografts of soft tissues are specially recognised in
multiple ligament injuries that require reconstructions.
Nowadays, the most utilised are those employed in surgery
of the anterior cruciate ligament although they can be used
for filling any ligament or tendon defect.
The principal difficulties of the cortical allografts are
in the consolidation of the ends with the bone itself and in
tumour surgery, given that these are patients immunodepressed
by the treatment, the incidence of infection is
increased with respect to spongy grafts and soft tissues,
which is irrelevant.
In short, the increasingly widespread use of allografts
is an essential therapeutic weapon in orthopaedic
surgery and traumatology. It must be used by expert
hands
Hybrid quantization of an inflationary universe
We quantize to completion an inflationary universe with small inhomogeneities
in the framework of loop quantum cosmology. The homogeneous setting consists of
a massive scalar field propagating in a closed, homogeneous scenario. We
provide a complete quantum description of the system employing loop
quantization techniques. After introducing small inhomogeneities as scalar
perturbations, we identify the true physical degrees of freedom by means of a
partial gauge fixing, removing all the local degrees of freedom except the
matter perturbations. We finally combine a Fock description for the
inhomogeneities with the polymeric quantization of the homogeneous background,
providing the quantum Hamiltonian constraint of the composed system. Its
solutions are then completely characterized, owing to the suitable choice of
quantum constraint, and the physical Hilbert space is constructed. Finally, we
consider the analog description for an alternate gauge and, moreover, in terms
of gauge-invariant quantities. In the deparametrized model, all these
descriptions are unitarily equivalent at the quantum level.Comment: 16 pages, no figure
Unique Fock quantization of scalar cosmological perturbations
We investigate the ambiguities in the Fock quantization of the scalar
perturbations of a Friedmann-Lema\^{i}tre-Robertson-Walker model with a massive
scalar field as matter content. We consider the case of compact spatial
sections (thus avoiding infrared divergences), with the topology of a
three-sphere. After expanding the perturbations in series of eigenfunctions of
the Laplace-Beltrami operator, the Hamiltonian of the system is written up to
quadratic order in them. We fix the gauge of the local degrees of freedom in
two different ways, reaching in both cases the same qualitative results. A
canonical transformation, which includes the scaling of the matter field
perturbations by the scale factor of the geometry, is performed in order to
arrive at a convenient formulation of the system. We then study the
quantization of these perturbations in the classical background determined by
the homogeneous variables. Based on previous work, we introduce a Fock
representation for the perturbations in which: (a) the complex structure is
invariant under the isometries of the spatial sections and (b) the field
dynamics is implemented as a unitary operator. These two properties select not
only a unique unitary equivalence class of representations, but also a
preferred field description, picking up a canonical pair of field variables
among all those that can be obtained by means of a time-dependent scaling of
the matter field (completed into a linear canonical transformation). Finally,
we present an equivalent quantization constructed in terms of gauge-invariant
quantities. We prove that this quantization can be attained by a mode-by-mode
time-dependent linear canonical transformation which admits a unitary
implementation, so that it is also uniquely determined.Comment: 19 pages, minor impovementes included, typos correcte
Racetrack Potentials and the de Sitter Swampland Conjectures
We show that one can find de Sitter critical points (saddle points) in models
of flux compactification of Type IIB String Theory without any uplifting terms
and in the presence of several moduli. We demonstrate this by giving explicit
examples following some of the ideas recently presented by Conlon in [1], as
well as more generic situations where one can violate the strong form of the de
Sitter Swampland Conjecture. We stabilize the complex structure and the dilaton
with fluxes, and we introduce a racetrack potential that fixes the K\"ahler
moduli. The resultant potentials generically exhibit de Sitter critical points
and satisfy several consistency requirements such as flux quantization, large
internal volume, and weak coupling, as well as a form of the so-called Weak
Gravity Conjecture. Furthermore, we compute the form of the potential around
these de Sitter saddle points and comment on these results in connection to the
refined and more recent version of the de Sitter Swampland Conjecture.Comment: 23 pages, 4 figures; updated to reflect version accepted to JHE
Reduction of Murine Cutaneous UVB-Induced Tumor-Infiltrating T Lymphocytes by Dietary Canthaxanthin
The effect of dietary canthaxanthin, retinyl palmitate, or their combination on the tumor-infiltrating T-lymphocyte response (T-TIL) in de novo murine ultraviolet type B irradiation-induced tumors was investigated to elucidate potential mechanisms of action of these compounds. We found that dietary canthaxanthin greatly reduced the number of tumor-infiltrating helper/inducer, suppressor/cytotoxic, and interleukin-2 receptor-positive T lymphocytes and also observed a concomitant statistically significant increase in tumour incidence in canthaxanthin-fed animals. The addition of retinyl palmitate to the canthaxanthin diet ameliorated this negative effect on TIL and the development of skin tumors. We conclude that dietary retinyl palmitate and canthaxanthin can modulate the host T-cell immune response within a growing tumor and may affect tumorigenicity
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