5,945 research outputs found
Number of spanning clusters at the high-dimensional percolation thresholds
A scaling theory is used to derive the dependence of the average number
of spanning clusters at threshold on the lattice size L. This number should
become independent of L for dimensions d<6, and vary as log L at d=6. The
predictions for d>6 depend on the boundary conditions, and the results there
may vary between L^{d-6} and L^0. While simulations in six dimensions are
consistent with this prediction (after including corrections of order loglog
L), in five dimensions the average number of spanning clusters still increases
as log L even up to L = 201. However, the histogram P(k) of the spanning
cluster multiplicity does scale as a function of kX(L), with X(L)=1+const/L,
indicating that for sufficiently large L the average will approach a finite
value: a fit of the 5D multiplicity data with a constant plus a simple linear
correction to scaling reproduces the data very well. Numerical simulations for
d>6 and for d=4 are also presented.Comment: 8 pages, 11 figures. Final version to appear on Physical Review
Continuum corrections to the level density and its dependence on excitation energy, n-p asymmetry, and deformation
In the independent-particle model, the nuclear level density is determined
from the neutron and proton single-particle level densities. The
single-particle level density for the positive-energy continuum levels is
important at high excitation energies for stable nuclei and at all excitation
energies for nuclei near the drip lines. This single-particle level density is
subdivided into compound-nucleus and gas components. Two methods were
considered for this subdivision. First in the subtraction method, the
single-particle level density is determined from the scattering phase shifts.
In the Gamov method, only the narrow Gamov states or resonances are included.
The level densities calculated with these two methods are similar, both can be
approximated by the backshifted Fermi-gas expression with level-density
parameters that are dependent on A, but with very little dependence on the
neutron or proton richness of the nucleus. However, a small decrease in the
level-density parameter was predicted for some nuclei very close to the drip
lines. The largest difference between the calculations using the two methods
was the deformation dependence on the level density. The Gamov method predicts
a very strong peaking of the level density at sphericity for high excitation
energies. This leads to a suppression of deformed configurations and,
consequently, the fission rate predicted by the statistical model is reduced in
the Gamov method.Comment: 18 pages 24 figure
Expression of Semaphorin 3F and Its Receptors in Epithelial Ovarian Cancer, Fallopian Tubes, and Secondary Müllerian Tissues
While semaphorins and their receptors appear to play a role in tumor carcinogenesis, little
is known about the role of semaphorin 3F (S3F) in epithelial ovarian cancer (EOC)
development. Therefore, we sought to determine the clinical relationship between S3F
and its receptors, neuropilin-2 (NP-2) and neuropilin-1 (NP-1) with EOC progression.
We analyzed the immunohistological expression of S3F, NP-2, and NP-1 in clinical
specimens of normal ovaries (N), benign cystadenomas (Cy), well-differentiated
adenocarcinomas (WD), poorly-differentiated adenocarcinomas (PD), inclusion cysts
(IC), paraovarian cysts (PC), and fallopian tubes (FT). Tissue sections were evaluated for
staining intensity and percentage of immunoreactive epithelia. We found that expression
of S3F and NP-2 decreased while NP-1 expression increased with EOC progression.
Interestingly, we also found elevated expression of S3F, NP-2, and NP-1 in epithelia of
ICs, PCs, and FT. Our findings indicate that loss or deregulation of semaphorin signaling
may play an important role in EOC development
Plant communities as a tool in temporary ponds conservation in SW Portugal
Temporary ponds are seasonal wetlands
annually subjected to extreme and unstable ecological conditions, neither truly aquatic nor truly terrestrial. This habitat and its flora have been poorly studied and documented because of the ephemeral character of the flora, the changeable annual weather that has a great effect on the small, herbaceous taxa and the declining abundance of temporary ponds. The objectives of this study are:
(a)to define plant community diversity in terms of floristic composition of ephemeral wetlands in SW Portugal,
(b) to identify temporary pond types according to their vegetation composition and
(c) to identify those ponds that configure the European community priority habitat (3170* – Mediterranean temporary ponds).
Vegetation sampling was conducted in 29 ponds, identifying 168 species grouped among 15 plant communities. Soil texture, pH, organic C and N
content were measured, but only N and percent of clay appear to be related with the distribution of each community type. The results showed that ephemeral wetlands could be classified into four type: vernal pools, marshlands, deep ponds and disturbed wetlands. Vernal pools correspond to the Mediterranean temporary ponds (3170*), protected as priority hab-
itat under the EU Habitats Directive. Submersed Isoetes species (Isoetes setaceum and Isoetes velatum) represents, together with Eryngium corniculatum, the indicator species for vernal pools. We
identify also indicator plant communities of this priority habitat, namely I. setaceum and E. corniculatum–Baldellia ranunculoides plant communities. In
this region, the conservation of temporary ponds has so far been compatible with traditional agricultural activities, but today these ponds are endangered by the intensification of agriculture and the loss of traditional land use practices and by the development of tourism
Dilepton and Photon Emission Rates from a Hadronic Gas
We analyze the dilepton and photon emission rates from a hadronic gas using
chiral reduction formulas and a virial expansion. The emission rates are
reduced to pertinent vacuum correlation functions, most of which can be
assessed from experiment. Our results indicate that in the low mass region, the
dilepton and photon rates are enhanced compared to most of the calculations
using chiral Lagrangians. The enhancement is further increased through a finite
pion chemical potential. An estimate of the emission rates is also made using
Haag's expansion for the electromagnetic current. The relevance of these
results to dilepton and photon emission rates in heavy-ion collisions is
discussed.Comment: 7 pages, LaTeX using revTeX, 6 figures imbedded in text. Figures
slightly changed, text left unchange
Development of a shape specification based on the waviness parameter of tapered roller bearing
Tapered roller bearings can accommodate high radial loads as well as high axial loads. The manufacturing process consists of rings machining processes and components assembly, followed by an intense quality control. In this contribution, a study of the parameters of influence in the inspection procedure has been carried out. The main objective of this work is to develop a shape specification using real parts and to optimize the process of specification development. This requires to study the influence of several parameters in the inspection and to determine how they affect the waviness specification
Early predictive response to multi-tyrosine kinase inhibitors in advanced refractory radioactive-iodine differentiated thyroid cancer: A new challenge for [18 f]fdg pet/ct
Differentiated thyroid cancer (DTC) represents the most common thyroid cancer histotype. Generally, it exhibits a good prognosis after conventional treatments; nevertheless, about 20% of patients can develop a local recurrence and/or distant metastasis. In one-third of advanced DTC, the metastatic lesions lose the ability to take up iodine and become radioactive iodine-refractory (RAI-R) DTC. In this set of patients, the possibility to perform localized treatments should always be taken into consideration before the initiation of systemic therapy. In the last decade, some multi-tyrosine kinase inhibitor (MKI) drugs were approved for advanced DTC, impacting on patient’s survival rate, but at the same time, these therapies have been associated with several adverse events. In this clinical context, the role of 2-deoxy-2-[18 F]fluoro-D-glucose positron emission tomography/computed tomography ([18 F]FDG PET/CT) in the early treatment response to these innovative therapies was investigated, in order to assess the potentiality of this diagnostic tool in the early recognition of non-responders, avoiding unnecessary therapy. Herein, we aimed to present a critical overview about the reliability of [18 F]FDG PET/CT in the early predictive response to MKIs in advanced differentiated thyroid cancer
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