6,623 research outputs found
Effects of nanoscale spatial inhomogeneity in strongly correlated systems
We calculate ground-state energies and density distributions of Hubbard
superlattices characterized by periodic modulations of the on-site interaction
and the on-site potential. Both density-matrix renormalization group and
density-functional methods are employed and compared. We find that small
variations in the on-site potential can simulate, cancel, or even
overcompensate effects due to much larger variations in the on-site interaction
. Our findings highlight the importance of nanoscale spatial inhomogeneity
in strongly correlated systems, and call for reexamination of model
calculations assuming spatial homogeneity.Comment: 5 pages, 1 table, 4 figures, to appear in PR
Magnetic Susceptibility of an integrable anisotropic spin ladder system
We investigate the thermodynamics of a spin ladder model which possesses a
free parameter besides the rung and leg couplings. The model is exactly solved
by the Bethe Ansatz and exhibits a phase transition between a gapped and a
gapless spin excitation spectrum. The magnetic susceptibility is obtained
numerically and its dependence on the anisotropy parameter is determined. A
connection with the compounds KCuCl3, Cu2(C5H12N2)2Cl4 and (C5H12N)2CuBr4 in
the strong coupling regime is made and our results for the magnetic
susceptibility fit the experimental data remarkably well.Comment: 12 pages, 12 figures included, submitted to Phys. Rev.
European cancer mortality predictions for the year 2012
Background: Estimating current cancer mortality figures is important for defining priorities for prevention and treatment. Materials and methods: Using logarithmic Poisson count data joinpoint models on mortality and population data from the World Health Organization database, we estimated numbers of deaths and age-standardized rates in 2012 from all cancers and selected cancer sites for the whole European Union (EU) and its six more populated countries. Results: Cancer deaths in the EU in 2012 are estimated to be 1 283 101 (717 398 men and 565 703 women) corresponding to standardized overall cancer death rates of 139/100 000 men and 85/100 000 women. The fall from 2007 was 10% in men and 7% in women. In men, declines are predicted for stomach (−20%), leukemias (−11%), lung and prostate (−10%) and colorectal (−7%) cancers, and for stomach (−23%), leukemias (−12%), uterus and colorectum (−11%) and breast (−9%) in women. Almost stable rates are expected for pancreatic cancer (+2-3%) and increases for female lung cancer (+7%). Younger women show the greatest falls in breast cancer mortality rates in the EU (−17%), and declines are expected in all individual countries, except Poland. Conclusion: Apart for lung cancer in women and pancreatic cancer, continuing falls are expected in mortality from major cancers in the E
Alginate Formulations: Current Developments in the Race for Hydrogel-Based Cardiac Regeneration
Cardiovascular diseases, including myocardial infarction (MI), represent the main worldwide cause of mortality and morbidity. In this scenario, to contrast the irreversible damages following MI, cardiac regeneration has emerged as a novel and promising solution for in situ cellular regeneration, preserving cell behavior and tissue cytoarchitecture. Among the huge variety of natural, synthetic, and hybrid compounds used for tissue regeneration, alginate emerged as a good candidate for cellular preservation and delivery, becoming one of the first biomaterial tested in pre-clinical research and clinical trials concerning cardiovascular diseases. Although promising results have been obtained, recellularization and revascularization of the infarcted area present still major limitations. Therefore, the demand is rising for alginate functionalization and its combination with molecules, factors, and drugs capable to boost the regenerative potential of the cardiac tissue. The focus of this review is to elucidate the promising properties of alginate and to highlight its benefits in clinical trials in relation to cardiac regeneration. The definition of hydrogels, the alginate characteristics, and recent biomedical applications are herewith described. Afterward, the review examines in depth the ongoing developments to refine the material relevance in cardiac recovery and regeneration after MI and presents current clinical trials based on alginate
The Critical Behaviour of Potts models with symmetry breaking fields
The -state Potts model in two dimensions in the presence of external
magnetic fields is studied. For general special choices of these
magnetic fields produce effective models with smaller symmetry . The phase diagram of these models and their critical behaviour are
explored by conventional finite-size scaling and conformal invariance. The
possibility of multicritical behavior, for finite values of the symmetry
breaking fields, in the cases where is also analysed. Our results
indicate that for effective models with symmetry the
multicritical point occurs at zero field. This last result is also corroborated
by Monte Carlo simulations.Comment: 15 pages (standart LaTex), 2 figure (PostScript) available by request
to [email protected]
The Critical Behaviour of the Spin-3/2 Blume-Capel Model in Two Dimensions
The phase diagram of the spin-3/2 Blume-Capel model in two dimensions is
explored by conventional finite-size scaling, conformal invariance and Monte
Carlo simulations. The model in its -continuum Hamiltonian version is
also considered and compared with others spin-3/2 quantum chains. Our results
indicate that differently from the standard spin-1 Blume-Capel model there is
no multicritical point along the order-disorder transition line. This is in
qualitative agreement with mean field prediction but in disagreement with
previous approximate renormalization group calculations. We also presented new
results for the spin-1 Blume-Capel model.Comment: latex 18 pages, 4 figure
Critical Behaviour of Mixed Heisenberg Chains
The critical behaviour of anisotropic Heisenberg models with two kinds of
antiferromagnetically exchange-coupled centers are studied numerically by using
finite-size calculations and conformal invariance. These models exhibit the
interesting property of ferrimagnetism instead of antiferromagnetism. Most of
our results are centered in the mixed Heisenberg chain where we have at even
(odd) sites a spin-S (S') SU(2) operator interacting with a XXZ like
interaction (anisotropy ). Our results indicate universal properties
for all these chains. The whole phase, , where the models change
from ferromagnetic to ferrimagnetic behaviour is
critical. Along this phase the critical fluctuations are ruled by a c=1
conformal field theory of Gaussian type. The conformal dimensions and critical
exponents, along this phase, are calculated by studying these models with
several boundary conditions.Comment: 21 pages, standard LaTex, to appear in J.Phys.A:Math.Ge
A new measurement of the antiproton-to-proton flux ratio up to 100 GeV in the cosmic radiation
A new measurement of the cosmic ray antiproton-to-proton flux ratio between 1
and 100 GeV is presented. The results were obtained with the PAMELA experiment,
which was launched into low-earth orbit on-board the Resurs-DK1 satellite on
June 15th 2006. During 500 days of data collection a total of about 1000
antiprotons have been identified, including 100 above an energy of 20 GeV. The
high-energy results are a ten-fold improvement in statistics with respect to
all previously published data. The data follow the trend expected from
secondary production calculations and significantly constrain contributions
from exotic sources, e.g. dark matter particle annihilations.Comment: 10 pages, 4 figures, 1 tabl
- …