Analytical and numerical studies of disordered spin-1 Heisenberg chains with aperiodic couplings

We investigate the low-temperature properties of the one-dimensional spin-1 Heisenberg model with geometric fluctuations induced by aperiodic but deterministic coupling distributions, involving two parameters. We focus on two aperiodic sequences, the Fibonacci sequence and the 6-3 sequence. Our goal is to understand how these geometric fluctuations modify the physics of the (gapped) Haldane phase, which corresponds to the ground state of the uniform spin-1 chain. We make use of different adaptations of the strong-disorder renormalization-group (SDRG) scheme of Ma, Dasgupta and Hu, widely employed in the study of random spin chains, supplemented by quantum Monte Carlo and density-matrix renormalization-group numerical calculations, to study the nature of the ground state as the coupling modulation is increased. We find no phase transition for the Fibonacci chain, while we show that the 6-3 chain exhibits a phase transition to a gapless, aperiodicity-dominated phase similar to the one found for the aperiodic spin-1/2 XXZ chain. Contrary to what is verified for random spin-1 chains, we show that different adaptations of the SDRG scheme may lead to different qualitative conclusions about the nature of the ground state in the presence of aperiodic coupling modulations.Comment: Accepted for publication in Physical Review

The Venus ionosphere in the northern polar region

PLASLIFE is a computer simulation which assists in the interpretation of high latitude ionospheric observations and, in this study, is applied to the polar regions of Venus. The Venus Express spacecraft samples the high latitude ionosphere in the northern hemisphere of the planet. On 4 August 2008 it was inserted into a new orbit with pericentre located below 200 km close to 86° N. The ASPERA-4 instrument on the spacecraft records the first extended in situ data set of the plasma environment in this sector. The observed ionospheric ion and electron populations exhibit significant variation between orbits and, by compensating for the effects of solar zenith angle and altitude, the relative contributions of photoionisation and plasma transport can be investigated. These variations are discussed with respect to parameters including local time and solar flux. Comparisons are drawn with the terrestrial ionosphere

What is there in the black box of dark energy: variable cosmological parameters or multiple (interacting) components?

The coincidence problems and other dynamical features of dark energy are studied in cosmological models with variable cosmological parameters and in models with the composite dark energy. It is found that many of the problems usually considered to be cosmological coincidences can be explained or significantly alleviated in the aforementioned models.Comment: 6 pages, 1 figure, talk given at IRGAC2006 (Barcelona, July 11-15, 2006), to appear in J. Phys.

Tyrosine kinase inhibitors for the therapy of anaplastic thyroid cancer

Anaplastic thyroid cancer (ATC) is often incurable so new therapeutic approaches are needed. Tyrosine kinases inhibitors (such as imanitib, sunitinib or sorafenib) are under evaluation for the treatment of ATC. Other vascular disrupting agents, such as combretastatin A4 phosphate, and antiangiogenic agents, such as aplidin, PTK787/ZK222584 and human VEGF monoclonal antibodies (bevacizumab, cetuximab), have been evaluated. Small-molecule adenosine triphosphate competitive inhibitors directed intracellularly at EGFRs tyrosine kinase, such as erlotinib or gefitinib, are also studied. Furthermore, new molecules have been shown to be active against ATC, such as CLM94 and CLM3. However, more research is needed to finally identify therapies able to control and to cure this disease

Cosmologies with a time dependent vacuum

The idea that the cosmological term, Lambda, should be a time dependent quantity in cosmology is a most natural one. It is difficult to conceive an expanding universe with a strictly constant vacuum energy density, namely one that has remained immutable since the origin of time. A smoothly evolving vacuum energy density that inherits its time-dependence from cosmological functions, such as the Hubble rate or the scale factor, is not only a qualitatively more plausible and intuitive idea, but is also suggested by fundamental physics, in particular by quantum field theory (QFT) in curved space-time. To implement this notion, is not strictly necessary to resort to ad hoc scalar fields, as usually done in the literature (e.g. in quintessence formulations and the like). A "running" Lambda term can be expected on very similar grounds as one expects (and observes) the running of couplings and masses with a physical energy scale in QFT. Furthermore, the experimental evidence that the equation of state of the dark energy could be evolving with time/redshift (including the possibility that it might currently behave phantom-like) suggests that a time-variable Lambda term (possibly accompanied by a variable Newton's gravitational coupling G=G(t)) could account in a natural way for all these features. Remarkably enough, a class of these models (the "new cosmon") could even be the clue for solving the old cosmological constant problem, including the coincidence problem.Comment: LaTeX, 15 pages, 4 figure

The non-archimedean space BC(X) with the strict topology

Let X be a zero-dimensional, Hausdorff topological space and K a field with a non-trivial, non-archimedean valuation under which it is complete. Then BC(X) is the vector space of the bounded continuous functions from X to K. We obtain necessary and sufficient conditions for BC(X), equipped with the strict topology, to be of countable type and to be nuclear in the non-archimedean sense

Perturbations in the relaxation mechanism for a large cosmological constant

Recently, a mechanism for relaxing a large cosmological constant (CC) has been proposed [arxiv:0902.2215], which permits solutions with low Hubble rates at late times without fine-tuning. The setup is implemented in the LXCDM framework, and we found a reasonable cosmological background evolution similar to the LCDM model with a fine-tuned CC. In this work we analyse analytically the perturbations in this relaxation model, and we show that their evolution is also similar to the LCDM model, especially in the matter era. Some tracking properties of the vacuum energy are discussed, too.Comment: 18 pages, LaTeX; discussion improved, accepted by CQ

Cosmologies with variable parameters and dynamical cosmon: implications on the cosmic coincidence problem

Dynamical dark energy (DE) has been proposed to explain various aspects of the cosmological constant (CC) problem(s). For example, it is very difficult to accept that a strictly constant Lambda-term constitutes the ultimate explanation for the DE in our Universe. It is also hard to acquiesce in the idea that we accidentally happen to live in an epoch where the CC contributes an energy density value right in the ballpark of the rapidly diluting matter density. It should perhaps be more plausible to conceive that the vacuum energy, is actually a dynamical quantity as the Universe itself. More generally, we could even entertain the possibility that the total DE is in fact a mixture of vacuum energy and other dynamical components (e.g. fields, higher order terms in the effective action etc) which can be represented collectively by an effective entity X (dubbed the ``cosmon''). The ``cosmon'', therefore, acts as a dynamical DE component different from the vacuum energy. While it can actually behave phantom-like by itself, the overall DE fluid may effectively appear as standard quintessence, or even mimic at present an almost exact CC behavior. Thanks to the versatility of such cosmic fluid we can show that a composite DE system of this sort (``LXCDM'') may have a key to resolving the mysterious coincidence problem.Comment: LaTeX, 13 pages, 5 figure

The New Elderly Patient: A Necessary Upgrade

The elderly individual is becoming the most common patient in clinical practice due to the increasing average life span, especially in developed countries. The current elderly patients are different from those of some decades ago. They usually have an active social life, want to be informed, and are actively involved in the current society with consequent high expectations for medical and dental treatment. However, not all the elderly patients are like this. Some of them show limited financial resources, reduced mental and manual skills, and poor motivation. The purpose of this communication is to make a brief characterization of the new elderly population in view of prosthetic and dental management

Water quality in the Municipality of São Domingos (Santiago island, Cape Verde)

O presente estudo tem como objetivo avaliar a qualidade da água e potencialidades de uso no concelho de São Domingos, na ilha de Santiago (Cabo Verde). Os resultados obtidos mostram, o carácter mineralizado destas águas, com valor médio de condutividade elétrica de 1361 µS/cm. A classificação hidroquímica, de acordo com o diagrama de Piper, conduziu à discriminação dos seguintes tipos: águas mistas (bicarbonatadas, cloretadas) e mistas sódicas (cloretadas e bicarbonatadas). Considerando o que está estabelecido na legislação Cabo-verdiana e Portuguesa relativamente à qualidade da água, verificouse que apenas 36 % das amostras têm qualidade suficiente para consumo humano. No que respeita à utilização da água para rega, cerca de 68 % das amostras apresentam evidências de risco de salinização alto a muito alto.This research aims the evaluation of water quality and potential uses at São Domingos municipality, at Santiago Island (Cape Verde). The results show the mineralized nature of these waters, with an average electrical conductivity of 1361 μS/cm. The hydrochemical classification, according to the Piper diagram, led to the following types: mixed (bicarbonate and chloride) and mixed with sodium (chloride and bicarbonate). Considering what is established for water quality in the Cape Verde and Portuguese legislation, only 36 % of the water samples are able for human consumption. Regarding irrigation use, approximately 68 % of the samples present high-to-very-high salinization risk.(undefined)info:eu-repo/semantics/publishedVersio