On Useful Conformal Tranformations In General Relativity

Local conformal transformations are known as a useful tool in various applications of the gravitational theory, especially in cosmology. We describe some new aspects of these transformations, in particular using them for derivation of Einstein equations for the cosmological and Schwarzschild metrics. Furthermore, the conformal transformation is applied for the dimensional reduction of the Gauss-Bonnet topological invariant in $d=4$ to the spaces of lower dimensions.Comment: 17 pages, LaTeX. The paper is intended mainly for pedagogical purposes and represents a collection of exercises concerning local conformal transformations and dimensional reduction. To be published in "Gravitation and Cosmology

Arterial spin labelling: initial experience, clinical impact and difficulties

RESUMO O arterial spin labeling (ASL) é uma técnica de perfusão por ressonância magnética (RM) que usa os protões das moléculas de água do sangue arterial como marcador endógeno. As suas principais vantagens residem no facto de ser um método não invasivo, rápido e que dispensa a administração de contraste. Actualmente os seus resultados são reprodutíveis de modo robusto, o que o torna uma ferramenta cada vez mais utilizada na prática clínica. O objectivo deste trabalho é apresentar a nossa experiência inicial com o ASL, salientando os aspectos técnicos, as principais solicitações clínicas, os resultados obtidos e as dificuldades experimentadas. Métodos: Foi efectuada uma revisão dos exames realizados durante um período de oito meses, usando uma técnica de ASL pulsado, num aparelho de 3T. A avaliação dos mapas de perfusão foi realizada de modo qualitativo. Resultados: As principais indicações clínicas para a realização de ASL foram epilepsia, doenças neuro-degenerativas e tumores intra-parenquimatosos. Embora o ASL não tenha sido, em nenhum dos casos, a principal ferramenta diagnóstica, contribuiu, por vezes, com dados fisiológicos importantes para o diagnóstico e para a orientação terapêutica. Salientam-se os casos de doentes com múltiplas crises epilépticas nos quais foi possível identificar focos de hiperperfusão pós-ictal (cujos resultados foram concordantes com o SPECT). Destacam-se ainda casos de doenças neuro-degenerativas nos quais o ASL identificou áreas de hipoperfusão típicas das respectivas entidades nosológicas. As principais dificuldades estiveram relacionadas com o carácter qualitativo da avaliação e com a valorização clínica dos achados. Conclusão: O estudo da perfusão cerebral por ASL tem um potencial diagnóstico importante. Com este trabalho mostramos que, com uma aquisição rápida e pós-processamento simples, pode facilmente integrar os estudos de RM de rotina. Abstract Arterial spin labelling (ASL) is a MR perfusion technique that uses protons from water molecules of the arterial blood as an endogenous tracer. It is fast, non-invasive and does not require gadolinium administration. Due to the increasing robustness of the results, it is becoming an important clinical tool. In this article we present our initial experience with ASL, highlighting some technical aspects, the main clinical applications, some achieved results and most important difficulties. Methods: Review of the examinations performed during eight months, using a pulsating ASL technique in a 3T machine. Perfusion maps were evaluated qualitatively. Results: The most frequent clinical applications were epilepsy, neurodegenerative disorders and tumours. Although perfusion data from ASL had never been crucial for diagnosis, it still provided substantial information. We highlight two epileptic patients who had had recent seizures, in which ASL depicted distinct post-ictal hyperperfusion areas (with the results being confirmed by SPECT studies). The impact was also remarkable in patients with neurodegenerative disorders in which ASL depicted hypoperfusion areas, typical of each nosological entity. The main difficulties were related to the lack of quantitative evaluation and to the clinical interpretation of the results obtained. Conclusion: ASL perfusion studies have a great potential in several clinical conditions. In this article we show that, with a fast acquisition and easy post-processing, it can integrate routine MRI examinations

Symmetries and Ambiguities in the linear sigma model with light quarks

We investigate the role of undetermined finite contributions generated by radiative corrections in a $SU(2)\times SU(2)$ linear sigma model with quarks. Although some of such terms can be absorbed in the renormalization procedure, one such contribution is left in the expression for the pion decay constant. This arbitrariness is eliminated by chiral symmetry.Comment: 9 pages. Added references through the text; an author was added due to an important contribution; corrected typos; the title also was changed. Submitted to Modern Physics Letter

Agrobacterium-mediated genetic transformation of a tropical elite maize line.

ABSTRACT: The efficiency of maize transformation mediated by Agrobacterium tumefaciens is influenced by various factors. The aim of this study was to test the effect of different concentrations of N6 salts (50% ? half strength, and 100% - full strength) in the infection and cocultivation media on genetic transformation efficiency of the L3 tropical elite maize line. Immature embryos were transformed via A. tumefaciens harboring the binary vector pTF102 containing the genes uidA and BAR under control of the CaMV35S promoter. The efficiency of the transgenic events produced was 3% for full strength and 1.1% for half strength N6 salts. Although under a lower concentration of salts, GUS expression was stronger; under this concentration, regeneration was less efficient. Thus, the results showed that the presence of 100% N6 salts in the infection and cocultivation media favored genetic transformation of the L3 maize inbred line mediated by A. tumefaciens

Levantamento e intensidade de ocorrência de insetos nocivos e seus inimigos naturais em culturas temporárias.

bitstream/item/59272/1/CPATU-ComTec45.pd

Evidence of Two Distinct Dynamic Critical Exponents in Connection with Vortex Physics

The dynamic critical exponent $z$ is determined from numerical simulations for the three-dimensional (3D) lattice Coulomb gas (LCG) and the 3D XY models with relaxational dynamics. It is suggested that the dynamics is characterized by two distinct dynamic critical indices $z_0$ and $z$ related to the divergence of the relaxation time $\tau$ by $\tau\propto \xi^{z_0}$ and $\tau\propto k^{-z}$, where $\xi$ is the correlation length and $k$ the wavevector. The values determined are $z_0\approx 1.5$ and $z\approx 1$ for the 3D LCG and $z_0\approx 1.5$ and $z\approx 2$ for the 3D XY model. It is argued that the nonlinear $IV$ exponent relates to $z_0$, whereas the usual Hohenberg-Halperin classification relates to $z$. Possible implications for the interpretation of experiments are pointed out. Comparisons with other existing results are discussed.Comment: to appear in PR