Vacuum fluctuations of a scalar field near a reflecting boundary and their effects on the motion of a test particle

The contribution from quantum vacuum fluctuations of a real massless scalar field to the motion of a test particle that interacts with the field in the presence of a perfectly reflecting flat boundary is here investigated. There is no quantum induced dispersions on the motion of the particle when it is alone in the empty space. However, when a reflecting wall is introduced, dispersions occur with magnitude dependent on how fast the system evolves between the two scenarios. A possible way of implementing this process would be by means of an idealized sudden switching, for which the transition occurs instantaneously. Although the sudden process is a simple and mathematically convenient idealization it brings some divergences to the results, particularly at a time corresponding to a round trip of a light signal between the particle and the wall. It is shown that the use of smooth switching functions, besides regularizing such divergences, enables us to better understand the behavior of the quantum dispersions induced on the motion of the particle. Furthermore, the action of modifying the vacuum state of the system leads to a change in the particle energy that depends on how fast the transition between these states is implemented. Possible implications of these results to the similar case of an electric charge near a perfectly conducting wall are discussed.Comment: 17 pages, 8 figure

Espumas cerâmicas como suportes catalíticos

Espumas reticulares de cordierite desenvolvidas por um método de polimerização “in situ” revelaram propriedades de elevado interesse para a aplicação como suportes catalíticos. Estas espumas são caracterizadas por possuírem porosidades superiores (>90%) às obtidas pelo método de replicação polimérica (70-85%). O desenvolvimento de um método de revestimento de espumas cerâmicas com catalisadores zeolíticos, e a optimização de parâmetros como teor de sólidos, ligante, surfactante ou pré-revestimento da espuma, tem estado a ser efectuado. As melhores características foram observadas para espumas com aproximadamente 17% (p/p) de revestimento obtidas a partir de suspensões com cerca de 16% de teor de sólidos. Espumas revestidas com zeólitos Pt/ZSM5 estão a ser utilizadas como catalisadores para a combustão catalítica de COVs, nomeadamente isopropanol e toluen

Five-Dimensional QED, Muon Pair Production and Correction to the Coulomb Potential

We consider QED in five dimensions in a configuration where matter is localized on a 3-brane while foton propagates in the bulk. The idea is to investigate the effects of the Kaluza-Klein modes of the photon in the relativistic regime, but in low energy, and in the nonrelativistic regime. In the relativistic regime, we calculate the cross section for the reaction $e^+ + e^- \to \mu^+ + \mu^-$. We compare our theoretical result with a precise measurement of this cross section at $\sqrt{s}=57.77$ GeV. As result, we extract a lower bound on the size of the extra dimension. In the nonrelativistic regime, we derive the contribution for the Coulomb potential due to the whole tower of the Kaluza-Klein excited modes of the photon. We use the modified potential to calculate the Rutherford scattering differential cross section.Comment: minor changes, three new refs. added, to appear in IJMP

On the relation between Transversal and Longitudinal Scaling in Cities

Given that a group of cities follows a scaling law connecting urban population with socio-economic or infrastructural metrics (transversal scaling), should we expect that each city would follow the same behavior over time (longitudinal scaling)? This assumption has important policy implications, although rigorous empirical tests have been so far hindered by the lack of suitable data. Here, we advance the debate by looking into the temporal evolution of the scaling laws for 5507 municipalities in Brazil. We focus on the relationship between population size and two urban variables, GDP and water network length, analyzing the time evolution of the system of cities as well as their individual trajectory. We find that longitudinal (individual) scaling exponents are city-specific, but they are distributed around an average value that approaches to the transversal scaling exponent when the data are decomposed to eliminate external factors, and when we only consider cities with a sufficiently large growth rate. Such results give support to the idea that the longitudinal dynamics is a micro-scaling version of the transversal dynamics of the entire urban system. Finally, we propose a mathematical framework that connects the microscopic level to global behavior, and, in all analyzed cases, we find good agreement between theoretical prediction and empirical evidence

Anisotropic superconducting properties of aligned MgB2 crystallites

Samples of aligned MgB2 crystallites have been prepared, allowing for the first time the direct identification of an upper critical field anisotropy Hc2^{ab}/Hc2^{c}= xi_{ab}/xi_{c} ~ 1.73; with xi_{o,ab} ~ 70 A, xi_{o,c} ~ 40 A, and a mass anisotropy ratio m_{ab}/m_{c} ~ 0.3. A ferromagnetic background signal was identified, possibly related to the raw materials purity.Comment: 4 pages, 4 figures; Revised version to appear in Phys. Rev. Let

Long-term survival in a patient with brain metastases of papillary thyroid carcinoma

We present the case of a 43-year-old woman who underwent total thyroidectomy with bilateral lymphadenectomy for a papillary thyroid carcinoma (PTC), solid variant (T4bN1bMx), with V600E BRAF mutation. After ablative therapy, she presented undetectable thyroglobulin (Tg) but progressively increasing anti-Tg antibodies (TgAbs). During follow-up, nodal, lung and brain metastases were identified. She was submitted to surgical excision of lung lesions, radiosurgery of brain metastases and five radioiodine treatments. The latest brain MRI showed no lesions, pulmonary CT showed stable micronodules and there was progressive reduction in TgAbs. This is a peculiar case of a PTC with lung and brain metastatic lesions detected through TgAbs. Initial histological and molecular study suggested a more aggressive clinical behaviour, which was eventually confirmed. Although PTC brain metastases are extremely rare and present poor prognosis, our patient presented a good response to treatment and longer survival than usually reported for similar cases.info:eu-repo/semantics/publishedVersio

Produção de pólen por abelhas melíferas (Apis mellifera) em área de cultivo de manga (Mangifera indica L.) no projeto irrigado de Maniçoba, Juazeiro-BA.

Para incrementar a produção da manga em áreas irrigadas no Vale do Submédio São Francisco, os produtores utilizam colmeias de abelhas Apis mellifera, que realizam sua polinização. Entretanto, não se sabe se paralelamente os apicultores poderiam aproveitar as abelhas nas áreas de cultivo também para a produção de pólen apícola. Desta forma, este trabalho foi realizado com o objetivo de avaliar a produção de pólen por colmeias de A. mellifera em área de cultivo de manga no projeto irrigado de Maniçoba, Juazeiro-BA. O pólen foi coletado por meio de coletor de pólen frontal em duas colmeias previamente padronizadas quanto à quantidade de áreas de cria e alimento estocado. As coletas foram realizadas a cada 24 horas, por cinco dias consecutivos, em outubro de 2011. Os grãos de pólen retirados dos coletores foram armazenados em embalagens plásticas individuais, secados em estufa a 40-50ºC, durante 24 horas e, em seguida, pesados em balança de precisão. A coleta de pólen foi baixa em ambas as colônias durante todo o período experimental. No entanto, em cada dia, a colônia 1 coletou relativamente mais pólen que a colônia 2, embora estas diferenças não foram significativas. Seria necessário repetir o experimento em maior número de áreas de cultivo para confirmar que a produção é realmente muito baixa, e assim, não indicar esta atividade como alternativa para os apicultores da região

Lande g-tensor in semiconductor nanostructures

Understanding the electronic structure of semiconductor nanostructures is not complete without a detailed description of their corresponding spin-related properties. Here we explore the response of the shell structure of InAs self-assembled quantum dots to magnetic fields oriented in several directions, allowing the mapping of the g-tensor modulus for the s and p shells. We found that the g-tensors for the s and p shells show a very different behavior. The s-state in being more localized allows the probing of the confining potential details by sweeping the magnetic field orientation from the growth direction towards the in-plane direction. As for the p-state, we found that the g-tensor modulus is closer to that of the surrounding GaAs, consistent with a larger delocalization. These results reveal further details of the confining potentials of self-assembled quantum dots that have not yet been probed, in addition to the assessment of the g-tensor, which is of fundamental importance for the implementation of spin related applications.Comment: 4 pages, 4 figure