Vacuum Polarization by a Magnetic Flux Tube at Finite Temperature in the Cosmic String Spacetime

In this paper we analyse the effect produced by the temperature in the vacuum polarization associated with charged massless scalar field in the presence of magnetic flux tube in the cosmic string spacetime. Three different configurations of magnetic fields are taken into account: $(i)$ a homogeneous field inside the tube, $(ii)$ a field proportional to $1/r$ and $(iii)$ a cylindrical shell with $\delta$-function. In these three cases, the axis of the infinitely long tube of radius $R$ coincides with the cosmic string. Because the complexity of this analysis in the region inside the tube, we consider the thermal effect in the region outside. In order to develop this analysis, we construct the thermal Green function associated with this system for the three above mentioned situations considering points in the region outside the tube. We explicitly calculate in the high-temperature limit, the thermal average of the field square and the energy-momentum tensor.Comment: 16 pages, 1 figur

From vortex molecules to the Abrikosov lattice in thin mesoscopic superconducting disks

Stable vortex states are studied in large superconducting thin disks (for numerical purposes we considered with radius R = 50 \xi). Configurations containing more than 700 vortices were obtained using two different approaches: the nonlinear Ginzburg-Landau (GL) theory and the London approximation. To obtain better agreement with results from the GL theory we generalized the London theory by including the spatial variation of the order parameter following Clem's ansatz. We find that configurations calculated in the London limit are also stable within the Ginzburg-Landau theory for up to ~ 230 vortices. For large values of the vorticity (typically, L > 100), the vortices are arranged in an Abrikosov lattice in the center of the disk, which is surrounded by at least two circular shells of vortices. A Voronoi construction is used to identify the defects present in the ground state vortex configurations. Such defects cluster near the edge of the disk, but for large L also grain boundaries are found which extend up to the center of the disk.Comment: 15 pages, 10 figures, RevTex4, submitted to Phys. Rev.

Multiple glomus tumors and segmental neurofibromatosis: there are no coincidences

Segmental neurofibromatosis is a rare subtype of neurofibromatosis type 1 (NF1). Glomus tumors are uncommon benign tumors. The authors report the association between these two rare conditions, not yet reported

Revisões de próteses da anca: Reconstrução das lises ósseas com enxertos alógenos

O desprendimento ou "descolamento" asséptico das próteses totais da anca e a lise óssea do leito da prótese, são as complicações mais frequentes das artroplastias da anca. Factores mecânicos, biológicos e, sobretudo, reacções do organismo às partículas de desgaste dos diferentes componentes das próteses estão, com certeza, envolvidos neste processo. As lises ósseas acetabulares e femurais podem revestir características e intensidades variáveis, obrigando a estratégias de reconstrução diferentes. Com base na gravidade das lises ósseas considerámos três graus para o acetábulo e igualmente três graus para o fémur. Para preenchimento das lises ósseas recorremos a enxertos alógenos, do Banco de Ossos dos Hospitais da Universidade de Coimbra, colhidos e conservados segundo as normas internacionalmente aceites. Nas lises acetabulares do grau I e grau II utilizámos enxerto esponjoso sob a forma de pequenos fragmentos ou grânulos e nas lises do grau III enxertos maciços talhados na extremidade distal do fémur. Como implantes temos utilizado cúpulas "primárias" ou anéis metálicos de reforço acetabular nas lises do grau I anéis metálicos nas lises do grau II e, cúpulas cimentadas directamente no enxerto maciço ou anéis metálicos cujos parafusos transfixam o enxerto, nas lises do grau III. Nas lises femurais temos utilizado enxerto esponjoso para preenchimento das perdas de substância óssea e como implante as hastes de Wagner, de forma quase sistemática. Como vias de abordagem da anca utilizámos a via postero-externa ou a via transfemoral. Esta metodologia tem-nos permitido a recolocação de nova prótese, mesmo em situações de extrema fragilidade e perda de substância óssea. De Outubro de 1990 a Dezembro de 1994 a mesma equipa tratou, segundo estes critérios, 185 ancas, sendo a lise óssea acetabular classificada do grau I em 35 casos, do grau II em 128 casos e do grau III em 16. A lise femoral foi do grau I em 38 casos, do grau II em 75 e do grau III em 47. O tempo de evolução pós-operatório variou entre o máximo de 4 anos e 9 meses e o mínimo de 6 meses, sendo a média de 2 anos e 11 meses. Como complicações mais significativas referimos 5 casos de infecção, 23 de luxação da prótese, 1 de reabsorção marcada do enxerto maciço com desprendimento do componente acetabular, 5 de afundamento da haste de Wagner que foi necessário substituir por outra de maior calibre e 3 casos de ausência de consolidação da "janela" óssea extensa (via transfemoral) sem repercussões clínicas. Os resultados clínicos foram considerados satisfatórios, pois que, segundo os critérios de Harris, pré-operatoriamente os doentes tinham em média uma pontuação de 40 e na última avaliação uma média de 76. Segundo a opinião do doente, 58°/o encontram-se entusiasmados com o resultado, 36% satisfeitos e apenas 6°/o decepcionados

Thermal Pair Production from Photon-Photon Collision: Breit-Wheeler Process at Finite Temperature

In this paper we examine the pair production through the Breit-Wheeler process $\gamma~\gamma \to e^+ e^-$ in a thermal background. We compute the thermal contribution to the Breit-Wheeler differential cross section within the thermofield dynamics formalism. We evaluate in details the cross section for this process, which possess a surprisingly simple expression valid for any temperature $\beta$, from which we discuss some physically relevant aspects. We also consider the high temperature regime of the cross section in order to have a better understanding about its thermal behavior.Comment: 13 pages, accepted for publication in EPJ

Vacuum Polarization for a Massless Spin-1/2 Field in the Global Monopole Spacetime at Nonzero Temperature

In this paper we present the effects produced by the temperature in the renormalized vacuum expectation value of the zero-zero component of the energy-momentum tensor associated with massless left-handed spinor field in the pointlike global monopole spacetime. In order to develop this calculation we had to obtain the Euclidean thermal Green function in this background. Because the expression obtained for the thermal energy density cannot be expressed in a closed form, its explicit dependence on the temperature is not completely evident. So, in order to obtain concrete information about its thermal behavior, we develop a numerical analysis of our result in the high-temperature limit for specific values of the parameter $\alpha$ which codify the presence of the monopole.Comment: 22 pages, LaTex format, 5 figure

Structural Responses of Quasi-2D Colloid Fluids to Excitations Elicited by Nonequilibrium Perturbations

We investigate the response of a dense monodisperse quasi-two-dimensional (q2D) colloid suspension when a particle is dragged by a constant velocity optical trap. Consistent with microrheological studies of other geometries, the perturbation induces a leading density wave and trailing wake, and we use Stokesian Dynamics (SD) simulations to parse direct colloid-colloid and hydrodynamic interactions. We go on to analyze the underlying individual particle-particle collisions in the experimental images. The displacements of particles form chains reminiscent of stress propagation in sheared granular materials. From these data, we can reconstruct steady-state dipolar flow patterns that were predicted for dilute suspensions and previously observed in granular analogs to our system. The decay of this field differs, however, from point Stokeslet calculations, indicating that the finite size of the colloids is important. Moreover, there is a pronounced angular dependence that corresponds to the surrounding colloid structure, which evolves in response to the perturbation. Put together, our results show that the response of the complex fluid is highly anisotropic owing to the fact that the effects of the perturbation propagate through the structured medium via chains of colloid-colloid collisions

Non-newtonian flow and pressure drop of pineapple juice in a plate heat exchanger

The study of non-Newtonian flow in plate heat exchangers (PHEs) is of great importance for the food industry. The objective of this work was to study the pressure drop of pineapple juice in a PHE with 50º chevron plates. Density and flow properties of pineapple juice were determined and correlated with temperature (17.4 < T < 85.8ºC) and soluble solids content (11.0 < Xs < 52.4 ºBrix). The Ostwald-de Waele (power law) model described well the rheological behavior. The friction factor for non-isothermal flow of pineapple juice in the PHE was obtained for diagonal and parallel/side flow. Experimental results were well correlated with the generalized Reynolds number (20 < Re g < 1230) and were compared with predictions from equations from the literature. The mean absolute error for pressure drop prediction was 4% for the diagonal plate and 10% for the parallel plate.(FAPESP) São Paulo Research Foundatio

Effect of pre-treatment on açaí pulp microfiltration process.

Açaí (Euterpe oleracea Mart.) is a palm tree from north region of Brazil. Its small fruit is rich in bioactive compounds making it an attractive product. The aim of this work was to evaluate the effect of pre-treatments on microfiltration of açaí pulp. Raw material was acaí pulp from Belém, Brazil. Pre-treatments were centrifugation, conducted in a basket centrifuge; refining, in a depulper with a 0.5 ?m mesh; and enzymatic hydrolysis with DSM Rapidase and Picantase for 30 min at 35oC. Microfiltration was conducted in tubular membranes with 0.1?m pore size and 0.022m2 of surface. Processes were carried out at 35oC/3bar in batch mode. Permeate flux was determined during the process. Total and soluble solids, pH and acidity were determined on initial and treated pulp, permeate and retentate. Initial pulp contained 13.89 (w/w), 2.85oBrix, 0.19g/100g (malic acid) and 4.93 of pH. Total solids of treated pulp from centrifugation (5.71%) were lower than the others (13.83 and 13.84%) which consequently caused lower total solids in retentate and permeate fractions. Acidity and pH of treated pulp were different (p<0.05) for the different pre-treatments. Similar behaviors were also verified to retentate and permeate fractions. Values varied from 0.10 to 0.29 g/100g malic acid and pH from 4.17 to 4.98, with no correlation to total solids content. Soluble solids were different for each fraction although there was no significant difference in the same fraction in function of used pre-treatment. The values were 2.87, 1.63 and 4.77oBrix for treated pulp, permeate and retentate, respectively. Average flux was affected by pre-treatment being the lowest values, around 70 L/hm2, obtained after centrifugation and the highest, 110 L/hm2, with the enzymatic action. As physical-chemical parameters did not present a behavior that contributes for the pre-treatment selection, permeate flux results suggest the use of enzyme as the recommended option