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  • Author: F. Vázquez x
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Abstract

The equilibrium Rayleigh-Brillouin spectrum for a Maxwell fluid in which heat conduction is governed by the classical Fourier law is computed. This is done by using fluctuating hydrodynamics and by the alternative procedure used by Mountain. It is found that both calculations render the same results only if the fluctuation-dissipation relations in the former are the ones prescribed by Landau and Lifshitz for the case where a dispersive dissipation coefficient is present. This result brings up the question of whether extended irreversible thermodynamics is the proper underlying nonequilibrium thermodynamic framework for the Maxwell fluid. It also suggests that at least the version of fluctuating hydrodynamics based on extended irreversible thermodynamics as introduced by Jou and Casas-Vázquez many years ago [18] must be revised, since it leads to a different form for the fluctuation-dissipation relations.

Abstract

During a histopathological survey of the geoduck, Panopea abbreviata (Hiatellidae), and the razor clam, Ensis macha (Pharidae), in northern Patagonian gulfs (Argentina), turbellarian worms were found in the intestine lumen. In this work, we described a new species of Paravortex (Platyhelminthes, Graffillidae). We collected the hosts by scuba diving and dissected alive for studying the turbellarians. In this new species, the pharynx continues in a short esophagus and the latter in a saccular intestine. Gravid specimens have from 2 to 8 twin embryos in the parenchyma. A short penis papilla arises from the seminal vesicle and the gonopore presents a strong sphincter. This species resembled P. nicolli Szidat, 1965, which was described paraziting Mytilus edulis platensis in Buenos Aires, Argentina. The new species can be differentiated from P. nicolli mainly by the presence of a penis papilla and a sphincter between genital atrium and gonopore. This turbellarian species was significantly more prevalent in geoducks (28 %, n = 210) than in razor clams (6 %, n = 480) (KW, p < 0.0001). For both host species, no evidence of direct physical damage caused by turbellarians was observed.

Abstract

A surface radio frequency coil was developed for small animal image acquisition in a pre-clinical magnetic resonance imaging system at 7 T. A flexible coil composed of two circular loops was developed to closely cover the object to be imaged. Electromagnetic numerical simulations were performed to evaluate its performance before the coil construction. An analytical expression of the mutual inductance for the two circular loops as a function of the separation between them was derived and used to validate the simulations. The RF coil is composed of two circular loops with a 5 cm external diameter and was tuned to 300 MHz and 50 Ohms matched. The angle between the loops was varied and the Q factor was obtained from the S11 simulations for each angle. B1 homogeneity was also evaluated using the electromagnetic simulations. The coil prototype was designed and built considering the numerical simulation results. To show the feasibility of the coil and its performance, saline-solution phantom images were acquired. A correlation of the simulations and imaging experimental results was conducted showing a concordance of 0.88 for the B1 field. The best coil performance was obtained at the 90° aperture angle. A more realistic phantom was also built using a formaldehyde-fixed rat phantom for ex vivo imaging experiments. All images showed a good image quality revealing clearly defined anatomical details of an ex vivo rat.

The philosophy of green chemistry has been very well received in Latin America’s research and development programs. In this review we describe the green chemistry contributions of Brazilian research groups over the last three years.