A criterion for the equivalence of the Birkhoff-Rott and Euler descriptions of vortex sheet evolution

In this article we consider the evolution of vortex sheets in the plane both as a weak solution of the two dimensional incompressible Euler equations and as a (weak) solution of the Birkhoff-Rott equations. We begin by discussing the classical Birkhoff-Rott equations with respect to arbitrary parametrizations of the sheet. We introduce a notion of weak solution to the Birkhoff-Rott system, and we prove consistency of this notion with the classical formulation of the equations. Our main purpose in this paper is to present a sharp criterion for the equivalence of the weak Euler and weak Birkhoff-Rott descriptions of vortex sheet dynamics.35994125414

Amniocentesis and biochemical evaluation of amniotic fluid in ewes at 70, 100 and 145 days of pregnancy

The objectives of this study were to determine the technical viability of amniocentesis in sheep and to observe biochemical changes in the amniotic fluid components. Amniotic fluid samples were collected by puncture in the greatest curvature of the uterine hum at days 70, 100, and 145 of pregnancy. The surgical procedure for collection of amniotic fluid samples was safe and efficient. For three stages of pregnancy, the following results were obtained: pH values 8.36, 7.34 and 7.37; glucose concentrations, 16.06. 8.58, and 3.79 g/dl; urea values, 42.68, 33.53, and 25.49 mg/dl; creatinine, 0.85, 5.04, and 11.25 g/dl; Gama-GT enzyme, 12.58, 14.20, and 12.30 UI/l; sodium concentrations, 146.60, 129.42, and 103.8 mmol/l: potassium concentrations, 9.79, 6.15, and 8.65 mmol/l; chloride, 96.59, 85.28, and 65.35 mmol/l; total protein, 0.14, 0.23, and 0.24 g/dl, respectively. (C) 2001 Elsevier B.V. B.V. All rights reserved

Effect of Mo concentration and aging time on the magnetic and mechanical hardness of Fe-xMo-5Ni-0.05C alloys (x = 5, 8, 11 and 15 wt. (%))

Changes to the microestructure during thermal aging treatment at 610 ºC in Fe-xMo-5Ni-0.05C alloys were studied for different aging times with different Mo concentrations. The heat treatment at 610 ºC induces carbide precipitation into the metallic matrix near Fe2Mo phase. The X-ray diffraction studies revealed a more intense precipitation of α-FeMo, Fe3Mo, R(Fe63Mo37) phases and MoC, Fe2MoC carbides for the alloys containing 15 and 11% Mo, respectively. This work shows that hardness and coercive force changes are function of the molybdenum content and aging time variation. Vickers hardness and coercive force both increase with the increase of molybdenum content and reach maximum values at 4 and 1h of aging, respectively

Brain single-photon emission computed tomography and magnetic resonance imaging in Machado-Joseph disease

Background: Machado-Joseph disease (MJD) is one of the most frequently encountered spinocerebellar ataxias. However, few reports on brain single-photon emission computed tomographic (SPECT) imaging (BSI) with hexylmethylpropylene amineoxine labled with technetium Tc99m and magnetic resonance imaging (MRI) have been performed for the evaluation of patients with MJD. Objectives: To investigate possible abnormalities with BSI and MRI in patients with MJD and to correlate these findings with the duration of symptoms; cerebellar, extrapyramidal, and pyramidal syndromes; and the molecular characteristics of the MJD mutation. Patients and Methods: Twelve patients (8 males and 4 females [mean age, 39 years]) with genetically proven MJD were studied. The patients underwent BST and MRI on the same day. Brain SPECT imaging was performed after an intravenous injection of Tc-99m-hexylniethylpropylene amineoxine. The transaxial, coronal, and sagittal BSIs obtained were submitted to visual and semiquantitative analyses. Magnetic resonance imaging was obtained in a 2-T system with coronal, sagittal, transaxial, and 3-dimensional (volumetric) acquisitions. The volumes of the cerebellar hemispheres and vermis were calculated. Control groups for BSI (22 female and 20 male subjects [mean age, 33 years]) and MRI (13 female and 4 male subjects [mean age, 32.2 years]) were included for comparison. Results: Correlation was observed between the perfusion abnormalities identified by visual analysis in the BSI with the structural abnormalities observed on MRI in the parietal lobes and vermis. Brain SPECT imaging identified (by visual analysis) more perfusion abnormalities in the inferior portion of the frontal lobes, mesial and lateral portions of the temporal lobes, basal ganglia, and cerebellar hemispheres. Magnetic resonance imaging identified more abnormalities in the pons and superior portions of the frontal lobes. Olivary atrophy was identified by MRI. Semiquantitative analysis showed a statistically significant difference of perfusion in the inferior and superior portions of the frontal lobes, lateral portion of the temporal lobes, parietal lobes, left basal ganglia, cerebellar hemispheres, and vermis when compared with the control group. A significant difference was noted between the vermis and cerebellar volumes on MRI when compared with the control group. A significant relationship was observed between the perfusion of the left parietal lobe (P=.05) and extrapyramidal syndrome. There was a tendency toward an inverse relationship between the duration of symptoms and the perfusion of the cerebellar hemispheres (rho=-0.37; P=.24) and volume of the vermis (rho=-0.30; P=34); between the length of the expanded (CAG)(n) repeat and the perfusion of the left parietal lobe (rho=-0.32; P =36), vermis (rho=-0.28; P =.43), and pons (rho=-0.28; P=.42). A direct association was observed between the length of the expanded (CAG), repeat and the perfusion of the lateral portion of the right temporal lobe (rho =0.67; P=.03). Conclusions: Brain SPECT imaging and MRI were capable of identifying subclinical abnormalities in individuals with MJD. These findings may be helpful for a better understanding of the pathophysiology of this disease.5881257126