El problema de dos fases en materiales heterogéneos. Aplicaciones

El propósito de este trabajo es extender la metodología desarrollada por Nochetto y colaboradores1-" para resolver el problema de Stefan al caso de materiales heterogéneos, es decir, aquellos para los cuales las propiedades físicas dependen de la ubicación espacial. Es éste un caso de particular interés práctico. Luego de la presentación de aspectos teóricos y computacionales, se describe la resolución de algunos problemas asociados al modelado de situaciones de incendio originadas por accidentes en el transporte de hexafluoruro de uranio.In this paper we present an extension of the methodology developed by R.H. Nochetto et to solve the Stefan problem, to situations for which the physical properties depend on the spatial point (thermically non-homogeneous materials). This is certainly a case of practica1 interest. After facing the theoretical and computational aspects, we describe the resolution of some problems associated to the modelling of fires originated by accidents in the transport of containers filled with uranium hexafluoride.Peer Reviewe

Simulación por elementos finitos de los primeros instantes de la extrusión de vainas de combustible para centrales nucleares

Se simularon los primeros instantes del proceso de extrusión de vainas de ZRY-4, utilizando el código de Elementos Finitos VELPEF, y un modelo para el material de tipo viscoelástico seudoplástico. Se estudiaron los campos de tensiones, presiones y velocidades, presiones en la matriz, el mandril, el contenedor y el pistón, la influencia en las anteriores de la fricción, la geometría y la temperatura.ZRY-4 cladding estrusion first moments were simulated, by VELPEF finite elements code, and a viscoelastic pseudoplastic model for the material. Stress, strain, presure and velocity fields, pressure on the die, mandrel, container and piston were studied, as weii as the influence of friction, geometry and temperature on the former.Peer Reviewe

Simulación por elementos finitos de los primeros instantes de la extrusión de vainas de combustible para centrales nucleares

Se simularon los primeros instantes del proceso de extrusión de vainas de ZRY-4, utilizando el código de Elementos Finitos VELPEF, y un modelo para el material de tipo viscoelástico seudoplástico. Se estudiaron los campos de tensiones, presiones y velocidades, presiones en la matriz, el mandril, el contenedor y el pistón, la influencia en las anteriores de la fricción, la geometría y la temperatura.ZRY-4 cladding estrusion first moments were simulated, by VELPEF finite elements code, and a viscoelastic pseudoplastic model for the material. Stress, strain, presure and velocity fields, pressure on the die, mandrel, container and piston were studied, as weii as the influence of friction, geometry and temperature on the former.Peer Reviewe

Fourier analysis of an equal‐order incompressible flow solver stabilized by pressure gradient projection

Fourier analysis techniques are applied to the stabilized finite element method (FEM) recently proposed by Codina and Blasco for the approximation of the incompressible Navier–Stokes equations, here denoted by pressure gradient projection (SPGP) method. The analysis is motivated by spurious waves that pollute the computed pressure in start‐up flow simulation. An example of this spurious phenomenon is reported. It is shown that Fourier techniques can predict the numerical behaviour of stabilized methods with remarkable accuracy, even though the original Navier–Stokes setting must be significantly simplified to apply them. In the steady state case, good estimates for the stabilization parameters are obtained. In the transient case, spurious long waves are shown to be persistent when the element Reynolds number is large and the Courant number is small. This can be avoided by treating the pressure gradient projection implicitly, though this implies additional computing effort. Standard extrapolation variants are unfortunately unstable. Comparisons with Galerkin–least‐squares (GLS) method and Chorin's projection method are also addresse

The costs of preventing and treating chagas disease in Colombia

Background: The objective of this study is to report the costs of Chagas disease in Colombia, in terms of vector disease control programmes and the costs of providing care to chronic Chagas disease patients with cardiomyopathy. Methods: Data were collected from Colombia in 2004. A retrospective review of costs for vector control programmes carried out in rural areas included 3,084 houses surveyed for infestation with triatomine bugs and 3,305 houses sprayed with insecticide. A total of 63 patient records from 3 different hospitals were selected for a retrospective review of resource use. Consensus methodology with local experts was used to estimate care seeking behaviour and to complement observed data on utilisation. Findings: The mean cost per house per entomological survey was $4.4 (in US$ of 2004), whereas the mean cost of spraying a house with insecticide was $27. The main cost driver of spraying was the price of the insecticide, which varied greatly. Treatment of a chronic Chagas disease patient costs between$46.4 and $7,981 per year in Colombia, depending on severity and the level of care used. Combining cost and utilisation estimates the expected cost of treatment per patient-year is$1,028, whereas lifetime costs averaged $11,619 per patient. Chronic Chagas disease patients have limited access to healthcare, with an estimated 22% of patients never seeking care. Conclusion: Chagas disease is a preventable condition that affects mostly poor populations living in rural areas. The mean costs of surveying houses for infestation and spraying infested houses were low in comparison to other studies and in line with treatment costs. Care seeking behaviour and the type of insurance affiliation seem to play a role in the facilities and type of care that patients use, thus raising concerns about equitable access to care. Preventing Chagas disease in Colombia would be cost-effective and could contribute to prevent inequalities in health and healthcare.Wellcome Trus

El problema de dos fases en materiales heterogéneos. Aplicaciones

El propósito de este trabajo es extender la metodología desarrollada por Nochetto y colaboradores1-" para resolver el problema de Stefan al caso de materiales heterogéneos, es decir, aquellos para los cuales las propiedades físicas dependen de la ubicación espacial. Es éste un caso de particular interés práctico. Luego de la presentación de aspectos teóricos y computacionales, se describe la resolución de algunos problemas asociados al modelado de situaciones de incendio originadas por accidentes en el transporte de hexafluoruro de uranio.In this paper we present an extension of the methodology developed by R.H. Nochetto et to solve the Stefan problem, to situations for which the physical properties depend on the spatial point (thermically non-homogeneous materials). This is certainly a case of practica1 interest. After facing the theoretical and computational aspects, we describe the resolution of some problems associated to the modelling of fires originated by accidents in the transport of containers filled with uranium hexafluoride.Peer Reviewe

Simulación por elementos finitos de los primeros instantes de la extrusión de vainas de combustible para centrales nucleares

Se simularon los primeros instantes del proceso de extrusión de vainas de ZRY-4, utilizando el código de Elementos Finitos VELPEF, y un modelo para el material de tipo viscoelástico seudoplástico. Se estudiaron los campos de tensiones, presiones y velocidades, presiones en la matriz, el mandril, el contenedor y el pistón, la influencia en las anteriores de la fricción, la geometría y la temperatura.ZRY-4 cladding estrusion first moments were simulated, by VELPEF finite elements code, and a viscoelastic pseudoplastic model for the material. Stress, strain, presure and velocity fields, pressure on the die, mandrel, container and piston were studied, as weii as the influence of friction, geometry and temperature on the former.Peer Reviewe

Gene-deleted live-attenuated Trypanosoma cruzi parasites as vaccines to protect against Chagas disease

© Informa UK, Ltd. Chagas disease is a neglected tropical disease caused by the protozoan parasite Trypanosoma cruzi. This illness is now becoming global, mainly due to congenital transmission, and so far, there are no prophylactic or therapeutic vaccines available to either prevent or treat Chagas disease. Therefore, different approaches aimed at identifying new protective immunogens are urgently needed. Live vaccines are likely to be more efficient in inducing protection, but safety issues linked with their use have been raised. The development of improved protozoan genetic manipulation tools and genomic and biological information has helped to increase the safety of live vaccines. These advances have generated a renewed interest in the use of genetically attenuated parasites as vaccines against Chagas disease. This review discusses the protective capacity of genetically attenuated parasite vaccines and the challenges and perspectives for the development of an effective whole-parasi

Serological Evaluation of Specific-Antibody Levels in Patients Treated for Chronic Chagas' Disease▿†

Serological tests are the main laboratory procedures used for diagnosis during the indeterminate and chronic stages of Chagas' disease. A serological regression to negativity is the main criterion used to define parasitological cure in treated patients. The aim of this work was to monitor the individual specificities of antibody levels for 3 years posttreatment in 18 adult patients. Conventional serological techniques (hemagglutination assays and enzyme-linked immunosorbent assay [ELISA]) were modified by using recombinant antigens to detect early markers of treatment effectiveness. For this purpose, serum samples were taken before and during treatment and every 6 months after treatment for at least 3 years. When hemagglutination assays were used, a decrease in antibody levels was observed in only one patient. When ELISA with serum dilutions was used, antibody clearance became much more apparent: in 77.7% (14/18) of the patients, antibody titers became negative with time. This was observed at serum dilutions of 1/320 and occurred between the 6th and the 30th months posttreatment. The immune response and the interval for a serological regression to negativity were different for each patient. For some of the recombinant antigens, only 50% (9/18) of the patients reached the serological regression to negativity. Recombinant antigen 13 might be a good marker of treatment effectiveness, since 66.6% (six of nine) of the patients presented with an early regression to negativity for specific antibodies to this antigen (P = 0.002)

A monoallelic deletion of the TcCRT gene increases the attenuation of a cultured Trypanosoma cruzi strain, protecting against an in vivo virulent challenge.

Trypanosoma cruzi calreticulin (TcCRT) is a virulence factor that binds complement C1, thus inhibiting the activation of the classical complement pathway and generating pro-phagocytic signals that increase parasite infectivity. In a previous work, we characterized a clonal cell line lacking one TcCRT allele (TcCRT+/-) and another overexpressing it (TcCRT+), both derived from the attenuated TCC T. cruzi strain. The TcCRT+/- mutant was highly susceptible to killing by the complement machinery and presented a remarkable reduced propagation and differentiation rate both in vitro and in vivo. In this report, we have extended these studies to assess, in a mouse model of disease, the virulence, immunogenicity and safety of the mutant as an experimental vaccine. Balb/c mice were inoculated with TcCRT+/- parasites and followed-up during a 6-month period. Mutant parasites were not detected by sensitive techniques, even after mice immune suppression. Total anti-T. cruzi IgG levels were undetectable in TcCRT+/- inoculated mice and the genetic alteration was stable after long-term infection and it did not revert back to wild type form. Most importantly, immunization with TcCRT+/- parasites induces a highly protective response after challenge with a virulent T. cruzi strain, as evidenced by lower parasite density, mortality, spleen index and tissue inflammatory response. TcCRT+/- clones are restricted in two important properties conferred by TcCRT and indirectly by C1q: their ability to evade the host immune response and their virulence. Therefore, deletion of one copy of the TcCRT gene in the attenuated TCC strain generated a safe and irreversibly gene-deleted live attenuated parasite with high immunoprotective properties. Our results also contribute to endorse the important role of TcCRT as a T. cruzi virulence factor