La consultation pour le test sérologique de dépistage VIH : enjeux pour le couple et pour le médecin

La pratique du test au centre de dépistage anonyme VIH de la Policlinique médicale universitaire de Lausanne semble indiquer que de plus en plus de personnes demandent à être testées, souvent au moment inaugural de la constitution de la vie du couple. L'indication au test de dépistage devrait être le résultat d'une négociation entre le patient et son médecin. Ce dernier est en outre confronté à la complexité des enjeux sociétaux et éthiques que le test représente. Il s'agit d'une tâche difficile, d'autant plus que la requête d'un test n'implique pas le seul devenir du sujet, mais aussi, dans la dimension sexuelle, le devenir de la personne qu'il rencontre. L'avènement du Sida a modifié la vie du couple en rendant la sexualité plus problématique et en donnant un caractère impératif l'exigence de négociation entre les partenaires du couple. La pratique de la prévention révèle aussi comment le Sida met en jeu la responsabilité que les médecins ont de négocier avec leurs patients, à l'instar de ce que ces derniers devraient faire avec leur partenaire dans un but de protection.

Calibration of high-resolution geophysical data with tracer test measurements to improve hydrological predictions

Relationships between porosity and hydraulic conductivity tend to be strongly scale- and site-dependent and are thus very difficult to establish. As a result, hydraulic conductivity distributions inferred from geophysically derived porosity models must be calibrated using some measurement of aquifer response. This type of calibration is potentially very valuable as it may allow for transport predictions within the considered hydrological unit at locations where only geophysical measurements are available, thus reducing the number of well tests required and thereby the costs of management and remediation. Here, we explore this concept through a series of numerical experiments. Considering the case of porosity characterization in saturated heterogeneous aquifers using crosshole ground-penetrating radar and borehole porosity log data, we use tracer test measurements to calibrate a relationship between porosity and hydraulic conductivity that allows the best prediction of the observed hydrological behavior. To examine the validity and effectiveness of the obtained relationship, we examine its performance at alternate locations not used in the calibration procedure. Our results indicate that this methodology allows us to obtain remarkably reliable hydrological predictions throughout the considered hydrological unit based on the geophysical data only. This was also found to be the case when significant uncertainty was considered in the underlying relationship between porosity and hydraulic conductivity.

test

test

A pseudo-spectral method for simulating of poro-elastic seismic wave propagation in complex borehole environments

We present a novel numerical approach for the comprehensive, flexible, and accurate simulation of poro-elastic wave propagation in cylindrical coordinates. An important application of this method is the modeling of complex seismic wave phenomena in fluid-filled boreholes, which represents a major, and as of yet largely unresolved, computational problem in exploration geophysics. In view of this, we consider a numerical mesh consisting of three concentric domains representing the borehole fluid in the center, the borehole casing and the surrounding porous formation. The spatial discretization is based on a Chebyshev expansion in the radial direction, Fourier expansions in the other directions, and a Runge-Kutta integration scheme for the time evolution. A domain decomposition method based on the method of characteristics is used to match the boundary conditions at the fluid/porous-solid and porous-solid/porous-solid interfaces. The viability and accuracy of the proposed method has been tested and verified in 2D polar coordinates through comparisons with analytical solutions as well as with the results obtained with a corresponding, previously published, and independently benchmarked solution for 2D Cartesian coordinates. The proposed numerical solution also satisfies the reciprocity theorem, which indicates that the inherent singularity associated with the origin of the polar coordinate system is handled adequately.

Qualidade do solo avaliada pelo "Soil Quality Kit Test" em dois experimentos de longa duração no Rio Grande do Sul

A avaliação da qualidade do solo (QS) é importante estratégia no planejamento agrícola, possibilitando a identificação e o aprimoramento de sistemas de manejo com características de alta produtividade e de preservação ambiental. O presente estudo foi realizado em dois experimentos de longa duração (10 e 15 anos) conduzidos no Sul do Brasil e teve por objetivo avaliar o efeito de sistemas de manejo na QS, utilizando um kit de análise expedita de qualidade de solo (KQS), desenvolvido pelo Instituto de Qualidade do Solo-USDA-ARS. A eficiência desse kit foi avaliada pela comparação com os métodos tradicionais utilizados na ciência do solo. Nas duas áreas experimentais investigou-se um total de 12 tratamentos, os quais englobaram sistemas de preparo com diferentes intensidades de revolvimento do solo (preparo convencional, preparo reduzido e plantio direto) e sistemas de culturas com ampla faixa de adição de resíduos vegetais ao solo, além da aplicação de doses anuais de N-uréia, variando de 0 a 144 kg ha-1. Em cada base experimental uma área sob campo natural foi avaliada, servindo como referência da condição do solo na ausência de interferência antrópica. Como indicadores de QS, foram avaliados infiltração de água, respiração do solo, densidade do solo, teor de nitrato+nitrito (N-NO3- + N-NO2-), estabilidade de agregados em água e pH. De maneira geral, os coeficientes de correlação entre os métodos do KQS e os métodos tradicionais foram elevados, sendo o mais alto para o indicador pH (r = 0,98) e o menor para o indicador infiltração de água no solo (r = 0,42). Os tratamentos selecionados foram teoricamente ordenados em ordem crescente de QS, a qual foi reproduzida de forma eficiente pelo índice de estoque de carbono (IEC), calculado pela razão entre o estoque de C orgânico do solo, na camada de 0-5 cm, de cada tratamento e o estoque de C orgânico no solo sob campo natural. Os indicadores estabilidade de agregados, N-NO3- + N-NO2- e respiração do solo foram os mais eficientes em discriminar a QS. O KQS foi eficiente em avaliar a QS dos tratamentos nas duas áreas experimentais. Os níveis mais elevados de QS foram alcançados nos tratamentos com plantio direto e consórcio de gramíneas e leguminosas tropicais, devido à cobertura do solo e às elevadas adições de C e N via resíduos culturais.

Numerical analysis of wave-induced fluid flow effects on seismic data: Application to monitoring of CO2 storage at the Sleipner Field

In this work we analyze how patchy distributions of CO2 and brine within sand reservoirs may lead to significant attenuation and velocity dispersion effects, which in turn may have a profound impact on surface seismic data. The ultimate goal of this paper is to contribute to the understanding of these processes within the framework of the seismic monitoring of CO2 sequestration, a key strategy to mitigate global warming. We first carry out a Monte Carlo analysis to study the statistical behavior of attenuation and velocity dispersion of compressional waves traveling through rocks with properties similar to those at the Utsira Sand, Sleipner field, containing quasi-fractal patchy distributions of CO2 and brine. These results show that the mean patch size and CO2 saturation play key roles in the observed wave-induced fluid flow effects. The latter can be remarkably important when CO2 concentrations are low and mean patch sizes are relatively large. To analyze these effects on the corresponding surface seismic data, we perform numerical simulations of wave propagation considering reservoir models and CO2 accumulation patterns similar to the CO2 injection site in the Sleipner field. These numerical experiments suggest that wave-induced fluid flow effects may produce changes in the reservoir's seismic response, modifying significantly the main seismic attributes usually employed in the characterization of these environments. Consequently, the determination of the nature of the fluid distributions as well as the proper modeling of the seismic data constitute important aspects that should not be ignored in the seismic monitoring of CO2 sequestration problems.

Level shifts in a panel data based unit root test : an application to the rate of unemployment

Several unit root tests in panel data have recently been proposed. The test developed by Harris and Tzavalis (1999 JoE) performs particularly well when the time dimension is moderate in relation to the cross-section dimension. However, in common with the traditional tests designed for the unidimensional case, it was found to perform poorly when there is a structural break in the time series under the alternative. Here we derive the asymptotic distribution of the test allowing for a shift in the mean, and assess the small sample performance. We apply this new test to show how the hypothesis of (perfect) hysteresis in Spanish unemployment is rejected in favour of the alternative of the natural unemployment rate, when the possibility of a change in the latter is considered.

Ambient seismic noise monitoring of a clay landslide: Toward failure prediction

Given that clay-rich landslides may become mobilized, leading to rapid mass movements (earthflows and debris flows), they pose critical problems in risk management worldwide. The most widely proposed mechanism leading to such flow-like movements is the increase in water pore pressure in the sliding mass, generating partial or complete liquefaction. This solid-to-liquid transition results in a dramatic reduction of mechanical rigidity in the liquefied zones, which could be detected by monitoring shear wave velocity variations. With this purpose in mind, the ambient seismic noise correlation technique has been applied to measure the variation in the seismic surface wave velocity in the Pont Bourquin landslide (Swiss Alps). This small but active composite earthslide-earthflow was equipped with continuously recording seismic sensors during spring and summer 2010. An earthslide of a few thousand cubic meters was triggered in mid-August 2010, after a rainy period. This article shows that the seismic velocity of the sliding material, measured from daily noise correlograms, decreased continuously and rapidly for several days prior to the catastrophic event. From a spectral analysis of the velocity decrease, it was possible to determine the location of the change at the base of the sliding layer. These results demonstrate that ambient seismic noise can be used to detect rigidity variations before failure and could potentially be used to predict landslides.

Effect of the environment inside and outside the cage on the activity and behaviour test performance of silver foxes

Selostus: Kasvatushäkin ympäristön vaikutus hopeakettujen käyttäytymiseen

Level shifts in a panel data based unit root test : an application to the rate of unemployment

Several unit root tests in panel data have recently been proposed. The test developed by Harris and Tzavalis (1999 JoE) performs particularly well when the time dimension is moderate in relation to the cross-section dimension. However, in common with the traditional tests designed for the unidimensional case, it was found to perform poorly when there is a structural break in the time series under the alternative. Here we derive the asymptotic distribution of the test allowing for a shift in the mean, and assess the small sample performance. We apply this new test to show how the hypothesis of (perfect) hysteresis in Spanish unemployment is rejected in favour of the alternative of the natural unemployment rate, when the possibility of a change in the latter is considered.