12,725 research outputs found
Improving sensitivity of oral fluid testing in IgG prevalence studies: application of mixture models to a rubella antibody survey
A method for the analysis of age-stratified antibody prevalence surveys is applied to a previously reported survey of antibody to rubella virus using oral fluid samples in which the sensitivity of the assay used was shown to be compromised. The age-specific distribution of the quantitative results of antibody tests using oral fluids is modelled as a mixture of strong positive, weak positive and negative components. This yields maximum likelihood estimates of the prevalence at each age and demonstrates that, when used in conjunction with mixture modelling techniques, the results of antibody prevalence studies using oral fluids accurately reflect those obtained using sera
Variational principles for spin systems and the Kirchhoff rod
We obtain the affine Euler-Poincar\'e equations by standard Lagrangian
reduction and deduce the associated Clebsch-constrained variational principle.
These results are illustrated in deriving the equations of motion for continuum
spin systems and Kirchhoff's rod, where they provide a unified geometric
interpretation.Comment: Submitted to Journal of Geometric Mechanics, 29 pages, no figure
Cavitation-induced force transition in confined viscous liquids under traction
We perform traction experiments on simple liquids highly confined between
parallel plates. At small separation rates, we observe a simple response
corresponding to a convergent Poiseuille flow. Dramatic changes in the force
response occur at high separation rates, with the appearance of a force plateau
followed by an abrupt drop. By direct observation in the course of the
experiment, we show that cavitation accounts for these features which are
reminiscent of the utmost complex behavior of adhesive films under traction.
Surprisingly enough, this is observed here in purely viscous fluids.Comment: Submitted to Physical Review Letters on May 31, 2002. Related
informations on http://www.crpp.u-bordeaux.fr/tack.htm
Geometric analysis of noisy perturbations to nonholonomic constraints
We propose two types of stochastic extensions of nonholonomic constraints for
mechanical systems. Our approach relies on a stochastic extension of the
Lagrange-d'Alembert framework. We consider in details the case of invariant
nonholonomic systems on the group of rotations and on the special Euclidean
group. Based on this, we then develop two types of stochastic deformations of
the Suslov problem and study the possibility of extending to the stochastic
case the preservation of some of its integrals of motion such as the Kharlamova
or Clebsch-Tisserand integrals
Preliminary hidrological results from Sarennes glacier basin, French Alps
Located in the French Alps, Glacier de Sarennes is a small glacier which has its mass balance, measured since 1948. Now since 1992, the Snow Engineenng and Avalanche control department of Cemagref Grenoble measures water leve1 in the emissary of this glacier at the altitude of 2800 meters. The time step of these records is 10 minutes. The aim of this study is to realize the first hydrological assessment, despite having few records until now, to be able to control the new experimental discharge station, and to extract the first scientific results
Sensitivity of the superconducting state in thin films
For more than two decades, there have been reports on an unexpected metallic state separating the established superconducting and insulating phases of thin-film superconductors. To date, no theoretical explanation has been able to fully capture the existence of such a state for the large variety of superconductors exhibiting it. Here, we show that for two very different thin-film superconductors, amorphous indium oxide and a single crystal of 2H-NbSe2, this metallic state can be eliminated by adequately filtering external radiation. Our results show that the appearance of temperature-independent, metallic-like transport at low temperatures is sufficiently described by the extreme sensitivity of these superconducting films to external perturbations. We relate this sensitivity to the theoretical observation that, in two dimensions, superconductivity is only marginally stable
SIRT1 overexpression in the rheumatoid arthritis synovium contributes to proinflammatory cytokine production and apoptosis resistance
Preliminary hidrological results from Sarennes glacier basin, French Alps
Located in the French Alps, Glacier de Sarennes is a small glacier which has its mass balance, measured since 1948. Now since 1992, the Snow Engineenng and Avalanche control department of Cemagref Grenoble measures water leve1 in the emissary of this glacier at the altitude of 2800 meters. The time step of these records is 10 minutes. The aim of this study is to realize the first hydrological assessment, despite having few records until now, to be able to control the new experimental discharge station, and to extract the first scientific results
Un-reduction
This paper provides a full geometric development of a new technique called
un-reduction, for dealing with dynamics and optimal control problems posed on
spaces that are unwieldy for numerical implementation. The technique, which was
originally concieved for an application to image dynamics, uses Lagrangian
reduction by symmetry in reverse. A deeper understanding of un-reduction leads
to new developments in image matching which serve to illustrate the
mathematical power of the technique.Comment: 25 pages, revised versio
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