795 research outputs found
Homogenization of Periodic Semilinear Parabolic Degenerate PDEs
International audienc
Electrohydraulic Crimping of 316L Tube in a 316L Thick Ring
During the electrohydraulic forming process a high current, up to one hundred of kilo amperes, is discharged between two electrodes immersed in a water tank. This creates
plasma that generates a primary shock wave and secondary pressure waves. If these
pressures are applied in a tube, it is then possible to deform dynamically this tube against
a ring, leading to crimping. This process presents several advantages: it is possible to
deform internally tubes of diameters ranging from a few millimetres to several centimetres,
no lubrication is needed and because the process is dynamic, the spring back is limited and
some materials can present an improved behaviour compared to quasi-static forming.
In this paper, we present an original electrohydraulic crimping device. We successively
present the operating principle of our system, the time evolution of the crimping pressure
and the strain rate in the tube for two kinds of pulse shaper. Finally crimping tests are
done to evaluate the efficiency of the process
Determining Pair Interactions from Structural Correlations
We examine metastable configurations of a two-dimensional system of
interacting particles on a quenched random potential landscape and ask how the
configurational pair correlation function is related to the particle
interactions and the statistical properties of the potential landscape.
Understanding this relation facilitates quantitative studies of magnetic flux
line interactions in type II superconductors, using structural information
available from Lorentz microscope images or Bitter decorations.
Previous work by some of us supported the conjecture that the relationship
between pair correlations and interactions in pinned flux line ensembles is
analogous to the corresponding relationship in the theory of simple liquids.
The present paper aims at a more thorough understanding of this relation. We
report the results of numerical simulations and present a theory for the low
density behavior of the pair correlation function which agrees well with our
simulations and captures features observed in experiments. In particular, we
find that the resulting description goes beyond the conjectured classical
liquid type relation and we remark on the differences.Comment: 7 pages, 6 figures. See also http://rainbow.uchicago.edu/~grier
Direct observation of the influence of the As-Fe-As angle on the Tc of superconducting SmFeAsOF
The electrical resistivity, crystalline structure and electronic properties
calculated from the experimentally measured atomic positions of the compound
SmFeAsOF have been studied up to pressures ~20GPa. The
correlation between the pressure dependence of the superconducting transition
temperature (Tc) and crystallographic parameters on the same sample shows
clearly that a regular FeAs tetrahedron maximizes Tc, through
optimization of carrier transfer to the FeAs planes as indicated by the
evolution of the electronic band structures.Comment: 15pages, 4 figure
Hepatitis B testing and treatment in HIV patients in The Gambia - compliance with international guidelines and clinical outcomes
Background Compliance with WHO guidelines on HBV screening and treatment in HIV-coinfected patients is often challenging in resource limited countries and has been poorly assessed in sub-Saharan Africa. Methods Between 2015 and 2016, we assessed physician’s compliance with WHO guidelines on HIV-HBV coinfection in the largest HIV clinic in The Gambia, and the hepatic outcomes in HIV-HBV coinfected patients as compared to randomly selected HIV-monoinfected controls. Results 870 HIV-infected patients regularly seen in this clinic agreed to participate in our study. Only 187 (21.5%, 95% CI 18.8–24.3) had previously been screened for HBsAg, 23 (12.3%, 95% CI 8.0–17.9) were positive of whom none had liver assessment and only 6 (26.1%) had received Tenofovir. Our HBV testing intervention was accepted by all participants and found 94/870 (10.8%, 95% CI 8.8–13.1) positive, 78 of whom underwent full liver assessment along with 40 HBsAg-negative controls. At the time of liver assessment, 61/78 (78.2%) HIV-HBV coinfected patients received ART with 7 (11.5%) on Tenofovir and 54 (88.5%) on Lamivudine alone. HIV-HBV coinfected patients had higher APRI score compared to controls (0.58 vs 0.42, p = 0.002). HBV DNA was detectable in 52/53 (98.1%) coinfected patients with 14/53 (26.4%) having HBV DNA >20,000 IU/L. 10/12 (83.3%) had at least one detectable 3TC-associated HBV resistance, which tended to be associated with increase in liver fibrosis after adjusting for age and sex (p = 0.05). Conclusions Compliance with HBV testing and treatment guidelines is poor in this Gambian HIV programme putting coinfected patients at risk of liver complications. However, the excellent uptake of HBV screening and linkage to care in our study suggests feasible improvements
Effects of kinked linear defects on planar flux line arrays
In the hard core limit, interacting vortices in planar type II
superconductors can be modeled as non-interacting one dimensional fermions
propagating in imaginary time. We use this analogy to derive analytical
expressions for the probability density and imaginary current of vortex lines
interacting with an isolated bent line defect and to understand the pinning
properties of such systems. When there is an abrupt change of the direction of
the pinning defect, we find a sinusoidal modulation of the vortex density in
directions both parallel and perpendicular to the defect.Comment: 13 figure
Bioenergy and African Transformation
Among the world’s continents, Africa has the highest incidence of food insecurity and poverty and the highest rates of population growth. Yet Africa also has the most arable land, the lowest crop yields, and by far the most plentiful land resources relative to energy demand. It is thus of interest to examine the potential of expanded modern bioenergy production in Africa. Here we consider bioenergy as an enabler for development, and provide an overview of modern bioenergy technologies with a comment on application in an Africa context. Experience with bioenergy in Africa offers evidence of social benefits and also some important lessons. In Brazil, social development, agricultural development and food security, and bioenergy development have been synergistic rather than antagonistic. Realizing similar success in African countries will require clear vision, good governance, and adaptation of technologies, knowledge, and business models to myriad local circumstances. Strategies for integrated production of food crops, livestock, and bioenergy are potentially attractive and offer an alternative to an agricultural model featuring specialized land use. If done thoughtfully, there is considerable evidence that food security and economic development in Africa can be addressed more effectively with modern bioenergy than without it. Modern bioenergy can be an agent of African transformation, with potential social benefits accruing to multiple sectors and extending well beyond energy supply per se. Potential negative impacts also cut across sectors. Thus, institutionally inclusive multi-sector legislative structures will be more effective at maximizing the social benefits of bioenergy compared to institutionally exclusive, single-sector structures
- …