257 research outputs found
Funding for Universal Service Obligations in Electricity Sector : the case of green power development
The process of deregulation in network industries, in particular in the electric sector, raises the problem of Ăžnancing the Universal Service Obligations (USO) corresponding to the production, transport and distribution operations. In this paper, we study three ways of funding for an USO of production, especially the "green" electricity development: the Ăžnancing with cross-subsidies, the implementation of a fund (financing by a tax) and finally a voluntary funding system by direct subscriptions of consumers. We notably show that this last one Pareto dominates mostly, from a welfare point of view, the other scenarios.ELECTRICITY ; ENVIRONMENT ; REGULATION ; NETWORK ; UNIVERSAL SERVICE,
Specific lipid recruitment by the retroviral gag protein upon HIV-1 assembly : from model membranes to infected cells
The retroviral Gag protein targets the plasma membrane of infected cells for viral particle formation and release. The matrix domain (MA) of Gag is myristoylated for membrane anchoring but also contains a highly basic region that recognizes acidic phospholipids. Gag targets lipid molecules at the inner leaflet of the plasma membrane including phosphatidylinositol (4,5) bisphosphate (PI(4,5)P2) and cholesterol. Here, we addressed the question whether HIV-1 Gag was able to trap PI(4,5)P2 and/or other lipids during HIV-1 assembly in silico, in vitro on reconstituted membranes and in cellulo at the plasma membrane of the host CD4+ T cells. In silico, we could observe the first PI(4,5)P2 preferential recruitment by HIV-1 MA or Gag while protein docked on artificial membranes. In vitro, using biophysical techniques, we observed the specific trapping of PI(4,5)P2, and, to a lesser extent, cholesterol and the exclusion of sphingomyelin, during HIV-1 myr(-)Gag self-assembly on LUVs and SLBs. Finally, in infected living CD4+ T cells, we measured lipid dynamics within and away from HIV-1 assembly sites using super-resolution stimulated emission depletion (STED) microscopy coupled with scanning Fluorescence Correlation Spectroscopy (sSTED-FCS). The analysis of HIV-1 infected CD4+ T lymphocytes revealed that, upon virus assembly, HIV-1 is able to specifically trap PI(4,5)P2, and cholesterol but not phosphatidylethanolamine (PE) or sphingomyelin (SM) at the cellular membrane. Furthermore, analyzing CD4+ T cells expressing only HIV-1 Gag protein showed that Gag is the main driving force restricting the mobility of PI(4,5)P2 and cholesterol at the cell plasma membrane. Our data provide the first direct evidence showing that HIV-1 Gag creates its own specific lipid environment for virus assembly by selectively recruiting lipids to generate PI(4,5)P2/cholesterol-enriched nanodomains favoring virus assembly, and that HIV-1 does not assemble on pre-existing lipid domains
Recommended from our members
HIV-1 Gag specifically restricts PI(4,5)P2 and cholesterol mobility in living cells creating a nanodomain platform for virus assembly
HIV-1 Gag protein assembles at the plasma membrane of infected cells for viral particle formation. Gag targets lipids, mainly PI(4,5)P2, at the inner leaflet of this membrane. Here, we address the question whether Gag is able to trap specifically PI(4,5)P2 or other lipids during HIV-1 assembly in the host CD4+ T lymphocytes. Lipid dynamics within and away from HIV-1 assembly sites were determined using super-resolution microscopy coupled with scanning fluorescence correlation spectroscopy in living cells. Analysis of HIV-1–infected cells revealed that, upon assembly, HIV-1 is able to specifically trap PI(4,5)P2 and cholesterol, but not phosphatidylethanolamine or sphingomyelin. Furthermore, our data showed that Gag is the main driving force to restrict the mobility of PI(4,5)P2 and cholesterol at the cell plasma membrane. This is the first direct evidence highlighting that HIV-1 creates its own specific lipid environment by selectively recruiting PI(4,5)P2 and cholesterol as a membrane nanoplatform for virus assembly
Adiabatic passage and ensemble control of quantum systems
This paper considers population transfer between eigenstates of a finite
quantum ladder controlled by a classical electric field. Using an appropriate
change of variables, we show that this setting can be set in the framework of
adiabatic passage, which is known to facilitate ensemble control of quantum
systems. Building on this insight, we present a mathematical proof of
robustness for a control protocol -- chirped pulse -- practiced by
experimentalists to drive an ensemble of quantum systems from the ground state
to the most excited state. We then propose new adiabatic control protocols
using a single chirped and amplitude shaped pulse, to robustly perform any
permutation of eigenstate populations, on an ensemble of systems with badly
known coupling strengths. Such adiabatic control protocols are illustrated by
simulations achieving all 24 permutations for a 4-level ladder
E2-quasi-exact solvability for non-Hermitian models
We propose the notion of E2-quasi-exact solvability and apply this idea to find explicit solutions to the eigenvalue problem for a non-Hermitian Hamiltonian system depending on two parameters. The model considered reduces to the complex Mathieu Hamiltonian in a double scaling limit, which enables us to compute the exceptional points in the energy spectrum of the latter as a limiting process of the zeros for some algebraic equations. The coefficient functions in the quasi-exact eigenfunctions are univariate polynomials in the energy obeying a three-term recurrence relation. The latter property guarantees the existence of a linear functional such that the polynomials become orthogonal. The polynomials are shown to factorize for all levels above the quantization condition leading to vanishing norms rendering them to be weakly orthogonal. In two concrete examples we compute the explicit expressions for the Stieltjes measure
The ANTARES Optical Beacon System
ANTARES is a neutrino telescope being deployed in the Mediterranean Sea. It
consists of a three dimensional array of photomultiplier tubes that can detect
the Cherenkov light induced by charged particles produced in the interactions
of neutrinos with the surrounding medium. High angular resolution can be
achieved, in particular when a muon is produced, provided that the Cherenkov
photons are detected with sufficient timing precision. Considerations of the
intrinsic time uncertainties stemming from the transit time spread in the
photomultiplier tubes and the mechanism of transmission of light in sea water
lead to the conclusion that a relative time accuracy of the order of 0.5 ns is
desirable. Accordingly, different time calibration systems have been developed
for the ANTARES telescope. In this article, a system based on Optical Beacons,
a set of external and well-controlled pulsed light sources located throughout
the detector, is described. This calibration system takes into account the
optical properties of sea water, which is used as the detection volume of the
ANTARES telescope. The design, tests, construction and first results of the two
types of beacons, LED and laser-based, are presented.Comment: 21 pages, 18 figures, submitted to Nucl. Instr. and Meth. Phys. Res.
The impact of Stieltjes' work on continued fractions and orthogonal polynomials
Stieltjes' work on continued fractions and the orthogonal polynomials related
to continued fraction expansions is summarized and an attempt is made to
describe the influence of Stieltjes' ideas and work in research done after his
death, with an emphasis on the theory of orthogonal polynomials
- …