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Search Results: 1 - 10 of 117988 matches for " T. Lasserre "
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EROS2 microlensing search towards the Magellanic Clouds
T. Lasserre,EROS Collaboration
Physics , 1999,
Abstract: EROS2 is a second generation microlensing experiment operating since mid-1996 at the European Southern Observatory (ESO) at La Silla (Chile). We present the two year analysis from our microlensing search towards the Small Magellanic Cloud (SMC) and report on the intensive observation of the caustic crossing event MACHO-SMC-98-1 and the limit derived on t he location of the lens. We also give preliminary results from our search towards the Large Magellanic Cloud (LMC); 25 square degrees are being analyzed and two candidates have been found. This allows us to set another limit on the halo mass fraction comprised of compact objects.
Not enough stellar Mass Machos in the Galactic Halo
T. Lasserre,EROS Collaboration
Physics , 2000,
Abstract: We combine new results from the search for microlensing towards the Large Magellanic Cloud (LMC) by EROS2 (Experience de Recherche d'Objets Sombres) with limits previously reported by EROS1 and EROS2 towards both Magellanic Clouds. The derived upper limit on the abundance of stellar mass MACHOs rules out such objects as an important component of the Galactic halo if their mass is smaller than 1 solar mass.
Modified Bean Seed Protein Phaseolin Did Not Accumulate Stably in Transgenic Tobacco Seeds after Methionine Enhancement Mutations  [PDF]
Eric Lasserre, T. S. Ko, John M. Dyer, Norimoto Murai
American Journal of Plant Sciences (AJPS) , 2015, DOI: 10.4236/ajps.2015.65069
Abstract: The major seed storage protein phaseolin of common bean (Phaseolus vulgaris L.) is deficient in methionine, an essential amino acid for human and animal health. To improve the nutritional quality of common bean, we designed methionine enhancement of phaseolin based on the three-dimensional structure of protein, de novo design principles and genetic information. Amino acid substitution and loop insertion were targeted to the interior and exterior, respectively, of the protein’s β-barrels. First, we introduced the methionine enhancement mutations into phaseolin cDNA, expressed cDNA in Escherichia coli and purified monomeric non-glycosylated proteins. Biophysical analysis of E. coli-expressed proteins demonstrated a similar structural stability of wild-type and mutant phaseolin monomers. Here, we attempted to test the structural stability of the methionine-enhanced phaseolin by introducing phaseolin cDNA to tobacco via Agrobacterium tumefaciens-mediated transformation of leaf disks, regenerating transgenic tobacco plants, and examining the accumulation of phaseolin protein in mature transgenic tobacco seeds. We used seven constructs containing different extents of methionine enhancement, ranging from the original 3 to maximum 33 methionines per 397 amino acid residues. ELISA analyses indicated that the methionine-enhanced phaseolins did not accumulate as stably in mature transgenic tobacco seeds as the wild-type phaseolin. It seems likely that the methionine-enhanced phaseolin proteins were under the stringent scrutiny of the protein quality control mechanism in the endoplasmic reticulum (ER), Golgi complex and/or vacuolar protein bodies. The protein degradation is probably to occur in the vacuolar protein bodies due to the instability of the trimer assembly caused by the methionine enhancement mutations targeting either amino-acids substitutions or/and loop insertions to the interior β-sheets and tum/loop regions, respectively, of N- and C-barrel structures.
Not enough stellar mass Machos in the Galactic halo
A. Milsztajn,T. Lasserre,for the EROS collaboration
Physics , 2000, DOI: 10.1016/S0920-5632(00)00970-1
Abstract: We present an update of results from the search for microlensing towards the Large Magellanic Cloud (LMC) by EROS (Experience de Recherche d'Objets Sombres). We have now monitored 25 million stars over three years. Because of the small number of observed microlensing candidates (four), our results are best presented as upper limits on the amount of dark compact objects in the halo of our Galaxy. We discuss critically the candidates and the possible location of the lenses, halo or LMC . We compare our results to those of the MACHO group. Finally, we combine these new results with those from our search towards the Small Magellanic Cloud as well as earlier ones from the EROS1 phase of our survey. The combined data is sensitive to compact objects in the broad mass range $ 10^{-7} - 10 $ solar masses. The derived upper limit on the abundance of stellar mass MACHOs rules out such objects as the dominant component of the Galactic halo if their mass is smaller than 2 solar masses.
KamLAND, terrestrial heat sources and neutrino oscillations
G. Fiorentini,T. Lasserre,M. Lissia,B. Ricci,S. Schonert
Physics , 2003, DOI: 10.1016/S0370-2693(03)00240-5
Abstract: We comment on the first indication of geo-neutrino events from KamLAND and on the prospects for understanding Earth energetics. Practically all models of terrestrial heat production are consistent with data within the presently limited statistics, the fully radiogenic model being closer to the observed value ($\approx 9$ geo-events). In a few years KamLAND should collect sufficient data for a clear evidence of geo-neutrinos, however discrimination among models requires a detector with the class and size of KamLAND far away from nuclear reactors. We also remark that the event ratio from Thorium and Uranium decay chains is well fixed $N(Th)/N(U) \simeq 0.25$, a constraint that can be useful for determining neutrino oscillation parameters. We show that a full spectral analysis, including this constraint, further reduces the oscillation parameter space compared to an analysis with an energy threshold $E_{vis}>2.6 MeV$.
Convergent Semidefinite Programming Relaxations for Global Bilevel Polynomial Optimization Problems
V. Jeyakumar,J. B. Lasserre,G. Li,T. S. Pham
Mathematics , 2015,
Abstract: In this paper, we consider a bilevel polynomial optimization problem where the objective and the constraint functions of both the upper and the lower level problems are polynomials. We present methods for finding its global minimizers and global minimum using a sequence of semidefinite programming (SDP) relaxations and provide convergence results for the methods. Our scheme for problems with a convex lower-level problem involves solving a transformed equivalent single-level problem by a sequence of SDP relaxations; whereas our approach for general problems involving a non-convex polynomial lower-level problem solves a sequence of approximation problems via another sequential SDP relaxations.
Chasing $θ_{13}$ with new reactor neutrino experiments
Th. Lasserre
Physics , 2004, DOI: 10.1016/j.nuclphysbps.2005.05.005
Abstract: It is now widely accepted that a new middle baseline disappearance reactor neutrino experiment with multiple detectors could provide a clean measurement of the $\theta_{13}$ mixing angle, free from any parameter degeneracies and correlations induced by matter effect and the unknown leptonic Dirac CP phase. The current best constraint on the third mixing angle comes from the Chooz reactor neutrino experiment $\sin^{2}(2\theta_{13})<0.2$ (90$ %$ C.L., $\Delta m_{\rm atm}^{2}=2.0 10^{-3}$ eV$^{2}$). Several projects of experiment, with different timescales, have been proposed over the last two years all around the world. Their sensitivities range from $\sin^{2}(2\theta_{13})<$ 0.01 to 0.03, having thus an excellent discovery potential of the $\nu_e$ fraction of $\nu_3$.
Double-Chooz: a search for Theta13
Th. Lasserre
Physics , 2004, DOI: 10.1016/j.nuclphysbps.2005.05.040
Abstract: The Double-Chooz experiment goal is to search for a non-vanishing value of the Theta13 neutrino mixing angle. This is the last step to accomplish prior moving towards a new era of precision measurements in the lepton sector. The current best constraint on the third mixing angle comes from the CHOOZ reactor neutrino experiment $\sin(2\theta_{13})^{2}<0.2$ (90% C.L., $\Delta m_{atm}^{2}=2.0$ eV$^{2}$). Double-Chooz will explore the range of $\sin(2\theta_{13})^{2}$ from 0.2 to 0.03-0.02, within three years of data taking. The improvement of the CHOOZ result requires an increase in the statistics, a reduction of the systematic error below one percent, and a careful control of the backgrounds. Therefore, Double-Chooz will use two identical detectors, one at 150 m and another at 1.05 km distance from the Chooz nuclear cores. In addition, we will to use the near detector as a ``state of the art'' prototype to investigate the potential of neutrinos for monitoring the civil nuclear power plants. The plan is to start operation with two detectors in 2008, and to reach a sensitivity sin$^{2}$$(2\theta_{13})$ of 0.05 in 2009, and 0.03-0.02 in 2011.
Testing the Reactor and Gallium Anomalies with Intense (Anti)Neutrino Emitters
Th. Lasserre
Physics , 2012, DOI: 10.1016/j.nuclphysbps.2013.04.013
Abstract: Several observed anomalies in neutrino oscillation data could be explained by a hypothetical fourth neutrino separated from the three standard neutrinos by a squared mass difference of a few 0.1 eV$^2$ or more. This hypothesis can be tested with MCi neutrino electron capture sources ($^{51}$Cr) or kCi antineutrino $\beta$-source ($^{144}$Ce) deployed inside or next to a large low background neutrino detector. In particular, the compact size of this source coupled with the localization of the interaction vertex lead to an oscillating pattern in event spatial (and possibly energy) distributions that would unambiguously determine neutrino mass differences and mixing angles.
Light Sterile Neutrinos in Particle Physics: Experimental Status
Thierry Lasserre
Physics , 2014,
Abstract: Most of the neutrino oscillation results can be explained by the three-neutrino paradigm. However several anomalies in short baseline oscillation data could be interpreted by invoking a hypothetical fourth neutrino, separated from the three standard neutrinos by a squared mass difference of more than 0.1 eV$^2$. This new neutrino, often called sterile, would not feel standard model interactions but mix with the others. Such a scenario calling for new physics beyond the standard model has to be either ruled out or confirmed with new data. After a brief review of the anomalous oscillation results we discuss the world-wide experimental proposal aiming to clarify the situation.
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