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Search Results: 1 - 10 of 144462 matches for " F. Piquemal "
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Start-up of the nemo3 experiment
F. Piquemal,NEMO collaboration
Physics , 2002,
Abstract: The NEMO collaboration is looking to measure neutrinoless double beta decay down to a lower limit of 0.1 eV for the effective neutrino mass. The NEMO 3 detector is now operating in the Frejus Underground Laboratory. The expected performance and the data of the first runs are presented here.
Magnetic nanowires as permanent magnet materials
T. Maurer,F. Ott,G. Chaboussant,Y. Soumare,J. -Y. Piquemal,G. Viau
Physics , 2007, DOI: 10.1063/1.2800786
Abstract: We present the fabrication of metallic magnetic nanowires using a low temperature chemical process. We show that pressed powders and magnetically oriented samples exhibit a very high coercivity (6.5 kOe at 140 K and 4.8 kOe at 300 K). We discuss the magnetic properties of these metamaterials and show that they have the suitable properties to realize "high temperature magnets" competitive with AlNiCo or SmCo permanent magnets. They could also be used as recording media for high density magnetic recording.
RK/100 and RK/200 Quantum Hall Array Resistance Standards
W. Poirier,A. Bounouh,K. Hayashi,H. Fhima,F. Piquemal,G. Geneves,J. P. Andre
Physics , 2002, DOI: 10.1063/1.1495893
Abstract: It is theoretically possible to combine several Hall bars in arrays to define new quantum standards with perfectly quantized resistance values. We have thus, for the first time, developed and fabricated novel Quantum Hall Array Resistance Standards (QHARS) made of a large number N (N=100, 50) of Hall bars placed in parallel using a triple connections technique. The Hall resistance of these quantum standards is found to be very well quantized. On the i=2 Hall plateau, the resistance of specific good arrays stays equal to RK/2N within 5 parts in 10^9 for supplying currents up to 2 mA at a 1.3 K temperature. The mean longitudinal resistance of the Hall bars which constitute the arrays has been determined through the analysis of the array equivalent electrical circuit. This measurement shows that the carrier transport in the Hall bars is dissipation-less. This work therefore demonstrates the efficiency of the multiple connections technique and consequently that QHARS are likely to extend the QHE metrological applications.
Heating process in the pre-Breakdown regime of the Quantum Hall Efect : a size dependent effect
Y. M. Meziani,C. Chaubet,B. Jouault,S. Bonifacie,A. Raymond,W. Poirier,F. Piquemal
Physics , 2003, DOI: 10.1016/j.physb.2004.01.124
Abstract: Our study presents experimental measurements of the contact and longitudinal voltage drops in Hall bars, as a function of the current amplitude. We are interested in the heating phenomenon which takes place before the breakdown of the quantum Hall effect, i.e. the pre-breakdown regime. Two types of samples has been investigated, at low temperature (4.2 and 1.5K) and high magnetic field (up to 13 T). The Hall bars have several different widths, and our observations clearly demonstrate that the size of the sample influences the heating phenomenon. By measuring the critical currents of both contact and longitudinal voltages, as a function of the filling factor (around $i=2$), we highlight the presence of a high electric field domain near the source contact, which is observable only in samples whose width is smaller than 400 microns.
Behavior of the contacts of Quantum Hall Effect devices at high currents : an electronic thermometer
Y. M. Meziani,C. Chaubet,S. Bonifacie,B. Jouault,A. Raymond,W. Poirier,F. Piquemal
Physics , 2003, DOI: 10.1063/1.1748853
Abstract: This paper reports on an experimental study of the contact resistance of Hall bars in the Quantum Hall Effect regime while increasing the current through the sample. These measurements involve also the longitudinal resistance and they have been always performed before the breakdown of the Quantum Hall Effect. Our investigations are restricted to the $i=2$ plateau which is used in all metrological measurements of the von Klitzing constant $R_K$. A particular care has been taken concerning the configuration of the measurement. Four configurations were used for each Hall bar by reversing the current and the magnetic field polarities. Several samples with different width have been studied and we observed that the critical current for the contact resistance increases with the width of the Hall bar as previously observed for the critical current of the longitudinal resistance. The critical currents exhibit either a linear or a sublinear increase. All our observations are interpreted in the current understanding of the Quantum hall effect brekdown. Our analysis suggests that a heated region appears at the current contact, develops and then extends in the whole sample while increasing the current. Consequently, we propose to use the contact resistance as an electronic thermometer for the Hall fluid.
The quantum metrology triangle experiment: quantization tests of an electron pump
Sassine, S;Steck, B;Feltin, N;Devoille, L;Chenaud, B;Poirier, W;Schopfer, F;Spengler, G;Séron, O;Piquemal, F;Lotkhov, S;
Sba: Controle & Automa??o Sociedade Brasileira de Automatica , 2010, DOI: 10.1590/S0103-17592010000600006
Abstract: we present our experimental set-up and discuss the results obtained with the quantum metrological triangle (qmt) experiment. this experiment consists in realizing ohm's law with the three effects used and investigated in quantum electrical metrology: the josephson effect (je), the quantum hall effect (qhe) and the single electron tunneling effect (set). the aim is to check the consistency of the phenomenological constants kj, rk and qx associated with these effects and theoretically expressed with the fundamental constants e and h (elementary charge and planck constant, respectively). such an experiment is a contribution for a new definition of electrical units in the international system (si)
Temperature dependence of alpha-induced scintillation in the 1,1,4,4-tetraphenyl-1,3-butadiene wavelength shifter
L. M. Veloce,M. Ku?niak,P. C. F. Di Stefano,A. J. Noble,M. G. Boulay,P. Nadeau,T. Pollmann,M. Clark,M. Piquemal,K. Schreiner
Physics , 2015,
Abstract: Liquid noble gas based particle detectors often use the organic wavelength shifter 1,1,4,4-tetraphenyl-1,3-butadiene (TPB) which shifts UV scintillation light to the visible regime, facilitating its detection, but which also can scintillate on its own. Dark matter searches based on this type of detector commonly rely on pulse-shape discrimination (PSD) for background mitigation. Alpha-induced scintillation therefore represents a possible background source in dark matter searches. The timing characteristics of this scintillation determine whether this background can be mitigated through PSD. We have therefore characterized the pulse shape and light yield of alpha induced TPB scintillation at temperatures ranging from 300 K down to 4 K, with special attention given to liquid noble temperatures. We find that the pulse shapes and light yield depend strongly on temperature. In addition, the significant contribution of long time constants above ~50 K provides an avenue for discrimination between alpha decay events in TPB and nuclear-recoil events in noble liquid detectors.
Measurements of Absolute Atomic Nitrogen Density by Two-Photon Absorption Laser-Induced Fluorescence Spectroscopy in Hot Air Plasma Generated by Microwave Resonant Cavity  [PDF]
Frédéric Marchal, Nofel Merbahi, Gaétan Wattieaux, Alain Piquemal, Mohammed Yousfi
Journal of Analytical Sciences, Methods and Instrumentation (JASMI) , 2017, DOI: 10.4236/jasmi.2017.74008
Abstract: For the first time, absolute densities of atomic nitrogen in its ground state (N4S) have been measured in hot dry and humid air plasma columns under post-discharge regime. The determination of space-resolved absolute densities leads to obtain the dissociation degrees of molecular nitrogen in the plasma. The hot plasmas are generated inside an upstream gas-conditioning cell at 600 mbar when the air gas flow is directly injected at 10 slm in a microwave resonant cavity (2.45 GHz, 1 kW) placed in the downstream side. Density measurements based on laser induced fluorescence spectroscopy with two-photon excitation (TALIF), are more particularly performed along the radial and axial positions of the plasma column. Calibration of TALIF signals is performed in situ (i.e. in the same gas-conditioning cell but without plasma) using an air gas mixture containing krypton. Optical emission spectroscopy is considered to estimate the rotational gas temperature by adding a small amount of H2 in dry air to better detect OH (A-X) spectra. The rotational temperatures in humid air plasma column (50% of humidity) are larger than those of dry air plasma column by practically 30% near the nozzle of resonant cavity on the axis of the plasma column. This is partly due to attachment heating processes initiated by water vapor. A maximum of the measured absolute nitrogen density is also observed near the nozzle which is also larger for humid air plasma column. The obtained dissociation degrees of molecular nitrogen in both dry and humid air plasma along the air plasma column are lower than the cases where only thermodynamic equilibrium is assumed. This is characteristic of the absence of chemical and energetic equilibria not yet reached in the air plasma column dominated by recombination processes.
Background optimization for a new spherical gas detector for very light WIMP detection
Ali Dastgheibi-Fard,I. Giomataris,G. Gerbierb,J. Derree,M. Gros,P. Magnier,D. Jourde,E . Bougamont,X-F. Navick,T. Papaevangelou,J. Galan,G. Tsiledakis,F. Piquemal,M. Zampaolo,P. Loaiza,I. Savvidis
Physics , 2014,
Abstract: The Spherical gaseous detector (or Spherical Proportional Counter, SPC) is a novel type of par- ticle detector, with a broad range of applications. Its main features include a very low energy threshold independent of the volume (due to its very low capacitance), a good energy resolution, robustness and a single detection readout channel, in its simplest version. Applications range from radon emanation gas monitoring, neutron flux and gamma counting and spectroscopy to dark matter searches, in particular low mass WIMPs and coherent neutrino scattering measure- ment. Laboratories interested in these various applications share expertise within the NEWS (New Experiments With Sphere) network. SEDINE, a low background prototype installed at underground site of Laboratoire Souterrain de Modane is currently being operated and aims at measuring events at very low energy threshold, around 100 eV. We will present the energy cali- bration with 37Ar, the surface background reduction, the measurement of detector background at sub-keV energies, and show anticipated sensitivities for light dark matter search.
Low-Temperature Scintillation Properties of CaWO4 Crystals for Rare-Event Searches
M. v. Sivers,M. Clark,P. C. F. Di Stefano,A. Erb,A. Gütlein,J. -C. Lanfranchi,A. Münster,P. Nadeau,M. Piquemal,W. Potzel,S. Roth,K. Schreiner,R. Strauss,S. Wawoczny,M. Willers,A. Z?ller
Physics , 2015,
Abstract: In prospect of its application in cryogenic rare-event searches, we have investigated the low-temperature scintillation properties of CaWO4 crystals down to 3.4 K under {\alpha} and {\gamma} excitation. Concerning the scintillation decay times, we observe a long component in the ms range which significantly contributes to the light yield below 40K. For the first time we have measured the temperature dependence of the {\alpha}/{\gamma}- ratio of the light yield. This parameter which can be used to discriminate {\alpha} and {\gamma} events in scintillating bolometers is found to be about 8-15% smaller at low temperatures compared to room temperature.
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