69 research outputs found
Resistance noise scaling in a 2D system in GaAs
The 1/f resistance noise of a two-dimensional (2D) hole system in a high
mobility GaAs quantum well has been measured on both sides of the 2D
metal-insulator transition (MIT) at zero magnetic field (B=0), and deep in the
insulating regime. The two measurement methods used are described: I or V
fixed, and measurement of resp. V or I fluctuations. The normalized noise
magnitude SR/R^2 increases strongly when the hole density is decreased, and its
temperature (T) dependence goes from a slight increase with T at the largest
densities, to a strong decrease at low density. We find that the noise
magnitude scales with the resistance, SR /R^2 ~ R^2.4. Such a scaling is
expected for a second order phase transition or a percolation transition. The
possible presence of such a transition is investigated by studying the
dependence of the conductivity as a function of the density. This dependence is
consistent with a critical behavior close to a critical density p* lower than
the usual MIT critical density pc.Comment: 13 pages, 8 figures, Proceedings of SPIE: Fluctuations and noise in
materials, D. Popovic, M.B. Weissman, Z.A. Racz Eds., Vol. 5469, pp. 101-113,
Mspalomas, Spain, 200
Experimental Evidence of Fluctuation-Dissipation Theorem Violation in a Superspin Glass
We present the experimental observation of the fluctuation-dissipation theorem (FDT) violation in an assembly of interacting magnetic nanoparticles in the low temperature superspin glass phase. The magnetic noise is measured with a two-dimension electron gas Hall probe and compared to the out of phase ac susceptibility of the same ferrofluid. For "intermediate" aging times of the order of 1 h, the ratio of the effective temperature to the bath temperature T grows from 1 to 6.5 when T is lowered from to 0.3 , regardless of the noise frequency. These values are comparable to those measured in an atomic spin glass as well as those calculated for a Heisenberg spin glass
meson production in = 200 GeV Au+Au and pp collisions at RHIC
We present the results for the measurement of meson production in
= 200 GeV Au+Au and pp collisions at the Relativistic Heavy Ion
Collider (RHIC). Using the event mixing technique, spectra and yields are
obtained from the decay channel for different centrality
bins in Au+Au collisions and in pp collisions. We observe that the spectrum
shape in Au+Au collisions depends weakly on the centrality and the shape of the
spectrum in pp collisions is significantly different from that in Au+Au
collisions. In Au+Au collisions, the extracted yield of meson is flat as
a function of rapidity; The of , extracted from the fit function
to the spectra, shows a different behavior as a function of centrality than
that of , and Comment: Proceedings for the 7th International Conference on Strangeness in
Quark Matte
Background discrimination capabilities of a heat and ionization germanium cryogenic detector
The discrimination capabilities of a 70 g heat and ionization Ge bolometer
are studied. This first prototype has been used by the EDELWEISS Dark Matter
experiment, installed in the Laboratoire Souterrain de Modane, for direct
detection of WIMPs. Gamma and neutron calibrations demonstrate that this type
of detector is able to reject more than 99.6% of the background while retaining
95% of the signal, provided that the background events distribution is not
biased towards the surface of the Ge crystal. However, the 1.17 kg.day of data
taken in a relatively important radioactive environment show an extra
population slightly overlapping the signal. This background is likely due to
interactions of low energy photons or electrons near the surface of the
crystal, and is somewhat reduced by applying a higher charge-collecting inverse
bias voltage (-6 V instead of -2 V) to the Ge diode. Despite this
contamination, more than 98% of the background can be rejected while retaining
50% of the signal. This yields a conservative upper limit of 0.7
event.day^{-1}.kg^{-1}.keV^{-1}_{recoil} at 90% confidence level in the 15-45
keV recoil energy interval; the present sensitivity appears to be limited by
the fast ambient neutrons. Upgrades in progress on the installation are
summarized.Comment: Submitted to Astroparticle Physics, 14 page
Phi meson production in Au+Au and p+p collisions at sqrt (s)=200 GeV
We report the STAR measurement of Phi meson production in Au+Au and p+p
collisions at sqrt (s)=200 GeV. Using the event mixing technique, the Phi
spectra and yields are obtained at mid-rapidity for five centrality bins in
Au+Au collisions and for non-singly-diffractive p+p collisions. It is found
that the Phi transverse momentum distributions from Au+Au collisions are better
fitted with a single-exponential while the p+p spectrum is better described by
a double-exponential distribution. The measured nuclear modification factors
indicate that Phi production in central Au+Au collisions is suppressed relative
to peripheral collisions when scaled by the number of binary collisions. The
systematics of versus centrality and the constant Phi/K- ratio versus beam
species, centrality, and collision energy rule out kaon coalescence as the
dominant mechanism for Phi production.Comment: 6 pages, 3 figures, submitted to Phys. Rev. Let
Nasal Bone Shape Is under Complex Epistatic Genetic Control in Mouse Interspecific Recombinant Congenic Strains
Genetic determinism of cranial morphology in the mouse is still largely unknown, despite the localization of putative QTLs and the identification of genes associated with Mendelian skull malformations. To approach the dissection of this multigenic control, we have used a set of interspecific recombinant congenic strains (IRCS) produced between C57BL/6 and mice of the distant species Mus spretus (SEG/Pas). Each strain has inherited 1.3% of its genome from SEG/Pas under the form of few, small-sized, chromosomal segments.The shape of the nasal bone was studied using outline analysis combined with Fourier descriptors, and differential features were identified between IRCS BcG-66H and C57BL/6. An F2 cross between BcG-66H and C57BL/6 revealed that, out of the three SEG/Pas-derived chromosomal regions present in BcG-66H, two were involved. Segments on chromosomes 1 (∼32 Mb) and 18 (∼13 Mb) showed additive effect on nasal bone shape. The three chromosomal regions present in BcG-66H were isolated in congenic strains to study their individual effect. Epistatic interactions were assessed in bicongenic strains.Our results show that, besides a strong individual effect, the QTL on chromosome 1 interacts with genes on chromosomes 13 and 18. This study demonstrates that nasal bone shape is under complex genetic control but can be efficiently dissected in the mouse using appropriate genetic tools and shape descriptors
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