620 research outputs found
Measuring the distribution of current fluctuations through a Josephson junction with very short current pulses
We propose to probe the distribution of current fluctuations by means of the
escape probability histogram of a Josephson junction (JJ), obtained using very
short bias current pulses in the adiabatic regime, where the low-frequency
component of the current fluctuations plays a crucial role. We analyze the
effect of the third cumulant on the histogram in the small skewness limit, and
address two concrete examples assuming realistic parameters for the JJ. In the
first one we study the effects due to fluctuations produced by a tunnel
junction, finding that the signature of higher cumulants can be detected by
taking the derivative of the escape probability with respect to current. In
such a realistic situation, though, the determination of the whole distribution
of current fluctuations requires an amplification of the cumulants. As a second
example we consider magnetic flux fluctuations acting on a SQUID produced by a
random telegraph source of noise.Comment: 6 pages, 6 figures; final versio
Occupational lead neurotoxicity: Improvement in behavioural effects after reduction of exposure.
To evaluate critical exposure levels and the reversibility of lead neurotoxicity a group of lead exposed foundry workers and an unexposed reference population were followed up for three years. During this period, tests designed to monitor neurobehavioural function and lead dose were administered. Evaluations of 160 workers during the first year showed dose dependent decrements in mood, visual/motor performance, memory, and verbal concept formation. Subsequently, an improvement in the hygienic conditions at the plant resulted in striking reductions in blood lead concentrations over the following two years. Attendant improvement in indices of tension (20% reduction), anger (18%), depression (26%), fatigue (27%), and confusion (13%) was observed. Performance on neurobehavioural testing generally correlated best with integrated dose estimates derived from blood lead concentrations measured periodically over the study period; zinc protoporphyrin levels were less well correlated with function. This investigation confirms the importance of compliance with workplace standards designed to lower exposures to ensure that individual blood lead concentrations remain below 50 micrograms/dl
Complete genome sequences of erwinia amylovora phages vB_EamP-S2 and vB_EamM-Bue1
Phages vB_EamP-S2 (S2) and vB_EamM-Bue1 (Bue1) infect the plant pathogen Erwinia amylovora. S2 has a genome size of 45,495 bp and belongs to the genus SP6virus. The genome size of Bue1, related to Salmonella phage Vil, is 164,037 bp. Both phages possess a depolymerase enzyme, a frequent feature of E. amylovora phages
Probing interactions in mesoscopic gold wires
We have measured in gold wires the energy exchange rate between
quasiparticles, the phase coherence time of quasiparticles and the resistance
vs. temperature, in order to probe the interaction processes which are relevant
at low temperatures. We find that the energy exchange rate is higher than
expected from the theory of electron-electron interactions, and that it has a
different energy dependence. The dephasing time is constant at temperatures
between 8 K and 0.5 K, and it increases below 0.5 K. The magnetoresistance is
negative at large field scales, and the resistance decreases logarithmically
with increasing temperatures, indicating the presence of magnetic impurities,
probably Fe. Whereas resistivity and phase coherence measurements can be
attributed to magnetic impurities, the question is raised whether these
magnetic impurities could also mediate energy exchanges between quasiparticles.Comment: latex pothier.tex, 12 files, 15 pages in: Proceedings of the NATO
Advanced Research Workshop on Size Dependent Magnetic Scattering, Pesc,
Hungary, May 28 - June 1st, 2000 Chandrasekhar V., Van Haesendonck C. eds
(Kluwer, 2001) [SPEC-S00/083
Density of States in Superconductor - Normal Metal - Superconductor Junctions
We consider the chi_0 dependence of the density of states inside the normal
metal of a superconductor - normal metal - superconductor (SNS) junction.Here
chi_0 is the phase difference of two superconductors of the junction. It is
shown that in the absence of electron-electron interaction the energy
dependence of the density of states has a gap which decreases as chi_0
increases and closes at chi_0= pi. Both the analytical expressions for the
chi_0 dependence of the density of states and the results of numerical
simulations are presented.Comment: 7 pages with 4 included epsf figures, published version with small
change
Sub-gap conductance in ferromagnetic-superconducting mesoscopic structures
We study the sub-gap conductance of a ferromagnetic mesoscopic region
attached to a ferromagnetic and a superconducting electrode by means of tunnel
junctions. In the absence of the exchange field, the ratio of the two tunnel junction resistances determines the behaviour of
the sub-gap conductance which possesses a zero-bias peak for and for
a peak at finite voltage. We show that the inclusion of the exchange
field leads to a peak splitting for , while it shifts the zero-bias
anomaly to finite voltages for .Comment: 5 pages revte
Magnetoresistance of proximity coupled Au wires
We report measurements of the magnetoresistance (MR) of narrow Au wires
coupled to a superconducting Al contact on one end, and a normal Au contact on
the other. The MR at low magnetic field is quadratic in , with a
characteristic field scale determined by phase coherent paths which
encompass not only the wire, but also the two contacts. is essentially
temperature independent at low temperatures, indicating that the area of the
phase coherent paths is not determined by the superconducting coherence length
in the normal metal, which is strongly temperature dependent at low
temperatures. We identify the relevant length scale as a combination of the
electron phase coherence length in the normal metal and the coherence
length in the superconductor
Diffusive conductors as Andreev interferometers
We present a novel mechanism of phase-dependent electric transport in
diffusive normal metal-superconductor structures. We provide a detailed
theoretical and numerical analysis of recent unexplained experiments
essentially explaining them.Comment: Self extracting file, 7 pages latex and 4 postscript figures. The
paper is also available at http://www.tn.tudelft.nl/tn/thspap.html In this
revision we resolved some printing problems concerning figures 2 and
Conductance Fluctuations in a Metallic Wire Interrupted by a Tunnel Junction
The conductance fluctuations of a metallic wire which is interrupted by a
small tunnel junction has been explored experimentally. In this system, the
bias voltage V, which drops almost completely inside the tunnel barrier, is
used to probe the energy dependence of conductance fluctuations due to disorder
in the wire. We find that the variance of the fluctuations is directly
proportional to V. The experimental data are consistently described by a
theoretical model with two phenomenological parameters: the phase breaking time
at low temperatures and the diffusion coefficient.Comment: 9 pages RevTeX and 4 PS figures (accepted for publication in Physical
Review Letters
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