571 research outputs found
Proximity effect in planar TiN-Silicon junctions
We measured the low temperature subgap resistance of titanium nitride
(superconductor, Tc=4.6K)/highly doped silicon (degenerated semiconductor) SIN
junctions, where I stands for the Schottky barrier. At low energies, the subgap
conductance is enhanced due to coherent backscattering of the electrons towards
the interface by disorder in the silicon (''reflectionless tunneling''). This
Zero Bias Anomaly (ZBA) is destroyed by the temperature or the magnetic field
above 250mK or 0.04T respectively. The overall differential resistance behavior
(vs temperature and voltage) is compared to existing theories and values for
the depairing rate and the barrier transmittance are extracted. Such an
analysis leads us to introduce an effective temperature for the electrons and
to discuss heat dissipation through the SIN interface.Comment: 23 pages, 6 figures, added references and minor corrections. Accepted
to Journal of Low Temperature Physic
Doubled Full Shot Noise in Quantum Coherent Superconductor - Semiconductor Junctions
We performed low temperature shot noise measurements in Superconductor (TiN)
- strongly disordered normal metal (heavily doped Si) weakly transparent
junctions. We show that the conductance has a maximum due to coherent multiple
reflections at low energy and that shot noise is then twice the Poisson noise
(S=4eI). The shot noise changes to the normal value (S=2eI) due to a large
quasiparticle contribution.Comment: published in Physical Review Letter
Modulation of hippocampal acetylcholine release - a potent central action of interleukin-2
The potential of the T-cell growth factor interleukin-2 (IL-2) to modulate the release of ACh from rat hippocampus was studied in vitro, as a means to investigate the possible functional significance of this cytokine in the CNS. Hippocampal slices were superfused with Krebs' buffer medium, and endogenous ACh released into the superfusate was measured using a radioenzymatic assay. Recombinant human IL-2 present during a stimulation with 25 mM KCl altered, in a concentration-dependent manner, the evoked transmitter release. At a concentration of 15 U/ml (< or = 1 nM), IL-2 inhibited ACh release by more than 50% of the control level (evoked ACh release from the untreated contralateral hemispheres). Inhibition was observed within 20 min of tissue exposure to IL-2 and lasted for up to 1 hr. The inhibitory effect of IL-2 was reversible since transient tissue exposure to IL-2 did not affect subsequent evoked ACh release. IL-2 at this concentration also significantly decreased evoked ACh in frontal cortical slices, but was ineffective in the parietal cortex and striatum, revealing that IL-2 selectively modulates the release of ACh from certain, but not all, cholinergic nerve terminals in the CNS. At very low concentrations (1.5 mU/ml, < or = 0.1 pM), IL-2 transiently increased hippocampal evoked ACh release, resulting in a biphasic dose-response profile with no significant effect observed at 0.015 mU/ml (< or = 1 fM). Other cytokines (IL-1 alpha, IL-3, IL-5, IL-6, interferon alpha), tested in hippocampal slice incubations, failed to modulate ACh release
3D sensors for the HL-LHC
In order to increase its discovery potential, the Large Hadron Collider (LHC)
accelerator will be upgraded in the next decade. The high luminosity LHC
(HL-LHC) period demands new sensor technologies to cope with increasing
radiation fluences and particle rates. The ATLAS experiment will replace the
entire inner tracking detector with a completely new silicon-only system. 3D
pixel sensors are promising candidates for the innermost layers of the Pixel
detector due to their excellent radiation hardness at low operation voltages
and low power dissipation at moderate temperatures. Recent developments of 3D
sensors for the HL-LHC are presented.Comment: 8 pages, 5 figures, International Workshops on Radiation Imaging
Detectors 201
Silicon-based three-dimensional microstructures for radiation dosimetry in hadrontherapy
In this work, we propose a solid-state-detector for use in radiation microdosimetry. This device improves the performance of existing dosimeters using customized 3D-cylindrical microstructures etched inside silicon. The microdosimeter consists of an array of micro-sensors that have 3D-cylindrical electrodes of 15 μm diameter and a depth of 5 μm within a silicon membrane, resulting in a well-defined micrometric radiation sensitive volume. These microdetectors have been characterized using an 241Am source to assess their performance as radiation detectors in a high-LET environment. This letter demonstrates the capability of this microdetector to be used to measure dose and LET in hadrontherapy centers for treatment plan verification as part of their patient-specific quality control program
Characterization of the first true coaxial 18-fold segmented n-type prototype detector for the GERDA project
The first true coaxial 18-fold segmented n-type HPGe prototype detector
produced by Canberra-France for the GERDA neutrinoless double beta-decay
project was tested both at Canberra-France and at the Max-Planck-Institut fuer
Physik in Munich. The main characteristics of the detector are given and
measurements concerning detector properties are described. A novel method to
establish contacts between the crystal and a Kapton cable is presented.Comment: 21 pages, 16 Figures, to be submitted to NIM
Toward a New Kind of Asteroseismic Grid Fitting
Recent developments in instrumentation (e.g., in particular the Kepler and
CoRoT satellites) provide a new opportunity to improve the models of stellar
pulsations. Surface layers, rotation, and magnetic fields imprint erratic
frequency shifts, trends, and other non-random behavior in the frequency
spectra. As our observational uncertainties become smaller, these are
increasingly important and difficult to deal with using standard fitting
techniques. To improve the models, new ways to compare their predictions with
observations need to be conceived. In this paper we present a completely
probabilistic (Bayesian) approach to asteroseismic model fitting. It allows for
varying degrees of prior mode identification, corrections for the discrete
nature of the grid, and most importantly implements a treatment of systematic
errors, such as the "surface effects." It removes the need to apply semi-
empirical corrections to the observations prior to fitting them to the models
and results in a consistent set of probabilities with which the model physics
can be probed and compared. As an example, we show a detailed asteroseismic
analysis of the Sun. We find a most probable solar age, including a 35 +- 5
million year pre-main sequence phase, of 4.591 billion years, and initial
element mass fractions of X_0 = 0.72, Y_0 = 0.264, Z_0 = 0.016, consistent with
recent asteroseismic and non-asteroseismic studies.Comment: 15 pages, 5 figures, accepted for publication in The Astrophysical
Journal; v2 contains minor changes made in the proofs (updated references &
corrected typos
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