8,603 research outputs found
Split-Stirling-cycle displacer linear-electric drive
The retrofit of a 1/4-W split-Stirling cooler with a linear driven on the displacer was achieved and its performance characterized. The objective of this work was to demonstrate that a small linear motor could be designed to meet the existing envelope specifications of the cooler and that an electric linear drive on the displacer could improve the cooler's reliability and performance. The paper describes the characteristics of this motor and presents cooler test results
H2 molecule in strong magnetic fields
The Pauli-Hamiltonian of a molecule with fixed nuclei in a strong constant
magnetic field is asymptotic, in norm-resolvent sense, to an effective
Hamiltonian which has the form of a multi-particle Schr\"odinger operator with
interactions given by one-dimensional \delta-potentials. We study this
effective Hamiltonian in the case of the H2 -molecule and establish existence
of the ground state. We also show that the inter-nuclear equilibrium distance
tends to 0 as the field-strength tends to infinity
Systematic search for high-energy gamma-ray emission from bow shocks of runaway stars
Context. It has been suggested that the bow shocks of runaway stars are
sources of high-energy gamma rays (E > 100 MeV). Theoretical models predicting
high-energy gamma-ray emission from these sources were followed by the first
detection of non-thermal radio emission from the bow shock of BD+43^\deg 3654
and non-thermal X-ray emission from the bow shock of AE Aurigae. Aims. We
perform the first systematic search for MeV and GeV emission from 27 bow shocks
of runaway stars using data collected by the Large Area Telescope (LAT) onboard
the Fermi Gamma-ray Space Telescope (Fermi). Methods. We analysed 57 months of
Fermi-LAT data at the positions of 27 bow shocks of runaway stars extracted
from the Extensive stellar BOw Shock Survey catalogue (E-BOSS). A likelihood
analysis was performed to search for gamma-ray emission that is not compatible
with diffuse background or emission from neighbouring sources and that could be
associated with the bow shocks. Results. None of the bow shock candidates is
detected significantly in the Fermi-LAT energy range. We therefore present
upper limits on the high-energy emission in the energy range from 100 MeV to
300 GeV for 27 bow shocks of runaway stars in four energy bands. For the three
cases where models of the high-energy emission are published we compare our
upper limits to the modelled spectra. Our limits exclude the model predictions
for Zeta Ophiuchi by a factor 5.Comment: 5 pages, 5 figures, 1 table, accepted by A&
The Phenion (R) Full-Thickness Skin Model for Percutaneous Absorption Testing
In recent years many efforts have been made to replace dermal toxicity testing of chemicals in the animal by in vitro assays. As a member of a German research consortium, we have previously contributed to the validation of an in vitro test protocol for percutaneous absorption studies on the basis of reconstructed human epidermis and both human and pig skin ex vivo. Aiming to assess the barrier properties of a newly developed reconstructed skin model, this protocol has now been transferred to the Phenion (R) Full-Thickness Skin Model (FT model). The permeation of testosterone and caffeine was quantified in parallel to that of pig skin using Franz-type diffusion cells. In addition, the permeation of benzoic acid and nicotine was studied. As expected, the FT model is more permeable than pig skin, yet its barrier properties are well in accordance with those of reconstructed human epidermis when compared to previous data. In fact, the FT model most efficiently retards testosterone as the compound of highest lipophilicity, which can be explained by an additional uptake by a reservoir formed by the dermis equivalent. Thus, the structure closely parallels human skin. In consequence, the Phenion FT model appears to be suitable for percutaneous absorption studies in hazard analysis and should be subjected to a catch-up validation study. Copyright (C) 2009 S. Karger AG, Base
The design of a small linear-resonant, split Stirling cryogenic refrigerator compressor
The development of a small linear-resonant compressor for use in a 1/4-watt, 78K, split Stirling cryogenic refrigerator is discussed. The compressor contains the following special features: (1) a permanent-magnet linear motor; (2) resonant dynamics; (3) dynamic balancing; and (4) a close-clearance seal between the compressor piston and cylinder. This paper describes the design of the compressor, and presents component test data and system test data for the compressor driving a 1/4-watt expander
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