8,376 research outputs found
Low energy proton bidirectional anisotropies and their relation to transient interplanetary magnetic structures: ISEE-3 observations
It is known that the interplanetary medium in the period approaching solar maximum is characterized by an enhancement in the occurrence of transient solar wind streams and shocks and that such systems are often associated with looplike magnetic structures or clouds. There is observational evidence that bidirectional, field aligned flows of low energy particles could be a signature of such looplike structures, although detailed models for the magnetic field configuration and injection mechanisms do not exist at the current time. Preliminary results of a survey of low energy proton bidirectional anisotropies measured on ISEE-3 in the interplanetary medium between August 1978 and May 1982, together with magnetic field data from the same spacecraft are presented
Local regulation of the coronary circulation in health and disease: role of nitric oxide and endothelin
Coronary artery disease is the leading cause of morbidity and mortality in western countries. Its pathogenesis is unknown, but involves enhanced vasoconstriction, increased interaction of platelets and monocytes with the vessel wall, as well as proliferation, migration and extracellular matrix formation of vascular smooth muscle. The endothelium lies in a strategic anatomical position between circulating blood and vascular smooth muscle cells. This supports the concept that dysfunction of these cells significantly contributes to coronary artery disease. Besides other mediators, endothelial cells are a source of nitric oxide and endothelin. Nitric oxide is a vasodilator, an inhibitor of both platelet function and proliferation and migration of vascular smooth muscle. Endothelin is a potent vasoconstrictor that facilitates proliferation. Under pathological conditions, in particular the presence of cardiovascular risk factors, endothelial dysfunction occurs and is a major contributor to the increase in platelet vessel wall interaction, vasoconstriction and proliferation in the coronary system. Endothelium-dependent vasodilation is usually reduced and endothelium-dependent constrictor responses, as well as endothelin production, are augmented. Hence, endothelial cells are important targets and mediators of coronary artery diseas
Pre-selectable integer quantum conductance of electrochemically fabricated silver point contacts
The controlled fabrication of well-ordered atomic-scale metallic contacts is
of great interest: it is expected that the experimentally observed high
percentage of point contacts with a conductance at non-integer multiples of the
conductance quantum G_0 = 2e^2/h in simple metals is correlated to defects
resulting from the fabrication process. Here we demonstrate a combined
electrochemical deposition and annealing method which allows the controlled
fabrication of point contacts with pre-selectable integer quantum conductance.
The resulting conductance measurements on silver point contacts are compared
with tight-binding-like conductance calculations of modeled idealized junction
geometries between two silver crystals with a predefined number of contact
atoms
Raman solitons in transient SRS
We report the observation of Raman solitons on numerical simulations of
transient stimulated Raman scattering (TSRS) with small group velocity
dispersion. The theory proceeds with the inverse scattering transform (IST) for
initial-boundary value problems and it is shown that the explicit theoretical
solution obtained by IST for a semi-infinite medium fits strikingly well the
numerical solution for a finite medium. We understand this from the rapid
decrease of the medium dynamical variable (the potential of the scattering
theory). The spectral transform reflection coefficient can be computed directly
from the values of the input and output fields and this allows to see the
generation of the Raman solitons from the numerical solution. We confirm the
presence of these nonlinear modes in the medium dynamical variable by the use
of a discrete spectral analysis.Comment: LaTex file, to appear in Inverse Problem
LIDAR Metrology for Prescription Characterization and Alignment of Large Mirrors
We describe the use of LIDAR, or "laser radar," (LR) as a fast, accurate, and non-contact tool for the measurement of the radius of curvature (RoC) of large mirrors. We report the results of a demonstration of this concept using a commercial laser radar system. We measured the RoC of a 1.4m x 1m spherical mirror with a nominal RoC of 4.6 m with a manufacturing tolerance of 4600mm +/- 6mm. The prescription of the mirror is related to its role as ground support equipment used in the test of part of the James Webb Space Telescope (JWST). The RoC of such a large mirror is not easily measured without contacting the surface. From a position near the center of curvature of the mirror, the LIDAR scanned the mirror surface, sampling it with 1 point per 3.5 sq cm. The measurement consisted of 3983 points and lasted only a few minutes. The laser radar uses the LIDAR signal to provide range, and encoder information from angular azimuth and elevation rotation stages provide the spherical coordinates of a given point. A best-fit to a sphere of the measured points was performed. The resulting RoC was within 20 ppm of the nominal RoC, also showing good agreement with the results of a laser tracker-based, contact metrology. This paper also discusses parameters such as test alignment, scan density, and optical surface type, as well as future possible application for full prescription characterization of aspherical mirrors, including radius, conic, off-axis distance, and aperture
Isabelle/DOF: Design and Implementation
This is the author accepted manuscript. The final version is available from Springer Verlag via the DOI in this record17th International Conference, SEFM 2019
Oslo, Norway, September 18–20, 2019DOF is a novel framework for defining ontologies and enforcing them during document development and evolution. A major goal of DOF is the integrated development of formal certification documents (e. g., for Common Criteria or CENELEC 50128) that require consistency across both formal and informal arguments. To support a consistent development of formal and informal parts of a document, we provide Isabelle/DOF, an implementation of DOF on top of the formal methods framework Isabelle/HOL. A particular emphasis is put on a deep integration into Isabelleâs IDE, which allows for smooth ontology development as well as immediate ontological feedback during the editing of a document. In this paper, we give an in-depth presentation of the design concepts of DOFâs Ontology Definition Language (ODL) and key aspects of the technology of its implementation. Isabelle/DOF is the first ontology language supporting machine-checked links between the formal and informal parts in an LCF-style interactive theorem proving environment. Sufficiently annotated, large documents can easily be developed collabo- ratively, while ensuring their consistency, and the impact of changes (in the formal and the semi-formal content) is tracked automatically.IRT SystemX, Paris-Saclay, Franc
Designable electron transport features in one-dimensional arrays of metallic nanoparticles: Monte Carlo study of the relation between shape and transport
We study the current and shot noise in a linear array of metallic
nanoparticles taking explicitly into consideration their discrete electronic
spectra. Phonon assisted tunneling and dissipative effects on single
nanoparticles are incorporated as well. The capacitance matrix which determines
the classical Coulomb interaction within the capacitance model is calculated
numerically from a realistic geometry. A Monte Carlo algorithm which
self-adapts to the size of the system allows us to simulate the single-electron
transport properties within a semiclassical framework. We present several
effects that are related to the geometry and the one-electron level spacing
like e.g. a negative differential conductance (NDC) effect. Consequently these
effects are designable by the choice of the size and arrangement of the
nanoparticles.Comment: 13 pages, 12 figure
A new two-pole accretion polar: RX J1846.9+5538
We report the discovery of a new, bright (V = 17 mag) AM Her system as the
optical counterpart of the soft ROSAT All-Sky-Survey source RX J1846.9+5538 (=
1RXS J184659.4+553834). Optical photometric and spectroscopic follow-up
observations reveal a single period of 128.7 min, consistent with a high degree
of spin-orbit synchronization, and a low polar field strength ( MG) of
the primary accretion region. The system was observed in optical intermediate
and high states that differ by about 1 mag. These brightness variations were
accompanied by a correlated change of the optical light curve, which we
interpret as a switch between one- and two-pole accretion. This explanation is
also supported by the X-ray light curves, which at two different epochs display
emission from two equally bright accretion regions separated by 160 degrees.
Both spots possess distinct spectral X-ray properties as seen from the X-ray
hardness ratio, where the secondary accretion region appears significantly
softer, thus probably indicating a higher field strength compared to the
primary region. In all ROSAT pointings a deep dip is present during the primary
flux maxima, very likely caused by absorption in one of the accretion streams.Comment: 11 pages, 9 figures; accepted for publication in Astronomy &
Astrophysic
Topography driven spreading
Roughening a hydrophobic surface enhances its nonwetting properties into superhydrophobicity. For liquids other than water, roughness can induce a complete rollup of a droplet. However, topographic effects can also enhance partial wetting by a given liquid into complete wetting to create superwetting. In this work, a model system of spreading droplets of a nonvolatile liquid on surfaces having lithographically produced pillars is used to show that superwetting also modifies the dynamics of spreading. The edge speed-dynamic contact angle relation is shown to obey a simple power law, and such power laws are shown to apply to naturally occurring surfaces
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