9,499 research outputs found
Photomechanical Investigation of Structural Behavior of Gyroscope Components. Task IV - Analysis of Initial Redesign of AB5-K8 GYROSCOPE
Photomechanics of structure and materials in redesigned AB5-K8 gyroscope component
The evolution of pebble size and shape in space and time
We propose a mathematical model which suggests that the two main geological
observations about shingle beaches, i.e. the emergence of predominant pebble
size ratios and strong segregation by size are interrelated. Our model is a
based on a system of ODEs called the box equations, describing the evolution of
pebble ratios. We derive these ODEs as a heuristic approximation of Bloore's
PDE describing collisional abrasion. While representing a radical
simplification of the latter, our system admits the inclusion of additional
terms related to frictional abrasion. We show that nontrivial attractors
(corresponding to predominant pebble size ratios) only exist in the presence of
friction. By interpreting our equations as a Markov process, we illustrate by
direct simulation that these attractors may only stabilized by the ongoing
segregation process.Comment: 22 pages, 8 figure
IBIS/PICsIT in-flight performances
PICsIT (Pixellated Imaging CaeSium Iodide Telescope) is the high energy
detector of the IBIS telescope on-board the INTEGRAL satellite. PICsIT operates
in the gamma-ray energy range between 175 keV and 10 MeV, with a typical energy
resolution of 10% at 1 MeV, and an angular resolution of 12 arcmin within a
\~100 square degree field of view, with the possibility to locate intense point
sources in the MeV region at the few arcmin level. PICsIT is based upon a
modular array of 4096 independent CsI(Tl) pixels, ~0.70 cm^2 in cross-section
and 3 cm thick. In this work, the PICsIT on-board data handling and science
operative modes are described. This work presents the in-flight performances in
terms of background count spectra, sensitivity limit, and imaging capabilities.Comment: 8 pages, 4 figures. Accepted for publication on A&A, special issue on
First Science with INTEGRA
Shape of the Galactic Orbits in Clusters
A kinematical analysis applied to a sample of galaxy clusters indicates that
the differences between the velocity distribution of elliptical and spiral
galaxies are associated with the shape of their orbit families. The orbital
anisotropies present on each morphological population could be measured with
the use of a parameter which is the ratio of the radial and tangential velocity
dispersions, and can be recovered through the observed line-of-sight velocity
distribution. When a Gaussian velocity distribution is assumed, having
different dispersions along the radial and tangential directions, we conclude
that the orbits of elliptical galaxies in clusters are close to radial, while
spirals have more circular shaped or isotropic orbits. Lenticulars galaxies
shares an intermediate orbital parameter, between spirals and ellipticals.Comment: 23 pages including 6 EPS-figures, and 4 tables. Accepted for
publication by ApJ, April 199
Spurious diffusion in particle simulations of the Kolmogorov flow
Particle simulations of the Kolmogorov flow are analyzed by the
Landau-Lifshitz fluctuating hydrodynamics. It is shown that a spurious
diffusion of the center of mass corrupts the statistical properties of the
flow. The analytical expression for the corresponding diffusion coefficient is
derived.Comment: 10 pages, no figure
Urban transportation: Perspectives on mobility and choice
A study of urban transportation systems are presented characterized by intensive scrutiny of many ideas, philosophies, and academic perspectives. This report is intended to communicate some dimensions of the urban transportation problem to the general public
Short-time inertial response of viscoelastic fluids measured with Brownian motion and with active probes
We have directly observed short-time stress propagation in viscoelastic
fluids using two optically trapped particles and a fast interferometric
particle-tracking technique. We have done this both by recording correlations
in the thermal motion of the particles and by measuring the response of one
particle to the actively oscillated second particle. Both methods detect the
vortex-like flow patterns associated with stress propagation in fluids. This
inertial vortex flow propagates diffusively for simple liquids, while for
viscoelastic solutions the pattern spreads super-diffusively, dependent on the
shear modulus of the medium
Impedance model for the polarization-dependent optical absorption of superconducting single-photon detectors
We measured the single-photon detection efficiency of NbN superconducting
single photon detectors as a function of the polarization state of the incident
light for different wavelengths in the range from 488 nm to 1550 nm. The
polarization contrast varies from ~5% at 488 nm to ~30% at 1550 nm, in good
agreement with numerical calculations. We use an optical-impedance model to
describe the absorption for polarization parallel to the wires of the detector.
For lossy NbN films, the absorption can be kept constant by keeping the product
of layer thickness and filling factor constant. As a consequence, we find that
the maximum possible absorption is independent of filling factor. By
illuminating the detector through the substrate, an absorption efficiency of
~70% can be reached for a detector on Si or GaAs, without the need for an
optical cavity.Comment: 15 pages, 5 figures, submitted to Journal of Applied Physic
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