23,533 research outputs found
The IBIS view of the galactic centre: INTEGRAL's imager observations simulations
The Imager on Board Integral Satellite (IBIS) is the imaging instrument of
the INTEGRAL satellite, the hard-X/soft-gamma ray ESA mission to be launched in
2001. It provides diagnostic capabilities of fine imaging (12' FWHM), source
identification and spectral sensitivity to both continuum and broad lines over
a broad (15 keV--10 MeV) energy range. It has a continuum sensitivity of
2~10^{-7} ph cm^{-2} s^{-1} at 1 MeV for a 10^6 seconds observation and a
spectral resolution better than 7 % at 100 keV and of 6 % at 1 MeV. The imaging
capabilities of the IBIS are characterized by the coupling of the above quoted
source discrimination capability with a very wide field of view (FOV), namely 9
x 9 degrees fully coded, 29 x 29 degrees partially coded FOV. We present
simulations of IBIS observations of the Galactic Center based on the results of
the SIGMA Galactic Center survey. They show the capabilities of this instrument
in discriminating between different sources while at the same time monitoring a
huge FOV. It will be possible to simultaneously take spectra of all of these
sources over the FOV even if the sensitivity decreases out of the fully coded
area. It is envisaged that a proper exploitation of both the FOV dimension and
the source localization capability of the IBIS will be a key factor in
maximizing its scientific output.Comment: 5 pages, LaTeX, to be published in the 4th Compton Symposium
Conference Proceedings, uses aipproc.cls, aipproc.sty (included
Relative periodic orbits in point vortex systems
We give a method to determine relative periodic orbits in point vortex
systems: it consists mainly into perform a symplectic reduction on a fixed
point submanifold in order to obtain a two-dimensional reduced phase space. The
method is applied to point vortices systems on a sphere and on the plane, but
works for other surfaces with isotropy (cylinder, ellipsoid, ...). The method
permits also to determine some relative equilibria and heteroclinic cycles
connecting these relative equilibria.Comment: 27 pages, 17 figure
Time and frequency transfer with a microwave link in the ACES/PHARAO mission
The Atomic Clocks Ensemble in Space (ACES/PHARAO mission), which will be
installed on board the International Space Station (ISS), uses a dedicated
two-way Micro-Wave Link (MWL) in order to compare the timescale generated on
board with those provided by many ground stations disseminated on the Earth.
Phase accuracy and stability of this long range link will have a key role in
the success of the ACES/PHARAO experiment. SYRTE laboratory is heavily involved
in the design and development of the data processing software : from
theoretical modelling and numerical simulations to the development of a
software prototype. Our team is working on a wide range of problems that need
to be solved in order to achieve high accuracy in (almost) real time. In this
article we present some key aspects of the measurement, as well as current
status of the software's development.Comment: Proceedings of the European Frequency and Time Forum (EFTF) 2012 held
in Gothenburg, Sweden, April 201
Plastic deformation of rough rolling contact: An experimental and numerical investigation
Quantifying the surface roughness evolution in contacts is a crucial step in the fatigue prediction process. Surfaces are initially conditioned by the running-in process and later altered by surface fatigue. The aim of this study is to understand and predict the evolution of the micro-geometry in the first few over-rolling cycles. Numerical predictions are validated by experiments. A major difficulty in understanding surface degradation is the measurement of the surface roughness evolution at the relevant scales. A twin disc micro-test rig, called ÎŒMag, was specially designed for this kind of analysis. The ÎŒMag allows the âin situâ observation of changes in the disc surface during interrupted tests, thus avoiding dismounting the specimens, which is a major cause of inaccuracy. The new method also maintains the relative position of the two discs. The precision of the measurements allows one to use the initial surface micro-geometry as input for the numerical contact calculation. Thus, the plastic deformation of the surfaces can be measured during the first cycles and compared to the numerical prediction. Results show a very good agreement between numerical predictions and experimental measurements
The Physiological Basis for Altered Na\u3csup\u3e+\u3c/sup\u3e and Cl\u3csup\u3e-\u3c/sup\u3e Movement Across the Gills of Rainbow Trout (\u3cem\u3eOncorhynchus mykiss\u3c/em\u3e) in Alkaline (pH=9.5) Water
To test the hypothesis that internal ion imbalances at high pH are caused by altered branchial ion transporting capacity and permeability, radiotracers (24Na+ and 36Cl-) were used to measure ion movements across the gills of intact rainbow trout (Oncorhynchus mykiss) during 3 d exposure to pH 9.5. At control pH (pH 8.0), the trout were in net ion balance, but by 8 h at high pH, 60%â70% reductions in Cl- influx (Cl) and Na+ influx (JNa/in) led to net Cl- and Na+ losses of -200 ”mol kg-1 h-1. Outflux (diffusive efflux plus renal ion losses) was not initially altered. By 72 h, net Cl- balance was reestablished because of a restoration of JCl/in. Although JNa/in remained 50% lower at this time, counterbalancing reductions in Na+ outflux restored net Na+ balance. One-substrate ion-uptake kinetics analyses indicated that reduced ion influx after 8 h at pH 9.5 was caused by 50% decreases in Cl- and Na+ maximal transport rates (JCl/max, JNa/max), likely reflecting decreased numbers of functional transport sites. Two-substrate kinetic analyses indicated that reduced internal HCO3- and H+ supply for respective branchial Cl-/base and Na+/acid transport systems also contributed to lower JCl/in and, to a lesser extent, lower JNa/in at pH 9.5. Recovery in in of JCl/in after 3 d accounted for restoration of Cl- balance and max likely reflected increased numbers of transport sites. In contrast, JNa/in remained 33% lower after 3 d, but a lower affinity of the max gills for Na+ (fourfold greater KNa/m) accounted for the chronic m reduction in Na+ influx at pH 9.5. Thus, reestablishment of Cl- uptake capacity and counterbalancing reductions in Na+ outflux allows rainbow trout to reestablish net ion balance in alkaline waters
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