8,936 research outputs found
The CANADA-FRANCE REDSHIFT SURVEY XIII: The luminosity density and star-formation history of the Universe to z ~ 1
The comoving luminosity density of the Universe is estimated from the CFRS
faint galaxy sample in three wavebands (2800A, 4400A and 1 micron) over the
redshift range 0 < z < 1. In all three wavebands, the comoving luminosity
density increases markedly with redshift. For a (q_0 = 0.5, Omega = 1.0)
cosmological model, the comoving luminosity density increases as at 1 micron, as at 4400A and as at 2800A, these exponents being reduced by 0.43 and 1.12 for (0.05,0.1)
and (-0.85,0.1) cosmological models respectively. The variation of the
luminosity density with epoch can be reasonably well modelled by an actively
evolving stellar population with a Salpeter initial mass function (IMF)
extending to 125 M_sun, a star-formation rate declining with a power 2.5, and a
turn-on of star-formation at early epochs. A Scalo (1986) IMF extending to the
same mass limit produces too many long-lived low mass stars. This rapid
evolution of the star-formation rate and comoving luminosity density of the
Universe is in good agreement with the conclusions of Pei and Fall (1995) from
their analysis of the evolving metallicity of the Universe. One consequence of
this evolution is that the physical luminosity density at short wavelengths has
probably declined by two orders of magnitude since z ~ 1.Comment: uuencoded compressed tar file containing 8 page Tex file, 2
postscript figures and 2 tables. Ap J Letters, in press. Also available at
http://www.astro.utoronto.ca/~lilly/CFRS/papers.htm
Pilot interaction with automated airborne decision making systems
The use of advanced software engineering methods (e.g., from artificial intelligence) to aid aircraft crews in procedure selection and execution is investigated. Human problem solving in dynamic environments as effected by the human's level of knowledge of system operations is examined. Progress on the development of full scale simulation facilities is also discussed
Rare Pionium Decays and Pion Polarizability
We calculate the decay of pionium atoms into two photons. The pion
polarizability gives rise to a 10% correction to the corresponding decay width
for pointlike pions. This opens the possibility to obtain the difference
between the electric and magnetic polarizability of the charged pion from a
future measurement of the branching fraction of pionium into two photons. For
such an experiment the \pi\pi-scattering lengths would have to be known to
better than 5% precision. We also comment on the contribution of the axial
anomaly to the decay of pionium into \gamma\pi^0.Comment: 7 pages, Latex, no figures, discussion and references added, version
to appear in EPJ
Star formation rates of distant luminous infrared galaxies derived from Halpha and IR luminosities
We present a study of the star formation rate (SFR) for a sample of 16
distant galaxies detected by ISOCAM at 15um in the CFRS0300+00 and CFRS1400+52
fields. Their high quality and intermediate resolution VLT/FORS spectra have
allowed a proper correction of the Balmer emission lines from the underlying
absorption. Extinction estimates using the Hbeta/Hgamma and the Halpha/Hbeta
Balmer decrement are in excellent agreement, providing a robust measurement of
the instantaneous SFR based on the extinction-corrected Halpha luminosity. Star
formation has also been estimated exploiting the correlations between IR
luminosity and those at MIR and radio wavelengths. Our study shows that the
relationship between the two SFR estimates follow two distinct regimes: (1) for
galaxies with SFRIR below ~ 100Msolar/yr, the SFR deduced from Halpha
measurements is a good approximation of the global SFR and (2) for galaxies
near of ULIRGs regime, corrected Halpha SFR understimated the SFR by a factor
of 1.5 to 2. Our analyses suggest that heavily extincted regions completely
hidden in optical bands (such as those found in Arp 220) contribute to less
than 20% of the global budget of star formation history up to z=1.Comment: (1) GEPI, Obs. Meudon, France ;(2) CEA-Saclay, France ;(3) ESO,
Gemany ;(4) IAC, Spain. To appear in A&
An optical fibre dynamic instrumented palpation sensor for the characterisation of biological tissue
AbstractThe diagnosis of prostate cancer using invasive techniques (such as biopsy and blood tests for prostate-specific antigen) and non-invasive techniques (such as digital rectal examination and trans-rectal ultrasonography) may be enhanced by using an additional dynamic instrumented palpation approach to prostate tissue classification. A dynamically actuated membrane sensor/actuator has been developed that incorporates an optical fibre Fabry–Pérot interferometer to record the displacement of the membrane when it is pressed on to different tissue samples. The membrane sensor was tested on a silicon elastomer prostate model with enlarged and stiffer material on one side to simulate early stage prostate cancer. The interferometer measurement was found to have high dynamic range and accuracy, with a minimum displacement resolution of ±0.4μm over a 721μm measurement range. The dynamic response of the membrane sensor when applied to different tissue types changed depending on the stiffness of the tissue being measured. This demonstrates the feasibility of an optically tracked dynamic palpation technique for classifying tissue type based on the dynamic response of the sensor/actuator
Deformation of grain boundaries in polar ice
The ice microstructure (grain boundaries) is a key feature used to study ice
evolution and to investigate past climatic changes. We studied a deep ice core,
in Dome Concordia, Antarctica, which records past mechanical deformations. We
measured a "texture tensor" which characterizes the pattern geometry and
reveals local heterogeneities of deformation along the core. These results
question key assumptions of the current models used for dating
Pilot interaction with automated airborne decision making systems
Two project areas were pursued: the intelligent cockpit and human problem solving. The first area involves an investigation of the use of advanced software engineering methods to aid aircraft crews in procedure selection and execution. The second area is focused on human problem solving in dynamic environments, particulary in terms of identification of rule-based models land alternative approaches to training and aiding. Progress in each area is discussed
Generalized Swiss-cheese cosmologies: Mass scales
We generalize the Swiss-cheese cosmologies so as to include nonzero linear
momenta of the associated boundary surfaces. The evolution of mass scales in
these generalized cosmologies is studied for a variety of models for the
background without having to specify any details within the local
inhomogeneities. We find that the final effective gravitational mass and size
of the evolving inhomogeneities depends on their linear momenta but these
properties are essentially unaffected by the details of the background model.Comment: 10 pages, 14 figures, 1 table, revtex4, Published form (with minor
corrections
An axis-free overset grid in spherical polar coordinates for simulating 3D self-gravitating flows
A type of overlapping grid in spherical coordinates called the Yin-Yang grid
is successfully implemented into a 3D version of the explicit Eulerian
grid-based code PROMETHEUS including self-gravity. The modified code
successfully passed several standard hydrodynamic tests producing results which
are in very good agreement with analytic solutions. Moreover, the solutions
obtained with the Yin-Yang grid exhibit no peculiar behaviour at the boundary
between the two grid patches. The code has also been successfully used to model
astrophysically relevant situations, namely equilibrium polytropes, a
Taylor-Sedov explosion, and Rayleigh-Taylor instabilities. According to our
results, the usage of the Yin-Yang grid greatly enhances the suitability and
efficiency of 3D explicit Eulerian codes based on spherical polar coordinates
for astrophysical flows.Comment: 15 pages, 17 figures, 2 tables, accepted for publication in A&
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