279 research outputs found
La croissance ne fait pas le bonheur : les Ă©conomistes le savent-ils ?
Malgré une croissance économique continue, des enquêtes révèlent que la “satisfaction de vie” des Occidentaux stagne. Pourquoi le bien-être ne progresse-t-il pas - ou plus - avec les revenus ? Qu'en disent les économistes ?
Recommended from our members
Complementary Dualities: The Significance of East/West Architectural Difference in Paquimé
This thesis provides the first formal and phenomenological analysis of the architecture in Paquimé, otherwise known as Casas Grandes, Chihuahua, Mexico. The eastern and western halves of the city are divided by a stone wall and reservoirs. The monuments on the east are rectilinear, puddled adobe structures used primarily for domestic and manufacturing purposes. The buildings on the west, on the other hand, are open earth mounds lined in stone for public displays. This thesis analyzes each building individually, the relationship of the structures to one another, and the entire layout of Paquimé in order to better understand Paquimian visual culture
X-ray Point Sources in the Sombrero Galaxy: Supersoft sources, the globular cluster/LMXB connection, and an overview
We report on the population of point sources discovered during an 18.5 ksec
Chandra ACIS-S observation of the Sombrero Galaxy. We present the luminosity
function, the spectra of the 6 brightest sources, consider correlations with
globular clusters (GCs) and with planetary nebulae (PNe), and study the
galaxy's population of SSSs. We detected 122 sources, 22 of them are identified
as luminous supersoft X-ray sources (SSSs). There is an over density of SSSs
within 1.5 kpc of the nucleus, which is itself the brightest X-ray source. SSSs
are also found in the disk and halo, with 1 SSS in a globular cluster (GC).
Several sources in Sombrero's halo are good candidates for SSS models in which
the accretor is a nuclear-burning white dwarf. In total, 32 X-ray sources are
associated with GCs. The majority of sources with luminosity > 1e38 erg/s are
in GCs. These results for M104, an Sa galaxy, are similar to what has been
found for elliptical galaxies and for the late-type spiral M31. We find that
those optically bright GCs with X-ray sources house only the brightest X-ray
sources. We find that, in common with other galaxies, there appears to be a
positive connection between young (metal-rich) GCs and X-ray sources, but that
the brightest X-ray sources are equally likely to be in metal-poor GCs. We
propose a model which can explain the trends seen in the data sets from the
Sombrero and other galaxies. Thermal-time scale mass transfer can occur in some
of the the younger clusters in which the turn-off mass is slightly greater than
; multiplicity may play a role in some of the most massive
clusters; accretion from giant stars may be the dominant mechanism in some
older, less massive and less centrally concentrated clusters.Comment: 13 pages, 7 figures. ApJ submitte
Development of a Life History Database for Upper Mississippi River Fishes
This report summarizes the development of a life history database for Upper Mississippi River System fishes. It provides the rationale for its development within the Long Term Resource Monitoring Program, describes it, outlines standards for its development. and demonstrates how it can be linked to the LTRMP fisheries database and used to address a host of new questions relevant to management and science in the basin.U.S. Army Corps of Engineers District, Rock Island Clock Tower BuildingOpe
The Far-Infrared Spectral Energy Distributions of X-ray-selected Active Galaxies
[Abridged] We present ISO far-infrared (IR) observations of 21 hard X-ray
selected AGN from the HEAO-1 A2 sample. We compare the far-IR to X-ray spectral
energy distributions (SEDs) of this sample with various radio and optically
selected AGN samples. The hard-X-ray selected sample shows a wider range of
optical/UV shapes extending to redder near-IR colors. The bluer objects are
Seyfert 1s, while the redder AGN are mostly intermediate or type 2 Seyferts.
This is consistent with a modified unification model in which the amount of
obscuring material increases with viewing angle and may be clumpy. Such a
scenario, already suggested by differing optical/near-IR spectroscopic and
X-ray AGN classifications, allows for different amounts of obscuration of the
continuum emission in different wavebands and of the broad emission line region
which results in a mixture of behaviors for AGN with similar optical emission
line classifications. The resulting limits on the column density of obscuring
material through which we are viewing the redder AGN are 100 times lower than
for the standard optically thick torus models. The resulting decrease in
optical depth of the obscuring material allows the AGN to heat more dust at
larger radial distances. We show that an AGN-heated, flared, dusty disk with
mass 10^9 solar and size of few hundred pc is able to generate optical-far-IR
SEDs which reproduce the wide range of SEDs present in our sample with no need
for an additional starburst component to generate the long-wavelength, cooler
part of the IR continuum.Comment: 40 pages, 14 figures, accepted for publication in Astrophysical
Journal, V. 590, June 10, 200
The End of the Rainbow: What Can We Say About the Extragalactic Sub-Megahertz Radio Sky?
The Galactic disc is opaque to radio waves from extragalactic sources with
frequencies nu less than ~3 MHz. However, radio waves with kHz, Hz, and even
lower frequencies may propagate through the intergalactic medium (IGM). I argue
that the presence of these waves can be inferred by using the Universe as our
detector. I discuss possible sub-MHz sources and set new non-trivial upper
limits on the energy density of sub-MHz radio waves in galaxy clusters and the
average cosmic background. Limits based on five effects are considered: (1)
changes in the expansion of the Universe from the radiation energy density (2)
heating of the IGM by free-free absorption; (3) radiation pressure squeezing of
IGM clouds by external radio waves; (4) synchrotron heating of electrons in
clusters; and (5) Inverse Compton upscattering of sub-MHz radio photons. Any
sub-MHz background must have an energy density much smaller than the CMB at
frequencies below 1 MHz. The free-free absorption bounds from the Lyman-alpha
forest are potentially the strongest, but are highly dependent on the
properties of sub-MHz radio scattering in the IGM. I estimate an upper limit of
6 * 10^4 L_sun Mpc^-3 for the emissivity within Lyman-alpha forest clouds in
the frequency range 5 - 200 Hz. The sub-MHz energy density in the Coma cluster
is constrained to be less than ~10^-15 erg cm^-3. At present, none of the
limits is strong enough to rule out a maximal T_b = 10^12 K sub-MHz synchrotron
background, but other sources may be constrained with a better knowledge of
sub-MHz radio propagation in the IGM.Comment: Accepted by MNRAS, 4 figures, 20 pages
The diffuse radio emission around NGC 5580 and NGC 5588
The galaxy pair NGC 5580 and NGC 5588 is part of a loose group of galaxies. They are surrounded by steep-spectrum, extended radio emission which was previously suggested to be a down-scaled example of Mpc-size radio haloes present in galaxies clusters. We present a multifrequency study of the radio emission aimed to clarify its nature. The source has been observed with the Giant Metrewave Radio Telescope at 235, 325 and 610 MHz and the images obtained were combined with archival data to cover the frequency range 150-1400 MHz. The new observations revealed the presence of a second, fainter lobe on the south-east of NGC 5580. The spectral index study of the source shows a flattening of the spectrum (which implies a younger particle population) close to the two galaxies. We argue that the extended radio emission is the remnant of a past activity cycle of the active galactic nucleus present in NGC 5580 and therefore a notable example of a dying radio galaxy located outside dense environments. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
- …