7,306 research outputs found
Research project Mauretania: Satellites as development aids
A general discussion is presented of how satellite images and ground surveys are used to define land use. Specifically it deals with the Tagant region in Mauretania, West Africa
Task rules, working memory, and fluid intelligence
Many varieties of working memory have been linked to fluid intelligence. In Duncan et al. (Journal of Experimental Psychology:General 137:131–148, 2008), we described limited working memory for new task rules: When rules are complex, some may fail in their control of behavior, though they are often still available for explicit recall. Unlike other kinds of working memory, load is determined in this case not by real-time performance demands, but by the total complexity of the task instructions. Here, we show that the correlation with fluid intelligence is stronger for this aspect of working memory than for several other, more traditional varieties—including simple and complex spans and a test of visual short-term memory. Any task, we propose, requires construction of a mental control program that aids in segregating and assembling multiple task parts and their controlling rules. Fluid intelligence is linked closely to the efficiency of constructing such programs, especially when behavior is complex and novel
Deconfinement to Quark Matter in Neutron Stars - The Influence of Strong Magnetic Fields
We use an extended version of the hadronic SU(3) non-linear realization of
the sigma model that also includes quarks to study hybrid stars. Within this
approach, the degrees of freedom change naturally as the temperature/density
increases. Different prescriptions of charge neutrality, local and global, are
tested and the influence of strong magnetic fields and the anomalous magnetic
moment on the particle population is discussed.Comment: To appear in the proceedings of conference XII HADRON PHYSICS April,
22-27, 2012, Bento Goncalves, Wineyards Valley Region, Rio Grande do Sul,
Brazil Revised version with corrections made to the text in page
Cosmic microwave background constraints on the epoch of reionization
We use a compilation of cosmic microwave anisotropy data to constrain the
epoch of reionization in the Universe, as a function of cosmological
parameters. We consider spatially-flat cosmologies, varying the matter density
(the flatness being restored by a cosmological constant), the Hubble
parameter and the spectral index of the primordial power spectrum. Our
results are quoted both in terms of the maximum permitted optical depth to the
last-scattering surface, and in terms of the highest allowed reionization
redshift assuming instantaneous reionization. For critical-density models,
significantly-tilted power spectra are excluded as they cannot fit the current
data for any amount of reionization, and even scale-invariant models must have
an optical depth to last scattering of below 0.3. For the currently-favoured
low-density model with and a cosmological constant, the
earliest reionization permitted to occur is at around redshift 35, which
roughly coincides with the highest estimate in the literature. We provide
general fitting functions for the maximum permitted optical depth, as a
function of cosmological parameters. We do not consider the inclusion of tensor
perturbations, but if present they would strengthen the upper limits we quote.Comment: 9 pages LaTeX file with ten figures incorporated (uses mn.sty and
epsf). Corrects some equation typos, superseding published versio
Stationarity of SLE
A new method to study a stopped hull of SLE(kappa,rho) is presented. In this
approach, the law of the conformal map associated to the hull is invariant
under a SLE induced flow. The full trace of a chordal SLE(kappa) can be studied
using this approach. Some example calculations are presented.Comment: 14 pages with 1 figur
Light Propagation in Inhomogeneous Universes. IV. Strong Lensing and Environmental Effects
We study the gravitational lensing of high-redshift sources in a LCDM
universe. We have performed a series of ray-tracing experiments, and selected a
subsample of cases of strong lensing (multiple images, arcs, and Einstein
rings). For each case, we identify a massive galaxy that is primarily
responsible for lensing, and studied how the various density inhomogeneities
along the line of sight (other galaxies, background matter) affect the
properties of the image. The matter located near the lensing galaxy, and
physically associated with it, has a small effect. The background matter
increases the magnification by a few percents at most, while nearby galaxies
can increase it by up to about 10 percent. The effect on the image separation
is even smaller. The only significant effect results from the random alignment
of physically unassociated galaxies, which can increase the magnification by
factors of several, create additional images, and turn arcs into rings. We
conclude that the effect of environment on strong lensing in negligible in
general, and might be important only in rare cases. We show that our conclusion
does not depend on the radial density profile of the galaxies responsible for
lensing.Comment: 23 pages, 7 figures (one in color). Accepted for publication in The
Astrophysical Journal. Minor typos correcte
- …