398 research outputs found
Correlation energies of inhomogeneous many-electron systems
We generalize the uniform-gas correlation energy formalism of Singwi, Tosi,
Land and Sjolander to the case of an arbitrary inhomogeneous many-particle
system. For jellium slabs of finite thickness with a self-consistent LDA
groundstate Kohn-Sham potential as input, our numerical results for the
correlation energy agree well with diffusion Monte Carlo results. For a helium
atom we also obtain a good correlation energy.Comment: 4 pages,1 figur
Evolution of the Luminosity Function and Colors of Galaxies in a Lambda-CDM Universe
The luminosity function of galaxies is derived from a cosmological
hydrodynamic simulation of a Lambda cold dark matter (CDM) universe with the
aid of a stellar population synthesis model. At z=0, the resulting B band
luminosity function has a flat faint end slope of \alpha \approx -1.15 with the
characteristic luminosity and the normalization in a fair agreement with
observations, while the dark matter halo mass function is steep with a slope of
\alpha \approx -2. The colour distribution of galaxies also agrees well with
local observations. We also discuss the evolution of the luminosity function,
and the colour distribution of galaxies from z=0 to 5. A large evolution of the
characteristic mass in the stellar mass function due to number evolution is
compensated by luminosity evolution; the characteristic luminosity increases
only by 0.8 mag from z=0 to 2, and then declines towards higher redshift, while
the B band luminosity density continues to increase from z=0 to 5 (but only
slowly at z>3).Comment: 6 pages, including 4 figures, mn2e style. Accepted to MNRAS pink
page
Gamma Ray Bursts as Probes of Quantum Gravity
Gamma ray bursts (GRBs) are short and intense pulses of -rays
arriving from random directions in the sky. Several years ago Amelino-Camelia
et al. pointed out that a comparison of time of arrival of photons at different
energies from a GRB could be used to measure (or obtain a limit on) possible
deviations from a constant speed of light at high photons energies. I review
here our current understanding of GRBs and reconsider the possibility of
performing these observations.Comment: Lectures given at the 40th winter school of theretical physics:
Quantum Gravity and Phenomenology, Feb. 2004 Polan
The Still Bay points of Apollo 11 Rock Shelter, Namibia : an inter-regional perspective
Abstract: Dating to roughly 80,000 to 70,000 years ago, components of the Still Bay technocomplex of southern Africa and their potential behavioural implications have been widely discussed. Stone points with invasive retouch, as defined over 90 years ago by Goodwin and van Riet Lowe, serve as markers for Still Bay assemblages, yet many Still Bay sites remain undated and comprehensive, comparable sets of data for their point assemblages remain unpublished. Much of the Middle Stone Age at the site of Apollo 11 in Namibia was undated until 2010, when a potential Still Bay component was announced. Although a Still Bay assemblage at Apollo 11 would represent the most northwesterly and inland expression of this technocomplex, its points have never been fully analysed. This paper presents their morphometric data and an interpretation of point-production strategies. These results are then compared with data obtained for two South African sites: Hollow Rock Shelter in the Western Cape and Umhlatuzana in KwaZulu-Natal. This comparison demonstrates that whereas there are no statistically significant differences in the morphometric data sets between the three sites, there are both similarities and differences in point-production strategies, cross-section shapes and the use of raw materials for knapping. It is suggested that these similarities and variations represent aspects of how knowledge-transfer systems and knapping conventions were followed on both intra-regional and inter-regional scales
Microlensing as a probe of the Galactic structure; 20 years of microlensing optical depth studies
Microlensing is now a very popular observational astronomical technique. The
investigations accessible through this effect range from the dark matter
problem to the search for extra-solar planets. In this review, the techniques
to search for microlensing effects and to determine optical depths through the
monitoring of large samples of stars will be described. The consequences of the
published results on the knowledge of the Milky-Way structure and its dark
matter component will be discussed. The difficulties and limitations of the
ongoing programs and the perspectives of the microlensing optical depth
technique as a probe of the Galaxy structure will also be detailed.Comment: Accepted for publication in General Relativity and Gravitation.
General Relativity and Gravitation in press (2010) 0
Atomic diffraction from nanostructured optical potentials
We develop a versatile theoretical approach to the study of cold-atom
diffractive scattering from light-field gratings by combining calculations of
the optical near-field, generated by evanescent waves close to the surface of
periodic nanostructured arrays, together with advanced atom wavepacket
propagation on this optical potential.Comment: 8 figures, 10 pages, submitted to Phys. Rev.
Hidrólise da uréia em latossolos: efeito da concentração de uréia, temperatura, pH, armazenamento e tempo de incubação
Chikungunya risk assessment for europe: recommendations for action
Since March 2005, 255 000 cases of chikungunya fever are estimated to have occurred on the island of RĂ©union, a French overseas department in the Indian Ocean [1]. An huge increase in estimated cases occurred at the end of December 2005, culminating in an estimated peak incidence of more than 40 000 cases in week 5 of 2006 [2]. Since then, the estimated weekly incidence trend is downwards, although there have been an estimated 3000 new cases per week since week 13 of 2006. In total, 213 deaths have been linked to the disease [1]. In Mayotte, the nearby French territorial collectivity, 5834 cases have been notified [3]. Chikungunya cases have also been reported on other islands in the Indian Ocean, and imported cases have been confirmed in several European countrie
Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
We review HB stars in a broad astrophysical context, including both variable
and non-variable stars. A reassessment of the Oosterhoff dichotomy is
presented, which provides unprecedented detail regarding its origin and
systematics. We show that the Oosterhoff dichotomy and the distribution of
globular clusters (GCs) in the HB morphology-metallicity plane both exclude,
with high statistical significance, the possibility that the Galactic halo may
have formed from the accretion of dwarf galaxies resembling present-day Milky
Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the
second-parameter problem is presented. A technique is proposed to estimate the
HB types of extragalactic GCs on the basis of integrated far-UV photometry. The
relationship between the absolute V magnitude of the HB at the RR Lyrae level
and metallicity, as obtained on the basis of trigonometric parallax
measurements for the star RR Lyrae, is also revisited, giving a distance
modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are
studied. Finally, the conductive opacities used in evolutionary calculations of
low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and
Space Scienc
Do precocial mammals develop at a faster rate? A comparison of rates of skull development in Sigmodon fulviventer and Mus musculus domesticus
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72993/1/j.1420-9101.2003.00568.x.pd
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