21,385 research outputs found
The two gap transitions in GeSn: effect of non-substitutional complex defects
The existence of non-substitutional -Sn defects in GeSn
was confirmed by emission channeling experiments [Decoster et al., Phys. Rev. B
81, 155204 (2010)], which established that although most Sn enters
substitutionally (-Sn) in the Ge lattice, a second significant fraction
corresponds to the Sn-vacancy defect complex in the split-vacancy configuration
( -Sn ), in agreement with our previous theoretical study [Ventura et
al., Phys. Rev. B 79, 155202 (2009)]. Here, we present our electronic structure
calculation for GeSn, including substitutional -Sn as
well as non-substitutional -Sn defects. To include the presence of
non-substitutional complex defects in the electronic structure calculation for
this multi-orbital alloy problem, we extended the approach for the purely
substitutional alloy by Jenkins and Dow [Jenkins and Dow, Phys. Rev. B 36, 7994
(1987)]. We employed an effective substitutional two-site cluster equivalent to
the real non-substitutional -Sn defect, which was determined by a
Green's functions calculation. We then calculated the electronic structure of
the effective alloy purely in terms of substitutional defects, embedding the
effective substitutional clusters in the lattice. Our results describe the two
transitions of the fundamental gap of GeSn as a function of the
total Sn-concentration: namely from an indirect to a direct gap, first, and the
metallization transition at higher . They also highlight the role of
-Sn in the reduction of the concentration range which corresponds to the
direct-gap phase of this alloy, of interest for optoelectronics applications.Comment: 11 pages, 9 Figure
Isocausal spacetimes may have different causal boundaries
We construct an example which shows that two isocausal spacetimes, in the
sense introduced by Garc\'ia-Parrado and Senovilla, may have c-boundaries which
are not equal (more precisely, not equivalent, as no bijection between the
completions can preserve all the binary relations induced by causality). This
example also suggests that isocausality can be useful for the understanding and
computation of the c-boundary.Comment: Minor modifications, including the title, which matches now with the
published version. 12 pages, 3 figure
Molecular and Genetic Regulation of Sensory Quality of Climacteric Fruit
The sensory quality of fruit has become a major criterion in making the
purchasing decision by consumers. Breeding programs have mainly been directed,
from the post-harvest stand point, towards improving shelf-life. Chance seedlings or
mutants with improved agronomic traits and/or extended shelf-life have been used
for introgressing the long shelf-life character and eventually improved sensory
quality traits in commercial genotypes of apple, melon or tomato. Because the plant
hormone ethylene plays a central role in both storability and ripening of climacteric
fruit, the generation by biotechnology of ethylene-inhibited fruit has offered a
powerful tool to better understand, at the molecular and genetic level, the interrelations
between storability and sensory quality. In the melon, inhibition of ethylene
synthesis results is a strong inhibition of the synthesis of aroma volatiles while the
accumulation of sugars is not affected or is even improved. The softening of the flesh
is strongly affected but not abolished. Mid or long shelf-life melons generated by
classical breeding present the same behavior. The generation of recombinant inbred
lines by crossing a typical climacteric melon (Cantaloupe Charentais of the
cantalupensis group) with a non climacteric melon (PI161375 of the agrestis
chinensis group) allowed to demonstrate that the climacteric character is conferred
by 2 duplicated loci only, which are of great importance for the regulation of
storability and sensory quality. Due to the importance of aroma volatiles in sensory
quality and to the strong negative correlation between aroma production and
ethylene synthesis, we have developed a research program aimed at isolating genes
involved in the synthesis of aroma volatiles. We will report on the recent advances in
the field with special emphasis on the characterization of genes responsible for the
synthesis of esters, a family of compounds crucial for the flavor of many fruit
Dusty Starbursts and the Growth of Cosmic Structure
Dusty starbursts were more numerous around z~1 than today and appear to be
responsible for the majority of cosmic star formation over the Hubble time. We
suggest that they represent a common phase within galaxies in general which is
triggered by the growth of cosmic structure. We discuss the origin of the
luminosity of luminous infrared galaxies at z~1. Are these galaxies dominated
by star formation or nuclear activity ? What is triggering their strong
activity ? Is it triggered by external interactions or did it happen naturally
within isolated galaxies ? We present HST-ACS high resolution optical images of
luminous infrared galaxies at z~0.7 showing the evolution of the morphology of
these galaxies as a function of infrared luminosity, or star formation rate,
and discuss the effect of the environment on their activity.Comment: 4 pages, 2 figures, to appear in Proceeding of the "Multi-Wavelength
Cosmology" Conference held in Mykonos, Greece, June 2003, ed.M. Plionis
(Kluwer
A Prediction of Observable Rotation in the ICM of Abell 3266
We present a numerical Hydro+N-body model of A3266 whose X-ray surface
brightness, temperature distribution, and galaxy spatial and velocity
distribution data are consistent with the A3266 data. The model is an old (~3
Gyr), off-axis merger having a mass ratio of ~2.5:1. The less massive
subcluster in the model is moving on a trajectory from southwest to northeast
passing on the western side of the dominant cluster while moving into the plane
of the sky at ~45 degrees. Off-axis mergers such as this one are an effective
mechanism for transferring angular momentum to the intracluster medium (ICM),
making possible a large scale rotation of the ICM. We demonstrate here that the
ICM rotation predicted by our fully 3-dimensional model of A3266 is observable
with current technology. As an example, we present simulated observations
assuming the capabilities of the high resolution X-ray spectrometer (XRS) which
was to have flown on Astro-E.Comment: 9 pages, 7 postscript figures, Fig. 3 and 6 are color postscript,
Accepted for publication in the Astrophysical Journa
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