25,527 research outputs found
Excited State Specific Multi-Slater Jastrow Wave Functions
We combine recent advances in excited state variational principles, fast
multi-Slater Jastrow methods, and selective configuration interaction to create
multi-Slater Jastrow wave function approximations that are optimized for
individual excited states. In addition to the Jastrow variables and linear
expansion coefficients, this optimization includes state-specific orbital
relaxations in order to avoid the compromises necessary in state-averaged
approaches. We demonstrate that, when combined with variance matching to help
balance the quality of the approximation across different states, this approach
delivers accurate excitation energies even when using very modest multi-Slater
expansions. Intriguingly, this accuracy is maintained even when studying a
difficult chlorine-anion-to- charge transfer in which traditional
state-averaged multi-reference methods must contend with different states that
require drastically different orbital relaxations.Comment: 16 pages, 6 figures, 2 table
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
Retinoic acid as a modulator of T cell immunity
Indexación: Scopus. DOAJ.Vitamin A, a generic designation for an array of organic molecules that includes retinal, retinol and retinoic acid, is an essential nutrient needed in a wide array of aspects including the proper functioning of the visual system, maintenance of cell function and differentiation, epithelial surface integrity, erythrocyte production, reproduction, and normal immune function. Vitamin A deficiency is one of the most common micronutrient deficiencies worldwide and is associated with defects in adaptive immunity. Reports from epidemiological studies, clinical trials and experimental studies have clearly demonstrated that vitamin A plays a central role in immunity and that its deficiency is the cause of broad immune alterations including decreased humoral and cellular responses, inadequate immune regulation, weak response to vaccines and poor lymphoid organ development. In this review, we will examine the role of vitamin A in immunity and focus on several aspects of T cell biology such as T helper cell differentiation, function and homing, as well as lymphoid organ development. Further, we will provide an overview of the effects of vitamin A deficiency in the adaptive immune responses and how retinoic acid, through its effect on T cells can fine-tune the balance between tolerance and immunity.http://www.mdpi.com/2072-6643/8/6/34
Hydraulic conductivity and swelling pressure of GCLs using polymer treated clays to high concentration CaCl(2) solutions
A Geosynthetic Clay Liner (GCL) is a frequently used h ydraulic barrier system designed to impede the flow of contaminated leachate into the environment. The main objective of this barrier system is to maintain a low hydraulic conductivity that is determined by the bentonite fraction. In this study, calcium bentonite, natural sodium bentonites, and sodium activated bentonite were treated with the HYPER clay technique. This involves the adsorption of an anionic polymer, Sodium CarboxyMethylCellulose (Na-CMC) onto the surface
of the clay material. The purpose of this research was to show the beneficial effect of the HYPER clay treatment on the swelling and hydraulic performance, while the bentonite is permeated with high concentration CaCl2 solutions. The test results showed that swelling and hydraulic performance increased with Na-CMC treatment, regardless of the type of bentonite that was used. Additionally, a powdered Na CMC configuration provided higher swelling and hydraulic performance compared to a granular configuration
Preliminary test on modified clays for seawater resistant drilling fluids
The quality of a drilling fluid declines in salt water conditions. An engineered clay (HYPER clay) was developed for geosynthetic clay liners with enhanced resistance to aggressive conditions. This study investigates the potential of this superior clay for drilling fluids applied in salt water conditions. A sodium bentonite was treated with a carboxymethyl cellulose (CMC) polymer following the HYPER clay process method. Preliminary tests were performed to investigate suitability of HYPER clay for seawater resistant drilling fluids. Fluid performance was characterized by its thixotropic behavior, rheological properties (gel strength, yield point and viscosity), swell and bleeding behavior. Drilling fluid performance was analyzed at various polymer dosages and electrolyte concentrations. Polymer treatment improved the gel strength and swelling ability of the fluid, especially in electrolyte solutions. Moreover, filter press tests (API 13B-1, 76% seawater) showed that filtrate loss decreased due to polymer treatment
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
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