111 research outputs found
Local Behavior of the First-Order Gradient Correction to the Thomas-Fermi Kinetic Energy Functional
The first order gradient correction to the Thomas-Fermi functional, proposed
by Haq, Chattaraj and Deb (Chem. Phys. Lett. vol. 81, 8031, 1984) has been
studied by evaluating both the total kinetic energy and the local kinetic
energy density. For testing the kinetic energy density we evaluate its
deviation from an exact result through a quality factor, a parameter that
reflects the quality of the functionals in a better way than their relative
errors. The study is performed on two different systems: light atoms (up to
Z=18) and a noninteracting model of fermions confined in a Coulombic-type
potential. It is found than this approximation gives very low relative errors
and a better local behavior than any of the usual generalized gradient
approximation semilocal kinetic density functionals.Comment: 7 pages, 2 tables, 4 figure
Assessment of density-functional approximations: Long-range correlations and self-interaction effects
The complex nature of electron-electron correlations is made manifest in the very simple but nontrivial problem of two electrons confined within a sphere. The description of highly nonlocal correlation and self-interaction effects by widely used local and semilocal exchange-correlation energy density functionals is shown to be unsatisfactory in most cases. Even the best such functionals exhibit significant errors in the Kohn-Sham potentials and density profiles
Kinetic Energy Density Study of Some Representative Semilocal Kinetic Energy Functionals
There is a number of explicit kinetic energy density functionals for
non-interacting electron systems that are obtained in terms of the electron
density and its derivatives. These semilocal functionals have been widely used
in the literature. In this work we present a comparative study of the kinetic
energy density of these semilocal functionals, stressing the importance of the
local behavior to assess the quality of the functionals. We propose a quality
factor that measures the local differences between the usual orbital-based
kinetic energy density distributions and the approximated ones, allowing to
ensure if the good results obtained for the total kinetic energies with these
semilocal functionals are due to their correct local performance or to error
cancellations. We have also included contributions coming from the laplacian of
the electron density to work with an infinite set of kinetic energy densities.
For all the functionals but one we have found that their success in the
evaluation of the total kinetic energy are due to global error cancellations,
whereas the local behavior of their kinetic energy density becomes worse than
that corresponding to the Thomas-Fermi functional.Comment: 12 pages, 3 figure
Ergotropy and entanglement in critical spin chains
A subsystem of an entangled ground state is in a mixed state. Thus, if we
isolate this subsystem from its surroundings we may be able to extract work
applying unitary transformations, up to a maximal amount which is called
ergotropy. Once this work has been extracted, the subsystem will still contain
some bound energy above its local ground state, which can provide valuable
information about the entanglement structure. We show that the bound energy for
half a free fermionic chain decays as the square of the entanglement entropy
divided by the chain length, thus approaching zero for large system sizes, and
we conjecture that this relation holds for all 1D critical states
No evidence of association between genetic variants of the PDCD1 ligands and SLE
To access publisher full text version of this article. Please click on the hyperlink in Additional Links fieldPDCD1, an immunoreceptor involved in peripheral tolerance has previously been shown to be genetically associated with systemic lupus erythematosus (SLE). PDCD1 has two ligands whose genes are located in close proximity on chromosome 9p24. Our attention was drawn to these ligands after finding suggestive linkage to a marker (gata62f03, Z=2.27) located close to their genes in a genome scan of Icelandic families multiplex for SLE. Here, we analyse Swedish trios (N=149) for 23 single nucleotide polymorphisms (SNPs) within the genes of the PDCD1 ligands. Initially, indication of association to eight SNPs was observed, and these SNPs were therefore also analysed in Mexican trios (N=90), as well as independent sets of patients and controls from Sweden (152 patients, 448 controls) and Argentina (288 patients, 288 controls). We do not find support for genetic association to SLE. This is the first genetic study of SLE and the PDCD1 ligands and the lack of association in several cohorts implies that these genes are not major risk factors for SLE.Genes and Immunity (2007) 8, 69-74. doi:10.1038/sj.gene.6364360; published online 30 November 2006
Fasting and postprandial plasma ghrelin levels are decreased in patients with liver failure previous to liver transplantation
[Abstract] Anorexia is a problem of paramount importance in patients with advanced liver failure. Ghrelin has important actions on feeding and weight homeostasis. Concentrations of ghrelin are controversial in liver cirrhosis. Our aim was to study fasting ghrelin and their response to an oral glucose tolerance test (OGTT) in liver failure patients and normal subjects. Methods We included 16 patients with severe liver failure prior to liver transplantation. As a control group we included 10 age- and BMI-matched healthy subjects. After an overnight fast, 75 g of oral glucose were administered; glucose, insulin, and ghrelin were obtained at baseline and at times 30, 60, 90, and 120 min, respectively. Results Fasting ghrelin (median and range) were statistically significantly lower for patients compared to the controls, 527 (377–971) pg/ml vs. 643 (523–2163) pg/ml, P = 0.045, for patients and controls, respectively. The area under the curve for total ghrelin post-OGTT were lower in end-stage liver failure patients than in the control group, 58815 (44730–87420) pg/ml min vs. 76560 (56160–206385) pg/ml min, for patients and controls, respectively, P = 0.027. Conclusions Ghrelin levels are significantly decreased both fasting and post-OGTT in patients with liver failure candidates for transplantation. Decreased ghrelin levels could contribute to anorexia in patients with cirrhosis.Instituto de Salud Carlos III; PI051024Instituto de Salud Carlos III; PI070413Xunta de Galicia; PS07/12Xunta de Galicia; PGIDT05PXIC91605PNXunta de Galicia; INCITE08ENA916110E
- …