456 research outputs found
Lattice-based QCD equation of state at finite baryon density: Cluster Expansion Model
The QCD equation of state at finite baryon density is studied in the framework of a Cluster Expansion Model (CEM), which is based on the fugacity expansion of the net baryon density. The CEM uses the two leading Fourier coefficients, obtained from lattice simulations at imaginary mu(B), as the only model input and permits a closed analytic form. Excellent description of the available lattice data at both mu(B) = 0 and at imaginary mu(B) is obtained. We also demonstrate how the Fourier coefficients can be reconstructed from baryon number susceptibilities
Masses and Phase Structure in the Ginzburg-Landau Model
We study numerically the phase structure of the Ginzburg-Landau model, with
particular emphasis on mass measurements. There is no local gauge invariant
order parameter, but we find that there is a phase transition characterized by
a vanishing photon mass. For type I superconductors the transition is of 1st
order. For type II 1st order is excluded by susceptibility analysis, but the
photon correlation length suggests 2nd order critical behaviour with \nu ~ 1/2.
The scalar mass, in contrast, does not show clear critical behaviour in the
type II regime for V \to \infty, contrary to the conventional picture.Comment: 16 pages, 6 figures. More data gathered, allowing more definite
conclusion
Assessing the Performance of Recent Density Functionals for Bulk Solids
We assess the performance of recent density functionals for the
exchange-correlation energy of a nonmolecular solid, by applying accurate
calculations with the GAUSSIAN, BAND, and VASP codes to a test set of 24 solid
metals and non-metals. The functionals tested are the modified
Perdew-Burke-Ernzerhof generalized gradient approximation (PBEsol GGA), the
second-order GGA (SOGGA), and the Armiento-Mattsson 2005 (AM05) GGA. For
completeness, we also test more-standard functionals: the local density
approximation, the original PBE GGA, and the Tao-Perdew-Staroverov-Scuseria
(TPSS) meta-GGA. We find that the recent density functionals for solids reach a
high accuracy for bulk properties (lattice constant and bulk modulus). For the
cohesive energy, PBE is better than PBEsol overall, as expected, but PBEsol is
actually better for the alkali metals and alkali halides. For fair comparison
of calculated and experimental results, we consider the zero-point phonon and
finite-temperature effects ignored by many workers. We show how Gaussian basis
sets and inaccurate experimental reference data may affect the rating of the
quality of the functionals. The results show that PBEsol and AM05 perform
somewhat differently from each other for alkali metal, alkaline earth metal and
alkali halide crystals (where the maximum value of the reduced density gradient
is about 2), but perform very similarly for most of the other solids (where it
is often about 1). Our explanation for this is consistent with the importance
of exchange-correlation nonlocality in regions of core-valence overlap.Comment: 32 pages, single pdf fil
Adsorption of CO on a Platinum (111) surface - a study within a four-component relativistic density functional approach
We report on results of a theoretical study of the adsorption process of a
single carbon oxide molecule on a Platinum (111) surface. A four-component
relativistic density functional method was applied to account for a proper
description of the strong relativistic effects. A limited number of atoms in
the framework of a cluster approach is used to describe the surface. Different
adsorption sites are investigated. We found that CO is preferably adsorbed at
the top position.Comment: 23 Pages with 4 figure
Relativistic calculations to assess the ability of the generalized gradient approximation to reproduce trends in cohesive properties of solids
Unicystic ameloblastoma of the mandible - an unusual case report and review of literature
Ameloblastoma is a true neoplasm of odontogenic epithelial origin. It is the second most common odontogenic neoplasm, and only odontoma outnumbers it in reported frequency of occurrence. Its incidence, combined with its clinical behavior, makes ameloblastoma the most significant odontogenic neoplasm. Unicystic ameloblastoma (UA) refers to those cystic lesions that show clinical, radiographic, or gross features of a mandibular cyst, but on histologic examination show a typical ameloblastomatous epithelium lining part of the cyst cavity, with or without luminal and/or mural tumor growth. It accounts for 5-15% of all intraosseous ameloblastomas. We report a case of unicystic ameloblastoma in a 30-year-old female, and review the literature
Static SU(3) potentials for sources in various representations
The potentials and string tensions between static sources in a variety of
representations (fundamental, 8, 6, 15-antisymmetric, 10, 27 and 15-symmetric)
have been computed by measuring Wilson loops in pure gauge SU(3). The
simulations have been done primarily on anisotropic lattices, using a tadpole
improved action improved to O(a_{s}^4). A range of lattice spacings (0.43 fm,
0.25 fm and 0.11 fm) and volumes (, , and ) has been used in an attempt to control
discretization and finite volume effects. At intermediate distances, the
results show approximate Casimir scaling. Finite lattice spacing effects
dominate systematic error, and are particularly large for the representations
with the largest string tensions.Comment: Version to appear in PR
Connection between Chiral Symmetry Restoration and Deconfinement
We propose a simple explanation for the connection between chiral symmetry
restoration and deconfinement in QCD at high temperature. In the Higgs
description of the QCD vacuum both spontaneous chiral symmetry breaking and
effective gluon masses are generated by the condensate of a color octet
quark-antiquark pair. The transition to the high temperature state proceeds by
the melting of this condensate. Quarks and gluons become (approximately)
massless at the same critical temperature. For instanton-dominated effective
multiquark interactions and three light quarks with equal mass we find a first
order phase transition at a critical temperature around 170 MeV.Comment: New section on vortices,33 pages,LaTe
Quintessential Kination and Cold Dark Matter Abundance
The generation of a kination-dominated phase by a quintessential exponential
model is investigated and the parameters of the model are restricted so that a
number of observational constraints (originating from nucleosynthesis, the
present acceleration of the universe and the dark-energy-density parameter) are
satisfied. The decoupling of a thermal cold dark matter particle during the
period of kination is analyzed, the relic density is calculated both
numerically and semi-analytically and the results are compared with each other.
It is argued that the enhancement, with respect to the standard paradigm, of
the cold dark matter abundance can be expressed as a function of the
quintessential density parameter at the onset of nucleosynthesis. We find that
values of the latter quantity close to its upper bound require the
thermal-averaged cross section times the velocity of the cold relic to be
almost three orders of magnitude larger than this needed in the standard
scenario so as compatibility with the cold dark matter constraint is achieved.Comment: Published versio
Pseudopotential study of binding properties of solids within generalized gradient approximations: The role of core-valence exchange-correlation
In ab initio pseudopotential calculations within density-functional theory
the nonlinear exchange-correlation interaction between valence and core
electrons is often treated linearly through the pseudopotential. We discuss the
accuracy and limitations of this approximation regarding a comparison of the
local density approximation (LDA) and generalized gradient approximations
(GGA), which we find to describe core-valence exchange-correlation markedly
different. (1) Evaluating the binding properties of a number of typical solids
we demonstrate that the pseudopotential approach and namely the linearization
of core-valence exchange-correlation are both accurate and limited in the same
way in GGA as in LDA. (2) Examining the practice to carry out GGA calculations
using pseudopotentials derived within LDA we show that the ensuing results
differ significantly from those obtained using pseudopotentials derived within
GGA. As principal source of these differences we identify the distinct behavior
of core-valence exchange-correlation in LDA and GGA which, accordingly,
contributes substantially to the GGA induced changes of calculated binding
properties.Comment: 13 pages, 6 figures, submitted to Phys. Rev. B, other related
publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm
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