161 research outputs found
Pressure-Driven Metal-Insulator Transition in Hematite from Dynamical Mean-Field Theory
The Local Density Approximation combined with Dynamical Mean-Field Theory
(LDA+DMFT method) is applied to the study of the paramagnetic and magnetically
ordered phases of hematite FeO as a function of volume. As the volume
is decreased, a simultaneous 1st order insulator-metal and high-spin to
low-spin transition occurs close to the experimental value of the critical
volume. The high-spin insulating phase is destroyed by a progressive reduction
of the charge gap with increasing pressure, upon closing of which the high spin
phase becomes unstable. We conclude that the transition in FeO at
50 GPa can be described as an electronically driven volume collapse.Comment: 5 pages, 4 figure
Pentraxin 3(PTX 3): An Endogenous Modulator of the Inflammatory Response
Inflammatory or anti-inflammatory? That is the question as far as the acute-phase response and its mediators, the pentraxins, are concerned. Only some ten years ago, the classical or short pentraxin C-reactive protein and the newly discovered long pentraxin PTX3 were considered to exert most of the detrimental effects of acute inflammation, whether microbial or sterile in origin. However, accumulating evidence suggests an at least dichotomous, context-dependent outcome attributable to the pentraxins, if not a straightforward anti-inflammatory nature of the acute-phase response. This paper is focused on the inherent effects of pentraxin 3 in inflammatory responses, mainly in coronary artery disease and in Aspergillus fumigatus infection. Both are examples of inflammatory reactions in which PTX3 is substantially involved; the former sterile, the latter infectious in origin. Apart from different inducing noxae, similarities in the pathogenesis of the two are striking. All the same, the introductory question still persists: is the ultimate impact of PTX3 in these conditions inflammatory or anti-inflammatory, paradoxical as the latter might appear? We try to provide an answer such as it emerges in the light of recent findings
Testing the effect of site selection and parameter setting on REVEALS-model estimates of plant abundance using th Czech Quaternary Palynological database
International audiencetypes, PFTs) is used in the LANDCLIM project to assess the effect of human-induced land-cover change on past climate in NW Europe. Using the Czech Quaternary Pollen Database, this case study evaluates the extent to which selection of data and input parameters for the REVEALS model applications would affect reconstruction outcomes. The REVEALS estimates of PFTs (grid-cell based REVEALS PFT estimates, GB REVEALS PFT-s) are calculated for five time windows of the Holocene using fossil pollen records available in each 1°×1°grid cell of the Czech Republic. The input data and parameters selected for testing are: basin type and size, number of 14C dates used to establish the chronology of the pollen records, number of taxa, and pollen productivity estimates (PPE). We used the Spearman correlation coefficient to test the hypothesis that there is no association between GB REVEALS PFT-s using different data and parameter inputs. The results show that differences in the basin size and type, number of dates, number and type of taxa (entomophilous included or not), and PPE dataset do not affect the rank orders of the GB REVEALS PFT-s significantly, except for the cases when entomophilous taxa are included. It implies that, given careful selection of data and parameter and interpretation of results, REVEALS applications can use pollen records from lakes and bogs of different sizes together for reconstruction of past land cover at the regional to sub-continental spatial scales for purposes such as the study of past land cover-climate interactions. Our study also provides useful criteria to set up protocols for data compilation REVEALS applications of this kind
A Density Functional Study of Atomic Hydrogen and Oxygen Chemisorption on the Relaxed (0001) Surface of Double Hexagonal Close Packed Americium
Ab initio total energy calculations within the framework of density
functional theory have been performed for atomic hydrogen and oxygen
chemisorption on the (0001) surface of double hexagonal packed americium using
a full-potential all-electron linearized augmented plane wave plus local
orbitals method. Chemisorption energies were optimized with respect to the
distance of the adatom from the relaxed surface for three adsorption sites,
namely top, bridge, and hollow hcp sites, the adlayer structure corresponding
to coverage of a 0.25 monolayer in all cases. Chemisorption energies were
computed at the scalar-relativistic level (no spin-orbit coupling NSOC) and at
the fully relativistic level (with spin-orbit coupling SOC). The two-fold
bridge adsorption site was found to be the most stable site for O at both the
NSOC and SOC theoretical levels with chemisorption energies of 8.204 eV and
8.368 eV respectively, while the three-fold hollow hcp adsorption site was
found to be the most stable site for H with chemisorption energies of 3.136 eV
at the NSOC level and 3.217 eV at the SOC level. The respective distances of
the H and O adatoms from the surface were found to be 1.196 Ang. and 1.164 Ang.
Overall our calculations indicate that chemisorption energies in cases with SOC
are slightly more stable than the cases with NSOC in the 0.049-0.238 eV range.
The work functions and net magnetic moments respectively increased and
decreased in all cases compared with the corresponding quantities of bare dhcp
Am (0001) surface. The partial charges inside the muffin-tins, difference
charge density distributions, and the local density of states have been used to
analyze the Am-adatom bond interactions in detail. The implications of
chemisorption on Am 5f electron localization-delocalization are also discussed.Comment: 9 Tables, 5 figure
Anharmonicity in one-dimensional electron-phonon system
We investigate the effect of anharmonicity on the one-dimensional half-filled
Holstein model by using the determinant quantum Monte Carlo method. By
calculating the order parameters we find that with and without anharmonicity
there is always an transition from a disorder phase to a dimerized phase.
Moreover, in the dimerized phase a lattice dimerization and a charge density
wave coexist. The anharmonicity represented by the quartic term suppresses the
dimerization as well as the charge density wave, while a double-well potential
favors the dimerization. In addition, by calculating the correlation exponents
we show that the disorder phase is metallic with gapless charge excitations and
gapful spin excitations while in the dimerized phase both excitations are
gapful.Comment: 5 page
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