Coulomb correlation effects in zinc monochalcogenides

Electronic structure and band characteristics for zinc monochalcogenides with zinc-blende- and wurtzite-type structures are studied by first-principles density-functional-theory calculations with different approximations. It is shown that the local-density approximation underestimates the band gap and energy splitting between the states at the top of the valence band, misplaces the energy levels of the Zn-3d states, and overestimates the crystal-field-splitting energy. Regardless of the structure type considered, the spin-orbit-coupling energy is found to be overestimated for ZnO and underestimated for ZnS with wurtzite-type structure, and more or less correct for ZnSe and ZnTe with zinc-blende-type structure. The order of the states at the top of the valence band is found to be anomalous for ZnO in both zinc-blende- and wurtzite-type structure, but is normal for the other zinc monochalcogenides considered. It is shown that the Zn-3d electrons and their interference with the O-2p electrons are responsible for the anomalous order. The typical errors in the calculated band gaps and related parameters for ZnO originate from strong Coulomb correlations, which are found to be highly significant for this compound. The LDA+U approach is by and large found to correct the strong correlation of the Zn-3d electrons, and thus to improve the agreement with the experimentally established location of the Zn-3d levels compared with that derived from pure LDA calculations

Obesogenic dietary intake in families with 1-year-old infants at high and low obesity risk based on parental weight status: baseline data from a longitudinal intervention (Early STOPP)

PURPOSE: To compare dietary intake in 1-year-old infants and their parents between families with high and low obesity risk, and to explore associations between infant dietary intake and relative weight. METHODS: Baseline analyses of 1-year-old infants (n = 193) and their parents participating in a longitudinal obesity intervention (Early STOPP) were carried out. Dietary intake and diet quality indicators were compared between high- and low-risk families, where obesity risk was based on parental weight status. The odds for high diet quality in relation to parental diet quality were determined. Associations between measured infant relative weight and dietary intake were examined adjusting for obesity risk, socio-demographics, and infant feeding. RESULTS: Infant dietary intake did not differ between high- and low-risk families. The parents in high-risk families consumed soft drinks, French fries, and low-fat spread more frequently, and fish and fruits less frequently (p < 0.05) compared to parents in low-risk families. Paternal intake of vegetables and fish increased the odds for children being consumers of vegetables (OR 1.7; 95 % CI 1.0-2.9) and fish, respectively (OR 2.5; 95 % CI 1.4-4.4). Infant relative weight was weakly associated with a high intake of milk cereal drink (r = 0.15; p < 0.05), but not with any other aspect of dietary intake, obesity risk, or early feeding patterns. CONCLUSIONS: At the age of one, dietary intake in infants is not associated with family obesity risk, nor with parental obesogenic food intake. Milk cereal drink consumption but no other infant dietary marker reflects relative weight at this young age.published_or_final_versio

Analysis of SSIM performance for Digital Cinema applications

Visual quality is one of the most important issues in digital cinema applications, and the most practical method to measure visual quality is using objective metrics. Several objective metrics that take into account perceived visual quality have been developed in the past few years; one of them is based on the structural similarity paradigm. To analyze the performance of these objective metrics for digital cinema applications, a subjective visual quality assessment in digital cinema environments using contents from the digital cinema initiative (DCI) standard evaluation material has been conducted in a previous study. Since in practice digital cinema utilizes only high quality imagery, in this paper we analyze further a subset of high- quality stimuli from the previous stud

Particle Dark Matter Constraints from the Draco Dwarf Galaxy

It is widely thought that neutralinos, the lightest supersymmetric particles, could comprise most of the dark matter. If so, then dark halos will emit radio and gamma ray signals initiated by neutralino annihilation. A particularly promising place to look for these indicators is at the center of the local group dwarf spheroidal galaxy Draco, and recent measurements of the motion of its stars have revealed it to be an even better target for dark matter detection than previously thought. We compute limits on WIMP properties for various models of Draco's dark matter halo. We find that if the halo is nearly isothermal, as the new measurements indicate, then current gamma ray flux limits prohibit much of the neutralino parameter space. If Draco has a moderate magnetic field, then current radio limits can rule out more of it. These results are appreciably stronger than other current constraints, and so acquiring more detailed data on Draco's density profile becomes one of the most promising avenues for identifying dark matter.Comment: 13 pages, 6 figure

Electronic structure and band parameters for ZnX (X = O, S, Se, Te)

First-principles density-functional calculations have been performed for zinc monochalcogenides with zinc-blende- and wurtzite-type structures. It is shown that the local-density approximation underestimates the band gap, misplaces the energy levels of the Zn-3d states, and overestimates the crystal-field splitting energy. Without spinorbit coupling, the order of the states at the top of VB is found to be normal for all the ZnX phases considered. Upon inclusion of the spinorbit coupling in calculations, ZnO in zinc-blende- and wurtzite-type phases become anomalous. It is shown that the Zn-3d electrons are responsible for the anomalous order. The effective masses of electrons and holes have been calculated and found that holes are much anisotropic and heavier than the electrons in agreement with experimental findings. The typical errors in calculated band gaps and related parameters originate from strong Coulomb correlations, which are found to be highly significant in ZnO. The LDA+U approach is found to correct the strong correlation of the Zn-3d electrons, and thus improves the agreement with the experimentally established location of the Zn-3d levels. Consequently, it increases significantly the parameters underestimated in the pure LDA calculations.Comment: 7 pages, 3 figures, 2 tables, ICAM-ICMAT conference, 200

Identifying Gamma-Ray Burst Remnants Through Positron Annihilation Radiation

We model the annihilation of relic positrons produced in a gamma-ray burst (GRB) after its afterglow has faded. We find that the annihilation signal from at least one GRB remnant in the Milky Way galaxy should be observable with future space missions such as INTEGRAL and EXIST, provided that the gas surrounding the GRB source has the typical density of the interstellar medium, < 1 cm^-3. Three fortunate circumstances conspire to make the signal observable. First, unlike positrons in a standard supernova, the GRB positrons initially travel at a relativistic speed and remain ahead of any non-relativistic ejecta until the ejecta become rarefied and the annihilation time becomes long. Second, the GRB remnant remains sufficiently hot (T > 5 x 10^5 K) for a strong annihilation line to form without significant smearing by three-photon decay of positronium. Third, the annihilation signal persists over a time longer than the average period between GRB events in the Milky Way galaxy.Comment: 5 pages, 2 figures, submitted to ApJL (fixed Latex figure referencing

Typing Late Prehistoric Cows and Bulls—Osteology and Genetics of Cattle at the Eketorp Ringfort on the Öland Island in Sweden

Human management of livestock and the presence of different breeds have been discussed in archaeozoology and animal breeding. Traditionally osteometrics has been the main tool in addressing these questions. We combine osteometrics with molecular sex identifications of 104 of 340 morphometrically analysed bones in order to investigate the use of cattle at the Eketorp ringfort on the Öland island in Sweden. The fort is dated to 300–1220/50 A.D., revealing three different building phases. In order to investigate specific patterns and shifts through time in the use of cattle the genetic data is evaluated in relation to osteometric patterns and occurrence of pathologies on cattle metapodia. Males were genotyped for a Y-chromosomal SNP in UTY19 that separates the two major haplogroups, Y1 and Y2, in taurine cattle. A subset of the samples were also genotyped for one SNP involved in coat coloration (MC1R), one SNP putatively involved in resistance to cattle plague (TLR4), and one SNP in intron 5 of the IGF-1 gene that has been associated to size and reproduction

Solubility limit and precipitate formation in Al-doped 4H-SiC epitaxial material

Heavily Al-doped 4H–SiC structures have been prepared by vapor phase epitaxy. Subsequent anneals have been carried out in an Ar atmosphere in a rf-heated furnace between 1500 °C and 2000 °C for 0.5 to 3 h. Secondary ion mass spectrometry has been utilized to obtain Al concentration versus depth as well as lateral distributions (ion images). Transmission electron microscopy(TEM) has been employed to study the crystallinity and determine phase composition after heat treatment. A solubility limit of ∼2×10²⁰ Al/cm³ (1900 °C) is extracted. Three-dimensional ion images show that the Al distribution does not remain homogeneous in layers heat treated at 1700 °C or above when the Al concentration exceeds 2×10²⁰ cm⁻³. Al-containing precipitates are identified by energy-filtered TEM.Financial support was partly received from the Swedish Foundation for Strategic Research (SSF) SiCEP program