828 research outputs found
A new model for the structure of the DACs and SACs regions in the Oe and Be stellar atmospheres
In this paper we present a new mathematical model for the density regions
where a specific spectral line and its SACs/DACs are created in the Oe and Be
stellar atmospheres. In the calculations of final spectral line function we
consider that the main reasons of the line broadening are the rotation of the
density regions creating the spectral line and its DACs/SACs, as well as the
random motions of the ions. This line function is able to reproduce the
spectral feature and it enables us to calculate some important physical
parameters, such as the rotational, the radial and the random velocities, the
Full Width at Half Maximum, the Gaussian deviation, the optical depth, the
column density and the absorbed or emitted energy. Additionally, we can
calculate the percentage of the contribution of the rotational velocity and the
ions' random motions of the DACs/SACs regions to the line broadening. Finally,
we present two tests and three short applications of the proposed model.Comment: 9 pages, 5 figures, accepted for publication in PAS
Mesoscopic Behavior Near a Two-Dimensional Metal-Insulator Transition
We study conductance fluctuations in a two-dimensional electron gas as a
function of chemical potential (or gate voltage) from the strongly insulating
to the metallic regime. Power spectra of the fluctuations decay with two
distinct exponents (1/v_l and 1/v_h). For conductivity , we find a third exponent (1/v_i) in the shortest samples, and
non-monotonic dependence of v_i and v_l on \sigma. We study the dependence of
v_i, v_l, v_h, and the variances of corresponding fluctuations on \sigma,
sample size, and temperature. The anomalies near
indicate that the dielectric response and screening length are critically
behaved, i.e. that Coulomb correlations dominate the physics.Comment: Revised according to referee remark
The influence of powder particle size on properties of Cu-Al2O3 composites
Inert gas atomized prealloyed copper powder containing 2 wt.% Al (average particle size ā 30 Ī¼m) and a mixture consisting of copper (average particle sizes ā 15 Ī¼m and 30 Ī¼m) and 4 wt.% of commercial Al2O3 powder particles (average particle size ā 0.75 Ī¼m) were milled separately in a high-energy planetary ball mill up to 20 h in air. Milling was performed in order to strengthen the copper matrix by grain size refinement and Al2O3 particles. Milling in air of prealloyed copper powder promoted formation of finely dispersed nano-sized Al2O3 particles by internal oxidation. On the other side, composite powders with commercial micro-sized Al2O3 particles were obtained by mechanical alloying. Following milling, powders were treated in hydrogen at 400 0C for 1h in order to eliminate copper oxides formed on their surface during milling. Hot-pressing (800 0C for 3 h in argon at pressure of 35 MPa) was used for compaction of milled powders. Hot-pressed composite compacts processed from 5 and 20 h milled powders were additionally subjected to high temperature exposure (800Ā°C for 1 and 5h in argon) in order to examine their thermal stability. The results were discussed in terms of the effects of different size of starting powders, the grain size refinement and different size of Al2O3 particles on strengthening, thermal stability and electrical conductivity of copper-based composites
Low dose gamma-irradiation alters the expression of p53 protein in the rat hippocampus
The tumor-suppressor p53 protein and glucocorticoid receptor (GR) respond to different types of stress. In an attempt to reveal the possibility that p53 protein is involved in the regulation of GR gene expression after low dose cranial irradiation (CI) with 2 Gy, we examined the expression of p53 mRNA and protein as well as expression of GR mRNA and protein in the hippocampus of 18-days-old rats. We found that p53 mRNA expression was unchanged after CI, while induction of p53 protein was rapid, leading to the accumulation of p53 protein in the cytoplasm. Irradiation leads to stimulated GR gene expression in a time-dependent manner, whereas the level of GR protein was unchanged after CI. Co-immunoprecipitation has not showed that wild type p53 protein physically interacts with the GR in the cytoplasm. Our data suggest that the low dose cranial irradiation leads to stabilization of the 53 protein, without interaction with GR protein the cytoplasm.Physical chemistry 2006 : 8th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 26-29 September 200
Tuning from failed superconductor to failed insulator with magnetic field
Do charge modulations compete with electron pairing in high-temperature
copper-oxide superconductors? We investigated this question by suppressing
superconductivity in a stripe-ordered cuprate compound at low temperature with
high magnetic fields. With increasing field, loss of three-dimensional
superconducting order is followed by reentrant two-dimensional
superconductivity and then an ultra-quantum metal phase. Circumstantial
evidence suggests that the latter state is bosonic and associated with the
charge stripes. These results provide experimental support to the theoretical
perspective that local segregation of doped holes and antiferromagnetic spin
correlations underlies the electron-pairing mechanism in cuprates.Comment: 20 pp, 4 figs.; accepted version; for open-access published version,
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Infrared and Raman spectra of LiV2O5 single crystals
The phonon dynamics of LiV2O5 single crystals is studied using infrared and
Raman spectroscopy techniques. The infrared-active phonon frequencies and
dielectric constants are obtained by oscillator fitting procedure of the
reflectivity data measured at room temperature. The Raman scattering spectra
are measured at room temperature and at T=10 K in all nonequivalent polarized
configurations. The assignment of the phonons is done by comparing the infrared
and Raman spectra of LiV2O5 and NaV2O5. The factor-group-analysis of the LiV2O5
crystal symmetry and of its constituent layers is performed to explain the
symmetry properties of the observed modes. We concluded that layer symmetry
dominates in the vibrational properties of this compound.Comment: 10 pages, 5 figure
Effects of long-term fertilization on yield of siderates and organic matter content of soil in the process of recultivation
The aim of this research was to determine the possibility of increasing organic matter content in humusless deposol topsoil and forming of a more favourable adsorptive complex by introducing green manure. Green manure biomass came from these compound plant species: winter rye + common vetch, forage pea + rapeseed mustard and Sudan grass. Compound feed was sown on degraded soil (type deposol) of the Stanari coal mine. Applied cultivation practices included primary and secondary tillage and additional plant nutrition. Mineral fertilizers were applied: NPK 7:20:30 (400 kg ha(-1)) and CAN 27% (200 kg ha(-1)). One of the treatments included addition of bentonite clay as absorbent of nutrients. During intensive vegetation the growth of the green biomass was measured, the crops were harvested, cut and ploughed in deposol topsoil. Organic matter content in deposol was determined when soil samples were taken 6 months after green manure incorporation. The results show that the mineral fertilization of siderates significantly increased green biomass yield and Sudan grass gave two cuts, which positively affected the increase of organic matter content in soil
Impact of climatic factors to the percentage of young in the population of brown hare (Lepus europaeus P) in the BaÄka district
Climatic factors, especially temperature and precipitations, greatly affect the dynamics of the hare number and population. Climatic factors directly affect the physiological and reproductive processes of both individuals and entire populations, or indirectly, through the availability of food, competition with other species, predators and other. The age structure of the hare population at the end of the period of reproduction is an important indicator of the population growth that is used for planning the level of explotation of the hare population (hunting). The rational use of the hare's population is one of the most important protection procedures and it should be well monitored and controlled by the hunting professionals. We used the average monthly temperature and the sum of monthly precipitations in the hare reproductive period (March-September) during ten years (2000 - 2009), together with the percent of young in the hare population, on the territory of BaÄka, for multiple regression (stepwise) analysis. Results of the regression analysis show an association between the percentage of young hares and the influence of climatic factors. The average temperature and sum of precipitation in June, are the strongest predictor of the percent of young in the hareās population in BaÄka. According to the coefficient of determination (R2=0.50) climatic parameters account for 50% of variance in the percentage of young hares in BaÄka. The regression correlation coefficient of all factors was R=0.70, which is on the border line between medium and high correlation
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