			Home About us Contact

Parameter R (parameter + r)

Distribution by Scientific Domains

Physics and Astronomy	37%
Engineering	25%
Chemistry	25%

Selected Abstracts

Numerical modeling of frequency influence on the electromagnetic stirring of semiconductor melts

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2006
C. Stelian
Abstract Alternating magnetic fields can be used in order to increase the level of convection and to mix the doped semiconductor alloys. A numerical analysis of the electromagnetic induced convection in GaInSb semiconductor melts is performed by using the software package CrysVUn. The magnetic field parameters are varied in order to obtain a maximum efficiency of the induced convection with a minimum quantity of the heat released in the melt. The influence of the electrical current frequency on the convection intensity is analyzed for samples with various radii (R = 0.5 , 3cm). Numerical procedure is validated by comparing the numerical results obtained in mercury samples with the experimental data given from the literature, which show a maximum stirring for a magnetic skin depth , = 0.2R , in the case of a mercury sample with the radius R = 10 cm. This maximum corresponds to a shielding parameter R, = 40. Our numerical results show that the value of the shielding parameter for which the convection intensity reaches the maximum depends on the sample radius and increases when the sample radius increases. The results of this analysis are important in the case of samples with small radius, when a good mixing of the melt can be obtained for frequencies much lower than those corresponding to a shielding parameter R, = 40. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Natural convection heat transfer along a vertical flat plate with a projection in the turbulent region

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2001
Katsuo Komori
Abstract In the present study, the heat transfer coefficients occurring with a projection in the turbulent region of a vertical flat plate were measured experimentally for various projection heights in the range of 0 to 20 mm. The wall temperature and fluid flow fields were also visualized using a liquid crystal sheet and nylon 12 powder, respectively. The average and local Nusselt numbers reach 1.07 to 1.22 and 1.2 to 1.7 times those for pure turbulent natural convection, respectively. The maximum enhancement rates of heat transfer are attained at a position of 2.3 to 3.3 times the projection height from the upper projection surface toward the downstream, and these positions are in good agreement with those of the reattachment of the fluid flow and with centers of dark red regions in the liquid crystal. On the other hand, the heat transfer coefficients in the just upstream and downstream regions of the projection are small compared with those for no projection. By introducing the nondimensional parameter R, the present experimental results are rearranged quantitatively and effectively. © 2001 Scripta Technica, Heat Trans Asian Res, 30(3): 222,233, 2001 [source]

Detecting introgressive hybridization between free-ranging domestic dogs and wild wolves (Canis lupus) by admixture linkage disequilibrium analysis

MOLECULAR ECOLOGY, Issue 10 2006
A. VERARDI
Abstract Occasional crossbreeding between free-ranging domestic dogs and wild wolves (Canis lupus) has been detected in some European countries by mitochondrial DNA sequencing and genotyping unlinked microsatellite loci. Maternal and unlinked genomic markers, however, might underestimate the extent of introgressive hybridization, and their impacts on the preservation of wild wolf gene pools. In this study, we genotyped 220 presumed Italian wolves, 85 dogs and 7 known hybrids at 16 microsatellites belonging to four different linkage groups (plus four unlinked microsatellites). Population clustering and individual assignments were performed using a Bayesian procedure implemented in structure 2.1, which models the gametic disequilibrium arising between linked loci during admixtures, aiming to trace hybridization events further back in time and infer the population of origin of chromosomal blocks. Results indicate that (i) linkage disequilibrium was higher in wolves than in dogs; (ii) 11 out of 220 wolves (5.0%) were likely admixed, a proportion that is significantly higher than one admixed genotype in 107 wolves found previously in a study using unlinked markers; (iii) posterior maximum-likelihood estimates of the recombination parameter r revealed that introgression in Italian wolves is not recent, but could have continued for the last 70 (± 20) generations, corresponding to approximately 140,210 years. Bayesian clustering showed that, despite some admixture, wolf and dog gene pools remain sharply distinct (the average proportions of membership to wolf and dog clusters were Qw = 0.95 and Qd = 0.98, respectively), suggesting that hybridization was not frequent, and that introgression in nature is counteracted by behavioural or selective constraints. [source]

Thermo- and galvanomagnetic measurements of semiconductors at ultrahigh pressure

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003
Vladimir V. Shchennikov
Abstract The thermoelectric power, magnetoresistance, and thermomagnetic effects were measured for Te and Se micro-samples in the vicinity of semiconductor,metal phase transitions at high pressure. From longitudinal and transverse Nernst-Ettingshausen effects the scattering parameter r of holes was estimated and a decrease of the effective mass of holes was found during the closing of semiconductor gap. After the high pressure treatment an inversion of the sign of parameter r corresponding to a change of scattering mechanism was observed for the Te sample due to an increase of the density of lattice defects. [source]

Thomas,Fermi approximation for the quasi-two-dimensional electron gas

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2001
M. Moreno
Abstract To take into account static correlation effects in the quasi-two-dimensional electron gas a screened Coulombic interaction between particles is studied. The Thomas,Fermi approximation is used and the potential screening appears as a function of the Wigner,Seitz density parameter rs and the effective width t of the system. With the self-consistent field theory applied to the modified deformable jellium, the ground-state energy per particle and the conditions for electron localization are obtained in terms of the interparticle distance and the screening parameter ,. A critical minimum characteristic width tc is obtained; below tc no long-range order is obtained. For larger widths a stable localized state is predicted at finite densities. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 82: 269,276, 2001 [source]

Effect of electron,electron interaction and plasmon excitation on the density-of-states for a two-dimensional electron liquid

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2007
Godfrey Gumbs
Abstract We calculate the Green's function for an interacting two-dimensional electron liquid whose strength of interaction is characterized by the electron density parameter rs. The screened electron,electron interaction is expressed in terms of a frequency and wave vector-dependent dielectric function , (q, w). If this screening is neglected, the tunneling density of states (DOS) is strongly modified by the electron,electron interaction. This modification is seen as a dip near the Fermi energy. This dip becomes deeper and narrower as rs is increased. When screening is included, the DOS is considerably affected by the collective plasma excitations. In particular, the range of frequencies where the plasmon excitations contribute increases with rs. Also, the DOS near the Fermi energy for the screened electron liquid depends on the electron density. We treat , (q, w) in the hydrodynamical approximation in order to investigate the way in which the tunneling DOS is modified at various electron densities. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

A hybrid integral equation and neural network approach for fast extraction of frequency dependent parameters of multiconductor transmission lines

INTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 1 2002
G. Pan
Abstract Multiconductor transmission lines (MTL) have been modeled by the distributed parameters R, L, C, and G in many commercial CAD packages, where most of the parameters are assumed to be frequency independent or at most . At gigahertz frequencies, such assumptions may introduce significantly large errors in the waveform simulation and timing. In this article, we present a new and fast technique based on a combination of neural network techniques and the integral equation method (IEM) to evaluate frequency dependences accurately, while dramatically reducing the computation time. © 2002 John Wiley & Sons, Inc. Int J RF and Microwave CAE 12: 37,50, 2002. [source]

Lipophilicity of some guaianolides isolated from two endemic subspecies of Amphoricarpos neumayeri (Asteraceae) from Montenegro

BIOMEDICAL CHROMATOGRAPHY, Issue 3 2009
Abubaker A. B. Atrrog
Abstract In this study 10 guaianolide-type sesquiterpene , -lactones named amphoricarpolides, isolated from the aerial parts of two endemic subspecies of Amphoricarpos neumayeri (ssp. neumayeri and ssp. murbeckii Bo,njak), were investigated by means of reversed-phase thin-layer chromatography. Methanol,water and tetrahydrofuran,water binary mixtures were used as mobile phase in order to determine lipophilicity parameters R and C0. Some of the investigated compounds were screened for their cytotoxic activity against HeLa and B16 cells. Chromatographically obtained lipophilicity parameters were correlated with calculated logP values and IC50 values. Principal component analysis identified the dominant pattern in the chromatographically obtained data. Copyright © 2008 John Wiley & Sons, Ltd. [source]