2,145 research outputs found
Signature of the Overhauser field on the coherent spin dynamics of donor-bound electron in a single CdTe quantum well
We have studied the coherent spin dynamics in an oblique magnetic field of
electrons localized on donors and placed in the middle of a single CdTe quantum
well, by using a time-resolved optical technique: the photo-induced Faraday
rotation. We showed that this dynamics is affected by a weak Overhauser field
created via the hyperfine interaction of optically spin-polarized donor-bound
electrons with the surrounding nuclear isotopes carrying non-zero spins. We
have measured this nuclear field, which is on the order of a few mT and can
reach a maximum experimental value of 9.4 mT. This value represents 13 % of the
maximal nuclear polarization, and corresponds also to 13 % of maximal
electronic polarization.Comment: 15 pages, 4 figure
Hole spin dephasing time associated to hyperfine interaction in quantum dots
The spin interaction of a hole confined in a quantum dot with the surrounding
nuclei is described in terms of an effective magnetic field. We show that, in
contrast to the Fermi contact hyperfine interaction for conduction electrons,
the dipole-dipole hyperfine interaction is anisotropic for a hole, for both
pure or mixed hole states. We evaluate the coupling constants of the
hole-nuclear interaction and demonstrate that they are only one order of
magnitude smaller than the coupling constants of the electron-nuclear
interaction. We also study, theoretically, the hole spin dephasing of an
ensemble of quantum dots via the hyperfine interaction in the framework of
frozen fluctuations of the nuclear field, in absence or in presence of an
applied magnetic field. We also discuss experiments which could evidence the
dipole-dipole hyperfine interaction and give information on hole mixing.Comment: 35 pages, 7 figures and 2 table
Recommended from our members
Syk-dependent Phosphorylation of CLEC-2: A Novel Mechanism of Hem-Immunoreceptor Tyrosine-Based Activation Motif Signaling
The C-type lectin-like receptor CLEC-2 signals via phosphorylation of a single cytoplasmic YXXL sequence known as a hem-immunoreceptor tyrosine-based activation motif (hemITAM). In this study, we show that phosphorylation of CLEC-2 by the snake toxin rhodocytin is abolished in the absence of the tyrosine kinase Syk but is not altered in the absence of the major platelet Src family kinases, Fyn, Lyn, and Src, or the tyrosine phosphatase CD148, which regulates the basal activity of Src family kinases. Further, phosphorylation of CLEC-2 by rhodocytin is not altered in the presence of the Src family kinase inhibitor PP2, even though PLCγ2 phosphorylation and platelet activation are abolished. A similar dependence of phosphorylation of CLEC-2 on Syk is also seen in response to stimulation by an IgG mAb to CLEC-2, although interestingly CLEC-2 phosphorylation is also reduced in the absence of Lyn. These results provide the first definitive evidence that Syk mediates phosphorylation of the CLEC-2 hemITAM receptor with Src family kinases playing a critical role further downstream through the regulation of Syk and other effector proteins, providing a new paradigm in signaling by YXXL-containing receptors
Compositional Variations in the \u3cem\u3eFire Clay Coal Bed\u3c/em\u3e of Eastern Kentucky: Geochemistry, Petrography, Palynology, and Paleoecology
Bench samples of the Fire Clay coal bed, collected from 28 localities in a study area of eight 7.5-minute quadrangles in the Eastern Kentucky Coal Field, were analyzed geochemically, petrographically, and palynologically to determine any spatial or temporal trends among the studied parameters.
At most sample sites the Fire Clay is split by a flint-clay parting of probable volcanic origin. The upper bench of the Fire Clay coal generally is thick, laterally continuous, low in ash yield and sulfur content, has a moderate to high calorific value, and is high in total vitrinite content. In contrast, the lower bench generally is thin, laterally discontinuous, moderate to high in ash yield and sulfur content, has a low to moderate calorific value, and has high liptinite and inertinite contents. Rider coals, present at two sample sites, are thin, laterally discontinuous, and high in both ash yield and sulfur content.
Fire Clay coal extracted from underground mines typically contains roof and floor rock, which is separated by conventional coal-cleaning methods. The analytical data were grouped into categories of increasing coal purity to approximate a cleaned coal product. Results indicate that some parameters (Btu and total vitrinite content) increase along a trend from higher ash to lower ash coal. Other parameters (ash yield, total sulfur content, and several minor elements) decrease. Still others (thickness and total moisture) show no trend at all. A comparison of these data with previously accumulated data from 64 cleaned coal samples (collected from preparation plants) confirms these trends. This is significant, especially with regard to Titles III and IV of the Clean Air Act Amendments of 1990, in that many deleterious components of coal appear to be removable by conventional coal-cleaning methods prior to combustion in an industrial furnace. Examples of these undesirable constituents include pyrite, chromium, cobalt, and nickel.
The Fire Clay coal was grouped into four compositional categories for paleoecological interpretation. The categories are (1) a Lycospora-dominant group with high vitrinite contents that is interpreted to have formed in areas of the Fire Clay paleomire that were kept very wet, to the point of having standing water, a majority of the time (this group probably developed in areas of the mire that were dominantly rheotrophic and planar); (2) a mixed-palynoflora group with high vitrinite contents that is defined by having a more diverse palynoflora than the first group (increased percentages of small lycopsid, fern, and calamite spores), and high percentages of vitrinite (this group is also interpreted to have formed in areas that were very wet most of the time, and were predominantly rheotrophic and planar); (3) a mixed-palynoflora group with moderate to low vitrinite contents that contains increased percentages of inertinite compared to the first two groups and a diverse palynoflora, possibly because the mire became more ombrotrophic and domed; and (4) a mixed-palynoflora group with high ash yield whose palynoflora is marked by various mixtures of lycopsids (trees and small forms), ferns (tree-like and small forms), calamites, and cordaite spores; samples defined by this group contain elevated percentages of liptinite and inertinite macerals, as well as higher ash yields. The conditions under which group 4 formed probably were rheotrophic and planar. Group 4 defines all the samples in the lower bench of the Fire Clay coal bed
Geochemistry, Petrology, and Palynology of the Princess No. 3 Coal, Greenup County, Kentucky
The high volatile C bituminous-rank, Bolsovian-age Princess No. 3 coal, a correlative of the heavily-mined Hazard No. 7 coal and the Peach Orchard and Coalburg Lower Split coals, was investigated three sites at a mine in Greenup County, Kentucky. The coal exhibits a “dulling upwards” trend, with decreasing vitrinite and a greater tendency towards dull clarain and bone lithotypes towards the top of the coal. The relatively vitrinite-rich basal lithotype is marked by a dominance of lycopod tree spores. The palynology transitions upwards to a middle parting co-dominated by tree fern and small lycopod spores and an upper bench dominated by tree ferns with contributions from small ferns, cordaites, and calamites. The lithotypes generally have a moderate- to high-S content with a variable ash yield. Sulfur, Fe2O3, and certain siderophile elements are highest near the top of the coal. As observed in other coals, uranium and Ge are enriched at the top and bottom margins of the coal. The rare earth chemistry at the top of the coal has a significantly lighter distribution (higher LREE/HREE) than at the base of the coal
Utility of cytokeratin 20 and Ki-67 as markers of urothelial dysplasia
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74783/1/j.1440-1827.2005.01821.x.pd
The environmental implications of upper Paleozoic plant-fossil assemblages with mixtures of wetland and drought-tolerant taxa in tropical Pangea
Possibilitiesof additive technologies for manufacturing of gradient materials with record high mechanical characteristics
- …