9,117 research outputs found
Phase separation and pairing in coupled chains and planes
A generalization of the model in a system of two coupled chains or
planes is studied by numerical diagonalization of small clusters. In
particular, the effect of density fluctuations between these one- or
two-dimensional coupled layerson intralayer phase separation and pairing is
analyzed. The most robust signals of superconductivity are found at quarter
filling for couplings just before the fully interlayer phase separated regime.
The possibility of an enhancement of the intralayer superconducting pairing
correlations by the interlayer couplings is investigated.Comment: 13 pages + 3 figures, available upon request, LATEX, preprint
ORNL/CCIP/93/1
A new early occurrence of Cervidae in North America from the Miocene-Pliocene Ellensburg Formation in Washington, USA
A new fossil cervid from the Craig’s Hill locality of the Miocene-Pliocene Ellensburg Formation in the State of Washington, USA, may be one of the oldest fossil deer yet found in North America, underlying a date of 4.9 Ma ± 0.1 Ma. This mandible fragment with m2, m3, and associated p2 has a size that does not distinguish it from Bretzia pseudalces, Odocoileus hemionus, or Capreolus constantini, and distinguishes it from Eocoileus gentryorum and Odocoileus lucasi only in having a thinner p2. A strong paraconid on the p2, and ectostylids and cingulids on the m2 and m3 link it most strongly with Bretzia pseudalces, but these are also intermittently present in Odocoileus hemionus. Because of the close geographic and temporal proximity of Bretzia pseudalces in the Ringold Formation, and its shared morphology with Bretzia, we are tentatively assigning this specimen to cf. Bretzia
Measurement of the Hyperfine Structure and Isotope Shifts of the 3s23p2 3P2 to 3s3p3 3Do3 Transition in Silicon
The hyperfine structure and isotope shifts of the 3s23p2 3P2 to 3s3p3 3Do3
transition in silicon have been measured. The transition at 221.7 nm was
studied by laser induced fluorescence in an atomic Si beam. For 29Si, the
hyperfine A constant for the 3s23p2 3P2 level was determined to be -160.1+-1.3
MHz (1 sigma error), and the A constant for the 3s3p3 3Do3 level is -532.9+-0.6
MHz. This is the first time that these constants were measured. The isotope
shifts (relative to the abundant isotope 28Si) of the transition were
determined to be 1753.3+-1.1 MHz for 29Si and 3359.9+-0.6 MHz for 30Si. This is
an improvement by about two orders of magnitude over a previous measurement.
From these results we are able to predict the hyperfine structure and isotope
shift of the radioactive 31Si atom, which is of interest in building a scalable
quantum computer
Superconductivity in the Cuo Hubbard Model with Long-Range Coulomb Repulsion
A multiband CuO Hubbard model is studied which incorporates long-range (LR)
repulsive Coulomb interactions. In the atomic limit, it is shown that a
charge-transfer from copper to oxygen ions occurs as the strength of the LR
interaction is increased. The regime of phase separation becomes unstable, and
is replaced by a uniform state with doubly occupied oxygens. As the holes
become mobile a superfluid condensate is formed, as suggested by a numerical
analysis of pairing correlation functions and flux quantization. Although most
of the calculations are carried out on one dimensional chains, it isComment: LATEX, 14 pages, 4 figures available as postcript files or hard copy,
preprint ORNL-CCIP/93/1
An introduction to the EULAR–OMERACT rheumatoid arthritis MRI reference image atlas
This article gives a short overview of the development and characteristics of the OMERACT rheumatoid arthritis MRI scoring system (RAMRIS), followed by an introduction to the use of the EULAR–OMERACT rheumatoid arthritis MRI reference image atlas. With this atlas, MRIs of wrist and metacarpophalangeal joints of patients with rheumatoid arthritis can be scored for synovitis, bone oedema, and bone erosion, guided by standard reference images
Biological Characterization of Gene Response to Insulin-Induced Hypoglycemia in Mouse Retina.
Glucose is the most important metabolic substrate of the retina and maintenance of normoglycemia is an essential challenge for diabetic patients. Chronic, exaggerated, glycemic excursions could lead to cardiovascular diseases, nephropathy, neuropathy and retinopathy. We recently showed that hypoglycemia induced retinal cell death in mouse via caspase 3 activation and glutathione (GSH) decrease. Ex vivo experiments in 661W photoreceptor cells confirmed the low-glucose induction of death via superoxide production and activation of caspase 3, which was concomitant with a decrease of GSH content. We evaluate herein retinal gene expression 4 h and 48 h after insulin-induced hypoglycemia. Microarray analysis demonstrated clusters of genes whose expression was modified by hypoglycemia and we discuss the potential implication of those genes in retinal cell death. In addition, we identify by gene set enrichment analysis, three important pathways, including lysosomal function, GSH metabolism and apoptotic pathways. Then we tested the effect of recurrent hypoglycemia (three successive 4h periods of hypoglycemia spaced by 48 h recovery) on retinal cell death. Interestingly, exposure to multiple hypoglycemic events prevented GSH decrease and retinal cell death, or adapted the retina to external stress by restoring GSH level comparable to control situation. We hypothesize that scavenger GSH is a key compound in this apoptotic process, and maintaining "normal" GSH level, as well as a strict glycemic control, represents a therapeutic challenge in order to avoid side effects of diabetes, especially diabetic retinopathy
Quantum Chemistry, Anomalous Dimensions, and the Breakdown of Fermi Liquid Theory in Strongly Correlated Systems
We formulate a local picture of strongly correlated systems as a Feynman sum
over atomic configurations. The hopping amplitudes between these atomic
configurations are identified as the renormalization group charges, which
describe the local physics at different energy scales. For a metallic system
away from half-filling, the fixed point local Hamiltonian is a generalized
Anderson impurity model in the mixed valence regime. There are three types of
fixed points: a coherent Fermi liquid (FL) and two classes of self-similar
(scale invariant) phases which we denote incoherent metallic states (IMS). When
the transitions between the atomic configurations proceed coherently at low
energies, the system is a Fermi liquid. Incoherent transitions between the low
energy atomic configurations characterize the incoherent metallic states. The
initial conditions for the renormalization group flow are determined by the
physics at rather high energy scales. This is the domain of local quantum
chemistry. We use simple quantum chemistry estimates to specify the basin of
attraction of the IMS fixed points.Comment: 12 pages, REVTE
Colossal Magnetoresistance in the Mn2+ Oxypnictides NdMnAsO1-xFx
Colossal magnetoresistance (CMR) is a rare phenomenon in which the electronic
resistivity of a material can be decreased by orders of magnitude upon
application of a magnetic field. Such an effect could be the basis of the next
generation of magnetic memory devices. Here we report CMR in the
antiferromagnetic oxypnictide NdMnAsO1-xFx as a result of competition between
an antiferromagnetic insulating phase with strong electron correlations and a
paramagnetic semiconductor upon application of a magnetic field. The discovery
of CMR in antiferromagnetic Mn2+ oxypnictide materials could open up an array
of materials for further investigation and optimisation for technological
applications
Experimental evidence of s-wave superconductivity in bulk CaC
The temperature dependence of the in-plane magnetic penetration depth,
, has been measured in a c-axis oriented polycrystalline
CaC bulk sample using a high-resolution mutual inductance technique. A
clear exponential behavior of has been observed at low
temperatures, strongly suggesting isotropic s-wave pairing. Data fit using the
standard BCS theory yields Angstroem and
meV. The ratio
gives indication for a conventional weakly coupled superconductor.Comment: To appear in Phys. Rev. Let
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