1,418 research outputs found
High-temperature Superconductivity in Layered Nitrides \beta-LiMNCl (M = Ti, Zr, Hf): Insights from Density-functional Theory for Superconductors
We present an ab initio analysis with density functional theory for
superconductors (SCDFT) to understand the superconducting mechanism of doped
layered nitrides \beta-LiMNCl (M=Ti, Zr, and Hf). The current version of
SCDFT is based on the Migdal-Eliashberg theory and has been shown to reproduce
accurately experimental superconducting-transition temperatures Tc of a wide
range of phonon-mediated superconductors. In the present case, however, our
calculated Tc4.3 K (M=Zr) and 10.5 K (M=Hf) are found to be less
than a half of the experimental Tc. In addition, Tc obtained in the present
calculation increases with the doping concentration x, opposite to that
observed in the experiment. Our results indicate that we need to consider some
elements missing in the present SCDFT based on the Migdal-Eliashberg theory.Comment: 18 pages, 13 figures, submitted to Physical Review
Epithelioid hemangioendothelioma of the temporal artery presenting as temporal arteritis: case report and literature review
<span style="font-size: small; font-family: ArialUnicodeMS;"><span style="font-size: small; font-family: ArialUnicodeMS;"><p align="left">Hemangioendotheliomas are classified as epithelioid hemangioendothelioma</p><p align="left">(EHE), retiform hemangioendothelioma, composite hemanioendothelioma, Kaposiform hemangioendothelioma (with or without Kasabach-Merritt syndrome), and Spindle cell hemangioendothelioma. The latter two types of hemangioendotheliomas usually follow a benign course, in contrast to the other types of hemangioendotheliomas, which are considered as a low grade malignant sarcoma with unpredictable prognosis. EHE's are rare tumors, mostly described in organs particularly the lungs and liver. Though endothelial in origin, EHE's reported to originate from small sized arteries are extremely rare. We report a very rare case of EHE arising from the temporal artery showing a peculiar presentation.</p></span></span
Minor shift in background substitutional patterns in the Drosophila saltans and willistoni lineages is insufficient to explain GC content of coding sequences
BACKGROUND: Several lines of evidence suggest that codon usage in the Drosophila saltans and D. willistoni lineages has shifted towards a less frequent use of GC-ending codons. Introns in these lineages show a parallel shift toward a lower GC content. These patterns have been alternatively ascribed to either a shift in mutational patterns or changes in the definition of preferred and unpreferred codons in these lineages. RESULTS AND DISCUSSION: To gain additional insight into this question, we quantified background substitutional patterns in the saltans/willistoni group using inactive copies of a novel, Q-like retrotransposable element. We demonstrate that the pattern of background substitutions in the saltans/willistoni lineage has shifted to a significant degree, primarily due to changes in mutational biases. These differences predict a lower equilibrium GC content in the genomes of the saltans/willistoni species compared with that in the D. melanogaster species group. The magnitude of the difference can readily account for changes in intronic GC content, but it appears insufficient to explain changes in codon usage within the saltans/willistoni lineage. CONCLUSION: We suggest that the observed changes in codon usage in the saltans/willistoni clade reflects either lineage-specific changes in the definitions of preferred and unpreferred codons, or a weaker selective pressure on codon bias in this lineage
Amplified biochemical oscillations in cellular systems
We describe a mechanism for pronounced biochemical oscillations, relevant to
microscopic systems, such as the intracellular environment. This mechanism
operates for reaction schemes which, when modeled using deterministic rate
equations, fail to exhibit oscillations for any values of rate constants. The
mechanism relies on amplification of the underlying stochasticity of reaction
kinetics within a narrow window of frequencies. This amplification allows
fluctuations to beat the central limit theorem, having a dominant effect even
though the number of molecules in the system is relatively large. The mechanism
is quantitatively studied within simple models of self-regulatory gene
expression, and glycolytic oscillations.Comment: 35 pages, 6 figure
Relationship between amino acid composition and gene expression in the mouse genome
<p>Abstract</p> <p>Background</p> <p>Codon bias is a phenomenon that refers to the differences in the frequencies of synonymous codons among different genes. In many organisms, natural selection is considered to be a cause of codon bias because codon usage in highly expressed genes is biased toward optimal codons. Methods have previously been developed to predict the expression level of genes from their nucleotide sequences, which is based on the observation that synonymous codon usage shows an overall bias toward a few codons called major codons. However, the relationship between codon bias and gene expression level, as proposed by the translation-selection model, is less evident in mammals.</p> <p>Findings</p> <p>We investigated the correlations between the expression levels of 1,182 mouse genes and amino acid composition, as well as between gene expression and codon preference. We found that a weak but significant correlation exists between gene expression levels and amino acid composition in mouse. In total, less than 10% of variation of expression levels is explained by amino acid components. We found the effect of codon preference on gene expression was weaker than the effect of amino acid composition, because no significant correlations were observed with respect to codon preference.</p> <p>Conclusion</p> <p>These results suggest that it is difficult to predict expression level from amino acid components or from codon bias in mouse.</p
The Red Rectangle: Its Shaping Mechanism and its Source of Ultraviolet Photons
The proto-planetary Red Rectangle nebula is powered by HD 44179, a
spectroscopic binary (P = 318 d), in which a luminous post-AGB component is the
primary source of both luminosity and current mass loss. Here, we present the
results of a seven-year, eight-orbit spectroscopic monitoring program of HD
44179, designed to uncover new information about the source of the
Lyman/far-ultraviolet continuum in the system as well as the driving mechanism
for the bipolar outflow producing the current nebula. Our observations of the
H-alpha line profile around the orbital phase of superior conjunction reveal
the secondary component to be the origin of the fast (max. v~560^{-1}\sun_{max} \ge 17,0002 -
5\times10^{-5}\sun^{-1}\sun$, about 5% of the
luminosity of the entire system. (abridged)Comment: Accepted for publication in Ap
Dendritic cell expression of the transcription factor T-bet regulates mast cell progenitor homing to mucosal tissue
The transcription factor T-bet was identified in CD4+ T cells, and it controls interferon γ production and T helper type 1 cell differentiation. T-bet is expressed in certain other leukocytes, and we recently showed (Lord, G.M., R.M. Rao, H. Choe, B.M. Sullivan, A.H. Lichtman, F.W. Luscinskas, and L.H. Glimcher. 2005. Blood. 106:3432–3439) that it regulates T cell trafficking. We examined whether T-bet influences homing of mast cell progenitors (MCp) to peripheral tissues. Surprisingly, we found that MCp homing to the lung or small intestine in T-bet−/− mice is reduced. This is reproduced in adhesion studies using bone marrow–derived MCs (BMMCs) from T-bet−/− mice, which showed diminished adhesion to mucosal addresin cellular adhesion molecule–1 (MAdCAM-1) and vascular cell adhesion molecule–1 (VCAM-1), endothelial ligands required for MCp intestinal homing. MCp, their precursors, and BMMCs do not express T-bet, suggesting that T-bet plays an indirect role in homing. However, adoptive transfer experiments revealed that T-bet expression by BM cells is required for MCp homing to the intestine. Furthermore, transfer of WT BM-derived dendritic cells (DCs) to T-bet−/− mice restores normal MCp intestinal homing in vivo and MCp adhesion to MAdCAM-1 and VCAM-1 in vitro. Nonetheless, T-bet−/− mice respond vigorously to intestinal infection with Trichinella spiralis, eliminating a role for T-bet in MC recruitment to sites of infection and their activation and function. Therefore, remarkably, T-bet expression by DCs indirectly controls MCp homing to mucosal tissues
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