1,013 research outputs found
Orbital Degeneracy and Peierls Instability in Triangular Lattice Superconductor IrPtTe
We have studied electronic structure of triangular lattice
IrPtTe superconductor using photoemission spectroscopy and
model calculations. Ir core-level photoemission spectra show that Ir
charge modulation established in the low temperature phase of IrTe
is suppressed by Pt doping. This observation indicates that the suppression of
charge modulation is related to the emergence of superconductivity.
Valence-band photoemission spectra of IrTe suggest that the Ir charge
modulation is accompanied by Ir orbital reconstruction. Based on the
photoemission results and model calculations, we argue that the
orbitally-induced Peierls effect governs the charge and orbital instability in
the IrPtTe.Comment: 5 pages,4 figure
Ground State and Magnetization Process of the Mixture of Bond-Alternating and Uniform S=1/2 Antiferromagnetic Heisenberg Chains
The mixture of bond-alternating and uniform S=1/2 antiferromagnetic
Heisenberg chains is investigated by the density matrix renormalization group
method. The ground state magnetization curve is calculated and the exchange
parameters are determined by fitting to the experimentally measured
magnetization curve of \CuClBr(-pic). The low
field behavior of the magnetization curve and low temperature behavior of the
magnetic susceptibility are found to be sensitive to whether the
bond-alternation pattern (parity) is fixed all over the sample or randomly
distributed. The both quantities are compatible with the numerical results for
the random parity model.Comment: 5 pages, 7 figures. Final and enlarged version accepted for
publication in J. Phys. Soc. Jp
Excitonic Bose-Einstein condensation in Ta2NiSe5 above room temperature
We show that finite temperature variational cluster approximation (VCA)
calculations on an extended Falicov-Kimball model can reproduce angle-resolved
photoemission spectroscopy (ARPES) results on Ta2NiSe5 across a
semiconductor-to-semiconductor structural phase transition at 325 K. We
demonstrate that the characteristic temperature dependence of the flat-top
valence band observed by ARPES is reproduced by the VCA calculation on the
realistic model for an excitonic insulator only when the strong excitonic
fluctuation is taken into account. The present calculations indicate that
Ta2NiSe5 falls in the Bose-Einstein condensation regime of the excitonic
insulator state.Comment: 21 pages(5 figures
Antiferromagnetic Heisenberg chains with bond alternation and quenched disorder
We consider S=1/2 antiferromagnetic Heisenberg chains with alternating bonds
and quenched disorder, which represents a theoretical model of the compound
CuCl_{2x}Br_{2(1-x)}(\gamma-{pic})_2. Using a numerical implementation of the
strong disorder renormalization group method we study the low-energy properties
of the system as a function of the concentration, x, and the type of
correlations in the disorder. For perfect correlation of disorder the system is
in the random dimer (Griffiths) phase having a concentration dependent
dynamical exponent. For weak or vanishing disorder correlations the system is
in the random singlet phase, in which the dynamical exponent is formally
infinity. We discuss consequences of our results for the experimentally
measured low-temperature susceptibility of
CuCl_{2x}Br_{2(1-x)}(\gamma-{pic})_2
Effect of IGF-I and PDGF administered in vivo on the expression of osteoblast-related genes in old rats
Abstract In order to establish the cellular basis for using growth factors as possible therapeutic agents for the age-dependent deficit in bone formation activity, we examined the individual and combined effects of IGF-I and/or plateletderived growth factor (PDGF) on the gene expression of osteoblast-related markers in male rats. The expression of osteoblast markers was examined in the femurs of adult and old rats following marrow ablation, which amplifies gene expression activity. The mRNA levels of collagen 1 (I) (COLI), alkaline phosphatase (AP), osteopontin (OP) and osteocalcin (OC) were significantly lower in the old as compared with the adult rats. To determine whether growth factors can abolish the agerelated deficits in mRNA expression in old bone, PDGF and/or IGF-I were infused directly into the right femur for 5 days following marrow ablation. The contralateral femur was infused with vehicle only and used as a control. PDGF stimulated the expression of OP mRNA in both adult and old rats, whereas COLI, AP and OC mRNAs were not affected. IGF-I infusion did not have a significant effect on mRNA expression in adult rats. In contrast, treatment with IGF-I significantly enhanced the mRNA levels of COLI, AP and OP in old rats. To examine whether the combination of both factors could affect the expression of osteoblast markers synergistically, PDGF and IGF-I were infused together. In adult bones, the combined treatment with PDGF and IGF-I caused a slight increase in the level of OP gene expression but no change in AP, OC or COLI genes. Although neither IGF-I nor PDGF alone was effective in stimulating the expression of OC, the combined treatment in old bones enhanced OC expression significantly. The expression of COLI, AP and OP was also stimulated, but the stimulation was no different from that of IGF-I alone. In PDGF plus IGF-I treatment with a high dose, no dose-response effects were observed. Within the limits of the present study, it is suggested that IGF-I and, to a much lesser extent, PDGF may partially restore the deficit in the expression of osteoblast markers in old bones, and that the combination of both factors is slightly better than IGF-I alone in stimulating OC expression
Epstein-Barr Virus latent membrane protein 1 induces Snail and epithelial–mesenchymal transition in metastatic nasopharyngeal carcinoma
Background:Epstein-Barr Virus (EBV)-associated nasopharyngeal carcinoma (NPC) is distinctive among head-and-neck cancers in its undifferentiated histopathology and highly metastatic character. We have recently investigated the involvement of epithelial–mesenchymal transition (EMT) in NPC. In a previous study, we found a close association of expression of LMP1, the principal EBV oncoprotein, with expression of Twist and induction of EMT.Methods:We analysed expression of Snail in 41 NPC tissues by immunohistochemistry. The role of Twist as well as Snail in EMT of NPC was investigated by using NP69SV40T human nasopharyngeal cells.Results:In NPC tissues, overexpression of Snail is associated with expression of LMP1 in carcinomatous cells. In addition, expression of Snail positively correlated with metastasis and independently correlated inversely with expression of E-cadherin. Expression of Twist had no association with expression of E-cadherin. Further, in a human nasopharyngeal cell line, LMP1 induces EMT and its associated cellular motility and invasiveness. Expression of Snail is induced by LMP1 in these cells, and small hairpin RNA (shRNA) to Snail reversed the cellular changes. By contrast, Twist did not produce EMT in these nasopharyngeal cells.Conclusions:This study strengthens the association of EMT with the metastatic behaviour of NPC. These results suggest that induction of Snail by the EBV oncoprotein LMP1 has a pivotal role in EMT in NPC
MUC1 Induced by Epstein-Barr Virus Latent Membrane Protein 1 Causes Dissociation of the Cell-Matrix Interaction and Cellular Invasiveness via STAT Signaling
Disruption of cellular adhesion is an essential pathobiologic step leading to tumor dissemination. Mucin 1 (MUC1) is a mucinous glycoprotein expressed at the surfaces of epithelial cells in many tissues and their carcinomas. MUC1 plays crucial roles in tumor invasion and metastasis, especially in opposing cell adhesion. We have shown that virus infection, specifically by the human tumor virus Epstein-Barr virus (EBV) induces a spectrum of cellular invasiveness and metastasis factors. Here we show that expression of MUC1 is increased in diverse latently EBV-infected cell lines that express latent membrane protein 1 (LMP1), the main viral oncoprotein, and that the level of MUC1 was suppressed by expression of a dominant-negative mutant of LMP1. Expression of LMP1 in EBV-negative nasopharyngeal cell lines induces expression of MUC1 through activation of the MUC1 promoter via binding of STAT1 and STAT3. Finally, LMP1 reduces cell adhesion ability, which is restored by inhibition of MUC1 expression with MUC1 small interfering RNA (siRNA). In addition, LMP1 increases cell invasiveness, which is suppressed by MUC1 siRNA. Thus, LMP1 induces MUC1, a factor important in an early step of detachment and release of tumor cells, which along with induction of other invasiveness and angiogenic factors may combine to act in a complex sequential process that culminates in metastasis of EBV-infected tumor cells
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