15 research outputs found
First Order Bipolaronic Transition at Finite Temperature in the Holstein Model
We investigate the Holstein model by using the dynamical mean-field theory
combined with the exact diagonalization method. Below a critical temperature
Tcr, a coexistence of the polaronic and the bipolaronic solutions is found for
the same value of the electron-phonon coupling $ in the range gc1(T)<g<gc2(T).
In the coexistence region, the system shows a first order phase transition from
the bipolaronic to the polaronic states as T decreases at T=Tp(<Tcr), where the
double occupancy and the lattice fluctuation together with the anharmonicity of
the effective ion potential change discontinuously without any symmetry
breaking. The obtained bipolaronic transition seems to be consistent with the
rattling transition in the beta-pyrochlore oxide KOs2O6.Comment: 5 pages, 5 figures, J. Phys. Soc. Jpn. 79 (2010) 09370
The Superconducting Instabilities of the non half-filled Hubbard Model in Two Dimensions
The problem of weakly correlated electrons on a square lattice is formulated
in terms of one-loop renormalization group. Starting from the action for the
entire Brillouin zone (and not with a low-energy effective action) we reduce
successively the cutoff about the Fermi surface and follow the
renormalization of the coupling as a function of three energy-momenta. We
calculate the intrinsic scale where the renormalization group flow
crosses over from the regime () where the electron-electron
(e-e) and electron-hole (e-h) terms are equally important to the regime
() where only the e-e term plays a role. In the low energy
regime only the pairing interaction is marginally relevant, containing
contributions from all renormalization group steps of the regime . After diagonalization of , we identify its most
attractive eigenvalue . At low filling,
corresponds to the representation ( symmetry), while near half
filling the strongest attraction occurs in the representation
( symmetry). In the direction of the van Hove singularities, the
order parameter shows peaks with increasing strength as one approaches half
filling. Using the form of pairing and the structure of the renormalization
group equations in the low energy regime, we give our interpretation of ARPES
experiments trying to determine the symmetry of the order parameter in the
Bi2212 high- compound.Comment: 24 pages (RevTeX) + 11 figures (the tex file appeared incomplete
E-Cadherin Expression Is Regulated by miR-192/215 by a Mechanism That Is Independent of the Profibrotic Effects of Transforming Growth Factor-β
OBJECTIVE--Increased deposition of extracellular matrix (ECM) within the kidney is driven by profibrotic mediators including transforming growth factor-[beta] (TGF-[beta]) and connective tissue growth factor (CTGF). We investigated whether some of their effects may be mediated through changes in expression of certain microRNAs (miRNAs). RESEARCH DESIGN AND METHODS--Proximal tubular cells, primary rat mesangial cells, and human podocytes were analyzed for changes in the expression of key genes, ECM proteins, and miRNA after exposure to TGF-[beta] (1-10 ng/[micro]l). Tubular cells were also infected with CTGF-adenovirus. Kidneys from diabetic apoE mice were also analyzed for changes in gene expression and miRNA levels. RESULTS--TGF-[beta] treatment was associated with morphologic and phenotypic changes typical of epithelial-mesenchymal transition (EMT) including increased fibrogenesis in all renal cell types and decreased E-cadherin expression in tubular cells. TGF-[beta] treatment also modulated the expression of certain miRNAs, including decreased expression of miR-192/215 in tubular cells, mesangial cells, which are also decreased in diabetic kidney. Ectopic expression of miR-192/215 increased E-cadherin levels via repressed translation of ZEB2 mRNA, in the presence and absence of TGF-[beta], as demonstrated by a ZEB2 3'-untranslated region luciferase reporter assay. However, ectopic expression of miR-192/215 did not affect the expression of matrix proteins or their induction by TGF-[beta]. In contrast, CTGF increased miR-192/215 levels, causing a decrease in ZEB2, and consequently increased E-cadherin mRNA. CONCLUSIONS--These data demonstrate the linking role of miRNA-192/215 and ZEB2 in TGF-[beta]/CTGF-mediated changes in E-cadherin expression. These changes appear to occur independently of augmentation of matrix protein synthesis, suggesting that a multistep EMT program is not necessary for fibrogenesis to occur.Bo Wang, Michal Herman-Edelstein, Philip Koh, Wendy Burns, Karin Jandeleit-Dahm, Anna Watson, Moin Saleem, Gregory J. Goodall, Stephen M. Twigg, Mark E. Cooper and Phillip Kantharidi
Heavy-Electron Formation and Bipolaronic Transition in the Anharmonic Holstein Model
The emergence of the bipolaronic phase and the formation of the
heavy-electron state in the anharmonic Holstein model are investigated using
the dynamical mean-field theory in combination with the exact diagonalization
method. For a weak anharmonicity, it is confirmed that the first-order
polaron-bipolaron transition occurs from the observation of a discontinuity in
the behavior of several physical quantities. When the anharmonicity is
gradually increased, the polaron-bipolaron transition temperature is reduced as
well as the critical values of the electron-phonon coupling constant for
polaron-bipolaron transition. For a strong anharmonicity, the polaron-bipolaron
transition eventually changes to a crossover behavior. The effect of
anharmonicity on the formation of the heavy-electron state near the
polaron-bipolaron transition and the crossover region is discussed in detail.Comment: 11 pages, 13 figure
Optical symmetries and anisotropic transport in high-Tc superconductors
A simple symmetry analysis of in-plane and out-of-plane transport in a family
of high temperature superconductors is presented. It is shown that generalized
scaling relations exist between the low frequency electronic Raman response and
the low frequency in-plane and out-of-plane conductivities in both the normal
and superconducting states of the cuprates. Specifically, for both the normal
and superconducting state, the temperature dependence of the low frequency
Raman slope scales with the axis conductivity, while the
Raman slope scales with the in-plane conductivity. Comparison with experiments
in the normal state of Bi-2212 and Y-123 imply that the nodal transport is
largely doping independent and metallic, while transport near the BZ axes is
governed by a quantum critical point near doping holes per
CuO plaquette. Important differences for La-214 are discussed. It is also
shown that the axis conductivity rise for is a consequence of
partial conservation of in-plane momentum for out-of-plane transport.Comment: 16 pages, 8 Figures (3 pages added, new discussion on pseudogap and
charge ordering in La214
Easy Derivatisation of Group 10 N-Heterocyclic Carbene Complexes and In Vitro Evaluation of an Anticancer Oestradiol Conjugate
In the search for novel metal-based pharmaceuticals, ruthenium-catalysed 1,3-dipolar cycloaddition is used to functionalise a series of palladium and platinum N-heterocyclic carbene complexes. This strategy was applied to the conjugation of amino acid, polyethylene glycol and oestradiol derivatives with the aim of enhancing chemical diversity and introducing specific features (e.g., water solubility, cell targeting). Antiproliferative activities of the different complexes were assayed against several cancer cell lines (KB, MCF7, HCT116, PC3, SKOV3, OVCAR8, HL60) and healthy cell lines (MRC5, VERO, EPC), which established their efficiency. The ease of the structural derivatisation thus renders these complexes attractive metal-based systems for the development of selective targeted metal-hybrid anticancer drugs
N-Heterocyclic Carbene-Polyethyleneimine (PEI) Platinum Complexes Inducing Human Cancer Cell Death: Polymer Carrier Impact
The high interest in N-Heterocyclic platinum carbene complexes in cancer research stems from their high cytotoxicity to human cancer cells, their stability, as well as their ease of functionalization. However, the development of these new molecules as anticancer agents still faces multiple challenges, in particular solubility in aqueous media. Here, we synthesized platinum-NHC bioconjugates that combine water-solubility and cytotoxicity by using polyethyleneimine as polymer carrier. We showed on 8 different types of cells that the activity of these conjugates is modulated by the size of the polymer and the overall density of metal ions onto polymer chains. Using HCT116 cells, the conjugates displayed an effective activity after only 45 min of exposure in vitro correlated with a quick uptake by the cells as shown by the use of various fluorescent-tagged derivatives