94 research outputs found
Thermoelectric properties of the degenerate Hubbard model
We investigate the thermoelectric properties of a system near a pressure
driven Mott-Hubbard transition. The dependence of the thermopower and the
figure of merit on pressure and temperature within a degenerate Hubbard model
for integer filling n=1 is calculated using dynamical mean field theory.
Quantum Monte Carlo method is used to solve the impurity model. Obtained
results can qualitatively explain thermoelectric properties of various strongly
correlated materials.Comment: RevTex, 7 pages, 6 figure
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Endothelin-1 down-regulates matrix metalloproteinase 14 and 15 expression in human first trimester trophoblasts via endothelin receptor type B
: Does endothelin-1 (ET-1) regulate matrix metalloproteinase (MMP) 14 and 15 production and invasion of human first trimester trophoblasts?
: ET-1 in pathophysiological concentrations down-regulates MMP14 and MMP15 expression via endothelin receptor (ETR) type B and decreases trophoblast migration and invasion.
: MMP14 and MMP15 are involved in trophoblast invasion. Impairment of invasion has been linked to pregnancy complications such as pre-eclampsia (PE). ET-1 is up-regulated in PE.
: study using primary human trophoblasts from 50 first trimester placentas (gestational week 7-12).
: Trophoblasts were cultured in the absence or presence of 10-100 nM ET-1. MMP14 and MMP15 mRNA and protein were quantified by RT-qPCR and Western blotting, respectively. Selective antagonists for ETRA (BQ-123) or ETRB (BQ-788) were used to identify ETR subtypes involved. Functional ET-1 effects were tested in first trimester chorionic villous explants and transwell invasion assays. The roles of tumor necrosis factor (TNF)-α (25 ng/ml) and oxygen (1%) in ET-1 regulation of MMP14 and 15 expression were assessed by Western blotting.
: ET-1 down-regulated MMP14 and MMP15 mRNA (-21% and -26%, respectively, < 0.05) and protein levels (-18% and -22%, respectively, < 0.05). This effect was mediated via ETRB. ET-1 decreased trophoblast outgrowth in placental explants (-24%, < 0.05) and trophoblast invasion (-26%, ≤ 0.01). TNF-α enhanced ET-1 mediated MMP15 down-regulation (by 10%, < 0.05), whereas hypoxia abolished the effect of ET-1 on both MMPs.
: N/A.
: Only primary trophoblasts were used in this study. Since trophoblast yield from first trimester placental material is limited, further aspects of MMP14 and 15 regulation could not be characterized. Other anti-invasive factors may be altered by ET-1 in trophoblasts and, thus, contribute to the reduced invasion, but have not been investigated. Oxygen levels similar to those found in the decidua (5-8% O2) were not analyzed in this study.
: ET-1 modifies placental function already during the first trimester of pregnancy, the time-window when the placental changes implicated in PE occur. Thus, our results improve the understanding of the placental mechanisms underlying trophoblast invasion and PE.The study was funded by the Oesterreichische Nationalbank (Anniversary Fund, project number: 14796) and the Herzfelder'sche Familienstiftung (to J.P.; number: 00685). AMM received funding from the Austrian Science Fund FWF (W1241) and the Medical University Graz through the PhD Program Molecular Fundamentals of Inflammation (DK-MOLIN)
Random Scattering by Atomic Density Fluctuations in Optical Lattices
We investigate hitherto unexplored regimes of probe scattering by atoms
trapped in optical lattices: weak scattering by effectively random atomic
density distributions and multiple scattering by arbitrary atomic
distributions. Both regimes are predicted to exhibit a universal semicircular
scattering lineshape for large density fluctuations, which depend on
temperature and quantum statistics.Comment: 4 pages, 2 figure
Theoretical Study on Superconductivity in Boron-Doped Diamond
We consider superconductivity in boron (B) doped diamond using a simplified
model for the valence band of diamond. We treat the effects of substitutional
disorder of B ions by the coherent potential approximation (CPA) and those of
the attractive force between holes by the ladder approximation under the
assumption of instantaneous interaction with the Debye cutoff. We thereby
calculate the quasiparticle life time, the evolution of the single-particle
spectra due to doping, and the effect of disorder on the superconducting
critical temperature . We in particular compare our results with those for
supercell calculations to see the role of disorder, which turns out to be of
crucial importance to .Comment: 9 pages, 13 figures, submitted to J. Phys. Soc. Jpn., Errors in
embedded eps figure files have been correcte
Influence of s-d interfacial scattering on the magnetoresistance of magnetic tunnel junctions
We propose the two-band s-d model to describe theoretically a diffuse regime
of the spin-dependent electron transport in magnetic tunnel junctions (MTJ's)
of the form F/O/F where F's are 3d transition metal ferromagnetic layers and O
is the insulating spacer. We aim to explain the strong interface sensitivity of
the tunneling properties of MTJ's and investigate the influence of electron
scattering at the nonideal interfaces on the degradation of the TMR magnitude.
The generalized Kubo formalism and the Green's functions method were used to
calculate the conductance of the system. The vertex corrections to the
conductivity were found with the use of "ladder" approximation combined with
the coherent-potential approximation (CPA) that allowed to consider the case of
strong electron scattering. It is shown that the Ward identity is satisfied in
the framework of this approximation that provides the necessary condition for a
conservation of a tunneling current. Based on the known results of ab-initio
calculations of the TMR for ballistic junctions, we assume that exchange split
quasi-free s-like electrons with the density of states being greater for the
majority spin sub-band give the main contribution to the TMR effect. We show
that, due to interfacial inter-band scattering, the TMR can be substantially
reduced even down to zero value. This is related to the fact that delocalized
quasi-free electrons can scatter into the strongly localized d sub-band with
the density of states at the Fermi energy being larger for minority spins
compared to majority spins. It is also shown that spin-flip electron scattering
on the surface magnons within the interface leads to a further decrease of the
TMR at finite temperature.Comment: REVTeX4, 20 pages, 9 figures, 1 table, submitted to Phys.Rev.B; In
Version 2 the text is substantially improved, the main results and
conclusions left the sam
Quantum oscillation of magnetoresistance in tunneling junctions with a nonmagnetic spacer
We make a theoretical study of the quantum oscillations of the tunneling
magnetoresistance (TMR) as a function of the spacer layer thickness. Such
oscillations were recently observed in tunneling junctions with a nonmagnetic
metallic spacer at the barrier-electrode interface. It is shown that momentum
selection due to the insulating barrier and conduction via quantum well states
in the spacer, mediated by diffusive scattering caused by disorder, are
essential features required to explain the observed period of oscillation in
the TMR ratio and its asymptotic value for thick nonmagnetic spacer.Comment: 4 pages, 5 figures, two column, REVTex4 styl
Electron transport in a quantum wire with realistic Coulomb interaction
Electron transport in a quantum wire with leads is investigated with actual
Coulomb interaction taken into account. The latter includes both the direct
interaction of electrons with each other and their interaction via the image
charges induced in the leads. Exact analytical solution of the problem is found
with the use of the bosonization technique for one-dimensional electrons and
three-dimensional Poisson equation for the electric field. The Coulomb
interaction is shown to change significantly the electron density distribution
along the wire as compared with the Luttinger liquid model with short-range
interactions. In DC and low frequency regimes, the Coulomb interaction causes
the charge density to increase strongly in the vicinity of the contacts with
the leads. The quantum wire impedance shows an oscillating behavior versus the
frequency caused by the resonances of the charge waves. The Coulomb interaction
produces a frequency dependent renormalization of the charge wave velocity.Comment: 10 two-colomn revtex pages, 6 postscript figures; one figure changed,
some typos corrected, to be published in Phys.Rev.
AC-conductance of a quantum wire with electron-electron interaction
The complex ac-response of a quasi-one dimensional electron system in the
one-band approximation with an interaction potential of finite range is
investigated. It is shown that linear response is exact for this model. The
influence of the screening of the electric field is discussed. The complex
absorptive conductance is analyzed in terms of resistive, capacitive and
inductive behaviors.Comment: 13 pages, REVTeX, 7 eps figures, to appear in Phys. Rev.
Control of human endometrial stromal cell motility by PDGF-BB, HB-EGF and trophoblast-secreted factors
Human implantation involves extensive tissue remodeling at the fetal-maternal interface. It is becoming increasingly evident that not only trophoblast, but also decidualizing endometrial stromal cells are inherently motile and invasive, and likely contribute to the highly dynamic processes at the implantation site. The present study was undertaken to further characterize the mechanisms involved in the regulation of endometrial stromal cell motility and to identify trophoblast-derived factors that modulate migration. Among local growth factors known to be present at the time of implantation, heparin-binding epidermal growth factor-like growth factor (HB-EGF) triggered chemotaxis (directed locomotion), whereas platelet-derived growth factor (PDGF)-BB elicited both chemotaxis and chemokinesis (non-directed locomotion) of endometrial stromal cells. Supernatants of the trophoblast cell line AC-1M88 and of first trimester villous explant cultures stimulated chemotaxis but not chemokinesis. Proteome profiling for cytokines and angiogenesis factors revealed neither PDGF-BB nor HB-EGF in conditioned media from trophoblast cells or villous explants, while placental growth factor, vascular endothelial growth factor and PDGF-AA were identified as prominent secretory products. Among these, only PDGF-AA triggered endometrial stromal cell chemotaxis. Neutralization of PDGF-AA in trophoblast conditioned media, however, did not diminish chemoattractant activity, suggesting the presence of additional trophoblast-derived chemotactic factors. Pathway inhibitor studies revealed ERK1/2, PI3 kinase/Akt and p38 signaling as relevant for chemotactic motility, whereas chemokinesis depended primarily on PI3 kinase/Akt activation. Both chemotaxis and chemokinesis were stimulated upon inhibition of Rho-associated, coiled-coil containing protein kinase. The chemotactic response to trophoblast secretions was not blunted by inhibition of isolated signaling cascades, indicating activation of overlapping pathways in trophoblast-endometrial communication. In conclusion, trophoblast signals attract endometrial stromal cells, while PDGF-BB and HB-EGF, although not identified as trophoblast-derived, are local growth factors that may serve to fine-tune directed and non-directed migration at the implantation site
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