2,353 research outputs found
First-Principles Modeling of Pt/LaAlO3/SrTiO3 Capacitors Under an External Bias Potential
We study the electrical properties of Pt/LaAlO3/SrTiO3 capacitors under the
action of an external bias potential, using first-principles simulations
performed at constrained electric displacement field. A complete set of band
diagrams, together with the relevant electrical characteristics (capacitance
and built-in fields), are determined as a function of LaAlO3 thickness and the
applied potential.We find that the internal field in LaAlO3 monotonically
decreases with increasing thickness; hence, the occurrence of spontaneous Zener
tunneling is ruled out in this system.We discuss the implications of our
results in the light of recent experimental observations on biased
LaAlO3/SrTiO3 junctions involving metallic top electrodes.Comment: 5 pages, 4 figure
Predicting polarization and nonlinear dielectric response of arbitrary perovskite superlattice sequences
We carry out first-principles calculations of the nonlinear dielectric
response of short-period ferroelectric superlattices. We compute and store not
only the total polarization, but also the Wannier-based polarizations of
individual atomic layers, as a function of electric displacement field, and use
this information to construct a model capable of predicting the nonlinear
dielectric response of an arbitrary superlattice sequence. We demonstrate the
successful application of our approach to superlattices composed of SrTiO,
CaTiO, and BaTiO layers.Comment: 5 pages, 4 figures, 2 table
Accurate polarization within a unified Wannier function formalism
We present an alternative formalism for calculating the maximally localized
Wannier functions in crystalline solids, obtaining an expression which is
extremely simple and general. In particular, our scheme is exactly invariant
under Brillouin zone folding, and therefore it extends trivially to the
Gamma-point case. We study the convergence properties of the Wannier functions,
their quadratic spread and centers as obtained by our simplified technique. We
show how this convergence can be drastically improved by a simple and
inexpensive ``refinement'' step, which allows for very efficient and accurate
calculations of the polarization in zero external field.Comment: 9 pages, 4 figure
Entropy and typical properties of Nash equilibria in two-player games
We use techniques from the statistical mechanics of disordered systems to
analyse the properties of Nash equilibria of bimatrix games with large random
payoff matrices. By means of an annealed bound, we calculate their number and
analyse the properties of typical Nash equilibria, which are exponentially
dominant in number. We find that a randomly chosen equilibrium realizes almost
always equal payoffs to either player. This value and the fraction of
strategies played at an equilibrium point are calculated as a function of the
correlation between the two payoff matrices. The picture is complemented by the
calculation of the properties of Nash equilibria in pure strategies.Comment: 6 pages, was "Self averaging of Nash equilibria in two player games",
main section rewritten, some new results, for additional information see
http://itp.nat.uni-magdeburg.de/~jberg/games.htm
Carrier-mediated magnetoelectricity in complex oxide heterostructures
While tremendous success has been achieved to date in creating both single
phase and composite magnetoelectric materials, the quintessential
electric-field control of magnetism remains elusive. In this work, we
demonstrate a linear magnetoelectric effect which arises from a novel
carrier-mediated mechanism, and is a universal feature of the interface between
a dielectric and a spin-polarized metal. Using first-principles density
functional calculations, we illustrate this effect at the SrRuO/SrTiO
interface and describe its origin. To formally quantify the magnetic response
of such an interface to an applied electric field, we introduce and define the
concept of spin capacitance. In addition to its magnetoelectric and spin
capacitive behavior, the interface displays a spatial coexistence of magnetism
and dielectric polarization suggesting a route to a new type of interfacial
multiferroic
A field deployable method for a rapid screening analysis of inorganic arsenic in seaweed
The authors thank the support for getting the seaweed samples from the projects funded under the Department of Agriculture, Food and the Marine’s Competitive research programmes in Ireland. Reference number 14 SF 860. The authors thank Corny Brombach for the graphical abstract.Peer reviewedPublisher PD
Nitric oxide modulates expression of extracellular matrix genes linked to fibrosis in kidney mesangial cells
Mesangial cells are thought to be important mediators of glomerular inflammation and fibrosis. Studies have established a direct role for nitric oxide (NO) in the regulation of gene expression in mesangial cells. Representational difference analysis was used to investigate changes in gene expression elicited by the treatment of S-nitroso-L-glutathione in rat mesangial cells. Seven upregulated and 11 downregulated genes were identified. Four out of 11 downregulated genes (connective tissue growth factor, thrombospondin-1, collagen type I all and collagen type I alpha 2) are known to be linked to inflammation and fibrosis. Results were verified across species in mesangial cells treated with a series of NO donors using Northern blot analysis, quantitative real-time PCR and protein analysis methods. Induction of endogenous NO production by cytokine stimulation also triggered regulation of the genes. One example gene, connective tissue growth factor, was studied at the promoter level. Promoter-reporter gene studies in mesangial cells demonstrated that NO acts at the transcriptional level to suppress gene expression. Our results reveal a complex role of NO in regulating gene expression in mesangial cells and suggest an antifibrotic potential for NO
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