29,596 research outputs found
Point contact tunnelling spectroscopy of the density of states in Tb-Mg-Zn quasicrystals
According to theoretical predictions the quasicrystalline (QC) electronic
density of states (DOS) must have a rich and fine spiky structure which
actually has resulted elusive. The problem with its absence may be related to
poor structural characteristics of the studied specimens, and/or to the
non-existence of this spike characteristic. Recent calculations have shown that
the fine structure indeed exists, but only for two dimensional approximants
phases. The aim of the present study is to show our recent experimental studies
with point contacts tunnel junction spectroscopy performed in samples of very
high quality. The studies were performed in icosahedral QC alloys with
composition TbMgZn. We found the presence of a pseudogap
feature at the Fermi level, small as compared to the pseudogap of other
icosahedral materials. This study made in different spots on the QC shows quite
different spectroscopic features, where the observed DOS was a fine non-spiky
structure, distinct to theoretical predictions. In some regions of the
specimens the spectroscopic features could be related to Kondo characteristics
due to Tb magnetic atoms acting as impurities. Additionally, we observed that
the spectroscopic features vanished under magnetic field.Comment: 9 pages, 8 figures, accepted in Journal of Non-Crystalline Solid
Fixed point theorems for a class of mappings depending of another function and defined on cone metric spaces
In this paper we study the existence and uniqueness of fixed points of a
class of mappings defined on complete, (sequentially compact) cone metric
spaces, without continuity conditions and depending on another function.Comment: 11 pages, submitte
Stochastic stability of sectional-Anosov flows
A {\em sectional-Anosov flow} is a vector field on a compact manifold
inwardly transverse to the boundary such that the maximal invariant set is
sectional-hyperbolic (in the sense of \cite{mm}). We prove that any
transitive sectional-Anosov flow has a unique SRB measure which is
stochastically stable under small random perturbations.Comment: 10 page
On the Existence of Fixed Points of Contraction Mappings Depending of Two Functions on Cone Metric Spaces
In this paper, we study the existence of fixed points for mappings defined on
complete, (sequentially compact) cone metric spaces, satisfying a general
contractive inequality depending of two additional mappings.Comment: 9 pages, submitte
Cone metric spaces and fixed point theorems of T-Kannan contractive mappings
The purpose of this paper is to obtain sufficient conditions for the
existence of a unique fixed point of T-Kannan type mappings on complete cone
metric spaces depended on another function.Comment: 9 page
T-Zamfirescu and T-weak contraction mappings on cone metric spaces
The purpose of this paper is to obtain sufficient conditions for the
existence of a unique fixed point of T-Zamfirescu and T-weak contraction
mappings in the framework of complete cone metric spaces.Comment: 9 pages, submitte
Common fixed points for a pair of commuting mappings in complete cone metric spaces
This paper is devoted to prove the S. L. Singh's common fixed point Theorem
for commuting mappings in cone metric spaces. In this framework, we introduce
the notions of Generalized Kannan Con- traction, Generalized Zamfirescu
Contraction and Generalized Weak Contraction for a pair of mappings, proving
afterward their respective fixed point results.Comment: submitte
Searching for spiral shocks
Spiral shocks in cataclysmic variables (CVs) are the result of tidal
interactions of the mass donor star with the accretion disc. Their study is
fundamental for our understanding of angular momentum transfer in discs. In our
quest to learn how widespread amongst binaries spiral shocks are, and how their
presence depends upon orbital period and mass ratio (as they are created by
direct interaction with the donor star), we have obtained spectra of a large
sample of CVs during their high-mass-transfer states. We find that 24 out of
the 63 systems observed are candidates for containing spiral shocks. 5 out of
those 24 CVs have been confirmed as showing shocks in the disc during outburst.Comment: 2 pages. Proceedings of the Goettingen conference on Cataclysmic
Variable Stars, Goettingen, August 200
Tilting Theory and Functor Categories III. The Maps Category
In this paper we continue the project of generalizing tilting theory to the
category of contravariant functors , from a skeletally small
preadditive category to the category of abelian groups. We introduced the
notion of a a generalized tilting category , and extended Happel's theorem
to . We proved that there is an equivalence of triangulated categories
. In the case of dualizing varieties, we proved
a version of Happel's theorem for the categories of finitely presented
functors. We also proved in this paper, that there exists a relation between
covariantly finite coresolving categories, and generalized tilting categories.
Extending theorems for artin algebras. In this article we consider the category
of maps, and relate tilting categories in the category of functors, with
relative tilting in the category of maps. Of special interest is the category
with an artin algebra
Applying the Inverse Average Magnitude Squared Coherence Index for Determining Order-Chaos Transition in a System Governed by H\'enon Mapping Dynamics
The quantitative determination of the order-chaos transition in a nonlinear
dynamical system described by H\'enon mapping defined as
, where , and is an
adjustable control parameter, was made. This was achieved by applying the
Inverse Average Magnitude-Squared Coherence Index (IAMSCI). This method is
based on the Welch average periodogram technique and it has the advantage
respect to nonlinear dynamical methods that it may be applied to any stationary
signal by using discrete Fourier transform (DFT) representation which allows to
operate on a short discrete-time series. Its effectiveness was demonstrated by
comparing the results obtained by applying IAMSCI method with those obtained by
calculating the largest Lyapounov exponent (LLE), both applied to the same
discrete-time series set derived from the H\'enon mapping.Comment: 20 pages, 7 figure
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