4,172 research outputs found
Empirical stationary correlations for semi-supervised learning on graphs
In semi-supervised learning on graphs, response variables observed at one
node are used to estimate missing values at other nodes. The methods exploit
correlations between nearby nodes in the graph. In this paper we prove that
many such proposals are equivalent to kriging predictors based on a fixed
covariance matrix driven by the link structure of the graph. We then propose a
data-driven estimator of the correlation structure that exploits patterns among
the observed response values. By incorporating even a small fraction of
observed covariation into the predictions, we are able to obtain much improved
prediction on two graph data sets.Comment: Published in at http://dx.doi.org/10.1214/09-AOAS293 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Mesoscovic magnetic/semiconductor heterostructures
We report the experimental results of Fe and Fe3O4 nanostructures on GaAs(100) surfaces and hybrid Ferromagnetic/Semiconductor/Ferromagnetic (FM/SC/FM) spintronic devices. Element specific x-ray magnetic circular dichroism (XMCD) measurements have shown directly that Fe atoms on the GaAs(100)-4 x 6 surface are ferromagnetic. Within coverages of 2.5 to 4.8 ML superparamagnetic nanoclusters are formed and exhibiting strong uniaxial anisotropy, of the order of 6.0 x 10(5) erg/cm(3). The coercivities of epitaxial Fe dot arrays films grown on GaAs(100) were observed to be dependent on the separation and size of the dots indicating that interdot dipolar coupling affects the magnetization processes in these dots. In addition Fe3O4 films grown on deformed GaAs(100) substrates have been observed to form nanostripes following the topography of the substrate and magneto-optical Kerr effect (MOKE) measurements showed that these nanostripes have uniaxial magnetic anisotropy with easy axis perpendicular to the length of the nanostripes. Meanwhile the FM/SC/FM vertical device has exhibited a biasing current dependent on MR characteristics, with a maximum change of 12% in the MR observed, indicating for the first time a large room temperature spin injection and detection
Temperature and impurity effects of the polaron in an asymmetric quantum dot
We study the temperature and impurity effects of the ground state energy and the ground state binding energy in an asymmetric quantum dot by using the liner combination operator method. It is found that the ground state energy and the ground state binding energy will increase with increasing the temperature. The ground state ener-gy is a decreasing function of the Coulomb bound potential, whereas the ground state binding energy is an in-creasing one of it
Effective conductivity of 2D isotropic two-phase systems in magnetic field
Using the linear fractional transformation, connecting effective
conductivities sigma_{e} of isotropic two-phase systems with and without
magnetic field, explicit approximate expressions for sigma_{e} in a magnetic
field are obtained. They allow to describe sigma_{e} of various inhomogeneous
media at arbitrary phase concentrations x and magnetic fields. the x-dependence
plots of sigma_e at some values of inhomogeneity and magnetic field are
constructed. Their behaviour is qualitatively compatible with the existing
experimental data. The obtained results are applicable for different two-phase
systems (regular and nonregular as well as random), satisfying the symmetry and
self-duality conditions, and admit a direct experimental checking.Comment: 9 pages, 2 figures, Latex2e, small corrections and new figure
Phase Transition in Strongly Degenerate Hydrogen Plasma
Direct fermionic path-integral Monte-Carlo simulations of strongly coupled
hydrogen are presented. Our results show evidence for the hypothetical plasma
phase transition. Its most remarkable manifestation is the appearance of
metallic droplets which are predicted to be crucial for the electrical
conductivity allowing to explain the rapid increase observed in recent shock
compression measurments.Comment: 1 LaTeX file using jetpl.cls (included), 5 ps figures. Manuscript
submitted to JETP Letter
Using Energy Conditions to Distinguish Brane Models and Study Brane Matter
Current universe (assumed here to be normal matter on the brane) is
pressureless from observations. In this case the energy condition is
and . By using this condition, brane models can be
distinguished. Then, assuming arbitrary component of matter in DGP model, we
use four known energy conditions to study the matter on the brane. If there is
nonnormal matter or energy (for example dark energy with ) on the
brane, the universe is accelerated.Comment: 5pages, no figures; Accepted by Communications in Theoretical Physic
Coupling of the lattice and superlattice deformations and hysteresis in thermal expansion for the quasi one-dimensional conductor TaS
An original interferometer-based setup for measurements of length of
needle-like samples is developed, and thermal expansion of o-TaS crystals
is studied. Below the Peierls transition the temperature hysteresis of length
is observed, the width of the hysteresis loop being up to . The behavior of the loop is anomalous: the length changes so
that it is in front of its equilibrium value. The hysteresis loop couples with
that of conductivity. The sign and the value of the length hysteresis are
consistent with the strain dependence of the charge-density waves (CDW) wave
vector. With lowering temperature down to 100 K the CDW elastic modulus grows
achieving a value comparable with the lattice Young modulus. Our results could
be helpful in consideration of different systems with intrinsic
superstructures.Comment: 4 pages, 3 figures. Phys. Rev. Lett., accepted for publicatio
On the injectivity of the circular Radon transform arising in thermoacoustic tomography
The circular Radon transform integrates a function over the set of all
spheres with a given set of centers. The problem of injectivity of this
transform (as well as inversion formulas, range descriptions, etc.) arises in
many fields from approximation theory to integral geometry, to inverse problems
for PDEs, and recently to newly developing types of tomography. The article
discusses known and provides new results that one can obtain by methods that
essentially involve only the finite speed of propagation and domain dependence
for the wave equation.Comment: To appear in Inverse Problem
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