119 research outputs found
Mass transfer characteristic from a rotating cylinder
Paper presented at the 6th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 30 June - 2 July, 2008.vk201
Nature of phase transition in magnetic thin films
We study the critical behavior of magnetic thin films as a function of the
film thickness. We use the ferromagnetic Ising model with the high-resolution
multiple histogram Monte Carlo (MC) simulation. We show that though the 2D
behavior remains dominant at small thicknesses, there is a systematic
continuous deviation of the critical exponents from their 2D values. We observe
that in the same range of varying thickness the deviation of the exponent
is very small from its 2D value, while exponent suffers a larger
deviation. Moreover, as long as the film thickness is fixed, i. e. no finite
size scaling is done in the direction perpendicular to the film, the 3D
values of the critical exponents cannot be attained even with very large (but
fixed) thickness. The crossover to 3D universality class cannot therefore take
place without finite size scaling applied in the direction, in the limit of
numerically accessible thicknesses. From values of exponent obtained
by MC, we estimate the effective dimension of the system. We conclude that with
regard to the critical behavior, thin films behave as systems with effective
dimension between 2 and 3.Comment: 8 pages, 17 figures, submitted to Phys. Rev.
Study of Loschmidt Echo for a qubit coupled to an XY-spin chain environment
We study the temporal evolution of a central spin-1/2 (qubit) coupled to the
environment which is chosen to be a spin-1/2 transverse XY spin chain. We
explore the entire phase diagram of the spin-Hamiltonian and investigate the
behavior of Loschmidt echo(LE) close to critical and multicritical point(MCP).
To achieve this, the qubit is coupled to the spin chain through the anisotropy
term as well as one of the interaction terms. Our study reveals that the echo
has a faster decay with the system size (in the short time limit) close to a
MCP and also the scaling obeyed by the quasiperiod of the collapse and revival
of the LE is different in comparison to that close to a QCP. We also show that
even when approached along the gapless critical line, the scaling of the LE is
determined by the MCP where the energy gap shows a faster decay with the system
size. This claim is verified by studying the short-time and also the collapse
and revival behavior of the LE at a quasicritical point on the ferromagnetic
side of the MCP. We also connect our observation to the decoherence of the
central spin.Comment: Accepted for publication in EPJ
Predicted Infrared and Raman Spectra for Neutral Ti_8C_12 Isomers
Using a density-functional based algorithm, the full IR and Raman spectra are
calculated for the neutral Ti_8C_12 cluster assuming geometries of Th, Td, D2d
and C3v symmetry. The Th pentagonal dodecahedron is found to be dynamically
unstable. The calculated properties of the relaxed structure having C3v
symmetry are found to be in excellent agreement with experimental gas phase
infrared results, ionization potential and electron affinity measurements.
Consequently, the results presented may be used as a reference for further
experimental characterization using vibrational spectroscopy.Comment: 6 pages, 5 figures. Physical Review A, 2002 (in press
Stability, Electronic Structure and Vibrational Modes of Ti_8C_12 Dimer
We present our density functional results of the geometry, electronic
structure and dissociation energy of Ti_8C_12 dimer. We show that as opposed to
the currently held view that Ti_8C_12 are highly stable monodispersed clusters,
the neutral Ti_8C_12 clusters form covalent bonds and form stable dimers. We
determine that the Ti atoms bond weakly (0.9 eV/bond) to organic ligands such
as ammonia. Alternatively the Met-Car dimer has a cohesive energy of 4.84 eV or
approximately 1.2 eV per bond. While Met-Car dimers are stable, formation of
these dimers may be quenched in an environment that contains a significant
population of organic ligands. The ionization and dissociation energies of the
dimer are of same order which prevents the observation of the dimer in the ion
mass spectroscopy. The analysis of the vibrational frequencies show the
lowest-energy structure to be dynamically stable. We also present infrared
absorption and Raman scattering spectra of the Ti_8C_12 dimer.Comment: 5 pages, 3 figures (Better quality figures available on request).
Physical Review B (Rapid Communication) (2002, in press
Genetic variability of Brazilian phytoplasma and spiroplasma isolated from maize plants
COSNet : a cost sensitive neural network for semi-supervised learning in graphs
The semi-supervised problem of learning node labels in graphs consists, given a partial graph labeling, in inferring the unknown labels of the unlabeled vertices. Several machine learning algorithms have been proposed for solving this problem, including Hopfield networks and label
propagation methods; however, some issues have been only partially considered, e.g. the preservation of the prior knowledge and the unbalance
between positive and negative labels. To address these items, we propose
a Hopfield-based cost sensitive neural network algorithm (COSNet). The
method factorizes the solution of the problem in two parts: 1) the sub-
network composed by the labelled vertices is considered, and the net-
work parameters are estimated through a supervised algorithm; 2) the
estimated parameters are extended to the subnetwork composed of the
unlabeled vertices, and the attractor reached by the dynamics of this
subnetwork allows to predict the labeling of the unlabeled vertices. The
proposed method embeds in the neural algorithm the \u201da priori\u201d knowl-
edge coded in the labelled part of the graph, and separates node labels
and neuron states, allowing to differentially weight positive and nega-
tive node labels. Moreover, COSNet introduces an efficient cost-sensitive
strategy which allows to learn the near-optimal parameters of the net-
work in order to take into account the unbalance between positive and
negative node labels. Finally, the dynamics of the network is restricted to
its unlabeled part, preserving the minimization of the overall objective
function and significantly reducing the time complexity of the learning
algorithm. COSNet has been applied to the genome-wide prediction of
gene function in a model organism. The results, compared with those ob-
tained by other semi-supervised label propagation algorithms and super-
vised machine learning methods, show the effectiveness of the proposed
approach
Genetic loci influencing kidney function and chronic kidney disease
Using genome-wide association, we identify common variants at 2p12-p13, 6q26, 17q23 and 19q13 associated with serum creatinine, a marker of kidney function (P = 10 10 to 10 15). Of these, rs10206899 (near NAT8, 2p12-p13) and rs4805834 (near SLC7A9, 19q13) were also associated with chronic kidney disease (P = 5.0 × 10 5 and P = 3.6 × 10 4, respectively). Our findings provide insight into metabolic, solute and drug-transport pathways underlying susceptibility to chronic kidney disease
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