5,022 research outputs found
On the Kinetic Roughening in Polymer Film Growth by Vapor Deposition
This is a Comment on a recent publication: Y.-P. Zhao et al., Phys. Rev.
Lett. 85, 3229 (2000). In the Letter, the authors report on an experimental
investigation of polymeric (p-xylene) thin film growth and propose a new
universality class not previously known. Here, we point out that the critical
exponents reported in the Letter are consistent with the critical exponents of
Das Sarma-Tamborenea growth model.Comment: 2 pages, 1 figure include
Phase Transitions in Confined Antiferromagnets
Confinement effects on the phase transitions in antiferromagnets are studied
as a function of the surface coupling v and the surface field h for bcc(110)
films. Unusual topologies for the phase diagram are attained for particular
combinations of v and h. It is shown that some of the characteristics of the
finite-temperature behavior of the system are driven by its low-temperature
properties and consequently can be explained in terms of a ground-state
analysis. Cluster variation free energies are used for the investigation of the
finite temperature behavior.Comment: 4 pages, 2 figures, Conference proceedings (SLAFES-XV), Phys. Stat.
Sol.(b), in pres
Transport properties of diluted magnetic semiconductors: Dynamical mean field theory and Boltzmann theory
The transport properties of diluted magnetic semiconductors (DMS) are
calculated using dynamical mean field theory (DMFT) and Boltzmann transport
theory. Within DMFT we study the density of states and the dc-resistivity,
which are strongly parameter dependent such as temperature, doping, density of
the carriers, and the strength of the carrier-local impurity spin exchange
coupling. Characteristic qualitative features are found distinguishing weak,
intermediate, and strong carrier-spin coupling and allowing quantitative
determination of important parameters defining the underlying ferromagnetic
mechanism. We find that spin-disorder scattering, formation of bound state, and
the population of the minority spin band are all operational in DMFT in
different parameter range. We also develop a complementary Boltzmann transport
theory for scattering by screened ionized impurities. The difference in the
screening properties between paramagnetic () and ferromagnetic ()
states gives rise to the temperature dependence (increase or decrease) of
resistivity, depending on the carrier density, as the system goes from the
paramagnetic phase to the ferromagnetic phase. The metallic behavior below
for optimally doped DMS samples can be explained in the Boltzmann theory
by temperature dependent screening and thermal change of carrier spin
polarization.Comment: 15 pages, 15 figure
Fast Distributed PageRank Computation
Over the last decade, PageRank has gained importance in a wide range of
applications and domains, ever since it first proved to be effective in
determining node importance in large graphs (and was a pioneering idea behind
Google's search engine). In distributed computing alone, PageRank vector, or
more generally random walk based quantities have been used for several
different applications ranging from determining important nodes, load
balancing, search, and identifying connectivity structures. Surprisingly,
however, there has been little work towards designing provably efficient
fully-distributed algorithms for computing PageRank. The difficulty is that
traditional matrix-vector multiplication style iterative methods may not always
adapt well to the distributed setting owing to communication bandwidth
restrictions and convergence rates.
In this paper, we present fast random walk-based distributed algorithms for
computing PageRanks in general graphs and prove strong bounds on the round
complexity. We first present a distributed algorithm that takes O\big(\log
n/\eps \big) rounds with high probability on any graph (directed or
undirected), where is the network size and \eps is the reset probability
used in the PageRank computation (typically \eps is a fixed constant). We
then present a faster algorithm that takes O\big(\sqrt{\log n}/\eps \big)
rounds in undirected graphs. Both of the above algorithms are scalable, as each
node sends only small (\polylog n) number of bits over each edge per round.
To the best of our knowledge, these are the first fully distributed algorithms
for computing PageRank vector with provably efficient running time.Comment: 14 page
- …