24,692 research outputs found
A method for enhancing the stability and robustness of explicit schemes in astrophysical fluid dynamics
A method for enhancing the stability and robustness of explicit schemes in
computational fluid dynamics is presented. The method is based in reformulating
explicit schemes in matrix form, which cane modified gradually into semi or
strongly-implicit schemes. From the point of view of matrix-algebra, explicit
numerical methods are special cases in which the global matrix of coefficients
is reduced to the identity matrix . This extreme simplification leads to
severer stability range, hence of their robustness. In this paper it is shown
that a condition, which is similar to the Courant-Friedrich-Levy (CFL)
condition can be obtained from the stability requirement of inversion of the
coefficient matrix. This condition is shown to be relax-able, and that a class
of methods that range from explicit to strongly implicit methods can be
constructed, whose degree of implicitness depends on the number of coefficients
used in constructing the corresponding coefficient-matrices. Special attention
is given to a simple and tractable semi-explicit method, which is obtained by
modifying the coefficient matrix from the identity matrix into a
diagonal-matrix . This method is shown to be stable, robust and it can be
applied to search for stationary solutions using large CFL-numbers, though it
converges slower than its implicit counterpart. Moreover, the method can be
applied to follow the evolution of strongly time-dependent flows, though it is
not as efficient as normal explicit methods. In addition, we find that the
residual smoothing method accelerates convergene toward steady state solutions
considerably and improves the efficiency of the solution procedure.Comment: 33 pages, 15 figure
On Nonrigid Shape Similarity and Correspondence
An important operation in geometry processing is finding the correspondences
between pairs of shapes. The Gromov-Hausdorff distance, a measure of
dissimilarity between metric spaces, has been found to be highly useful for
nonrigid shape comparison. Here, we explore the applicability of related shape
similarity measures to the problem of shape correspondence, adopting spectral
type distances. We propose to evaluate the spectral kernel distance, the
spectral embedding distance and the novel spectral quasi-conformal distance,
comparing the manifolds from different viewpoints. By matching the shapes in
the spectral domain, important attributes of surface structure are being
aligned. For the purpose of testing our ideas, we introduce a fully automatic
framework for finding intrinsic correspondence between two shapes. The proposed
method achieves state-of-the-art results on the Princeton isometric shape
matching protocol applied, as usual, to the TOSCA and SCAPE benchmarks
Monte Carlo Methods for Equilibrium and Nonequilibrium Problems in Interfacial Electrochemistry
We present a tutorial discussion of Monte Carlo methods for equilibrium and
nonequilibrium problems in interfacial electrochemistry. The discussion is
illustrated with results from simulations of three specific systems: bromine
adsorption on silver (100), underpotential deposition of copper on gold (111),
and electrodeposition of urea on platinum (100).Comment: RevTex, 14 pages, 8 figures. To appear in book _Interfacial
Electrochemisty
Chemical vapor deposition modeling for high temperature materials
The formalism for the accurate modeling of chemical vapor deposition (CVD) processes has matured based on the well established principles of transport phenomena and chemical kinetics in the gas phase and on surfaces. The utility and limitations of such models are discussed in practical applications for high temperature structural materials. Attention is drawn to the complexities and uncertainties in chemical kinetics. Traditional approaches based on only equilibrium thermochemistry and/or transport phenomena are defended as useful tools, within their validity, for engineering purposes. The role of modeling is discussed within the context of establishing the link between CVD process parameters and material microstructures/properties. It is argued that CVD modeling is an essential part of designing CVD equipment and controlling/optimizing CVD processes for the production and/or coating of high performance structural materials
Information Filtering on Coupled Social Networks
In this paper, based on the coupled social networks (CSN), we propose a
hybrid algorithm to nonlinearly integrate both social and behavior information
of online users. Filtering algorithm based on the coupled social networks,
which considers the effects of both social influence and personalized
preference. Experimental results on two real datasets, \emph{Epinions} and
\emph{Friendfeed}, show that hybrid pattern can not only provide more accurate
recommendations, but also can enlarge the recommendation coverage while
adopting global metric. Further empirical analyses demonstrate that the mutual
reinforcement and rich-club phenomenon can also be found in coupled social
networks where the identical individuals occupy the core position of the online
system. This work may shed some light on the in-depth understanding structure
and function of coupled social networks
Spectral Generalized Multi-Dimensional Scaling
Multidimensional scaling (MDS) is a family of methods that embed a given set
of points into a simple, usually flat, domain. The points are assumed to be
sampled from some metric space, and the mapping attempts to preserve the
distances between each pair of points in the set. Distances in the target space
can be computed analytically in this setting. Generalized MDS is an extension
that allows mapping one metric space into another, that is, multidimensional
scaling into target spaces in which distances are evaluated numerically rather
than analytically. Here, we propose an efficient approach for computing such
mappings between surfaces based on their natural spectral decomposition, where
the surfaces are treated as sampled metric-spaces. The resulting spectral-GMDS
procedure enables efficient embedding by implicitly incorporating smoothness of
the mapping into the problem, thereby substantially reducing the complexity
involved in its solution while practically overcoming its non-convex nature.
The method is compared to existing techniques that compute dense correspondence
between shapes. Numerical experiments of the proposed method demonstrate its
efficiency and accuracy compared to state-of-the-art approaches
Tag-Aware Recommender Systems: A State-of-the-art Survey
In the past decade, Social Tagging Systems have attracted increasing
attention from both physical and computer science communities. Besides the
underlying structure and dynamics of tagging systems, many efforts have been
addressed to unify tagging information to reveal user behaviors and
preferences, extract the latent semantic relations among items, make
recommendations, and so on. Specifically, this article summarizes recent
progress about tag-aware recommender systems, emphasizing on the contributions
from three mainstream perspectives and approaches: network-based methods,
tensor-based methods, and the topic-based methods. Finally, we outline some
other tag-related works and future challenges of tag-aware recommendation
algorithms.Comment: 19 pages, 3 figure
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