155,335 research outputs found
Scalar and vector Slepian functions, spherical signal estimation and spectral analysis
It is a well-known fact that mathematical functions that are timelimited (or
spacelimited) cannot be simultaneously bandlimited (in frequency). Yet the
finite precision of measurement and computation unavoidably bandlimits our
observation and modeling scientific data, and we often only have access to, or
are only interested in, a study area that is temporally or spatially bounded.
In the geosciences we may be interested in spectrally modeling a time series
defined only on a certain interval, or we may want to characterize a specific
geographical area observed using an effectively bandlimited measurement device.
It is clear that analyzing and representing scientific data of this kind will
be facilitated if a basis of functions can be found that are "spatiospectrally"
concentrated, i.e. "localized" in both domains at the same time. Here, we give
a theoretical overview of one particular approach to this "concentration"
problem, as originally proposed for time series by Slepian and coworkers, in
the 1960s. We show how this framework leads to practical algorithms and
statistically performant methods for the analysis of signals and their power
spectra in one and two dimensions, and, particularly for applications in the
geosciences, for scalar and vectorial signals defined on the surface of a unit
sphere.Comment: Submitted to the 2nd Edition of the Handbook of Geomathematics,
edited by Willi Freeden, Zuhair M. Nashed and Thomas Sonar, and to be
published by Springer Verlag. This is a slightly modified but expanded
version of the paper arxiv:0909.5368 that appeared in the 1st Edition of the
Handbook, when it was called: Slepian functions and their use in signal
estimation and spectral analysi
Highlighting Entanglement of Cultures via Ranking of Multilingual Wikipedia Articles
How different cultures evaluate a person? Is an important person in one
culture is also important in the other culture? We address these questions via
ranking of multilingual Wikipedia articles. With three ranking algorithms based
on network structure of Wikipedia, we assign ranking to all articles in 9
multilingual editions of Wikipedia and investigate general ranking structure of
PageRank, CheiRank and 2DRank. In particular, we focus on articles related to
persons, identify top 30 persons for each rank among different editions and
analyze distinctions of their distributions over activity fields such as
politics, art, science, religion, sport for each edition. We find that local
heroes are dominant but also global heroes exist and create an effective
network representing entanglement of cultures. The Google matrix analysis of
network of cultures shows signs of the Zipf law distribution. This approach
allows to examine diversity and shared characteristics of knowledge
organization between cultures. The developed computational, data driven
approach highlights cultural interconnections in a new perspective.Comment: Published in PLoS ONE
(http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0074554).
Supporting information is available on the same webpag
Directed Transmission Method, A Fully Asynchronous approach to Solve Sparse Linear Systems in Parallel
In this paper, we propose a new distributed algorithm, called Directed
Transmission Method (DTM). DTM is a fully asynchronous and continuous-time
iterative algorithm to solve SPD sparse linear system. As an architecture-aware
algorithm, DTM could be freely running on all kinds of heterogeneous parallel
computer. We proved that DTM is convergent by making use of the final-value
theorem of Laplacian Transformation. Numerical experiments show that DTM is
stable and efficient.Comment: v1: poster presented in SPAA'08; v2: full paper; v3: rename EVS to
GNBT; v4: reuse EVS. More info, see my web page at
http://weifei00.googlepages.co
Dynamic Selection of Symmetric Key Cryptographic Algorithms for Securing Data Based on Various Parameters
Most of the information is in the form of electronic data. A lot of
electronic data exchanged takes place through computer applications. Therefore
information exchange through these applications needs to be secure. Different
cryptographic algorithms are usually used to address these security concerns.
However, along with security there are other factors that need to be considered
for practical implementation of different cryptographic algorithms like
implementation cost and performance. This paper provides comparative analysis
of time taken for encryption by seven symmetric key cryptographic algorithms
(AES, DES, Triple DES, RC2, Skipjack, Blowfish and RC4) with variation of
parameters like different data types, data density, data size and key sizes.Comment: 8 pages, 4 figures, Fifth International Conference on Communications
Security & Information Assurance (CSIA 2014) May 24~25, 2014, Delhi, Indi
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