52,189 research outputs found
Predicting Item Popularity: Analysing Local Clustering Behaviour of Users
Predicting the popularity of items in rating networks is an interesting but
challenging problem. This is especially so when an item has first appeared and
has received very few ratings. In this paper, we propose a novel approach to
predicting the future popularity of new items in rating networks, defining a
new bipartite clustering coefficient to predict the popularity of movies and
stories in the MovieLens and Digg networks respectively. We show that the
clustering behaviour of the first user who rates a new item gives insight into
the future popularity of that item. Our method predicts, with a success rate of
over 65% for the MovieLens network and over 50% for the Digg network, the
future popularity of an item. This is a major improvement on current results.Comment: 25 pages, 11 figure
Identifying Influential Nodes in Bipartite Networks Using the Clustering Coefficient
The identification of influential nodes in complex network can be very
challenging. If the network has a community structure, centrality measures may
fail to identify the complete set of influential nodes, as the hubs and other
central nodes of the network may lie inside only one community. Here we define
a bipartite clustering coefficient that, by taking differently structured
clusters into account, can find important nodes across communities
Role of spatial coherence in polarization tomography
We analyze an experimental setup in which a quasi-monochromatic spatially
coherent beam of light is used to probe a paraxial optical scatterer. We
discuss the effect of the spatial coherence of the probe beam on the Mueller
matrix representing the scatterer. We show that according to the degree of
spatial coherence of the beam, the \emph{same} scattering system can be
represented by \emph{different} Mueller matrices. This result should serve as a
warning for experimentalists.Comment: 3 pages, 1 figur
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In-situ Neutron Diffraction Studies of Various Metals on Engin-X at ISIS
Unsupervised Bump Hunting Using Principal Components
Principal Components Analysis is a widely used technique for dimension
reduction and characterization of variability in multivariate populations. Our
interest lies in studying when and why the rotation to principal components can
be used effectively within a response-predictor set relationship in the context
of mode hunting. Specifically focusing on the Patient Rule Induction Method
(PRIM), we first develop a fast version of this algorithm (fastPRIM) under
normality which facilitates the theoretical studies to follow. Using basic
geometrical arguments, we then demonstrate how the PC rotation of the predictor
space alone can in fact generate improved mode estimators. Simulation results
are used to illustrate our findings.Comment: 24 pages, 9 figure
On the explanatory power of principal components
We show that if we have an orthogonal base () in a
-dimensional vector space, and select vectors and
such that the vectors traverse the origin, then the probability of
being to closer to all the vectors in the base than to is at
least 1/2 and converges as increases to infinity to a normal distribution
on the interval [-1,1]; i.e., . This result has
relevant consequences for Principal Components Analysis in the context of
regression and other learning settings, if we take the orthogonal base as the
direction of the principal components.Comment: 10 pages, 3 figure
A search for diffuse bands in fullerene planetary nebulae: evidence of diffuse circumstellar bands
Large fullerenes and fullerene-based molecules have been proposed as carriers
of diffuse interstellar bands (DIBs). The recent detection of the most common
fullerenes (C60 and C70) around some planetary nebulae (PNe) now enable us to
study the DIBs towards fullerene-rich space environments. We search DIBs in the
optical spectra towards three fullerene-containing PNe (Tc 1, M 1-20, and IC
418). Special attention is given to DIBs which are found to be unusually
intense towards these fullerene sources. In particular, an unusually strong
4428A absorption feature is a common charateristic of fullerene PNe. Similar to
Tc 1, the strongest optical bands of neutral C60 are not detected towards IC
418. Our high-quality (S/N > 300) spectra for PN Tc 1, together with its large
radial velocity, permit us to search for the presence of diffuse bands of
circumstellar origin, which we refer to as diffuse circumstellar bands (DCBs).
We report the first tentative detection of two DCBs at 4428 and 5780 A in the
fullerene-rich circumstellar environment around the PN Tc 1. Laboratory and
theoretical studies of fullerenes in their multifarious manifestations (carbon
onions, fullerene clusters, or even complex species formed by fullerenes and
other molecules like PAHs or metals) may help solve the mystery of some of the
diffuse band carriers.Comment: Accepted for publication in Astronomy & Astrophysics (16 pages, 10
figures, and 7 Tables); final version (changes regarding PN M 1-20 and
language corrected
Diffuse Neutron Scattering Study of Magnetic Correlations in half-doped La0.5Ca0.5-xSrxMnO3 (x = 0.1, 0.3 and 0.4) Manganites
The short range ordered magnetic correlations have been studied in half doped
La0.5Ca0.5-xSrxMnO3 (x = 0.1, 0.3 and 0.4) compounds by polarized neutron
scattering technique. On doping Sr2+ for Ca2+ ion, these compounds with x =
0.1, 0.3, and 0.4 exhibit CE-type, mixture of CE-type and A-type, and A-type
antiferromagnetic ordering, respectively. Magnetic diffuse scattering is
observed in all the compounds above and below their respective magnetic
ordering temperatures and is attributed to magnetic polarons. The correlations
are primarily ferromagnetic in nature above T\_N, although a small
antiferromagnetic contribution is also evident. Additionally, in samples x =
0.1 and 0.3 with CE-type antiferromagnetic ordering, superlattice diffuse
reflections are observed indicating correlations between magnetic polarons. On
lowering temperature below T\_N the diffuse scattering corresponding to
ferromagnetic correlations is suppressed and the long range ordered
antiferromagnetic state is established. However, the short range ordered
correlations indicated by enhanced spin flip scattering at low Q coexist with
long range ordered state down to 3K. In x = 0.4 sample with A-type
antiferromagnetic ordering, superlattice diffuse reflections are absent.
Additionally, in comparison to x = 0.1 and 0.3 sample, the enhanced spin flip
scattering at low Q is reduced at 310K, and as temperature is reduced below
200K, it becomes negligibly low. The variation of radial correlation function,
g(r) with temperature indicates rapid suppression of ferromagnetic correlations
at the first nearest neighbor on approaching TN. Sample x = 0.4 exhibits growth
of ferromagnetic phase at intermediate temperatures (~ 200K). This has been
further explored using SANS and neutron depolarization techniques.Comment: 13 pages, 12 figures, To appear in Physical Review
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