239 research outputs found
Solving non-uniqueness in agglomerative hierarchical clustering using multidendrograms
In agglomerative hierarchical clustering, pair-group methods suffer from a
problem of non-uniqueness when two or more distances between different clusters
coincide during the amalgamation process. The traditional approach for solving
this drawback has been to take any arbitrary criterion in order to break ties
between distances, which results in different hierarchical classifications
depending on the criterion followed. In this article we propose a
variable-group algorithm that consists in grouping more than two clusters at
the same time when ties occur. We give a tree representation for the results of
the algorithm, which we call a multidendrogram, as well as a generalization of
the Lance and Williams' formula which enables the implementation of the
algorithm in a recursive way.Comment: Free Software for Agglomerative Hierarchical Clustering using
Multidendrograms available at
http://deim.urv.cat/~sgomez/multidendrograms.ph
Variability of behaviour in electricity load profile clustering: who does things at the same time each day?
UK electricity market changes provide opportunities to alter
households' electricity usage patterns for the benet of the overall electricity network. Work on clustering similar households has concentrated on daily load proles and the variability in regular household behaviours has not been considered. Those households with most variability in reg-
ular activities may be the most receptive to incentives to change timing. Whether using the variability of regular behaviour allows the creation of more consistent groupings of households is investigated and compared with daily load prole clustering. 204 UK households are analysed to nd
repeating patterns (motifs). Variability in the time of the motif is used as the basis for clustering households. Dierent clustering algorithms are assessed by the consistency of the results.
Findings show that variability of behaviour, using motifs, provides more consistent groupings of households across dierent clustering algorithms and allows for more ecient targeting of behaviour change interventions
Unsupervised classemes
The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-642-33885-4_41Proceedings of Information Fusion in Computer Vision for Concept Recognition at the ECCV 2012In this paper we present a new model of semantic features that, unlike previously presented methods, does not rely on the presence of a labeled training data base, as the creation of the feature extraction function is done in an unsupervised manner.
We test these features on an unsupervised classification (clustering) task, and show that they outperform primitive (low-level) features, and that have performance comparable to that of supervised semantic features, which are much more expensive to determine relying on the presence of a labeled training set to train the feature extraction function
Fuzzy Sphere Dynamics and Non-Abelian DBI in Curved Backgrounds
We consider the non-Abelian action for the dynamics of -branes in the
background of -branes, which parameterises a fuzzy sphere using the SU(2)
algebra. We find that the curved background leads to collapsing solutions for
the fuzzy sphere except when we have branes in the background, which
is a realisation of the gravitational Myers effect. Furthermore we find the
equations of motion in the Abelian and non-Abelian theories are identical in
the large limit. By picking a specific ansatz we find that we can
incorporate angular momentum into the action, although this imposes restriction
upon the dimensionality of the background solutions. We also consider the case
of non-Abelian non-BPS branes, and examine the resultant dynamics using
world-volume symmetry transformations. We find that the fuzzy sphere always
collapses but the solutions are sensitive to the combination of the two
conserved charges and we can find expanding solutions with turning points. We
go on to consider the coincident 5-brane background, and again construct
the non-Abelian theory for both BPS and non-BPS branes. In the latter case we
must use symmetry arguments to find additional conserved charges on the
world-volumes to solve the equations of motion. We find that in the Non-BPS
case there is a turning solution for specific regions of the tachyon and radion
fields. Finally we investigate the more general dynamics of fuzzy
in the -brane background, and find collapsing solutions
in all cases.Comment: 49 pages, 3 figures, Latex; Version to appear in JHE
A series of algebras generalizing the octonions and Hurwitz-Radon identity
International audienceWe study non-associative twisted group algebras over (ℤ2)n with cubic twisting functions. We construct a series of algebras that extend the classical algebra of octonions in the same way as the Clifford algebras extend the algebra of quaternions. We study their properties, give several equivalent definitions and prove their uniqueness within some natural assumptions. We then prove a simplicity criterion. We present two applications of the constructed algebras and the developed technique. The first application is a simple explicit formula for the following famous square identity: (a21+⋯+a2N)(b21+⋯+b2ρ(N))=c21+⋯+c2N , where c k are bilinear functions of the a i and b j and where ρ(N) is the Hurwitz-Radon function. The second application is the relation to Moufang loops and, in particular, to the code loops. To illustrate this relation, we provide an explicit coordinate formula for the factor set of the Parker loop
An Integrated Modeling Approach for Predicting Process Maps of Residual Stress and Distortion in a Laser Weld: A Combined CFD–FE Methodology
Laser welding has become an important joining methodology within a number of industries for the structural joining of metallic parts. It offers a high power density welding capability which is desirable for deep weld sections, but is equally suited to performing thinner welded joints with sensible amendments to key process variables. However, as with any welding process, the introduction of severe thermal gradients at the weld line will inevitably lead to process-induced residual stress formation and distortions. Finite element (FE) predictions for weld simulation have been made within academia and industrial research for a number of years, although given the fluid nature of the molten weld pool, FE methodologies have limited capabilities. An improvement upon this established method would be to incorporate a computational fluid dynamics (CFD) model formulation prior to the FE model, to predict the weld pool shape and fluid flow, such that details can be fed into FE from CFD as a starting condition. The key outputs of residual stress and distortions predicted by the FE model can then be monitored against the process variables input to the model. Further, a link between the thermal results and the microstructural properties is of interest. Therefore, an empirical relationship between lamellar spacing and the cooling rate was developed and used to make predictions about the lamellar spacing for welds of different process parameters. Processing parameter combinations that lead to regions of high residual stress formation and high distortion have been determined, and the impact of processing parameters upon the predicted lamellar spacing has been presented
Pion, kaon, proton and anti-proton transverse momentum distributions from p+p and d+Au collisions at GeV
Identified mid-rapidity particle spectra of , , and
from 200 GeV p+p and d+Au collisions are reported. A
time-of-flight detector based on multi-gap resistive plate chamber technology
is used for particle identification. The particle-species dependence of the
Cronin effect is observed to be significantly smaller than that at lower
energies. The ratio of the nuclear modification factor () between
protons and charged hadrons () in the transverse momentum
range GeV/c is measured to be
(stat)(syst) in minimum-bias collisions and shows little
centrality dependence. The yield ratio of in minimum-bias d+Au
collisions is found to be a factor of 2 lower than that in Au+Au collisions,
indicating that the Cronin effect alone is not enough to account for the
relative baryon enhancement observed in heavy ion collisions at RHIC.Comment: 6 pages, 4 figures, 1 table. We extended the pion spectra from
transverse momentum 1.8 GeV/c to 3. GeV/
Demonstration of the temporal matter-wave Talbot effect for trapped matter waves
We demonstrate the temporal Talbot effect for trapped matter waves using
ultracold atoms in an optical lattice. We investigate the phase evolution of an
array of essentially non-interacting matter waves and observe matter-wave
collapse and revival in the form of a Talbot interference pattern. By using
long expansion times, we image momentum space with sub-recoil resolution,
allowing us to observe fractional Talbot fringes up to 10th order.Comment: 17 pages, 7 figure
Características morfológicas, físicas e químicas de frutos de populações de umbu-cajazeira no Estado da Bahia
Azimuthal anisotropy and correlations in p+p, d+Au and Au+Au collisions at 200 GeV
We present the first measurement of directed flow () at RHIC. is
found to be consistent with zero at pseudorapidities from -1.2 to 1.2,
then rises to the level of a couple of percent over the range . The latter observation is similar to data from NA49 if the SPS rapidities
are shifted by the difference in beam rapidity between RHIC and SPS.
Back-to-back jets emitted out-of-plane are found to be suppressed more if
compared to those emitted in-plane, which is consistent with {\it jet
quenching}. Using the scalar product method, we systematically compared
azimuthal correlations from p+p, d+Au and Au+Au collisions. Flow and non-flow
from these three different collision systems are discussed.Comment: Quark Matter 2004 proceeding, 4 pages, 3 figure
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