91,948 research outputs found
Cosmic void exclusion models and their impact on the distance scale measurements from large scale structure
Baryonic Acoustic Oscillations (BAOs) studies based on the clustering of
voids and matter tracers provide important constraints on cosmological
parameters related to the expansion of the Universe. However, modelling the
void exclusion effect is an important challenge for fully exploiting the
potential of these kind of analyses. We thus develop two numerical methods to
describe the clustering of cosmic voids. Neither model requires additional
cosmological information beyond that assumed within the galaxy de-wiggled
model. The models consist in power spectra whose performance we assess in
comparison to a parabolic model on both Patchy boxes and light-cones. Moreover,
we test their robustness against systematic effects and the reconstruction
technique. The void model power spectra and the parabolic model with a fixed
parameter provide strongly correlated values for the Alcock-Paczynski
() parameter, for boxes and light-cones likewise. The resulting
values - for all three models - are unbiased and their uncertainties
are correctly estimated. However, the numerical models show less variation with
the fitting range compared to the parabolic one. The Bayesian evidence suggests
that the numerical techniques are often favoured compared to the parabolic
model. Moreover, the void model power spectra computed on boxes can describe
the void clustering from light-cones as well as from boxes. The same void model
power spectra can be used for the study of pre- and post-reconstructed
data-sets. Lastly, the two numerical techniques are resilient against the
studied systematic effects. Consequently, using either of the two new void
models, one can more robustly measure cosmological parameters.Comment: 18 pages, 24 figure
Two Algorithms for Orthogonal Nonnegative Matrix Factorization with Application to Clustering
Approximate matrix factorization techniques with both nonnegativity and
orthogonality constraints, referred to as orthogonal nonnegative matrix
factorization (ONMF), have been recently introduced and shown to work
remarkably well for clustering tasks such as document classification. In this
paper, we introduce two new methods to solve ONMF. First, we show athematical
equivalence between ONMF and a weighted variant of spherical k-means, from
which we derive our first method, a simple EM-like algorithm. This also allows
us to determine when ONMF should be preferred to k-means and spherical k-means.
Our second method is based on an augmented Lagrangian approach. Standard ONMF
algorithms typically enforce nonnegativity for their iterates while trying to
achieve orthogonality at the limit (e.g., using a proper penalization term or a
suitably chosen search direction). Our method works the opposite way:
orthogonality is strictly imposed at each step while nonnegativity is
asymptotically obtained, using a quadratic penalty. Finally, we show that the
two proposed approaches compare favorably with standard ONMF algorithms on
synthetic, text and image data sets.Comment: 17 pages, 8 figures. New numerical experiments (document and
synthetic data sets
A General Spatio-Temporal Clustering-Based Non-local Formulation for Multiscale Modeling of Compartmentalized Reservoirs
Representing the reservoir as a network of discrete compartments with
neighbor and non-neighbor connections is a fast, yet accurate method for
analyzing oil and gas reservoirs. Automatic and rapid detection of coarse-scale
compartments with distinct static and dynamic properties is an integral part of
such high-level reservoir analysis. In this work, we present a hybrid framework
specific to reservoir analysis for an automatic detection of clusters in space
using spatial and temporal field data, coupled with a physics-based multiscale
modeling approach. In this work a novel hybrid approach is presented in which
we couple a physics-based non-local modeling framework with data-driven
clustering techniques to provide a fast and accurate multiscale modeling of
compartmentalized reservoirs. This research also adds to the literature by
presenting a comprehensive work on spatio-temporal clustering for reservoir
studies applications that well considers the clustering complexities, the
intrinsic sparse and noisy nature of the data, and the interpretability of the
outcome.
Keywords: Artificial Intelligence; Machine Learning; Spatio-Temporal
Clustering; Physics-Based Data-Driven Formulation; Multiscale Modelin
Appointment scheduling model in healthcare using clustering algorithms
In this study we provided a scheduling procedure which is combination of
machine learning and mathematical programming. Outpatients who request for
appointment in healthcare facilities have different priorities. Determining the
priority of outpatients and allocating the capacity based on the priority
classes are important concepts that have to be considered in scheduling of
outpatients. Two stages are defined for scheduling an incoming patient. In the
first stage, We applied and compared different clustering methods such as
k-mean clustering and agglomerative hierarchical clustering methods to classify
outpatients into priority classes and suggested the best pattern to cluster the
outpatients. In the second stage, we modeled the scheduling problem as a Markov
Decision Process (MDP) problem that aims to decrease waiting time of higher
priority outpatients. Due to the curse of dimensionality, we used fluid
approximation method to estimate the optimal solution of the MDP. We applied
our methodology on a dataset of Shaheed Rajaei Medical and Research Center in
Iran, and we showed how our models work in prioritizing and scheduling of
outpatients
Linear Precoding in Cooperative MIMO Cellular Networks with Limited Coordination Clusters
In a cooperative multiple-antenna downlink cellular network, maximization of
a concave function of user rates is considered. A new linear precoding
technique called soft interference nulling (SIN) is proposed, which performs at
least as well as zero-forcing (ZF) beamforming. All base stations share channel
state information, but each user's message is only routed to those that
participate in the user's coordination cluster. SIN precoding is particularly
useful when clusters of limited sizes overlap in the network, in which case
traditional techniques such as dirty paper coding or ZF do not directly apply.
The SIN precoder is computed by solving a sequence of convex optimization
problems. SIN under partial network coordination can outperform ZF under full
network coordination at moderate SNRs. Under overlapping coordination clusters,
SIN precoding achieves considerably higher throughput compared to myopic ZF,
especially when the clusters are large.Comment: 13 pages, 5 figure
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