3,451 research outputs found
High-Dimensional Regression with Gaussian Mixtures and Partially-Latent Response Variables
In this work we address the problem of approximating high-dimensional data
with a low-dimensional representation. We make the following contributions. We
propose an inverse regression method which exchanges the roles of input and
response, such that the low-dimensional variable becomes the regressor, and
which is tractable. We introduce a mixture of locally-linear probabilistic
mapping model that starts with estimating the parameters of inverse regression,
and follows with inferring closed-form solutions for the forward parameters of
the high-dimensional regression problem of interest. Moreover, we introduce a
partially-latent paradigm, such that the vector-valued response variable is
composed of both observed and latent entries, thus being able to deal with data
contaminated by experimental artifacts that cannot be explained with noise
models. The proposed probabilistic formulation could be viewed as a
latent-variable augmentation of regression. We devise expectation-maximization
(EM) procedures based on a data augmentation strategy which facilitates the
maximum-likelihood search over the model parameters. We propose two
augmentation schemes and we describe in detail the associated EM inference
procedures that may well be viewed as generalizations of a number of EM
regression, dimension reduction, and factor analysis algorithms. The proposed
framework is validated with both synthetic and real data. We provide
experimental evidence that our method outperforms several existing regression
techniques
Hadronization revisited : the dynamics behind hadro-chemical equilibrium
The multiplicity of hadronic species created in elementary, and in nucleus-nucleus collisions, are known to be well reproduced by the statistical hadronization model, in its canonical and grand-canonical versions.To understand the origin of the implied equilibrium we revisit the hadronization models developed for e+e- annihilation to hadrons which imply spatial color pre-confinement clusters forming at the end of the pQCD evolution, which decays into on-shell hadrons/resonances. The classical ensemble description arises as a consequence of decoherence and phase space dominance during cluster formation, and decay.For A+A collisions we assume that hadronization occurs from similar singlet clusters which will overlap spatially owing to the extreme density. This is imaged in the transition to the grand-canonical ensemble.This transition sets in with increasing A and collision centrality. It can be described by a percolation model
Automatic vehicle monitoring systems study. Report of phase O. Volume 2: Problem definition and derivation of AVM system selection techniques
A set of planning guidelines is presented to help law enforcement agencies and vehicle fleet operators decide which automatic vehicle monitoring (AVM) system could best meet their performance requirements. Improvements in emergency response times and resultant cost benefits obtainable with various operational and planned AVM systems may be synthesized and simulated by means of special computer programs for model city parameters applicable to small, medium and large urban areas. Design characteristics of various AVM systems and the implementation requirements are illustrated and cost estimated for the vehicles, the fixed sites and the base equipments. Vehicle location accuracies for different RF links and polling intervals are analyzed. Actual applications and coverage data are tabulated for seven cities whose police departments actively cooperated in the study
Properties of quasi-relaxed stellar systems in an external tidal field
In a previous paper, we have constructed a family of self-consistent triaxial
models of quasi-relaxed stellar systems, shaped by the tidal field of the
hosting galaxy, as an extension of the well-known spherical King models. For a
given tidal field, the models are characterized by two physical scales (such as
total mass and central velocity dispersion) and two dimensionless parameters
(the concentration parameter and the tidal strength). The most significant
departure from spherical symmetry occurs when the truncation radius of the
corresponding spherical King model is of the order of the tidal radius, which,
for a given tidal strength, is set by the maximum concentration value admitted.
For such maximally extended (or "critical") models the outer boundary has a
generally triaxial shape, given by the zero-velocity surface of the relevant
Jacobi integral, which is basically independent of the concentration parameter.
In turn, the external tidal field can give rise to significant global
departures from spherical symmetry (as measured, for example, by the quadrupole
of the mass distribution of the stellar system) only for low-concentration
models, for which the allowed maximal value of the tidal strength can be
relatively high. In this paper we describe in detail the intrinsic and the
projected structure and kinematics of the models, covering the entire parameter
space, from the case of sub-critical (characterized by "underfilling" of the
relevant Roche volume) to that of critical models. The intrinsic properties can
be a useful starting point for numerical simulations and other investigations
that require initialization of a stellar system in dynamical equilibrium. The
projected properties are a key step in the direction of a comparison with
observed globular clusters and other candidate stellar systems.Comment: 13 pages, 11 figures, uses emulateapj.cls with apjfonts.sty. Accepted
for publication in The Astrophysical Journa
Using GPS bistatic signal for land and ocean remote sensing in South Africa
Includes bibliographical references (leaves 73-77).This project discusses the basic principles and theory of this new technology, and concentrates on reflection points and Fresnel zones. The CPS receivers are placed at different coastal regions within South Africa, and the simulation of the reflection points and Fresnel zones are observed as the CPS satellites pass over South Africa. The East London area was chosen as the location to place the receiver throughout my analysis
A users guide for A344: A program using a finite difference method to analyze transonic flow over oscillating airfoils
The design and usage of a pilot program for calculating the pressure distributions over harmonically oscillating airfoils in transonic flow are described. The procedure used is based on separating the velocity potential into steady and unsteady parts and linearizing the resulting unsteady differential equations for small disturbances. The steady velocity potential which must be obtained from some other program, was required for input. The unsteady equation, as solved, is linear with spatially varying coefficients. Since sinusoidal motion was assumed, time was not a variable. The numerical solution was obtained through a finite difference formulation and either a line relaxation or an out of core direct solution method
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