11,050 research outputs found
Pastoral women’s rights and leadership forums, Tanzania: Experience, impact and lessons learned
The supervised hierarchical Dirichlet process
We propose the supervised hierarchical Dirichlet process (sHDP), a
nonparametric generative model for the joint distribution of a group of
observations and a response variable directly associated with that whole group.
We compare the sHDP with another leading method for regression on grouped data,
the supervised latent Dirichlet allocation (sLDA) model. We evaluate our method
on two real-world classification problems and two real-world regression
problems. Bayesian nonparametric regression models based on the Dirichlet
process, such as the Dirichlet process-generalised linear models (DP-GLM) have
previously been explored; these models allow flexibility in modelling nonlinear
relationships. However, until now, Hierarchical Dirichlet Process (HDP)
mixtures have not seen significant use in supervised problems with grouped data
since a straightforward application of the HDP on the grouped data results in
learnt clusters that are not predictive of the responses. The sHDP solves this
problem by allowing for clusters to be learnt jointly from the group structure
and from the label assigned to each group.Comment: 14 page
Entropy production for coarse-grained dynamics
Systems out of equilibrium exhibit a net production of entropy. We study the
dynamics of a stochastic system represented by a Master Equation that can be
modeled by a Fokker-Planck equation in a coarse-grained, mesoscopic
description. We show that the corresponding coarse-grained entropy production
contains information on microscopic currents that are not captured by the
Fokker-Planck equation and thus cannot be deduced from it. We study a
discrete-state and a continuous-state system, deriving in both the cases an
analytical expression for the coarse-graining corrections to the entropy
production. This result elucidates the limits in which there is no loss of
information in passing from a Master Equation to a Fokker-Planck equation
describing the same system. Our results are amenable of experimental
verification, which could help to infer some information about the underlying
microscopic processes
Flory theory for Polymers
We review various simple analytical theories for homopolymers within a
unified framework. The common guideline of our approach is the Flory theory,
and its various avatars, with the attempt of being reasonably self-contained.
We expect this review to be useful as an introduction to the topic at the
graduate students level.Comment: Topical review appeared J. Phys.: Condens. Matter, 46 pages, 8
Figures. Sec. VIF added. Typos fixed. Few references adde
A Simplified Mathematical Model for the Formation of Null Singularities Inside Black Holes I - Basic Formulation and a Conjecture
Einstein's equations are known to lead to the formation of black holes and
spacetime singularities. This appears to be a manifestation of the mathematical
phenomenon of finite-time blowup: a formation of singularities from regular
initial data. We present a simple hyperbolic system of two semi-linear
equations inspired by the Einstein equations. We explore a class of solutions
to this system which are analogous to static black-hole models. These solutions
exhibit a black-hole structure with a finite-time blowup on a characteristic
line mimicking the null inner horizon of spinning or charged black holes. We
conjecture that this behavior - namely black-hole formation with blow-up on a
characteristic line - is a generic feature of our semi-linear system. Our
simple system may provide insight into the formation of null singularities
inside spinning or charged black holes in the full system of Einstein
equations.Comment: 39 pages, 3 figures, extended versio
Zenithal bistable device: comparison of modeling and experiment
A comparative modeling and experimental study of the zenithal bistable liquid crystal device is presented. A dynamic Landau de Gennes theory of nematic liquid crystals is solved numerically to model the electric field induced latching of the device and the results are compared with experimental measurements and theoretical approximations. The study gives a clear insight into the latching mechanism dynamics and enables the dependence of the device latching on both material parameters and surface shape to be determined. Analytical approximation highlights a route to optimize material selection in terms of latching voltages and the numerical model, which includes an accurate surface representation, recovers the complex surface shape effects. Predictions of device performance are presented as a function of both surface anchoring strength and surface shape and grating pitch. A measurement of the homeotropic anchoring energy has been undertaken by comparing the voltage response as a function of cell gap; we find the homeotropic anchoring energies can be varied in the range 0.5 to 4 (10-44 J m-2)
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