3,111 research outputs found
Geometric analysis of noisy perturbations to nonholonomic constraints
We propose two types of stochastic extensions of nonholonomic constraints for
mechanical systems. Our approach relies on a stochastic extension of the
Lagrange-d'Alembert framework. We consider in details the case of invariant
nonholonomic systems on the group of rotations and on the special Euclidean
group. Based on this, we then develop two types of stochastic deformations of
the Suslov problem and study the possibility of extending to the stochastic
case the preservation of some of its integrals of motion such as the Kharlamova
or Clebsch-Tisserand integrals
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On the optimality of double-bracket flows
We analyze the optimality of the stable fixed point of the double-bracket equations. We introduce different types of optimality and prove local and global optimality results with respect to the Schattenp-norms.Peer Reviewe
Mechanical Systems with Symmetry, Variational Principles, and Integration Algorithms
This paper studies variational principles for mechanical systems with symmetry and their applications to integration algorithms. We recall some general features of how to reduce variational principles in the presence of a symmetry group along with general features of integration algorithms for mechanical systems. Then we describe some integration algorithms based directly on variational principles using a
discretization technique of Veselov. The general idea for these variational integrators is to directly discretize Hamilton’s principle rather than the equations of motion in a way that preserves the original systems invariants, notably the symplectic form and, via a discrete version of Noether’s theorem, the momentum map. The resulting mechanical integrators are second-order accurate, implicit, symplectic-momentum algorithms. We apply these integrators to the rigid body and the double spherical pendulum to show that the techniques are competitive with existing integrators
The Social and Political Dimensions of the Ebola Response: Global Inequality, Climate Change, and Infectious Disease
The 2014 Ebola crisis has highlighted public-health vulnerabilities in Liberia, Sierra
Leone, and Guinea – countries ravaged by extreme poverty, deforestation and
mining-related disruption of livelihoods and ecosystems, and bloody civil wars in
the cases of Liberia and Sierra Leone. Ebola’s emergence and impact are grounded
in the legacy of colonialism and its creation of enduring inequalities within African
nations and globally, via neoliberalism and the Washington Consensus. Recent
experiences with new and emerging diseases such as SARS and various strains of
HN influenzas have demonstrated the effectiveness of a coordinated local and
global public health and education-oriented response to contain epidemics. To what
extent is international assistance to fight Ebola strengthening local public health and
medical capacity in a sustainable way, so that other emerging disease threats, which
are accelerating with climate change, may be met successfully? This chapter
considers the wide-ranging socio-political, medical, legal and environmental factors
that have contributed to the rapid spread of Ebola, with particular emphasis on the
politics of the global and public health response and the role of gender, social
inequality, colonialism and racism as they relate to the mobilization and
establishment of the public health infrastructure required to combat Ebola and other
emerging diseases in times of climate change
The role of brand loyalty and social media in e-commerce interfaces: survey results and implications for user interfaces
This paper explores the role of brand loyalty and social media in e-commerce interfaces. A survey consisting of 118 respondents was contacted to address the questions relating to online shopping and brand loyalty. Link between the frequency of access and time spent on an e-commerce user interface, and brand loyalty, gender and age profile differences, and the role of social media to branding and on-line shopping was analyzed. It was found that online loyalty differs from offline loyalty and loyalty also differed across genders, showing men were more loyal than women when shopping online. Information shared about products on social media by friends and family played an important role in purchase decision making. Website interface and ease of navigation were also key aspects for online shopping. The research concluded with recommendations to create multimodal websites which are more interactive and targeted so customer experience is enhanced and loyalty is achieved through the use of interactivity and social media
Quantum States and Phases in Driven Open Quantum Systems with Cold Atoms
An open quantum system, whose time evolution is governed by a master
equation, can be driven into a given pure quantum state by an appropriate
design of the system-reservoir coupling. This points out a route towards
preparing many body states and non-equilibrium quantum phases by quantum
reservoir engineering. Here we discuss in detail the example of a \emph{driven
dissipative Bose Einstein Condensate} of bosons and of paired fermions, where
atoms in an optical lattice are coupled to a bath of Bogoliubov excitations via
the atomic current representing \emph{local dissipation}. In the absence of
interactions the lattice gas is driven into a pure state with long range order.
Weak interactions lead to a weakly mixed state, which in 3D can be understood
as a depletion of the condensate, and in 1D and 2D exhibits properties
reminiscent of a Luttinger liquid or a Kosterlitz-Thouless critical phase at
finite temperature, with the role of the ``finite temperature'' played by the
interactions.Comment: 9 pages, 2 figure
Level spacings for weakly asymmetric real random matrices and application to two-color QCD with chemical potential
We consider antisymmetric perturbations of real symmetric matrices in the
context of random matrix theory and two-color quantum chromodynamics. We
investigate the level spacing distributions of eigenvalues that remain real or
become complex conjugate pairs under the perturbation. We work out analytical
surmises from small matrices and show that they describe the level spacings of
large random matrices. As expected from symmetry arguments, these level
spacings also apply to the overlap Dirac operator for two-color QCD with
chemical potential.Comment: 23 pages, 6 figures, 1 animation; minor corrections, references
added, as published in JHE
The rolling problem: overview and challenges
In the present paper we give a historical account -ranging from classical to
modern results- of the problem of rolling two Riemannian manifolds one on the
other, with the restrictions that they cannot instantaneously slip or spin one
with respect to the other. On the way we show how this problem has profited
from the development of intrinsic Riemannian geometry, from geometric control
theory and sub-Riemannian geometry. We also mention how other areas -such as
robotics and interpolation theory- have employed the rolling model.Comment: 20 page
Exponential Random Graph Modeling for Complex Brain Networks
Exponential random graph models (ERGMs), also known as p* models, have been
utilized extensively in the social science literature to study complex networks
and how their global structure depends on underlying structural components.
However, the literature on their use in biological networks (especially brain
networks) has remained sparse. Descriptive models based on a specific feature
of the graph (clustering coefficient, degree distribution, etc.) have dominated
connectivity research in neuroscience. Corresponding generative models have
been developed to reproduce one of these features. However, the complexity
inherent in whole-brain network data necessitates the development and use of
tools that allow the systematic exploration of several features simultaneously
and how they interact to form the global network architecture. ERGMs provide a
statistically principled approach to the assessment of how a set of interacting
local brain network features gives rise to the global structure. We illustrate
the utility of ERGMs for modeling, analyzing, and simulating complex
whole-brain networks with network data from normal subjects. We also provide a
foundation for the selection of important local features through the
implementation and assessment of three selection approaches: a traditional
p-value based backward selection approach, an information criterion approach
(AIC), and a graphical goodness of fit (GOF) approach. The graphical GOF
approach serves as the best method given the scientific interest in being able
to capture and reproduce the structure of fitted brain networks
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