9,968 research outputs found
Kinematic Equations for Front Motion and Spiral-Wave Nucleation
We present a new set of kinematic equations for front motion in bistable
media. The equations extend earlier kinematic approaches by coupling the front
curvature with the order parameter associated with a parity breaking front
bifurcation. In addition to naturally describing the core region of rotating
spiral waves the equations can be be used to study the nucleation of
spiral-wave pairs along uniformly propagating fronts. The analysis of
spiral-wave nucleation reduces to the simpler problem of droplet, or domain,
nucleation in one space dimension.Comment: 8 pages. Aric Hagberg: http://cnls.lanl.gov/~aric; Ehud Meron:
http://www.bgu.ac.il/BIDR/research/staff/meron.htm
Rett Syndrome: Revised diagnostic criteria and nomenclature
Objective: Rett syndrome (RTT) is a severe neurodevelopmental disease that affects approximately 1 in 10,000 live female births and is often caused by mutations in Methyl-CpG-binding protein 2 (MECP2). Despite distinct clinical features, the accumulation of clinical and molecular information in recent years has generated considerable confusion regarding the diagnosis of RTT. The purpose of this work was to revise and clarify 2002 consensus criteria for the diagnosis of RTT in anticipation of treatment trials. Method: RettSearch members, representing the majority of the international clinical RTT specialists, participated in an iterative process to come to a consensus on a revised and simplified clinical diagnostic criteria for RTT. Results: The clinical criteria required for the diagnosis of classic and atypical RTT were clarified and simplified. Guidelines for the diagnosis and molecular evaluation of specific variant forms of RTT were developed. Interpretation These revised criteria provide clarity regarding the key features required for the diagnosis of RTT and reinforce the concept that RTT is a clinical diagnosis based on distinct clinical criteria, independent of molecular findings. We recommend that these criteria and guidelines be utilized in any proposed clinical research
Order Parameter Equations for Front Transitions: Nonuniformly Curved Fronts
Kinematic equations for the motion of slowly propagating, weakly curved
fronts in bistable media are derived. The equations generalize earlier
derivations where algebraic relations between the normal front velocity and its
curvature are assumed. Such relations do not capture the dynamics near
nonequilibrium Ising-Bloch (NIB) bifurcations, where transitions between
counterpropagating Bloch fronts may spontaneously occur. The kinematic
equations consist of coupled integro-differential equations for the front
curvature and the front velocity, the order parameter associated with the NIB
bifurcation. They capture the NIB bifurcation, the instabilities of Ising and
Bloch fronts to transverse perturbations, the core structure of a spiral wave,
and the dynamic process of spiral wave nucleation.Comment: 20 pages. Aric Hagberg: http://cnls.lanl.gov/~aric; Ehud
Meron:http://www.bgu.ac.il/BIDR/research/staff/meron.htm
Stratified spatiotemporal chaos in anisotropic reaction-diffusion systems
Numerical simulations of two dimensional pattern formation in an anisotropic
bistable reaction-diffusion medium reveal a new dynamical state, stratified
spatiotemporal chaos, characterized by strong correlations along one of the
principal axes. Equations that describe the dependence of front motion on the
angle illustrate the mechanism leading to stratified chaos
Subversion of host innate immunity by uropathogenic Escherichia coli
Uropathogenic Escherichia coli (UPEC) cause the majority of community-onset urinary tract infections (UTI) and represent a major etiologic agent of healthcare-associated UTI. Introduction of UPEC into the mammalian urinary tract evokes a well-described inflammatory response, comprising pro-inflammatory cytokines and chemokines as well as cellular elements (neutrophils and macrophages). In human UTI, this inflammatory response contributes to symptomatology and provides means for diagnosis by standard clinical testing. Early in acute cystitis, as demonstrated in murine models, UPEC gains access to an intracellular niche that protects a population of replicating bacteria from arriving phagocytes. To ensure the establishment of this protected niche, UPEC employ multiple strategies to attenuate and delay the initiation of host inflammatory components, including epithelial secretion of chemoattractants. Recent work has also revealed novel mechanisms by which UPEC blunts neutrophil migration across infected uroepithelium. Taken together, these attributes distinguish UPEC from commensal and nonpathogenic E. coli strains. This review highlights the unique immune evasion and suppression strategies of this bacterial pathogen and offers directions for further study; molecular understanding of these mechanisms will inform the development of adjunctive, anti-virulence therapeutics for UTI
Optimal Interdiction of Unreactive Markovian Evaders
The interdiction problem arises in a variety of areas including military
logistics, infectious disease control, and counter-terrorism. In the typical
formulation of network interdiction, the task of the interdictor is to find a
set of edges in a weighted network such that the removal of those edges would
maximally increase the cost to an evader of traveling on a path through the
network.
Our work is motivated by cases in which the evader has incomplete information
about the network or lacks planning time or computational power, e.g. when
authorities set up roadblocks to catch bank robbers, the criminals do not know
all the roadblock locations or the best path to use for their escape.
We introduce a model of network interdiction in which the motion of one or
more evaders is described by Markov processes and the evaders are assumed not
to react to interdiction decisions. The interdiction objective is to find an
edge set of size B, that maximizes the probability of capturing the evaders.
We prove that similar to the standard least-cost formulation for
deterministic motion this interdiction problem is also NP-hard. But unlike that
problem our interdiction problem is submodular and the optimal solution can be
approximated within 1-1/e using a greedy algorithm. Additionally, we exploit
submodularity through a priority evaluation strategy that eliminates the linear
complexity scaling in the number of network edges and speeds up the solution by
orders of magnitude. Taken together the results bring closer the goal of
finding realistic solutions to the interdiction problem on global-scale
networks.Comment: Accepted at the Sixth International Conference on integration of AI
and OR Techniques in Constraint Programming for Combinatorial Optimization
Problems (CPAIOR 2009
Dynamic Front Transitions and Spiral-Vortex Nucleation
This is a study of front dynamics in reaction diffusion systems near
Nonequilibrium Ising-Bloch bifurcations. We find that the relation between
front velocity and perturbative factors, such as external fields and curvature,
is typically multivalued. This unusual form allows small perturbations to
induce dynamic transitions between counter-propagating fronts and nucleate
spiral vortices. We use these findings to propose explanations for a few
numerical and experimental observations including spiral breakup driven by
advective fields, and spot splitting
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