6,138 research outputs found
A map-based place-browser for a PDA
This article describes PlaceBrowser, a PDA based application that allows the user of the application to navigate around an area of geographical interest, such as a city, using a zoomable, panable hierarchy of aerial images, in a fashion similar to Google Maps. The novel aspect to the work is that an area of precise interest within the map can be pin-pointed by the user by directly dragging out a rectangular area on the map. This forms the source to a spatial search that returns landmarks that are then used to trigger a Web based query. The results of this query are displayed to the user. The net effect is that, in response to dragging out a rectangular area, web pages that are relevant to this area but have not been explicitly geo-spatially tagged with metadata (longitude,latitude) are shown to the user
Sparse Stochastic Inference for Latent Dirichlet allocation
We present a hybrid algorithm for Bayesian topic models that combines the
efficiency of sparse Gibbs sampling with the scalability of online stochastic
inference. We used our algorithm to analyze a corpus of 1.2 million books (33
billion words) with thousands of topics. Our approach reduces the bias of
variational inference and generalizes to many Bayesian hidden-variable models.Comment: Appears in Proceedings of the 29th International Conference on
Machine Learning (ICML 2012
Properties of the Lindemann Mechanism in Phase Space
We study the planar and scalar reductions of the nonlinear Lindemann
mechanism of unimolecular decay. First, we establish that the origin, a
degenerate critical point, is globally asymptotically stable. Second, we prove
there is a unique scalar solution (the slow manifold) between the horizontal
and vertical isoclines. Third, we determine the concavity of all scalar
solutions in the nonnegative quadrant. Fourth, we establish that each scalar
solution is a centre manifold at the origin given by a Taylor series. Moreover,
we develop the leading-order behaviour of all planar solutions as time tends to
infinity. Finally, we determine the asymptotic behaviour of the slow manifold
at infinity by showing that it is a unique centre manifold for a fixed point at
infinity.Comment: 27 pages, 6 figure
Environmental statistics and optimal regulation
Any organism is embedded in an environment that changes over time. The
timescale for and statistics of environmental change, the precision with which
the organism can detect its environment, and the costs and benefits of
particular protein expression levels all will affect the suitability of
different strategies-such as constitutive expression or graded response-for
regulating protein levels in response to environmental inputs. We propose a
general framework-here specifically applied to the enzymatic regulation of
metabolism in response to changing concentrations of a basic nutrient-to
predict the optimal regulatory strategy given the statistics of fluctuations in
the environment and measurement apparatus, respectively, and the costs
associated with enzyme production. We use this framework to address three
fundamental questions: (i) when a cell should prefer thresholding to a graded
response; (ii) when there is a fitness advantage to implementing a Bayesian
decision rule; and (iii) when retaining memory of the past provides a selective
advantage. We specifically find that: (i) relative convexity of enzyme
expression cost and benefit influences the fitness of thresholding or graded
responses; (ii) intermediate levels of measurement uncertainty call for a
sophisticated Bayesian decision rule; and (iii) in dynamic contexts,
intermediate levels of uncertainty call for retaining memory of the past.
Statistical properties of the environment, such as variability and correlation
times, set optimal biochemical parameters, such as thresholds and decay rates
in signaling pathways. Our framework provides a theoretical basis for
interpreting molecular signal processing algorithms and a classification scheme
that organizes known regulatory strategies and may help conceptualize
heretofore unknown ones.Comment: 21 pages, 7 figure
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