1,030,946 research outputs found
A Selection Criterion for Patterns in Reaction-Diffusion Systems
Alan Turing's work in Morphogenesis has received wide attention during the
past 60 years. The central idea behind his theory is that two chemically
interacting diffusible substances are able to generate stable spatial patterns,
provided certain conditions are met. Turing's proposal has already been
confirmed as a pattern formation mechanism in several chemical and biological
systems and, due to their wide applicability, there is a great deal of interest
in deciphering how to generate specific patterns under controlled conditions.
However, techniques allowing one to predict what kind of spatial structure will
emerge from Turing systems, as well as generalized reaction-diffusion systems,
remain unknown. Here, we consider a generalized reaction diffusion system on a
planar domain and provide an analytic criterion to determine whether spots or
stripes will be formed. It is motivated by the existence of an associated
energy function that allows bringing in the intuition provided by phase
transitions phenomena. This criterion is proved rigorously in some situations,
generalizing well known results for the scalar equation where the pattern
selection process can be understood in terms of a potential. In more complex
settings it is investigated numerically. Our criterion can be applied to
efficiently design Biotechnology and Developmental Biology experiments, or
simplify the analysis of hypothesized morphogenetic models.Comment: 19 pages, 10 figure
Microscopic Selection of Fluid Fingering Pattern
We study the issue of the selection of viscous fingering patterns in the
limit of small surface tension. Through detailed simulations of anisotropic
fingering, we demonstrate conclusively that no selection independent of the
small-scale cutoff (macroscopic selection) occurs in this system. Rather, the
small-scale cutoff completely controls the pattern, even on short time scales,
in accord with the theory of microscopic solvability. We demonstrate that
ordered patterns are dynamically selected only for not too small surface
tensions. For extremely small surface tensions, the system exhibits chaotic
behavior and no regular pattern is realized.Comment: 6 pages, 5 figure
Kanerva's sparse distributed memory with multiple hamming thresholds
If the stored input patterns of Kanerva's Sparse Distributed Memory (SDM) are highly correlated, utilization of the storage capacity is very low compared to the case of uniformly distributed random input patterns. We consider a variation of SDM that has a better storage capacity utilization for correlated input patterns. This approach uses a separate selection threshold for each physical storage address or hard location. The selection of the hard locations for reading or writing can be done in parallel of which SDM implementations can benefit
Coalescence, genetic diversity in sexual populations under selection
In sexual populations, selection operates neither on the whole genome, which
is repeatedly taken apart and reassembled by recombination, nor on individual
alleles that are tightly linked to the chromosomal neighborhood. The resulting
interference between linked alleles reduces the efficiency of selection and
distorts patterns of genetic diversity. Inference of evolutionary history from
diversity shaped by linked selection requires an understanding of these
patterns. Here, we present a simple but powerful scaling analysis identifying
the unit of selection as the genomic "linkage block" with a characteristic
length determined in a self-consistent manner by the condition that the rate of
recombination within the block is comparable to the fitness differences between
different alleles of the block. We find that an asexual model with the strength
of selection tuned to that of the linkage block provides an excellent
description of genetic diversity and the site frequency spectra when compared
to computer simulations. This linkage block approximation is accurate for the
entire spectrum of strength of selection and is particularly powerful in
scenarios with many weakly selected loci. The latter limit allows us to
characterize coalescence, genetic diversity, and the speed of adaptation in the
infinitesimal model of quantitative genetics
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Consumer decision making in mobile-banking service selection
This paper reports on the findings of a study of 267 consumers on the first order selection criteria within a decision making model that utilizes the Analytic Hierarchy Process (AHP) to evaluate mobile banking service selection. The AHP analysis of the first order selection criteria for the full data sample identified ‘Time Saving’ as the highest ranked factor followed by ‘Control’ then ‘Any Place’ and lastly ‘Cost’. The survey also reports on consumer usage patterns for internet and mobile services as well as exploring their experiences with mobile banking services
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