96 research outputs found
Complex patterns of spontaneous initiations and terminations of reentrant circulation in a loop of cardiac tissue
A two-component model is developed that consists of a discrete loop of
cardiac cells that circulates action potentials together with a cardiac pacing
mechanism. Physiological properties of cells such as restitutions of
refractoriness and of conduction velocity are given via experimentally measured
functions. The dynamics of circulating pulses and their interactions with the
pacer are regulated by two threshold relations. Patterns of spontaneous
initiations and terminations of reentry (SITR) generated by this system are
studied through numerical simulations and analytical observations. These
patterns can be regular or irregular; causes of irregularities are identified
as the threshold bistability of reentrant circulation (T-bistability) and in
some cases, also phase-resetting interactions with the pacer.Comment: 27 pages, 10 figures, 61 references; A version of this paper (same
results) is to appear in the Journal of Theoretical Biology; arXiv V2 adds
helpful commments to facilitate reading and corrects minor errors in
presentatio
Numerical verification of universality for the Anderson transition
We analyze the scaling behavior of the higher Lyapunov exponents at the
Anderson transition. We estimate the critical exponent and verify its
universality and that of the critical conductance distribution for box,
Gaussian and Lorentzian distributions of the random potential
Ecological Invasion, Roughened Fronts, and a Competitor's Extreme Advance: Integrating Stochastic Spatial-Growth Models
Both community ecology and conservation biology seek further understanding of
factors governing the advance of an invasive species. We model biological
invasion as an individual-based, stochastic process on a two-dimensional
landscape. An ecologically superior invader and a resident species compete for
space preemptively. Our general model includes the basic contact process and a
variant of the Eden model as special cases. We employ the concept of a
"roughened" front to quantify effects of discreteness and stochasticity on
invasion; we emphasize the probability distribution of the front-runner's
relative position. That is, we analyze the location of the most advanced
invader as the extreme deviation about the front's mean position. We find that
a class of models with different assumptions about neighborhood interactions
exhibit universal characteristics. That is, key features of the invasion
dynamics span a class of models, independently of locally detailed demographic
rules. Our results integrate theories of invasive spatial growth and generate
novel hypotheses linking habitat or landscape size (length of the invading
front) to invasion velocity, and to the relative position of the most advanced
invader.Comment: The original publication is available at
www.springerlink.com/content/8528v8563r7u2742
‘Filip’ or flop? Managing public relations and the Latin American reaction to the 1966 FIFA World Cup
The 1966 FIFA World Cup has become part of the iconography of its hosts and champions, England. Extant literature has tended to focus on the cultural and symbolic legacy of the tournament, or engaged with diplomatic relations between Britain and North Korea. Contrastingly, we use archival sources from footballing and government institutions to explore the less studied topic of how the tournament was reported and perceived in Latin America, where England had commercial interests and influence, but where there were allegations that FIFA, the FA and even the UK government manipulated the tournament to the advantage of England and other European teams. We provide fresh perspectives on the social and cultural significance of the 1966 FIFA World Cup by analysing how the tournament’s organizers attempted to manage the situation and resulting negative public relations, and how 1966 fits within longer-term footballing and diplomatic relations between England and Latin America
First-principles characterization of a heteroceramic interface: ZrO2(001) deposited on an alpha-Al2O3(1(1)over-bar02) substrate
Uso do plasma suíno ultrafiltrado na recuperação de leitões com sinais clínicos de circovirose
Uso de plasma suíno desidratado por Spray-Dryer na dieta de leitões desmamados precocemente
Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents
Life-form spectra of quartzite and itabirite rocky outcrop sites, Minas Gerais, Brazil
Automatic presentations and semigroup constructions
An automatic presentation for a relational structure is, informally, an abstract representation of the elements of that structure by means of a regular language such that the relations can all be recognized by finite automata. A structure admitting an automatic presentation is said to be FA-presentable. This paper studies the interaction of automatic presentations and certain semigroup constructions, namely: direct products, free products, finite Rees index extensions and subsemigroups, strong semilattices of semigroups, Rees matrix semigroups, Bruck-Reilly extensions, zero-direct unions, semidirect products, wreath products, ideals, and quotient semigroups. For each case, the closure of the class of FA-presentable semigroups under that construction is considered, as is the question of whether the FA-presentability of the semigroup obtained from such a construction implies the FA-presentability of the original semigroup[s]. Classifications are also given of the FA-presentable finitely generated Clifford semigroups, completely simple semigroups, and completely 0-simple semigroups.PostprintPeer reviewe
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