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MR Evans

Publications and source records attributed to MR Evans.

7 recordsLinked to original sources
PubMed2000

Stochastic ballistic annihilation and coalescence

We study a class of stochastic ballistic annihilation and coalescence models with a binary velocity distribution in one dimension. We obtain an exact solution for the density which reveals a universal phase diagram for the asymptotic density decay. By universal we mean that all models in the class are described by a single phase diagram spanned by two reduced parameters. The phase diagram reveals four regimes, two of which contain the previously studied cases of ballistic annihilation. The two new phases are a direct consequence of the stochasticity. The solution is obtained through a matrix product approach and builds on properties of a q-deformed harmonic oscillator algebra.

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PubMed2000

Male wrens with large testes breed early.

To display to females, male wrens, Troglodytes troglodytes, use cock nests built on their territories. Nest building starts about a month before the first females begin egg laying. The timing of nest building is highly variable between males with up to 8 weeks separating the earliest from the latest males to initiate this display activity. Males that weigh more before the breeding season initiate nest building earlier than lighter males. We measured testis size in male wrens in the prebreeding period during which seasonal testicular recrudescence is occurring. The initiation of nest building was predicted by male age and by testis size. This suggests that variation in the start of courtship activity may reflect variation between males in the rate of testicular recrudescence. Variation in male prebreeding body mass was influenced by variation in testis size, which suggests that the relation reported earlier between body mass and timing of nest construction could be explained, in part, by variation in testis size. Alternatively, if body mass reflects body condition then both the extent of testes recrudescence and the timing of courtship activity could be condition-dependent traits. Copyright 2000 The Association for the Study of Animal Behaviour.

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PubMed2000

Coarsening of a class of driven striped structures

The coarsening process in a class of driven systems exhibiting striped structures is studied. The dynamics is governed by the motion of the driven interfaces between the stripes. When two interfaces meet they coalesce thus giving rise to a coarsening process in which l(t), the average width of a stripe, grows with time. This is a generalization of the reaction-diffusion process A+A-->A to the case of extended coalescing objects, namely, the interfaces. Scaling arguments which relate the coarsening process to the evolution of a single driven interface are given, yielding growth laws for l(t), for both short and long times. We introduce a simple microscopic model for this process. Numerical simulations of the model confirm the scaling picture and growth laws. The results are compared to the case where the stripes are not driven and different growth laws arise.

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PubMed1997

The influence of habitat and male morphology on a mate-choice cue: the display nests of wrens

Wrens, Troglodytes troglodytesare highly polygynous passerines. Males build cock nests that are displayed to females and function as a mate-choice cue. Males with large numbers of nests are more likely to attract females than males with fewer nests. To be useful to females a cue used in mate choice must contain information. One way to evaluate the information content of such a cue may be to examine the factors that influence its size. The number of nests was predicted on territories with known building rates (immigration) and nest destruction rates (death) using an immigration-death function. This analysis suggested that if only building rate and destruction rates were considered then the number of nests on territories was consistently overestimated. In 1994 an experiment was conducted in which nest-site availability was manipulated. Males provided with additional nest sites built more nests and continued to build later in the year resulting in longer nest-building periods than controls. The converse was found when nest sites were experimentally removed. This suggested that the number of nests that could be constructed on a territory was limited by habitat structure. None of the morphological characters considered here significantly influenced the number of nests built by males. Therefore, the information content of this mate-choice cue will be primarily about characteristics of the habitat on the territory rather than characteristics of the male.1997The Association for the Study of Animal Behaviour

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