18,467 research outputs found
Frequency-dependent fitness induces multistability in coevolutionary dynamics
Evolution is simultaneously driven by a number of processes such as mutation,
competition and random sampling. Understanding which of these processes is
dominating the collective evolutionary dynamics in dependence on system
properties is a fundamental aim of theoretical research. Recent works
quantitatively studied coevolutionary dynamics of competing species with a
focus on linearly frequency-dependent interactions, derived from a
game-theoretic viewpoint. However, several aspects of evolutionary dynamics,
e.g. limited resources, may induce effectively nonlinear frequency
dependencies. Here we study the impact of nonlinear frequency dependence on
evolutionary dynamics in a model class that covers linear frequency dependence
as a special case. We focus on the simplest non-trivial setting of two
genotypes and analyze the co-action of nonlinear frequency dependence with
asymmetric mutation rates. We find that their co-action may induce novel
metastable states as well as stochastic switching dynamics between them. Our
results reveal how the different mechanisms of mutation, selection and genetic
drift contribute to the dynamics and the emergence of metastable states,
suggesting that multistability is a generic feature in systems with
frequency-dependent fitness.Comment: 12 pages, 6 figures; J. R. Soc. Interface (2012
Female impersonation as an alternative reproductive strategy in giant cuttlefish
Out of all the animals, cephalopods possess an unrivalled ability to change their shape and body patterns. Our observations of giant cuttlefish (Sepia apama) suggest this ability has allowed them to evolve alternative mating strategies in which males can switch between the appearance of a female and that of a male in order to foil the guarding attempts of larger males. At a mass breeding aggregation in South Australia, we repeatedly observed single small males accompanying mating pairs. While doing so, the small male assumed the body shape and patterns of a female. Such males were never attacked by the larger mate-guarding male. On more than 20 occasions, when the larger male was distracted by another male intruder, these small males, previously indistinguishable from a female, were observed to change body pattern and behaviour to that of a male in mating display. These small males then attempted to mate with the female, often with success. This potential for dynamic sexual mimicry may have played a part in driving the evolution of the remarkable powers of colour and shape transformation which characterize the cephalopods
Orbital periods of the binary sdB stars PG0940+068 and PG1247+554
We have used the radial velocity variations of two sdB stars previously
reported to be binaries to establish their orbital periods. They are
PG0940+068, (P=8.33d) and PG1247+554 (P=0.599d). The minimum masses of the
unseen companions, assuming a mass of 0.5 solar masses for the sdB stars, are
0.090 +/- 0.003 solar masses for PG1247+554 and 0.63 +/- 0.02 solar masses for
PG0940+068. The nature of the companions is not constrained further by our
data.Comment: 5 pages, 2 figure
The UK National Prolapse Survey: 10Â years on
INTRODUCTION AND HYPOTHESIS: To assess trends in the surgical management of pelvic organ prolapse (POP) amongst UK practitioners and changes in practice since a previous similar survey. METHODS: An online questionnaire survey (Typeform Pro) was emailed to British Society of Urogynaecology (BSUG) members. They included urogynaecologists working in tertiary centres, gynaecologists with a designated special interest in urogynaecology and general gynaecologists. The questionnaire included case scenarios encompassing contentious issues in the surgical management of POP and was a revised version of the questionnaire used in the previous surveys. The revised questionnaire included additional questions relating to the use of vaginal mesh and laparoscopic urogynaecology procedures. RESULTS: Of 516 BSUG members emailed, 212 provided completed responses.. For anterior vaginal wall prolapse the procedure of choice was anterior colporrhaphy (92% of respondents). For uterovaginal prolapse the procedure of choice was still vaginal hysterectomy and repair (75%). For posterior vaginal wall prolapse the procedure of choice was posterior colporrhaphy with midline fascial plication (97%). For vault prolapse the procedure of choice was sacrocolpopexy (54%) followed by vaginal wall repair and sacrospinous fixation (41%). The laparoscopic route was preferred for sacrocolpopexy (62% versus 38% for the open procedure). For primary prolapse, vaginal mesh was used by only 1% of respondents in the anterior compartment and by 3% in the posterior compartment. CONCLUSION: Basic trends in the use of native tissue prolapse surgery remain unchanged. There has been a significant decrease in the use of vaginal mesh for both primary and recurrent prolapse, with increasing use of laparoscopic procedures for prolapse
A candidate optical counterpart to the middle-aged gamma-ray pulsar PSR J1741-2054
We carried out deep optical observations of the middle-aged -ray
pulsar PSR J1741-2054 with the Very Large Telescope (VLT). We identified two
objects, of magnitudes and , at positions
consistent with the very accurate Chandra coordinates of the pulsar, the
faintest of which is more likely to be its counterpart. From the VLT images we
also detected the known bow-shock nebula around PSR J1741-2054. The nebula is
displaced by \sim 0\farcs9 (at the confidence level) with respect
to its position measured in archival data, showing that the shock propagates in
the interstellar medium consistently with the pulsar proper motion. Finally, we
could not find evidence of large-scale extended optical emission associated
with the pulsar wind nebula detected by Chandra, down to a surface brightness
limit of magnitudes arcsec. Future observations are needed
to confirm the optical identification of PSR J1741-2054 and characterise the
spectrum of its counterpart.Comment: 8 pages, 3 figures, Astrophysical Journal, in pres
Flow of nitrogen-pressurized Halon 1301 in fire extinguishing systems
Halon 1301 which is a halocarbon fire extinguishing agent (CBrF3) used by the U.S. Army for vehicle fire suppression is discussed. Halon 1301 is discharged under nitrogen pressure, and the Halon-nitrogen mixture is a two phase, two component mixture that obeys compressible fluid laws and exhibits choking effects. A computer model was developed to analyze the discharge of Halon and nitrogen from a storage bottle through pipes and nozzles. The model agrees well with data from Halon 1301 discharge tests. The discharge time depends mainly on nozzle area and pipe volume, for given initial conditions. Graphs were developed for estimating discharge times. A nozzle employing multiple concentric converging/diverging nozzles was developed which gave hemispherical coverage
Random division of an interval
The well-known relation between random division of an interval and the Poisson process is interpreted as a Laplace transformation. With the use of this interpretation a number of (in part known) results is derived very easily
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