209 research outputs found
Oscillatory behaviour in a lattice prey-predator system
Using Monte Carlo simulations we study a lattice model of a prey-predator
system. We show that in the three-dimensional model populations of preys and
predators exhibit coherent periodic oscillations but such a behaviour is absent
in lower-dimensional models. Finite-size analysis indicate that amplitude of
these oscillations is finite even in the thermodynamic limit. In our opinion,
this is the first example of a microscopic model with stochastic dynamics which
exhibits oscillatory behaviour without any external driving force. We suggest
that oscillations in our model are induced by some kind of stochastic
resonance.Comment: 7 pages, 10 figures, Phys.Rev.E (Nov. 1999
DREAM: III.A helium survey in exoplanets on the edge of the hot Neptune desert with GIANO-B@TNG
The population of close-in exoplanets features a desert of hot Neptunes whose
origin is uncertain. These planets may have lost their atmosphere, eroding into
mini-Neptunes and super-Earths. Direct observations of evaporating atmospheres
are essential to derive mass-loss estimates and constrain this scenario. The
metastable 1083.3nm HeI triplet represents a powerful diagnostic of atmospheric
evaporation since it traces the hot gas in extended exoplanet atmospheres, is
observable from the ground, and is weakly affected by interstellar medium
absorption. We conducted a uniform HeI transmission spectroscopy survey,
focusing on 9 planets located at the edges of the Neptunian desert, aiming to
gain insights into the role of photo-evaporation in its formation. We observed
one transit per planet using the high-resolution, near-infrared spectrograph
GIANO-B on the Telescopio Nazionale Galileo. We focused our analysis on the HeI
triplet by computing high-resolution transmission spectra. We then employed the
p-winds model to interpret the observed transmission spectra. We found no sign
of planetary absorption in the HeI triplet in any of the investigated targets.
We thus provided 3sigma upper-limit estimations on the thermosphere absorption,
temperature, and mass loss, and combined them with past measurements to search
for correlations with parameters thought to be drivers in the formation of the
HeI triplet. Our results strengthen the importance of performing homogeneous
surveys and analyses to bring clarification in the HeI detection and hence in
the Neptunian desert origin. Our findings corroborate the literature
expectations that the HeI absorption signal correlates with the stellar mass
and the received XUV flux. However, these trends seem to disappear in terms of
mass-loss rates; further studies are essential to shed light on this aspect and
to understand better the photo-evaporation process.Comment: 23 pages, 13 figures, accepted for publication in A&A, after language
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Axial Vector Coupling Constant in Chiral Colour Dielectric Model
The axial vector coupling constants of the decay processes of neutron
and hyperon are calculated in SU(3) chiral colour dielectric model (CCDM).
Using these axial coupling constants of neutron and hyperon, in CCDM we
calculate the integrals of the spin dependent structure functions for proton
and neutron. Our result is similar to the results obtained by MIT bag and
Cloudy bag models.Comment: 9 pages, Latex file, no figure, to appear in Phys. Rev.
Prior Mating Experience Modulates the Dispersal of Drosophila in Males More Than in Females
Cues from both an animal’s internal physiological state and its local environment may influence its decision to disperse. However, identifying and quantifying the causative factors underlying the initiation of dispersal is difficult in uncontrolled natural settings. In this study, we automatically monitored the movement of fruit flies and examined the influence of food availability, sex, and reproductive status on their dispersal between laboratory environments. In general, flies with mating experience behave as if they are hungrier than virgin flies, leaving at a greater rate when food is unavailable and staying longer when it is available. Males dispersed at a higher rate and were more active than females when food was unavailable, but tended to stay longer in environments containing food than did females. We found no significant relationship between weight and activity, suggesting the behavioral differences between males and females are caused by an intrinsic factor relating to the sex of a fly and not simply its body size. Finally, we observed a significant difference between the dispersal of the natural isolate used throughout this study and the widely-used laboratory strain, Canton-S, and show that the difference cannot be explained by allelic differences in the foraging gene
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