98 research outputs found
Social learning and culture in bees: Simple mechanisms, complex outcomes
\ua9 Indian Academy of Sciences 2024. Bees have been excellent model systems to study social learning – the ability of animals to change their behaviour based on observations of other individuals. Researchers have investigated several aspects of social learning in bees, including how it can lead to cultural traditions. A recent study also argues that bees have the capacity to socially learn behaviours that they could not innovate on their own. To understand these findings better, I review what we know about the mechanisms underlying social learning in bees and use these findings to compare social learning and culture in bees and humans. The findings suggest that the seemingly complex social behaviours of bees could arise from simple mechanisms underlying learning in general. I highlight the importance of investigating cognitive mechanisms and how they might differ across animals
Different Effects of Reward Value and Physical Saliency During Bumblebee Visual Search for Multiple Rewarding Targets
Several animals, including bees, use visual search to distinguish targets of interest and ignore distractors. While bee flower choice is well studied, we know relatively little about how they choose between multiple rewarding flowers in complex floral environments. Two factors that could influence bee visual search for multiple flowers are the saliency (colour contrast against the background) and the reward value of flowers. We here investigated how these two different factors contribute to bee visual search. We trained bees to independently recognize two rewarding flower types that, in different experiments, differed in either saliency, reward value or both. We then measured their choices and attention to these flowers in the presence of distractors in a test without reinforcement. We found that bees preferred more salient or higher rewarding flowers and ignored distractors. When the high-reward flowers were less salient than the low-reward flowers, bees were nonetheless equally likely to choose high-reward flowers, for the reward and saliency values we used. Bees were also more likely to attend to these high-reward flowers, spending higher inspection times around them and exhibiting faster search times when choosing them. When flowers differed in reward, we also found an effect of the training order with low-reward targets being more likely to be chosen if they had been encountered during the more immediate training session prior to the test. Our results parallel recent findings from humans demonstrating that reward value can attract attention even when targets are less salient and irrelevant to the current task
Radial density profiles of time-delay lensing galaxies
We present non-parametric radial mass profiles for ten QSO strong lensing
galaxies. Five of the galaxies have profiles close to ,
while the rest are closer to r^{-1}, consistent with an NFW profile. The former
are all relatively isolated early-types and dominated by their stellar light.
The latter --though the modeling code did not know this-- are either in
clusters, or have very high mass-to-light, suggesting dark-matter dominant
lenses (one is a actually pair of merging galaxies). The same models give
H_0^{-1} = 15.2_{-1.7}^{+2.5}\Gyr (H_0 = 64_{-9}^{+8} \legacy), consistent
with a previous determination. When tested on simulated lenses taken from a
cosmological hydrodynamical simulation, our modeling pipeline recovers both H_0
and within estimated uncertainties. Our result is contrary to some
recent claims that lensing time delays imply either a low H_0 or galaxy
profiles much steeper than r^{-2}. We diagnose these claims as resulting from
an invalid modeling approximation: that small deviations from a power-law
profile have a small effect on lensing time-delays. In fact, as we show using
using both perturbation theory and numerical computation from a
galaxy-formation simulation, a first-order perturbation of an isothermal lens
can produce a zeroth-order change in the time delays.Comment: Replaced with final version accepted for publication in ApJ; very
minor changes to text; high resolution figures may be obtained at
justinread.ne
Cosmological Model Predictions for Weak Lensing: Linear and Nonlinear Regimes
Weak lensing by large scale structure induces correlated ellipticities in the
images of distant galaxies. The two-point correlation is determined by the
matter power spectrum along the line of sight. We use the fully nonlinear
evolution of the power spectrum to compute the predicted ellipticity
correlation. We present results for different measures of the second moment for
angular scales \theta \simeq 1'-3 degrees and for alternative normalizations of
the power spectrum, in order to explore the best strategy for constraining the
cosmological parameters. Normalizing to observed cluster abundance the rms
amplitude of ellipticity within a 15' radius is \simeq 0.01 z_s^{0.6}, almost
independent of the cosmological model, with z_s being the median redshift of
background galaxies.
Nonlinear effects in the evolution of the power spectrum significantly
enhance the ellipticity for \theta < 10' -- on 1' the rms ellipticity is \simeq
0.05, which is nearly twice the linear prediction. This enhancement means that
the signal to noise for the ellipticity is only weakly increasing with angle
for 2'< \theta < 2 degrees, unlike the expectation from linear theory that it
is strongly peaked on degree scales. The scaling with cosmological parameters
also changes due to nonlinear effects. By measuring the correlations on small
(nonlinear) and large (linear) angular scales, different cosmological
parameters can be independently constrained to obtain a model independent
estimate of both power spectrum amplitude and matter density \Omega_m.
Nonlinear effects also modify the probability distribution of the ellipticity.
Using second order perturbation theory we find that over most of the range of
interest there are significant deviations from a normal distribution.Comment: 38 pages, 11 figures included. Extended discussion of observational
prospects, matches accepted version to appear in Ap
Rhythmic abilities in humans and non-human animals: a review and recommendations from a methodological perspective
Rhythmic behaviour is ubiquitous in both human and non-human animals, but it is unclear whether the cognitive mechanisms underlying the specific rhythmic behaviours observed in different species are related. Laboratory experiments combined with highly controlled stimuli and tasks can be very effective in probing the cognitive architecture underlying rhythmic abilities. Rhythmic abilities have been examined in the laboratory with explicit and implicit perception tasks, and with production tasks, such as sensorimotor synchronization, with stimuli ranging from isochronous sequences of artificial sounds to human music. Here, we provide an overview of experimental findings on rhythmic abilities in human and non-human animals, while critically considering the wide variety of paradigms used. We identify several gaps in what is known about rhythmic abilities. Many bird species have been tested on rhythm perception, but research on rhythm production abilities in the same birds is lacking. By contrast, research in mammals has primarily focused on rhythm production rather than perception. Many experiments also do not differentiate between possible components of rhythmic abilities, such as processing of single temporal intervals, rhythmic patterns, a regular beat or hierarchical metrical structures. For future research, we suggest a careful choice of paradigm to aid cross-species comparisons, and a critical consideration of the multifaceted abilities that underlie rhythmic behaviour. This article is part of the theme issue 'Synchrony and rhythm interaction: from the brain to behavioural ecology'.Animal science
Wavefronts, Caustic Sheets, and Caustic Surfing in Gravitational Lensing
Very little attention has been paid to the properties of optical wavefronts
and caustic surfaces due to gravitational lensing. Yet the wavefront-based
point of view is natural and provides insights into the nature of the caustic
surfaces on a gravitationally lensed lightcone. We derive analytically the
basic equations governing the wavefronts, lightcones, caustics on wavefronts,
and caustic surfaces on lightcones in the context of weak-field, thin-screen
gravitational lensing. These equations are all related to the potential of the
lens. In the process, we also show that the standard single-plane gravitational
lensing map extends to a new mapping, which we call a wavefront lensing map.
Unlike the standard lensing map, the Jacobian matrix of a wavefront lensing map
is not symmetric. Our formulas are then applied to caustic ``surfing.'' By
surfing a caustic surface, a space-borne telescope can be fixed on a
gravitationally lensed source to obtain an observation of the source at very
high magnification over an extended time period, revealing structure about the
source that could not otherwise be resolved. Using our analytical expressions
for caustic sheets, we present a scheme for surfing a caustic sheet of a lensed
source in rectilinear motion. Detailed illustrations are also presented of the
possible types of wavefronts and caustic sheets due to nonsingular and singular
elliptical potentials, and singular isothermal spheres, including an example of
caustic surfing for a singular elliptical potential lens.Comment: To appear in J. Math. Phys., 31 pages, 15 figure
Mathematics of Gravitational Lensing: Multiple Imaging and Magnification
The mathematical theory of gravitational lensing has revealed many generic
and global properties. Beginning with multiple imaging, we review
Morse-theoretic image counting formulas and lower bound results, and
complex-algebraic upper bounds in the case of single and multiple lens planes.
We discuss recent advances in the mathematics of stochastic lensing, discussing
a general formula for the global expected number of minimum lensed images as
well as asymptotic formulas for the probability densities of the microlensing
random time delay functions, random lensing maps, and random shear, and an
asymptotic expression for the global expected number of micro-minima. Multiple
imaging in optical geometry and a spacetime setting are treated. We review
global magnification relation results for model-dependent scenarios and cover
recent developments on universal local magnification relations for higher order
caustics.Comment: 25 pages, 4 figures. Invited review submitted for special issue of
General Relativity and Gravitatio
Semi analytic approach to understanding the distribution of neutral hydrogen in the universe: Comparison of simulations with observations
Following Bi & Davidsen (1997), we perform one dimensional semi analytic
simulations along the lines of sight to model the intergalactic medium (IGM).
Since this procedure is computationally efficient in probing the parameter
space -- and reasonably accurate -- we use it to recover the values of various
parameters related to the IGM (for a fixed background cosmology) by comparing
the model predictions with different observations. For the currently favoured
LCDM model (\Omega_m=0.4, \Omega_{\Lambda}=0.6 and h=0.65), we obtain, using
statistics obtained from the transmitted flux, constraints on (i) the
combination f=(\Omega_B h^2)^2/J_{-12}, where \Omega_B is the baryonic density
parameter and J_{-12} is the total photoionisation rate in units of 10^{-12}
s^{-1}, (ii) temperature T_0 corresponding to the mean density and (iii) the
slope \gamma of the effective equation of state of the IGM at a mean redshift z
\simeq 2.5. We find that 0.8 <(T_0/10^4 K)< 2.5 and 1.3<\gamma<2.3. while the
constraint obtained on f is 0.020^2<f<0.032^2. A reliable lower bound on
J_{-12} can be used to put a lower bound on \Omega_B h^2, which can be compared
with similar constraints obtained from Big Bang Nucleosynthesis (BBN) and CMBR
studies. We find that if J_{-12}>1.2, the lower bound on \Omega_B h^2 is in
violation of the BBN value.Comment: Revised version; accepted for publication in Ap
TreePM Method for Two-Dimensional Cosmological Simulations
We describe the two-dimensional TreePM method in this paper. The 2d TreePM
code is an accurate and efficient technique to carry out large two-dimensional
N-body simulations in cosmology. This hybrid code combines the 2d Barnes and
Hut Tree method and the 2d Particle-Mesh method. We describe the splitting of
force between the PM and the Tree parts. We also estimate error in force for a
realistic configuration. Finally, we discuss some tests of the code.Comment: 12 pages, 3 figures, uses jaa.sty. To be submitted to JA
- …