2,824 research outputs found
Modelling collective foraging by means of individual behaviour rules in honey-bees
An individual-oriented model is constructed
which simulates the collective foraging behaviour of a
colony of honey-bees, Apis mellifera. Each bee follows
the same set of behavioural rules. Each rule consists of a
set of conditions followed by the behavioural act to be
performed if the conditions are fulfilled. The set of
conditions comprises the state of external information
available to the bee (e.g. the dancing of other bees) and
internal information variables (like memorised location
of a food source and homing motivation). The rules are
partly observational (i.e. they capture the observable
regularities between the present external information
and the individual bee's behaviour), and partly involve
hypothesised internal-state variables (e.g. abandoning
tendency and homing motivation), because no observ-
able (physiological) aspect has as yet been detected in the
bee which correlates with changes in the internal moti-
vation. Our aim is to obtain a set of rules that is nec-
essary and sufficient for the generation of the collective
foraging behaviour observed in real bees. We simulated
an experiment performed by Seeley et al. in which a
colony of honey-bees chooses between two nectar
sources of different profitabilities which are switched at
intervals. A good fit between observed and simulated
collective forager patterns was obtained when the model
included rules in which the bees (1) relied on the infor-
mation acquired from previous fiights to a source (e.g.
profitability and time of day when the source was
found), (2) used positional information obtained by at-
tending recruitment dances and (3) did not abandon a
(temporarily) deteriorated source too fast or too slowly.
The significance of the following issues is discussed: the
role of internal and external information, source prof-
itability, the spatial precision of the dance communica-
tion, the ability to search for a source after the source
position has been transmitted, the tendency to abandon
a deteriorated source, and the concepts of scout, recruit,
(un)employed forager, and foraging history
Symmetry breaking in collective honeybee foraging: a simulation study
Symmetry breaking is the phenomenon that the numbers of foragers exploiting two equally profitable food sources will diverge. This
phenomenon has been investigated in ants [1,4,5], but hardly in honeybees. It is even not clear whether in honeybees symmetry breaking
can occur [3, p.190]. We present results of an individual-oriented simulation model showing that under specific circumstances symmetry
breaking in the numbers of honeybee workers exploiting two or four identical nectar sources can occur. We studied factors that influence
the occurrence of symmetry breaking, which include: size of the forager pool, number of bees initially exploiting the sources, and size of
the flower patch. This study is part of an ongoing study which aims at developing an individual-oriented simulation model capturing the
necessary and sufficient behavioural rules to generate the collective foraging patterns observed in bee
Exploration and exploitation of food sources by social insect colonies: a revision of the scout-recruit concept
Social insect colonies need to explore and exploit
multiple food sources simultaneously and efficiently.
At the individual level, this colony-level behaviour
has been thought to be taken care of by two types of individual:
scouts that independently search for food, and
recruits that are directed by nest mates to a food source.
However, recent analyses show that this strict division of
labour between scouts and recruits is untenable. Therefore,
a modified concept is presented here that comprises
the possible behavioural states of an individual forager
(novice forager, scout, recruit, employed forager, unemployed
experienced forager, inspector and reactivated
forager) and the transitions between them. The available
empirical data are reviewed in the light of both the old
and the new concept, and probabilities for the different
transitions are derived for the case of the honey-bee. The
modified concept distinguishes three types of foragers
that may be involved in the exploration behaviour of the
colony: novice bees that become scouts, unemployed experienced
bees that scout, and lost recruits, i.e. bees that
discover a food source other than the one to which they
were directed to by their nest mates. An advantage of the
modified concept is that it allows for a better comparison
of studies investigating the different roles performed by
social insect foragers during their individual foraging
histories
Extracting Muon Momentum Scale Corrections for Hadron Collider Experiments
We present a simple method for the extraction of corrections for bias in the
measurement of the momentum of muons in hadron collider experiments. Such bias
can originate from a variety of sources such as detector misalignment, software
reconstruction bias, and uncertainties in the magnetic field. The two step
method uses the mean for muons from $Z\to \mu\mu$ decays to
determine the momentum scale corrections in bins of charge, $\eta$ and $\phi$.
In the second step, the corrections are tuned by using the average invariant
mass of events in the same bins of charge
and . The forward-backward asymmetry of pairs
as a function of mass, and the distribution of bosons
in the Collins-Soper frame are used to ascertain that the corrections remove
the bias in the momentum measurements for positive versus negatively charged
muons. By taking the sum and difference of the momentum scale corrections for
positive and negative muons, we isolate additive corrections to
that may originate from misalignments and multiplicative corrections that may
originate from mis-modeling of the magnetic field . This method has recently been used in the CDF experiment at
Fermilab and in the CMS experiment at the Large Hadron Collider at CERNComment: 6 pages, 3 figures, to be published in EPJC 201
Numerical investigation of conjugated heat transfer in a channel with a moving depositing front
This article presents numerical simulations of conjugated heat transfer in a fouled channel with a moving depositing front. The depositing front separating the fluid and the deposit layer is captured using the level-set method. Fluid flow is modeled by the incompressible Navier–Stokes equations. Numerical solution is performed on a fixed mesh using the finite volume method. The effects of Reynolds number and thermal conductivity ratio between the deposit layer and the fluid on local Nusselt number as well as length-averaged Nusselt number are investigated. It is found that heat transfer performance, represented by the local and length-averaged Nusselt number reduces significantly in a fouled channel compared with that in a clean channel. Heat transfer performance decreases with the growth of the deposit layer. Increases in Reynolds, Prandtl numbers both enhance heat transfer. Besides, heat transfer is enhanced when the thermal conductivity ratio between the deposit layer and the fluid is lower than 20 but it decreases when the thermal conductivity ratio is larger than 2
Angular momentum spatial distribution symmetry breaking in Rb by an external magnetic field
Excited state angular momentum alignment -- orientation conversion for atoms
with hyperfine structure in presence of an external magnetic field is
investigated. Transversal orientation in these conditions is reported for the
first time. This phenomenon occurs under Paschen Back conditions at
intermediate magnetic field strength. Weak radiation from a linearly polarized
diode laser is used to excite Rb atoms in a cell. The laser beam is polarized
at an angle of pi/4 with respect to the external magnetic field direction.
Ground state hyperfine levels of the 5S_1/2 state are resolved using
laser-induced fluorescence spectroscopy under conditions for which all excited
5P_3/2 state hyperfine components are excited simultaneously. Circularly
polarized fluorescence is observed to be emitted in the direction perpendicular
to both to the direction of the magnetic field B and direction of the light
polarization E. The obtained circularity is shown to be in quantitative
agreement with theoretical predictions.Comment: Accepted for publication in Phys. Rev.
Constraining models of the large scale Galactic magnetic field with WMAP5 polarization data and extragalactic Rotation Measure sources
We introduce a method to quantify the quality-of-fit between data and
observables depending on the large scale Galactic magnetic field. We combine
WMAP5 polarized synchrotron data and Rotation Measures of extragalactic sources
in a joint analysis to obtain best fit parameters and confidence levels for GMF
models common in the literature. None of the existing models provide a good fit
in both the disk and halo regions, and in many instances best-fit parameters
are quite different than the original values. We note that probing a very large
parameter space is necessary to avoid false likelihood maxima. The thermal and
relativistic electron densities are critical for determining the GMF from the
observables but they are not well constrained. We show that some
characteristics of the electron densities can already be constrained using our
method and with future data it may be possible to carry out a self-consistent
analysis in which models of the GMF and electron densities are simultaneously
optimized.Comment: 27 pages, 13 figures. Accepted for publication in JCAP; arXiv version
updated to include minor revision
Nanolithography and manipulation of graphene using an atomic force microscope
We use an atomic force microscope (AFM) to manipulate graphene films on a
nanoscopic length scale. By means of local anodic oxidation with an AFM we are
able to structure isolating trenches into single-layer and few-layer graphene
flakes, opening the possibility of tabletop graphene based device fabrication.
Trench sizes of less than 30 nm in width are attainable with this technique.
Besides oxidation we also show the influence of mechanical peeling and
scratching with an AFM of few layer graphene sheets placed on different
substrates.Comment: 11 pages text, 5 figure
The seesaw mechanism at TeV scale in the 3-3-1 model with right-handed neutrinos
We implement the seesaw mechanism in the 3-3-1 model with right-handed
neutrinos. This is accomplished by the introduction of a scalar sextet into the
model and the spontaneous violation of the lepton number. We identify the
Majoron as a singlet under symmetry, which makes it
safe under the current bounds imposed by electroweak data. The main result of
this work is that the seesaw mechanism works already at TeV scale with the
outcome that the right-handed neutrino masses lie in the electroweak scale, in
the range from MeV to tens of GeV. This window provides a great opportunity to
test their appearance at current detectors, though when we contrast our results
with some previous analysis concerning detection sensitivity at LHC, we
conclude that further work is needed in order to validate this search.Comment: about 13 pages, no figure
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