612 research outputs found
Assessment of pollen rewards by foraging bees
This is the author accepted manuscript. The final version is available from Wiley via the DOI in this record.The removal of pollen by flower-visiting insects is costly to plants, not only in
terms of production, but also via lost reproductive potential. Modern
angiosperms have evolved various reward strategies to limit these costs, yet
many plant species still offer pollen as a sole or major reward for pollinating
insects.
2. The benefits plants gain by offering pollen as a reward for pollinating are
defined by the behaviour of their pollinators, some of which feed on the pollen
at the flower, while others collect pollen to provision offspring.
3. We explore how pollen impacts on the behaviour and foraging decisions of
pollen-collecting bees, drawing comparisons with what is known for nectar
rewards. This question is of particular interest since foraging bees typically do
not ingest pollen during collection, meaning the sensory pathways involved in
evaluating this resource are not immediately obvious.
4. Previous research focussed on whether foraging bees can determine the quality
of pollen sources offered by different plant species, and attempted to infer the
mechanisms underpinning such evaluations, mainly through observations of
collection preferences in the field
5. More recent experimental research has started to focus on if pollen itself can
mediate the detection of, and learning about, pollen sources and associated
floral cues.
6. We review advancements in the understanding of how bees forage for pollen
and respond to variation in pollen quality, and discuss future directions for
studying how this ancestral floral food reward shapes the behaviour of
pollinating insects
Quantum control of Sr in a miniature linear Paul trap
We report on the construction and characterization of an apparatus for
quantum information experiments using Sr ions. A miniature linear
radio-frequency (rf) Paul trap was designed and built. Trap frequencies above 1
MHz in all directions are obtained with 50 V on the trap end-caps and less than
1 W of rf power. We encode a quantum bit (qubit) in the two spin states of the
electronic ground-state of the ion. We constructed all the necessary
laser sources for laser cooling and full coherent manipulation of the ions'
external and internal states. Oscillating magnetic fields are used for coherent
spin rotations. High-fidelity readout as well as a coherence time of 2.5 ms are
demonstrated. Following resolved sideband cooling the average axial vibrational
quanta of a single trapped ion is and a heating rate of
ms is measured.Comment: 8 pages,9 figure
Sympathetic cooling of and for quantum logic
We demonstrate the cooling of a two species ion crystal consisting of one
and one ion. Since the respective cooling transitions of
these two species are separated by more than 30 nm, laser manipulation of one
ion has negligible effect on the other even when the ions are not individually
addressed. As such this is a useful system for re-initializing the motional
state in an ion trap quantum computer without affecting the qubit information.
Additionally, we have found that the mass difference between ions enables a
novel method for detecting and subsequently eliminating the effects of radio
frequency (RF) micro-motion.Comment: Submitted to PR
Atmospheric effects on extensive air showers observed with the Surface Detector of the Pierre Auger Observatory
Atmospheric parameters, such as pressure (P), temperature (T) and density,
affect the development of extensive air showers initiated by energetic cosmic
rays. We have studied the impact of atmospheric variations on extensive air
showers by means of the surface detector of the Pierre Auger Observatory. The
rate of events shows a ~10% seasonal modulation and ~2% diurnal one. We find
that the observed behaviour is explained by a model including the effects
associated with the variations of pressure and density. The former affects the
longitudinal development of air showers while the latter influences the Moliere
radius and hence the lateral distribution of the shower particles. The model is
validated with full simulations of extensive air showers using atmospheric
profiles measured at the site of the Pierre Auger Observatory.Comment: 24 pages, 9 figures, accepted for publication in Astroparticle
Physic
The Fluorescence Detector of the Pierre Auger Observatory
The Pierre Auger Observatory is a hybrid detector for ultra-high energy
cosmic rays. It combines a surface array to measure secondary particles at
ground level together with a fluorescence detector to measure the development
of air showers in the atmosphere above the array. The fluorescence detector
comprises 24 large telescopes specialized for measuring the nitrogen
fluorescence caused by charged particles of cosmic ray air showers. In this
paper we describe the components of the fluorescence detector including its
optical system, the design of the camera, the electronics, and the systems for
relative and absolute calibration. We also discuss the operation and the
monitoring of the detector. Finally, we evaluate the detector performance and
precision of shower reconstructions.Comment: 53 pages. Submitted to Nuclear Instruments and Methods in Physics
Research Section
Interactions between temperature and energy supply drive microbial communities in hydrothermal sediment
Temperature and bioavailable energy control the distribution of life on Earth, and interact with each other due to the dependency of biological energy requirements on temperature. Here we analyze how temperature-energy interactions structure sediment microbial communities in two hydrothermally active areas of Guaymas Basin. Sites from one area experience advective input of thermogenically produced electron donors by seepage from deeper layers, whereas sites from the other area are diffusion-dominated and electron donor-depleted. In both locations, Archaea dominate at temperatures >45 °C and Bacteria at temperatures <10 °C. Yet, at the phylum level and below, there are clear differences. Hot seep sites have high proportions of typical hydrothermal vent and hot spring taxa. By contrast, high-temperature sites without seepage harbor mainly novel taxa belonging to phyla that are widespread in cold subseafloor sediment. Our results suggest that in hydrothermal sediments temperature determines domain-level dominance, whereas temperature-energy interactions structure microbial communities at the phylum-level and below
Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter
Data collected by the Pierre Auger Observatory through 31 August 2007 showed
evidence for anisotropy in the arrival directions of cosmic rays above the
Greisen-Zatsepin-Kuz'min energy threshold, \nobreak{eV}. The
anisotropy was measured by the fraction of arrival directions that are less
than from the position of an active galactic nucleus within 75 Mpc
(using the V\'eron-Cetty and V\'eron catalog). An updated
measurement of this fraction is reported here using the arrival directions of
cosmic rays recorded above the same energy threshold through 31 December 2009.
The number of arrival directions has increased from 27 to 69, allowing a more
precise measurement. The correlating fraction is , compared
with expected for isotropic cosmic rays. This is down from the early
estimate of . The enlarged set of arrival directions is
examined also in relation to other populations of nearby extragalactic objects:
galaxies in the 2 Microns All Sky Survey and active galactic nuclei detected in
hard X-rays by the Swift Burst Alert Telescope. A celestial region around the
position of the radiogalaxy Cen A has the largest excess of arrival directions
relative to isotropic expectations. The 2-point autocorrelation function is
shown for the enlarged set of arrival directions and compared to the isotropic
expectation.Comment: Accepted for publication in Astroparticle Physics on 31 August 201
Advanced functionality for radio analysis in the Offline software framework of the Pierre Auger Observatory
The advent of the Auger Engineering Radio Array (AERA) necessitates the
development of a powerful framework for the analysis of radio measurements of
cosmic ray air showers. As AERA performs "radio-hybrid" measurements of air
shower radio emission in coincidence with the surface particle detectors and
fluorescence telescopes of the Pierre Auger Observatory, the radio analysis
functionality had to be incorporated in the existing hybrid analysis solutions
for fluoresence and surface detector data. This goal has been achieved in a
natural way by extending the existing Auger Offline software framework with
radio functionality. In this article, we lay out the design, highlights and
features of the radio extension implemented in the Auger Offline framework. Its
functionality has achieved a high degree of sophistication and offers advanced
features such as vectorial reconstruction of the electric field, advanced
signal processing algorithms, a transparent and efficient handling of FFTs, a
very detailed simulation of detector effects, and the read-in of multiple data
formats including data from various radio simulation codes. The source code of
this radio functionality can be made available to interested parties on
request.Comment: accepted for publication in NIM A, 13 pages, minor corrections to
author list and references in v
Search for First Harmonic Modulation in the Right Ascension Distribution of Cosmic Rays Detected at the Pierre Auger Observatory
We present the results of searches for dipolar-type anisotropies in different
energy ranges above eV with the surface detector array of
the Pierre Auger Observatory, reporting on both the phase and the amplitude
measurements of the first harmonic modulation in the right-ascension
distribution. Upper limits on the amplitudes are obtained, which provide the
most stringent bounds at present, being below 2% at 99% for EeV
energies. We also compare our results to those of previous experiments as well
as with some theoretical expectations.Comment: 28 pages, 11 figure
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