4,719 research outputs found
Collective action and the intensity of between-group competition in nonhuman primates
The importance of between-group competition in the social evolution of animal societies is controversial, particularly with respect to understanding the origins and maintenance of cooperation in our own species. Among primates, aggressive between-group encounters are often rare or strikingly absent, a phenomenon that in some species has been ascribed to the presence of collective action problems. Here, we report on a series of comparative tests that show that the intensity of between-group contest competition is indeed lower in species that experience a collective action problem while controlling for predictions from an "ideal gas” model of animal encounters and general species' ecology. Species that do not succumb to the collective action problem are either cooperative breeders, are characterized by philopatry of the dominant sex, or live in relatively small groups with few individuals of this dominant sex. This implies that collective action problems are averted either through shared genes and benefits or a by-product mutualism in which the territorial behavior of some privileged individuals is not affected by the behavior of others. We conclude that across the primate taxon, the intensity of between-group competition is predominantly constrained by a social dilemma among group members, rather than ecological conditions, and that the collective action problem is thus an important selective pressure in the evolution of primate (including human) cooperation and socialit
Saprolegnia diclina IIIA and S. parasitica employ different infection strategies when colonizing eggs of Atlantic salmon, Salmo salar L.
Acknowledgements The work has been funded by the European Commission through the EU Marie Curie ITN project SAPRO (238550) (MMS, AW). We would also like to acknowledge support from the BBSRC and the University of Aberdeen (PvW) and Landcatch and AquaGen for providing salmon eggs. Elin Rolen's assistance with sequencing of the strains is highly appreciated.Peer reviewedPublisher PD
Precise calibration of LIGO test mass actuators using photon radiation pressure
Precise calibration of kilometer-scale interferometric gravitational wave
detectors is crucial for source localization and waveform reconstruction. A
technique that uses the radiation pressure of a power-modulated auxiliary laser
to induce calibrated displacements of one of the ~10 kg arm cavity mirrors, a
so-called photon calibrator, has been demonstrated previously and has recently
been implemented on the LIGO detectors. In this article, we discuss the
inherent precision and accuracy of the LIGO photon calibrators and several
improvements that have been developed to reduce the estimated voice coil
actuator calibration uncertainties to less than 2 percent (1-sigma). These
improvements include accounting for rotation-induced apparent length variations
caused by interferometer and photon calibrator beam centering offsets, absolute
laser power measurement using temperature-controlled InGaAs photodetectors
mounted on integrating spheres and calibrated by NIST, minimizing errors
induced by localized elastic deformation of the mirror surface by using a
two-beam configuration with the photon calibrator beams symmetrically displaced
about the center of the optic, and simultaneously actuating the test mass with
voice coil actuators and the photon calibrator to minimize fluctuations caused
by the changing interferometer response. The photon calibrator is able to
operate in the most sensitive interferometer configuration, and is expected to
become a primary calibration method for future gravitational wave searches.Comment: 13 pages, 6 figures, accepted by Classical and Quantum Gravit
Precise calibration of LIGO test mass actuators using photon radiation pressure
Precise calibration of kilometer-scale interferometric gravitational wave
detectors is crucial for source localization and waveform reconstruction. A
technique that uses the radiation pressure of a power-modulated auxiliary laser
to induce calibrated displacements of one of the ~10 kg arm cavity mirrors, a
so-called photon calibrator, has been demonstrated previously and has recently
been implemented on the LIGO detectors. In this article, we discuss the
inherent precision and accuracy of the LIGO photon calibrators and several
improvements that have been developed to reduce the estimated voice coil
actuator calibration uncertainties to less than 2 percent (1-sigma). These
improvements include accounting for rotation-induced apparent length variations
caused by interferometer and photon calibrator beam centering offsets, absolute
laser power measurement using temperature-controlled InGaAs photodetectors
mounted on integrating spheres and calibrated by NIST, minimizing errors
induced by localized elastic deformation of the mirror surface by using a
two-beam configuration with the photon calibrator beams symmetrically displaced
about the center of the optic, and simultaneously actuating the test mass with
voice coil actuators and the photon calibrator to minimize fluctuations caused
by the changing interferometer response. The photon calibrator is able to
operate in the most sensitive interferometer configuration, and is expected to
become a primary calibration method for future gravitational wave searches.Comment: 13 pages, 6 figures, accepted by Classical and Quantum Gravit
Using a quantum dot as a high-frequency shot noise detector
We present the experimental realization of a Quantum Dot (QD) operating as a
high-frequency noise detector. Current fluctuations produced in a nearby
Quantum Point Contact (QPC) ionize the QD and induce transport through excited
states. The resulting transient current through the QD represents our detector
signal. We investigate its dependence on the QPC transmission and voltage bias.
We observe and explain a quantum threshold feature and a saturation in the
detector signal. This experimental and theoretical study is relevant in
understanding the backaction of a QPC used as a charge detector.Comment: 4 pages, 4 figures, accepted for publication in Physical Review
Letter
Differential activation of lumbar and sacral motor pools during walking at different speeds and slopes
Organization of spinal motor output has become of interest for investigating differential activation of lumbar and sacral motor pools during locomotor tasks. Motor pools are associated with functional grouping of motoneurons of the lower limb muscles. Here we examined how the spatiotemporal organization of lumbar and sacral motor pool activity during walking is orchestrated with slope of terrain and speed of progression. Ten subjects walked on an instrumented treadmill at different slopes and imposed speeds. Kinetics, kinematics, and electromyography of 16 lower limb muscles were recorded. The spinal locomotor output was assessed by decomposing the coordinated muscle activation profiles into a small set of common factors and by mapping them onto the rostrocaudal location of the motoneuron pools. Our results show that lumbar and sacral motor pool activity depend on slope and speed. Compared with level walking, sacral motor pools decrease their activity at negative slopes and increase at positive slopes, whereas lumbar motor pools increase their engagement when both positive and negative slope increase. These findings are consistent with a differential involvement of the lumbar and the sacral motor pools in relation to changes in positive and negative center of body mass mechanical power production due to slope and speed.NEW & NOTEWORTHY In this study, the spatiotemporal maps of motoneuron activity in the spinal cord were assessed during walking at different slopes and speeds. We found differential involvement of lumbar and sacral motor pools in relation to changes in positive and negative center of body mass power production due to slope and speed. The results are consistent with recent findings about the specialization of neuronal networks located at different segments of the spinal cord for performing specific locomotor tasks
Spatio-temporal impact of climate change on the groundwater system
Given the importance of groundwater for food production
and drinking water supply, but also for the survival
of groundwater dependent terrestrial ecosystems (GWDTEs)
it is essential to assess the impact of climate change on this
freshwater resource. In this paper we study with high temporal
and spatial resolution the impact of 28 climate change
scenarios on the groundwater system of a lowland catchment
in Belgium. Our results show for the scenario period
2070–2101 compared with the reference period 1960–
1991, a change in annual groundwater recharge between
−20% and +7%. On average annual groundwater recharge
decreases 7%. In most scenarios the recharge increases during
winter but decreases during summer. The altered recharge
patterns cause the groundwater level to decrease significantly
from September to January. On average the groundwater
level decreases about 7 cm with a standard deviation between
the scenarios of 5 cm. Groundwater levels in interfluves and
upstream areas are more sensitive to climate change than
groundwater levels in the river valley. Groundwater discharge
to GWDTEs is expected to decrease during late summer and
autumn as much as 10%, though the discharge remains at
reference-period level during winter and early spring. As
GWDTEs are strongly influenced by temporal dynamics of
the groundwater system, close monitoring of groundwater
and implementation of adaptive management measures are
required to prevent ecological loss
Interacting Binaries with Eccentric Orbits. Secular Orbital Evolution Due To Conservative Mass Transfer
We investigate the secular evolution of the orbital semi-major axis and
eccentricity due to mass transfer in eccentric binaries, assuming conservation
of total system mass and orbital angular momentum. Assuming a delta function
mass transfer rate centered at periastron, we find rates of secular change of
the orbital semi-major axis and eccentricity which are linearly proportional to
the magnitude of the mass transfer rate at periastron. The rates can be
positive as well as negative, so that the semi-major axis and eccentricity can
increase as well as decrease in time. Adopting a delta-function mass-transfer
rate of 10^{-9} M_\sun {\rm yr}^{-1} at periastron yields orbital evolution
timescales ranging from a few Myr to a Hubble time or more, depending on the
binary mass ratio and orbital eccentricity. Comparison with orbital evolution
timescales due to dissipative tides furthermore shows that tides cannot, in all
cases, circularize the orbit rapidly enough to justify the often adopted
assumption of instantaneous circularization at the onset of mass transfer. The
formalism presented can be incorporated in binary evolution and population
synthesis codes to create a self-consistent treatment of mass transfer in
eccentric binaries.Comment: 16 pages, 8 figures, Accepted by The Astrophysical Journa
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