413 research outputs found
Cue-conflict experiments between magnetic and visual cues in dunlin Calidris alpina and curlew sandpiper Calidris ferruginea
Despite our extensive knowledge on various aspects of their lives, there has been limited investigation into the hierarchical relationships among different compass systems in shorebirds. The aim of this study was to investigate the relationship between magnetic and celestial compasses in two species of shorebirds, the curlew sandpiper (Calidris ferruginea; prebreeding migration) and the dunlin (Calidris alpina; postbreeding migration) using cue-conflict experiments. Birds were captured in a Mediterranean stopover site, after which their magnetic orientation was determined under simulated overcast conditions at sunset using modified Emlen funnels fitted with infrared video cameras. Birds that demonstrated a well-defined directional preference were then exposed over two sunsets to conflicting directional information between the local geomagnetic field and the ±90° shifted band of maximum polarisation. These individuals were tested again for magnetic orientation at sunset in the same conditions as previous test, to determine whether their directional choices had changed after the cue-conflict. Our results showed that individuals from both species did not recalibrate their magnetic compass from visual cues after the cue-conflict, even though at least dunlins did not appear to completely disregard the information derived from celestial cues. This study is one of the few experimental studies on the migratory orientation of Charadriiformes and on the hierarchical relationships between the different compasses used by these birds during their extensive migratory movements
New cue-conflict experiments suggest a leading role of visual cues in the migratory orientation of Pied Flycatchers Ficedula hypoleuca
Migratory birds use both geomagnetic and celestial cues to select and maintain their seasonally appropriate migratory direction. The integration of the different compass cues is still poorly understood. Previous cue-conflict experiments suggested that Pied Flycatchers Ficedula hypoleuca did not recalibrate their magnetic compass against the polarization pattern at twilight, but the available evidence is problematic given the high variability of birdsâ directional preferences. We performed a new set of cue-conflict experiments where (1) we modified the protocol in order to try to reduce scatter of data and (2) we integrated the results of two experimental approaches, i.e. orientation cages and releases of radio-tagged birds. Pied Flycatchers were tested in Emlen funnels without access to celestial cues before and after being exposed to conflicting visual and geomagnetic information. After the second test, birds were equipped with radio-transmitters and followed until the vanishing of the radio signal. Contrary to previous experiments, our data showed a general dominance of celestial cues: polarized light sun-related pattern in captive birds tested without access to stars and stellar
dominance in free-flying birds released under a starry sky at night-time. These results underline the importance of experimental protocols when testing ways in which birds integrate their compass systems
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All-sky search for short gravitational-wave bursts in the second Advanced LIGO and Advanced Virgo run
We present the results of a search for short-duration gravitational-wave transients in the data from the second observing run of Advanced LIGO and Advanced Virgo. We search for gravitational-wave transients with a duration of milliseconds to approximately one second in the 32-4096 Hz frequency band with minimal assumptions about the signal properties, thus targeting a wide variety of sources. We also perform a matched-filter search for gravitational-wave transients from cosmic string cusps for which the waveform is well modeled. The unmodeled search detected gravitational waves from several binary black hole mergers which have been identified by previous analyses. No other significant events have been found by either the unmodeled search or the cosmic string search. We thus present the search sensitivities for a variety of signal waveforms and report upper limits on the source rate density as a function of the characteristic frequency of the signal. These upper limits are a factor of 3 lower than the first observing run, with a 50% detection probability for gravitational-wave emissions with energies of âŒ10-9 Mc2 at 153 Hz. For the search dedicated to cosmic string cusps we consider several loop distribution models, and present updated constraints from the same search done in the first observing run
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Search for intermediate mass black hole binaries in the first and second observing runs of the Advanced LIGO and Virgo network
Gravitational-wave astronomy has been firmly established with the detection of gravitational waves from the merger of ten stellar-mass binary black holes and a neutron star binary. This paper reports on the all-sky search for gravitational waves from intermediate mass black hole binaries in the first and second observing runs of the Advanced LIGO and Virgo network. The search uses three independent algorithms: two based on matched filtering of the data with waveform templates of gravitational-wave signals from compact binaries, and a third, model-independent algorithm that employs no signal model for the incoming signal. No intermediate mass black hole binary event is detected in this search. Consequently, we place upper limits on the merger rate density for a family of intermediate mass black hole binaries. In particular, we choose sources with total masses M=m1+m2Ï”[120,800] M and mass ratios q=m2/m1Ï”[0.1,1.0]. For the first time, this calculation is done using numerical relativity waveforms (which include higher modes) as models of the real emitted signal. We place a most stringent upper limit of 0.20 Gpc-3 yr-1 (in comoving units at the 90% confidence level) for equal-mass binaries with individual masses m1,2=100 M and dimensionless spins Ï1,2=0.8 aligned with the orbital angular momentum of the binary. This improves by a factor of âŒ5 that reported after Advanced LIGO's first observing run
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Search for Eccentric Binary Black Hole Mergers with Advanced LIGO and Advanced Virgo during Their First and Second Observing Runs
When formed through dynamical interactions, stellar-mass binary black holes (BBHs) may retain eccentric orbits (e > 0.1 at 10 Hz) detectable by ground-based gravitational-wave detectors. Eccentricity can therefore be used to differentiate dynamically formed binaries from isolated BBH mergers. Current template-based gravitational-wave searches do not use waveform models associated with eccentric orbits, rendering the search less efficient for eccentric binary systems. Here we present the results of a search for BBH mergers that inspiral in eccentric orbits using data from the first and second observing runs (O1 and O2) of Advanced LIGO and Advanced Virgo. We carried out the search with the coherent WaveBurst algorithm, which uses minimal assumptions on the signal morphology and does not rely on binary waveform templates. We show that it is sensitive to binary mergers with a detection range that is weakly dependent on eccentricity for all bound systems. Our search did not identify any new binary merger candidates. We interpret these results in light of eccentric binary formation models. We rule out formation channels with rates âȘ100 Gpc-3 yr-1 for e > 0.1, assuming a black hole mass spectrum with a power-law index âČ2
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Search for gravitational waves from Scorpius X-1 in the second Advanced LIGO observing run with an improved hidden Markov model
We present results from a semicoherent search for continuous gravitational
waves from the low-mass X-ray binary Scorpius X-1, using a hidden Markov model
(HMM) to track spin wandering. This search improves on previous HMM-based
searches of LIGO data by using an improved frequency domain matched filter, the
-statistic, and by analysing data from Advanced LIGO's second
observing run. In the frequency range searched, from to
, we find no evidence of gravitational radiation. At
, the most sensitive search frequency, we report an upper
limit on gravitational wave strain (at 95\% confidence) of when marginalising over source inclination angle. This is the
most sensitive search for Scorpius X-1, to date, that is specifically designed
to be robust in the presence of spin wandering
First narrow-band search for continuous gravitational waves from known pulsars in advanced detector data
Spinning neutron stars asymmetric with respect to their rotation axis are potential sources of
continuous gravitational waves for ground-based interferometric detectors. In the case of known pulsars a
fully coherent search, based on matched filtering, which uses the position and rotational parameters
obtained from electromagnetic observations, can be carried out. Matched filtering maximizes the signalto-
noise (SNR) ratio, but a large sensitivity loss is expected in case of even a very small mismatch
between the assumed and the true signal parameters. For this reason, narrow-band analysis methods have
been developed, allowing a fully coherent search for gravitational waves from known pulsars over a
fraction of a hertz and several spin-down values. In this paper we describe a narrow-band search of
11 pulsars using data from Advanced LIGOâs first observing run. Although we have found several initial
outliers, further studies show no significant evidence for the presence of a gravitational wave signal.
Finally, we have placed upper limits on the signal strain amplitude lower than the spin-down limit for 5 of
the 11 targets over the bands searched; in the case of J1813-1749 the spin-down limit has been beaten for
the first time. For an additional 3 targets, the median upper limit across the search bands is below the
spin-down limit. This is the most sensitive narrow-band search for continuous gravitational waves carried
out so far
The governance of justice and internal security in Scotland: Between the Scottish independence referendum and British decisions on the EU
This article examines how the governance of justice and internal security in Scotland could be affected by the outcome of the Scottish independence referendum in September 2014. The article argues that it is currently impossible to equate a specific result in the referendum with a given outcome for the governance of justice and internal security in Scotland. This is because of the complexities of the current arrangements in that policy area and the existence of several changes that presently affect them and are outside the control of the government and of the people of Scotland. This article also identifies an important paradox. In the policy domain of justice and internal security, a ânoâ vote could, in a specific set of circumstances, actually lead to more changes than a victory of the âyesâ camp
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