6,130 research outputs found
Historical factors associated with past environments influence the biogeography of thermophilic endospores in Arctic marine sediments
Selection by the local, contemporary environment plays a prominent role in shaping the biogeography of microbes. However, the importance of historical factors in microbial biogeography is more debatable. Historical factors include past ecological and evolutionary circumstances that may have influenced present-day microbial diversity, such as dispersal and past environmental conditions. Diverse thermophilic sulphate-reducing Desulfotomaculum are present as dormant endospores in marine sediments worldwide where temperatures are too low to support their growth. Therefore, they are dispersed to here from elsewhere, presumably a hot, anoxic habitat. While dispersal through ocean currents must influence their distribution in cold marine sediments, it is not clear whether even earlier historical factors, related to the source habitat where these organisms were once active, also have an effect. We investigated whether these historical factors may have influenced the diversity and distribution of thermophilic endospores by comparing their diversity in 10 Arctic fjord surface sediments. Although community composition varied spatially, clear biogeographic patterns were only evident at a high level of taxonomic resolution (>97% sequence similarity of the 16S rRNA gene) achieved with oligotyping. In particular, the diversity and distribution of oligotypes differed for the two most prominent OTUs (defined using a standard 97% similarity cutoff). One OTU was dominated by a single ubiquitous oligotype, while the other OTU consisted of ten more spatially localised oligotypes that decreased in compositional similarity with geographic distance. These patterns are consistent with differences in historical factors that occurred when and where the taxa were once active, prior to sporulation. Further, the influence of history on biogeographic patterns was only revealed by analysing microdiversity within OTUs, suggesting that populations within standard OTU-level groupings do not necessarily share a common ecological and evolutionary history
Faking on a situational judgment test in a medical school selection setting: Effect of different scoring methods?
We examined the occurrence of faking on a rating situational judgment test (SJT) by
comparing SJT scores and response styles of the same individuals across two natuâ
rally occurring situations. An SJT for medical school selection was administered twice
to the same group of applicants (N = 317) under lowâstakes (T1) and highâstakes (T2)
circumstances. The SJT was scored using three different methods that were differâ
entially affected by response tendencies. Applicants used significantly more extreme
responding on T2 than T1. Faking (higher SJT score on T2) was only observed for
scoring methods that controlled for response tendencies. Scoring methods that do
not control for response tendencies introduce systematic error into the SJT score,
which may lead to inaccurate conclusions about the existence of faking
Molecular outflows towards O-type young stellar objects
We have searched for massive molecular outflows in a sample of high-mass star
forming regions, and we have characterised both the outflow properties and
those of their associated molecular clumps. With a sample composed largely of
more luminous objects than previous ones, this work complements analogous
surveys performed by other authors by adding the missing highest luminosity
sources. The sample under study has been selected so as to favour the earliest
evolutionary phases of star formation, and is composed of very luminous objects
(L_bol > 2x10^4 L_sun and up to ~10^6 L_sun), possibly containing O-type stars.
Each source has been mapped in 13CO(2-1) and C18O(2-1) with the IRAM-30m
telescope on Pico Veleta (Spain). The whole sample shows high-velocity wings in
the 13CO(2-1) spectra, indicative of outflowing motions. In addition, we have
obtained outflow maps in 9 of our 11 sources, which display well-defined blue
and/or red lobes. For these sources, the outflow parameters have been derived
from the line wing 13CO(2-1) emission. An estimate of the clump masses from the
C18O(2-1) emission is also provided and found to be comparable to the virial
masses. From a comparison between our results and those found by other authors
at lower masses, it is clear that the outflow mechanical force increases with
the bolometric luminosity of the clump and with the ionising photon rate of the
associated HII regions, indicating that high-mass stars drive more powerful
outflows. A tight correlation between outflow mass and clump mass is also
found. Molecular outflows are found to be as common in massive star forming
regions as in low-mass star forming regions. This, added to the detection of a
few tentative large-scale rotating structures suggests that high-mass stars may
generally form via accretion, as low-mass stars.Comment: 16 pages, 10 figures, accepted by Astronomy and Astrophysic
Setting upper limits on the strength of periodic gravitational waves from PSR J1939+2134 using the first science data from the GEO 600 and LIGO detectors
Data collected by the GEO 600 and LIGO interferometric gravitational wave detectors during their first observational science run were searched for continuous gravitational waves from the pulsar J1939+2134 at twice its rotation frequency. Two independent analysis methods were used and are demonstrated in this paper: a frequency domain method and a time domain method. Both achieve consistent null results, placing new upper limits on the strength of the pulsar's gravitational wave emission. A model emission mechanism is used to interpret the limits as a constraint on the pulsar's equatorial ellipticity
First LIGO search for gravitational wave bursts from cosmic (super)strings
We report on a matched-filter search for gravitational wave bursts from
cosmic string cusps using LIGO data from the fourth science run (S4) which took
place in February and March 2005. No gravitational waves were detected in 14.9
days of data from times when all three LIGO detectors were operating. We
interpret the result in terms of a frequentist upper limit on the rate of
gravitational wave bursts and use the limits on the rate to constrain the
parameter space (string tension, reconnection probability, and loop sizes) of
cosmic string models.Comment: 11 pages, 3 figures. Replaced with version submitted to PR
Astrophysically Triggered Searches for Gravitational Waves: Status and Prospects
In gravitational-wave detection, special emphasis is put onto searches that
focus on cosmic events detected by other types of astrophysical observatories.
The astrophysical triggers, e.g. from gamma-ray and X-ray satellites, optical
telescopes and neutrino observatories, provide a trigger time for analyzing
gravitational wave data coincident with the event. In certain cases the
expected frequency range, source energetics, directional and progenitor
information is also available. Beyond allowing the recognition of gravitational
waveforms with amplitudes closer to the noise floor of the detector, these
triggered searches should also lead to rich science results even before the
onset of Advanced LIGO. In this paper we provide a broad review of LIGO's
astrophysically triggered searches and the sources they target
First upper limits from LIGO on gravitational wave bursts
We report on a search for gravitational wave bursts using data from the first
science run of the LIGO detectors. Our search focuses on bursts with durations
ranging from 4 ms to 100 ms, and with significant power in the LIGO sensitivity
band of 150 to 3000 Hz. We bound the rate for such detected bursts at less than
1.6 events per day at 90% confidence level. This result is interpreted in terms
of the detection efficiency for ad hoc waveforms (Gaussians and sine-Gaussians)
as a function of their root-sum-square strain h_{rss}; typical sensitivities
lie in the range h_{rss} ~ 10^{-19} - 10^{-17} strain/rtHz, depending on
waveform. We discuss improvements in the search method that will be applied to
future science data from LIGO and other gravitational wave detectors.Comment: 21 pages, 15 figures, accepted by Phys Rev D. Fixed a few small typos
and updated a few reference
Analysis of LIGO data for gravitational waves from binary neutron stars
We report on a search for gravitational waves from coalescing compact binary
systems in the Milky Way and the Magellanic Clouds. The analysis uses data
taken by two of the three LIGO interferometers during the first LIGO science
run and illustrates a method of setting upper limits on inspiral event rates
using interferometer data. The analysis pipeline is described with particular
attention to data selection and coincidence between the two interferometers. We
establish an observational upper limit of 1.7 \times 10^{2}M_\odot$.Comment: 17 pages, 9 figure
All-sky LIGO Search for Periodic Gravitational Waves in the Early S5 Data
We report on an all-sky search with the LIGO detectors for periodic
gravitational waves in the frequency range 50--1100 Hz and with the frequency's
time derivative in the range -5.0E-9 Hz/s to zero. Data from the first eight
months of the fifth LIGO science run (S5) have been used in this search, which
is based on a semi-coherent method (PowerFlux) of summing strain power.
Observing no evidence of periodic gravitational radiation, we report 95%
confidence-level upper limits on radiation emitted by any unknown isolated
rotating neutron stars within the search range. Strain limits below 1.E-24 are
obtained over a 200-Hz band, and the sensitivity improvement over previous
searches increases the spatial volume sampled by an average factor of about 100
over the entire search band. For a neutron star with nominal equatorial
ellipticity of 1.0E-6, the search is sensitive to distances as great as 500
pc--a range that could encompass many undiscovered neutron stars, albeit only a
tiny fraction of which would likely be rotating fast enough to be accessible to
LIGO. This ellipticity is at the upper range thought to be sustainable by
conventional neutron stars and well below the maximum sustainable by a strange
quark star.Comment: 6 pages, 1 figur
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