6,770 research outputs found
Measurement of the threshold sensitivity of honeybees to weak, extremely low-frequency magnetic fields
Experiments reported previously demonstrate that free-flying honeybees are able to detect static intensity fluctuations as weak as 26 nT against the background, earth-strength magnetic field. We report here an extension of this work to weak, alternating fields at frequencies of 10 and 60 Hz. Our results indicate that the sensitivity of the honeybee magnetoreception system decreases rapidly with increasing frequency. At 60 Hz, alternating field strengths above 100 µT are required to elicit discrimination. These results are consistent with biophysical predictions of a magnetite-based magnetoreceptor
Separation of biological materials in microgravity
Partition in aqueous two phase polymer systems is a potentially useful procedure in downstream processing of both molecular and particulate biomaterials. The potential efficiency of the process for particle and cell isolations is much higher than the useful levels already achieved. Space provides a unique environment in which to test the hypothesis that convection and settling phenomena degrade the performance of the partition process. The initial space experiment in a series of tests of this hypothesis is described
Demixing of aqueous polymer two-phase systems in low gravity
When polymers such as dextran and poly(ethylene glycol) are mixed in aqueous solution biphasic systems often form. On Earth the emulsion formed by mixing the phases rapidly demixes because of phase density differences. Biological materials can be purified by selective partitioning between the phases. In the case of cells and other particulates the efficiency of these separations appears to be somewhat compromised by the demixing process. To modify this process and to evaluate the potential of two-phase partitioning in space, experiments on the effects of gravity on phase emulsion demixing were undertaken. The behavior of phase systems with essentially identical phase densities was studied at one-g and during low-g parabolic aircraft maneuvers. The results indicate the demixing can occur rather rapidly in space, although more slowly than on Earth. The demixing process was examined from a theoretical standpoint by applying the theory of Ostwald ripening. This theory predicts demizing rates many orders of magnitude lower than observed. Other possible demixing mechanisms are considered
J0316+4328: a Probable "Asymmetric Double" Lens
We report a probable gravitational lens J0316+4328, one of 19 candidate
asymmetric double lenses (2 images at a high flux density ratio) from CLASS.
Observations with the Very Large Array (VLA), MERLIN and the Very Long Baseline
Array (VLBA) imply that J0316+4328 is a lens with high confidence. It has 2
images separated by 0.40", with 6 GHz flux densities of 62 mJy and 3.2 mJy. The
flux density ratio of ~19 (constant over the frequency range 6-22 GHz) is the
largest for any 2 image gravitational lens. High resolution optical imaging and
deeper VLBI maps should confirm the lensing interpretation and provide inputs
to detailed lens models. The unique configuration will give strong constraints
on the lens galaxy's mass profile.Comment: Accepted to MNRAS Letters. 5 pages, 6 figures, 3 table
Ultra-High-Resolution Marine 2D-3D Seismic Investigation of the Liman Tepe/Karantina Island Archaeological Site (Urla/Turkey)
Cataloged from PDF version of article.2D and 3D high-resolution seismic investigations were performed on submerged coastal archaeological sites
at Iskele and near to Karantina Island in the Bay of Izmir in western Turkey. Tectonic subsidence of the
coastline has submerged a number of archaeological features associated with an important Early Bronze
Archaic settlement (Liman Tepe) and the classical Ionian city of Clazomenae. Seismic surveys were focused
on imaging of an Archaic harbour structure and other submerged Hellenistic and Roman architectural
features. Seismic data were acquired with the SEAMAP-3D ultra-high-resolution 3D marine seismic
acquisition system developed for detailed archaeological site investigation.
A 2D reconnaissance survey was performed over a 2 km2 area around Karantina Island to evaluate the
seismic penetrability and to locate sites for further 3D investigation. This survey predominantly revealed
marine sediment layers covering the local bedrock, which is characterized by scattering of seismic energy
showing its rocky nature.
Two ultra-high-resolution 3D seismic surveys were performed. The first covered a 350 m × 30 m area in the
modern harbour targeting a prominent Archaic harbour structure. The second was acquired across a
120 m × 40 m area on the southeast shore of the Karantina Island close to a Roman architectural feature. The
3D surveys were acquired with nominal line spacings of 1 m, using a 8× 4 pseudo-rigid hydrophone array
and a Boomer source firing at 3 Hz shot frequency. Automated processing of the seismic data using a portable
Linux cluster provided stacked 3D seismic volumes with 25 cm × 25 cm bin size on-site.
The 3D seismic survey of the harbour clearly imaged the submerged Archaic structure and the underlying
sediment sequence. The seismic time slices reveal two seismic anomalies (2–3 m in diameter) in the harbour
basin sediments. The 3D surveys southeast of Karantina identified a thicker marine sediment sequence
overlying steeply dipping bedrock reflectors. The sediment sequence records the rapid accumulation and
progradation of the coastline following the construction the Alexander causeway linking the mainland with
the island in 334 B.C
Children's biobehavioral reactivity to challenge predicts DNA methylation in adolescence and emerging adulthood.
A growing body of research has documented associations between adverse childhood environments and DNA methylation, highlighting epigenetic processes as potential mechanisms through which early external contexts influence health across the life course. The present study tested a complementary hypothesis: indicators of children's early internal, biological, and behavioral responses to stressful challenges may also be linked to stable patterns of DNA methylation later in life. Children's autonomic nervous system reactivity, temperament, and mental health symptoms were prospectively assessed from infancy through early childhood, and principal components analysis (PCA) was applied to derive composites of biological and behavioral reactivity. Buccal epithelial cells were collected from participants at 15 and 18 years of age. Findings revealed an association between early life biobehavioral inhibition/disinhibition and DNA methylation across many genes. Notably, reactive, inhibited children were found to have decreased DNA methylation of the DLX5 and IGF2 genes at both time points, as compared to non-reactive, disinhibited children. Results of the present study are provisional but suggest that the gene's profile of DNA methylation may constitute a biomarker of normative or potentially pathological differences in reactivity. Overall, findings provide a foundation for future research to explore relations among epigenetic processes and differences in both individual-level biobehavioral risk and qualities of the early, external childhood environment
A multi-beam HI survey of the Virgo Cluster - two isolated HI clouds ?
We have carried out a fully sampled large area ()
21cm \HI line survey of part of the Virgo cluster using the Jodrell Bank
multi-beam instrument. The survey has a sensitivity some 3 times better than
the standard HIJASS and HIPASS surveys. We detect 31 galaxies, 27 of which are
well known cluster members. The four new detections have been confirmed in the
HIPASS data and by follow up Jodrell Bank pointed observations. One object lies
behind M86, but the other 3 have no obvious optical counter parts upon
inspection of the digital sky survey fields. These 3 objects were mapped at
Arecibo with a smaller \am{3}{6} HPBW and a 4 times better sensitivity than the
Jodrell Bank data, which allow an improved determination of the dimensions and
location of two of the objects, but surprisingly failed to detect the third.
The two objects are resolved by the Arecibo beam giving them a size far larger
than any optical images in the nearby field. To our mass limit of and column density limit of
atoms cm these new
detections represent only about 2% of the cluster atomic hydrogen mass. Our
observations indicate that the \HI mass function of the cluster turns down at
the low mass end making it very different to the field galaxy \HI mass
function. This is quite different to the Virgo cluster optical luminosity
function which is much steeper than that in the general field. Many of the
sample galaxies are relatively gas poor compared to \HI selected samples of
field galaxies, confirming the 'anaemic spirals' view of Virgo cluster late
type galaxies.Comment: Accepted for publication in MNRA
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