1,397 research outputs found
Completing HI observations of galaxies II. The Coma Supercluster
High sensitivity 21-cm HI line observations, with an rms noise level of \sim
0.5 mJy, were made of 35 spiral galaxies in the Coma Supercluster, using the
refurbished Arecibo telescope, which resulted in the detection of 25 objects.
These data, combined with the measurements available from the literature,
provide the set of HI data for 94% of all late-type galaxies in the Coma
Supercluster with an apparent photographic magnitude m_p <15.7 mag. We confirm
that the typical scale of HI deficiency around the Coma cluster is 2 Mpc, i.e.
one virial radius. Comparing the HI mass function (HIMF) of cluster with
non-cluster members of the Coma Supercluster we detect a shortage of high HI
mass galaxies among cluster members that can be ascribed to the pattern of HI
deficiency found in rich clusters.Comment: 16 pages, 8 figures, 4 tables. Accepted for publication on A&
The characteristics of electronic training collars for dogs
A wide range of electronic dog training collars (e-collars) is available in the UK, yet there is no means by which purchasers can meaningfully compare their electrical characteristics at the point of sale. In this research the electrical characteristics of 13 models of e-collar were examined and an approach to ranking the strength of the electrical stimuli was developed. The electrical impedance of dogs’ necks was measured so that e-collars could be tested under realistic conditions. This impedance was found to be about 10kΩ for wet dogs and 640kΩ for dry dogs. Two copies of each of eight e-collar models and one copy of a further five models were tested. The stimuli generated by these collars comprised sequences of short high voltage pulses. There were large differences between e-collar models in the peak voltage, number of pulses and duration of the pulses but little variation between the duplicates. The peak voltage varied with the impedance of the dog, from 6000V at an impedance of 500kΩ to 100V at 5kΩ. The highest voltages were generated for only a few millionths of a second. A stimulus strength ranking index (SSRI) was developed based on the subjective response of human subjects to electrical stimuli. This index is used to compare the strength of e-collars with diverse electrical characteristics. It shows a wide range in the stimulus strengths of collars and that the relationships between ‘momentary’ and ‘continuous’ stimuli for various models differ significantly
Signatures of Interchange Reconnection: STEREO, ACE and Hinode Observations Combined
Combining STEREO, ACE and Hinode observations has presented an opportunity to
follow a filament eruption and coronal mass ejection (CME) on the 17th of
October 2007 from an active region (AR) inside a coronal hole (CH) into the
heliosphere. This particular combination of `open' and closed magnetic
topologies provides an ideal scenario for interchange reconnection to take
place. With Hinode and STEREO data we were able to identify the emergence time
and type of structure seen in the in-situ data four days later. On the 21st,
ACE observed in-situ the passage of an ICME with `open' magnetic topology. The
magnetic field configuration of the source, a mature AR located inside an
equatorial CH, has important implications for the solar and interplanetary
signatures of the eruption. We interpret the formation of an `anemone'
structure of the erupting AR and the passage in-situ of the ICME being
disconnected at one leg, as manifested by uni-directional suprathermal electron
flux in the ICME, to be a direct result of interchange reconnection between
closed loops of the CME originating from the AR and `open' field lines of the
surrounding CH.Comment: 13 pages, 13 figures, accepted Annales Geophysica
Benefits of an out-of-school time program on social-emotional learning among disadvantaged adolescent youth:A retrospective analysis
Strongly nonexponential time-resolved fluorescence of quantum-dot ensembles in three-dimensional photonic crystals
We observe experimentally that ensembles of quantum dots in three-dimensional (3D) photonic crystals reveal strongly nonexponential time-resolved emission. These complex emission decay curves are analyzed with a continuous distribution of decay rates. The log-normal distribution describes the decays well for all studied lattice parameters. The distribution width is identified with variations of the radiative emission rates of quantum dots with various positions and dipole orientations in the unit cell. We find a striking sixfold change of the width of the distribution by varying the lattice parameter. This interpretation qualitatively agrees with the calculations of the 3D projected local density of states. We therefore conclude that fluorescence decay of ensembles of quantum dots is highly nonexponential to an extent that is controlled by photonic crystals
Completing HI observations of galaxies in the Virgo cluster
High sensitivity (rms noise mJy) 21-cm HI line observations were
made of 33 galaxies in the Virgo cluster, using the refurbished Arecibo
telescope, which resulted in the detection of 12 objects. These data, combined
with the measurements available from the literature, provide the first set of
HI data that is complete for all 355 late-type (Sa-Im-BCD) galaxies in the
Virgo cluster with mag. The Virgo cluster HI mass function
(HIMF) that was derived for this optically selected galaxy sample is in
agreement with the HIMF derived for the Virgo cluster from the blind HIJASS HI
survey and is inconsistent with the Field HIMF. This indicates that both in
this rich cluster and in the general field, neutral hydrogen is primarily
associated with late-type galaxies, with marginal contributions from early-type
galaxies and isolated HI clouds. The inconsistency between the cluster and the
field HIMF derives primarily from the difference in the optical luminosity
function of late-type galaxies in the two environments, combined with the HI
deficiency that is known to occur in galaxies in rich clusters.Comment: accepted for publication on A&
Plasma composition in a sigmoidal anemone active region
Using spectra obtained by the EIS instrument onboard Hinode, we present a
detailed spatially resolved abundance map of an active region (AR)-coronal hole
(CH) complex that covers an area of 359 arcsec x 485 arcsec. The abundance map
provides first ionization potential (FIP) bias levels in various coronal
structures within the large EIS field of view. Overall, FIP bias in the small,
relatively young AR is 2-3. This modest FIP bias is a consequence of the AR
age, its weak heating, and its partial reconnection with the surrounding CH.
Plasma with a coronal composition is concentrated at AR loop footpoints, close
to where fractionation is believed to take place in the chromosphere. In the
AR, we found a moderate positive correlation of FIP bias with nonthermal
velocity and magnetic flux density, both of which are also strongest at the AR
loop footpoints. Pathways of slightly enhanced FIP bias are traced along some
of the loops connecting opposite polarities within the AR. We interpret the
traces of enhanced FIP bias along these loops to be the beginning of
fractionated plasma mixing in the loops. Low FIP bias in a sigmoidal channel
above the AR's main polarity inversion line where ongoing flux cancellation is
taking place, provides new evidence of a bald patch magnetic topology of a
sigmoid/flux rope configfiuration.Comment: For on-line animation, see
http://www.mssl.ucl.ac.uk/~db2/fip_intensity.gif. Accepted by Ap
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