8,318 research outputs found
A study of purely astrometric selection of extragalactic point sources with Gaia
Selection of extragalactic point sources, e.g. QSOs, is often hampered by
significant selection effects causing existing samples to have rather complex
selection functions. We explore whether a purely astrometric selection of
extragalactic point sources, e.g. QSOs, is feasible with the ongoing Gaia
mission. Such a selection would be interesting as it would be unbiased in terms
of colours of the targets and hence would allow selection also with colours in
the stellar sequence. We have analyzed a total of 18 representative regions of
the sky by using GUMS, the simulator prepared for ESAs Gaia mission, both in
the range of mag and mag. For each region we
determine the density of apparently stationary stellar sources, i.e. sources
for which Gaia cannot measure a significant proper motion. The density is
contrasted with the density of extragalactic point sources, e.g. QSOs, in order
to establish in which celestial directions a pure astrometric selection is
feasible. When targeting regions at galactic latitude
the ratio of QSOs to apparently stationary stars is above 50\% and when
observing towards the poles the fraction of QSOs goes up to about \%.
We show that the proper motions from the proposed Gaia successor mission in
about 20 years would dramatically improve these results at all latitudes.
Detection of QSOs solely from zero proper motion, unbiased by any assumptions
on spectra, might lead to the discovery of new types of QSOs or new classes of
extragalactic point sources.Comment: 4 pages, 4 figures, sent in and accepted for publishing to A&
The Digital Divide and Courtroom Technology: Can David Keep Up With Goliath?
The federal judiciary recently embraced the technological revolution. Select courts are now equipped with state-of-the-art technology to aid in trial presentations. Before the judiciary made the improvements, litigants had to keep pace with the technological advancements themselves, often at a great cost. One might think that the recent technological improvements made to federal courtrooms would have widened the gap between large and small firms where the available resources are vastly different, but that is not the case. In fact, the installation of new technology into courtrooms serves to equalize what would otherwise be a digital divide.
Part II of this Note introduces the technologies available to lawyers when trying cases in the Electronic Courtrooms, and provides a brief overview of the types of technologies available in a judge\u27s chambers to facilitate caseload management. Part III of this Note analyzes whether large firms have any advantage over small firms or solo practitioners in effectively using the new, increasingly available technology. This portion of the Note compares the actual use of technology by large and small firms, examines reactions from practitioners who used the new systems, and analyzes why small firms and solo practitioners are not disadvantaged when litigating in an Electronic Courtroom
The Digital Divide and Courtroom Technology: Can David Keep Up With Goliath?
The federal judiciary recently embraced the technological revolution. Select courts are now equipped with state-of-the-art technology to aid in trial presentations. Before the judiciary made the improvements, litigants had to keep pace with the technological advancements themselves, often at a great cost. One might think that the recent technological improvements made to federal courtrooms would have widened the gap between large and small firms where the available resources are vastly different, but that is not the case. In fact, the installation of new technology into courtrooms serves to equalize what would otherwise be a digital divide.
Part II of this Note introduces the technologies available to lawyers when trying cases in the Electronic Courtrooms, and provides a brief overview of the types of technologies available in a judge\u27s chambers to facilitate caseload management. Part III of this Note analyzes whether large firms have any advantage over small firms or solo practitioners in effectively using the new, increasingly available technology. This portion of the Note compares the actual use of technology by large and small firms, examines reactions from practitioners who used the new systems, and analyzes why small firms and solo practitioners are not disadvantaged when litigating in an Electronic Courtroom
Genetic lineage tracing defines distinct neurogenic and gliogenic stages of ventral telencephalic radial glial development
<p>Abstract</p> <p>Background</p> <p>Radial glia comprise a molecularly defined neural progenitor population but their role in neurogenesis has remained contested due to the lack of a single universally accepted genetic tool for tracing their progeny and the inability to distinguish functionally distinct developmental stages.</p> <p>Results</p> <p>By direct comparisons of Cre/<it>loxP </it>lineage tracing results obtained using three different radial glial promoters (<it>Blbp</it>, <it>Glast</it>, and <it>hGFAP</it>), we show that most neurons in the brain are derived from radial glia. Further, we show that <it>hGFAP </it>promoter induction occurs in ventral telencephalic radial glia only after they have largely completed neurogenesis.</p> <p>Conclusion</p> <p>These data establish the major neurogenic role of radial glia in the developing central nervous system and genetically distinguish an early neurogenic <it>Blbp</it><sup>+</sup><it>Glast</it><sup>+</sup><it>hGFAP</it><sup>- </sup>stage from a later gliogenic <it>Blbp</it><sup>+</sup><it>Glast</it><sup>+</sup><it>hGFAP</it><sup>+ </sup>stage in the ventral telencephalon.</p
The high A_V Quasar Survey: A z=2.027 metal-rich damped Lyman-alpha absorber towards a red quasar at z=3.21
To fully exploit the potential of quasars as probes of cosmic chemical
evolution and the internal gas dynamics of galaxies it is important to
understand the selection effects behind the quasar samples and in particular if
the selection criteria exclude foreground galaxies with certain properties
(most importantly a high dust content). Here we present spectroscopic follow-up
from the 10.4-m GTC telescope of a dust-reddened quasar, eHAQ0111+0641, from
the extended High A_V Quasar (HAQ) survey. We find that the z=3.21 quasar has a
foreground Damped Lyman-alpha Absorber (DLA) at z=2.027 along the line of
sight. The DLA has very strong metal lines due to a moderately high metallicity
(with an inferred lower limit of 25% of the solar metallicity), but a very
large gas column density along the line-of-sight in its host galaxy. This
discovery is further evidence that there is a dust bias affecting the census of
metals, caused by the combined effect of dust obscuration and reddening, in
existing samples of z>2 DLAs. The case of eHAQ0111+0641 illustrates that dust
bias is not only caused by dust obscuration, but also dust reddening.Comment: 7 pages, 4 figures. Accepted for publication in A&A. A few typos have
been correcte
Serendipitous discovery of a projected pair of QSOs separated by 4.5 arcsec on the sky
We present the serendipitous discovery of a projected pair of quasi-stellar
objects (QSOs) with an angular separation of arcsec. The
redshifts of the two QSOs are widely different: one, our programme target, is a
QSO with a spectrum consistent with being a narrow line Seyfert 1 AGN at
. For this target we detect Lyman-, \ion{C}{4}, and
\ion{C}{3]}. The other QSO, which by chance was included on the spectroscopic
slit, is a Type 1 QSO at a redshift of , for which we detect
\ion{C}{4}, \ion{C}{3]} and \ion{Mg}{2}. We compare this system to previously
detected projected QSO pairs and find that only about a dozen previously known
pairs have smaller angular separation.Comment: 4 pages, 3 figures. Accepted for publication in A
Determining the fraction of reddened quasars in COSMOS with multiple selection techniques from X-ray to radio wavelengths
The sub-population of quasars reddened by intrinsic or intervening clouds of
dust are known to be underrepresented in optical quasar surveys. By defining a
complete parent sample of the brightest and spatially unresolved quasars in the
COSMOS field, we quantify to which extent this sub-population is fundamental to
our understanding of the true population of quasars. By using the available
multiwavelength data of various surveys in the COSMOS field, we built a parent
sample of 33 quasars brighter than mag, identified by reliable X-ray to
radio wavelength selection techniques. Spectroscopic follow-up with the
NOT/ALFOSC was carried out for four candidate quasars that had not been
targeted previously to obtain a 100\% redshift completeness of the sample. The
population of high quasars (HAQs), a specific sub-population of quasars
selected from optical/near-infrared photometry, is found to contribute
of the parent sample. The full population of bright spatially
unresolved quasars represented by our parent sample consists of
reddened quasars defined by having , and
of the sample having assuming the extinction
curve of the Small Magellanic Cloud. We show that the HAQ selection works well
for selecting reddened quasars, but some are missed because their optical
spectra are too blue to pass the color cut in the HAQ selection. This is
either due to a low degree of dust reddening or anomalous spectra. We find that
the fraction of quasars with contributing light from the host galaxy is most
dominant at . At higher redshifts the population of spatially
unresolved quasars selected by our parent sample is found to be representative
of the full population at mag. This work quantifies the bias against
reddened quasars in studies that are based solely on optical surveys.Comment: 22 pages, 10 figures, accepted for publication in A&A. The ArXiv
abstract has been shortened for it to be printabl
New high-sensitivity, milliarcsecond resolution results from routine observations of lunar occultations at the ESO VLT
(Abridged) Lunar occultations (LO) are a very efficient and powerful
technique, that achieves the best combination of high angular resolution and
sensitivity possible today at near-infrared wavelengths. Given that the events
are fixed in time, that the sources are occulted randomly, and that the
telescope use is minimal, the technique is very well suited for service mode
observations. We have established a program of routine LO observations at the
VLT observatory, especially designed to take advantage of short breaks
available in-between other programs. We have used the ISAAC instrument in burst
mode, capable of producing continuous read-outs at millisecond rates on a
suitable subwindow. Given the random nature of the source selection, our aim
has been primarily the investigation of a large number of stellar sources at
the highest angular resolution in order to detect new binaries. Serendipitous
results such as resolved sources and detection of circumstellar components were
also anticipated. We have recorded the signal from background stars for a few
seconds, around the predicted time of occultation by the Moon's dark limb. At
millisecond time resolution, a characteristic diffraction pattern can be
observed. Patterns for two or more sources superimpose linearly, and this
property is used for the detection of binary stars. The detailed analysis of
the diffraction fringes can be used to measure specific properties such as the
stellar angular size and the presence of extended light sources such as a
circumstellar shell. We present a list of 191 stars for which LO data could be
recorded and analyzed. Results include the detection of 16 binary and 2 triple
stars, all but one of which were previously unknown. The projected angular
separations are as small as 4 milliarcseconds and magnitude differences as high
as ?K=5.8 mag...Comment: 10 pages, 3 figures, to be published in A&
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