283 research outputs found
Possible High-Redshift, Low-Luminosity AGN Activity in the Hubble Deep Field
In the Hubble Deep Field (HDF), twelve candidate sources of high-redshift (z
> 3.5) AGN activity have been identified. The color selection criteria were
established by passing spectra of selected quasars and Seyfert galaxies
(appropriately redshifted and modified for "Lyman forest" absorption), as well
as stars, observed normal and starburst galaxies, and galaxy models for various
redshifts through the filters used for the HDF observations. The actual
identification of AGN candidates also involved convolving a
Laplacian-of-Gaussian filter with the HDF images, thereby removing relatively
flat galactic backgrounds and leaving only the point-like components in the
centers. Along with positions and colors, estimated redshifts and absolute
magnitudes are reported, with the candidates falling toward the faint end of
the AGN luminosity function. One candidate has been previously observed
spectroscopically, with a measured redshift of 4.02. The number of sources
reported here is consistent with a simple extrapolation of the observed quasar
luminosity function to magnitude 30 in B_Johnson. Implications for ionization
of the intergalactic medium and for gravitational lensing are discussed.Comment: 10 pages LaTex plus 2 separate files (Table 1 which is a two-page
landscape LaTex file; and Figure 6 which is a large (0.7 MB) non-encapsulated
postscript file). Accepted for publication in the Astronomical Journa
Multiple sclerosis or neuromyelitis optica? Re-evaluating an 18th-century illness using 21st-century software
In this paper we report the application of an extensive database of symptoms, signs, laboratory findings and illnesses, to the diagnosis of an historical figure. The medical diagnosis of Augustus d'Este (1794â1848) â widely held to be the first documented case of multiple sclerosis â is reviewed, using the detailed symptom diary, which he kept over many years, as clinical data. Some of the reported features prompted the competing claim that d'Este suffered from acute porphyria, which in turn was used in support of the hypothesis that his grandfather, King George III, also suffered from the disease. We find that multiple sclerosis is statistically the most likely diagnosis, with neuromyelitis optica a strong alternative possibility. The database did not support a diagnosis of any of the acute porphyrias
Trapped Ion Imaging with a High Numerical Aperture Spherical Mirror
Efficient collection and analysis of trapped ion qubit fluorescence is
essential for robust qubit state detection in trapped ion quantum computing
schemes. We discuss simple techniques of improving photon collection efficiency
using high numerical aperture (N.A.) reflective optics. To test these
techniques we placed a spherical mirror with an effective N.A. of about 0.9
inside a vacuum chamber in the vicinity of a linear Paul trap. We demonstrate
stable and reliable trapping of single barium ions, in excellent agreement with
our simulations of the electric field in this setup. While a large N.A.
spherical mirror introduces significant spherical aberration, the ion image
quality can be greatly improved by a specially designed aspheric corrector lens
located outside the vacuum system. Our simulations show that the spherical
mirror/corrector design is an easy and cost-effective way to achieve high
photon collection rates when compared to a more sophisticated parabolic mirror
setup.Comment: 5 figure
Carbon stars at high Galactic latitude
Photometry and kinematics are presented for a sample of objective prism selected carbon stars towards the north and south Galactic poles. Distances are determined by fitting the infrared colors to a giant branch. If these stars are like the carbon stars seen in dwarf spheroidal galaxies, the median distance of the sample is 28 kpc. If they are more like the carbon stars found recently in the Galactic bulge, they may be only half as distant. The surface density of carbon stars as a function of distance is remarkably consistent with an R^(1/4) density profile for the Galactic halo. This density profile can be traced to â 15 scale radii and fills a volume similar to that occupied by globular clusters. The data yield an effective
radius of either 7.0 or 3.5 kpc depending on choice of distance scale. The velocity dispersion of the sample is 96 + 12 km/s. A kinematic model in which vertical velocity dispersion is independent of height above the Galactic plane seems in best accord with the data
Emission-Line Galaxy Surveys as Probes of the Spatial Distribution of Dwarf Galaxies. I. The University of Michigan Survey
Objective-prism surveys which select galaxies on the basis of line-emission
are extremely effective at detecting low-luminosity galaxies and constitute
some of the deepest available samples of dwarfs. In this study, we confirm that
emission-line galaxies (ELGs) in the University of Michigan (UM)
objective-prism survey (MacAlpine et al. 1977-1981) are reliable tracers of
large-scale structure, and utilize the depth of the samples to examine the
spatial distribution of low-luminosity (M -18.0) dwarfs relative to
higher luminosity giant galaxies (M -18.0) in the Updated Zwicky
Catalogue (Falco et al. 1999). New spectroscopic data are presented for 26 UM
survey objects. We analyze the relative clustering properties of the overall
starbursting ELG and normal galaxy populations, using nearest neighbor and
correlation function statistics. This allows us to determine whether the
activity in ELGs is primarily caused by gravitational interactions. We conclude
that galaxy-galaxy encounters are not the sole cause of activity in ELGs since
ELGs tend to be more isolated and are more often found in the voids when
compared to their normal galaxy counterparts. Furthermore, statistical analyses
performed on low-luminosity dwarf ELGs show that the dwarfs are less clustered
when compared to their non-active giant neighbors. The UM dwarf samples have
greater percentages of nearest neighbor separations at large values and lower
correlation function amplitudes relative to the UZC giant galaxy samples. These
results are consistent with the expectations of galaxy biasing.Comment: 17 pages, 4 tables, 10 figures. Accepted for publication in the Ap
Species and Genotype Effects of Bioenergy Crops on Root Production, Carbon and Nitrogen in Temperate Agricultural Soil
Bioenergy crops have a secondary benefit if they increase soil organic C (SOC) stocks through capture and allocation below-ground. The effects of four genotypes of short-rotation coppice willow (Salix spp., âTerra Novaâ and âToraâ) and Miscanthus (M. Ă giganteus (âGiganteusâ) and M. sinensis (âSinensisâ)) on roots, SOC and total nitrogen (TN) were quantified to test whether below-ground biomass controls SOC and TN dynamics. Soil cores were collected under (âplantâ) and between plants (âgapâ) in a field experiment on a temperate agricultural silty clay loam after 4- and 6-yearsâ management. Root density was greater under Miscanthus for plant (up to 15.5 kg mâ3) compared with gap (up to 2.7 kg mâ3) whereas willow had lower densities (up to 3.7 kg mâ3). Over two years, SOC increased below 0.2 m depth from 7.1 to 8.5 kg mâ3 and was greatest under Sinensis at 0-0.1 m depth (24.8 kg mâ3). Miscanthus-derived SOC, based on stable isotope analysis, was greater under plant (11.6 kg mâ3) than gap (3.1 kg mâ3) for Sinensis. Estimated SOC stock change rates over the two-year period to 1-m depth were 6.4 for Terra Nova, 7.4 for Tora, 3.1 for Giganteus and 8.8 Mg haâ1 yearâ1 for Sinensis. Rates of change of TN were much less. That SOC matched root mass down the profile, particularly under Miscanthus, indicated that perennial root systems are an important contributor. Willow and Miscanthus offer both biomass production and C sequestration when planted in arable soil
Rothamsted Research willow (Salix spp.) breeding programme: multi-site yield trial results 2014
On the application of radio frequency voltages to ion traps via helical resonators
Ions confined using a Paul trap require a stable, high voltage and low noise
radio frequency (RF) potential. We present a guide for the design and
construction of a helical coil resonator for a desired frequency that maximises
the quality factor for a set of experimental constraints. We provide an
in-depth analysis of the system formed from a shielded helical coil and an ion
trap by treating the system as a lumped element model. This allows us to
predict the resonant frequency and quality factor in terms of the physical
parameters of the resonator and the properties of the ion trap. We also compare
theoretical predictions with experimental data for different resonators, and
predict the voltage applied to the ion trap as a function of the Q-factor,
input power and the properties of the resonant circuit
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