10,294 research outputs found
The Color-Magnitude Relation in Coma: Clues to the Age and Metallicity of Cluster Populations
We have observed three fields of the Coma cluster of galaxies with a narrow
band (modified Stromgren) filter system. Observed galaxies include 31 in the
vicinity of NGC 4889, 48 near NGC 4874, and 60 near NGC 4839 complete to
M_5500=-18 in all three subclusters. Spectrophotometric classification finds
all three subclusters of Coma to be dominated by red, E type (ellipticals/S0's)
galaxies with a mean blue fraction, f_B, of 0.10. The blue fraction increases
to fainter luminosities, possible remnants of dwarf starburst population or the
effects of dynamical friction removing bright, blue galaxies from the cluster
population by mergers. We find the color-magnitude (CM) relation to be well
defined and linear over the range of M_5500=-13 to -22. After calibration to
multi-metallicity models, bright ellipticals are found to have luminosity
weighted mean [Fe/H] values between -0.5 and +0.5, whereas low luminosity
ellipticals have [Fe/H] values ranging from -2 to solar. The lack of CM
relation in our continuum color suggests that a systematic age effect cancels
the metallicity effects in this bandpass. This is confirmed with our age index
which finds a weak correlation between luminosity and mean stellar age in
ellipticals such that the stellar populations of bright ellipticals are 2 to 3
Gyrs younger than low luminosity ellipticals.Comment: 26 pages AAS LaTeX, 6 figures, accepted for publication in A
Special Education in Juvenile Residential Facilities: Can Animals Help?
Children with emotional/behavioral disorders (EBD) are arguably one of the highest at-risk groups for dropping out before graduating high school. They are the group of students with disabilities who are most likely to be educated in residential facilities. Residential facilities such as Green Chimneys have incorporated animals into the treatment milieu with success. Animals have been used in various settings to improve the quality of life as well as the emotional and physical needs of people served by these facilities. This article describes the requirements for using animals in residential treatment, the limitations of such programs, and the research findings for the use of animal-assisted therapy or activities (AAT/AAA). Using Gardner’s (1999) iteration of his theory of multiple intelligence, the authors proposed an understanding of how these treatments might be improve the intelligence of a child with EBD. Requirements for effective treatment of special needs children were discussed
Testing A (Stringy) Model of Quantum Gravity
I discuss a specific model of space-time foam, inspired by the modern
non-perturbative approach to string theory (D-branes). The model views our
world as a three brane, intersecting with D-particles that represent stringy
quantum gravity effects, which can be real or virtual. In this picture, matter
is represented generically by (closed or open) strings on the D3 brane
propagating in such a background. Scattering of the (matter) strings off the
D-particles causes recoil of the latter, which in turn results in a distortion
of the surrounding space-time fluid and the formation of (microscopic, i.e.
Planckian size) horizons around the defects. As a mean-field result, the
dispersion relation of the various particle excitations is modified, leading to
non-trivial optical properties of the space time, for instance a non-trivial
refractive index for the case of photons or other massless probes. Such models
make falsifiable predictions, that may be tested experimentally in the
foreseeable future. I describe a few such tests, ranging from observations of
light from distant gamma-ray-bursters and ultra high energy cosmic rays, to
tests using gravity-wave interferometric devices and terrestrial particle
physics experients involving, for instance, neutral kaons.Comment: 25 pages LATEX, four figures incorporated, uses special proceedings
style. Invited talk at the third international conference on Dark Matter in
Astro and Particle Physics, DARK2000, Heidelberg, Germany, July 10-15 200
POPULATION RECOVERY OF THE WHOOPING CRANE WITH EMPHASIS ON REINTRODUCTION EFFORTS: PAST AND FUTURE
The U.S. Fish and Wildlife Service (USFWS) began building a captive whooping crane (Grus americana) colony at Patuxent Wildlife Research Center (patuxent), Maryland, in 1966. From 1976 to 1984, 73 eggs from this colony and 216 eggs from Wood Buffalo National Park (Wood Buffalo), Canada, nests were placed in sandhill crane (G. canadensis) nests at Grays Lake National Wildlife Refuge (Grays Lake), Idaho, the site of the first whooping crane reintroduction attempt. Although 84 chicks fledged from the 289 eggs, the egg transfer program has been discontinued because of inordinately high mortality (only ca. 13 birds remain in the wild in 1991) and lack of breeding in survivors. In recent decades new methods have emerged for introducing captive-produced offspring to the wild. Surrogate studies with sandhill cranes, particularly the endangered Mississippi sandhill cranes (G. c. pulla), have shown that young cranes, raised either by captive, conspecific foster parents, or by costumed humans and in close association with live cranes and lifelike crane taxidermic dummies, have high post-release survival rates. These techniques will likely be used in future Whooping crane reintroduction programs. Current recovery objectives for the Whooping crane include expansion of the 2 captive colonies, establishment of a third captive colony in Canada, and reintroduction of 2 additional wild populations. The Kissimmee Prairie in central Florida has been selected for the next release experiment. Evaluation of this site began in 1984, and risk assessment is expected to begin in 1992 with the transfer and monitoring of a group of captivereared, juvenile whooping cranes. These tests of the environment will, if results are favorable, be followed by a full-scale reintroduction effort of at least 20 birds/year beginning in 1994 or 1995
Characterization of hexabundles: Initial results
New multi-core imaging fibre bundles -- hexabundles -- being developed at the
University of Sydney will provide simultaneous integral field spectroscopy for
hundreds of celestial sources across a wide angular field. These are a natural
progression from the use of single fibres in existing galaxy surveys.
Hexabundles will allow us to address fundamental questions in astronomy without
the biases introduced by a fixed entrance aperture. We have begun to consider
instrument concepts that exploit hundreds of hexabundles over the widest
possible field of view. To this end, we have compared the performance of a
61-core fully-fused hexabundle and 5 lightly-fused bundles with 7 cores each.
All fibres in the bundles have 100 micron cores. In the fully-fused bundle, the
cores are distorted from a circular shape in order to achieve a higher fill
fraction. The lightly-fused bundles have circular cores and five different
cladding thicknesses which affect the fill fraction. We compare the optical
performance of all 6 bundles and find that the advantage of smaller
interstitial holes (higher fill fraction) is outweighed by the increase in
modal coupling, cross-talk and the poor optical performance caused by the
deformation of the fibre cores. Uniformly high throughput and low cross-talk
are essential for imaging faint astronomical targets with sufficient resolution
to disentangle the dynamical structure. Devices already under development will
have between 100 and 200 lightly-fused cores, although larger formats are
feasible. The light-weight packaging of hexabundles is sufficiently flexible to
allow existing robotic positioners to make use of them.Comment: Accepted for publication in MNRAS. See also a complimentary paper on
the development of hexabundles - Bland-Hawthorn et al. 2011, Optics Express,
vol. 19, p. 2649
(http://www.opticsinfobase.org/abstract.cfm?URI=oe-19-3-2649
Prime focus spectrograph: Subaru's future
The Prime Focus Spectrograph (PFS) of the Subaru Measurement of Images and Redshifts (SuMIRe) project has been endorsed by Japanese community as one of the main future instruments of the Subaru 8.2-meter telescope at Mauna Kea, Hawaii. This optical/near-infrared multi-fiber spectrograph targets cosmology with galaxy surveys, Galactic archaeology, and studies of galaxy/AGN evolution. Taking advantage of Subaru’s wide field of view, which is further extended with the recently completed Wide Field Corrector, PFS will enable us to carry out multi-fiber spectroscopy of 2400 targets within 1.3 degree diameter. A microlens is attached at each fiber entrance for F-ratio transformation into a larger one so that difficulties of spectrograph design are eased. Fibers are accurately placed onto target positions by positioners, each of which consists of two stages of piezo-electric rotary motors, through iterations by using back-illuminated fiber position measurements with a widefield metrology camera. Fibers then carry light to a set of four identical fast-Schmidt spectrographs with three color arms each: the wavelength ranges from 0.38 μm to 1.3 μm will be simultaneously observed with an average resolving power of 3000. Before and during the era of extremely large telescopes, PFS will provide the unique capability of obtaining spectra of 2400 cosmological/astrophysical targets simultaneously with an 8-10 meter class telescope. The PFS collaboration, led by IPMU, consists of USP/LNA in Brazil, Caltech/JPL, Princeton, and JHU in USA, LAM in France, ASIAA in Taiwan, and NAOJ/Subaru
Supersymmetry and primordial black hole abundance constraints
We study the consequences of supersymmetry for primordial black hole (PBH)
abundance constraints. PBHs with mass less than about 10^{11}g will emit
supersymmetric particles when they evaporate. In most models of supersymmetry
the lightest of these particles, the lightest supersymmetric particle (LSP), is
stable and will hence survive to the present day. We calculate the limit on the
initial abundance of PBHs from the requirement that the present day LSP density
is less than the critical density. We apply this limit, along with those
previously obtained from the effects of PBH evaporation on nucleosynthesis and
the present day density of PBHs, to PBHs formed from the collpase of
inflationary density perturbations, in the context of supersymmetric inflation
models. If the reheat temperature after inflation is low, so as to avoid the
overproduction of gravitinos and moduli, then the lightest PBHs which are
produced in significant numbers will be evaporating around the present day and
there are therefore no constraints from the effects of the evaporation products
on nucleosynthesis or from the production of LSPs. We then examine models with
a high reheat temperature and a subsequent period of thermal inflation. In
these models avoiding the overproduction of LSPs limits the abundance of low
mass PBHs which were previously unconstrained. Throughout we incorporate the
production, at fixed time, of PBHs with a range of masses, which occurs when
critical collapse is taken into account.Comment: 8 pages RevTeX file with 3 figures incorporated (uses RevTeX and
epsf). Version to appear in Phys. Rev. D: minor change to calculation and
added discussio
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