8,771 research outputs found
The New Zealand Thrush: An Extinct Oriole
The New Zealand Thrush, or Piopio, is an extinct passerine that was endemic to New Zealand. It has often been placed in its own family (Turnagridae), unresolved relative to other passerines, but affinities with thrushes, Australaian magpies, manucodes, whistlers, birds-of-paradise and bowerbirds has been suggested based on morphological data. An affinity with the bowerbirds was also indicated in an early molecular study, but low statistical support make this association uncertain. In this study we use sequence data from three nuclear introns to examine the phylogenetic relationships of the piopios. All three genes independently indicate an oriole (Oriolidae) affinity of the piopios, and the monophyly of the typical orioles (Oriolus), figbirds (Sphecotheres), and the piopios is strongly supported in the Bayesian analysis of the concatenated data set (posterior probability = 1.0). The exact placement of the piopios within Oriolidae is, however, more uncertain but in the combined analysis and in two of the gene trees the piopios are placed basal to the typical orioles while the third gene suggest a sister relationship with the figbirds. This is the first time an oriole affinity has been proposed for the piopios. Divergence time estimates for the orioles suggest that the clade originated ca 20 million years ago, and based on these estimates it is evident that the piopios must have arrived on New Zealand by dispersal across the Tasman Sea and not as a result of vicariance when New Zealand separated from Gondwana in the late Cretaceous
Hypergolic ignitor
An ignitor for use with the MC-1 rocket engine has a cartridge bounded by two end caps with rupture disc assemblies connected thereto. A piston assembly within the cartridge moves from one end of the cartridge during the ignition process. The inlet of the ignitor communicates with a supply taken from the discharge of the fuel pump. When the pump is initially started, the pressure differential bursts the first rupture disc to begin the movement of the piston assembly toward the discharge end. The pressurization of the cartridge causes the second rupture disc to rupture and hypergolic fluid contained within the cartridge is discharged out the ignitor outlet
Parity Doubling in the Meson Spectrum
A simple argument for the restoration of parity symmetry high in the hadron
spectrum is presented. The restoration scale is estimated to be 2.5 GeV. This
in turn implies that typical quark model phenomenology such as scalar
confinement or the decay model are only useful for low lying states.
Minimal requirements for constructing more general phenomenologies are
discussed. An additional mass degeneracy between and states
is shown to occur and an isovector state is predicted at roughly 1700
MeV, in contradiction with the naive quark model. Similarly, isovector and
isoscalar states are predicted at 2000 MeV. Finally, these results
imply that Regge trajectories must become nonlinear at high spin.Comment: 5 pages, revtex, no figures, no tables. Version to appear in PL
Youth Definitions of Success, Obstacles to Success, and How Significant Others Can Help: Providing Youth a Voice in Their Own Development
Positive Youth Development (PYD) programmes are often conceptualized and led by adults with little or no youth input. The purpose of this study was to better understand youth definitions of success, obstacles they face in achieving success, and how they perceive others can help. Interviews were conducted with 24 youth from three different contexts (swim club, church group, and reform home) in Trinidad and Tobago. The results indicated that youth have a varied understanding of success. Further, many youths’ definitions mirror those prescribed in PYD literature. Youth identified a variety of obstacles in their quest for success, and though similarities existed, several obstacles were context dependent. Finally, youth identified support and assistance as the best mechanisms to propel them to success. Support, both informal and formal, points to the significant role non-parent adults serve in the lives of youth. Implications for youth programmes and future research are discussed
The Far-infrared Continuum of Quasars
ISO provides a key new far-infrared window through which to observe the
multi-wavelength spectral energy distributions (SEDs) of quasars and active
galactic nuclei (AGN). It allows us, for the first time, to observe a
substantial fraction of the quasar population in the far-IR, and to obtain
simultaneous, multi-wavelength observations from 5--200 microns. With these
data we can study the behavior of the IR continuum in comparison with
expectations from competing thermal and non-thermal models. A key to
determining which mechanism dominates, is the measurement of the peak
wavelength of the emission and the shape of the far-IR--mm turnover. Turnovers
which are steeper than frequency^2.5 indicate thermal dust emission in the
far-IR.
Preliminary results from our ISO data show broad, fairly smooth, IR continuum
emission with far-IR turnovers generally too steep to be explained by
non-thermal synchrotron emission. Assuming thermal emission throughout leads to
a wide inferred temperature range of 50-1000 K. The hotter material, often
called the AGN component, probably originates in dust close to and heated by
the central source, e.g. the ubiquitous molecular torus. The cooler emission is
too strong to be due purely to cool, host galaxy dust, and so indicates either
the presence of a starburst in addition to the AGN or AGN-heated dust covering
a wider range of temperatures than present in the standard, optically thick
torus models.Comment: 4 pages, to be published in the proceedings of "The Universe as Seen
by ISO," ed. M. Kessler. This and related papers can be found at
http://hea-www.harvard.edu/~ehooper/ISOkp/ISOkp.htm
Infrared Properties of High Redshift and X-ray Selected AGN Samples
The NASA/ISO Key Project on active galactic nuclei (AGN) seeks to better
understand the broad-band spectral energy distributions (SEDs) of these sources
from radio to X-rays, with particular emphasis on infrared properties. The ISO
sample includes a wide variety of AGN types and spans a large redshift range.
Two subsamples are considered herein: 8 high-redshift (1 < z < 4.7) quasars;
and 22 hard X-ray selected sources.
The X-ray selected AGN show a wide range of IR continuum shapes, extending to
cooler colors than the optical/radio sample of Elvis et al. (1994). Where a
far-IR turnover is clearly observed, the slopes are < 2.5 in all but one case
so that non-thermal emission remains a possibility. The highest redshift
quasars show extremely strong, hot IR continua requiring ~ 100 solar masses of
500 - 1000 Kelvin dust with ~ 100 times weaker optical emission. Possible
explanations for these unusual properties include: reflection of the optical
light from material above/below a torus; strong obscuration of the optical
continuum; or an intrinsic deficit of optical emission.Comment: 8 pages, 3 figures (2 color), to be published in the Springer Lecture
Notes of Physics Series as part of the proceedings for "ISO Surveys of a
Dusty Universe," a workshop held at Ringberg Castle, Germany, November 8 -
12, 1999. Requires latex style files for this series: cl2emult.cls,
cropmark.sty, lnp.sty, sprmindx.sty, subeqnar.sty (included with submission
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