3,593 research outputs found
A limit on the detectability of the energy scale of inflation
We show that the polarization of the cosmic microwave background can be used
to detect gravity waves from inflation if the energy scale of inflation is
above 3.2 times 10^15 GeV. These gravity waves generate polarization patterns
with a curl, whereas (to first order in perturbation theory) density
perturbations do not. The limiting ``noise'' arises from the second--order
generation of curl from density perturbations, or rather residuals from its
subtraction. We calculate optimal sky coverage and detectability limits as a
function of detector sensitivity and observing time.Comment: 4 pages, 3 figures, submitted to PR
Far-flung Filaments of Ejecta in the Young Supernova Remnant G292.0+1.8
New optical images of the young SNR G292.0+1.8, obtained from the 0.9-m
telescope at CTIO, show a more extensive network of filaments than had been
known previously. Filaments emitting in [O III] are distributed throughout much
of the 8 arcmin diameter shell seen in X-ray and radio images, including a few
at the very outermost shell limits. We have also detected four small complexes
of filaments that show [S II] emission along with [OIII]. In a single long-slit
spectrum we find variations of almost an order of magnitude in the relative
strengths of oxygen and sulfur lines, which must result from abundance
variations. None of the filaments, with or without [S II], shows any evidence
for hydrogen, so all appear to be fragments of pure SN ejecta. The [S II]
filaments provide the first evidence for undiluted products of oxygen burning
in the ejecta from the supernova that gave rise to G292.0+1.8. Some oxygen
burning must have occurred, but the paucity of [S II]-emitting filaments
suggests that either the oxygen burning was not extensive or that most of its
products have yet to be excited. Most of the outer filaments exhibit radial,
pencil-like morphologies that suggest an origin as Rayleigh-Taylor fingers of
ejecta, perhaps formed during the explosion. Simulations of core-collapse
supernovae predict such fingers, but these have never before been so clearly
observed in a young SNR. The total flux from the SNR in [OIII] 5007 is 5.4 *
10**-12 ergs/cm**2/s. Using a distance of 6 kpc and an extinction correction
corresponding to E(B-V) = 0.6 (lower than previous values but more consistent
both with our data and radio and X-ray estimates of NH), this leads to a
luminosity of 1.6 * 10**35 ergs/s in the 5007 Ang. line.Comment: 32 pages including 10 figures, and 3 tables, accepted for publication
in AJ. Vol 132, July 2006. Higher resolution versions of the figures and a
pdf of the manuscript can be found at
http://www-int.stsci.edu/~long/papers/g292_optical
Ab initio many-body calculation of excitons in solid Ne and Ar
Absorption spectra, exciton energy levels and wave functions for solid Ne and
Ar have been calculated from first principles using many-body techniques.
Electronic band structures of Ne and Ar were calculated using the GW
approximation. Exciton states were calculated by diagonalizing an exciton
Hamiltonian derived from the particle-hole Green function, whose equation of
motion is the Bethe-Salpeter equation. Singlet and triplet exciton series up to
n=5 for Ne and n=3 for Ar were obtained. Binding energies and
longitudinal-transverse splittings of n=1 excitons are in excellent agreement
with experiment. Plots of correlated electron-hole wave functions show that the
electron-hole complex is delocalised over roughly 7 a.u. in solid Ar.Comment: 6 page
Supervisor Cultural Responsiveness and Unresponsiveness in Cross-Cultural Supervision
Thirteen supervisees’ of color and 13 European American supervisees’ experiences of culturally responsive and unresponsive cross-cultural supervision were studied using consensual qualitative research. In culturally responsive supervision, all supervisees felt supported for exploring cultural issues, which positively affected the supervisee, the supervision relationship, and client outcomes. In culturally unresponsive supervision, cultural issues were ignored, actively discounted, or dismissed by supervisors, which negatively affected the supervisee, the relationship, and/or client outcomes. European American supervisees’ and supervisees’ of color experiences diverged significantly, with supervisees of color experiencing unresponsiveness more frequently and with more negative effects than European American supervisees. Implications for research and supervision practice are discussed
Can inflationary models of cosmic perturbations evade the secondary oscillation test?
We consider the consequences of an observed Cosmic Microwave Background (CMB)
temperature anisotropy spectrum containing no secondary oscillations. While
such a spectrum is generally considered to be a robust signature of active
structure formation, we show that such a spectrum {\em can} be produced by
(very unusual) inflationary models or other passive evolution models. However,
we show that for all these passive models the characteristic oscillations would
show up in other observable spectra. Our work shows that when CMB polarization
and matter power spectra are taken into account secondary oscillations are
indeed a signature of even these very exotic passive models. We construct a
measure of the observability of secondary oscillations in a given experiment,
and show that even with foregrounds both the MAP and \pk satellites should be
able to distinguish between models with and without oscillations. Thus we
conclude that inflationary and other passive models can {\em not} evade the
secondary oscillation test.Comment: Final version accepted for publication in PRD. Minor improvements
have been made to the discussion and new data has been included. The
conclusions are unchagne
Anisotropy in the Cosmic Microwave Background at Degree Angular Scales: Python V Results
Observations of the microwave sky using the Python telescope in its fifth
season of operation at the Amundsen-Scott South Pole Station in Antarctica are
presented. The system consists of a 0.75 m off-axis telescope instrumented with
a HEMT amplifier-based radiometer having continuum sensitivity from 37-45 GHz
in two frequency bands. With a 0.91 deg x 1.02 deg beam the instrument fully
sampled 598 deg^2 of sky, including fields measured during the previous four
seasons of Python observations. Interpreting the observed fluctuations as
anisotropy in the cosmic microwave background, we place constraints on the
angular power spectrum of fluctuations in eight multipole bands up to l ~ 260.
The observed spectrum is consistent with both the COBE experiment and previous
Python results. There is no significant contamination from known foregrounds.
The results show a discernible rise in the angular power spectrum from large (l
~ 40) to small (l ~ 200) angular scales. The shape of the observed power
spectrum is not a simple linear rise but has a sharply increasing slope
starting at l ~ 150.Comment: 5 page
Measuring CMB polarisation with the Planck mission
In this paper, we discuss why and how the Planck mission, originally designed
and proposed for mapping CMB intensity fluctuations, has been revised for
polarisation measurement capability as well
Hubble Space Telescope Observations of UV Oscillations in WZ Sagittae During the Decline from Outburst
We present a time series analysis of Hubble Space Telescope observations of
WZ Sge obtained in 2001 September, October, November and December as WZ Sge
declined from its 2001 July superoutburst. Previous analysis of these data
showed the temperature of the white dwarf decreased from ~29,000 K to ~18,000
K. In this study we binned the spectra over wavelength to yield ultraviolet
light curves at each epoch that were then analyzed for the presence of the
well-known 27.87 s and 28.96 s oscillations. We detect the 29 s periodicity at
all four epochs, but the 28 s periodicity is absent. The origin of these
oscillations has been debated since their discovery in the 1970s and competing
hypotheses are based on either white dwarf non-radial g-mode pulsations or
magnetically-channelled accretion onto a rotating white dwarf. By analogy with
the ZZ Ceti stars, we argue that the non-radial g-mode pulsation model demands
a strong dependence of pulse period on the white dwarf's temperature. However,
these observations show the 29 s oscillation is independent of the white
dwarf's temperature. Thus we reject the white dwarf non-radial g-mode pulsation
hypothesis as the sole origin of the oscillations. It remains unclear if
magnetically-funnelled accretion onto a rapidly rotating white dwarf (or belt
on the white dwarf) is responsible for producing the oscillations. We also
report the detection of a QPO with period ~18 s in the September light curve.
The amplitudes of the 29 s oscillation and the QPO vary erratically on short
timescales and are not correlated with the mean system brightness nor with each
other.Comment: 20 pages, 3 figures, 1 table; accepted for publication in Ap
The Terrestrial Carbon (Terra C) Information System to facilitate carbon synthesis across heterogeneous landscapes.
There are urgent needs to better synthesize knowledge and data across large regions and time periods to address global climate change, conduct soil/terrestrial carbon accounting, model carbon dynamics, assess carbon sequestration, and develop strategies for mitigation and adaptation. To address these needs we developed the Terrestrial Carbon (TerraC) Information System dedicated to advance soil/terrestrial carbon science. TerraC offers user-friendly tools to upload, store, manage, query, analyze, and download lab and field data characterizing carbon in soils, plants/biomass, atmosphere, water, and whole ecosystems. The purpose of TerraC is three-fold to: (i) advance carbon science through sharing of carbon and ancillary environmental data; (ii) facilitate environmental synthesis; and (iii) enhance collaboration among students, faculty, scientists, and extension specialists through shared resources. Data and metadata stored in TerraC can be shared privately among selected users (groups) or publicly with any user. We integrated various spatially-explicit soil carbon and ancillary environmental data collected in Florida representing different time periods, and conducted a synthesis analysis on soil carbon that will be presented as a case study. Detailed information about TerraC and data sharing options are available at: http://TerraC.ifas.ufl.edu
CMB Anisotropy Induced by Cosmic Strings on Angular Scales
We have computed an estimate of the angular power spectrum of the Cosmic
Microwave Background (CMB) induced by cosmic strings on angular scales , using a numerical simulation of a cosmic string network; and decomposed
this pattern into scalar, vector, and tensor parts. We find no evidence for
strong acoustic oscillations in the scalar anisotropy but rather a broad peak.
The anisotropies from vector modes dominate except on very small angular scales
while the tensor anisotropies are sub-dominant on all angular scales. The
anisotropies generated after recombination are even more important than in
adiabatic models. We expect that these qualitative features are robust to the
varying of cosmological parameters, a study which has not yet been done.Comment: 4 pages, 2 figure
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