21,004 research outputs found
Experimental Performance of a Solar Air Collector with a Perforated Back Plate in New Zealand
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Late time tails from momentarily stationary, compact initial data in Schwarzschild spacetimes
An L-pole perturbation in Schwarzschild spacetime generally falls off at late
times t as t^{-2L-3}. It has recently been pointed out by Karkowski,
Swierczynski and Malec, that for initial data that is of compact support, and
is initially momentarily static, the late-time behavior is different, going as
t^{-2L-4}. By considering the Laplace transforms of the fields, we show here
why the momentarily stationary case is exceptional. We also explain, using a
time-domain description, the special features of the time development in this
exceptional case.Comment: 7 pages, 5 figure
A view of Large Magellanic Cloud HII regions N159, N132, and N166 through the 345 GHz window
We present results obtained towards the HII regions N159, N166, and N132 from
the emission of several molecular lines in the 345 GHz window. Using ASTE we
mapped a 2.4' 2.4' region towards the molecular cloud N159-W in the
CO J=3-2 line and observed several molecular lines at an IR peak very
close to a massive young stellar object. CO and CO J=3-2 were
observed towards two positions in N166 and one position in N132. The CO
J=3-2 map of the N159-W cloud shows that the molecular peak is shifted
southwest compared to the peak of the IR emission. Towards the IR peak we
detected emission from HCN, HNC, HCO, CH J=4-3, CS J=7-6, and
tentatively CO J=3-2. This is the first reported detection of these
molecular lines in N159-W. The analysis of the CH line yields more
evidence supporting that the chemistry involving this molecular species in
compact and/or UCHII regions in the LMC should be similar to that in Galactic
ones. A non-LTE study of the CO emission suggests the presence of both cool and
warm gas in the analysed region. The same analysis for the CS, HCO, HCN,
and HNC shows that it is very likely that their emissions arise mainly from
warm gas with a density between to some cm. The
obtained HCN/HNC abundance ratio greater than 1 is compatible with warm gas and
with an star-forming scenario. From the analysis of the molecular lines
observed towards N132 and N166 we propose that both regions should have similar
physical conditions, with densities of about 10 cm.Comment: accepted in MNRAS (October 5, 2015
Applying black hole perturbation theory to numerically generated spacetimes
Nonspherical perturbation theory has been necessary to understand the meaning
of radiation in spacetimes generated through fully nonlinear numerical
relativity. Recently, perturbation techniques have been found to be successful
for the time evolution of initial data found by nonlinear methods. Anticipating
that such an approach will prove useful in a variety of problems, we give here
both the practical steps, and a discussion of the underlying theory, for taking
numerically generated data on an initial hypersurface as initial value data and
extracting data that can be considered to be nonspherical perturbations.Comment: 14 pages, revtex3.0, 5 figure
Surface parameters of stannic oxide in powder, ceramic, and gel form by nitrogen adsorption techniques Interim report
Surface parameters of stannic oxide in powder, ceramic, and gel form by nitrogen adsorption techniques - analysis of adsorption isotherm
ASTE observations in the 345 GHz window towards the HII region N113 of the Large Magellanic Cloud
N113 is an HII region located in the central part of the Large Magellanic
Cloud (LMC) with an associated molecular cloud very rich in molecular species.
Most of the previously observed molecular lines cover the frequency range
85-270 GHz. Thus, a survey and study of lines at the 345 GHz window is required
in order to have a more complete understanding of the chemistry and excitation
conditions of the region. We mapped a region of 2.5' x 2.5' centered at N113
using the Atacama Submillimeter Telescope Experiment in the 13CO J=3-2 line
with an angular and spectral resolution of 22" and 0.11 km/s, respectively. In
addition, we observed 16 molecular lines as single pointings towards its
center. For the molecular cloud associated with N113, from the 13CO J=3-2 map
we estimate LTE and virial masses of about 1x10^4 and 4.5x10^4 M_sun,
respectively. Additionally, from the dust continuum emission at 500 micron we
obtain a mass of gas of 7x10^3 M_sun. Towards the cloud center we detected
emission from: 12CO, 13CO, C18O (3-2), HCN, HNC, HCO+, C2H (4-3), and CS (7-6);
being the first reported detection of HCN, HNC, and C2H (4-3) lines from this
region. The CS (7-6) which was previously tentatively detected is confirmed in
this study. By analyzing the HCN, HNC, and C2H, we suggest that their emission
may arise from a photodissociation region (PDR). Moreover, we suggest that the
chemistry involving the C2H in N113 can be similar to that in Galactic PDRs.
Using the HCN J=4-3, J=3-2, and J=1-0 lines in a RADEX analysis we conclude
that we are observing very high density gas, between some 10^5 and 10^7 cm-3.Comment: accepted for publication in A&A, September 9, 201
Elemental Abundances in M31: Alpha and Iron Element Abundances from Low-Resolution Resolved Stellar Spectroscopy in the Stellar Halo
Measurements of [Fe/H] and [/Fe] can probe the minor merging history
of a galaxy, providing a direct way to test the hierarchical assembly paradigm.
While measurements of [/Fe] have been made in the stellar halo of the
Milky Way, little is known about detailed chemical abundances in the stellar
halo of M31. To make progress with existing telescopes, we apply spectral
synthesis to low-resolution DEIMOS spectroscopy (R 2500 at 7000
Angstroms) across a wide spectral range (4500 Angstroms 9100
Angstroms). By applying our technique to low-resolution spectra of 170 giant
stars in 5 MW globular clusters, we demonstrate that our technique reproduces
previous measurements from higher resolution spectroscopy. Based on the
intrinsic dispersion in [Fe/H] and [/Fe] of individual stars in our
combined cluster sample, we estimate systematic uncertainties of 0.11 dex
and 0.09 dex in [Fe/H] and [/Fe], respectively. We apply our
method to deep, low-resolution spectra of 11 red giant branch stars in the
smooth halo of M31, resulting in higher signal-to-noise per spectral resolution
element compared to DEIMOS medium-resolution spectroscopy, given the same
exposure time and conditions. We find [/Fe] = 0.49
0.29 dex and [Fe/H] = 1.59 0.56 dex for our
sample. This implies that---much like the Milky Way---the smooth halo of M31 is
likely composed of disrupted dwarf galaxies with truncated star formation
histories that were accreted early in the halo's formation.Comment: 21 pages, 14 figures, accepted to Ap
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