714 research outputs found
Observations of the 51.8 micron (O III) emission line in Orion
The 51.8 micron fine structure transition P2:3P2 3P1 for doubly ionized oxygen was observed in the Orion nebula. The observed line strength is of 5 plus or minus 3 times 10 to the minus 15th power watt/sq cm is in good agreement with theoretical predictions. Observations are consistent with the newly predicted 51.8 micron line position. The line lies close to an atmospheric water vapor feature at 51.7 micron, but is sufficiently distant so that corrections for this feature are straightforward. Observations of the 51.8 (O III) line are particularly important since the previously discovered 88 micron line from the same ion also is strong. This pair of lines should, therefore, yield new data about densities in observed H II regions; or else, if density data already are available from radio or other observations, the lines can be used to determine the differential dust absorption between 52 and 88 micron in front of heavily obscured regions
Diagrammatic Monte Carlo for Correlated Fermions
We show that Monte Carlo sampling of the Feynman diagrammatic series (DiagMC)
can be used for tackling hard fermionic quantum many-body problems in the
thermodynamic limit by presenting accurate results for the repulsive Hubbard
model in the correlated Fermi liquid regime. Sampling Feynman's diagrammatic
series for the single-particle self-energy we can study moderate values of the
on-site repulsion () and temperatures down to . We
compare our results with high temperature series expansion and with single-site
and cluster dynamical mean-field theory.Comment: 4 pages, 5 figures, stylistic change
Exploring optimum percentage of fly-ash as a replacement of cement for enhancement of concrete properties
Researchers and decision makers are continuously looking out to determine the potential and effectiveness of fly-ash as a partial replacement of cement in concrete. The current study is carried out to check the optimum or nearly optimum quantity of fly-ash with which cement should be replaced to get most of the properties of concrete enhanced and to give the idea about the quantities of fly-ash that can be used in a better way and better cause so that a proper management scheme of its usage and disposal can be implied. Further, a comparison is given between normal concrete and fly-ash concrete to show the properties which can be enhanced by proper utilization of fly-ash as a partial replacement of cement. After carrying out the lab experiments, it has been seen that the replacement of fly-ash in concrete has resulted in general increase in compressive strength, flexural strength and splitting tensile strength up to 15% replacement and after then the strength is decreased considerably than that of normal concrete. Addition of fly-ash in concrete has resulted in decrease in the water absorption of concrete and hence decreases in permeability of concrete. There is a progressive increase in workability with increase in percentage of fly-ash in concrete. The current study has led to a conclusion that in order to achieve best results in use of fly-ash concrete, the fly-ash used for replacing cement in concrete should have the required properties as specified by the standards and proper techniques of processing fly-ash as well as mixing of fly-ash with cement must be employed
Archaeal phylogenomics provides evidence in support of a methanogenic origin of the Archaea and a thaumarchaeal origin for the eukaryotes
We have developed a machine-learning approach to identify 3537 discrete orthologue protein sequence groups distributed across all available archaeal genomes. We show that treating these orthologue groups as binary detection/non-detection data is sufficient to capture the majority of archaeal phylogeny. We subsequently use the sequence data from these groups to infer a method and substitution-model-independent phylogeny. By holding this phylogeny constrained and interrogating the intersection of this large dataset with both the Eukarya and the Bacteria using Bayesian and maximum-likelihood approaches, we propose and provide evidence for a methanogenic origin of the Archaea. By the same criteria, we also provide evidence in support of an origin for Eukarya either within or as sisters to the Thaumarchaea
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Optimal gridding and degridding in radio interferometry imaging
In radio interferometry imaging, the gridding procedure of convolving
visibilities with a chosen gridding function is necessary to transform
visibility values into uniformly sampled grid points. We propose here a
parameterised family of "least-misfit gridding functions" which minimise an
upper bound on the difference between the DFT and FFT dirty images for a given
gridding support width and image cropping ratio. When compared with the widely
used spheroidal function with similar parameters, these provide more than 100
times better alias suppression and RMS misfit reduction over the usable dirty
map. We discuss how appropriate parameter selection and tabulation of these
functions allow for a balance between accuracy, computational cost and storage
size. Although it is possible to reduce the errors introduced in the gridding
or degridding process to the level of machine precision, accuracy comparable to
that achieved by CASA requires only a lookup table with 300 entries and a
support width of 3, allowing for a greatly reduced computation cost for a given
performance
Detection of the (OIII)88.16Mu line in M17
The detection of a predicted transition, the fine structure line of O3 at 88.16 microns in the H 2 region M17, was reported. Line intensity was measured at 2.2 sub + 7 sub -0.7 times 10 to the 15th power
Mapping the Kinematics of the Narrow-Line Region in the Seyfert Galaxy NGC 4151
Using The Hubble Space Telescope's Space Telescope Imaging Spectrograph HST's
STIS, observations of the OIII emission from the narrow-line region (NLR) of
NGC 4151 were obtained and radial velocities determined. Five orbits of HST
time were used to obtain spectra at five parallel slit configurations, at a
position angle of 58 degrees, with spatial resolution 0.2 arcseconds across and
0.1 arcseconds along each slit. A spectral resolving power of ~ 9,000 with the
G430M grating gave velocity measurements accurate to ~ 34 km/s. A kinematic
model was generated to match the radial velocities, for comparison to previous
kinematic models of biconical radial outflow developed for low-dispersion
spectra at two slit positions. The new high-resolution spectra permit the
measurement of accurate velocity dispersions for each radial-velocity
component. The full-width at half-maximum (FWHM) reaches a maximum of 1000 km/s
near the nucleus, and generally decreases with increasing distance to about 100
km/s in the extended narrow-line region (ENLR), starting at about 6 arcseconds
from the nucleus. In addition to the bright emission knots, which generally fit
our model, there are faint high velocity clouds which do not fit the biconical
outflow pattern of our kinematic model. These faint clouds occur at the
turnover points of the outflowing bright clouds. We suggest possible scenarios
that could explain these rogue clouds: (1) backflow resulting from shocks and
(2) outflow outside of the bicones, although the latter does not explain how
the knots are ionized and accelerated. A comparison of our observations with a
high-resolution radio map shows that there is no evidence that the kinematics
of the NLR clouds are affected by the radio lobes that comprise the inner jet.Comment: 30 pages, 15 figures (some color), accepted for publication in the
Astronomical Journal. Downloadable versions of the paper with high resolution
figures/images are available here:
http://www.chara.gsu.edu/~crenshaw/NGC4151_kinematics.pdf <--PDF Version
http://www.chara.gsu.edu/~crenshaw/NGC4151_kinematics.ps <--PS Versio
Improved Si:As BIBIB (Back-Illuminated Blocked-Impurity-Band) hybrid arrays
Results of a program to increase the short wavelength (less than 10 microns) detective quantum efficiency, eta/beta, of Si:As Impurity Band Conduction arrays are presented. The arrays are epitaxially grown Back-Illuminated Blocked (BIB) Impurity-Band (BIBIB) 10x50 detectors bonded to switched-FET multiplexers. It is shown that the 4.7 microns detective quantum efficiency increases proportionately with the thickness of the infrared active layer. A BIB array with a thick active layer, designed for low dark current, exhibits eta/beta = 7 to 9 percent at 4.7 microns for applied bias voltages between 3 and 5 V. The product of quantum efficiency and photoelectric gain, etaG, increases from 0.3 to 2.5 as the voltage increases from 3 to 5 V. Over this voltage range, the dark current increases from 8 to 120 e(-)s(-1) at a device temperature of 4.2 K and is under 70 e(-)s(-1) for all voltages at 2 K. Because of device gain, the effective dark current (equivalent photon rate) is less than 3 e(-)s(-1) under all operating conditions. The effective read noise (equivalent photon noise) is found to be less than 12 electrons under all operating conditions and for integration times between 0.05 and 100 seconds
Probing the Kinematics of the Narrow-Line Region in Seyfert Galaxies with Slitless Spectroscopy: Observational Results
We present slitless spectra of 10 Seyfert galaxies observed with the Space
Telescope Imaging Spectrograph on the Hubble Space Telescope. The spectra cover
the [OIII] 4959, 5007 emission lines at a spectral resolving power of ~9000 and
a spatial resolution of 0.1". We compare the slitless spectra with previous HST
narrow-band images to determine the velocity shifts and dispersions of the
bright emission-line knots in the narrow-line regions (NLRs) of these Seyferts.
Many knots are spatially resolved with sizes of tenths of arcsecs,
corresponding to tens of pcs, and yet they appear to move coherently with
radial velocities between zero and +/- 1200 km/s with respect to the systemic
velocities of their hostgalaxies. The knots also show a broad range in velocity
dispersion, ranging from ~30 km/s (the velocity resolution) to ~1000 km/s FWHM.
Most of the Seyfert galaxies in this sample show an organized flow pattern,
with radial velocities near zero at the nucleus (defined by the optical
continuum peak) and increasing to maximum blueshifts and redshifts within ~1''
of the nucleus, followed by a decline to the systemic velocity. The
emission-line knots also follow a general trend of decreasing velocity
dispersion with increasing distance. In the Seyfert 2 galaxies, the presence of
blueshifts and redshifts on either side of the nucleus indicates that rotation
alone cannot explain the observed radial velocities, and that radial outflow
plays an important role. Each of the Seyfert galaxies in this sample (with the
exception of Mrk 3) shows a bright, compact (FWHM < 0.5") [O III] knot at the
position of its optical nucleus. These nuclear emission-line knots have
radial-velocity centroids near zero, but they typically have the highest
velocity dispersions.Comment: 28 pages, 5 figures (on 9 pages), accepted for A
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