4,091 research outputs found
ALMA Temporal Phase Stability and the Effectiveness of Water Vapor Radiometer
Atacama Large Millimeter/submillimeter Array (ALMA) will be the world largest
mm/submm interferometer, and currently the Early Science is ongoing, together
with the commissioning and science verification (CSV). Here we present a study
of the temporal phase stability of the entire ALMA system from antennas to the
correlator. We verified the temporal phase stability of ALMA using data, taken
during the last two years of CSV activities. The data consist of integrations
on strong point sources (i.e., bright quasars) at various frequency bands, and
at various baseline lengths (up to 600 m). From the observations of strong
quasars for a long time (from a few tens of minutes, up to an hour), we derived
the 2-point Allan Standard Deviation after the atmospheric phase correction
using the 183 GHz Water Vapor Radiometer (WVR) installed in each 12 m antenna,
and confirmed that the phase stability of all the baselines reached the ALMA
specification. Since we applied the WVR phase correction to all the data
mentioned above, we also studied the effectiveness of the WVR phase correction
at various frequencies, baseline lengths, and weather conditions. The phase
stability often improves a factor of 2 - 3 after the correction, and sometimes
a factor of 7 improvement can be obtained. However, the corrected data still
displays an increasing phase fluctuation as a function of baseline length,
suggesting that the dry component (e.g., N2 and O2) in the atmosphere also
contributes the phase fluctuation in the data, although the imperfection of the
WVR phase correction cannot be ruled out at this moment.Comment: Proc. SPIE 8444-125, in press (7 pages, 4 figures, 1 table
'Special K' and a loss of cell-to-cell adhesion in proximal tubule-derived epithelial cells: modulation of the adherens junction complex by ketamine
Ketamine, a mild hallucinogenic class C drug, is the fastest growing âparty drugâ used by 16â24 year olds in the UK. As the recreational use of Ketamine increases we are beginning to see the signs of major renal and bladder complications. To date however, we know nothing of a role for Ketamine in modulating both structure and function of the human renal proximal tubule. In the current study we have used an established model cell line for human epithelial cells of the proximal tubule (HK2) to demonstrate that Ketamine evokes early changes in expression of proteins central to the adherens junction complex. Furthermore we use AFM single-cell force spectroscopy to assess if these changes functionally uncouple cells of the proximal tubule ahead of any overt loss in epithelial cell function. Our data suggests that Ketamine (24â48 hrs) produces gross changes in cell morphology and cytoskeletal architecture towards a fibrotic phenotype. These physical changes matched the concentration-dependent (0.1â1 mg/mL) cytotoxic effect of Ketamine and reflect a loss in expression of the key adherens junction proteins epithelial (E)- and neural (N)-cadherin and ÎČ-catenin. Down-regulation of protein expression does not involve the pro-fibrotic cytokine TGFÎČ, nor is it regulated by the usual increase in expression of Slug or Snail, the transcriptional regulators for E-cadherin. However, the loss in E-cadherin can be partially rescued pharmacologically by blocking p38 MAPK using SB203580. These data provide compelling evidence that Ketamine alters epithelial cell-to-cell adhesion and cell-coupling in the proximal kidney via a non-classical pro-fibrotic mechanism and the data provides the first indication that this illicit substance can have major implications on renal function. Understanding Ketamine-induced renal pathology may identify targets for future therapeutic intervention
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High-Frequency Measurements Of The Spectrum Of Sagittarius A*
We report near-simultaneous interferometric measurements of the spectrum of Sagittarius A* over the 5-354 GHz range and single-dish observations that have yielded the first detection of Sgr A* at 850 GHz. We confirm that Sgr A*'s spectrum rises more steeply at short millimeter wavelengths than at centimeter wavelengths, leading to a near-millimeter/submillimeter excess that dominates its luminosity. Below 900 GHz, Sgr A*'s observed luminosity is 70 +/- 30 L.. A new upper limit to Sgr A*'s 24.3 mu m flux, together with a compilation of other extant IR data, imply a far-infrared spectral turnover, which can result from either an intrinsic synchrotron cutoff or excess extinction near Sgr A*. If the former applies, Sgr A*'s total synchrotron luminosity is <10(3) L., while in the latter case it is <3 x 10(4) L. if spherical symmetry also applies.NSF AST96-15025, AST96-13717Astronom
Measurement of Antenna Surfaces from In- and Out-Of-Focus Beam Maps using Astronomical Sources
We present a technique for the accurate estimation of large-scale errors in
an antenna surface using astronomical sources and detectors. The technique
requires several out-of-focus images of a compact source and the
signal-to-noise ratio needs to be good but not unreasonably high. For a given
pattern of surface errors, the expected form of such images can be calculated
directly. We show that it is possible to solve the inverse problem of finding
the surface errors from the images in a stable manner using standard numerical
techniques. To do this we describe the surface error as a linear combination of
a suitable set of basis functions (we use Zernike polynomials). We present
simulations illustrating the technique and in particular we investigate the
effects of receiver noise and pointing errors. Measurements of the 15-m James
Clerk Maxwell telescope made using this technique are presented as an example.
The key result is that good measurements of errors on large spatial scales can
be obtained if the input images have a signal-to-noise ratio of order 100 or
more. The important advantage of this technique over transmitter-based
holography is that it allows measurements at arbitrary elevation angles, so
allowing one to characterise the large scale deformations in an antenna as a
function of elevation.Comment: 6 pages, 5 figures (accepted by Astronomy & Astrophysics
Out-Of-Focus Holography at the Green Bank Telescope
We describe phase-retrieval holography measurements of the 100-m diameter
Green Bank Telescope using astronomical sources and an astronomical receiver
operating at a wavelength of 7 mm. We use the technique with parameterization
of the aperture in terms of Zernike polynomials and employing a large defocus,
as described by Nikolic, Hills & Richer (2006). Individual measurements take
around 25 minutes and from the resulting beam maps (which have peak signal to
noise ratios of 200:1) we show that it is possible to produce low-resolution
maps of the wavefront errors with accuracy around a hundredth of a wavelength.
Using such measurements over a wide range of elevations, we have calculated a
model for the wavefront-errors due to the uncompensated gravitational
deformation of the telescope. This model produces a significant improvement at
low elevations, where these errors are expected to be the largest; after
applying the model, the aperture efficiency is largely independent of
elevation. We have also demonstrated that the technique can be used to measure
and largely correct for thermal deformations of the antenna, which often exceed
the uncompensated gravitational deformations during daytime observing.
We conclude that the aberrations induced by gravity and thermal effects are
large-scale and the technique used here is particularly suitable for measuring
such deformations in large millimetre wave radio telescopes.Comment: 10 pages, 7 figures (accepted by Astronomy & Astrophysics
Dose-area product measurements during Barium enema radiograph examinations -a Western Cape study
The aim of this study was to obtain a direct measurement of the typical dose delivered to an average adult patient during a barium enema examination. Measurement was done on a sample of 50 patients at three departments, using a dose-area product (DAP) meter. The comparison of the results with UK median levels indicates that the doses measured in South Africa are higher (41 Gy cm2 (dose x area) v. 48 Gy cm2 ). Patient protection can be improved by comparing local practice with national reference levels. The values obtained in this study (first quartile 35 Gy cm2, median 48 Gy cm2, third quartile 84 Gy cm2) are recommended as initial reference dose levels for barium enemas in South Africa
Interferometric Observations of the Nuclear Region of Arp220 at Submillimeter Wavelengths
We report the first submillimeter interferometric observations of an
ultraluminous infrared galaxy. We observed Arp220 in the CO J=3-2 line and
342GHz continuum with the single baseline CSO-JCMT interferometer consisting of
the Caltech Submillimeter Observatory (CSO) and the James Clerk Maxwell
Telescope (JCMT). Models were fit to the measured visibilities to constrain the
structure of the source. The morphologies of the CO J=3-2 line and 342GHz
continuum emission are similar to those seen in published maps at 230 and
110GHz. We clearly detect a binary source separated by about 1 arcsec in the
east-west direction in the 342GHz continuum. The CO J=3-2 visibility
amplitudes, however, indicate a more complicated structure, with evidence for a
compact binary at some velocities and rather more extended structure at others.
Less than 30% of the total CO J=3-2 emission is detected by the interferometer,
which implies the presence of significant quantities of extended gas. We also
obtained single-dish CO J=2-1, CO J=3-2 and HCN J=4-3 spectra. The HCN J=4-3
spectrum, unlike the CO spectra, is dominated by a single redshifted peak. The
HCN J=4-3/CO J=3-2, HCN J=4-3/HCN J=1-0 and CO J=3-2/2-1 line ratios are larger
in the redshifted (eastern) source, which suggests that the two sources may
have different physical conditions. This result might be explained by the
presence of an intense starburst that has begun to deplete or disperse the
densest gas in the western source, while the eastern source harbors undispersed
high density gas.Comment: 17 pages, 9 figures, 4 Tables. accepted by Ap
Blue Straggler Stars: The Spectacular Population in M80
Using HST-WFPC2 observations in two ultraviolet (UV) filters (F225W and
F336W) of the central region of the high density Galactic Globular cluster
(GGC) M80 we have identified 305 Blue Straggler Stars (BSS) which represents
the largest and most concentrated population of BSS ever observed in a GGC. We
also identify the largest, clean sample of evolved BSS yet found. The high
stellar density alone cannot explain the BSS, and we suggest that in M80 we are
witnessing a transient dynamical state, during which stellar interactions are
delaying the core-collapse process leading to an exceptionally large population
of collisional-BSS.Comment: 15 pages, 5 figures, Astrophysical Journal Letters, in pres
Characterizing the early vocabulary profiles of preverbal and minimally verbal children with autism spectrum disorder
Abstract
Children with autism spectrum disorder (ASD) often have significant language delays. But do they learn language differently than neurotypical toddlers? We compared the lexical skills of 64 preverbal and minimally verbal children with ASD, to 461 vocabulary-size-matched typically developing (TD) toddlers. We also examined social features of verb knowledge using a novel collection of social ratings. Children with ASD produced proportionally more verbs than TD toddlers. Children with ASD produced proportionally more action and food words, while TD toddlers produced proportionally more animal, people words, and animal sounds and sound effects. Children with ASD also produced âmommyâ and âdaddyâ at lower rates. We discuss how these differences may reflect an association between lexical development and weaknesses in social communication.
Lay abstract
Although preverbal and minimally verbal (PV-MV) children with autism spectrum disorder (ASD) represent a significant portion of the ASD population, we have a limited understanding of and characterization of them. Though it is a given that their lexical profiles contain fewer words, it is important to determine whether: a) the words PV-MV children with ASD produce are similar to the first words typically developing (TD) children produce, or b) there are unique features of the limited words that PV-MV children with ASD produce. The current study compared the early word profiles of PV-MV children with ASD to vocabulary-matched TD toddlers. Children with ASD produced proportionally more verbs than TD toddlers. Also, children with ASD produced proportionally more action and food words, while TD toddlers produced proportionally more animal words, animal sounds and sound effects, and people words. Children with ASD also produced âmommyâ and âdaddyâ at lower rates. Our findings identified several areas of overlap in early word learning; however, our findings also point to differences that may be connected to core weaknesses in social communication (i.e., people words). The findings highlight words and categories that could serve as useful targets for communication intervention with PV-MV children with ASD
Another Non-segregated Blue Straggler Population in a Globular Cluster: the Case of NGC 2419
We have used a combination of ACS-HST high-resolution and wide-field SUBARU
data in order to study the Blue Straggler Star (BSS) population over the entire
extension of the remote Galactic globular cluster NGC 2419. The BSS population
presented here is among the largest ever observed in any stellar system, with
more than 230 BSS in the brightest portion of the sequence. The radial
distribution of the selected BSS is essentially the same as that of the other
cluster stars. In this sense the BSS radial distribution is similar to that of
omega Centauri and unlike that of all Galactic globular clusters studied to
date, which have highly centrally segregated distributions and, in most cases,
a pronounced upturn in the external regions. As in the case of omega Centauri,
this evidence indicates that NGC 2419 is not yet relaxed even in the central
regions. This observational fact is in agreement with estimated half-mass
relaxation time, which is of the order of the cluster age.Comment: in press in the Ap
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