3,420 research outputs found
The Magnetic Field of the H~II Region NGC 6334A
We have studied the polarization characteristics and Faraday rotation of the
extragalactic radio source J172043554, that appears projected on the north
lobe of the galactic H II region NGC 6334A. From observations made with the
Very Large Array at 6.0 and 3.6 cm in three different epochs (1994, 1997, and
2006), we estimate a rotation measure of +5100900 rad m for the
extragalactic source. This large rotation measure implies a line-of-sight
average magnetic field of G, the largest
obtained by this method for an H II region. NGC 6334A is significantly denser
than other H II regions studied and this larger magnetic field is expected on
the grounds of magnetic flux conservation. The ratio of thermal to magnetic
pressure is 5, in the range of values determined for more diffuse H II
regions.Comment: 5 pages, 0 figure
NN interaction in a Goldstone boson exchange model
Adiabatic nucleon-nucleon potentials are calculated in a six-quark
nonrelativistic chiral constituent quark model where the Hamiltonian contains a
linear confinement and a pseudoscalar meson (Goldstone boson) exchange
interaction between quarks. Calculations are performed both in a cluster model
and a molecular orbital basis, through coupled channels. In both cases the
potentials present an important hard core at short distances, explained through
the dominance of the [51]_{FS} configuration, but do not exhibit an attractive
pocket. We add a scalar meson exchange interaction and show how it can account
for some middle-range attraction.Comment: 32 pages with 12 eps figures incorporated, RevTeX. Final version
published in PR
Production, purification, and characterization of recombinant hFSH glycoforms for functional studies
Previously, our laboratory demonstrated the existence of a ÎČ-subunit glycosylation-deficient human FSH glycoform, hFSH21. A third variant, hFSH18, has recently been detected in FSH glycoforms isolated from purified pituitary hLH preparations. Human FSH21 abundance in individual female pituitaries progressively decreased with increasing age. Hypo-glycosylated glycoform preparations are significantly more active than fully-glycosylated hFSH preparations. The purpose of this study was to produce, purify and chemically characterize both glycoform variants expressed by a mammalian cell line. Recombinant hFSH was expressed in a stable GH3 cell line and isolated from serum-free cell culture medium by sequential, hydrophobic and immunoaffinity chromatography. FSH glycoform fractions were separated by Superdex 75 gel-filtration. Western blot analysis revealed the presence of both hFSH18 and hFSH21 glycoforms in the low molecular weight fraction, however, their electrophoretic mobilities differed from those associated with the corresponding pituitary hFSH variants. Edman degradation of FSH21/18 -derived ÎČ-subunit before and after peptide-N-glycanase F digestion confirmed that it possessed a mixture of both mono-glycosylated FSHÎČ subunits, as both Asn7 and Asn24 were partially glycosylated. FSH receptor-binding assays confirmed our previous observations that hFSH21/18 exhibits greater receptor-binding affinity and occupies more FSH binding sites when compared to fully-glycosylated hFSH24. Thus, the age-related reduction in hypo-glycosylated hFSH significantly reduces circulating levels of FSH biological activity that may further compromise reproductive function. Taken together, the ability to express and isolate recombinant hFSH glycoforms opens the way to study functional differences between them both in vivo and in vitro
Faraday rotation of the supernova remnant G296.5+10.0: Evidence for a Magnetized Progenitor Wind
We present spectropolarimetric radio images of the supernova remnant (SNR)
G296.5+10.0 at frequencies near 1.4 GHz, observed with the Australia Telescope
Compact Array. By applying rotation measure (RM) synthesis to the data, a
pixel-by-pixel map of Faraday rotation has been produced for the entire
remnant. We find G296.5+10.0 to have a highly ordered RM structure, with mainly
positive RMs (mean RM of +28 rad/m**2) on the eastern side and negative RMs
(mean RM of -14 rad/m**2) on the western side, indicating a magnetic field
which is directed away from us on one side and toward us on the other. We
consider several possible mechanisms for creating the observed RM pattern.
Neither Faraday rotation in foreground interstellar gas nor in a homogeneous
ambient medium swept up by the SNR shell can easily explain the magnitude and
sign of the observed RM pattern. Instead, we propose that the observed RMs are
the imprint of an azimuthal magnetic field in the stellar wind of the
progenitor star. Specifically, we calculate that a swept-up magnetized wind
from a red supergiant can produce RMs of the observed magnitude, while the
azimuthal pattern of the magnetic field at large distances from the star
naturally produces the anti-symmetric RM pattern observed. Expansion into such
a wind can possibly also account for the striking bilateral symmetry of the
SNR's radio and X-ray morphologies.Comment: Accepted for publication in The Astrophysical Journa
The Octave (Birmingham - Sheffield Hallam) automated pipeline for extracting oscillation parameters of solar-like main-sequence stars
The number of main-sequence stars for which we can observe solar-like
oscillations is expected to increase considerably with the short-cadence
high-precision photometric observations from the NASA Kepler satellite. Because
of this increase in number of stars, automated tools are needed to analyse
these data in a reasonable amount of time. In the framework of the asteroFLAG
consortium, we present an automated pipeline which extracts frequencies and
other parameters of solar-like oscillations in main-sequence and subgiant
stars. The pipeline uses only the timeseries data as input and does not require
any other input information. Tests on 353 artificial stars reveal that we can
obtain accurate frequencies and oscillation parameters for about three quarters
of the stars. We conclude that our methods are well suited for the analysis of
main-sequence stars, which show mainly p-mode oscillations.Comment: accepted by MNRA
The c2d Spitzer Spectroscopic Survey Of Ices Around Low-Mass Young Stellar Objects. I. H2O And The 5-8 Mu M Bands
To study the physical and chemical evolution of ices in solar-mass systems, a spectral survey is conducted of a sample of 41 low-luminosity YSOs (L similar to 0.1-10 L-circle dot) using 3-38 mu m Spitzer and ground-based spectra. The sample is complemented with previously published Spitzer spectra of background stars and with ISO spectra of well-studied massive YSOs (L similar to 10(5) L-circle dot). The long-known 6.0 and 6.85 mu m bands are detected toward all sources, with the Class 0-type YSOs showing the deepest bands ever observed. The 6.0 mu m band is often deeper than expected from the bending mode of pure solid H2O. The additional 5-7 mu m absorption consists of five independent components, which, by comparison to laboratory studies, must be from at least eight different carriers. Much of this absorption is due to simple species likely formed by grain surface chemistry, at abundances of 1%-30% for CH3OH, 3%-8% for NH3, 1%-5% for HCOOH, similar to 6% for H2CO, and similar to 0.3% for HCOO- relative to solid H2O. The 6.85 mu m band has one or two carriers, of which one may be less volatile than H2O. Its carrier(s) formed early in the molecular cloud evolution and do not survive in the diffuse ISM. If an NH4+- containing salt is the carrier, its abundance relative to solid H2O is similar to 7%, demonstrating the efficiency of low-temperature acid-base chemistry or cosmic-ray-induced reactions. Possible origins are discussed for enigmatic, very broad absorption between 5 and 8 mu m. Finally, the same ices are observed toward massive and low-mass YSOs, indicating that processing by internal UV radiation fields is a minor factor in their early chemical evolution.NWO SpinozaNOVAEuropean Research Training Network PLANETS HPRN-CT-2002-00308NASA Origins NAG5-13050NASA Hubble Fellowship 01201.01NASA NAS 5-26555Astronom
Global asteroseismic properties of solar-like oscillations observed by Kepler : A comparison of complementary analysis methods
We present the asteroseismic analysis of 1948 F-, G- and K-type main-sequence
and subgiant stars observed by the NASA {\em Kepler Mission}. We detect and
characterise solar-like oscillations in 642 of these stars. This represents the
largest cohort of main-sequence and subgiant solar-like oscillators observed to
date. The photometric observations are analysed using the methods developed by
nine independent research teams. The results are combined to validate the
determined global asteroseismic parameters and calculate the relative precision
by which the parameters can be obtained. We correlate the relative number of
detected solar-like oscillators with stellar parameters from the {\em Kepler
Input Catalog} and find a deficiency for stars with effective temperatures in
the range \,K and a drop-off in
detected oscillations in stars approaching the red edge of the classical
instability strip. We compare the power-law relationships between the frequency
of peak power, , the mean large frequency separation,
, and the maximum mode amplitude, , and show that
there are significant method-dependent differences in the results obtained.
This illustrates the need for multiple complementary analysis methods to be
used to assess the robustness and reproducibility of results derived from
global asteroseismic parameters.Comment: 14 pages, 9 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Moisture susceptibility of high and low compaction dry process crumb rubber modified asphalt mixtures
The field performance of dry process crumb rubber-modified (CRM) asphalt mixtures has been reported to be inconsistent with stripping and premature cracking on the surfacing. One of the concerns is that, because achieving field compaction of CRM material is difficult due to the inherent resilient nature of the rubber particle, nonuniform field compaction may lead to a deficient bond between rubber and bitumen. To assess the influence of compaction, a series of CRM and control mixtures was produced and compacted at two levels: 4% (low, optimum laboratory compaction) and 8% (high, field experience) air void content. The long-term durability, in regard to moisture susceptibility of the mixtures, was assessed by conducting repeated moisture conditioning cycles. Mechanical properties (stiffness, fatigue, and resistance to permanent deformation) were determined in the Nottingham Asphalt Tester. Results indicated that compared with conventional mixtures, the CRM mixtures, regardless of compaction effort, are more susceptible to moisture with the degree of susceptibility primarily depending on the amount of rubber in the mixture, rather than the difference in compaction. This behavior is different from that of conventional mixtures in which, as expected, poorly compacted mixtures were found to be more susceptible to moisture than were well-compacted mixtures
The Spitzer c2d Survey of Weak-Line T Tauri Stars. III. The Transition from Primordial Disks to Debris Disks
We present 3.6 to 70 {\mu}m Spitzer photometry of 154 weak-line T Tauri stars
(WTTS) in the Chamaeleon, Lupus, Ophiuchus and Taurus star formation regions,
all of which are within 200 pc of the Sun. For a comparative study, we also
include 33 classical T Tauri stars (CTTS) which are located in the same star
forming regions. Spitzer sensitivities allow us to robustly detect the
photosphere in the IRAC bands (3.6 to 8 {\mu}m) and the 24 {\mu}m MIPS band. In
the 70 {\mu}m MIPS band, we are able to detect dust emission brighter than
roughly 40 times the photosphere. These observations represent the most
sensitive WTTS survey in the mid to far infrared to date, and reveal the
frequency of outer disks (r = 3-50 AU) around WTTS. The 70 {\mu}m photometry
for half the c2d WTTS sample (the on-cloud objects), which were not included in
the earlier papers in this series, Padgett et al. (2006) and Cieza et al.
(2007), are presented here for the first time. We find a disk frequency of 19%
for on-cloud WTTS, but just 5% for off- cloud WTTS, similar to the value
reported in the earlier works. WTTS exhibit spectral energy distributions
(SEDs) that are quite diverse, spanning the range from optically thick to
optically thin disks. Most disks become more tenuous than Ldisk/L* = 2 x 10^-3
in 2 Myr, and more tenuous than Ldisk/L* = 5 x 10^-4 in 4 Myr.Comment: 40 pages, 13 figures, 4 tables. Accepted for publication in ApJ on
September 20, 201
A rightward shift in the visuospatial attention vector with healthy aging
The study of lateralised visuospatial attention bias in non-clinical samples has revealed a systematic group-level leftward bias (pseudoneglect), possibly as a consequence of right hemisphere dominance for visuospatial attention. Pseudoneglect appears to be modulated by age, with a reduced or even reversed bias typically present in elderly participants. It has been suggested that this shift in bias may arise due to disproportionate aging of the right hemisphere and/or an increase in complementary functional recruitment of the left hemisphere for visuospatial processing. In this study, we report rightward shifts in subjective midpoint judgement relative to healthy young participants whilst elderly participants performed a computerized version of the landmark task (in which they had to judge whether a transection mark appeared closer to the right or left end of a line) on three different line lengths. This manipulation of stimulus properties led to a similar behavioural pattern in both the young and the elderly: a rightward shift in subjective midpoint with decreasing line length, which even resulted in a systematic rightward bias in elderly participants for the shortest line length (1.98° of visual angle). Overall performance precision for the task was lower in the elderly participants regardless of line length, suggesting reduced landmark task discrimination sensitivity with healthy aging. This rightward shift in the attentional vector with healthy aging is likely to result from a reduction in right hemisphere resources/dominance for attentional processing in elderly participants. The significant rightward bias in the elderly for short lines may even suggest a reversal of hemisphere dominance in favour of the left hemisphere/right visual field under specific conditions
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