107 research outputs found
The Visibility of Galactic Bars and Spiral Structure At High Redshifts
We investigate the visibility of galactic bars and spiral structure in the
distant Universe by artificially redshifting 101 B-band CCD images of local
spiral galaxies from the Ohio State University Bright Spiral Galaxy Survey. Our
artificially redshifted images correspond to Hubble Space Telescope I-band
observations of the local galaxy sample seen at z=0.7, with integration times
matching those of both the very deep Northern Hubble Deep Field data, and the
much shallower Flanking Field observations. The expected visibility of galactic
bars is probed in two ways: (1) using traditional visual classification, and
(2) by charting the changing shape of the galaxy distribution in "Hubble
space", a quantitative two-parameter description of galactic structure that
maps closely on to Hubble's original tuning fork. Both analyses suggest that
over 2/3 of strongly barred luminous local spirals i.e. objects classified as
SB in the Third Reference Catalog) would still be classified as strongly barred
at z=0.7 in the Hubble Deep Field data. Under the same conditions, most weakly
barred spirals (classified SAB in the Third Reference Catalog) would be
classified as regular spirals. The corresponding visibility of spiral structure
is assessed visually, by comparing luminosity classifications for the
artificially redshifted sample with the corresponding luminosity
classifications from the Revised Shapley Ames Catalog. We find that for
exposures times similar to that of the Hubble Deep Field spiral structure
should be detectable in most luminous low-inclination spiral galaxies at z=0.7
in which it is present. [ABRIDGED]Comment: Accepted for publication in The Astronomical Journa
The stellar content of the super star clusters in NGC 1569
We discuss HST FOS ultraviolet spectroscopy and NICMOS near-infrared
photometry of four young super star clusters in the central region of the
irregular starburst galaxy NGC 1569. The new observations coupled with previous
HST WFPC2 photometry and ground-based optical spectroscopy allow us to isolate
and age-date the hot and cool stellar components of these massive clusters. We
analyze the two components A1 and A2 of the brightest super star cluster NGC
1569-A. This cluster received previous attention due to the simultaneous
presence of Wolf-Rayet stars and red supergiants. The FOS spectra provide the
first evidence for O-stars in NGC 1569-A, indicating a young (5 Myr) stellar
component in A1 and/or A2. Comparison with other high-mass star-forming regions
suggests that the O- and Wolf-Rayet stars are spatially coincident. If so,
cluster A2 could be the host of the very young O- and Wolf-Rayet population,
and the somewhat older red supergiants could be predominantly located in A1.
The mass-to-light ratio of NGC 1569-A1 is analyzed in five optical and infrared
photometric bands and compared to evolutionary synthesis models. No indications
for an anomalous initial mass function are found, consistent with a scenario
where this cluster is the progenitor of present-day globular clusters. The
clusters A1 and A2 are compared to clusters B and #30. The latter two clusters
are older and fully dominated by red supergiants. All four super star clusters
provide a significant fraction (20 - 25%) of the total optical and
near-infrared light in the central region of the galaxy. The photometric
properties of the super star cluster population in NGC 1569 resemble those of
the populous clusters in the Magellanic Clouds
Correction: Large cortical bone pores in the tibia are associated with proximal femur strength
[This corrects the article DOI: 10.1371/journal.pone.0215405.
Thermal study of the effect of several solvents on polymerization of acrylonitrile and their subsequent pyrolysis
The polymerization of acrylonitrile to polyacrylonitrile (PAN) has been studied using several solvents: N,N-dimethylformamide (DMF), hexane, toluene, water, and in bulk form (no solvent). The addition of DMF is the only case where both monomer and polymer are soluble in the solvent. Thermal analyses of the resultant products after polymerization have been performed by differential scanning calorimetry and pyrolysisâgas chromatography:
mass spectrometry. The effect of the solvents employed as media for polymerization is interpreted from the results of the thermal and structural (X-ray diffraction) methods. The polymer samples obtained when using water or toluene as solvents have the greater content of amorphous components compared to the others. The amide molecules are difficult to
completely eliminate in the product obtained after the polymerization reaction and even after prolonged heating at 110°C and remain occluded. DMF can be considered to exert a
plasticized effect on PAN and is even capable of forming complexes by dipolar bonding. As a result of this interaction, the thermogram is quite different from the other samples studied in the present work, showing a single sharp exothermic peak. This is associated with nitrile group polymerization (cyclization) of PAN. It is deduced that the amount of heat evolved as
well as the temperature interval over which it is released are influenced by the chemical
processing of PAN, in particular when using DMF as solvent for both monomer and polymer. Pyrolysis of the different PAN samples revealed the release of occluded solvent
molecules, mainly when using DMF, and compounds produced from the thermal degradation processes. Different types of cyclized compounds, such as pyridine derivatives and aromatic nitriles were identified. All these compounds could be derived from cyclized PAN structures which are not completely degraded by the thermal treatment of pyrolysis. Alkyldinitriles have also been tentatively identified associated with the final molecular breakdown of cyclized structures with six-member rings by pyrolysis. Valuable complementary information on the structure of the PAN samples (homopolymer) obtained using the
different processing approaches involving several solvent media has been provided by
pyrolysis. The present results will improve our understanding of the evolution of the
structure and properties of carbon and activated carbon fibres which will enable us to establish processing strategies in order to obtain these materials under adequate and
reproducible conditions.Peer reviewe
The Hubble Space Telescope Extragalactic Distance Scale Key Project. X. The Cepheid Distance to NGC 7331
The distance to NGC 7331 has been derived from Cepheid variables observed
with HST/WFPC2, as part of the Extragalactic Distance Scale Key Project.
Multi-epoch exposures in F555W (V) and F814W (I), with photometry derived
independently from DoPHOT and DAOPHOT/ALLFRAME programs, were used to detect a
total of 13 reliable Cepheids, with periods between 11 and 42 days. The
relative distance moduli between NGC 7331 and the LMC, imply an extinction to
NGC 7331 of A_V = 0.47+-0.15 mag, and an extinction-corrected distance modulus
to NGC 7331 of 30.89+-0.14(random) mag, equivalent to a distance of 15.1 Mpc.
There are additional systematic uncertainties in the distance modulus of +-0.12
mag due to the calibration of the Cepheid Period-Luminosity relation, and a
systematic offset of +0.05+-0.04 mag if we applied the metallicity correction
inferred from the M101 results of Kennicutt et al 1998.Comment: To be published in The Astrophysical Journal, 1998 July 1, v501 note:
Figs 1 and 2 (JPEG files) and Fig 7 (multipage .eps file) need to be
viewed/printed separatel
The ACS Virgo Cluster Survey X. Half-light Radii of Globular Clusters in Early-Type Galaxies: Environmental Dependencies and a Standard Ruler for Distance Estimation
We have measured half-light radii, r_h, for globular clusters (GCs) belonging
to the 100 early-type galaxies observed in the ACS Virgo Cluster Survey and the
elliptical galaxy NGC 4697. An analysis of the dependencies of the measured r_h
on both the properties of the GCs themselves and their host galaxies reveals
that the average r_h increases with increasing galactocentric distance or,
alternatively, with decreasing galaxy surface brightness. For the first time,
we find that the average r_h decreases with the host galaxy color. We also show
that there is no evidence for a variation of r_h with the luminosity of the
GCs. Finally, we find in agreement with previous observations that the average
r_h depends on the color of GCs, with red GCs being ~17% smaller than their
blue counterparts. We show that this difference is probably a consequence of an
intrinsic mechanism, rather than projection effects, and that it is in good
agreement with the mechanism proposed in Jordan (2004). We discuss these
findings in light of two simple pictures for the origin of the r_h of GCs and
show that both lead to a behavior in rough agreement with the observations.
After accounting for the dependencies found we show that the average GC
half-light radii can be successfully used as a standard ruler for
distance estimation. We outline the methodology, and provide a calibration for
its use. We find = 2.7 +- 0.35 pc for GCs with (g-z)=1.2 mag in a galaxy
with color (g-z)_{gal}=1.5 mag and at an underlying surface z-band brightness
of mu_z = 21 mag arcsec^{-2}. Using this technique, we place an upper limit of
3.4 Mpc on the 1-sigma line-of-sight depth of the Virgo Cluster. Finally, we
examine the form of the r_h distribution for our sample galaxies and provide an
analytic expression which successfully describes this distribution. (Abridged)Comment: 18 pages, 13 figures. Accepted for publication in ApJ. Also available
at http://www.physics.rutgers.edu/~pcote/acs/publications.htm
Panel 4 : Report of the Microbiology Panel
Objective. To perform a comprehensive review of the literature from July 2011 until June 2015 on the virology and bacteriology of otitis media in children. Data Sources. PubMed database of the National Library of Medicine. Review Methods. Two subpanels comprising experts in the virology and bacteriology of otitis media were created. Each panel reviewed the relevant literature in the fields of virology and bacteriology and generated draft reviews. These initial reviews were distributed to all panel members prior to meeting together at the Post-symposium Research Conference of the 18th International Symposium on Recent Advances in Otitis Media, National Harbor, Maryland, in June 2015. A final draft was created, circulated, and approved by all panel members. Conclusions. Excellent progress has been made in the past 4 years in advancing our understanding of the microbiology of otitis media. Numerous advances were made in basic laboratory studies, in animal models of otitis media, in better understanding the epidemiology of disease, and in clinical practice. Implications for Practice. (1) Many viruses cause acute otitis media without bacterial coinfection, and such cases do not require antibiotic treatment. (2) When respiratory syncytial virus, metapneumovirus, and influenza virus peak in the community, practitioners can expect to see an increase in clinical otitis media cases. (3) Biomarkers that predict which children with upper respiratory tract infections will develop otitis media may be available in the future. (4) Compounds that target newly identified bacterial virulence determinants may be available as future treatment options for children with otitis media.Peer reviewe
Electrodiagnostic subtyping in GuillainâBarrĂ© syndrome patients in the International GuillainâBarrĂ© Outcome Study
Background and purpose: Various electrodiagnostic criteria have been developed in GuillainâBarrĂ© syndrome (GBS). Their performance in a broad representation of GBS patients has not been evaluated. Motor conduction data from the International GBS Outcome Study (IGOS) cohort were used to compare two widely used criterion sets and relate these to diagnostic amyotrophic lateral sclerosis criteria. Methods: From the first 1500 patients in IGOS, nerve conduction studies from 1137 (75.8%) were available for the current study. These patients were classified according to nerve conduction studies criteria proposed by Hadden and Rajabally. Results: Of the 1137 studies, 68.3% (Nâ=â777) were classified identically according to criteria by Hadden and Rajabally: 111 (9.8%) axonal, 366 (32.2%) demyelinating, 195 (17.2%) equivocal, 35 (3.1%) inexcitable and 70 (6.2%) normal. Thus, 360 studies (31.7%) were classified differently. The areas of differences were as follows: 155 studies (13.6%) classified as demyelinating by Hadden and axonal by Rajabally; 122 studies (10.7%) classified as demyelinating by Hadden and equivocal by Rajabally; and 75 studies (6.6%) classified as equivocal by Hadden and axonal by Rajabally. Due to more strictly defined cutoffs fewer patients fulfilled demyelinating criteria by Rajabally than by Hadden, making more patients eligible for axonal or equivocal classification by Rajabally. In 234 (68.6%) axonal studies by Rajabally the revised El Escorial (amyotrophic lateral sclerosis) criteria were fulfilled; in axonal cases by Hadden this was 1.8%. Conclusions and discussion: This study shows that electrodiagnosis in GBS is dependent on the criterion set utilized, both of which are based on expert opinion. Reappraisal of electrodiagnostic subtyping in GBS is warranted
- âŠ