6,061 research outputs found
Spectroscopic and Vibrational Energy Transfer Studies in Molecular Bromine
Vibrational transfer and electronic quenching in the lower vibrational levels (v\u27 \u3c 3) of the B3π(0u+) state of 79Br2 were investigated using spectrally resolved, temporally resolved laser induced fluorescence techniques. Spectrally resolved emissions from collisionally populated Br2(B) vibrational levels were observed for Br2 and rare gas collision partners. Vibrational transfer was efficient in the non-predissociative vibrational levels and was adequately described by the Montroll-Shuler model for harmonic oscillators. A single fundamental rate coefficient for vibrational transfer from v\u27 = 1 to v\u27 = 0, kv(1,0), characterizes vibrational relaxation. For Br2, the value was k,(1,0) = 3.6 ± 0.4 x 10-11 cm3/molec-sec. For rare gas collisions, values ranged from kv(1,0) = 2.5 ± 0.3 x 10-11 cm3/molec-sec for helium to kv(1,0) = 3.1 ± 0.4 x 10-1 cm3/molec-sec for xenon. Electronic quenching rates for the observed vibrational levels were obtained from the same data. For Br2, the quenching rate coefficient was kq = 3.7 ± 1.2 x 1011 cm 3/molec-sec. Quenching rate coefficients for the rare gases were smaller, kq = 8.0 ± 1.2 x 1012 cm 3/molec-sec. Additionally, the spectroscopy of high vibrational levels in the 79Br81Br X1 Σg+ ground electronic state was investigated using spectrally resolved, pulsed laser induced fluorescence Vrom low J levels in the B3Π(0u+) state. Over 100 bandheads were identified for transitions from 15 ≤ v\u27 ≤ 21 to 1 ≤ v ≤ 27. The calculated spectroscopic constants, ωe = 323.1 ± 1.5 cm-1, ωe = 1.02 ± 0.1 cm-1 and ωeYe = -3.77 ± 0.2 x 10-3 cm-1, are valid for v ≤ 27
Astrophysicists on Twitter: An in-depth analysis of tweeting and scientific publication behavior
This paper analyzes the tweeting behavior of 37 astrophysicists on Twitter
and compares their tweeting behavior with their publication behavior and
citation impact to show whether they tweet research-related topics or not.
Astrophysicists on Twitter are selected to compare their tweets with their
publications from Web of Science. Different user groups are identified based on
tweeting and publication frequency. A moderate negative correlation (p=-0.390*)
is found between the number of publications and tweets per day, while retweet
and citation rates do not correlate. The similarity between tweets and
abstracts is very low (cos=0.081). User groups show different tweeting behavior
such as retweeting and including hashtags, usernames and URLs. The study is
limited in terms of the small set of astrophysicists. Results are not
necessarily representative of the entire astrophysicist community on Twitter
and they most certainly do not apply to scientists in general. Future research
should apply the methods to a larger set of researchers and other scientific
disciplines. To a certain extent, this study helps to understand how
researchers use Twitter. The results hint at the fact that impact on Twitter
can neither be equated with nor replace traditional research impact metrics.
However, tweets and other so-called altmetrics might be able to reflect other
impact of scientists such as public outreach and science communication. To the
best of our knowledge, this is the first in-depth study comparing researchers'
tweeting activity and behavior with scientific publication output in terms of
quantity, content and impact.Comment: 14 pages, 5 figures, 7 table
The identification of physical close galaxy pairs
A classification scheme for close pairs of galaxies is proposed. The scheme
is motivated by the fact that the majority of apparent close pairs are in fact
wide pairs in three-dimensional space. This is demonstrated by means of
numerical simulations of random samples of binary galaxies and the scrutiny of
the resulting projected and spatial separation distributions.
Observational strategies for classifying close pairs according to the scheme
are suggested. As a result, physical (i.e., bound and spatially) close pairs
are identified.Comment: 16 pages, 5 figures, accepted for publication in The Astronomical
Journal, added text corrections on proof
The Structure of the Outer Halo of the Galaxy and its Relationship to Nearby Large-Scale Structure
We present evidence to support an earlier indication that the Galaxy is
embedded in an extended, highly inclined, triaxial halo outlined by the spatial
distribution of companion galaxies to the Milky Way. Signatures of this spatial
distribution are seen in 1) the angular variation of the radial-velocity
dispersion of the companion galaxies, 2) the spatial distribution of the M~31
sub-group of galaxies, 3) the spatial distribution of the isolated, mainly
dwarf irregular, galaxies of the Local Group, 4) the velocity anisotropy
quadrupole of a sub-group of high-velocity clouds, and 5) the spatial
distribution of galaxies in the Coma-Sculptor cloud. Tidal effects of M~31 and
surrounding galaxies on the Galaxy are not strong enough to have affected the
observed structure. We conclude that this distribution is a reflection of
initial conditions. A simple galaxy formation scenario is proposed which ties
together the results found here with those of Holmberg (1969) and Zaritsky et
al. (1997) on the peculiar distribution of satellites around a large sample of
spiral galaxies.Comment: Accepted for publication in the Astron J., March 2000, 12 pages with
1 figur
Completeness of case ascertainment and survival time error in English cancer registries: impact on 1-year survival estimates.
BACKGROUND: It has been suggested that cancer registries in England are too dependent on processing of information from death certificates, and consequently that cancer survival statistics reported for England are systematically biased and too low. METHODS: We have linked routine cancer registration records for colorectal, lung, and breast cancer patients with information from the Hospital Episode Statistics (HES) database for the period 2001-2007. Based on record linkage with the HES database, records missing in the cancer register were identified, and dates of diagnosis were revised. The effects of those revisions on the estimated survival time and proportion of patients surviving for 1 year or more were studied. Cases that were absent in the cancer register and present in the HES data with a relevant diagnosis code and a relevant surgery code were used to estimate (a) the completeness of the cancer register. Differences in survival times calculated from the two data sources were used to estimate (b) the possible extent of error in the recorded survival time in the cancer register. Finally, we combined (a) and (b) to estimate (c) the resulting differences in 1-year cumulative survival estimates. RESULTS: Completeness of case ascertainment in English cancer registries is high, around 98-99%. Using HES data added 1.9%, 0.4% and 2.0% to the number of colorectal, lung, and breast cancer registrations, respectively. Around 5-6% of rapidly fatal cancer registrations had survival time extended by more than a month, and almost 3% of rapidly fatal breast cancer records were extended by more than a year. The resulting impact on estimates of 1-year survival was small, amounting to 1.0, 0.8, and 0.4 percentage points for colorectal, lung, and breast cancer, respectively. INTERPRETATION: English cancer registration data cannot be dismissed as unfit for the purpose of cancer survival analysis. However, investigators should retain a critical attitude to data quality and sources of error in international cancer survival studies
Tweets as impact indicators: Examining the implications of automated bot accounts on Twitter
This brief communication presents preliminary findings on automated Twitter
accounts distributing links to scientific papers deposited on the preprint
repository arXiv. It discusses the implication of the presence of such bots
from the perspective of social media metrics (altmetrics), where mentions of
scholarly documents on Twitter have been suggested as a means of measuring
impact that is both broader and timelier than citations. We present preliminary
findings that automated Twitter accounts create a considerable amount of tweets
to scientific papers and that they behave differently than common social bots,
which has critical implications for the use of raw tweet counts in research
evaluation and assessment. We discuss some definitions of Twitter cyborgs and
bots in scholarly communication and propose differentiating between different
levels of engagement from tweeting only bibliographic information to discussing
or commenting on the content of a paper.Comment: 9 pages, 4 figures, 1 tabl
Anisotropic Distribution of SDSS Satellite Galaxies: Planar (not Polar) Alignment
The distribution of satellite galaxies relative to isolated host galaxies in
the Sloan Digital Sky Survey (SDSS) is investigated. Host-satellite systems are
selected using three different methods, yielding samples of ~3300, ~1600, and
\~950 satellites. In the plane of the sky, the distributions of all three
samples show highly significant deviations from circular symmetry (> 99.99%, >
99.99%, and 99.79% confidence levels, respectively), and the degree of
anisotropy is a strong function of the projected radius, r_p, at which the
satellites are found. For r_p < 100 kpc, the SDSS satellites are aligned
preferentially with the major axes of the hosts. This is in stark contrast to
the Holmberg effect, in which satellites are aligned with the minor axes of
host galaxies. The degree of anisotropy in the distribution of the SDSS
satellites decreases with r_p and is consistent with an isotropic distribution
at of order the 1-sigma level for 250 kpc < r_p < 500 kpc.Comment: ApJ Letters (in press); Discussion section substantially revised,
SDSS DR3 included in the analysis, no significant changes to the result
Platybunus triangularis and Paroligolophus agrestis: two phalangids introduced to North America (Arachnida, Opiliones)
Volume: 2Start Page: 127End Page: 12
A Hubble Space Telescope Snapshot Survey of Dynamically Close Galaxy Pairs in the CNOC2 Redshift Survey
We compare the structural properties of two classes of galaxies at
intermediate redshift: those in dynamically close galaxy pairs, and those which
are isolated. Both samples are selected from the CNOC2 Redshift Survey, and
have redshifts in the range 0.1 < z <0.6. Hubble Space Telescope WFPC2 images
were acquired as part of a snapshot survey, and were used to measure bulge
fraction and asymmetry for these galaxies. We find that paired and isolated
galaxies have identical distributions of bulge fractions. Conversely, we find
that paired galaxies are much more likely to be asymmetric (R_T+R_A >= 0.13)
than isolated galaxies. Assuming that half of these pairs are unlikely to be
close enough to merge, we estimate that 40% +/- 11% of merging galaxies are
asymmetric, compared with 9% +/- 3% of isolated galaxies. The difference is
even more striking for strongly asymmetric (R_T+R_A >= 0.16) galaxies: 25% +/-
8% for merging galaxies versus 1% +/- 1% for isolated galaxies. We find that
strongly asymmetric paired galaxies are very blue, with rest-frame B-R colors
close to 0.80, compared with a mean (B-R)_0 of 1.24 for all paired galaxies. In
addition, asymmetric galaxies in pairs have strong [OII]3727 emission lines. We
conclude that close to half of the galaxy pairs in our sample are in the
process of merging, and that most of these mergers are accompanied by triggered
star formation.Comment: Accepted for publication in the Astronomical Journal. 40 pages,
including 15 figures. For full resolution version, please see
http://www.trentu.ca/physics/dpatton/hstpairs
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