7,030 research outputs found
The Effect of Use and Access on Citations
It has been shown (S. Lawrence, 2001, Nature, 411, 521) that journal articles
which have been posted without charge on the internet are more heavily cited
than those which have not been. Using data from the NASA Astrophysics Data
System (ads.harvard.edu) and from the ArXiv e-print archive at Cornell
University (arXiv.org) we examine the causes of this effect.Comment: Accepted for publication in Information Processing & Management,
special issue on scientometric
The NASA Astrophysics Data System: Data Holdings
Since its inception in 1993, the ADS Abstract Service has become an
indispensable research tool for astronomers and astrophysicists worldwide. In
those seven years, much effort has been directed toward improving both the
quantity and the quality of references in the database. From the original
database of approximately 160,000 astronomy abstracts, our dataset has grown
almost tenfold to approximately 1.5 million references covering astronomy,
astrophysics, planetary sciences, physics, optics, and engineering. We collect
and standardize data from approximately 200 journals and present the resulting
information in a uniform, coherent manner. With the cooperation of journal
publishers worldwide, we have been able to place scans of full journal articles
on-line back to the first volumes of many astronomical journals, and we are
able to link to current version of articles, abstracts, and datasets for
essentially all of the current astronomy literature. The trend toward
electronic publishing in the field, the use of electronic submission of
abstracts for journal articles and conference proceedings, and the increasingly
prominent use of the World Wide Web to disseminate information have enabled the
ADS to build a database unparalleled in other disciplines.
The ADS can be accessed at http://adswww.harvard.eduComment: 24 pages, 1 figure, 6 tables, 3 appendice
The NASA Astrophysics Data System: Architecture
The powerful discovery capabilities available in the ADS bibliographic
services are possible thanks to the design of a flexible search and retrieval
system based on a relational database model. Bibliographic records are stored
as a corpus of structured documents containing fielded data and metadata, while
discipline-specific knowledge is segregated in a set of files independent of
the bibliographic data itself.
The creation and management of links to both internal and external resources
associated with each bibliography in the database is made possible by
representing them as a set of document properties and their attributes.
To improve global access to the ADS data holdings, a number of mirror sites
have been created by cloning the database contents and software on a variety of
hardware and software platforms.
The procedures used to create and manage the database and its mirrors have
been written as a set of scripts that can be run in either an interactive or
unsupervised fashion.
The ADS can be accessed at http://adswww.harvard.eduComment: 25 pages, 8 figures, 3 table
The NASA Astrophysics Data System: The Search Engine and its User Interface
The ADS Abstract and Article Services provide access to the astronomical
literature through the World Wide Web (WWW). The forms based user interface
provides access to sophisticated searching capabilities that allow our users to
find references in the fields of Astronomy, Physics/Geophysics, and
astronomical Instrumentation and Engineering. The returned information includes
links to other on-line information sources, creating an extensive astronomical
digital library. Other interfaces to the ADS databases provide direct access to
the ADS data to allow developers of other data systems to integrate our data
into their system.
The search engine is a custom-built software system that is specifically
tailored to search astronomical references. It includes an extensive synonym
list that contains discipline specific knowledge about search term
equivalences.
Search request logs show the usage pattern of the various search system
capabilities. Access logs show the world-wide distribution of ADS users.
The ADS can be accessed at http://adswww.harvard.eduComment: 23 pages, 18 figures, 11 table
The NASA Astrophysics Data System: Overview
The NASA Astrophysics Data System Abstract Service has become a key component
of astronomical research. It provides bibliographic information daily, or near
daily, to a majority of astronomical researchers worldwide.
We describe the history of the development of the system and its current
status.
We show several examples of how to use the ADS, and we show how ADS use has
increased as a function of time. Currently it is still increasing
exponentially, with a doubling time for number of queries of 17 months.
Using the ADS logs we make the first detailed model of how scientific
journals are read as a function of time since publication.
The impact of the ADS on astronomy can be calculated after making some simple
assumptions. We find that the ADS increases the efficiency of astronomical
research by 333 Full Time Equivalent (2000 hour) research years per year, and
that the value of the early development of the ADS for astronomy, compared with
waiting for mature technologies to be adopted, is 2332 FTE research years.
The ADS is available at http://adswww.harvard.edu/.Comment: 19 pages, 22 figure
Proper Motion of Pulsar B1800-21
We report high angular resolution, multi-epoch radio observations of the
young pulsar PSR B1800-21. Using two pairs of data sets, each pair spanning
approximately a ten year period, we calculate the proper motion of the pulsar.
We obtain a proper motion of mu_alpha=11.6 +- 1.8 mas/yr, mu_delta=14.8 +- 2.3
mas/yr, which clearly indicates a birth position at the extreme edge of the W30
supernova remnant. Although this does not definitively rule out an association
of W30 and PSR B1800-21, it does not support an association.Comment: 13 pages, 1 color figure. Replaced with version accepted for
publication in Astrophysical Journa
MOST observations of the roAp stars HD 9289, HD 99563, and HD 134214
We report on the analysis of high-precision space-based photometry of the
roAp (rapidly oscillating Ap) stars HD 9289, HD 99563, and HD134214. All three
stars were observed by the MOST satellite for more than 25 days, allowing
unprecedented views of their pulsation. We find previously unknown candidate
frequencies in all three stars. We establish the rotation period of HD 9289
(8.5 d) for the first time and show that the star is pulsating in two modes
that show different mode geometries. We present a detailed analysis of HD
99563's mode multiplet and find a new candidate frequency which appears
independent of the previously known mode. Finally, we report on 11 detected
pulsation frequencies in HD 134214, 9 of which were never before detected in
photometry, and 3 of which are completely new detections. Thanks to the
unprecedentedly small frequency uncertainties, the p-mode spectrum of HD 134214
can be seen to have a well-defined large frequency spacing similar to the
well-studied roAp star HD 24712 (HR 1217).Comment: 11 pages, 12 figures, accepted for publication in A&
On the understanding of pulsations in the atmosphere of roAp stars: phase diversity and false nodes
Studies based on high-resolution spectroscopic data of rapidly oscillating Ap
stars show a surprising diversity of pulsation behavior in the atmospheric
layers, pointing, in particular, to the co-existence of running and standing
waves. The correct interpretation of these data requires a careful modelling of
pulsations in these magnetic stars. In light of this, in this work we present a
theoretical analysis of pulsations in roAp stars, taking into account the
direct influence of the magnetic field. We derive approximate analytical
solutions for the displacement components parallel and perpendicular to the
direction of the magnetic field, that are appropriate to the outermost layer.
From these, we determine the expression for the theoretical radial velocity for
an observer at a general position, and compute the corresponding pulsation
amplitude and phase as function of height in the atmosphere. We show that the
integral for the radial velocity has contributions from three different types
of wave solutions, namely, running waves, evanescent waves, and standing waves
of nearly constant amplitude. We then consider a number of case studies to
illustrate the origin of the different pulsational behaviour that is found in
the observations. Concerning pulsation amplitude, we find that it generally
increases with atmospheric height. Pulsation phase, however, shows a diversity
of behaviours, including phases that are constant, increasing, or decreasing
with atmospheric height. Finally, we show that there are situations in which
the pulsation amplitude goes through a zero, accompanied by a phase jumps of
, and argue that such behaviour does not correspond to a pulsation node in
the outermost layers of the star, but rather to a visual effect, resulting from
the observers inability to resolve the stellar surface.Comment: 21 pages, 25 figure
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