844 research outputs found
An Evaluation of Physical Disk I/Os for Complex Object Processing
In order to obtain the performance required for nonstandard database environments, a hierarchical complex object model with object references is used as a storage structure for complex objects. Several storage models for these complex objects, as well as a benchmark to evaluate their performance, are described. A cost model for analytical performance evaluation is developed, and the analytical results are validated by means of measurements on the DASDBS, complex object storage system. The results show which storage structures for complex objects are the most efficient under which circumstance
The Danish National Passenger Model – model specification and results
The paper describes the structure of the new Danish National Passenger model and provides on this basis a general discussion of large-scale model design, cost-damping and model validation. The paper aims at providing three main contributions to the existing literature. Firstly, at the general level, the paper provides a description of a large-scale forecast model with a discussion of the linkage between population synthesis, demand and assignment. Secondly, the paper gives specific attention to model specification and in particular choice of functional form and costdamping. Specifically we suggest a family of logarithmic spline functions and illustrate how it is applied in the model. Thirdly and finally, we evaluate model sensitivity and performance by evaluating the distance distribution and elasticities. In the paper we present results where the spline-function is compared with more traditional function types and it is indicated that the spline-function provides a better description of the data. Results are also provided in the form of a back-casting exercise where the model is tested in a back-casting scenario to 2002
Kinematics and Composition of the Galactic Bulge: Recent Progress
We present recent results from a Keck study of the composition of the
Galactic bulge, as well as results from the bulge Bulge Radial Velocity Assay
(BRAVA). Culminating a 10 year investigation, Fulbright, McWilliam, & Rich
(2006, 2007) solved the problem of deriving the iron abundance in the Galactic
bulge, and find enhanced alpha element abundances, consistent with the earlier
work of McWilliam & Rich (1994). We also report on a radial velocity survey of
{\sl 2MASS}-selected M giant stars in the Galactic bulge, observed with the
CTIO 4m Hydra multi-object spectrograph. This program is to test dynamical
models of the bulge and to search for and map any dynamically cold substructure
in the Galactic bulge. We show initial results on fields at and . We construct a longitude-velocity plot for
the bulge stars and the model data, and find that contrary to previous studies,
the bulge does not rotate as a solid body; from the
rotation curve has a slope of and flattens considerably
at greater and reaches a maximum rotation of
(heliocentric) or (Galactocentric). This rotation is
slower than that predicted by the dynamical model of Zhao (1996).Comment: 6 pages, 6 figures, contributed paper at IAU Symposium 245 "Formation
and Evolution of Galactic Bulges
Bringing it all together: a multi-method evaluation of Tanum 247:1
This paper presents the results of a photogrammetric survey of the rock art panel Tanum 247:1 in Kalleby, which revealed an entirely new boat that had previously been missed in a documentation history over 50 years long. Through the combined use of digital and traditional methods the results could be verified. It is therefore argued that collating documentations, both past and present, can help to create a better picture of Bronze Age rock art carvings. In addition to using new and traditional documentation methods together, panels should be recorded beyond what is known, both in terms of discovering unknown carvings, as well as creating better data for future researchers
Alpha Enhancement and the Metallicity Distribution Function of Plaut's Window
We present Fe, Si, and Ca abundances for 61 giants in Plaut's Window
(l=-1,b=-8.5) and Fe abundances for an additional 31 giants in a second, nearby
field (l=0,b=-8) derived from high resolution (R~25,000) spectra obtained with
the Blanco 4m telescope and Hydra multifiber spectrograph. The median
metallicity of red giant branch (RGB) stars in the Plaut field is ~0.4 dex
lower than those in Baade's Window, and confirms the presence of an iron
abundance gradient along the bulge minor axis. The full metallicity range of
our (biased) RGB sample spans -1.5<[Fe/H]<+0.3, which is similar to that found
in other bulge fields. We also derive a photometric metallicity distribution
function for RGB stars in the (l=-1,b=-8.5) field and find very good agreement
with the spectroscopic metallicity distribution. The radial velocity and
dispersion data for the bulge RGB stars are in agreement with previous results
of the BRAVA survey, and we find evidence for a decreasing velocity dispersion
with increasing [Fe/H]. The [alpha/Fe] enhancement in Plaut field stars is
nearly identical to that observed in Baade's window, and suggests that an
[alpha/Fe] gradient does not exist between b=-4 and -8. Additionally, a subset
of our sample (23 stars) appear to be foreground red clump stars that are very
metal--rich, exhibit small metallicity and radial velocity dispersions, and are
enhanced in alpha elements. While these stars likely belong to the Galactic
inner disk population, they exhibit [alpha/Fe] ratios that are enhanced above
the thin and thick disk.Comment: Accepted for publication in ApJ. 38 pages, 11 figures, and 2 tables.
Requests for higher resolution figures and electronic versions of tables 1
and/or 2 in advance of publication may be sent to cijohnson[at]astro.ucla.ed
Metallicity Distribution Functions, Radial Velocities, and Alpha Element Abundances in Three Off-Axis Bulge Fields
We present radial velocities and chemical abundance ratios of [Fe/H], [O/Fe],
[Si/Fe], and [Ca/Fe] for 264 red giant branch (RGB) stars in three Galactic
bulge off-axis fields located near (l,b)=(-5.5,-7), (-4,-9), and (+8.5,+9). The
results are based on equivalent width and spectrum synthesis analyses of
moderate resolution (R~18,000), high signal-to-noise ratio (S/N~75-300) spectra
obtained with the Hydra spectrographs on the Blanco 4m and WIYN 3.5m
telescopes. The targets were selected from the blue side of the giant branch to
avoid cool stars that would be strongly affected by CN and TiO; however, a
comparison of the color-metallicity distribution in literature samples suggests
our selection of bluer targets should not present a significant bias against
metal-rich stars. We find a full range in metallicity that spans
[Fe/H]\approx-1.5 to +0.5, and that, in accordance with the previously observed
minor-axis vertical metallicity gradient, the median [Fe/H] also declines with
increasing Galactic latitude in off-axis fields. The off-axis vertical [Fe/H]
gradient in the southern bulge is estimated to be ~0.4 dex/kpc. The (+8.5,+9)
field exhibits a higher than expected metallicity, with a median [Fe/H]=-0.23,
that might be related to a stronger presence of the X--shaped bulge structure
along that line-of-sight. All fields exhibit an identical, strong decrease in
velocity dispersion with increasing metallicity that is consistent with
observations in similar minor-axis outer bulge fields. Additionally, the
[O/Fe], [Si/Fe], and [Ca/Fe] versus [Fe/H] trends are identical among our three
fields, and are in good agreement with past bulge studies. [abridged]Comment: Accepted for Publication in the Astrophysical Journal; 120 pages
(main text ends on page 24); 22 figures (figures end on page 46); 6 tables;
electronic versions of the tables can be made available upon request to
author C. Johnso
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