730 research outputs found
Radiation-Hydrodynamic Simulations of Collapse and Fragmentation in Massive Protostellar Cores
We simulate the early stages of the evolution of turbulent, virialized,
high-mass protostellar cores, with primary attention to how cores fragment, and
whether they form a small or large number of protostars. Our simulations use
the Orion adaptive mesh refinement code to follow the collapse from ~0.1 pc
scales to ~10 AU scales, for durations that cover the main fragmentation phase,
using three-dimensional gravito-radiation hydrodynamics. We find that for a
wide range of initial conditions radiation feedback from accreting protostars
inhibits the formation of fragments, so that the vast majority of the collapsed
mass accretes onto one or a few objects. Most of the fragmentation that does
occur takes place in massive, self-shielding disks. These are driven to
gravitational instability by rapid accretion, producing rapid mass and angular
momentum transport that allows most of the gas to accrete onto the central star
rather than forming fragments. In contrast, a control run using the same
initial conditions but an isothermal equation of state produces much more
fragmentation, both in and out of the disk. We conclude that massive cores with
observed properties are not likely to fragment into many stars, so that, at
least at high masses, the core mass function probably determines the stellar
initial mass function. Our results also demonstrate that simulations of massive
star forming regions that do not include radiative transfer, and instead rely
on a barotropic equation of state or optically thin heating and cooling curves,
are likely to produce misleading results.Comment: 23 pages, 18 figures, emulateapj format. Accepted to ApJ. This
version has minor typo fixes and small additions, no significant changes.
Resolution of images severely degraded to fit within size limit. Download the
full paper from http://www.astro.princeton.edu/~krumholz/recent.htm
Observations of Trip Generation, Route Choice, and Trip Chaining with Private-Sector Probe Vehicle GPS Data
This paper presents an exploratory study of GPS data from a private-sector data provider for analysis of trip generation, route choice, and trip chaining. The study focuses on travel to and from the Indianapolis International Airport. GPS data consisting of nearly 1 billion waypoints for 12 million trips collected over a 6-week period in the state of Indiana. Within this data, there were approximately 10,000 trip records indicating travel to facilities associated with the Indianapolis airport. The analysis is based the matching of waypoints to geographic areas that define the extents of roadways and various destinations. A regional analysis of trip ends finds that travel demand for passenger services at the airport extends across a region spanning about 950 km. Local travel between land uses near the airport is examined by generation of an origin-destination matrix, and route choice between the airport and downtown Indianapolis is studied. Finally, the individual trips are scanned to identify trip chaining behavior. Several observations are made regarding these dynamics from the data. There is some sample bias (types of vehicles) and opportunities to further refine some of the land use definitions, but the study results suggest this type of data will provide a new frontier for characterizing travel demand patterns at a variety of scales
Sequence Optimization at Signalized Diamond Interchanges Using High-Resolution Event-Based Data
Performance Ranking of Arterial Corridors Using Travel Time and Travel Time Reliability Metrics
Performance measures are important for managing transportation systems and demonstrating accountability. This session presents a scalable methodology for analyzing arterial travel times, taking into account both the central tendency of the travel time and its reliability. Findings will be presented from a pilot analysis that was carried out for 28 arterials including a total of 341 signalized intersections from across the state of Indiana
Using WebGIS to Develop a Spatial Bibliography for Organizing, Mapping, and Disseminating Research Information: A Case Study of Quaking Aspen
On the Ground • Spatial data is valuable to researchers for locating studies that occur in a particular area of interest, or one with similar attributes. • Without a standard in publishing protocol, spatial data largely goes unreported, or is difficult to find without searching the publication. • Assigning location data and displaying points on a public web map makes locating publications based on spatial location possible
XO-3b: A Massive Planet in an Eccentric Orbit Transiting an F5V Star
We report the discovery of a massive (Mpsini = 13.02 +/- 0.64 Mjup; total
mass 13.25 +/- 0.64 Mjup), large (1.95 +/- 0.16 Rjup) planet in a transiting,
eccentric orbit (e = 0.260 +/- 0.017) around a 10th magnitude F5V star in the
constellation Camelopardalis. We designate the planet XO-3b, and the star XO-3,
also known as GSC 03727-01064. The orbital period of XO-3b is 3.1915426 +/-
0.00014 days. XO-3 lacks a trigonometric distance; we estimate its distance to
be 260 +/- 23 pc. The radius of XO-3 is 2.13 +/- 0.21 Rsun, its mass is 1.41
+/- 0.08 Msun, its vsini = 18.54 +/- 0.17 km/s, and its metallicity is [Fe/H] =
-0.177 +/- 0.027. This system is unusual for a number of reasons. XO-3b is one
of the most massive planets discovered around any star for which the orbital
period is less than 10 days. The mass is near the deuterium burning limit of 13
Mjup, which is a proposed boundary between planets and brown dwarfs. Although
Burrows et al. (2001) propose that formation in a disk or formation in the
interstellar medium in a manner similar to stars is a more logical way to
differentiate planets and brown dwarfs, our current observations are not
adequate to address this distinction. XO-3b is also unusual in that its
eccentricity is large given its relatively short orbital period. Both the
planetary radius and the inclination are functions of the spectroscopically
determined stellar radius. Analysis of the transit light curve of XO-3b
suggests that the spectroscopically derived parameters may be over estimated.
Though relatively noisy, the light curves favor a smaller radius in order to
better match the steepness of the ingress and egress. The light curve fits
imply a planetary radius of 1.25 +/- 0.15 Rjup, which would correspond to a
mass of 12.03 +/- 0.46 Mjup.Comment: 26 pages, 10 figures. Accepted by ApJ. Current version has several
small corrections as a result of a bug in the fitting softwar
An improved synthesis, crystal structures, and metallochromism of salts of [Ru(tolyl-terpy)(CN)(3)](-)
The previously reported complex [Ru(ttpy)(CN)(3)] [ttpy = 4'(p-tolyl)-2,2':6',2"-terpyridine] is conveniently synthesised by reaction of ttpy with Ru(dmso)(4)Cl-2 to give [Ru(ttpy)(dmso)Cl-2], which reacts in turn with KCN in aqueous ethanol to afford [Ru(ttpy)(CN)(3)] which was isolated and crystallographically characterised as both its (PPN)(+) and K+ salts. The K+ salt contains clusters containing three complex anions and three K+ cations connected by end-on and side-on cyanide ligation to the K+ ions. The solution speciation behaviour of [Ru(ttpy)(CN)(3)] was investigated with both Zn2+ and K+ salts in MeCN, a solvent sufficiently non-competitive to allow the added metal cations to associate with the complex anion via the externally-directed cyanide lone pairs. UV-Vis spectroscopic titration of (PPN)[Ru(ttpy)(CN)(3)] with Zn(ClO4)(2) showed a blue shift of 2900 cm (1) in the (MLCT)-M-1 absorption manifold due to the ` metallochromism' effect; a series of distinct binding events could be discerned corresponding to formation of 4:1, 1:1 and then 1:3 anion: cation adducts, all with high formation constants, as the titration proceeded. In contrast titration of (PPN)[Ru(ttpy)(CN)(3)] with the more weakly Lewis-acidic KPF6 resulted in a much smaller blue-shift of the 1MLCT absorptions, and the titration data corresponded to formation of 1:1 and then 2: 1 cation: anion adducts with weaker stepwise association constants of the order of 10(4) and then 10(3) M (1). Although association of [Ru(ttpy)(CN)(3)] resulted in a blue-shift of the (MLCT)-M-1 absorptions, the luminescence was steadily quenched, as raising the (MLCT)-M-3 level makes radiationless decay via a lowlying (MC)-M-3 state possible. (C) 2010 Elsevier B. V. All rights reserved
Near-infrared Spectral Characterization of Solar-type Stars in the Northern Hemisphere
Although solar-analog stars have been studied extensively over the past few
decades, most of these studies have focused on visible wavelengths, especially
those identifying solar-analog stars to be used as calibration tools for
observations. As a result, there is a dearth of well-characterized solar
analogs for observations in the near-infrared, a wavelength range important for
studying solar system objects. We present 184 stars selected based on
solar-like spectral type and V-J and V-K colors whose spectra we have observed
in the 0.8-4.2 micron range for calibrating our asteroid observations. Each
star has been classified into one of three ranks based on spectral resemblance
to vetted solar analogs. Of our set of 184 stars, we report 145 as reliable
solar-analog stars, 21 as solar analogs usable after spectral corrections with
low-order polynomial fitting, and 18 as unsuitable for use as calibration
standards owing to spectral shape, variability, or features at low to medium
resolution. We conclude that all but 5 of our candidates are reliable solar
analogs in the longer wavelength range from 2.5 to 4.2 microns. The average
colors of the stars classified as reliable or usable solar analogs are
V-J=1.148, V-H=1.418, and V-K=1.491, with the entire set being distributed
fairly uniformly in R.A. across the sky between -27 and +67 degrees in decl.Comment: 19 pages, 8 figures, 2 table
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