889 research outputs found
tert-Butyl 5-methoxy-3-pentylindole-1-carboxylate
he molecule of the title compound, C₁₉H₂₇NO₃, is essentially planar, with all non-H atoms within 0.2 Å of the nine-membered indole plane, except for the three tert-butyl C atoms. The C₅ pentyl chain is in an extended conformation, with three torsion angles of 179.95 (13), 179.65 (13) and -178.95 (15)° (the latter two angles include the C atoms of the C5 chain only). Three intramolecular C-H...O=C contacts are present (C...O 115°), and an intermolecular C-H...O=C contact and π-π stacking complete the intermolecular interactions
An analysis of the duties of general clerical workers in the General Electric Company
Thesis (M.A.)--Boston University 1949. This item was digitized by the Internet Archive
Radio or newspaper advertising for retailers
This item was digitized by the Internet Archive
The archaeology of scattered wreck-sites: formation processes and shallow water archaeology in western Lake Huron
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74939/1/j.1095-9270.2002.tb01415.x.pd
The First Population II Stars Formed in Externally Enriched Mini-halos
We present a simulation of the formation of the earliest Population II stars,
starting from cosmological initial conditions and ending when metals created in
the first supernovae are incorporated into a collapsing gas-cloud. This occurs
after a supernova blast-wave collides with a nearby mini-halo, inducing further
turbulence that efficiently mixes metals into the dense gas in the center of
the halo. The gas that first collapses has been enriched to a metallicity of Z
~ 2e-5 Zsun. Due to the extremely low metallicity, collapse proceeds similarly
to metal-free gas until dust cooling becomes efficient at high densities,
causing the cloud to fragment into a large number of low mass objects. This
external enrichment mechanism provides a plausible origin for the most
metal-poor stars observed, such as SMSS J031300.36-670839.3, that appear to
have formed out of gas enriched by a single supernova. This mechanism operates
on shorter timescales than the time for low-mass mini-halos (M < 5e5 Msun) to
recover their gas after experiencing a supernova. As such, metal-enriched stars
will likely form first via this channel if the conditions are right for it to
occur. We identify a number of other externally enriched halos that may form
stars in this manner. These halos have metallicities as high as 0.01 Zsun,
suggesting that some members of the first generation of metal-enriched stars
may be hiding in plain sight in current stellar surveys.Comment: Accepted for publication in MNRAS. Minor updates and one additional
figure. Movies and images available at http://www.roe.ac.uk/~brs/pop2prim
Late Pop III Star Formation During the Epoch of Reionization: Results from the Renaissance Simulations
We present results on the formation of Pop III stars at redshift 7.6 from the
Renaissance Simulations, a suite of extremely high-resolution and physics-rich
radiation transport hydrodynamics cosmological adaptive-mesh refinement
simulations of high redshift galaxy formation performed on the Blue Waters
supercomputer. In a survey volume of about 220 comoving Mpc, we found 14
Pop III galaxies with recent star formation. The surprisingly late formation of
Pop III stars is possible due to two factors: (i) the metal enrichment process
is local and slow, leaving plenty of pristine gas to exist in the vast volume;
and (ii) strong Lyman-Werner radiation from vigorous metal-enriched star
formation in early galaxies suppresses Pop III formation in ("not so") small
primordial halos with mass less than 3 10 M. We
quantify the properties of these Pop III galaxies and their Pop III star
formation environments. We look for analogues to the recently discovered
luminous Ly emitter CR7 (Sobral et al. 2015), which has been
interpreted as a Pop III star cluster within or near a metal-enriched star
forming galaxy. We find and discuss a system similar to this in some respects,
however the Pop III star cluster is far less massive and luminous than CR7 is
inferred to be.Comment: 8 pages, 4 figures, 3 tables. Accepted by Ap
Probing The Ultraviolet Luminosity Function of the Earliest Galaxies with the Renaissance Simulations
In this paper, we present the first results from the Renaissance Simulations,
a suite of extremely high-resolution and physics-rich AMR calculations of high
redshift galaxy formation performed on the Blue Waters supercomputer. These
simulations contain hundreds of well-resolved galaxies at , and
make several novel, testable predictions. Most critically, we show that the
ultraviolet luminosity function of our simulated galaxies is consistent with
observations of high-z galaxy populations at the bright end of the luminosity
function (M), but at lower luminosities is essentially flat
rather than rising steeply, as has been inferred by Schechter function fits to
high-z observations, and has a clearly-defined lower limit in UV luminosity.
This behavior of the luminosity function is due to two factors: (i) the strong
dependence of the star formation rate on halo virial mass in our simulated
galaxy population, with lower-mass halos having systematically lower star
formation rates and thus lower UV luminosities; and (ii) the fact that halos
with virial masses below M do not universally
contain stars, with the fraction of halos containing stars dropping to zero at
M. Finally, we show that the brightest of our
simulated galaxies may be visible to current and future ultra-deep space-based
surveys, particularly if lensed regions are chosen for observation.Comment: 7 pages, 4 figures, accepted by The Astrophysical Journal Letter
Validating Semi-Analytic Models of High-Redshift Galaxy Formation using Radiation Hydrodynamical Simulations
We use a cosmological hydrodynamic simulation calculated with Enzo and the
semi-analytic galaxy formation model (SAM) GAMMA to address the chemical
evolution of dwarf galaxies in the early universe. The long-term goal of the
project is to better understand the origin of metal-poor stars and the
formation of dwarf galaxies and the Milky Way halo by cross-validating these
theoretical approaches. We combine GAMMA with the merger tree of the most
massive galaxy found in the hydrodynamic simulation and compare the star
formation rate, the metallicity distribution function (MDF), and the
age-metallicity relationship predicted by the two approaches. We found that the
SAM can reproduce the global trends of the hydrodynamic simulation. However,
there are degeneracies between the model parameters and more constraints (e.g.,
star formation efficiency, gas flows) need to be extracted from the simulation
to isolate the correct semi-analytic solution. Stochastic processes such as
bursty star formation histories and star formation triggered by supernova
explosions cannot be reproduced by the current version of GAMMA. Non-uniform
mixing in the galaxy's interstellar medium, coming primarily from
self-enrichment by local supernovae, causes a broadening in the MDF that can be
emulated in the SAM by convolving its predicted MDF with a Gaussian function
having a standard deviation of ~0.2 dex. We found that the most massive galaxy
in the simulation retains nearby 100% of its baryonic mass within its virial
radius, which is in agreement with what is needed in GAMMA to reproduce the
global trends of the simulation.Comment: 26 pages, 13 figures, 2 tables, submitted to ApJ (version 2
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