2,839 research outputs found
Influence of baryonic physics in galaxy simulations: a semi-analytic treatment of the molecular component
Recent work in galaxy formation has enlightened the important role of baryon
physics, to solve the main problems encountered by the standard theory at the
galactic scale, such as the galaxy stellar mass functions, or the missing
satellites problem. The present work aims at investigating in particular the
role of the cold and dense molecular phase, which could play a role of gas
reservoir in the outer galaxy discs, with low star formation efficiency.
Through TreeSPH simulations, implementing the cooling to low temperatures, and
the inclusion of the molecular hydrogen component, several feedback
efficiencies are studied, and results on the gas morphology and star formation
are obtained. It is shown that molecular hydrogen allows some slow star
formation (with gas depletion times of about 5 Gyr) to occur in the outer parts
of the discs. This dense and quiescent phase might be a way to store a
significant fraction of dark baryons, in a relatively long time-scale, in the
complete baryonic cycle, connecting the galaxy discs to hot gaseous haloes and
to the cosmic filaments.Comment: Accepted for publication in Astronomy and Astrophysics, 21 pages, 29
figure
Quantifying stellar radial migration in an N-body simulation: blurring, churning, and the outer regions of galaxy discs
Radial stellar migration in galactic discs has received much attention in
studies of galactic dynamics and chemical evolution, but remains a dynamical
phenomenon that needs to be fully quantified. In this work, using a Tree-SPH
simulation of an Sb-type disc galaxy, we quantify the effects of blurring
(epicyclic excursions) and churning (change of guiding radius). We quantify
migration (either blurring or churning) both in terms of flux (the number of
migrators passing at a given radius), and by estimating the population of
migrators at a given radius at the end of the simulation compared to
non-migrators, but also by giving the distance over which the migration is
effective at all radii. We confirm that the corotation of the bar is the main
source of migrators by churning in a bar-dominated galaxy, its intensity being
directly linked to the episode of a strong bar, in the first 1-3 Gyr of the
simulation. We show that within the outer Lindblad resonance (OLR), migration
is strongly dominated by churning, while blurring gains progressively more
importance towards the outer disc and at later times. Most importantly, we show
that the OLR limits the exchange of angular momentum, separating the disc in
two distinct parts with minimal or null exchange, except in the transition
zone, which is delimited by the position of the OLR at the epoch of the
formation of the bar, and at the final epoch. We discuss the consequences of
these findings for our understanding of the structure of the Milky Way disc.
Because the Sun is situated slightly outside the OLR, we suggest that the solar
vicinity may have experienced very limited churning from the inner disc.Comment: Accepted for publication in Astronomy and Astrophysics (acceptance
date: 27/04/15), 24 pages, 24 figure
Earned Value Analysis Lesson Plan and Activity
At California Polytechnic State University, in the Construction Management Department there is a need for a lesson plan which teaches students the concepts of earned value analysis as it applies to construction projects. As many construction management students from Cal Poly go into industry and take part in complex projects, it will be beneficial to understand project management tools such as earned value. Earned value analysis focuses on two critical components, time and money and how they relate to each other and compare to the original estimate throughout the duration of a project. Comparing the estimated values to actual values during construction provides variables to calculate the schedule performance index and cost performance index. These indexes give an accurate estimate as to if the project is ahead or behind schedule and over or under budget. Understanding how to calculate these values will allow for timely action by the project team to keep projects on schedule and on budget
The COMPLETE Survey of Outflows in Perseus
We present a study on the impact of molecular outflows in the Perseus
molecular cloud complex using the COMPLETE survey large-scale 12CO(1-0) and
13CO(1-0) maps. We used three-dimensional isosurface models generated in
RA-DEC-Velocity space to visualize the maps. This rendering of the molecular
line data allowed for a rapid and efficient way to search for molecular
outflows over a large (~ 16 sq. deg.) area. Our outflow-searching technique
detected previously known molecular outflows as well as new candidate outflows.
Most of these new outflow-related high-velocity features lie in regions that
have been poorly studied before. These new outflow candidates more than double
the amount of outflow mass, momentum, and kinetic energy in the Perseus cloud
complex. Our results indicate that outflows have significant impact on the
environment immediately surrounding localized regions of active star formation,
but lack the energy needed to feed the observed turbulence in the entire
Perseus complex. This implies that other energy sources, in addition to
protostellar outflows, are responsible for turbulence on a global cloud scale
in Perseus. We studied the impact of outflows in six regions with active star
formation within Perseus of sizes in the range of 1 to 4 pc. We find that
outflows have enough power to maintain the turbulence in these regions and
enough momentum to disperse and unbind some mass from them. We found no
correlation between outflow strength and star formation efficiency for the six
different regions we studied, contrary to results of recent numerical
simulations. The low fraction of gas that potentially could be ejected due to
outflows suggests that additional mechanisms other than cloud dispersal by
outflows are needed to explain low star formation efficiencies in clusters.Comment: Published in The Astrophysical Journa
As newly returned New York Police Commissioner, Bill Bratton’s first task will be to regain the trust of the city’s most heavily policed groups
Last week, Bill Bratton was sworn in as New York City’s police commissioner, as part of the administration of new mayor, Bill de Blasio. David Halle, Andrew A. Beveridge, and Sydney Beveridge, take a closer look at Bill Bratton’s policy success in reducing crime, in both New York and Los Angeles, through the use of the COMPSTAT program and its successors. They write that, now that he has returned to New York, Bratton’s challenge will be to keep crime rates low while reducing the widespread hatred of the police among black residents that has been created by ‘Stop & Frisk’ policies
Linguistics
Contains reports on three research projects.National Science Foundation (Grant GP-2495)National Institutes of Health (Grant MH-04737-04)U. S. Air Force. Electronics Systems Division (Contract AFl9(628)-2487)National Aeronautics and Space Administration (Grant NsG-496
Linguistics
Contains research objectives and reports on one research project.National Institutes of Health (Grant 1 P01 MH-13390-02
- …