4,761 research outputs found
The Formation of Star Clusters II: 3D Simulations of Magnetohydrodynamic Turbulence in Molecular Clouds
(Abridged) We present a series of decaying turbulence simulations that
represent a cluster-forming clump within a molecular cloud, investigating the
role of magnetic fields on the formation of potential star-forming cores. We
present an exhaustive analysis of numerical data from these simulations that
includes a compilation of all of the distributions of physical properties that
characterize bound cores - including their masses, radii, mean densities,
angular momenta, spins, magnetizations, and mass-to-flux ratios. We also
present line maps of our models that can be compared with observations. Our
simulations range between 5-30 Jeans masses of gas, and are representative of
molecular cloud clumps with masses between 100-1000 solar masses. The cores
have mass-to-flux ratios that are generally less than that of the original
cloud, and so a cloud that is initially highly supercritical can produce cores
that are slightly supercritical, similar to that seen by Zeeman measurements of
molecular cloud cores. Clouds that are initially only slightly supercritical
will instead collapse along the field lines into sheets, and the cores that
form as these sheets fragment have a different mass spectrum than what is
observed. The spin rates of these cores suggests that subsequent fragmentation
into multiple systems is likely. The sizes of the bound cores that are produced
are typically 0.02-0.2 pc and have densities in the range 10^4-10^5 cm^{-3} in
agreement with observational surveys. Finally, our numerical data allow us to
test theoretical models of the mass spectrum of cores, such as the turbulent
fragmentation picture of Padoan-Nordlund. We find that while this model gets
the shape of the core mass spectrum reasonably well, it fails to predict the
peak mass in the core mass spectrum.Comment: Accepted by MNRAS. 28 pages, 16 figures. Substantial revision since
last versio
Dynamics of rapidly rotating Bose-Einstein condensates in a harmonic plus quartic trap
A two-dimensional rapidly rotating Bose-Einstein condensate in a harmonic
plus quartic trap is expected to have unusual vortex states that do not occur
in a pure harmonic trap. At a critical rotation speed , a central
hole appears in the condensate, and at some faster rotation speed ,
the system undergoes a transition to a giant vortex state with pure
irrotational flow. Using a time-dependent variational analysis, we study the
behavior of an annular condensate with a single concentric ring of vortices.
The transition to a giant vortex state is investigated by comparing the energy
of the two equilibrium states (the ring of vortices and the giant vortex) and
also by studying the dynamical stability of small excitation modes of the ring
of vortices.Comment: 12pages, 4figure
Energy Loss from Reconnection with a Vortex Mesh
Experiments in superfluid 4He show that at low temperatures, energy
dissipation from moving vortices is many orders of magnitude larger than
expected from mutual friction. Here we investigate other mechanisms for energy
loss by a computational study of a vortex that moves through and reconnects
with a mesh of small vortices pinned to the container wall. We find that such
reconnections enhance energy loss from the moving vortex by a factor of up to
100 beyond that with no mesh. The enhancement occurs through two different
mechanisms, both involving the Kelvin oscillations generated along the vortex
by the reconnections. At relatively high temperatures the Kelvin waves increase
the vortex motion, leading to more energy loss through mutual friction. As the
temperature decreases, the vortex oscillations generate additional reconnection
events between the moving vortex and the wall, which decrease the energy of the
moving vortex by transfering portions of its length to the pinned mesh on the
wall.Comment: 9 pages, 10 figure
An AI approach for scheduling space-station payloads at Kennedy Space Center
The Payload Processing for Space-Station Operations (PHITS) is a prototype modeling tool capable of addressing many Space Station related concerns. The system's object oriented design approach coupled with a powerful user interface provide the user with capabilities to easily define and model many applications. PHITS differs from many artificial intelligence based systems in that it couples scheduling and goal-directed simulation to ensure that on-orbit requirement dates are satisfied
Alien Registration- Tilley, Lewis R. (Fort Fairfield, Aroostook County)
https://digitalmaine.com/alien_docs/35773/thumbnail.jp
Investment Performance of Common Stock in Relation to their Price-Earnings Ratios: BASU 1977 Extended Analysis
In this study, the work of Basu 1977 is partly replicated using subsequent market data. A trading strategy of investing in assets based on their price-earnings ratio is back-tested, thus also testing the efficient market hypothesis. Market data over the past twenty-five years (1989-2014) was gathered, cleaned, and modeled to test for unexplained return to five portfolios ranked by PE ratio. The data was tested using the single-factor Capital Asset Pricing Model and the Fama-French three-factor model. The dataset was then decomposed by price and similarly modeled to test whether the effectiveness of using PE as a leading indicator is limited by the price level of an asset. I conclude that investing in a portfolio comprised of the lowest PE ratio assets yields the highest unexplained returns over the period examined. I also find that this strategy is primarily driven by low and mid-priced stocks, and does not hold at high price levels. In this analysis, the efficient market hypothesis does not hold
Do individuals consuming a vegetarian diet suffer less chronic disease than the general public in a Midwestern county?.
The main purpose of this study was to determine if vegetarians living in Oklahoma County suffered from less heart disease, stroke, cancer, and diabetes than the general public of Oklahoma County. The secondary purpose of the study was to collect descriptive statistics on vegetarians living in Oklahoma County. Criteria for participation were adults living in Oklahoma County consuming any type of vegetarian diet
Determinants of Students’ First Impressions of Instructors and Courses
Students evaluated instructors and courses in the first two weeks of the fall semester to determine the factors that form impressions in the early stages of the semester. Results indicate differences exist between upper and lower division courses with presentation of material and perceived workload as key factors that students use to form first impressions.Teaching/Communication/Extension/Profession,
Perturbations in inflationary cosmologies with smooth exit
We give a comprehensive analysis of how scalar and tensor perturbations evolve in cosmologies with a smooth transition from power-law-like and de Sitter-like inflation to a radiation era. Analytic forms for the super-horizon and sub-horizon perturbations in the inflationary and radiation dominated eras are found
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