12,455 research outputs found
A centrally heated dark halo for our Galaxy
We construct a new family of models of our Galaxy in which dark matter and
disc stars are both represented by distribution functions that are analytic
functions of the action integrals of motion. The potential that is
self-consistently generated by the dark matter, stars and gas is determined,
and parameters in the distribution functions are adjusted until the model is
compatible with observational constraints on the circular-speed curve, the
vertical density profile of the stellar disc near the Sun, the kinematics of
nearly 200 000 giant stars within 2 kpc of the Sun, and estimates of the
optical depth to microlensing of bulge stars. We find that the data require a
dark halo in which the phase-space density is approximately constant for
actions |J| \lesssim 140 kpc km ^-1. In real space these haloes have core radii
~ 2 kpc.Comment: 14 pages, 11 figures, accepted for publication in MNRA
Art, Artists and Pedagogy
This volume has been brought together to generate new ideas and provoke discussion about what constitutes arts education in the twenty-first century, both within the institution and beyond. Art, Artists and Pedagogy is intended for educators who teach the arts from early childhood to tertiary level, artists working in the community, or those studying arts in education from undergraduate to Masters or PhD level
Systematic Development of Trans-Theoretically Based Behavioral Risk Management Programs
The authors explain the development and use of a behavioral Risk management strategy. It is designed for developing interventions to change behaviors, e.g., to lower the Risk of AIDS. The advantage of their strategy is said to be its structure combined with flexibility. Intervenors are not restricted to a single model in determining factors most relevant to changing Risky behavior
Probing the helium-graphite interaction
Two separate lines of investigation have recently converged to produce a highly detailed picture of the
behavior of helium atoms physisorbed on graphite basal plane surfaces. Atomic beam scattering experiments
on single crystals have yielded accurate values for the binding energies of several· states for both (^4)He and (^3)He, as well as matrix elements of the largest Fourier component of the periodic part of the interaction potential.
From these data, a complete three-dimensional description of the potential has been constructed, and the
energy band structure of a helium atom moving in this potential calculated. At the same time, accurate
thermodynamic measurements were made on submonolayer helium films adsorbed on Grafoil. The binding
energy and low-coverage specific heat deduced from these measurements are in excellent agreement with
those calculated from the band structures
The mass distribution of the Fornax dSph: constraints from its globular cluster distribution
Uniquely among the dwarf spheroidal (dSph) satellite galaxies of the Milky
Way, Fornax hosts globular clusters. It remains a puzzle as to why dynamical
friction has not yet dragged any of Fornax's five globular clusters to the
centre, and also why there is no evidence that any similar star cluster has
been in the past (for Fornax or any other dSph). We set up a suite of 2800
N-body simulations that sample the full range of globular-cluster orbits and
mass models consistent with all existing observational constraints for Fornax.
In agreement with previous work, we find that if Fornax has a large dark-matter
core then its globular clusters remain close to their currently observed
locations for long times. Furthermore, we find previously unreported behaviour
for clusters that start inside the core region. These are pushed out of the
core and gain orbital energy, a process we call 'dynamical buoyancy'. Thus a
cored mass distribution in Fornax will naturally lead to a shell-like globular
cluster distribution near the core radius, independent of the initial
conditions. By contrast, CDM-type cusped mass distributions lead to the rapid
infall of at least one cluster within \Delta t = 1-2Gyr, except when picking
unlikely initial conditions for the cluster orbits (\sim 2% probability), and
almost all clusters within \Delta t = 10Gyr. Alternatively, if Fornax has only
a weakly cusped mass distribution, dynamical friction is much reduced. While
over \Delta t = 10Gyr this still leads to the infall of 1-4 clusters from their
present orbits, the infall of any cluster within \Delta t = 1-2Gyr is much less
likely (with probability 0-70%, depending on \Delta t and the strength of the
cusp). Such a solution to the timing problem requires that in the past the
globular clusters were somewhat further from Fornax than today; they most
likely did not form within Fornax, but were accreted.Comment: 12 pages, 8 figures, 3 tables, submitted to MNRA
EXPORT ENHANCEMENT STRATEGIES FOR SMALL AND MEDIUM RURAL AND AGRICULTURAL FIRMS
Literature reports that small and medium firms face greater difficulty in obtaining the necessary export market information and in obtaining financing than do larger firms. Accordingly, the United States has many export promotion and enhancement services, but there is little documentation on the impacts of these services on small and medium rural and agricultural firms. The objectives of this project were to 1) analyze the export assistance needs of small and medium rural and agricultural firms operating in the Northern Plains region at different stages of the export or internationalization process, 2) identify available export assistance and promotion services offered at the federal and state levels to meet the needs of these firms, and 3) identify factors that may increase the effectiveness of export assistance programs. The primary assistance these firms wanted from the government was help in documenting their exports. The primary reasons firms did not seek government assistance were a lack of knowledge of the service and the service is not useful. The most often used non-government information sources were trade or industry associations and banks. Accordingly, policy makers should emphasize programs that complement efforts of private organizations and that target the needs and interests of the firms.export, rural, agriculture, export assistance, Northern Plains, government, Community/Rural/Urban Development, International Development,
A kiloparsec-scale nuclear stellar disk in the milky way as a possible explanation of the high velocity peaks in the galactic bulge
The Apache Point Observatory Galactic Evolution Experiment has measured the stellar velocities of red giant stars in the inner Milky Way. We confirm that the line of sight velocity distributions (LOSVDs) in the mid-plane exhibit a second peak at high velocities, whereas those at | b| =2^\circ do not. We use a high resolution simulation of a barred galaxy, which crucially includes gas and star formation, to guide our interpretation of the LOSVDs. We show that the data are fully consistent with the presence of a thin, rapidly rotating, nuclear disk extending to ∼1 kpc. This nuclear disk is orientated perpendicular to the bar and is likely to be composed of stars on x2 orbits. The gas in the simulation is able to fall onto such orbits, leading to stars populating an orthogonal disk
- …