1,586 research outputs found
MOND and the Galaxies
We review galaxy formation and dynamics under the MOND hypothesis of modified
gravity, and compare to similar galaxies in Newtonian dynamics with dark
matter. The aim is to find peculiar predictions both to discriminate between
various hypotheses, and to make the theory progress through different
constraints, touching the interpolation function, or the fundamental
acceleration scale. Galaxy instabilities, forming bars and bulges at longer
term, evolve differently in the various theories, and help to bring
constraints, together with the observations of bar frequency. Dynamical
friction and the predicted merger rate could be a sensitive test of theories.
The different scenarios of galaxy formation are compared within the various
theories and observations.Comment: 8 pages, 7 figures, Invited paper to "The Invisible Universe
International Conference", ed. J-M. Alimi, A. Fuzfa, P-S. Corasaniti, AIP pu
Gaseous Flows in Galaxies
The gas component plays a major role in the dynamics of spiral galaxies,
because of its dissipative character, and its ability to exchange angular
momentum with stars in the disk. Due to its small velocity dispersion, it
triggers gravitational instabilities, and the corresponding non-axisymmetric
patterns produce gravity torques, which mediate these angular momentum
exchanges. When a srong bar pattern develops with the same pattern speed all
over the disk, only gas inside corotation can flow towards the center. But
strong bars are not long lived in presence of gas, and multiple-speed spiral
patterns can develop between bar phases, and help the galaxy to accrete
external gas flowing from cosmic filaments. The gas is then intermittently
driven to the galaxy center, to form nuclear starbursts and fuel an active
nucleus. The various time-scales of these gaseous flows are described.Comment: 10 pages, 6 figures, review paper in the Proceedings of the IAU
Symposium 245, "Formation and Evolution of Galaxy Bulges", held at Oxford,
U.K., July 2007, Eds. M. Bureau, E. Athanassoula, B. Barbu
Rx for Health Referral Toolkit to Promote Extension Programs
The Cooperative Extension National Framework for Health and Wellness calls for the Cooperative Extension Service (CES) to partner with healthcare professionals to support their patients in preventing illness and promoting health through community education. Strategies to connect the healthcare system with coordinated referrals to community-based health programs can help patients improve health outcomes. The Rx for Health Referral Toolkit pilot project was developed as part of a strategy to align CES’s strengths with the medical community to promote quality healthcare experiences for patients. The toolkit educates healthcare providers about the many health programs offered by CES in Michigan. It helps ease the burden on healthcare providers by providing a ready-to-use, simple referral tool. Extension staff were recruited to serve as the point of contact for healthcare provider referrals and conduct outreach with primary care practices utilizing the Rx for Health Referral Toolkit. As a result of the pilot project, CES educators had 56 new participant referrals directly from healthcare providers. Prior to this pilot, referrals from healthcare providers were rare. Feedback showed that patients also needed to know what CES is and what it has to offer. Partnerships between healthcare providers and CES can improve the health of patients nationwide
Evolution of spiral galaxies in modified gravity: II- Gas dynamics
The stability of spiral galaxies is compared in modified Newtonian Dynamics
(MOND) and Newtonian dynamics with dark matter (DM). We extend our previous
simulations that involved pure stellar discs without gas, to deal with the
effects of gas dissipation and star formation. We also vary the interpolating
function between the MOND and Newtonian regime. Bar formation is compared in
both dynamics, from initial conditions identical in visible component. One
first result is that the MOND galaxy evolution is not affected by the choice of
the mu-function, it develops bars with the same frequency and strength. The
choice of the mu-function significantly changes the equivalent DM models, in
changing the dark matter to visible mass ratio and, therefore, changing the
stability. The introduction of gas shortens the timescale for bar formation in
the DM model, but is not significantly shortened in the MOND model. As a
consequence, with gas, the MOND and DM bar frequency histograms are now more
similar than without gas. The thickening of the plane occurs through vertical
resonance with the bar and peanut formation, and even more quickly with gas.
Since the mass gets more concentrated with gas, the radius of the peanut is
smaller, and the appearance of the pseudo-bulge is more boxy. The bar strength
difference is moderated by saturation, and feedback effects, like the bar
weakening or destruction by gas inflow due to gravity torques. Averaged over a
series of models representing the Hubble sequence, the MOND models have still
more bars, and stronger bars, than the equivalent DM models, better fitting the
observations. Gas inflows driven by bars produce accumulations at Lindblad
resonances, and MOND models can reproduce observed morphologies quite well, as
was found before in the Newtonian dynamics.Comment: 9 pages, 11 figures, accepted in A&
Polar ring galaxies as tests of gravity
Polar ring galaxies are ideal objects with which to study the
three-dimensional shapes of galactic gravitational potentials since two
rotation curves can be measured in two perpendicular planes. Observational
studies have uncovered systematically larger rotation velocities in the
extended polar rings than in the associated host galaxies. In the dark matter
context, this can only be explained through dark halos that are systematically
flattened along the polar rings. Here, we point out that these objects can also
be used as very effective tests of gravity theories, such as those based on
Milgromian dynamics (MOND). We run a set of polar ring models using both
Milgromian and Newtonian dynamics to predict the expected shapes of the
rotation curves in both planes, varying the total mass of the system, the mass
of the ring with respect to the host, as well as the size of the hole at the
center of the ring. We find that Milgromian dynamics not only naturally leads
to rotation velocities being typically higher in the extended polar rings than
in the hosts, as would be the case in Newtonian dynamics without dark matter,
but that it also gets the shape and amplitude of velocities correct. Milgromian
dynamics thus adequately explains this particular property of polar ring
galaxies.Comment: 9 pages, 8 Figures, 1 Table, Accepted for publication by MNRA
Quasi-linear formulation of MOND
A new formulation of MOND as a modified-potential theory of gravity is
propounded. In effect, the theory dictates that the MOND potential phi produced
by a mass distribution rho is a solution of the Poisson equation for the
modified source density rho*=-(1/4 pi G)divergence(g), where g=nu(|gN|/a0)gN,
and gN is the Newtonian acceleration field of rho. This makes phi simply the
scalar potential of the algebraic acceleration field g. The theory thus
involves solving only linear differential equations, with one nonlinear,
algebraic step. It is derivable from an action, satisfies all the usual
conservation laws, and gives the correct center-of-mass acceleration to
composite bodies. The theory is akin in some respects to the nonlinear Poisson
formulation of Bekenstein and Milgrom, but it is different from it, and is
obviously easier to apply. The two theories are shown to emerge as natural
modifications of a Palatini-type formulation of Newtonian gravity, and are
members in a larger class of bi-potential theories.Comment: 23 pages. Published in MNRAS. Minor changes to match the published
versio
RELAX to Relajarse: A Framework for Culturally Adapting Educational Programming in Extension
Family life and Extension family and consumer science educators are encouraged to adapt existing curricula to effectively use with ethnically diverse audiences. Scholars have described different methods for culturally adapting programming; however, few have documented the process by which Extension educators may tackle this endeavor. The purpose of this article is to provide a framework and step-by-step example for how one Extension program was translated and culturally adapted for U.S. Latino participants. Lessons learned and recommendations are provided
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