4,754 research outputs found
A Structured Framework and Resources to Use to Get Your Medical Education Work Published.
IntroductionMedical educators often have great ideas for medical education scholarship but have difficulty converting their educational abstract or project into a published manuscript.MethodsDuring this workshop, participants addressed common challenges in developing an educational manuscript. In small-group case scenarios, participants discovered the importance of the "So what?" in making the case for their project. Incorporating conceptual frameworks, participants chose appropriate outcome metrics, discussed how to frame the discussion section, and ensured appropriate journal fit. After each small-group exercise, large-group discussions allowed the small groups to report back so that facilitators could highlight and reinforce key learning points. At the conclusion of the workshop, participants left with a checklist for creating an educational manuscript and an additional resources document to assist them in avoiding common pitfalls when turning their educational abstract/project into a publishable manuscript.ResultsThis workshop was presented in 2016 and 2017. Presenter evaluations were completed by 33 participants; 11 completed conference evaluations. The mean overall rating on presenter evaluations was 4.55 out of 5, while the conference evaluations mean was 3.73 out of 4. Comments provided on both evaluation tools highlighted the perceived effectiveness of the delivery and content. More than 50% of respondents stated that they planned to incorporate the use of conceptual frameworks in future work.DiscussionThis workshop helped participants address common challenges by providing opportunities for hands-on practice as well as tips and resources for use when submitting a medical education manuscript for publication
Sub-Alfvenic Non-Ideal MHD Turbulence Simulations with Ambipolar Diffusion: I. Turbulence Statistics
Most numerical investigations on the role of magnetic fields in turbulent
molecular clouds (MCs) are based on ideal magneto-hydrodynamics (MHD). However,
MCs are weakly ionized, so that the time scale required for the magnetic field
to diffuse through the neutral component of the plasma by ambipolar diffusion
(AD) can be comparable to the dynamical time scale. We have performed a series
of 256^3 and 512^3 simulations on supersonic but sub-Alfvenic turbulent systems
with AD using the Heavy-Ion Approximation developed in Li, McKee, & Klein
(2006). Our calculations are based on the assumption that the number of ions is
conserved, but we show that these results approximately apply to the case of
time-dependent ionization in molecular clouds as well. Convergence studies
allow us to determine the optimal value of the ionization mass fraction when
using the heavy-ion approximation for low Mach number, sub-Alfvenic turbulent
systems. We find that ambipolar diffusion steepens the velocity and magnetic
power spectra compared to the ideal MHD case. Changes in the density PDF, total
magnetic energy, and ionization fraction are determined as a function of the AD
Reynolds number. The power spectra for the neutral gas properties of a strongly
magnetized medium with a low AD Reynolds number are similar to those for a
weakly magnetized medium; in particular, the power spectrum of the neutral
velocity is close to that for Burgers turbulence.Comment: 37 pages, 11 figures, 4 table
On the Transfer of Metric Fluctuations when Extra Dimensions Bounce or Stabilize
In this report, we study within the context of general relativity with one
extra dimension compactified either on a circle or an orbifold, how radion
fluctuations interact with metric fluctuations in the three non-compact
directions. The background is non-singular and can either describe an extra
dimension on its way to stabilization, or immediately before and after a series
of non-singular bounces. We find that the metric fluctuations transfer
undisturbed through the bounces or through the transients of the
pre-stabilization epoch. Our background is obtained by considering the effects
of a gas of massless string modes in the context of a consistent 'massless
background' (or low energy effective theory) limit of string theory. We discuss
applications to various approaches to early universe cosmology, including the
ekpyrotic/cyclic universe scenario and string gas cosmology.Comment: V2. Minor Clarifications V3. appendix and 2 figures added, typos
corrected, conclusions unchanged 12 pages, 6 figure
Black Rings, Boosted Strings and Gregory-Laflamme
We investigate the Gregory-Laflamme instability for black strings carrying
KK-momentum along the internal direction. We demonstrate a simple kinematical
relation between the thresholds of the classical instability for the boosted
and static black strings. We also find that Sorkin's critical dimension depends
on the internal velocity and in fact disappears for sufficiently large boosts.
Our analysis implies the existence of an analogous instability for the
five-dimensional black ring of Emparan and Reall. We also use our results for
boosted black strings to construct a simple model of the black ring and argue
that such rings exist in any number of space-time dimensions.Comment: 26 pages, 6 figure
Ariel - Volume 5 Number 5
Editors
Mark Dembert
J. D. Kanofsky
Entertainment
Robert Breckenridge
Joe Conti
Gary Kaskey
Photographer
Scot Kastner
Overseas Editor
Mike Sinason
Circulation
Jay Amsterdam
Humorist
Jim McCann
Staff
Ken Jaffe
Bob Sklaroff
Janet Welsh
Dave Jacoby
Phil Nimoityn
Frank Chervane
On the Hydrodynamic Interaction of Shock Waves with Interstellar Clouds. II. The Effect of Smooth Cloud Boundaries on Cloud Destruction and Cloud Turbulence
The effect of smooth cloud boundaries on the interaction of steady planar
shock waves with interstellar clouds is studied using a high-resolution local
AMR technique with a second-order accurate axisymmetric Godunov hydrodynamic
scheme. A 3D calculation is also done to confirm the results of the 2D ones. We
consider an initially spherical cloud whose density distribution is flat near
the cloud center and has a power-law profile in the cloud envelope. When an
incident shock is transmitted into a smooth cloud, velocity gradients in the
cloud envelope steepen the smooth density profile at the upstream side,
resulting in a sharp density jump having an arc-like shape. Such a ``slip
surface'' forms immediately when a shock strikes a cloud with a sharp boundary.
For smoother boundaries, the formation of slip surface and therefore the onset
of hydrodynamic instabilities are delayed. Since the slip surface is subject to
the Kelvin-Helmholtz and Rayleigh-Taylor instabilities, the shocked cloud is
eventually destroyed in cloud crushing times. After complete cloud
destruction, small blobs formed by fragmentation due to hydrodynamic
instabilities have significant velocity dispersions of the order of 0.1 ,
where is the shock velocity in the ambient medium. This suggests that
turbulent motions generated by shock-cloud interaction are directly associated
with cloud destruction. The interaction of a shock with a cold HI cloud should
lead to the production of a spray of small HI shreds, which could be related to
the small cold clouds recently observed by Stanimirovic & Heiles (2005). The
linewidth-size relation obtained from our 3D simulation is found to be
time-dependent. A possibility for gravitational instability triggered by shock
compression is also discussed.Comment: 62 pages, 16 figures, submitted to Ap
Vertex Sparsifiers: New Results from Old Techniques
Given a capacitated graph and a set of terminals ,
how should we produce a graph only on the terminals so that every
(multicommodity) flow between the terminals in could be supported in
with low congestion, and vice versa? (Such a graph is called a
flow-sparsifier for .) What if we want to be a "simple" graph? What if
we allow to be a convex combination of simple graphs?
Improving on results of Moitra [FOCS 2009] and Leighton and Moitra [STOC
2010], we give efficient algorithms for constructing: (a) a flow-sparsifier
that maintains congestion up to a factor of , where , (b) a convex combination of trees over the terminals that maintains
congestion up to a factor of , and (c) for a planar graph , a
convex combination of planar graphs that maintains congestion up to a constant
factor. This requires us to give a new algorithm for the 0-extension problem,
the first one in which the preimages of each terminal are connected in .
Moreover, this result extends to minor-closed families of graphs.
Our improved bounds immediately imply improved approximation guarantees for
several terminal-based cut and ordering problems.Comment: An extended abstract appears in the 13th International Workshop on
Approximation Algorithms for Combinatorial Optimization Problems (APPROX),
2010. Final version to appear in SIAM J. Computin
Vertical integration and firm boundaries : the evidence
Since Ronald H. Coase's (1937) seminal paper, a rich set of theories has been developed that deal with firm boundaries in vertical or input–output structures. In the last twenty-five years, empirical evidence that can shed light on those theories also has been accumulating. We review the findings of empirical studies that have addressed two main interrelated questions: First, what types of transactions are best brought within the firm and, second, what are the consequences of vertical integration decisions for economic outcomes such as prices, quantities, investment, and profits. Throughout, we highlight areas of potential cross-fertilization and promising areas for future work
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