22 research outputs found
Observation of magnetocoriolis waves in a liquid metal Taylor-Couette experiment
The first observation of fast and slow magnetocoriolis (MC) waves in a
laboratory experiment is reported. Rotating nonaxisymmetric modes arising from
a magnetized turbulent Taylor-Couette flow of liquid metal are identified as
the fast and slow MC waves by the dependence of the rotation frequency on the
applied field strength. The observed slow MC wave is damped but the observation
provides a means for predicting the onset of the Magnetorotational Instability
Laboratory Study of Magnetorotational Instability and Hydrodynamic Stability at Large Reynolds Numbers
Two plausible mechanisms have been proposed to explain rapid angular momentum transport during accretion processes in astrophysical disks: nonlinear hydrodynamic instabilities and magnetorotational instability (MRI). A laboratory experiment in a short Taylor-Couette flow geometry has been constructed in Princeton to study both mechanisms, with novel features for better controls of the boundary-driven secondary flows (Ekman circulation). Initial results on hydrodynamic stability have shown negligible angular momentum transport in Keplerian-like flows with Reynolds numbers approaching one million, casting strong doubt on the viability of nonlinear hydrodynamic instability as a source for accretion disk turbulence
Stability of the Submillimeter Brightness of the Atmosphere Above Mauna Kea, Chajnantor and the South Pole
The summit of Mauna Kea in Hawaii, the area near Cerro Chajnantor in Chile,
and the South Pole are sites of large millimeter or submillimeter wavelength
telescopes. We have placed 860 GHz sky brightness monitors at all three sites
and present a comparative study of the measured submillimeter brightness due to
atmospheric thermal emission. We report the stability of that quantity at each
site.Comment: 6 figure
The Influence of Horizontal Boundaries on Ekman Circulation and Angular Momentum Transport in a Cylindrical Annulus
We present numerical simulations of circular Couette flow in axisymmetric and
fully three-dimensional geometry of a cylindrical annulus inspired by Princeton
MRI liquid gallium experiment. The incompressible Navier-Stokes equations are
solved with the spectral element code Nek5000 incorporating realistic
horizontal boundary conditions of differentially rotating rings. We investigate
the effect of changing rotation rates (Reynolds number) and of the horizontal
boundary conditions on flow structure, Ekman circulation and associated
transport of angular momentum through the onset of unsteadiness and
three-dimensionality. A mechanism for the explanation of the dependence of the
Ekman flows and circulation on horizontal boundary conditions is proposed.Comment: 23 pages, 7 figures; to be published in the Topical Issue of the
Physica Scripta in 200
Stability of quasi-Keplerian shear flow in a laboratory experiment
Context: Subcritical transition to turbulence has been proposed as a source
of turbulent viscosity required for the associated angular momentum transport
for fast accretion in Keplerian disks. Previously cited laboratory experiments
in supporting this hypothesis were performed either in a different type of flow
than Keplerian or without quantitative measurements of angular momentum
transport and mean flow profile, and all of them appear to suffer from Ekman
effects, secondary flows induced by nonoptimal axial boundary conditions. Such
Ekman effects are expected to be absent from astronomical disks, which probably
have stress-free vertical boundaries unless strongly magnetized. Aims: To
quantify angular momentum transport due to subcritical hydrodynamic turbulence,
if exists, in a quasi-Keplerian flow with minimized Ekman effects. Methods: We
perform a local measurement of the azimuthal--radial component of the Reynolds
stress tensor in a novel laboratory apparatus where Ekman effects are minimized
by flexible control of axial boundary conditions. Results: We find significant
Ekman effects on angular momentum transport due to nonoptimal axial boundary
conditions in quasi-Keplerian flows. With the optimal control of Ekman effects,
no statistically meaningful angular momentum transport is detected in such
flows at Reynolds number up to two millions. Conclusions: Either a subcritical
transition does not occur, or, if a subcritical transition does occur, the
associated radial transport of angular momentum in optimized quasi-Keplerian
laboratory flows is too small to directly support the hypothesis that
subcritical hydrodynamic turbulence is responsible for accretion in
astrophysical disks. Possible limitations in applying laboratory results to
astrophysical disks due to experimental geometry are discussed.Comment: 24 pages, 13 figures, published in Astron. Astrophy
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Genetic counseling for congenital heart disease – Practice resource of the national society of genetic counselors
Congenital heart disease (CHD) is an indication which spans multiple specialties across various genetic counseling practices. This practice resource aims to provide guidance on key considerations when approaching counseling for this particular indication while recognizing the rapidly changing landscape of knowledge within this domain. This resource was developed with consensus from a diverse group of certified genetic counselors utilizing literature relevant for CHD genetic counseling practice and is aimed at supporting genetic counselors who encounter this indication in their practice both pre- and postnatally
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Observation of Magnetocoriolis Waves in a Liquid Metal Taylor-Couette Experiment
The first observation of fast and slow magnetocoriolis (MC) waves in a laboratory experiment is reported. Rotating nonaxisymmetric modes arising from a magnetized turbulent Taylor-Couette flow of liquid metal are identified as the fast and slow MC waves by the dependence of the rotation frequency on the applied field strength. The observed slow MC wave is marginally damped but will become destabilized by the magnetorotational instability with a modest increase in rotation rate