Browsing by Subject "fields"

Now showing 1 - 7 of 7

Central Rotations of Milky Way Globular Clusters
(2014-06) Fabricius, Maximilian H.; Noyola, Eva; Rukdee, Surangkhana; Saglia, Roberto P.; Bender, Ralf; Hopp, Ulrich; Thomas, Jens; Opitsch, Michael; Williams, Michael J.; Noyola, Eva
Most Milky Way globular clusters (GCs) exhibit measurable flattening, even if on a very low level. Both cluster rotation and tidal fields are thought to cause this flattening. Nevertheless, rotation has only been confirmed in a handful of GCs, based mostly on individual radial velocities at large radii. We are conducting a survey of the central kinematics of Galactic GCs using the new Integral Field Unit instrument VIRUS-W. We detect rotation in all 11 GCs that we have observed so far, rendering it likely that a large majority of the Milky Way GCs rotate. We use published catalogs of GCs to derive central ellipticities and position angles. We show that in all cases where the central ellipticity permits an accurate measurement of the position angle, those angles are in excellent agreement with the kinematic position angles that we derive from the VIRUS-W velocity fields. We find an unexpected tight correlation between central rotation and outer ellipticity, indicating that rotation drives flattening for the objects in our sample. We also find a tight correlation between central rotation and published values for the central velocity dispersion, most likely due to rotation impacting the old dispersion measurements.
The Dallas-Fort Worth Earthquake Sequence: October 2008 through May 2009
(2011-02) Frohlich, Cliff; Hayward, Chris; Stump, Brian; Potter, Eric; Potter, Eric
This paper describes a sequence of small earthquakes (m(b) <= 3.3) that occurred at the Dallas-Fort Worth Airport, Texas, between 30 October 2008 and 31 May 2009. Analysis of records at regional station WMOK identified more than 180 earthquakes in the sequence; about 90 percent occurred in four clusters on 30 October-1 November, 20 November, 26 December and 15-17 May. After the sequence began, a six-station temporary local network obtained high-quality three-component records for 11 earthquakes occurring between 20 November and 1 December. Analysis of these data demonstrated that all 11 earthquakes originated from a focus near 32.855 degrees N, 97.051 degrees W, with an estimated depth similar to 4.4 km. This location is less than 0.5 km from a well completed in August 2008 that extends to a depth of 4.2 km, drilled to dispose of brines collected during flowback of hydraulic fracturing fluids associated with the production of natural gas. Brine disposal commenced at the well on 12 September 2008. Seismograms and (S-P) intervals for the earthquakes are similar though not identical, and relative locations indicate they occurred along a north-northeast-south-southwest trend with horizontal and vertical dimensions of similar to 1.1 km and 0.2 km, respectively. This trend is approximately coincident with that of a mapped normal fault in the subsurface, and consistent with the maximum horizontal in situ stress direction. Because of the absence of previous historical earthquakes, the proximity of the brine disposal well, and the similarity with other documented cases of induced seismicity, it seems likely that fluid injection induced the 2008-2009 sequence.
The Deep Boring at Spur
(University of Texas at Austin, 1914-10-05) University of Texas at Austin
Evidence For Decay Of Turbulence By MHD Shocks In The ISM via CO Emission
(2015-06) Larson, Rebecca L.; Evans, Neal J.; Green, Joel D.; Yang, Lao-Lun; Larson, Rebecca L.; Evans, Neal J.; Green, Joel D.; Yang, Lao-Lun
We utilize observations of sub-millimeter rotational transitions of CO from a Herschel Cycle 2 open time program ("COPS", PI: J. Green) to identify previously predicted turbulent dissipation by magnetohydrodynamic (MHD) shocks in molecular clouds. We find evidence of the shocks expected for dissipation of MHD turbulence in material not associated with any protostar. Two models fit about equally well: model 1 has a density of 10(3) cm(-3), a shock velocity of 3 km s(-1), and a magnetic field strength of 4 mu G; model 2 has a density of 10(3.5) cm(-3), a shock velocity of 2 km s(-1), and a magnetic field strength of 8 mu G. Timescales for decay of turbulence in this region are comparable to crossing times. Transitions of CO up to J of 8, observed close to active sites of star formation, but not within outflows, can trace turbulent dissipation of shocks stirred by formation processes. Although the transitions are difficult to detect at individual positions, our Herschel-SPIRE survey of protostars provides a grid of spatially distributed spectra within molecular clouds. We averaged all spatial positions away from known outflows near seven protostars. We find significant agreement with predictions of models of turbulent dissipation in slightly denser (10(3.5) cm(-3)) material with a stronger magnetic field (24 mu G) than in the general molecular cloud.
Global Axisymmetric Magnetorotational Instability With Density Gradients
(2008-05) Pino, Jesse; Mahajan, S. M.; Pino, Jesse; Mahajan, S. M.
We examine global incompressible axisymmetric perturbations of a differentially rotating MHD plasma with radial density gradients. It is shown that the standard magnetorotational instability (MRI) criterion drawn from the local dispersion relation is often misleading. If the equilibrium magnetic field is either purely axial or purely toroidal, the problem reduces to finding the global radial eigenvalues of an effective potential. The standard Keplerian profile including the origin is mathematically ill-posed, and thus any solution will depend strongly on the inner boundary. We find a class of unstable modes localized by the form of the rotation and density profiles, with reduced dependence on boundary conditions.
Institutional Logics And Institutional Pluralism: The Contestation Of Care And Science Logics In Medical Education, 1967-2005
(2010-03) Dunn, M. B.; Jones, C.; Dunn, Mary B.
Although most studies underscore institutional change as replacement of one dominant logic for another and assume that professions are guided by a single logic, professions that operate in multiple institutional spheres often have plural logics. We focus on medical education, the supplier of medical professionals, which resides at the interstices between academia and healthcare. Using archival sources from 1910 to 2005, we identify two logics central to the profession that persisted over time: care and science. We found that jurisdictional competition with rivals such as public health, contestation among physicians, the rise of managed care, and increasing numbers of women entering medical schools are associated with increased attention to the care logic. Differentiation in the missions of medical schools is associated with reduced attention to the science logic. Our study reveals that plural logics of care and science in medical education are supported by distinct groups and interests, fluctuate over time, and create dynamic tensions about how to educate future professionals.(circle)
Location and Felt Reports for the 25 April 2010 mbLg 3.9 Earthquake Near Alice, Texas: Was it Induced by Petroleum Production?
(2012-04) Frohlich, Cliff; Glidewell, Jennifer; Brunt, Michael; Frohlich, Cliff; Glidewell, Jennifer; Brunt, Michael
This study examines seismograms and felt reports for the 25 April 2010 Alice, Texas, earthquake and explores its possible relationship with gas and oil production in the Stratton field. We identified P arrivals at seven broadband stations situated within similar to 100 km of the epicentral region and determined a location of 27.72 degrees N, 97.95 degrees W, about 11 km east of the location reported by the National Earthquake Information Center but coincident with the region of highest intensity (modified Mercalli intensity V-VI) felt reports. We compare arrivals for observed secondary P and S arrivals with predictions from a published Gulf Coast velocity model. At nearby stations, the secondary arrivals are much stronger than primary arrivals; the arrival times and the presence of high-amplitude phases traveling at the Love-wave velocity of the uppermost model layer suggest the focal depth was shallow, 3 km or less. This places the 2010 hypocenter approximately along the mapped trace of the Vicksburg fault zone and at the depth of the Frio formation, the principal productive member in the Stratton field, which has produced at least 2.7 trillion cubic feet of gas and about 100 million barrels of oil since production commenced in 1938. We conclude it is plausible, although not proven definitively, that production in the Stratton field contributed to the occurrence of the 2010 Alice earthquake and an earlier similar earthquake that occurred on 24 March 1997.