567 research outputs found
Low-dimensional dynamics embedded in a plane Poiseuille flow turbulence : Traveling-wave solution is a saddle point ?
The instability of a streak and its nonlinear evolution are investigated by
direct numerical simulation (DNS) for plane Poiseuille flow at Re=3000. It is
suggested that there exists a traveling-wave solution (TWS). The TWS is
localized around one of the two walls and notably resemble to the coherent
structures observed in experiments and DNS so far. The phase space structure
around this TWS is similar to a saddle point. Since the stable manifold of this
TWS is extended close to the quasi two dimensional (Q2D) energy axis, the
approaching process toward the TWS along the stable manifold is approximately
described as the instability of the streak (Q2D flow) and the succeeding
nonlinear evolution. Bursting corresponds to the escape from the TWS along the
unstable manifold. These manifolds constitute part of basin boundary of the
turbulent state.Comment: 5 pages, 6 figure
Definitive Management of Failure After Pyeloplasty
Introduction: Failure after pyeloplasty is difficult to manage. We report our experience managing pyeloplasty failures. Methods: We retrospectively reviewed the case log of a single surgeon, from August 1996 to August 2014, to identify all patients undergoing a surgical procedure after failed pyeloplasty. We excluded patients without follow-up exceeding 1 year from initial postpyeloplasty procedure. Failure was defined as a need for additional definitive intervention. Results: Of 247 laparoscopic pyeloplasties, 68 endopyelotomies and 305 simple laparoscopic nephrectomies reviewed, 41 were performed after previous pyeloplasty and had sufficient follow-up. Laparoscopic nephrectomy was performed in nine patients. All three secondary laparoscopic pyeloplasties were successful. Of 29 secondary endopyelotomies, 10 (34%) were successful. Of the 19 failures after secondary endopyelotomy, 12 patients had tertiary pyeloplasty (5 laparoscopic and 7 open surgical), 5 (26%) underwent tertiary endopyelotomy, and 2 (11%) required nephrectomy. Our overall endopyelotomy success rate was 38% (13/34) vs 100% (11/11) for secondary or tertiary pyeloplasty (4 patients lost to follow-up). Median time to failure was 5 months for endopyelotomy. Median follow-up for patients free from intervention was 40.2 months. Conclusions: Secondary pyeloplasty (including both laparoscopic and open surgical approach) is more than twice as successful as endopyelotomy after failed pyeloplasty. Secondary pyeloplasty is an excellent alternative to endopyelotomy in select patients with failure after initial pyeloplasty.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140085/1/end.2015.0837.pd
Resolving the gap and AU-scale asymmetries in the pre-transitional disk of V1247 Orionis
Pre-transitional disks are protoplanetary disks with a gapped disk structure,
potentially indicating the presence of young planets in these systems. In order
to explore the structure of these objects and their gap-opening mechanism, we
observed the pre-transitional disk V1247 Orionis using the Very Large Telescope
Interferometer, the Keck Interferometer, Keck-II, Gemini South, and IRTF. This
allows us spatially resolve the AU-scale disk structure from near- to
mid-infrared wavelengths (1.5 to 13 {\mu}m), tracing material at different
temperatures and over a wide range of stellocentric radii. Our observations
reveal a narrow, optically-thick inner-disk component (located at 0.18 AU from
the star) that is separated from the optically thick outer disk (radii >46 AU),
providing unambiguous evidence for the existence of a gap in this
pre-transitional disk. Surprisingly, we find that the gap region is filled with
significant amounts of optically thin material with a carbon-dominated dust
mineralogy. The presence of this optically thin gap material cannot be deduced
solely from the spectral energy distribution, yet it is the dominant
contributor at mid-infrared wavelengths. Furthermore, using Keck/NIRC2 aperture
masking observations in the H, K', and L' band, we detect asymmetries in the
brightness distribution on scales of about 15-40 AU, i.e. within the gap
region. The detected asymmetries are highly significant, yet their amplitude
and direction changes with wavelength, which is not consistent with a companion
interpretation but indicates an inhomogeneous distribution of the gap material.
We interpret this as strong evidence for the presence of complex density
structures, possibly reflecting the dynamical interaction of the disk material
with sub-stellar mass bodies that are responsible for the gap clearing.Comment: 16 pages, 17 Figures, accepted by Astrophysical Journa
Panchromatic Imaging of a Transitional Disk: The Disk of GM Aur in Optical and FUV Scattered Light
We have imaged GM Aur with HST, detected its disk in scattered light at 1400A
and 1650A, and compared these with observations at 3300A, 5550A, 1.1 microns,
and 1.6 microns. The scattered light increases at shorter wavelengths. The
radial surface brightness profile at 3300A shows no evidence of the 24AU radius
cavity that has been previously observed in sub-mm observations. Comparison
with dust grain opacity models indicates the surface of the entire disk is
populated with sub-micron grains. We have compiled an SED from 0.1 microns to 1
mm, and used it to constrain a model of the star+disk system that includes the
sub-mm cavity using the Monte Carlo Radiative Transfer code by Barbara Whitney.
The best-fit model image indicates that the cavity should be detectable in the
F330W bandpass if the cavity has been cleared of both large and small dust
grains, but we do not detect it. The lack of an observed cavity can be
explained by the presence of sub-microns grains interior to the sub-mm cavity
wall. We suggest one explanation for this which could be due to a planet of
mass <9 Jupiter masses interior to 24 AU. A unique cylindrical structure is
detected in the FUV data from the Advanced Camera for Surveys/Solar Blind
Channel. It is aligned along the system semi-minor axis, but does not resemble
an accretion-driven jet. The structure is limb-brightened and extends 190 +/-
35 AU above the disk midplane. The inner radius of the limb-brightening is 40
+/- 10 AU, just beyond the sub-millimeter cavity wall.Comment: 40 pages, 11 figures, 4 tables, accepted to Ap
Planting Food or Fuel: Developing an Interdisciplinary Approach to Understanding the Role of Culture in Farmers’ Decisions to Grow Second-Generation Biofuel Feedstock Crops
Recent interest in biofuels as an alternative energy source has spurred considerable changes in agricultural practice worldwide. These changes will be more pronounced as second-generation biofuels, such as switch grass, gain prominence; this article examines the cultural factors associated with the decisions U.S. farmers face in targeting crops for fuel production instead of food. Through an interdisciplinary assessment of the dynamics of farmers' behavior, developed herein is a theoretical framework to analyze how farmers grapple with shifting expectations of their function.National Science Foundation EPS-0903806, KU-Transportation Research Institut
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