Enhancement and Analysis of Real-Time Radiography Images

Shuttle Redesigned Solid Rocket Motor (RSRM) nozzle interiors fabricated from carbon phenolic composite exhibit "ply lift" when hot fired. The composite surface is smooth when fabricated, but the individual plies separate and lift away from the surface when exposed to high temperature and high-pressure exhaust gas. It shows a cross section of a post-fired composite in which ply lift is evident as dark fissures. Surface charring is also visible as a darker band about 0.2 inches thick. Charring is normal, but ply lift is not desirable since the fissures could possibly initiate an abnormal exhaust path from the RSRM. The underlying mechanisms of ply lift are under investigation as part of the Shuttle Return-To-Flight Program

Three-dimensional flaw reconstruction using a real-time X-ray imaging system

A system has been developed for making three-dimensional flaw measurements in materials using a real-time X-ray imaging laboratory. This environment affords precise control over all positional variables, offers multiple degrees of freedom for sample movement, and the continuous nature of the real-time image eliminates ambiguity in determining correspondence points among multiple views of the sample. This system is based on film stereography in which two stereo projections are obtained of a sample either by translating the X-ray source or by translating the sample. The three-dimensional coordinates of features of interest such as crack endpoints and centroids of void-like flaws are determined by measuring the disparity between corresponding points in the stereo pair and triangulating to find the depth of the point within the sample. This new system generalizes the sample motion for arbitrary shifts and rotations, and easily accommodates more than two views to yield a least-squares estimate of the three-dimensional point locations. The system is implemented by a set of software modules which augments an existing real-time laboratory. All sub-systems to manipulate the sample position, process the image, select feature points from the display screen, and compute three-dimensional feature coordinates were seamlessly integrated. Calibration routines were implemented to accurately determine the X-ray source, sample, and detector geometry. The spatial distortion and blurring effects of the X-ray detector were characterized and modelled. An image warp was applied to correct spatial nonlinearities, and image restoration was used to increase the resolution of the detector. A high-speed digital signal processing board was used to implement on-line image processing routines for detector corrections and contrast enhancement. The performance of the complete system was determined by measuring fabricated samples and industrial samples containing crack-like defects. The three-dimensional measurements were accurate to ±0.02 cm. This system delivers much of the information found in a computed tomography image at much lower cost, and is faster and more accurate than film-based stereography

Laminar and turbulent dissipation in shear flow with suction

The rate of viscous energy dissipation in a shear layer of incompressible Newtonian fluid with injection and suction is studied by means of exact solutions, nonlinear and linearized stability theory, and rigorous upper bounds. For large enough values of the injection angle a steady laminar flow is nonlinearly stable for all Reynolds numbers, while for small but nonzero angles the laminar flow is linearly unstable at high Reynolds numbers. The upper bound on the energy dissipation rate—valid even for turbulent solutions of the Navier-Stokes equations—scales precisely the same as that in the steady laminar solution with regard to the viscosity in the vanishing viscosity limit. Both the laminar dissipation and the upper bound on turbulent dissipation display scaling in which the energy dissipation rate becomes independent of the viscosity for high Reynolds numbers. Hence the laminar energy dissipation rate and the largest possible turbulent energy dissipation rate for flows in this geometry differ by just a prefactor that depends only on injection angle. This result establishes the sharpness of the upper bound’s scaling in the vanishing viscosity limit for these boundary conditions, and this system provides an analytic illustration of the delicacy of corrections to scaling (e.g., logarithmic terms as appearing in the “law of the wall”) to perturbations in the boundary conditions. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87605/2/497_1.pd

Energy dissipation in a shear layer with suction

The rate of viscous energy dissipation in a shear layer of incompressible Newtonian fluid with injection and suction is studied by means of exact solutions, nonlinear and linearized stability theory, and rigorous upper bounds. The injection and suction rates are maintained constant and equal and this leads to solutions with constant throughput. For strong enough suction, expressed in terms of the entry angle between the injection velocity and the boundaries, a steady laminar flow is nonlinearly stable for all Reynolds numbers. For a narrow range of small but nonzero angles, the laminar flow is linearly unstable at high Reynolds numbers. The upper bound on the energy dissipation rate—valid even for turbulent solutions of the Navier–Stokes equations—scales with viscosity in the same way as the laminar dissipation in the vanishing viscosity limit. For both the laminar and turbulent flows, the energy dissipation rate becomes independent of the viscosity for high Reynolds numbers. Hence the laminar energy dissipation rate and the largest possible turbulent energy dissipation rate for flows in this geometry differ by only a prefactor that depends only on the angle of entry. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69712/2/PHFLE6-12-8-1955-1.pd

Destabilizing Taylor-Couette flow with suction

We consider the effect of radial fluid injection and suction on Taylor-Couette flow. Injection at the outer cylinder and suction at the inner cylinder generally results in a linearly unstable steady spiralling flow, even for cylindrical shears that are linearly stable in the absence of a radial flux. We study nonlinear aspects of the unstable motions with the energy stability method. Our results, though specialized, may have implications for drag reduction by suction, accretion in astrophysical disks, and perhaps even in the flow in the earth's polar vortex.Comment: 34 pages, 9 figure

Approaching the Problem of Time with a Combined Semiclassical-Records-Histories Scheme

I approach the Problem of Time and other foundations of Quantum Cosmology using a combined histories, timeless and semiclassical approach. This approach is along the lines pursued by Halliwell. It involves the timeless probabilities for dynamical trajectories entering regions of configuration space, which are computed within the semiclassical regime. Moreover, the objects that Halliwell uses in this approach commute with the Hamiltonian constraint, H. This approach has not hitherto been considered for models that also possess nontrivial linear constraints, Lin. This paper carries this out for some concrete relational particle models (RPM's). If there is also commutation with Lin - the Kuchar observables condition - the constructed objects are Dirac observables. Moreover, this paper shows that the problem of Kuchar observables is explicitly resolved for 1- and 2-d RPM's. Then as a first route to Halliwell's approach for nontrivial linear constraints that is also a construction of Dirac observables, I consider theories for which Kuchar observables are formally known, giving the relational triangle as an example. As a second route, I apply an indirect method that generalizes both group-averaging and Barbour's best matching. For conceptual clarity, my study involves the simpler case of Halliwell 2003 sharp-edged window function. I leave the elsewise-improved softened case of Halliwell 2009 for a subsequent Paper II. Finally, I provide comments on Halliwell's approach and how well it fares as regards the various facets of the Problem of Time and as an implementation of QM propositions.Comment: An improved version of the text, and with various further references. 25 pages, 4 figure

Challenges and Opportunities in the Hydrologic Sciences

This is the Table of Contents and Introduction of a Report published as Hornberger, G. M., E. Bernhardt, W. E. Dietrich, D. Entekhabi, G. E. Fogg, E. Foufoula-Georgiou, W. J. Gutowski, W. B. Lyons, K. W. Potter, S. W. Tyler, H. J. Vaux, C. J. Vorosmarty, C. Welty, C. A. Woodhouse, C. Zheng, Challenges and Opportunities in the Hydrologic Sciences. 2012: Water Science and Technology Board, Division on Earth and Life Studies, National Academy of Sciences, Washington, DC. 173 pp. Posted with permission.</p

Phospholipids Trigger Cryptococcus neoformans Capsular Enlargement during Interactions with Amoebae and Macrophages

A remarkable aspect of the interaction of Cryptococcus neoformans with mammalian hosts is a consistent increase in capsule volume. Given that many aspects of the interaction of C. neoformans with macrophages are also observed with amoebae, we hypothesized that the capsule enlargement phenomenon also had a protozoan parallel. Incubation of C. neoformans with Acanthamoeba castellanii resulted in C. neoformans capsular enlargement. The phenomenon required contact between fungal and protozoan cells but did not require amoeba viability. Analysis of amoebae extracts showed that the likely stimuli for capsule enlargement were protozoan polar lipids. Extracts from macrophages and mammalian serum also triggered cryptococcal capsular enlargement. C. neoformans capsule enlargement required expression of fungal phospholipase B, but not phospholipase C. Purified phospholipids, in particular, phosphatidylcholine, and derived molecules triggered capsular enlargement with the subsequent formation of giant cells. These results implicate phospholipids as a trigger for both C. neoformans capsule enlargement in vivo and exopolysaccharide production. The observation that the incubation of C. neoformans with phospholipids led to the formation of giant cells provides the means to generate these enigmatic cells in vitro. Protozoan- or mammalian-derived polar lipids could represent a danger signal for C. neoformans that triggers capsular enlargement as a non-specific defense mechanism against potential predatory cells. Hence, phospholipids are the first host-derived molecules identified to trigger capsular enlargement. The parallels apparent in the capsular response of C. neoformans to both amoebae and macrophages provide additional support for the notion that certain aspects of cryptococcal virulence emerged as a consequence of environmental interactions with other microorganisms such as protists

Genetic variants in novel pathways influence blood pressure and cardiovascular disease risk.

Blood pressure is a heritable trait influenced by several biological pathways and responsive to environmental stimuli. Over one billion people worldwide have hypertension (≥140 mm Hg systolic blood pressure or  ≥90 mm Hg diastolic blood pressure). Even small increments in blood pressure are associated with an increased risk of cardiovascular events. This genome-wide association study of systolic and diastolic blood pressure, which used a multi-stage design in 200,000 individuals of European descent, identified sixteen novel loci: six of these loci contain genes previously known or suspected to regulate blood pressure (GUCY1A3-GUCY1B3, NPR3-C5orf23, ADM, FURIN-FES, GOSR2, GNAS-EDN3); the other ten provide new clues to blood pressure physiology. A genetic risk score based on 29 genome-wide significant variants was associated with hypertension, left ventricular wall thickness, stroke and coronary artery disease, but not kidney disease or kidney function. We also observed associations with blood pressure in East Asian, South Asian and African ancestry individuals. Our findings provide new insights into the genetics and biology of blood pressure, and suggest potential novel therapeutic pathways for cardiovascular disease prevention