3,139 research outputs found
Redundant actuator development study
Current and past supersonic transport configurations are reviewed to assess redundancy requirements for future airplane control systems. Secondary actuators used in stability augmentation systems will probably be the most critical actuator application and require the highest level of redundancy. Two methods of actuator redundancy mechanization have been recommended for further study. Math models of the recommended systems have been developed for use in future computer simulations. A long range plan has been formulated for actuator hardware development and testing in conjunction with the NASA Flight Simulator for Advanced Aircraft
Measurement of retinal vessel widths from fundus images based on 2-D modeling
Changes in retinal vessel diameter are an important sign of diseases such as hypertension, arteriosclerosis and diabetes mellitus. Obtaining precise measurements of vascular widths is a critical and demanding process in automated retinal image analysis as the typical vessel is only a few pixels wide. This paper presents an algorithm to measure the vessel diameter to subpixel accuracy. The diameter measurement is based on a two-dimensional difference of Gaussian model, which is optimized to fit a two-dimensional intensity vessel segment. The performance of the method is evaluated against Brinchmann-Hansen's half height, Gregson's rectangular profile and Zhou's Gaussian model. Results from 100 sample profiles show that the presented algorithm is over 30% more precise than the compared techniques and is accurate to a third of a pixel
Optic nerve head segmentation
Reliable and efficient optic disk localization and segmentation are important tasks in automated retinal screening. General-purpose edge detection algorithms often fail to segment the optic disk due to fuzzy boundaries, inconsistent image contrast or missing edge features. This paper presents an algorithm for the localization and segmentation of the optic nerve head boundary in low-resolution images (about 20 /spl mu//pixel). Optic disk localization is achieved using specialized template matching, and segmentation by a deformable contour model. The latter uses a global elliptical model and a local deformable model with variable edge-strength dependent stiffness. The algorithm is evaluated against a randomly selected database of 100 images from a diabetic screening programme. Ten images were classified as unusable; the others were of variable quality. The localization algorithm succeeded on all bar one usable image; the contour estimation algorithm was qualitatively assessed by an ophthalmologist as having Excellent-Fair performance in 83% of cases, and performs well even on blurred image
Relations between Kauffman and Homfly satellite invariants
We extend a mod 2 relation between the Kauffman and Homfly polynomials, first
observed by Rudolph in 1987, to the general Kauffman and Homfly satellite
invariants.Comment: 9 page
Classical Physics and Quantum Loops
The standard picture of the loop expansion associates a factor of h-bar with
each loop, suggesting that the tree diagrams are to be associated with
classical physics, while loop effects are quantum mechanical in nature. We
discuss examples wherein classical effects arise from loop contributions and
display the relationship between the classical terms and the long range effects
of massless particles.Comment: 15 pages, 3 figure
Topologically Massive Gauge Theory: A Lorentzian Solution
We obtain a lorentzian solution for the topologically massive non-abelian
gauge theory on AdS space by means of a SU(1, 1) gauge transformation of the
previously found abelian solution. There exists a natural scale of length which
is determined by the inverse topological mass. The topological mass is
proportional to the square of the gauge coupling constant. In the topologically
massive electrodynamics the field strength locally determines the gauge
potential up to a closed 1-form via the (anti-)self-duality equation. We
introduce a transformation of the gauge potential using the dual field strength
which can be identified with an abelian gauge transformation. Then we present
the map from the AdS space to the pseudo-sphere including the topological mass.
This is the lorentzian analog of the Hopf map. This map yields a global
decomposition of the AdS space as a trivial circle bundle over the upper
portion of the pseudo-sphere which is the Hyperboloid model for the Lobachevski
geometry. This leads to a reduction of the abelian field equation onto the
pseudo-sphere using a global section of the solution on the AdS space. Then we
discuss the integration of the field equation using the Archimedes map from the
pseudo-sphere to the cylinder over the ideal Poincare circle. We also present a
brief discussion of the holonomy of the gauge potential and the dual-field
strength on the upper portion of the pseudo-sphere.Comment: 23 pages, 1 postscript figur
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