18,909 research outputs found
New procedure for design of self-adaptive control systems
Adaptive control system compensates for changes in the dynamic characteristics of linear controlled elements. It is mechanized so that the actual input of each control approaches the ideal input
Approximation in quantale-enriched categories
Our work is a fundamental study of the notion of approximation in
V-categories and in (U,V)-categories, for a quantale V and the ultrafilter
monad U. We introduce auxiliary, approximating and Scott-continuous
distributors, the way-below distributor, and continuity of V- and
(U,V)-categories. We fully characterize continuous V-categories (resp.
(U,V)-categories) among all cocomplete V-categories (resp. (U,V)-categories) in
the same ways as continuous domains are characterized among all dcpos. By
varying the choice of the quantale V and the notion of ideals, and by further
allowing the ultrafilter monad to act on the quantale, we obtain a flexible
theory of continuity that applies to partial orders and to metric and
topological spaces. We demonstrate on examples that our theory unifies some
major approaches to quantitative domain theory.Comment: 17 page
Sharp rate of average decay of the Fourier transform of a bounded set
We prove that the spherical mean of the Fourier transform of the
characteristic function of a bounded convex set (without any additional
assumptions) or a bounded set with a C^{3/2} boundary decays at infinity at the
same rate as the Fourier transform of the characteristic function of the ball.Comment: 10 pages. GAFA (to appear
Investigation of nonlinear motion simulator washout schemes
An overview is presented of some of the promising washout schemes which have been devised. The four schemes presented fall into two basic configurations; crossfeed and crossproduct. Various nonlinear modifications further differentiate the four schemes. One nonlinear scheme is discussed in detail. This washout scheme takes advantage of subliminal motions to speed up simulator cab centering. It exploits so-called perceptual indifference thresholds to center the simulator cab at a faster rate whenever the input to the simulator is below the perceptual indifference level. The effect is to reduce the angular and translational simulation motion by comparison with that for the linear washout case. Finally, the conclusions and implications for further research in the area of nonlinear washout filters are presented
Intensity dependence of Rydberg states
We investigate numerically and analytically the intensity dependence of the
fraction of electrons that end up in a Rydberg state after strong-field
ionization with linearly polarized light. We find that including the intensity
dependent distribution of ionization times and non-adiabatic effects leads to a
better understanding of experimental results. Furthermore, we observe using
Classical Trajectory Monte Carlo simulations that the intensity dependence of
the Rydberg yield changes with wavelength and that the previously observed
power-law dependence breaks down at longer wavelengths. Our work suggests that
Rydberg yield measurements can be used as an independent test for
non-adiabaticity in strong field ionization
New methods in adaptive flight control
New methods for design of adaptive flight control system
Vehicle design considerations for active control application to subsonic transport aircraft
The state of the art in active control technology is summarized. How current design criteria and airworthiness regulations might restrict application of this emerging technology to subsonic CTOL transports of the 1980's are discussed. Facets of active control technology considered are: (1) augmentation of relaxed inherent stability; (2) center-of-gravity control; (3) ride quality control; (4) load control; (5) flutter control; (6) envelope limiting, and (7) pilot interface with the control system. A summary and appraisal of the current state of the art, design criteria, and recommended practices, as well as a projection of the risk in applying each of these facets of active control technology is given. A summary of pertinent literature and technical expansions is included
Solution to the problem of the poor cyclic fatigue resistance of bulk metallic glasses
The recent development of metallic glass-matrix composites represents a particular milestone in engineering materials for structural applications owing to their remarkable combination of strength and toughness. However, metallic glasses are highly susceptible to cyclic fatigue damage, and previous attempts to solve this problem have been largely disappointing. Here, we propose and demonstrate a microstructural design strategy to overcome this limitation by matching the microstructural length scales (of the second phase) to mechanical crack-length scales. Specifically, semisolid processing is used to optimize the volume fraction, morphology, and size of second-phase dendrites to confine any initial deformation (shear banding) to the glassy regions separating dendrite arms having length scales of ≈2 μm, i.e., to less than the critical crack size for failure. Confinement of the damage to such interdendritic regions results in enhancement of fatigue lifetimes and increases the fatigue limit by an order of magnitude, making these “designed” composites as resistant to fatigue damage as high-strength steels and aluminum alloys. These design strategies can be universally applied to any other metallic glass systems
Engine Data Interpretation System (EDIS), phase 2
A prototype of an expert system was developed which applies qualitative constraint-based reasoning to the task of post-test analysis of data resulting from a rocket engine firing. Data anomalies are detected and corresponding faults are diagnosed. Engine behavior is reconstructed using measured data and knowledge about engine behavior. Knowledge about common faults guides but does not restrict the search for the best explanation in terms of hypothesized faults. The system contains domain knowledge about the behavior of common rocket engine components and was configured for use with the Space Shuttle Main Engine (SSME). A graphical user interface allows an expert user to intimately interact with the system during diagnosis. The system was applied to data taken during actual SSME tests where data anomalies were observed
Controlling the quantum number distribution and yield of Rydberg states via the duration of the laser pulse
We show that the distribution of quantum numbers of Rydberg states does not
only depend on the field strength and wavelength of the laser which the atom is
exposed to, but that it also changes significantly with the duration of the
laser pulse. We provide an intuitive explanation for the underlying mechanism
and derive a scaling law for the position of the peak in the quantum number
distribution on the pulse duration. The new analytic description for the
electron's movement in the superposed laser and Coulomb field (applied in the
study of quantum numbers) is then used to explain the decrease of the Rydberg
yield with longer pulse durations. This description stands in contrast to the
concepts that explained the decrease so far and also reveals that
approximations which neglect Coulomb effects during propagation are not
sufficient in cases such as this.Comment: 8 pages, 8 figure
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