SEARCH · Search NASA
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
A factorization approach to the linear regulator quadratic cost problem is developed. This approach makes some new connections between optimal control, factorization, Riccati equations and certain Wiener-Hopf operator equations. Applications of the theory to systems describable by evolution equations in Hilbert space and differential delay equations in Euclidean space are presented.
The significance of machine and natural vision is discussed together with the need for a general approach to image acquisition and processing aimed at recognition. An exploratory scheme is proposed which encompasses the definition of spatial primitives, intrinsic image properties and sampling, 2-D edge detection at the smallest scale, the construction of spatial primitives from edges, and the isolation of contour information from textural information. Concepts drawn from or suggested by natural vision at both perceptual and physiological levels are relied upon heavily to guide the development of the overall scheme. The scheme is intended to provide a larger context in which to place the emerging technology of detector array focal-plane processors. The approach differs from many recent efforts in edge detection and image coding by emphasizing smallest scale edge detection as a foundation for multi-scale symbolic processing while diminishing somewhat the importance of image convolutions with multi-scale edge operators. Cursory treatments of information theory illustrate that the direct application of this theory to structural information in images could not be realized.
The viscosities of carbon dioxide and xenon have been measured near their critical points and the critical exponent y characterizing the asymptotic divergence has been determined. Both fluids yielded exponents in the range y = 0.041 + or - 0.001 and thus also fell in the range y = 0.042 + or - 0.002 from an earlier study of four binary liquids. This agreement between experiments is the first evidence that pure fluids and binary liquids are in the same dynamic universality class. A recent theoretical value for y is 0.032. The 30 percent discrepancy is much greater than the combined errors from experiment and theory. The torsion oscillator viscometer operated at low frequency and low shear rate to avoid systematic errors caused by critical slowing down. Far from T(c) the analysis accounted for the crossover from critical to noncritical temperature dependence, where the latter was obtained from previously published correlations. Corrections for gravitational stratification were included close to T(c).
The stability characteristics of various compact fourth and sixth order spatial operators are assessed using the theory of Gustafsson, Kreiss and Sundstrom (G-K-S) for the semi-discrete Initial Boundary Value Problem (IBVP). These results are then generalized to the fully discrete case using a recently developed theory of Kreiss. In all cases, favorable comparisons are obtained between the G-K-S theory, eigenvalue determination, and numerical simulation. The conventional definition of stability is then sharpened to include only those spatial discretizations that are asymptotically stable. It is shown that many of the higher order schemes which are G-K-S stable are not asymptotically stable. A series of compact fourth and sixth order schemes, which are both asymptotically and G-K-S stable for the scalar case, are then developed.
A 3-cable crane mechanism has been designed for incorporation into a highly loaded Lunar crane for planetary construction. This 3-cable crane must maintain a positive stability margin in all phases of the loading/unloading, assembly, or installation operations. A 2D kinematic curvature theory is applied to: (1) derive a general stability criterion to prevent the 3-cable crane from instability; and (2) determine a simple equation of natural frequency for two planar models of 3-cable crane. Investigation of the 2D vibrational characteristics of the planar models provides valuable insight toward understanding of 3D dynamic behavior of the 3-cable crane. Also, precision in natural frequency from this simple kinematic equation due to the exclusion of the radius-of-gyration of a suspended article is discussed. Multibody dynamics of the 3D 3-cable crane is presented and simulated to study the resulting vibrational characteristics under external disturbances and to verify the feasibility of the stability criterion for the 3-cable crane.
Zone plate lenses are a type of focusing element which function essentially as differential phase shifters, having a relatively few, coarsely quantized phase delays across the incident beam of radiation. The major advantages are ease of fabrication and much reduced thickness, compared to conventional refractive focusing elements. These considerations are both of particular importance for the submillimeter range, in which manufacturing tolerances for curved optical elements can pose significant problems, and where the absorption of readily available dielectric materials is quite large. In this presentation we briefly review the theory of zone plate lens operations, present a relatively simple method for calculating the aperture efficiency of zone plate lenses used as antennas, and show some theoretical and measured results in the 100 GHz range.
A new analytical approach to study linear magnetoacoustic waves propagating in an isothermal, stratified, and uniformly magnetized atmosphere is presented. The approach is based on Dirac equations, and the theory of Sturm-Liouville operators is used to investigate spectral properties of the obtained Dirac Hamiltonians. Two cases are considered: (1) the background magnetic field is vertical, and the waves are separated into purely magnetic (transverse) and purely acoustic (longitudinal) modes; and (2) the field is tilted with respect to the vertical direction and the magnetic and acoustic modes become coupled giving magnetoacoustic waves. For the first case, the Dirac Hamiltonian possesses either a discrete spectrum, which corresponds to standing magnetic waves, or a continuous spectrum, which can be clearly identified with freely propagating acoustic waves. For the second case, the quantum mechanical perturbation calculus is used to study coupling and energy exchange between the magnetic and acoustic components of magnetoacoustic waves. It is shown that this coupling may efficiently prevent trapping of magnetoacoustic waves instellar atmospheres.
This paper presents the basic understanding of the friction stir welding process. It covers process description, pin tool operation and materials, metal flow theory, mechanical properties, and materials welded using the process. It also discusses the thermal stir welding process and the differences between thermal stir and friction stir welding. MSFC weld tools used for development are also presented.
The experimental ion-beam behavior obtained without neutralizers is compared with both simple collision theory and plasma-wave theory. This comparison indicates that plasma waves play an important part in beam behavior, although the present state of plasma-wave theory does not permit more than a qualitative comparison. The theories of immersed-emitter and electron-trap neutralizer operation are discussed; and, to the extent permitted by experimental data, the theory is compared with experimental results. Experimental data are lacking completely at the present time for operation in space. The results that might be expected in space and the means of simulating such operation in Earth-bound facilities, however, are discussed.
The operation of collecting and emitting Langmuir probes and double probes within time-stationary strong electrostatic potential structures is analyzed. The cross sections of spherical and cylindrical probes to charged particles within the structures are presented and used to obtain the current-voltage characteristics of idealized probes. The acquisition of plasma parameters from these characteristics is outlined, and the operation of idealized floating double-probe systems is analyzed. Probe surface effects are added to the idealized theory, and some surface effects pertinent to spacecraft probes are quantified. Magnetic field effects on idealized probes are examined, and the time required for floating probes to change their potentials by collecting charge and by emitting photoelectrons is discussed. Calculations on the space-charge effects of probe-perturbed beams and on the space-charge limiting of electron emission are given in an appendix.
Energy minimization for trial wave function constrained to give expectation value of operator
The report presents the application of fixed lag smoothing algorithms to the problem of estimation of the phase and frequency of a sinusoidal carrier received in the presence of process noise and additive observation noise. A suboptimal structure consists of a phase-locked loop (PLL) followed by post-loop correction to the phase and frequency estimates. When the PLL is operating under high signal-to-noise ratio, the phase detector is approximately linear, and the smoother equations then correspond to the optimal linear equations for an equivalent linear signal model. The performance of such a smoother can be predicted by linear filtering theory. However, if the PLL is operating near the threshold region of the signal-to-noise ratio, the phase detector cannot be assumed to be linear. Then the actual performance of the smoother can significantly differ from that predicted by linear theory. In this report we present both the theoretical and simulated performance of such smoothers derived on the basis of various models for the phase and frequency processes.
The application of fixed lag smoothing algorithms are presented for the problem of estimation of the phase and frequency of a sinusoidal carrier received in the presence of process noise and additive observation noise. A suboptimal structure consists of a phase-locked loop (PLL) followed by a post loop correction to the phase and frequency estimates. When the PLL is operating under a high signal-to-noise ratio, the phase detector is approximately linear, and the smoother equations then correspond to the optimal linear equations for an equivalent linear signal model. The performance of such a smoother can be predicted by the linear filtering theory. However, if the PLL is operating near the threshold region of the signal to noise ratio, the phase detector cannot be assumed to be linear. Then the actual performance of the smoother can significantly differ from that predicted by linear filtering theory. Both the theoretical and simulated performance of such smoothers derived on the basis of various models for the phase of frequency processes are presented.
The Atmosphere Explorer satellites carry a quasi-open source neutral mass spectrometer which has the capability to operate in a nonstagnating or 'fly-through' mode. Technical information on the operating characteristics of fly-through along with considerable scientific data have been acquired in this mode. When the vehicle is spun, the fly-through signal contains information on the kinetic temperature as well as the neutral density. Both quantities can be extracted from the data once the theory of operation is formulated in terms of the ambient gas velocity distribution and the angular response of the instrument.
The stability of elastic flap bending, lead-lag bending, and torsion of uniform, untwisted, cantilever rotor blades without chordwise offsets between the elastic, mass, tension, and areodynamic center axes is investigated for the hovering flight condition. The equations of motion are obtained by simplifying the general, nonlinear, partial differential equations of motion of an elastic rotating cantilever blade. The equations are adapted for a linearized stability analysis in the hovering flight condition by prescribing aerodynamic forces, applying Galerkin's method, and linearizing the resulting ordinary differential equations about the equilibrium operating condition. The aerodynamic forces are obtained from strip theory based on a quasi-steady approximation of two-dimensional unsteady airfoil theory. Six coupled mode shapes, calculated from free vibration about the equilibrium operating condition, are used in the linearized stability analysis. The study emphasizes the effects of two types of structural coupling that strongly influence the stability of hingeless rotor blades. The first structural coupling is the linear coupling between flap and lead-lag bending of the rotor blade. The second structural coupling is a nonlinear coupling between flap bending, lead-lag bending, and torsion deflections. Results are obtained for a wide variety of hingeless rotor configurations and operating conditions in order to provide a reasonably complete picture of hingeless rotor blade stability characteristics.
The key characteristics of an intelligent advisory system is explored. A central feature is that human-machine cooperation should be based on a metaphor of human-to-human cooperation. ALLY, a computer-based operator's associate which is based on a preliminary theory of human-to-human cooperation, is discussed. ALLY assists the operator in carrying out the supervisory control functions for a simulated NASA ground control system. Experimental evaluation of ALLY indicates that operators using ALLY performed at least as well as they did when using a human associate and in some cases even better.
Regimes of Lorentz-violating effective field theories are studied in which departures from Lorentz symmetry are nonperturbative. Within a free toy theory exhibiting Lorentz breakdown involving an operator of mass dimension three, it is shown that conventional methods suffice to achieve field quantization and Fock-space construction. However, the absence of an observer-invariant energy-positivity condition requires physical input beyond the free theory for the unambiguous identification of a ground state. An investigation of the role of thermodynamics in this context is instigated.
This review discusses Operator Inference, a nonintrusive reduced modeling approach that incorporates physical governing equations by defining a structured polynomial form for the reduced model, and then learns the corresponding reduced operators from simulated training data. The polynomial model form of Operator Inference is sufficiently expressive to cover a wide range of nonlinear dynamics found in fluid mechanics and other fields of science and engineering, while still providing efficient reduced model computations. The learning steps of Operator Inference are rooted in classical projection-based model reduction; thus, some of the rich theory of model reduction can be applied to models learned with Operator Inference. This connection to projection-based model reduction theory offers a pathway toward deriving error estimates and gaining insights to improve predictions. Furthermore, through formulations of Operator Inference that preserve Hamiltonian and other structures, important physical properties such as energy conservation can be guaranteed in the predictions of the reduced model beyond the training horizon. This review illustrates key computational steps of Operator Inference through a large-scale combustion example.