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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.

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At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Discrete square root smoothing.

The basic techniques applied in the square root least squares and square root filtering solutions are applied to the smoothing problem. Both conventional and square root solutions are obtained by computing the filtered solutions, then modifying the results to include the effect of all measurements. A comparison of computation requirements indicates that the square root information smoother (SRIS) is more efficient than conventional solutions in a large class of fixed interval smoothing problems.

Kaminski, P. G.↗
NASA NTRS1971

ELF propagation in the plasmasphere based on satellite observations of discrete and continuous forms

The propagation of electromagnetic waves in a nonhomogeneous anisotropic medium is examined from the point of view of geometrical optics. In particular, the propagation of ELF waves in the magnetosphere is described in terms of the electron and ion densities and the intensity and inclination of the earth's magnetic field. The analysis of the variations of wave normal angle along the ray path is extended to include the effects of ions. A comparison of the relative importance of each of the above parameters in controlling the orientation of the wave normals is made in the region of the magnetosphere where most of the ion whistlers have been detected.

Muzzio, J. L. R.↗
NASA NTRS1973

A comparison of discrete linear filtering algorithms.

Seven filter algorithms were presented in a recent survey paper (Kaminski, 1971), and were compared computationally (operations count) when relatively few observations were to be processed. These algorithms are now elaborated further. Details of the computations are presented, and it is shown that for problems with even moderately large amounts of data, the information matrix and square-root information matrix formulations are computationally more efficient than the other methods considered (conventional Kalman, stabilized Kalman, and square-root covariance mechanizations). It is pointed out that Schmidt's matrix factorization-Householder transformation technique leads to the same equations as those obtained via Potter's method. Several improvements in the equation mechanization are given.

Bierman, G. J.↗
NASA NTRS1973

Design and performance of a large vocabulary discrete word recognition system. Volume 1: Technical report

The development, construction, and test of a 100-word vocabulary near real time word recognition system are reported. Included are reasonable replacement of any one or all 100 words in the vocabulary, rapid learning of a new speaker, storage and retrieval of training sets, verbal or manual single word deletion, continuous adaptation with verbal or manual error correction, on-line verification of vocabulary as spoken, system modes selectable via verification display keyboard, relationship of classified word to neighboring word, and a versatile input/output interface to accommodate a variety of applications.

Source record↗
NASA NTRS1974

Discrete wall jets in quiescent air

An experimental investigation was made of turbulent jet flows resulting from small, round nozzles discharging parallel to a smooth, flat wall in quiescent air. Nozzle axes were located 3.0 nozzle diameters above the wall surface. The case of a single nozzle and the case of a spanwise array of equally spaced nozzles were investigated. Several forms of approximate velocity profile similarity were noted, and the flow from the array of nozzles was seen to approach the form of a two-dimensional wall jet.

Mclean, J. D.↗
NASA NTRS1974

Engineering information on an Analog Signal to Discrete Time Interval Converter (ASDT-IC)

An electronic control system for nondissipative dc power converters is presented which improves (1) the routinely attainable static output voltage accuracy to the order of + or - 1% for ambient temperatures from -55 to 100 C and (2) the dynamic stability by utilizing approximately one tenth of the feedback gain needed otherwise. Performance is due to a functional philosophy of deterministic pulse modulation based on pulse area control and to an autocompensated signal processing principle. The system can be implemented with commercially available unselected components.

Schwarz, F. C.↗
NASA NTRS1974

Flow in a discrete slotted nozzle with massive injection

An experimental investigation has been conducted to determine the effect of massive wall injection on the flow characteristics in a slotted nozzle. Some of the experiments were performed on a water table with a slotted-nozzle test section. This has 45 deg and 15 deg half angles of convergence and divergence, respectively, throat radius of 2.5 inches, and throat width of 3 inches. The hydraulic analogy was employed to qualitatively extend the results to a compressible gas flow through the nozzle. Experimental results from the water table include contours of constant Froude and Mach number with and without injection. Photographic results are also presented for the injection through slots of CO2 and Freon-12 into a main-stream air flow in a convergent-divergent nozzle in a wind tunnel. Schlieren photographs were used to visualize the flow, and qualititative agreement between the results from the gas tunnel and water table is good.

Perkins, H. C.↗
NASA NTRS1973

A constrained discrete optimal guidance strategy for low-thrust space flight

A low-thrust guidance algorithm suitable for operational use is formulated. Using linear stochastic control theory, a linear feedback control law is obtained for a minimum terminal miss performance criterion. The control variables are restricted to constant values over specified time intervals and are explicitly limited. Both fixed and variable time-of-arrival guidance are considered. Guidance equations are presented in deterministic (operational) and in statistical form; and computational procedures necessary for implementation are outlined. The performance of the guidance algorithm is evaluated by applying it to the approach phase of the 1980 rendezvous mission with the comet Encke.

Jacobson, R. A.↗
NASA NTRS1973

Further discrete variable results for a panel flutter optimization problem

Numerical solutions are presented for the problem of minimum weight design of a thin one-dimensional, simply supported, solid panel in compression, with one side exposed to a parallel high supersonic air flow. The flutter speed is held fixed and a minimum thickness constraint is imposed.

Pierson, B. L.↗
NASA NTRS1974

Theory of discrete vortex noise

A solution is obtained for the noise induced by vortex shedding from the trailing edge of a semiinfinite flat plate. The method of solution for the potential flow is based on a procedure whereby an inner incompressible flow is matched to an outer acoustic field. Acoustic wave fronts are calculated and compared qualitatively with schlieren photographs of similar flows. The acoustic directivity pattern is obtained, and the extreme sensitivity of this parameter to the incompressible flow near the trailing edge of the plate is investigated.

Davis, S. S.↗
NASA NTRS1974

Sequential square root filtering and smoothing of discrete linear systems

A square root information filter/smoother is derived using recursive least-squares arguments. The combined filter/smoother algorithm has the following attributes: (1) it has a square root structure, which enhances numerical accuracy; (2) filter and smoother mechanizations are identical in form, facilitating implementation of the smoother; and (3) storage and computation requirements are modest compared with other smoothing algorithms. Partitioning the results to separate bias parameters provides further computational economies and reduction of storage requirements.

Bierman, G. J.↗
NASA NTRS1974

NCUBE - A clustering algorithm based on a discretized data space

Cluster analysis involves the unsupervised grouping of data. The process provides an automatic procedure for generating known training samples for pattern classification. NCUBE, the clustering algorithm presented, is based upon the concept of imposing a gridwork on the data space. The NCUBE computer implementation of this concept provides an easily derived form of piecewise linear discrimination. This piecewise linear discrimination permits the separation of some types of data groups that are not linearly separable.

Eigen, D. J.↗
NASA NTRS1974

Observations of discrete gamma ray sources with SAS-2

Compact gamma ray sources centered on the Crab nebula and the Vela X supernova remnant are considered. An excess in the galactic radiation was observed in both regions. Data indicate that a large fraction of this flux is pulsed. The excess from the Vela region could reflect either a large-scale galactic feature, such as a superposition of spiral arm segments, or it could be associated with the Vela supernova remnant. Low-energy gamma ray bursts were observed in the SAS-2 anticoincidence shielding.

Thompson, D. J.↗
NASA NTRS1974

Discretized partial differential equations - Examples of control systems defined on modules

The purpose of this paper is to show how the important problems of linear system theory can be solved concisely for a particular class of linear systems, namely block circulant systems, by exploiting the algebraic structure. This type of system arises in lumped approximations to linear partial differential equations. The computation of the transition matrix, the variation of constants formula, observability, controllability, pole allocation, realization theory, stability and quadratic optimal control are discussed. In principle, all questions which are solved here could also be solved by standard methods; the present paper clearly exposes the structure of the solution, and thus permits various savings in computational effort.

Brockett, R. W.↗