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At least 433 records · Page 24

Input-output characterization of fiber reinforced composites by P waves

Input-output characterization of fiber composites is studied theoretically by tracing P waves in the media. A new path motion to aid in the tracing of P and the reflection generated SV wave paths in the continuum plate is developed. A theoretical output voltage from the receiving transducer is calculated for a tone burst. The study enhances the quantitative and qualitative understanding of the nondestructive evaluation of fiber composites which can be modeled as transversely isotropic media.

Renneisen, John D.↗

On the sensitivity of a residual circulation model to differences in input temperature data

The residual mean circulation (RMC) formulation of zonally averaged transport in the middle atmosphere produces a circulation which depends on the distributions of net diabatic heating and temperature. Such circulations are from two temperature data sets, using the same radiative transfer code (Rosenfield et al. 1987). These circulations are then used to transport N2O in a photochemical model. The circulations and the resulting N2O distributions are notably different during the Northern Hemisphere winter, with that based on the NMC temperatures producing too much upward transport in the tropical stratosphere, as judged by comparison with the stratospheric and mesoscale sounder data. The experiment demonstrates that model calculations, in general, and perturbation assessments, in particular, are likely to be quite sensitive to the choice of input temperature data (where this is not computed self-consistently). It also reveals what appears to be a seasonally dependent bias in NMC zonally averaged temperatures with respect to those obtained from the LIMS instrument during 1978/1979.

Guthrie, Paul D.↗

Space market model space industry input-output model

The goal of the Space Market Model (SMM) is to develop an information resource for the space industry. The SMM is intended to contain information appropriate for decision making in the space industry. The objectives of the SMM are to: (1) assemble information related to the development of the space business; (2) construct an adequate description of the emerging space market; (3) disseminate the information on the space market to forecasts and planners in government agencies and private corporations; and (4) provide timely analyses and forecasts of critical elements of the space market. An Input-Output model of market activity is proposed which are capable of transforming raw data into useful information for decision makers and policy makers dealing with the space sector.

Hodgin, Robert F.↗

The program on radiative inputs of the sun to the Earth (rise)

General concerns about changes in the Earth's climate and in the ozone layer have increased the importance of measuring and understanding variations in the sun's radiative outputs. These outputs appear, for instance, at the top of the list of global change forcing agents in the recent FY-90 document on the U.S. Global Change Program. Significant advances have been made over the past decade in radiometry of the total solar irradiance. Photometry of light variations in stars similar to the sun, but much younger, is providing new insights into the sun's variations in luminosity and UV radiation at previous epochs of interest to paleoclimate studies. Measurement of the sun's 11-year output variability in the ultraviolet and extreme ultraviolet still possess a challenge of great importance. All of these topics are addressed by the program on Radiative Inputs of the Sun to Earth (RISE). RISE is a 5-year program of observations, data analysis, and theory, that has been defined at two workshops held in Boulder, Colorado in November 1987, and in Tucson, Arizona in October 1989. These meetings involved about 60 solar and atmospheric physicists, and stellar astronomers. A proceedings of the 1987 workshop was issued in early 1988. A substantial component of the program, consisting of ground-based observations, data analysis, and theory, is directed at the National Science Foundation (NSF) and the program is seeking a FY-92 funding start at the NSF. RISE also makes recommendations on measurements required from NASA and NOAA satellites.

Foukal, Peter V.↗

Development and testing of controller performance evaluation methodology for multi-input/multi-output digital control systems

Described here is the development and implementation of on-line, near real time controller performance evaluation (CPE) methods capability. Briefly discussed are the structure of data flow, the signal processing methods used to process the data, and the software developed to generate the transfer functions. This methodology is generic in nature and can be used in any type of multi-input/multi-output (MIMO) digital controller application, including digital flight control systems, digitally controlled spacecraft structures, and actively controlled wind tunnel models. Results of applying the CPE methodology to evaluate (in near real time) MIMO digital flutter suppression systems being tested on the Rockwell Active Flexible Wing (AFW) wind tunnel model are presented to demonstrate the CPE capability.

Pototzky, Anthony↗

Suggestions for CAP-TSD mesh and time-step input parameters

Suggestions for some of the input parameters used in the CAP-TSD (Computational Aeroelasticity Program-Transonic Small Disturbance) computer code are presented. These parameters include those associated with the mesh design and time step. The guidelines are based principally on experience with a one-dimensional model problem used to study wave propagation in the vertical direction.

Bland, Samuel R.↗

Remotely sensed soil moisture input to a hydrologic model

The possibility of using detailed spatial soil moisture maps as input to a runoff model was investigated. The water balance of a small drainage basin was simulated using a simple storage model. Aircraft microwave measurements of soil moisture were used to construct two-dimensional maps of the spatial distribution of the soil moisture. Data from overflights on different dates provided the temporal changes resulting from soil drainage and evapotranspiration. The study site and data collection are described, and the soil measurement data are given. The model selection is discussed, and the simulation results are summarized. It is concluded that a time series of soil moisture is a valuable new type of data for verifying model performance and for updating and correcting simulated streamflow.

Engman, E. T.↗

Indirect techniques for adaptive input-output linearization of non-linear systems

A technique of indirect adaptive control based on certainty equivalence for input output linearization of nonlinear systems is proven convergent. It does not suffer from the overparameterization drawbacks of the direct adaptive control techniques on the same plant. This paper also contains a semiindirect adaptive controller which has several attractive features of both the direct and indirect schemes.

Teel, Andrew↗

Comments on Frequency Swept Rotating Input Perturbation Techniques and Identification of the Fluid Force Models in Rotor/bearing/seal Systems and Fluid Handling Machines

Perturbation techniques used for identification of rotating system dynamic characteristics are described. A comparison between two periodic frequency-swept perturbation methods applied in identification of fluid forces of rotating machines is presented. The description of the fluid force model identified by inputting circular periodic frequency-swept force is given. This model is based on the existence and strength of the circumferential flow, most often generated by the shaft rotation. The application of the fluid force model in rotor dynamic analysis is presented. It is shown that the rotor stability is an entire rotating system property. Some areas for further research are discussed.

Muszynska, Agnes↗

Statistical linearization for multi-input/multi-output nonlinearities

Formulas are derived for the computation of the random input-describing functions for MIMO nonlinearities; these straightforward and rigorous derivations are based on the optimal mean square linear approximation. The computations involve evaluations of multiple integrals. It is shown that, for certain classes of nonlinearities, multiple-integral evaluations are obviated and the computations are significantly simplified.

Lin, Ching-An↗

Summary of astronaut inputs on automation and robotics for Space Station Freedom

Astronauts and payload specialists present specific recommendations in the form of an overview that relate to the use of automation and robotics on the Space Station Freedom. The inputs are based on on-orbit operations experience, time requirements for crews, and similar crew-specific knowledge that address the impacts of automation and robotics on productivity. Interview techniques and specific questionnaire results are listed, and the majority of the responses indicate that incorporating automation and robotics to some extent and with human backup can improve productivity. Specific support is found for the use of advanced automation and EVA robotics on the Space Station Freedom and for the use of advanced automation on ground-based stations. Ground-based control of in-flight robotics is required, and Space Station activities and crew tasks should be analyzed to assess the systems engineering approach for incorporating automation and robotics.

Weeks, David J.↗

Convergence characteristics of the multiple input, multiple output LMS algorithm

The convergence characteristics of the multiple input, multiple output LMS algorithm, as applied to active noise and vibration control systems, are examined. The mean square error during the convergence process, as well as the final converged value, are examined analytically and in computer simulation. It is shown that the ratio of number of error sensors to number of control sources has a significant influence upon both the converging and converged value of the mean square error. Other active control system variables, such as the inherent time delays and structural/acoustic transfer functions, are also shown to have a significant influence upon the convergence process.

Snyder, Scott D.↗

Inferring heuristic classification hierarchies from natural language input

A methodology for inferring hierarchies representing heuristic knowledge about the check out, control, and monitoring sub-system (CCMS) of the space shuttle launch processing system from natural language input is explained. Our method identifies failures explicitly and implicitly described in natural language by domain experts and uses those descriptions to recommend classifications for inclusion in the experts' heuristic hierarchies.

Hull, Richard↗

Atmospheric chemistry in the Arctic and subarctic - Influence of natural fires, industrial emissions, and stratospheric inputs

Layers with enhanced concentrations of trace gases intercepted by the NASA Electra aircraft over Alaska during the Arctic Boundary Layer Expedition (ABLE 3A) in July-August 1988 are discussed. Haze layers apparently associated with boreal fires were enriched in hydrocarbons and NO(y), with emission factors corresponding closely to laboratory data for smoldering combustion. It is argued that atmospheric composition was strongly modified by wildfires during several periods of the ABLE 3A mission. The associated enhancement of NO(y) was smaller than observed for most other combustion processes but was nonetheless significant in the context of very low background concentrations. Ozone production in fire plumes was negligible. Ambient O3 was supplied by the stratosphere, with little direct input from midlatitude source during summer. It is argued that NO(y) was supplied about equally by the stratosphere and by wildfires. Hydrocarbons and CO appear to derive from biomass fires and from human activities.

Wofsy, S. C.↗

Input impedance of coaxially fed rectangular microstrip antenna on electrically thick substrate

A full-wave spectral domain analysis has been used to obtain input-impedance results for a probe-fed rectangular-patch antenna, modeling the source as a magnetic-current frill. Multiple modes are used in the probe surface current to account for axial and azimuthal variations. It is established that maximum resistance is dependent on the substrate loss tangent. The axial variation of the probe current must be taken into account for substrate thicknesses greater than about 0.02 wavelengths.

Chen, Wei↗

The quality of photometric information in the Hipparcos Input Catalog

Comparison with independent photoelectric photometry is used to assess the quality of magnitudes and colors in the Hipparcos Input Catalog. These magnitudes and colors will play an important role in the luminosity calibration of Hipparcos stars. We conclude that photoelectric photometry, available for about 37 percent of the catalog, is of uniformly good quality, and the error estimates in the Catalog are very accurate. On the other hand, colors determined from poor spectral classes suffer from very significant errors, also correctly estimated in the Catalog, which make them essentially unsuited for the purpose of luminosity calibration. Only stars with either photoelectric colors or good 2D spectral classes can be used in a high-accuracy luminosity calibration.

Casertano, Stefano↗

Atmospheric energy input and ionization by energetic electrons during the geomagnetic storm of 8-9 November 1991

The Atmospheric X-ray Imaging Spectrometer (AXIS) of the Particle Environment Monitor investigation aboard the Upper Atmosphere Research Satellite monitors energy input to the upper atmosphere due to energetic electrons. Analysis of the AXIS data from the major geomagnetic storm of 8-9 November 1991 is presented. During the November storm, electrons above a few keV flowing into a substantially expanded auroral zone provided the bulk of the ionizing power to the upper atmosphere. At the peak of the disturbance the total AXIS-observed power reached 40 GW. On 9 November the whole day average atmospheric ionization rate in the auroral zone at 80 km altitude exceeded the rate due to solar UV and solar X-rays by a factor of over 10 to 100.

Chenette, D. L.↗

Comparison of several methods for obtaining the time response of linear systems to either a unit impulse or arbitrary input from frequency-response data

Several methods of obtaining the time response of Linear systems to either a unit impulse or an arbitrary input from frequency-response data are described and compared. Comparisons indicate that all the methods give good accuracy when applied to a second-order system; the main difference is the required computing time. The methods generally classified as inverse Laplace transform methods were found to be most effective in determining the response to a unit impulse from frequency-response data of higher order systems. Some discussion and examples are given of the use of such methods as flight-data-analysis techniques in predicting loads and motions of a flexible aircraft on the basis of simple calculations when the aircraft frequency response is known.

Donegan, James J↗