Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Localization”

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.

At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

The role of technetium-99m stannous pyrophosphate in myocardial imaging to recognize, localize and identify extension of acute myocardial infarction in patients

The ability of technetium-99m stannous pyrophosphate myocardial scintigrams to aid diagnostically in recognizing, localizing, and identifying extension of acute myocardial infarction in patients was evaluated. The present study is an extension of previous animal and patient evaluations that were recently performed utilizing this myocardial imaging agent.

Willerson, J. T.↗
NASA NTRS1976

Locally stabilizable large-scale systems

A class of large scale linear systems, stabilizable by local feedback control applied around each decoupled subsystem, is established. The control scheme, outlined in the paper, is based upon the decomposition-aggregation method, and involves only operations on the subsystem level. The systems, stabilized by the proposed method, have a tolerance to a wide class of non-linearities, and are reliable with respect to the structural perturbations.

Vukcevic, M. B.↗
NASA NTRS1977

Intense localized photoelectric charging in the lunar sunset terminator region. I - Development of potentials and fields. II - Supercharging at the progression of sunset

Numerical computations show that locally sunlit areas in the dark lunar sunset terminator region can acquire large electric potentials and fields due to the retention of photoelectrons emitted from sunlit areas by surrounding dark areas of the highly resistive lunar surface. It is shown that the potential can increase or decrease depending on the rates of photoelectron emission and areal contraction. It is concluded that in the lunar situation, the likely result is an increase in the potential, or a 'supercharging' of the sunlit area.

Criswell, D. R.↗
NASA NTRS1977

Localized induced electric field within the magnetotail

The conversion of magnetic energy, stored within the magnetotail during the growth phase, into particle kinetic energy is studied by taking induced electric fields, due to explicit time dependence of magnetic fields, into consideration. The polarization of a plasma in the presence of such a field is discussed, and the topological difference between a polarized and an induced electric field, namely that one is irrotational and the other is not, is pointed out. A localized perturbation in neutral sheet current is also discussed.

Heikkila, W. J.↗
NASA NTRS1977

Localization of an experimental ecological unit in the Maradi region of Nigeria

A detailed topographical and geomorphological description of a specific ecological unit in the Maradi region of the Sahel in the Niger Republic is presented. Sandy structures are classified into active dunes and covered dunes and an extensives vocabulary is developed to describe sub-categories. The descriptions are based on meteorological data (anemometric and rainfall) from local weather stations, ground observations, aerial photographs and LANDSAT pictures. The problem of dune reactivation and desertification is discussed both from the standpoint of causes and possible counter measures.

Mainguet, M.↗
NASA NTRS1977

The evaluation of a HgCdTe photomixer with a Tunable Diode Laser (TDL) and the evaluation of TDL's as a local oscillator in a heterodyne detection system

Heterodyne systems would be much more versatile if a broadly tunable laser, such as a semiconductor diode laser (TDL), could be used as the local oscillator (LO). Previous studies have shown that while a TDL can be used as an LO, the TDL lack sufficient power to cause the signal-to-noise ratio to be shot noise limited. The heterodyne system with a HgCdTe photodiode as the LO was characterized and the beat frequency response of the heterodyne systems was mapped out.

Harward, C. N.↗
NASA NTRS1977

On the localness of the spectral energy transfer in turbulence

Data for the energy transfer function are used to estimate the degree of localness of energy transfer in homogeneous turbulence. It is found that in regions where the energy which enters a wavenumber band is greater than the energy leaving, much of the energy entering the band is produced by wavenumbers an order of magnitude smaller. Thus for both low and high Reynolds numbers, spectral energy transfer is nonlocal. The tendency of the energy to jump between separated wavenumber regions agrees with the theory that turbulence forms concentrated regions of large velocity gradients. It is also felt that the universal equilibrium theory may be applicable if the Reynolds number of the turbulence is very high.

Deissler, R. G.↗
NASA NTRS1977

A satellite interpretation of the dynamics of a severe local storms area using 5 minute interval SMS data

Wind fields derived from cloud-tracking on the visible digital data of the Synchronous Meteorological Satellite-2 are used to study the onset of local severe storms. The study is based on an assessment of several dynamic parameters of lower tropospheric wind fields, including the divergence, relative vorticity, and deformation. The automated cloud-tracking proves capable of detecting a preferred area of flow convergence located ahead of a dry line; the detection of this convergence aids in monitoring the onset of a hail-producing thunderstorm.

Peslen, C. A.↗
NASA NTRS1978

Evaluation of a locally homogeneous model of spray evaporation

Measurements were conducted on an evaporating spray in a stagnant environment. The spray was formed using an air-atomizing injector to yield a Sauter mean diameter of the order of 30 microns. The region where evaporation occurred extended approximately 1 m from the injector for the test conditions. Profiles of mean velocity, temperature, composition, and drop size distribution, as well as velocity fluctuations and Reynolds stress, were measured. The results are compared with a locally homogeneous two-phase flow model which implies no velocity difference and thermodynamic equilibrium between the phases. The flow was represented by a k-epsilon-g turbulence model employing a clipped Gaussian probability density function for mixture fraction fluctuations. The model provides a good representation of earlier single-phase jet measurements, but generally overestimates the rate of development of the spray. Using the model predictions to represent conditions along the centerline of the spray, drop life-history calculations were conducted which indicate that these discrepancies are due to slip and loss of thermodynamic equilibrium between the phases.

Shearer, A. J.↗
NASA NTRS1978

A local proton irradiation model for isotopic anomalies in the solar system

An attempt is made to explain the O-16 and Al-26 anomalies observed in solar-system bodies in the framework of a local irradiation model wherein a small amount of solar system matter of normal isotopic composition was irradiated by energetic protons from the primeval sun. Several isotopic constraints are summarized with which the model should be consistent, and a proton energy distribution and fluence and a target elemental composition are chosen such that the extraordinary component produced by irradiation satisfies the constraints. Detailed attention is given to the relevant oxygen reactions, Al-26 production, and effects of proton irradiation on isotopes of Mg, Ca, and Ba. A scenario is outlined which satisfies all the constraints. Consequences of the model are discussed with respect to the isotopic anomalies observed in Allende inclusions.

Lee, T.↗
NASA NTRS1978

Local precision nets for monitoring movements of faults and large engineering structures

Along Bocono Fault were installed local high precision geodetic nets to observe the possible horizontal crustal deformations and movements. In the fault area there are few big structures which are also included in the mentioned investigation. In the near future, measurements shall be extended to other sites of Bocono Fault and also to the El Pilar Fault. In the same way and by similar methods high precision geodetic nets are applied in Venezuela to observe the behavior of big structures, as bridges and large dams and of earth surface deformations due to industrial activities.

Henneberg, H. G.↗
NASA NTRS1978

Local and global processes which impact solar wind electrons

A detailed first principle kinetic theory for solar wind electrons which is neither fluid not exospheric in nature is presented. The global and local properties of the solar wind expansion and coulomb collisions that are reflected in the observed electron velocity distribution function are: its bifurcation, skewness, and the differential temperatures of the thermal and suprathermal subpopulations. Predictions of correlations amongst electron solar wind parameters which were previously reported are shown.

Scudder, J. D.↗
NASA NTRS1979

Geosynchronous satellite operating anomalies caused by interaction with the local spacecraft environment

The dependence of a spacecraft anomaly or event upon geophysical parameters established on the basis of statistical analysis is presented. Examples are provided for establishing relationships between events and parameters such as geomagnetic activity, local time, and events on other spacecraft. Examples illustrated the potential dangers of not using quantitative statistical techniques it was recommended that the data collection planning and statistical analysis planning be done together. Results demonstrate a high correlation between the events and the goephysical parameter being investigated.

Grajek, M. A.↗
NASA NTRS1979

Local neighborhood transition probability estimation and its use in contextual classification

The problem of incorporating spatial or contextual information into classifications is considered. A simple model that describes the spatial dependencies between the neighboring pixels with a single parameter, Theta, is presented. Expressions are derived for updating the posteriori probabilities of the states of nature of the pattern under consideration using information from the neighboring patterns, both for spatially uniform context and for Markov dependencies in terms of Theta. Techniques for obtaining the optimal value of the parameter Theta as a maximum likelihood estimate from the local neighborhood of the pattern under consideration are developed.

Chittineni, C. B.↗
NASA NTRS1979

Preliminary report on DSN system performance under local weather effects

Local effects of precipitation are studied, and a simplified working model is developed. Experimental results obtained by simulation are in good agreement with the model, showing that it could be an important contribution to system degradation. If this is confirmed, some suggestions for improvement are presented.

Urech, J. M.↗
NASA NTRS1979

Evaluation of a locally homogeneous model of spray evaporation

A model of spray evaporation which employs a second-order turbulence model in conjunction with the locally homogeneous flow approximation, which implies infinitely fast interphase transport rates is presented. Measurements to test the model were completed for single phase constant and variable density jets, as well as an evaporating spray in stagnant air. Profiles of mean velocity, composition, temperature and drop size distribution as well as velocity fluctuations and Reynolds stress, were measured within the spray. Predictions were in agreement with measurements in single phase flows and also with many characteristics of the spray, e.g. flow width, radial profiles of mean and turbulent quantities, and the axial rate of decay of mean velocity and mixture fraction.

Shearer, A. J.↗
NASA NTRS1979

Analysis of the helium component of the local interstellar medium

Observations of the extraterrestrial He I 584-A emission made with an EUV experiment aboard OSO 8 are analyzed and compared with previous data from a similar experiment aboard the STP 72 1 satellite. The observations are also compared with an exhaustive set of emission models, and an envelope of possible velocities and temperatures is defined for the local interstellar medium. This envelope begins near 9 km/s with temperatures of 6000 to 8000 K, continues upward through 15 km/s with temperatures of 6000 to 15,000 K, and finally terminates near 27 km/s with temperatures of 11,000 to 14,000 K; the densities corresponding to these velocities and temperatures cover the range from 0.008 to 0.02 per cu cm. Previous observations of hydrogen L-alpha emission from the interstellar wind are reviewed and compared with the 584-A observations. With a typical value of 12% assumed for the cosmic helium abundance, the present observations imply a hydrogen density of 0.067 to 0.17 per cu cm, in good agreement with the values obtained from the L-alpha measurements.

Weller, C. S.↗