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Lee, K.

Publications and source records attributed to Lee, K..

248 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Convective amplification of type I irregularities in the equatorial electrojet.

Wave propagation and refraction of 'type I' irregularities in the equatorial electrojet are investigated. Quantitative calculation of wave refraction in a model electrojet shows that the direction of wave refraction must change sign at one altitude. Waves propagating with the electrons rotate their wave vectors upward in the upper electrojet and downward in the lower electrojet during the day, and vice versa at night. Furthermore, the altitude region of largest linear growth rate is also the one with the weakest refraction rate. Consequently, computations of the ray-path integrated wave growth show that this region would dominate the backscatter spectrum from the electrojet if linear theory were valid, and it is further noted that the maximum amplitude wave should have phase velocities exceeding the ion acoustic speed. It is therefore concluded that propagation alone, without inclusion of nonlinear effects, cannot explain backscatter observations of a constant Doppler frequency shift given by the ion acoustic speed.

Lee, K.↗
NASA NTRS1973

Application of remote sensor data to geologic analysis of the Bonanza Test Site Colorado

A geologic map of the Bonanza Test Site is nearing completion. Using published large scale geologic maps from various sources, the geology of the area is being compiled on a base scaled at 1:250,000. Sources of previously published geologic mapping include: (1) USGS Bulletins; (2) professional papers and geologic quadrangle maps; (3) Bureau of Mines reports; (4) Colorado School of Mines quarterlies; and (5) Rocky Mountain Association of Geologist Guidebooks. This compilation will be used to evaluate ERTS, Skylab, and remote sensing underflight data.

Lee, K.↗
NASA NTRS1973

Effect of surface asperity on elastohydrodynamic lubrication

The important aspects of elastohydrodynamic lubrication, with a single, one-dimensional asperity, have been found by solving numerically the coupled transient Reynolds equation and the elasticity equation. Even though the assumption of a single asperity is highly ideal, this study sheds some light on the effect of surface roughness on elastohydrodynamic lubrication. The results show that the film pressure tends to increase more than the steady state pressure, and in particular, the increase in pressure reaches a maximum as the asperity approaches the inlet of the contact region. The asperity height and the pressure increase above the steady state pressure are closely related to each other; the higher the asperity height, the larger the pressure increase. In the pure rolling case, it has been found that a local pressure peak is not developed. However, in the cases of sliding and rolling, a small, local pressure peak is developed on the pressure profile when the asperity moves into the contact region. In general, the overall film thickness profile increases with increasing asperity height, but is not significantly affected by the asperity width. Moreover, the slope of the overall film thickness profile for the transient cases is much greater than the steady state profile, which is approximately constant across the contact width. The increase in the center film thickness also depends upon the width and height of the asperity.

Lee, K.↗
NASA NTRS1972

Application of remote sensor data to geologic analysis of the Bonanza test site, Colorado

A variety of remote sensor data has aided geologic mapping in central Colorado. This report summarizes the application of sensor data to both regional and local geologic mapping and presents some conclusions on the practical use of remote sensing for solving geologic mapping problems. It is emphasized that this study was not conducted primarily to test or evaluate remote sensing systems or data, but, rather, to apply sensor data as an accessory tool for geologic mapping. The remote sensor data used were acquired by the NASA Earth Observations Aircraft Program. Conclusions reached on the utility of the various sensor data and interpretation techniques for geologic mapping were by-products of attempts to use them.

Lee, K.↗
NASA NTRS1972

Convective amplification of Type 1 irregularities in the equatorial electrojet

Wave propagation and refraction of Type 1 irregularities in the equatorial electrojet were investigated. Quantitative calculation of wave refraction in a model electrojet showed that the direction of wave refraction must change sign at one altitude. Waves propagating with the electrons rotate their wave vectors upwards in the upper electrojet and downwards in the lower electrojet during the day, and vice versa at night. Furthermore, the altitude region of largest linear growth rate is also the one with the weakest refraction rate. Consequently, computations of the ray-path integrated wave growth shows that this region would dominate the backscatter spectrum from the electrojet if linear theory were valid, and it is further noted that the maximum amplitude wave should have phase velocities exceeding the ion acoustic speed. It was concluded that propagation alone, without inclusion of nonlinear effects, cannot explain backscatter observations of a constant Doppler frequency shift given by the ion acoustic speed.

Lee, K.↗
NASA NTRS1972

Effects of propagation parallel to the magnetic field on the type 1 electrojet irregularity instability

A simple analysis is presented which indicates that Type 1 irregularities which have a slight component of propagation along the magnetic field may be more unstable than those which propagate across the field. It was found that significant irregularity amplitudes may occur at the northern or southern extremities of the equatorial electrojet from those modes with large north-south group velocity, and they could significantly change our understanding of nonlinear solutions of the electrojet instability.

Lee, K.↗
NASA NTRS1972

External production and control of electrojet irregularities.

Analytical investigation of parametric coupling of a large-amplitude 'pump' wave to a natural plasma mode of the ionospheric E layer. It is shown that the E layer plasma mode can be either stabilized or destabilized by the parametric process. Two necessary conditions for parametric interaction are (1) near frequency matching (i.e., the pump wave frequency should be near the local upper hybrid frequency) and (2) a finite electric field component of the pump wave perpendicular to the background static magnetic field. An investigation of the propagation characteristics of the pump wave in the magnetic equatorial region indicates that an obliquely propagating O mode in the magnetic meridian plane meets the two necessary conditions in an optimal manner. From typical values of ionospheric parameters it is estimated that the required incident energy flux of the pump wave for parametric stabilization or destabilization of the E layer plasma mode (near its natural marginal stability) is much less than 1 mW/sq m. Thus parametric coupling experiments for the ionospheric E layer are technically feasible.

Lee, K.↗
NASA NTRS1972

Bonanza project, 1971

Research on the application of remote sensing techniques to the mineral industry stresses photointerpretation by human interpreter experienced in the extraction of geological information from aerial color and multiband photographs and from thermal scanner imagery. Also considered are optical and digital image enhancement, multiband color additive projection, video image processing, and computer reduction and analysis of infrared spectrometry. Evaluation of those parameters which have the most contrast between adjacent rock formations and which can be remotely sensed establish the following most useful geological characteristics: Topographic landform, color, albedo, and surface temperature.

Lee, K.↗
NASA NTRS1971

The pressure and deformation profile between two colliding lubricated cylinders

The pressure and deformation profiles between two colliding lubricated cylinders are obtained by solving the coupled, time-dependent elastohydrodynamic equations with an iterative procedure. The analysis includes effects which were not considered in a previous solution, namely, the effect of the lubricant compressibility and the effect of a lubricant with composite pressure-viscosity coefficients. It is found that the local approach velocity plays an important role during final stages of normal approach. It causes the lubricant to be entrapped within the contact region; neither the pressure nor the deformation profile converges to the Hertzian profile for a dry contact. The use of a smaller pressure-viscosity coefficient at high pressures reduces the sharp pressure gradient at the center of the contact and produces a much milder variation of load with respect to the film thickness. The effect of compressibility of the lubricant is found to be relatively small.

Lee, K.↗
NASA NTRS1970

High frequency Hall current instability

The Hall current electrojet instability was studied to determine if it generates VLF hiss in the auroral zone of magnetic substorms. Using the kinetic equations with particle conserving Krook collision operator for electrons and ions, and Poisson's equation, it is shown that in the low frequency region, the range of frequency of unstable modes increases as the electron density increases, and that the high frequency component must be taken into account in calculations of turbulent saturation of the Hall current instability driven beyond threshold. It is concluded that Hall currents can generate waves in the VLF hiss frequency band which are related to local auroral electrojet activity.

Lee, K.↗
NASA NTRS1969

Studies of cycles for liquid-metal magnetohydrodynamic generation of power

Studies of liquid-metal magnetohydrodynamic power cycles indicate that the overall efficiency of a binary cycle, employing a liquid-metal topping cycle and a bottoming steam cycle, may reach 60 percent. Details of analyses and data on cycles are presented, and the commercial potential of the binary cycle is discussed.

Lee, K.↗