Engineering topics
Publications and source records attributed to Walker, J. C. G..
Ambipolar diffusion is discussed for the case of a weakly-ionized, multicomponent plasma. Shortcomings of some of the previous formulations of this problem are pointed out. In particular, it is shown that the polarization electrostatic field acts to couple the motion of the various ions with the result that the diffusion velocity of each ion depends on the density gradients of all the ions.
The probability that a star has a habitable planet with a communicative civilization is investigated. One approach to the search problem is to assume that the other civilization will do most of the work, which implies that the search is limited to 'supercivilizations' able to transmit detectable signals in all directions all the time. The development of an optimal search strategy is discussed together with questions of the probability of success.
The thermal structure of the earth's upper atmosphere is examined in detail, with emphasis on the physical processes that govern the behavior of charged-particle temperatures. The characteristic features of and competition between the heating, cooling, and thermal conduction processes that govern electron and ion temperatures in the mid-latitude and auroral ionospheric regions are theoretically analyzed, and appropriate comparisons are made with experimental data. The proposed elaborate theory is considered qualitatively successful in accounting for the thermal structure of the ionosphere, and points requiring quantitative verification are delineated.
Analysis of the departure of oxygen and nitrogen molecules from the Boltzmann distribution in the thermosphere. It is concluded that the daytime production rates are too low to cause departures from the Boltzmann distribution at altitudes below about 300 km for vibrational levels containing a significant fraction of total population. It is also pointed out that diffusion cannot perturb significantly the Boltzmann distribution at altitudes below about 370 km.
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Measurements of the vertical flux of oxygen ions, when combined with simultaneous measurements of electron density and of electron and ion temperatures, present a unique opportunity to examine conditions in the topside ionosphere. The measured fluxes and densities may be used directly to evaluate terms in the O+ continuity equation without requiring any assumptions to be made about neutral winds, electric fields, or the ambipolar diffusion coefficient. From observations at Millstone Hill we have, in this way, derived the rate of loss of O+ in the charge-exchange reaction with hydrogen, the rate of photoionization of atomic oxygen, and the rate of loss of O+ in reactions with N2 and O2. In combination with laboratory and theoretical results, these rates can be interpreted to yield number densities of the corresponding neutral species. When the measured fluxes are examined for consistency with measured density gradients and temperature profiles, we find clear evidence of wind-induced or electrodynamic vertical drifts larger than 60 m/sec.
Plasma transport processes role in E region from midlatitude nocturnal and auroral ionospheric models in terms of transport equations
Auroral electron temperature, noting field aligned energy transport current effects
Thermoelectric transport properties of ionospheric electron gas above 100 km
Minor ion diffusion coefficients in F 2 region, noting Coulomb collisions role in ion density sensitivity to ionospheric fluxes
Auroral enhancement of IR oxygen band, considering electric field excitation mechanisms
Venus deep mantle water degassing rate from atmospheric hydrogen escape data
Thermal diffusion effects on F 2 region ion densities, deriving diffusion coefficients for partially ionized atomic oxygen plasma
Thermospheric molecular nitrogen vibrational temperature, studying various chemical reactions and collisions as energy sources
Thermal diffusion coefficient for fully ionized plasma containing mixture of arbitrary charge ions in topside ionosphere
Electron, ion and neutral particle temperatures of upper atmosphere
Nocturnal electron concentrations and temperature at Manitoba measured by rocket-borne Langmuir probe, compared with F 1 region
Oxygen electron cooling effect on ionospheric electron temperatures, noting discrepancy removal throughout day at all altitudes