Results 241 to 250 of about 884,628 (273)

Enantioselective cobalt-catalyzed [4.pi.+2.pi.+2.pi.] cycloadditions

The Journal of Organic Chemistry, 1993
Cobalt-catalyzed [4π+2π+2π] cycloaddition reactions are reported. Various 2-substituted butadienes have been shown to undergo cycloaddition with enantioselectivities of up to 79 to ...
Mark Lautens, William Tam, Christian Sood   +2 more
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Pi 2 pulsations and the auroral electrojet

Planetary and Space Science, 1975
Abstract Measurements of the properties of Pi 2 pulsations along a magnetic meridian at high latitudes during a number of substorms have been analyzed for their relationship to the auroral electrojet. It is found that the maximum Pi 2 pulsation amplitudes are closely associated with the instantaneous position of the electrojet.
John V. Olson, Gordon Rostoker
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Harmonics in spectra of PI 2 pulsations

Planetary and Space Science, 1973
Abstract Spectral analysis of Earth current records at South Uist, Eskdalemuir and East Anglia has revealed a harmonic frequency content in some Pi 2 spectra. The fundamental period is approximately 150 sec and in each case 4 or 5 harmonic components are present. These events were recorded during December 1969 and December 1970 and all occurred for
Bruce Roth, David Orr
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On the occurrence of Pi 2 micropulsations

Planetary and Space Science, 1973
Abstract Related investigations concerning the source and occurrence of Pi 2 micropulsations indicate that (1) Pi 2 peak occurrence is near 2230 LMT, before (after) which the initial disturbance vector orientation is primarily northeast (northwest) in the northern hemisphere; (2) peak occurrence is near 2330 (2030) LMT during intervals of low ...
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Concerning the structure of Pi 2 pulsations

Journal of Geophysical Research: Space Physics, 1985
We look at some simple theoretical considerations relevant to the origin of Pi 2 geomagnetic pulsations observed on the ground with the onset of geomagnetic activity. Using a basic model, we examine how subsidiary current flows are created by auroral ionospheric conductivity enhancements in the electrojet regions.
D. J. Southwood, W. J. Hughes
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Nighttime equatorial Pi 2 micropulsations

Journal of Geophysical Research, 1969
The analysis of nighttime Pi 2 micropulsations recorded at Colombo, over an uninterrupted period of one year from October 17, 1964, to October 16, 1965, indicates that (1) Pi 2 events are most prominent, especially about midnight, during the equinoxes; (2) the rate of occurrence of Pi 2 events increases almost linearly with Kp up to a Kp level of at ...
M. L. T. Kannangara, P. C. B. Fernando
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Statistical study of the polarisation of Pi 2 micropulsations

Journal of Atmospheric and Terrestrial Physics, 1973
The polarisation, properties of Pi 2 micropulsations are studied at certain 'low', 'middle', and 'high' latitude sites, and it is shown that left-hand polarised signals predominate at the low and high latitudes, whilst neither sense of polarisation is preferred at the middle latitude.
Doobov A.L., Mainstone J.S.
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Pi 2 pulsations and the westward traveling surge

Journal of Geophysical Research: Space Physics, 1986
A model is developed that relates the poleward leaps of the westward traveling surge (WTS) and the generation of Pi 2 pulsations. The feedback instability developed by Sato and coworkers is combined with the dynamic surge model of Rothwell et al. (1984).
Paul L. Rothwell, Michael B. Silevitch, Lars P. Block   +2 more
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A transient‐response theory of Pi 2 pulsations

Journal of Geophysical Research: Space Physics, 1985
The cause of Pi 2 pulsations at substorm onset can be understood in terms of the transient ionospheric response to an enhanced convection in the plasma sheet. A two‐dimensional model is presented to demonstrate how the transient ionospheric response can lead to damped oscillations similar to the Pi 2 pulsations observed at substorm onset.
W. Sun, J. R. Kan
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