Deriving the normalised ion-neutral collision frequency from EISCAT observations
Common programme observations by the EISCAT UHF radar revealed an extended interval, post geomagnetic local noon on 03 April 1992, during which the F-region ion velocity orthogonal to the geomagnetic field was significantly enhanced, to values exceeding 2 km s−1 corresponding to a perpendicular electric field of some 100 mV m−1. Observations from this interval are used to illustrate a method by which estimates of the E-region ion-neutral collision frequency may be derived in the presence of enhanced electric field. From both the rotation of the ion velocity vector and the reduction in the ion velocity magnitude relative to that in the F-region, independent estimates of the normalised ion-neutral collision frequency are made at the UHF E-region tristatic altitudes; the derived values are, in general, lower than model predictions. Although initial calculations assume a stationary neutral atmosphere, first-order estimates of the E-region neutral wind are subsequently employed to calculate revised estimates of the normalised ion-neutral collision frequency; these neutral winds are derived by attributing the difference between predicted and observed enhancements in field-parallel ion temperature to thermospheric motion. The inclusion of neutral winds, which are themselves not inconsiderable, appears to have only a limited effect on the normalised collision frequencies derived.
High resolution EISCAT observations of the ion-neutral collision frequency in the lower E-region
Abstract A multichannel Barker coded EISCAT experiment with basic spatial and temporal resolutions of 600 m and 10 s, respectively, is described. The experiment was run on 13–17 February 1984 and data obtained in a diffuse aurora as well as in an auroral arc are used for determining the ion-neutral collision frequency in the lower E -region. Post-integration over 20 and 3 min, respectively, is carried out in the two cases and the plasma parameters are fitted with the assumption of equal ion and electron temperatures. The effect of varying the temperature ratio is discussed. The obtained collision frequencies are generally found to be in accordance with profiles based on the CIRA (1972) model atmosphere. In addition to collision frequencies, vertical ion velocities and electron temperature profiles are presented. It is found that the velocities are consistent with the observed electric fields.
Evaluation of antioxidants by a rapid polarographic method
A simple, rapid, precise, and reproducible method and an adaptable apparatus for polarographic measurement of lipid peroxidation and antioxidant activity is described. This method measures antioxidant activity within a few min time as compared to the hours or days needed for several widely used methods. Peroxidation rates were measured for different lipids as a function of amount of lipid, and amount of biocatalyst. The method is applicable to the detection and measurement of the antioxidant effects exhibited by weak antioxidants and has been satisfactorily used for the measurement of the antioxidant activity of different concentrations of powerful antioxidants.