Oblique Resonance Research Articles

Oblique resonances in the ionosphere

A new diagnostic tool for space plasmas is presented. The oblique resonance excited by an antenna in a magnetoplasma has been detected in the ionosphere with a rocket experiment. The instrument is simple and consists of a fixed frequency transmitter and a receiver. The resonance cone and its fine structure are used to deduce the plasma density and the electron temperature. The possibility of measuring field‐aligned currents is briefly discussed.

Resonance cone and Bernstein wave interference patterns in a magnetoplasma

General dispersion relations for a hot magnetoplasma are used to explain the interference observed between electrostatic waves and the electromagnetic field in an afterglow plasma. Observations are made near both oblique resonance cones (connected with whistler and Z‐propagation modes) and in the frequency region corresponding to “Bernstein” waves. Independent measurements of the lower (whistler) and upper (Z‐mode) resonance cones, for a particular case, lead to the same isotropic temperature in the late afterglow, namely 540 K. Independent measurements of the lower resonance cone and of Bernstein waves in the early afterglow also lead to consistent isotropic temperatures. As the real and imaginary components of the wave number increase, a point of inflection is reached on the various dispersion curves for homogeneous plane waves beyond which these curves can no longer be used to explain the observed interference fringes. For homogeneous waves with a wave number smaller than that corresponding to the inflection point, reasonable values of Landau damping are obtained which agree roughly with observed damping.

Plasmapause crossings determined by using the oblique plasma resonance excited by a Satellite-Borne RF Antenna

The location of the plasmapause has been measured by an oblique plasma resonance technique. The angle with respect to the geomagnetic field at which this resonance occurs is sensitive to the ambient electron density. During magnetically quiet conditions, abrupt changes in this angle, implying a steep electron density gradient, occur between L=3.2 and L=3.6 between 0400 and 0500 LT. This location agrees with the expected location of the plasmapause at that time as measured by the whistler dispersion technique.

Isokinetic External Rotation Strength of Shoulder: Correlation with Age and Muscle Size

The purpose of this study was to determine the correlation between quantitative (cross sectional areas) evaluation of the posterior cuff muscles and mechanical strength in asymptomatic shoulders with special reference to aging. The cross-sectional area of the combined infraspinatus and teres minor muscles were measured, in the sagittal oblique magnetic resonance images, in eighty-one patients with a mean age of 44.06 years (range 19 - 74). These areas were correlated with the measured isokinetic strength in external rotation at angular velocities of 60 deg/s and 180 deg/s using Cybex 770 NORM. The results show that there was a gradual decrease in size of the muscles as the age of the individual increases. A strong correlation was found between aging and combined cross-sectional area and peak torque as well. The correlation between combined cross-sectional area and peak torques at both angular velocities were less strong. Further, the correlation between the peak torque/cross-sectional area ratio with aging was also less significant, which may imply that the decrease in the muscle strength was greater than the change in muscle area. Our results suggest that there may be other qualitative and biochemical factors that may determine the true strength of the muscles in the aged population.