Solar activity dependence of interplanetary disturbances

Interplanetary scintillation measurements obtained inside 200 R using the Ooty Radio Telescope during August 1986–April 1991 have been analysed to study the interplanetary disturbances (or events) and their occurrence rates at various phases of the solar cycle. The disturbances are identified by the increase in the level of scintillation compared with the expected value. In total, 735 events have been identified. The results show a rate of 0.49 events per day near solar maximum and a low rate of 0.16 events per day during minimum of activity. The results are compared with coronal mass ejection (CME) rates and transients rates obtained from the Doppler scintillation measurements.     

Extensive-Dilatancy Anisotropy (Eda) Inferred From Observations of Crustal Shear Waves Generated By A Refraction Experiment In Northern Scandinavia

Summary. Particle-motion plots of shear waves have been studied for the section FG of the FENNOLORA seismic experiment. Shear-wave splitting is observed on some records and the polarization of the first arriving shear waves show two peaks at about N35°W and N65°E. These results can be interpreted as being due to crack-induced anisotropy with the crack direction dominated by a (dominant) horizontal stress around N35°W. This is consistent with in situ stress measurements and focal mechanism studies in Scandinavia. the results show that seismic refraction experiments may be useful in providing evidence of crack-induced anisotropy in the stable continental crust.     

High-resolution ion-microprobe measurement of lead isotopes: Variations within single zircons from Lac Seul,northwestern Ontario

Selected-area measurements of lead-isotope ratios in zircons have been made at high mass resolution using a modified A.E.I. IM20 ion-microprobe. At a working resolution of 3200 it is shown that the important interfering molecular peaks generated from the zircon matrix may be separated from atomic lead peaks. Corrections for overlapping peaks, which are necessary in measurements of lead isotopes at low mass resolution, are then only required for ²⁰⁸Pb.Measurements on N.B.S. standards show no isotope discrimination within counting statistics. Determination of ²⁰⁷Pb/²⁰⁶Pb on 29 single zircon grains from a tonalite gneiss and a granite from Lac Seul, northwestern Ontario, give very variable ratios with mean values close to those of bulk separates. Peaks in the distribution of 207/206 ratios obtained from the tonalite gneiss may be interpreted as evidence for two stages of lead loss. High 207/206 ratios are shown to be significant for at least two zircons and probably record a minimum age of formation of 3.3 ± 0.1 b.y. for the gneiss.     

Human-induced Changes in the Groundwater Chemical Composition within an Oil Field Area

The effect of highly saline oil-field water on soils and potable groundwater is considered. Three phases of the hydrochemical evolution of groundwater quality affected by transborder pollution and field development that has deteriorated potable groundwater in the two topmost aquifers are identified.     

On the temperature distribution in the solar corona

An improved value of coronal temperature is obtained by the degree of ionization method taking various processes into consideration. Comparison with some of the existing results has also been made.     

Invariant manifolds, phase correlations of chaotic orbits and the spiral structure of galaxies

In the presence of a strong   m = 2  component in a rotating galaxy, the phase-space structure near corotation is shaped to a large extent by the invariant manifolds of the short-period family of unstable periodic orbits terminating at L ₁ or L ₂. The main effect of these manifolds is to create robust phase correlations among a number of chaotic orbits large enough to support a spiral density wave outside corotation. The phenomenon is described theoretically by soliton-like solutions of a Sine–Gordon equation. Numerical examples are given in an N -body simulation of a barred spiral galaxy. In these examples, we demonstrate how the projection of unstable manifolds in configuration space reproduces essentially the entire observed bar–spiral pattern.