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.     

Geoeffective Disturbances in the Solar Wind near the Solar Activity Minimum according to the Data of a Two-year Series of Observations of Interplanetary Scintillations with the BSA LPI Radio Telescope

Astronomy Reports - A joint analysis of the monitoring data of interplanetary scintillations with solar and geophysical data showed that at the descending phase of the 24 solar activity cycle, the...     

Semi-automatic delineation of badlands using contrast in vegetation activity: a case study in the lower Chambal valley,India

Population growth worldwide leads to an increasing pressure on the land. Recent studies reported that many areas covered by badlands are decreasing because parts of badlands are being levelled and converted into arable land. It is important to monitor these changes for environmental planning. This paper proposes a remote-sensing-based detection method which allows mapping of badland dynamics based on seasonal vegetation changes in the lower Chambal valley, India. Supervised classification was applied on three Landsat (Thematic Mapper) images, from 3 different seasons; January (winter), April (summer) and October (post-monsoon). Different band selection methods were applied to get the best classification. Validation was done by ground referencing and a GeoEye-1 satellite image. The image from January performed best with overall accuracy of 87% and 0.69 of kappa. This method opens the possibilities of using semi-automatic classification for the Chambal badlands which is so far mapped with manual interpretations only.