A comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials: Some results from lake sediments

A new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility (χ_ARM, i.e. specific ARM obtained in a 1 Oe steady field), which is particularly sensitive to the single domain (SD) and small pseudo-single domain (PSD) grains of the finer magnetite fraction. A second parameter, low-field susceptibility (χ), is relatively more sensitive to the coarser magnetite fraction (larger PSD and smaller multidomain (MD) grains). We can then obtain a measure of the ratio of coarse- to fine-grain magnetite for large numbers of samples by plotting χ_ARversusχ. A simple idealized model based on sized magnetite samples is proposed to explain the use of the χ_ARMversusχ plot for detecting relative grain-size changes in the magnetic content of natural materials. The sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of χ_ARM and χ are used to test the model.The model is used to interpret the magnetic variations observed, and the interpretations are supported by high-field hysteresis measurements of the same sediments. The combination of the high-field hysteresis method of Day et al. [1] and the χ_ARM vs. χ method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite. The χ_ARMvs.χ method should be used as an intial means of identifying distinct groups of samples.The high-field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation.     

Dynamic analysis of piles and pile groups embedded in homogeneous soils

A boundary element formulation for the dynamic analysis of axially and laterally loaded single piles and pile groups is presented. The piles are represented by compressible beam-column elements and the soil as a hysteretic elastic half-space. The governing equations of motion for the pile domain have been solved exactly for distributed periodic loading intensities. These solutions are then coupled with a numerical solution for the motion of the soil domain by satisfying equilibrium and compatibility at the pile-soil interface. The results obtained from the analysis compare favourably with those from alternative analyses, e.g. finite element, but at greatly reduced computational costs.     

The geochemistry of beryllium and fluorine in the gem fields of Sri Lanka

A study of the abundance of Be in the gem sediments of Sri Lanka shows that Be is found in the range of 1–13 ppm. Be shows an irregular distribution among sediments. It occurs in the silicate form and due to the proximity to the beryllium bearing rocks, namely granites and pegmatites of the Highland and Southwest Groups of Sri Lanka, very little decomposition of the Be-bearing minerals had taken place. This is further aided by the high resistance to weathering of the beryllium minerals, particularly beryl and chrysoberyl.The beryllian granites and pegmatites of the Precambrian of Sri Lanka are presumed to have been formed due to the magmatic activity associated and related to charnockitic rocks abundant in the main gem bearing areas of Sri Lanka.Fluorine is found in the range of 400–2,000 ppm and the F/Be ratios for all the areas studied show a range of 54–441. The analysis of the averages of these ratios do not show any particular anomaly in any of the areas studied. The narrow ranges of the F/Be ratios indicate the similar conditions under which weathering and geochemical transportation had taken place in the gem fields of Sri Lanka.     

Transient elastodynamic analysis of three-dimensional problems by boundary element method

An advanced implementation of the direct boundary element method applicable to transient problems involving three-dimensional solids of arbitrary shape and connectivity is presented. The work first focuses on the formulation of the method, followed by a discussion of the fundamental singular solutions. Subsequently, a family of isoparametric boundary elements is introduced, along with the necessary numerical integration techniques as well as the solution algorithm. Numerical examples are presented, which demonstrate the unconditional stability and high accuracy of this dynamic analysis technique.     

Numerical hysteresis model for intermittent studies in unsaturated soils

In the present study, the use of one of the recent dependent domain models of capillary hysteresis in the numerical analysis of intermittent infiltration and redistribution of water in two types of soils (a sand and Rubicon Sandy Loam) has been shown. The numerical results for both the soils have been presented in terms of pressure head depth, moisture content depth and the pressure head-moisture content relationships. The capillary hysteresis model has been found to be very useful for the prediction of both wetting and drying scanning curves of various orders.     

Lunar paleointensity from three Apollo 15 crystalline rocks using an A.R.M. method

Three Apollo 15 crystalline rocks were used for determining lunar paleointensity at 3.3 AE using a new ARM-method of paleointensity determination. The values were found to be 4900 γ, 2200 γ, and 7600 γ. Thus an average lunar paleointensity of 4900 γ is concluded for this period.     

Long-term seismic observations along Myanmar–Sunda subduction margin: insights for 2004 Mw > 9.0 earthquake

International Journal of Earth Sciences - The present study investigates the temporal variation of few seismic parameters between the Myanmar (Zone I), Andaman–Nicobar–Northwest Sumatra...