The structures of three centers of trivalent iron in α-quartz

Trivalent iron is known to occur in amethysts in three different environments: substitutional with an as yet unidentified alkali ion in an adjacent interstitial site on the twofold axis (so-called S ₁ center), substitutional with a proton on one of the four oxygen neighbors (S ₂ center) and without detectable charge compensation (so-called I center because it was proposed to be in interstitial sites, but its nature is still disputed). The alkali ion in the S ₁ center was now identified as Li and the Li and Fe superhyperfine (shf) tensors were determined by electron paramagnetic resonance at low temperatures in samples of unusually high quality. The fine structure and ¹H shf structure tensors for the S ₂ center with the proton on an oxygen with longer bond distance were evaluated and the geometry of the oxygen coordination was estimated by application of the superposition model. For the I center the ⁵⁷Fe and ²⁹Si shf splittings were determined and the evidence in favor of assignment to an interstitial site is reviewed.     

Disaster vulnerability: Scale,power and daily life

The author gratefully acknowledges the stimulation over a number of years of his co-authors in a project about to appear in 1994 under the title,At Risk: Natural Hazards, People's Vulnerability and Disasters, Routledge, London & New York — Piers Blaikie, Terry Cannon, and Ian Davis.Earlier versions of this paper were discussed by session on disasters organized by Tony Oliver-Smith at the annual meeting of the Society for Applied Anthropology, Memphis, March, 1992 and at the Famine and Food Systems Study Group of the International Geographical Union, convened at Tufts University, July, 1992, by John Field and Hans Bohle. My thanks as well to colleagues who participated in these two discussions.     

Solid Waste Management in Ohio*

State environmental protection agencies are being forced to assume more responsibility for solid waste management. Ohio took the lead in mandating the state control of waste by implementing a statewide, integrated solid waste management plan. This paper discusses the shift in management responsibility and key factors affecting variations in the amounts of waste managed by Ohio's 48 solid waste management districts. Accessibility, population characteristics, location, and open landfill availability are factors that influence managed volumes of solid waste.     

The method of free-positioned point masses — geoid studies on the Gulf of Bothnia

Gravity data inversion methods using spatial source distributions are frequently investigated and applied in Geodesy. Nearly all of them construct a fixed geometry for the sources. It was shown that this is not at all necessary. We give an approach to the problem of geoid determination based on free-positioned point masses. The algorithm available is extended and refined in order to make it applicable to more ill-designed and complex problems than addressed so far. We introduce concepts to handle different data accuracies, non-uniform data coverages, and different data types. The Gulf of Bothnia serves as an area of investigation. We determine a pure gravimetric geoid solution as well as a combined solution based on gravimetric and altimetric data. The problem of gross error detection in the altimetry is treated. The prediction accuracies obtained prove the method to be suitable for such a problem.