Continuum energy dissipation of 48 Persei

Self-similar solutions for one-dimensional unsteady flow of a non-ideal gas behind an exponential shock propagating into a uniform atmosphere are investigated. The equation of state in the suitable form for such gases is found to be fairly accurate at low-density region.     

Some early Russian studies of subsurface storm‐flow processes

Subsurface flow is an important component of the catchment hydrological cycle. Various mechanisms of this process and their role in storm‐flow generation attracted the attention of many researchers throughout the twentieth century. The results of most of these studies are well documented. However, similar studies conducted in the past by many Russian hydrologists have never been made available to the English speaking hydrological community. This paper attempts to fill this gap and briefly review some of these investigations, focusing on their main results. It starts with the review of the early experimental studies (after 1930s–1950s), which allow the main characteristics of subsurface storm flow to be established. This is followed by a review of the research conducted in 1960s, which resulted in some conceptualization of the subsurface flow mechanisms. The paper also draws some parallels between this, mostly unknown, subsurface flow research in Russia and the better‐known contemporary studies of this process. Copyright © 2002 John Wiley & Sons, Ltd.     

Stabilisation of divalent rare earth elements in natural fluorite

Summary ?The occurrence of divalent rare earth elements (Sm²⁺, Yb²⁺, Tm²⁺, and Ho²⁺) in natural fluorite is evaluated using a suite of 37 samples deriving mainly from Sn–W deposits in the Erzgebirge (Germany), Central Kazakhstan, and the Mongolian Altai. Trace element composition was determined by ICP-AES and ICP-MS. The defect structure of the samples was studied by cathodoluminescence (CL), electron paramagnetic resonance (EPR), and optical absorption spectroscopy. Reduction of cubic Sm³⁺, Yb³⁺, Tm³⁺, and Ho³⁺ under radioactive irradiation produces the corresponding divalent centres. Our data suggest a preferable formation of Sm²⁺ and Yb²⁺ under thorium and of Tm²⁺ and Ho²⁺ under uranium irradiation. Irradiation (indicated by intense brownish (thorium) and deep purple (uranium) coloration of fluorite) gives rise to a population of divalent centres in equilibrium with their decay. However, sporadic radioactive irradiation and stabilisation of the divalent state of the REE by other electron defects were found in most cases. Three models of stabilisation of Sm²⁺, Yb²⁺, Tm²⁺, and Ho²⁺ are discussed. The most effective mechanism for Sm, Yb, Tm, and Ho is coupling with Fe³⁺ centres (REE³⁺+Fe²⁺ → REE²⁺+Fe³⁺). Accordingly, the occurrence of Fe³⁺ centres in natural fluorite is regarded to indicate not an oxidising, but rather a reducing environment during fluorite precipitation. Originally incorporated in the divalent form, Fe²⁺ was converted to Fe³⁺ by radioactive irradiation. Such a conclusion is in agreement with the finding of high contents of interstitial fluorine providing tetragonal local compensation of trivalent REE centres in crystals with high Fe³⁺. If Fe is not present, compensation of divalent Sm, Yb, and Tm is achieved by radiogenic oxidation of Ce(Pr, Tb)³⁺ accompanied by charge transfer (REE³⁺+Ce(Pr, Tb)³⁺ → REE²⁺+ Ce(Pr, Tb)⁴⁺). Ho²⁺ is sometimes stabilised by a hole trapped by an electron localised on a F vacancy (Ho³⁺+e⁻ on □_F → REE²⁺+ self-trapped exciton). Because Sm²⁺ is optically active, the stabilisation by Fe³⁺ (stable up to temperatures above 350 °C) or Ce(Pr, Tb)⁴⁺ (unstable even under visible light) in samples may be determined by careful observations in the field. Institut für Geotechnik, ETH Zürich, ETH-H?nggerberg, Zürich, Switzerland Stanford Linear Accelerator Center, Menlo Park, CA, USA Received January 8, 2002; revised version accepted June 10, 2002     

Subsurface grout barriers for ground stabilization in dolomite areas near Carletonville, South Africa

 Artificial lowering of the groundwater level in dolomitic aquifers of the Far West Rand gold mining area has led to the formation of hundreds of sinkholes and subsidences. Where ground movements develop in or around important structures, it has become standard practice to drill boreholes for exploration and to inject mine tailings (slimes), cement and water to fill cavernous zones and arrest further ground movements. Although this method of grouting has mostly been effective, some boreholes accepted such large quantities of grout that the operation became prohibitively expensive. This paper describes an experiment to construct subsurface barriers by pouring wet (high slump) concrete via closely-spaced lines of boreholes into cavernous zones beneath a depression on a provincial road. The barriers required a small quantity of concrete and the zone between barriers was quickly filled by grout. The lack of further ground movements confirmed the success of the project. Received: 22 May 2000 · Accepted: 18 July 2000