Solubility of corundum in supercritical water

Isothermal (670–700°C) solubility of corundum in supercritical water, within the stability range of corundum as a phase of the system Al₂O₃-H₂O, has been determined by the weight loss method. Experiments were performed in the pressure range 2.5 to 6 kbar in cold seal hydrothermal equipment at 670 ± 5°C using gold tubing. The overall uncertainty of the solubility values obtained was 8%. Experiments in the pressure range 10 to 20 kbar were performed in a piston cylinder apparatus at 700°C using sealed gold capsules held by supporting steel containers. The overall uncertainty of the solubility values obtained was estimated to be 10%.All data could be fitted by the linear equation S_[ppmAl2O3] = ?12.37 + 7.24 · p[_kbar] with correlation coefficient r = 0.9963. Separate fits of hydrothermal and piston cylinder results yielded a small difference between the two data sets, which is due rather to the experimental uncertainty than to the small temperature difference.     

A discussion of world-wide measurements of tidal gravity with respect to oceanic interactions,lithosphere heterogeneities,Earth's flattening and inertial forces

By the end of 1981 the International Center of Earth Tides (ICET) had collected and evaluated a considerable amount of data from 180 stations, including those of the Trans-World Profile which ensure for the first time a world-wide distribution including the tropical areas and the southern hemisphere. In 1979–80, new oceanic cotidal maps of high quality, established by Schwiderski, became available. These maps fit “on-land” tidal-gravity measurements quite successfully. A new theoretical approach developed by Wahr in 1981 has resulted in a set of theoretical formulae establishing the latitude-dependence of the classical elastic amplitude factors for tidal deformations.We calculate here, for six tidal waves, the correlations between the observed gravity variations and those resulting from a calculation based upon the Schwiderski maps. These correlations are highly significant. After subtraction of these oceanic effects we calculate the latitude-dependences of the experimentally determined amplitude factors, which are found to fit Wahr's theoretical formulae. There remains, however, a serious discrepancy in the constant terms of the various formulae. The effects of heterogeneities in the lithosphere on tidal deformations are also clearly identified.     

Shock-induced devolatilization of calcite

The amounts of CO₂ and CO evolved upon shock compression and decompression of calcite to 18 GPa (180 kbar) have been determined using a new gas phase shock recovery technique and gas source mass spectrometry. The data demonstrate that from ～0.03 to 0.3 mole percent of calcite is devolatilized at shock pressures significantly lower than those predicted (30 GPa) for the onset of volatilization by continuum thermodynamic theory and are in qualitative agreement with release adiabat data for calcite and aragonite. Carbon and oxygen isotope ratios in the shock-released CO₂ are the same as those in the unshocked (hydrothermal) calcite, demonstrating that the CO₂ comes from the calcite rather than other potential sources.     

Oxidation of sulphur compounds in the atmosphere: I. Rate constants of OH radical reactions with sulphur dioxide,hydrogen sulphide,aliphatic thiols and thiophenol

The reactions of OH radicals with SO₂, H₂S, thiophenol, and a series of aliphatic thiols (1–5 C-atoms) have been investigated in 201 and 381 reaction chambers at 1 atm total pressure and 300 K using a competitive kinetic technique. Initially, OH radicals were produced by photolysis of CH₃ONO/NO mixtures in air. Applying this OH source rate constants for OH with SO₂, H₂S, and thiophenol in synthetic air were determined to be (1.1±0.2)×10^-12, (5.5±0.8)×10^-12 and (1.1±0.2)×10^-11 cm³ s^-1, respectively. However, when this method was applied to the aliphatic thiols the rate constants obtained were found to be dependent on the partial pressures of O₂ and NO. These effects have been attributed to the built-up of a radical species, not yet identified, which leads to uncontrolled chain reactions in the system. Using the photolysis of H₂O₂ at wavelengths greater than 260 nm as the OH source in 1 atm N₂, rate constants for the 1–5 aliphatic thiols in the range 2.9 to 5.6×10^-11 cm³ s^-1 were obtained. The rate constants obtained in the present study are compared with recent literature values.     

The Prince of Wales Formation – post-flood basalt alkali volcanism in the Tertiary of East Greenland

 In the nunataks of the Prince of Wales Mountains the tholeiite flood basalts of the East Greenland Tertiary Province are unconformably overlain by alkaline lavas. The majority of the alkaline lavas are strongly porphyritic picrites, ankaramites and hawaiites. These rocks have lower ¹⁴³Nd/¹⁴⁴Nd and higher ⁸⁷Sr/⁸⁶Sr than the tholeiitic flood basalts and are isotopically akin to ocean island basalts. The alkaline lavas also have high concentrations of incompatible elements which on normalised plots have a pattern which is similar in shape to that of enriched oceanic island basalts. The isotopic and chemical characteristics of these late-stage representatives of the East Greenland volcanic activity are attributed to their derivation from the peripheral regions of the East Greenland plume, the axial region of which was moving progressively eastwards relative to the westwards drift of the Greenland plate. It is proposed that the incompatible element contents of the magmas so produced were dominated by small degree melts formed beneath a cap of continental lithosphere in the marginal regions of the plume. Received: 5 June 1995 / Accepted: 11 December 1995     

Spatially simplified scatterplots for large raster datasets

Abstract

Scatterplots are essential tools for data exploration. However, this tool poorly scales with data-size, with overplotting and excessive delay being the main problems. Generalization methods in the attribute domain focus on visual manipulations, but do not take into account the inherent nature of information redundancy in most geographic data. These methods may also result in alterations of statistical properties of data. Recent developments in spatial statistics, particularly the formulation of effective sample size and the fast approximation of the eigenvalues of a spatial weights matrix, make it possible to assess the information content of a georeferenced data-set, which can serve as the basis for resampling such data. Experiments with both simulated data and actual remotely sensed data show that an equivalent scatterplot consisting of point clouds and fitted lines can be produced from a small subset extracted from a parent georeferenced data-set through spatial resampling. The spatially simplified data subset also maintains key statistical properties as well as the geographic coverage of the original data.     

Liquidus temperatures and phase compositions in the system Qz-Ab-Or at 5 kbar and very low water activities

Liquidus phase relations have been experimentally determined in the systems Qz-Ab-Or-(H₂O), Qz-Ab-(H₂O) and Qz-Or-(H₂O) at H₂O-undersaturated conditions (a _H2O = 0.07) and P = 5 kbar. Starting materials were homogeneous synthetic glasses containing 1 wt% H₂O. The liquidus temperatures were bracketed by crystallization and dissolution experiments. The results of kinetic studies showed that crushed glasses are the best starting materials to overcome undercooling and to minimize the temperature difference between the lowest temperature of complete dissolution (melting) and the highest temperature at which crystallization can be observed. At P = 5 kbar and a _H2O = 0.07, the Qz-Ab eutectic composition is Qz₃₂Ab₆₈ at 1095 °C (±10 °C) and the Qz-Or eutectic is Qz₃₈Or₆₂ at 1030 °C (±10 °C). The minimum temperature of the ternary system Qz-Ab-Or is 990 °C (±10 °C) and the minimum composition is Qz₃₂Ab₃₅‐ Or₃₃. The Qz content of the minimum composition in the system Qz-Ab-Or-H₂O remains constant with changing a _H2O. The normative Or content, however, increases by approximately 10 wt% with decreasing a _H2O from 1 to 0.07. Such an increase has already been observed in the system Qz-Ab-Or-H₂O-CO₂ at high a _H2O and it is concluded that the use of CO₂ to reduce water activities does not influence the composition of the minima in quartz-feldspar systems. The determined liquidus temperature in melts with 1 wt% H₂O is very similar to that obtained in previous nominally “dry” experiments. This discrepancy is interpreted to be due to problems in obtaining absolutely dry conditions. Thus, the hitherto published solidus and liquidus temperatures for “dry” conditions are probably underestimated. Received: 27 March 1997 / Accepted: 1 October 1997