Electron paramagnetic resonance spectroscopy: A suggested approach to trace metal analysis in marine environments

Electron paramagnetic resonance (EPR) spectroscopy analysis of marine samples from different environments appears to differentiate between adsorbed and structural Mn (II) and Fe (III) sites in the sediment. This suggests that EPR may provide a means of distinguishing different environmental influences on sediment. Acid extract solutions from sediment samples exhibit clearly defined EPR spectra due to Mn(II), Ti(III), Fe(III), and VO(IV), which are amenable to qualitative and quantitative analysis at concentrations below one part per million. Spectra of several shellfish vary considerably, both between species, and within a species, depending on sampling localities. Resonances from Mn(II), Mo(V), and Fe(III) can be obtained. Mn(II) is substituted for Ca(II) in the calcite structure of some shells. The low detection limits, small sample size, required and identification of oxidation states by EPR complement other analytical techniques and may prove useful in marine systems.     

Graded-Density Reservoirs for Accessing High Stress Low Temperature Material States

In recently developed laser-driven shockless compression experiments an ablatively driven shock in a primary target is transformed into a ramp compression wave in a secondary target via unloading followed by stagnation across an intermediate vacuum gap. Current limitations on the achievable peak longitudinal stresses are limited by the ability of shaping the temporal profile of the ramp compression pulse. We report on new techniques using graded density reservoirs for shaping the loading profile and extending these techniques to high peak pressures.     

ISO SWS Spectroscopy of Proto-Planetary Nebulae

We are obtaining low- (SWS01) and medium-resolution (SWS06) spectra of PPNe to investigate spectral features arising in these transitional objects. Three sources with the 21 μm feature have been confirmed, one new source found, and evidence of some substructure seen. This revised version was published online in August 2006 with corrections to the Cover Date.     

The effect of orbital eccentricity and nodal regression on spin-stabilized satellites

The gyroscopic motion of a spin-stabilized satellite due to gravity gradient torques in a circular orbit has been analyzed to varying degrees in numerous publications. This paper shows that the restriction to a circular orbit is, in fact, not essential and with a slight increase in complexity, noncircular orbits may be treated. More importantly, a uniform regression of the orbital node can also be accounted for. The general results are expressed in closed form using Jacobian elliptic functions. Finally, and this is perhaps most important, certain algebraic integrals of the precession are given which can be used to place limits on the excursions of the spin axis without actually solving for the motion. This allows one to design orientations such that the maximum angle between the orbit normal and spin axis never exceeds a specific amount even though the orbit normal is in precession.     

An evaluation of the genesis and suitability of groundwater for irrigation in the Volta Region,Ghana

Stable isotope data and concentrations of the major cations and anions of groundwater from the northern part of the Volta Region, Ghana, were used to determine the source of recharge and the suitability of groundwater in the area for irrigation. This study finds that the delta deuterium (δD) and delta Oxygen-18 (δ¹⁸O) data from the area fall along the global meteoric water line (GMWL). An equation of regression derived for the relationship between δD and δ¹⁸O bears very close semblance to the equation which describes the GMWL. On the basis of this, groundwater in the study area is probably meteoric and fresh. The apparently low salinities and sodicities of the groundwater seem to support this interpretation. The suitability of groundwater for domestic and irrigation purposes is related to its source, which determines its constitution. A plot of the sodium adsorption ratio (SAR) and electrical conductivity (EC) data on a semilog axis, suggests that groundwater serves good irrigation quality in the area. Sixty percent (60%), 20% and 20% of the 67 data points used in this study fall within the medium salinity–low sodicity (C2–S1), low salinity–low sodicity (C1–S1) and high salinity–low sodicity (C3–S1) fields, which ascribe good irrigation quality to groundwater from this area. Salinities range from 28.1 to 1,956 μS/cm, whilst SAR values fall within the range 0–3. Extremely low sodicity waters of this kind, with salinities lower than 600 μS/cm, have the tendency to affect the dispersive properties of irrigation soils when used for irrigation. About 50% of the groundwater in the study area fall within this category and need prior treatment before usage.     

Basalt contamination by continental crust: Some experiments and models

Chemical interaction between molten basalt and felsic minerals of the continental crust (quartz, K-feldspar, and oligoclase) was examined in static and dynamic experiments at 1,200°–1,400° C. Under circumstances of continuous stirring at 1,400°, -quartz dissolves in tholeiite melt at a rate of 3.3×10^–6 g/s per cm² of contact area; at 1,300°, the solution rate is 1.5×10^–6 g/cm{cm2}s. The feldspars are molten at the experimental conditions, and interact with contacting basalt melt by diffusion in the liquid state. This is a complex process characterized by rapid initial diffusion of alkalies to establish a distribution between felsic melt and basalt similar to that observed in cases of actual two-liquid equilibrium (both alkalies reach concentrations in the felsic melt 1.5–3 times those in the basalt). Alkali diffusion may be uphill or downhill, depending on which direction of net flux is required to produce a two-liquid type distribution. Once this distribution is attained, subsequent diffusion of all melt species is slow and apparently limited by the diffusivity of SiO₂, which is 10^–9-l0^–10 cm²/s at 1,200° C. Interdiffusion experiments involving molten basalt and synthetic granite confirm the behavior illustrated by the feldspar/basalt results, and give similar SiO₂ diffusivities.The solution rates and interdiffusion data can be used to model basalt contamination processes likely to occur in the continental crust. For the restricted case of solid quartzitic xenoliths, the uptake of SiO₂ in a well-mixed basalt magma is quite fast: appreciable SiO₂ contamination may occur over exposure times of only days to years. If basalt magma induces local melting of crustal rocks, the assimilation process becomes one of liquid-state interdiffusion. In this case, the varying diffusivities of ions and their differing preferences for silicic relative to basaltic melts can produce marked selective contamination effects. Selective contamination of ascending basaltic magmas is particularly likely in the case of K₂O, which may be introduced in substantial amounts even when other elements remain unaffected. The Na₂O content of mantle-derived magmas is buffered against contamination by crustal materials, and K₂O is buffered against further increases once it reaches a level of 1–1.5 wt.%.     

Mineralogy and origin of stichtite in chromite-bearing serpentinites

Stichtite, a rare (14 known localities worldwide) hydrated carbonate-hydroxide of Mg and Cr with ideal formula Mg₆Cr₂ (OH)₁₆ CO₃ · 4H₂O, occurs exclusively in Cr-rich serpentinites of ophiolites or greenstone belts. Physical properties (hardness = 1.5–2, specific gravity = 2.16–2.2, perfect basal [0001] cleavage, grain size commonly < 100 μm) resemble talc, but the mineral has an attractive purple to lilac color; chemical analyses demonstrate it to be a non-silicate. Stichtite generally occurs as irregular to rounded masses (< 1 cm – 30 cm across) and as veinlets (< 1 mm – > 2 cm wide) within serpentinite. Macroscopic and microscopic textures, such as crosscutting veinlets and stringers, demonstrate that stichtite formation invariably post-dated serpentinization. In some specimens stichtite surrounds relict grains of Cr-rich spinel; in others stichtite has completely replaced euhedral or subhedral chromites. Chemical analyses of stichtites reveal substantial substitution of Al and Fe³⁺ for Cr in specimens from many localities, reflecting a possible compositional continuum between stichtite and rhombohedral polymorphs hydrotalcite (Mg₆Al₂ (OH)₁₆ CO₃ · 4H₂O) and pyroaurite (Mg₆Fe₂ (OH)₁₆ CO₃ · 4H₂O). We report the first electron microprobe analyses of stichtites from seven localities, and summarize all available published chemical data. Stichtites very likely inherited part of their trivalent cation chemistry from precursor Cr-rich spinels, but stichtite growth apparently post-dated characteristic “ferritchromit” alteration, as demonstrated by the depletion of Al and enrichment in Fe³⁺ in stichtite relative to primary chromite core compositions. Stichtite appears to form by reaction between serpentine and altered chromite, during addition of substantial fluid, either as separate H₂O and CO₂ phases, or as a mixed volatile phase. Such reactions must involve removal of substantial SiO₂, possibly by transport and remote deposition of silica by throughgoing aqueous and carbonic fluid. Received: 4 April 1996 / Accepted: 16 September 1996     

When is it sensible not to use XML?

This paper considers the problem of comparing the read time for a file containing an array of one-half million one-byte data values using a direct read time with the time required to read an equivalent XML file. The XML file uses a variable-length string encoding of the identifiers associated with each of the byte values. The XML file is about 180 times larger than the original file of byte values. Because the XML file is much larger and because the XML parsing requires substantially more computational work, reading the XML file on a Windows-based PC takes about 3,700 times longer than the direct read. The experimental study shows that the XML read time increases linearly with the size of the file. Given the increased read time and the increased probability of programming errors for the XML encoding, it appears that in cases where data archives are providing simple binary or text files of data that may be readily understood and read with short programs, then XML may not be an optimal choice for serving users or for preserving data.