Laboratory studies of the interaction of carbon monoxide with water ice

The interaction of carbon monoxide (CO) with vapour-deposited water(H₂O) ices has been studied using temperature programmed desorption (TPD) and Fourier transform reflection-absorption infrared spectroscopy (FT-RAIRS) over a range of astrophysically relevant temperatures. Such measurements have shown that CO desorption from amorphous H₂Oices is a much more complex process than current astrochemical models suggest. Re-visiting previously reported laboratory experiments (Collings et al., 2003), a rate model has been constructed to explain, in a phenomenological manner, the desorption of CO over astronomically relevant time scales. The model presented here can be widely applied to a range of astronomical environments where depletion of CO from the gas phase is relevant. The model accounts for the two competing processes of CO desorption and migration, and also enables the entrapment of some of the CO in the ice matrix and its subsequent release as the water ice crystallises and then desorbs. The astronomical implications of this model are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Application of environmental groundwater tracers at the Sulphur Bank Mercury Mine, California, USA

Boron, chloride, sulfate, δD, δ¹⁸O, and ³H concentrations in surface water and groundwater samples from the Sulphur Bank Mercury Mine (SBMM), California, USA were used to examine geochemical processes and provide constraints on evaporation and groundwater flow. SBMM is an abandoned sulfur and mercury mine with an underlying hydrothermal system, adjacent to Clear Lake, California. Results for non-³H tracers (i.e., boron, chloride, sulfate, δD, and δ¹⁸O) identify contributions from six water types at SBMM. Processes including evaporation, mixing, hydrothermal water input and possible isotopic exchange with hydrothermal gases are also discerned. Tritium data indicate that hydrothermal waters and other deep groundwaters are likely pre-bomb (before ~1952) in age while most other waters were recharged after ~1990. A boron-based steady-state reservoir model of the Herman Impoundment pit lake indicates that 71–79% of its input is from meteoric water with the remainder from hydrothermal contributions. Results for groundwater samples from six shallow wells over a 6–month period for δD and δ¹⁸O suggests that water from Herman Impoundment is diluted another 3% to more than 40% by infiltrating meteoric water, as it leaves the site. Results for this investigation show that environmental tracers are an effective tool to understand the SBMM hydrogeologic regime.

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Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.

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Résumé Les concentrations en bore, chlorure, sulfate, δD, δ¹⁸O, et ³H d’échantillons d’eaux de surface et souterraine prélevés dans le banc de soufre de la mine de mercure (SBMM en anglais) en Californie, USA, ont été utilisées pour étudier les processus géochimiques et pour fournir des contraintes à l’évaporation et à l’écoulement des eaux souterraines. La SBMM est une mine de soufre et de mercure abandonnée, adjacente au lac Clear en Californie et sous laquelle se trouve un système hydrothermal.Les résultats des traceurs autres que le tritium (bore, chlorure, sulfate, δD, et δ¹⁸O) ont permis d’identifier des contributions de six types d’eaux à SBMM. Des processus tels que l’évaporation, le mélange, l’entrée d’eau hydrothermale et de possibles échanges isotopiques avec des gaz hydrothermaux ont également été identifiés. Les données de tritium montrent que les eaux hydrothermales et d’autres eaux profondes sont probablement d’age antérieure à la bombe (avant ~1952), alors que la plupart des autres eaux sont issues de la recharge après ~1990. Un modèle de réservoir représentant le lac situé dans la partie Herman Impoundment de l’ancienne mine, en régime permanent et basé sur le bore, montre que 71–79% de l’eau provient des précipitations, le reste provenant de contributions hydrothermales. Les résultats de δD et δ¹⁸O pour des échantillons d’eau souterraine de six puits peu profonds sur une période de 6 mois suggèrent que l’eau de Hermann Impoundment est encore diluée entre 3% jusqu’à plus de 40% lorsqu’elle quitte le site du fait de l’infiltration d’eau météorique. Les résultats de cette étude montrent que les traceurs environnementaux constituent un outil efficace pour comprendre le régime hydrogéologique de la SBMM.

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Resumen Se han utilizado datos de concentraciones de boro, cloruros, sulfatos, δD, δ¹⁸O, y ³H en muestras de aguas superficiales y subterráneas procedentes de la Mina de Mercurio Sulphur Bank (SBMM), California, USA, para estudiar los procesos geoquímicos y caracterizar la evaporación y el flujo del agua subterránea. SBMM es una mina abandonada de azufre y mercurio con un sistema hidrotermal subyacente, cercano al Lago Clear, California.Los resultados de los trazadores que no son ³H (por ejemplo, boro, cloruros, sulfatos δD, y δ¹⁸O) identifican las contribuciones de seis tipos de agua en la SBMM. Se han identificado diversos procesos, como evaporación, mezcla, entrada de agua hidrotermal y la posibilidad de intercambios isotópicos con gases hidrotermales. Los datos de tritio indican que las aguas hidrotermales y otras aguas subterráneas profundas son probablemente pre-bombas (previas a ~1952) en edad mientras que la mayoría de las otras aguas se han recargado después de ~1990. Un modelo estacionario basado en el boro de la fosa del lago Herman Impoundment indica que el 71–79% de su entrada procede de agua meteórica con restos de contribución hidrotermal. Los resultados para las muestras de aguas subterráneas procedentes de seis pozos superficiales en un periodo de 6 meses para δD y δ¹⁸O sugieren que el agua procedente de Herman Impoundment se diluye en otro 3% hasta más del 40% debido a la infiltración de agua meteórica., que sale del sitio. Los resultados de esta investigación muestran que los trazadores ambientales son una herramienta efectiva para entender el régimen hidrogeológico de la SBMM.

     

Hyper Redundancy for Accuracy Enhancement in Automated Close Range Photogrammetry

A generic network design in close range photogrammetry is one where optimal multi-ray intersection geometry is obtained with as few camera stations as practicable. Hyper redundancy is a concept whereby, once the generic network is in place, many additional images are recorded, with the beneficial impact upon object point precision being equivalent to the presence of multiple exposures at each camera position within the generic network. The effective number of images per station within a hyper redundant network might well be in the range of 10 to 20 or more. As is apparent when it is considered that a hyper redundant network may comprise hundreds of images, the concept is only applicable in practice to fully automatic vision metrology systems, where it proves to be a very effective means of enhancing measurement accuracy at the cost of minimal additional work in the image recording phase. This paper briefly reviews the network design and accuracy aspects of hyper redundancy and illustrates the technique by way of the photogrammetric measurement of surface deformation of a radio telescope of 26 m diameter. This project required an object point measurement accuracy of σ  = 0·065 mm, or 1/400 000 of the diameter of the reflector.     

Atmospheric Methyl Iodide at Cape Grim, Tasmania, from AGAGE Observations

Atmospheric mixing ratios of methyl iodide (CH₃I) and other methyl halides have been measured at Cape Grim, Tasmania (41°S, 145°E), since early 1998 as part of the Advanced Global Atmospheric Gases Experiment (AGAGE). This paper analyses about 1700 ambient air CH₃I measurements from the 14-month period (March 1998–April 1999). Mixing ratios peaked during the summer, despite faster photolytic loss, suggesting local oceanic emissions were about 2.2–3.6 times stronger in summer than in winter. Back trajectories show that CH₃I levels are strongly dependent on air mass origin, with highest mixing ratios in air from the Tasman Sea/Bass Strait region and lowest levels in air originating from the Southern Ocean at higher latitudes. CH₃I mixing ratios were not well correlated with other methyl halides in unpolluted marine air. The large variations with season and air mass origin suggest that high frequency, continuous data from key locations will make a significant contribution to the understanding of sources and sinks of this important short-lived atmospheric species.     

Background simulations for the Large Area Detector onboard LOFT

The Large Observatory For X-ray Timing (LOFT), currently in an assessment phase in the framework the ESA M3 Cosmic Vision programme, is an innovative medium-class mission specifically designed to answer fundamental questions about the behaviour of matter, in the very strong gravitational and magnetic fields around compact objects and in supranuclear density conditions. Having an effective area of ～10 m² at 8 keV, LOFT will be able to measure with high sensitivity very fast variability in the X-ray fluxes and spectra. A good knowledge of the in-orbit background environment is essential to assess the scientific performance of the mission and optimize the design of its main instrument, the Large Area Detector (LAD). In this paper the results of an extensive Geant-4 simulation of the instrumentwillbe discussed, showing the main contributions to the background and the design solutions for its reduction and control. Our results show that the current LOFT/LAD design is expected to meet its scientific requirement of a background rate equivalent to 10 mCrab in 2?30 keV, achieving about 5 mCrab in the most important 2–10 keV energy band. Moreover, simulations show an anticipated modulation of the background rate as small as 10 % over the orbital timescale. The intrinsic photonic origin of the largest background component also allows for an efficient modelling, supported by an in-flight active monitoring, allowing to predict systematic residuals significantly better than the requirement of 1 %, and actually meeting the 0.25 % science goal.     

Exploration drilling and reservoir model of the Platanares geothermal system, Honduras, Central America

Results of drilling, logging, and testing of three exploration core holes, combined with results of geologic and hydrogeochemical investigations, have been used to present a reservoir model of the Platanares geothermal system, Honduras. Geothermal fluids circulate at depths ≥ 1.5 km in a region of active tectonism devoid of Quaternary volcanism. Large, artesian water entries of 160 to 165°C geothermal fluid in two core holes at 625 to 644 m and 460 to 635 m depth have maximum flow rates of roughly 355 and 560 l/min, respectively, which are equivalent to power outputs of about 3.1 and 5.1 MW(thermal). Dilute, alkali-chloride reservoir fluids (TDS ≤ 1200 mg/kg) are produced from fractured Miocene andesite and Cretaceous to Eocene redbeds that are hydrothermally altered. Fracture permeabillity in producing horizons is locally greater than 1500 and bulk porosity is ≤ 6%. A simple, fracture-dominated, volume-impedance model assuming turbulent flow indicates that the calculated reservoir storage capacity of each flowing hole is approximately 9.7 × 10⁶ l/(kg cm⁻²), Tritium data indicate a mean residence time of 450 yr for water in the reservoir. Multiplying the natural fluid discharge rate by the mean residence time gives an estimated water volume of the Platanares system of ≥ 0.78 km³. Downward continuation of a 139°C/km “conductive” gradient at a depth of 400 m in a third core hole implies that the depth to a 225°C source reservoir (predicted from chemical geothermometers) is at least 1.5 km. Uranium-thorium disequilibrium ages on calcite veins at the surface and in the core holes indicate that the present Platanares hydrothermal system has been active for the last 0.25 m.y.     

极隙区Pc3频段脉动的传播特性

南极中山站和戴维斯站 (不变磁纬 74.5°S)白天中午位于磁层极隙区 ,夜间位于极盖区或极光带的极向边沿。两站均安装了完全相同的感应式磁力计。选择两站 1 997年 3月和 1 996年 6、9、1 2月的数据 ,运用快速傅立叶变换和波形检查方法选择 Pc3频段脉动事件 ,然后用信号互谱技术进行统计分析 ,结果如下 :在中山站 -戴维斯站 ,Pc3频段脉动主要出现于白天中午 /磁中午和磁午夜附近 ;白天 ,Pc3频段脉动振幅、出现率和出现的时间范围均有一定的季节变化 ,冬季最小 ,但在夜间 ,Pc3频段脉动没有这种变化 ;夜间 ,Pc3频段脉动振幅比在白天大许多 ;Pc3频段脉动传播方向 ,白天主要向西 ,夜间不太规则。这些可能反映了电离层电导率和日侧电离层电流系统对 Pc3频段脉动的影响。