Lithification of gas-rich chondrite regolith breccias by grain boundary and localized shock melting

We studied the fine-grained matrices (< 150 μm) of 14 gas-rich ordinary chondrite regolith breccias in an attempt to decipher the nature of the lithification process that converted loose regolith material into consolidated breccias. We find that there is a continuous gradation in matrix textures from nearly completely clastic (class A) to highly cemented (class C) breccias in which the remaining clasts are completely surrounded by interstitial, shock-melted material. We conclude that this interstitial material formed by shock melting in the porous regolith. In general, the abundances of solar-wind-implanted ⁴He and ²⁰Ne are inversely correlated with the abundance of interstitial, shock-melted, feldspathic material. Chondrites with the highest abundance of interstitial, melted material (class C) experienced the highest shock pressures and temperatures and suffered the most extensive degassing. It is this interstitial, feldspathic melt that lithifies and cements the breccias together; those breccias with very little interstitial melt (class A) are the most porous and least consolidated.     

Occurrence and distribution of bacteria indicators,chemical tracers and pathogenic vibrios in Singapore coastal waters

Water quality in Singapore's coastal area was evaluated with microbial indicators, pathogenic vibrios, chemical tracers and physico-chemical parameters. Sampling sites were grouped into two clusters (coastal sites at (i) northern and (ii) southern part of Singapore). The coastal sites located at northern part of Singapore along the Johor Straits exhibited greater pollution. Principal component analysis revealed that sampling sites at Johor Straits have greater loading on carbamazepine, while turbidity poses greater influence on sampling sites at Singapore Straits. Detection of pathogenic vibrios was also more prominent at Johor Straits than the Singapore Straits. This study examined the spatial variations in Singapore's coastal water quality and provided the baseline information for health risk assessment and future pollution management.     

Comparison of LiDAR waveform processing methods for very shallow water bathymetry using Raman,near‐infrared and green signals

Airborne light detection and ranging (LiDAR) bathymetry appears to be a useful technology for bed topography mapping of non‐navigable areas, offering high data density and a high acquisition rate. However, few studies have focused on continental waters, in particular, on very shallow waters (<2 m) where it is difficult to extract the surface and bottom positions that are typically mixed in the green LiDAR signal. This paper proposes two new processing methods for depth extraction based on the use of different LiDAR signals [green, near‐infrared (NIR), Raman] of the SHOALS‐1000T sensor. They have been tested on a very shallow coastal area (Golfe du Morbihan, France) as an analogy to very shallow rivers. The first method is based on a combination of mathematical and heuristic methods using the green and the NIR LiDAR signals to cross validate the information delivered by each signal. The second method extracts water depths from the Raman signal using statistical methods such as principal components analysis (PCA) and classification and regression tree (CART) analysis. The obtained results are then compared to the reference depths, and the performances of the different methods, as well as their advantages/disadvantages are evaluated. The green/NIR method supplies 42% more points compared to the operator process, with an equivalent mean error (?4·2 cm verusu ?4·5 cm) and a smaller standard deviation (25·3 cm verusu 33·5 cm). The Raman processing method provides very scattered results (standard deviation of 40·3 cm) with the lowest mean error (?3·1 cm) and 40% more points. The minimum detectable depth is also improved by the two presented methods, being around 1 m for the green/NIR approach and 0·5 m for the statistical approach, compared to 1·5 m for the data processed by the operator. Despite its ability to measure other parameters like water temperature, the Raman method needed a large amount of reference data to provide reliable depth measurements, as opposed to the green/NIR method. Copyright © 2010 John Wiley & Sons, Ltd.     

Earth rotation and network geometry optimization for very long baseline interferometers

Very Long Baseline Interferometry (VLBI) is one of the new techniques which will probably dominate geodesy and geophysics in the near future. Its main advantage lies in the fact that it brings the accuracy of direction measurements to a level previously possible only for range measurements. This closes the gap between powerful range determination techniques such as laser ranging and the much less accurate determination of directions through photographic tracking of artificial earth satellites. The technique is geometric in the sense that the relevant observations are independent of the gravity field of the earth. However, the “orbits” of the observed extragalactic radio sources with respect to an earth-fixed system are dominated and perturbed by the rotation of the earth with respect to inertial frame. This allows the determination of polar motion, precession-nutation and length-of-the-day variations, and the technique becomes also “dynamic” in this respect. The capability of determining the geometry of a network of stations within a short time interval and with a centimeter level accuracy also allows the study of the variation of network geometry with time caused by earth tides and other periodic or secular station drifts. The main objective of the present work is the exploration of the capabilities of VLBI for the recovery of earth rotation and network geometry parameters. For this purpose, a number of characteristic experimental designs based on present and candidate for the near future station locations is chosen. The results from the analysis of simulated observations for each particular design are presented in the paper. Presented at IAG International Symposium on “Optimization of Design and Computation of Control Networks”, Sopron, Hungary, 4–10 July 1977.     

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Deformation und Umwandlung von Plagioklas durch Stoßwellen in den Gesteinen des Nördlinger Ries

Plagioclase from fragments of crystalline basement rocks in breccias found in the area of the Nördlinger Ries crater displays characteristic plastic deformation and phase transition phenomena due to shock metamorphism at different pressures in the range of 100 to 1000 kilobars.These phenomena are discussed in the scope of a progressive impact metamorphism the degree of metamorphism reflecting a radial gradient of pressure and temperature diminishing outward from the point of meteorite impact.Within the lowest pressure range of about 100 to 300 kilobars (shock stage I) strong fracturing and plastic deformation such as bending of crystals, deformation bands and planar features (lamellae of lowered refractive index and of lowered or no birefringence) are to be found. The lamellae which are mostly isotropic, are interpreted as slip bands the glide planes of which are low indices planes of the plagioclase lattice such as (001), (010), (100), (1¯20), (130) and others. These slip bands are unknown from feldspar formed by normal processes within the earth's crust. Plagioclase of such a stage of deformation shows an unusual strong decrease of refraction and birefringence. Its optical properties are those of a highly disordered plagioclase. It may be called diaplectic plagioclase.Total isotropization of plagioclase is a typical feature of the pressure range from 300 to 500 kilobars (shock stage II). This glass which is called diaplectic glass differs strongly from the normal glass in physical properties and structural state. It is formed by a kind of solid state transformation without actual melting.Shock pressures in the order of 500 to 650 kilobars (shock stage III) are able to cause selective melting of plagioclase grains in a crystalline rock. Normal glasses with vesicles and streaks are formed by this process.Within the pressure range of about 650 to 1000 kilobars (shock stage IV) residual temperatures are so high that total melting of rocks occurs. Plagioclase melts are mixed inhomogenously with other silicate melts forming rock melts which can be found in suevite as flat glassy bombs. Vaporization of silicates must be expected in the upper pressure range of this shock stage.Statistical universal stage measurements on the fabric of plagioclase support theoretical considerations after which the deformation pattern of a single crystal should depend on the fabric relations to the surrounding minerals and on their physical properties. Strongly inhomogenous deformation of plagioclase minerals within the microscopic rock scale was observed because polycrystalline rocks are disorganizing a unique shock front by interaction of wave fronts at interfaces and free surfaces and perhaps by multiwave shocks. Directions of compressive and tensile stresses on a mineral are therefore changing from grain to grain.     

Avalanche risk assessment for mountain roads: a case study from Iceland

This paper presents an assessment of the avalanche hazard potential and the resulting risks on mountain roads for a 38.7-km-long section of road no 76 (Siglufjarearvegur) in northern Iceland following a regional scale approach developed in the Alps. The assessment of the individual avalanche death risk proved applicable to distinguish areas of avalanche hazard with a risk above the accepted level, which should be given priority in following detailed investigations and the planning of possible protective measures, from road sections where the avalanche death risk is low and accepted according to international practice. The cumulative individual and collective avalanche death risks in the investigated road section provide a comparable measure for assessing the avalanche hazard both within the Icelandic public road network and on an international scale. The case study on road no 76 in northern Iceland shows that a standardised regional scale risk-based approach is practical to determine, analyse and assess the avalanche hazard situation on mountain roads in Iceland and guarantees comprehensible, reproducible and comparable results as a basis for a sustainable planning of measures.     

Policy concerns in Bulgarian food distribution

The Bulgarian food distribution system, like those of its Central and East European neighbours, lags behind the West in critical performance areas. Previous research quantified Central and East European food distribution deficiencies on the basis of a five factor model. This study investigates the attitudes of 250 Bulgarian consumers using these same five factors: food processing, quality, cost, availability and retailing. The findings show that the Bulgarian food distribution system does not satisfy consumer wants as well as do systems in other former communist countries in four of the five factors. At the same time, Bulgarian consumers are more satisfied than UK and US consumers in the system's ability to make some foods available. The study also shows that Bulgarian consumers who use privatised shops perceive the system more positively than those who use state and cooperative outlets. The implications of these and other findings are discussed in terms of critical policy concerns for government and industry stakeholders.