On the relation between GDOP and the volume described by the user-to-satellite unit vectors for GNSS positioning

GPS Solutions - The geometric dilution of precision (GDOP) is related to the satellite geometry. Thus far, research has focused on minimizing the GDOP by selecting a set of satellites that...     

Polymetamorphic evolution of the Lewisian complex,NW Scotland,as recorded by U-Pb isotopic compositions of zircon,titanite and rutile

U-Pb isotopic relations in zircon and titanite of granulite and amphibolite gneisses in the Lewisian complex and bordering Laxford Front reveal complex discordance patterns indicating multiple Late Archean and Early Proterozoic crystallization, overgrowth and Pb-loss events. The earliest stages in the evolution of the complex remain poorly resolved. Zircon ages of 2710 Ma date high-grade metamorphism and magmatism probably related to tectonic and magmatic accretion in a continental arc setting. A distinct event at 2490–2480 Ma, possibly initiated by metamorphism and deformation at high-grade conditions, caused amphibolitization of the granulites and emplacement of granitic pegmatites. This event can be correlated with development of Inverian shear zones and formation of granitoid layers along the Laxford Front. The emplacement of a younger generation of granitoid sheets during the Laxfordian event fromed hydrothermal titanite at 1754 Ma in gneisses south of the Laxford Bridge and partially reset older titanite at Scourie. Growth of secondary titanite and rutile also occurred during subsequent low-grade metamorphism at 1690–1670 Ma.     

Cross-sectional areas of mid-ocean ridge axes bounding the Easter and Juan Fernandez microplates

We have calculated cross-sectional areas for the ridges bounding the Easter and Juan Fernandez microplates, 22°–28°S and 31°–35°S, obtaining accurate results where complete bathymetric data exist and estimates in other regions with partial bathymetric coverage and predicted bathymetry. We consider the reliability and usefulness of global predicted bathymetry in these calculations and the possible application of this dataset in other localities. The spreading rates on ridges bounding these microplates span the range from slow to superfast, allowing an investigation of ridge axis inflation over most of the rates active on Earth today. The across-axis areas of the Easter microplate ridge axes range from –29 km² to 7 km², while the Juan Fernandez ridge axis areas range from –27 km² to 8 km². Positive values correlate with regions usually interpreted as magmatically robust. Negative values arise from calculations in areas of propagating rift tips and deep grabens, such as Pito and Endeavor Deeps. Geochemical trends of Easter microplate axial basalts show decreasing MgO toward propagating rift tips and slight positive correlations between variables such as MgO vs. cross-sectional area, Na_8.0 vs. axial depth, and Na_8.0 vs. cross-sectional area. We document the decrease in the axial area approaching segment ends and propagating rift tips along both the West and East ridges of the microplates. On the Easter microplate both East and West ridge systems undergo large variations in spreading rate from >130 km Myr^–1 to <50 km Myr^–1. Inflation on these ridge segments is highly variable and only weakly correlated with spreading rate. On the Juan Fernandez microplate, West ridge spreading rates vary only between 115–140 km Myr^–1 and are systematically faster than on the East ridge, where rates vary between 10–35 km Myr^–1. Cross axis areas are systematically greater and significantly less variable on the faster spreading West ridge. Overall, compared to oceanic spreading centers bounding major plates with similar spreading rates, the axial areas are smaller on the microplate ridge systems, possibly because their rapidly changing configurations create a lag in the mantle response to the rigid plate boundary.     

Evaluation of the seismic risk of the unreinforced masonry building stock in Antioquia,Colombia

This work focuses on the exploitation of very high-resolution (VHR) satellite imagery coupled with multi-criteria analysis (MCA) to produce flood hazard maps. The methodology was tested over a portion of the Yialias river watershed basin (Nicosia, Cyprus). The MCA methodology was performed selecting five flood-conditioning factors: slope, distance to channels, drainage texture, geology and land cover. Among MCA methods, the analytic hierarchy process technique was chosen to derive the weight of each criterion in the computation of the flood hazard index (FHI). The required information layers were obtained by processing a VHR GeoEye-1 image and a digital elevation model. The satellite image was classified using an object-based technique to extract land use/cover data, while GIS geoprocessing of the DEM provided slope, stream network and drainage texture data. Using the FHI, the study area was finally classified into seven hazard categories ranging from very low to very high in order to generate an easily readable map. The hazard seems to be severe, in particular, in some urban areas, where extensive anthropogenic interventions can be observed. This work confirms the benefits of using remote sensing data coupled with MCA approach to provide fast and cost-effective information concerning the hazard assessment, especially when reliable data are not available.     

The first meteorological observations at a tropical high elevation site: Antisana, 1846

Antisana is a stratovolcano with an associated glacier located in the Ecuadorian Andes. Dr Aguirre made meteorological readings every day, at every hour from sunrise to sunset, from December 1845 to December 1846, at Antisana using a meteorological station at 4060 mamsl (meters above mean sea level). Unfortunately, only the monthly average data have been preserved. These meteorological data are here studied and compared with the closest modern stations for monthly values of temperature, rainfall, and pressure. According to these comparisons, the year 1846 was rainy and cold in comparison with the current climate. Moreover, these observations have been useful to help resolve a debate about a possible El Niño event in 1846 with the high precipitation in Antisana and Quito in 1846 discarding the occurrence of an El Niño event. The probable occurrence of a La Niña event is discussed. These data are the earliest known systematic instrumental meteorological observations taken at above 4000 mamsl.     

Life in the Goldilocks Zone: Perceptions of Place Disruption on the Periphery of the Bakken Shale

Community impacts from oil development in the Bakken Shale, located in the north central region of the United States, have been well reported in the press, including highly publicized accounts of social disruption. Less examined are communities on the periphery of such development, which experience related impacts unique to their location. Twenty-eight long-time residents from three Bakken periphery communities were interviewed to evaluate social and environmental impact perceptions, including perceived risks of place disruption. Findings suggest that whereas place meanings and identities were disrupted by the oil boom in Bakken core communities, they remain intact in these periphery communities. Findings further suggest periphery residents view their proximal location to the Bakken region as a social and economic “Goldilocks Zone:” close enough to benefit from spillover economic impacts, yet far enough away to avoid serious negative social impacts. This research extends understanding of place disruption and development impacts in energy periphery communities.     

Towards a standard measure of sea anemone size: assessing the accuracy and precision of morphological measures for cantilever‐like animals

Our capacity to detect and interrogate patterns in nature depends on the use of standard methods for measuring biological units. Consensus methods to quantify the size of individual animals and characteristics of biological communities are critical for comparisons across time and space. Nowhere is this more important than when dealing with organisms such as sea anemones that display high plasticity in body shape. Despite the need for accurate measures of anemone size for ecological comparisons, there is little consensus on the accuracy and precision of size inferences for these animals. We assessed several morphological parameters to determine which in‐field measure accurately and reliably reflects the reference size of an anemone measured in the laboratory: (i) column height, (ii) column diameter, (iii) limbus diameter, (iv) pedal disc diameter, (v) pedal disc area or (vi) pedal disc perimeter. The results revealed large variability in the accuracy and precision amongst measures, which have implications for their suitability as a standard method for in situ measurements. In general, measures of diameter were preferable to those of height, area and perimeter; and those associated with attachment (i.e. the limbus and pedal disc diameter) performed the best. Overall, considering concurrence with measures obtained from two differing but useful reference states, pedal disc diameter was the most accurate parameter (mean percentage difference = 0.6) with which to estimate the size of sea anemones in the field, and we thus recommend its use as an effective, non‐destructive means of gaining insights into their behavioural and evolutionary ecology.