Anelastic deformation in Iceland studied using GPS: with special reference to post-tectonic motion following the 1975-1985 krafla rifting episode, and isostatic rebound

The Krafla volcanic system is a spreading segment in north Iceland. A decade-long crustal spreading episode began there in 1975. Up to 8 m of rift-normal surface widening occurred along an 80-90 km-long section of the plate boundary. Isostatic uplift in the vicinity of the melting icecap Vatnajōkull has been proposed. A third GPS survey of a regional network surrounding the Krafla system was conducted in 1992. In 1991 a 10-point GPS network was installed and measured for the first time around Vatnajōkull. The 1991 and 1992 GPS data were processed using the Bernese software. Differencing the 1992 results with those from 1987 and 1990 revealed a regional deformation field with a maximum, rift-normal expansion rate of 4.4 cm/yr near the rift, decreasing to 3 cm/yr at large distances. The time-averaged spreading rate in north Iceland, 1.8 cm/yr, cannot account for this deformation. The vertical deformation field reveals regional uplift throughout the network area, at its maximum closest to the rift and decreasing with distance. Three different models were applied to study the postdyking ground deformation, (1) continued opening at depth on the dyke plane in an elastic halfspace, (2) stress redistribution in an elastic-viscous layered medium, and (3) stress redistribution in an elastic layer over a viscoelastic halfspace. The latter model was developed by extending mathematical techniques previously used to model surface displacements resulting from thrust faulting to the case of dyke emplacement. For the model of continuous dyking at depth, a range of dykes will fit the deformation field. Using the elastic-viscous model, the motion 1987-1990 and 1990-1992 is simulated adequately given the survey errors, but the 1987-1992 deformation is poorly fitted, suggesting that a more realistic geophysical model is required. Using the elastic-viscoelastic approach the effects of historical episodes in the region were subtracted from the observed displacement fields and the remaining motion was modelled as relaxation following the recent Krafla rifting episode. The best-fit model involves a halfspace viscosity of 1.1 x 10(^18) Pa s. The vertical field is noisy, but indicates that the Krafla dyke complex rifted the entire elastic layer. Isostatic uplift centred on Vatnajőkull is inconsistent with the vertical deformation field. The model suggests that the Krafla volcano became inactive after 1988/1989. The model further predicts that the width of the "plate boundary zone" is greater than that of Iceland itself

Graph layout using subgraph isomorphisms

Today, graphs are used for many things. In engineering, graphs are used to design circuits in very large scale integration. In computer science, graphs are used in the representation of the structure of software. They show information such as the flow of data through the program (known as the data flow graph [1]) or the information about the calling sequence of programs (known as the call graph [145]). These graphs consist of many classes of graphs and may occupy a large area and involve a large number of vertices and edges. The manual layout of graphs is a tedious and error prone task. Algorithms for graph layout exist but tend to only produce a 'good' layout when they are applied to specific classes of small graphs. In this thesis, research is presented into a new automatic graph layout technique. Within many graphs, common structures exist. These are structures that produce 'good' layouts that are instantly recognisable and, when combined, can be used to improve the layout of the graphs. In this thesis common structures are given that are present in call graphs. A method of using subgraph isomorphism to detect these common structures is also presented. The method is known as the ANHOF method. This method is implemented in the ANHOF system, and is used to improve the layout of call graphs. The resulting layouts are an improvement over layouts from other algorithms because these common structures are evident and the number of edge crossings, clusters and aspect ratio are improved

Lavfloraen på dødt organisk materiale under overhengende berg og steinblokker

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Flame spectroscopic studies of bismuth, lanthanum, lead and silver with particular reference to their determination in steels.

This thesis discusses the atomic spectroscopy of bismuth, lanthanum, lead and silver and describes the determination of trace amounts of the four metals in steel after the preliminary solvent extraction of the metals. A study of the interference effects of the matrix elements upon both the extraction and determination of each metal is included. The thesis also describes an investigation into lock-in amplification systems in both atomic absorption and fluorescence spectrometry and discusses their effect upon the detection limits for bismuth, lead and silver, as well as the advantages of spectrometers incorporating lock-in amplifiers in the analysis of steel

DESDynI Lidar for Solid Earth Applications

As part of the NASA's DESDynI mission, global elevation profiles from contiguous 25 m footprint Lidar measurements will be made. Here we present results of a performance simulation of a single pass of the multi-beam Lidar instrument over uplifted marine terraces in southern Alaska. The significance of the Lidar simulations is that surface topography would be captured at sufficient resolution for mapping uplifted terraces features but it will be hard to discern I-2m topographic change over features less than tens of meters in width. Since Lidar would penetrate most vegetation, the accurate bald Earth elevation profiles will give new elevation information beyond the standard 30-m OEM

Use of waveform lidar and hyperspectral sensors to assess selected spatial and structural patterns associated with recent and repeat disturbance and the abundance of sugar maple (Acer saccharum Marsh.) in a temperate mixed hardwood and conifer forest.

Abstract Waveform lidar imagery was acquired on September 26, 1999 over the Bartlett Experimental Forest (BEF) in New Hampshire (USA) using NASA\u27s Laser Vegetation Imaging Sensor (LVIS). This flight occurred 20 months after an ice storm damaged millions of hectares of forestland in northeastern North America. Lidar measurements of the amplitude and intensity of ground energy returns appeared to readily detect areas of moderate to severe ice storm damage associated with the worst damage. Southern through eastern aspects on side slopes were particularly susceptible to higher levels of damage, in large part overlapping tracts of forest that had suffered the highest levels of wind damage from the 1938 hurricane and containing the highest levels of sugar maple basal area and biomass. The levels of sugar maple abundance were determined through analysis of the 1997 Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) high resolution spectral imagery and inventory of USFS Northern Research Station field plots. We found a relationship between field measurements of stem volume losses and the LVIS metric of mean canopy height (r2 = 0.66; root mean square errors = 5.7 m3/ha, p \u3c 0.0001) in areas that had been subjected to moderate-to-severe ice storm damage, accurately documenting the short-term outcome of a single disturbance event

Integrative taxonomy reveals a new species, Nephroma orvoi, in the N. parile species complex (lichenized Ascomycota)

Our knowledge of the diversity and distribution of many groups of lichens remains poor due to unclear species boundaries and challenging species identification. We have studied the medium sized to large foliose lichen Nephroma parile, which is known to be heterogeneous in chemistry and genetics. Our aim has been to assess the potential presence of evolutionary significant units within the Nephroma parile species complex that may be worthy of recognition at species level. Using phylogenetic analysis of the fungal DNA-barcode marker (ITS) in combination with studies of morphology and chemistry, we discover two distinct lineages in the N. parile species complex. For the strongly supported clade that corresponds to chemotype II, we describe the new species Nephroma orvoi. The new species is known from Norway, Sweden, Finland, Switzerland, Canada (Alberta and British Columbia), USA (Washington), and Greenland.publishedVersio

Integrative taxonomy reveals a new species, Nephroma orvoi, in the N. parile species complex (lichenized Ascomycota)

Our knowledge of the diversity and distribution of many groups of lichens remains poor due to unclear species boundaries and challenging species identification. We have studied the medium sized to large foliose lichen Nephroma parile, which is known to be heterogeneous in chemistry and genetics. Our aim has been to assess the potential presence of evolutionary significant units within the Nephroma parile species complex that may be worthy of recognition at species level. Using phylogenetic analysis of the fungal DNA-barcode marker (ITS) in combination with studies of morphology and chemistry, we discover two distinct lineages in the N. parile species complex. For the strongly supported clade that corresponds to chemotype II, we describe the new species Nephroma orvoi. The new species is known from Norway, Sweden, Finland, Switzerland, Canada (Alberta and British Columbia), USA (Washington), and Greenland.publishedVersio

Fusing simulated GEDI, ICESat-2 and NISAR data for regional aboveground biomass mapping

Accurate mapping of forest aboveground biomass (AGB) is critical for better understanding the role of forests in the global carbon cycle. NASA's current GEDI and ICESat-2 missions as well as the upcoming NISAR mission will collect synergistic data with different coverage and sensitivity to AGB. In this study, we present a multi-sensor data fusion approach leveraging the strength of each mission to produce wall-to-wall AGB maps that are more accurate and spatially comprehensive than what is achievable with any one sensor alone. Specifically, we calibrate a regional L-band radar AGB model using the sparse, simulated spaceborne lidar AGB estimates. We assess our data fusion framework using simulations of GEDI, ICESat-2 and NISAR data from airborne laser scanning (ALS) and UAVSAR data acquired over the temperate high AGB forest and complex terrain in Sonoma County, California, USA. For ICESat-2 and GEDI missions, we simulate two years of data coverage and AGB at footprint level are estimated using realistic AGB models. We compare the performance of our fusion framework when different combinations of the sparse simulated GEDI and ICEsat-2 AGB estimates are used to calibrate our regional L-band AGB models. In addition, we test our framework at Sonoma using (a) 1-ha square grid cells and (b) similarly sized irregularly shaped objects. We demonstrate that the estimated mean AGB across Sonoma is more accurately estimated using our fusion framework than using GEDI or ICESat-2 mission data alone, either with a regular grid or with irregular segments as mapping units. This research highlights methodological opportunities for fusing new and upcoming active remote sensing data streams toward improved AGB mapping through data fusion.</p