A 3D Time Domain CSEM Forward Modeling Code using custEM and FEniCS

A new 3D time domain CSEM forward modeling code TDcustEM built upon the recently published open-source frequency domain code custEM and the open-source finite element toolbox FEniCS is presented. The transformation of the frequency domain data provided by custEM is performed by a Fast Hankel Transform using 80 digital filter coefficients. 3D edge-based tetrahedral meshes generated by TetGen facilitate the calculation of syn- thetic data using topography, arbitrary source geometries and complex subsurface structures. To ensure precision and reliability of the new algorithm, calculated results of different CSEM setups and electromagnetic field components are cross-validated against analytic solutions as well as 1D and 3D time domain modeling codes. Certain modeling studies are conducted regarding possible interpolation and extrapola- tion techniques to reduce the number of necessary frequencies and therefore the compu- tational runtime, which is still an issue of convolutional time domain CSEM approaches. Additional modeling studies showed the importance of precise receiver positioning for measuring the horizontal components of the time derivative of the magnetic field. As the present thesis is embedded in the Collaborative Research Centre 806 – Our Way to Europe, three sedimentary deposits in the East African Rift Valley were subject to mul- tidimensional TEM surveys in the framework of this project. Common 1D (EMUPLUS) as well as laterally and spatially constrained (AarhusInv) in- version techniques were applied to the TEM field data. Sediment thicknesses as well as stratigraphic sequences of the investigated sedimentary basins were derived. An extensive 3D modeling study of one of the target areas representing a volcanically-formed basin including topography was performed using the newly developed TDcustEM code

Evaluation of three approaches for simulating 3D time-domain electromagnetic data

We implemented and compared the implicit Euler time-stepping approach, the inverse Fourier Transform-based approach, and the Rational Arnoldi method for simulating 3D transient electromagnetic data. We utilize the finite-element method with unstructured tetrahedral meshes for the spatial discretization supporting irregular survey geometries and anisotropic material parameters. Both, switch-on and switch-off current waveforms, can be used in combination with direct current solutions of Poisson problems as initial conditions. Moreover, we address important topics such as the incorporation of source currents and opportunities to simulate impulse as well as step response magnetic field data with all approaches for supporting a great variety of applications. Three examples ranging from simple to complex real-world geometries and validations against external codes provide insight into the numerical accuracy, computational performance, and unique characteristics of the three applied methods. We further present an application of logarithmic Fourier transforms to convert transient data into the frequency domain. We made all approaches available in the open-source Python toolbox custEM, which previously supported only frequency-domain electromagnetic data. The object-oriented software implementation is suited for further elaboration on distinct modeling topics and the presented examples can serve for benchmarking other codes

Isotropic clustering for hierarchical radiosity - implementation and experiences

Although Hierarchical Radiosity was a big step forward for finite element computations in the context of global illumination, the algorithm can hardly cope with scenes of more than medium complexity. The reason is that Hierarchical Radiosity requires an initial linking step, comparing all pairs of initial objects in the scene. These initial objects are then hierarchically subdivided in order to accurately represent the light transport between them. Isotropic Clustering, as introduced by Sillion, in addition creates a hierarchy above the input objects. Thus, it allows for the interaction of complete clusters of objects and avoids the costly initial linking step. In this paper, we describe our implementation of the isotropic clustering algorithm and discuss some of the problems that we encountered. The complexity of the algorithm is examined and clustering strategies are compared

Lithium Content of 160 Beverages and Its Impact on Lithium Status in Drosophila melanogaster

Lithium (Li) is an important micronutrient in human nutrition, although its exact molecular function as a potential essential trace element has not yet been fully elucidated. It has been previously shown that several mineral waters are rich and highly bioavailable sources of Li for human consumption. Nevertheless, little is known about the extent in which other beverages contribute to the dietary Li supply. To this end, the Li content of 160 different beverages comprising wine and beer, soft and energy drinks and tea and coffee infusions was analysed by inductively coupled plasma mass spectrometry (ICP-MS). Furthermore, a feeding study in Drosophila melanogaster was conducted to test whether Li derived from selected beverages changes Li status in flies. In comparison to the average Li concentration in mineral waters (108 µg/L; reference value), the Li concentration in wine (11.6 ± 1.97 µg/L) and beer (8.5 ± 0.77 µg/L), soft and energy drinks (10.2 ± 2.95 µg/L), tea (2.8 ± 0.65 µg/L) and coffee (0.1 ± 0.02 µg/L) infusions was considerably lower. Only Li-rich mineral water (~1600 µg/L) significantly increased Li concentrations in male and female flies. Unlike mineral water, most wine and beer, soft and energy drink and tea and coffee samples were rather Li-poor food items and thus may only contribute to a moderate extent to the dietary Li supply. A novelty of this study is that it relates analytical Li concentrations in beverages to Li whole body retention in Drosophila melanogaster

Computing the bounded subcomplex of an unbounded polyhedron

We study efficient combinatorial algorithms to produce the Hasse diagram of the poset of bounded faces of an unbounded polyhedron, given vertex-facet incidences. We also discuss the special case of simple polyhedra and present computational results.Comment: 16 page

Tackling Cost Drivers of Maritime UXO Surveys

During UXO survey and clearance campaigns, a large number of false positive target points drive costs and efforts. This paper presents three approaches for the improvement of maritime UXO surveys that allow for the immediate execution of target point investigations. (1) Data quality factors were generated to help determine, whether UXO can be detected in the acquired multibeam echosounder (MBES), side-scan sonar, subbottom profiler and magnetic data. (2) Artificial intelligence was developed to rapidly identify target points with potential UXO objects in MBES data. (3) Magnetometers and a high-resolution camera were integrated on an AUV to allow for autonomous target point investigation, that does not require permanent supervision of survey personnel

Between umbra and penumbra

International audienceComputing shadow boundaries is a difficult problem in the case of non-point light sources. A point is in the umbra if it does not see any part of any light source; it is in full light if it sees entirely all the light sources; otherwise, it is in the penumbra. While the common boundary of the penumbra and the full light is well understood, less is known about the boundary of the umbra. In this paper we prove various bounds on the complexity of the umbra and the penumbra cast by a segment or polygonal light source on a plane in the presence of polygon or polytope obstacles. In particular, we show that a single segment light source may cast on a plane, in the presence of two triangles, four connected components of umbra and that two fat convex obstacles of total complexity n can engender Omega(n) connected components of umbra. In a scene consisting of a segment light source and k disjoint polytopes of total complexity n, we prove an Omega(nk^2+k^4) lower bound on the maximum number of connected components of the umbra and a O(nk^3) upper bound on its complexity. We also prove that, in the presence of k disjoint polytopes of total complexity n, some of which being light sources, the umbra cast on a plane may have Omega(n^2k^3 + nk^5) connected components and has complexity O(n^3k^3). These are the first bounds on the size of the umbra in terms of both k and n. These results prove that the umbra, which is bounded by arcs of conics, is intrinsically much more intricate than the full light/penumbra boundary which is bounded by line segments and whose worst-case complexity is in Omega(n alpha(k) +km +k^2) and O(n alpha(k) +km alpha(k) +k^2), where m is the complexity of the polygonal light source

Boron Contents of German Mineral and Medicinal Waters and Their Bioavailability in Drosophila melanogaster and Humans

Scope Boron is a trace element that naturally occurs in soil, making mineral and medicinal water important contributors to overall intake. Thus, in a systematic screening, the mean boron concentrations of 381 German mineral and medicinal waters are determined. Methods and results Boron concentrations in mineral and medicinal waters are analyzed by inductively coupled mass spectrometry (ICP-MS). Highest boron values find in waters from the southwest of Germany. The boron content of the waters is positively correlated with the concentration of most other analyzed bulk elements, including calcium, potassium, magnesium, and sodium. Mineral waters with either low (7.9 µg L-1 ), medium (113.9 µg L-1 ), or high (2193.3 µg L-1 ) boron content are chosen for boron exposure experiments in fruit flies (Drosophila melanogaster) and humans. In flies, boron-rich mineral water significantly increases boron accumulation, with the accumulation predominantly occurring in the exoskeleton. In humans, serum boron and 24-h urinary boron excretion significantly increase only in response to the intake of boron-rich mineral water. Conclusion Overall, the current data demonstrate that mineral and medicinal waters vary substantially in the content of boron and that boron-rich mineral water can be used to elevate the boron status, both in flies and humans

Brane Decay of a (4+n)-Dimensional Rotating Black Hole. II: spin-1 particles

The present works complements and expands a previous one, focused on the emission of scalar fields by a (4+n)-dimensional rotating black hole on the brane, by studying the emission of gauge fields on the brane from a similar black hole. A comprehensive analysis of the particle, energy and angular momentum emission rates is undertaken, for arbitrary angular momentum of the black hole and dimensionality of spacetime. Our analysis reveals the existence of a number of distinct features associated with the emission of spin-1 fields from a rotating black hole on the brane, such as the behaviour and magnitude of the different emission rates, the angular distribution of particles and energy, the relative enhancement compared to the scalar fields, and the magnitude of the superradiance effect. Apart from their theoretical interest, these features can comprise clear signatures of the emission of Hawking radiation from a brane-world black hole during its spin-down phase upon successful detection of this effect during an experiment.Comment: 35 pages, 19 figures, Latex fil