Computation of optimized arrays for 3-D electrical imaging surveys

3-D electrical resistivity surveys and inversion models are required to accurately resolve structures in areas with very complex geology where 2-D models might suffer from artefacts. Many 3-D surveys use a grid where the number of electrodes along one direction (x) is much greater than in the perpendicular direction (y). Frequently, due to limitations in the number of independent electrodes in the multi-electrode system, the surveys use a roll-along system with a small number of parallel survey lines aligned along the x-direction. The ‘Compare R' array optimization method previously used for 2-D surveys is adapted for such 3-D surveys. Offset versions of the inline arrays used in 2-D surveys are included in the number of possible arrays (the comprehensive data set) to improve the sensitivity to structures in between the lines. The array geometric factor and its relative error are used to filter out potentially unstable arrays in the construction of the comprehensive data set. Comparisons of the conventional (consisting of dipole-dipole and Wenner-Schlumberger arrays) and optimized arrays are made using a synthetic model and experimental measurements in a tank. The tests show that structures located between the lines are better resolved with the optimized arrays. The optimized arrays also have significantly better depth resolution compared to the conventional array

Adaptive time-lapse optimized survey design for electrical resistivity tomography monitoring

Adaptive optimal experimental design methods use previous data and results to guide the choice and design of future experiments. This paper describes the formulation of an adaptive survey design technique to produce optimal resistivity imaging surveys for time-lapse geoelectrical monitoring experiments. These survey designs are time-dependent and, compared to dipole–dipole or static optimized surveys that do not change over time, focus a greater degree of the image resolution on regions of the subsurface that are actively changing. The adaptive optimization method is validated using a controlled laboratory monitoring experiment comprising a well-defined cylindrical target moving along a trajectory that changes its depth and lateral position. The algorithm is implemented on a standard PC in conjunction with a modified automated multichannel resistivity imaging system. Data acquisition using the adaptive survey designs requires no more time or power than with comparable standard surveys, and the algorithm processing takes place while the system batteries recharge. The results show that adaptively designed optimal surveys yield a quantitative increase in image quality over and above that produced by using standard dipole–dipole or static (time–independent) optimized surveys

A Function Based on Chebyshev Polynomials as an Alternative to the Sinc Function in FIR Filter Design

The sinc function is often used as the basis for the design of discrete linear-phase FIR filters. However the Fourier transform of the truncated sinc function exhibits ripple in the pass band due to the Gibbs phenomenon. This paper introduces an alternative function based on Chebyshev polynomials whose Fourier transform decreases monotonically in the pass band. Furthermore this function features an intrinsic window function with an adjustable parameter influencing the Fourier transform in the transition and stop bands.Comment: 25 pages, 5 figures, 9 tables. Revised to incorporate a comprehensive analysis of the Fourier transform of the proposed alternative to the sinc functio

Recorded captures of American lobster (Homarus Americanus) in Swedish waters and an observation of predation on the European lobster (Homarus Gammarus)

publishedVersio

PCIe Riser Extension Assembly

The PCIe Riser Extension provides geometric flexibility and the capability to expose all PCIe lanes from four processors on a single four socket motherboard to the chassis ends that may be a significant distance away, yet meet the electrical specifications required. The PCIe Riser Extension utilizes standard commercially available connectors and cabling to achieve this task

Adaptive time-lapse optimized survey design for electrical resistivity tomography monitoring

Adaptive optimal experimental design methods use previous data and results to guide the choice and design of future experiments. This paper describes the formulation of an adaptive survey design technique to produce optimal resistivity imaging surveys for time-lapse geoelectrical monitoring experiments. These survey designs are time-dependent and, compared to dipole-dipole or static optimized surveys that do not change over time, focus a greater degree of the image resolution on regions of the subsurface that are actively changing. The adaptive optimization method is validated using a controlled laboratory monitoring experiment comprising a well-defined cylindrical target moving along a trajectory that changes its depth and lateral position. The algorithm is implemented on a standard PC in conjunction with a modified automated multichannel resistivity imaging system. Data acquisition using the adaptive survey designs requires no more time or power than with comparable standard surveys, and the algorithm processing takes place while the system batteries recharge. The results show that adaptively designed optimal surveys yield a quantitative increase in image quality over and above that produced by using standard dipole-dipole or static (time-independent) optimized survey

Optimization of orthogonal separations for the analysis of oligonucleotides using 2D-LC

Oligonucleotides are commonly analysed using one dimensional chromatography (1D-LC) to resolve and characterise manufacturing impurities, structural isomers and (in respect to emerging oligonucleotide therapeutics) drug substance and drug product. Due to low selectivity and co-elution of closely related oligonucleotides using 1D-LC, analyte resolution is challenged. This leads to the requirement for improved analytical methods. Multidimensional chromatography has demonstrated utility in a range of applications as it increases peak capacity using orthogonal separations, however there are limited studies demonstrating the 2D-LC analysis of closely related oligonucleotides. In this study we optimised OGN size and sequence based separations using a variety of 1D-LC methods and coupled these orthogonal modes of chromatography within a 2D-LC workflow. Theoretical 2D-LC workflows were evaluated for optimal orthogonality using the minimum convex hull metric. The most orthogonal workflow identified in this study was ion-pair reversed phase using tributylammonium acetate (IP-RP-TBuAA) coupled with strong anion exchange in conjunction with sodium perchlorate (SAX-NaClO4) at high mobile phase pH. We developed a heart-cut (IP-RP-TBuAA)-(SAX-NaClO4) 2D-LC method for analysis of closely related size and sequence variant OGNs and OGN manufacturing impurities. The 2D-LC method resulted in an increased orthogonality and a reduction in co-elution (or close elution). Application of a UV based reference mapping strategy in conjunction with the 2D-LC method demonstrated a reduction in analytical complexity by reducing the reliance on mass based detection methods

Livestock Raiding Among the Pastoral Turkana of Kenya:

Summaries The long?persisting and erroneous conception of famine among the pastoral Turkana of Kenya as an essentially ‘drought?driven’ event has given way to growing recognition today of the key role which livestock raiding plays in the breakdown of coping strategies. However, this article argues that the phenomenon of cattle raids per se is not the problem. Rather it is the fashion in which raiding has been transformed over the years, from a quasi?cultural practice with important livelihood?enhancing functions, into more predatory forms driven by an economic logic and modern forms of violence. This article seeks to understand predatory raiding and its effects in terms of the changing functions which raiding serves within pastoral society and, increasingly, outside it. The article uses a model of armed conflict and livelihood vulnerability to illustrate how violence and the threat of violence interact with drought to undermine the coping strategies of herders

Fulani cattle productivity and management in the Kachia grazing reserve, Nigeria

Kachia Grazing Reserve (KGR) in northern Nigeria was home to some 10,000 Fulani pastoralists and their 40,000 cattle in June 2011. This study examines productivity and management of cattle belonging to livestock keepers within the reserve before and after a mass immigration event when 3,000 refugees moved into the reserve with their cattle to escape inter-community violence during May 2011. Data, on livestock management strategies (transhumance) and production parameters (herd size, composition, fertility, dynamics), were collected in March, June and October 2011.Cattle productivity in KGR is geared to supporting Fulani households while maintaining herd wealth. High offtake of young animals, especially the selling of heifers, was an unusual finding and may indicate that KGR pastoralists have been restricting their herd size voluntarily as well as limiting milk production to household requirements. This is probably due to the absence of a commercial milk market and a higher reliance on the sale of young stock to meet cash needs.Despite the widespread perception that grazing reserves are promoting sedentarisation of Fulani pastoralists and curbing transhumance, the inhabitants of the KGR were observed to practise wide-ranging transhumance both during wet and dry seasons driven by the limited availability of grazing. Some households selected a sub-sample of animals for transhumance rather than sending their whole herd, and some maintained cattle on alternative land-holdings outside the reserve. KGR households described modifying their usual transhumance practices in response to the mass immigration event and insecurity.Nevertheless, the herd demography results from this study are broadly similar to data obtained from other studies over the past 40 years, indicating that productivity and management practices have remained relatively unchanged