Controlled source electromagnetic (CSEM) geophysics has been used with a fair amount of success in near surface hydrogeological studies. Recently, these investigations have been conducted frequently in human impacted field sites containing cultural conductors such as metal fences and buried pipes. Cultural noise adds an element of complexity to the geological interpretation of this type of data. This research investigates the influence of mutual induction between two buried targets in a CSEM experiment. In particular, it looks at the mutual coupling between a buried cultural conductor and a geological heterogeneity. We attempt to isolate the Hz field induced by tertiary currents in targets caused by mutual coupling. This is achieved with a Texas A&M 3D CSEM finite element code, which calculates the secondary Hz fields emanating from a target buried in a halfspace. Buried geological targets and cultural conductors are modeled as volumetric slabs embedded in a halfspace. A series of models have been simulated to study the effect of varying parameters such as target conductivity, transmitter location and shape of a target on the mutual inductance. In each case, the secondary Hz field is calculated for a model with two slabs, and two models with individual slabs. The mutual coupling is calculated by removing the secondary fields from the individual slab models from the response of a two slab model. The calculations of mutual inductance from a variety of such models suggests a complicated interaction of EM fields between the two targets. However, we can explain most of these complexities by adapting a simple approach to Maxwell’s equations. Although the tertiary Hz field is complicated, it may be useful in the characterization and delineation of electrical heterogeneities in the subsurface, which can then be related to geological features such as fractures or joints. It is seen that the most important factor affecting the mutual coupling is the host conductivity. The results have also shown that mutual coupling is very sensitive to transmitter (TX) location, especially when the TX is positioned near one of the targets.

Acoustic point-source reflection from an unperturbed seabed with a continuously varying density and sound speed profile in a fluid-like sediment layer overlying an elastic basement is considered in this paper. This fundamental problem has illuminated many interesting phenomena about the effects of sediment stratification on acoustic wave interactions with the seabeds. The analysis employs the analytical solutions for the Helmholtz equation in the sediment layer, in which the density and the sound speed are, respectively, described by three kinds of geological models. The results have demonstrated that the effects of sediment stratifacation are confined in a region in range, where the reflection field is dominated by the reflected ray bundles containing ray components with the grazing angles which are neither too steep nor too shallow. The effects of many other factors, such as frequency, sediment thickness, basement elasticity, on the reflection fields are investigated, in particular, the interface wave component may become important in the region close to the seabed, if the sediment thickness is relatively thin in comparison with the acoustic wave length.

Fachhochsch. Oldenburg/Ostfriesland/Wilhelmshaven, Diplomarbeit--Oldenburg, 2007.

This study has been performed with an aim to provide an insight into how Node.js is used and the Node.js technology adaptation in the open source community. This research displays the diversity of Node.js and can inspire the reader to further development or continued research. Studies into different usages of Node.js have been missing in academic research and therefore this study gives a new, important insight into this technology. The authors used the exploratory case study methodology. For data collection, the authors created a JQuery and HTML script that fetched the desired dataset from Github and that were used as a static base for the study. Based on the usage areas extracted from the literature study, the authors specified different categories of usage. The dataset was manually investigated and placed into the categories, if they were relevant. The results show that web applications is by far the most well represented category with over 50% of all usages falling into this category. Network applications and Web servers come in at second and third position with 14% and 13% respectively. This study provided further categories and the authors could generate a set of diagrams, showing a trend on how the different usage areas changed from 2010 to 2015.

Tandem source-channel coding is proven to be optimal by Shannon given unlimited delay and complexity in the coders. Under low delay and low complexity constraints, joint source-channel coding may achieve better performance. Although digital joint source-channel coding has shown a noticeable gain in terms of reconstructed signal quality, coding delay, and complexity, it suffers from the leveling-off effect. However, analog systems do not suffer from the leveling-off effect. In this thesis, we investigate the advantage of analog systems based on the Shannon-Kotel’nikov approach and hybrid digital-analog coding systems, which combine digital and analog schemes to achieve a graceful degradation/improvement over a wide range of channel conditions. First, we propose a low delay and low complexity hybrid digital-analog coding that is able to achieve high (integer) expansion ratios ( >3). This is achieved by combining the spiral mapping with multiple stage quantizers. The system is simulated for a 1 : 3 bandwidth expansion and the behavior for a 1 : M (with M an integer >3) system is studied in the low noise level regime. Next, we propose an analog joint source-channel coding system that is able to achieve a low (fractional) expansion ratio between 1 and 2. More precisely, this is an N : M bandwidth expansion system based on combining uncoded transmission and a 1 : 2 bandwidth expansion system (with N < M < 2N).Finally, a 1 : 2 analog bandwidth expansion system using the (Shannon-Kotel’nikov) Archimedes’ spiral mapping is used in the compressed sensing context, which is inherently analog, to increase the system’s immunity against channel noise. The proposed system is compared to a conventional compressed sensing system that assumes noiseless transmission and a compressed sensing based system that account for noise during signal reconstruction. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2011-07-29 02:30:11.978

In this thesis, we introduce three new approaches for solving the single source shortest path (SSSP) problem in nearly acyclic directed graphs, and algorithms based on these approaches. In the first approach, we extend a technique of strongly connected components (sc-components) decomposition by Takaoka [23], and the generalized decomposition approach is called a higher-order decomposition. According to Takaoka's definition of acyclicity, the degree of cyclicity of a graph G, cyc(G), is defined by the maximum cardinality of the strongly connected components of G. Based on the higher-order decomposition, we give a generalization of Takaoka's definition of acyclicity. That is, the degree of cyclicity cych(G) is the maximum cardinality of the hth order strongly connected components of G, where h is the number of times that the graph has been decomposed. Then, the original definition introduced by Takaoka [23] can be presented as: The degree of cyclicity cyc(G) is the maximum cardinality of the 1th order strongly connected components of G. The second approach presents a new method for measuring acyclicity based on modifications to two existing methods. In the new method, we decompose the given graph into a 1-dominator set, which is a set of acyclic subgraphs, where each sub-graph is dominated by one trigger vertex. Meanwhile we compute sc-components of a degenerated graph derived from triggers. Using this preprocessing, we can efficiently compute the single source shortest paths (SSSPs) for nearly acyclic graphs in O(m + r logl ) time, where r is the size of the 1-dominator set, and l is the size of the largest sc-component. In the third approach, we modify the concept of a 1-dominator set to that of a 1-2-dominator set, and achieve O(m + r²) time to compute a 1- 2-dominator set in a graph. Each of acyclic sub-graphs obtained by the 1-2-dominator set are dominated by one or two trigger vertices cooperatively. Such sub-graphs are potentially larger than those decomposed by the 1-dominator set. Thus fewer trigger vertices are needed to cover the graph, that is, rʹ ≤ r, where rʹ is the number of triggers in the 1-2-dominator set. When rʹ is much smaller than r, we can efficiently compute SSSPs in O(m + rʹlogrʹ) time.

Marine seismic source arrays are directional. Source directivity is used to attenuate coherent noise, but primary reflected data may be degraded. Source directivity is ignored in a standard processing sequence, so directional source signature deconvolution may be required. In the frequency-wavenumber (f-k) directional deconvolution method, a filter is calculated from far-field source signatures and is applied to the f-k transform of common-receiver gathers. Reflections on common-receiver gathers are often spatially aliased, and this causes practical problems with the technique. Directional deconvolution may also be performed in combination with prestack migration because the prestack Kirchhoff summation migration operator is a function of source take-off angle. The constant-offset section is deconvolved separately with a full range of filters for source signatures radiated in different directions; then the migration summation operator sums across the deconvolved sections, selecting the section which has been deconvolved for the correct source signature at each point. Physical model data, which were acquired over simple models using a directional source, are used to evaluate directional deconvolution assuming constant velocity. Reflector continuity and resolution are improved by using directional deconvolution. Directional deconvolution combined with prestack migration is extended to media in which the velocity varies with depth, and is applied to two datasets from the Southern North Sea. The second dataset, which has shallow steeply dipping reflectors, is improved by using directional deconvolution. Directional deconvolution may be combined with a Kirchhoff migration technique which assumes a linear velocity-depth model. Results are superior to conventional Kirchhoff migration because ray bending is honoured. Directional deconvolution cannot synthesise fully point-source equivalent data from data acquired with a source array without excessive noise amplification. Source arrays with a short in-line dimension should be used where possible. For data which have been acquired with a long source array, directional deconvolution is desirable.

Based on collaboration rather than competition, Open Source Software provides a new dynamic in the development and use of software systems. As such it has the potential to make a significant legal, social and economic impact on the industry. While its origins trace back to the start of the software industry, the recent success of the Linux operation system, Apache web server or the Mozilla Firefox Internet Browser provide impetus to the growth of interest in this movement. However, while a number of studies have been conducted on its development, few have provided empirical evidence of its adoption within the South East Asian context. This study aims to investigate factors leading to the adoption of Open Source Software in Singaporean Organisations. The research has found that the adoption of Open Source Software is driven by the perception of a cost advantage. The organisations interviewed have acknowledged cost as being one of their biggest concerns and top priorities. While costs were stated to be of major concern to the organisations, objective measures of cost such as Total Cost of Ownership (TCO) and Return on Investment (ROI) were rarely used by the organisations studied. This perception of cost saving is found to be led by industry sources such as publications, conferences and websites. The next significant finding is the need for increased open source software skills in the industry. One of the major drivers of Open Source Software Adoption in the organisations is that they posses pre-existing skills in Open Source Software use. This enables them to better mitigate risk and to lower their training costs. The final principal finding is that Open Source Software appears to be used mainly in systems infrastructure applications. Organisations reported a large degree of satisfaction including increased stability, scalability and cost effectiveness. Issues remain with Open Source Software’s manageability, its quality of support and ease of use.

Zugl.: Heidelberg, Univ., Diplomarbeit, 2006 / Hergestellt on demand

Thesis (M.S. - Department of Soil, Water and Environmental Science) - University of Arizona. / Includes bibliographical references (leaves 80-81