<p>Context awareness is an important aspect of pervasive and ubiquitous computing. By utilizing contextual information gathered from the environment, applications can adapt to the user’s specific situation. In this thesis, user context is used to automatically discover multimedia devices and services that can be used by a mobile Session Initiation Protocol (SIP) user agent. The location of the user is captured using various sensing technologies to allow users of our SIP user agent to interact with network attached projectors, speakers, and cameras in a home and office environment. In order to determine the location of the user, we have developed and evaluated a context aggregation framework that gathers and analyzes contextual information from various sources such as passive infrared sensors, infrared beacons, light intensity, and temperature sensors. Once the location of the user is determined, the Service Location Protocol (SLP) is used to search for services. For this purpose, we have implemented a mobile SLP user agent and integrated it with an existing SIP user agent. The resulting mobile SIP user agent is able to dynamically utilize multimedia devices around it without requiring the user to do any manual configuration. This thesis also addressed the challenge of building trust relationship between the user agent and the multimedia services. We propose a mechanism which enables the user agent authenticate service advertisements before starting to redirect media streams. The measurements we have performed indicate that the proposed context aggregation framework provides more accurate location determination when additional sensors are incorporated. Furthermore, the performance measurements indicate that the delay incurred by introducing context awareness to the SIP user agent is acceptable for a small deployment such as home and office environment. In order to realize large scale deployments, future investigations are recommended to further improve the performance of the framework. Keywords: SIP, context-awareness, service discovery, trust establishment</p>

<p>Four samples of galvanized steel armour for sub sea power cables are tested with an electric steel tester. The samples exhibit different remanence magnetization and permeability. The effects of permeability on loss in sub sea cables is found to be insignificant. Slight increase of conductor inductance due to increase in permeability of armour wires is observed. Mutual cancellation of inductance between circuits that are twisted opposite to each other, or with respect to one circuit, is confirmed with laboratory tests and measurements on full scale sub sea power cables. The parameters of one cable is calculated using IEC’s analytical approach and found to be inaccurate for conductor resistance. The Calculations places 22% of total cable loss in the armour. Measurements on two sub sea cables and analysis using finite element method contradict the calculated armour loss. Parameters for two sub sea power cables are calculated based on measurements performed on the actual cables. The calculated values are compared with values computed using finite element analysis. Derived physics from laboratory experiments and measurements on the cables is applied in finite element analysis and found to be accurate compared with calculated values from measurements and computed values using Flux 2.5D.</p>

Despite the availability of distance education technology, Oregon State University Extension Service educators have made limited use of this equipment for delivery of educational programs to clients of the state's 36 county Extension Service offices. Some Extension educators may be hesitant to use distance technology because they are unsure whether clients will accept distance delivered programming. This project explored this issue, framed in the question: Is distance education received favorably or unfavorably by volunteer adult learners? A volunteer learner is defined as one who seeks to gain knowledge while interacting with others who share like interests, a description that fits many Extension Service clients. Other questions in the project were: How much do volunteer learners learn from distance delivered instruction compared to traditional instruction? and How much do volunteer learners interact with instructors and each other in the distance classroom compared to the traditional classroom? Participants in the project were adults taking part in the MG training program in February 1993 in five Oregon counties. These adult learners participated in two 90-minute instructional segments; part one, 'Landscaping for Wildlife' and part two, 'Controlling Wildlife in the Home Landscape.' Part one was delivered via satellite delivery. Part two was delivered to participants in person by the instructor. In both parts, learners were pre- and post-tested on the subject matter presented. Learners also completed opinion surveys for each session. Audio tapes were made of each session for analysis of learner-learner, and learner-instructor interaction. Also, the Extension agents acting as downlink site coordinators in the project were interviewed to assess their opinions of the distance education session. Comparison of the data indicate that learners felt the quality of learning experience in both modes of program delivery was about equal. Also, the testing component indicated that participants learned about the same amount of material. Interaction analysis results indicated little or no difference in the amount of interaction in both the traditional and distance sessions. The results show that the effectiveness of distance delivery of Master Gardener training instruction to adult learners is equivalent to traditional delivery of training instruction for participants in this study. / Graduation date: 1997

ABSTRACT AN ANALYSIS OF THE DISCIPLESHIP STRATEGY OF ROBERT EMERSON COLEMAN John Thomas Green IV, Ph. D. The Southern Baptist Theological Seminary, 2012 Chair: Dr. Charles E. Lawless, Jr. This dissertation examines the discipleship strategy of Robert Emerson Coleman. Chapter 1 introduces the ministry and work of Robert Coleman. The chapter also discusses the call to discipleship given by Jesus Christ in the Great Commission and the need for the local church to effectively disciple its members. Chapter 2 presents a biography of Coleman. This chapter highlights his conversion and call to ministry. It also includes details of his ministry as a pastor, professor, and author. Chapter 3 provides an historical analysis of Coleman's discipleship strategy. This chapter notes influences upon Coleman's strategy, including the work of John Wesley. It also describes the historical context in which Coleman's strategy was developed, particularly the states of the evangelical church and the Methodist church. Chapter 4 addresses Coleman's practice of discipleship in his ministry. The chapter includes insight into Coleman's personal discipleship, as well as, his discipleship of his family, churches that he has pastored, and students that he led while teaching. Chapter 5 offers a biblical analysis of Coleman's discipleship strategy, dissecting Scripture used by Coleman to support his principles of discipleship outlined in The Master Plan of Evangelism. The chapter also notes several other works by Coleman to show how he consistently communicated his discipleship strategy. The conclusion offers application of Coleman's strategy in the North American church. Positive contributions of Coleman's work for discipleship in the local church are enumerated. Challenges to implementing his strategy are also shared. This work contends that Coleman has provided a biblical and effective model for discipleship in The Master Plan of Evangelism. His strategy is faithful to the model of Christ with His disciples. Coleman's work provides helpful contributions to discipleship in the local church though it has its challenges in implementation. Although Coleman's discipleship ministry has been conducted largely outside of the local church, his strategy can and should be used in the local church for discipleship.

In this master thesis the theory and practical use of modal analysis is explained, giving an introduction to the possibilities of modal analysis. The master thesis starts with a look at wind power and the design of a modern wind turbine. Two models, one for constant wind speed wind turbines and one for variable speed wind turbines, are presented. An example shows how modal analysis can be utilized to evaluate a network's dynamic stability. Simulations are performed on a two-area network where different wind power models are tested and compared. A two-mass model is used to model a constant wind turbine. The model consists of an asynchronous generator, a turbine, and a low speed shaft with a tensional stiffness. The model representing the variable speed wind turbine is based on a DFIG model included in the simulation software. The two-area network consists of two areas connected together through a long line between Bus 5 and Bus 6. Area 1 has two production sources, one placed in Bus 1 and one placed in Bus 2. The second area represents a large network modelled as a very large synchronous generator with a high inertia. The calculations have showed how modal analysis can be used to evaluate a system by using linearized differential equations and how the systems robustness against small disturbances can be altered by changing the systems parameters. Simulations have verified that a two-mass model must be used when modelling a constant speed wind turbine. The inertia of the turbine will greatly influence the model's behaviour and must therefore be included in the model. Eigenvalues analysis performed during different wind speeds have documented that wind power will not become less stable towards small disturbances when operated at low wind speed conditions.

With the recent developments in semiconductors and control equipment, Voltage Source Converter based High Voltage Direct Current (VSC-HVDC) has attracted the growing interest of researchers. The use of VSC technology and Pulse Width Modulation (PWM) has a number of potential advantages: short circuit current reduction; rapid and independent control of the active and reactive power, etc. With such highly favourable advantages, VSC-HVDC is definitely going to be a large part of future transmission and distribution systems. HVDC technology based on VSC technology has been an area of growing interest recently because of its suitability in forming a transmission link for transmitting bulk amount of wind power. This thesis deals with the control of VSC-HVDC. The objective of the work is to understand the control structure of the VSC-HVDC system, and establish the tuning criteria for the PI controllers of the converter controllers. A model of a VSC based dc link using PWM Technology is developed. A mathematical model of the control system based on the relationships between voltage and current is described for the VSC. A control system is developed combining an inner current loop controller and outer dc voltage controller. The vector control strategy is studied and corresponding dynamic performance under step changes and system fault is investigated in PSCAD/EMTDC simulation package. The simulation results verify that the model can fulfill bi-directional power transfers, fast response control and that the system has good steady state performance. The controller parameters tuned according to the developed tuning criteria is found to provide acceptable system performances.

The North Sea has a vast amount of wind energy with largest energy per area densities located about 100-300Km of distance from shore. Should this energy be tapped by offshore wind farms, HVDC transmission would be the more feasible solution at such long subsea distances. On the other hand Norwegian oil/gas platforms in the North Sea use electricity from gas fired turbines at offshore sites. These gas turbines have much less efficiency than onshore generation of electricity and also release large amounts of green house gases. Therefore supplying the platforms with power from onshore transmitted by HVDC will result in benefits both from economic and environmental protection perspectives. Given these two interests for HVDC in the Norwegian offshore, the use of Multiterminal HVDC (MTDC) is a potential solution for the integration of the wind farms and oil/gas platforms into the onshore grid system. Hence, this thesis focuses on the operation and control of MTDC systems. The MTDC system is desired to be capable of interfacing with all kinds of AC grids namely: stiff, weak and passive grid systems. Compared to the classical thyristor based converter, VSC has several features that make it the most suitable converter for making of MTDC, the most decisive being its ability of bidirectional power transfer for fixed voltage polarity. VSC-HVDC is also suitable for implementing control of active and reactive current in synchronously rotating d-q reference frame which in turn results in decoupled control of active and reactive power. In the first two chapters of the thesis literatures are reviewed to understand operation of VSC and its use in HVDC systems. Afterwards controllers are developed for different AC connections (stiff, weak and passive) and for different DC parameter (power, DC voltage) control modes. DC voltage and active power control are implemented by active current control and AC voltage and reactive power control are achieved by reactive power compensation. Tuning techniques for the PI controllers are discussed and used in the simulation models. Finally control techniques for reliable operation of MTDC are developed. In order to validate theoretical arguments, each of the control schemes was developed and simulated in PSCAD/EMTDC simulation software. Simulation results indicate that satisfactory performance of VSC-HVDC was obtained with the proposed active/reactive power controllers, AC/DC voltage controllers, frequency and DC overvoltage controllers. For coordinated multiterminal operation, voltage margin control method and DC voltage droop characteristic were used. These are control methods based upon realization of desired P-UDC characteristic curves of converter terminals. Four-terminal MTDC system with different AC grid connections was used to study the multiterminal operation. Simulations have shown that voltage margin control method results in reliable operation of MTDC during loss of a terminal connection without the need for communication between terminals. The use of DC voltage droop control along with voltage margin control enabled load sharing among VSC-HVDC terminals in DC voltage control mode according to predetermined participation factor.

Direct electrical heating (DEH) of pipelines is a flow assurance method that has proven to be a good and reliable solution for preventing the formation of hydrates and wax in multiphase flow lines. The technology is installed on several pipelines in the North Sea and has become StatoilHydros preferred method for flow assurance. Tyrihans is the newest installation with 10 MW DEH for a 43 km pipline. However, the pipeline represents a considerable single-phase load which makes the power system dependent on a balancing unit for providing symmetrical conditions. This limits the step out distance and is not suitable for subsea installation. Aker Solutions has proposed several specially connected transformers for subsea power supply of DEH systems, Scott-T being one of them. The Scott-T transformer is a three-to-two-phase transformer which provides balanced electrical power between the two systems when the two secondary one-phase loads are equal. By implementing this transformer, it can be possible to install the power supply subsea as there is no need for a balancing unit. In addition, the system may be applicable for long step out distances. This is because the pipeline is inductive and can use the reactive power produced by the long cable which also can increase the critical cable length. There are however some limitations on this system using the Scott-T transformer. There is a large variation in the magnetic permeability between individual joints of the pipeline. This can result in different load impedance of the two pipe sections connected to the Scott-T transformer. The result is unbalance in the power system. The method of symmetrical components is applied to investigate the behavior during unbalanced loading of the Scott-transformer. The relationship between the negative- and the positive sequence component of the current is used to express the degree of unsymmetry. For the simulations in SIMPOW, the Scott-T transformer is modelled by the use of Dynamic Simulation Language. The simulations on the DSL model give correct and reliable results for analysing the the degree of unsymmetry in the Scott-T transformer. When the load impedance of one pipe section is varied, simulation proves that it can change between 0.75 and 1.34 per unit of the other pipe impedance. The Scott-T transformer does still provide electrical power between the two systems which is below the limit for the degree of unsymmetry (15%). Case 1 and Case 2 introduce two possible configurations for a subsea DEH system with the Scott-T transformer implemented. The configurations include an onshore power supply which is connected to a subsea power system for direct electrical heating and a subsea load at the far end of the subsea cable. The pipeline in Case 1 is 100 km long and is divided into two pipe sections of 50 km which are connected to a Scott-T transformer. The pipeline in Case 2 is 200 km long and is divided into four pipe sections of 50 km each. There are two Scott-T transformers in Case 2. For normal operation of the subsea load (50 MW, cosfi=0.9) and heating the pipe content from the ambient sea emperature, the results indicate that tap changers are necessary to keep the Scott-T transformers secondary terminal voltage at 25 kV. This meets the requirement in both cases for heating the pipe content from 4 to 25 degrees celsius within 48 hours after a shutdown of the process. The degree of unsymmetry is zero for both cases when the system is operated as normal. However, all system simulations indicate that reactive power compensation has to be included for Case 1 as well as for Case 2 in order to have a power factor of unity at the onshore grid connection. The fault scenarios indicate that the degree of unsymmetry is dependent on both the type of fault and the power supply in the system. For Case 1, the relationship (I-/I+) is only of 3.3% in the subsea cable when there is a short-circuit at DEHBUS3, but as much as 87% at the grid connection. The degree of unsymmetry in the Scott-T transformer is then 67%. This is far beyond the limit for maximum negative sequence component of 15%. The significant unsymmetry in the line between the grid and BUS1 is most likely due to the large power delivered to the fault. During the fault, the reactive power delivered to the system increases from 10.6 Mvar to 131.9 Mvar after the fault, but the active power increases only from 75.2 MW to 87.1 MW. This means that it is most likely the reactive power that contributes to the consequent unsymmetry and negative sequence component of the current. There are two Scott-T transformers installed in Case 2. If the DEH system is only heating the pipe section closest to shore (at DEHBUS33), simulations show that the three-phase power system becomes unsymmetric which results in different phase currents. The degree of unsymmetry at the grid connection is 32% when only the pipe section at DEHBUS33 is heated. In addition, the unbalance in the three-phase system caused by SCOTT1 involves unbalance in the SCOTT2 transformer as well. The load voltages are not equal in magnitude and dephased of 90 degrees for this mode, but are 32 kV and 35 kV respectively and dephased of 88 degrees. This concludes a very important behavior of the Scott-T transformer. The simulations conclude that the Scott-T transformer provides symmetrical conditions for both configurations when the two load impedances are equal. However, Case 2 shows an important result when installing two Scott-T transformers in the same system. Unbalanced loading of one of the specially connected transformers gives unsymmetrical conditions in the three-phase system which results in unbalanced load voltages for the other Scott-T transformer. The analysis is limited to the configurations given for Case 1 and Case 2, but shows typical results when an alternative transformer connection is implemented in a DEH system.

There is an increasing amount of power processed through power electronics in the areas of generation interface, energy storage and loads. This increment enables possibilities for improved solutions for efficient generation and use of electric power. Traditionally loads in AC distribution systems have been seen as passive and individual elements rather than active components of the system. An AC distribution system with high percentage of power electronic loads can be susceptible for instability under abnormal operation conditions if the converter controls are not designed for such conditions. This thesis introduces a solution of reactive current control for a constant power load (CPL) in an AC distribution system. A CPL is a load that draws a constant amount of active power without regard to any drops in system voltage. The resistance seen from the AC distribution system to the CPL is known as a negative input resistance which is characteristic for this kind of load. A drop in AC system voltage will result in increased current and vice versa. Hence the resulting resistance will be negative. Negative resistance behaviour is not favourable for system stability and the work has focused on a control of the converter that reduces the instability effect of the load. By controlling the reactive current component to inject current for support of the AC distribution system voltage during faults and other interferences, the load becomes an active participant in the AC distribution system. An AC distribution system has been built in PSCAD/EMTDC. An asynchronous generator and a fixed capacitor are used as distributed generation. The CPL consists of an AC/DC converter and a voltage dependent current source in order to keep constant DC power at the load. Focus has been on the converter control implementing a voltage oriented vector control based on a two phase rotational reference frame. Measurements of current and voltage with different voltage drop levels have been done for comparison of a CPL with and without reactive current control. The simulation example has verified the negative resistance phenomenon of the CPL. Results shows that the AC system voltage is less vulnerable in case of faults if the converter control is designed to inject reactive current into the AC distribution system.

Offshore wind power has proven to be a renewable energy source with a high potential, especially in the North Sea, where an important development is going on. The location of the wind farms tends to move far from the coast to benefit stronger and more constant wind. In the same time, the power output of the wind farm is increasing to several hundreds of MW up to 1 GW. In the European liberalized electricity market, the interconnection of the countries become very important to facilitate the cross-border trade of electricity but also to improve the reliability of the grid. Combining this both aspects into one, a big offshore HVDC grid connecting countries and large wind farms spread allover the North Sea is currently being studied and developed. So in addition of the challenge given by a high penetration of the wind power production in the European power production scheme, new challenges are opened especially for the offshore transmission. This master thesis presents the integration to grid of a single 1 GW or a cluster of wind farms connected to an oil rig with different connection scheme based on HVDC transmission using the Voltage Source Converter (VSC) technology. The connection of the offshore wind farms is done either with a single HVDC transmission or two HVDC transmissions connected to the main grid at two different Points of Common Connection situated in the south-west of Norway. The wind farms are not represented in detail but by a single generator. They are equipped for the simulation with Double Fed Induction Generators (DFIG) to be representative of the reality, almost half of the wind turbines are today equipped with DFIG technology. Two disturbances are used to test the electrical stability of the system: a classical 150ms three fault phase in agreement with the grid code requirements on the ride fault through requirements and 100ms fault leading to the tripping of a line. The impact of using different types of generator is also investigated with the simulation of cluster wind farm where a wind farm is equipped with Fixed Speed Generator (FIG). The emphasis is put on the response of the VSC-converter and to a lesser extent on the behaviour of the wind turbine generator. It is demonstrated the capacity of the VSC-converter to stabilize a small grid alone and to “isolate” a disturbance. The voltage and the frequency offshore are practically unaffected by a fault onshore and vice versa. As expected, it is demonstrated that the multiplication of the VSC-HVDC converter in a grid improves the stability of the system. Finally, it has been noticed that there maybe some interactions if several different types of generators are used. The replacement of a generator by another type inside the wind farm cluster may change completely the dynamic behaviour after a disturbance. Simulations are performed with PSS/E.