Development and characterization of a distributed measurement system for the evaluation of voltage quality in electric power networks

The research activity carried out during the PhD course in Electrical Engineering belongs to the branch of electric and electronic measurements. The main subject of the present thesis is a distributed measurement system to be installed in Medium Voltage power networks, as well as the method developed to analyze data acquired by the measurement system itself and to monitor power quality. In chapter 2 the increasing interest towards power quality in electrical systems is illustrated, by reporting the international research activity inherent to the problem and the relevant standards and guidelines emitted. The aspect of the quality of voltage provided by utilities and influenced by customers in the various points of a network came out only in recent years, in particular as a consequence of the energy market liberalization. Usually, the concept of quality of the delivered energy has been associated mostly to its continuity. Hence the reliability was the main characteristic to be ensured for power systems. Nowadays, the number and duration of interruptions are the “quality indicators” commonly perceived by most customers; for this reason, a short section is dedicated also to network reliability and its regulation. In this contest it should be noted that although the measurement system developed during the research activity belongs to the field of power quality evaluation systems, the information registered in real time by its remote stations can be used to improve the system reliability too. Given the vast scenario of power quality degrading phenomena that usually can occur in distribution networks, the study has been focused on electromagnetic transients affecting line voltages. The outcome of such a study has been the design and realization of a distributed measurement system which continuously monitor the phase signals in different points of a network, detect the occurrence of transients superposed to the fundamental steady state component and register the time of occurrence of such events. The data set is finally used to locate the source of the transient disturbance propagating along the network lines. Most of the oscillatory transients affecting line voltages are due to faults occurring in any point of the distribution system and have to be seen before protection equipment intervention. An important conclusion is that the method can improve the monitored network reliability, since the knowledge of the location of a fault allows the energy manager to reduce as much as possible both the area of the network to be disconnected for protection purposes and the time spent by technical staff to recover the abnormal condition and/or the damage. The part of the thesis presenting the results of such a study and activity is structured as follows: chapter 3 deals with the propagation of electromagnetic transients in power systems by defining characteristics and causes of the phenomena and briefly reporting the theory and approaches used to study transients propagation. Then the state of the art concerning methods to detect and locate faults in distribution networks is presented. Finally the attention is paid on the particular technique adopted for the same purpose during the thesis, and the methods developed on the basis of such approach. Chapter 4 reports the configuration of the distribution networks on which the fault location method has been applied by means of simulations as well as the results obtained case by case. In this way the performance featured by the location procedure firstly in ideal then in realistic operating conditions are tested. In chapter 5 the measurement system designed to implement the transients detection and fault location method is presented. The hardware belonging to the measurement chain of every acquisition channel in remote stations is described. Then, the global measurement system is characterized by considering the non ideal aspects of each device that can concur to the final combined uncertainty on the estimated position of the fault in the network under test. Finally, such parameter is computed according to the Guide to the Expression of Uncertainty in Measurements, by means of a numeric procedure. In the last chapter a device is described that has been designed and realized during the PhD activity aiming at substituting the commercial capacitive voltage divider belonging to the conditioning block of the measurement chain. Such a study has been carried out aiming at providing an alternative to the used transducer that could feature equivalent performance and lower cost. In this way, the economical impact of the investment associated to the whole measurement system would be significantly reduced, making the method application much more feasible.

Evaluation of fluid transport processes in dental enamel. Methods to assess the relevance of enamel permeability in caries prevention and etching treatments.

This thesis evaluated in vivo and in vitro enamel permeability in different physiological and clinical conditions by means of SEM inspection of replicas of enamel surface obtained from polyvinyl siloxane impressions subsequently later cast in polyether impression ma-terial. This technique, not invasive and risk-free, allows the evaluation of fluid outflow from enamel surface and is able to detect the presence of small quantities of fluid, visu-alized as droplets. Fluid outflow on enamel surface represents enamel permeability. This property has a paramount importance in enamel physiolgy and pathology although its ef-fective role in adhesion, caries pathogenesis and prevention today is still not fully under-stood. The aim of the studies proposed was to evaluate enamel permeability changes in differ-ent conditions and to correlate the findings with the actual knowledge about enamel physiology, caries pathogenesis, fluoride and etchinhg treatments. To obtain confirmed data the replica technique has been supported by others specific techniques such as Ra-man and IR spectroscopy and EDX analysis. The first study carried out visualized fluid movement through dental enamel in vivo con-firmed that enamel is a permeable substrate and demonstrated that age and enamel per-meability are closely related. Examined samples from subjects of different ages showed a decreasing number and size of droplets with increasing age: freshly erupted permanent teeth showed many droplets covering the entire enamel surface. Droplets in permanent teeth were prominent along enamel perikymata. These results obtained through SEM inspection of replicas allowed innovative remarks in enamel physiology. An analogous testing has been developed for evaluation of enamel permeability in primary enamel. The results of this second study showed that primary enamel revealed a substantive permeability with droplets covering the entire enamel sur-face without any specific localization accordingly with histological features, without changes during aging signs of post-eruptive maturation. These results confirmed clinical data that showed a higher caries susceptibility for primary enamel and suggested a strong relationship between this one and enamel permeability. Topical fluoride application represents the gold standard for caries prevention although the mechanism of cariostatic effect of fluoride still needs to be clarified. The effects of topical fluoride application on enamel permeability were evaluated. Particularly two dif-ferent treatments (NaF and APF), with different pH, were examined. The major product of topical fluoride application was the deposition of CaF2-like globules. Replicas inspec-tion before and after both treatments at different times intervals and after specific addi-tional clinical interventions showed that such globule formed in vivo could be removed by professional toothbrushing, sonically and chemically by KOH. The results obtained in relation to enamel permeability showed that fluoride treatments temporarily reduced enamel water permeability when CaF2-like globules were removed. The in vivo perma-nence of decreased enamel permeability after CaF2 globules removal has been demon-strated for 1 h for NaF treated teeth and for at least 7 days for APF treated teeth. Important clinical consideration moved from these results. In fact the caries-preventing action of fluoride application may be due, in part, to its ability to decrease enamel water permeability and CaF2 like-globules seem to be indirectly involved in enamel protection over time maintaining low permeability. Others results obtained by metallographic microscope and SEM/EDX analyses of or-thodontic resins fluoride releasing and not demonstrated the relevance of topical fluo-ride application in decreasing the demineralization marks and modifying the chemical composition of the enamel in the treated area. These data obtained in both the experiments confirmed the efficacy of fluoride in caries prevention and contribute to clarify its mechanism of action. Adhesive dentistry is the gold standard for caries treatment and tooth rehabilitation and is founded on important chemical and physical principles involving both enamel and dentine substrates. Particularly acid etching of dental enamel enamel has usually employed in bonding pro-cedures increasing microscopic roughness. Different acids have been tested in the litera-ture suggesting several etching procedures. The acid-induced structural transformations in enamel after different etching treatments by means of Raman and IR spectroscopy analysis were evaluated and these findings were correlated with enamel permeability. Conventional etching with 37% phosphoric acid gel (H3PO4) for 30 s and etching with 15 % HCl for 120 s were investigated. Raman and IR spectroscopy showed that the treatment with both hydrochloric and phosphoric acids induced a decrease in the carbonate content of the enamel apatite. At the same time, both acids induced the formation of HPO42- ions. After H3PO4 treatment the bands due to the organic component of enamel decreased in intensity, while in-creased after HCl treatment. Replicas of H3PO4 treated enamel showed a strongly reduced permeability while replicas of HCl 15% treated samples showed a maintained permeability. A decrease of the enamel organic component, as resulted after H3PO4 treatment, involves a decrease in enamel permeability, while the increase of the organic matter (achieved by HCl treat-ment) still maintains enamel permeability. These results suggested a correlation between the amount of the organic matter, enamel permeability and caries. The results of the different studies carried out in this thesis contributed to clarify and improve the knowledge about enamel properties with important rebounds in theoretical and clinical aspects of Dentistry.

How valuable are multiple treatment comparison methods in evidence-based health-care evaluation?

Objectives To compare the use of pair-wise meta-analysis methods to multiple treatment comparison (MTC) methods for evidence-based health-care evaluation to estimate the effectiveness and cost-effectiveness of alternative health-care interventions based on the available evidence. Methods Pair-wise meta-analysis and more complex evidence syntheses, incorporating an MTC component, are applied to three examples: 1) clinical effectiveness of interventions for preventing strokes in people with atrial fibrillation; 2) clinical and cost-effectiveness of using drug-eluting stents in percutaneous coronary intervention in patients with coronary artery disease; and 3) clinical and cost-effectiveness of using neuraminidase inhibitors in the treatment of influenza. We compare the two synthesis approaches with respect to the assumptions made, empirical estimates produced, and conclusions drawn. Results The difference between point estimates of effectiveness produced by the pair-wise and MTC approaches was generally unpredictable—sometimes agreeing closely whereas in other instances differing considerably. In all three examples, the MTC approach allowed the inclusion of randomized controlled trial evidence ignored in the pair-wise meta-analysis approach. This generally increased the precision of the effectiveness estimates from the MTC model. Conclusions The MTC approach to synthesis allows the evidence base on clinical effectiveness to be treated as a coherent whole, include more data, and sometimes relax the assumptions made in the pair-wise approaches. However, MTC models are necessarily more complex than those developed for pair-wise meta-analysis and thus could be seen as less transparent. Therefore, it is important that model details and the assumptions made are carefully reported alongside the results.

Financial decision making about found oil and gas in Ghana : real options vs. traditional methods

This research is a study of the use of capital budgeting methods for investment decisions. It uses both the traditional methods and the newly introduced approach called the real options analysis to make a decision. The research elucidates how capital budgeting can be done when analysts encounter projects with high uncertainty and are capital intensive, for example oil and gas production. It then uses the oil and gas find in Ghana as a case study to support its argument. For a clear understanding a thorough literature review was done, which highlights the advantages and disadvantages of both methods. The revenue that the project will generate and the costs of production were obtained from the predictions by analysts from GNPC and compared to others experts’ opinion. It then applied both the traditional and real option valuation on the oil and gas find in Ghana to determine the project’s feasibility. Although, there are some short falls in real option analysis that are presented in this research, it is still helpful in valuing projects that are capital intensive with high volatility due to the strategic flexibility management possess in their decision making. It also suggests that traditional methods of evaluation should still be maintained and be used to value projects that have no options or those with options yet the options do not have significant impact on the project. The research points out the economic ripples the production of oil and gas will have on Ghana’s economy should the project be undertaken. These ripples include economic growth, massive job creation and reduction of the balance of trade deficit for the country. The long run effect is an eventually improvement of life of the citizens. It is also belief that the production of gas specifically can be used to generate electricity in Ghana which would enable the country to have a more stable and reliable power source necessary to attract more foreign direct investment.

Percutaneous transluminal angioplasty and stent placement in acute vessel occlusion: evaluation of new methods for interventional stroke treatment

BACKGROUND AND PURPOSE: The major goal of acute ischemic stroke treatment is fast and sufficient recanalization. Percutaneous transluminal balloon angioplasty (PTA) and/or placement of a stent might achieve both by compressing the thrombus at the occlusion site. This study assesses the feasibility, recanalization rate, and complications of the 2 techniques in an animal model. MATERIALS AND METHODS: Thirty cranial vessels of 7 swine were occluded by injection of radiopaque thrombi. Fifteen vessel occlusions were treated by PTA alone and 15, by placement of a stent and postdilation. Recanalization was documented immediately after treatment and after 1, 2, and 3 hours. Thromboembolic events and dissections were documented. RESULTS: PTA was significantly faster to perform (mean, 16.6 minutes versus 33.0 minutes for stent placement; P < .001), but the mean recanalization rate after 1 hour was significantly better after stent placement compared with PTA alone (67.5% versus 14.6%, P < .001). Due to the self-expanding force of the stent, vessel diameter further increased with time, whereas the recanalization result after PTA was prone to reocclusion. Besides thromboembolic events related to the passing maneuvers at the occlusion site, no thrombus fragmentation and embolization occurred during balloon inflation or stent deployment. Flow to side branches could also be restored at the occlusion site because it was possible to direct thrombus compression. CONCLUSIONS: Stent placement and postdilation proved to be much more efficient in terms of acute and short-term vessel recanalization compared with PTA alone.

Quality controls for two heel bone ultrasounds used in the Swiss Evaluation of the Methods of Measurement of Osteoporotic Fracture Risk Study

Because of the important morbidity and mortality associated with osteoporosis, it is essential to detect subjects at risk by screening methods, such as bone quantitative ultrasounds (QUSs). Several studies showed that QUS could predict fractures. None, however, compared prospectively different QUS devices, and few data of quality controls (QCs) have been published. The Swiss Evaluation of the Methods of Measurement of Osteoporotic Fracture Risk is a prospective multicenter study that compared three QUSs for the assessment of hip fracture risk in a population of 7609 women age >/=70 yr. Because the inclusion phase lasted 20 mo, and because 10 centers participated in this study, QC became a major issue. We therefore developed a QC procedure to assess the stability and precision of the devices, and for their cross-calibration. Our study focuses on the two heel QUSs. The water bath system (Achilles+) had a higher precision than the dry system (Sahara). The QC results were highly dependent on temperature. QUS stability was acceptable, but Sahara must be calibrated regularly. A sufficient homogeneity among all the Sahara devices could be demonstrated, whereas significant differences were found among the Achilles+ devices. For speed of sound, 52% of the differences among the Achilles+ was explained by the water s temperature. However, for broadband ultrasound attenuation, a maximal difference of 23% persisted after adjustment for temperature. Because such differences could influence measurements in vivo, it is crucial to develop standardized phantoms to be used in prospective multicenter studies.

Comparative Evaluation of Pelvic Allograft Selection Methods

This paper presents a firsthand comparative evaluation of three different existing methods for selecting a suitable allograft from a bone storage bank. The three examined methods are manual selection, automatic volume-based registration, and automatic surface-based registration. Although the methods were originally published for different bones, they were adapted to be systematically applied on the same data set of hemi-pelvises. A thorough experiment was designed and applied in order to highlight the advantages and disadvantages of each method. The methods were applied on the whole pelvis and on smaller fragments, thus producing a realistic set of clinical scenarios. Clinically relevant criteria are used for the assessment such as surface distances and the quality of the junctions between the donor and the receptor. The obtained results showed that both automatic methods outperform the manual counterpart. Additional advantages of the surface-based method are in the lower computational time requirements and the greater contact surfaces where the donor meets the recipient.

Evaluation and Comparison of Anatomical Landmark Detection Methods for Cephalometric X-Ray Images: A Grand Challenge

Cephalometric analysis is an essential clinical and research tool in orthodontics for the orthodontic analysis and treatment planning. This paper presents the evaluation of the methods submitted to the Automatic Cephalometric X-Ray Landmark Detection Challenge, held at the IEEE International Symposium on Biomedical Imaging 2014 with an on-site competition. The challenge was set to explore and compare automatic landmark detection methods in application to cephalometric X-ray images. Methods were evaluated on a common database including cephalograms of 300 patients aged six to 60 years, collected from the Dental Department, Tri-Service General Hospital, Taiwan, and manually marked anatomical landmarks as the ground truth data, generated by two experienced medical doctors. Quantitative evaluation was performed to compare the results of a representative selection of current methods submitted to the challenge. Experimental results show that three methods are able to achieve detection rates greater than 80% using the 4 mm precision range, but only one method achieves a detection rate greater than 70% using the 2 mm precision range, which is the acceptable precision range in clinical practice. The study provides insights into the performance of different landmark detection approaches under real-world conditions and highlights achievements and limitations of current image analysis techniques.

Evaluation of Non-Survey International IO Construction Methods with the Asian-Pacific Input-Output Table

This paper presents four non-survey methods to construct a full-information international input-output table from national IO tables and international import and export statistics, and this paper tests these four methods against the semi-survey international IO table for nine East-Asian countries and the USA, which is constructed by the Institute of Developing Economies in Japan. The tests show that the impact on the domestic flows of using self-sufficiency ratios is small, except for Singapore and Malaysia, two countries with large volumes of smuggling and transit trade. As regards the accuracy of the international flows, all methods show considerable errors, of 10%-40% for commodities and of 10%-70% for services. When more information is added, i.e. going from Method 1 to 4, the accuracy increases, except for Method 2 that generally produces larger errors than Method 1. In all, it seems doubtful whether replacing the semi-survey Asian-Pacific IO table with one of the four non-survey tables is justified, except when the semi-survey table itself is also considered to be just another estimate.

A bi-cubic transformation for the numerical evaluation of the Cauchy principal value integrals in boundary methods

The numerical strategies employed in the evaluation of singular integrals existing in the Cauchy principal value (CPV) sense are, undoubtedly, one of the key aspects which remarkably affect the performance and accuracy of the boundary element method (BEM). Thus, a new procedure, based upon a bi-cubic co-ordinate transformation and oriented towards the numerical evaluation of both the CPV integrals and some others which contain different types of singularity is developed. Both the ideas and some details involved in the proposed formulae are presented, obtaining rather simple and-attractive expressions for the numerical quadrature which are also easily embodied into existing BEM codes. Some illustrative examples which assess the stability and accuracy of the new formulae are included.

Simulation-based evaluation of susceptibility distortion correction methods in diffusion MRI for connectivity analysis

Connectivity analysis on diffusion MRI data of the whole-brain suffers from distortions caused by the standard echo-planar imaging acquisition strategies. These images show characteristic geometrical deformations and signal destruction that are an important drawback limiting the success of tractography algorithms. Several retrospective correction techniques are readily available. In this work, we use a digital phantom designed for the evaluation of connectivity pipelines. We subject the phantom to a “theoretically correct” and plausible deformation that resembles the artifact under investigation. We correct data back, with three standard methodologies (namely fieldmap-based, reversed encoding-based, and registration- based). Finally, we rank the methods based on their geometrical accuracy, the dropout compensation, and their impact on the resulting connectivity matrices.

Métodos diferenciales e interferométricos para la evaluación de deformaciones de la corteza terrestre mediante técnicas GNSS e InSAR = Differential and interferometric methods for evaluation of crustal deformation using GNSS and InSAR techniques

La actividad volcánica interviene en multitud de facetas de la propia actividad humana, no siempre negativas. Sin embargo, son más los motivos de peligrosidad y riesgo que incitan al estudio de la actividad volcánica. Existen razones de seguridad que inciden en el mantenimiento del seguimiento y monitorización de la actividad volcánica para garantizar la vida y la seguridad de los asentamientos antrópicos en las proximidades de los edificios volcánicos. En esta tesis se define e implementa un sistema de monitorización de movimientos de la corteza en las islas de Tenerife y La Palma, donde el impacto social que representa un aumento o variación de la actividad volcánica en las islas es muy severo. Aparte de la alta densidad demográfica del Archipiélago, esta población aumenta significativamente, en diferentes periodos a lo largo del año, debido a la actividad turística que representa la mayor fuente de ingresos de las islas. La población y los centros turísticos se diseminan predominantemente a lo largo de las costas y también a lo largo de los flancos de los edificios volcánicos. Quizá el mantenimiento de estas estructuras sociales y socio-económicas son los motivos más importantes que justifican una monitorización de la actividad volcánica en las Islas Canarias. Recientemente se ha venido trabajando cada vez más en el intento de predecir la actividad volcánica utilizando los nuevos sistemas de monitorización geodésica, puesto que la actividad volcánica se manifiesta anteriormente por deformación de la corteza terrestre y cambios en la fuerza de la gravedad en la zona donde más tarde se registran eventos volcánicos. Los nuevos dispositivos y sensores que se han desarrollado en los últimos años en materias como la geodesia, la observación de la Tierra desde el espacio y el posicionamiento por satélite, han permitido observar y medir tanto la deformación producida en el terreno como los cambios de la fuerza de la gravedad antes, durante y posteriormente a los eventos volcánicos que se producen. Estos nuevos dispositivos y sensores han cambiado las técnicas o metodologías geodésicas que se venían utilizando hasta la aparición de los mismos, renovando métodos clásicos y desarrollando otros nuevos que ya se están afianzando como metodologías probadas y reconocidas para ser usadas en la monitorización volcánica. Desde finales de la década de los noventa del siglo pasado se han venido desarrollando en las Islas Canarias varios proyectos que han tenido como objetivos principales el desarrollo de nuevas técnicas de observación y monitorización por un lado y el diseño de una metodología de monitorización volcánica adecuada, por otro. Se presenta aquí el estudio y desarrollo de técnicas GNSS para la monitorización de deformaciones corticales y su campo de velocidades para las islas de Tenerife y La Palma. En su implementación, se ha tenido en cuenta el uso de la infraestructura geodésica y de monitorización existente en el archipiélago a fin de optimizar costes, además de complementarla con nuevas estaciones para dar una cobertura total a las dos islas. Los resultados obtenidos en los proyectos, que se describen en esta memoria, han dado nuevas perspectivas en la monitorización geodésica de la actividad volcánica y nuevas zonas de interés que anteriormente no se conocían en el entorno de las Islas Canarias. Se ha tenido especial cuidado en el tratamiento y propagación de los errores durante todo el proceso de observación, medida y proceso de los datos registrados, todo ello en aras de cuantificar el grado de fiabilidad de los resultados obtenidos. También en este sentido, los resultados obtenidos han sido verificados con otros procedentes de sistemas de observación radar de satélite, incorporando además a este estudio las implicaciones que el uso conjunto de tecnologías radar y GNSS tendrán en un futuro en la monitorización de deformaciones de la corteza terrestre. ABSTRACT Volcanic activity occurs in many aspects of human activity, and not always in a negative manner. Nonetheless, research into volcanic activity is more likely to be motivated by its danger and risk. There are security reasons that influence the monitoring of volcanic activity in order to guarantee the life and safety of human settlements near volcanic edifices. This thesis defines and implements a monitoring system of movements in the Earth’s crust in the islands of Tenerife and La Palma, where the social impact of an increase (or variation) of volcanic activity is very severe. Aside from the high demographic density of the archipelago, the population increases significantly in different periods throughout the year due to tourism, which represents a major source of revenue for the islands. The population and the tourist centres are mainly spread along the coasts and also along the flanks of the volcanic edifices. Perhaps the preservation of these social and socio-economic structures is the most important reason that justifies monitoring volcanic activity in the Canary Islands. Recently more and more work has been done with the intention of predicting volcanic activity, using new geodesic monitoring systems, since volcanic activity is evident prior to eruption because of a deformation of the Earth’s crust and changes in the force of gravity in the zone where volcanic events will later be recorded. The new devices and sensors that have been developed in recent years in areas such as geodesy, the observation of the Earth from space, and satellite positioning have allowed us to observe and measure the deformation produced in the Earth as well as the changes in the force of gravity before, during, and after the volcanic events occur. The new devices and sensors have changed the geodetic techniques and methodologies that were used previously. The classic methods have been renovated and other newer ones developed that are now vouched for as proven recognised methodologies to be used for volcanic monitoring. Since the end of the 1990s, in the Canary Islands various projects have been developed whose principal aim has been the development of new observation and monitoring techniques on the one hand, and the design of an appropriate volcanic monitoring methodology on the other. The study and development of GNSS techniques for the monitoring of crustal deformations and their velocity field is presented here. To carry out the study, the use of geodetic infrastructure and existing monitoring in the archipelago have been taken into account in order to optimise costs, besides complementing it with new stations for total coverage on both islands. The results obtained in the projects, which are described below, have produced new perspectives in the geodetic monitoring of volcanic activity and new zones of interest which previously were unknown in the environment of the Canary Islands. Special care has been taken with the treatment and propagation of errors during the entire process of observing, measuring, and processing the recorded data. All of this was done in order to quantify the degree of trustworthiness of the results obtained. Also in this sense, the results obtained have been verified with others from satellite radar observation systems, incorporating as well in this study the implications that the joint use of radar technologies and GNSS will have for the future of monitoring deformations in the Earth’s crust.