As Redes Neurais Artificiais (RNAs) vêm sendo empregadas com cada vez mais sucesso em diversas áreas de pesquisa, no campo da engenharia e em outros campos diversos. Neste trabalho foram modeladas séries fluviométricas relativas às afluências a quatro reservatórios, localizados em quatro bacias hidrográficas distintas que compõem a Bacia Metropolitana de Fortaleza, Ceará, Brasil. Tais afluências apresentam peculiaridades relativas à ocorrência de magnitudes nulas, que dificultam sua modelagem através dos convencionais modelos estatísticos da família Box-Jenkins. Neste estudo foram trabalhadas duas abordagens distintas, a primeira univariada, em que cada série era modelada de forma individual, e a segunda multivariada, em que as séries fluviométricas eram modeladas simultaneamente. Os resultados obtidos, segundo ambas as modelagens, demonstram que a técnica apresenta potencial para a aplicação pretendida. Estudos futuros merecem ser desenvolvidos ainda no sentido de verificar a melhor maneira de se enquadrar a componente aleatória nas séries sintéticas produzidas via RNAs. / Artificial Neural Networks (ANNs) are being used more and more in many different fields of research, in engineering applications or other applications. This research deals with modeling of inflows to four reservoirs, located in different watersheds that belong to the Metropolitan Watershed of Fortaleza city, Brazil. These discharge sequences have particular characteristics in that they have frequent occurence of null discharges which makes it difficult to use traditional statistical models such as those Box-Jenkis family. Two different modeling approaches were adopted in this study, the first univariate, in which each time series was modeled individually, and the second multivariate, in which the four time series were modeled simultaneously. The results from the both approaches show that the technique has potential for use in water resources planning and management. Future studies are required to propose better means of incorporing the random component in the generation of synthetic time series through ANNs.

Le dioxyde de carbone, principal gaz à effet de serre lié aux activités humaines, est considéré comme l’un des gaz les plus problématiques pour notre environnement ces dernières années, principalement à cause du réchauffement climatique qu’il engendre. C’est pour cette raison que l’augmentation de sa teneur dans l’atmosphère nous concerne tous quant aux conséquences futures pour notre planète. Afin de limiter l’émission de CO2, sa conversion en composés à valeur ajoutée présente un grand intérêt et est possible notamment via des procédés plasmas. Plus particulièrement, les décharges à barrière diélectrique (DBD) sont utilisées depuis quelques années pour générer des plasmas froids opérant à pression atmosphérique, principalement pour des applications en traitement de surface, mais également pour le traitement d’effluents gazeux.Lors de cette thèse, nous nous sommes focalisés sur le processus de dissociation du CO2 en CO et O2 via un réacteur DBD à flux continu et avons analysé sa conversion et son efficacité énergétique via différentes études. Celles-ci ont été réalisées grâce à plusieurs méthodes de diagnostic, comme par exemple la spectrométrie de masse utilisée pour déterminer la conversion et l’efficacité du processus, la spectroscopie d’émission optique, l’oscilloscope pour une caractérisation électrique, etc. afin d’avoir une meilleure compréhension du comportement des décharges CO2.Dans un premier temps, nous avons réalisé une étude détaillée d’un plasma CO2 pur où nous avons fait varier différents paramètres, tels que le temps de résidence, la fréquence, la puissance, la pulsation de la haute tension et l’épaisseur et la nature du diélectrique. Le CO2 donne lieu généralement à une décharge filamentaire, consistant en de nombreuses microdécharges réparties au niveau de la zone du plasma. Celles-ci constituent la principale source de réactivité dans une DBD. Un aperçu détaillé de l’aspect physique de ces microdécharges a été réalisé grâce à la caractérisation électrique, permettant de mieux comprendre les propriétés électriques de la décharge et des microdécharges. En effet, nous avons pu déterminer l’importance de la tension présente au niveau du plasma, de l’intensité du courant plasma, du nombre de microdécharges et de leur temps de vie sur l’efficacité du processus de dissociation de CO2.Ensuite, nous avons conclu ce travail avec des études combinant le CO2 en phase plasma avec de l’eau ou du méthane afin de produire des molécules à valeur ajoutée telles que les syngas (CO et H2), mais aussi des hydrocarbures (C2H6, C2H4, C2H2 et CH2O) dans le cas de l’ajout du méthane. A travers ces études, nous avons obtenu une meilleure connaissance de la chimie et de la physique qui ont lieu dans ce type de plasma. / Carbon dioxide appears as one of the most problematic gases for the environment, mostly because it is responsible for global warming. This is why its increasing concentration into the atmosphere, mainly due to anthropogenic activities, is a real concern for planet Earth. In order to prevent the release of large amounts of CO2, its conversion into value-added products is of great interest. In this context, plasma-based treatments using dielectric barrier discharges (DBDs) are nowadays more and more used for the conversion of this gas. In this thesis, we investigated the CO2 splitting process into CO and O2 via a flowing cylindrical DBD and we studied its conversion and energy efficiency by means of several diagnostic methods, such as mass spectrometry to determine the conversion and energy efficiency of the process, optical emission spectroscopy for gas temperature measurements, and an oscilloscope for electrical characterization, in order to obtain a better understanding of the CO2 discharge itself.First, we focused on an extensive experimental study of a pure CO2 plasma where different parameters were varied, such as the gas residence time, the operating frequency, the applied power, the pulsation of the AC signal, the thickness and the nature of the dielectric. CO2 discharges typically exhibit a filamentary behavior, consisting of many microdischarges, which act as the main source of reactivity in a DBD. A detailed insight in the physical aspects was achieved by means of an in-depth electrical characterization, allowing more insight in the electrical properties of the discharge and more specifically in the microdischarges, which are spread out throughout the active zone of the plasma. It was found throughout this work that the plasma voltage, which reflects the electric field and thus determines how the charged particles are accelerated, the plasma current, which reflects the electron density, but also the number of microdischarges and their average lifetime, play an important role in the efficiency of the CO2 dissociation process. It was revealed that the microdischarge number is important as it represents the repartition of the locations of reactivity. Indeed, as the microfilaments are more spread out in the same discharge volume, the probability for the CO2 molecules to pass through the reactor and interact with at least one microdischarge filament becomes more important at a larger number of microfilaments.The second part of the thesis was dedicated to discharges combining CO2 and H2O or CH4, both being hydrogen source molecules. The combined CO2/H2O or CO2/CH4 conversion allows forming value-added products like syngas (CO and H2), but also hydrocarbons (C2H6, C2H4, C2H2 and CH2O), at least in the presence of methane. Throughout this study, we tried to obtain a better knowledge of the chemistry and physic behind these conversion processes. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

With the development of electricity transmission systems, more and more insulators have been used in the system to isolate the high potential conductors from the earth. In order to secure the reliability of power system, it is necessary to understand the ageing mechanism of the insulators. A model for energy (heat) transfer between low current discharges and insulation surfaces has been built in this project which contributes to the understanding and prediction of insulator ageing. Within the experimental work, the temperature of low current discharges under different conditions has been measured with the “Best-fit” method. The temperature was found to vary between 1200 K and 2300 K with current level, sub cycle duration, gap length, electrode conductivity and polarity of DC discharges. The discharge temperature increases with the growth of current and sub cycle duration by means of the elevation of energy, while the discharge temperature is hotter between salt water droplets than between tap water droplets even though the former has a lower energy (I^2 Rt). The temperature is insensitive to a change of gap length and a positive discharge has a higher temperature than an equivalent negative one. The specific measurement shows the middle part is hotter than the electrode areas. Within the simulation work, the presence of water droplet(s) on the insulation surface concentrates and enhances the electric field over the surface which increases the risk of partial discharge. For practical insulators, this means the core, rather than the sheds, suffers more from discharges between water droplets as they are aligned to the electric field. This highlights the importance of keeping the core dry. The simulation of heat transfer between low current discharges insulation surface was achieved using COMSOL software. The simulated results show that the surface temperature increases rapidly in the first few seconds and arrives at a thermal equilibrium state after 20 seconds of discharge, which meets the experimental observation. The insulation surface temperature distribution under AC discharge is symmetric and the surface centre has the highest temperature which decreases towards the water droplets. In DC, the surface around the cathode is the hottest and the anode area is the coldest.

No description available.

Ester liquids including natural ester and synthetic ester are considered as potential substitutes for mineral oil, due to their good biodegradability and high fire points. Although these liquids have been widely used in distribution and traction transformers, research efforts are required for the purposes of design and manufacture of high voltage and large power transformers which are filled by esters. Indeed, it would be risky to apply esters in large power transformers without thorough understandings of their behaviours in large gaps and/or when combined with pressboard insulation. Therefore, investigations of creepage discharges along the surface of pressboard in esters are vitally important and their behaviours should be compared with those of mineral oils. This thesis is aimed to investigate the creepage discharges along pressboard in esters and mineral oil under ac divergent electric field. Apparent charges, current signals and images of streamer channels were obtained synchronously to identify whether and how the introduction of pressboard surface would influence the inception and propagation of discharges as compared to tests in open gap. When over-stressed by higher voltages, the surface tracking along the pressboard-ester interface, triggered by sustaining creepage discharges, was studied and the evolutions of accompanying creepage discharge patterns were investigated. In these experiments, both esters and mineral oil impregnated pressboards were comparatively studied. The test results indicated that at the inception stage, the presence of pressboard or any other solid types in different liquids under test do not influence the PD inception voltages; in the propagation stage, solid surface tends to promote the development of discharges, especially those occurring in negative half cycles, and shifts more discharges towards the zero-crossing phase angles. This discharge promotion effect is much more evident in esters than in mineral oil, probably because of higher discharge intensity in esters and higher viscosity of esters. The space charge effect and the residual low density channel effect are proved as the mechanisms best explaining the influences of solids on creepage discharges. Under higher voltages, it was found that the impregnated pressboard is susceptible to discharge erosion characterized by “white and carbonized tree-shaped marks”, due to intense discharges occurring on or near the pressboard surface. The “white mark” appears at a lower voltage and propagates more easily on ester impregnated pressboard. The gaseous “white mark” channels will attract the subsequent discharges to follow the same discharge routes; the accumulative energy dissipation in these channels will then result in the carbonization of the channels. Once formed, the surface tree-shaped mark can continue to grow even under reduced voltage levels until it bridges the gap and causes the final flashover.

The thesis is focused on electrical discharge in liquid solutions, in particular in ethanol solutions. In the theoretical section, the plasma is defined along with its important parameters, types of plasma generation and usage of plasma technologies. Main part is focused on the discharges in water solutions. Electric discharges in liquid solutions enable physical processes (shock waves, UV radiaton, electric current) as well as chemical ones (generation of radicals and ions). Both types of the processes are used in many fields – medicine (tool sterilization, destruction of pathogens), consumer technologies (surface adjustemen, processing of the textiles, surface clearing) of environmental protection (clearing water, decomposition of organic compounds). Goal of the thesis was to analyze discharge products on ethanol solution. Multiple samples were measured and concentration od selected products was monitored during the measurement – ethanol, acetone and acetaldehyde. PTR-TOF-MS method was used to collect and analyze the data. This method is well used thanks to quick response and immediate measurement. It produce the reset accurate enough for our purpose. It would be more efficient to use this method in combination with another analytical metohod in the future research, e.g. gas chromatography.

The presented diploma thesis deals with the issue of wire electrical discharge machining of SiSiC ceramics. The first part explains the principles of electrical discharge machining, describes the WEDM technology and presents the properties of the advanced ceramics. The second part consists of a detailed analysis of the cutting process of eighteen samples obtained with systematically changing process parameters. Based on the obtained results from EDX analysis, SEM electron microscopy and topography there was performed an analysis of the influence of process parameters on the cutting speed, surface roughness, kerf width and number of wire breaks with usage of the selected brass cutting wire. From the evaluated results it was possible to select a combination of parameters that ensured a stable machining process.

The aim of this dissertation are future trends of electrical discharge machining in conditions of a small tool factory. In the introduction is presented the theory of non-conventional machining. The practical part is focused on valuation the current level of electrical discharge machining, the importance of the use in a tool Nástrojárna Ryšavý. It also compares the level of leading global manufacturers of electrical discharge machines and future trends of electro-discharge technology.

No description available.

Bakgrund Första januari 2018 kom en ny lag om samverkan vid utskrivning från sjukhuset till Primärvård, där Primärvården har huvudansvaret för utskrivningsplaneringen. Då samverkanslagen är ny, var det svårt att finna studier om hur distriktssköterskorna/sjuksköterskorna upplever att vara ansvariga vid utskrivningsplaneringen. Syfte Syftet med studien var att beskriva hur distriktssköterskor/sjuksköterskor upplevde att arbeta med utskrivningsplanering från sjukhus till primärvård och hur de upplevde att vara ansvariga för denna planering utifrån den nya samverkanslagen.  Metod Studien använde en kvalitativ ansats och deskriptiv design. Semistrukturerade intervjuer med elva distriktssköterskor/sjuksköterskor användes som datainsamlingsmetod. Data analyserades med kvalitativ innehållsanalys Huvudresultat Resultatet visade att det som påverkade distriktssköterskorna/sjuksköterskorna mest i arbetet med utskrivningsplanering var bristen på kommunikation och information från sjukhuset. Att få information om patientens tillstånd och behov av insatser efter hemgång, var en stor utmaning. Sökandet efter information var mycket tidskrävande och innefattade flera olika sökvägar. Samtliga distriktssköterskor/sjuksköterskor uppgav att de ofta ringde sjukhuset och anhöriga till patienten för att få information. När sjukhuset hade en vårdplanerare med erfarenhet och kompetens, upplevde deltagarna att information gällande patientens status och planerade åtgärder var tydligare, vilket bidrog till en tryggare hemgång för patienten.   Slutsats Studien har visat att distriktssköterskor/sjuksköterskor i Primärvården tyckte det var svårt att vara ansvariga vid utskrivningsplanering. Problem med att få information från sjukhuset, avsaknad av rätt kompetens hos vårdplaneraren på sjukhuset, utbildning i kommunikationssystemet Lifecare, samt tidsbrist var bekymmersamt. / Abstract Background January first 2018, a new law came into force on discharge from the hospital to primary healthcare, where primary healthcare was responsible for the discharge planning. When the collaboration law is new, there were difficulties finding studies of how the districtnurses/registered nurses find themselves responsible for the discharge planning. Aim The aim of the study was to describe how districtnurses/registered nurses experienced working with discharge planning from hospital to primary healthcare and how they felt responsible for this planning based on the new collaboration law. Method The study used a qualitative approach and descriptive design. Semi-structured interviews with eleven districtnurses/nurses were used as a data collection method. Data was analyzed with qualitative content analysis. Main findings The result showed that what influenced the districtnurses/nurses most in the work on dischargeplanning was the lack of communication and information from the hospital. Getting information about the patient's condition and the need for intervention after the return home was a great challenge. The search for information was very timeconsuming and included several different paths. All districtnurses/nurses stated that they often called the hospital and relatives to the patient for information. When the hospital had a dischargeplanning nurse with experience and expertise, the participants experienced that information regarding the patient's status and planned measures was clearer, which contributed to a safer homecoming for the patient. Conclusion The study has shown that districtnurses/nurses in primary health care felt it was difficult to be responsible for dischargeplanning. Problems with getting information from the hospital, lack of proper competence of the dischargeplanning nurse at the hospital, training in the communication system Lifecare, and time shortage were worrying.