L'adolescence, marquée par l'éclosion de la puberté et la résurgence des pulsions sexuelles et agressives, engage, un travail interne lié aux transformations psychiques et à l'émergence de la sexualité génitale. La puberté peut alors faire intrusion et trauma, blessant le sujet qui est plus ou moins prêt à supporter la contrainte au changement induit par le processus pubertaire. En référence au modèle théorique psychanalytique, nous nous intéressons dans cette étude à la manière dont les adolescents font face aux afflux d'excitations, tant externes qu'internes, selon un traitement psychique, par un travail de mentalisation et de symbolisation, ou bien comportemental ou somatique, par le langage du corps ou le recours à la sensorialité. En effet, quelles que soient les capacités d'élaboration mentale de l'adolescent, une vulnérabilité transitoire de l'appareil mental est attendue à cet âge de la vie. Notre travail se propose ainsi d'explorer le traitement de l'excitation à l'adolescence, mis en évidence par l'étude de la qualité de quatre mouvements psychiques : le narcissisme, le système pare-excitation, le recours au corps par la sensorialité et le langage du corps, ainsi que les processus de pensée à travers l'étude de la mentalisation et de la symbolisation. Notre objet de recherche questionne ainsi la qualité du traitement de l'excitation, à travers la mise en perspective de ces différentes dimensions conceptuelles, susceptible d'exposer une meilleure approche processuelle de l'adolescence. Partant de l'hypothèse principale selon laquelle le traitement de l'excitation est multifactoriel, l'objectif de cette étude est de dégager la manière dont l'articulation des différents concepts étudiés est à même de rendre compte, de manière plus sensible, du traitement de l'excitation à l'adolescence. La méthodologie projective a été choisie pour mettre à l'épreuve cette hypothèse à l'aide de grilles référées aux quatre dimensions précitées. Nous avons rencontré 17 adolescents tout-venants âgés de 14 à 18 ans auxquels nous avons proposé le Rorschach et le TAT. Dans une approche comparative, nous avons étudié le traitement de l'excitation auprès de deux groupes d'âge (14-16 ans et 16-18 ans). Les résultats mettent en avant des différences dans le traitement de l'excitation à l'adolescence entre les deux groupes d'âge, les plus jeunes ayant préférentiellement recours à l'inhibition, les plus âgés étant davantage en mesure de mentaliser et symboliser l'excitation. Conformément à notre hypothèse générale, l'analyse projective des quatre dimensions de notre travail permet une approche plus fine pour chaque adolescent des spécificités du traitement de l'excitation. / Adolescence, marked by the emergence of puberty and the resurgence of sexual and aggressive drives, engages an internal work linked to psychic transformations and to the emergence of genital sexuality. Puberty can therefore intrude and cause trauma, hurting the subject who is more or less ready to bear the constraint to change induced by the pubertal process. In reference to the theoretical psychoanalytic model, we are interested in the study of the way in which adolescents are confronted with the influx of excitations, both external and internal, through a psychic treatment, by a work of mentalisation and symbolisation, or behavioural, or somatic, by the language of the body or the use of sensoriality. Indeed, whatever the mental capacity of the adolescent, a transient vulnerability of the mental apparatus is expected at this age of life. Our work thus proposes to explore the treatment of excitation in adolescence, evidenced by the study of the quality of several psychic movements: narcissism, protective-shield system, sensoriality and body language, as well as the processes of thought through the study of mentalisation and symbolisation. Our research object thus questions the quality of the treatment of excitation, through the putting into perspective of these four conceptual dimensions, likely to expose a better process approach of adolescence. On the basis of the main hypothesis that the processing of the excitation is multifactorial, the objective of this study is to determine how the articulation of the different concepts studied is able to account more sensibly for the treatment of excitation in adolescence. The projective methodology was chosen to test this hypothesis using grids referred to the above four dimensions. We met 17 teenagers aged 14 to 18 years old who passed the Rorschach and TAT. In a comparative approach, we studied the treatment of excitation with two age groups (14-16 years and 16-18 years). The results highlight differences in the treatment of adolescent arousal between the two age groups, with the younger ones preferring inhibition, the older age groups being more able to mentalise and symbolize the excitation. According to our general hypothesis, the projective analysis of the four dimensions of our work allows a finer approach for each adolescent to the specificities of the treatment of excitation.

The Norwegian Network Code FIKS from the Norwegian Transmission System Operator (TSO) Statnett, states that synchronous generators ≥ 25 MVA must have a static excitation system. It also includes requirements on the step time response and the available field winding ceiling voltage of the excitation system. An improved brushless excitation system is in operation in some pilot power plants. A rotating thyristor bridge is controlled via Bluetooth. The step time response is as fast as conventional static excitation systems. However, a ceiling voltage factor of 2 requires the thyristor bridge to operate at firing angles about 60 degrees. High torque pulsations, low power factor and low utilization of the exciter is the end result. New power electronic interfaces on the shaft results in a betterutilization of the designed exciter and improves the mechanical performance as well as the controllability of the generator field winding. Permanent magnet rotating exciters increase the field forcing strength of the synchronous generator, yielding improved transient stability (Fault Ride-Through req.). Brushless exciters also reduces regular maintenance of the generator. The thesis includes experiments on a state of the art synchronous generator test setup including constructed PM exciter and different power electronic solutions. Some investigations has been done on industrial power plants as well.

Doppler ultrasound imaging modalities arguably represent one of the most complex task performed (usually in real time) by ultrasound scanners. At the heart of these techniques lies the ability to detect and estimate soft tissues or blood motion within the human body. As they have become an invaluable tool in a wide range of clinical applications, these techniques have fostered an intensive effort of research in the field of signal processing for more than thirty years, with a push towards more accurate velocity or displacement estimation. Coded excitation has recently received a growing interest in the medical ultrasound community. The use of these techniques, originally developed in the radar field, makes it possible to increase the depth of penetration in B-mode imaging, while complying with safety standards. These standards impose strict limits on the peak acoustic intensity which can be transmitted into the body. Similar solutions were proposed in the early developments of Doppler flow-meters to improve the resolution / sensitivity trade-off from which typical pulsed Doppler systems suffer. This work discusses the potential improvements in resolution, sensitivity and accuracy achievable in the context of modern Doppler ultrasound imaging modalities (taken in its broadest sense, that is, all the techniques involving the estimation of displacements, or velocities). A theoretical framework is provided for discussing this potential improvements, along with simulations for a more quantitative assessment. Colour Flow Imaging (CFI) modalities are taken as the main reference technique for discussion, due to their historical importance, and their relevance in many clinical applications. The potential achievable improvement in accuracy is studied in the context of modern velocity estimation strategies, which can be broadly classified into narrowband estimators (such as the “Kasai” estimator still widely used in CFI) and time shift based wideband strategies (normalised crosscorrelation estimator used, for instance, in applications like strain or strain rate estimation, elastography, etc.). Finally, simulations and theoretical results are compared to experimental data obtained with a simple custom-designed experimental set-up, using a single-element transducer.

Vibrational and electronic absorption spectra of metal alloy molecules and small particles have been measured. The matrix isolation technique was used to produce the samples. Dissimilar metals were combined to provide far infrared vibrational activity. Through the study of the electronic and vibrational excitation spectra, metallic interatomic binding potential characteristics could be investigated. The absorption spectra of the molecular systems were modelled using the extended Hueckel method, for the electronic excitations, and a dynamical matrix-normal mode technique for the vibrational excitations. Surface plasmon absorption, from the metal alloy particles, could not be measured but surface phonon absorption was measured. Electronic and vibrational absorption lines in alloyed metal molecules were measured and compared to the calculations. A surface diffusion model was developed to explain the dependences of molecule and particle size on the experimentally controlled system parameters.

Thesis (MSc)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: The radionuclide 75Se (T1/2= 119.8 days) decays to the stable isotope 75As by 100 % electron capture. Applications of this radioisotope include its use as a radiotracer in agricultural investigations and as a potential irradiation source in high-activity brachytherapy. The application of this isotope as a radiotracer in clinical studies has been limited due to a lack of availability of carrier-free 75Se. In this study the excitation functions for the production of carrier-free 75Se, other selenium radioisotopes and radiocontaminants produced via natBr(p,x) nuclear reactions were measured by the use of the stacked foil technique. Three separate stacks were assembled from aluminium and copper monitor foils and potassium bromide tablets. The latter were prepared by pressing KBr salt into tablets with a thickness of 200 mg/cm2 and a diameter of 20 mm, which are sandwiched between thin Al foils. The monitor foils, with a diameter of 19 mm, were punched from foil sheets. The stacks were irradiated at proton beam energies of 100.9 MeV, 66.8 MeV and 40.4 MeV respectively at the National Accelerator Centre cyclotron facility. After bombardment the KBr tablets were sealed in plastic bags to prevent the loss of any krypton isotopes produced. The gamma-ray spectra of the induced radioactivity in each of the target foils were recorded by means of a Ge-detector coupled with a SILENA 16-k multichannel analyser. The measured excitation functions for the above-mentioned isotopes are presented. Where applicable the cross-section values are compared with previously published values, while the others are presented as new data. Theoretical calculations by means of the computer code ALICE (IPPE) were also done for comparison. / AFRIKAANSE OPSOMMING: Die radionuklied 75Se (T1/2= 119.8 dae) verval deur 100 % elektronvangs na die stabiele isotoop 75As. Toepassings vir hierdie radioisotoop sluit in sy gebruik as 'n radiospoormiddel in landbou-ondersoeke en as 'n potensiële stralingsbron in hoë aktiwiteit bragiterapie. Die aanwending van hierdie isotoop as 'n radiospoorder in kliniese studies word egter beperk deur die gebrek aan beskikbaarheid van draer-vry 75Se. In hierdie studie is die opwekkingskrommes vir die produksie van draer-vry 75Se, ander selenium radioistope en radiokontaminante bepaal deur die natBr(p,x) kernreaksies te meet met behulp van die foelie-stapel metode. Drie verskillende stapels, bestaande uit aluminium- en koper-monitor foelies en kalium-bromied tablette, is saamgestel. Laasgenoemde is voorberei deur KBr sout saam te pers tot tablette met 'n dikte van 200 mg/cm2 en 'n deursnit van 20 mm en wat omsluit is met dun Al-foelies. Die monitor-foelies, met 'n deursnit van 19 mm, is gepons uit foelieplate. Die stapels is bestraal met protonbundels met energieë van onderskeidelik 100.9 MeV, 66.8 MeV en 40.4 MeV by die Nasionale Versneller Sentrum, Faure, se siklotron-fasiliteit. Na bombardering is die KBr tablette verseël in plastieksakkies om verliese van enige vervaardigde kripton isotope te verhoed. Die gamma-straal spektra van die geinduseeerde radioaktiwiteit in elke teiken is opgeneem met behulp van 'n Ge-detektor wat gekoppel was aan 'n SILENA 16-k multikanaal-analiseerder. Bogenoemde isotope se gemete opwekkingskrommes word aangebied. Waar van toepassing word die kansvlakwaardes vergelyk met vorige gepubliseerde waardes terwyl ander aangebied word as die eerste data bekend. 'n Vergelyking met die teoreties berekende kansvlakwaardes van die rekenaar kode ALICE (IPPE) word ook gedoen.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

No description available.

The purpose of this experiment was to make positive assignment of the Cs133 energy levels excited by the inelastic scattering of neutrons.

X-ray crystallography is an important analytical method for the characterisation of materials in the solid state. During the last decade, it has become important as a tool in the new field of photocrystallography. This combines both crystallography and photochemistry and is used to monitor the formation of light-induced metastable and transient species, so that structural information can be obtained during the change of a material. This is an important area of research as solid state chemistry can display new phenomena and reveal properties that are not possible in solution. Chapter 1 of this thesis commences with a brief introduction to the different methods used to achieve and measure the excitation within crystalline compounds, while Chapter 2 contains an introduction into diffraction methods. In Chapters 3-5 new photocrystallographic studies were performed on two series of compounds. The first one consists of a systematic study on metal complexes with different pyridylethylene ligands. The focus was to align complexes in the solid state so that they can undergo photo induced cycloaddition reactions. These solid state reactions are important as they present “green synthetic chemistry”. The second study involves the photoinduced linkage isomerisation of [Ni(L)2(NO2)2] complexes. Structural characterisation shows that the NO2 ligands change their coordination mode when irradiated with light of different wavelengths. Conditions for the metastable isomerisation were optimised by altering temperature and wavelengths. In Chapters 6 and 7 a systematic study of structural changes in a series of lanthanide complexes and their use as triboluminescence materials, is described. The proposed mechanism of triboluminescence for these complexes is discussed. To summarise, in this thesis, systematic investigations have been carried out in different aspects of crystallography using appropriate series of compounds. The nature of and the conditions required for the change to occur within the solid state have been established.

This thesis work aims at developing a model in Visual Basic for Applications and Microsoft Excel that can be used to predict temperatures in semiconductor devices for two commercial products made by Voith Hydro AB, and via simulation of the model determine the maximum current that can be conducted through the two products. The two products are called field exciters. A field exciter controls the rotor current of a generator with the help of semiconductor devices. When used in a power converter, such devices give rise to losses. A certain amount of the electrical energy passing through the converter is lost in form of heat. If the thermal energy is not dissipated, the temperature in the semiconductor device will rise. This will eventually lead to device failure when the temperature exceeds a certain temperature threshold which depends on the semiconductor material. The proposed model allows to predict these losses and the corresponding temperatures for a specified field current and ambient temperature. The model was validated experimentally. A simplified brushless excitation system was designed and constructed, temperature measurements were carried out for different field currents and later used to validate the model. This thesis concludes that the model developed in Visual Basic predicts temperatures with good results for the PWM-30A but not as good for the PWM-150A. The model simulations show that the PWM-30A can operate with a continuous current of 30 A, for a short duration of 10 seconds it can step up the current to 60 A at an ambient temperature of 50 °C. When the PWM-30A is cooled by forced convection, it can conduct a continuous current of 50 A at an ambient temperature of 50 °C. During field forcing, the PWM-30A can step up the current to 100 A for a duration of 10 seconds. It has been concluded that the PWM-150A cannot, without further testing, conduct a larger current than it was originally designed for, which is 150 A continuously at an ambient temperature of 40 °C. During field forcing it can step up the current to 240 A for 10 seconds.