Preliminary studies have stirred the hope that sound-field stimulation through auditory steady state evoked potentials can be used to assess aided thresholds in the difficult-to-test population. Before the introduction of ASSEP into the clinical field, as a technique for the prediction of aided thresholds in the difficult-to-test population, a question arises concerning its clinical validation. The application of ASSEP through sound field stimulation, in the determination of aided thresholds and for the evaluation of amplification fittings, is dependent on the determination of unaided responses. Subsequently the estimation of unaided thresholds in the hearing impaired population is dependent on the establishment of normative data from the normal hearing population. The aim of this study was to determine the influence of insert earphones and sound field speaker presentation on threshold estimations using monotic auditory steady state evoked potentials, in a group of normal hearing adults. To achieve the aim of the study, a comparative, within-group experimental design was selected. The results of the current study indicated that the monotic single ASSEP technique under both insert earphone- and sound field conditions provided a reasonable estimation (25-35 dB HL for inset earphones; 20-33 dB HL for sound field speaker presentation) of the behavioural pure tone thresholds. The minimum response levels obtained under insert earphone conditions differed significantly from those obtained under sound field conditions for all the frequencies tested except 2 kHz (p < 0.01). Subsequently, the current study indicates that minimum response levels obtained using a specific transducer should serve as the basis of comparison with behavioural thresholds obtained under the same transducer. Therefore, behavioural pure tone thresholds obtained under insert earphone conditions will not suffice as a basis of comparison for minimum response levels obtained for the ASSEP technique under sound field conditions, and vice versa. This research endeavour concluded that the monotic ASSEP technique under both insert earphone and sound field conditions provide useful information for the estimation of frequency specific thresholds, but that the results are transducer specific and that comparison across transducers should be avoided. / Dissertation (M (Communication Pathology))--University of Pretoria, 2006. / Speech-Language Pathology and Audiology / Unrestricted

Cette recherche s’articule en deux parties. L’objectif de la première partie est d’analyser par voie expérimentale et numérique la phénoménologie du décollement interne, dit décollement de jet (en regimes transitoire et établi) dans les tuyères supersoniques refroidies par film fluide. La deuxième partie porte sur la réinterprétation des concepts de tuyère existants pour aboutir à la proposition d’un nouveau dispositif de détente supersonique, qui offre une résistance accrue au décollement de jet. La première partie de cette thèse est basée sur l’analyse des résultats expérimentaux obtenus lors de la campagne d’essais réalisée à l’ONERA. Ces essais, ont mis en évidence des spécificités de comportement de la tuyère, inhérentes à la manière d’amorcer le jet supersonique principal par rapport à l’établissement du film pariétal. Ces mêmes expériences ont permis d’étudier le comportement instationnaire du décollement de jet lorsque les conditions d’alimentation sont maintenues en régime établi. L’apparition de fréquences caractéristiques a été mise en évidence et leur origine a été étudiée à l’aide de simulations numériques. En nous appuyant sur les considérations issues de la première partie de l’étude, une revue critique des concepts de tuyère existants a été menée. Ce travail a permis d’identifier une lacune majeure dans la définition des tuyères à écoulement interne, à savoir l’absence d’une « barrière » qui puisse prévenir l’occurrence du décollement de jet. Ainsi, nous avons proposé la conjonction d’un dispositif à écoulement externe (aerospike) et d’une tuyère classique afin de résoudre cette problématique in nuce, en créant une barrière fluidique continue tout autour du plan de sortie de la tuyère principale. L’efficacité de ce concept a donc été prouvée par calcul, puis une campagne expérimentale a été organisée afin de valider les résultats obtenus. / This research is in two parts. The objective of the first part is to analyse by experimental and numerical means the phenomenology of nozzle flow separation in transient and steady state conditions. The second part of this research work focuses on the reinterpretation of existing concepts of converging-diverging nozzles, leading to the proposal of a new supersonic expansion device, with improved flow separation characteristics.Experimental data, collected during the test campaign conducted at ONERA, have been analysed and are presented in the first part of this thesis. Obtained results highlight some peculiarities of the transient behavior of the nozzle, mostly dependent on the synchronisation between the start-up phase of the main jet and the grow-up of the wall film. These same experiments have been also used to investigate the unsteadiness of the flow separation, when nozzle feeding conditions are maintained constant. Appearance of characteristic frequencies has been highlighted and their origin has been investigated by CFD simulations.In the second part, a critical review of existing nozzle concepts was conducted. This allowed identifying a major gap in the definition of traditional supersonic nozzles, namely the absence of a "barrier" that can prevent the occurrence of the flow separation. Thus, in the second part of this thesis we propose a new nozzle concept. It is based on the combination of a small aerospike and a conventional nozzle (main flow). Such an arrangement allows solving the flow separation problem in nuce. The effectiveness of this concept has been proved by calculation and by an experimental test campaign.

La croissance cristalline de KH2PO4(KDP)and K(H1-xDx)2PO4(DKDP)a été fortement étudiée depuis de nombreuses années. Les propriétés optiques nonlinéaires (conversion de fréquence: doublage pour le KDP et triplage pour le DKDP)et les études fondamentales sur les mécanismes de croissance sont à la base du développement important de la croissance de ces cristaux. Au début des années 90, un fort intérêt s'est porté sur le KDP et DKDP pour les dispositifs optiques à large ouverture pour les applications industrielles de fusion inertielle comme au NAtional Ignition Facility (NIF) aux USA ou pour le laser MégaJoule en France. La dimension de ces optiques (40*40 cm²) nécessite des cristaux géants crûs en solution. Une technique de croissance rapide a été développé par abaissement de température dans un réacteur de 1000L et par une filtration en continu afin d'éviter la nucléation spontanée. Cette méthode est très robuste et fiable pour la croissance rapide de cristaux géants de KDP mais néanmoins montre des limitations inhérentes à cette méthode. En effet, cela mène à des cristaux inhomogènes (défauts, inhomogénéités isotopiques)ce qui est rédhibitoire pour des solutions solides intermédiaires comme le DKDP : la composition en début de croissance peut varier significativement de celle en fin de croissance. Très récemment, des méthodes par circulation de solution en conditions stationnaires ont été développées pour palier à ce problèmeet sont considérées comme les plus pertinentes. C'est pourquoi nous avons développé un système par circulation en conditions stationnaires avec un traitement original de la solution. Dans un premier temps, le système a été testé sur un composé modèle KDP puis dans un deuxième sur le composé utilisé pour l'application DKDP. / Crystal Growth of KH2PO4(KDP)and K(H1-xDx)2PO4(DKDP)has been extensively covered over the years. For decades KDP and DKDP crystals have been grown either for their nonlinear optical properties (frequency conversion : doubling for KDP and tripling for DKDP) or for fundamental studies on crystal growth mechanisms. At the beginning of the 90's, a special interest arose for KDP for large aperture optical elements for laser fusion facilities such as the National Ignition Facility (NIF)in the USA or for the laser MegaJoule in France. The size of such optics(40*40 cm²)requires giant crystals to be grown in solution. A rapid growth technique has been developed based on the temperature lowering of a 1000L solution and its continuous filtration to avoid spurious nucleation. While this method is very robust and fully mature for the rapid growth of giant KDPs it nonetheless suffers from the limitations inherent to the Temperature Lowering Method(TLM).It does not provide stable growth conditions(temperature and supersaturation change).This can lead to inhomogeneous crystals (defects, isotopic inhomogeneity)and this is critical for intermediate of a solid solutions as the DKDP : the composition grown at the beginning can differ significantly from the one crystallizing later. Very early, transport methods growing crystals in stationary conditions, were considered to be "the most pertinent ones". That's why we have developed a growth system in stationary conditions with an original treatment of the solution. The grown compound selected was firstly KDP (model compound)then DKDP (KDP deuterated) for the desired application.

ABSTRACT This thesis is concerned with a technical modification of design of the electrical power systems for Modřice and its surroundings. The thesis describes a basic theoretical distribution of the electricity network and the distribution network itself. Following chapters are devoted to the development and construction of the HV networks and to the methods and ways of calculating the steady operation of the network. These methods are then used in the computational programs that are presented in the next chapter of this paper. The aim of the practical part of the thesis is to first determine the current state of the network in the given location. Furthermore, several modifications are proposed according to the requirements for increasing the power consumption or connecting the new supply places. The proposed modifications are further assessed for the different operating conditions. The result is a network that is functional, operational and reliable. The whole analysis is carried out in the PAS DAISY Off-line V4 Bizon computing program.

Disertační práce se zabývá chováním a odezvou elastohydrodynamického (EHD) mazacího filmu za neustálených provozních podmínek. V úvodní části práce jsou shrnuty poznatky z oblasti EHD mazání; od jeho historie, přes základní mechanismy mazání a používané experimentální metody, až po nedávno publikované studie zaměřené na transientní podmínky. Hlavním cílem práce bylo experimentálně objasnit vliv provozních parametrů a reologických vlastností maziv na chování mazacího filmu v bodovém kontaktu při jeho nárazovém zatěžování a vystavení příčným vibracím. Za tímto účelem byla vyvinuta laboratorní zařízení umožňující měření rozložení mazacího filmu a tření za kontrolovaných nestacionárních podmínek. Experimenty odhalili zásadní roli přibližovacích a zatěžovacích rychlostí na formování stlačených mazacích filmů při nárazovém zatěžování. Výsledky byly srovnávány s nedávným teoretickým řešením. Bylo ukázáno na jeho nedostatky, jež byly následně odstraněny implementací empirických vztahů zohledňujících reologii maziv. V případě příčných vibrací byly nalezeny hranice selhání mazacího filmu a určeny vztahy popisující vliv příčných vibrací na centrální tloušťku filmu a její fluktuace jednotně pro všechny maziva. Závěrečná část práce poskytuje nový pohled na reologii maziv pomocí inovativního přístupu měření třecích reakcí maziva současně ve dvou směrech kontaktu za podmínek příčných vibrací. Tyto původní výsledky rozšiřují pochopení mechanizmů EHD mazání a mohou být použity k dokonalejším návrhům strojů, a vylepšit tak jejich účinnost, spolehlivost a životnost.

The goal of this Master thesis is to design a power convertor for BLDC motor 48V/2kW. Emphasis is placed on the small dimensions of the final printed circuit board. Therefore, power SMD transistors STL135N8F7AG are used in small packages PowerFlat 5x6. To reduce area of the PCB, electrolytic capacitors are mounted on a separate board, which is located above the main PCB. Small high-capacity 22F/100V ceramic capacitors are used in the DC-LINK as well. They are located as close as possible to the power SMD tranzistors. Control logic will be provided by microprocesor STM32G474RE. High resolution timer HRTIM1 is used. The first part of this thesis is devoted to the brief description of BLDC motor construction and driving. Next parts are focused on the design itself.

Knowlege of elektric power, power dissipation and voltage conditions in every single segments and elektric power system nodes is necessary for operations control and designing of another elektric power system expansion. In this Thesis, we will handle with steady state of system calculation using PAS-DAISY-OFF LINE software, solving various power network configurations and their verification.

This thesis deals with the steady operation and short-circuit conditions in the 110 kV network E.ON in a separate and parallel operation of nodal areas of Otrokovice substation and Sokolnice substation. The theoretical part is devoted to the calculation of steady state high-voltage systems using Newton's iterative method, transient phenomena that may occur in the power system short-circuit calculations and theories. The practical part deals with the actual calculations of steady state and short-circuit conditions in a separate and parallel operation of nodal areas Sokolnice-Otrokovice, which were calculated using the dispatching program. These calculations are then evaluated for possible use of involvement in actual operation. At the end there are suggestions on operational measures in the network 110 kV.

Freshwater lakes constrain its methane (CH4) emissions through CH4 oxidation. CH4 includes three carbon (C) isotopes; the stable isotopes 12C,13C and the unstable and more uncommon isotope 14C. Methanotrophs (i.e. methane oxidizing bacteria) oxidize the lighter isotope more rapidly. Changes in relative isotopic composition can therefore be used to calculate how much CH4 is oxidized in a system. This study investigates an annual CH4 oxidation in a freshwater lake. Water samples and bubbles of CH4 gas were collected once a month, from March to November, in lake Gundlebosjön. The CH4 gas was separated from the water samples with a headspace extraction technique. The concentration and isotopic composition of CH4 was analyzed in a cavity ring down spectrometer. The isotopic data was used in two mathematical models, based on open-steady state and closed systems. It was found that the stable isotope method to estimate CH4 oxidation was only useful during periods when clear concentration and isotope differences could be observed in the water column. CH4 oxidation could only be estimated in the water column in August, and in the surface layer in June and July. / Utsläppen av metan (CH4) från sötvattensjöar begränsas genom CH4 oxidation. Det är två stabila kolisotoper som dominerar i CH4; 12C och 13C. Den ostabila kolisotopen 14C finns även i CH4, men den är mer ovanlig i naturen. Metantrofer (metanoxiderande bakterier) oxiderar den lättare kolisotopen snabbare. Förändringar i isotopsammansättningen kan användas för att beräkna hur mycket CH4 som oxideras i ett system. Denna studie undersöker en årlig CH4 oxidation i en sötvattensjö. Vattenprover och bubblor av CH4-gas samlades en gång i månaden, från mars till november, i Gundlebosjön. CH4 gasen separerades från vattenproverna med en ”headspace extraction” teknik. Koncentration och isotopsammansättningen av CH4 analyserades i en ”cavity ring down spectrometer”. Isotopdata användes i två matematiska modeller, baserade på öppet-stabilt tillstånd och stängt system. Den stabila isotopmetoden för att uppskatta CH4 oxidation var endast användbar under perioder då tydliga skillnader i koncentrationen och isotopsammansättningen kunde observeras i vattenpelaren. CH4 oxidation kunde endast uppskattas i vattenpelaren i augusti, och i vattenpelarens ytskikt i juni och juli.

<p>Early processes following photon absorption by the photosynthetic pigment-protein complex photosystem I (PS I) have been the subject of decades of research, yet many questions remain in this area of study. Among the trickiest to investigate is the role of the PS I reaction center’s (RC’s) two accessory (A_‑1) chlorophyll (Chl) cofactors as primary electron donors or acceptors, oxidizing the special pair (P₇₀₀) of Chls or reducing a nominal primary electron acceptor (A₀) Chl in the first electron transfer step. Such processes, which occur on a picosecond timescale, have long been studied via ultrafast spectroscopy, though difficulty lies in distinguishing among signals from early processes, which have similar lifetimes and involve many identical pigments. In this work, we used steady-state and ultrafast optical pump-probe spectroscopies on PS I trimers from wildtype and mutant strains of the cyanobacterium <i>Synechocystis</i> sp. PCC 6803 in which an asparagine amino acid residue near A_‑1 had been replaced with methionine on one or both sides of the RC. We also conducted an identical set of experiments on mutants in which A₀ was similarly targeted, as well as studied the effects on the A₀ absorption spectrum of a third category of mutations in which a peripheral H‑bond to A₀ was lost. Steady-state absorption spectroscopy revealed that many of these mutations caused mild Chl deficiencies in the light-capturing antenna of PS I without necessarily preventing organisms’ growth. More importantly, we determined that contrary to certain hypotheses, A_‑1 is the most likely true first electron acceptor, as reasoned from observing rapid triplet state formation in double A_‑1 mutants. We also concluded from non-additive detrimental effects of single-side mutations that if one RC branch is damaged at the level of A₀ or A_‑1, electron transfer may be redirected along the intact branch. This may help explain the conservation of two functional RC branches in PS I over many generations of natural selection, despite the additional cost to organisms of manufacturing both.</p>