Einleitung Erkrankungen des Bewegungsapparates haben bei Milchkühen eine hohe wirtschaftliche Bedeutung sowie enorme Auswirkungen auf das Tierwohl. Etwa 90 % der Lahmheiten beim Rind werden durch Klauenerkrankungen hervorgerufen. Die Ursachen dieser Klauenerkrankungen sind multifaktoriell und umfassen tier- und umweltassoziierte Faktoren. Die Pododermatitis aseptica diffusa ist eine der wichtigsten Ursachen für die Entstehung von umschriebenen Klauenlederhautentzündungen. In ihrer Pathogenese spielen Veränderungen der Zehendurchblutung eine zentrale Rolle. Die Pulsed-Wave (PW)-Dopplersonographie ist eine nicht invasive Technik zur Beurteilung des Blutflusses an Gefäßen und zur Untersuchung der Durchblutung von Organen. Jedoch liegen keine PW-Dopplersonographischen Untersuchungen an der Zehe des Rindes in der Literatur vor. Ziele der Untersuchungen Ziel der Untersuchungen war es, die Zehendurchblutung bei Rindern, die an einer Pododermatitis circumscripta solearis oder parietalis litten, im Milchviehbetrieb zu erfassen. Dazu wurde in einem ersten Schritt die Methodik der PW-Dopplersonographie an der Zehe der Hintergliedmaßen von gesunden Kühen etabliert. In einem zweiten Schritt wurden Blutflussmerkmale an den Hintergliedmaßen lahmer Kühe, die an einer Pododermatitis circumscripta solearis oder parietalis litten, erfasst, um Auswirkungen der Entzündung sowie weiterer als relevant erscheinender Einflussfaktoren für die Zehendurchblutung zu untersuchen. Material und Methoden In der Publikation 1 wurden 22 gesunde Deutsch Holstein Kühe einbezogen. Die Versuchstiere wurden im Betrieb einer klinischen Untersuchung inklusive einer Lahmheitsbeurteilung sowie einer Klauenpflege aller Gliedmaßen unterzogen. Am zweiten Versuchstag wurde eine sonographische Untersuchung beider Hintergliedmaßen am stehenden Tier durchgeführt. Zur sonographischen Untersuchung wurde das MyLab One (Esaote Deutschland GmbH) mit einem Linearschallkopf (10 MHz) ohne Vorlaufstrecke verwendet. Mittels Brightness(B)-Mode wurden Weichteilgewebe, synoviale Einrichtungen und Blutgefäße distal des Tarsus untersucht. In der Arteria (A.) interdigitalis wurde der Blutfluss mittels PW-Dopplersonographie beurteilt. Die Auswertung der Daten erfolgte mit dem Programm MyLap Desk auf einem Laptop. In die Publikation 2 wurden 33 lahme und 11 gesunde Deutsch Holstein Kühe einbezogen. Die lahmen Kühe litten an einer superfiziellen bis profunden Pododermatitis an der Außenklaue einer Hintergliedmaße. Die klinische und sonographische Untersuchung erfolgte wie in der Publikation 1 beschrieben. Für die statistische Bearbeitung der Daten wurde die procedure mixed (SAS, Version 9.4) verwendet. Ergebnisse In den Publikationen 1 und 2 konnte an 112 von 132 Hintergliedmaßen bei 66 Kühen ein auswertbares PW-Doppler-Signal gemessen werden. Bei 17 der 20 nicht auswertbaren Hintergliedmaßen lag nur eine mäßige B-Mode-Bildqualität vor. Die lahmen Kühe trippelten bei der sonographischen Untersuchung mehr als die gesunden Kühe. Blutflusskurventypen mit einem niedrigen peripheren Gefäßwiderstand liegen vor allem an den Hintergliedmaßen lahmer Kühe und Kurventypen mit einem hohen Widerstand am häufigsten bei gesunden Kühen vor. Lahme Kühe haben im Vergleich zu nicht-lahmen Kühen einen erhöhten Gefäßdurchmesser (D) und eine gesteigerte Blutflussrate (BF) sowie enddiastolische Blutflussgeschwindigkeit. Es bestehen keine Unterschiede zwischen der betroffenen Gliedmaße und der Gegengliedmaße lahmer Kühe. Ein numerisch höherer D, eine höhere BF sowie maximale systolische und maximale mittlere Blutflussgeschwindigkeit liegen bei Kühen mit einer mittelgradigen Lahmheit vor. Schlussfolgerungen Die PW-Dopplersonographie in Kombination mit dem in der Studie verwendeten Untersuchungsgang ist für die Messung des Blutflusses in der A. interdigitalis an den Hintergliedmaßen des Rindes sehr gut geeignet. Sowohl die bei den Kühen gefundenen Blutflusskurvenprofile als auch die quantitativen Blutflussmerkmale sind mit Werten von Pferden vergleichbar. Es liegt eine gesteigerte Durchblutung an den betroffenen Zehen und denen der Gegengliedmaße von lahmen Kühen im Vergleich zu gesunden Kühen vor. Nicht nur das Vorliegen einer umschriebenen Klauenlederhautentzündung, sondern auch ihr zeitlicher Verlauf, die Auswirkungen einer aktivierten Entzündungskaskade, das Vorliegen einer chronischen Klauenrehe und vor allem die Gewichtsbelastung und die Gewichtsverschiebung zwischen den Hintergliedmaßen müssen in die Beurteilung des digitalen Blutflusses einbezogen werden. Die erstmalig an der Rinderzehe ermittelten Blutflussdaten stellen eine gute Grundlage für weitere Forschungen auf dem Gebiet der Klauenrehe-Pathogenese dar.:Inhaltsverzeichnis 1 Einleitung 1 2 Literaturübersicht 3 2.1 Pododermatitis aseptica diffusa beim Rind 3 2.1.1 Definition 3 2.1.2 Symptomatik 3 2.1.2.1 Klinisches Stadium 3 2.1.2.1.1 Akute Form 3 2.1.2.1.2 Subakute Form 4 2.1.2.1.3 Chronische Form 4 2.1.2.2 Subklinisches Stadium 5 2.1.3 Ätiologie 5 2.1.3.1 Fütterung 5 2.1.3.1.1 Zusammenhang zwischen Fütterung und Dysfunktion des Blutgefäßsystems der Zehe 5 2.1.3.1.2 Kohlenhydrate 7 2.1.3.1.3 Proteine und Aminosäuren 9 2.1.3.1.4 Lipide 10 2.1.3.1.5 Spurenelemente 10 2.1.3.1.5.1 Kupfer 10 2.1.3.1.5.2 Zink 10 2.1.3.1.5.3 Mangan 11 2.1.3.1.5.4 Selen 11 2.1.3.1.6 Vitamine 11 2.1.3.1.6.1 Biotin 11 2.1.3.1.6.2 Vitamine A, D, E 12 2.1.3.1.7 Toxine 12 2.1.3.1.8 Bewertung der Versorgung mit Mineralstoffen, Spurenelementen und Vitaminen für die Klauengesundheit 12 2.1.3.2 Mechanische Faktoren 13 2.1.3.2.1 Digitales Fettpolster 13 2.1.3.2.2 Hypertrophie der Außenklaue an den Hintergliedmaßen 14 2.1.3.2.3 Dünne Sohlen 14 2.1.3.3 Hormonelle Veränderungen während der Transitphase 15 2.1.3.4 Haltung 17 2.1.4 Pathogenese 18 2.1.5 Reheassoziierte Klauenlederhautentzündungen 19 2.2 Anatomie des Blutgefäßsystems beim Rind 20 2.2.1 Arterien der Hintergliedmaße 20 2.2.1.1 Arterien am Ober- und Unterschenkel 20 2.2.1.2 Arterien an Mittelfuß und Zehen 21 2.2.1.2.1 Plantares System 21 2.2.1.2.2 Dorsales System 21 2.2.2 Venen der Hintergliedmaße 21 2.2.2.1 Venen am Ober- und Unterschenkel 21 2.2.2.2 Venen an Mittelfuß und Zehen 22 2.2.2.2.1 Plantares System 22 2.2.2.2.2 Dorsales System 22 2.2.3 Blutgefäßsystem der Klauen 23 2.2.3.1 Arterien 23 2.2.3.2 Venen 23 2.2.3.3 Arterio-venöse Anastomosen 24 2.3 Bildgebende Verfahren zur Darstellung des Gefäßsystems 24 2.3.1 Allgemein 24 2.3.2 Brightness Mode Sonographie 25 2.3.2.1 Prinzip 25 2.3.2.2 Allgemeine Anwendung an der Gliedmaße 25 2.3.2.3 Spezielle Anwendung zur Untersuchung des Blutgefäßsystems an der Gliedmaße distal des Tarsus 26 2.3.3 Pulsed-Wave-Dopplersonographie 27 2.3.3.1 Prinzip 27 2.3.3.2 Merkmale 29 2.3.3.3 Allgemeine Anwendung 30 2.3.3.4 Anwendung an der Gliedmaße 30 2.3.4 Weitere bildgebende Verfahren 33 2.3.4.1 Angiographie 33 2.3.4.1.1 Prinzip 33 2.3.4.1.2 Anwendung an der Gliedmaße 34 2.3.4.2 Szintigraphie 34 2.4 Zusammenfassende Schlussfolgerungen aus dem Literaturstudium 35 3 Publikation 1 37 4 Publikation 2 47 5 Diskussion 59 5.1 Auswahl des Messpunktes und Messbarkeit des Blutflusses 59 5.2 Verhalten 60 5.3 Gliedmaßenstellung 60 5.4 Qualitative Blutflussmerkmale 61 5.5 Quantitative Blutflussmerkmale 62 6 Zusammenfassung 66 7 Summary 68 8 Literaturverzeichnis 70 9 Danksagung 96 / Introduction Diseases of the locomotor system in dairy cattle have a huge economic and welfare importance. Nearly 90 % of lameness in cattle is caused by claw disease. The reasons are multifactorial and include animal as well as environmental factors. Claw horn disruption is the main cause for the development of claw horn lesions. Changes in the blood circulation of the toes play an essential role in their pathogenesis. Pulsed-Wave (PW)-Doppler ultrasonography is a non-invasive technique to evaluate the flow in blood vessels and to examine the blood circulation of an organ. However, there have not been any PW-Doppler ultrasonographical investigations for the bovine limb in the literature yet. Aims The objective of this investigation is to measure the blood flow of the toes in dairy cattle suffering from sole ulcer or white line disease in dairy farms. In a first step the PW-Doppler ultrasonography was established at the toe of hindlimbs in healthy dairy cattle. In a second step blood flow variables in the hindlimbs of lame cows affected by a sole ulcer or white line disease were recorded to evaluate the consequence of inflammation as well as to examine further factors seem to influence the blood flow of the toes. Material and Methods Twenty-two German Holstein cows were included in the first publication. The cows were examined clinically in the farm including an evaluation of the lameness score as well as a claw trimming of all limbs. One day after an ultrasonography was performed in standing position in both hind limbs. For the examination a MyLabOne (Esaote Deutschland GmbH) with a linear transducer without a standoff pad was used. Soft tissue, synovial structures and blood vessels distal of the tarsal region were examined by using a Brightness (B)-mode ultrasonography. In the interdigital arteria the blood flow was measured by PW-Doppler ultrasonography. The analysis of the data was carried out by the program MyLabDesk on a laptop. The second publication included 33 lame and 11 healthy German Holstein cows. The lame cows suffered from a superficial too profound sole ulcer or white line disease at the outer claw of one hind limb. The clinical and ultrasonographical examination took place analogically to the first publication. For the statistical analyses the MIXED procedure (SAS, version 9.4) was used. Results Combining both publications in 112 of 132 hindlimbs a usable PW-Doppler signal was generated. Seventeen of the 20 not usable signals the B-mode quality was moderate. During the ultrasonography lame cows pattered their limbs more often than healthy cows. Blood flow profiles with a low peripheral resistance are more common in the hindlimbs of lame cows and profiles with a high peripheral resistance are most frequent in healthy cows. Lame cows have a higher vessel diameter (D), blood flow rate (BF) and end-diastolic blood flow velocity compared to healthy cows. There was no difference in the affected compared to the opposite limbs of lame cows. A numerical higher D, BF as well as maximum systolic and maximum time-averaged mean blood flow velocity occurred in moderate lame cows compared to mild lame cows. Conclusions The PW-Doppler ultrasonography is well suited for the evaluation of the blood flow in the bovine interdigital artery at the hindlimbs. The observed blood flow profiles as well as quantitative blood flow parameters are comparable to data in horses. There is an increased blood circulation in the affected and the opposite limb of lame cows compared to healthy cows. Not only the existence of the claw horn lesions but also their chronological progress, the influence of the inflammatory cascade, the availability of chronic claw horn disruption and especially weight bearing and weight shifting between hindlimbs have to be considered in the assessment of the blood flow of toes. The for the first-time generated blood flow parameters provide a good basis for further investigations in the topic of claw horn disruption pathogenesis.:Inhaltsverzeichnis 1 Einleitung 1 2 Literaturübersicht 3 2.1 Pododermatitis aseptica diffusa beim Rind 3 2.1.1 Definition 3 2.1.2 Symptomatik 3 2.1.2.1 Klinisches Stadium 3 2.1.2.1.1 Akute Form 3 2.1.2.1.2 Subakute Form 4 2.1.2.1.3 Chronische Form 4 2.1.2.2 Subklinisches Stadium 5 2.1.3 Ätiologie 5 2.1.3.1 Fütterung 5 2.1.3.1.1 Zusammenhang zwischen Fütterung und Dysfunktion des Blutgefäßsystems der Zehe 5 2.1.3.1.2 Kohlenhydrate 7 2.1.3.1.3 Proteine und Aminosäuren 9 2.1.3.1.4 Lipide 10 2.1.3.1.5 Spurenelemente 10 2.1.3.1.5.1 Kupfer 10 2.1.3.1.5.2 Zink 10 2.1.3.1.5.3 Mangan 11 2.1.3.1.5.4 Selen 11 2.1.3.1.6 Vitamine 11 2.1.3.1.6.1 Biotin 11 2.1.3.1.6.2 Vitamine A, D, E 12 2.1.3.1.7 Toxine 12 2.1.3.1.8 Bewertung der Versorgung mit Mineralstoffen, Spurenelementen und Vitaminen für die Klauengesundheit 12 2.1.3.2 Mechanische Faktoren 13 2.1.3.2.1 Digitales Fettpolster 13 2.1.3.2.2 Hypertrophie der Außenklaue an den Hintergliedmaßen 14 2.1.3.2.3 Dünne Sohlen 14 2.1.3.3 Hormonelle Veränderungen während der Transitphase 15 2.1.3.4 Haltung 17 2.1.4 Pathogenese 18 2.1.5 Reheassoziierte Klauenlederhautentzündungen 19 2.2 Anatomie des Blutgefäßsystems beim Rind 20 2.2.1 Arterien der Hintergliedmaße 20 2.2.1.1 Arterien am Ober- und Unterschenkel 20 2.2.1.2 Arterien an Mittelfuß und Zehen 21 2.2.1.2.1 Plantares System 21 2.2.1.2.2 Dorsales System 21 2.2.2 Venen der Hintergliedmaße 21 2.2.2.1 Venen am Ober- und Unterschenkel 21 2.2.2.2 Venen an Mittelfuß und Zehen 22 2.2.2.2.1 Plantares System 22 2.2.2.2.2 Dorsales System 22 2.2.3 Blutgefäßsystem der Klauen 23 2.2.3.1 Arterien 23 2.2.3.2 Venen 23 2.2.3.3 Arterio-venöse Anastomosen 24 2.3 Bildgebende Verfahren zur Darstellung des Gefäßsystems 24 2.3.1 Allgemein 24 2.3.2 Brightness Mode Sonographie 25 2.3.2.1 Prinzip 25 2.3.2.2 Allgemeine Anwendung an der Gliedmaße 25 2.3.2.3 Spezielle Anwendung zur Untersuchung des Blutgefäßsystems an der Gliedmaße distal des Tarsus 26 2.3.3 Pulsed-Wave-Dopplersonographie 27 2.3.3.1 Prinzip 27 2.3.3.2 Merkmale 29 2.3.3.3 Allgemeine Anwendung 30 2.3.3.4 Anwendung an der Gliedmaße 30 2.3.4 Weitere bildgebende Verfahren 33 2.3.4.1 Angiographie 33 2.3.4.1.1 Prinzip 33 2.3.4.1.2 Anwendung an der Gliedmaße 34 2.3.4.2 Szintigraphie 34 2.4 Zusammenfassende Schlussfolgerungen aus dem Literaturstudium 35 3 Publikation 1 37 4 Publikation 2 47 5 Diskussion 59 5.1 Auswahl des Messpunktes und Messbarkeit des Blutflusses 59 5.2 Verhalten 60 5.3 Gliedmaßenstellung 60 5.4 Qualitative Blutflussmerkmale 61 5.5 Quantitative Blutflussmerkmale 62 6 Zusammenfassung 66 7 Summary 68 8 Literaturverzeichnis 70 9 Danksagung 96

Energy storage systems will likely be needed for future shipboard power systems that supply loads with high power variability such as pulsed power loads. The power generation in shipboard power systems may not be sufficient to satisfy the energy demands of the pulsed power load systems operating in conjunction with other ship service loads. Two fundamental items in evaluating the requirements of an energy storage system are the energy storage capacity and the ratings of the power conversion equipment that interfaces the energy device to the power system. The supply current of pulsed power load systems is aperiodic and cannot be described in terms of active power. Also, the RMS value and thus apparent power are only defined for periodic quantities. Therefore traditional methods of rating power equipment cannot be used. This thesis describes an approach to determine the ratings of an energy storage interface and the energy storage capacity of an energy storage device as a function of load and supply parameters. The results obtained using the proposed approach are validated with the results obtained from the simulation model of the generator supplying a pulsed power load in conjunction with an energy storage system. The energy storage system requirements for various pulsed power load profiles are obtained using the proposed approach. The method used for determining the ratings of an energy storage system utilizes an orthogonal decomposition of pulsed power load system supply current evaluated within a sliding window. The signals obtained from the decomposition are also useful in generating the control reference signals for the energy storage interface. Although the approach and methods are focused on a particular structure of the pulsed power load system, they may be generalized for use in any type of configuration of a pulsed power load system.

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Thesis (MSc)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: In this investigation the formation of thin film manganites and their electrical characteristics is studied. In order to see the effect of oxidation states on magneto-resistivity, 80% of Mn is replaced by Fe. Pulsed laser deposition (3 J/cm2), carried out in oxygen partial pressures ranging from 0.01 mbar to 1.00 mbar was used to fabricate the thin films from two target compositions, namely La2CaMn2.94Feo.0609 and La2CaMno.6Fe2.409. Films were deposited on Si< 100 >, MgO< 100 >, SrTi03< 100 > and LaAl03< 100 > single crystal substrates. Samples were characterized by RBS, AFM, SEM, and XRD. Electrical measurements were also carried out. One of the main characterization techniques in this investigation is Rutherford Backscattering Spectrometry (RBS). It has been shown that RBS is a very powerful characterization technique when used in conjunction with the RUMP simulation program. The effect of various parameters can be determined beforehand by RUMP simulation of the thin film structures to be investigated. Simulation shows that RBS is an excellent characterization tool for determining film thickness and stoichiometry. The role of oxygen uptake in La2CaMn3_xFexOg was investigated as the oxidation states of elements in manganite materials have a large effect on their magnetoresistive properties. The height of the La signal can be used as a measure of the oxygen content. RBS spectra of films deposited on single crystal silicon substrates at different ambient pressures show that the fit between simulated and measured RBS spectra improves with higher oxygen pressures, thereby indicating better quality manganite material. The RBS spectra also show that the films have good stoichiometry. Atomic force microscopy was used to determine the roughness of the thin films. The annealed film (average roughness 4.5 nm) shows a surface smoother than the non-annealed film (average roughness 5.3 nm). SEM measurements show that in the case of samples having a high Fe content, the crystallite size varies between about 0.04 11m and 0.10 11m, while for samples with high manganese content, the crystallinity varies between 0.03 jJ,m and 0.06jLm. Manganites were analyzed using Bragg-Brentano (28) X-ray diffraction. Measurements show that manganite films cannot be grown epitaxially on Si< 100 > and MgO< 100 > single crystals due to a large lattice mismatch. In the case of SrTi03 and LaAl03 several reflections and sharp peaks from the film can be seen, indicating reasonable epitaxial growth. SEM measurements of the samples however show polycrystallinity. Complete epitaxy has thus not occurred, but many grains have an epitaxial orientation. Resistance versus temperature (the room temperature to about 100 K) in zero magnetic field was measured for a La2CaMno.06Fe2.409 thin film and maximum resistance corresponding to about 108 K was found. At higher temperatures the resistance decreases as temperature increases. The manganite thin film therefore shows semiconductor behaviour. Resistance measurements carried out at different magnetic fields (0 - 1 T) show a small positive magnetoresistance of 0.83 %. Usually the magnetoresistance phenomenon is measured at higher magnetic fields and this could be the reason for our low value as well as the fact that the iron content could be too high. / AFRIKAANSE OPSOMMING: In hierdie ondersoek is die formasie en karakterisering van dunlagie manganiete ondersoek. Om die effek van oksidasie-toestand op magnetoresistiwiteit te bepaal, is 80% van die Mn verplaas deur Fe. Pulseerde laser deposissie(3 J/cm2), is uitgevoer by 'n parsiële suurstof druk tussen 0.10 en 1.00 mbar deur gebruik te maak van La2Ca Mn2.94Feo.o609 en La2CaMno.6Fe2.409 teiken skywe. Dunlagies was gedeponeer op Si<IOO>, MgO<IOO>, SrTi03<100> en LaAl03<100> enkelkristal substrate. Die dunlagies is daarna ge-karakteriseer met behulp van Rutherford terugverstrooing (RBS), atoom krag mikroskopie(AFM), skandeer elektronmikroskopie (SEM) en xstraal diffraksie(XRD). Elektriese metings is ook uitgevoer. Een van die hoof tegnieke wat gebruik is in hierdie ondersoek is Rutherford terugverstrooing (RBS) van 2 Mev alfa-deeltjies. In hierdie navorsing is aangetoon dat RBS saam met spektra simulasie(RUMP), 'n besondere kragtige metode is om die stoichiometrie en dikte van manganiet lagies te bepaal. Die rol van die opname van suurstof in die dunlagies was ondersoek, aangesien die oksidasie toestand van manganiet lagies 'n groot effek het op hulle magnetoresistiwiteit. Die hoogte van die La sein is gebruik as 'n maatstaf van suurstof inhoud. RBS spektra van dunlagies gevorm op enkelkristal silikon substrate by verskillende parsiële suurstof drukke wys dat die passing tussen gemete en gesimuleerde spektra verbeter by hoër suurstof drukke, wat beter kwaliteit manganiet materiaal aandui. Die RBS spektra het ook aangetoon dat die stoichiometrie van die lagies uitstekend is. Atoom krag mikroskopie(AFM) is gebruik om die grofheid van die oppervlaktes van die dunlagies te bepaal. Lagies wat by 750 grade celsius uitgegloei is ( gemiddelde gladheid van 4.5 nm) was gladder as films wat nie na ablasie uitgegloei is nie (gemiddelde gladheid van 5.3 nm). SEM metings toon ook dat dunlagies met 'n hoë Fe inhoud 'n kristalliet deursnit het van 0.04 tot 0.10 mikrometer en die met 'n hoë mangaan inhoud 'n poli-kristalliniteit het van tussen 0.03 en 0.06 mikrometer het. Bragg-Brentano(twee-theta) X-straal diffraksie meting wys dat manganiet films nie epitaksieël op Si<IOO> en MgO<IOO> enkelkristal substrate gevorm kan word nie, weens 'n groot verskil in die kristal-rooster parameters. SEM metings van die monsters wys polikristalliniteit. Algehele epitaksie het dus nie plaasgevind nie, maar verskeie kristalliete het 'n epitaksiële orientasie. Weerstand metings is gemaak by temperature so laag as 100 Kelvin vir La2CaMno.o6Fe2.409dunlagies en 'n maksimum weerstand is by 108 Kelvin gevind. By hoër temperature het die weerstand afgeneem soos die temperatuur toeneem, wat halfgeleier gedrag aandui. Weerstand metings by verskillende magneetvelde (0 tot I Tesla) wys 'n klein magnetoresistiwiteits effek van 0.83%. Gewoonlik word magnetoresistiwiteit gemeet by hoë magneet velde (ongeveer 6 Tesla). Dit, sowel as die hoë Fe samestelling van die monsters kan die rede wees vir die lae magnetoresistiwiteit wat waargeneem word.

Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: With technological advances in solid-state switches the modernization of conventional pulsed power supplies utilizing thyratrons has become possible. A novel pulsed power supply is designed where two series-stacked IGBTs (rated at 1700 V and 300 A each) are used to replace a thryatrondriven pulsed power supply for a mini CO2 TEA laser. The mini CO2 TEA laser is firstly characterized in order to optimize the design of the pulsed power supply. It is found that stable laser discharges can be obtained with electrode voltage rise-times of 150 ns or less. Furthermore, the optical output energy and the efficiency of the laser have been significantly increased by reducing the peaking capacitor size of the pulsed power supply. The two stacked IGBTs switch a C-C transfer loop and the generated pulse is stepped up by a pulse transformer and is compressed by a two-stage magnetic pulse compression unit. Theoretically and through measurements it is shown that automatic voltage sharing between the two IGBTs can be obtained if the turn-on time of the IGBTs is much faster than the transfer time of the switched C-C transfer loop. Lifetime tests reveal that high-power IGBTs are able to reliably switch pulses with peak currents between 4 and 5 times the rated average current of the device. Under laser fault conditions, i.e. laser arcing or missing laser discharges, the reliability of the pulser can be increased by using over-voltage snubbers. In addition, it was found that the internal diode of IGBT modules can eventually fail under the prevalence of laser fault conditions. A modular construction approach is used where components of the pulsed power supply are preassembled. A new rectangular layout of the magnetic pulse compression unit is utilized in order to minimize size and simplify the final construction and assembly. / AFRIKAANSE OPSOMMING: Nuwe ontwikkeling in vastetoestand-skakelaars het die modernisering van laser-pulskragbronne moontlik gemaak. ’n Nuwe kragbron wat gebruik maak van twee seriegeskakelde IGBT’s is ontwerp om ’n Tiratron-gedrewe laserkragbron te vervang, wat vir ’n mini-C02-TEA-laser gebruik word. Die laser is vooraf eers gekarakteriseer om sodoende die laserkragbron te optimeer. Daar is bevind dat stabiele laserontladings verkry kan word met spanningstygtye van 150 ns of minder. Verder kan die uittree-energie van die laser beduidend verhoog word deur die uittreekapasitore (eng.: peaking capacitors) van die laserkragbron te verminder. Die twee serie-geskakelde IGBT’s skakel ’n C-C oordraglus. Die spanning van die gegenereerde puls word deur ’n pulstransformator verhoog en die stygtyd van die puls word met ’n twee-stadium magnetiese pulskompressor verlaag. Teoreties en deur metings kan getoon word dat eweredige spanningsverdeling tussen die twee IGBT’s outomaties verkry kan word indien die skakeltye van die IGBT’s baie vinniger as die oordragstyd van die C-C oordraglus is. Toetse het getoon dat IGBT’s pulse met piekstrome van tussen vier tot vyf keer die gespesifiseerde gemiddelde stroom betroubaar kan skakel. Tydens laserfouttoestande kan die betroubaarheid van die IGBT verhoog word deur oorspanningsgapsers te gebruik, maar onder fouttoestande wat voortduur, kan die IGBT se interne diode vemietig word. Die komponente van die laserkragbron is as modules vervaardig, wat op ’n maklike wyse gemonteer kan word. ’n Nuwe reghoekige uitleg is gebruik vir die konstruksie van die magnetiese pulskompressor, waarmee die grootte van die pulskompressor geminimeer en die konstruksie vergemaklik is.

This thesis presents experimental studies of various non-thermal atmospheric pressure gas discharges generated using short pulsed excitation as an alternative to widely used sinusoidal excitation. Several pulse generators are detailed that provide high voltage pulses ranging from hundreds of microseconds to less than ten nanoseconds in duration. A key enabler to the generation of a stable discharge is a suitably high repetition rate; this prerequisite precludes many conventional pulsed power technologies. Fortunately, recent advances in semiconductor technology have made it possible to construct solid state switches capable of producing high voltage pulses with repetition rates of many kilohertz. Pulsed excitation introduces many opportunities to tailor the applied voltage and consequently enhance the discharge which are not possible with sinusoidal excitation sources. Through detailed electrical and optical analysis it is shown that pulsed excitation is not only more energy efficient than a comparable sinusoidal source but produces a higher flux of excited species that are essential in many applications. When pulse widths are reduced to a sub-microsecond timescale a novel barrier-free mode of operation is observed. It is shown that diffuse large area plasmas are easily produced at kilohertz repetition rates without the usually indispensable dielectric barriers. Experimental results show that a short pulse width prevents the onset of the undesirable glow-to-arc transition thus introducing an added degree of stability. A further benefit of pulsed excitation is the ability to produce gas discharges with a high instantaneous peak power yet low average power consumption, resulting in a high density plasma that exhibits roomtemperature characteristics. Finally, as an acid test to highlight the many benefits of pulsed excitation several real-world applications are considered. It is shown that in all cases pulsed gas discharges provide real benefits compared to their sinusoidal counterparts.

Thesis (PhD (Physics))--University of Stellenbosch, 2002. / Includes bibliography. / ENGLISH ABSTRACT: High temperature superconductivity is an important topic in contemporary solid state physics, and an area of very active research. Due to it’s potential for application in low temperature electronic devices, the material has attracted the attention of researchers in the electronic engineering and material science fields alike. Moreover, from a fundamental point of view, several questions remain unanswered, related to the origin of superconductivity of this class of materials and the nature of quantised magnetic flux present in magnetised samples. In this work, flux creep phenomena in a thin superconducting YBa₂Cu₃O₇ film deposited by pulsed laser deposition, is investigated near the critical temperature 0 ≤ Tc – T ≤ 10 K. Creep activation energy U0 and critical current density jc were determined as a function of temperature close to Tc, providing important data to a problem of high-Tc superconductivity which is still a matter of debate. In particular it is still an open question whether restoring the temperature in a creep freezing experiment in fact restores the film to it's original state before the freezing. The most important novel results concern the regime of critical fluctuations in the vicinity Tc - T < 1 K. We studied the isothermal relaxation of trapped magnetic flux, and determined that the long time decay follows a power law, where the exponent is inversely proportional to the creep activation energy. The temperature dependence of the critical current density jc(T) of the YBa₂Cu₃O₇ film close to Tc was obtained during warming runs. It was determined that jc(T) follows a square root dependence on T to high accuracy in the range 0.2 ≤ Tc – T ≤ 1.5 K. During flux creep experiments an interesting phenomenon called creep freezing related to the strong temperature dependence of the relaxation rate was observed. A pronounced slowing of relaxation with only a small drop in temperature from a starting temperature close to Tc was detected. Experiments were conducted by initiating an isothermal flux decay run. At a certain point the temperature was slightly lowered, and the flux decay stopped within experimental accuracy. When the temperature was restored to the initial value, the flux decay resumed at the previous rate before cooling. An argument based on vortex drift velocity was employed to explain the phenomenon qualitatively. During the course of this investigation, a pulsed laser deposition (PLD) system was designed and built from scratch. PLD involves the interaction of a focussed laser pulse with a multielemental solid target material. Material ablated from the target forms a fast moving plume consisting of atomic and molecular particles, directed away from the target, and towards a usually heated substrate on which the particles condense layer by layer to form a thin film. The substrate temperature and background gas are carefully controlled to be conductive to the growth of a desired phase of the multi-elemental compound. The PLD system proved to be quite versatile in the range of materials that could be deposited. It was used to deposit thin films of different materials, most notable were good quality superconducting YBa₂Cu₃O₇, thermochromic VO2, and magnetoresistive LaxCa1-xMnO3. Metallic Au and Ag layers were also successfully deposited on YBa2Cu3O7 thin films, to serve as protective coatings. The critical temperatures of the best superconducting films were 90 K as determined by resistivity measurement. The optimal deposition conditions to deposit high quality superconducting YBa₂Cu₃O₇ thin films was found to be: deposition temperature 780°C, laser energy density 2-3 J/cm2, oxygen partial pressure 0.2 mbar, and target-substrate distance 35 mm. This yields film with Tc ~ 90 K. It was found that deposition temperature plays the predominant role in determining the quality of YBa₂Cu₃O₇ thin films deposited by PLD. / AFRIKAANSE OPSOMMING: Hoë temperatuur supergeleiding is tans ’n aktuele onderwerp van vastetoestandfisika en dit is ’n gebied van baie aktiewe navorsing. Weens die potensiaal vir toepassings van hoë temperatuur supergeleiers in elektronika, het dié klas materiale die aandag van fisici and elektronici getrek. Verskeie fundamentele vraagstukke bly steeds onbeantwoord, veral met betrekking tot die oorsprong van supergeleiding in hierdie materiale en die gedrag van gekwantiseerde magnetiese vloed (“vortekse”) in gemagnetiseerde monsters. In hierdie werk word diffusie van vortekse in dun supergeleidende YBa₂Cu₃O₇ films ondersoek naby die kritieke temperatuur (0 ≤ Tc - T ≤ 10 K). Die temperatuur afhanklikheid van die diffusie aktiveringsenergie U0 en die kritieke stroomdigtheid jc word bepaal naby Tc. Dit verskaf belangrike inligting tot probleme in hoë temperatuur supergeleiding wat tans nog onbeantwoord bly. In die besonder is dit steeds ’n ope vraag of die herstel van die aanvanklike temperatuur in ’n vloedstollings eksperiment waarlik die film tot die oorspronklike toestand herstel. Die belangrikste nuwe resultate hou verband met die gebied van kritieke fluktuasies van die orde parameter in die omgewing 0 < Tc - T < 1 K. Ons het die isotermiese ontspanning van vortekse verstrik in die kristalstruktuur bestudeer, en bepaal dat die lang tydsverval ’n magsverwantskap handhaaf, waar die eksponent omgekeerd eweredig is aan U0. Die temperatuur afhanklikheid van die kritieke stroomdigtheid jc(T) van die YBa₂Cu₃O₇ film naby Tc is bepaal tydens verhittingslopies. Daar is bevind dat naby Tc, jc ’n vierkantswortel verband met T volg, tot hoë noukeurigheid in die gebied 0.2 ≤ Tc – T ≤ 1.5 K. Gedurende vorteksdiffusie eksperimente is ’n interessante verskynsel naamlik vloedstolling (“flux freezing”) waargeneem. Dit hou verband met die sterk temperatuur afhanklikheid van die vervaltempo van die magnetiese moment van ’n gemagnetiseerde film. ’n Skerp daling van die vervaltempo, weens slegs ’n klein temperatuurdaling vanaf die begin temperatuur naby Tc, is waargeneem. Gedurende eksperimente is daar aanvanklik ’n isotermiese vloedontspanning teweeg gebring. Op ’n sekere tydstip is die temperatuur effens verlaag, waarby die vloedontspanning tot stilstand gekom het binne grense van waarneming. Wanneer die temperatuur weer herstel is na die oorspronklike, het die vloedontspanning voortgegaan teen die tempo voor die temperatuurverlaging. ’n Verklaring wat gebaseer is op vorteks dryfsnelheid was aan die hand gedoen om hierdie gedrag te verklaar. ’n Groot komponent van die projek was om die dun YBa₂Cu₃O₇ films self te vervaardig. Tydens hierdie ondersoek, is ’n gepulseerde laser deposisie (“PLD”) sisteem eiehandig ontwerp en gebou. PLD behels die interaksie van ’n gefokuseerde laser puls met ’n teiken bestaande uit ’n multi-element vastestofverbinding. Materiaal wat verdamp (“ablate”) word, vorm ’n snelbewegende pluim bestaande uit atomiese en molekulêre deeltjies. Dit beweeg vanaf die teiken na ’n verhitte substraat, waarop die deeltjies kondenseer om laag vir laag ’n dun film te vorm. Die substraat temperatuur en agtergrond gas word sorgvuldig beheer om die groei van die verlangde fase van die multi-element verbinding teweeg te bring. Die PLD sisteem is baie veeldoelig ten opsigte van die verskeidenheid materiale wat suksesvol neergeslaan kan word. Dit was aangewend om verskillende materiale neer te slaan, onder andere supergeleidende YBa₂Cu₃O₇, termochromiese VO2, en magnetoresistiewe LaxCa1-xMnO3. Geleidende Au en Ag lagies is ook suksesvol neergeslaan op YBa₂Cu₃O₇ dun films, om te dien as beskermingslagies. Die kritieke temperatuur van die beste supergeleidende films was 90 K soos bepaal deur weerstandsmetings. Die optimale neerslaan toestand vir hoë kwaliteit YBa₂Cu₃O₇ dun films was: substraat temperatuur 780°C, laser energiedigtheid 2 - 3 J/cm2, suurstofdruk 0.2 mbar, en teiken-substraat afstand 35 mm. Daar is bevind dat die substraat temperatuur die deurslaggewende rol speel tydens die neerslaan proses om die kwaliteit van die supergeleidende films te bepaal.

Thesis (MEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / The Josephson effect of high-temperature superconducting nanobridge structures is studied worldwide. Until now, nanobridges are generally fabricated with focused ion beam milling on planar thin films. These nanobridges are employed as weak links in superconducting quantum interference devices (SQUIDs) and used in superconducting flux flow transistors and devices. This project had two main objectives: to improve the sidewall angle of photoresist lines, with the aid of atomic force microscopy (AFM) nanolithography; and to fabricate hightemperature Josephson junctions by constricting superconductive YBCO lines on MgO substrates with AFM nanolithography. The entire fabrication process is explained including photolithography, deposition of the YBCO thin films with pulsed laser deposition (PLD), nanolithography and wet etching. Although the testing of the junctions did not show any Josephson behaviour, it could be demonstrated that nanobridge structures can successfully be created by AFM nanolithography. The entire fabrication process has been demonstrated in detail for the benefit of future research.

Pulsed plasma jets (also called "SparkJets'") were investigated for use in controlling the mean separation location induced by shock wave-boundary layer interaction. These synthetic jet actuators are driven by electro-thermal heating from an electrical discharge in a small cavity, which forces the gas in the cavity to exit through a small hole as a high-speed jet. With this method of actuation, pulsed plasma jets can achieve pulsing frequencies on the order of kilohertz, which is on the order of the instability frequency of many lab-scale shock wave-boundary layer interactions (SWBLI). The interaction under investigation was generated by a 20° compression ramp in a Mach 3 flow. The undisturbed boundary layer is transitional with Re[subscript theta] of 5400. Surface oil streak visualization is used in a parametric study to determine the optimum pulsing frequency of the jet, the optimum distance of the jet from the compression corner, and the optimum injection angle of the jets. Three spanwise-oriented arrays of three plasma jets are tested, each with a different pitch and skew angle on the jet exit port. The three injection angles tested were 22° pitch and 45° skew, 20° pitch and 0° skew, and 45° pitch and 0° skew. Jet pulsing frequency is varied between 2 kHz and 4 kHz, corresponding to a Strouhal number based on separation length of 0.012 and 0.023. Particle image velocimetry is used to characterize the effect that the actuators have on the reattached boundary layer profile on the ramp surface. Results show that plasma jets pitched at 20° from the wall, and pulsed at a Strouhal number of 0.018, can reduce the size of an approximate measure of the separation region by up to 40% and increase the integrated momentum in the downstream reattached boundary layer, albeit with a concomitant increase in the shape factor. / text

As the ultimate fate of nearly all stars, including our Sun, white dwarfs (WDs) hold rich and informative histories in their observable light. To determine a fundamental parameter of WDs, mass, we perform the first measurement of the average gravitational redshift of an ensemble of WDs. We find a larger mean mass than that determined from the primary and expansive technique known as the spectroscopic method. The potential inaccuracy of this method has broad astrophysical implications, including for our understanding of Type 1a supernova progenitors and for constraining the age of the Universe. This motivates us to investigate the WD atmosphere models used with the spectroscopic method, particularly the input theoretical line profiles, by developing a new experimental platform to create plasmas at WD photospheric conditions (T_e ~ 1 eV, n_e ~ 10^17 cm^-3). Instead of observing WD spectra to infer the plasma conditions at the surface of the star, we set the conditions and measure the emergent spectra in the laboratory. X-rays from a z-pinch dynamic hohlraum generated at the Z Pulsed Power Facility at Sandia National Laboratories irradiate a gas cell to initiate formation of a large (120x20x10 mm or 24 cm^3) plasma. We observe multiple Balmer lines from our plasma in emission and in absorption simultaneously along relatively long (~120 mm) lines of sight perpendicular to the heating radiation. Using a large, radiation-driven plasma aides us to achieve homogeneity along our observed lines of sight. With time-resolved spectroscopy we measure lines at a range of electron densities that spans an order of magnitude, and we do this within one pulsed power shot experiment. Observing our plasma in absorption not only provides the signal-to-noise to measure relative line shapes, it allows us to measure relative line strengths because the lines share the same lower level population. This constrains the theoretical reduction factors used to describe ionization potential depression or the occupation probabilities associated with these Balmer lines. We compare our measured line shapes with the theoretical ones used in WD atmosphere models as part of the first fruits of this rich experimental platform. / text