Thesis (MScEng (Electrical and Electronic Engineering))--Stellenbosch University, 2008. / This thesis relates to the analysis and design of a SQUID microscope. Superconductor theory is discussed in depth to provide a thorough understanding of Josephson junctions and of dc SQUID magnetometers. The behaviour and suitability of different types of single-layer dc SQUIDs are looked at. The quality of the superconducting material patterned onto a substrate and the Josephson junction design used affect the behaviour of a practical dc SQUID. Noise and cooling play an integral part in the design and operation of a dc SQUID. The source of noise is looked at in an effort to minimize its effect. Cryocooling is essential to real world operation so different cooling strategies and their consequences are analyzed. This thesis focuses on modeling the behaviour of the dc SQUID to creating a practical system for use inside a SQUID microscope. Operating the dc SQUID with the appropriate electronics will linearize the device, reduce the effect of noise, and create a device with wide bandwidth. Each step in creating a practical system is discussed in detail. Simulations are used to create models predicting the behaviour of the dc SQUID and the electronics. They are then used to design and create practical electronic systems. Measurements are performed on Josephson junctions and dc SQUID magnetometers using the designed electronics. The Josephson junctions behave as predicted and were successfully tested. The dc SQUIDs did not behave as predicted and were not successfully tested. The SQUIDs were damaged, either by a malfunction in the cryocooler or through age related deterioration. A full test of the flux-locked loop was not possible and the dc SQUID was not linearized.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: This thesis presents an attempt at creating a fully functional SQUID for the purposes of a predefined application. The goal of the work is to provide a method of development, primarily utilising the facilities of the Engineering Faculty of the University of Stellenbosch, with minimal assistance from other departments. This method is then analysed and the successes and failures discussed in order to provide guidelines and recommendations for future research. The device consists of a gradiometric SQUID, as well as electronics which provide the SQUID bias current, output linearisation and output signal filtering. YBCO is used for the superconducting material, allowing the use of liquid nitrogen as coolant which eases the operation and portability of the device. Various methods of creating Josephson junctions are tested, such as constriction bridges using AFM lithography and step-edge junctions, with and without different buffer layers. Proof of concept simulations demonstrate the viability of the device. Unfortunately, a functional device could not be constructed, mostly due to the design requiring higher levels of resolution and process control than some of the available facilities can provide. Recommendations are provided for future researchers. / AFRIKAANSE OPSOMMING: Hierdie tesis beskryf ’n poging om ’n volledige funksionele SQUID te vervaardig vir die doeleindes van ’n vasgestelde toepassing. Die doel van die werk is om ’n metode te voorsien wat hoofsaaklik gebruik maak van die fasiliteite van die Ingenieurswese Fakulteit van die Universiteit van Stellenbosch, met minimale hulp van ander departemente. Hierdie metode word dan ondersoek en die suksesse en mislukkings bespreek om riglyne en voorstellings te voorsien vir toekomstige navorsing. Die toestel bestaan uit ’n gradiometriese SQUID, sowel as elektronika wat voorsiening maak vir voorspanning, uittree-linearisering en ’n uittree-filter. YBCO is as supergeleidende materiaal gebruik, wat die gebruik van vloeibare stikstof as verkoeler moontlik maak en dus die hantering en draagbaarheid van die toestel vergemaklik. Verskillende metodes om Josephson-vlakke te vervaardig is getoets, onder andere vernouingsbrugvlakke deur middel van AFM litografie en stapvlakke met en sonder bufferlae. Bewys van konsep simulasies demonstreer die lewensvatbaarheid van die toestel. Ongelukkig kon ’n funksionele weergawe van die toestel nie vervaardig word nie, hoofsaaklik as gevolg van die ontwerp wat hoër resolusievlakke en beter prosesbeheer benodig as wat sekere van die beskikbare fasiliteite kan voorsien. Aanbevelings word voorsien vir toekomstige navorsers.

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Thesis (MTech (Oceanography))Cape Peninsula University of Technology, 2010 / The current dynamics along the Tsitsikamma coast is described from a combination of acoustic current measurements. satellite-tracked surface drifters and underwater temperature recordings made between November 2006 and March 2008. The Tsitsikamma coast is largely a Marine Protected Area (MPA) that protects a rich marine biodiversity. The nearshore currents are important in the dispersal of eggs and larvae of many marine species. including the paralarvae of the commercially caught chokka squid. LoNgo reynaudii. Changes in the environment, including the currents. can affect the successful recruitment of chokka squid, and can bring about large annual fluctuations in biomass that creates economic uncertainty in the squid fishery. Results confirm the existence of a predominantly alongshore current off the Tsitsikamma coast. At Middelbank eastward flow was slightly dominant, with a percentage occurrence of 58% vs. 41% westward flow near the surface. The percentage eastward flow decreased with depth, with 41% vs. 58% westward flow near the seabed. At Thyspunt westward and eastward flow occurred at near equal percentages. but westward flow was slightly dominant throughout the water column. The alongshore current was strongest near the surface during eastward flow (maximum = 141 crn.s1: average = 27 crn.s '). while westward surface currents were weaker (maximum velocity = 78 cm.s1: average = 19 crn.s1). Current speed generally decreased with depth and opposing surface and bottom currents, associated with a thermal stratified water column, were occasionally recorded. The nearshore flow regime was characterised by frequent barotropic alongshore reversals that occurred year round. An increase in strong eastward episodes, and opposing surface and bottom currents during spring and summer months have implications for the dispersal of squid paralarvae during the summer and winter spawning seasons. In summer, the combination of strong eastward pulses in the current and upwelling at the capes favoured dispersal onto the midshelf of the Agulhas Bank. In winter, alongshore oscillations without the offshore displacement associated with upwelling. restricted offshore dispersal which caused surface particles to be retained inshore. Drifter trajectories show that both the eastward and westward nearshore current can link the inshore spawning grounds with the nursery grounds, offshore on the central Agulhas Bank; and that passive, neutrally buoyant material in the surface layer can reach the vicinity of the cold ridge in as little as eight days. The wind-driven processes of upwelling and coastal trapped waves (CTWs). and the influence of the greater shelf circulation are discussed as possible driving forces of variability in the currents off the Tsitsikamma coast. The occurrence of coastal trapped waves during thermal stratification appears to drive the jet-like, eastward pulses in the current. and results suggest that the propagation of CTWs may regulate and even enhance upwelling and downwelling along the Tsitsikamma coast.

abstract: Seeking an upper limit of the Neutron Electric Dipole Moment (nEDM) is a test of charge-parity (CP) violation beyond the Standard Model. The present experimentally tested nEDM upper limit is 3x10^(26) e cm. An experiment to be performed at the Oak Ridge National Lab Spallation Neutron Source (SNS) facility seeks to reach the 3x10^(28) e cm limit. The experiment is designed to probe for a dependence of the neutron's Larmor precession frequency on an applied electric eld. The experiment will use polarized helium-3 (3He) as a comagnetometer, polarization analyzer, and detector. Systematic influences on the nEDM measurement investigated in this thesis include (a) room temperature measurements on polarized 3He in a measurement cell made from the same materials as the nEDM experiment, (b) research and development of the Superconducting QUantum Interference Devices (SQUID) which will be used in the nEDM experiment, (c) design contributions for an experiment with nearly all the same conditions as will be present in the nEDM experiment, and (d) scintillation studies in superfluid helium II generated from alpha particles which are fundamentally similar to the nEDM scintillation process. The result of this work are steps toward achievement of a new upper limit for the nEDM experiment at the SNS facility. / Dissertation/Thesis / Doctoral Dissertation Physics 2019

La presente investigación busca determinar cuáles fueron los factores que influyeron en el crecimiento de las exportaciones de Calamar Gigante congelado al mercado español durante los años 2012 – 2016. Primer capítulo, iniciamos con la evolución que ha venido desarrollándose la industria pesquera a nivel internacional y posteriormente como se ha desempeñado la industria en el Perú sobre la extracción, comercialización y exportación de Calamar Gigante congelado. Se investiga si: el cambio climático (niño o niña), el tratado de libre comercio con la Unión Europea, la competitividad, el aporte de las instituciones privadas o públicas al sector pesquero y el mercado de destino y su tendencia de consumo contribuyeron a la exportación de Calamar Gigante Congelado. Segundo capítulo, se determina el planteamiento de la investigación (Problemática e hipótesis), metodológica y tipo de investigación. Las entrevistas fueron realizadas a: Exportadores, Gremio, Instituciones Gubernamentales y Trader. Estos fueron escogidos por ser entidades o empresas representativas al sector. Tercer capítulo, se analizará la información brindada por los entrevistados, la cual nos permitirá obtener un panorama real del sector pesquero potero sobre el problema planteado y nos contribuirá al final del estudio. Cuarto capítulo, se procederá a contrastar las opiniones vertidas en cada entrevista y validar la pertinencia de cada factor con respecto al crecimiento de las exportaciones de pota congelada al mercado español en el periodo de tiempo especificado. Por último, en el quinto capítulo como resultado de la investigación, se presentan conclusiones y recomendaciones. / The following research tries to determinate the factors that influenced the growth of frozen giant squid exports to Spain from 2012 to 2016. First chapter, we begin with the evolution of the fishing industry which has been developing internationally and subsequently how is the situation of the industry in Peru about the extraction, commercialization and export of Frozen Giant Squid. It is investigated whether: climate change (el niño), the free trade agreement with the European Union, competitiveness, the contribution of private or public institutions to the fishing sector and the destination market and its consumption trend contributed to the Export of Frozen Giant Squid. Second chapter, the approach of the research (Problematic and hypothesis), methodological and type of research is determined. The interviews were conducted with: Exporters, Guild, Government Institutions and Trader. These were chosen because they are entities or companies that are representative for the fishery sector. Third chapter, the information provided by the interviewees will be analyzed, which will allow us to obtain a real picture of the fishing sector in the area of the problem and contribute to the end of the study. Fourth chapter, we will proceed to contrast the opinions expressed in each interview and validate the relevance of each factor with respect to the growth of exports of frozen squid to the Spanish market in the specified period of time. Finally, in the fifth chapter as a result of the investigation, conclusions and recommendations are presented. / Tesis

Cephalopods are an important component of many marine ecosystems and support large fisheries. Their active lifestyles and complex behaviors are thought to be driven in large part by competition with fishes. Although cephalopods appear to compete successfully with fishes, a number of their important physiological traits are arguably inferior, such as an inefficient mode of locomotion via jet propulsion and a phylogenetically limited means of blood-borne gas transport. In active shallow-water cephalopods, these traits result in an interesting combination of very high oxygen demand and limited oxygen supply. The ability to maintain active lifestyles despite these metabolic constraints makes cephalopods a fascinating subject for metabolic physiology. This dissertation focuses on the physiological adaptations that allow coleoid cephalopods to maintain a balance of oxygen supply and demand in a variety of environmental conditions. A critical component of understanding oxygen supply in any animal is knowing the means of oxygen delivery from the environment to the mitochondria. Squids are thought to obtain a fairly large portion of their oxygen via simple diffusion across the skin in addition to uptake at the gills. Although this hypothesis has support from indirect evidence and is widely accepted, no empirical examinations have been conducted to assess the validity of this hypothesis. In Chapter 2, I examined cutaneous respiration in two squid species, Doryteuthis pealeii and Lolliguncula brevis, by using a divided chamber to physically separate the mantle cavity and gills from the outer mantle surface. I measured the oxygen consumption rate in the two compartments and found that, at rest, squids only obtain enough oxygen cutaneously to meet demand of the skin tissue locally (12% of total). The majority of oxygen is obtained via the traditional branchial pathway. In light of these findings, I re-examine and discuss the indirect evidence that has supported the cutaneous respiration hypothesis. Ocean acidification is believed to limit the performance of squids due to their exceptional oxygen demand and pH-sensitivity of blood-oxygen binding, which may reduce oxygen supply in acidified waters. The critical oxygen partial pressure (Pcrit), defined as the PO2 below which oxygen supply cannot match basal demand, is a commonly reported index of hypoxia tolerance. Any CO2-induced reduction in oxygen supply should be apparent as an increase in Pcrit. In Chapter 3, I assessed the effects of CO2 (40 to 140 Pa) on the metabolic rate and Pcrit of two squid species: Dosidicus gigas and Doryteuthis pealeii. Carbon dioxide had no effect on metabolic rate or hypoxia tolerance in either species. Furthermore, considering oxygen transport parameters (e.g. Bohr coefficient, blood P50) and blood PCO2 values from the literature, I estimated an increase in seawater PCO2 to 100 Pa (≈1000 μatm/ppmv) would result in a maximum drop in hemocyanin-O2 saturation by 6% at normoxia and a Pcrit increase of ≈1 kPa (≈5% air saturation) in the absence of active extracellular pH compensation. Such changes are unlikely given the capacity for acid-base regulation in many cephalopods. Moreover, this estimated change is within the 95% confidence intervals of the Pcrit measurements reported here. Squid blood-O2 binding is more sensitive to pH than most other marine animals measured to date. Therefore, the lack of effect in squids suggests that ocean acidification is unlikely to have a limiting effect on blood-O2 supply in most marine animals. The pelagic octopod, Japetella diaphana, is known to inhabit meso- and bathypelagic depths worldwide. Across its range, individuals encounter oxygen levels ranging from nearly air-saturated to nearly anoxic. In Chapter 4, we assessed the physiological adaptations of individuals from the eastern tropical Pacific (ETP) where oxygen is extremely low. Ship-board measurements of metabolic rate and hypoxia tolerance were conducted and a metabolic index was constructed to model suitable habitat for aerobic metabolism. I found that animals from the ETP had a higher metabolic rate than animals from more oxygen-rich habitats. Despite their higher oxygen demand, they maintained better hypoxia tolerance than conspecifics from oxygen-rich Hawaiian waters. Furthermore, I found that hypoxia tolerance in Japetella has a reverse temperature dependence from most marine ectotherms, a characteristic that uniquely suits the physical characteristics of its oxygen-poor environment. Even with their high tolerance to hypoxia, the OMZ core likely has insufficient oxygen supply to meet the basal oxygen demand of Japetella. Despite the limited aerobic habitat in this region, species abundance was comparable to more oxygenated ocean regions, suggesting that physiological or behavioral plasticity such as altered hypoxia tolerance or hypoxic avoidance in this globally-distributed species is sufficient to maintain species fitness in this extreme environment. These findings contribute towards our understanding of the impacts of climate change on cephalopod physiology and biogeography. The study of environmental physiology provides a mechanistic basis for the understanding and prediction of ecological responses to climate change.

L'électronique moléculaire et la spintronique moléculaire sont deux domaines émergeant de la nanophysique, prometteurs pour réaliser de nouveaux types de dispositifs utiles tant pour le stockage d'information que pour l'information quantique. Ce travail de thèse a pour objet de contribuer à ces deux domaines de recherche par la réalisation de jonctions moléculaires à base de nanotubes de carbone, faisant intervenir des nanostructures magnétiques. Nous avons choisi deux approches: (i) le transport électronique à travers des nanotubes de carbone remplis de matériaux magnétiques (nanotubes hybrides) et (ii) le développement du nano-SQUID composé de jonctions supraconductrices à nanotube de carbone. Ce magnétomètre devrait être suffisamment sensible pour étudier les propriétés magnétiques de molécules individuelles attachées au nanotube de carbone.

Dans les composés antiferromagnétiques Heisenberg à géométrie kagomé, la frustration des interactions est à l'origine d'un état liquide de spins à T=0. Un état RVB, originalement proposé par Anderson dans les réseaux triangulaires puis dans les cuprates, décrit probablement ce fondamental, dont l'état singulet est dégénéré exponentiellement dans un faible gap singulet-triplet. Peu de composés expérimentaux se rapprochent aujourd'hui du système idéal et l'existence de perturbations ou d'anisotropie lève souvent la dégénérescence du fondamental lorsque T->0. Une étude par RMN, MuSR et SQUID, a été réalisée dans les composés à géométrie de bicouches kagomé de spin 3/2, Ba2Sn2ZnGa10-7pCr7pO22 et SrCr9pGa12-9pO19, considérés comme les archétypes d'un hamiltonien de spins purement Heisenberg sur un réseau kagomé. Outre l'absence caractéristique de transition jusqu'à une température Tg~2 K bien plus basse que la température de Curie-Weiss thetaCW~250 K, des propriétés physiques semblables dans ces deux systèmes sont mesurées malgré des défauts radicalement différent. Les propriétés intrinsèques de cette géométrie en sont déduites, à savoir: - une décroissance de la susceptibilité en dessous de 45 K (RMN) interprétée par de très faibles longueurs de corrélations magnétiques, au moins pour T>10 K, malgré les fortes interactions antiferromagnétiques (thetaCW~250 K). Ce maximum de la susceptibilité reste compatible avec l'existence d'un gap de spin; - l'existence de fluctuations quantiques pour T>30 mK, beaucoup plus bas que Tg (MuSR); - la corrélation entre l'apparition de ces fluctuations et celle d'un état de type verre de spin à Tg. Un modèle phénoménologique décrivant la relaxation des muons est présenté, pour la première fois dans ces systèmes, et suggère la stabilisation d'un état de type RVB en dessous de Tg.