Plus de vingt ans après la découverte de la supraconductivité à haute température critique, le mécanisme physique sous-jacente n'est pas encore bien cerné. En 2008, la découverte d'une nouvelle famille de supraconducteurs à haute température critique, les supraconducteurs à base de fer, a donné l'espoir de trouver une compréhension plus profonde des mécanismes de ce type de supraconductivité. Synthétiser des l'échantillons de grande qualité, la caractérisation des propriétés supraconductrices, l'étude des symétrices du gap et du paramètre d'ordre sont des étapes essentielles pour révéler le mécanisme. La connaissance précise du mécanisme permettra de profiter pleinement des propriétés remarquables de ces matériaux dans leurs applications industrielles si prometteuses. La thèse décrit d'abord la croissance de monocristaux de Ba$_{1-x}$K$_x$Fe$_2$As$_2$ et l'étude de leurs propriétés supraconductrices, menant vers la proposition d'une structure de gap du supraconducteur et d'un paramètre d'ordre pour les supraconducteurs à base de fer Ba-122 à partir de mesures de résistivité, de sondes à effect Hall, de spectroscopie d'Andreev en mode point-contact et de l'imagerie magnétique par la microscopie à nano-squid.Dans le chapitre 1, les événements historiques les plus marquants de la supraconductivité sont rappelés, les propriétés essentielles des supraconducteurs et le dévelopment des théories de la supraconductivité sont esquissés avant de présenter brièvement la découverte des supraconducteurs à base de fer et de donner un aperçu des questions actuelles de recherche dans ce domaine.Dans le chapitre 2, la procédure de croissance de monocristaux de Ba$_{1-x}$K$_x$Fe$_2$As$_2$ par la méthode de "self-flux", leur caractérisation par diffraction et par l'analyse de dispersion d'énergie des rayons X et la sensibilité des mesures de résistivité et de susceptibilité AC sont décrites. Puis nous présentons quelques résultats des mesures de la résistivité dépendante de la température de monocristaux du composé Ba$_{1-x}$K$_x$Fe$_2$As$_2$ (0,23 $\leq x \leq$ 0,4) sous champs magnétiques allant jusqu'à 9 T et dépendante de l'angle.Dans le chapitre 3, nous exposons quelques points essentiels du système de mesure à base de sonde de Hall que nous avons construit. Ensuite, nous présentons des mesures d'aimantation locale et globale sur des polycristaux de SmFeAsO$_{0.9}$F$_{0.1}$ synthétisés à haute pression, et de monocristaux de Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ effectuées par sonde de Hall et VSM.Dans le chapitre 4, nous donnons une brève introduction à la spectroscopie d'Andreev en mode point-contact, puis nous appliquons cette technique à des monocristaux de Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ et à une série de monocristaux de BaFe$_{2-x}$Ni$_x$As$_2$ couvrant une large gamme de dopage.Dans le chapitre 5, le développement d'un microscope de force à nano-SQUID et les mesures effectuées sur un film Rhénium d'épaisseur de 80 nm sont présentés. Le microscope peut acquérir des images topographiques et magnétiques simultanément. La plage de balayage maximale à 0.8 K est de \unit{70} {\micro\meter} $\times$ \unit{85}{\micro\meter} et sa résolution magnétique est d'environ $1,5 \times10^{-4}\Phi_0/\sqrt{\textrm{Hz}}$. Dans le chapitre 6, nous présentons quelques résultats des mesures de $\lambda$ par imagerie par microscopie de force à nano-squid sur des monocristaux de Ba(Fe$_{1-x}$Ni$_x$)$_2$As$_2$, couvrant tout le diagramme de phase. Sur les m\^{e}mes cristaux ont été effectuées des mesures du premier champ critique, de la variation de fréquence d'un oscillateur à diode tunnel et de la capacité calorifique.Enfin, au chapitre 7, un résumé détaillé et critique est présenté.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Geomagnetic storms are primarily driven by the rapid transfer of energy from the solar wind to the magnetosphere. The mechanism of energy transfer involves the merging of the interplanetary magnetic field to the geomagnetic field in a process known as magnetic reconnection. This leads to an influx of energetic, charged particles into the magnetosphere so that current systems are enhanced. Specifically, an increase in the equatorial ring current leads to a decrease in the surface field. Geomagnetic storms are thus characterized by a strong decline in the horizontal components of the geomagnetic field, lasting from several hours to days. The intensity of a storm is described by the disturbed storm-time index, which is essentially a measure of the deviation from the typical quiet day variation along the equator. Severe storms can lead to the disruption of high frequency (HF) communications as a consequence of a strongly perturbed ionosphere. By the same token, the global positioning system (GPS) can become highly unreliable during magnetically disturbed conditions, yielding distance errors as large as 50 meters. The impact of geomagnetic activity and other solar-driven processes on technology systems are collectively known as space weather. Magnetic field sensing thus forms an important part of space weather forecasting and is vital to space science research as a means of improving our understanding of solar wind-magnetosphere interactions. This study examines the use of magnetometers built as SQUIDs (Superconducting Quantum Interference Devices) for monitoring the geomagnetic field for space weather forecasting purposes. A basic theory of superconductivity is presented and subsequently the key aspects governing the operation of SQUIDs are discussed. Space weather is also introduced with respect to the various processes on the sun that perturb the magnetosphere and hence the geomagnetic field. The method of analysis was basically to Fourier-transform the data using the Wiener-Khintchine theorem. A systematic approach to Fourier analysis is thus presented, demonstrating the superiority of the Wiener-Khintchine theorem in noise reduction. The suitability of SQUID magnetometers for space science research is demonstrated by a comparative study between SQUID and fluxgate datasets for magnetic storms during 2011. Strong correlation was observed between the frequency content of the SQUID and fluxgate signals. This result supports South Africa’s SQUID project, currently undertaken as a collaborative effort between SANSA Space Science and the Department of Electrical and Electronic Engineering at Stellenbosch University. This thesis thus lays a foundation for future research involving advanced magnetometry using SQUIDs. / AFRIKAANSE OPSOMMING: Geomagnetiese storms word hoofsaaklik gedryf deur die vinnige oordrag van energie van die sonwind na die magnetosfeer. Die meganisme van energie oordrag behels die samesmelting van die interplanetêre magneetveld met die geomagneetveld, in 'n proses wat bekend staan as magnetiese heraansluiting. Dit lei tot 'n instroming van energieke elektries-gelaaide deeltjies, tot in die magnetosfeer, met die gevolg dat magnetosferiese elektriese stroomstelsels versterk word. 'n Toename in die ekwatoriale ringstrome lei spesifiek tot 'n afname in die horisontale komponent van die geomagnetiese veld. Geomagnetiese storms word dus gekenmerk deur 'n sterk afname in die horisontale komponent van die geomagnetiese veld, ‘n afname wat etlike ure tot dae kan duur. Die intensiteit van 'n storm word beskryf deur die storm-tyd versteurings indeks , 'n maatstaf van die afwyking van die tipiese stil dag magnetiese variasie langs die ewenaar. Ernstige storms kan lei tot die ontwrigting van hoë frekwensie (HF) kommunikasie as 'n gevolg van 'n erg versteurde ionosfeer. Soortgelyk kan die Globale Posisionering Stelsel (GPS) hoogs onbetroubaar word tydens magneties versteurde toestande, en posisiefoute so groot as 50 meter veroorsaak. Die impak van geomagnetiese aktiwiteit en ander sonkrag gedrewe prosesse op tegnologie is gesamentlik bekend as ruimteweer. Magneetveldmetinge vorm dus 'n belangrike deel van ruimteweervoorspelling en is noodsaaklik vir ruimtewetenskaplike navorsing as 'n middel om die sonwind-magnetosfeer interaksies beter te verstaan. Hierdie studie ondersoek die gebruik van SQUID (Engels: Superconducting Quantum Interference Device) magnetometers vir die monitering van die geomagnetiese veld vir ruimteweervoorspellingsdoeleindes. ’n Basiese teorie van supergeleiding word aangebied, waarvolgens die sleutelaspekte van SQUIDs bespreek word. Ruimteweer word ook voorgestel in terme van die verskillende prosesse op die son wat die aarde se magnetosfeer en dus die geomagnetiese veld versteur. Die analisemetode wat hier gebruik word, is om die Fourier-transform van data met die Wiener-Khintchine theorema te bereken. A sistematiese metode vir Fourier-analise word aangebied, wat die superiorireit van die Wiener-Khintchine teorema vir ruisvermindering demonstreer. Die geskiktheid van SQUID magnetometers vir ruimtewetenskaplike navorsing word gedemonstreer deur ’n vergelykende studie tussen SQUID- en vloedhek-datastelle vir magnetiese storms gedurende 2011. Sterk korrelasie is waargeneem tussen die frekwensie-inhoud van die SQUID- en vloedhekseine. Hierdie resultate ondersteun Suid-Afrika se SQUID-projek, wat tans as ’n samewerkingspoging tussen SANSA Space Science en die Departement Elektriese en Elektroniese Ingenieurswese aan die Universiteit van Stellenbosch bedryf word. Hierdie tesis lê ’n fondasie vir toekomstige navorsing oor gevorderde magnetometrie met SQUIDs.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Superconducting QUantum Interference Devices (SQUIDs) are fairly recent types of magnetometers that use flux quantization combined with Josephson tunnelling to detect very faint (< 10¯15 T) magnetic fields. Recent scientific studies have shown that these highly sensitive magnetometers, located in an ultra-low-noise environment, are capable of observing Earth-ionosphere couplings, such as P waves emitted during earthquakes or magnetic storms in the upper atmosphere, S and T breathing modes of the Earth during quiet magnetic and seismic periods, signals in time correlating with sprites. Since SQUIDs are much more sensitive than conventional magnetometers, they are arguably the best tool for understanding space weather and natural hazards, whether they are produced from space or within the ionosphere by magnetic storms for instance, or natural disturbances, including magnetic disturbances produced by earthquakes or as a result of the dynamics of the earth's core. A study was conducted at SANSA Space Science in Hermanus, Western Cape, in 2012, to find the correlation between SQUID and Fluxgate data-sets, with the aim of validating the use of a SQUID as a reliable instrument for Space Weather observations. In that study, SQUID data obtained from the Low Noise Laboratory (LSBB) in France was compared to Fluxgate data-sets from the three closest magnetic observatories to LSBB, namely Chambon la For êt (France), Ebro (Spain) and Fürstenfeldbruck (Germany), all further than 500 km from LSBB. As a follow-up study, our aim is to correlate the SANSA Space Science SQUID data at Hermanus with Fluxgate magnetic data also recorded on-site (at Hermanus). There are notable di_erences between the previous study and the current study. In the previous study, the three-axis SQUID used comprised of three low-Tc devices operated in liquid helium (4.2 K) in an underground, low noise environment shielded from most human interferences. The SQUID magnetometer operated at Hermanus for the duration of this study is a high-Tc two-axis device (measuring the x and z components of the geomagnetic field). This SQUID magnetometer operates in liquid nitrogen (77 K), and is completely unshielded in the local geomagnetic field of about 26 uT. The environment is magnetically clean to observatory standards, but experiences more human interference than that at LSBB. The high-Tc SQUIDs also experience excessive 1/f noise at low frequencies which the low-Tc SQUIDs do not suffer from, but the big advantage of the current study is that the SQUIDs are located within 50 m from the observatory's fluxgate. We thus expect far better correlation between SQUID and fluxgate data than what was obtained in the previous study, which should improve the isolation of signals detected by the SQUID but not by the fluxgate. / AFRIKAANSE OPSOMMING: SQUIDs (supergeleidende kwantuminterferensietoestelle) is redelik onlangse tipes magnetometers wat vloedkwantisering saam met Josephson-tonneling gebruik om baie klein (< 10¯15 T) magnetiese velde waar te neem. Onlangse wetenskaplike studies het getoon dat hierdie hoogs sensitiewe magnetometers die vermoë het om Aarde-ionosfeerkoppeling waar te neem wanneer dit in 'n ultra-laeruisomgewing geplaas word. Sodanige koppeling sluit in: P-golwe wat deur aardbewings or magnetiese storms in die boonste atmosfeer veroorsaak word; S- en T-asemhalingsmodusse van die Aarde gedurende stil magnetiese en seismiese periodes; en seine in tyd wat korreleer met weerligeffekte in die boonste atmosfeer. Aangesien SQUIDs heelwat meer sensistief is as konvensionele magnetometers, is dit moontlik die beste gereedskap om ruimteweer en geassosieerde natuurlike gevare mee te analiseer; hetsy sulke toestande veroorsaak word vanaf die ruimte (deur die son) of binne die ionosfeer deur magnetiese storms of natuurlike steurings wat deur aardbewings of die dinamika van die Aardkern veroorsaak word. 'n Studie is in 2012 gedoen by SANSA Space Science in Hermanus in die Wes-Kaap om die korrelasie tussen SQUID- en vloedhekdatastelle te vind met die doel om SQUIDs as betroubare instrumente vir ruimteweerwaarneming te bevestig. In daardie studie is SQUID-data verkry vanaf die Laeruis Ondergrondse Laboratorium (LSBB) in Frankryk, en is dit vergelyk met vloedhekdatastelle vanaf die drie naaste magnetiese observatoriums aan LSBB, naamlik: Chambon la Forêt (Frankryk), Ebro (Spanje) en Fürstenfeldbruck (Duitsland). Al drie hierdie observatoriums is verder as 500 km vanaf LSBB. As 'n opvolgstudie is ons doelwit om SQUID- en vloedhekdata wat beide op die terrein van SANSA Space Science in Hermanus waargeneem word, te korreleer. Daar is merkbare verskille tussen hierdie en die vorige studies. In die vorige studie is 'n drie-as lae-Tc SQUID-magnetometer in vloeibare helium (4.2 K) in 'n laeruis ondergrondse laboratorium, afgeskerm teen menslike steurings, gebruik. Die SQUID-magnetometer wat vir die duur van die huidige studie by Hermanus gebruik is, is 'n hoë-Tc twee-as toestel (wat die x - en z -komponente van die geomagnetiese veld meet). Hierdie SQUID-magnetometer opereer in vloeibare stikstof teen 77 K, sonder enige afskerming in die geomagnetiese veld van ongeveer 26 uT. Die omgewing is magneties skoon volgens observatoriumstandaarde, maar ondervind meer menslik-veroorsaakde steurings as LSBB. Die hoë-Tc SQUIDs tel ook heelwat 1/f ruis op (wat lae-frekwensiemetings beïnvloed); iets wat nie 'n rol speel by die lae-Tc SQUIDs nie. Die groot voordeel van die huidige studie is dat die SQUIDs binne 50 meter vanaf die observatorium vloedhekke geleë is. Ons verwag dus heelwat beter korrelasie tussen SQUID- en vloedhekdata as wat met die vorige studie verkry is, wat dit makliker sal maak om die isolasie te verbeter van seine wat deur die SQUIDs waargeneem is, maar nie deur die vloedhekke nie.

Cold bosonic atoms trapped in optical lattices formed by standing wave interference patterns of multiple laser beams constitute excellent emulators of models of strongly correlated quantum systems of bosons. In this thesis, we develop and deploy strong-coupling expansion (i.e., an expansion in terms of the ratio of the inter-site hopping amplitude of the bosons to the strength of their interactions) techniques for studying the properties of three different instances of such systems. In the first instance, we have used strong coupling expansion techniques to calculate the density pro le for bosonic atoms trapped in an optical lattice with an overall harmonic trap at finite temperatures and large on site interaction in the presence of super fluid regions. Our results match well with quantum Monte Carlo simulations at finite temperature. We present calculations for the entropy per particle as a function of temperature which can be used to calibrate the temperature in experiments. Our calculations for the scaled density in the vacuum-to-super fluid transition agree well with the experimental data for appropriate temperatures. We also discuss issues connected with the demonstration of universal quantum critical scaling in the experiments. Experimental realizations of “atomtronic" Josephson junctions have recently been created in annular traps in relative rotation with respect to potential barriers that generate the weak links. If these devices are additionally subjected to optical lattice potentials, then they can incorporate strong-coupling Mott physics within the design, which can modify the behaviour and can allow for interesting new configurations of system generated barriers and of super fluid ow patterns. we have examined theoretically the behavior of a Bose super fluid in an optical lattice in the presence of an annular trap and a barrier across the annular region which acts as a Josephson junction. As the fluid is rotated relative to the barrier, it generates circulating super-currents until, at larger speeds of rotation, it develops phase slips which are typically accompanied by vortices. We use a finite temperature strong-coupling expansion about the mean- held solution of the Bose Hubbard model to calculate various properties of the device. In addition, we discuss some of the rich behavior that can result when there are Mott regions within the system. Rubidium-Cesium dipolar molecule formation through Feshbach resonance is an area of great current interest, for, the dipolar molecules, once formed, interact via v long range dipolar forces, leading to possibilities of novel phases. Experimentalists currently make such systems mostly using trial and error, and the resulting efficiencies for molecule formation tend to be low. With a goal to assist cold-atom experimentalists to achieve higher e ciencies of molecule formation, we have estimated the trap parameters for Rb and Cs atoms in a 3D optical lattice required to create single occupancy per site Mott phase for both the species in the same regions of the trap. We thus identify the ne tuning of the external magnetic held near Rb-Cs Feshbach resonance required to achieve highest probability for creating single Rb-Cs Feshbach molecules in the system. We have used the Falicov-Kimball model to describe the relevant system and strong-coupling expansions about the mean- held solution to calculate the density pro les for both species and efficiency for molecule formation, determined by overlapping regions of single occupancy for both Rb and Cs, up to second order in the expansion. We also calculate the entropy per particle which serves as an estimation of the temperature in the experimental system

URhGe has garnered interest recently as one of the few known ferromagnetic superconductors. The superconductivity in this material appears to arise from magnetic fluctuations rather than phonons, and take a triplet form which is remarkably resistant to field. In this thesis, a number of measurements on the material are presented. Some probe the Fermiology, with strong evidence appearing for a model which as both light open sheets and heavy, small, closed pockets. The open sheets, associated with chains of real-space electron density running along the b axis, dominate the conductivity in most circumstances. Evidence for their existence arises from the general large and non-saturating magnetoresistance, and from the unusual observation of negative temperature coefficient of resistance at high fields. The closed pockets have provided a few Shubnikov-de Haas oscillations, but mostly they remain inferred from the high specific heat γ and their role in the magnetism. In order to better probe the superconductivity, a high precision low noise DC resistance measurement bridge was built using a SQUID. Along with conventional measurements, this provides evidence that the two pockets of superconductivity on the phase diagram are the same phase. The re-entrance an be understood simply as a result of magnetic field being a tuning parameter, but also suppressing bulk superconductivity through orbital limiting. The SQUID bridge allowed the detection of domain wall superconductivity linking up these two pockets. The SQUID bridge was also used to study the highly structured superconducting transition in BiPd. This material lacks inversion symmetry in its crystal structure, so is a good candidate for unusual forms of superconductivity. Here again non-bulk superconductivity is considered the most likely cause for the structure. Unusual and distinctive IV curves have been measured, and a simple model of inhomogeneous conductivity channels with different critical currents is proposed as an explanation.

mRNA localisation is a widely used mechanism for achieving temporal-spatial restriction of protein expression and is essential during development to establish cell polarity. mRNA localisation is particularly well studied in the Drosophila egg chamber where gurken mRNA is localised to the dorsal-anterior corner of the oocyte in a Dynein-dependent process that establishes the anterior-posterior and dorsal-ventral axes of the future embryo. An RNA stem-loop called the gurken localisation signal is necessary and sufficient to drive gurken localisation through interactions with a specific complement of protein factors. However, the exact RNA sequence and structural features required to promote each stage of gurken localisation are unknown. Using a live-cell injection assay I have dissected regions of the mRNA signal that are responsible for driving gurken transport and anchoring through their association with Egalitarian, Me31B and Squid proteins. I show the structure of an AU-rich stem and a purine stack are essential for gurken transport, and demonstrate that the size of the internal loop between these stems is important. These features of the localisation signal are essential for recruitment of Egalitarian, which links the mRNA to the Dynein transport machinery. I also show that these mRNA sequence and structural elements are present in several other Dynein-transported mRNAs. The bulge at the distal end of the gurken localisation signal is important for anchoring grk at the dorsal-anterior of the oocyte, possibly through Squid binding, and the proximal third of the signal is essential for recruitment of the translation component Me31B. These studies indicate that the role of the gurken localisation signal in controlling gurken transport, anchoring and translation can be mapped to distinct regions of the signal and provide insights into how the signal carries out these numerous functions at a molecular level. Determining the molecular interactions involved in mRNA localisation improves our understanding of how specificity is generated to direct different mRNAs to distinct regions of the cell to restrict protein expression.

As principais propriedades físico-químicas da quitosana dependem da massa molar média, grau médio de acetilação (<span style=\"text-decoration: overline\">GA) e do parâmetro de acetilação (PA) que expressa o padrão de distribuição das unidades 2-acetamido-2-desoxi-D-glucopiranose (GlcNAc) e 2-amino-2-desoxi-D-glucopiranose ( GlcN) ao longo de suas cadeias. A distribuição alternada, randômica ou em blocos das unidades GlcN e GlcNAc ao longo das cadeias poliméricas está diretamente relacionada com as condições de preparação da quitosana, sendo que as reações executadas em condições homogêneas geram quitosanas em cujas cadeias há o predomínio da distribuição randômica, enquanto que nas quitosanas produzidas em condições heterogêneas a distribuição em blocos predomina. Neste trabalho &beta;-quitina extraída de gládios de lulas (Loligo sp) foi submetida a 3 etapas consecutivas do processo de desacetilação assistida por irradiação de ultrassom de alta intensidade (processo DAIUS), resultando em quitosana extensivamente desacetilada (<span style=\"text-decoration: overline\">GA &asymp; 2%) e de elevada massa molar média viscosimétrica (<span style=\"text-decoration: overline\">Mv &asymp; 354000 g/mol) comparada a quitosanas obtidas por outros métodos. Essa amostra, denominada amostra QSo, foi dissolvida em ácido acético aquoso e então submetida à reação de N-acetilação por 24 h à temperatura ambiente. A ocorrência de O-acetilação foi evitada pela adição de 1,2-propanodiol ao meio reacional e a variação da razão molar anidrido acético/grupos amino permitiu a obtenção de cinco amostras de quitosanas N-acetiladas, as quais foram caracterizadas por espectroscopia de RMN 1H, espectroscopia na região do infravermelho, difração de raios X, viscosimetria capilar, microscopia eletrônica de varredura e análise termogravimétrica. O parâmetro de acetilação (PA) das quitosanas N-acetiladas foi determinado a partir dos espectros de RMN 1H de modo a permitir a avaliação do tipo de distribuição de unidades 2-acetamido-2-desoxi-D-glucopiranose (GlcNAc) e 2-amino-2-desoxi-D-glucopiranose (GlcN) predominante nos produtos. As reações de N-acetilação foram executadas em duplicata gerando as amostras dos conjuntos 1 e 2, as quais apresentaram <span style=\"text-decoration: overline\">GA variando no intervalo 25%&lt; <span style=\"text-decoration: overline\">GA &lt;55%, sendo constatada variação linear de <span style=\"text-decoration: overline\">GA com a razão molar anidrido acético/grupos amino. As quitosanas N-acetiladas apresentaram parâmetro de acetilação variando com 0,9&lt;PA&lt;1,5, indicando o predomínio da distribuição randômica das unidades GlcNAc e GlcN. As quitosanas N-acetiladas apresentaram maior estabilidade térmica em comparação com a quitosana de partida (amostra QSo), devido a porcentagem de unidades GlcNAc nas cadeias dos polímeros que provocaram alterações na sua estrutura cristalina. Os ângulos de Bragg característicos de &beta;-quitina (amostra QTo) extraída de gládios de lulas foram identificados nos difratogramas das quitosanas N-acetiladas com 30%&lt; <span style=\"text-decoration: overline\">GA &lt;55%, o que sugere que essas amostras adquiriram características semelhantes a da &beta;-quitina. Outra evidência desse fato foi comprovada através da análise das micrografias das amostras de quitosana N-acetiladas, que revelaram que as características das superfícies das partículas das amostras mais acetiladas são semelhantes a da &beta;-quitina. / The main physichochemical properties of chitosan rely on its average molar mass, average degree of acetylation (<span style=\"text-decoration: overline\">GA) and the parameter of acetylation (PA), which expresses the distribution pattern of 2-deoxy-2-acetamido-D-glucopyranose (GlcNAc) and 2-deoxy-2-amino-D-glucopyranose (GlcN) units along its chains. The occurrence of alternated, random or block-like distribution of GlcN and GlcNAc along the polymer chains is directly related to preparation conditions of chitosan. When homogeneous conditions are applied chitosan chains exhibiting random distribution are produced, while the chitosan generated from heterogeneous reactions presents block-like distribution. In this work, &beta;-chitin extracted from squid pens (Loligo sp.) was submitted to three consecutive steps of ultrasound-assisted deacetylation process (USAD process), resulting in an extensively deactylated chitosan (DA=2%) with high viscosity average molar mass (<span style=\"text-decoration: overline\">Mv= 354,000 g/mol) compared to chitosan obtained by other methods. This chitosan, named sample CSo, was dissolved in aqueous acetic acid and then it was submitted to N-acetylation reaction for 24 hours at room temperature. The occurrence of O-acetylation was prevented by adding 1,2-propanediol to the reaction nedium and the variation of the molar ratio acetic anhydride/amino groups allowed the preparation of five N-acetylated chitosans, named as samples RCSon, which were characterized by 1H NMR spectroscopy, infrared spectroscopy, X-ray diffraction, viscometry, scanning electron microscopy and thermogravimetric analysis. The parameter of acetylation (PA) of N-acetylated chitosans was determined from the 1H NMR spectra, allowing the assessment to the distribution pattern of GlcNAc and GlcN units. The N-acetylation reactions were carried out in duplicate, generating two independent sets of N-acetylated chitosans whose average degree of acetylation ranged as 25% &lt; DA &lt; 55%, a linear increase of DA with increasing molar ratio acetic anhydride/amino groups being observed. The N-acetylated chitosans presented parameter of acetylation ranging as 0,9 &lt; PA &lt; 1,5, indicating the predominance of random distribution of GlcNAc and GlcN units. The N-acetylated chitosans showed higher thermal stability as compared to the parent chitosan (CSo sample), probably due to the changes in the degree of order resulting from the higher content of GlcNAc units present in former samples. The Bragg angles characteristic of beta-chitin (CTo sample) were identified in the XRD patterns of N-acetylated chitosans, suggesting that these samples acquired similar characteristics as beta-chitin. Further evidence of this fact was observed through the SEM analyses, which revealed that the characteristics of particle\'s surfaces of N-acetylated chitosans are similar to those of beta-chitin.

Made available in DSpace on 2014-08-20T14:31:31Z (GMT). No. of bitstreams: 1 dissertacao_tony_da_silveira.pdf: 2236842 bytes, checksum: 944d753a4ecf58121a6ca37c8589d2f5 (MD5) Previous issue date: 2014-02-21 / Pontoporia blainvillei is a cetacean popularly know in Brasil as toninha. Its distribution is restrict for estuarine and coastal waters of south-west of Atlantic. Studies of gastrintestinalparasitology of toninhas indicate a component community formed for less species, including nematodes, trematodes and acantocephalans. However, despite knowing that the course of infection is the ingestion of infected prey, intermediate hosts are unknown. The toninhas s diet is composed mainly for fishes, squids and shrimps. Many of these fishes in various areas of distribution of the cetacean have been reported with parasites that attack the species in some stage of development. However, larval forms of the trematode Synthesium pontoporiae and the acantocephalan Bolbosoma turbinella were not identified in any of the food items of P. blainvillei. The present study aimed to evaluate three components of the diet of P. blainvillei as possible sources transmission of parasitiasis. Fifty specimens of Doryteuthis sanpaulensis; forty-three specimens of Paralonchurus brasiliensis and fifty specimens of Trachurus lathami were necropsied. The organs were individually, washed in tamis (150μm) and examined under a stereomicroscope. Helminths were collected, counted, fixed in AFA, stained with Delafield s hematoxylin or Gomori s trichrome, clarified in Amman s lactophenol or Beech creosote and mounted on slides. Parasitological indices were calculated. None of the food items analyzed showed infection by metacercariae of S. pontoporiae. Helminths found in D. sanpaulensis did not have records of infection of P. blainvillei. Cistacanths of C. australe were found in the coelomic cavity and mesentery of P. brasiliensis (P=53,49%; IMI=6,74) and of T. lathami (P=4%; IMI=1,50). Cistacanths of B. turbinella were on same sites of T. lathami (P=14%; IMI=2,14). Paralonchurus brasiliensis and T. lathami are recorded in this study as new paratenics hosts for C. australe, as well as T. lathami is to B. turbinella. In addition to the parasites that infect P. blainvillei, the nematodes Hysterothylacium sp., Dichelyne (D.) spinicaudatus and Procamallanus pereirai, and trematodes Diphterostomum brusinae, Opecoeloides catarinensis, O. stenosomae, Pachycreadium gastrocotylum, Aponurus laguncula, A. pyriformis and Lecithochirum sp. are registered as members of the component community of P. brasiliensis and five new records of parasitism on fish and a new record of parasite species to brazilian waters. The use of nematodes as biomarkers for distinguishing the populations of P. brasiliensis is discussed. Through the present study more about the ecology and parasitology of final and paratenic hosts were revealed, as well as aspects of the biology of parasites, contributing to the knowledge about the marine biology of the south Atlantic. / Pontoporia blainvillei é um cetáceo conhecido popularmente no Brasil como toninha, cuja distribuição é restrita às águas estuarinas e costeiras do sudoeste do Atlântico. Estudos sobre parasitologia gastrintestinalde toninhas indicam uma comunidade componente formada por poucas espécies, incluindo nematódeos, trematódeos e acantocéfalos. Entretanto, apesar de se saber que a forma de infecção é a ingestão de presas infectadas, os hospedeiros intermediários são pouco conhecidos. A dieta da toninha é composta principalmente por peixes, lulas e camarões. Muitos desses peixes em várias áreas da distribuição do cetáceo já foram reportados com parasitos que acometem a espécie em algum estágio de desenvolvimento. Contudo, formas larvais do trematódeo Synthesium pontoporiae e do acantocéfalo Bolbosoma turbinella não foram identificadas em nenhum dos itens alimentares de P. blainvillei. O presente estudo teve como objetivo avaliar três espécies componentes da dieta de P. blainvillei como possíveis fontes transmissoras de parasitíases. Cinquenta espécimes de Doryteuthis sanpaulensis; quarenta e três espécimes de Paralonchurus brasiliensis e cinquenta espécimes de Trachurus lathami foram necropsiados. Os órgãos foram individualizados, lavados em tamis (150μm) e examinados sob estereomicroscópio. Os helmintos coletados foram contados, fixados em AFA, corados com hematoxilina de Delafield ou tricrômico de Gomori, clarificados em lactofenol de Amman ou creosoto de Faia e montados em lâminas. Índices parasitológicos foram calculados. Nenhum dos itens alimentares analisados apresentou infecção por metacercárias de S. pontoporiae. Helmintos encontrados em D. sanpaulensis não têm registros de infecção em P. blainvillei. Acantocistos de C. australe foram encontrados na cavidade celômica e mesentério de P. brasiliensis (P=53,49%; IMI=6,74) e de T. lathami (P=4%; IMI=1,50). Acantocistos de B. turbinella estiveram nos mesmos sítios de T. lathami (P=14%; IMI=2,14). Paralonchurus brasiliensis e T. lathami são registrados no presente estudo como novos hospedeiros paratênicos para C. australe, assim como T. lathami é para B. turbinella. Além dos parasitos que infectam P. blainvillei, os nematódeos Hysterothylacium sp., Dichelyne (D.) spinicaudatus e Procamallanus (S.) pereirai, e os trematódeos Diphterostomum brusinae, Opecoeloides catarinensis, O. stenosomae, Pachycreadium gastrocotylum, Aponurus laguncula, A. pyriformis e Lecithochirum sp. são registrados como membros da comunidade componente de P. brasiliensis sendo cinco novos registros de parasitismo para o peixe e um novo registro de espécie parasita para águas brasileiras. A utilização de nematódeos como biomarcadores para a distinção de populações de P. brasiliensis é abordada. Através do presente estudo mais informações sobre a ecologia e parasitologia dos hospedeiros definitivo e paratênicos foram reveladas, assim como aspectos da biologia dos parasitos, contribuindo para o conhecimento sobre a biologia marinha do Atlântico sul.

Inorganic macrocycles have stimulated interest in recent years for their magnetic properties, their associated host-guest chemistry and their aesthetically appealing structures. These characteristics have led to suggestions that they could be exploited for the purposes of ion recognition, catalysis, as single molecule magnets, MRI agents, antibacterial agents and as part of larger architectures in a molecular machine. This thesis explores the properties of a group of chromium(III) macrocycles, with functionality tailored towards different pursuits. Firstly the magnetic properties of a newly synthesised family of ring dimers are investigated. The nature of magnetic exchange within each ring leads to a net electronic spin which, it has been proposed, could represent a quantum binary digit within a quantum information processing system. By linking together pairs of rings, the degree of inter ring communication can be determined. Such interactions are important for the correlation of spin as initiation of quantum entanglement, a pre-requisite for quantum computing. The rings can also act as fluoro-metallocrowns, hosting the molecule which templated their formation. A range of rings with different guests are synthesised and their solid and solution state structures are explored. On templating about bulky dialkyl amines hybrid organic-inorganic rotaxanes are formed where the guest is fixed. In contrast when using small amines and alkali metals, exchange of guests is possible. The dynamics of all of these systems are investigated with proton NMR, quite remarkable for such highly paramagnetic complexes.

It is currently hypothesised that the chokka squid (Loligo reynaudi) consist of a single stock. This was tested through a spatial comparison of the morphology of this species. Forty three morphometric characters were measured from 1079 chokka squid collected from three regions: the south coast of South Africa, the west coast of South Africa, and southern Angola. While no significant differences were found for the hard body parts, results from discriminant function analyses showed the soft body morphometric characters from each of the three regions differed, with an overall correct classification rate of 100% for males and 99% for females in all three regions. Due to the existing model being used to assess the resource currently being updated it was not feasible to apply this model to the area-disaggregated data from this study. Rather, the CPUE trends and catches from the area-disaggregated data were compared against those of the area-aggregated data, as a first attempt to discern any appreciable differences which would suggest the use of disaggregated data in future assessments. Both the trawl and jig CPUE trends from the area-disaggregated analysis differed only slightly from those of the area-aggregated data. Similarly, the spring and autumn biomass trends for the main spawning area (east of 22°E) followed the same trends as for the full area. It is therefore concluded that there is currently no need to assess the resource on an area-disaggregated basis.