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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
621

Electrifying the Molecules of Life : Peptide and Protein Analysis by Capillary Electrophoresis Coupled to Electrospray Ionization Mass Spectrometry

Wetterhall, Magnus January 2004 (has links)
This thesis describes the current status and novel aspects of the analysis of the molecules of life, i.e. peptides and proteins, using capillary electrophoresis (CE) coupled to mass spectrometry (MS) via (sheathless) electrospray ionization (ESI). Early reports of sheathless CE-ESI-MS were plagued by limited lifetimes of the electrospray emitter. In this thesis, two new approaches, the Black Dust and the Black Jack methods, utilizing polymer-embedded graphite instead of noble metals are presented. These emitters have shown improved long-term stability and proven excellent for sheathless electrospray operation. Failure of an emitter is often caused by electrochemical reactions occurring at the emitter-liquid interface. The electrochemical properties of the graphite coated emitters were therefore evaluated by classical electrochemical methods, such as cyclic voltammetry and chronoamperometry. The graphite coated emitters showed excellent electrochemical stability and properties compared to noble metal and polymer configurations. Analyte-wall interactions have long been known to cause problems in the CE analysis of biomolecules. This can be circumvented by internal modification of the capillary walls. Additionally, it is of outermost importance to have a stable and sufficiently high electroosmotic flow (EOF) to sustain the electrospray, when using a sheathless approach. New monomer and polymer coatings are presented for rapid and high-efficient CE-ESI-MS separations of peptides and proteins. Furthermore, the use of CE-ESI coupled to Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) shows great potential for rapid proteomic probing of human cerebrospinal fluid. The results are comparable with more established techniques, such as liquid chromatography and two-dimensional gel electrophoresis coupled to MS. However, the CE-ESI-FTICRMS analysis has significantly lower sample consumption and faster analysis time compared to the other techniques. The applications and use of CE-ESI-MS is expected to have a bright future with continued growth as current trends of multidimensional hyphenation and microfabricated devices are further developed and explored.
622

Carbon-based magnetic nanomaterials

Zagaynova, Valeria January 2012 (has links)
Magnetism of carbon-based materials is a challenging area for both fundamental research and possible applications. We present studies of low-dimensional carbon-based magnetic systems (fullerene-diluted molecular magnets, carbon nanotubes, graphite fluoride, and nanoporous carbon) by means of SQUID magnetometer, X-ray diffraction and vibrational spectroscopy, the latter techniques used as complementary instruments to find a correlation between the magnetic behaviour and the structure of the samples.In the first part of the thesis, characteristic features of the magnetization process in aligned films of carbon nanotubes with low concentration of iron are discussed. It is shown that the magnetism of such structures is influenced by quantum effects, and the anisotropy behaviour is opposite to what is observed in heavily doped nanotubes.In the second part, Mn12-based single molecular magnets with various carboxylic ligands and their 1:1 fullerene-diluted complexes are studied. We prove that magnetic properties of such systems strongly depend on the environment, and, in principle, it is possible to design a magnet with desirable properties. One of the studied compounds demonstrated a record blocking temperature for a single molecular magnet. Both fullerene-diluted complexes demonstrated “magnetization training” effect in alternating magnetic fields and the ability to preserve magnetic moment.The third and the fourth parts of the thesis are dedicated to the analysis of various contributions to the magnetic susceptibility of metal-free carbon-based systems – intercalated compounds of graphite fluorides and nanoporous oxygen-eroded graphite. The magnetic properties of these systems are strongly dependent on structure, and can be delicately tuned by altering the π-electron system of graphite, i. e. by degree of fluorination of intercalated compounds and by introduction of boron impurity to the host matrix of nanoporous graphite. / Magnetism av kolbaserade material är ett utmanande område för både grundforskning och möjliga tillämpningar. Vi presenterar studier med låg-dimensionella kolbaserade magnetiska system (fulleren-utspädda molekylära magneter, kolnanorör, grafit fluorid och nanoporösa kol) med hjälp av SQUID magnetometer, röntgendiffraktion och vibrerande spektroskopi, de senare tekniker som används som komplement instrument för att finna sambandet mellan den magnetiska uppträdande och strukturen hos proven. I den första delen av avhandlingen är egenheter från magnetisering processen i linje filmer av kolnanorör med låg koncentration av järn diskuteras. Det visas att magnetism av sådana strukturer påverkas av kvantmekaniska effekter och anisotropin beteende är motsatsen till vad som observerats i kraftigt dopade nanorör. I den tvåa delen är Mn12-baserade enda-molekyl magneter med olika karboxylsyror ligander och deras 1:1 fulleren-utspädda komplex studeras. Vi visar att magnetiska egenskaperna hos sådana system beror i hög grad på miljön, och i princip är det möjligt att utforma en magnet med önskvärda egenskaper. En av de studerade föreningarna visade en post blockeringstemperaturen för en enda molekylär magnet. Både fulleren-utspädda komplex visade "magnetisering utbildning" effekt i alternerande magnetfält och möjligheten att bevara magnetiskt moment. Den tredje och fjärde delarna av avhandlingen är avsedda för inneboende magnetism av analys av olika bidrag till magnetisk susceptibilitet av metall-fritt kol-baserade system -inskjutna föreningar grafit fluorider och nanoporösa O2-eroderade grafit. Magnetiska egenskaperna hos dessa system är starkt beroende av strukturen, och kan fint avstämmas genom att man ändrar π-elektronsystem av grafit, i. e. med graden av fluorering av inskjutna föreningar och genom införandet av bor föroreningar till värd matris av nanoporösa grafit.
623

Towards Safer Lithium-Ion Batteries

Herstedt, Marie January 2003 (has links)
Surface film formation at the electrode/electrolyte interface in lithium-ion batteries has a crucial impact on battery performance and safety. This thesis describes the characterisation and treatment of electrode interfaces in lithium-ion batteries. The focus is on interface modification to improve battery safety, in particular to enhance the onset temperature for thermally activated reactions, which also can have a negative influence on battery performance. Photoelectron Spectroscopy (PES) and Differential Scanning Calorimetry (DSC) are used to investigate the surface chemistry of electrodes in relation to their electrochemical performance. Surface film formation and decomposition reactions are discussed. The upper temperature limit for lithium-ion battery operation is restricted by exothermic reactions at the graphite anode; the onset temperature is shown to be governed by the composition of the surface film on the anode. Several electrolyte salts, additives and an anion receptor have been exploited to modify the surface film composition. The most promising thermal behaviour is found for graphite anodes cycled with the anion receptor, tris(pentafluorophenyl)borane, which reduces salt reactions and increases the onset temperature from ~80 °C to ~150 °C. The electrochemical performance and surface chemistry of Swedish natural graphite, carbon-treated LiFePO4 and anodes from high-power lithium-ion batteries are also investigated. Jet-milled Swedish natural graphite exhibits a high capacity and rate capability, together with a decreased susceptibility to solvent co-intercalation. Carbon-treated LiFePO4 shows promising results: no solvent reaction products are detected. The amount of salt compounds increases, with power fade occurring for anodes from high-power lithium-ion batteries; the solvent reduction products comprise mainly Li-carboxylate type compounds.
624

Stories from a Chair: A Life Exquisite

Blinkhorn, Jessica Elaine 04 April 2010 (has links)
Exquisite is defined as carefully selected or sought out. I believe myself to be a selected soul placed in a body of circumstance. My work is self-explorative and telling of those circumstances in hopes of evoking empathy. Our bodies function and exist on many different levels. What I understand as normal for most differs vastly from what is normal for me. I aim to offer my perspective on the world, establish understanding, and blur the lines of normalcy.
625

An Investigation Of Compacted Graphite Cast Iron Production By Means Of Thermal Analysis Technique And Other Process Control Windows

Elmabrouk, Omar Mustafa 01 January 2007 (has links) (PDF)
ABSTRACT AN INVESTIGATION OF COMPACTED GRAPHITE IRON PRODUCTION BY MEANS OF THERMAL ANALYSIS TECHNIQUE AND OTHER PROCESS CONTROL WINDOWS El-mabrouk, Omar PhD, Metallurgical and Material Engineering Department Supervisor: Prof. Dr. Ali Kalkanli January 2007, 123 pages Compacted graphite irons have been proved valuable in many applications such as exhaust manifolds, hydraulic valves, and diesel engine blocks, the process of producing compacted graphite irons is not a straight forward process because of its narrow processing windows and its high sensitivity to the section thickness, treatment reaction time, pouring temperatures and charge composition. In this thesis, compacted graphite was produced with minimum variations through all section thickness and the effect of Mg/S ratio, section thickness, and treatment agents on the graphite morphology, electrical resistivity property and fracture strength at high temperatures was investigated. The range of Mg/S ratio and the section thickness was from 2/3 to 7/1 and 5 mm to 40 mm respectively. FeSiMg and FeSiMg cermish metal were used as a treatment agent. Optical metallographic method was implemented to investigate the graphite morphology change. For being a distinguishable characteristic for compacted graphite iron over ductile iron, thermal conductivity changes at high temperatures ranging from room temperature to 500 0C was examined by a suitable electrical setup in the manner of electrical conductivity changes by measuring the electrical resistance. On the other hand, due to the higher values of mechanical properties of compacted graphite iron over those of gray iron, tensile strength was also examined by means of tensile test. The relation between the compacted graphite shape and the alloy properties such as fracture strength and thermal conductivity was investigated. The most important controlling parameters to produce compacted graphite are Mg/S ratio and oxygen activity. The relation between these parameters with both fracture strength and thermal conductivity was established by means of multiple regression analysis technique.
626

Characterization of factors interacting in CGI machining : machinability - material microstructure - material physical properties

Berglund, Anders January 2008 (has links)
<p>The Swedish truck industry is forced to find new material solutions to achieve lighter engines with increased strength. Customers and new environmental regulations demand both higher specific power and more environmentally friendly trucks, and this places a rising pressure on the manufactures. This demand could be met by increasing the peak pressure in the cylinders. Consequently, a more efficient combustion is obtained and the exhaust lowered. This however exposes the engine to higher loads and material physical properties must therefore be enhanced.</p><p>Today, alloyed gray iron is the predominantly used engine material. This material cannot meet the requirements of tomorrow’s engines. Compacted Graphite Iron has good potential to be the replacement; it opens new design opportunities with its superior strength, which can lead to smaller, more efficient engines and additional power. The question is: how will manufacturing be affected?</p><p>The main goal of this thesis is to identify and investigate the main factors’ effect and their individual contributions on CGI machining.  When the relationship between the fundamental features; machinability, material microstructure, and material physical properties, are revealed, then the CGI material can be optimized, both regarding the manufacturing process and design requirements. The basic understanding is developed mainly through experimental analysis. No attempt has been made to optimize the material to be used as engine material in this thesis.</p><p>The thesis demonstrates the importance of having good casting process control. It also illustrates the microstructural properties’ effects on CGI machinability, and what new aspects of machining must be taken into account, compared to gray iron.</p> / OPTIMA CGI
627

Matériaux carbonés sp2/sp3 intercalés sous pression : le cas du graphite et des clathrates.

Rey, N. 29 October 2007 (has links) (PDF)
L'objectif de ce travail de thèse est d'étudier l'évolution du graphite intercalé avec des atomes alcalins (Li, Rb et Cs) sous haute pression et haute température, procédé susceptible de conduire aux clathrates de carbone, matériaux formés de nano-cages de type sp3 aux propriétés mécaniques proches du diamant et potentiellement supraconducteur à haute température. L'évolution complexe des propriétés structurales et électroniques sous pression des composés CsC8 et RbC8 a été mise en évidence grâce à l'utilisation de sondes locales (spectroscopies d'absoprtion X et Raman) et de sondes à longue distance (diffraction de rayons X et de neutrons). Des nouvelles informations jusqu'à 32 GPa et 16 GPa portant sur le transfert de charge, l'équation d'état, les transitions structurales de CsC8 et RbC8 respectivemement sont apportées. Des calculs ab initio réalisés sur ces clathrates de carbone afin d'étudier leur stabilité ainsi que leurs propriétés sous pression ont permis d'obtenir des indications concernant leur synthèse.
628

Untersuchung der Physisorption von Wasserstoff in porösen Materialien mit einer neuartigen volumetrischen Apparatur

Khvostikova, Olga 01 April 2011 (has links) (PDF)
Wasserstoff ist der ideale Energieträger, da er völlig schadstofffrei verbrennt und einen potentiell hohen Energiegehalt pro Masse besitzt. Die größte Herausforderung für den Gebrauch von Wasserstoff als Kraftstoff ist die Wasserstoffspeicherung in sicheren und kostengünstigen Systemen. Die Ziele und Aufgaben der vorliegenden Doktorarbeit sind, poröse Materialien, die unterschiedliche Struktur und Zusammensetzung besitzen, für die Physisorption von Wasserstoff mittels einer neuartigen volumetrischen Apparatur zu untersuchen. Das Erreichen maximaler Speicherdaten stand nicht im Vordergrund dieser Arbeit. Viel wichtiger war es, einen Struktur – Eigenschafts – (Sorptions) – Zusammenhang zu verstehen, auf deren Basis eine systematische Entwicklung von Wasserstoffspeichermaterialien erfolgen könnte. Zwei Klassen von potentiellen Wasserstoffspeichern wurden erforscht: expandierte Graphitmaterialien und Metallorganische Netzwerke. Neue experimentelle Methoden zur Untersuchung der Wasserstoffspeicherkapazität an modifizierter volumetrischer Apparatur wurden erfolgreich entwickelt und geprüft. Das Verwenden einer der Kammern als Referenzkammer ermöglicht das Ausschließen der experimentellen Artefakte aus der Auswertung der gespeicherten Wasserstoffmenge. Es wurde keine Gaszustandgleichung bei tiefen Temperaturen verwendet, was sehr wichtig bei den Experimenten mit Wasserstoff ist.
629

Spéciation chimique et immunotoxicologie du béryllium : effets thérapeutiques des agents complexants NTA, NTP et tiron

Stephan, Chadi H. January 2008 (has links)
Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal
630

Optimisation du dépôt par ablation laser de films minces d'alumine et de carbone tétraédrique amorphe pure et dopé; propriétés des couches et intégration dans le fabrication de composants MEMS RF

Orlianges, Jean-Christophe 28 November 2003 (has links) (PDF)
Ce travail consiste en l'optimisation des conditions de dépôt par ablation laser à température ambiante du carbone et de l'alumine. Il se divise en huit parties principales. Le premier chapitre est une présentation du contexte de l'émergence des couches de carbone et d'alumine par ablation laser. le deuxième chapitre décrit les dispositifs expérimentaux et modes opératoires mis en œuvre, qu'ils concernent l'élaboration des films aussi bien que la détermination de leurs propriétés. Les deux chapitres suivants s'intéressent à résoudre les principaux défauts de l'ablation laser à savoir : La projection de particules solides lors du dépôt (chapitre 3) L'inhomogénéité en épaisseur des couches réalisées sur sustrat fixe (chapitre 4) le cinquième chapitre est consacré à l'étude des propriétés structurelles, électriques et mécaniques des couches de ta-C en fonction des conditiond de dépôt. Ce travail s'appuie sur une étude de l'énergie des ions dans le panache plasma (spectroscopie, imagerie résolue temporellement et spectralement) et leur rôle dans la croissance des films de ta-C (analyses Raman, XPS, MET...). le sixième chapitre reprend une étude similaire à ce qui a été présenté dans le chapitre précédent en l'applicant aux couches minces d'alumine par ablation laser. Enfin le dernier chapitre est consacré à l'intégration, dans les composants MEMS RF, des films d'alumine et de ta-C déposés par ablation laser. Ce chapitre rapporte les résultats de la collaboration menée avec l'IRCOM pour réaliser des composants fonctionnels (microcommutateurs RF, filtres accordables ...) à base de couches minces déposées par ablation laser.

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