The results of cross polarized pump-probe experiments in preformed He plasma waveguides are reported. Pump and probe have same wavelength and duration of 800nm and 80fs respectively. Peak pump intensity is I[subscript guided] = 0.2X10¹⁸W/cm² ~1000 I[subscript probe]. Single shot probe spectra and mode profiles at the channel exit are discriminated from the pump with a polarization analyzer and captured at various relative time delays [Delta]t. Frequency-domain interference (FDI) between the probe and a weak depolarized component of the pump is observed for [scientific equation]. Although the depolarized component is nearly undetectable through measurement of pump leakage alone, FDI sensitively reveals its substantially non-Gaussian structure. The possible depolarization mechanisms are analyzed. When probe is positioned at the leading edge of the pump, [scientific equation], its spectrum suffers a blue shift not measurable in the transmitted pump itself. The evidence suggests the channel interior is fully ionized and the partially formed channel ends are the origin of both depolarization and blue shift. A robust, pulsed, differentially-pumped plasma channel generation cell for high intensity guiding experiments has been developed. The design includes an axicon lens, windows for transverse interferometry, and permits injection of one or two different gases (main gas plus high Z seed gas) with several millisecond injection times and simultaneous 0.1ms pressure sensing resolution. Very well formed plasma waveguides have been formed in helium as well as hydrogen, at repeatable and well controlled pressures up to 1000Torr, with very uniform interior density, rapid density drop at boundaries, and very low exterior density. The possible danger associated with the use of large amounts of hydrogen was considered and a complex safety system was designed, constructed and used. Extensive analysis of channel profile reconstruction through transverse interferometry was performed. This includes an intuitive, efficient reformulation and extension of the Phase Locked Loop (PLL) carrier fringe demodulation method. It is also demonstrated and explained how and under which conditions artificial fringe frequency multiplication can reduce demodulation distortions in both PLL and Fast Fourier Transform (FFT) methods. / text

No description available.

Due to climate change and arctic amplification, the avalanche activity is expected to increase at higher latitudes (Hall et al., 1994). The arctic settlement of Longyearbyen, Svalbard, situated inside the valley Longyeardalen, is yearly threatened by avalanche activity (Eckerstorfer & Christiansen, 2011a). The surrounding slopes are known to produce avalanche, and during the last century they have proven to be able to cause substantial damages and even fatalities (Hallerstig, 2010). Previous studies investigated magnitude and forcing of the avalanches, including a meteorological perspective (Eckerstorfer & Christiansen, 2011b). This allowed for the usage of forecasts from the weather model AROME-Arctic in order to have an avalanche bulletin.The forecast for the area of Longyearbyen suffers from the location and the insufficient resolution of its source data. The data are obtained from an AWS located at the local airport, at the mouth of a relatively wide NW/SE oriented valley. Conversely, Longyeardalen is oriented NE/SW and is narrower. Because of the topography, channeling of winds is expected to produce difference weather conditions at the two sites, generating two distinct local weather conditions (Whiteman, 2000). If these different weather conditions are not taken into account, the weather model may provide forecasts that are not reliable for the area of Longyeardalen, hence resulting in biased avalanche bulletins.In this work I compare the data from the airport, from Longyeardalen and from the plateau above in order to assess if relevant differences exist in some important meteorological parameters (temperature, wind speed and direction, precipitation) between these sites. The weather station at the airport is an official AWS while the data from the other two sites were obtained using portable weather stations deployed during a field campaign between March 1st and April 11th 2018. During this time, snow data from the slopes surrounding Longyeardalen were also obtained. These data have been used to look for correlations among the wind conditions in the valley and the depth of the snow, as it is known that snow transport is a major factor determining snow accumulation in the area (Jaedicke and Sandvik, 2002; Hestnes, 2000).Temperature and precipitation have been found to be consistent among the two investigated valleys, while wind parameters differed significantly. Wind speed in Longyeardalen is on average overestimated by 3 m/s if only the data from the airport are used while the direction data are uncorrelated. This is due to the different circulations that occur at the two sites. Adventdalen is mostly influenced by southeasterly winds that are forcedly channeled or induced by the synoptic circulation, while in the smaller Longyeardalen southerly winds prevail due a thermal circulation induced by the presence of two glaciers on the top part of the valley. Snow depth is altered by the wind transport but it was not possible to find any correlation due to the low resolution of the snow depth data.

No description available.

<p> This project is concerned with medium energy heavy ion (60 KEV 75As, 40Ar, 120 KEV 150As2) implantation into single crystal iron at room temperature and 35°K. Resulting crystal properties are measured using the technique of high energy light ion (1.0 MEV 4He) channeling and backscattering. The phenomenon of oxygen recoil implantation by the bombarding ion is found to be an important effect to avoid if radiation damage is to be measured. In cases where oxygen recoil implantation has been eliminated, radiation damage was evident from an increase in the minimum channeling yield. The existence of damage beyond the expected damage range at room temperature is attributed to diffusion of defects. Some annealing of damage is observed in samples which have been damaged at 35°K and warmed to room temperature. At doses of about 10^16 atoms/cm^2, 80(±10)% of the implanted As is found to be at lattice sites.</p> <p> The merits and limitations of this technique as a simulation of 14 MEV neutron radiation damage are also discussed.</p> / Thesis / Master of Engineering (MEngr)

No description available.

Homogene Immunoassays sind immunologische Testverfahren, bei deren Durchführung vollständig auf Separations- und Waschschritte verzichtet werden kann. Der Substrate Channeling Immunoassay beruht auf der Weitergabe eines Substrates in einem immunologischen Komplex aus zwei Enzymen. Das Produkt des ersten Enzyms dient dem zweiten Enzym als Substrat zur Generierung eines photometrisch nachweisbaren Produktes. Voraussetzung für diese Weitergabe ist die enge räumliche Nähe beider Enzyme. Diese Nähe wird durch eine Bindung zwischen Analyt und anti-Analyt Antikörper vermittelt. Ein solcher Substrate Channeling Immunoassay wurde unter Verwendung der Enzyme Glucoseoxidase und Peroxidase aufgebaut. Das so etablierte System war funktionstüchtig, jedoch blieb seine Sensitivität hinter der normaler, heterogener Immunoassays zurück. Die Grundlage eines Fluorescence Quenching Immunoassays ist der gegenseitige Ausschluß zweier Antikörper bei der Bindung eines Dihapten-Konjugates. Das Konjugat besteht dabei aus dem Analyten und einem Fluorophor. Die beiden um die Konjugatbindung konkurrierenden Antikörper sind ein anti-Analyt Antikörper und ein anti-Fluorophor Antikörper, der zudem über die Eigenschaft verfügt, bei Bindung des Fluorophors dessen Fluoreszenz zu löschen. Externe Gaben des freien Analyten verschieben das eingestellte Gleichgewicht in Richtung Fluorophor-Bindung und damit Fluoreszenz-Löschung. Die Änderung der Fluoreszenz ist direkt an die Konzentration des freien Analyten gekoppelt und dient zu deren Bestimmung. Ein solcher Fluorescence Quenching Immunoassays wurde für die Konzentrationsbestimmung des Herbizides Diuron etabliert. Die erreichten Sensitivitäten erlauben die praktische, immundiagnostische Anwendung des Systems. Ein Dihapten-Konjugat wurde ebenfalls zum Aufbau eines Verfahrens zur Selektion Antikörper produzierender Zellen eingesetzt. Die Selektion der Antikörper produzierenden Zellen erfolgt unter Verwendung eines Toxinkonjugates. Dieses Konjugat besteht aus einem Liganden und einem Toxin. Die Antikörperbindung des Liganden behindert sterisch die Wechselwirkung der Toxinkomponente im Konjugat mit deren Zielstruktur in oder auf der Zelle. Nur Zellen die einen geeigneten Antikörper sezernieren, überleben die Selektion und reichern sich in der Kultur an. Das Selektionsverfahren wurde erfolgreich für die Selektion von E.coli Zellen eingesetzt, die einen rekombinanten, Fluorescein bindenden Antikörper produzierten. Das hierfür synthetisierte Toxinkonjugat bestand aus Fluorescein (Ligand) und Ampicillin (Toxinkomponente). Eine Ablösung der bisher für diese Aufgabe gebräuchlichen, außerordentlich kostenintensiven, Screening Methoden wird damit möglich. / Homogeneous immunoassays are test systems which do not depend on separation steps. The substrate channeling immunoassay is based on the product/substrate transfer in an immunological complex built up by two enzymes. The product of the first enzyme functions as substrate for the second enzyme. The second enzyme generates a photometrically detectable product. The close proximity of these two enzymes is the basis of the substrate channeling. This proximity is created by antibody binding to the corresponding analyte. The enzymes glucose oxidase and peroxidase were used for the development of such an assay system. The established homogeneous immunoassay was functional. But the sensitivity of the assay was much lower than that of conventional heterogeneous immunoassays. The principle of a fluorescence quenching immunoassay is based on the fact that two antibodies exclude each other from binding to a dihapten conjugate. The conjugate consists of the analyte and the fluorophore. The two antibodies which compete for the conjugate binding are an anti-analyte antibody and an anti-fluorophore antibody. This anti-fluorophore antibody quenches the fluorescence of the fluorophore after binding. The addition of free analyte alters the equilibrium of the system so that the anti-fluorophore antibody is bound to the fluorophore and the fluorescence is quenched. The change in fluorescence is therefore an indicator of the concentration of free analyte added. A homogeneous fluorescence quenching immunoassay was established for the determination of the herbicide diuron. The sensitivities obtained allow the practical immunodiagnostic application of the system. A dihapten conjugate was also employed for the development of a selection method for antibody-producing cells. Toxin conjugates were used in this system. Each conjugate consisted of a ligand and a toxin. Antibody binding to the ligand sterically inhibits the toxin component to interact with its target structure. Only cells secreting a binding antibody will survive the selection and will accumulate in culture. The system was applied to the selection of E.coli cells producing a recombinant fluorescein-binding antibody. The toxin conjugate used in experiment consisted of fluorescein (ligand) and ampicillin (toxin component). This selection procedure allowed the isolation of recombinant antibody-producing E.coli cells. It has the potential to replace the time-consuming and labour-intensive methods used so far.

"May 2002." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Le travail développé dans cette thèse concerne un type particulier de sources de positrons utilisant le rayonnement de canalisation dans un cristal ainsi que d'autres effets cristallins observes le long des axes du cristal ; ces effets produisent un grand nombre de photons qui, à leur tour, génèrent un grand nombre de paires e+e- dans une cible amorphe. Les photons et les paires sont créés dans deux cibles différentes séparées par une certaine distance permettant l'installation d'un aimant pour dévier les particules chargées avant la cible amorphe. Une telle source est appelée source hybride de positrons ; elle a été choisie par le CERN pour le projet CLIC. Ce type de sources présente de réels avantages par rapport aux cibles conventionnelles qui ont une grande emittance ainsi qu'un niveau important de dépôt d'énergie dans la cible. Apres un rappel des phénomènes physiques qui concernent notre étude, des simulations détaillées utilisant d'une part le programme de V .Strakhovenko pour les effets cristallins et d'autre part le code GEANT4 pour la génération des positrons conduisent à une description complète pour les photons et les positrons avec, notamment, les espaces de phase longitudinal et transverse, le spectre en énergie, la distribution temporelle,.. Nous avons particulièrement insiste sur deux points : d'abord sur les dispositifs de capture des positrons -après la cible- qui sont essentiels pour avoir de bons rendements de positrons acceptes et ensuite sur la densité de l'énergie déposée dans la cible qui représente un paramètre important pour la survie des cibles. En ce qui concerne le premier point, trois dispositifs de capture ont été étudiés : le système adiabatique (AMD), le système quart d'onde (QWT) et la lentille de lithium. Pour le deuxième point qui concerne l'énergie déposée et l'échauffement de la cible, on a cherché à optimiser la densité d'énergie déposée en diminuant son maximum (PEDD) ; l'énergie moyenne déposée a aussi été optimisée en utilisant une solution spéciale pour le convertisseur : un convertisseur granulaire forme de petites sphères, comme cela avait été considéré précédemment pour les usines à neutrinos. Des résultats très prometteurs nous ont conduits à envisager la source hybride de positrons avec un convertisseur granulaire comme une solution au difficile problème d'ILC. Cette solution est étudiée moyennant une transformation des impulsions du faisceau avant la cible, comme cela avait été envisage par l'équipe du KEK. Le transport du faisceau de positrons au-delà du solénoïde a été étudié avec la première partie de l'optique quadrupolaire.

<p>Resistance to antimicrobials is an increasing problem in the world of today, and develops faster than man can counter. It is therefore of importance to study metabolic pathways in order to develop new antibiotics, but also to understand how resistance spreads and stabilizes in microbial populations.</p><p>The commensal flora could be an important factor in the spread of antimicrobial resistance, as drugs aimed at other targets also hit the harmless commensal bacteria. If stable resistance develops in such a population, it could seriously impair a later treatment with the same drug. After a treatment with the macrolide clarithromycin, resistance to this antibiotic increased markedly in the untargeted throat flora, and resistance levels did not recede until at least one year later. </p><p>Another example of stable resistance can also be seen in sulfonamide resistant <i>Streptococcus pyogenes</i>. Sequence determinations of the dihydropteroate synthase (<i>dhps</i>) gene conferring this resistance revealed a mosaic organisation implying that the it had been brought there by horizontal transfer. Molecular characterization of this gene showed that the sulfonamide resistance was due to mutations of structurally important amino acids in position 65 and 213.</p><p>The folate synthesis pathway has potential for being exploited further as a drug target. One possible new drug target is hydroxymethyl-dihydropterin pyrophosphokinase (<i>hppk</i>). In the malaria parasite <i>Plasmodium falciparum</i> this enzyme is part of a polyfunctional entity, also encoding <i>dhps</i>. The HPPK part can be separated from DHPS, but that the opposite is not possible. The PfHPPK has two insertions: one also present in other plasmodia, and one apparently unique to <i>P. falciparum</i>. Both are crucial for enzyme activity.</p><p>To further characterize HPPK, we developed a spectrophotometric activity assay and a method to measure substrate channelling of hydroxymethyl-dihydropterin diphosphate.</p>