No description available.

The prevention and control of salmonellae in commercial swine operations are becoming increasingly important. The current approach focuses on identifying sources and/or origins of salmonellae contamination before swine are processed for human consumption. The objective of the current study was to assess strain variability among salmonellae grouped by serotype and to determine common origins of contamination (farm or slaughter plant). Salmonellae were previously collected from swine at slaughter, serotyped by the National Veterinary Services Laboratory and stored at - 70??C. Pulsed-field gel electrophoresis (PFGE) was performed to genotypically characterize serotypic isolates using restriction endonuclease XbaI. Dendrogram comparisons were also used to assess genotypic similarity when multiple genotypes existed. This study found PFGE to be more discriminatory than serotyping indicating that multiple genotypic strains existed among selected serotypes. On the basis of PFGE results alone, origins of contamination could not be determined in this study. It is suggested by the author, that origins of contamination could be further defined pending future research, in which in-depth longitudinal studies are included. When used as an adjunct to conventional typing methods, PFGE may prove to be a substantial subtyping system in epidemiologic investigations to identify point-of-entry contaminants to the food chain.

The prevention and control of salmonellae in commercial swine operations are becoming increasingly important. The current approach focuses on identifying sources and/or origins of salmonellae contamination before swine are processed for human consumption. The objective of the current study was to assess strain variability among salmonellae grouped by serotype and to determine common origins of contamination (farm or slaughter plant). Salmonellae were previously collected from swine at slaughter, serotyped by the National Veterinary Services Laboratory and stored at - 70??C. Pulsed-field gel electrophoresis (PFGE) was performed to genotypically characterize serotypic isolates using restriction endonuclease XbaI. Dendrogram comparisons were also used to assess genotypic similarity when multiple genotypes existed. This study found PFGE to be more discriminatory than serotyping indicating that multiple genotypic strains existed among selected serotypes. On the basis of PFGE results alone, origins of contamination could not be determined in this study. It is suggested by the author, that origins of contamination could be further defined pending future research, in which in-depth longitudinal studies are included. When used as an adjunct to conventional typing methods, PFGE may prove to be a substantial subtyping system in epidemiologic investigations to identify point-of-entry contaminants to the food chain.

Invented in the 1950s, gel electrophoresis has now become a routine analytical method to verify the size of nucleic acids and proteins in molecular biology labs. Conventional gel electrophoresis can successfully separate DNA fragments from several base pairs to a few tens of kilo base pairs, beyond which a point is reached that DNA molecules cannot be resolved due to the size independent mobility. In this case, pulsed field gel electrophoresis (PFGE) was introduced to extend the range of DNA fragment sizes that can be effectively separated. But despite the incredible success of PFGE techniques, some important drawbacks remain. First, separation time is extremely long, ranging from several hours to a few days. Second, detection methods still rely on staining the gel after the run. Real time observation and study of band migration behavior is impossible due to the large size of the PFGE device. Finally, many commercial PFGE instruments are relatively expensive, a factor that can limit their accessibility both for routine analytical and preparative use as well as for performing fundamental studies. In this research, a miniaturized PFGE device was constructed with dimension 2cm x 2.6cm, capable of separating DNA fragments ranging from 2.5kb to 32kb within three hours using low voltage. The separation process can be observed in real time under a fluorescence microscope mounted with a cooled CCD camera. Resolution and mobility of the sample were measured to test the efficiency of the device. We also explored manipulating DNA fragments by end labeling DNA molecules with quantum dot nanocrystals. The quantum dot-DNA conjugates can be further modified through binding interactions with biotinylated single-stranded DNA primers. Single molecule visualization was performed during gel electrophoresis and the extension length, entanglement probability and reorientation time of different conjugates were measured to study their effect on DNA migration through the gel. Finally, electrophoresis of DNA conjugates was performed in the miniaturized PFGE device, and shaper bands were observed compared with the non end-labeled sample. Furthermore, by end-labeling DNA with quantum dots, the migration distance of shorter fragments is reduced, providing the possibility of separating a wider range of DNA fragment sizes on the same gel to achieve further device miniaturization.

Invented in the 1950s, gel electrophoresis has now become a routine analytical method to verify the size of nucleic acids and proteins in molecular biology labs. Conventional gel electrophoresis can successfully separate DNA fragments from several base pairs to a few tens of kilo base pairs, beyond which a point is reached that DNA molecules cannot be resolved due to the size independent mobility. In this case, pulsed field gel electrophoresis (PFGE) was introduced to extend the range of DNA fragment sizes that can be effectively separated. But despite the incredible success of PFGE techniques, some important drawbacks remain. First, separation time is extremely long, ranging from several hours to a few days. Second, detection methods still rely on staining the gel after the run. Real time observation and study of band migration behavior is impossible due to the large size of the PFGE device. Finally, many commercial PFGE instruments are relatively expensive, a factor that can limit their accessibility both for routine analytical and preparative use as well as for performing fundamental studies. In this research, a miniaturized PFGE device was constructed with dimension 2cm x 2.6cm, capable of separating DNA fragments ranging from 2.5kb to 32kb within three hours using low voltage. The separation process can be observed in real time under a fluorescence microscope mounted with a cooled CCD camera. Resolution and mobility of the sample were measured to test the efficiency of the device. We also explored manipulating DNA fragments by end labeling DNA molecules with quantum dot nanocrystals. The quantum dot-DNA conjugates can be further modified through binding interactions with biotinylated single-stranded DNA primers. Single molecule visualization was performed during gel electrophoresis and the extension length, entanglement probability and reorientation time of different conjugates were measured to study their effect on DNA migration through the gel. Finally, electrophoresis of DNA conjugates was performed in the miniaturized PFGE device, and shaper bands were observed compared with the non end-labeled sample. Furthermore, by end-labeling DNA with quantum dots, the migration distance of shorter fragments is reduced, providing the possibility of separating a wider range of DNA fragment sizes on the same gel to achieve further device miniaturization.

No description available.

Diffusion is an omnipresent, most fundamental phenomenon in nature and thus critical for the performance of numerous technologies. This is in particular true for nanoporous materials with manifold applications for matter upgrading by separation, purification and conversion. The path lengths of molecular transportation within the industrial plants range from the elementary steps of diffusion within the micropores of the individual particles up to the matter flow over macroscopic distances. Each of them might be decisive in determining overall performance so that detailed knowledge of all modes of mass transfer is crucial for a knowledge-based optimization of the devices with reference to their transport properties. The rate of mass transfer is particularly complicated to be assessed within the individual (adsorbent) particles/crystallites with pore sizes of the order of molecular dimensions. We are going to present two powerful techniques exactly for this application, operating under both equilibrium (Pulsed Field Gradient (PFG) NMR) and non-equilibrium (Microimaging by interference microscopy and IR microscopy) conditions. The potentials of these techniques are demonstrated in a few showcases, notably including the options of transport enhancement in pore hierarchies. The contribution concludes with a survey on present activities within an IUPAC initiative aiming at the elaboration of “guidelines for measurements and reporting of diffusion properties of chemical compounds in nanoporous materials”.

Water and ion transport critically determine the performance of many functional materials and devices, from fuel cells to lithium ion batteries to soft mechanical actuators. This dissertation aims to address some fundamental issues regarding transport and anisotropy, structural heterogeneity and molecular interactions inside ionic polymers. I first discuss a main deficiency of a standard protocol for calibrating high pulsed-field-gradient NMR. I show that high gradient calibration using low γ nuclei is not amenable to measurements on slow diffusing high γ nuclei. Then I employ NMR diffusometry to investigate transport and anisotropy for a series of ionic polymers, from poly(arylene ether sulfone) hydrophilic-hydrophobic multi-block copolymers to polymer blends to perfluorosulfonate random copolymers. For the multi-block copolymers, NMR diffusion measurements yield diffusion anisotropy as a function of water uptake and block lengths. ²H NMR spectroscopy on absorbed D₂O probes membrane alignment modes. These measurements also provide insights into average defect distributions. For the blend membranes, we examine the impact of compatibilizer on their transport properties. An increase in compatibilizer significantly improves the membrane phase homogeneity confirmed by SEM and transport studies. Theories of diffusion in porous media yield changes in domain size and tortuosity that correspond to drastic changes in local restrictions to water diffusion among different blend membranes. NMR relaxometry studies yield multi-component T₁ values, which further probe structural heterogeneities on smaller scales than diffusion experiments. For the random copolymer, the exploration of ion transport reveals inter-ionic associations of ionic liquids (ILs) modulated by hydration level and ionic medium. When ILs diffuse inside ionic polymers, isolated anions diffuse faster (≥ 4X) than cations at high hydration whereas ion associations result in substantially faster cation diffusion (≤ 3X) at low hydration inside membranes, revealing prevalent anionic aggregates. Finally, I present the strategy and analytical protocol for studying ionomer membranes using ILs. The normal cation diffusion contrasts to the anomalous anion diffusion caused by local confinement structures inside the membranes, which vary drastically with temperature and hydration level. These structures correspond to a density variation of SO₃⁻ groups, which define a distribution of local electrical potentials that fluctuate with temperature and nature of ionic media. / Ph. D.

No description available.

Les pastilles supraconductrices peuvent produire des forts champs magnétiques très supérieurs aux aimants permanents. Plusieurs méthodes d’aimantation de ces pastilles existent néanmoins une seule est principalement utilisée pour les applications en génie électrique, l’aimantation par champ magnétique impulsionnel (Pulsed Field Magnetization). Afin de maîtriser l’aimantation de ces pastilles supraconductrices par PFM, nous avons étudié l’influence de la forme de l’inducteur sur le champ magnétique piégé où nous trouvons une influence significative de la forme de l’inducteur sur le champ piégé dans la pastille supraconductrice. Afin de prévoir la mise en oeuvre des pastilles supraconductrices dans des applications en génie électrique, nous avons étudié l’aimantation de ces pastilles dans un circuit magnétique et l’influence de ce circuit sur le champ piégé. Nous remarquons une nette amélioration du champ piégé dans la pastille en utilisant le circuit magnétique. Nous avons étudié, également, l’influence d’un champ démagnétisant impulsionnel et alternatif sur le champ piégé dans une pastille supraconductrice aimantée. Les dégradations observées ne montrent pas de contre-indication à l’utilisation des pastilles supraconductrices aimantées dans les applications en génie électrique. / The superconducting bulks can produce very strong magnetic fields greater than those of permanent magnets can. Several methods of magnetization of the superconducting bulks exist, however one is mainly used for the electrical applications, the Pulsed Field Magnetization. In order to control the magnetization of the superconducting bulks by PFM, we studied the influence of the shape of the inductor on the trapped magnetic field where we find a significant influence of the shape of the inductor on the trapped magnetic field in the anticipate superconducting bulk. In order to the implementation of the superconducting bulk in the electrical applications, we studied the magnetization of these bulks in a magnetic core and the influence of this magnetic core on the trapped magnetic field. We notice an important improvement of the trapped magnetic field in the superconducting bulk by using the magnetic core. We studied also the influence of a pulsed and an alternating demagnetizing field on the trapped magnetic field in a superconducting bulk. The observed degradation does not show any contraindication to use the superconducting magnetic bulks in the electrical engineering applications.