Strong magnetic field pulse generator

High magnetic fields and extremely low temperatures are essential in the study of new semiconductor materials for example in the field of spintronics. Typical phenomenons that arise in such conditions are: Hall Effect, Anomalous Hall effect and Shubnikov de-Haas effect. In this thesis a device capable for such conditions was described. A strong magnetic field pulse generator situated in the laboratory of physics and the Lappeenranta University of Technology was studied. The device is introduced in three parts. First one is the pulsed field magnetic generator, which is responsible for generating the high magnetic field. Next one is the measurement systems, which are responsible for monitoring the sample and the system itself. The last part describes the cryostat system, which allows the extremely cold temperatures in the system.

Evolution of Bordetella pertussis post vaccination

Evolution of Bordetella pertussis post vaccination Whooping cough or pertussis is caused by the gram-negative bacterium Bordetella pertussis. It is a highly contiguous disease in the human respiratory tract. Characteristic of pertussis is a paroxysmal cough with whooping sound during gasps of breath after coughing episodes. It is potentially fatal to unvaccinated infants. The best approach to fight pertussis is to vaccinate. Vaccinations against pertussis have been available from the 1940s. Traditionally vaccines were whole-cell pertussis (wP) preparations as part of the combined diphtheria-tetanus-pertussis (DTP) vaccines. More recently acellular pertussis (aP) vaccines have replaced the wP vaccines in many countries. The aP vaccines are less reactogenic and can also be administered to school children and adults. There are several publications reporting variation in the i>B. pertussis virulence factors that are also aP vaccine antigens. This has occurred in the genes coding for pertussis toxin and pertactin about 15 to 30 years after the introduction of pertussis vaccines to immunisation programs. Resurgence of pertussis has also been reported in many countries with high vaccination coverage. In this study the evolution of B. pertussis was investigated in Finland, the United Kingdom, Poland, Serbia, China, Senegal and Kenya. These represent countries with a long history of high vaccination coverage with stable vaccines or changes in the vaccine formulation; countries which established high vaccination coverage late; and countries where vaccinations against pertussis were started late. With bacterial cytotoxicity and cytokine measurements, comparative genomic hybridisation, pulsed-field gel electrophoresis (PFGE), genotyping and serotyping it was found that changes in the vaccine composition can postpone the emergence of antigenic variants. It seems that the change in PFGE profiles and the loss of genetic material in the genome of B. pertussis are similar in most countries and the vaccine-induced immunity is selecting non-vaccine type strains. However, the differences in the formulation of the vaccines, the vaccination programs and in the coverage of pertussis vaccination have affected the speed and timing of these changes.

Pulsed electric field assisted sol-gel preparation of TiO2 particles and their photocatalytic properties

The objective of this thesis was to study the effect of pulsed electric field on the preparation of TiO2 nanoparticles via sol-gel method. The literature part deals with properties of different TiO2 crystal forms, principles of photocatalysis, sol-gel method and pulsed electric field processing. It was expected that the pulsed electric field would have an influence on crystallite size, specific surface area, polymorphism and photocatalytic activity of produced particles. TiO2 samples were prepared by using different frequencies and treatment times of pulsed electric field. The properties of produced TiO2 particles were examined X-ray diffraction (XRD), Raman spectroscopy and BET surface area analysis. The photocatalytic activities of produced TiO2 particles were determined by using them as photocatalysts for the degradation of formic acid under UVA-light. The photocatalytic activities of samples produced with sol-gel method were also compared with the commercial TiO2 powder Aeroxide® (Evonic Degussa GmbH). Pulsed electric field did not have an effect on the morphology of particles. Results from XRD and Raman analysis showed that all produced TiO2 samples were pure anatase. However, pulsed electric field did have an effect on crystallite size, specific surface area and photocatalytic activity of TiO2 particles. Generally, the crystallite sizes were smaller, specific surface areas larger and initial formic acid degradation rates higher for samples that were produced by applying the pulsed electric field. The higher photocatalytic activities were attributed to larger surface areas and smaller crystallite sizes. Though, with all of the TiO2 samples produced by the sol-gel method the initial formic acid degradation rates were significantly slower than with the commercial TiO2 powder.

Influence of Pulsed-Electric Field Irradiation in Crystallization

The growing pharmaceutical interest, among others, in the polymorphic composition of the emerging solid end-products from production processes has been traced to the need for attainment of high product purity. This is more so as the presence of different polymorphs may constitute physical impurity of the product. Hence, the need for optimization of the yield of desired product component(s) through controlled crystallization kinetics for instance. This study was carried out to investigate the impact of pulsed electric field (PEF) irradiation on the crystal morphology of glycine obtained by cooling crystallization (without seeding) from commercial glycine sample in distilled deionized water solution. In doing so, three different pulse frequencies (294, 950 and 145 Hz) and a case without PEF were studied at three cooling rates (5, 10 and 20 ºC/h). The crystal products obtained were analyzed for polymorphic composition by powder x-ray diffraction (PXRD) and Fourier transform infrared (FTIR) spectroscopy while the particles characterization was done on Morphologi G3. The results obtained from this study showed that pulsed electric field irradiation had significant impact on metastability of the aqueous solution as well as on the polymorphic composition of the end product. With increasing PEF frequency applied, nucleation started earlier and the γ-glycine polymorph content of the product crystals increased. These were found to have been aided by cooling rate, as the most significant effect was observed at 5 ºC/h. It was also discovered that PEF application had no measurable impact on the pH of the aqueous solution as well as the size distribution of the particles. Cooling on the contrary was believed to be responsible for the broadening of the particle size distribution with a downward shift of the lower limit of the raw material from about 100 μm to between 10 and 50 μm.

Photocatalysis Studies under Visible Light Irradiation with TiO2 Obtained by Pulsed Electric Field Assisted Sol-Gel Method

The objective of this thesis was to study the effect of pulsed electric field on the preparation of TiO2 nanoparticles via sol-gel method under the visible light irradiation. The literature part introduces properties of different TiO2 crystal forms and principle of photocatalysis. It was expected that pulsed electric field would have an influence on degradation for oxalic acid and formic acid. TiO2 samples were prepared by using three frequencies (50Hz, 294Hz, and 963Hz) and two treatment times (12 minutes and 24 minutes) of pulsed electric field. The photocatalytic activities of TiO2 samples produced with sol-gel method were also compared with the TiO2 particles made by previous study and with the commercial TiO2 powder Aeroxide® (Evonic Degussa GmbH) at the same condition. Results show that pulsed electric field does have an effect on degradation for oxalic acid and formic acid. Generally, higher photocatalytic activities for oxalic acid and formic acid were obtained with lower frequency and longer treatment time of pulsed electric field.

Superconducting properties and their enhancement in ReBa2Cu3O7-delta (RE = Y and Gd) films prepared by pulsed laser deposition

Due to font problem on the tilte field the titlte of the thesis is corrected here. The title of the thesis is: Superconducting properties and their enhancement in ReBa₂Cu₃O₇-delta (RE = Y and Gd) films prepared by pulsed laser deposition

Design of Pulsed Electroacoustic Measurement System for Space Charge Characterisation

Pulsed electroacoustic (PEA) method is a commonly used non-destructive technique for investigating space charges. It has been developed since early 1980s. These days there is continuing interest for better understanding of the influence of space charge on the reliability of solid electrical insulation under high electric field. The PEA method is widely used for space charge profiling for its robust and relatively inexpensive features. The PEA technique relies on a voltage impulse used to temporarily disturb the space charge equilibrium in a dielectric. The acoustic wave is generated by charge movement in the sample and detected by means of a piezoelectric film. The spatial distribution of the space charge is contained within the detected signal. The principle of such a system is already well established, and several kinds of setups have been constructed for different measurement needs. This thesis presents the design of a PEA measurement system as a systems engineering project. The operating principle and some recent developments are summarised. The steps of electrical and mechanical design of the instrument are discussed. A common procedure for measuring space charges is explained and applied to verify the functionality of the system. The measurement system is provided as an additional basic research tool for the Corporate Research Centre of ABB (China) Ltd. It can be used to characterise flat samples with thickness of 0.2–0.5 mm under DC stress. The spatial resolution of the measurement is 20 μm.

Oxidation of Aqueous Thiosulfate Solutions by Pulsed Corona Discharge

The aim of this Master’s thesis focused on the oxidation of sodium thiosulfate using non thermal plasma technology as an advance oxidation process (AOP). By using this technology we can degrade certain toxic chemical compounds present in mining wastewaters as pollutants. Different concentrations of thiosulfate and pulse frequencies were used in the PCD experiments and the results in terms of various delivered energies (kWh/m3) and degradation kinetics were compared. Pulsed corona discharge is an energy efficient process compared to other oxidation processes using for the treatment of waste water pollutants. Due to its simplicity and low energy costs make it attractive in the field of waste water treatment processes. This technology of wastewater treatment has been tested mainly on pilot scale level and in future the attempts are to be focus on PCD investigations on larger process scale. In this research work of oxidation of thiosulfate using pulsed corona discharge, the main aim of this research was to study degradation of a studied toxic and not environmental friendly chemical compound. The focus of this research was to study the waste waters coming from the gold mines containing leachate compound thiosulfate. Literature review contained also gold leaching process when cyanide is used as the leachate. Another objective of this work was to compare PCD process with other processes based on their energy efficiencies. In the experimental part two concentrations of sodium thiosulfate, 1000ppm and 400ppm, were used. Two pulse generator frequencies of 833 and 200 pulses per second (pps) were used. The chemical analyses of the samples taken during semi-batch PCD oxidation process were analyzed by ion chromatographic (IC). It is observed after the analyses that among different frequencies and concentrations, the most suitable ones for the process is 200pps and 1000ppm respectively because the pollutants present in the waste water has more time to react with the OH radicals which are the oxidants and the process is energy efficient compared to other frequencies.

Seasonal occurrence of Lygus bugs on field crops in Finland

Selostus: Niittyluteiden esiintyminen viljelykasveissa kasvukauden eri aikoina

Long-term fertilizer field trials: comparison of three mathematical response models

Selostus: Lannoituksen pitkäaikaiset kenttäkokeet: kolmen matemaattisen mallin vertailu

Drought response of modern and old oat lines in greenhouse and long-term field trials

Selostus: Vanhojen ja uusien kauralajikkeiden reagointi kuivuuteen kasvihuone- ja peltokokeissa

Effect of fertilization on soil phosphorus in a long-term field experiment in southern Finland

Selostus: Maan fosforitilan muutos pitkäaikaisessa kenttäkokeessa hietamaalla