Simulation of the Interaction Mean Free Path between Neutrons and TRISO Particles

The interaction mean free path between neutrons and TRISO particles is simulated using scripts written in MATLAB to solve the increasing error present with an increase in the packing factor in the reactor physics code Serpent. Their movement is tracked both in an unbounded and in a bounded space. Their track is calculated, depending on the program, linearly directly using the position vectors of the neutrons and the surface equations of all the fuel particles; by dividing the space in multiple subspaces, each of which contain a fraction of the total number of particles, and choosing the particles from those subspaces through which the neutron passes through; or by choosing the particles that lie within an infinite cylinder formed on the movement axis of the neutron. The estimate from the current analytical model, based on an exponential distribution, for the mean free path, utilized by Serpent, is used as a reference result. The results from the implicit model in Serpent imply a too long mean free path with high packing factors. The received results support this observation by producing, with a packing factor of 17 %, approximately 2.46 % shorter mean free path compared to the reference model. This is supported by the packing factor experienced by the neutron, the simulation of which resulted in a 17.29 % packing factor. It was also observed that the neutrons leaving from the surfaces of the fuel particles, in contrast to those starting inside the moderator, do not follow the exponential distribution. The current model, as it is, is thus not valid in the determination of the free path lengths of the neutrons.

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.

Situations charta öfver Orrjärvi grufva med kringliggande koppar- och järnmalms skärpningar, uti Kisko sokn, Raseborgs wästra härad och Nylands län

Kartta kuuluu A. E. Nordenskiöldin kokoelmaan

Carta universal en que se contiene todo lo que del mundo se ha descubierto fasta agora

Kartta kuuluu A. E. Nordenskiöldin kokoelmaan

Atomic Force Microscopy Investigation of NI Particles Deposited on Porous Silicon

In this thesis properties and influence of modification techniques of porous silicon were studied by Atomic Force Microscope (AFM). This device permits to visualize the surface topography and to study properties of the samples on atomic scale, which was necessary for recent investigation. Samples of porous silicon were obtained by electrochemical etching. Nickel particles were deposited by two methods: electrochemical deposition and extracting from NiCl2 ethanol solution. Sample growth was conducted in Saint-Petersburg State Electrotechnical University, LETI. Kelvin probe force microscopy (KPFM) and Magnetic force microscopy (MFM) were utilized for detailed information about surface properties of the samples. Measurements showed the difference in morphology correlating with initial growth conditions. Submicron size particles were clearly visible on surfaces of the treated samples. Although their nature was not clarified due to limitations of AFM technique. It is expected that surfaces were covered by nanometer scale Ni particles, which can be verified by implication of RAMAN device.

Att ha en studerande i klassen : en studie i hur elever i Vasa övningsskola uppfattar klasslärarstuderandes närvaro i skolan

Syftet med denna avhandling är att undersöka hur elever i grundskolan F–6 (förskola till årskurs 6) i Vasa övningsskola uppfattar klasslärarstuderande och deras närvaro i skolan. Den fenomenografiska forskningsansatsen ligger som grund för arbetet och undersökningen är i huvudsak kvalitativ men har även kvantitativa inslag. De forskningsfrågor vi med vår undersökning önskar få svar på är följande: 1. Vilken uppfattning har eleverna om klasslärarstuderandenas uppgifter under praktikperioderna? 2. Vilken uppfattning har eleverna om klasslärarstuderandenas beredskap för läraryrket? 3. Vilka faktorer påverkar elevernas relation till klasslärarstuderandena? För att besvara forskningsfrågorna har vi använt två datainsamlingsmetoder. I den första undersökningen har vi gjort intervjuer med 14 elever i F–6 i Vasa övningsskola. I tillägg till detta har även en enkät delats ut i tre klasser i övningsskolan; en sammansatt klass 5–6, en klass i årskurs 5 och en klass i årskurs 6. Det sammanlagda antalet respondenter och insamlade enkätsvar i den andra undersökningen är 50 stycken. Våra resultat visar att eleverna uppfattar att det under praktikperioderna bland annat hör till klasslärarstuderandenas uppgifter att bekanta sig med eleverna, auskultera, planera och undervisa. Gällande den andra forskningsfrågan visar resultaten att eleverna bedömer studerandenas lärarberedskap exempelvis utgående från om studerandena kan skapa ordning i klassen, hurdana ämneskunskaper de har, hur de ger instruktioner, vilka metoder de använder samt hur väl de kan anpassa sig till skolans organisation och klassens arbete. Faktorer som enligt elevernas uppfattning påverkar deras relation till klasslärarstuderandena är bland annat vilka förväntningar eleverna har på relationen, vilket bemötande de får av studerandena, praktikens ramar samt elevernas relation till den egna klassläraren. Slutsatserna av vår avhandling är att relationerna till lärarstuderandena är betydelsefulla för eleverna även om de begränsas både tidsmässigt och organisatoriskt av praktikperiodernas ramar. På basis av vår undersökning konstaterar vi också att eleverna vid Vasa övningsskola skulle ha fördel av att studerandena i högre grad än nu fokuserar på att utveckla relationer till eleverna och vågar använda personligheten som ett verktyg under praktikperioderna.