Mastergradsoppgaver i fysikk
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Mastergradsoppgaver i fysikk
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Høydalsvik, Stein (Master thesis; Mastergradsoppgave, Jan-1980)[+][-]
Abstract: Analyser av okkultasjonskurvene frå fotoelektriske observasjonar viser at ein stor del av dei observerte stjernene er dobbelstjerner. Okkultasjonsteknikken kan lett åtskilje stjerner som har ein vinkelavstand større enn 0",01 og under gunstige tilhøve kan oppløysinga vere 0",001. I tillegg kan analysen av observasjonen gje vinkeldiameteren til stjerna dersom han er større enn 0",001. Utfrå vinkeldiameteren kan vi bestemme den effektive temperaturen som er ein fundamental storleik for ei stjerne. Ved observasjonar av okkultasjonar kan vi såleis få verdifull informasjon om stjernene som vert okkultert. Eg har valt å konsentrere meg om den okkulterte stjerna og kva informasjon ein analyse av okkultasjonskurva kan gje om ho. Ein vesentleg del av arbeidet har vore å prøve ut observasjonsutstyret i Skibotn på slike observasjonar og eventuelt kome med forslag om forbetringar av dette. Eit viktig siktemål med dette arbeidet var å tilretteleggje ei enkel observasjonsprosedyre slik at ein seinare kan observere okkultasjonar utan stor arbeidsinnsats, nærmast som ein rutineobservasjon. I kapittel 2, 3 og 4 viser eg korleis vi kan bruke generell diffraksjonsteori i tolkinga av ei okkultasjonskurve. Eg diskuterer også mogelege feilkjelder i denne tolkinga. Kapittel 5 viser instrumentasjonen som vart brukt til observasjonane og gjev ei prosedyre for slike observasjonar. Kapittel 6 forklarar kort analyseprogrammet, og eg diskuterer mogelege forbetringar av det. Kapittel 7 presenterer dei einskilde observasjonane og analyseresultata av dei. Eg gjev ei vurdering av kor gyldige desse resultata er. Kapittel 8 er så ein diskusjon av observasjonskvaliteten og kva innverknad ulike faktorar har på denne. Særleg ser eg på kva innverknad scintillasjonen kan ha. Til slutt gjev eg så i kapittel 9 ei oppsummering av dei viktigaste resultata samt ei vurdering av kva rolle okkultasjonsobservasjonar kan/bør ha ved observatoriet i Skibotn i framtida. Description: Dette er ei hovudfagsoppgåve URI: http://hdl.handle.net/10037/3444 File(s) in this item: 1
thesis.pdf (10.80Mb) -
Dullo, Firehun Tsige (Master thesis; Mastergradsoppgave, 18-May-2011)[+][-]
Abstract: Over the last few years, the notion that links optical trapping with strong intensity of light (high energy photon) not only forced the modification of optical tweezer, but it also open up the door for evanescent wave field trapping. While optical tweezer is merely suitable for trapping micro-sized particles, trapping by evanescent field of a channel waveguide enables both micro and nanosized particles to be trapped and propel as well. Indeed, nowadays, various structures of channel wave guides are designed to secure higher intensity of light for significantly better trapping purposes. The goal of this study is mainly to examine and better understand features related to trapping of particles on three different structures of a waveguides: straight, loop and ring resonators. We also propose new method to characterize the ring resonator waveguide. Though there are limitations to this method, it is possible to measure power in and out of the ring. Besides, the characteristics result shows too much power loss. From the straight waveguide experiment we confirm that gold particles of diameter 200nm and 500nm are trapped and propelled above the waveguide by the evanescent field. The speed obtained from the 200nm diameter analysis reaches up to 420µm/s for 700mW laser power, which considerably faster than the previously reported values. Given the advantages of the applications of loop waveguides, to stop particles by standing waves or counter propagating beams, we are able to clearly observe this phenomenon in our experiment for 1.02µm diameter polyester particles, in contrast to gold nanoparticles due to weak gradient forces. Maintaining similar analysis for ring resonator waveguides, however, the lacking of particle trapping or propulsion is observed for gallium arsenide nanowires, due to their asymmetric structure besides the low power. Weak gradient force and low power in the gold, and low power though strong gradient force in polystyrene ring waveguides are responsible for lack of trapping and propulsion in the nanoparticles. Even though the priority is of this thesis is the experimental essence, the theories of optical waveguides and optical trapping forces are briefly reviewed. URI: http://hdl.handle.net/10037/3419 File(s) in this item: 1
thesis.pdf (3.754Mb) -
Anelli, Marco (Master thesis; Mastergradsoppgave, 15-Nov-2010)[+][-]
Abstract: This work discusses the theory of the magnetizability. The magnetizability is a molecular property defined as the second-order perturbation of the energy in the presence of an external magnetic field. When the magnetic field is static, perturbation and multipole theories lead to an origin-independent expression for the magnetizability, whereas for a frequency-dependent magnetic field its expression turns out to be origin dependent. Since the magnetizability in the static case is an observable quantity, the expression obtained in the dynamic case is clearly unphysical. My work discusses several approaches in order to solve this issue. The magnetizability has been analyzed in the microscopic case, within both the non-relativistic and the relativistic framework. The expression for the magnetizability proposed by Raab and de Lange has been considered, pointing out the weak points of their non-relativistic theory, and trying to recover an alternative expression in the relativistic framework. The macroscopic case has also been discussed in detail, and an origin-independent expression for the inverse permeability has been derived within a fully relativistic approach. The problem of finding an origin-independent expression for the magnetizability in the microscopic case remains unresolved, however the results obtained in the macroscopic case and the analysis done in this thesis are good starting points for further studies, and suggests that future work should start from the relativistic theory of the property. URI: http://hdl.handle.net/10037/2961 File(s) in this item: 1
thesis.pdf (630.1Kb) -
Rønningen, Petter (Master thesis; Mastergradsoppgave, 18-May-2010)[+][-]
Abstract: Interchange driven propagation of so-called "blobs" arises in basic laboratory plasmas, in the scrape-off layer of fusion plasmas and as Equatorial Spread-F (ESF) phenomena. The propagation of such blobs has been demonstrated in the VTF experiment at MIT and in earlier simulations. Experimental results show that the velocity of these blobs is inverse proportional to the neutral gas pressure. These blobs have also shown the tendency to form mushroom-like shapes. We here develop a two-field model for the interchange mechanism in magnetised plasma in toroidal chambers. This model is then used to simulate the dynamics of propagating blobs using a two dimensional advection-diffusion solver. Studying the effects of ion-neutral collisions and blob amplitudes, we observe the separation between an inertia dominated and one collisionally dominated regime. We also observe that this separation persists for all simulated amplitudes. We further perform simulations with parameters set to closely resemble the VTF experiments. These simulations show that the experimental result of the velocity being inversely proportional to the neutral gas pressure is in a qualitative match with the simulated results for the collisionally dominant regime. URI: http://hdl.handle.net/10037/2579 File(s) in this item: 1
thesis.pdf (1.391Mb) -
Kube, Ralph Arthur (Master thesis; Mastergradsoppgave, May-2010)[+][-]
Abstract: Numerical studies of radial filament motions in the SOL of toroidally confined plasmas are studies. We use a two dimensional two-field model to characterize blob-like structures in the radial-poloidal domain. These structures are observed to achieve velocities in the order of the ion acoustic velocity in the SOL of tokamaks and other toroidal confinement devices. By numerical means we find a scaling of the radial blob velocity that is inversely proportional to the square of the characteristic blob length. Comparison to an analytic solution show that the analytic solutions overestimates radial blob velocities. We also compare the numerical studies to experimental results and find good agreement. URI: http://hdl.handle.net/10037/2573 File(s) in this item: 2
errata (2).pdf (94.88Kb)thesis_opt.pdf (2.910Mb)
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