Støyreduksjon har blitt utført på hyperspektrale bilder i både spektral retning og romlige retninger. Algoritmene som har blitt benyttet for å oppnå støyreduksjon er Principal Component Analysis (PCA), Maximum Noise Fraction (MNF) og wavelet-transform. MNF-algoritmen har blitt kjørt med mange forskjellige støyestimatorer for å bestemme hvilke av disse som gir høye signal-støy-forhold. Å utføre støyestimatet i fourierrommet har også blitt undersøkt. Dette ga gode resultater når man benyttet fasedifferansen med nærliggende piksler som estimator for hyperspektrale bilder tatt under hvitt lys. Ble derimot kilden endret til en 355nm laserkilde fikk man langt dårligere resultater. Det er bare Haar-transformen som har blitt brukt til wavelet-transformasjon. Haar-transformen ga dårlig støydempning i både spektral retning og romlige retninger. Algoritmene PCA og MNF fungerer bra til støyreduksjon. I spektral retning er det liten forskjell mellom PCA og de ulike støyestimatene som er brukt under MNF. Ser man derimot på det romlige planet finner en større forskjeller mellom dem. Dette gjelder spesielt for spektralbånd med lav intensitet og mye støy. Her gir PCA bedre støydempning enn MNF. Støyreduksjonen ved PCA og MNF kommer som en direkte følge av å begrense antallet prinsipalkomponenter under tilbaketransformasjonen. Hvor grensen bør settes for hvilke prinsipalkomponenter som skal bevares, ble også vurdert. Når lyskildeforholdene for de hyperspektrale bildene blir sammenlignet er grensen valgt slik at 99,25% av det opprinnelige signalet blir bevart. Spekteret til hyperspektrale bilder tatt under hvitt lys har høy intensitet for lange bølgelengder, og lav intensitet ved korte bølgelengder. Endres derimot lyskilden til en 355nm laserkilde får man lav intensitet for lange bølgelengder og høy intensitet for korte.

Blind spectrum sensing in cognitive radio is being addressed in this thesis. Particular emphasis is put on performance in the low signal to noise range. It is shown how methods relying on traditional sample based estimation methods, such as the energy detector and autocorrelation based detectors, suffer at low SNRs. This problem is attempted to be solved by investigating how higher order statistics and information theoretic distance measures can be applied to do spectrum sensing. Results from a thorough literature survey indicate that the information theoretic distance gls{kl} divergence is promising when trying to devise a novel cognitive radio spectrum sensing scheme. Two novel detection algorithms based on Kullback-Leibler divergence estimation are proposed. However, unfortunately only one of them has a fully proven theoretical foundation. The other has a partial theoretical framework, supported by empirical results. Detection performance of the two proposed detectors in comparison with two reference detectors is assessed. The two reference detectors are the energy detector, and an autocorrelation based detector. Through simulations, it is shown that the proposed KL divergence based algorithms perform worse than the energy detector for all the considered scenarios, while one of them performs better than the autocorrelation based detector for certain signals. The reason why the detectors perform worse than the energy detector, despite the good properties of the estimators at low signal to noise ratios, is that the KL divergence between signal and noise is small. The low divergence stems from the fact that both signal and noise have very similar probability density distributions. Detection performance is also assessed by applying the detectors to raw data of a downconverted UMTS signal. It is shown that the noise distribution deviates from the standard assumption (circularly symmetric complex white Gaussian). Due to this deviation, the autocorrelation based reference detector and the two proposed Kullback-Leibler divergence based detectors are challenged. These detectors rely heavily on the aforementioned assumption, and fail to function properly when applied to signals with deviating characteristics.

Grunnlaget for det arbeidet som er utført i denne rapporten er påstanden om LoranCsrobusthet som navigasjonssystem. Robustheten til systemet måles i systemets egen evnetil å motstå interferens (absolutt robusthet) og hvor robust LoranC er i forhold til andre navigasjonssystemer(relativ robusthet). Fokuset i denne rapporten er å gi en beskrivelse av navigasjonssystemet LoranC, hvilke faktorer som påvirker signalet langs utbredelsesveien og hva som skal til for å interferere med disse signalene. For å avdekke hva som kan gjøres for å interferer med LoranC signalene er det utført praktiske målinger/jammetest. De teoretiske beregningene sammen med observasjonene i det praktiske forsøket skal danne grunnlaget for et hensiktsmessig oppsett av en mobil LoranC jammerenhet.Ønsker man å påvirke en mottakers posisjonsangivelse er det viktig at man kjennertil virkemåten til systemet og prinsippene brukt i mottakerene. Kapittel 4.2 tar for segde teoretiske aspektene ved LoranC systemet og kap 4.3 omhandler virkemåten til enLoranC mottaker. Søken etter å finne sårbarheten til systemet startes med å se på de potensielle feilkildene som systemet må ta høyde for under normal drift. LoranC signalene påvirkes av underlaget(den elektriske ledeevnen), topografien, årstiden og de aktuelle atmosfæriske forholdene. Dette er degraderende faktorer som LoranC-systemet må ta med i beregningene for å oppnå systemkravene til posisjonsnøyaktighet. For å gi en bedre forståelse for hva LoranC signalene ved normal drift påvirkes av vil kap.4 gi en gjennomgang av utbredelse av LoranC-signaler og hvordan den atmosfæriske støyen påvirker disse signalene.Videre gir kap 4.8 en introduksjon av generelle signaltyper og modulasjoner som kanbenyttes til å interferere med LoranC-signalene. Dette er signaler som videre skal benyttes som jamme/narre signaler i de praktiske målingene.Grensesnittet mellom det elektriske interferenssignalet(jamming/spoofing) og utbredelsesmediumet(eteren) er antennen, og på grunn av at LoranC er et lavfrekvent navigasjonssystem vil signalenes lange bølgelengden skape utfordringer ved antennedesignet.I denne rapporten vi dette gjøre seg mest gjeldende ved at størrelsen til LoranC senderantennen begrenses av kravet til mobilitet hos jammeenheten, mens god antenneeffektivitet krever en fysisk stor antenne. Kap 4.9 gir en oversikt over disse utfordringene og viser beregninger av en antenne som kan benyttes i et slikt mobilt jammeoppsett.For beregning av feltstyrkeverdiene til LoranC-signalene og den atmosfæriske støyen vedmålestasjonen ble det utviklet og brukt et Excel-program med utgangspunkt i drøftet bølge- og støy-teori. Kapittel 5 gir en gjennomgang av dette Excel-programmet. Beregningene i dette programmet danner grunnlaget for hva som kreves av en jammeenhetsom skal kunne interferere med LoranC signaler fra tre valgte sendere. Hva som krevesav en slik jammerenhet er presentert i dette kapittel.I kapittel 6 beskriver de praktiske målingene som ble utført på Frøya. For å avdekke hvasom er den mest effektive formen for interferens med LoranC-signaler ble interferensmålingene utført ved bruk av to typer antenner, forskjellige signaltyper/modulasjoner og varierende signalstyrke/avstand. Videre ble de teoretiske signalberegninger for LoranCsignalet og den atmosfæriske støyen sammenlignet med signal-verdier observert under jammemålingene. Egenskapene og ytelsen til jammeantennene og posisjonsplottet fra LoranC mottakeren ble også observert og benyttet til å fastslå effektiviteten av interferensen med LoranC-signalene og jamme-effektivitet. Denne rapporten avsluttes med at de teoretiske resultatene i kombinasjon med de praktiske undersøkelsene gir en bedømmelse av LoranC sin robusthet samt et oppsett av et mobilt LoranC-jammesystem.

The increase in the world’s demand for energy, and the fact that at one point we will run out of oil and gas which are two major contributers of the world supply of energy toady, are two reasons for why new and reliable energy sources are needed. The solar industry is one of the fastest growing industires, but the price of energy delivered by solar cells is still too high compared to other alternatives. More research is therefore needed in order to drive the price of solar energy down.In this report seven silicon nitride films with different stoichiometry are deposited on silicon substrate by the plasma enhanced chemical vapor de- position (PECVD) method. The deposition conditions are selected in order to enhance the formation of silicon nanoclusters. Silicon nanostructures have interesting properties due quantum effects observed at these dimensions. The most interesting of these properties is the ability to tune the silicon nanos- tructures to absrob ligth at different wavelengths. High energy light cannot be utilized in silicon solar cells. With the application of silicon nanostruc- tures, this light can be absorbed and down-converted to usable light which is then transmitted into the solar cell. This would increase the efficiency of the soalr cell, which results in cheaper energy. Two ensembles of as-deposited and annealed (annealed at 1050◦ C) samples were characterized with dif- ferent techniques in order to find the thickness, composition, light emitting sources and optical constants of the films. The techniques used were ellipsom- etry, photo-luminescence (PL) and transmission electron microscopy (TEM).The results obtained shows that all films are porous (indicated by the low index of refraction). One of the effects of annealing is an increase in the refractive index for all samples, which is an indication that the films have become more compact as a result of the annealing process. PL is obtained for samples with a high flow of ammonia, while samples of a low flow have little or no PL. The annealing process increase the PL observed for samples with a high ammonia flow, while a reduction is observed for the samples with a low flow. TEM images reveals that only one sample has any nanostructures present, so the observed PL is likely related to defect states.

A literature review of relevant luminescence spectra for silicon solar cell materials has been performed. Three multi crystalline silicon samples in particular has been the focus of attention, one electronic grade sample R6, and two solar grade samples ES1, and MH2, where MH2 has added chromium. A list of relevant luminescence spectra has been compiled, and can be found in the appendix.The samples was measured using low temperature micro photoluminescence. They where cooled down by liquid helium in a cryostat, and excited using a laser. Photoluminescence was captured by a camera mounted on a spectrometer. Noise components was measured and removed, but are subject to changes in between measurements, causing some unwanted artifacts to appear in the end result.Luminescence due to P and B doping atoms are identified in ES1, and MH2 as expected, and a weak boron bound exciton line is also present in the clean sample R6. R6 also show signs of having a carbon-carbon complex impurity forming at grain boundaries. Lines attributed to chromium boron pairs where not observed in MH2, presumably due to the lack of such pairs. ES1 exhibits a luminescence attributed to a higher quality material, than both MH2, and R6. Expected behavior is for R6 to have such traits, but this is not the case. The reason for ES1 to show this enhanced luminescence is not known. Lines attributed to dislocations are observed in all the samples, but consist of less intense peaks than expected.Local heating is a severe problem using micro photoluminescence. Bound excitons, impurity lines, and dislocation related lines, all loose intensity at higher temperatures. The intrinsic TO line also have a substantial broadening with respect to energies, suggesting that local temperatures are as much as 70K higher than the sample holder temperature, when exciting with 128 mW using a 2 µm spot diameter.

Over the recent years semiconductor nanowires have gained much attention for their potential to either improve existing technology or create novel devices. This potential has been realized in devices such as semiconductor nanowire lasers[2-3] and nanowire single-photon detectors[4]. With nanowire technology it could be possible to create single-photon nanowire lasers that emit photons in the near infrared region. Such devices should prove very interesting for telecommunications and quantum cryptography.The purpose of this master thesis was the study of the optical properties of GaAs nanowires with GaAsSb inserts. For this reason, both nanowires with and without an AlGaAs coating to increase the nanowire Quantum Efficiency (QE) have been subjected to low temperature PL spectroscopy. In an attempt to determine the physical origin of the different optical properties of different nanowires, µ-PL spectroscopy, Scanning Transmission Electron Microscopy (STEM) and Transmission Electron Microscopy (TEM) was carried out on the same nanowires of a sample with AlGaAs shell nanowires. Through these measurements, it was found that STEM at 30 kV did not change the optical properties of the nanowire, but 200 kV TEM had a detrimental effect on nanowire PL. Through the structurally and optically correlated examination, it was found that stacking faults near the insert was not the origin of the power dependent behavior of the insert emission, and in combination with PL measurements of both zincblende (ZB) and wurtzite (WZ) GaAs nanowires the electronic band structure of the nanowire inserts was determined to very likely be type-II. Also, a theoretical explanation of the origin of the observed insert emission behavior was presented, and polarization dependent PL measurements were presented and discussed.

One of the leading causes of death in the western world today is heart diseases, and atherosclerotic plaque that ruptures in the coronary arteries is believed to be one of the main causes of heart attacks.The Capacitive Micromachined Transducer has good acoustic matching with fluids, and is considered a good candidate for improving intravascular ultrasound diagnostics.Further evaluation and characterization of a CMUT operating in immersion has been the objective of this thesis, and it is a continuation of the work started in the project Characterization of Capacitive Ultrasound Transducers. The same CMUT have been studied in both, but a backing layer was added to it for the testing done during the work on this thesis.Pulse-echo measurements with the CMUT immersed in rapeseed oil have been performed, and there has also been conducted measurements to find the attenuation of the oil. The results from the attenuation measurements have then been employed to simplify the analysis of the pulse-echo measurements.Any definitive characteristics for the CMUT was not found during these tests due to disturbances in the frequency responses. This is suspected to be because of line resistances and parasitic capacitances in the system. This suspicion is supported by the findings from studying the impedance response of the system.The backing layer added to the CMUT have proved to be very effective in dampening the ringing effect on the pulses emitted by the CMUT. There have also been signs of unexpected alteration of the CMUTs frequency characteristics. One possible source of this is that the process of adding the backing layer have resulted in that the layer exerts force on the CMUT, and by this changing the tension of the membranes.

Robots shaped as snakes – snake robots – have a vast potential within areas such as seach and rescue, and inspection and maintenance. Snake robots with active wheels are a specialized form of snake robots. The active wheels are advantageous in made-made environments such as office floors, factories and ventilation systems. The active wheels and the articulated body of the robots offer an efficient platform for moving both horizontally and vertically. A snake robot needs to be able to perform advanced motions in order to navigate complex man- made environments such as pipe-structures. The topic of this master’s thesis is to develop control strategies for snake robot motions on flat planes and in pipe structures. A previously developed simulator for simulation of wheeled snake robot locomotion with a snake robot called Piko [1] will be available. Suggested work 1. Get acquainted with the simulator and make a short tutorial how to, e.g.: install the simulator for development, read sensor signals, control the various degrees of freedom, and perform simulations without visualization. 2. Develop and implement necessary improvements of the simulator. 3. Perform a short literature study within the following topics relevant to the thesis: a. Reinforcement learning b. Function approximators for reinforcement learning c. Current pipe inspection robots and their capabilities (degree of autonomy, design, etc) 4. Formulate one or more motion primitives (controllers) and investigate how to optimize control strategies based on the motion primitives by the use of robot learning. a. In particular, investigate by using the simulator a motion primitive which endows a wheeled snake robot with the capability to lift its head as high as possible. Notes - The robot learning strategies may be based on results from [2]. - If another type of learning framework than reinforcement learning is employed (e.g. evolutionary algorithms), the literature study should reflect this. 1. Fjerdingen, S.A., Liljebäck, P. and Transeth, A.A., A snake-like robot for internal inspection of complex pipe structures (PIKo), in ‘Proc. IEEE/RSJ Int. Conf. on Intelligent Robots and Systems’, St. Louis, USA, Oct 11-15, 2009, pp. 5665-5671. 2. Fjerdingen, S.A., Kyrkjebø, E., Transeth, A.A., AUV Pipeline Following using Reinforcement Learning, in ‘Proc. Int. Symp. on Robotics’, München, Germany, June 8-11, 2010, to appear.

CLIC is an international study of a future multi-TeV electron-positron linear collider, where the energy of a high-intensity drive beam is extracted and transferred to the main beam via Power Extraction and Transfer Structures (PETS) in the form of rf power. The study of power production is therefore essential for the feasibility of CLIC. Power production in PETS has been studied, and experiments have been performed in the decelerator Test Beam Line in the CLIC Test Facility 3.In particular, the correlation of the power production and the beam position inside the structure has been studied. It is shown that the total produced power is constant when the beam has a position offset through the PETS. In addition, the difference between the measured phases from each side is independent of the beam position, which allows for efficient combination of the fields. However, the ratio of the power on each side of the PETS unexpectedly shows a linear dependence on the horizontal offset, with a correlation value of 0.87. This can potentially affect the power transferred to the main linac, and should be taken into account in the design of the high power rf system.A graphical user interface was developed for the Test Beam Line, and the functionality is described in detail. The program is used in the operation of the Test Beam Line for monitoring, matching, steering and power production experiments, and has interfaces to MAD-X and PLACET. A documentation is also given of the Test Beam Line and the methods of the power measurements.

The optimization of piezoelectric ultrasonic transducers has tradisionally been done through trial and error, somewhat guided by one-dimentional simulations. This can often be a very time-consuming and expensive process, hence a more extensive simulation method is desired.A series of finite element models of piezoelectric ultrasonic transducer has been made in COMSOL Multiphysics. The initial models were designed to emulate the conditions assumed in a one-dimentional transducer model, and their validity could thus be confirmed by said model. Later models did not emulate these conditions, and a lossless model of a spherical disc with backing and a single matching layer was successfully implemented. Attemps had been made to include mechanical loss in the initial models, but was only partially achieved. All loss was thus excluded from later models. A final model with a piezoelectric layer poled in the radial direction was not successfully designed, as the varying poling direction proved to be difficult to implement.