Diss. (sammanfattning) Uppsala : Uppsala universitet, 2006. / Härtill 3 uppsatser.

<p>Accelerator-driven systems (ADS) are being investigated and designed for transmutation of the long-lived nuclear waste. Application of ADS allows to safely transmute large fractions of minor actinides (MA) per reactor core, while the fraction in critical reactors is limited to a few percent due to the safety constraints. Additional imposed costs of ADS introduction into the nuclear fuel cycle can be decreased by improving their effciency, particularly the external source effciency.</p><p>Design of the European Facility for Industrial Transmutation (EFIT) with transuranium (TRU) oxide fuel has been recently developed in the frame of  the EUROTRANS project. In this thesis it is shown that the neutron and proton source effciency of EFIT can be significantly improved by application of advanced TRU nitride fuel. Thanks to the good neutron economy of the nitride fuel, the EFIT core size can be reduced, which permits reducing the size of the spallation target. This provides a twice higher proton source effciency and therefore lowers the demand for the proton accelerator current. Additionally, the nitride version of EFIT features two times lower coolant void worth improving the core safety.</p><p>The pulsed neutron source (PNS) methods for ADS reactivity control have been studied experimentally at the YALINA facility in Minsk (Belarus) and shown good agreement with numerical simulation. The PNS methods will be most probably used for calibration of online reactivity monitoring system in future ADS.</p><p> </p>

<p>The main aim of the study was the assessment of the changes in tumouroxygenation based on FMISO PET imaging as one of the radiobiologicalbases for adaptive radiation therapy. The particular goal of the projectwas to create the platform for quantitative analysis of the distribution ofoxygenation and the radiation sensitivity associated with it at different timepoints during the treatment.</p> / QC 20100708

<p>The structure of the halo nucleus⁶He has been investigated in a pionic fusion experiment at the CELSIUS storage ring facility in Uppsala. The ⁴He(d, ⁶He)π⁺ reaction was studied 0.6 - 5.0 MeV above threshold in the centre-of-mass frame with a deuteron beam incident on a ⁴He gas target. The ⁶He ions were detected in a ΔE - E solid-state detector telescope inserted into the CELSIUS ring. The results for the total and differential cross section are presented and compared to results for the analogue reaction producing the 3.56 MeV analogue state in ⁶Li. A simple model of the reaction gives results consistent with earlier findings of ⁶He as having a spatial extent considerably exceeding that of the alpha particle. It is also shown that information about the high momentum part of the halo wave function can be extracted from the results of this pionic fusion measurement.</p>

The main topic of this dissertation is electronic charge transport in polymeric and molecular organic materials and material blends intended for solar cell applications. Charge transport in polymers is a strange beast and carrier mobility is rarely a well-defined number. Measurements on different sample geometries and under different conditions tend to give different results and when everything is to be related to solar cell performance it is imperative that there is a way to correlate the results from different measurements. Polymer solar cells utilize composite materials for their function. This puts an additional twist on charge transport studies, as there will also be interaction between the different phases to take into account. Several measurement techniques have been used and their interrelationships as well as information on their relevance for solar cells have been investigated. Field effect transistors (FET) with an organic active layer have proved to be one of the more versatile measurement geometries and are also an interesting topic in itself. FETs are discussed both as a route for material characterization and as components. A main result correlates bias stress in organic field effect transistors with the electronic structure of the material. Power conversion efficiency in solar cells is discussed with respect to electrical properties. The interaction of different blend materials and the impact of stoichiometry on transport properties in the active layer have been investigated. Results indicate that charge transport properties frequently are a key determining factor for which material combinations and ratios that works best. Some work on the conductive properties of nano-fibers coated with semiconducting polymers has also been done and is briefly discussed. The conductive properties of nano-fibers have been studied through potential imaging.

<p>Recent observational achievements within cosmology and astrophysics have lead to a concordance model in which the energy content in our Universe is dominated by presumably fundamentally new and exotic ingredients – dark energy and dark matter. To reveal the nature of these ingredients is one of the greatest challenges in physics.</p><p>The detection of a signal in gamma rays from dark matter annihilation would significantly contribute to revealing the nature of dark matter. This thesis presents derived imprints in gamma-ray spectra that could be expected from dark matter annihilation. In particular, dark matter particle candidates emerging in models with extra space dimensions, extending the standard model to be supersymmetric, and introducing an inert Higgs doublet are investigated. In all these scenarios dark matter annihilation induces sizeable and distinct signatures in their gamma-ray spectra. The predicted signals are in the form of monochromatic gamma-ray lines or a pronounced spectrum with a sharp cutoff at the dark matter particle’s mass. These signatures have no counterparts in the expected astrophysical background and are therefore well suited for dark matter searches.</p><p>Furthermore, numerical simulations of galaxies are studied to learn how baryons, that is, stars and gas, affect the expected dark matter distribution inside disk galaxies such as the Milky Way. From regions of increased dark matter concentrations, annihilation signals are expected to be the strongest. Estimations of dark matter induced gamma-ray fluxes from such regions are presented.</p><p>The types of dark matter signals presented in this thesis will be searched for with existing and future gamma-ray telescopes.</p><p>Finally, a claimed detection of dark matter annihilation into gamma rays is discussed and found to be unconvincing.</p>

<p>A quantum computer is an information processing machine, much like an ordinary classical computer, but its function is based on quantum mechanical principles. To be able to construct such a machine would be a fantastic accomplishment---to have total control over a quantum system is a dream for both physicists and science-fiction enthusiasts. The basic information unit in a quantum computer is the quantum bit, or qubit for short. A quantum computer consists of many coupled qubits. To get a single qubit to work properly, would be a major step towards building this machine.</p><p>Here we study two different qubit ideas. The central element in both setups is the superconducting tunnel junction---the Josephson junction. By connecting the Josephson junctions to standard electronics in a clever way, a qubit can be realised. With these constructions it is in principle very easy to manipulate and read out the quantum probabilities, by varying voltages and currents in time. However, this ease of manipulation has a cost: strong interactions with uncontrolled degrees of freedom of the environment transfer information from the qubit. For superconducting qubits this decoherence is typically very fast.</p><p>There are ways to deal with the decoherence. One way is to tune the circuit parameters so that the decoherence becomes minimal. Another way is to engineer the qubits so fast so that the effect of decoherence becomes small. In this thesis, we will apply both these strategies. Specifically, the measurement speed of the second qubit we study, turns out to be very sensitive to the topology of the phase space of the detector variables.</p>

No description available.

<p>Solar radiation is the main driving force for the Earth’s weather and climate. It is also the prime source for renewable energy technologies.Solar energy technologies can satisfy the current energy demand and at the same time reduce anthropogenic greenhouse gas emissions. It follows from scientific and engineering research within the field that accurate terrestrial solar radiation data and derived models can improve the detection of longterm climate change, the validation of Earth radiation budget estimates, and the deployment of solar energy systems. But, accurate assessment of solar energy at the Earth’s surface is difficult due to spatial, temporal and angular variability. These variations emphasise the need for localised solar radiation measurements and models.</p><p>In light of the above, this work has aimed at improving the quality of radiation data at two specific locations; one in Trondheim, Norway and the other in Durban, South Africa. This has entailed the development of an automatic data logging system, and frequent radiometer calibrations with traceability to the World Radiometric Reference. In addition, a radiometer called the Direct-Diffuse Solar Radiometer has been developed for the mapping of sky radiance. Supplementary work has been done to re-affirm the need for quality ground-based data.</p><p>The work done is twofold, the first on the measurements of solar irradiance and the second on the implementation of solar radiation models. So, the presentation of the work is divided into two parts. Chapters 1 to 5 are included in Part A under the heading “Measurement of Solar Irradiance”. Chapters 6 is given in Part B, “Data Modelling”.</p><p>Chapter 1 describes the concept of solar irradiance, discusses the components of solar radiation and introduces the radiometers in common use for the measurements of solar irradiance. Motivations for the development of the Direct-Diffuse Solar Radiometer are also included.</p><p>Chapter 2 describes the radiation mapping at the two sites, with particular emphasis on methods implemented for higher accuracy sampling, data reliability and continuity. </p><p>Regular radiometer calibration is necessary to ensure the data quality. Therefore the methodology for and results from calibration of the site radiometers are given in Chapter 3.</p><p>The acquired direct and global data for the sites are presented in Chapter 4. Diurnal 1-minute variations are discussed along with estimates of monthly and annual trends, with particular emphasis on atmospheric transmittance and the clearness index.</p><p>The last chapter in Part A, i.e. Chapter 5, presents the work done on the Direct-Diffuse Solar Radiometer (DDSR-1B). The instrument is designed for measuring sky irradiance as well as direct solar irradiance. The DDSR-1B is a prototype ground based instrument which is mounted on a remotely controlled solar tracker/sky positioner. The Chapter discusses the DDSR- 1B’s design, control, calibration and field tests in detail.</p><p>Chapter 6 in Part B considers 2 available software products that can generate estimates of direct normal solar irradiances for any ground location. This chapter also concludes the work for this thesis by reemphasising the need for localised solar radiation measurements and models.</p><p>Finally, Chapter 7 collects the major conclusions given through the course of this text.</p>

<p>For an idealized one-dimensional crystal it is possible to have energy levels whose wave functions are localized at the surface. These states are called surface states. There is one surface state for each energy gap between the ordinary allowed bands of energies. These electron states are called Tamm states. This Tamm state has an energy that lies almost at the middle of the energy gap and is mainly localized at the surface atomic layer. The image potential states are generated by a potential well formed by the Coulomb-like image potential barrier. These image states that are also called Shockley states are localized in a slowly decaying tail in the vacuum.</p><p>I also studied the lateral (in-plane) motion of electrons confined to terraces between steps on a vicinal Cu (111) surface. The local density of states showed a number of peaks at energies where electrons can occupy new quantum-well states on a step. I also tested the influence of the electron lifetime on the local density of states.</p>