<p>In this thesis, the first determination of the electric charge of the top quark is presented using 370pb^-1 of data recorded by the DØ detector at the Fermilab Tevatron accelerator. ttbar events are selected with one isolated electron or muon and at least four jets out of which two are <i>b</i>-tagged by reconstruction of a secondary decay vertex (SVT). The method is based on the discrimination between <i>b</i>- and <i>b</i>-quark jets using a jet charge algorithm applied to SVT-tagged jets. A method to calibrate the jet charge algorithm with data is developed. A constrained kinematic fit is performed to associate the <i>W</i> bosons to the correct <i>b</i>-quark jets in the event and extract the top quark electric charge. The data is in good agreement with the Standard Model top quark electric charge of 2e/3. The scenario where the selected sample is solely composed of an exotic quark Q with charge 4e/3 is excluded at 92% confidence level. Using a Bayesian approach, an upper limit on the fraction of exotic quarks <i>p</i> < 0.80 at 90% confidence level is obtained.</p>

<p>The overall focus of this thesis is on fluorescence flicker processes of fluorescent molecules, e.g. protonation-deprotonation or singlet-triplet electronic state transitions, intrinsic or generated by their interaction with their environment, monitored by fluorescence spectroscopy.</p><p>Understanding proton migration along membranes and membrane proteins in cells is essential for understanding energy metabolism. It has been seen that certain membrane-spanning proton-transporter proteins in the respiratory chain in the mitochondrial inner membrane take up protons faster than the rate limited by diffusion. To explain these observations it has been suggested that there is a proton-collecting antenna, consisting of negatively and protonatable residues on the surface of these proteins, which increases the rate of uptake. Using fluorescence correlation spectroscopy and artificial biological membranes the proton collecting antenna effect is verified, as well as the proton migration properties on these membranes at various surface buffer concentrations.</p><p>Fluorescence flicker due to singlet-triplet electronic state transitions in a fluorescent molecule is interesting because of the long transition time between the two states. This means that the molecule has a long time to interact with the local environment, and can therefore be used as a microenvironmental sensor. A novel method for monitoring photo-induced, transient, long-lived, non- or weakly fluorescent states, e.g. the triplet state, was developed. With this method, only the time averaged intensity is detected and used for determining the triplet state kinetics. This method has several advantages, in particular it lends itself well for parallelization, over traditional methods including fluorescence correlation spectroscopy.</p>

<p>In this thesis visible spectroscopy is developed and used for two applications.</p><p>Studies of motional Stark effect spectra for diagnosing the current distribution in the fusion plasmas with two different spectroscopic diagnostic systems: ratiometry and interferometry. Both systems provide non-invasive method for diagnosis of the internal plasma properties, e.g. magnetic field. Pitch angle of magnetic field lines are obtained from polarisation of Stark split <i>H</i>αspectral lines emitted by energetic hydrogen atoms injected into the plasma volume by neutral beam. Several methods of calibration of the systems on TEXTOR and JET are discussed. The main result of this work is the first measurement of the safety factor radial profile with new ratiometric MSE system on TEXTOR.</p><p>Studies of molecular fragmentation of free molecules <i>CH</i>₄ and <i>NH</i>₃excited with synchrotron radiation by detection of the fluorescence from the fragments. The results give the decay path ways for the molecules when excited below the<i> N</i> and <i>C i</i>onisation edges.</p>

<p>This thesis deals with the detection and analysis of low-level natural and induced radioactivity. Using high energy-resolution Ge detectors in low-level counting areas airborne radioactivity’s like Be-7 and Cs-137 have been investigated. The experimental facilities and techniques are described in some detail.</p><p>One of the aims in this work is the studying of change detection in the amount of the activity received on the earth from events that happen at the solar system. Information about this is achieved by measuring the activity of the Be-7 isotope, which is a very good indicator of the solar protons that reach the atmosphere of the Earth. Therefore Be-7 probes the variation of the boundary conditions on the Earth related to solar events as well as transportation between the atmospheric layers, troposphere and stratosphere, which are the layers nearest to the ground. Results obtained by this work refer to the seasonal variation and the eleven years sun cycle in addition to the two to three years cycle expected by some scientists. These results are shown in many figures of the activity measurements and the Fourier transformation of the intensity of the Be-7.</p><p>The effect of the man-made radiation in the air was studied by collection of Cs-137, which was contaminating most of countries in the world after the Chernobyl accident. Our search for low levels of Cs-137 shows how important it is to use a Low Level Laboratory, like the one at AlbaNova, for measurements of novelty and change.</p><p>Studying the airborne activity in Sweden and Finland at the same time and time interval gives us a possibility to look for correlations of the fall down of the Be-7 activity from the upper layers of the atmosphere simultaneously in both countries.</p><p>This thesis also involves the results of Neutron Activation Analysis Technique applied to the general human food, milk, vegetables and grains. The experiments were performed at the neutron beam of the Iraqi reactor IRT 5000 at Baghdad. The goal of the experiments was to determine iodine and other trace elements after the Chernobyl accident compared to results from different countries.</p><p>An exploratory, preliminary study of airborne activities, following e.g. an accident at a nuclear power plant, or leakage of radiation from any source of contamination at any region, using a small, expendable unmanned aerial vehicle is also discussed briefly.</p>

<p>PoGOLite is a balloon-borne experiment which will study polarised soft gamma-ray emission from astrophysical targets in the 25 keV – 80 keV energy range by applying well-type phoswich detector technology. Polarised gamma-rays are expected from a wide variety of sources including rotation-powered pulsars, accreting black holes and neutron stars, and jet-dominated active galaxies. Polarisation measurements provide a powerful probe of the gamma-ray emission mechanism and the distribution of magnetic and radiation fields around the source. The polarisation is determined using Compton scattering and photoelectric absorption in an array of 217 plastic scintillators. The sensitive detector is surrounded by a segmented Bismuth Germanium Oxide (BGO) anticoincidence shield. The function of this shield is to reduce backgrounds from charged cosmic rays, primary and atmospheric gamma-rays, and atmospheric and instrumental neutrons. The anticoincidence shield consists of 427 BGO crystals with three different geometries. The characteristics of the BGO crystals of the bottom anticoincidence shield have been studied with particular focus on the light yield.</p><p>The PoGOLite polarimeter has a field of view of 2.4° x 2.4° and must be kept aligned to objects of interest on the sky. A star tracker forms part of the attitude control system. The star tracker system comprises a CCD camera, lens, and a baffle system. Preliminary studies have been made concerning optimization of the focus, flat field correction, map of hot pixel and CCD response. An estimate of the star magnitude limit is also derived and found to be compatible with the environment around the Crab, which is the first observational target. These studies pave the way toward an autonomous star tracking device which together with the other attitude control devices will reconstruct the pointing solution.</p>

<p>Abstract</p><p>This thesis presents methods to combine 3D cell culture, microfluidics and gradients on a controlled cellular scale. 3D cultures in biological extracellular matrix gels or synthetic gels bridge the gap between organ-tissue cultures and traditional 2D cultures. A device for embedding, anchoring and culturing cells in a controlled 3D flow through micro-environment was designed and evaluated. The device was realized using an etched silicon pillar flow chamber filled with gel mixed with cells. The pillars anchor and stabilize the gel as well as increase the surface to volume ratio, permitting higher surface flow rates and improving diffusion properties. Within the structure cells were still viable and proliferating after six days of cultivation, showing that it is possible to perform medium- to-long term cultivation of cells in a controlled 3D environment.</p><p>This concept was further developed to include controllable and time stable 3D microgradient environments. In this system stable diffusion gradients can be generated by the application of two parallel fluid flows with different composition against opposite sides of a gel plug with embedded cells. Culture for up to two weeks was performed showing cells still viable and proliferating. The cell tracer dye calcein was used to verify gradient formation as the fluorescent intensity in exposed cells was proportional to the position in the chamber. Cellular response to an applied stimulus was demonstrated by use of an adenosine triphosphate gradient where the onset of an intracellular calcium release also depends on cell position.</p>

<p>The Polarized Gamma-ray Observer (PoGOLite) is a balloon-borne instrument capable of measuring as low as 10% polarization from a 200 mCrab source in a sixhour °ight. A wide array of sources can be studied, including pulsars, neutron stars, accretion discs and jets from active galactic nuclei. The two new observational parameters provided by such measurements, polarization angle and degree, will allow these objects to be studied in a completely new way, providing information both about the emission mechanisms and the geometries of the emitting objects. The instrument measures anisotropies in azimuthal scattering angles of gammarays with a close-packed array of 217 well-type phoswich detector cells (PDCs) by coincident detection of Compton scattering and photoelectric absorption. Each PDC comprises a \slow" plastic scintillator tube, a \fast" plastic scintillator rod and a BGO crystal. The fast scintillator is the main detector component, whereas the slow scintillator and the BGO crystal act as an active collimator and a bottom anticoincidence shield, respectively. The three parts are viewed by a single photomultiplier tube (PMT) and pulse shape discrimination is used to identify signals from each part.</p><p> The detector array is surrounded by a 54-segment side anticoincidence shield (SAS) made of BGO crystals. Each segment is 60 cm long and consists of three crystals. A total of 187 crystals have been procured and tested for light yield, energy resolution, dimensions and surface ¯nish. All crystals have been found to be of excellent quality and measured characteristics have been within speci¯ed limits. The performance of the instrument has also been evaluated in several beam tests with polarized synchrotron photons irradiating a prototype detector array. Front-end electronics have been tested and a modulation in the observed scattering angles has been observed in line with expectations. Geant4-based Monte Carlo simulations of the instrument performance have shown that a 10 cm thick polyethylene shield is required around the detector array in order to su±ciently reduce the background from atmospheric neutrons. To validate these simulations, a simple detector array with four plastic scintillators and three BGO crystals was irradiated with 14 MeV neutrons. The array was shielded with polyethylene, mimicking the PoGOLite instrument design. Measured results could be accurately recreated in Geant4 simulations, demonstrating that the treatment of neutron interaction processes in Geant4 is reliable.</p>

<p>Steel is an important structural material in nuclear reactors used for example in pressure vessels and fast reactor cladding. In reactor environments it has been observed that ferritic steels are more resistant to swelling than the austenitic steels typically used. Much effort has been put into developing basic models of FeCr alloys which can serve as model alloys for describing ferritic steels. As a result, a number of interatomic potentials for Fe and FeCr alloys exist today.</p><p>For the work in this thesis, basic material properties coming from experiments or ab initio calculations were used to fit interatomic potentials for Fe, Cr and FeCr implementing both the embedded atom method and the Finnis-Sinclair formalisms. The potentials were then validated by molecular dynamic calculations of material properties such as defect formation energies, migration energies and thermal expansion. Further studies of potential performance were carried out in simulations of radiation damage cascades and thermal aging.</p><p>The influence of the interatomic potential on the primary defect state in materials under irradiation was analyzed in a study comparing results obtained using four different potentials. The objective of the study was to find correlations between potential properties and the primary damage state produced in simulations of displacement cascades. The defect evolution and clustering during different cascade stages were also investigated to try to gain a better understanding of these processes.</p>

<p>This thesis is devoted to the study of various examples of exactly solved quantum many-body systems in one-dimension. It is divided into two parts: the ¯rst provides background and complementary results to the second, which consists of three scienti¯c papers. The ¯rst paper concerns a particu- lar extension, corresponding to the root system CN, of the delta-interaction model. We prove by construction that its exact solution, even in the gen- eral case of distinguishable particles, can be obtained by the coordinate Bethe ansatz. We also elaborate on the physical interpretation of this model. It is well known that the delta-interaction is included in a four parameter family of local interactions. In the second paper we interpret these parameters as cou- pling constants of certain momentum dependent interactions and determine all cases leading to a many-body system of distinguishable particles which can be solved by the coordinate Bethe ansatz. In the third paper we consider the so-called rational Calogero-Sutherland model, describing an arbitrary number of particles on the real line, con¯ned by a harmonic oscillator potential and interacting via a two-body interaction proportional to the inverse square of the inter-particle distance. We construct a novel solution algorithm for this model which enables us to obtain explicit formulas for its eigenfunctions. We also show that our algorithm applies, with minor changes, to all extensions of the rational Calogero-Sutherland model which correspond to a classical root system.</p>

<p>Dark matter (DM) constitutes one of the most intriguing but so far unresolved issues in physics. In many extensions of the Standard Model of particle physics, the existence of a stable Weakly Interacting Massive Particle (WIMP) is predicted. The WIMP is an excellent DM particle candidate and one of the most interesting scenarios include an annihilation of two WIMPs into two gamma-rays. If the WIMPs are assumed to be non-relativistic, the resulting photons will both have an energy equal to the mass of the WIMP and will manifest themselves as a monochromatic spectral line in the energy spectrum. This type of signal would represent a “smoking gun” for DM, since no other known astrophysical process should be able to produce it. When searching for a line, the energy resolution and performance of the calorimeter are key factors. In this thesis, these are investigated using beam test data, taken at CERN in 2006. Four statistical methods that can be used to search for DM spectral lines are, then, studied in terms of their power and coverage. The methods are based on both hypothesis tests and confidence interval calculations. Two peak finding methods are also tested on a simulated data set representing one year of realistic data, obtained with the Large Area Telescope (LAT) on-board the Gamma-ray Large Area Space Telescope (GLAST). The data set is called Service Challenge 2 (SC2) and contains a variety of gamma-ray sources, including different DM components. Finally, an upper limit on < σν > γγ, based on SC2, is calculated.</p>