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The electroweak standard model (Salam-Weinberg) is well-known to be a satisfactory and consistent theoretical description of all the experimental data we have obtained so far. In this thesis, we discuss possible phenomenology which goes beyond the standard model, with particular emphasis on the neutral current effects. First of all, the left-right symmetric extension of the standard model is discussed and we find limits on its parameters. We show that this model cannot explain certain newly reported and highly speculative events at the CERN collider [3], which in principle could be caused by the decay into two W's of a new heavy Z. We then discuss composite models where there is a strong expectation that there should be two neutral Z's of similar mass. We study the effects of these on neutral current phenomenology and show that in general the extra Z would be very hard to detect. A comparison of our model with a particular superstring model [6] is also made.

The standard model of particle physics is introduced, and extensions of it, which may be of cosmological relevance, are considered. The inflationary paradigm is reviewed as an extension of the standard cosmological model. In particular, the natural inflation mechanism resulting from a thermal phase change in a field theory with a spontaneous symmetry breaking potential, is examined. The question of when thermal equilibrium is likely to be a valid assumption in the early universe is considered in some detail. For inflation models, this question is answered by a self-consistency argument involving the total number of interactions per inflaton particle. In order to describe thermal-phase-change inflation models further, the temperature-dependent effective potential resulting from finite-temperature field theory is reviewed. The self-consistency test is developed into a numerical procedure which may be used to discuss the likelihood of thermal state generation in specific inflation models in a quantitative way. Alternatively, the method can be used to provide bounds on the parameters in the inflation potential from the requirement that a thermal state should occur. This procedure is applied to several example potentials and in particular it is easily verified that the "new inflation" model (relying on a phase change) is not viable. The method is quite general and can be applied to any inflation model for which a finite temperature effective potential can be defined. The procedure is generalised to the recently proposed extended inflation. Bounds on the extra free parameters which must be introduced in extended inflation are discussed. It is concluded that despite these extra free parameters the difficulties of generating a thermal state are just as great as they are in conventional inflation.

This thesis comprises two parts. In the first part an overview is given of the Standard Model, Supersymmetry and R-hadrons. R-hadrons are predicted within the framework of the Split-SUSY theory, in which the gluino can have a sufficiently long lifetime to hadronise into so-called R-hadrons. These will then propagate through the ATLAS detector as (meta)stable particles. The R-hadrons, which interact strongly, have the property of changing electric charge in interactions as they move through matter. In this thesis a strategy to search for R-hadrons with the ATLAS detcector is developed. The second part describes the ATLAS detector and the developement of the digitizer system of the ATLAS hadronic calorimeter. The digitizer system is the digitial readout system, in which data is read out from the detector to data buffers via an optical link. In the LHC environment, the operation of radiation-hard circuitry is essential. Therefore a quality control program was used to control that the design conforms to the requirements of radiation tolerance. An important part of the work was to test the devices to study their functionality and properties. This work is described in this thesis.

The chromatographic behaviour of a new column packing for high performance size exclusion chromatography based on crosslinked polyacrylamide particles was studied. Experimental retention data for poly(ethylene glycol)and poly(ethylene oxide) standards in water and water-methanol mixtures showed that the separation mechanism is size exclusion, since a universal calibration plot based on hydrodynamic volume was obtained. For polysaccharide standards in water and water-methanol (80/20), the universal calibration was valid for molecular weights above 4 * 10~. Below this value, secondary mechanisms appear to be taking part in the separation since water-methanol (80/20) is a poor solvent for polysaccharides. Crosslinked polyacrylamide packings showed an interactive behaviour with tetrahydrofuran and dimethylformamide as eluents with polystyrene and poly( ethylene glycol )/poly(ethylene oxide) standards and the universal calibration was not valid.

Unmanned vehicles being used more and more for tasks that need to be done in environ- ments that are hard to access, or dangerous for humans. Because the vehicles are unmanned they need some way of conveying information to the operator about where it is located. In some cases visual feedback to the operator might be enough, but in environments with low visibility other techniques are required. This thesis will address the issue of localization in an underwater environment by means of side-scan sonars and an inertial measurement unit (IMU). It will explore whether it is possible to localize a remotely operated vehicle (ROV) in a known environment by fusing data from the different sensors. A particle filter is applied to the translational motion of the ROV and an extended kalman filter is used to estimate the vehicles attitude. The focus of the thesis lies in statistical mod- eling and simulation of the ROV and its sensors rather than in validation and testing in the physical realm. Results show that a particle filter localization is plausible in environments given varied enough readings. For cases where measurements are similar, such as close to the floor of a pool the filter tends to diverge.