This thesis presents studies of the low energy properties of nseveral frustrated spin-1/2 Heisenberg antiferromagnets using various analytic and computational methods. The models studied include the union jack model, the alternating Heisenberg chain, the Heisenberg bilayer model, and the spin-Peierls model. The union jack model is a Heisenberg antiferromagnetic spin model with frustration, and is analyzed using spin-wave theory. For small values of the frustrating coupling $\alpha$, the system is N{\' e}el ordered, while for large $\alpha$ the frustration is found to induce a canted phase. Spin wave theory with second order corrections finds the critical coupling at $\alpha \simeq 0.645$,which agrees quantitatively with series expansion results. No intermediate spin-liquid phase is found to exist between the two phases. The alternating Heisenberg chain is studied using an alternative triplet-wave expansion formalism for dimerized spin systems, modification of the ??bond operator?? formalism of Sachdev and Bhatt. Projection operators are used to confine the system to the physical subspace, rather than constraint equations. Comparisons are made with the results of dimer series expansions and exact diagonalization. The S=1/2 Heisenberg bilayer spin model at zero temperature is studied in the dimerized phase using analytic triplet-wave expansions and dimer series expansions. The occurrence of two-triplon bound states in the S=0 and S=1 channels, and antibound states in the S=2 channel, is predicted with triplet-wave theory and confirmed by series expansions. All bound states are found to vanish at or before the critical coupling separating the dimerized phase from the N{\' e}el phase. The critical behavior of the total and single-particle static transverse structure factors is also studied by series expansion methods and found to conform with theoretical expectations. The Heisenberg spin-Peierls model with dispersive, gapless phonons is studied with Density Matrix Renormalization Group methods. We investigate the zero temperature properties of the model using the crossover method. The calculations were found to converge poorly and no conclusive results could be found using this method. An analysis of the convergence problems and the discovery of an anomalous triplet ground state is presented in this chapter.

Measurements of atomic parity violation provide important cross-tests of the standard model of electroweak interactions by probing these interactions in the domain of low energies. The effects of parity nonconservation in atoms, both dependent and not dependent on nuclear spin, have been successfully measured in experiments. The existence of permanent electric dipole moment (EDM) of a quantum particle requires that fundamental parity (P) and time-reversal (T) symmetries are violated. By the CPT theorem, this would mean violation of the combined CP (charge conjugation-parity) symmetry as well. Studies of T and CP violation in nature provide valuable information for theories of baryogenesis, and for understanding of fundamental interactions in general. Recently, a new wave of experiments has been initiated to measure the effects of P and T violation in solid state materials. The possibility to substantially increase the experimental sensitivity lies in the larger number of particles compared to the atomic experiments and in the specific collective effects in solids. The downside is the typically larger level of systematics. In the present work, the following effects due to violation of T and P at fundamental level in solids are considered: (a) effects due to the nuclear weak charge (violation of P) in rare-earth trifluorides, a possibility exists to measure the Weinberg angle with high precision; (b) effects due to the nuclear anapole moment (nuclear spin-dependent violation of P) in praseodymium and thulium garnets, the NMR-type experiments can possibly be used to measure nuclear anapole moments of Pr and Tm; (c) effects due to the electron EDM in gadolinium garnets, increase of the experimental sensitivity to the electron EDM of several orders of magnitude is possible; (d) effects due to the nuclear Schiff moment of 207Pb in ferroelectric lead-titanate; this possibility looks particularly promising, offering a potential 10 orders of magnitude increase of sensitivity to the nuclear Schiff moment, which puts the standard model prediction for this value within experimental reach. Also discussed are several other possibilities for experimental observation of these effects and the impact of some possible systematic effects on the proposed measurements.

To improve the replication of acoustic guitars, measurements of three Martin OOO style steel-string guitars were made at various stages of their construction. The guitars were constructed in parallel, as similar to each other as possible, with the exception of the soundboard material---which were made of Sitka spruce, Engelmann spruce and Western Red cedar. To improve the similarity of the instruments, methods were developed to measure and control the material properties of key components before their incorporation into the instruments, including a device to measure the thickness of a guitar soundboard attached to the back and sides of the instrument. Some of these measurements were compared to numerical models of the instrument and, after the establishment of a lexicon to describe guitar sounds, some physical factors contributing towards the timbre of guitar sounds were determined. The results of these investigations may be developed to improve the consistency in the manufacture of stringed musical instruments.

Precision cosmology challenges many aspects of fundamental physics. In particular, quasar absorption lines test the assumed constancy of fundamental constants over cosmological time-scales and distances. Until recently, the most reliable technique was the alkali doublet (AD) method where the measured doublet separation probes variations in the fine-structure constant, ???? e2/??c. However, the recently introduced many-multiplet (MM) method provides several advantages, including a demonstrated ???10-fold precision gain. This thesis presents detailed MM analyses of 3 independent Keck/HIRES samples containing 128 absorption systems with 0.2 &gt zabs &gt 3.7. We find 5.6 ?? statistical evidence for a smaller ?? in the absorption clouds: ????/?? = (-0.574 ?? 0.102) x 10-5. All three samples separately yield consistent, significant ????/??. The data marginally prefer constant d??/dt rather than constant ????/??. The two-point correlation function for ?? and the angular distribution of ????/?? give no evidence for spatial variations. We also analyse 21 Keck/HIRES Si iv doublets, obtaining a 3-fold relative precision gain over previous AD studies: ????/?? = (-0.5 ?? 1.3) x 10-5 for 2.0 &gt zabs &gt 3.1. Our statistical evidence for varying ?? requires careful consideration of systematic errors. Modelling demonstrates that atmospheric dispersion is potentially important. However, the quasar spectra suggest a negligible effect on ????/??. Cosmological variation in Mg isotopic abundances may affect ????/?? at zabs &gt 1.8. Galactic observations and theory suggest diminished 25;26Mg abundances in the low metallicity quasar absorbers. Removing 25;26Mg isotopes yields more negative ????/?? values. Overall, known systematic errors can not explain our results. We also constrain variations in y ?? ?? 2gp, comparing H i 21-cm and millimetrewave molecular absorption in 2 systems. Fitting both the H i and molecular lines yields the tightest, most reliable current constraints: ??y/y = (-0.20??0.44)x10-5 and (-0.16??0.54)x10-5 at zabs = 0.2467 and 0.6847 respectively. Possible line-ofsight velocity differences between the H i and molecular absorbing regions dominate these 1 ?? errors. A larger sample of mm/H i comparisons is required to reliably quantify this uncertainty and provide a potentially crucial check on the MM result.

Massive stars form in the dense optically thick cores of molecular clouds throughout the Galaxy. They actively participate in the heating of these molecular clouds and also in enriching the interstellar medium with heavy elements. Stellar winds may contribute to change the original cloud structure by in uencing nearby low mass star formation, or even by triggering the formation of new stars. Despite the fact that massive star formation is manifest throughout the Galaxy, the mechanisms involved in their formation are poorly understood. The coincidence of methanol masers and ultracompact (UC) HII regions with young massive stars, indicates their eectiveness in tracing the earliest stages of high-mass stellar evolution. This thesis concentrates on a multiwavelength study of massive star formation regions. The cornerstone of this thesis is a (sub)millimetre study of methanol maser and UC HII sources associated with massive star formation regions. The 15m Swedish ESO Submillimetre Telescope (SEST) and the 15m James Clerk Maxwell Telescope (JCMT) were used to survey continuum emission at 1.2mm and 450 & 850 m, respectively. The 1.2-mm continuum emission observations were undertaken with the SEST IMaging Bolometer Array (SIMBA) toward star-forming complexes associated with methanol maser and/or radio continuum sources. This survey detected emission toward all of the methanol maser and UC HII regions targeted, and revealed evidence of a handful of these tracers lying within the elds mapped without millimetre continuum emission. Interestingly, the SIMBA survey also revealed evidence of sources devoid of traditional star formation tracers (methanol/OH maser, UC HII regions, IRAS sources), detected solely from their millimetre continuum emission. These `mm-only' sources prompted a follow-up study with the JCMT. The 450 and 850m observations of mm-only cores discovered in the SIMBA survey, utilised the Submillimetre Common User Bolometer Array (SCUBA) on the JCMT, which detected submillimetre continuum emission toward 97 per cent of sources targeted. The SCUBA instrument also resolved a number of SIMBA sources into multiple components, and found evidence of submillimetre sources devoid of SIMBA emission. The (sub)millimetre data from the SIMBA and SCUBA surveys enabled study of the dust properties of the cores, and in particular the dust grain emissivity index , which is of order 2 for the sample. Spectral energy distribution (SED) diagrams were drawn for the SIMBA sources, employing MSX and IRAS data where possible. Eight parameters are reported for each of the sources in the sample: luminosity, temperature, mass, H2 number density (nH2 ), surface density (), radius, distance and luminosity-tomass ratio (L/M). These data show that the mm-only cores are of comparable mass to sources harbouring a methanol maser and/or radio continuum source, but are smaller, cooler, less luminous, with smaller luminosity-to-mass ratios, than these sources. This prompts the suggestion that the mm-only core is an example of the earliest stages of massive star formation prior to the onset of methanol maser emission. The mm-only sample was identied as comprising two populations, which are distinguished by temperature. The cool-mm sources are distinct from the warm-mm sources as well as from those sources with a methanol maser and/or a radio continuum source for all parameters tested but for the mass and in some instances the radius. The warm-mm on the other hand are similar to those sources with a methanol maser site and/or an UC HII region for all parameters tested. The cool-mm sources are less luminous, with lower luminosity-to-mass ratios, as well as higher H2 number and surface densities. This prompts hypotheses to be drawn regarding the nature of these two mm-only populations. The warm-mm sources are possible precursors to the methanol maser and are thus indicative of the earliest stages of massive star formation, whilst the cool-mm sources are possible examples of `failed' cores that will remain starless. It is, however, not yet clear which of these mm-only populations are forming massive stars and further work to test these hypotheses is required.

Naval submarines and surface ships are regularly subjected to a treatment called &quotdeperming&quot that seeks to design the vessel???s permanent magnetisation for optimal magnetic camouflage. A scaled model of a magnetic treatment facility (MTF) has been established as a valid system to simulate deperming and used to investigate various aspects of the deperm process including: magnetic anisotropy and demagnetising fields as factors in the physical modelling of magnetism in whole vessels; a comparison of current and alternative deperm procedures; the application of theoretical models of bulk magnetisation to calculate deperm outcomes in the physical model and in actual vessels. A &quotlaboratory MTF&quot was constructed to imitate the applied field geometry at a naval MTF. The system was calibrated and it was determined that the laboratory MTF could make magnetic measurements on a CU200T-G steel bar sample with an equivalent accuracy (error = ??5%) to that of standard magnetometric equipment. Experiments were conducted with emphasis on a holistic approach to modelling the deperm process and describing magnetisation changes in whole objects. The importance of the magnetic anisotropic changes to steel with cold rolling was confirmed. In CU200T-G steel sheet the initial susceptibility (ci) was found to increase by a factor of 3 ??0.1 in the rolling direction, from a value of ~ 110 in the un-rolled steel sheet (thickness dependent). ci in the rolled sheet transverse to the rolling direction was decreased by a factor of 0.94 ??0.09 to ci in the un-rolled sheet steel. Previous studies on hull steel have neglected to account for this transformation through cold work. The demonstration on mild steel here is expected to have an analogy in the final state of the hull sheet steel as it resides in a submarine pressure hull. Future studies either on hull material or on modelling whole vessels should include the same or similar magnetic anisotropic properties in the steel(s) under investigation. Hollow circular tubes made from CA2S-E and CU200T-G steel sheet were selected as models for vessels. It was shown that these steel tubes were a good choice in this regard: minimising the complexity of the experiment whilst maintaining the validity of a deperm simulation. During a deperm there was an excellent qualitative likeness in the permanent longitudinal magnetisation (PLM) for the steel tubes to PLM in both a submarine and a surface vessel. Permanent vertical magnetisation (PVM) deperm results from the tubes displayed a close qualitative match with PVM in a submarine but not in a surface vessel. A theoretical treatment for demagnetisation factors (Nd) in hollow ellipsoids was used in conjunction with a geometrical approximation to calculate Nd for finite hollow objects of revolution. Subsequent theoretical calculations correlated well with experimental results for measured effective ci (ceff) in hollow circular CU200T-G steel tubes of various lengths and aspect ratios. Using an estimate of 100 as ci for submarine hull steel, the same analysis produces Nd for the axial and transaxial directions in a submarine equal to 5.97??10-3 and 0.0142 respectively. Three items for potential improvement were identified in the current deperm protocol used on naval vessels (Flash-D): redundancy in the protocol; the duration of the deperm and a theoretical basis for predicting the final magnetisation or changes in magnetisation during a deperm. Simulations of a novel &quotanhysteretic deperm&quot method, designed to combat these issues, compared favourably to the Flash-D protocol. The standard deviation (s) of the final PVM from 30 Flash-D deperms on steel tubes was 206 A/m; for the final PVM from 30 anhysteretic deperms of the same duration, this was 60 A/m. The s for the final PLM for Flash-D and anhysteretic deperms of the same duration were 416 A/m and 670 A/m respectively. The conclusion is that adopting the anhysteretic deperm on actual vessels would improve the reliability of the PVM outcome. Though the procedure would demand the same duration as Flash-D, there is the advantage of saving time by not having to repeat deperms to obtain the desired result. Additionally the anhysteretic deperm is considerably more amenable to theoretical analysis. A modified version of Langevin???s equation was used to predict the final PLM and PVM results for anhysteretic deperms and to provide a useful analysis of the anhysteretic processes in the Flash-D procedure. Using a Preisach analysis of hysteresis, a mathematical description of bulk magnetic changes that occur to a specific object, within a deperm, has been developed. Theoretical calculations of PLM in a steel tube during and after both types of deperm are in excellent agreement with experimental data. The same theoretical approach was also used to retrospectively model PLM results from previous Flash-D deperms on a submarine with equal success. With this analysis it is proposed that anhysteretic deperm outcomes could be predicted a priori. The influence of magnetic cargo on hull magnetisation was demonstrated to be of significance during and after deperming. &quotSympathetic deperming&quot occurs where a magnetic source is located close to the hull during a deperm. It was found that a vessel or model vessel hull could still be demagnetised even when they contain magnetic cargo that would normally resist the direct application of the same magnetic fields. This was explained using the principles of demagnetising fields and anhysteretic magnetisation. A possible explanation was provided for a PVM measurement anomaly common to the model and vessel deperm results. From measurement, alternating longitudinal applied fields apparently induce corresponding changes in the PVM. This effect could be explained by the depermed object being offset longitudinally from the position expected by the measurement system. This offset could be estimated using an analysis of the changes to PLM and PVM after a longitudinal applied field. The offset displacements calculated for the vessels were too small to be verified experimentally (&gt 0.1m), but the predicted offset for the steel tubes coincided with the limit of precision for their placement in the laboratory MTF = 0.5mm The aim of this work was to look at the deperm process with reference to a system that demonstrated qualitative similarities to deperms on actual vessels. The laboratory MTF is a unique facility, permitting a useful practical analysis of deperming based on sound magnetostatic measurements The experimental and theoretical results gained here have direct application to future deperms on naval vessels with particular reference to submarines.

In this thesis we investigate the large-scale distribution of Ly alpha forest absorption, the effect of ionizing radiation from QSOs on their surrounding intergalactic medium and the primordial abundance of deuterium. We develop a new technique for detecting structure on Mpc scales in the Ly alpha forest. This technique does not rely on identifying individual absorption lines but is rather based on the statistics of the transmitted flux. We demonstrate that the new method is significantly more sensitive to the presence of large-scale structure in the Ly alpha forest than a two-point correlation function analysis. We apply this method to 2 A resolution spectra of ten QSOs which cover the redshift range 2.2 < z < 3.4. The QSOs form a closely spaced group on the sky and are concentrated within a 1-deg^2 field. We find evidence for large-scale structure in the distribution of Ly alpha forest absorption at the > 99 per cent confidence level. Along the line of sight we find overdense Ly alpha absorption on scales of up to 1200 km s^-1. There is also strong evidence for correlated absorption across line of sight pairs separated by < 3 h^-1 Mpc. For larger separations the cross-correlation signal becomes progressively less significant. Using the same technique and dataset we confirm the existence of the proximity effect. We derive a value for the mean intensity of the extragalactic background radiation at the Lyman limit of J = (3.6^+3.5_-1.3) x 10^-22 ergs s^-1 cm^-2 Hz^-1 sr^-1. This value assumes that QSO redshifts measured from high ionization lines differ from the true systemic redshifts by Delta v = 800 km s^-1. Allowing for known QSO variability we find evidence at a level of 2.1 sigma that the significance of the proximity effect is correlated with QSO Lyman limit luminosity. From the complete sample we find no evidence for the existence of a foreground proximity effect, implying either that J > 20 x 10^-22 ergs s^-1 cm^-2 Hz^-1 sr^-1 or that QSOs emit at least a factor of 1.4 less ionizing radiation in the plane of the sky than along the line of sight to Earth. We do, however, find one counter-example where a foreground QSO apparently depletes the absorbing gas in four surrounding lines of sight. We discuss the feasibility of pre-selecting absorption systems from low resolution data for a measurement of the primordial deuterium abundance. We present a new, low resolution spectroscopic survey of 101 high redshift QSOs aimed at identifying candidate D/H systems. We further present an echelle spectrum of a Lyman limit system at z = 2.917. We find that this system is most likely heavily contaminated and does not yield an interesting limit on D/H.

Integral membrane proteins perform a wide range of biological processes, including respiration, signal transduction and molecular transport. Structural information is necessary for a full understanding of the mechanisms by which integral membrane proteins work. Ferrous iron transporter protein B (FeoB) is an integral membrane protein of Escherichia coli which is considered to transport ferrous iron in to bacteria. But there are no definite proofs or clear indications of the precise mechanism of ferrous transport. By expressing and crystallizing the G-protein domain (FeoGP) and FeoB, it will be helpful to know about the iron transport system. In order to express FeoB and FeoGP, expression vector pFeoB (FeoB in pGEX-4T-1) and pFeoGP (FeoB in pGEX-4T-1) were made. FeoB and FeoGP proteins were expressed and purified. Using vapour diffusion method crystallization trials of FeoB and FeoGP were done. Crystals of FeoGP are observed and no crystal formation for FeoB. Native crystals of FeoGP diffracted to 2.2 ?? resolution, and mant-GMPPNP crystals to 2.6 ??. Preliminary data processing indicate space group P212121 for native crystals, with cell dimensions 46 x 119 x 146 ??. The data set is 100% complete, Rmerge 0.08, and I/ ?? 3.2.

In this thesis we study GaAs one dimensional hole systems with strong spin-orbit interaction effects. The primary focus is the Zeeman splitting of 1D subbands in the two orthogonal in-plane magnetic field directions. We study two types of 1D hole systems based on different (311)A grown heterostructures: a modulation doped GaAs/AlGaAs square quantum well and an undoped induced GaAs/AlGaAs triangular quantum well. The results from the modulation doped 1D wire show enhanced anisotropy of the effective Lande g-factor for the two in-plane field directions (parallel and perpendicular to the wire), compared to that in 2D hole systems. This enhancement is explained by the confinement induced reorientation of the total angular momentum ^ J from perpendicular to the 2D plane to in-plane and parallel to the wire. We use the intrinsic anisotropy of the in-plane g-factors to probe the 0:7 structure and the zero bias anomaly in 1D hole wires. We find that the behaviour of the 0:7 structure and the ZBA are correlated and depend strongly on the orientation of the in-plane field. This result proves the connection between the 0:7 and the ZBA and their relation to spin. We fabricate the first induced hole 1D wire with extremely stable gate characteristics and characterize this device. We also fabricate devices with two orthogonal induced hole wires on one chip, to study the interplay between the confinement, crystallographic anisotropy and spin-orbit coupling and their effect on the Zeeman splitting. We find that the ratios of the g-factors in the two orthogonal field directions for the two wires show opposite behaviour. We compare absolute values of the g-factors relative to the magnetic field direction. For B || [011] the g-factor is large for the wire along [011] and small for the wire along [233]. Whereas for B || [233], the g-factors are large irrespective of the wire direction. The former result can be explained by reorientation of ^ J along the wire, and the latter by an additional off-diagonal Zeeman term, which leads to the out-of-plane component of ^ J when B || [233], and as a result, to enhanced g-factors via increased exchange interactions.

This study investigates the Monte Carlo calculations of cell survival in metastatic subcutaneous melanoma cancer tumours. To achieve this goal, a Monte Carlo program called SLAB.FOR was developed by Prof. David Charlton. The program randomly places alphas from 213Bi in the medium, which is a cancer cell sized micro dosimeter with a SiO2 converter on the top and Si as the sensitive volume. Then the Monte Carlo program calculates the energy deposited by alphas and their chord length and also the dose deposited in the sensitive volume. To be able to use this program, some information was taken from phase one of a clinical trial conducted by the Centre of Experimental Radiation Oncology (CERO) in 2001. During the course of this study the administered activities on tumours with different diameters are determined. Using this information the number of alpha particles going through each m3 of the tumour was found. Based on this number, the program SLAB.FOR was run for different administered activities in the tumours. The output of the program yielded the energy deposited and the number of hits by the alpha particles as they go through the tumours. The output data was also used to calculate the cell survival values, energy and hit distribution probabilities. The cell survival values were then used to plot the cell survival curves. They were plotted against dose, number of hits and injected activity per volume of the tumours. These data were also used to plot the energy and hit distribution probability curves. Our results show that survival is dependent on the diameter of the cell and decreases when the dose deposited in the tumour increases. The survival also has a relationship with the number of hits that a cell receives and it also depends on the injected activity to the volume. The survival decreases as the number of hits and injected activity increases. Our results confirmed what was stated in the clinical trial conducted by the Centre of Experimental Radiation Oncology (CERO) in 2001.