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Optical polarimetry results are presented for four spiral galaxies: NGC 5194 (M51), NGC 1068, NGC 4565 and NGC 4594 (Ml04). M51 and NGC 1068 show spiral polar isation patterns which are interpreted as indicating a spiral magnetic field in each case. NGC 4565 and M104 show polar isations in their dust lanes which are parallel to their galactic planes, and which are interpreted in terms of a magnetic field in the plane of each. It is hypothesised that the observed magnetic fields may be linked to galactic shocks. A discussion of the origin of galactic magnetic fields concludes that there is no evidence which necessitates a primordial magnetic field.

No description available.

No description available.

Fast Field-Cycling (FFC) MRI allows the magnetic field to be switched during an imaging scan. FFC-MRI can be used to exploit a characteristic of contrast agents, i.e. the variation of its spin-lattice relaxation time (T1) or rate (R1= 1/T1) with magnetic field in order to increase contrast. Contrast agents play an essential role in MRI, allowing improved diagnosis and delineation of diseased tissue. However, the R1, and hence the effectiveness of contrast agents, varies significantly with magnetic field. Thus, Fast Field-Cycling (FFC) MRI can be used to take advantage of this variation to improve image contrast, allowing more sensitive detection of the agent. In this project new contrast agents, developed by a collaborating group (Invento S.r.l., Italy) were investigated for use with FFC-MRI. R1 dispersion curves of samples containing a range of contrast agents were first obtained using both a commercial relaxometer and a home-built whole-body FFC-MRI system, and the accuracy of the home-built FFC-MRI system was verified. The magnetisation behaviour of these samples during field-cycling pulse sequences was modelled in order to predict the pulse sequence parameters necessary for maximum T1 contrast. Images were obtained, using a number of novel imaging techniques developed on the home-built whole-body FFC-MRI system, and also, using standard T1 weighted imaging on a 3 T Philips clinical MRI scanner. A new FFC-MRI imaging method, ΔR1 mapping was employed to show an increase in contrast using a novel Mn2+ based liposomal contrast agent compared with T1 weighted images at 5 mT, 59 mT and 3 T. The low concentrations of Mn2+ based liposomal contrast agents used with ΔR1 mapping indicate suitability for molecular imaging

Magnetisation Transfer Contrast (MTC) is a well-established magnetic resonance imaging (MRI) contrast-generating mechanism, and is widely used for clarifying MR-invisible macromolecular information indirectly via MR-detectable free protons using an offresonance pre-saturation radiofrequency (RF) pulse (or MT pulse). As a result of MT pulse irradiation, magnetisation between both proton pools is exchanged and the signal intensity of mobile protons is decreased in relation to the amount of macromolecules. MTC MRI is normally implemented at a fixed magnetic field; however, it may be useful to evaluate changes of the MT effect as a function of magnetic field (B0). In order to explore fielddependent MTC experiments using a single MR instrument, two techniques are required, which enable simultaneously shifting both B0 and the resonance frequency of an RF coil (f0) during MT pulse irradiation and returning them to the original condition during MR data acquisition. Switching of B0 is achieved by fast field-cycling (FFC). FFC is a novel technique allowing B0 to shift between levels rapidly during the pulse sequence. This makes it possible to perform a number of beneficial field-dependent studies and/or to provide new MR contrast mechanisms. Switching of f0 requires an actively frequencyswitchable RF coil. This coil was designed and constructed for frequencies at and below 2.5 MHz proton Larmor frequency. The design employed PIN diodes, and enabled switching f0 between five different values. Using these techniques and tools, fielddependent MTC experiments were carried out with a control sample and samples with different concentrations of agarose gel. Due to the absence of macromolecules in the control, the MT effect was almost zero, whereas the MT effect observed in agarose samples increased with increasing concentration of macromolecules. Furthermore, MT effects ((for a given set of MT pulse conditions) were larger at higher B0.

International Telemetering Conference Proceedings / October 25-28, 1993 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Highly reliable data storage for satellites and spacecraft is a challenging technology. The space environment is a unique combination of many environmental factors which impact the reliability and even the very survival of electronic systems. The need for space qualified memory is becoming even more important with the advent of on-board data processing which requires rapid access to large data bases. This paper describes the unique environmental and design considerations that must be taken into account for a magnetic disk that is designed to operate for years in the space environment.

A field-gradient torque magnetometer has been designed and constructed which measures the magnetic moment of isotropic superconductors using a Quantum Design torque chip. The magnetometer fits onto the base of an Oxford Instruments Heliox probe; thus the temperature range is 300 mK to 20 K, in magnetic fields up to 15 T. The superconductors measured on the torque magnetometer in vacuum were NbTi wire, PbMo(_6)S(_8), and Pb(_0.75)Eu(_0.25)Mo(_6)S(_8) as a function of magnetic field, magnetic field- gradient and temperature. The utility of the torque magnetometer was demonstrated by determining the critical current density (J(_c)) and the upper critical field (B(_c2)(0)) of the samples. These superconducting properties were compared with the vibrating sample magnetometer (VSM) values, for the same samples. The change in the superconducting parameters and properties of Pb(_1-x)Eu(_x)Mo(_6)S(_8), for x = 0.0 & 0.25 were investigated. The samples were fabricated using two different heat treatment methods, which finished with hot isostatic pressing (HIP'ing) at 2000 bar and 800 C for 8 hours. To characterise the superconductors, ac resistivity, ac susceptibility, specific heat and magnetic measurements were carried out, as a function of magnetic field and temperature. From the magnetisation data, the GL parameter (k) and the Sommerfeld constant (y) were determined for the magnetic superconductor x = 0.25. For both samples, k was determined in the temperature range 6 K to T(_c), from the magnetisation data. For x = 0.0 & 0.25, the critical temperature (T(_c)), the upper critical field (B(_c2(0)), the critical current density (J(_c)) and the irreversibility fields (B(_irr)) were determined from the experimental data.

Cardiovascular disease (CVD) is a term used to describe a variety of diseases and events that impact the heart and circulatory system. CVD is the United Kingdom's (UKs) biggest killer, causing more than 50,000 premature deaths each year. Early recognition of the potential for magnetic resonance imaging (MRI) to provide a versatile, non-ionising, non-invasive, technique for the assessment of CVD resulted in the modality becoming an area of intense interest in the research, radiology and cardiology communities. The first half of this thesis reviews some of the key developments in magnetic resonance hardware and software that have led to cardiac magnetic resonance imaging (CMRI) emerging as a reliable and reproducible tool, with a range of applications ideally suited for the evaluation of cardiac morphology, function, viability, valvular disease, perfusion, and congenital cardiomyopathies. In addition to this, the advantages and challenges of imaging at 3.0T in comparison to 1.5T are discussed. The second half of this thesis presents a number of investigations that were specifically designed to explore the capability of CMRI to accurately detect subtle age and disease related changes in the human heart. Our investigations begin with a study at 1.5T that explores the clinical and scientific significance of the less frequently used measure of right ventricular function to test the hypothesis that the inclusion of this data provides a more informative assessment of overall cardiac function. The focus then shifts to imaging at 3.0T and the challenges of optimising cardiac imaging at this field strength are discussed. Normal quantitative parameters of cardiac function are established at this field strength for the left ventricle and the left atrium of local volunteers. These values are used to investigate disease related changes in left ventricle and left atrium of distinct patient cohorts. This work concludes by investigating the impact of gadolinium-based contrast agents on the quantitative parameters of cardiac function.

This thesis is concerned with the effect of static and oscillatory magnetic fields on the yield of radical recombination reactions and the proposal that such effects may constitute a possible mechanism for the interaction of environmental electromagnetic fields with biological systems. A brief overview of research pertaining to the biological effects of environmental electromagnetic fields is presented. Next, the concept of the radical pair is introduced and the theory of its behaviour in solution is examined in order to illustrate the mechanism by which magnetic fields can affect its probability of separation. Three different experimental systems involving the attack of free-radicals on DNA are presented. The extent of DNA damage is assayed in the presence and absence of a static magnetic field. These systems involve the killing of yeast cells as observed by the growth of subsequent colonies, direct observation of strand breaks to DNA, in vitro, by gel electrophoresis and the direct observation of intra- nuclear DNA damage by microgel analysis. In all systems, magnetic field effects are observed but are difficult to reproduce consistently. The design of novel apparatus for the observation of resonant radiofrequency effects is described. The application of a 30-40 MHz oscillating magnetic field is found to alter the yield of exciplex fluorescence in the photoreaction of anthracene-d₁₀ and 1,3-dicyanobenzene. The effect is interpreted in terms of a change in the efficiency of singlet andleftrightarrow; triplet interconversion in the {anthracene cation - DCB anion} radical pair when the oscillating field is in resonance with hyperfine splittings in the DCB anion radical.