In The Prevention Of Cross Infection With Measles In An Acute, Paediatric Ward

A CAJM article on a measles vaccine

Universality and programmability of quantum computers

Manin, Feynman, and Deutsch have viewed quantum computing as a kind of universal physical simulation procedure. Much of the writing about quantum logic circuits and quantum Turing machines has shown how these machines can simulate an arbitrary unitary transformation on a finite number of qubits. The problem of universality has been addressed most famously in a paper by Deutsch, and later by Bernstein and Vazirani as well as Kitaev and Solovay. The quantum logic circuit model, developed by Feynman and Deutsch, has been more prominent in the research literature than Deutsch's quantum Turing machines. Quantum Turing machines form a class closely related to deterministic and probabilistic Turing machines and one might hope to find a universal machine in this class. A universal machine is the basis of a notion of programmability. The extent to which universality has in fact been established by the pioneers in the field is examined and this key notion in theoretical computer science is scrutinised in quantum computing by distinguishing various connotations and concomitant results and problems.Comment: 17 pages, expands on arXiv:0705.3077v1 [quant-ph

On improving the cost-effective dispersion of calcium carbonate in polypropylene for impact resistance

The potential to improve the performance of polymer composites cost-effectively has been researched across various aspects of development and manufacture. Each endeavour fell broadly into one of three categories; the principal ingredients and their required properties, the methods with which they were transformed into products and the means by which they were observed. It was determined that the ingredients with the highest potential as defined, each shared simplicity and abundance as material traits. The use of bespoke functionalised ingredients proved costly to implement, providing only modest property benefits compared to a standard formulation comprising polypropylene, 10 – 30 % w/w of 2 μm calcium carbonate with 0.5 – 1.0 % w/w stearic acid surface treatment. It was found that an apparent deterioration in impact resistance that was encountered on reducing the filler particle size was in each case observed, attributable to a coarsening of these fine particles that resulted from the mixing process. Finer particles could not be implemented more cost-effectively than standard formulations; an effect which was attributed to the tendency of the finest particles to form aggregates that could not be decomposed by mixing under high shear. However, the favourability of particle dispersion in standard formulations was used to implement a production method of polymer composites that required significantly less energy across the entire production stage and held other significant advantages. Concentrates comprising minerals in wax were produced and made to successfully re-disperse from loadings approaching those allowed by their theoretical packing maxima, in some cases up to 90 % w/w. Furthermore, a single injection moulding cycle with minimal back-mixing was used to combine concentrates and neat polymers to make commercially-competitive composite specimens, at final concentrations as low as 10 % w/w. A principal method to obtain in situ visual particle data from thin composite films was developed along with several derivative analyses. The techniques allowed rapid and representative data collection for high particle proportions at resolutions of 6 – 8 μm, accounting for particles most relevant to impact-resistance in standard formulations. As a whole, significant and realistic saving opportunities were identified in the expenditure of unnecessary resources, such as; processing energy, capital investment, transportation, labour and time. These findings were supported by experimental data

Integrated geophysical studies at Masaya volcano, Nicaragua

Research into the mechanisms responsible for the lasting, cyclic activity at Masaya volcano can lead to a better understanding of persistently degassing volcanoes. This study is greatly enhanced by the integration of dynamic micro-gravity, deformation and gas flux measurements. The acquisition of extended temporal and spatial geophysical data will also allow for the development of robust models for the dynamics of magmatic systems. Masaya volcano, Nicaragua, is one of the most active systems in Central America, making it an excellent natural laboratory for this study. It is noted for repeated episodes of lava lake formation, strong degassing and subsequent quiescence. Ground-based geophysical measurements show two episodes of similar magnitude gravity decreases in 1993-1994 and 1997-1999, separated by a period of minor gravity increase. A major increase in SO2 gas flux from 1997-1999 correlates well with the most recent episode of gravity decrease. The gravity changes are not accompanied by deformation in the summit areas and are interpreted in terms of sub-surface density changes. The persistent degassing at Masaya suggests that up to ~15 km3 of magma may have degassed over the last 150 years, only a minute fraction of which has been erupted. Furthermore, thermal flux calculations suggest that 0.5 km3 of magma (the estimated volume of the shallow reservoir) would cool from liquidus to just above solidus temperatures in only 5 years. The high rates of degassing and cooling at open-system volcanoes such as Masaya raise questions as to the ultimate fate of this degassed and cooled magma. A number of models have been proposed to explain this, but the most likely mechanism to explain persistent activity at Masaya and other similar volcanoes is convective removal of cooled and degassed magma and subsequent recharge by volatile-rich magma from depth. Another fundamental question in modem volcanology concerns the manner in which a volcanic eruption is triggered; the intrusion of fresh magma into a reservoir is thought to be a key component. The amount by which previously ponded reservoir magma interacts with a newly intruded magma will determine the nature and rate of eruption as well as the chemistry of erupted lavas and shallow dykes. The physics of this interaction can be investigated through a conventional monitoring procedure that incorporates the Mogi model relating ground deformation (∆h) to changes in volume of a magma reservoir. Gravity changes (∆g)combined with ground deformation provides information on magma reservoir mass changes. Models developed here predict how, during inflation, the observed .1.gI~ gradient will evolve as a volcano develops from a state of dormancy through unrest into a state of explosive activity

Cyclic factorizability theories

Let r denote a finite group and R a commutative ring. Factorizability theories seek to describe similarities between the local structure of R1-modules M and N, where M and N are related by, for example, being isomorphic when tensored up with Q. In the first three chapters of this thesis, we define two families of factorizability theories, the invariance and coinvariance factorizability theories. We will consider three members of these families. We demonstrate that monomial invariance factorizability is equivalent to monomial factorizability as defined in [19]. We go on to consider the two cyclic cases. We demonstrate that the weak cyclic invariance factorizability theory is strict and is identical to the weak cyclic coinvariance factorizability theory. We also demonstrate that the strong cyclic invariance factorizability theory and the strong cyclic coinvariance factorizability theory are not identical but are equivalent. In chapters 4 and 5, we discuss C.M.M. F-functors over R. Thus we find relations which can simplify the calculation of the invariance and coinvariance factorizability theories. An index of the less well known definitions used in this thesis is included as an appendix

Investigation of the structure and phase transitions in the novel A-site substituted perovskite series (Na1-xKx)0.5Bi0.5TiO

An extensive study of the crystal structure and phase transitions in Na0.5Bi0.5TiO3 has been carried out using neutron/x-ray powder, and single-crystal x-ray, diffraction techniques. This has been complemented with optical and Raman studies. The sequence of phase transitions from the high-temperature prototypic cubic structure (above 813 K), to one of tetragonal (673-773 K) and then rhombohedral structure (5-528 K) has been established in Na0.5Bi0.5TiO3. Coexisting tetragonal/cubic (773-813 K) and rhombohedral/tetragonal (528-673 K) phases have also been observed. Rietveld refinements have revealed the rhombohedral phase, space group Ric, exhibits an antiphase, a-a-a- oxygen octahedra tilt system, with parallel cation displacements. The tetragonal phase, space group P4bm, possesses an unusual combination of in-phase, a0a0c+ oxygen octahedra tilts and antiparallel cation displacements along the polar axis. This structure type is unprecedented amongst the perovskites. A high-pressure study using synchrotron and neutron diffraction has revealed the ambient pressure rhombohedral structure undergoes a phase transition to an orthorhombic structure with Pnma symmetry and the a-b+a- oxygen octahedra tilt system together with antiparallel A-cation ordering along [010]. The pure rhombohedral structure persists up to 8 kbar; between 10-19.4 kbar a rhombohedral/orthorhombic coexistence region was observed and above 26.2 kbar the purely orthorhombic phase was seen. Structural variations as a function of temperature, pressure and doping across the (Na1-xKx)0.5Bi0.5TiO3 series are also presented. With increasing potassium doping across this series, phase transitions from the rhombohedral structure with octahedral tilting to a non-tilted rhombohedral structure (space group, Ram) and then to a tetragonal structure (space group P4mm) was observed. A basic phase diagram for this series has been assembled outlining phase boundaries across the series and as a function of temperature. In this study, the optimum conditions used for the fabrication of powders, ceramics and single crystals of the perovskite compound Na0.5Bi0.5TiO3 and the solid solution across the (Na1-xKx)0.5Bi0.5TiO3 series have been established. A detailed analysis of this A-site substituted distorted perovskite compound is made with structural variations, cation displacements and octahedral distortions for the different phases being reported. The A-site substituted compounds are thoroughly discussed in the context of modem perovskite science

Volcanic eruption prediction: Magma chamber physics from gravity and deformation measurements

One of the greatest remaining problems in modern volcanology is the process by which volcanic eruptions are triggered. It is generally accepted that eruptions are preceded by magma intrusion [Sigurdsson and Sparks, 1978]. The degree of interaction between previously ponded magma in a chamber and newly intruded magma determines the nature and rate of eruption and also the chemistry of erupted lavas and shallow dykes. Here, we investigate the physics of this interaction. Volcano monitoring at its most effective is a synergy between basic science and risk assessment, while hazard mitigation depends on reliable interpretation of eruption precursors. The simple and much used Mogi model relates ground deformation (?h) to changes in magma chamber volume. Gravity changes (?g) combined with ground deformation provide information on magma chamber mass changes. Our new models predict how the ?g/?h gradient will evolve as a volcano develops from a state of dormancy through unrest into a state of explosive activity. Thus by simultaneous measurement of deformation and gravity at a few key stations, magma chamber processes can be identified prior to the onset of conventional eruption precursors

Heathland responses to nitrogen deposition : exploring the role of habitat management and soil biochemistry

Elevated levels of nitrogen deposition are altering the normal functioning of seminatural ecosystems around the world. Of concern in Europe are the nitrogen driven changes occurring to (semi)-natural ecosystems such as obrotrophic bogs, upland moors and lowland heathland. Lowland heathland is a particularly vulnerable oligotrophic habitat, with a narrow climatic optimum that restricts the remaining fragmented patches to a small corner of highly populated northwestern Europe. Increased nitrogen availability reduces the competitiveness of characteristic heathland plants, such as Calluna vulgaris, that are adapted to situations where nitrogen is the limiting nutrient. Resulting changes such as accelerated productivity, increased herbivore and frost damage, and changes in the nutrient limitation status of heathlands can lead to invasion by nitrophilous graminoid species, but this process may be dependent on (1) the intensity and duration of elevated nitrogen inputs, (2) the relative availability of other nutrients and (3) conservation management intended to reduce overall nutrient levels. The present study investigated the effects of nitrogen deposition in N and P limited vegetation, and in heathlands around the UK that are experiencing anthropogenically enhanced background levels of nitrogen deposition. Physical and biochemical parameters of vegetation, litter and soil were used as indicators. A long-term fieldscale manipulation study at Thursley Common, Surrey was used to quantify the effect of nitrogen inputs to an N limited system and, in particular, determine how these effects were modified by a gradient of management intensity, and an unplanned wildfire. The process of vegetation recovery, following a cessation of nitrogen inputs was also investigated. The effects of nitrogen deposition to P limited heathland were investigated using heathland mesocosms. Two nationwide heathland surveys investigated how the effect of nitrogen deposition within a gradient of background deposition in England was modified by environmental factors, such as geology or soil type. The first survey examined the effect of stand age (and management) on responses to nitrogen deposition. The second survey focused on the physical and biochemical responses to nitrogen deposition in Calluna, litter, bryophytes and soil to quantify its impact on heathlands across England. The Thursley nitrogen manipulation investigation showed clear ongoing responses in rates of canopy development and shoot growth to nitrogen deposition, which were reduced by increasing levels of management intensity. Historical nitrogen inputs in the recovery experiment continued to significantly increase rates of Calluna canopy development 9 years after inputs had ceased. These effects were re-invigorated by the unplanned wildfire. The mesocosm experiment indicated that P limited heathlands are susceptible to the detrimental effects of nitrogen deposition, particularly, altering shoot phenology and increasing drought stress. Both the nationwide surveys indicated that, at a national scale, heathland vegetation and soil biochemical indices are responsive to background nitrogen deposition levels within (and exceeding) the critical load range, despite environmental influences, such as geology and soil type which were also found to have significant effects on these parameters