The optical properties of automatically darkening welding filters based on liquid crystal technology

This thesis addresses the problem of the poor optical angular properties displayed by the majority of automatically darkening welding filters currently on the market that are based on liquid crystal technology. It is shown that by reducing the twist-angle present in the liquid crystal cell to below that of 90 together with employment of a novel polariser arrangement, an optical shutter design based on a double-cell construction is obtained that boasts a reduced angular transmittance variation when in the activated phase. This gives an optical filter possessing a wide central viewing cone whilst maintaining the remaining optical parameters at a high level. The only point of compromise comes from the voltage increase requirement upon reduction of the twist- angle in order to maintain cell contrast. Although this inflates the power consumption of the system, beneficial effects upon the total light scattering provoked by the device are also observed. The final sections deal with a new mode of operation for a twisted-nematic liquid crystal cell when placed between crossed polarisers together with an interference filter possessing a high optical transmittance over the central part of the visible spectrum. This mode of operation means that the cell is in a dark state when inactivated. Application of a small stimulating voltage transmutes the unit into the light state, where upon further increment of the driving electronics beyond this point reverts the system back into a low transmittance phase. Such a mode of operation for a twisted-nematic cell offers several advantages over that of the normally white mode when considering the optical lens of an automatically darkening welding filter. In particular, a dark, fail-safe state is provided should the controlling electronics malfunction preventing the unit from holding in a potentially hazardous light phase, a property usually associated with the normally black mode of operation, whilst the fast switching speed from the light to the dark state associated with the normally white mode of operation is maintained. It is shown that there are only two cell types that display this phenomenon and the optical properties of these two systems are analysed in some detail with the view of developing an automatically darkening welding filter based on this technology. This thesis is submitted to the University of Durham for the degree of Master of Science. All work contained within this thesis was carried out by the author at Hornell Innovation AB in Sweden. No material contained within has been submitted for a previous degree and the copyright of this thesis rests with the author. No quotation from it should be published without his prior written consent and information derived from it should be acknowledged

Outer-Sphere Effects on Reduction Potentials of Copper Sites in Proteins: The Curious Case of High Potential Type 2 C112D/M121E Pseudomonas aeruginosa Azurin

Redox and spectroscopic (electronic absorption, multifrequency electron paramagnetic resonance (EPR), and X-ray absorption) properties together with X-ray crystal structures are reported for the type 2 Cu^(II) C112D/M121E variant of Pseudomonas aeruginosa azurin. The results suggest that Cu^(II) is constrained from interaction with the proximal glutamate; this structural frustration implies a “rack” mechanism for the 290 mV (vs NHE) reduction potential measured at neutral pH. At high pH (~9), hydrogen bonding in the outer coordination sphere is perturbed to allow axial glutamate ligation to Cu^(II), with a decrease in potential to 119 mV. These results highlight the role played by outer-sphere interactions, and the structural constraints they impose, in determining the redox behavior of transition metal protein cofactors

Improving reintroduction success in large carnivores through individual-based modelling: how to reintroduce Eurasian lynx (<i>Lynx lynx</i>) to Scotland

Globally, large carnivores have been heavily affected by habitat loss, fragmentation and persecution, sometimes resulting in local extinctions. With increasing recognition of top-down trophic cascades and complex predator- prey dynamics, reintroductions are of growing interest for restoration of ecosystem functioning. Many re- introductions have however failed, in part due to poor planning and inability to model complex eco-evolutionary processes to give reliable predictions. Using the case study of Eurasian lynx (Lynx lynx), a large predator being considered for reintroduction to Scotland, we demonstrate how an individual-based model that integrates demography with three distinct phases of dispersal (emigration, transfer and settlement) can be used to explore the relative suitability of three geographically-distant potential reintroduction sites, multi-site reintroductions and two founding population sizes. For a single-site reintroduction of 10 lynx, our simulation results show a clear hierarchy of suitability across all metrics. Reintroduction in the Kintyre Peninsula (west coast) consistently performed best, with a probability of population persistence at year 100 of 83%, and the Scottish component of Kielder Forest (southern Scotland) worst, with only a 21% chance of population persistence to year 100. Simultaneous two-site reintroduction in the Kintyre Peninsula and in Aberdeenshire (near the east coast) of 32 lynx gave a 96% persistence at 100 years. Our model was highly sensitive to survival, particularly of adults, highlighting this parameter's importance for reintroduction success. The results strongly indicate the potential viability of Eurasian lynx reintroduction to Scotland given the current cover of suitable woodland habitat. More generally, our work demonstrates how emerging modelling approaches incorporating increased realism in re- presenting species' demography, ecology and dispersal can have high value for quick, inexpensive assessment of likely reintroduction success and for selection between alternative strategies

Aspects of Sporinite Chemistry

With the recent advent of the ability to separate coal into maceral concentrates of high purity, the individual constituents of coal can now be analyzed separately, without their mutual interference, giving a much better understanding of the macromolecular structure of coal. The sporinites from two Pennsylvanian age coal samples (Illinois Basin, U.S.A.) were studied, one from a vitrinite-rich high-volatile bituminous coal, the other from a liptinite-rich high-volatile bituminous coal of slightly higher rank. Sporinites were isolated from each coal by density gradient centrifugation. The sporinite of the vitrinite-rich coal was compared chemically and petrographically with the parent coal and with the sporinite of the liptinite-rich coal. The fluorescence spectrum of the sporinite from the liptinite-rich coal is shifted to the red end of the spectrum, which may be accounted for by the somewhat higher rank of the sample and/or by differences in the original assemblage of spores. The lack of chemical differences between the extracts of the sporinite and its whole coal reinforce the concept of bitumen as an homogeneous mobile phase pervading the coal. Thus, extract chemistry seems an unsuitable technique for distinguishing between macerals from the same coal. Hopane and sterane distributions in the sporinite and parent coal pyrolyzates are very similar, but the two materials can be readily distinguished by the distribution of tetracyclic diterpanes of the phyllocladane type, which are biological marker compounds derived from higher plant material. Overall, the sporinite is considerably more paraffinic in character and has a greater preponderance of straight-chain alkane moieties than the coal as a whole. In the case of the vitrinite-rich coal, the whole-coal structure appears significantly more polyaromatic than the sporinite. The distributions of thiophenic compounds differ in the pyrolyzates of the two materials. The sporinite from the liptinite-rich coal is even less polycondensed than the sporinite from the vitrinite-rich sample. The chemical and petrographic differences of the two sporinites probably reflect the different assemblages of spores in the original peats and their different diagenetic histories

Characterization of Organic Sulfur Compounds in Coals and Coal Macerals

Peroxyacetic acid oxidation has been used to investigate the type and distribution of organic sulfur species in samples of vitrinite, sporinite and inertinite, separated from the Herrin No.6 and an Indiana No.5 coal seam. It was established that organic sulfur species were selectively preserved during oxidation and their analysis led to some of the first sulfur-33 NMR spectra obtained for coal. The effects of maceral separation processes on model compounds were also studied. Results from our studies support the following conclusions: 1). Different macerals have different distributions and types of organic sulfur species. 2). Organic sulfur compounds in coal occur at the ends of macromolecular structures. 3). Maceral separation techniques do not affect organic sulfur species in coal. 4). Maceral separation is essential for the chemical characterization of coal. 5). GC-MS and sulfur-33 NMR data agree

Towards a radiocarbon calibration for oxygen isotope stage 3 using New Zealand kauri (Agathis australis)

It is well known that radiocarbon years do not directly equate to calendar time. As a result, considerable effort has been devoted to generating a decadally resolved calibration curve for the Holocene and latter part of the last termination. A calibration curve that can be unambiguously attributed to changes in atmospheric ¹⁴C content has not, however, been generated beyond 26 kyr cal BP, despite the urgent need to rigorously test climatic, environmental, and archaeological models. Here, we discuss the potential of New Zealand kauri (Agathis australis) to define the structure of the ¹⁴C calibration curve using annually resolved tree rings and thereby provide an absolute measure of atmospheric ¹⁴C. We report bidecadally sampled ¹⁴C measurements obtained from a floating 1050-yr chronology, demonstrating repeatable ¹⁴C measurements near the present limits of the dating method. The results indicate that considerable scope exists for a high-resolution ¹⁴C calibration curve back through OIS-3 using subfossil wood from this source

Mapping the Galactic Halo. V. Sgr dSph Tidal Debris 60 degrees from the Main Body

As part of the Spaghetti Project Survey (SPS) we have detected a concentration of giant stars well above expectations for a smooth halo model. The position (l~350, b~50) and distance (~50 kpc) of this concentration match those of the Northern over-density detected by SDSS (Yanny et al. 2000, Ivezic et al. 2000). We find additional evidence for structure at ~80 kpc in the same direction. We present radial velocities for many of these stars, including the first published results from the 6.5m Magellan telescope. The radial velocities for stars in these structures are in excellent agreement with models of the dynamical evolution of the Sgr dwarf tidal debris, whose center is 60 degrees away. The metallicity of stars in these streams is lower than that of the main body of the Sgr dwarf, which may indicate a radial metallicity gradient prior to disruption.Comment: 10 pages, 3 figures accepted in Astrophysical Journal Letter

Improving reintroduction success in large carnivores through individual-based modelling: How to reintroduce Eurasian lynx (Lynx lynx) to Scotland

Globally, large carnivores have been heavily affected by habitat loss, fragmentation and persecution, sometimes resulting in local extinctions. With increasing recognition of top-down trophic cascades and complex predator- prey dynamics, reintroductions are of growing interest for restoration of ecosystem functioning. Many re- introductions have however failed, in part due to poor planning and inability to model complex eco-evolutionary processes to give reliable predictions. Using the case study of Eurasian lynx (Lynx lynx), a large predator being considered for reintroduction to Scotland, we demonstrate how an individual-based model that integrates demography with three distinct phases of dispersal (emigration, transfer and settlement) can be used to explore the relative suitability of three geographically-distant potential reintroduction sites, multi-site reintroductions and two founding population sizes. For a single-site reintroduction of 10 lynx, our simulation results show a clear hierarchy of suitability across all metrics. Reintroduction in the Kintyre Peninsula (west coast) consistently performed best, with a probability of population persistence at year 100 of 83%, and the Scottish component of Kielder Forest (southern Scotland) worst, with only a 21% chance of population persistence to year 100. Simultaneous two-site reintroduction in the Kintyre Peninsula and in Aberdeenshire (near the east coast) of 32 lynx gave a 96% persistence at 100 years. Our model was highly sensitive to survival, particularly of adults, highlighting this parameter's importance for reintroduction success. The results strongly indicate the potential viability of Eurasian lynx reintroduction to Scotland given the current cover of suitable woodland habitat. More generally, our work demonstrates how emerging modelling approaches incorporating increased realism in re- presenting species' demography, ecology and dispersal can have high value for quick, inexpensive assessment of likely reintroduction success and for selection between alternative strategies.REF Compliant by Deposit in Stirling's Repositor

Neighbourhood green space, physical function and participation in physical activities among elderly men: the Caerphilly Prospective study

Background: The built environment in which older people live plays an important role in promoting or inhibiting physical activity. Most work on this complex relationship between physical activity and the environment has excluded people with reduced physical function or ignored the difference between groups with different levels of physical function. This study aims to explore the role of neighbourhood green space in determining levels of participation in physical activity among elderly men with different levels of lower extremity physical function. Method: Using data collected from the Caerphilly Prospective Study (CaPS) and green space data collected from high resolution Landmap true colour aerial photography, we first investigated the effect of the quantity of neighbourhood green space and the variation in neighbourhood vegetation on participation in physical activity for 1,010 men aged 66 and over in Caerphilly county borough, Wales, UK. Second, we explored whether neighbourhood green space affects groups with different levels of lower extremity physical function in different ways. Results: Increasing percentage of green space within a 400 meters radius buffer around the home was significantly associated with more participation in physical activity after adjusting for lower extremity physical function, psychological distress, general health, car ownership, age group, marital status, social class, education level and other environmental factors (OR = 1.21, 95% CI 1.05, 1.41). A statistically significant interaction between the variation in neighbourhood vegetation and lower extremity physical function was observed (OR = 1.92, 95% CI 1.12, 3.28). Conclusion: Elderly men living in neighbourhoods with more green space have higher levels of participation in regular physical activity. The association between variation in neighbourhood vegetation and regular physical activity varied according to lower extremity physical function. Subjects reporting poor lower extremity physical function living in neighbourhoods with more homogeneous vegetation (i.e. low variation) were more likely to participate in regular physical activity than those living in neighbourhoods with less homogeneous vegetation (i.e. high variation). Good lower extremity physical function reduced the adverse effect of high variation vegetation on participation in regular physical activity. This provides a basis for the future development of novel interventions that aim to increase levels of physical activity in later life, and has implications for planning policy to design, preserve, facilitate and encourage the use of green space near home