The effect of nutritional supplementation on visual function

The aim of this research was to determine the effect of a lutein-based nutritional supplemented on measures of visual function in normal and ARMD-affected eyes. Thirty participants were recruited to the ARMD cohort (aged between 55 and 82 years, mean ± SD: 69.2 ± 7.8) and 46 were recruited into the normal cohort (aged between 22 and 73 years, mean ± SD: 50.0 ± 15.9). Outcome measures were distance (DVA) and near (NVA) visual acuity, contrast sensitivity (CS), photostress recovery time measured with the Eger Macular Stressometer (EMS), central visual function assessed with the Macular Mapping test (MMT), and fundus photography. Reliability studies were carried out for the EMS and the MMT. A change of 14 s is required to indicate a clinically significant change in EMS time, and a change of 14 MMT points is required to indicate a clinically significant change in MMT score. Sample sizes were sufficient for the trial to have 80% power to detect a significant clinical effect at the 5% significance level for all outcome measures in the normal cohort, and for CS in the ARMD cohort. The study demonstrated that a nutritional supplement containing 6mg lutein, 750 mg vitamin A, 250 mg vitamin C, 34 mg vitamin E, 10 mg zinc, and 0.5 mg copper had no effect on the outcome measures over nine or 18 months in normal or ARMD affected participants. The finding that nine months of antioxidant supplementation, in this case, has no significant effect on CS in ARMD-affected participants adds to the literature, and contrasts with previous RCTs, the AREDS and the LAST. This project has added to the debate about the use of nutritional supplementation prior to the onset of ARMD.

The development of calibration and adaptive filtering procedures for neuromagnetic studies of human visual function

This thesis first considers the calibration and signal processing requirements of a neuromagnetometer for the measurement of human visual function. Gradiometer calibration using straight wire grids is examined and optimal grid configurations determined, given realistic constructional tolerances. Simulations show that for gradiometer balance of 1:104 and wire spacing error of 0.25mm the achievable calibration accuracy of gain is 0.3%, of position is 0.3mm and of orientation is 0.6°. Practical results with a 19-channel 2nd-order gradiometer based system exceed this performance. The real-time application of adaptive reference noise cancellation filtering to running-average evoked response data is examined. In the steady state, the filter can be assumed to be driven by a non-stationary step input arising at epoch boundaries. Based on empirical measures of this driving step an optimal progression for the filter time constant is proposed which improves upon fixed time constant filter performance. The incorporation of the time-derivatives of the reference channels was found to improve the performance of the adaptive filtering algorithm by 15-20% for unaveraged data, falling to 5% with averaging. The thesis concludes with a neuromagnetic investigation of evoked cortical responses to chromatic and luminance grating stimuli. The global magnetic field power of evoked responses to the onset of sinusoidal gratings was shown to have distinct chromatic and luminance sensitive components. Analysis of the results, using a single equivalent current dipole model, shows that these components arise from activity within two distinct cortical locations. Co-registration of the resulting current source localisations with MRI shows a chromatically responsive area lying along the midline within the calcarine fissure, possibly extending onto the lingual and cuneal gyri. It is postulated that this area is the human homologue of the primate cortical area V4.

The role of GABAergic modulation in motor function related neuronal network activity

At rest, the primary motor cortex (M1) exhibits spontaneous neuronal network oscillations in the beta (15–30 Hz) frequency range, mediated by inhibitory interneuron drive via GABA-A receptors. However, questions remain regarding the neuropharmacological basis of movement related oscillatory phenomena, such as movement related beta desynchronisation (MRBD), post-movement beta rebound (PMBR) and movement related gamma synchronisation (MRGS). To address this, we used magnetoencephalography (MEG) to study the movement related oscillatory changes in M1 cortex of eight healthy participants, following administration of the GABA-A modulator diazepam. Results demonstrate that, contrary to initial hypotheses, neither MRGS nor PMBR appear to be GABA-A dependent, whilst the MRBD is facilitated by increased GABAergic drive. These data demonstrate that while movement-related beta changes appear to be dependent upon spontaneous beta oscillations, they occur independently of one other. Crucially, MRBD is a GABA-A mediated process, offering a possible mechanism by which motor function may be modulated. However, in contrast, the transient increase in synchronous power observed in PMBR and MRGS appears to be generated by a non-GABA-A receptor mediated process; the elucidation of which may offer important insights into motor processes.

The effects of a lutein-based supplement on objective and subjective measures of retinal and visual function in eyes with age-related maculopathy - a randomised controlled trial

Lutein and zeaxanthin are lipid-soluble antioxidants found within the macula region of the retina. Links have been suggested between increased levels of these carotenoids and reduced risk for age-related macular disease (ARMD). Therefore, the effect of lutein-based supplementation on retinal and visual function in people with early stages of ARMD (age-related maculopathy, ARM) was assessed using multi-focal electroretinography (mfERG), contrast sensitivity and distance visual acuity. A total of fourteen participants were randomly allocated to either receive a lutein-based oral supplement (treated group) or no supplement (non-treated group). There were eight participants aged between 56 and 81 years (65·50 (sd 9·27) years) in the treated group and six participants aged between 61 and 83 years (69·67 (sd 7·52) years) in the non-treated group. Sample sizes provided 80 % power at the 5 % significance level. Participants attended for three visits (0, 20 and 40 weeks). At 60 weeks, the treated group attended a fourth visit following 20 weeks of supplement withdrawal. No changes were seen between the treated and non-treated groups during supplementation. Although not clinically significant, mfERG ring 3 N2 latency (P= 0·041) and ring 4 P1 latency (P= 0·016) increased, and a trend for reduction of mfERG amplitudes was observed in rings 1, 3 and 4 on supplement withdrawal. The statistically significant increase in mfERG latencies and the trend for reduced mfERG amplitudes on withdrawal are encouraging and may suggest a potentially beneficial effect of lutein-based supplementation in ARM-affected eyes. Copyright © 2012 The Authors.

Investigation of EDFA power transients in circuit-switched and packet-switched optical networks

Erbium-doped fibre amplifiers (EDFA’s) are a key technology for the design of all optical communication systems and networks. The superiority of EDFAs lies in their negligible intermodulation distortion across high speed multichannel signals, low intrinsic losses, slow gain dynamics, and gain in a wide range of optical wavelengths. Due to long lifetime in excited states, EDFAs do not oppose the effect of cross-gain saturation. The time characteristics of the gain saturation and recovery effects are between a few hundred microseconds and 10 milliseconds. However, in wavelength division multiplexed (WDM) optical networks with EDFAs, the number of channels traversing an EDFA can change due to the faulty link of the network or the system reconfiguration. It has been found that, due to the variation in channel number in the EDFAs chain, the output system powers of surviving channels can change in a very short time. Thus, the power transient is one of the problems deteriorating system performance. In this thesis, the transient phenomenon in wavelength routed WDM optical networks with EDFA chains was investigated. The task was performed using different input signal powers for circuit switched networks. A simulator for the EDFA gain dynamicmodel was developed to compute the magnitude and speed of the power transients in the non-self-saturated EDFA both single and chained. The dynamic model of the self-saturated EDFAs chain and its simulator were also developed to compute the magnitude and speed of the power transients and the Optical signal-to-noise ratio (OSNR). We found that the OSNR transient magnitude and speed are a function of both the output power transient and the number of EDFAs in the chain. The OSNR value predicts the level of the quality of service in the related network. It was found that the power transients for both self-saturated and non-self-saturated EDFAs are close in magnitude in the case of gain saturated EDFAs networks. Moreover, the cross-gain saturation also degrades the performance of the packet switching networks due to varying traffic characteristics. The magnitude and the speed of output power transients increase along the EDFAs chain. An investigation was done on the asynchronous transfer mode (ATM) or the WDM Internet protocol (WDM-IP) traffic networks using different traffic patterns based on the Pareto and Poisson distribution. The simulator is used to examine the amount and speed of the power transients in Pareto and Poisson distributed traffic at different bit rates, with specific focus on 2.5 Gb/s. It was found from numerical and statistical analysis that the power swing increases if the time interval of theburst-ON/burst-OFF is long in the packet bursts. This is because the gain dynamics is fast during strong signal pulse or with long duration pulses, which is due to the stimulatedemission avalanche depletion of the excited ions. Thus, an increase in output power levelcould lead to error burst which affects the system performance.

Vertical and horizontal scope economies in the regulated US electricity power industry

This paper investigates vertical economies between generation and distribution of electric power, and horizontal economies between different types of power generation in the U.S. electric utility industry. Our quadratic cost function model includes three generation output measures (hydro, nuclear and fossil fuels), which allows us to analyze the effect that generation mix has on vertical economies. Our results provide (sample mean) estimates of vertical economies of 8.1% and horizontal economies of 5.4%. An extensive sensitivity analysis is used to show how the scope measures vary across alternative model specifications and firm types. © 2012 Blackwell Publishing Ltd and the Editorial Board of The Journal of Industrial Economics.

NADPH oxidase signaling and cardiac myocyte function

The NADPH oxidase family of enzymes has emerged as a major source of reactive oxygen species (ROS) that is important in diverse cellular functions including anti-microbial defence, inflammation and redox signaling. Of the five known NADPH oxidase isoforms, several are expressed in cardiovascular cells where they are involved in physiological and pathological processes such as the regulation of vascular tone, cell growth, migration, proliferation, hypertrophy, apoptosis and matrix deposition. This article reviews current knowledge regarding the role of NADPH oxidases in cardiomyocyte function in health and disease. © 2009 Elsevier Inc. All rights reserved.

An interdisciplinary approach to designing and evaluating a hybrid solar-biomass power plant

Purpose: Energy security is a major concern for India and many rural areas remain un-electrified. Thus, innovations in sustainable technologies to provide energy services are required. Biomass and solar energy in particular are resources that are widely available and underutilised in India. This paper aims to provide an overview of a methodology that was developed for designing and assessing the feasibility of a hybrid solar-biomass power plant in Gujarat. Design/methodology/approach: The methodology described is a combination of engineering and business management studies used to evaluate and design solar thermal collectors for specific applications and locations. For the scenario of a hybrid plant, the methodology involved: the analytical hierarchy process, for solar thermal technology selection; a cost-exergy approach, for design optimisation; quality function deployment, for designing and evaluating a novel collector - termed the elevation linear Fresnel reflector (ELFR); and case study simulations, for analysing alternative hybrid plant configurations. Findings: The paper recommended that for a hybrid plant in Gujarat, a linear Fresnel reflector of 14,000 m2 aperture is integrated with a 3 tonne per hour biomass boiler, generating 815 MWh per annum of electricity for nearby villages and 12,450 tonnes of ice per annum for local fisheries and food industries. However, at the expense of a 0.3 ¢/kWh increase in levelised energy costs, the ELFR can increase savings of biomass (100 t/a) and land (9 ha/a). Research limitations/implications: The research reviewed in this paper is primarily theoretical and further work will need to be undertaken to specify plant details such as piping layout, pump sizing and structure, and assess plant performance during real operational conditions. Originality/value: The paper considers the methodology adopted proved to be a powerful tool for integrating technology selection, optimisation, design and evaluation and promotes interdisciplinary methods for improving sustainable engineering design and energy management. © Emerald Group Publishing Limited.

Reciprocating power generation in a chemically driven synthetic muscle

A scalable synthetic muscle has been constructed that transducts nanoscale molecular shape changes into macroscopic motion. The working material, which deforms affinely in response to a pH stimulus, is a self-assembled block copolymer comprising nanoscopic hydrophobic domains in a weak polyacid matrix. A device has been assembled where the muscle does work on a cantilever and the force generated has been measured. When coupled to a chemical oscillator this provides a free running chemical motor that generates a peak power of 20 mW kg 1 by the serial addition of 10 nm shape changes that scales over 5 orders of magnitude. It is the nanostructured nature of the gel that gives rise to the affine deformation and results in a robust working material for the construction of scalable muscle devices.

Mechanical properties and the evolution of matrix molecules in PTFE upon irradiation with MeV alpha particles

The morphology, chemical composition, and mechanical properties in the surface region of α-irradiated polytetrafluoroethylene (PTFE) have been examined and compared to unirradiated specimens. Samples were irradiated with 5.5 MeV 4He2+ ions from a tandem accelerator to doses between 1 × 106 and 5 × 1010 Rad. Static time-of-flight secondary ion mass spectrometry (ToF-SIMS), using a 20 keV C60+ source, was employed to probe chemical changes as a function of a dose. Chemical images and high resolution spectra were collected and analyzed to reveal the effects of a particle radiation on the chemical structure. Residual gas analysis (RGA) was utilized to monitor the evolution of volatile species during vacuum irradiation of the samples. Scanning electron microscopy (SEM) was used to observe the morphological variation of samples with increasing a particle dose, and nanoindentation was engaged to determine the hardness and elastic modulus as a function of a dose. The data show that PTFE nominally retains its innate chemical structure and morphology at a doses <109 Rad. At α doses ≥109 Rad the polymer matrix experiences increased chemical degradation and morphological roughening which are accompanied by increased hardness and declining elasticity. At  α doses >1010 Rad the polymer matrix suffers severe chemical degradation and material loss. Chemical degradation is observed in ToF-SIMS by detection of ions that are indicative of fragmentation, unsaturation, and functionalization of molecules in the PTFE matrix. The mass spectra also expose the subtle trends of crosslinking within the α-irradiated polymer matrix. ToF-SIMS images support the assertion that chemical degradation is the result of a particle irradiation and show morphological roughening of the sample with increased a dose. High resolution SEM images more clearly illustrate the morphological roughening and the mass loss that accompanies high doses of a particles. RGA confirms the supposition that the outcome of chemical degradation in the PTFE matrix with continuing irradiation is evolution of volatile species resulting in morphological roughening and mass loss. Finally, we reveal and discuss relationships between chemical structure and mechanical properties such as hardness and elastic modulus.

Effect of thermal residual stresses on fatigue crack opening and propagation behavior in an Al/SiCp metal matrix composite

The effects of a thermal residual stress field on fatigue crack growth in a silicon carbide particle-reinforced aluminum alloy have been measured. Stress fields were introduced into plates of material by means of a quench from a solution heat-treatment temperature. Measurements using neutron diffraction have shown that this introduces an approximately parabolic stress field into the plates, varying from compressive at the surfaces to tensile in the center. Long fatigue cracks were grown in specimens cut from as-quenched plates and in specimens which were given a stress-relieving overaging heat treatment prior to testing. Crack closure levels for these cracks were determined as a function of the position of the crack tip in the residual stress field, and these are shown to differ between as-quenched and stress-relieved samples. By monitoring the compliance of the specimens during fatigue cycling, the degree to which the residual stresses close the crack has been evaluated. © 1995 The Minerals, Metals & Material Society.

Comparison of the ageing behaviour of PM 2124 Al alloy and Al-SiCp metal-matrix composite

The ageing response of 2124 Al-SiC particulate metal-matrix composite (MMC) and unreinforced alloy has been examined using hardness measurements and Arrhenius analysis. The formation of phases during precipitation has been studied using differential scanning calorimetry (DSC). The MMC exhibits accelerated ageing compared to unreinforced alloy, due to enhanced S′ formation. The activation energy for diffusion is lower in the MMC than in the unreinforced alloy. DSC scans show Guinier-Preston B (GPB) zone nucleation to occur at a lower temperature in the MMC, whilst the total volume of GPB zones formed is smaller than in the unreinforced alloy. A model has been proposed to explain the GPB zone formation behaviour, in which ease of GPB zone nucleation varies within the MMC, as a function of ageing time and of position within the matrix. S′ formation is enhanced in the MMC because of improved diffusion and a large increase in density of heterogeneous nucleation sites compared to the unreinforced alloy. © 1994 Chapman & Hall.

The effect of microstructure on the fracture toughness of a metal-matrix composite

The fracture behaviour and plane strain fracture toughness, KIC, of four 8090-based metal-matrix composites containing 20 weight % SiC particles, 3, 6 and 23 μm in diameter, has been evaluated as a function of matrix ageing condition. Toughness values are found to be almost independent of reinforcement size. Ageing at 170°C results in a monotonic decrease in toughness with increasing strength up to the peak condition, with no subsequent recovery in toughness on overageing. However, unlike reinforced 8090, the composites are not found to be susceptible to intergranular embrittlement on overageing. The observed trends are found to be independent of reinforcement size. These findings are explained in terms of the strength, work hardening behaviour and nature and distribution of void-nucleating particles in the matrix. © 1993.

Heavy ion irradiation effects in zirconium nitride

Polycrystalline zirconium nitride (ZrN) samples were irradiated with He +, Kr ++, and Xe ++ ions to high (>1·10 16 ions/cm 2) fluences at ∼100 K. Following ion irradiation, transmission electron microscopy (TEM) and grazing incidence X-ray diffraction (GIXRD) were used to analyze the microstructure and crystal structure of the post-irradiated material. For ion doses equivalent to approximately 200 displacements per atom (dpa), ZrN was found to resist any amorphization transformation, based on TEM observations. At very high displacement damage doses, GIXRD measurements revealed tetragonal splitting of some of the diffraction maxima (maxima which are associated with cubic ZrN prior to irradiation). In addition to TEM and GIXRD, mechanical property changes were characterized using nanoindentation. Nanoindentation revealed no change in elastic modulus of ZrN with increasing ion dose, while the hardness of the irradiated ZrN was found to increase significantly with ion dose. Finally, He + ion implanted ZrN samples were annealed to examine He gas retention properties of ZrN as a function of annealing temperature. He gas release was measured using a residual gas analysis (RGA) spectrometer. RGA measurements were performed on He-implanted ZrN samples and on ZrN samples that had also been irradiated with Xe ++ ions, in order to introduce high levels of displacive radiation damage into the matrix. He evolution studies revealed that ZrN samples with high levels of displacement damage due to Xe implantation, show a lower temperature threshold for He release than do pristine ZrN samples.