Fibre Bragg gratings fabrication in four core fibres

Due to the limitation of the lens effect of the optical fibre and the inhomogeneity of the laser fluence on different cores, it is still challenging to controllably inscribe different fibre Bragg gratings (FBGs) in multicore fibres. In this article, we reported the FBG inscription in four core fibres (FCFs), whose cores are arranged in the corners of a square lattice. By investigating the influence of different inscription conditions during inscription, different results, such as simultaneous inscription of all cores, selectively inscription of individual or two cores, and even double scanning in perpendicular core couples by diagonal, are achieved. The phase mask scanning method, consisting of a 244nm Argon-ion frequencydoubled laser, air-bearing linear transfer stage and cylindrical lens and mirror setup, is used to precisely control the grating inscription in FCFs. The influence of three factors is systematically investigated to overcome the limitations, and they are the defocusing length between the cylindrical lens and the bare fibre, the rotation geometry of the fibre to the irritation beam, and the relative position of the fibre in the vertical direction of the laser beam.

Velocity distributions in a plate heat exchanger channel

The development of a Laser Doppler Anemometer technique to measure the velocity distribution in a commercial plate heat exchanger is described. Detailed velocity profiles are presented and a preliminary investigation is reported on flow behaviour through a single cell in the channel matrix. The objective of the study was to extend previous investigations of plate heat exchanger flow patterns in the laminar range with the eventual aim of establishing the effect of flow patterns on heat transfer performance, thus leading to improved plate heat exchanger design and design methods. Accurate point velocities were obtained by Laser Anemometry in a perspex replica of the metal channel. Oil was used as a circulating liquid with a refractive index matched to that of the perspex so that the laser beams were not distorted. Cell-by-cell velocity measurements over a range of Reynolds number up to ten showed significant liquid mal-distribution. Local cell velocities were found to be as high as twenty seven times average velocity, contrary to the previously held belief of four times. The degree of mal-distribution varied across the channel as well as in the vertical direction, and depended on the upward or downward direction of flow. At Reynolds numbers less than one, flow zig-zagged from one side of the channel to the other in wave form, but increases in Reynolds number improved liquid distribution. A detailed examination of selected cells showed velocity variations in different directions, together with variation within individual cells. Experimental results are also reported on the flow split when passing through a single cell in a section of a channel . These observations were used to explain mal-distribution in the perspex channel itself.

High stability interleaved fibre Michelson interferometer for on-line precision displacement measurements

A self-reference fiber Michelson interferometer measurement system, which employs fiber Bragg gratings (FBGs) as in-fiber reflective mirrors and interleaves together two fiber Michelson interferometers that share the common-interferometric-optical path, is presented. One of the fiber interferometers is used to stabilise the system by the use of an electronic feedback loop to compensate the influences resulting from the environmental disturbances, while the other one is used to perform the measurement task. The influences resulting from the environmental disturbances have been eliminated by the compensating action of the electronic feedback loop, this makes the system suitable for on-line precision measurement. By means of the homodyne phase-tracking technique, the linearity of the measurement results of displacement measurements has been very high.

Faster radial strain relaxation in InAs-GaAs core-shell heterowires

The structure of wurtzite and zinc blende InAs-GaAs (001) core-shell nanowires grown by molecular beam epitaxy on GaAs (001) substrates has been investigated by transmission electron microscopy. Heterowires with InAs core radii exceeding 11 nm, strain relax through the generation of misfit dislocations, given a GaAs shell thickness greater than 2.5 nm. Strain relaxation is larger in radial directions than axial, particularly for shell thicknesses greater than 5.0 nm, consistent with molecular statics calculations that predict a large shear stress concentration at each interface corner. © 2012 American Institute of Physics.

The activity of pH membrane disruptive pseudopeptides and their subcellular fate in mammalian cells cultured in-vitro

This thesis describes investigations upon pseudopeptides which were conducted to improve our understanding of the fate of synthetic macromolecules in cells and to develop approaches to influence that fate. The low uptake of molecules across the external cellular membrane is the principal barrier against effective delivery of therapeutic products to within the cell structure. In nature, disruption of this membrane by amphiphilic peptides plays a central role in the pathogenesis by bacterial and toxin infections. These amphiphilic peptides contain both hydrophobic and weakly charged hydrophilic amino acid residues and upon activation they become integrated into the lipid bilayers of the extracellular or endosomal membranes. The architectures of the pseudopeptides described here were designed to display similar pH dependent membrane rupturing activity to that of peptides derived from the influenza virus hemagglutinin HA-2. This HA protein promotes fusion of the influenza virus envelope with the cell endosome membrane due to a change in conformation in response to the acidic pH of the endosome lumen (pH 5.0-6.0). The pseudopeptides were obtained by the copolymerisation of L-lysine and L-lysine ethyl-ester with various dicarboxylic acid moieties. In this way a linear polyamide comprising of alternating pendant carboxylic acids and pendant hydrophobic moieties was made. At physiological pH (pH 7.4), electrostatic repulsion of pendant anionic carboxyl groups along the polymer backbone is sufficient to overcome the intramolecular association of the hydrophobic groups resulting in an extended conformation. At low pH (typically pH 4.8) loss of charge results in increased intramolecular hydrophobic association and the polymer chain collapses to a compact conformation, leading to precipitation of the polymer. Consequently, a conformation dependent functional property could be made to respond to small changes in the environmental pH. Pseudopepides were investigated for their cytoxicity towards a well known cell line, namely C26 (colorectal adenocarcinoma) and were shown through the use of a cell viability assay, MTT (3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide) to be well tolerated by C26 cells over a range of concentrations (2-500,μg/ml) at physiological pH (pH 7.4). A modified version of a shorter 30-minute coupled enzymatic assay, the LDH (lactate dehydrogenase) assay was used to evaluate the ability of the pseudopeptides to disrupt the membrane of two different cell lines (COS-1; African green monkey, kidney and A2780; human ovarian carcinoma) at low pH (pH 5.5). The cell membrane disruption property of the pseudopeptides was successfully demonstrated for COS-I and A2780 cell lines at this pH (pH 5.5). A variety of cell lines were chosen owing to limited availability and to compare the cytotoxic action of these pH responsive psudopeptides towards normal and tumorogenic cell lines. To investigate the intracellular delivery of one of the pseudopeptides, poly (L-lysine iso-phthalamide) and its subcellular location, a Cy3 bisamine fluorophore was conjugated into its backbone, at ratios of dye:lysine of 1:20, 1:30, 1:40, 1:60 and 1:80. Native polyacrylacrylamide gel electrophoresis (PAGE) and high voltage paper electrophoresis (HVPE) studies of the polydyes were conducted and provided evidence that that the Cy3 bisamine fluorophore was conjugated into the backbone of the polymer, poly (L-lysine iso-phthalamide). The subcellular fate of the fluorescentlylabelled "polydye" (hereafter PD20) was monitored by laser scanning confocal microscopy (LSCM) in CHO (Chinese hamster ovary) cells cultured in-vitro at various pH values (pH 7.4 and 5.0). LSCM images depicting time-dependent internalisation of PD20 indicated that PD20 traversed the extracellular membrane of CHO cells cultured in-vitro within ten minutes and migrated towards the endosomal regions where the pH is in the region of 5.0 to 6.0. Nuclear localisation of PD20 was demonstrated in a subpopulation of CHO cells. A further study was completed in CHO and HepG2 (hepatocellular carcinoma) cells cultured in-vitro using a lower molecular weight polymer to demonstrate that the molecular weight of "polydye" could be tailored to attain nuclear trafficking in cells. Prospective use of this technology encompasses a method of delivering a payload into a living cell based upon the hypercoiling nature of the pseudopeptides studied in this thesis and has led to a patent application (GB0228525.2; 20(2).

Some aspects of the interaction of humic substances with metal ions

Humic substances are the major organic constituents of soils and sediments. They are heterogeneous, polyfunctional, polydisperse, macromolecular and have no accurately known chemical structure. Their interactions with radionuclides are particularly important since they provide leaching mechanisms from disposal sites. The central theme to this research is the interaction of heavy metal actinide analogues with humic materials. Studies described focus on selected aspects of the characteristics and properties of humic substances. Some novel approaches to experiments and data analysis are pursued. Several humic substances are studied; all but one are humic acids, and those used most extensively were obtained commercially. Some routine characterisation techniques are applied to samples in the first instance. Humic substances are coloured, but their ultra-violet and visible absorption spectra are featureless. Yet, they fluoresce over a wide range of wavelengths. Enhanced fluorescence in the presence of luminescent europium(III) ions is explained by energy transfer from irradiated humic acid to the metal ion in a photophysical model. Nuclear magnetic resonance spectroscopy is applied to the study of humic acids and their complexes with heavy metals. Proton and carbon-13 NMR provides some structural and functionality information; Paramagnetic lanthanide ions affect these spectra. Some heavy metals are studied as NMR nuclei, but measurements are restricted by their sensitivity. A humic acid is fractionated yielding a broad molecular weight distribution. Electrophoretic mobilities and particle radii determined by Laser Doppler Electrophoretic Light Scattering are sensitive to the conditions of the supporting media, and the concentration and particle size distribution of humic substances. In potentiometric titrations of humate dispersions, the organic matter responds slowly and the mineral acid addition is buffered. Proton concentration data is modelled and a mechanism is proposed involving two key stages, both resulting in proton release after some conformational changes.

Wear of abrasion resisting materials

The wear behaviour of a series of chromium containing white irons has been investigated under conditions of high stress grinding abrasion using a specimen on track abrasion testing machine. The measured abrasion resistance of the irons has been explained in terms of microstructure and hardness and with respect to the wear damage observed at and beneath abraded surfaces. During abrasion material removal occurred by cracking and detachment from the matrix of eutectic carbides as well as by penetration and micromachining effects of the abrasive grits being crushed at the wearing surface. Under the particular test conditions used martensitic matrix structures gave higher resistance to abrasion than austenitic or pearlitic. However, no simple relationship was found between general hardness or matrix microhardness at wear surfaces and abrasion resistance, and the test yielded pessimistic results for austenitic irons. The fine structures of the 15% Cr and 30% Cr alloys were studied by thin foil transmission electron microscopy. It was found that both the matrix and carbide constituents could be thinned for examination at 100 Kv using conventional dishing followed by ion beam thinning. Flany of the rodlike eutectic N7C3 carbides were seen to consist of clusters of scalier rods with individual 117C3 crystals quite often containing central cores of matrix constituent. 3oth eutectic and secondary N7C3 carbides were found to contain stacking faults on planes normal to the basal plane. In the eutectic carbides in the 30A Cr iron there was evidence of an in-situ PI7C3 C. transition which had taken place during the hardening heat treatment of this alloy. In the as-cast austenitic matrix iron strain induced martensite was produced at the wear surface contributing to work hardening. The significance of these findings have been discussed in relation to wear performance.

Liquidity and portfolio optimisation

This thesis presents research within empirical financial economics with focus on liquidity and portfolio optimisation in the stock market. The discussion on liquidity is focused on measurement issues, including TAQ data processing and measurement of systematic liquidity factors (FSO). Furthermore, a framework for treatment of the two topics in combination is provided. The liquidity part of the thesis gives a conceptual background to liquidity and discusses several different approaches to liquidity measurement. It contributes to liquidity measurement by providing detailed guidelines on the data processing needed for applying TAQ data to liquidity research. The main focus, however, is the derivation of systematic liquidity factors. The principal component approach to systematic liquidity measurement is refined by the introduction of moving and expanding estimation windows, allowing for time-varying liquidity co-variances between stocks. Under several liability specifications, this improves the ability to explain stock liquidity and returns, as compared to static window PCA and market average approximations of systematic liquidity. The highest ability to explain stock returns is obtained when using inventory cost as a liquidity measure and a moving window PCA as the systematic liquidity derivation technique. Systematic factors of this setting also have a strong ability in explaining a cross-sectional liquidity variation. Portfolio optimisation in the FSO framework is tested in two empirical studies. These contribute to the assessment of FSO by expanding the applicability to stock indexes and individual stocks, by considering a wide selection of utility function specifications, and by showing explicitly how the full-scale optimum can be identified using either grid search or the heuristic search algorithm of differential evolution. The studies show that relative to mean-variance portfolios, FSO performs well in these settings and that the computational expense can be mitigated dramatically by application of differential evolution.

Dynamics in systematic liquidity

We develop a principal component approach to systematic liquidity measurement by introducing moving and expanding estimation windows. We evaluate these methods along with traditional estimation techniques (full sample PCA and market average) in terms of ability to explain (1) cross sectional stock liquidity and cross sectional stock returns. For several traditional liquidity measures our results suggest an expanding window specification for systematic liquidity estimation. The market average proxy of systematic liquidity produces the same degree of commonality, but does not have the same ability to explain stock returns as the PCA-estimates.

Clinical evaluation of the Oculus Keratograph

AIM: To determine the validity and reliability of the measurement of corneal curvature and non-invasive tear break-up time (NITBUT) measures using the Oculus Keratograph. METHOD: One hundred eyes of 100 patients had their corneal curvature assessed with the Keratograph and the Nidek ARKT TonorefII. NITBUT was then measured objectively with the Keratograph with Tear Film Scan software and subjectively with the Keeler Tearscope. The Keratograph measurements of corneal curvature and NITBUT were repeated to test reliability. The ocular sensitivity disease index questionnaire was completed to quantify ocular comfort. RESULTS: The Keratograph consistently measured significantly flatter corneal curvatures than the ARKT (MSE difference: +1.83±0.44D), but was repeatable (p>0.05). Keratograph NITBUT measurements were significantly lower than observation using the Tearscope (by 12.35±7.45s; pp < 0.001) and decreased on subsequent measurement (by -1.64 ± 6.03s; p < 0.01). The Keratograph measures the first time the tears break up anywhere on the cornea with 63% of subjects having NI-TBUT's <5s and a further 22% having readings between 5 and 10s. The Tearscope results were found to correlate better with the patients symptoms (r = -0.32) compared to the Keratograph (r = -0.19). Conclusions: The Keratograph requires a calibration off-set to be comparable to other keratometry devices. Its current software detects very early tear film changes, recording significantly lower NITBUT values than conventional subjective assessment. Adjustments to instrumentation software have the potential to enhance the value of Keratograph objective measures in clinical practice.

H-induced platelet and crack formation in hydrogenated epitaxial Si/Si0.98 B0.02 /Si structures

An approach to transfer a high-quality Si layer for the fabrication of silicon-on-insulator wafers has been proposed based on the investigation of platelet and crack formation in hydrogenated epitaxialSi/Si0.98B0.02/Si structures grown by molecular-beam epitaxy. H-related defect formation during hydrogenation was found to be very sensitive to the thickness of the buried Si0.98B0.02 layer. For hydrogenated Si containing a 130nm thick Si0.98B0.02 layer, no platelets or cracking were observed in the B-doped region. Upon reducing the thickness of the buried Si0.98B0.02 layer to 3nm, localized continuous cracking was observed along the interface between the Si and the B-doped layers. In the latter case, the strains at the interface are believed to facilitate the (100)-oriented platelet formation and (100)-oriented crack propagation.

A taxonomy of measures for consumer-based brand equity:drawing on the views of managers in Europe

Purpose: The purpose of this paper is to identify the components of consumer-based brand equity from the perspective of experts in brand management in the UK, Germany and Greece. Design/methodology/approach: Data were collected from semi-structured interviews with senior brand consultants and managers, five in the UK, five in Germany and five in Greece. Findings: The findings suggested four categories of measures which can be used to define brand equity. These are the consumers' understanding of brand characteristics; consumers' brand evaluation; consumers' affective response towards the brand; and consumers' behaviour towards the brand. Specific dimensions are identified as indicators of each category. Research limitations/implications: Although the focus of this study is Europe, data were only collected from the UK, Germany and Greece, countries representing three of the five European cultural clusters. The resultant taxonomy adds to the fragmented literature on brand equity measurement by proposing four categories to gauge brand equity. Practical implications: The suggested taxonomy provides indicators of a framework managers could use when assessing brand equity. Originality/value: There is little agreement on what constitutes brand equity and therefore measures of brand equity are fragmented. To date, the views of practicing managers have not been taken into account in research. This paper draws on the views of practitioners and academics to suggest a taxonomy of categories of measures for brand equity. © Emerald Group Publishing Limited.

The development of attenuation compensation models of fluorescence spectroscopy signals

This study examines the effect of blood absorption on the endogenous fluorescence signal intensity of biological tissues. Experimental studies were conducted to identify these effects. To register the fluorescence intensity, the fluorescence spectroscopy method was employed. The intensity of the blood flow was measured by laser Doppler flowmetry. We proposed one possible implementation of the Monte Carlo method for the theoretical analysis of the effect of blood on the fluorescence signals. The simulation is constructed as a four-layer skin optical model based on the known optical parameters of the skin with different levels of blood supply. With the help of the simulation, we demonstrate how the level of blood supply can affect the appearance of the fluorescence spectra. In addition, to describe the properties of biological tissue, which may affect the fluorescence spectra, we turned to the method of diffuse reflectance spectroscopy (DRS). Using the spectral data provided by the DRS, the tissue attenuation effect can be extracted and used to correct the fluorescence spectra.

Optical fiber cavity ring down measurement of refractive index with a microchannel drilled by femtosecond laser

A microchannel was inscribed in the fiber of a ring cavity which was constructed using two 0.1%:99.9% couplers and a 10-m fiber loop. Cavity ring down spectroscopy was used to measure the refractive index (RI) of gels infused into the microchannel. The ring down time discloses a nonlinear increase with respect to RI of the gel and sensitivity up to 300 µs/RI unit and an index resolution of 1.4 × 10 was obtained. © 2009 IEEE.

Optical fiber cavity ring down measurement of refractive index with a microchannel drilled by femtosecond laser

A microchannel was inscribed in the fiber of a ring cavity which was constructed using two 0.1%:99.9% couplers and a 10-m fiber loop. Cavity ring down spectroscopy was used to measure the refractive index (RI) of gels infused into the microchannel. The ring down time discloses a nonlinear increase with respect to RI of the gel and sensitivity up to 300 µs/RI unit and an index resolution of 1.4 × 10 was obtained. © 2009 IEEE.