Fabrication of Bonded Monolithic Porous Layer Open Tubular (monoPLOT) Columns in Wide Bore Capillary by Laminar Flow Thermal Initiation

A novel scalable procedure for the thermally initiated polymerisation of bonded monolithic porous layers of controlled thickness within open tubular fused silica capillaries (monoPLOT columns) is presented. Porous polymer layers of either polystyrene-divinylbenzene or butyl methacrylate-ethylene dimethacrylate, of variable thickness and morphology were polymerised inside fused silica capillaries utilising combined thermal initiation and laminar flow of the polymerisation mixture. The procedure enables the production through thermal initiation of monoPLOT columns of varying length, internal diameter, user defined morphology and layer thickness for potential use in both liquid and gas chromatography. The morphology and thickness of the bonded polymer layer on the capillary wall is strongly dependent on the laminar flow properties of the polymerisation mixture and the changing shear stress within the fluid across the inner diameter of the open capillary. Owing to the highly controlled rate of polymerisation and its dependence on fluid shear stress at the capillary wall, the procedure was demonstrably scalable, as illustrated by the polymerisation of identical layers within different capillary diameters.     

Fibre coupled micro-light emitting diode array light source with integrated band-pass filter for fluorescence detection in miniaturised analytical systems

In this work, a new type of miniaturized fibre-coupled solid-state light source is demonstrated as an excitation source for fluorescence detection in capillary electrophoresis. It is based on a parabolically shaped micro-light emitting diode (μ-LED) array with a custom band-pass optical interference filter (IF) deposited at the back of the LED substrate. The GaN μ-LED array consisted of 270 individual μ-LED elements with a peak emission at 470 nm, each about 14 μm in diameter and operated as a single unit. Light was extracted through the transparent substrate material, and coupled to an optical fibre (OF, 400 μm in diameter, numerical aperture NA = 0.37), to form an integrated μ-LED-IF-OF light source component. This packaged μ-LED-IF-OF light source emitted approximately 225 μW of optical power at a bias current of 20 mA. The bandpass IF filter was designed to reduce undesirable LED light emissions in the wavelength range above 490 nm. Devices with and without IF were compared in terms of the optical power output, spectral characteristics as well as LOD values. While the IF consisted of only 7.5 pairs (15 layers) of SiO₂/HfO₂ layers, it resulted in an improvement of the baseline noise as well as the detection limit measured using fluorescein as test analyte, both by approximately one order of magnitude, with a LOD of 1 × 10⁻⁸ mol L⁻¹ obtained under optimised conditions. The μ-LED-IF-OF light source was then demonstrated for use in capillary electrophoresis with fluorimetric detection. The limits of detection obtained by this device were compared to those obtained with a commercial fibre coupled LED device.     

An investigation of phase transformation and crystallinity in laser surface modified H13 steel

This paper presents a laser surface modification process of AISI H13 tool steel using 0.09, 0.2 and 0.4 mm size of laser spot with an aim to increase hardness properties. A Rofin DC-015 diffusion-cooled CO₂ slab laser was used to process AISI H13 tool steel samples. Samples of 10 mm diameter were sectioned to 100 mm length in order to process a predefined circumferential area. The parameters selected for examination were laser peak power, overlap percentage and pulse repetition frequency (PRF). X-ray diffraction analysis (XRD) was conducted to measure crystallinity of the laser-modified surface. X-ray diffraction patterns of the samples were recorded using a Bruker D8 XRD system with Cu?K _α (λ=1.5405 Å) radiation. The diffraction patterns were recorded in the 2θ range of 20 to 80°. The hardness properties were tested at 981 mN force. The laser-modified surface exhibited reduced crystallinity compared to the un-processed samples. The presence of martensitic phase was detected in the samples processed using 0.4 mm spot size. Though there was reduced crystallinity, a high hardness was measured in the laser-modified surface. Hardness was increased more than 2.5 times compared to the as-received samples. These findings reveal the phase source of the hardening mechanism and grain composition in the laser-modified surface.     

Laser machined macro and micro structures on glass for enhanced light trapping in solar cells

In order to increase the efficiency of solar cell modules it is necessary to make the optimum use of light incident upon them. Much research has been done on improving light absorption through front surface texturisation and light trapping schemes. Laser light is commonly used in industry for various applications including marking and texturisation. By controlling laser parameters, it is possible to tailor macro and micro structures in most materials. The CO₂ laser used in this investigation emits radiation at 10.6 μm with the ability to pulse in the micro-second range. The laser was used to ablate grooved textures in the fused quartz material, used in this study as the light trapping medium, following which an analysis of the effects of the laser parameters on the texture geometry and surface morphology was performed through a combination of cross sectioning and scanning electron microscopy. Transmission through the textured glass was improved for most samples after acid etching. The light trapping effects of the best performing textures were analysed by investigating the effects on a silicon solar cell’s performance at varying angles of incidence. Results indicated a significant increase in light trapping when light was incident at acute angles. For an angle of incidence of 10^° a relative increase in efficiency of up to 51 % was observed.     

Laser micro-processing of amorphous and partially crystalline Cu45Zr48Al7 alloy

This paper presents a microstructural study of laser micro-processed high-purity Cu₄₅Zr₄₈Al₇ alloys prepared by arc melting and Cu-mould casting. Microprocessing of the Cu₄₅Zr₄₈Al₇ alloy was performed using a Rofin DC-015 diffusion-cooled CO₂ slab laser system with 10.6-μm wavelength. The laser was defocused to a spot size of 0.2 mm on the sample surface. The laser parameters were set to give 300- and 350-W peak power, 30% duty cycle and a 3000-Hz laser pulse repetition frequency (PRF). About 100-micrometer-wide channels were scribed on the surfaces of disk-shaped amorphous and partially crystalline samples at traverse speeds of 500 and 5000 mm/min. These channels were analysed using scanning electron microscopy (SEM) and 2D stylus profilometry. The metallographic study and profile of these processed regions are discussed in terms of the applied laser processing parameters. The SEM micrographs showed that striation marks developed at the edge and inside these regions as a result of the laser processing. The results from this work showed that microscale features can be produced on the surface of amorphous Cu–Zr–Al alloys by CO₂ laser processing.     

Fabrication of Bonded Monolithic Porous Layer Open Tubular (monoPLOT) Columns in Wide Bore Capillary by Laminar Flow Thermal Initiation

A novel scalable procedure for the thermally initiated polymerisation of bonded monolithic porous layers of controlled thickness within open tubular fused silica capillaries (monoPLOT columns) is presented. Porous polymer layers of either polystyrene-divinylbenzene or butyl methacrylate-ethylene dimethacrylate, of variable thickness and morphology were polymerised inside fused silica capillaries utilising combined thermal initiation and laminar flow of the polymerisation mixture. The procedure enables the production through thermal initiation of monoPLOT columns of varying length, internal diameter, user defined morphology and layer thickness for potential use in both liquid and gas chromatography. The morphology and thickness of the bonded polymer layer on the capillary wall is strongly dependent on the laminar flow properties of the polymerisation mixture and the changing shear stress within the fluid across the inner diameter of the open capillary. Owing to the highly controlled rate of polymerisation and its dependence on fluid shear stress at the capillary wall, the procedure was demonstrably scalable, as illustrated by the polymerisation of identical layers within different capillary diameters.

     

Evolving technical trading rules for spot foreign-exchange markets using grammatical evolution

Grammatical Evolution (GE) is a novel, data-driven, model-induction tool, inspired by the biological gene-to-protein mapping process. This study provides an introduction to GE, and applies the methodology in an attempt to uncover useful technical trading rules which can be used to trade foreign exchange markets. In this study, each of the evolved rules (programs) represents a market trading system. The form of these programs is not specified ex-ante, but emerges by means of an evolutionary process. Daily US-DM, US-Stg and US-Yen exchange rates for the period 1992 to 1997 are used to train and test the model. The findings suggest that the developed rules earn positive returns in hold-out sample test periods, after allowing for trading and slippage costs. This suggests potential for future research to determine whether further refinement of the methodology adopted in this study could improve the returns earned by the developed rules. It is also noted that this novel methodology has general utility for rule-induction, and data mining applications.MSC codes: 91B84, 68W10, 62J02     

Demonstration of an optical biosensor for the detection of faecal indicator bacteria in freshwater and coastal bathing areas

ColiSense, an early warning system developed for Escherichia coli detection, is assessed using environmental samples. The system relies on the detection of β-glucuronidase (GUS), a biomarker enzyme for E. coli. In contrast with other rapid GUS-based methods, ColiSense is the only method that uses 6-chloro-4-methyl-umbelliferyl-β-d-glucuronide (6-CMUG) as a fluorogenic substrate. The system measures a direct kinetic response of extracted GUS, and the detection was carried out in the absence of particles or bacteria. It is necessary to evaluate the system with environmental samples to establish the relationship between faecal indicator bacteria E. coli and the response measured by the ColiSense. This paper presents the results of tests carried out with the ColiSense system for 2 trials, one conducted with freshwater samples collected from rivers in the Dublin area and a second conducted with seawater samples from coastal areas collected over the bathing season. A positive linear correlation was found between E. coli (MPN 100 mL⁻¹) and ColiSense response (R² = 0.85, N = 125, p < 0.01) for the seawater sample. A ColiSense response threshold was identified as 0–1.8 pmol min⁻¹ 100 mL⁻¹, equivalent to 0–500 E. coli 100 mL⁻¹. Using this threshold, 96.8% of the samples were correctly classified as being above or below 500 E. coli 100 mL⁻¹ by the ColiSense system. Results presented demonstrate that the ColiSense system can be used as an early warning tool with potential for active management of bathing areas by providing results in 75 min from sample collection.

     

Comparison of ANN and DoE for the prediction of laser-machined micro-channel dimensions

This paper presents four models developed for the prediction of the width and depth dimensions of CO₂ laser-formed micro-channels in glass. A 3³ statistical design of experiments (DoE) model was built and conducted with the power (P), pulse repetition frequency (PRF), and traverse speed (U) of the laser machine as the selected parameters for investigation. Three feed-forward, back-propagation artificial neural networks (ANNs) models were also generated. These ANN models were varied to investigate the influence of variations in the number and the selection of training data. Model A was constructed with 24 data randomly selected from the experimental results, leaving three data points for model testing; Model B was constructed with the eight corner points of the experimental data space, and seven other randomly selected data, leaving 12 data points for testing; and Model C was constructed with 15 randomly selected data leaving 12 data points for testing. These models were developed separately for both micro-channel width and depth prediction. These ANN models were constructed in LabVIEW coding. The performance of these ANN models and the DoE model were compared. When compared with the actual results two of the ANN models showed greater average percentage error than the DoE model. The other ANN model showed an improved predictive capability that was approximately twice as good as that provided from the DoE model.