DSpace Collection:

Gas-sensitive holographic sensors

Mon, 15 Apr 2013 23:00:00 GMT

Title: Gas-sensitive holographic sensors Authors: Martínez Hurtado, Juan Leonardo Abstract: Holographic sensors are photonic layered structures contained in analyte sensitive lms that upon illumination produce monochromatic reflections (λ). The present work reports the fabrication of oxygen and ammonia sensors in Nafi on membranes and hydrocarbon and volatile organic compound sensors in poly(dimethylsiloxane) (PDMS) films. A holographic recording technique was developed to suit these materials consisting of the in situ formation of nanoparticles of 18nm average diameter and their subsequent ordered ablation with a 300mJ laser. The wavelength of the monochromatic reflections depends principally on the refractive index of the resulting layers (n) and the separation between them (Λ). Changes in these parameters are generated by the analyte-sensor interactions and their magnitude can be correlated to the analyte concentration. The strength of these interactions is determined by the thermodynamic properties of the analytes, such as the cohesive energy density (δ^2), and this, was coupled with a photonic model for the prediction of the holographic response. After exposure to different concentrations of the analytes, the kinetics of the responses were determined and the lowest detection limits (LDL) established as follows: Hydrocarbons in PDMS holograms 1% (v/v) in 3s for a range of concentrations from 0-100%; ammonia in Nafi on holograms 0.16% in 100s in the 0-12.5% range; the LDL for oxygen sensing could not be determined although the response was recorded down to 12.5% and up to 100% in 100s. Holographic sensors show competitive responses comparable to commercially available gas sensors for biomedical diagnostics and industrial process monitoring because of their facile fabrication and their shared sensing platform allowing multiplexing. Description: Sensors for volatile organic compounds (VOC) and hydrocarbons made by photonic gratings in PDMS (poly dimethylsiloxane). Sensors for Ammonia and Oxygen attempted using Nafion membranes.

Microwave-assisted pyrolysis of HDPE using an activated carbon bed

Mon, 15 Apr 2013 23:00:00 GMT

Title: Microwave-assisted pyrolysis of HDPE using an activated carbon bed Authors: Russell, Alan Donald Abstract: Plastics play an enormous role in modern manufacturing, but the extraction and refining of raw materials, followed by the synthesis of plastics themselves, represents an enormous energy investment into a product that is all too often simply “thrown away” into a landfill after a single use. Microwave-assisted pyrolysis is a recycling technique that allows the recovery of chemical value from plastic waste by breaking down polymers into useful smaller hydrocarbons using microwave heat in the absence of oxygen. This dissertation examines the use of a catalytic activated carbon bed in this procedure, using high density polyethylene (HDPE) as a model plastic. Initial tests with the batch input of HDPE produced a condensed pyrolysis oil comprising 35.5–45.3% aromatics, with the remainder primarily short-chain aliphatics. This oil was approximately three times lighter than that produced in the absence of catalyst, with a narrower range of molecular masses that matched those of the liquid transport fuels petrol and diesel (C5–C21). The non-condensable gases that resulted were short-chain aliphatics that could be used as feedstock for the creation of new chemicals (such as virgin HDPE), or fuels such as natural gas and LPG. The development of apparatus capable of adding sample in a continuous fashion enabled the processing of larger quantities of HDPE, and resulted in condensed products with a significantly higher aromatic content (>80% at 450°C), and which encompassed a somewhat narrower range of molecular masses compared with those produced in the batch mode; this was due to differences in kinetics and residence time that resulted from the different modes of sample introduction. As a result of processing larger quantities of HDPE it became apparent that the activated carbon deactivated over time, with a bed able to process around 3.5 times its mass in HDPE at 450°C before any significant changes in output products occurred. The decomposition of HDPE proceeds via thermal scission and radical-mediated mechanisms; high energy surface active sites facilitate the transfer of hydrogen and radicals, and this enhances overall cracking and lowers the activation energy for the formation of aromatics. Analysis of material deposited on the surface of the activated carbon confirmed that deactivation occurred through coking, with both cracking and deactivation thought to be enhanced by the formation of microwave-induced microplasmas. Overall, the microwave-assisted pyrolysis of HDPE using activated carbon produces a much narrower range of more valuable products compared with non-catalytic processing. While the process is not likely to be economic in its current form owing to the relatively rapid deactivation of the activated carbon, future configurations incorporating online reactivation may be able to economically provide a second use cycle for these materials, avoiding expending energy to extract and process increasingly scarce new raw material from the surface of the earth.

Functional characterisation of LEA proteins from bdelloid rotifers

Tue, 13 Nov 2012 00:00:00 GMT

Title: Functional characterisation of LEA proteins from bdelloid rotifers Authors: Tripathi, Rashmi Abstract: ‘Anhydrobiosis’ or ‘life without water’ is a fascinating phenomenon that was first described by the eminent Dutch microscopist Antony van Leewenhoek in bdelloid rotifers in 1702. Despite being studied for over three hundred years, our understanding of its molecular basis remains largely elusive. Recently, two group 3 LEA (late embryogenesis abundant) proteins, ArLEA1A and ArLEA1B, have been identified in the desiccation-induced gene set in the bdelloid species Adineta ricciae that are hypothesised to protect these animals by preventing protein aggregation and stabilising membranes respectively. In this dissertation, the functional characteristics of bdelloid LEA proteins have been further explored using computational and experimental tools. Analysis of their phylogeny and domain composition reveals that ArLEA1A and ArLEA1B are evolutionarily distinct from other related group 3 LEA proteins. Moreover, unlike some LEA proteins that are unstructured, bdelloid LEA proteins are predicted to form a-helices, with ArLEA1B having an additional propensity to polymerise into tropomyosin like filaments. These proteins are also predicted to localise in the ER (endoplasmic reticulum) and interact with cell signalling molecules. Intracellular localisation analysis of ArLEA1A and ArLEA1B using confocal microscopy confirms that these proteins translocate into the ER as predicted and their distribution within the entire secretory system and the cell exterior is regulated by their N- and C-terminal signals. Preliminary results suggest that over-expressing ArLEA1A fails to provide protection against protein aggregation within the mammalian ER. Lastly, both ArLEA1A and ArLEA1B are found to provide partial protection against desiccation induced damage of fluorescence properties of the red fluorescent protein mCherry. Overall, the results in this dissertation provide important mechanistic insights into the mode of action of bdelloid LEA proteins during anhydrobiosis.

Detection of mycobacterial siderophores and implications for diagnostics

Tue, 13 Nov 2012 00:00:00 GMT

Title: Detection of mycobacterial siderophores and implications for diagnostics Authors: McBride, Nicholas S. Abstract: Mycobacterium tuberculosis (Mtb) is a pervasive human pathogen that continues to kill 1.8 million people every year. Acquisition of iron within the host is vital to the pathogenicity of Mtb and to accomplish this it produces siderophores called mycobactins and carboxymycobactins. This dissertation has sought to build a simple assay for detection and quantification of mycobacterial siderophores that has potential applications in tuberculosis (TB) diagnosis. This assay has been tested and was successfully able to detect mycobactin spiked into a biological specimen. Furthermore, the theoretical level of mycobactin production that occurs in the lungs of infected patients was estimated. Samples were obtained from infected animal models of TB and human patients and tested for presence of mycobactin and carboxymycobactin. These data provided information regarding the potential use of siderophores as diagnostic biomarkers for TB.

A sensor for combustion thermometry based on blue diode lasers.

Mon, 22 May 2006 23:00:00 GMT

Title: A sensor for combustion thermometry based on blue diode lasers. Authors: Burns, Iain Stewart Abstract: Spatially-resolved measurements of flame temperature have been demonstrated with diode lasers for the first time. The technique is based on the use of blue diode lasers to perform laser-induced fluorescence on indium atoms seeded to the flame. Temperature measurements have been carried out in laminar flames both by the two-line atomic fluorescence technique, and also by a novel line-shape thermometry method that requires the use of only a single diode laser. The first part of this work involved the development of blue extended cavity diode lasers with favourable tuning properties. Two custom-designed extended cavity diode lasers (ECDL) have been built, emitting at wavelengths of around 410 nm and 451 nm respectively. These devices are capable of mode-hop free tuning over ranges greater than 90 GHz. The performance of these devices exceeds that of commercially available systems and a patent application has been filed. High resolution fluorescence spectroscopy has been performed on both the 52P1/2→62S1/2 and 52P3/2→62S1/2 transitions of indium atoms seeded at trace quantities into atmospheric pressure flames. In both cases, the spectra obtained show excellent agreement with a theoretical fit based on the individual hyperfine components of the transition. The two ECDLs have been used to build a sensor for the measurement of temperature in combustion systems. It is much simpler, more compact, less expensive, and more versatile than any previously existing device. The two lasers were used sequentially to probe indium atoms seeded to the flame. The ratio of the resulting fluorescence signals is related to the relative populations in the two sub-levels of the spin-orbit split ground state of indium, and thus to the temperature. Temperature measurements have been successfully performed in a laminar flame and the data thus obtained do not need to be corrected by any ‘calibration constant’. This novel thermometry technique offers a robust alternative to traditional methods involving bulky high power lasers. A further development has been made by demonstrating a fluorescence line-shape thermometry technique requiring only a single diode laser excitation source. Progress has been made towards the goal of rapid temperature measurements appropriate to the study of turbulent flames. This involved the development of a simple technique for actively locking the wavelength of the blue diode laser to a resonance line of the tellurium molecule. A high-speed thermometry system would work by rapidly switching between the two locked laser beams using an optical modulator.

A biosynthetic approach to the discovery of novel bioactive peptides

Mon, 07 May 2012 23:00:00 GMT

Title: A biosynthetic approach to the discovery of novel bioactive peptides Authors: Wright, Oliver Evan Abstract: Peptides represent a source of novel therapeutics for recalcitrant human diseases, but screening for bioactivity from natural or synthetic sources can be uneconomic. In contrast, in vivo expression of peptides from DNA libraries in a heterologous host such as Escherichia coli may combine production with screening. This dissertation aimed to use such an approach to discover novel bioactive peptides in a high throughput and cost-effective manner, with a focus on antimicrobials and antiaggregants as proof-of-principle. Antimicrobial peptides (AMPs) are innate defence effectors that may combat antibiotic-resistant pathogens. An inducible, autocleaving fusion tag was utilised to produce the model murine cathelicidin K2C18, along with a number of variants, which exhibited varying degrees of antimicrobial activity against a panel of microbes. Importantly, K2C18 also exhibited a bacteriostatic effect in vivo when secreted to the periplasm. This allowed for the implementation of an in vivo whole cell screen for novel AMPs, using genomic DNA libraries as an input. One putative hit, the peptide S-H4, showed similar in vivo behaviour to K2C18 and was active when added exogenously to microbial cultures. A second in vivo screen was constructed to search for inhibitors of Aβ42 aggregation, a process implicated in Alzheimer’s disease. The aggregation state of Aβ42 was coupled to the fluorescence of a chromophore fusion partner, and used to screen co-expressed peptides from a random DNA library for putative antiaggregants. Additionally, the system incorporated an internal fluorescent reference to allow ratiometric comparison between samples. Several hits were identified and further validated using flow cytometry, with work ongoing to assess their activity in vitro. Proof-of-principle of these two screens was achieved, indicating that such in vivo approaches to bioactive peptide discovery could lead to the development of new and useful therapeutics.

Experimental characterisation of bubbly flow using MRI

Tue, 08 Nov 2011 00:00:00 GMT

Title: Experimental characterisation of bubbly flow using MRI Authors: Tayler, Alexander B. Abstract: This thesis describes the first application of ultra-fast magnetic resonance imaging (MRI) towards the characterisation of bubbly flow systems. The principle goal of this study is to provide a hydrodynamic characterisation of a model bubble column using drift-flux analysis by supplying experimental closure for those parameters which are considered difficult to measure by conventional means. The system studied consisted of a 31 mm diameter semi-batch bubble column, with 16.68 mM dysprosium chloride solution as the continuous phase. This dopant served the dual purpose of stabilising the system at higher voidages, and enabling the use of ultra-fast MRI by rendering the magnetic susceptibilities of the two phases equivalent. Spiral imaging was selected as the optimal MRI scan protocol for application to bubbly flow on the basis of its high temporal resolution, and robustness to fluid flow and shear. A velocimetric variant of this technique was developed, and demonstrated in application to unsteady, single-phase pipe flow up to a Reynolds number of 12,000. By employing a compressed sensing reconstruction, images were acquired at a rate of 188 fps. Images were then acquired of bubbly flow for the entire range of voidages for which bubbly flow was possible (up to 40.8%). Measurements of bubble size distribution and interfacial area were extracted from these data. Single component velocity fields were also acquired for the entire range of voidages examined. The terminal velocity of single bubbles in the present system was explored in detail with the goal of validating a bubble rise model for use in drift-flux analysis. In order to provide closure to the most sophisticated bubble rise models, a new experimental methodology for quantifying the 3D shape of rising single bubbles was described. When closed using shape information produced using this technique, the theory predicted bubble terminal velocities within 9% error for all bubble sizes examined. Drift-flux analysis was then used to provide a hydrodynamic model for the present system. Good predictions were produced for the voidage at all examined superficial gas velocities (within 5% error), however the transition of the system to slug flow was dramatically overpredicted. This is due to the stabilising influence of the paramagnetic dopant, and reflects that while drift-flux analysis is suitable for predicting liquid holdup in electrolyte stabilised systems, it does not provide an accurate representation of hydrodynamic stability. Finally, velocity encoded spiral imaging was applied to study the dynamics of single bubble wakes. Both freely rising bubbles and bubbles held static in a contraction were examined. Unstable transverse plane vortices were evident in the wake of the static bubble, which were seen to be coupled with both the path deviations and wake shedding of the bubble. These measurements demonstrate the great usefulness for spiral imaging in the study of transient multiphase flow phenomena.

Homeostasis and volume regulation in the Plasmodium falciparum infected red blood cell

Mon, 06 Jun 2011 23:00:00 GMT

Title: Homeostasis and volume regulation in the Plasmodium falciparum infected red blood cell Authors: Mauritz, Jakob Martin Andreas Abstract: The thesis reports on the application of advanced microanalytical techniques to answer a fundamental open question on the homeostasis of Plasmodium falciparum infected red blood cells, namely how infected cells retain their integrity for the duration of the parasite asexual reproduction cycle. The volume and shape changes of infected cells were measured and characterized at femtolitre resolution throughout the intraerythrocytic cycle using confocal microscopy. Fluorescence lifetime imaging and electron probe X-ray microanalysis were applied for the quantification of intracellular haemoglobin and electrolyte concentrations. The cytomechanical properties of uninfected and infected red cells were studied using a novel optical stretcher device, which enabled individual cells to be trapped and manipulated optomechanically in microfluidic channels. Combined, these methods offered a unique insight into the homeostatic and rheological behaviour of malaria-infected red cells. The results were analysed by comparison with predictions from a detailed physiological model of the homeostasis and volume regulation of infected cells, providing broad support to the view that excess haemoglobin consumptions by the parasite was necessary for the integrity of infected cells (the colloidosmotic hypothesis). The dissertation is introduced with an overview of malaria, red blood cells homeostasis and the changes induced by Plasmodium falciparum infection. In the following, this description is extended to an in-depth theoretical analysis of the infected red blood cell homeostasis, from which the need to characterise certain parameters arises. The subsequent chapters address sequentially the assessment of the haemoglobin and electrolyte concentration, cell shape and volume changes and ultimately alterations in cell elasticity. The experimental part is complemented with a comparison of the resulting data to the predictions from the theoretical analysis and an outlook on future work.

Fundamental and applied aspects of contact electrification

Sun, 01 Feb 1976 00:00:00 GMT

Title: Fundamental and applied aspects of contact electrification Authors: Elsdon, Ronald Abstract: Apparatus has been developed, which permits the measurement of electrification produced by rolling or sliding contact between a spherical specimen, and a plane dielectric sample. Measurements of the charge transferred to metal contact spheres, and the two-dimensional dielectric surface charge distribution, have been carried out under controlled conditions. The dissipation processes of air breakdown and bulk condution have been studied. The importance of metal work function, dielectric material, the normal force during contact, the mode of contact, and the time of contact has also been investigated. Contact electrification and charge dissipation occurring in a vibrated bed have been studied. The variables of interest were the bulk particle resistivity, the amplitude of vibration, and the. system electrode geometry. Theoretical models have been developed for the processes occurring, and the models could be used to interpret experimental observations. The relevance of the results to previous particle electrification studies, and to general particle handling situations has been discussed. Two new applications of particle charging have been examined. The first utilised particle contact electrification occurring naturally in a fluidised bed. By applying a suitable alternating electric field normal to an immersed heater surface, considerable increases in the heat transfer coefficient have been obtained, as a result of the imposed particle movement. The influence on the heat transfer coefficient, of the electric field magnitude and frequency, together with the fluidising air velocity, has been studied. The second application involved devising a novel means of electrostatic separation, using induction charging applied to the particles on the surface of a vibrated bed. A theoretical model for predicting particle collection rates has been developed, and verified by comparison with experimental observations. An efficient separation has been demonstrated on a combined size/resistivity basis.

Scale-up of oscillatory flow mixing

Tue, 15 Feb 2000 00:00:00 GMT

Title: Scale-up of oscillatory flow mixing Authors: Smith, Keith Buchanan Abstract: Oscillatory Flow Mixing is a recent development in mixing technology which has evolved over the past decade. It has a number of similarities to other mixing technologies, particularly pulsed and reciprocating plate columns, but at the laboratory scale has demonstrated a number of advantageous properties. These properties (such as control of residence time distribution, improved heat transfer and predictable mixing times) have been demonstrated at the laboratory scale for a wide range of different potential applications, but until now there has been a lack of firm understanding and research into how the technology could be scaled-up into an industrial scale process. This thesis addresses the problem of scale-up in Oscillatory Flow Mixing. It reports on a programme of experiments on geometrically scaled apparatus with the measurement of residence time distributions and flow visualisation as the principal methods of investigating the wide range of flow conditions that can be achieved by control of net flow and of oscillatory conditions. Results from these investigations are interpreted as axial dispersion coefficients and also compared with results obtained computationally using a fluid mechanics approach to simulate flow fields and the injection of inert tracers into those flow fields. Significant clarification is reported concerning the analysis of axial dispersion measurements using the diffusion model for which conflicting solutions were identified in the literature. The development of a flow visualisation technique using fluorescent dye streaklines is also reported. Using the latter technique stable manifolds in Oscillatory Flow Mixing have for the first time been experimentally observed as well as a range of other flow regimes. The study of scale-up was extended by the successful construction and investigation of an alternative reactor geometry with the potential for use in large-scale plant. From the work presented in the thesis it is concluded that Oscillatory Flow Mixing is a technology which in general lends itself readily to scaling-up from laboratory to pilot plant scale, and most probably to industrial scale. Experiments performed on small laboratory apparatus (containing less than one litre of fluid) can with confidence be used to predict mixing behaviour in much larger plant (containing hundreds of litres of fluid.)

Ultra-fast Imaging of Two-Phase Flow in Structured Monolith Reactors; Techniques and Data Analysis

Thu, 01 Mar 2007 00:00:00 GMT

Title: Ultra-fast Imaging of Two-Phase Flow in Structured Monolith Reactors; Techniques and Data Analysis Authors: Heras, Jonathan Jaime Abstract: This thesis will address the use of nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) techniques to probe the “monolith reactor”, which consists of a structured catalyst over which reactions may occur. This reactor has emerged as a potential alternative to more traditional chemical engineering systems such as trickle bed and slurry reactors. However, being a relatively new design, its associated flow phenomena and design procedures are not rigorously understood, which is retarding its acceptance in industry. Traditional observations are unable to provide the necessary information for design since the systems are opaque and dynamic. Therefore, NMR is proposed as an ideal tool to probe these systems in detail. The theory of NMR is summarised and the development of novel NMR techniques is presented. Novel techniques are validated in simple systems, and tested in more complex systems to ascertain their quantitative nature, and to find their limitations. These techniques are improvements over existing techniques in that they either decrease the acquisition time (allowing the observation of dynamically-changing systems) or allow us to probe systems in different ways to extract useful information. The goal of this research is to better understand the flow phenomena present in such systems, and to use this information to design better, more efficient, more controllable industrial reactors. The analysis of the NMR data acquired is discussed in detail, and several novel image-processing techniques have been developed to aid in the quantification of features within the images, and also to measure quantities such as holdup and velocity. These novel techniques are validated, and then applied to the systems of interest. Various configurations of monolith reactor, ranging from low flow rate systems to more challenging (and more industrially relevant) turbulent systems, are probed using these methods, and the contrasting flow phenomena and performance of these systems are discussed, with a view to optimisation of the choice of design parameters.

The production of pure hydrogen with simultaneous capture of carbon dioxide

Mon, 11 Oct 2010 23:00:00 GMT

Title: The production of pure hydrogen with simultaneous capture of carbon dioxide Authors: Bohn, Christopher Abstract: The need to stabilise or even reduce the production of anthropogenic CO2 makes the capture of CO2 during energy generation from carbonaceous fuels, e.g. coal or biomass, necessary for the future. For hydrogen, an environmentally-benign energy vector whose sole combustion product is water, to become a major energy source, it must be produced in an efficient, CO2-neutral manner. A process, which uses a packed bed of iron and its oxides, viz. Fe, Fe0:947O, Fe3O4 and Fe2O3, has been formulated to produce separate, pure streams of H2 and CO2. The process is exothermic and has the following stages: 1. Reduction of Fe2O3 to Fe0:947O or Fe in syngas (CO + H2) from gasifying coal or biomass. This stage generates pure CO2 for sequestration, once the water has been condensed. 2. Subsequent oxidation of Fe or Fe0:947O to Fe3O4 using steam. This stage generates H2 of sufficient purity for use in polymeric membrane fuel cells. 3. Further oxidation of Fe3O4 to Fe2O3 using air to return the oxide to step (1). It was shown that reduction to Fe0:947O in step (1) gave stable yields of H2 in step (2) after 40 cycles, near those predicted from reaction stoichiometry. By contrast, reduction to Fe, rather than Fe0:947O, in step (1) gave low levels of H2 in step (2) after just 10 cycles. This demonstrates that modifying the iron oxide is unnecessary unless reduction to Fe is performed. Wet-impregnation of Fe2O3 was performed with salts of Al, Cr and Mg or with tetraethyl orthosilicate for Si to give loadings of 1-30 mol % of the additive element. The addition of Al stabilised the quantity of H2 produced when the sample was reduced to Fe. Using a sol-gel method, composite particles with diff erent mass ratios of Fe2O3 and Al2O3 were prepared. For reduction to Fe over 40 cycles, 40 wt. % Al2O3 was required to give stable conversions near 75 % of that expected from reaction stoichiometry. Prior to this research, it had been assumed that the alumina acted as an inert support. However, this was shown to be incorrect since the formation of FeO.Al2O3 was quantitatively confirmed using X-ray diffraction. The presence of the compound, FeO.Al2O3, is significant since it reduces the loss in internal surface area but binds reactive iron, two contradictory e ects for the production of H2. The production of separate streams of pure H2 and CO2 from solid fuels, lignite and subbituminous coal, was demonstrated. Pure H2 with [CO] ~< 50 ppmv and [SO2] ~~ 0 ppmv was produced from a low-rank coal, showing that the process is e cacious with an impure fuel. Contaminants found in syngas which are gaseous above 273 K apparently do not adversely affect the iron oxide material or purity of the hydrogen. Subsequent oxidation of the Fe3O4 with air, step (3), removed sulphurous and carbonaceous contaminants deposited during reduction, generated useful heat and did not lead to a decrease in the H2 yield in step (2). It is therefore recommended that step (3) be included in the process. Rates of reaction are reported for the reduction of iron oxide particles by a mixture of CO, CO2 and N2. Importantly, rates were investigated over multiple cycles. Reduction of either Fe2O3 to Fe3O4 or of Fe3O4 to Fe0:947O was found to be first-order in CO. With the particle sizes used, the rates of reduction were controlled by intrinsic chemical kinetics. Activation energies and pre-exponential factors are reported. The rates were used to simulate, satisfactorily, the reduction of a packed bed of iron oxide. The rate of reduction was doubled by the addition of 1 mol. % Ce to the granulated iron oxide. The overall rate was shown to be dependent on the active surface area of the iron oxide. A lattice Boltzmann model, which incorporates hydrodynamics, mass transport and reaction, was developed. The composition of the solid changed with time. Quantitative agreement between the model and experiments for the reduction of a single particle of Fe2O3 to Fe3O4 in CO was achieved. Additionally, the model correctly predicted a sharp front in the CO concentration for reduction of a packed bed of Fe2O3 to Fe3O4.

Development of novel laser diagnostic techniques for the quantitative study of premixed flames

Thu, 01 Jan 2009 00:00:00 GMT

Title: Development of novel laser diagnostic techniques for the quantitative study of premixed flames Authors: Chrystie, Robin Simon Macpherson Abstract: The main topic of this thesis concerns the development and application of laser diagnostic techniques for accurate temperature measurements and for the determination of flamefront properties in premixed flames that can serve as input data for computational fluid dynamical (CFD) models in technical combustion. The work comprises of a number of related studies, to address problems of relevance in the field of combustion research. The first part of this work involves the development and testing of an improved method for the computation of flamefront curvature in lean premixed turbulent flames. Measurements of spatially resolved heat release rate along the flamefront were then compared with the curvature data and it could be shown that a significant correlation exists between local rate of heat release and flamefront curvature. The results here agree with predictions from CFD models and improve on previous experimental attempts to find a correlation between curvature and heat release. In the second part of this work, the focus was shifted towards the development and application of improved thermometry techniques. One study was on the improvement and application of a coherent anti-Stokes Raman spectroscopy (CARS) setup to an acoustically-forced turbulent lean premixed flame stabilised on a burner, whose design was modelled to mimic phenomena of relevance in industrial combustors. In a related previous study reported in the literature two-line OH planar laser induced fluorescence had been applied to this flame and it was suspected that the results were inaccurate. Using CARS, these inaccuracies could be verified, amounting to discrepancies in temperature of up to 47% compared to the true temperatures. A major effort towards the end of this project was focused on the improvement of traditional thermometry techniques, in order to make them more accurate, faster, and spatially resolved. A technique based on indium two-line atomic fluorescence (TLAF) thermometry was developed and applied, which employed a novel extended cavity diode laser design, and it was shown for the first time that temperature measurements with high accuracy and precision could be performed in low pressure sooting flames without recourse to calibration. Both the high precision and accuracy of the technique allowed for the deduction that the temperature in the flames studied here is relatively insensitive to changes in pressure in stark contrast to the soot volume fraction. Finally, it is shown for the first time that low power diode lasers can be used in combination with indium TLAF to measure spatially and temporally highly resolved temperatures in a quasi-continuous fashion. We demonstrated such measurements at effective rates of 3.5 kHz in a steady laminar test flame yielding an unprecedented precision of 1.5 % at ~2000 K at this measurement rate.

Selective cation-exchange adsorption of the two major whey proteins

Tue, 16 Mar 2010 00:00:00 GMT

Title: Selective cation-exchange adsorption of the two major whey proteins Authors: El-Sayed, Mayyada Abstract: Whey is a by-product of cheese manufacture, containing a mixture of proteins of commercial value, each having unique attributes for nutritional, biological and food ingredient applications. A tremendous amount of whey, normally treated as a waste product, is produced worldwide each year. This work describes the cation-exchange adsorption of the two major whey proteins, alpha-lactalbumin (ALA) and beta-lactoglobulin (BLG) with the purpose of optimising a process for isolating them from whey. Adsorption of pure BLG and ALA was studied onto SP Sepharose FF using 0.1M acetate buffer. Batch experiments were carried out at various pH values for ALA and BLG, and the relevant Langmuir isotherm parameters, dissociation constant, Kd, and maximum binding capacity, qm, were determined. The optimum pH for separation was chosen to be pH 3.7. At pH 3.7, both Kd and qm pertaining to ALA were found to have higher numerical values than those of BLG, implying different characteristics of adsorption of the two proteins on this adsorbent. The Kd for the former protein was almost four times larger than the latter, while qm was 1.3 times higher. Packed-bed column adsorption was performed using a 1-ml column at pH 3.7, flow rate 1 ml/min and initial concentration of 3 mg/ml for BLG and 1.5 mg/ml for ALA both in 0.1M sodium acetate buffer. The t1/2 for the resulting ALA breakthrough was 75% longer than its BLG counterpart. The above results suggest the possibility of the occurrence of competitive adsorption between the proteins when adsorbed simultaneously. In traditional batch uptake experiments, the kinetic rate constants of ALA and BLG in both the single- and two-component systems were determined using the simple kinetic model. The values so obtained implied that BLG was adsorbed faster than ALA. In the confocal laser scanning microscopy experiments, the different behaviour of ALA and BLG in the single-component system with regard to their penetration within the adsorbent beads suggested that the two proteins have different transport mechanisms governing their adsorption. The two-component system results showed that ALA was able to displace BLG in spite of the lower affinity of the former protein to the adsorbent. The packed-bed adsorption and elution of a mixture of ALA and BLG were then investigated under the above conditions but using a 5-ml column. BLG breakthrough occurred first, and its concentration in the outlet exceeded its feed value by 1.6 fold before declining to the feed value, followed by the breakthrough of ALA. ALA displaced and eluted all the BLG from the column in a pure form. Pure ALA could then be eluted with good recovery. The single- and two-component breakthrough curves for ALA and BLG were simulated by the simple kinetic model using the isotherm parameters, but the overshoot phenomenon could only be predicted after correcting these parameters. The evidence of the competitive nature of adsorption observed in binary mixtures was used to develop a facile separation procedure for the two proteins from aqueous solutions of whey concentrate powders. A novel consecutive two-stage separation process was developed to separate ALA and BLG from whey concentrate mixtures. Almost all the BLG in the feed was recovered, with 78% being recovered at 95% purity and a further 20% at 86% purity. In addition, 67% of ALA was recovered, 48% at 54% purity and 19% at 60% purity. The correction factors employed for the pure binary mixture were used to simulate the breakthrough curves of the two proteins in experiments conducted with whey concentrate in each of the two stages of the novel separation process, and there was agreement between the experimental and theoretical results.