A Novel Biosensor Using Nanolithographically-Produced Submicron Optical Sources for the Study of Cell Adhesion and Chemotaxis

Cell adhesion and chemotaxis are two key factors determining cell behaviour and differentiation which are currently analysed by microscopic examination of the cell or membrane-associated fluorescence labels. These analyses are often slow, labour intensive and of limited informational content. This thesis describes the physical theory and experimental aspects of an optical method suitable for monitoring cell contact, adhesion to a surface and chemotaxis beyond the conventional limit of optical microscopy by means of a device that utilises both a plain bare surface and arrays of apertures nanolithographically-produced in the surface of a Surface Plasmon Resonance (SPR) sensor structure. Any minute vertical movement of the cell, within the near-field of the SPR active surface or actual cell/surface contact, creates intensity fluctuations, detectable in the far-field. This was demonstrated during experiments with non-apertured devices. (A video demonstrating the biological features of the device accompanies this thesis and may be obtained by contacting University of Plymouth's LRC.) The light scattered by each nanolithographically-produced aperture also fluctuates as a consequence of the cell approaching to within a few hundred nanometres of the aperture bearing surface and demonstrated detection of minute vertical movement on the surface of the apertured device. The combination of apertured and non-apertured detection results in a highly spatially-sensitive 3-dimensional sensor. Digitising the output from a CCD camera allows patterns of intensity fluctuation to be correlated with the contact and adhesion of individual cells on the active surface over a short period of time (2-3 minutes). Initial trials of an apertured device (diameter (^) « wavelength of incident light ( X ) ) carried out by our collaborating partners Drs R. Carr and S. Al-shukri at the Centre for Applied Microbiology and Research, Porton Down demonstrated that the use of apertures etched in a SPR metal surface produced a highly sensitive dielectric monitor, i.e. sensitive to very small changes in the refractive index of the micro-environment adjacent to the aperture. This was proposed as being of potentially great value in the development of extremely sensitive probes of dielectric particulates of sub-micron dimensions, i.e. biological macromolecules and supramolecular structures. Characterisation of the associated radiative and non-radiative evanescent fields on the surface of the device was conducted in order to gain a greater knowledge of the mechanisms by which the interactions between the cells adjacent to and in direct contact with the apertures and evanescent fields produced such significant intensity fluctuations in the results at CAMR. A combinational Scanning Probe Microscope was developed and used in Scanning Nearfield Optical Microscope and Photon Scanning Tunnelling Microscope modes of operation to detect the evanescent and radiative fields respectively. Detailed mapping of the radiative pattern in the near-field of the large apertures {<p » X) demonstrated a diffraction of approximately 25% of the Surface Plasmon Wave (SPW) either side of the centre of the aperture with the remainder being contained within the metal layer. Scattering at the second aperture interface, i.e. air/metal, was shown to be of a lower magnitude as a result of non-surface plasmon enhancement within the non-resonant aperture. Characterisation of the intensity profile of small apertures (^ < A) was beyond the scope of this project due to its limited time and finance and was not undertaken. A section in the conclusions is dedicated to giving a possible cause of the intensity profiles IV detected during the initial studies at CAMR with possible procedures required to verify and expand such work. In order to investigate the potential of the device in the biological environment, biological trials were carried out with collaborating establishments at Salisbury and Exeter and demonstrated that this dual sensing microscopic technique had great potential in the 3-dimensional monitoring of cell movement together with the capability of extending our knowledge of cell behaviour with the view to a system of rapid screening for tumour cells. This technique has produced real-time images of cell behaviour, which to our knowledge has not been previously seen before by any other microscopy technique. The finding of these trials are documented in this thesis with possible theories as to what the biological effects responsible for these results may possibly be. Future work into the verification of these effects and more biological trials and procedures are described in the hope that afler further work the device may be developed into a commercial and readily available scientific unit for use in the laboratory.FORCE Cancer Research Centre, Exeter and Centre for Applied Microbiology and Research, Porton Dow

PARTIAL NEEDLE LIFT AND INJECTION RATE SHAPE EFFECT ON THE FORMATION AND COMBUSTION OF THE DIESEL SPRAY

Fuel direct injection represents one of the key turning points in the development of the Diesel engines. The appeal of this solution has been growing thanks to the parallel advancement in the technology of the injection hardware and in the knowledge of the physics involved in the spray formation and combustion. In the present thesis, the effect of partial needle lift and injection rate shaping has been investigated experimentally using a multi-orifice Diesel injector. Injection rate shaping is one of the most attractive alternatives to multiple injection strategies but its implementation has been for long time impeded by technological limitations. A novel direct-acting injector prototype made it possible to carry out the present research: this injector features a mechanical coupling between the nozzle needle and the piezo-stack actuator, allowing a fully flexible control on the nozzle needle movement and enabling partial needle lift as well as the implementation of alternative injection rate shapes typologies. Different optical diagnostics were applied to study the spray development and combustion in a novel continuous flow test chamber that allows an accurate control on a wide range of thermodynamic conditions (up to 1000K and 15MPa). In addition, hydraulic characterization tests were carried out to analyze the fuel flow through the injector nozzle. Partial needle lift has been found to affect the injection event, reducing the mass flow rate (as expected) but also causing a reduction in the effective orifice area and an increase on the spreading angle. Moreover, at this condition, higher hole-to-hole dispersion and flow instabilities were detected. Needle vibrations caused by the needle interactions with fuel flow and by the onset of cavitation in the needle seat are likely the causes of this behavior. Injection rate shaping has a substantial impact on the premixed phase of the combustion and on the location where the ignition takes place. Furthermore, the results proved that the modifications in the internal flow caused by the partial needle lift are reflected on the ignition timing. On the other hand, the analysis of the experimental data through a 1D spray model revealed that an increasing mass flow rate (e.g. ramp or boot injection rate profiles) causes an increase in the fuelair equivalence ratio at the lift-off length and a consequent higher soot formation during the diffusive phase of the combustion. Finally, the wide range of boundary conditions tested in all the experiments served to draw general conclusions about the physics involved in the injection/combustion event and, in some cases, to obtain statistical correlations.Bardi, M. (2014). PARTIAL NEEDLE LIFT AND INJECTION RATE SHAPE EFFECT ON THE FORMATION AND COMBUSTION OF THE DIESEL SPRAY [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/37374TESI

Study and Performance Enhancement of Fast Tool Servo Diamond Turning of Micro-structured Surfaces

Ph.DDOCTOR OF PHILOSOPH

Infra-red astronomical photometry : one to twenty microns

Imperial Users onl

A Fibre Optical Strain Sensor

Strain-sensing elements, fabricated in standard communications-grade single mode optical fibre, are increasingly being considered for application in structural health monitoring. The reason for this is the numerous advantages demonstrated by these devices compared with traditional indicators. This thesis describes work carried out on optical sensors at the University of Plymouth. The aim of this work was to achieve an optical fibre strain sensing system capable of measuring absolute strain with good resolution and having wide dynamic range, without bulky optical equipment and not susceptible to misalignment due to handling. Earlier work was devoted to study on an intrinsic Fabry-Perot interferometric sensor and an optical phase-shift detection technique. The sensing element investigated relied on the end face of an optical fibre as one mirror and the second mirror being a layer of Titanium Dioxide (TO2). Although some results are included, it was soon realised that this sensor had a number of problems, particularly with fabrication. As no simple solution presented itself, consideration was given to a sensor that made use of the change in reflectance of an intra-core fibre Bragg grating when the grating was subjected to strain. The bulk of work described in this thesis is concerned with this type of sensing element. The grating structure is inherently flexible and a number of structural formats were studied and investigated. The first and simplest grating considered was two linearly chirped Bragg gratings used in a Fabry-Perot configuration (a grating resonator). The sensor was tested using the sensing detection system and although the fabrication problems were overcome absolute strain measurement was unattainable. To achieve this end, a theoretical study of a number of grating structures was carried out using the T-matrix Formalism. Confidence in using this approach was gained by comparing the spectral behaviour of a proposed grating with results, which were given by another theoretical model for the same proposed grating. The outcome of this study was that two structures in particular showed promise with regard to absolutism (the measure of true strain) and linearity. Discussions held with the department of Applied Physics at Aston University about fabrication resulted in one of the proposed designs being abandoned due to difficulties of fabrication. The second structure showed more promise and fabrication attempts were put in hand. This grating is linearly-chirped with a Top-hat function and a sinusoidal perturbation as a taper function of the refractive index modulation. Experiments were performed, data were acquired and system performance for this sensor is presented. The thesis concludes that using such a fibre Bragg grating as the sensing element of a strain sensing system enables it to measure absolute strain without using bulky optical equipment. At present, the resolution of strain is limited by the quality of the grating being fabricated (anomalies on profile), this should improve once the fabrication technique is refined.British Aerospace System and Equipment, BASE and Department of Electronic Engineering and Applied Physics, Aston Universit

EUROSENSORS XVII : book of abstracts

Fundação Calouste Gulbenkien (FCG).Fundação para a Ciência e a Tecnologia (FCT)

Development of optical techniques for space-borne laser interferometric gravitational wave detectors

This thesis deals with aspects of gravitational wave detection relating directly to the proposed LISA mission. The thesis begins with a review of gravitational wave astrophysics, starting with a brief description of the prediction and nature of gravitational radiation as a consequence of General Relativity. A short description of possible astrophysical sources is given along with current estimates of signal sources and strengths. The history of gravitational wave detectors is then briefly outlined, from the early 1960s and the first resonant bar, through to the modern long baseline laser interferometers currently under construction. Discussion then turns to the joint ESA/NASA space-borne interferometer, LISA. LISA involves picometre precision laser interferometry between spacecraft separated by millions of kilometres. Among the considerable technical challenges involved are the need for laser and clock frequency stabilisation schemes, active phase-locked laser transponders and precision telescope design. After an overview of the mission concept, the thesis deals with the issue of gravitational wave signal extraction from the various interferometric data streams produced in the six LISA spacecraft. A scheme for obtaining the necessary transfer of clock stability around the set of spacecraft is presented. LISA is planned to use diode-pumped solid state lasers. Experiments carried out to characterise the frequency noise of such a laser over the timescales of interest to the LISA mission are then described. Active frequency stabilisation to a triangular Fabry-Perot reference cavity is undertaken, with independent measurements of residual frequency noise obtained from a second analyser cavity. In LISA, the divergence of the laser beams as they propagate along the long arms of the interferometer means that only a very small amount of light is received by any spacecraft. The phase locking system has to function with this low received intensity and should, ideally, produce a transponded beam with relative phase fluctuations determined by the photon shot noise of the weak received light. A test and demonstration of the phase-locked laser transponder scheme for LISA is then presented. The frequency stabilised laser is used as the master oscillator, and a second identical laser is used as the slave. Results are obtained both from within the stabilisation system and also from out-of-Ioop measurements using an independent optical path. At relative power levels approaching those in LISA, performance close to the shot noise limit was demonstrated over part of the frequency spectrum of interest. Some excess noise was, however, found at milliHertz frequencies, most probably due to thermal effects. The thesis then continues with an investigation of far-field wavefront aberrations caused by errors in the transmitting telescopes originally planned for LISA. Any phase variation across the near field wavefront (defined as the wavefront on the primary mirror), caused, for example, by a mis-alignment of the telescope mirrors, will produce phase variation in the far-field wavefront. Coupled with pointing fluctuations of the incoming light, these wavefront distortions can cause excess displacement noise in the interferometer readout. The starting point of the investigation was to redesign the LISA telescope in order to remove both spherical and coma aberrations. Using Gaussian ray tracing techniques, the effect of near field aberrations on the far field phase was explored. A revised Ritchey-Chretien telescope design is described and numerical simulations presented. Finally the thesis concludes with a summary of the work carried out, setting the results in the context of the development of the LISA mission

Modification of an ignition quality tester and its use in characterizing middle distillate fuels

The Ignition Quality Tester ( IQTTM ) is a constant volume combustion chamber based device which is used to determine the derived cetane number of diesel fuel oils when used in conjunction with ASTM D6890. During a test, the fuel sample is injected into heated, pressurised gas where it combusts. Suitable measurements are made during the combustion event to determine the ignition delay of the fuel and the latter is used with a correlation to determine the derived cetane number of the sample. The IQT offers improved repeatability and reproducibility when compared with the conventional method of determining cetane number, namely ASTM D613. Despite these advantages, the device features a fuel injection system not indicative of the state of the art, in terms of direct injection diesel components and associated fuel spray behavior. Therefore this project sought to make suitable mechanical, electrical and control modifications to incorporate a more technologically appropriate injector. It is believed that by improving the spray characteristics of the IQT along with the incorporation of a flexible control system, that it can be leveraged to a greater extent in a fuels research context. The modifications made to the system included the incorporation of a single hole common rail diesel injector along with a custom control system. The control system allowed flexible control of all variables considered to be significant to the study of auto-ignition delays. Additionally, an optical sensor was added to detect luminous emissions from the reacting fuels. The modified system was used to rate diesel fuels with varied composition including solvents, diesel primary reference fuels, crude derived as well as Low Temperature Fischer Tropsch (LTFT) products. These tests were performed at two temperatures and oxygen concentrations and the resulting data was used to redevelop correlations between the cetane number of the respective samples and their ignition delays in order to surmise the optimal operating conditions of the modified IQT