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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

The transfer of radionuclides from sea to land in sea spray

Nelis, Patrick M. January 1990 (has links)
This thesis reports on an investigation into the transport inland in sea spray of radionuclides discharged into the Irish Sea from the nuclear plant at Scllafield in Cumbria. The work was carried out in response to a concern about the increased incidence of childhood leukaemia in the vicinity of Britain's nuclear reprocessing facilities. It is proposed that the sea spray transfer is an important pathway of discharged radioactivity into the human environment. The inland transfer of contaminated sea spray was investigated on the beach at Drigg, between 6 and 10 km south of the BNFL Scllafield marine discharge pipeline, through which significant levels of radionuclides have been flushed since 1952. The radionuclide concentrations of coastal marram grass vegetation and collected on exposed muslin screen passive droplet collectors are reported. The method used to determine the mass of sea-salt collected by the exposed screens is described and the results of these measurements presented. The collection of the natural atmospheric radionuclide 7Bc on the exposed muslin screens was used to extract the effects of the changing wind flow on the collection of the spray droplets at different distances inland. This allowed an elucidation of the true reduction in the radionuclide air concentrations with distance from the sea. The Sellafield-produced radionuclides present on the exposed screens were found to decrease with distance inland at the same rate as the collected sea-salt, implicating the sea spray droplets as the carriers of the radioactivity. A model of the inland transfer of sea spray droplets produced in the turf zone along the shoreline is described. The collection of the contaminated spray in coastal soil, vegetation and muslin screen collectors is simulated. This model gives results which fit the measured reduction in radionuclide air concentrations with distance from the sea. A successful application to datasets of the inland transfer of spray and radioactivity reported elsewhere is also illustrated. The analysis of the changing surface air concentration with distance inland illustrated that the initially rapid reduction measured here and elsewhere is due more to the spray droplets being mixed to higher altitudes than their deposition to the ground. An analysis of a sea spray collection event in which very high radionuclide air concentrations were measured calculates that under certain conditions 1 km of coastline can produce 1.54xl05Bq of 239+240pu and 1.10xl05Bq of 241Am per hour. This material is thought to be efficiently transported inland in sea spray, and 60% of it is calculated to be still airborne 1 km from the coast. It is concluded that the sea spray transport of marine discharged radioactivity transfers significant levels of long-lived radionuclides to the land, much of it in the respirable size range, and that this material can be carried to large distances from the sea. This pathway merits further investigation as the causes of the increased leukaemia incidence in West Cumbria are sought.
12

Object tracking with a pan, tilt and zoom camera

Sinclair, Mark Macdonald January 2005 (has links)
This thesis reviews the existing work done on tracking with pan/tilt/zoom cameras and proposes a novel method of multiscale block tracking with perspective cameras using principles and methods from both computer vision and computer graphics. The theory of perspective transforms in 3D graphics is reviewed as well as relating real world cameras to synthetic cameras through camera calibration. Conventional 2D block tracking methods are reviewed and the expanded to track under pan, tilt and zoom conditions. Two methods of pan/tilt/zoom tracking are developed and then applied to blocks and blobs (connected regions of pixels). A novel offline technique of fitting contours to these track points is then explored with and without the presence of pan, tilt and zoom. A method of updating the multiscale reference block is presented and the tracker is evaluated without block updating (feed forward) and with block updating and position filtering. Experimental results for people following are presented using synthetic ray-traced data with absolute ground truth and real sequences taken with a commercial pan/tilt/zoom camera with hand estimated ground truth. All sequences were processed offline, however, with optimisation it appears to be feasible to implement a real-time solution. Applying position filtering and predictions, using a Kalman filter, improves results and robustness. The application of this method to existing vision techniques is discussed as well as the possible methods for real-time implementation of these algorithms.
13

A high performance distributed data acquisition system for the NA48 experiment on CP-violation

Mckay, Nicholas Ewen January 1995 (has links)
This thesis describes the data acquisition methods employed by the NA48 experiment at CERN. A brief overview of the physics behind NA48 and a description of the experimental apparatus are given in the introduction. The specification and the implementation of the data acquisition system is then detailed along with a discussion of the design 'philosophy' that influenced the design choices. The section of the data acquisition system on which I have been working, the Data Merger, is discussed in some detail. Next, my main contribution to NA48, the Input Buffer, is described along with its performance in laboratory tests and data taking runs. Alternative solutions to the problems of acquiring data are also discussed along with examples of similar experiments data taking schemes. Finally, the conclusions that can be drawn from the design and performance of the NA48 data acquisition system are discussed.
14

Design and applications of Fourier transform processors using surface acoustic wave and charge coupled devices

Jack, Mervyn A. January 1978 (has links)
The current availability of analogue surface acoustic wave (SAW) and charge coupled devices (CCD) permits the hardware realisation of real time Fourier transform processors as an alternative to use of the digital fast Fourier transform (FFT). This thesis demonstrates how such analogue Fourier transform processors have been designed, developed and applied to engineering systems since the initial work in the years 1974-1975. A rigorous mathematical analysis of the operation of the SAW (chirp) Fourier transform is presented. This demonstrates that recovery of transform components at baseband demands high tolerance components and circuit design. However, by holding the outputs on a carrier, considerable hardware simplification is possible. Specific applications in spectrum analysis, cepstrum analysis and signal correlation are considered since these permit operation with the transform components on a carrier. In addition, the design and application of CCD Fourier transform processors, based on the chirp-z-transform and prime transform algorithms is presented. The performance of these analogue processors is compared to that of the digital FFT. This work leads directly to consideration of the design and application of Fourier transform processors which incorporate combinations of SAW and CCD devices. Experimental results are included throughout to demonstrate the operation of the systems discussed in the thesis.
15

Breaking waves and the dispersion of surface films

Schlicke, Ted January 2001 (has links)
The techniques of Laser Induced Fluorescence (LIF) and Dual-Plane Particle Image Velocimetry (PIV) were applied to the investigation of breaking waves and the dispersion of surface films. LIF was used to obtain widescreen images of the concentration distribution of a methanol-rhodamine B film after breaking. Five different wave amplitudes were studied, corresponding to a range of breaker types from weakly spilling to strongly plunging. Spatial and temporal information to quantify the dispersion was extracted from these images, such as the depth reached and area covered by the film, the motion of its centre of mass, dispersion coefficients and exponents, and the fractal dimension of the film-water boundary. The depth measurements and fractal dimension calculations compared well with related work. All three velocity components of the water motion were measured using dual-plane PIV and a single camera. The vector maps obtained revealed the cascade from large to small scale vortices, and the transition from two to three dimensional flow after breaking. A 4-camera system was built, capable of producing sequences of images triggered in rapid succession up to a total of 120 frames per second. Each camera could be individually filtered, allowing the possibility of simultaneous PIV and LIF.
16

Coplanar interdigitated band electrodes for electrosynthesis

Belmont, Cecile January 1994 (has links)
The behaviour of coplanar cathodic and anodic band electrodes was investigated and their use for standard syntheses was proven to be considerably advantageous, when compared to other techniques. Electrode arrays were fabricated by screen printing platinum, silver or carbon inks. The inter-electrode distances were in the range 1 mm to 250μm for a constant band width of 1 mm. The mass transport was characterised for different inter-electrode distances and flow conditions. Figures compared positively with other cells. Two acceptable mathematical models were derived for the estimation of the resistance between coplanar band electrodes and were compared with results obtained experimentally or by simulation. Due to their excellent physical and chemical properties, platinum electrodes were found to be particularly well suited for the three syntheses investigated. The furan methoxylation, being carried out in a resistive solvent, was chosen to highlight the advantage of minimising the ohmic drop. It was also shown that the formation of by-product could be limited by acid neutralisation on the adjacent band. Vigorous mixing conditions were not crucial. With the 250 μm inter-electrode array, DHDMF could be produced with a current efficiency of 87%. This compared extremely well with other cells and furthermore the energy consumption could be reduced to 1.4kWh.kg<SUP>-1</SUP>, which represented a saving of at least 50%. The importance of having small ohmic losses was also encountered for the Kolbe reaction, where the applied voltage was set at high values. However the printed platinum film was too rugged and a passivation of the electrode was noticed. The advantage of having small inter-electrode distances was stressed by investigating the propylene epoxidation, which is a coupled reaction. Propylene oxide was produced at a rate of 0.12 mol.h<SUP>-1</SUP>.dm<SUP>-2 </SUP>for an energy consumption of 2.0 kWh.kg<SUP>-1</SUP>. This technique was thus found to be very competitive. Finally the possibility of using this method for the production of hypochlorite by electrolysis of sea water was investigated.
17

Atomic force microscopy on self-assembled polymer structures

Glynos, Emmanouil January 2007 (has links)
In Part A we started our studies by investigating the morphology of physisorbed linear and star polybutadiene (PB) on a freshly cleaved mica surface from dilute solution after solvent evaporation . For the case of linear PB, we found that the dependence of the M<sub>w </sub>on the observed polymer structures is crucial for samples with relatively high surface density where the interactions among the adsorbed polymers become significant. For a relatively high surface density we observed a tendency of the adsorbed polymers to aggregate for all the molecular weight molecules and an isotropic structural pattern was observed. We explained these structural phenomena with increasing surface density in terms of the molecular interactions of the adsorbed polymers when in good solvent conditions and after the abrupt solvent evaporation. For the case of star PB we present a study of the structure and growth of star shaped polymer monolayers on mica. The fine structure study revealed that the monolayer morphology depends strongly on the functionality (number of arms) of the star polymer. We studied poly(isoprene-<i>b</i>-ethylene oxide) block copolymer micelles on mica under ambient conditions (in our laboratory). We found that the time dependent behaviour of the polymeric islands arises from the surface 'aging’ of freshly cleaved muscovite mica from highly hydrophillic when freshly cleaved to less hydrophillic with the exposure time in ambient conditions. In part B the AFM is proposed for the first time as a tool to image the surface of polymer microbubbles at the nanometer range in liquid and to perform reproducible measurements on the nano/micro mechanical properties. We applied the AFM to assess structural aspects of the microbubble shell and probe their mechanical properties. As microbubbles are large objects compared to the overall size of usual AFM tips a convolution between the AFM tip and the microbubble was typical of the acquired topographies. However, a small part of the top of the bubble was imaged with nanometer resolution and roughness measurements are reported. Using contact mode AFM force-distance curves were captured and the range of stiffness (or effective spring constant) of BiSphere microbubbles was systematically measured.
18

Applications of laser desorption laser photoionisation time-of-flight mass spectrometry

Redpath, Craig Robertson January 1995 (has links)
This thesis describes the development and application of laser desorption laser photoinisation time-of-flight mass spectrometry (L<SUP>2</SUP>TOFMS) for the analysis of polymers and related systems. L<SUP>2</SUP>TOFMS has been little used in this area until now. In the past, this technique has been used extensively for the study of high mass, involatile and/or thermally labile species such as biomolecules, porphyrins and dyestuffs. The theory behind the main experimental principles is discussed and the equipment used is described in detail. The main body of the thesis is concerned with the generation of high quality polymer mass spectra. Utilising several ionisation wavelengths, the mass spectra of several aromatic polymers have been obtained for the first time. For two model polystyrene systems, polystyrene 800 and 2500, a series of intense oligomer peaks and some fragments were observed at each photoionisation wavelength employed. Fragments were shown to occur in the laser desorption event, a phenomenon previously documented. However, an intact oligomer series for these polymers had never previously been observed using this technique. The data obtained allowed a complete and unambiguous characterisation of the polystyrenes to be made. Molecular weight averages were calculated from the spectra. When 193 nm photoinisation was employed, these values compared favourably to those supplied by the manufacturer. However, photoinisation by either 248 nm or 266 nm UV radiation resulted in mass spectra which gave lower molecular weight averages. This was primarily due to oligomer fragmentation at these wavelengths. The analysis and characterisation of a fluorinated polystyrene and phenyl containing siloxane polymer was also carried out. L<SUP>2</SUP>TOF mass spectra were also recorded for several polymer additives in their pure form. Two compound classes of additive were studied, namely UV stabilisers and phenolic antioxidants.
19

Multiple CCD array digital particle image velocimetry

Dewhirst, Timothy Peter January 1998 (has links)
Digital image processing is a technologically limited subject, and has seen tremendous growth over the last ten years with the exponential increase in computing power commonly available. This tend can be seen in Particle Image Velocimetry (PIV) as the migration from traditional wet film cameras to fully digital systems. The use of digital cameras in PIV measurements has been commonplace for a number of years. However, the majority of the reported systems suffered from low spatial and temporal resolution due to the architecture of commonly available cameras. The aim of this thesis was to construct a system which was entirely digital, with high spatial resolution and flexible timing abilities, removing the need to use image shifting. In order to create such a system, a state of the art in digital imaging technology was reviewed. The conclusion of this study was that in order to achieve the aims set, a multiple CCD (Charge Coupled Device) system would be required. The prototyping and construction of both two- and four-CCD array cameras is described. The software required to analyse images from low spatial resolution sources (relative to film) is also described, including the precautions that must be taken to ensure unbiased and accurate velocity measurements. Finally, the multiple CCD-array systems were applied to a number of flows to prove the concept. These include the study of breaking waves, wave motion over submerged pipes, and extension of the PIV technique to enable the measurement of accelerations.
20

Particle image velocimetry applied to waves with surface active films

Pullen, John January 1999 (has links)
The technique of digital particle image velocimetry (DPIV) and the related technique of particle tracking velocimetry (PTV) are described. These techniques were extended and applied by the author to the study of surface active chemical films on the mechanics of capillary-gravity waves. The two custom-made facilities for these studies are described along with specialised image processing software developed by the author. Finally, results from a series of experiments are presented which detail the damping of wind waves by surface active films, measurements of wind induced surface drift and the alteration of surface particle trajectories. Results from all three experiments were compared with theoretical predictions.

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