2,248 results for 1900, Doctoral

  • Wavefront estimation in astronomical imaging.

    Irwan, Roy (1999)

    Doctoral thesis
    University of Canterbury Library

    The challenge in building astronomical telescopes is to obtain the clearest possible image of a distant star, which should appear as a single point. Extended objects, such as galaxies and planets can be regarded as collections of points. However, turbulence in the atmosphere degrades any optical signal that passes through it. The optical effects of the atmospheric turbulence arise from random inhomogeneities in the temperature distribution of the atmosphere. As a consequence of these temperature inhomogeneities, the index of refraction distribution of the atmosphere is random. Plane waves striking the atmosphere from space objects acquire an aberration as they propagate through the atmosphere. The plane wave's surface of constant phase is no longer planar when intercepted by a,n a.stronornica.l telescope. The prnctica.l consequence of a.tmospheric turbulence is that resolution is generally limited by turbulence rather than by optical design and quality of a telescope. There are a number of approaches to solving this problem, ranging from an orbiting telescope (the Hubble Space Telescope), adaptive optics, and post detection processing. The latter approaches have applications to less expensive ground based telescopes and have been the subject of many years of research. Adaptive optics is a general term for optical components whose characteristics can be modified in real time so as to alter the phase of an incident optical wavefront. An adaptive optics system can be used to correct for atmospheric induced distortions. Before any corrections can be applied, however, some measurement must be made of the phase distortions. It is the aim of this study to estimate the degradation of the wavefronts phase. Two approaches to do so are presented. Firstly, through wavefront sensors, which many adaptive optics systems have been devised from. Among them the Shack-Hartmann sensor is the most commonly used. The sensor requires a subdivision of the receiving pupil by means of sub-apertures, wherein the lowestorder deformation of the wavefront phase is estimated. This linearizes the problem of phase retrieval to solving a linear system of equations. A new analysis is presented which differs from previously published work in the estimation of the noise inherent in the centroid calculation used in this sensor. This analysis is supported by computer simulations. Secondly, the nonlinear approach of phase retrieval is discussed. The problem becomes how to relate the phase and magnitude of the Fourier transform. It is thus necessary to estimate the phase distortion in the instrument solely from measurements made at the image plane of the telescope. The process of phase retrieval is then divided into two distinct steps. The expression for the covariance of the phase distortion using a Kolmogorov model for the turbulence is derived first. This covariance is then employed as part of a formal Bayesian estimate of the phase distortion. It is also shown that phase retrieval can be employed as a robust technique for estimating the wavefront distortion using a lenslet array. The results obtained compare favorably with the alternative approach of phase diversity. Furthermore, the introduction of prior information, in the form of statistical information of the distortion, is shown to considerably enhance the success of the phase retrieval especially for very low light levels. A comparative evaluation shows the superiority of phase retrieval to Shack-Hartmann sensing, only if the local maxima are overcome. The principal drawback of phase retrieval is the relatively long computing time required to find the solution when general-purposed computer is used.

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  • The spectra of transition-metal ions in solids

    Johnstone, I.W. (1975)

    Doctoral thesis
    University of Canterbury Library

    The results of an investigation of the Raman and infrared spectra of cobaltous ions in cadmium-chloride, cadmium-bromide, and manganese-chloride, and of cobalt-chloride are presented. The cobalt ions substitute for the cation in these crystals and experience a trigonal crystal-field which splits the lowest ⁴T₁g (⁴F) cubic-field term into six Kramers doublets with energies in the range 0-1200 cm⁻¹. The Raman spectra, measured as a function of temperature and of cobalt concentration show all five single ion electronic transitions together with several lines due to cobalt ion pairs. The infrared spectra comprise both magnetic-dipole allowed electronic transitions and electric-dipole allowed vibronic lines and bands. They confirm the identity of the electronic transitions seen by Raman scattering and also yield information concerning the lattice modes of the host and the possible interactions within cobalt ion pairs. The strong field matrices of the trigonal crystal-field and Zeeman interactions are calculated for the d³ (d⁷) configuration and quantitatively explain the experimental data. The crystal-field analysis provides single ion wavefunctions for further calculations which successfully explain the spectra of antiferromagnetic CoCl₂ and exchange coupled colbalt pairs in CdCl₂ (Co²⁺) and CdBr₂ (Co²⁺). A preliminary investigation of the infrared absorption of an oxygen-induced impurity site in CdCl₂-type crystals is also presented.

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  • Upper atmospheric studies using radio meteors

    Wilkinson, Philip James (1973)

    Doctoral thesis
    University of Canterbury Library

    The atmospheric motions in the 80-110 km height region, and methods of measuring them are discussed. Wind measurements using radio meteor trails are then considered in greater detail and an account is given of the equipment at the field station of the Physics Department of Canterbury at Rolleston near Christchurch, as well as details of the data reduction methods used. An analysis of the errors associated with the collection of data indicates that approximately half the variance in an average of wind velocities observed in a thirty minute period is due to atmospheric variability. Results from the first year's observations suggest that the solar diurnal and semidiurnal tides are of roughly the same magnitude, this magnitude being in agreement with the latitudinal variations observed at other stations.

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  • The group theory of the harmonic oscillator with applications in physics.

    Haskell, T. G. (1972)

    Doctoral thesis
    University of Canterbury Library

    The possibility of the group SU₃ being used in the description of the (d+s)N and (d+s)npm many-electron complexes is examined by symmetrization of the Coulomb Hamiltonian. By dividing the Coulomb interaction into symmetry conserving and symmetry violating terms it is found that while the SU₃ scheme tends to give a better description in the (d+s)N case it shows no improvement over the configurational scheme in the (d+s)npm complex. The scheme is, however, very useful for the calculation of matrix elements of operators normally found in atomic spectroscopy and a complete set of symmetrized , scalar, Hermitian spin-independent two particle operators acting within (d+s)npm configurations is constructed. The radial wavefunctions of the harmonic oscillator are found to form a basis for the representations of the group 0(2,1) in the group scheme Sp(6,R) ⊃ S0(3) x 0(2,1). The operators Tkp = r2k are shown to transform simply under the action of the group generators. The matrix elements of Tkq and a selection rule similar to that of Pasternack and Sternheimer are derived. Finally the rich group structure of the harmonic oscillator is investigated and a dynamical group proposed which contains, as subgroups, the groups Sp(6,R), SU(3), H₄ and the direct product 0(2,1) x S0(3). Some remarks are made about contractions of groups, semidirect and direct products, and the generalization of the method to n-dimensions.

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  • Orbital characteristics of meteoroids

    Steel, Duncan (1984)

    Doctoral thesis
    University of Canterbury Library

    The bulk of meteoroidal particles follow pseudo-random orbits and are termed sporadic meteoroids. These are thought to be derived from the correlated streams of particles released by comets, although the mechanisms by which their orbits are dispersed have been the subject of some confusion. By developing techniques to compute the frequency of close encounters with each of the planets, and also the gross outcome of such events, it is shown that most sporadic orbits are a result of gravitational scattering by the giant planets. Jupiter plays the major role. Although catastrophic impacts with smaller particles limit the lifetimes of meteoroids, this mechanism is not responsible for the bulk of the stream disruption. With a simple model of the zodiacal cloud, the method is also used to find the collisional lifetime of meteoroids including for the first time the dependence upon inclination. The rate of meteoroid depletion by planetary collisions and hyperbolic ejections resulting from close approaches is calculated. It is found that for Jupiter-crossing meteoroids these losses are as rapid as those due to the PoyntingRobertson effect. This theory is also applied to six peculiar asteroids, including Hidalgo and Chiron. These prove to have extremely short-lived orbits: large orbital variations occur on a timescale of only ~10³ years. It is also shown that Pluto exists in its Neptune-crossing orbit solely because of the stable resonance which prohibits approaches between the two in the present epoch. The collision rate between the Apollo-Amor-Aten asteroids and each of the terrestrial planets is calculated using all 76 known objects. The result using this new procedure (4-6 Earth impacts per million years) is somewhat higher than previous estimates, indicating that these asteroids do not represent a steady-state population.

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  • Seismic resistant design of base isolated multistorey structures

    Andriono, Takim (1989)

    Doctoral thesis
    University of Canterbury Library

    The Base Isolation technique and its benefits in reducing the transmitted earthquake energy into a structure has gained increasing recognition during the last two decades. This recognition is indicated by the application of Base Isolation systems to a large number of bridges, several multistorey buildings and some power plants in countries which have high seismic risk. Unfortunately, the currently available design procedures, especially for multistorey structures, seem inadequate and too restrictive and as a result present practice still relies upon a series of deterministic time history analyses which are not only impractical for design purposes but appear unable to give the designer a clear insight into the seismic behaviour of the multistory structure. This research is carried out to investigate in more detail the effects of various structural parameters and ground motion characteristics on the seismic response of Base Isolated multistorey structures. It also reviews the shortcomings of the current design methods. The results are then used to develop two simplified analysis methods for practical design. The first method which is called the Code-Type approach can be used to accurately estimate the inertia forces, not only at the level of the isolation devices but throughout the height of the multistorey structure. It is recommended for use as a preliminary design tool or even a final design tool for simple Base Isolated multistorey structures. The second procedure which is based on the Component Mode Synthesis method is suggested for final design purposes of more complex Base Isolated multistorey structures. This method enables the designer to evaluate the effects of the isolation devices on the contribution of each mode of vibration to the total response of the structure.

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  • Ring laser dynamics.

    King, Benjamin Thomas (1999)

    Doctoral thesis
    University of Canterbury Library

    The departure of the behaviour of large ring laser gyros from the ideal is examined. A detailed description of the experimental operation of large ring lasers is provided along with several new innovations in equipment layout, data collection and especially in data reduction. The limits on gyro performance due to noise are investigated. A review of literature regarding the fundamental limit placed on gyro resolution is provided. This limit is due to spontaneous emission in the gain medium of the laser and it is demonstrated that our ring lasers approach this quantum limit. Two entirely independent methods for evaluating the quantum noise induced linewidth are demonstrated to agree well. One of the methods, which uses a second order autoregressive model, is able to make accurate linewidth estimates in sub-second gate times. A complex model is proposed which accounts for specific observed light scattering phenomena within a ring laser. This model is compared with dual beam data taken from C-I and is able to describe frequency shifts and waveform distortion accurately. The model also performs favourably when describing locking profiles for low rotation rates and externally induced perimeter modulation. When locked to an external signal the ring laser is found to be an extremely sensitive low frequency vibration detector. The commissioning of a very large (14 m perimeter) prototype ring laser gyro, GO, is described along with a comparison with the smaller ( 4 m perimeter) gyros C-I and C-II. This prototype has proven to be an invaluable testing ground for designs and techniques to be used on a proposed high precision 16 m perimeter gyro named the Grossring (G).

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  • Blind deconvolution and phase retrieval

    Lane, Richard George (1988)

    Doctoral thesis
    University of Canterbury Library

    Theoretical and practical aspects of identifying and deconvolving a convolution in more than one-dimension are presented. In contrast to conventional techniques which require knowledge of the blurring function, this thesis describes techniques for "blind" deconvolution. The techniques introduced differ from previous work in the field of blind deconvolution because they do not require an ensemble of similarly blurred images, i.e. they can be effectively employed upon a single convolution. The first method for blind deconvolution introduced relies on the analytic properties of the Fourier spectrum of a compact image. Rather than deal with continuous images, a discrete approximation is employed. It is argued, however, that approximation of the Fourier spectrum by a finite order polynomial model is a logical response to the practical constraints posed by limited a.mounts of noisy data. Since the convolution of two images is equivalent to a multiplication of their Fourier spectra, deconvolution is consequently equivalent to factorisation of their Fourier spectra. In one dimension it is always possible to factorise a polynomial, even when it is of infinite order. These factors correspond to isolated points, in the complex plane into which the Fourier spectra are analytically continued, where the spectra are zero. Since these points are distinct there are a large number of factors and hence there is usually a large number of ways of deconvolving a one-dimensional image. By contrast the analytically continued Fourier spectrum of a two-dimensional image exists in a four-dimensional space and is zero on a two-dimensional analytic surface, here called a zero-sheet. Because of the analytic nature of the zero-sheet it is not possible, in general, to factorise a two-dimensional spectrum or equivalently partition its zerosheet into separate analytic surfaces. The major exception is when the true image is a convolution in which case the zero-sheet is, in fact, the union of the zero-sheets of the components of the convolution. As a result the zero-sheet of a convolution can be partitioned into two zero-sheets which can be used to recover, to within a complex constant, the components of the convolution. The addition of noise is shown to link the zero-sheets of the components of the convolution. Consequently it is no longer possible to partition the zero-sheet without isolating and correcting these "bridges" between the zero-sheets of the components. The Fourier phase problem forms a special subclass of the blind deconvolution problem, one in which the true image and the blurring function are conjugate mirror images of each other. The data in the Fourier phase problem comprises the oversampled magnitude of the Fourier transform of the true image. Consequently, it is necessary to reconstruct the Fourier phase before an estimate of the true image can be formed. It is shown that a solution exists and the accuracy of the solution can be empirically related to the amount of noise present in the Fourier magnitude data. It is shown that a unique solution to the Fourier phase problem in more than one dimension exists except when the spectrum is the Fourier transform of a convolution. In this case, the number of solutions to the Fourier phase problem is related to the number of component images which have been convolved to produce the convolution. The second technique for deconvolution introduced in this thesis uses these multiple solutions to the Fourier phase problem to recover information about the phase of the spectra of the components of the convolution. The Fourier phase is, however, only recovered modulo π. The problems encountered in the modified magnitude problem, as it is called in this thesis, are analysed and techniques for overcoming these difficulties are described. A final result presented herein is an extension to an existing technique for blind deconvolution of ensembles of two-dimensional speckle images. It is shown that comparing the zero-sheets of the speckle spectra leads to a useful new approach to speckle imaging.

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  • Solid state spectroscopy : rare earth - hybride centres in the alkaline earth fluorides

    Jacobs, I.T. (1971)

    Doctoral thesis
    University of Canterbury Library

    Both the optical and infrared spectra of cerium and praseodymium tri-positive ions in the alkaline earth fluorines have been studied. Various charge compensation mechanisms have been employed including negative hydride, deuteride and tritide ions. For the hydride centres the degenerate local mode lines are resolved into more than one component. These splittings are attributed to electron-phonon interaction effects between the low lying rare earth 4f electronic states and the hydride ion local mode phonons. The 4f-5d electronic transitions of the cerium hydride type centres show large isotope shifts up to 50 cm⁻¹. Only the non-degenerate hydride ion vibration appears in the 4f-5d optical spectra and the vibrational interval is increased from absorption to fluorescence by as much as 15%. Both the isotope and vibronic shifts for the tetragonal cerium sites are attributed to electron-phonon interaction effects. Simple models involving point charges and point dipoles account in a semi-quantitative way for several features of the spectra but fail to account for either the sign or magnitude of the isotope and vibronic shifts.

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  • Upper atmospheric studies : some observations of the south tropical OI airglow phenomenon

    Malcolm, Roger K. (1972)

    Doctoral thesis
    University of Canterbury Library

    An account is presented of a series of observations of the dynamic behaviour of a region of the south tropical airglow·arcs made from Rarotonga (Lat. 21.2° south, long. 159.8° west) with the aid of a large aperture (90 cms), high resolution (½° beamwidth) scanning photometer. The night airglow is found to be strongly disturbed on many nights, characteristically by elliptical areas of lower than normal intensity drifting in an easterly direction. It was possible to associate their passage with the occurrence of 'spread-F' as observed by the Rarotongan ionosonde. An attempt is made to account for the airglow processes; suggestions are made concerning the possible origin of the disturbances; and their presence is examined in the light of the trans-equatorial propagation of V.H.F. signals from Hawaii, as recorded at Rarotonga.

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  • Solid state spectroscopy : the electron paramagnetic resonance spectra of gadolinium anderbium ions in hydrogenated alkaline earth fluoride crystals

    Edgar, A. (1974)

    Doctoral thesis
    University of Canterbury Library

    The Electron Paramagnetic Resonance technique has been used to study alkaline earth fluoride crystals doped with both hydride and gadolinium (or erbium) ions, and the spin Hamiltonian parameters have been determined for the various kinds of charge-compensated rare earth ion site which occur. In particular, two sites of tetragonal symmetry with the structures RE³⁺-FI⁻, RE³⁺-HI⁻ have been examined, and small shifts in the EPR spectra of the latter site have been measured when a deuteride or tritiide ion replaces the hydride ion. A crystal lattice model of point charges and point dipoles at distorted lattice sites predicts a value of the crystal field parameter B₀² for the tetraqonal sites which is only one half of that estimated from the observed spectra, but the model successfully accounts for the larger value of B₀² for the RE³⁺-HI⁻ site compared with the RE³⁺-FI⁻ site on the basis of the larger polarisability of the H⁻ ion. Isotope shifts are interpreted by the electron phonon interaction between the 4f electrons of the rare earth ion and the localised mode of vibration of the light anion. The magnitudes of the shifts, calculated on a point charge/point dipole model, are in good agreement with experiment. The reorientation of the tetragonal Gd³⁺-HI⁻ sites has been examined by EPR line broadening and dielectric loss techniques. No distinct dielectric loss peak corresponding to this site was observed, and it is proposed that it cannot be distinguished from that for Gd³⁺-FI⁻ sites. An interstitialcy model for the reorientation has been investigated and is found to be consistent with this explanation and with the observation of a metastable Gd³⁺-HS⁻-FI⁻ site in u.v. irradiated calcium fluoride.

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  • Some aspects of molybdenum halide chemistry

    Gainsford, G.J. (1969)

    Doctoral thesis
    University of Canterbury Library

    Chemical and X-ray crystallographic studies of molybdenum(II) halides, which are based on the well-known (Mo₆Cl₈)⁴⁺ cluster, have been carried out. Contrary to previous reports, the reactions of 2,2'-bipyridyl with the halides (Mo₆Cl₈)Cl₄ and (Mo₆Cl₈)I₄ yield, even under mild conditions, bipyridylium salts of chloromolybdic(II) and iodomolybdic(II) acids respectively: (BipyH)₂((Mo₆Cl₈)X₆) where X = Cl, I and Bipy = 2,2'-bipyridyl. The reactions are complicated by the formation of mixtures of products, which are mainly various crystalline forms of the bipyridylium salts. An amorphous product may be a true mono-bipyridyl complex. An unusual oxidation occurs during the reactions of triphenylphosphine (Ph₃P) and triphenylarsine (Ph₃As) with (Mo₆Cl₈)Cl₄ and (Mo₆Cl₈)I₄. Infra-red spectral and X-ray powder photographic studies show that the oxidized ligand complexes, (Mo₆Cl₈)X₄(Ph₃Z0)₂ (X = Cl, I; Z = As,P), are formed except under conditions in which both molecular and chemically-bound oxygen is rigorously excluded. The conditions required to coordinate more than two neutral unidentate ligands to the (Mo₆Cl₈)⁴⁺ cluster have been examined. It proved possible to obtain new ionic complexes under a range of conditions. The six-fold coordination of the (Mo₆Cl₈)⁴⁺ cluster is maintained in these compounds (e.g. ((Mo₆Cl₈)I₃(triphenylphosphine oxide)₂(pyridine))⁺I⁻) by the ionization of one or more of the terminal halogen atoms in the molybdenum(II) halide starting material (e.g.(Mo₆Cl₈)I₄). The X-ray single crystal structures of two isomorphous salts, (BipyH)₂(( (Mo₆Cl₈)X₆) (X = Cl,I), have been solved using the difference Patterson method. To solve another crystalline modification of the chloro-salt, the (Mo₆Cl₈) cluster was constrained to its established geometry with its centroid fixed at the origin of the unit cell. This rigid group of atoms was then rotated by the least-squares refinement of the three orientation-defining angles. The three structures contain discrete ((Mo₆Cl₈)X₆)²⁻(X = Cl,I) and (C₁₀H₉N₂)⁺ (bipyridylium) ions. The anions consist of highly-symmetric (Mo₆Cl₈) clusters (Mo-Mo = 2.606, Mo-Cl = 2.48 Ao), with six terminal halogen atoms (X) bound by single covalent bonds to the molybdenum atoms (Mo-Cl = 2.423, Mo-I = 2.737 Ao). The bipyridylium cations are twisted from perfect cis conformations in all three structures. The average dihedral angle between the two rings is 13 degrees. Further details of the geometries of the anion and cation are discussed. The ionic packing in the three crystals is dominated by the bulky anions. These are arranged in expanded "hexagonal close-packed" layers with the cations centred on approximately trigonal holes in this array. The two crystalline modifications of the chloro-salt differ in the orientation of the bipyridylium cations in these layers.

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  • Uranium luminescence

    Nicholas, J.V. (1966)

    Doctoral thesis
    University of Canterbury Library

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  • Some studies of the theory and application of continuous groups in atomic spectroscopy

    Cunningham, M.J. (1971)

    Doctoral thesis
    University of Canterbury Library

    This thesis is concerned with the representation theory of continuous groups both compact and non-compact and its application to atomic spectroscopy. In Chapter I some atomic wavefunctions for equivalent electrons in the group scheme SU2 x (U2l+1 R2l+1 R3) are constructed in terms of electron fermion creation and annihilation operators. The concept of semiconjugacy is defined and shown to reduce the number of states that must be explicitly calculated. The states of the d shell are calculated and tabulated. In Chapter II it is shown how to extract n-body cfp's associated with arbitrary auxiliary quantum numbers from the n-body generalisation of Redmond's formula. The method is applied to give explicit formulae for the squares of one body cfp's of the atomic d-shell. Group theory is applied in Chapter III to extend the quasiparticle formalism developed by Armstrong and Judd to expose the complete group structure of the eigenfunctions of the equivalent electron l shell. A simple method for relating quasiparticle states to determinantal states and for calculating quasiparticle matrix elements is developed. The need for fractional parentage coefficients in calculating these matrix elements is eliminated. In Chapter IV the technique and formalism is extended to describe general mixed configurations. The hydrogen atom is factorised according to the scheme 0(4,2) 0(2,1) x 0(3) in Chapter V and the radial group 0(2,1) studied. It is shown that rkD n/(n+q) , where Da is a dilatation operator, is proportional to a tensor operator in this scheme, allowing a group theoretical study of the radial matrix element rk, including an explanation of the Pasternack and Sternheimer selection rule. The technique is extended in Chapter VI to solve a differential equation directly related to the generalised Kepler equation of Infeld and Hull in an 0(2,1) x 0(3) group scheme. This equation contains as special cases the Schrodinger, Klein-Gordan, and Dirac (two forms) hydrogen atoms. A generalised Pasternack and Sternheimer selection rule exists and some matrix elements can be evaluated group theoretically.

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  • Lower ionospheric irregularities

    Vincent, R.A. (1967)

    Doctoral thesis
    University of Canterbury Library

    This thesis is a study of the structure of that part of the ionosphere lying between 60 and 120 km. In the usual terminology the ionized parts of the atmosphere in this altitude range are called the ionospheric D and E regions, the boundary between them occurring at a height of 90 km. Above this height the E region extends upwards to 140 km, the base of the F region. Since the ionization below 50 km is not enough to effect the propagation or radio waves this height effectively marks the bottom of the D region. There is also another system of nomenclature based on the neutral gas temperatures of the atmosphere. The mesosphere lies in the altitude range 50 to 85 km, which is a region of decreasing temperature with height. Because they refer to the same height range the terms mesosphere and D region are often used synonymously in the following work. Above 90 km the temperature increases, rapidly at first and then more slowly, in the thermosphere.

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  • Erwin Strittmatter in reference to the agarian novel of the nineteenth and twentieth centuries

    Gebbie, Ian William (1978)

    Doctoral thesis
    University of Canterbury Library

    This study deals with two aspects of German literature: the agrarian novel from the early nineteenth century to National Socialism, and a comparison of capitalist and socialist ideology, using the works of the DDR author Erwin Strittmatter. In the first part of the thesis, chosen works are analysed with the aim of establishing a pattern of bourgeois idealism and of tracing its development in reference to the changing historical background. The political implications of the nationalist transformation and radicalisation of the conservative agrarian ideology, which grew up as a middle-class reaction to the emergence of modern industrial Germany, are illustrated by the combination of the heroic and the idyllic in fascist literature. The second part deals with the socialist agrarian novel, which is discussed, in the light of Marxist theory, as a departure from the conservative model, and in relation to different political ideals and objectives. Three agrarian novels of Erwin Strittmatter Ochsenkutscher, Tinko and Ole Bienkopp - are examined in detail as the basis for contrast with capitalist doctrine and for observations on the role of literature in the DDR. The concluding chapter illustrates how, in the established East German state of the 1960's, the disregard for the demands of authority, which is a feature of Strittmatter's Ole Bienkopp, indicates a return to the traditional pattern of bourgeois idealism within the confines of socialist morality.

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  • An evaluation of the validity of multidimensional scaling methods : for the representation of cognitive processes

    Fraser, Christopher O (1980)

    Doctoral thesis
    University of Canterbury Library

    This study is an evaluation of the issues involved in providing a meaningful psychological interpretation of multidimensional scaling solutions, for example to regard them as valid representations of the cognitive processes involved in generating the data. The various metatheoretic approaches that have been developed to define appropriate procedures for the quantification of psychological attributes are discussed and evaluated. It is argued that much current psychological research is based on an inappropriate paradigm. In particular it is argued that the emphasis on magnitude estimation to generate psychological data is misplaced and scales derived from weak-ordered judgements are much to be preferred. Extending these arguments to the multidimensional case, it is argued that most applications of multivariate methods in psychology have shown insufficient recognition of the theoretical implications of using a particular technique. The application of any method of data analysis such as multidimensional scaling is only appropriate if it can be shown that the assumptions implicit in the scaling model are satisfied for that set of empirical data. In addition some variations in the scaling model, such as subjective metrics scaling, involve additional assumptions which need to be explicitly formulated and tested. These metatheoretic limitations, as well as evidence on the frequent occurrence of violations of its basic assumptions suggest that multidimensional scaling configurations can at best be attributed with only a limited degree of psychological significance. It is suggested that such value as it does possess is limited to the evaluation of non-dimensional structural hypotheses derived from some prior substantive theory. An empirical example is presented demonstrating that even when there appears an obvious and intuitive interpretation of the dimensions of a MDS configuration, the solution may be completely inappropriate as a model of the underlying cognitive processes. A second example however describes a more appropriate and successful application of multidimensional scaling methodology. A theoretical interpretation of emotion labelling based on Guttmans (1957 ) facet theory, was shown to be substantially confirmed in the structure of a MDS configuration.

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  • Regulation of microbial production in intertidal mudflats : the role of Amphibola crenata, a deposit feeding gastropod

    Juniper, S.K. (1982)

    Doctoral thesis
    University of Canterbury Library

    Interactions between the deposit feeding gastropod Amphibola crenata and the microbial community in intertidal mudflats were studied in laboratory and field experiments in two New Zealand estuaries. The study was mainly designed to reveal the effect of deposit feeding on bacterial and microalgal production and assess the importance of these microorganisms to the nutrition of the snail. The secondary aim was to compare the influence of Amphibola to external factors which regulate microbial production on the mudflat. Short-term effects of deposit feeding on bacterial production were examined by monitoring the recolonisation of Amphibola faeces by bacteria. Long-term effects on bacterial production were studied in artificial enclosures in the field where the effect of snail density on bacterial numbers and activity was monitored. These same enclosures were also used to study the effect of grazing by the snail on standing crop and productivity of the epibenthic algae. Assimilation of bacterial carborn by Amphibola was experimentally measured, and the contribution of bacterial and microalgal carbon to the snail’s carbon budget was estimated. The effect of microbial biomass on the feeding behaviour of Amphibola was also examined. It was found that a pulse in bacterial production occured during the recolonisation of Amphibola faeces by bacteria. This appeared to be similar in magnitude to the amount of bacterial biomass consumed by the snail - approximately 4. 5 mg C/m²/day. Amphibola also had a minor long-term influence on bacterial numbers and activity, but no clear effect on productivity was apparent. Grazing by Amphibola caused a substantial reduction in microalgal standing crop and productivity and affected the species composition of the microalgal community. Both the bacteria and microalgae serve as significant sources of carbon for the snail, but a large additional input of carbon is required to meet its nutritional needs. Other possible sources of carbon for the snail include meiofauna and non-living organic material. Amphibola was also found to alter its feeding rate in response to changes in microbial biomass, in a manner which may improve the return for feeding effort. In overview, it appears that Amphibola and the sediment bacteria similarly influence the other 's productivity while Amphibola has a greater effect on the microalgae than the microalgae have on Amphibola. Ultimate control of microbial productivity was concluded to be external to these relationships, with the snail acting only to modify seasonally determined levels of productivity.

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  • Phase manipulation of speech using FIR digital filters

    Stephen, R. D. C. (1987)

    Doctoral thesis
    University of Canterbury Library

    Three related investigations involving the fields of FIR digital filters, phase manipulation of speech, and speech coding via bandwidth compression are reported. The first investigation is aimed at providing a means of generating the impulse response coefficients of a non-linear phase FIR digital filter. Existing methods of designing linear-phase filters are discussed and compared from a defined common comparison base. The methods available for designing non-linear phase filters are examined. An existing linear phase design method is extended to the non-linear phase case and shown to be useful. The required impulse response length in the presence of non-linear phase is studied. Particular emphasis is placed on "random phase" filters and their generation because they are required by the second investigation. The second investigation examines in detail the ramifications of phase randomising a speech signal. The analytic zero representation of speech which forms the underlying base on which the discussion, and answers, are based is elucidated. The technique of using a non-linear phase FIR filter is shown to be feasible and as a minimum, offers at least the same level of performance as a very early reported technique. Significant differences in the behaviour of male and female speech is demonstrated. The third and final investigation reports some early and incomplete experiments on a radically different approach to achieving band width compression and expansion of a signal. The technique is referred to as "phase unwrapping". It is based on the application of a linear phase FIR digital filter in an adaptation of the traditional convolution relation. The motivation and validity of the basic idea is outlined and justified via application of the procedure to simple sinusoids and one experiment using real speech. The fundamental problem to be overcome is identified and the basis of a possible means of solution indicated.

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  • Atmospheric physics : electron density variations in the mesosphere

    Wratt, D.S. (1974)

    Doctoral thesis
    University of Canterbury Library

    The theory of the differential absorption and differential phase experiments is examined, and it is found that the differences in predicted electron densities due to different hypothetical reflection processes are in general no larger than experimental uncertainties. Results of differential absorption and differential phase measurements are compared. It is found that electron densities in the mesosphere above Christchurch can be affected by energetic particle precipitation. Evidence is also found for increases in electron concentration associated with a stratospheric warming, but apart from this there is no clear evidence for stratosphere-ionosphere coupling above Christchurch. Model studies show that much of the variation over time scales of four days or more above Christchurch could be accounted for by vertical transport of nitric oxide. However, other results make it likely that other processes, such as variations in loss rate, are also important.

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