87,603 results

  • Impact of War: a Diplomatic History of New Zealand's Economic Relations With Britain, 1939-1954

    McKinnon, Malcolm Arthur (1981)

    Doctoral thesis
    Victoria University of Wellington

    This study is a diplomatic history of Anglo-New Zealand economic relations through World War II and the postwar decade. During this tine Britain's priorities were such as to sharply alter her economic interests in New Zealand, compared both with the pre-war and post-1954 eras. It is this transformation which gives the period its distinctive coloration. Throughout these years Britain wanted New Zealand to conserve and direct her resources, initially to assist in the war effort, subsequently to aid the tasks of reconstruction. New Zealand gave active support to Britain. Nonetheless, she could not completely disregard her own interests. In the short-term, there was always pressure to buy on the cheapest and sell on the dearest market. In the long-term, New Zealand faced more fundamental decisions. Should she seek economic security through close association with Britain? Should she diversify her economic relations? Should she try to insulate her domestic from the international economy? These longstanding concerns can be traced through the period. They, too, moulded the course of events. Chapter one looks at the record of economic diplomacy before 1939. Chapters two to five look at the World War II period. Chapter two examines the period from the perspectives of the restraint Britain sought to impose on New Zealand in the consumption of resources. Chapters three to five trace the history of New Zealand's export industries - her major contribution to the struggle - through the war. Chapters six to ten span the post-war decade. Chapter six follows the theme of chapter two through to 1949. Chapter seven looks at Britain's concern about the commercial implications of New Zealand's import policies - a concern which had taken a back seat through the war. Chapters eight and ten take the history of the food export industries through to 1954. Chapter nine picks up the themes of chapters six and seven and takes them through to 1954, and also looks at the wool trade after 1946. Lastly, chapter eleven looks at how the relationship between the two countries evolved after 1954. The end of the long period of stringency meant a return in some, but certainly not in all, respects to pre-war conditions.

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  • On Ballance: a Biography of John Ballance, Journalist and Politician, 1839-1893

    McIvor, Timothy J (1984)

    Doctoral thesis
    Victoria University of Wellington

    This thesis is a biography of John Ballance, New Zealand's first Liberal Premier. It examines his career as journalist and politician, from his arrival in New Zealand and Wanganui in 1866 until his death in 1893. Ballance is viewed from a number of different perspectives: as editor and owner of a 'frontier' town's newspaper, as a prominent Wanganui personality closely involved in promoting local development, as Member of the House of Representatives and, finally, as a national political leader. The first chapter looks briefly at Ballance's early life in the north of Ireland and Birmingham. Chapter two then discusses his arrival in Wanganui, the establishment of the Evening Herald, and his participation in the war against Titokowaru. The following chapter begins with an examination of Ballance's attitude to political and economic issues of the 1870s, in particular his opposition to the provincial system, and ends with his entering Parliament for the first time in 1875. A little over two years later he became Colonial Treasurer in the Grey Government (chapter four). Chapter five covers the period 1879 to 1884, and Ballance's only electoral defeat, in 1881. Chapter six examines the broad base of his liberal philosophy, and shows how its different strands are inter-related, all pointing to a democratic, secular society, with considerable emphasis on individual and national self-reliance. In 1884 Ballance re-entered Parliament, and became Minister of Lands and Native Minister in the Stout-Vogel Government. His activities and initiatives when holding these two portfolios are the subject of chapter seven. Chapters eight and nine lead up to the crucial election of 1890. Ballance, after some initial hesitation, accepted the leadership of the Opposition in 1889. Land reform predominated his campaign at the election. Chapters ten to twelve discuss Ballance in power (1891-93). His major problem was to secure and consolidate the new Liberal regime, in the face of opposition to government measures from the Legislative Council and an alleged withdrawal of capital from the country. Ballance's reaction was to pursue a non-borrowing, self-reliant policy, and to establish a Liberal Federation to organise support for the Government at grass roots level. The conclusion discusses the 'Ballance tradition'.

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  • Facing the Past: Looking Back at Refugee Childhood in New Zealand

    Beaglehole, Ann (1990)

    Doctoral thesis
    Victoria University of Wellington

    The experiences of child refugees and children of refugees from Hitler growing up in New Zealand in the period from the late 1930s to the end of the 1960s are the subject of this study. By means of tape-recorded conversations with the former children, now men and women in their thirties, forties and fifties, the study focuses, in particular, on two issues. First, the lingering legacy of Nazi persecution, whether it was experienced directly or indirectly by the children or their parents; second, the effects of growing up, often isolated from others of a similar background, in a monocultural country by and large free from overt anti-Semitism but intolerant of cultural differences. The first chapter is concerned with the aims of the study, with methodology and with a survey of relevant literature. Some aspects of recent Jewish history and the Central and Eastern European refugee world are examined in Chapter 2. The features of New Zealand society most closely interwoven with the interviewees' experiences are also considered in that chapter. The third chapter turns to the memories, interpretations and explanations of the former refugees and children of refugees. It introduces the people in the study and some of the main concerns and preoccupations of their childhood. Chapter 4 is about refugee children and children of refugees at school, Chapter 5 about some aspects of a refugee adolescence and Chapter 6 about language, culture and identity. Chapter 7 looks specifically at the impact of a traumatic history on the people in the study. Chapter 8 is concerned with adult issues in the lives of the interviewees. It examines ethnic identity, cultural transmission and assimilation. The study concludes with biographical information about the interviewees which fill in some of the details not covered in the text.

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  • Coloured Views: Images of the New Zealand City and Town, 1880-1930

    Alessio, Dominic (1992)

    Doctoral thesis
    Victoria University of Wellington

    "Coloured Views" is a comparative and multidisciplinary examination of the motives and methods of New Zealand's urban boosters between 1880 and 1930. It looks at the positive image of the country's cities and towns rendered in the literature and art of the period, and compares it with other British Dominions as well as with America. Such optimistic images were considered vital to urban growth by promoters who were intent on inducing increased immigration, tourism and investment to their cities and towns. In addition to economic motivation, it will also be argued that the boosters in New Zealand were imbued to an unusual degree by dreams of creating an urban utopia in their New World, one that was free from the influences of vices typically associated with the Old World. In examining perceptions of urban New Zealand, this thesis also attempts to revert the imbalance in New Zealand historiography which has generally ignored cities and towns or which has assumed that all debate about them was negative. It undertakes a study of a wide array of promotional sources, including material which has never before been examined, such as motion pictures and foreign language texts. "Coloured Views" attempts to show that cities and towns had their ardent defenders in New Zealand as well as their critics. The study concludes with an examination of modern booster techniques in order to emphasise the topicality of the subject matter.

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  • Identification, Documentation and Control of Biological Contamination in Middle Distillate Fuel

    Hettige, Gloriah Emly Gres (1987)

    Doctoral thesis
    Victoria University of Wellington

    The present study was initiated under a contract with the New Zealand Defence Scientific Establishment to document the nature, extent and possible sources of microbial contamination of middle distillate fuel ('Dieso' ) held in storage tanks at Devonport, Auckland, and to study possible methods for control of such contamination. Thirty-one fungal species and five bacteria were isolated during the period 1982-1984. The principal contaminants were the fungi Cladosporium resinae (the anamorph of Amorphotheca resinae Parbery), Penicillium corylophilum and Paecilomyces variotii. All three fungi produced dark mycelial mats at the water/diesel fuel interface in laboratory studies. Interactions between these fungi were observed. In the presence of Bushnell.-Haas mineral salts/diesel fuel phases Cladosporium resinae predominated while in seawater/diesel fuel phases Penicillium corylophilum predominated. All New Zealand and Australian isolates of C. resinae grew profusely in Bushnell-Haas mineral salts/diesel fuel phases. The biostatic/biocidal effects of chemicals on the predominant fungi in diesel fuel were studied in laboratory and field tests during 1984-1985. The most effective biocides in controlling C. resinae were benomyl, imazalil and Kathon 886. Imazalil had no effect on Paecilomyces variotii but when used in combination with benomyl a synergistic effect occurred at 100 ppm. Biobor JF, DEGME and EGME performed poorly in laboratory tests regardless of the amount of water present, but gave temporary inhibition of C. resinae in the field tests. Isolates from tanks treated with Biobor JF and DEGME grew well in the presence of these compounds in the laboratory. DML-7 and Proxel AS inhibited C. resinae and Penicillium spp. in both laboratory and field tests at a high dose of 300 ppm but were less effective against P. variotii. The effects of the biocides on engine performance and carbon deposits on engine components were studied. Recommendations for control of microbiological contamination of stored diesel fuel are given. In electron microscope studies no difference was observed in the intracellular structures between jet and diesel fuel isolates of C. resinae and the non-hydrocarbon utilizing Cladosporium cladosporioides.

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  • A Bubble Rising in Viscous Fluid: Lagrange's Equations For Motion at a High Reynolds Number

    Harper, J F (2001)

    Scholarly text
    Victoria University of Wellington

    A gas bubble rising steadily in a pure liquid otherwise at rest at a moderate Weber number is, to a good approximation, of oblate spheroidal shape. Previous analytical calculations of that shape at high Reynolds numbers have ignored viscosity. This paper shows that if one includes viscosity by incorporating Rayleigh's dissipation integral in Lagrange's equations, then the speed of rise is that given by Moore, and the shape is that found for inviscid flow by El Sawi using the virial integral and by Benjamin using Hamiltonian theory.

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  • Stakeholder Perceptions of Tourism Development in Marahau/New Zealand: a Role for Participatory Approaches and GIS

    Hasse, Julia (2001)

    Doctoral thesis
    Victoria University of Wellington

    Abstract Tourism research is increasingly focusing on community participation and stakeholder collaboration in tourism planning. It is argued that sustainable development outcomes require the integration of community perspectives into the planning processes, and that the views of different stakeholders must be communicated effectively to interested parties. These core issues are explored in this thesis. I draw upon advances made in participatory research in development studies and introduce these to tourism planning. The thesis also introduces participatory approaches and GIS (PAGIS) as a tool that can be blended into a framework that facilitates a better understanding of stakeholders' perceptions towards tourism, and therefore has the potential to improve community participation and stakeholder interaction in tourism planning. The case study used in this thesis is Marahau, a small community in New Zealand located at the gateway to an icon of New Zealand's tourism industry, the Abel Tasman National Park. The community has undergone rapid transformation from an agriculture-based economy to an expanding tourism destination. The recent increase in visitor numbers, tourism businesses, and permanent residents in the community have resulted in major management and planning issues concerning the future of Marahau. This research highlights the changes that tourism development has brought to the community and presents the various perceptions of stakeholders in this particular setting. The research shows that to plan for more sustainable forms of tourism development the subjective perspectives and the roles of all stakeholders need to be understood and integrated into a responsive planning framework. PAGIS can increase the number and diversity of people able to participate in decision-making. PAGIS integrates 'expert' and 'local' knowledge that can result in more responsive planning procedures to enhance tourism's potential to act as a force for more sustainable development.

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  • Sexual Abuse Counsellors' Responses to Stress and Trauma: a Social Work Perspective

    Pack, Margaret (2004)

    Scholarly text
    Victoria University of Wellington

    Based on qualitative interviews with 36 ACC-approved counsellors, this research explores the range of social, organisational and theoretical factors that impact on sexual abuse counsellors. In this context the author explores the relevance of "vicarious traumatisation" and the strategies and theoretical approaches used to foster counsellors' well-being. Current literature about vicarious traumatisation suggests that counsellors' exposure to their clients' trauma may increase their risk of burn-out and secondary traumatisation. The relationship between counsellors' responses to their clients' trauma and the theoretical frameworks they use in practice, and the impact of the counsellors' work on their relationships with their partners, colleagues, friends and family, are explored. The model of stress and trauma developed highlights that counsellors experience stress when there are inconsistencies between their personal philosophies, their practice experience (or what they are exposed to in their dealings with dients) and the theoretical frameworks they use in practice. This sense of disjuncture provides the impetus for the development of alternative frameworks for practice that increase the resilience of counsellors who work intensively with traumatic material. The model of stress and trauma developed introduces a multi-level understanding of the challenges faced by sexual abuse counsellors and the implications for their relationships with their significant others.

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  • Vegetation and Landscape Dynamics in Eastern Taranaki Hill Country

    Blaschke, Paul Michael (1988)

    Doctoral thesis
    Victoria University of Wellington

    An ecological study of hill country landscapes in eastern Taranaki, New Zealand, was undertaken as part of a project concerning the implications of long-term soil mantle changes for sustainable land use. The study was undertaken in a 417 km2 area comprising uplifted and steeply dissected soft Tertiary sediments with a predominantly sandstone lithology. Rapid European settlement in the 1890s modified the natural vegetation cover greatly, so that most remaining forest in the study area occurs in patches surrounded by a matrix of pastoral land. Vegetational and successional patterns and environmental variation : The pattern of woody vegetation was investigated by extensive reconnaissance sampling incorporating semi-quantitative analysis of canopy cover, followed by intensive, environmentally stratified sampling. The vegetation was classified on a structural and floristic basis into 19 units of forest, treeland, scrub and shrubland. The effect of environmental variation on vegetation composition was investigated by reciprocal averaging ordination (DECORANA). The first ordination axis was correlated to vegetation structure and canopy height and was interpreted as a complex disturbance gradient relating to time since disturbance. The second and third axes were related to soil fertility and topographical gradients. Forest plots were dominated by Beilschmiedia tawa and Weinmannia racemosa and had basal area values of up to >250 m2/ha. Basal area, stem and seedling density varied greatly between vegetation structural groups. Regeneration of woody vegetation following various types of disturbance: The disturbance regime was comprehensively documented. Main factors of natural disturbance are landslide erosion and windthrow; main factors of cultural disturbance are direct clearance by felling and burning, and introduced animals. A chronology is presented of successional pathways for about 400 years following major disturbance. Succession proceeds through shrubland and scrub stages dominated by treeferns, Leptospermwn scoparium or other broadleaved woody shrubs, through treeland, to broadleaved forest dominated firstly by W. racemosa or Knightia excelsa, then by B. tawa. Podocarp trees are generally only prominent after a long period of uninterrupted succession. Seedling recruitment, mortality and growth were monitored for 2 years. Seedling dynamics varied considerably between and within sampling plots, some of which contained small exclosures that excluded possums and goats. The effects of introduced animals on seedling recruitment and vegetation growth is strongly modified by microtopography. Most dominant species showed continuous regeneration at the scale of the whole study area, despite local discontinuities. This pattern was consistent with a model of interrpted gap-phase regeneration, which may be widely applicable to New Zealand lowland forests. The vegetation turnover time is in the order of 150-250 years, a period consistent with comparable temperate forest ecosystems. The successional pathway is primarily dependent on topography, previous site history and location and area of disturbance. The existence of residual-soils on landslide scars, variations in plant propagule supply, and rapid loss of soil from steep slopes cleared for agriculture, all suggest that a rigid distinction between primary and secondary succession in the study area is not appropriate. Hillslope processes underlying vegetation and landscape change: Hillslope processes were studied in five 0.1 ha plots in which slope profiles were measured, vegetation and microtopography mapped in detail, vegetation age assessed and soil properties investigated. Ground surface age was assessed as an interpretation of the above data. Mean surface age was c. 450 years, but some swales had a surface age of several thousand years. There was a significant correlation between surface age and soil depth, soil depth increase being faster and continuing for much longer under forest than under pasture. Observations were made of near-surface erosion processes such as soil creep. A model of hillslope erosion is outlined, involving periodic evacuation of swales by landslides and refilling of swales by near-surface erosion. Evidence of past environments supports a fluvial origin for swales in an early Ohakean (glacial maximum) or pre-Ohakean period of high erosion. A concluding synthesis of vegetation, topography and soils emphasises the importance of selecting appropriate temporal and spatial scales at which to study landscape processes.

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  • Allozyme and Other Aspects of Variation in the Genus Bulbinella in New Zealand

    Milicich, Lesley Dawn (1993)

    Doctoral thesis
    Victoria University of Wellington

    This thesis examines some aspects of morphological, cytogenetic and allozyme variation in the six species of the genus Bulbinella in New Zealand. Because evidence was found suggesting that fragmentation and reduction of the habitat of some species of the study genus had occurred, aspects of the conservation status of Bulbinella were also investigated. Some of the morphological characters described and used by Moore (1964) to separate the species were employed in this study as well as other characters recorded by the author in actively glowing plants. Generally, the seven taxa could be successfully distinguished using selected morphological characters, although in some species or populations a range of morphological forms was observed. Increased human land use (mainly mining, farming and associated activities) has reduced some populations of Bulbinella to low numbers by destroying large areas of habitat. In some cases once vast areas of Bulbinella have been reduced to fragments or probably exterminated. The karyotypes of five of the seven taxa were determined and these were all consistent with published data. G-banding was achieved in only one slide from one plant. A total of four bands (restricted to two pairs of chromosomes) was observed in the entire chromosome complement of 14. Each band was located on a separate chromosome. Inflorescence material from 61 natural populations of Bulbinella in New Zealand was examined for enzyme activity using starch gel electrophoresis. Activity was detected for eight of a total of 43 enzyme stains. Three monomorphic and 11 polymorphic loci were resolved. While no completely fixed differences between all the taxa could be demonstrated, four almost fixed differences were found. In some instances where populations belonging to different species were not geographically separated by great distances (s unbiased genetic distances divided the genus into four groups, three of which corresponded to three currently recognised taxa. The other group contained the remaining four taxa. Although the component taxa of this cluster could be readily separated using morphological characters, they could not be distinguished using allozyme data. The endemic distribution of B. rossii (Campbell Island and Auckland Island Group) and fixed morphological differences justify its remaining a separate taxon. The formal raising of B. gibbsii var. gibbsii to a separate specific status is subject to the analysis of further samples of this taxon. B. angustifolia, B, talbotii, and B. gibbsii vat. balanifera also remain separate taxa, with B. gibbsii var. balanifera being raised to a separate specific status. B. modesta, which is genetically closely related to B. hookeri, becomes a sub-species of this taxon.

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  • Reducing Parabolic Partial Differential Equations to Canonical Form

    Harper, J F (1994)

    Scholarly text
    Victoria University of Wellington

    A simple method of reducing a parabolic partial differential equation to canonical form if it has only one term involving second derivatives is the following: find the general solution of the first-order equation obtained by ignoring that term and then seek a solution of the original equation which is a function of one more independent variable. Special cases of the method have been given before, but are not well known. Applications occur in fluid mechanics and the theory of finance, where the Black-Scholes equation yields to the method, and where the variable corresponding to time appears to run backwards, but there is an information-theoretic reason why it should.

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  • Bubbles Rising in Line: Why is the First Approximation So Bad?

    Harper, J F (1997)

    Scholarly text
    Victoria University of Wellington

    An analytical theory is given for the viscous wake behind a spherical bubble rising steadily in a pure liquid at high Reynolds number, and for that wake's effect on the motion of a second bubble rising underneath the first. Previous theoretical work on this subject consists of just two papers: a first approximation ignoring wake vorticity diffusion between the bubbles, and a full numerical solution avoiding simplifying approximations (apart from that of spherical shape of the bubbles). A second approximation is now found; it removes much of the discrepancy between the first approximation and the full solution. The leading-order calculation of wake vorticity diffusion uses a transformation of the independent variables which appears to be new. Experimental work to date has disagreed with all the theoretical work, but it addresses a somewhat different problem: a line of many bubbles.

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  • Stagnant-Cap Bubbles With Both Diffusion and Adsorption Rate-Determining

    Harper, J F (2004)

    Scholarly text
    Victoria University of Wellington

    When a gas bubble rises in an impure liquid, its surface often has an upper spherical cap with negligible shear stress, a lower spherical cap with negligible tangential velocity, and a very small transition region between the two caps. This paper gives the diffusion boundary-layer theory for the distribution of surfactant around a stagnant-cap bubble, allowing for slowness of both adsorption and diffusion. The resulting singular Volterra integrodifferential equations are solved numerically for creeping flow (small Reynolds number). The main result is the relation between the surface pressure of surfactant in the bulk solution, the cap angle and Peclet number of the bubble, and the adsorption depth and adsorption speed of the surfactant. The values of the latter two parameters affect the validity of the approximations much more than the numerical results.

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  • Bubble Rise in a Liquid With a Surfactant Gas, in Particular Carbon Dioxide

    Harper, J F (2007)

    Scholarly text
    Victoria University of Wellington

    When a gas bubble rises in a surfactant solution, the velocity field and the distribution of surfactant affect each other. This paper gives the theory for small Reynolds and internal Peclet numbers if the surfactant is gaseous or volatile, if its mass flux across the bubble and around its surface dominates its mass flux through the bulk liquid, and if slowness of both adsorption and convective diffusion must be allowed for. The theory is tested on the experiments of Kelsall et al. (J. Chem. Soc. Faraday Trans., vol. 92, 1996, p. 3879). Their bubbles rose as expected in a pure liquid until the apparatus was opened to the atmosphere. That significantly slowed the bubbles down. The effect is so sensitive to small concentrations of slowly adsorbing or reacting surfactants that atmospheric carbon dioxide could have caused it, even though it alters the equilibrium surface tension by less than four parts per million in pure air.

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  • The Axisymmetric Prandtl-Batchelor Eddy Behind a Circular Disc in a Uniform Stream

    Harper, J F (1998)

    Scholarly text
    Victoria University of Wellington

    Analytical support is given to Fornberg's numerical evidence that the steady axially symmetric flow of a uniform stream past a bluff body has a wake eddy which tends towards a large Hill's spherical vortex as the Reynolds number tends to infinity. The viscous boundary layer around the eddy resembles that around a liquid drop rising in a liquid, especially if the body is a circular disc, so that the boundary layer on it does not separate. This makes it possible to show that if the first-order perturbation of the eddy shape from a sphere is small then the eddy diameter is of order R1/5 times the disc diameter, where R is the Reynolds number based on the disc diameter. Previous authors had suggested R1/3 and ln R, but they appear to have made unjustified assumptions.

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  • Growing Bubbles Rising in Line

    Harper, J F (2001)

    Scholarly text
    Victoria University of Wellington

    Over many years the author and others have given theories for bubbles rising in line in a liquid. Theory has usually suggested that the bubbles will tend towards a stable distance apart, but experiments have often showed them pairing off and sometimes coalescing. However, existing theory seems not to deal adequately with the case of bubbles growing as they rise, which they do if the liquid is boiling, or is a supersaturated solution of a gas, or simply because the pressure decreases with height. That omission is now addressed, for spherical bubbles rising at high Reynolds numbers. As the flow is then nearly irrotational, Lagrange's equations can be used with Rayleigh's dissipation function. The theory also works for bubbles shrinking as they rise because they dissolve.

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  • What Really is a Continuous Function?

    Harper, J F (2007)

    Scholarly text
    Victoria University of Wellington

    There are surprisingly many essentially different definitions of continuity even of a real function of one real variable. This paper shows that the definitions in various textbooks published from 1893 to 1992 have some very different consequences, and that one error that was noticed and corrected in 1904 reappeared in a 1907 book.

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  • Fortran 95 for Fortran 77 Users

    Harper, J F (2007)

    Scholarly text
    Victoria University of Wellington

    For 50 years Fortran has been a computer language used mainly by engineers and scientists (but by few computer scientists), mainly for numerical work. Five versions were standardised and are commonly referred to as f66, f77, f90, f95 and f2003 to indicate the year. F95 has superseded f90, and no f2003 compilers exist yet. These notes concentrate on f77 and f95. They are written to show f77 users a number of the f95 features that I found so useful that I gave up f77 except when writing a program for someone with no f95 compiler. Some new features make programming easier, some allow the machine to detect bugs that f77 compilers cannot, and some make programs easier to read.

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  • Comparative Analysis of New Zealand Campylobacter Isolates Using MLST, PFGE and flaA PCR RFLP Genotyping

    McTavish, Sharla (2008)

    Masters thesis
    Victoria University of Wellington

    Campylobacter jejuni and Campylobacter coli are the most commonly identified sources of campylobacteriosis in New Zealand, yet little is known about the distribution of genotypes within the respective population structures. Using multi-locus sequence typing (MLST), pulsed-field gel electrophoresis (PFGE) and flaA genotyping, the current study identified the distribution of genotypes within New Zealand C. jejuni and C. coli isolates from an outbreak situation, as well as isolates present in the ESR Campylobacter collection. Although the most commonly identified MLST genotypes were similar to international genotypes, a number of internationally rare, or unique to New Zealand genotypes were observed. One rare dominant genotype, ST-474, arising from a point source outbreak, was found to cause a large proportion of human campylobacteriosis cases in New Zealand. A unique cluster of New Zealand genotypes were isolated only from river water, identifying a potentially water adapted C. jejuni strain. Frequent homologous recombination and horizontal gene transfer events were identified within the seven housekeeping genes characterised in the New Zealand sample and the MLST C. jejuni/C. coli database. The identified genetic instability within the current study questions the legitimacy of bacterial species boundaries, especially when examining closely related species such as C. jejuni and C. coli.

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  • The Effect of Opiates on the Developing Cerebral Cortex

    Sargeant, Timothy John (2008)

    Doctoral thesis
    Victoria University of Wellington

    Opiate drugs, such as codeine, morphine and heroin are powerful analgesics and drugs of abuse. The unborn child is invariably exposed to opiate drugs as a consequence of maternal use. Studies that have investigated the impact of opiate drugs demonstrated opioid system expression in proliferating regions of the developing brain, as well as on proliferative astroglia taken from the developing central nervous system. The effects of opiates on astroglial proliferation (largely mediated by the mu opioid receptor) are predominantly inhibitory, but are extremely context dependent. This context dependency exists because of the complexity resident within the opioid signalling system. However, since this previous research was conducted, there has been impressive progress made in the field of developmental neurobiology with the demonstration that cells of astrocytic lineage are responsible for the generation of the central nervous system. It was therefore the aim of the current research project to investigate the developmental impact of opiate exposure in the context of the foetal mouse cerebral cortex. This aim was divided into 3 separate aims that comprised of; determining the cellular localisation of the mu opioid receptor, the effects of opiate exposure on cortical progenitor cells, and to determine the effect of opiate exposure on the development of the cerebral cortex itself. The mu opioid receptor was expressed on proliferative radial glia of both the embryonic day 15.5 (neurogenic) and embryonic day 18.5 (gliogenic) ventricular zone of the dorsal forebrain. Interestingly and significantly, the mu opioid receptor-positive glia observed in the embryonic day 18.5 mouse forebrain were also observed at a comparable developmental stage in the foetal human forebrain. Morphine exposure slowed down G2 phase of the cell cycle at embryonic day 15.5 in the neurogenic murine cortical ventricular zone. This opiate-induced slowing in cell cycle progression was shown not to impact on proliferation in the ventricular zone, although future research should address whether this perturbation altered differentiation or developmental maturation of the radial glia. Morphine exposure throughout corticogenesis decreased levels of doublecortin expression (a migratory neuronal marker) at the end of gestation. Postnatally, mice exposed to morphine during corticogenesis also showed decreased numbers of neurons in layer V of the cerebral cortex. Collectively, this thesis presents the first evidence that shows morphine affects cortical progenitor cells in vivo. This research supports the possibility that the opioid system plays an endogenous role in corticogenesis. The clinical significance is morphine has the potential to perturb normal development of the cerebral cortex.

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