Showing papers by "University of Auckland published in 1980"

Explosive volcanic eruptions — IV. The control of magma properties and conduit geometry on eruption column behaviour

Abstract: Summary Plinian air-fall deposits and ignimbrites are the principal products of explosive eruptions of high viscosity magma. In this paper, the flow of gas/pyroclast dispersions and high viscosity magma through various magma chamber/conduit/vent geometries is considered. It is argued that after the first few minutes of an eruption magma fragmentation occurs at a shallow depth within the conduit system. Gas pressures at the fragmentation level are related to exsolved gas contents by consideration of the exsolution mechanism. The sizes of blocks found near vents imply that gas velocities of 200 to 600 m s−1 commonly occur. These velocities are greater than the effective speed of sound in an erupting mixture (90-200 m s−1) and the transition from subsonic to supersonic flow is identified as occurring at the depth at which the conduit has its minimum diameter. The range of values of this minimum diameter (∼ 5 to ∼ 100 m) is estimated from observed and theoretically deduced mass-eruption rates. The energy and continuity equations are solved, taking account of friction effects, for numerous geometries during the evolution, by wall erosion, of a conduit. Conduit erosion ceases, near the surface, when an exit pressure of one atmosphere is reached. Eruption velocities are found to depend strongly on exsolved magma gas content and weakly on radius of conduit and friction effects. Assuming water as the main volatile phase, velocities of 400-600 m s−1 for plinian events imply magma water contents of 3-6 per cent by weight. Three scenarios are presented of eruptions in which: (1) conduit radius increases but gas content remains constant; (2) conduit radius increases and gas content decreases with time; and (3) conduit radius remains fixed and gas content decreases. These models demonstrate that the reverse grading commonly observed in plinian air-fall deposits is primarily a consequence of conduit erosion, which always results in increasing eruption intensity and eruption column height with time. The models also show that a decrease in gas content as deeper levels in a magma chamber are tapped or an increasing vent radius as conduit walls are eroded leads to the prediction of a progression from air-fall activity through ignimbrite formation to cessation of eruption and caldera collapse.

Non-linear stability of a general class of differential equation methods

Abstract: For a class of methods sufficiently general as to include linear multistep and Runge-Kutta methods as special cases, a concept known as algebraic stability is defined. This property is based on a non-linear test problem and extends existing results on Runge-Kutta methods and on linear multistep and one-leg methods. The algebraic stability properties of a number of particular methods in these families are studied and a generalization is made which enables estimates of error growth to be provided for certain classes of methods.

Ultrastructural study of tension and pressure zones in a rabbit flexor tendon.

Abstract: The flexor digitorum profundus tendon of the rabbit hind limb is subject to tensional forces throughout most of its length but, within a localised area which is in contact with the calcaneum and talus, it is subjected to additional compressive forces. This pressure-bearing area, in marked contrast to the tensional areas, has a fibrocartilage-like organization and a high concentration of glycosaminoglycans (GAG). Ultrastructural features of the cells, collagen and matrix in the tension and pressure zones are also markedly different, with a full spectrum of transitional characteristics in the junctional region between the two zones. These findings support the concept that the cells in the various regions are sensitive and responsive to changes in physical load. In the tensional zone, elongated cells have extensive cytoplasmic flanges, which may contact flanges of neighbouring cells, and a scalloped cell surface that intimately conforms to the adjacent positively charged and tightly packed collagen fibrils of long periodicity (63 nm) and varying diameters. In the pressure zone, round and clustered fibrocartilage-like cells, characterized by dense arrays of 11-nm-diameter microfilaments and numerous lipid droplets, are surrounded by loosely packed collagen fibrils of short periodicity (53 nm) and predominantly small diameters, and an extensive matrix rich in GAG. It is suggested that these regional morphological variations in the extracellular components result from, and are indirectly the cause of, changes in the cellular synthetic activities which are known to occur in response to changes in the physical environment.

Metaplastic polyps and polyposis of the colorectum.

Abstract: Five hundred and fifty-four colorectal metaplastic polyps have been studied histologically. Whilst most lesions were small and sessile, 16.1% measured greater than 0.5 cm in diameter and 0.9% were greater than 1 cm. The larger polyps were frequently pedunculated and occasionally showed a tubulo-villous or villous pattern. A structural similarity between the larger metaplastic polyps and colorectal adenomas is illustrated and the importance of the distinction of metaplastic from dysplastic epithelium in the differentiation of these lesions is stressed. Other unusual features of metaplastic polyps are described. Evidence is given to suggest that males have a greater propensity to develop metaplastic polyps than females. A search for men adenomas, but relatively frequent (20.8%) in juvenile polyps. Finally, seven patients with multiple metaplastic polyps of the colorectum are described, in whom a diagnosis of adenomatous polyposis had been made at some stage in their management. Six of the seven patients were males and the mean age at presentation was 37.4 years. Larger metaplastic polyps were frequent in these cases. The necessity for histological confirmation in all cases of intestinal polyposis is stressed, and the possibility that 'metaplastic polyposis' is a pathological entity is discussed.

The Use of Self-Modeling to Improve the Swimming Performance of Spina Bifida Children.

Abstract: The use of edited videotape replay (which showed only "positive" behaviors) to improve the water skills of three spina bifida children, aged 5 to 10 years was examined. A multiple baseline across subjects design was used, and behavioral changes were observed to occur in close association with intervention. One child was given successive reapplications of videotaped self-modeling with continuing improvements. It appears that a useful practical technique has been developed.

Steroid and growth hormone levels in premature infants after prenatal betamethasone therapy to prevent respiratory distress syndrome.

Abstract: Steroid and Growth Hormone Levels in Premature Infants After Prenatal Betamethasone Therapy to Prevent Respiratory Distress Syndrome

Persisting effects of minor head injury observable during hypoxic stress

Abstract: Ten university students who had recovered from minor head injury between one and three years previously were given vigilance and memory tests at a simulated altitude of 3,800 metres. Their performance was significantly below that of a matched group of students who had never had a head injury. The finding supports the proposition that even minor head injury has persisting effects, though they may be subtle and only emerge under the effects of stress.

Comparative study of the erythrocytes and haemoglobins in nototheniid fishes from Antarctica

Abstract: The blood of seven Antarctic nototheniid species and representatives from three other families contained low haemoglobin concentrations compared with non-polar marine teleosts. Haematocrit values were slightly lower than values from other teleosts, while haemoglobin and erythrocyte counts were substantially reduced by comparison. Interspecific variation in haemoglobin concentration seemed to be a function of activity level. Mean corpuscular haemoglobin concentration of all Antarctic species was strikingly low by comparison with species from lower latitudes and was not correlated with the habits of the species. Haemoglobin componentry was compared using celluslose-acetate electrophoresis and, unlike many temperate species, only one major haemoprotein was isolated from each benthic species, but four components were evident in the pelagic species Trematomus borchgrevinki. The possible functional significance of these findings was discussed in relation to the ecology of each species.

Low-aspect ratio ignimbrites

Abstract: Conventionally1, three important characteristics of ignimbrites are that they show a very pronounced tendency to pond in topographic depressions, possess a flat, horizontal or gently sloping upper depositional surface, and have a thickness generally between 10 and 1,000 m. The youngest major ignimbrite, that of 1912 in the Valley of Ten Thousand Smokes (Alaska)2–4 shows these characteristics well, being ponded in a valley 25 km long with a flat upper surface sloping down-valley at an average of 1.3°, and having an estimated thickness exceeding 100 m in places. AU three characteristics are commonly used as field criteria to distinguish ignimbrites from other pyroclastic rock bodies. Here we look at certain ignimbrites which depart significantly from this conventional form in that a major part of them occurs as a thin layer mantling the landscape, resting on slopes as steep as 30°, and with an upper surface sensibly parallel with the underlying surface. We have studied two examples, the 1,800-yr-old5 Taupo ignimbrite (New Zealand), and the 1,400-yr-old Rabual ignimbrite (New Britain)6,7. We also cite several others. These ignimbrites have a remarkably low aspect ratio. This ratio, previously applied to lava extrusions8,9, provides a useful means of quantifying the overall geometry of rock bodies. The ratio is that of average thickness to lateral spread; conveniently the latter is taken as the diameter of the circle which covers the same area as the rock body.

Onset of convection in a layered porous medium heated from below

Abstract: The formalism required to determine the criterion for the onset of convection in a multi-layered porous medium heated from below is developed using a straightforward linear stability analysis. Detailed results for two- and three-layer configurations are presented. These results show that large permeability differences between the layers are required to force the system into an onset mode different from a homogeneous system.

A revision of the supraspecific classification of the orders dictyoceratida dendroceratida and verongida class demospongiae

Abstract: A reappraisal of all existing generic taxa within the group of Demospongiae lacking a mineral skeleton, and formerly referred to as the order Keratosa, has resulted n a new classification. Three or...

An implementation of singly-implicit Runge-Kutta methods

Abstract: A description is given ofSTRIDE, an algorithm for the numerical integration of ordinary differential equations. This algorithm, which is applicable to either stiff or non-stiff initial value problems, is based on the family of singly-implicit Runge-Kutta methods of Burrage [2]. The present paper is confined mainly to a theoretical discussion, but includes an overview of the structure of the algorithm together with a general description of how it is used. A companion report [5] contains more detailed documentation intended particularly for a potential user of the algorithm. The companion report also includes an Algol 60 procedure declaration forSTRIDE together with the listing of an equivalent Fortran subroutine.

A study of the structural response of wet hyaline cartilage to various loading situations.

Abstract: A direct view has been obtained of the manner in which the fibrous components and chondrocytes in hyaline cartilage respond to the application of uniaxial tensile loading and plane-strain compressive loading.A micro-mechanical testing device has been developed which inserts directly into the stage of a high-resolution optical microscope fitted with Nomarski interference contrast and this has permitted simultaneous morphological and mechanical observations to be conducted on articular cartilage maintained in its wet functional condition.Aligned and crimped fibrous arrays surround the deeper chondrocytes and can be observed to undergo well-defined geometric changes with applied stress. It is thought that these arrays may act as displacement or strain sensors transmitting mechanical information from the bulk matrix to their associated cells thus inducing a specific metabolic response.The process of tissue recovery following sustained high levels of compressive loading can also be observed with this experimen...

Density and distribution patterns of the temperate marine fish Cheilodactylus spectabilis (Cheilodactylidae) in a reef environment

Abstract: Cheilodactylus spectabilis (Hutton) is common over shallow reefs in north-eastern New Zealand. Replicated transect between-area differences in density and in size frequency. C. spectabilis is not nocturnally active. The between-area differences in density and size frequency remained constant over daylight hours, demonstrating that C. spectabilis does not undergo any systematic feeding migrations. Topographic complexity was shown to have a significant positive influence on fish density. Mean size was related to water depth at 5 localities investigated, with small (<200 mm standard length, SL) individuals being restricted to shallow water. All sizes of C. spectabilis examined had fed on small invertebrates, with gammarid amphipods predominating. No evidence of size-related differentiation in feeding patterns was observed, although small individuals spent significantly more time feeding than large ones. Small (<200 mm SL) individuals occupied feeding areas and shelter sites from which they excluded other small C. spectabilis. Large individuals showed no site-associated aggression, covered a greater area during daily movements and overlapped with other large and small C. spectabilis while feeding. No evidence of dawn or dusk peaks of feeding activity or movement was collected.

Effects of density on monospecific stands of marine algae

Abstract: Current ideas on intraspecific competition between plants in monospecific stands stem from work on terrestrial floras. The central tenet is that higher plant density exacts a price from the individuals in a stand: (1) total yield (biomass) per area reaches a constant value at high density (the law of constant final yield1–5); (2) the weight distribution of individuals becomes skewed, with few large and many small plants1,5–8; (3) survival rates may be reduced when plants are sown at higher densities1,9. The effects of density seem to be remarkably similar for primitive as well as higher plants1,2,9–11 and are often summarized by the 3/2 thinning law1,2,5–7,9–11, which indicates that if a stand of plants is sampled through time, the relationship between log weight and log density is a line of −1.5 slope. The basis of this is that mortality is density dependent, so that density is related to time through the thinning process due to crowding. We report here that these effects do not obtain for two species of subtidal marine algae. For the characters which we examined—total yield, plant length, plant dry weight and dry weight of reproductive parts—algae fared better at higher densities. We conclude that there is a difference between marine and terrestrial plants in their responses to density, and we suggest a difference in herbivory due to arthropod–plant associations in each system.

A note on modeling project interdependence in research and development

Abstract: This note is concerned with the problem of resource allocation under uncertainty in a research and development laboratory. A distinction is defined between project interrelationships that are specific (or internal) to certain projects and interrelationships resulting from external environmental factors. Formulations are introduced that allow both types of interrelationships to be formally included in a resource allocation optimization model. In the case of external environmental factors, an example is presented and analyzed.

Meditation training and essential hypertension: a methodological study.

Abstract: Meditation training appears to be a promising psychological approach to the control of hypertension However, most studies to date have had serious deficiencies This study attempted to correct many of these deficiencies Forty-one unmedicated hypertensives referred by general practitioners were randomly allocated to three groups The treatment group (SRELAX) underwent training procedures based on Transcendental Meditation; a placebo control group (NSRELAX) underwent identical training but withou a mantra Both procedures were compared with a no-treatment control group The results showed modest reductions in blood pressure in both SRELAX and NSRELAX groups, compared with the no-treatment controls, with diastolic percentage reductions reaching significance (p < 005) There was considerable subject variation in response, with overall a mean decline i diastolic blood presure of 8-10% on 3-month follow-up Possible indicators to predict the response of subjects are considered and reasons for the similarity in the effectiveness of the SRELAX and NSRELAX conditions are discussed

The ordinal and subclass classification of the Demospongiae (Porifera); appraisal of the present arrangement, and proposal of a new order

Abstract: The criteria for subclass diagnosis within the Demospongiae are evaluated, with particular reference to dependence on oviparous or viviparous reproductive sequence as a primary characteristic in defining the three subclasses. Emphasis on reproductive pattern and larval type has permitted the development of a more natural classification than ever before. New evidence confirming the occurrence of oviparity in three groups previously classified with the viviparous Ceractinomorpha, coupled with histological, biochemical, and paleontological studies, requires that a new order be established and that the diagnosis of the Ceractinomorpha be amended. The new order Nepheliospongida is diagnosed, and the genera Petrosia, Strongylophora, Xestospongia, Oceanapia, Foliolina, Calyx, Vagocia, and Biminia are assigned to it. It is suggested that the ancient reproductive pattern in subclass Ceractinomorpha was oviparity, and that this condition has been retained in at least two divergent lines represented by the ...