Showing papers by "Newcastle University published in 1976"

Sialons and related nitrogen ceramics

Abstract: Although silicon nitride is at present a leading contender for gas turbines and other hightemperature engineering applications, it is only the first of a wide field of nitrogen ceramics, other members of which offer better prospects for technological exploitation. “Sialons” are phases in the Si-Al-O-N and related systems and are comparable in variety and diversity with the mineral silicates. They are built up of one-, two-, and threedimensional arrangements of (Si, Al) (O, N)4 tetrahedra in the same way that the fundamental structural unit in the silicates is the SiO4 tetrahedron. These new oxynitrides include structure types based uponα andΒ silicon nitrides, silicon oxynitride, aluminium nitride and silicon carbide, eucryptite, spinel, melilite and apatite. They are being explored for their thermal, mechanical, chemical and electrical properties.

Instabilities in polymer processing

Abstract: Instabilities which arise in shear and extensional flows in the processing of polymeric liquids are reviewed. The experimental observations and the extent of theoretical understanding of the instabilities are discussed.

Early production of intracellular IgM by B-lymphocyte precursors in mouse.

Abstract: IN BALB/c mice, surface immunoglobulin (Ig)-bearing B lymphocytes are first detectable by immunofluorescence at 17 d gestation in the liver and spleen1. Explants of 14-d foetal liver1 and spleen2, and 15-d bone marrow (our unpublished observations), have been shown to generate Ig-bearing B cells in vitro after 4–7 d of culture, suggesting that B lymphocytes normally develop multifocally in the haemopoietic tissues of mice. We have used direct immunofluorescence to demonstrate cells with intracellular IgM and no detectable surface Ig in mouse foetal liver as early as 12 d gestation. Our results suggest that B lymphocyte precursors synthesise IgM several days before they incorporate these molecules into their plasma membranes as cell-surface receptors for antigen.

Colony interactions and hyphal interference between Septoria nodorum and phylloplane fungi

Abstract: Interactions between dual cultures of Septoria nodorum and several other cereal phylloplane fungi were studied in vitro to determine their antagonistic ability and their tolerance of antagonism. No fungi tested were outstandingly successful antagonists and interference reactions between opposed hyphae rarely occurred. Septoria caused the hyphae of some test fungi to fail to plasmolyse and others to burst. In experiments designed to examine volatile and non-volatile metabolites growth of Septoria was rarely affected by colonies of the test fungi.

The dispersal of young post-larval bivalve molluscs by byssus threads

Abstract: NEW observations, both in the marine environment and in the laboratory, indicate that the byssus in young post-larval bivalves has a hitherto unsuspected function—that of dispersal The method of transport is analogous to the gossamer flight of young spiders In the laboratory, small scale currents will induce the secretion of what seems to be a single long thread which, by increasing the viscous drag exerted on the young bivalves, enables them to be carried along on relatively small currents The threads, which stain readily in Alcian blue (a stain selective for acid mucopolysaccharides) are typically long compared with the length scale of the animal itself: for instance an Abra 1 mm long can produce a 2–4-µm diameter thread of length greater than 3 cm This mechanism, which we term byssus drifting, is functional from the late pediveliger stage up to at least 25 mm size in some species, and it has been found to be present in the 20 species tested so far and listed in Table 1 (a functional byssus has not been reported previously1 in post-larval bivalves of those genera marked with an asterisk)

Statistical Analysis of Spatial Point Patterns by Means of Distance Methods

Abstract: Summary Various distance-based methods of testing for randomness in a population of spatially distributed events are described. Special emphasis is placed upon preliminary analysis in which the complete enumeration of the events within the study area is not available. Analytical progress in assessing the power of the techniques against extremes of aggregation and regularity is reviewed and the results obtained from the Monte Carlo simulation of more realistic processes are presented. It is maintained that the method of T-square sampling can help to provide quick and informative results and is especially suited to large populations. Some comments on contiguous quadrat methods are made.

Equilibrium and kinetic studies of the aggregation of porphyrins in aqueous solution

Abstract: An investigation of the behavior of protoporphyrin IX, deuteroporphyrin IX, haematoporphyrin IX and coproporphyrin III in aqueous solution revealed extensive and complex aggregation processes Protoporphyrin appears to be highly aggregated under all conditions studied At concentrations below 4 muM, aggregation of deutero-, haemato- and coproporphyrin is probably restricted to dimerization At approx 4muM each of these three porphyrins exhibits sharp changes in spectra consistent with a "micellization" process to form large aggregates of unknown size This critical concentration increases with increasing temperature and pH, but is not very sensitive to variation in ionic strength Temperature-jump kinetic studies on deuteroporphyrin also imply an initial dimerization process, the rate constants for which are comparable with those for various synthetic porphyrins, followed by a further extensive aggragation The ability of a particular porphyrin to dimerize appears to parallel that of the corresponding iron(III) complexes (ferrihaems), although it is thought that ferrihaems do not exhibit further aggregation under these conditions

Plastic deformation below worn surfaces

Abstract: Large strains occur at and near the worn surface of a ductile material (e.g. ∼8 at a depth of 10 µm after trepanning, ∼2.5 at 2.5 µm below an abraded surface). The wear of such materials is thus controlled by their strain-hardening behavior. Measurements have been made of the strain and microhardness at points below the worn surface of copper-silver solder composite specimens. The results are consistent with a model of the abrasion process that suggests the strain below the surface should be proportional to the abrasive grit size and to the square root of the applied load, but the strain at the surface should be independent of these factors. A simple energy balance confirms the work done during wear is determined by the plastic deformation at and below the worn surface. The measured volume wear rate shows the linear dependence on load expected on the model of the abrasion process, but there is also some dependence on grit size at small grit sizes and possible reasons for this are discussed.

Central pontine myelinolysis. Two cases with associated electrolyte disturbance

Abstract: Two patients with central pontine myelinolysis are described. Both were middle aged women presenting with a history of protracted vomiting and drowsiness. Hyponatraemia (serum sodium 96 to 100 mmol/L) was a feature in both patients. No underlying malignancy, alcoholism, malnutrition or other serious disease was identified. Correction of electrolyte abnormalities was accompanied by deterioration in level of consciousness and development of a neurological syndrome characterized by quadriparesis, dysphasia and mutism. Death followed and histopathological examination confirmed classical myelinolysis in the central pons and extensive similar, though not identical, lesions in the cerebral hemispheres in both cases. The pathophysiological basis of the lesions is likely to be a special metabolic susceptibility of oligodendroglial cells in areas where neurones, glial cells and myelin sheaths lie in close proximity to one another.

The involvement of flavour volatiles in the resistance to downy mildew of wild and cultivated forms of brassica oleracea

Abstract: SUMMARY The possible involvement of flavour volatiles in the resistance of Brassica oleracea L. seedlings to cabbage downy mildew (Peronospora parasitica (Pers. ex Fr.) Fr.) was investigated using seedlings of a number of commercial Brassica oleracea cultivars. Flavour volatiles are primarily released as a result of tissue damage in brassicas. Only one cultivar tested was resistant to the disease and its tissue macerates yielded the greatest concentration of volatiles. One of these compounds, allyl isothiocyanate, proved to be highly toxic to the pathogen and was produced in much greater concentrations in macerates of cotyledon than first leaf tissue. The ability of seedlings to produce allyl isothiocyanate in large amounts following tissue damage may inhibit the growth of Peronospora parasitica in resistant seedlings. Wild populations of Brassva oleracea L. subsp. oleracea (wild cabbage) were also tested for disease resistance, and the highest proportions of resistant seedlings were found in those populations containing high levels of flavour volatiles. The longest established wild populations possessed the highest average concentrations of flavour volatiles, and it is suggested that selective breeding has resulted in a reduction in the amounts of these compounds in cultivated forms. This change may be a contributory factor towards the lack of resistance shown by modern cultivars.

Collisions between electrons and ions

Abstract: The topic of electron-ion collisions is discussed, primarily from the experimental viewpoint, with an emphasis on recent experiments and new techniques. The methods used in crossed-beam experiments, ion traps and sequential mass spectrometry are described with their application to the measurement of cross sections for electron impact ionization and excitation of positive ions, detachment from negative ions and dissociation of simple molecular ions.

Free Mycolic Acids as Criteria in the Classification of Nocardia and the ‘rhodochrous’ Complex

Abstract: SUMMARY: The methyl esters of free mycolic acids from representative strains of Nocardia asteroides, N. brasiliensis, N. caviae and the ‘rhodochrous’ complex were subjected to detailed mass spectral analysis. The anhydromycolic esters of the Nocardia strains consisted of homologous series containing from zero to three double bonds, with the main components of the parent mycolic acids centred on C52 to C54 (range C46 to C58). The anhydromycolates from one rhodochrous strain, Nocardia opaca, had a molecular weight range similar to the nocardiae (C46 to C57) but the remaining rhodochrous strains gave an homologous series of anhydromycolates containing from zero to two double bonds, with the main components of the parent mycolic acids centred on C38, C42, C44 or C46 (total range from C34 to C50). The mycolic acids from the rhodochrous strains with chain lengths centred around C40 form a group intermediate in size between corynomycolic acids (centred around C50) and nocardomycolic acids (centred around C50). These data weaken the case for retaining the ‘rhodochrous’ complex in the genus Mycobacterium, and also show that many rhodochrous strains can be distinguished from true nocardiae and corynebacteria. These results confirm the value of lipid characters in the classification of these organisms.

An Empirical Study of Some Spatial Interaction Models

Abstract: This paper attempts to focus attention away from a mathematical and theoretical perspective to one where empirical and statistical aspects can assume greater significance. The need for this change of emphasis is demonstrated by the results of an empirical study of a selection of nine spatial-interaction models. Not only do the theory-based models fail to achieve significantly better levels of performance than some empirically derived models, but both types of model fail to achieve satisfactory levels of descriptive performance. These models are shown to be sensitive to the choice of calibration procedure and various kinds of errors in the constant and independent variables. It is suggested that the use of these models should always be accompanied by estimates of confidence limits, and that there is an urgent need for the development of new model designs which can at least provide accurate descriptions of observed reality.

Model for the structure of the gastric mucous gel.

Abstract: THE surface of the stomach is covered by a layer of mucous gel which protects the underlying mucosa from the harmful, acidic stomach contents. The principal component of the gel has been isolated from pig gastric mucus, purified, and shown to be a glycoprotein of molecular weight 2×106 (Table 1)1,2. This glycoprotein consists of four equal sized subunits (molecular weight 5 × 105) joined by disulphide bridges3,4. Each glycoprotein subunit consists of a protein core, 14% by weight of the glycoprotein, with carbohydrate side chains attached. The protein core consists of two regions, one rich in serine, threonine and proline and bearing all the carbohydrate, the other having an amino acid composition characteristic of a globular protein. The latter contains cystine residues which bridge the four subunits. Mild reducing agents and proteolytic enzymes each split the glycoprotein into four subunits4,5. The carbohydrate chains, approximately 15 residues in a branched structure, account for 82% by weight of the glygoprotein and carry ester sulphate residues. The problem therefore is to explain how such a glycoprotein molecule can associate to form a gel which in vivo is essentially impermeable to proteolytic enzymes and which can act as a barrier to protons probably by supporting a pH gradient.

Thyroid-stimulating immunoglobulins and the control of thyroid function.

Abstract: Triiodothyronine (T3) suppression and thyrotropin-releasing hormone (TRH) tests were used to study thyroid function in 50 patients with thyroid disease. The results of the thyroid function tests were compared with the levels of serum thyroid-stimulating immunoglobulins (TSI) measured by a radio-receptor assay. In euthyroid and hyperthyroid patients, the presence of TSI corresponded with the absence of TSH control of thyroid function. However, in two hypothyroid patients with serum TSI levels readily detectable in the receptor assay, T3 suppression and TRH tests indicated that thyroid function was under TSH control.

Evidence that blackfly larvae can feed on particles of colloidal size.

Abstract: FILTRATION of colloidal particles has not previously been reported for animals living in flowing freshwaters. The observation that blackfly larvae (Diptera : Simuliidae) can filter such particles may alter our understanding of the nutrition of these suspension-feeding animals and also afford new possibilities for the control of the insect in areas where the adult females are vectors of onchocerciasis.

Studies on the mechanism of diurnal variation of proliferative indices in the small bowel mucosa of the rat

Abstract: In the rat small bowel mucosa significant variation was found in both the labelling and the mitotic indices with time of day. The zenith and the nadir of labelling and mitotic activity coincided at 15.00 and 02.00 hours respectively. Small changes were found in the ‘cut-off’ position, but this variation in proliferative compartment size was insufficient to account for the comparatively wider fluctuations in proliferative indices. Measurements of the rate of entry into mitosis, using metaphase arrest with vincristine at three widely separated times during the day, showed no significant change. Changes in the growth fraction or in the birth rate as measured cannot account for diurnal variation in the proliferative activity of the small bowel mucosa. We propose a hypothesis which involves diurnal fluctuations in the transit times through G1 and through G2.

The Influence of the Hatching Factor on the Water Uptake of the Second Stage Larva of the Potato Cyst Nematode Heterodera Rostochiensis

Abstract: 1. Larvae-containing eggs of the potato cyst nematode were soaked in root diffusate in artificial tap water or in artificial tap water alone. In one experiment, the eggs were still contained in intact cysts; in another experiment they were in a halved cyst. 2. Eggs were ruptured after 0–5 days treatment and the water content of the liberated larvae immediately estimated by interference microscopy. 3. Larvae from treated eggs from both the halved and intact cysts had a higher water content than controls. 4. Larvae liberated from treated eggs from the halved cyst reached their maximum water content after 24 h treatment; those from intact cysts attained the same value after 2 days. The delay, for the intact cyst, is in keeping with the hatching response for intact cysts and supports the view that the results for water content are due to the activity of the hatching factor. 5. Reasons are advanced for the view that the hatching factor may work via a neurosecretory mechanism.

A search strategy for the elementary cycles of a directed graph

Abstract: The most successful known algorithms enumerating the elementary cycles of a directed graph are based on a backtracking strategy. Such existing algorithms are discussed and a new backtracking algorithm is proposed which is bounded byO(N +M(C + 1)) time, for a directed graph withN vertices,M edges andC elementary cycles.