Showing papers by "University of Leeds published in 1979"

A physically based, variable contributing area model of basin hydrology / Un modèle à base physique de zone d'appel variable de l'hydrologie du bassin versant

Abstract: A hydrological forecasting model is presented that attempts to combine the important distributed effects of channel network topology and dynamic contributing areas with the advantages of simple lum...

Petrogenetic implications of Ti, Zr, Y, and Nb variations in volcanic rocks

Abstract: Data from experimental runs, coexisting phases in ultramafic rocks and phenocryst-matrix pairs in volcanic rocks have been used to compile a table of mineral-liquid distribution coefficients for Ti, Zr, Y, and Nb for basic, intermediate and acid melt compositions. These values have then been used to interpret variations of these elements, first in basalts and second, during fractional crystallization from basic to acid magmas. For basalts, petrogenetic modelling of Zr/Y, Zr/Ti, and Zr/Nb ratios, when used in conjunction with REE, Cr and isotopic variations, suggests that: (1) the increase in Zr/Y ratio from mid-ocean ridge to within plate basalts and the low Zr/Nb ratios of alkalic basalts are due to (fluid controlled) source heterogeneities; (2) the low Zr and Zr/Y ratio of volcanic arc basalts results from high degree of partial melting of a depleted source; and (3) the high Zr and similar Zr/Y ratio of basalts from fast spreading relative to slow spreading ridges results from open-system fractional crystallization. Modelling of fractionation trends in more evolved rocks using Y-Zr, Ti-Zr and Nb-Zr diagrams highlights in particular the change in crystallizing mafic phases from island arcs (clinopyroxene-dominated) to Andean-type arcs (amphibole±biotite-dominated). These methods can be applied to altered lavas of unknown affinities to provide additional information on their genesis and eruptive environment.

The Role of Theory in Uses and Gratifications Studies

Abstract: Although the uses and gratifications approach lacks a single general theory, it is not inherently atheoretical, and the author suggests how progress can be made in dealing with four conceptual issues facing this tradition: the nature of the "active" audience; the role of gratification orientations in mediating effects; the social origins of media needs and uses; and the interest shared with students of popular culture in perceptions of and cognitions about mass media content formed by audience members.

A simulation model of alluvial stratigraphy

Abstract: The quantitative model presented simulates the development of a two-dimensional alluvial sedimentary succession beneath a floodplain traversed by a single major river. Several inter-related effects which influence the distribution of channel-belt sand and gravel bodies within overbank fines are accounted for. These are (a) laterally variable aggradation, (b) compaction of fine sediment, (c) tectonic movement at floodplain margins, and (d) channel avulsion. Selected experiments with the model show how the interconnectedness and areal density of channel-belt deposits decrease with increasing floodplain width/channel-belt size, mean avulsion period, and channel-belt aggradation rate. Separation of stream patterns based on interconnectedness and channel deposit density is difficult. Tectonic movements do not have a significant influence upon the successions unless a preferred direction of tilting is maintained (half-graben). Then channel-belt deposits showing offlap tendencies tend to cluster adjacent to the active floodplain margin, leaving dominantly fine-grained alluvium to accumulate on the inactive side. Individual channel-belt deposits thicken during aggradation, although a self-regulating limit to such thickening is likely to operate. ‘Multistorey’features resulting from aggradation may be difficult to tell apart from those arising through superposition of distinct channel-belt deposits of avulsive origin.

Allometry of the limb bones of mammals from shrews (Sorex) to elephant (Loxodonta)

Abstract: Measurements have been made of the principal leg bones of 37 species representing almost the full range of sizes of terrestrial mammals. The lengths of corresponding bones tend to be proportional to (body mass)0·35 and the diameters to (body mass)0·36, except in the family Bovidae in which the exponents for length are much nearer the value of 0·25 predicted by McMahon's (1973) theory of elastic similarity. Comparisons are made between mammals of similar size belonging to different orders.

Reaction-bonded silicon nitride: its formation and properties

Abstract: The theme of the review is the construction of a model embracing the mechanism of formation of reaction-bonded silicon nitride, the development of microstructure and mechanical properties. Possible nitridation reactions are discussed, with emphasis on kinetics and on phase composition and microstructure of the reaction product. The influence of Fe, a common impurity in silicon powders, and of H2, as an additive to the nitriding atmosphere, is considered in some detail. The optical, electrical and thermal properties are briefly discussed and areas for further research and development studies identified.

Crustal contamination versus enriched mantle: 143 Nd/ 144 Nd and 87 Sr/ 86 Sr evidence from the Italian volcanics

Abstract: 143Nd/144Nd, 87Sr/86Sr, and REE analyses are presented on a wide variety of Pliocene-Recent volcanic rocks from central Italy. 143Nd/144Nd varies from 0.51214–0.51289 and 87Sr/86Sr from 0.7255-0.7036; while the rare earth elements are characterised by light RE enrichment and a significant negative Eu anomaly. These Italian volcanics are tentatively subdivided into three zones: (1) N. Tuscany where the magmas are believed to reflect crustal anatexis. (2) A central zone in which hybrid (crust/ mantle) rocks have been recognised. (3) A southern zone, south of Rome, where mantle-derived magmas are identified which have been largely unaffected by interaction with continental crust. At Roccamonfina, in zone 3, Rb/Sr and Sm/Nd pseudo isochrons are observed but since the calculated ages are 0.5 and 2.0 b.y. respectively it is argued that a simple isochron model is not applicable and that the data are most easily explained by a recent mixing event within the upper mantle. It is envisaged that this occurred during metasomatism of the upper mantle source region by a fluid that had high 87Sr/86Sr and low 143Nd/144Nd and was enriched in K, Rb, and LREE's but relatively depleted in Sr2+ and Eu2+.

Genetic studies of nitrate assimilation in Aspergillus nidulans

Abstract: Summary (1) In Aspergillus nidulans, at least 16 genes can mutate to affect the reduction of nitrate to ammonium, a process requiring two enzymes, nitrate reductase and nitrite reductase. (2) niaD is the only gene whose effects on enzyme structure are confined to nitrate reductase alone. It specifies a core polypeptide, one or more of which form the basic subunit of nitrate reductase, molecular weight 50000. (3) At least five cnx genes together specify a molybdenum co-factor, necessary for the activity of nitrate reductase, and of xanthine dehydrogenases I and II. The cnxH gene specifies a polypeptide component of this co-factor, and the cnxE and F gene products are involved in co-factor elaboration, The role of the remaining cnx genes is at present unknown. (4) Functional nitrate reductase has a molecular weight of 200000 and is likely to consist of four subunits, together with one or more molecules of the cnx-specified co-factor. (5) The co-factor plays a catalytic role in the aggregation of nitrate-reductase subunits. (6) The niiA gene is the structural gene for nitrite reductase. (7) Other genes affecting nitrate assimilation are either regulatory or bring about their effects indirectly. (8) Of the genes affecting nitrate assimilation, close linkage is found only between the niiA and niaD genes. (9) Nitrate and nitrite reductases are subject to control by nitrate induction and ammonium repression. (10) Nitrate induction is mediated by the nirA gene whose product must be active for the niiA and niaD genes to be expressed. Since most niaD mutants produce nitrite reductase constitutively, it is likely that the nirA gene product is normally inactivated by nitrate reductase, but only when the latter is not complexed with nitrate, (11) Ammonium repression is mediated by the areA gene, whose product must be active for the expression of the niiA and niaD genes, and which is inactive in the presence of ammonium. (12) The tamA gene may function similarly to the areA gene, both gene products being necessary for the expression of the niiA and niaD genes. (13) Although the niiA and niiD genes are probably contiguous, they are not likely to be organized into a structure equivalent to a bacterial operon. (14) Whereas the areA and nirA genes regulate the synthesis of nitrate and nitrite reductases, it is probable that at least nitrate reductase is also subject to post-translational control, the presence of active enzyme being correlated with high levels of NADPH. (15) The regulation of the pentose-phosphate pathway, of mannitol-I-phosphate dehydrogenase and of certain activities required for the catabolism of some nitrogen-containing compounds appears to be connected with that of nitrate assimilation. In all cases, it is probable that the nirA gene and nitrate reductase itself are involved.

Clinical Pharmacokinetics of Prednisone and Prednisolone

Abstract: Prednisone and prednisolone are used in a wide variety of diseases. The two compounds are metabolically interconvertible; prednisolone is assumed to be the pharmacologically active species. Prednisone and prednisolone plasma concentrations are commonly determined by either radioimmunoassay or competitive protein binding techniques. No relationship has been demonstrated between prednisolone plasma concentration (unbound or total concentration) and clinical response; alternate day dosage regimens with fluctuating plasma concentrations being considered generally to be as effective with less side effects than a daily dosage regimen. Both drugs are rapidly absorbed after oral administration, reaching peak plasma concentrations after 1 to 3 hours. In general, plasma half-lives for prednisone are slightly longer (3.4 to 3.8h) than for prednisolone (2.1 to 3.5h). Either drug can be prescribed in most situations. On average, however, the bioavailability of prednisolone after oral prednisone is approximately 80% of that after prednisolone. A wide intersubject variation in prednisolone concentration is evident after both drugs, which may suggest impaired drug absorption in some individuals. Prednisolone shows dose dependent pharmacokinetics; an increase in dose leading to an increase in volume of distribution and plasma clearance. This can be explained in terms of the non-linear binding of the drug to plasma proteins. The degree of binding will determine the distribution and clearance of free (i.e. pharmacologically active) drug. Reduced doses are recommended in patients with hypoalbuminaemia. Prednisolone pharmacokinetics are also dependent on age; the half-life being shorter in children. Liver disease prolongs the prednisolone half-life and, due to the frequently associated hypoalbuminaemia, also increases the percentage of unbound drug. It has been recommended by some that prednisolone rather than prednisone is the drug of choice in active liver disease owing to the poor conversion of prednisone to prednisolone in some patients. However, the reduced plasma concentration of prednisolone in such patients is compensated for by delayed clearance. Thus, there is little advantage of one preparation over the other. Pharmacokinetic drug interactions have been reported, particularly accelerated clearance of prednisolone due to enzyme inducing agents such as barbiturates, phenytoin, rifampicin and other corticosteroids. On the other hand, oral contraceptives have been reported to increase the half-life and to decrease distribution volume and clearance of prednisolone, due to the increased levels of corticosteroid binding globulin (transcortin).

K-Ar geochronology and palaeomagnetism of volcanic rocks in the Lesser Antilles island arc

Abstract: K-Ar age determinations, mainly whole rock, with some corroboration from mineral separates, are presented for lava flows, domes, minor intrusives and blocks in tuffs from 95 localities in the Lesser Antilles. Together with the much smaller number of previously published data, these show a distinction between a range 38-10 million years (Ma) in the outer arc (Limestone Caribbees) and less than 7.7 Ma in the inner arc (Volcanic Caribbees). From southern Martinique southwards, the two arcs are superposed, and the whole range is fragmentarily represented. The observed age ranges in the outer and inner arcs fit between discontinuities in sea floor spreading in the North Atlantic at ca. 38 and ca. 9 Ma and a causal connection between spreading change and relocation of arc volcanicity is suggested. Palaeomagnetic directions at 108 localities in ten of the islands fall into normal ( N = 56, k = 13.8, D = 359°, I = + 22°, pole position 229° E, 89° N with drjr = 3°, d X = 6°) and reversed groups ( N = 41, k = 14.1, D = 178°, I = -22°, pole position 18° E, 88° S with d xjr = 3°, dx = 6°) plus six sites of intermediate polarity and five sites indeterminate. The mean dipole axis is within 2° of the present rotation axis and is likely to be identical with it with a probability of 99%. The data are generally in accord with the established geomagnetic polarity time scale, but there is some suggestion of a normal polarity event at ca. 1.18 Ma within the Matuyama Reversed Epoch. The palaeomagnetic data relate mainly to be past 10 Ma and suggest that within that time the Lesser Antilles have not changed their latitude or geographic orientation, and that the geomagnetic field has averaged that of a centred axial dipole. The few older palaeomagnetic data are consistent with these same conclusions (though with less certainty) back to ca. 20 Ma ago. There is no evidence for oroclinal bending of the arc since then.

Computation of torque and current in doubly salient reluctance motors from nonlinear magnetisation data

Abstract: The paper presents a new method for accurately calculating the torque and current of a variable-reluctance stepping motor from measured or computed flux-linkage/current/rotor position data. The new method is more accurate and uses less input data than previously known procedures, and is computationally efficient. It can be applied to both steady-state and transient problems.

Muscle Strengths and Musculoskeletal Geometry of the Upper Limb

Abstract: A survey of past literature has shown that there is a lack of reliable data for use in prediction of joint forces in the upper limb although this is desirable when developing joint replacements. Upper limb geometry has been analysed, leading to muscle moment arm data at the wrist and elbow. The variation of these moment arms during elbow flexion has also been examined. Analysis of the dimensions of muscles has enabled their relative strengths to be predicted, based on their ‘physiological cross-sections’. When used in conjuction with published emg data, this information will enable elbow and wrist joint forces to be estimated more realistically than has previously been possible.

Transmission of the Load in the Knee Joint with Special Reference to the Role of the Menisci Part I: Anatomy, Analysis and Apparatus

Abstract: The menisci of the knee joint transmit a considerable fraction of the total load acting on the joint. This paper describes an investigation into the load carrying capacity of the individual meniscus. Interest is also directed to an examination of the function of the degenerate meniscus and that of the meniscus with different kinds of tears. Quantifying the meniscal loads is based on a four-spring model representing the load bearing areas in the knee with intact menisci. The assumptions underlying the model are discussed and the problems of loading associated with the four-spring model are described. These problems called for careful consideration of the methods of loading and aligning the joint. A loading machine with a special aligning device was built for the experimental work.The experimental procedure is described in Part II. The intact individual meniscus was shown to transmit 70-99 per cent of the load acting on the respective side. The load carrying capacity of the meniscus was shown to decrease fo...

143 Nd/ 144 Nd and 87 Sr/ 86 Sr ratios from the Azores and their significance in LIL-element enriched mantle

Abstract: Basalts from Sao Miguel are displaced to higher 87Sr/86Sr ratios, and have a significantly shallower slope, compared with the main correlation between 143Nd/144Nd and 87Sr/86Sr for most mantle-derived volcanic rocks. Available data on young magmatic rocks indicate that large ionic lithophile (LIL)-element enrichment in the upper mantle involves two readily distinguishable components which reflect different histories.

The development of endomycorrhizal root systems ii. effect of agronomic factors and soil conditions on the development of vesicular-arbuscular mycorrhizal infection in barley and on the endophyte spore density

Abstract: Summary The percentage of roots with vesicular-arbuscular mycorrhizal fungi and numbers of spores were measured over 2 years in a field experiment with different crop rotations of barley, kale and fallow. Spore numbers, and subsequent infections of barley crops, were largest following barley; both kale and fallow breaks reduced spore population and infection similarly. With all crop rotations there was a long delay before appreciable percentage infection of roots developed, followed by a rapid increase, and then a constant value. Such late infections appear unlikely to improve crop nutrition, and final yield was negatively related to per cent infection. A survey of barley crops in 2 years on commercial fields following at least 3 years barley showed that infection was rather similar in most fields. There was a very slight correlation between infection percentage, clay content and pH, but no other soil factor had any influence. Early-sown crops tended to have low infection.

Effect of anorexic drugs on food intake and the micro-structure of eating in human subjects

Abstract: Human volunteer subjects of normal weight received oral doses of (+)amphetamine (10 mg) or (±)fenfluramine (30 mg and 60 mg) together with a placebo control according to a within-subjects design. The effects of these treatments were monitored by measuring food intake in a test meal, subjective ratings of hunger motivation and the micro-structure of eating behaviour abstracted from videotaped recordings of the test meal. Various measures of the rate of feeding were computed from these recordings. Amphetamine and fenfluramine (60 mg) showed generally similar effects on food intake and on the subjective experience of hunger, but displayed differing actions on the fine structure of eating. Amphetamine increased latency to initiation of eating and increased the rate of food ingestion, whilst fenfluramine slowed the local rate of eating and eliminated the characteristic decline in the rate of feeding across the course of a meal. These findings display certain resemblance to the results of animal experiments involving similar pharmacological manipulations and emphasise the importance of measuring rate of feeding in animal and human studies. The results of this study suggest that the micro-analysis of feeding behaviour not only provides a tool for understanding systems involved in the modulation of food consumption but also reveals information which may be helpful for the use of drugs in the treatment of obesity.

Design of General Manifold Multiplexers

Abstract: The direct analytical design process for arbitrary multiplexers given in a previous paper is extended to the case of bandpass channel filters connected to a uniform-impedance manifold (e.g., a length of waveguide or transmission line). The previous approximations are greatly improved by adding immittance compensation in a way which not only preserves the canonic form of the network but also assists in the physical construction by spacing the filters along a manifold. The phase shifters between channels are themselves sufficient to compensate the filter interactions to such an extent that contiguous channeling cases are designable. The results are presented mainly in closed form requiring minimal computer optimization. Analysis of multiplexers with frequency-dependent manifolds indicate that there are restrictions on the total bandwidth, but a ten-channel multiplexer is probably feasible, suitable for input and output multiplexers required in typical communications systems. Practical results on a simple manifold triplexer are presented.

Identification of Pseudomonas tolaasi: the White Line in Agar and Mushroom Tissue Block Rapid Pitting Tests

Abstract: A sharply defined white line of precipitate forms in Pseudomonas Agar F (Difco) between the opaque white colonies of Pseudomonas tolaasi and translucent colonies of certain unidentified pseudomonads. This visible interaction has been utilized in a specific and reliable method for the identification of Ps. tolaasi. The white line test was positive when 113 isolates of Ps. tolaasi from five different countries were examined, whereas 154 isolates of pseudomonads other than Ps. tolaasi, including Ps. corrugata, Ps. delphinii, Ps. fluorescens, Ps. lachrymans, Ps. marginalis, Ps. pastinaceae, Ps. phaseolicola, Ps. aeruginosa, Ps. putida, Ps. syringae, Ps. mors-prunorum, Ps. cichorii, Ps. antirrhini, Ps. viridiflava, Ps. caryophylli, Ps. cepacia, Ps. mendocina, Ps. stutzeri, Ps. acidivorus and Ps. lemoignei did not give the white line reaction with a reacting translucent colony pseudomonad. Browning of mushrooms in host tests does not help in the identification of Ps. tolaasi, but a conspicuous pitting produced in less than 10 min at the cut surface of mushroom tissue is as specific as the white line test in detecting Ps. tolaasi in suspension in distilled water.

Mechanical stresses in fast locomotion of buffalo (Syncews coffer) and elephant (Loxodonta africana)

Abstract: Films of buffalo and elephant running, and detailed measurements on dissected legs, have been used to estimate the maximum stresses which occur in locomotion, in certain muscles, tendons and bones. These stresses are similar to stresses previously determined for some other, smaller mammals.

A Generalized Multiplexer Theory

Abstract: A general direct analytical design process is presented for multiplexers having any number of channels with arbitrary channel complexity, bandwidths, and interchannel spacings. The theory assumes initially that independent doubly terminated designs are available for the individual filters, and formulas for modifications to parameters associated with the first two resonators are developed to match the multiplexer. These formulas are approximate, and the Iimitations of the theory are indicated with several computed examples. The theory is applied to the design of a five-channel interdigital multiplexer. A first-stage immittance compensation scheme is described which improves the design for limiting cases, but the theory of complete immittance compensation which handles even contiguous channel operation is reserved for a companion paper.

Mechanics of running of the ostrich (Struthio camelus)

Abstract: Ostriches have been filmed running fast in their natural habitat. A female ostrich has been dissected and the principal bones, muscles and tendons in a leg have been measured. It is calculated that stresses up to 240 kN m−2 and 40 MN m−2, respectively, act in the digital flexor muscles and their tendons during running. Tensile and compressive stresses up to about 70MNm−2 and 110 MNm−2 act in the tibiotarsus. A large proportion of the energy which would otherwise be required for running is probably saved by elastic storage in tendons. Comparisons are made with the legs of flying birds and of antelopes.