Showing papers by "University of Leeds published in 1978"

Pupils and Paradigms: a Review of Literature Related to Concept Development in Adolescent Science Students

Abstract: (1978). Pupils and Paradigms: a Review of Literature Related to Concept Development in Adolescent Science Students. Studies in Science Education: Vol. 5, No. 1, pp. 61-84.

Synthesis of heat exchanger networks: I. Systematic generation of energy optimal networks

Abstract: A thermodynamically orientated method is presented for the synthesis of heat exchanger networks. With this method, the problem is solved in two stages. In the first stage, preliminary networks are generated which give maximum heat recovery. In the second stage, the most satisfactory final networks are evolved using the preliminary networks as starting points. In this paper, emphasis is given to the synthesis of the preliminary networks. Two four-stream examples are solved. In Part II, emphasis will be given to the synthesis of final networks.

Translocation and transfer of nutrients in vesicular‐arbuscular mycorrhizas

Abstract: SUMMARY Trifolium repens (white clover) or Allium cepa (onion) infected with the mycorrhizal fungus Glomus mosseae were grown in split-plate cultures, so that nutrients could be supplied to the external hyphae only. The uptake and translocation of 32P, 65Zn and 35S by hyphae of the fungus was measured. A lag phase of 2-3 days in the appearance of 32P in the shoot was caused by a delay in the uptake and translocation of P by the hyphae, rather than in transfer from fungus to host. The calculated maximum translocation rate of P for onion was 6.4 × 10−16 mole s−1, and the P flux in the hyphae about 2 × 10−10 mole cm−2 s−1. The molar amounts of P, S and Zn translocated were in the ratio of 35:5:1 and the mean fluxes in the ratio of 50:8:1 with clover.

Equilibrium values and dynamics of attractiveness terms in production-constrained spatial-interaction models

Abstract: A number of mechanisms are explored for modelling equilibrium values of attractiveness terms in production-constrained spatial-interaction models. They include revenue and facility-size balancing, a differential-equation representation of profit maximisation, and mathematical-programming formulations. The different methods turn out to be closely related but offer different and complementary insights. Some dynamic properties of such equilibrium points are explored, including the identification of circumstances which generate discrete changes for smooth changes in parameters. A number of possible algorithms for calculating the points are described.

Elastohydrodynamic Lubrication of Elliptical Contacts for Materials of Low Elastic Modulus I—Fully Flooded Conjunction

Abstract: Elastohydrodynamic lubrication concepts of conjunctions of elliptical form are applied to materials of low elastic modulus. The influence of the ellipticity parameter and the dimensionless speed, load, and material parameters on minimum film thickness for these materials has been investigated. The ellipticity parameter was varied from a ball on plate configuration to a configuration approaching a line contact. The dimensionless speed and load parameters were varied by 1 order of magnitude. Seventeen different cases were used to generate minimum and central film thickness relations. Contour plots are presented that illustrate the pressure distribution and film thickness in the conjunction.

Evolutionary Patterns and Processes in Ferns

Abstract: Publisher Summary The sole important development in fern cytological technique has been the development of a variety of squash methods for the study of fern chromosomes in somatic tissues. This chapter reviews the evolutionary patterns and processes in ferns. The fossil record of the polypodiaceous ferns in Mesozoic era and tertiary period are also reviewed. The Thelypteridaceae is a large and axonomically difficult family, whose classification is in an only partially resolved state, whereas, the Dryopteridaceae is a large and morphologically diverse but cytologically remarkably uniform family. The existence of a great natural group of genera, the Adiantaceae is also presented in the chapter. The cytology of some of the ancient ferns such as Psilotales, Ophioglossales, Marattiales, and Osmundales are discussed. The information necessary for evaluation of the contribution that cytology can make towards a true phylogenetic classification of the ferns is presented here showing the basic chromosome number or numbers determined for each genus. The different types of polyploidy found in ferns namely autopolyploidy, allopolyploidy, segmental alloploidy and autoallopolyploidy, and their occurrence in different species complexes are also discussed. The systematic and geographical distribution of polyploids, irrespective of their genetic nature, is also reviewed.

Factor analysis of a sleep evaluation questionnaire.

Abstract: A self-completion sleep evaluation questionnaire (SEQ), consisting of 10 cm line analogue rating scale questions, was constructed to investigate subjects' responses to aspects of sleep and early morning behaviour. The questions were grouped into 4 chronological areas: the ease of getting to sleep (GTS), the perceived quality of sleep (QOS), the ease of awakening from sleep (AFS), and the integrity of early morning behaviour following wakefulness (BFW). Five hundred and one SEQs were completed during several investigations into the comparative effectiveness of hypnotic drugs. The classical factor analysis produced 4 factors which corresponded to the 4 aspects of sleep and early morning behaviour listed above. The GTS and QOS factors were positively correlated (+0.57), as were the AFS and BFW factors (+0.48). The 2 sleeping state factors (GTS and QOS) were orthogonal to the 2 waking state factors (AFS and BFW).

Synthesis of heat exchanger networks: II. Evolutionary generation of networks with various criteria of optimality

Abstract: An evolutionary method is presented for the synthesis of heat exchanger networks. Starting from feasible solutions which preferably exhibit maximum energy recovery,1 the method allows systematic promotion of desired design features such as low overall cost, suitability for starting-up procedures, observation of safety constraints, etc. Seven examples based on standard literature problems are used to illustrate the method.

Hot-pressing and the ?-? phase transformation in silicon nitride

Abstract: The kinetics of densification and the kinetics of theα-β phase transformation have been measured during the hot-pressing of silicon nitride ceramics using magnesia as additive. Two mechanisms of densification have been identified. The first is a very rapid particle rearrangement, liquid-enhanced above 1550° C, which operates up to relative densities of about 0.65. The kinetics of the much slower decelerating second stage obey the Coble hot-pressing equation and the rate of densification is found to be proportional to the amount of additive. The controlling mechanism is believed to be diffusion in a boundary second phase, and values for the diffusion coefficient,D b, of the rate-controlling species in the boundary phase for temperatures above and below 1550° C are given. The kinetics of theα toβ transformation, the greater part of which occurs after densification is complete, are described by a first order reaction; the dependence of rate on the quantity of additive and on temperature is similar to that found for densification, and a similar controlling mechanism is believed to be responsible for the two processes.

Mechanics of locomotion of dogs (Canis familiaris) and sheep (Ovis aries)

Abstract: Records have been made of the forces exerted on the ground by dogs and a sheep, in walking, trotting, cantering and slow galloping. Film has been taken simultaneously. The difference between walking and trotting was much less marked for the sheep than for the dogs. Step length and stride length increase as speed increases. They are expressed as functions of the Froude number. The vertical component of the force exerted by a foot on the ground shows two main maxima in walking, except in the case of the fore feet of sheep. In this case and in other gaits there is only one main maximum. The vertical movements of the fore and hind quarters which occurred in examples of each gait have been calculated from the force records. The force exerted by a foot on the ground changes direction in the course of a step so as to remain more or less in line with a point fixed relative to the animal, but dorsal to its back. The force records show impact disturbances in the first 003 sec of contact of each foot with the ground. The point of application of the force on the sole of a foot tends to move posteriorly as the force increases. The results are discussed in relation to a theoretical account of the mechanics of locomotion on legs.

Some properties of clasical multi-dimesional scaling

Abstract: The paper gives a new optimal property of the classical method of multi-dimensional scaling when the distance matrix is non-Euclidean. We also examine robustness of the method under a linear model. A technique to estimate missing values is also given.

The α/β silicon nitride phase transformation

Abstract: The literature on the α/β silicon nitride transformation is reviewed briefly. Data are presented on the kinetics of the tranformation of 1600° C on low and high purity silicon nitride powders. The addition of magnesia increased the rate of transformation while the addition of yttria had no effect. Scanning electron photomicrographs show clearly the morphology changes that accompany the transformation. It is concluded that the transformation occurs via a solution-precipitation mechanism and that α and β are probably low and high temperature forms of silicon nitride.

A further contribution to the theory of the transient hot-wire technique for thermal conductivity measurements

Abstract: The paper presents rigorous working equations for an automatic Wheatstone bridge employed in fluid thermal conductivity measurements by the transient hot-wire technique. Particular attention is concentrated upon the inevitable small differences between the two wires employed for the cancellation of the end effects in the experimental arrangement. It is shown that from experimental measurements of the change in the difference of resistance of the two wires as a function of time during their transient heating, it is possible to determine the temperature rise of a wire acting as a finite section of an infinite wire. The correct expressions for the calculation of the heat flux in the wire are also given.

Parturition and Lactation in the Bitch: Serum Progesterone, Cortisol and Prolactin

Abstract: Concurrent changes in serum progesterone, cortisol and prolactin associated with the prepartum period and lactation of 6 suckling and 1 nonsuckling Beagle bitches were determined by radioimmunoassay. Progesterone in each bitch fell sharply prior to parturition and remained low during lactation. Mean progesterone at approximately 120, 36, 20 and 10 h prepartum was 4.5 ± 0.6, 3.1 ± 0.4, 1.2 ± 0.4 and 0.6 ± 0.1 ng/ml, respectively. In 6 of 7 bitches, serum cortisol was elevated above mean prepartum levels (23 ± 1 ng/ml) during the day prior to the Onset of parturition, reached peak levels of 63 ± 7 ng/ml at 8-24 h prepartum and fell to 19 ± 4 ng/ml at 8-12 h postpartum. Mean cortisol remained between 22 ± 1 and 27 ± 5 ng/ml during lactation and weaning. During the last week of pregnancy, serum prolactin levels (14-97 ng/ml) were variable within (50 ± 2 to 33 ± 8 ng/ml) and among (25 ± 2 to 80 ± 9 ng/ml) bitches and averaged 40 ± 7 ng/ml. In each bitch, prolactin increased by 195 ± 29% during the 16-56 h prepartum and reach peak levels (117 ± 24 ng/ml) at 8-32 (21 ± 3) h prepartum in 6 bitches and at 24 h postpartum in the remaining bitch. By 36 h after these peaks, prolactin levels were reduced to 37 ± 8 ng/ml before again increasing in response to suckling. Mean prolactin increased during the first week of lactation, peaked at 86 ± 19 ng/ml at 1.5 weeks of lactation, fell slowly to 43 ± 6 ng/ml at 5 weeks, shortly before weaning and then fell abruptly to 13 ± 2 ng/ml following weaning. The hormone changes observed were similar to those reported for several other speciesand suggest that the bitch may be a useful model for the study of maternal endocrine adjustments.

A mechanism for the nitridation of Fe-contaminated silicon

Abstract: The influence of iron impurity on both the oxidation and nitridation of high purity silicon has been investigated. It is shown that iron is effective in rapidly removing the protective silica film which normally covers silicon. Experimental evidence suggests that the removal is achieved by iron-induced devitrification and disruption of the silica, thus allowing the SiO (g) generated by the Si/SiO2 interface reaction to escape. During the nitridation of iron-contaminated silicon powder compacts it is found that iron significantly enhances the extent of reaction for contamination levels of <1000 p.p.m. Fe (by weight). Above this level there is a decrease in the rate of formation of extra nitride. At all levels of contamination the percentage of silicon converted to β-Si3N4 was observed to be directly proportional to the iron concentration, and it is shown that this β-growth occurs within an FeSix liquid phase. The possible implications of the findings for the optimization of strength of reaction-bonded silicon nitride are briefly discussed.

Detection and estimation of polyphosphate in vesicular‐arbuscular mycorrhizas

Abstract: Polyphosphates have been extracted from onion roots infected with Glomus mosseae by the technique of phenol-detergent extraction. The polyphosphate was separated from RNA and DNA and characterized by the technique of polyacrylamide gel electrophoresis. On gels stained with Toluidine Blue, the blue-purple nucleic acid bands (β-metachromatic) could be readily distinguished from the pink (γ-metachromatic) polyphosphate band, which ran faster than tRNA, and was coincident with synthetic, marker polyphosphate of chain length 200 ±10. By excising stained gel bands, dry-ashing and P determination, and by enzymic hydrolysis, the presence of condensed orthophosphate in this band has been confirmed. Polyphosphates could not be detected in uninfected roots and the content in infected roots increases several-fold when plants are supplied with orthophosphate 24 h before extraction. By calculation it has been shown that the polyphosphate forms a substantial proportion (40%) of the total P present in the fungal component of mycorrhizal roots, and that this concentration is sufficient to support the proposed phosphorus translocation.

Loess deposits associated with deserts

Abstract: Summary The division of loess deposits into warm/desert and cold/glacial is well entrenched in the literature. The nature and distribution of glacial loess are well accounted for but doubts have been cast on the existence of a true desert loess, i.e. a loess consisting of silt particles actually formed in a desert region. It appears that the loess deposits in Central Asia and North China were formed from silt particles transported out of adjacent deserts — but the particles themselves had their origins in glacial grinding and cold weathering processes in the adjacent mountains. Thus the deserts close to mountainous areas tend to have associated loess deposits. Deserts which are not particularly associated with mountains, e.g. the Sahara and Australian deserts, do not have large loess deposits nearby. Some loess deposits in the Persian/Arabian Gulf region have been observed which consist of silt-sized carbonate particles; a separate division of carbonate loess is proposed. Large scale silt formation is still one of the consequences of glacial action, however it is apparent from recent studies of quartz clasts that glacial grinding is not such an exclusive quartz silt producer as was once proposed. Much coarse-silt-sized quartz is produced directly by weathering of igneous rocks, but there appears to be little doubt that the vast majority of the silt particles for the loess deposits of the world were formed as a consequence of glacial action and cold weathering — and this includes the deposits in Central Asia and North China.

Effects of the anticonvulsant sodium valproate on gamma-aminobutyrate and aldehyde metabolism in ox brain.

Abstract: — Succinic semialdehyde dehydrogenase and NADPH-dependent aldehyde reductase have been purified from ox brain by affinity chromatography on 5′ AMP–Sepharose and 2′5′ ADP–Sepharose respectively. Aldehyde reductase has also been purified using chromatography on Procion Red HE3B–Sepharose. The effects of the anticonvulsant drug sodium valproate were examined on these enzymes, and also on GABA-aminotransferase partially purified from ox brain. Aldehyde reductase was inhibited by valproate in an uncompetitive manner with respect to aldehyde substrates (Ki= 38–85 μM). The inhibitions of succinic semialdehyde dehydrogenase and GABA aminotransferase were approx 2 orders of magnitude weaker, suggesting that aldehyde reductase may be an important site of action of anticonvulsant drugs.