Showing papers by "University of East Anglia published in 1974"

Flux of Gases across the Air-Sea Interface

Abstract: This article describes the use of a two-layer model to estimate the flux of various gases across the air-sea interface.

Reaction mechanism in chemisorption kinetics: nitrogen on the {100} plane of tungsten

Abstract: Kinetic models are developed for the formation of a chemisorbed overlayer on a homotattic surface with fourfold symmetry, taking into account the existence of short range order in the overlayer. It is shown that where the pairwise lateral interaction energy between nearest neighbour adatoms is large (repulsive or attractive), and the overlayer is consequently highly ordered, dissociative adsorption follows a pseudo first-order rate mechanism. Accurate sticking probabilities as a function of surface stoichiometry are reported for the interaction of nitrogen with the {100} plane of tungsten, obtained by a molecular beam technique, over a wide range of both surface and gas temperatures. The results are shown to be in quantitative agreement with the kinetic model, allowing for initial trapping into a mobile physisorbed state, and consistency is established with structural (low-energy electron diffraction) studies.

A Model for Oceanic Crystal Structure Developed

Abstract: Summary The plastic upward flow of asthenosphere at mid-ocean ridge crests implies a linear basaltic magma chamber at the base of the ocean crust at ridge crests. This in turn implies a mature oceanic crust composed of a unit of lavas and dykes, overlying a unit of isotropic gabbro, formed by upward cooling of the magma chamber, overlying a unit of cumulate gabbros and ultramafics, overlying residual mantle from which the basaltic magma has been removed. Analysis of this structure shows that it is asymmetric, with lavas and cumulates dipping towards the spreading centre, and dykes predominantly chilled away from the spreading centre. Increase in spreading rate leads to an increase in lava dips, to a separation of lavas and dykes into distinct units, to a thinning of the dyke unit, and to a narrowing of individual dykes. Metamorphic facies and seismic layering may, but do not necessarily, correspond with this lithological layering. The degree of rifting of oceanic crust and the depth of the median valley are related to an interplay of spreading rate and viscosity of the rising asthenospheric material. Measurement of such parameters as direction and extent of one-way chilling of dykes, dyke thickness, lava dip, and degree of separation of lavas and dykes, in sequence-type ophiolite complexes should allow the determination of direction and rate of spreading at the mid-ocean ridges at which they were formed. The model implies cogenetic liquid-solid relationships between ocean-floor rocks, and suggests changes in the shape of the liquid-solid phase diagram over the pressure range 0.5–2 kb, as well as extensive development of ocean-floor metamorphic rocks.

The control of the production of lactate and ethanol by higher plants.

Abstract: Factors controlling the production of ethanol and lactate have been examined using cell free extracts prepared from pea seeds (Pisum sativum var Alaska) and parsnip roots (Pastinaca sativa). The result suggest that under aerobic conditions pyruvate decarboxylase is inactive. With the onset of anaerobiosis glycolysis leads to an accumulation of lactate with a corresponding fall in pH. The fall in pH activates pyruvate decarboxylase and initiates competition between lactate dehydrogenase and pyruvate decarboxylase for pyruvate. The effect of pyruvate concentration on the partitioning has been analysed in terms of a modified Wegscheider rule and shows that the ratio lactate dehydrogenase activity/pyruvate decarboxylase activity bears an inverse relationship to the pyruvate concentration. The decrease in ratio which occurs when the pyruvate concentration rises is enhanced by the co-operativity which is exhibited by pyruvate decarboxylase. The pH optimum of lactate dehydrogenase is alkaline whilst the pH optimum of pyruvic decarboxylase is acid, thus the two enzymes function as a pH-stat. The possibility of excessive production of lactic acid is further controlled by the response of lactate dehydrogenase to ATP; the enzyme is inhibited by ATP and the inhibition increases as the pH decreases. It is suggested that this mechanism functions to protect the plant from excess production of acid.

Subglacial Shearing and Crushing, and the Role of Water Pressures in Tills from South-East Iceland

Abstract: Till exposed at the retreating margin of Breidamerkurjokull has a two-layer structure; an upper horizon of high void ratio and with a high concentration of fines, and an underlying, denser, less fi...

A critical examination of the physical and adrenergic factors affecting blood flow through the gills of the rainbow trout

Abstract: 1. Perfusion of the whole gill of Salmo gairdneri with a Newtonian medium under different afferent and efferent pressures has revealed considerable passive distensibility in the branchial vasculature. A capacity for autoregulation may exist. 2. Changes in dorsal aortic pressure are relatively more effective than changes in ventral aortic pressure in altering branchial vascular resistance. 3. Measurements of changes in vascular tone in the gills determined as the ratio of resistances in the experimental and the control states at one point on the pressure differential/flow profile can be extrapolated to the rest of the profile when the comparisons have been made at the same flow. 4. True catecholamines cause a maximum 60% decrease in vascular resistance (at the same flow) by stimulation of β 1 -adrenergic receptors in the gills. 5. Branchial dimensions and perfusate viscosities have been measured and, together with the pressure differential/flow data, have been used to evaluate the Muir-Brown model of vascular resistance in the teleost gill. The model, with some limitations, fits the present data and suggests that both active and passive resistance changes are best explained by alterations in the number of secondary lamellae perfused.

Thermo-mechanics of rubberlike materials

Abstract: A theoretical study is made in this paper of the formulation of constitutive equations describing the thermo-mechanical response of solid polymers in the temperature range in which they exhibit rubberlike behaviour. An expression for the Helmholtz free energy of such a material is first constructed on the basis of two assumptions which are motivated by physical arguments concerning the relation of the molecular structure of a cross-linked polymer to its bulk response. The constitutive equations for the stress and the entropy generated by the proposed form of the free energy function are then employed m a detailed investigation of the extension of a cylindrical specimen under prescribed conditions of temperature and pressure, a situation which serves as a model of the experimental arrangement most frequently used in laboratory studies of the mechanical and thermo-mechanical properties of rubberlike solids. Qualitative consistency of the theoretical predictions with observed behaviour is shown to be assured, over the full range of circumstances for which measurements have been reported, by two simple inequalities affecting one of the three response functions appearing in the stress-deformation-temperature relations. The function concerned is closely related to the strain energy governing isothermal deformations of the material at a selected reference temperature and it is associated, by the physical considerations referred to above, with the contribution to the stress of the polymer network. This conclusion shows that a rational macroscopic theory of rubberlike thermoelasticity can be developed in rather general terms. In particular, the requirement that the constitutive equations shall reproduce the anomalous thermo-mechanical effects which are characteristic of solid elastomers imposes restrictions on the response functions no more severe than those which ensure that the purely mechanical behaviour of the material is physically realistic. In the remainder of the paper the capability of the basic theory for furnishing results quantitatively agreeing with experiment is examined. Empirical forms of the three response functions are presented which accurately represent measurements made in tests involving compression at different fixed temperatures and stretching at the reference temperature. Numerical calculations relating to the analysis of the extension of a cylinder, given earlier, are then described and compared with the results of experiments in which thermoelastic inversion phenomena occur. Satisfactory agreement is secured, but it is noted that insufficiency of material data for the rubbers used in the tests precludes an exact correlation of theory and experiment. The final section of the paper is concerned with isothermal deformations of rubberlike materials which are mechanically incompressible (in the sense that volume changes can be brought about by thermal expansion but not by loading at fixed temperature). This property closely approximates the typical behaviour of natural and synthetic rubbers, but its incorporation into a general treatment of rubberlike thermoelasticity presents difficulties and places an undesirable limitation on the scope of the theory. An analogue is shown to exist between the constitutive equations for deformations at the reference temperature and their counterparts in respect of isothermal deformations at other temperatures, and with its aid the problem of the combined extension, torsion and uniform heating of a circular cylinder is solved. Again, a numerical evaluation of the solution is compared with available experimental data.

Studies on partially reduced mammalian cytochrome oxidase. Reactions with carbon monoxide and oxygen.

Abstract: A number of methods were used to prepare a species of mammalian cytochrome oxidase (EC 1.9.3.1, ferrocytochrome c –oxygen oxidoreductase) in which only cytochrome a 3 is reduced and in combination with CO. The kinetics of CO binding by cytochrome a 3 2+ in this species is significantly different from that exhibited by cytochrome a 3 2+ in the fully reduced enzyme. The second-order rate constant for combination was 5X10 4 m −1 ·s −1 and the ‘off’ constant was 3X10 −2 s −1 . The kinetic difference spectra cytochrome a 3 2+ –cytochrome a 3 2+ –CO reveal further differences between the mixed-valence and the fully reduced enzyme. The reaction between cytochrome a 3 2+ and oxygen in the mixed-valence species was followed in flow–flash experiments and reveals a fast, oxygen-dependent (8X10 7 m −1 ·s −1 at low oxygen) rate followed by a slow process, whose rate is independent of oxygen but whose amplitude is dependent on [O 2 ]. The fast oxygen-dependent reaction yields as the first product the so-called ‘oxygenated’ enzyme. We conclude from these experiments that the ligand-binding behaviour of cytochrome a 3 depends on the redox state of its partners, a fact which represents clear evidence for site–site interaction in this enzyme. The fact that oxygen reacts rapidly with this enzyme species in which only one component, namely cytochrome a 3 , is reduced represents clear and unequivocal evidence that this is indeed the O 2 -binding site in cytochrome oxidase and may indicate that reduction of oxygen can proceed via single electron steps.

Aromaticity of Heterocycles

Abstract: Publisher Summary This chapter discusses aromaticity of heterocycles. At a time when the validity of the concept of aromaticity is questioned, increasingly, it seems appropriate to review various definitions in common use and to survey their applications in heterocyclic chemistry. From a qualitative viewpoint the characteristics of an aromatic compound are easy to define. A compound is said to be aromatic if it is cyclic and unsaturated with an enhanced stability over simple olefinic compounds. The characteristic aromatic reactivity of the type described is clearly a matter of degree and is difficult to assess quantitatively. From a simple consideration of pyridine, which reacts less readily with electrophiles but more readily with nucleophiles at the ring carbon atoms than does benzene, it soon becomes apparent that attempts to discuss even relative aromatic character using kinetic criteria is fraught with difficulties; this is apart from the fundamental objection that chemical reactivity is not solely a function of ground-state stability.

Respiratory Responses to Long-Term Hypoxic Stress in the Crayfish Orconectes virilis

Abstract: 1. Changes in the rate and force of scaphognathite beating, irrigation volume, oxygen utilization, oxygen consumption and heart rate during acclimation in response to the experimental conditions and in response to long-term hypoxic exposure have been measured in the crayfish Orconectes virilis . 2. Immediately following placement in the experimental chamber the animals exhibited very high levels of respiratory and circulatory performance. These levels decreased slowly and stable minimal performance levels could be measured only after 2-3 days. A 3-day acclimation period under normoxic conditions thus routinely preceded hypoxic experiments to ensure measurement of unmasked hypoxic responses. 3. Two responses to hypoxia were routinely observed: an initial hyperirrigation response maintained oxygen consumption by increased branchial water flow. This response was not maintained, but oxygen consumption remained at pre-hypoxic levels while pumping rates decreased. 4. Possible mechanisms of acclimation to hypoxia are discussed.

Structural investigations of amorphous transition element films I. Scanning electron diffraction study of cobalt

Abstract: Thin films of cobalt, prepared in ultra-high-vacuum at 4 K and examined in situ by scanning electron diffraction, are shown to be amorphous with a radial distribution function similar to that obtained theoretically by serial deposition of atoms in the computer-simulated model developed by Bennett. The effects of removal of lossy electrons (by velocity filtering), subtraction of substrate background, and multiple scattering on the diffraction profile are investigated and discussed.

Structural investigations of amorphous transition element films: II. Chromium, iron, manganese and nickel

Abstract: Thin films of iron, chronium, manganese and nickel have been prepared in ultra high vacuum at 4 K and examined by scanning electron diffraction. Amorphous structures have been identified in iron, chromium and manganese and their respective interference functions found to be similar to each other and to that for cobalt. An argument is given supporting the concept of a truly amorphous phase devoid of crystalline order, as distinct from a miorocrystalline array. This argument is based not only on experimental structural results but on computer-simulated models together with magnetic and electron transport measurements. No evidence was found of an amorphous phase in clean nickel films. Some explanations are suggested for the inconsistencies between the present and earlier work, particularly in the case of nickel and iron.

Observations on shell form and its ecological significance in thaisid gastropods of the genus Lepsiella in New Zealand

Abstract: This paper is concerned with the ecological significance of variation in shell form within the thaisid gastropod genus Lepsiella in New Zealand. Shell form has been investigated by measurement of shell height and breadth, aperture length and width, the diameters of consecutive whorls, apical angle, shell weight, and shell capacity, although in many cases shell height and shell breadth could not be measured because of erosion. L.albomarginata has been studied intensively at 4 stations in the South Island, and L. scobina less intensively at 6 stations in the North and South Islands. Comparisons of pairs of characters between stations have been tested by regression analysis and analysis of covariance where appropriate. Shells of L. albomarginata are relatively taller and narrower, and have a thicker wall, at a very sheltered station (Hakahaka Bay) that at more wave-exposed stations. L. scobina (sensu stricto), characterised by the presence of spiral ribs on the shell, exhibits less striking but comparable differences in shell shape. In laboratory tests in a tidal tank the thicker-shelled L. albomarginata from a sheltered station (Hakahaka Bay in Port Underwood) was much better able to resist attack by the shore crab Hemigrapsus edwardsi than was L. albomarginata from a nearby wave-exposed station (Whites Bay, near Cape Campbell, South Island). L. scobina from both stations was resistant to attack. H. edwardsi abounds at sheltered stations, but is missing from wave-exposed rock reefs such as those at Whites Bay, so that the ability to survive encounters with shore crabs is ecologically important to L. albomarginata inhabiting sheltered stations. L. scobina occupies a lower zone on the shore, where it is probably liable to encounter other more powerful predators. Its spiral ribs probably strengthen the shell. We do not know to what extent differences in shell form and thickness depend on environmental factors, and to what extent they originate genetically. Thin shells are associated with an abundance of mussels (Mytilus edulis ssp. aoteanus or Modiolus neozelanicus). There is an interesting possibility that a scarcity of mussels or other food caused by superior nonspecific predators might result in the production of better-protected Lepsiella.

Properties of the assimilatory nitrate reductase from Aspergillus nidulans.

Abstract: 1. Nitrate reductase has been partially purified from Aspergillus nidulans. It has a sedimentation coefficient of 7.6 (± 0.1) S and a molecular weight of 190000 (± 10000) from sucrose density gradient centrifugation and gel-filtration studies. There is spectroscopic evidence for the presence of a haemoprotein component. 2. It possesses two associated activities, cytochrome c reductase and reduced viologen dye: nitrate reductase. A study of the effects of heat and inhibitors on the three activities suggests that the molecule consists of two functional parts. One of these is heat labile, contains FAD and a haemoprotein and catalyses the transfer of electrons from NADPH to cytochrome c. The other part is heat stable, contains molybdenum and catalyses the transfer of electrons from reduced viologen dyes to nitrate. 3. The Km values for nitrate, NADPH and cytochrome c are reported. In each case the Km for one substrate is not affected by varying the concentration of the other, suggesting a lack of interaction between their respective binding sites. Product inhibition by NADP+ and nitrate under saturating and non-saturating concentrations of NADPH and nitrate suggests a random order rapid-equilibrium mechanism for the enzyme.

Seasonal Rainfall in Southwestern Australia and the General Circulation

Abstract: Seasonal rainfall data at 56 stations in southwestern Australia covering the period 1876–1970 are analysed. The square-root transformation is used. Principal component analysis is used for an exploratory study; the first eigenvector and coefficient are particularly informative. Rainfall patterns of recent years are then individually compared with features of the general circulation. In winter there is good spatial correlation over the region except in a small area near Hopetoun where reverse anomalies often occur. Two fundamental types of winter rain are postulated: continuous rains due to widespread uplift in mid-troposphere associated with winds from north of west, and showery rains associated with airstream instability and enhanced by topography and coastal convergence. Rainfall of early winter is mainly of the first type, closely related to the intensity of the westerlies and probably also to the quasi-biennial osculation of the equatorial stratosphere. Rainfall of late winter is more of the ...

Rapid groundwater flow in fissures in the chalk: an example from south Hampshire

Abstract: Summary Projected road improvements in south Hampshire included plans to dispose of surface drainage into soakaways to be sited near an area of swallow holes in the Chalk. An experiment was undertaken to establish if there was a direct connection between the swallow holes, located near the junction of the Chalk and the Lower Tertiary strata, and major springs used for water supply in the Havant area. As the swallow holes are dry except in periods of storm rainfall a tracer, the fluorescent dye Rhodamine WT, was injected together with a large volume of water into one of the swallow holes. Water samples were collected from the springs at Havant and analysed for Rhodamine WT using a Turner fluorometer. The tracer was found at both sets of springs sampled and the straight line velocity from input point to spring was in excess of 2 km per day. Computations based on the concentration of dye recovered from the springs show that in the event of a tanker spillage within the proposed drainage scheme severe contamination would be expected to occur at the springs. The experiment and the results obtained make it clear that extreme caution should be exercised to avoid contamination of fissure-flow within the Chalk aquifer.

Inhibition and uncoupling of photophosphorylation in isolated chloroplasts by organotin, organomercury and diphenyleneiodonium compounds.

Abstract: 1. Trialkyltin, triphenyltin and diphenyleneiodonium compounds inhibited ADP-stimulated O(2) evolution by isolated pea chloroplasts in the presence of phosphate or arsenate. Tributyltin and triphenyltin were the most effective inhibitors, which suggests a highly hydrophobic site of action. Phenylmercuric acetate was a poor inhibitor of photophosphorylation, which suggests that thiol groups are not involved. 2. Triethyltin was a potent uncoupler of photophosphorylation by isolated chloroplasts in media containing Cl(-), but had little uncoupling activity when Cl(-) was replaced by NO(3) (-) or SO(4) (2-), which are inactive in the anion-hydroxide exchange. It is suggested that uncoupling by triethyltin is a result of the Cl(-)-OH(-) exchange together with a natural uniport of Cl(-). Tributyltin, triphenyltin and phenylmercuric acetate had low uncoupling activity, probably because in these compounds the uncoupling activity is partially masked by inhibitory effects. 3. At high concentrations the organotin compounds caused inhibition of electron transport uncoupled by carbonyl cyanide m-chlorophenylhydrazone or NH(4)Cl. At these high concentrations the organotin compounds may be producing a detergent-like disorganization of the membrane structure. In contrast, diphenyleneiodonium sulphate inhibited uncoupled electron transport at low concentrations; however, this inhibition is less than the inhibition of photophosphorylation, which suggests that the compound also inhibits the phosphorylation reactions as well as electron transport. 4. The effects of these compounds on basal electron transport were complex and depended on the pH of the reaction media. However, they can be explained on the basis of three actions: inhibition of the phosphorylation reactions, uncoupling and direct inhibition of electron transport. 5. The inhibition of cyclic photophosphorylation in the presence of phenazine methosulphate by diphenyleneiodonium sulphate shows that it inhibits in the region of photosystem 1.

Cytochrome-c reductases from wild-type and mutant strains of Aspergillus nidulans.

Abstract: The sedimentation coefficients of the NADPH: cytochrome-c oxidoreductase enzymes from wild-type and mutant strains of Aspergillus nidulans have been estimated by sucrose density gradient centrifugation. In the wild-type, two species of cytochrome-c reductase were found, with sedimentation coefficients of 13.7s and 7.6s respectively. The 13.7s species did not appear to be associated with the enzymes of nitrate reduction, whereas the 7.6s species was closely associated with NADPH: nitrate oxidoreductase. In mutant strains lacking nitrate reductase, a thir species of cytochrome-c reductase with a sedimentation coefficient of 4.5s was found. There is some evidence that this 4.5s cytochrome-c reductase is a subunit or breakdown product of nitrate reductase and a model is presented for the role of this 4.5s cytocnorome-c reductase in the assembly of the intact nitrate reductase molecule.

Gas exchange and its effect on blood gas concentrations in the amphibian, Xenopus laevis.

Abstract: 1. Unrestrained Xenopus with access to air had an oxygen consumption, as measured at 20 °C by manometric and electrode techniques, of approximately 4.5 ml O 2 100 g -1 h -1 of which 1.1 ml was taken in through the skin. 2. Measurements of body volume showed that the rate of oxygen uptake from the lungs was high when the animal was at the surface but fell rapidly during the first few minutes of a dive. 3. Oxygen tensions in systemic (80 mmHg) and pulmocutaneous (60 mmHg) vessels provided evidence for separation of blood flows in the ventricle of the animal when breathing air. The tensions fell in all parts of the circulation throughout a dive. 4. The above data, together with a conventionally determined oxygen dissociation curve, show that both blood and lungs are used to a limited extent as oxygen stores during a dive, the blood being more important. The stores do not permit tissue consumption to go on at a uniform rate throughout a normal breathing-diving cycle.

Host skin mucus as a hatching stimulant in Acanthocotyle lobianchi, a monogenean from the skin of Raja spp.

Abstract: When incubated at 13°C in alternating 12 h periods of light and darkness eggs of Acanthocotyle lobianchi rarely hatch. Hatching was not induced by shadowing or by mechanical disturbance. When skin mucus from the host ray was added to eggs which were more than 15 days old, hatching occurred almost immediately in about 60% of all eggs tested. Susceptibility to host mucus increased with the age of the eggs so that after 26–30 days of incubation over 80% of the eggs tested hatched. Some oncomiracidia were found to remain alive for up to 83 days in the egg, although they appeared to be fully developed at 15 days. Lipid droplets in the body of the 15-day-old oncomiracidia gradually disappeared as the eggs aged and it is suggested that these droplets serve as a food store for resting larvae.

Regulation of 'malic' enzyme of Solanum tuberosum by metabolites.

Abstract: A purification of `malic' enzyme from potato is described. The purified enzyme is specific for NADP and requires a bivalent cation for activity. At pH values below 7 the plot of rate versus malate concentration approximates to normal Michaelis–Menten kinetics. At pH values above 7 the plot of rate versus malate concentration is sigmoid. A number of dicarboxylic acids activate the enzyme and remove the sigmoidicity. The enzyme is inhibited by phosphate, triose phosphates and AMP. In general, effectors of the oxidative decarboxylation of malate behave in the same manner in the reductive carboxylation of pyruvate. The response of the enzyme to energy charge is reported and the physiological significance of the response to metabolites is discussed in relation to the proposed role of the enzyme in the control of pH.