Showing papers by "University of Liverpool published in 1978"

The calculation of lead-210 dates assuming a constant rate of supply of unsupported 210Pb to the sediment

Abstract: Summary The paper describes a method of calculating sediment age from 210Pb profiles where changes in accumulation rate have affected initial 210Pb concentration. Previously published age/depth profiles derived from 210Pb measurements have assumed a constant initial concentration of unsupported 210Pb per unit dry weight at each stage of accumulation, despite variations in accumulation rates. In sediments from three sites which have experienced rapid acceleration in accumulation in recent times, the assumption is not compatible with the measured unsupported 210Pb concentrations. the alternative assumption of a constant rate of supply of unsupported 210Pb to the sediments per unit time allows calculation of age throughout the profiles irrespective of evidence for rapidly accelerating accumulation. The methods of calculation used are outlined, illustrated and discussed in the light of evidence obtained from the sediments of Lough Erne and Lough Neagh, N. Ireland and lakes Ipea and Egari in the Highlands of Papua New Guinea. They provide a means of dating variations in accumulation rate resulting from human activity in the drainage basin.

Isolation, structure and biological activity of two cholecystokinin octapeptides from sheep brain

Abstract: SEVERAL peptides—for example, substance P and neurotensin—are now known to occur in both endocrine cells of the gut and in central or peripheral neurones1. The significance of this dual distribution is far from fully understood, but it seems possible that the same peptide might function as both hormone and neurotransmitter. Vanderhaeghen et al. have reported that radioimmunoassays (RIA) for the antral hormone gastrin have shown activity in extracts of brain, particularly cerebral cortex, of a wide range of vertebrate species2. However, gastrin has the same COOH-terminal pentapeptide sequence as the intestinal hormone cholecystokinin (CCK) and antisera specific for the COOH terminus of gastrin usually cross-react to some extent with CCK also. We found that the pattern of cross-reactivity of boiling water extracts of brain with six different antisera resembled that of a COOH-terminal fragment of CCK more closely than gastrin, and gel filtration studies have indicated that the main component in the extracts was compatible with the COOH-terminal octapeptide of CCK (CCK8)3; these findings have since been confirmed by others4–6. We have purified from sheep brain two octapeptides corresponding to the CCK-like component previously identified by RIA, and report here the isolation, sequence and some properties of these molecules.

The determination of relative growth in crustacea

Abstract: Relative growth in Crustacea is generally in accordance with the simple allometry rule, y = Bxα. The regulation of growth at each ecdysis is such as to result in the attainment, where possible, of the proportions dictated by this rule. Growth proceeds as a series of phases, each composed of from one to several instars. Within each phase there is simple allometric growth, but both the levels of allometry and the size of the variables often change at the transition between phases. These transition changes may be minimal, but they can be so prominent as to result in an obvious critical moult or metamorphosis. In Brachyura there is a consistent pattern of phases in the later post-larval life, the critical moults separating the final three phases being known as the pre-puberty and puberty moults respectively. There can be polymorphism of the terminal mature phase. The critical moults do not necessarily appear to have fixed positions in the sequence of post-larval instars.

On Coastal Trapped Waves: Analysis and Numerical Calculation by Inverse Iteration

Abstract: Waves of sub-inertial frequency in a continuously stratified ocean and trapped over a continental shelf and slope are considered. They form one infinite discrete sequence of modes with frequencies decreasing to zero. The mode frequencies increase with stratification. All modes progress with the coast on their right in the Northern Hemisphere. In three formal asymptotic limits the waves adopt special forms: (1) large longshore wavenumber [Rhines (1970) bottom–trapped waves]; (2) small stratification [barotropic continental shelf waves]; and (3) large stratification [baroclinic (internal) Kelvin-like waves]. These results are illustrated by numerical calculations using the method of inverse iteration, which avoids time integration. Further calculations demonstrate the strong influence of the depth and density profiles on the wave forms. In particular, a realistic context (i.e., a gently sloping shelf bounded by a steeper continental slope, together with greater stratification near to the surface) a...

The oxidation behavior of CoCrAI systems containing active element additions

Abstract: The effect of small amounts of yttrium (up to 1 wt. %) and hafnium (up to 1.5 wt.%) on the oxidation behavior of Co-Cr-Al alloys in the temperature range 1000–1200°C for times up to 1000 hr in air has been studied. The major portion of the study has been concerned with Co-10Cr-11Al base alloys. Both isothermal and cyclic tests have been carried out; the cycle used consisted of 20 hr at temperature, followed by cooling to room temperature. Both additions reduce the overall oxidation, Hf somewhat more so than Y. In part, this is due to the improved adhesion between scale and alloy reducing scale spallation at temperature, and in part due to possible modification of the Al2O3 grain size. The former factor is far more critical under thermal cycling conditions. Under isothermal conditions the oxidation rate increases with increasing Hf content with all but the 1.5 wt.% alloy oxidizing more slowly than the Hf-free alloy; increase in Y content has the reverse effect. Under thermal cycling conditions the 0.3 and 1.0 wt.% Hf alloys show the lowest overall weight gain. Metallographic evidence suggests that the improved scale adhesion is due principally to a pegging mechanism; the active elements promote the growth of intrusions of Al2O3 into the alloy. However, if the intrusions are too large, they can act as initiators of scale failure.

Role of intracellular calcium in promoting muscle damage: a strategy for controlling the dystrophic condition.

Abstract: It is suggested that various muscle diseases and examples of experimentally-induced muscle damage arise because of a high calcium level in the myoplasm. When [Ca2+]i is raised experimentally in amphibian or mammaliam muscle by treatment with A23187 or caffeine, myofilament degradation follows quickly. Such a rapid action suggests the involvement of a sequence of proteolytic activity that is stimulated by a rise in [Ca2+]i. Ca2+ might either trigger protease activity directly or indirectly, or promote the release of lysosomal enzymes. A high [Ca2+]i in dystrophic muscle is believed to be the resultant of a sequence of events that is summarized in the figure. Suggestions are presented for different ways in which the steady-state position of [Ca2+]i might ultimately be controlled for the clinical amelioration of some dystrophic conditions.

Antileishmanial activity of antimonials entrapped in liposomes

Abstract: THE use of liposomes in chemotherapy as a method of ensuring that drugs reach the diseased or defective tissues suffers from the drawback that, on intravenous injection, the bulk of the material is rapidly cleared by the phagocytic cells of the liver1, and does not reach the desired target. We report here a system in which advantage is taken of this behaviour to treat visceral leishmaniasis in mice, in which the amastigote parasites reside unharmed in vacuoles inside the Kupffer cells of the liver2.

Biolithogenesis of microcodium : elucidation.

Abstract: Petrographic studies of Tertiary and Pleistocene caliche from the western Mediterranean show some unusual calcite structures. These structures were designated Microcodium elegans Gluck 1912. New data are presented which question earlier interpretations with regard to the origin of this structure. The new discovery of Microcodium in Recent soils extends its stratigraphic range into the Holocene. Retention of fine detail in Recent samples, revealed by light microscopy and SEM, has suggested an origin hitherto unconsidered, calcification of mycorrhizal associations. Ancient and Recent Microcodium fabrics are compared; sufficient preservation of ultrastructure in the Ancient indicates a homologous origin. Environmental, stratigraphic and palaeoecological significance of Microcodium is discussed: correct recognition indicates existence of a palaeosol, and hence is a valuable criterion for recognition of continental conditions, cessation of sedimentation, subaerial exposure, and time-equivalent horizons. In particular. Microcodium is a characteristic component of caliche in the western Mediterranean. A review of the literature suggests that its presence may have been overlooked or misinterpreted in other parts of the world and, thus, may be more widespread than hitherto suspected. This study, in its embryonic stage of development. illumines the potential importance of biolithogenesis within terrestial carbonates.

Alternative 210 Pb dating: results from the New Guinea Highlands and Lough Erne

Abstract: RECENT lake sediments can be dated using 210Pb and fall-out 137Cs. Pennington et al.1, and Robbins and Edgington2 have set out the assumptions used in calculating dates and estimating accumulation rates from the declining concentration of unsupported 210Pb in the near-surface sediments of Blelham Tarn and Lake Michigan respectively. In both cases, as in other papers3,4, an essential assumption is a constant initial concentration (c.i.c.) of unsupported 210Pb per unit dry weight in the sediment at each depth, whether or not any variations may have occurred in the rate of accumulation. This assumption requires that in undisturbed cores, unsupported 210Pb concentrations should always decline monotonically with depth. Figure 1 shows unsupported 210Pb concentrations in cores from Lough Erne, Northern Ireland and Lake Ipea, Papua New Guinea. The profiles are ‘kinked’ and show at one or more points, a marked increase in unsupported 210Pb concentration with depth. The levels at which this occurs in the cores range from 6 to 30cm. The increases cannot, therefore, be the result of the anomalously low surface concentrations noted elsewhere4. Associated biological, chemical and geophysical studies show that the profiles have not been significantly disturbed by physical or biological mixing. These profiles are not consistent with the c.i.c. deposition model and are regarded as evidence for the dilution of unsupported 210Pb by accelerated sediment accumulation. If such dilution has taken place without leading to a kink in 210Pb concentrations, the assumption of c.i.c. will lead to underestimation of the true age of the sediment below the onset of acceleration. In the case of the ‘kinked’ profiles, dates are not calculable using the c.i.c. deposition model alone. We have adopted an alternative approach to calculating 210Pb dates using as our main assumption a constant rate of supply (c.r.s.) of unsupported 210Pb to the sediment per unit time and deriving dates from the integrated activity of the radionuclide. Previous authors have referred to the possibility of calculating dates using this assumption5,6 but have not given a full account of the method or evaluated the results of its application. Details of the methods used here are set out elsewhere7. This paper compares and briefly evaluates the two alternative models as applied to the sediments of Lough Erne and Lakes Ipea and Egari. The c.r.s. based dates obtained have been compared with those derived either from c.i.c. based 210Pb dates or, in the case of the ‘kinked’ profiles, from a combination of 137Cs dating8 and c.i.c. based calculations. Figure 2 plots the resulting age against depth curves from Lough Erne, Fig. 3, some of the results from Lakes Ipea and Egari.

Interpretation of the Mössbauer spectra of the four-iron ferredoxin from Bacillus stearothermophilus.

Abstract: The Mossbauer spectra of both oxidized and reduced ferredoxin from Bacillus stearothermophilus have been analysed using computer fits to theoretical spectra obtained from a spin Hamiltonian. A consistent set of parameters was obtained from fits to spectra obtained over a wide range of temperature and magnetic field. These results are interpreted in terms of a model for the active centre which is consistent with its electronic and magnetic properties in both redox states. In the model for the oxidized centre all four iron atoms have essentially the same valence, intermediate between ferric and ferrous, with one pair spin-up and the other pair spin-down. On reduction the extra electron goes predominantly to one pair of iron atoms which become ferrous with the other pair remaining substantially unchanged. Using this model it is possible to obtain relationships between the spin Hamiltonian parameters for individual iron atoms and those for the coupled centre. This can give further insight into the relation between the observed electron paramagnetic resonance and Mossbauer spectra.

On the role of grain boundary dislocations in high temperature creep

Abstract: The processes that occur at grain boundaries during high temperature creep at low strain rates have been studied by scanning electron microscopy of a fiducial grid and by transmission electron microscopy mainly of pure aluminium. These and other observations are interpreted in terms of a dislocation model for grain boundary behaviour during high temperature creep.

Kinetics of adsorption, desorption, and migration at singlecrystal metal surfaces

Abstract: This restricted review of a broad and expanding research field represents an attempt to provide an integrated approach to the three primary kinetic processes in chemisorption, emphasizing the interrelationship between structure and kinetics. Kinetic analyses alone are notoriously ambiguous; the success of a particular model is thus dependent on a full range of corroborative experimental information. Indeed, an understanding of the processes involved in the formation of chemisorbed overlayers, in adatom mobility, and in desorption is contingent on the application of structural techniques to chemisorption systems. On the other hand, results from kinetic studies—and desorption, in particular—can also play an important role in the determination of adsorbate structures.

Cocaine-induced conditioned taste aversions in rats

Abstract: In two separate studies cocaine hydrochloride at doses between 10–36 mg/kg was found to induce a dose-related conditioned taste aversion (C.T.A.) to saccharin, and to be an effective conditioning agent even when injections of the drug were delayed 90 min after saccharin intake. These data contrast with an earlier report [3] which suggested that cocaine was totally devoid of aversive properties. However, they do indicate that cocaine is only a weak aversion-inducing agent. In contrast to other drugs, the doses of cocaine which are required to induce a C.T.A. are very large relative to those commonly employed in behavioural studies. The weak potency of cocaine in inducing C.T.A. may be related to the drug's marked potency in the self-administration paradigm. Some possible determinants of cocaine's weak effects are discussed.

Vibrations and waves in physics

Abstract: For the third edition of this successful undergraduate text, the author has made a number of changes to improve the presentation and clarify some of the arguments, and has also brought several of the applications up to date. The new material includes an elementary, descriptive introduction to the ideas behind the new science of chaos. The overall objectives of the book are unchanged: to lead the student to a thorough understanding of the basic concepts of vibrations and waves, to show how these concepts unify a wide variety of familiar physics, and to open doors to advanced topics which they illuminate. Each section of the book contains a brief summary of its salient contents. There are approximately 180 problems to which all numerical answers are provided, together with hints for their solution. This book is designed both for use as a text for an initial undergraduate course on vibrations and waves, and for a reference at later stages when more advanced topics or applications are met.

Structural resistances to mass transfer in the lichen xanthoria parietina

Abstract: SUMMARY Quantitative morphological data obtained from Xanthoria parietina by light and electron microscopy is related to measurements of photosynthesis rate and estimates of biotrophic ribitol transfer. It is concluded (a) that diffusive CO2 flux into the alga is greatly reduced by the resistance of the fungal cortex, (b) that diffusion can easily account for the mass transfer of ribitol from alga to fungus, and (c) that haustoria have no role in the biotrophic transfer of carbohydrate in lichens.

Physical problems of the benthic boundary layer

Abstract: Since the boundary layer at the sea bed has a number of features in common with boundary layers found in laboratory scale flows and in meteology, a brief review is given first of the properties which may be inferred from experience in these fields or from theoretical studies. Measurements of velocity profiles, turbulence, and shearing stress which have been made near the bottom, in deep water, and on the continental shelf, are described in relation to this background. In particular, the logarithmic form of the velocity profile near the bed and deductions from it appear to be valid in certain conditions, but the occurrence of ripples and other bed forms is a complicating feature. The relation of the dynamical aspects of the flow to the transport of sediment as bed load and in suspension is discussed. The diflusive properties of the layer are then considered, in relation to fluxes near the sea-sediment interface and to the formation of nepheloid layers or layers well mixed in temperature and salinity.