Showing papers by "University of Liverpool published in 1986"

Repetitive transient rises in cytoplasmic free calcium in hormone-stimulated hepatocytes

Abstract: In the stressed animal, the vasoactive hormones vasopressin and angiotensin-II and the neurotransmitter noradrenaline induce liver cells to release glucose from glycogen. The intracellular signal that links the cell-surface receptors for noradrenaline (alpha 1) and vasoactive peptides to activation of glycogenolysis is known to be a rise in the cytoplasmic concentration of free calcium ions (free Ca). The receptors for these agonists induce the hydrolysis of phosphatidylinositol 4,5-bisphosphate, a minor plasmalemma lipid, to produce inositol trisphosphate and diacylglycerol. Inositol trisphosphate has been shown to mobilize intracellular calcium in hepatocytes. We show here, by means of aequorin measurements in single, isolated rat hepatocytes, that the free Ca response to these agonists consists of a series of transients. Each transient rose within 3 s to a peak free Ca of at least 600 nM and had a duration of approximately 7 s. The transients were repeated at intervals of 0.3-4 min, depending on agonist concentration. Between transients, free Ca returned to the resting level of approximately 200 nM. Clearly, the mechanisms controlling free Ca in hepatocytes are more complex than hitherto suspected.

210Pb dating by low background gamma counting

Abstract: Lead-210 and radium-226 measurements by direct gamma assay can now provide a record of changing concentrations in lake sedimemts sufficiently reliable and precise to form a suitable basis for age/depth and drysedimentation-rate calculations. There are additional benefits in terms of non destructive sample preparation and simultaneous assay for other environmentally significant gamma-emitting radioisotopes (e.g. 137Cs and 241 Am). Results from L. Fleet, S. W. Scotland illustrate the value of this approach especially in lakes with disturbed catchments where variable input of supported 210Pb has occurred.

Observation of a Discrete-Line Superdeformed Band up to 60 ℏ in Dy 152

Abstract: A rotational band of nineteen transitions with a moment of inertia ${\mathfrak{J}}_{\mathrm{band}}^{(2)}$ of $84{\ensuremath{\hbar}}^{2}$ ${\mathrm{MeV}}^{\ensuremath{-}1}$ has been observed in $^{152}\mathrm{Dy}$. The band feeds into the oblate yrast states between ${19}^{\ensuremath{-}}$ and ${25}^{\ensuremath{-}}$ and it is proposed that the lowest member of the band has a spin of ${22}^{+}$ and thus the band extends up to $60\ensuremath{\hbar}$. It is identified as the yrast superdeformed band and its intensity accounts for the whole of the ridge structure seen previously in continuum ${E}_{\ensuremath{\gamma}}\ensuremath{-}{E}_{\ensuremath{\gamma}}$ correlations.

Fault dimensions, displacements and growth

Abstract: Maximum total displacement (D) is plotted against fault or thrust width(W) for 65 faults, thrusts, and groups of faults from a variety of geological environments. Displacements range from 0.4 m to 40 km and widths from 150 m to 630 km, and there is a near linear relationship betweenD andW 2. The required compatibility strains (e s) in rocks adjacent to these faults increases linearly withW and with $$\sqrt D $$ and ranges frome s=2×10−4 toe s=3×10−1. These are permanent ductile strains, which compare with values ofe s=2×10−5 for the elastic strains imposed during single slip earthquake events, which are characterised by a linear relationship between slip (u) andW. The data are consisten with a simple growth model for faults and thrusts, in which the slip in successive events increases by increments of constant size, and which predicts a relationship between displacement and width of the formD=cW 2. Incorporation of constant ductile strain rate into the model shows that the repreat time for slip events remains constant throughout the life of a fault, while the displacement rate increases with time. An internally consistent model withe s=2×10−5, giving repeat times of 160 years and instantaneous displacement rates of 0.02 cm/yr, 0.2 cm/yr, and 2.0 cm/yr when total displacement is 1 m, 100 m, and 10 km, and slip increasing by 0.5 mm with each event, gives a good approximation of the data. The model is also applicable to stable sliding, the slip rate varying with ductile strain rate and withW 2.

Occurrence, Biochemistry and Physiology of Phenazine Pigment Production

Abstract: Publisher Summary This chapter describes the structural features, nomenclature, origin, metabolism, and some properties of phenazines. Naturally occurring phenazines are pigments formed exclusively by bacteria. The absorption spectra of phenazines are characteristic, with an intense peak in the range 250 to 290 nm and a weaker peak at 350 to 400 nm. Unlike the various carotenoid and other pigments that color many bacteria, the phenazine pigments are mostly water soluble and are excreted into the medium. The chapter discusses the biosynthetic origins of phenazine compounds followed by the metabolism of phenazines. The immediate precursors of the long-known products—namely, pyocyanine, chlororaphine and iodinin, attracted early attention. In addition, phenazines, along with most other secondary metabolites, are of uncertain physiological significance. There is little information on the physiological factors that regulate the initiation of phenazine biosynthesis and cause its cessation. Although many phenazines participate in redox reactions, there is no generally accepted evidence that any phenazine functions physiologically in a respiratory chain.

Seifert circles and knot polynomials

Abstract: In this paper I shall show how certain bounds on the possible diagrams presenting a given oriented knot or link K can be found from its two-variable polynomial PK defined in [3]. The inequalities regarding exponent sum and braid index of possible representations of K by a closed braid which are proved in [5] and [2] follow as a special case.

Crosscorrelation between the envelopes of 900 MHz signals received at a mobile radio base station site

Abstract: An experimental investigation is reported of the crosscorrelation of 900 MHz signals received by two spatially separated antennas at a base station. The investigation embraced vertical, horizontal and combined horizontal and vertical separation of the antennas, for transmission from test routes 1.3 km from the base station. It was found that a crosscorrelation ≤0.7 (i.e. when diversity improvement becomes significant) can best be achieved using vertical separation of the antennas of between 11 λ and 13 λ for the 1.3 km cell radius. At 900 MHz such an antenna separation is easily obtained and, in addition, the roof space required is small. Moreover, the crosscorrelation using vertically spaced antennas is independent of the incoming arrival angle (unlike horizontally spaced antennas), and hence low correlation can be achieved while maintaining omnidirectional coverage.

The electronic structure of the benzene molecule

Abstract: The Kekule description of benzene as a mixture of the two structures and was given a firm foundation in quantum theory as a ‘resonance hybrid’ (see, for example, ref. 1). As molecular orbital (MO) theory developed, it was felt that the aromatic character of benzene was explained more naturally in terms of delocalized orbitais. The view that delocalized electrons provide essentially the correct description for this type of system appears to be accepted at all levels2; however, we present here theoretical evidence which challenges this view. We show that the π-electrons in benzene are almost certainly localized and that the characteristic properties of such a system arise from the mode of spin coupling.

Finite group actions on 3-manifolds

Abstract: If G is a finite group acting smoothly on a closed surface F, it is well known that G leaves invariant some Riemannian metric of constant curvature on F. Thus any action of G on the 2-sphere S 2 is conjugate in Diff(S 2) to an orthogonal action. If G acts on the torus SX• S 1, there is a G-invariant flat metric on S a • S 1, and if G acts on a surface F with negative Euler number, then F admits a G-invariant hyperbolic metric. Recently Thurston, [Th 1, Th 2, Th 3], has described the eight 3-dimensional geometries which provide geometric structures for closed 3-manifolds in the same way that the 2-sphere S 2, the Euclidean plane E 2 and the hyperbolic plane H 2 provide geometric structures for surfaces. See also the survey article by Scott [Sc4]. Thurston also conjectured that if M is a closed 3-manifold with a geometric structure modelled on one of these eight geometries, say X, then any smooth action of a finite group G on M should leave invariant some metric on M inducing the geometry X. We will say that G preserves the geometric structure on M in this case. It should be noted that the restriction to smooth actions of G on M is essential. For Bing [Bi] showed that there are involutions of S 3 whose fixed set is a wild 2-sphere. However, in dimension two, it was proved by Eilenberg [Ei] that any action of a finite group on a surface is conjugate to a smooth action. In this paper, our main result asserts that Thurston's conjecture holds for five of the eight geometries. The result is the following.

Valence electronic structure of AuZn and AuMg alloys derived from a new way of analyzing Auger-parameter shifts.

Abstract: A new model is presented that makes it possible to determine the degree of electron transfer in alloys from measurements of the Auger parameter This approach is superior to the use of core-ionization-energy shifts in conjunction with a potential model The Auger parameter does not depend on any reference level, whereas ionization energies measured with respect to the Fermi level must be corrected to the vacuum level before they can be used in the potential model Furthermore, the new model does not require inclusion of contributions from Madelung, surface-dipole, or other bulk contributions, which must be considered in the potential model This new technique is applied to the alloys AuZn and AuMg to show that approximately 01e is transferred to the gold in the first case and about 02e in the second The analysis shows that there is a small increase in the gold 5d population through the series Au, AuZn, AuMg The results are combined with data on M\"ossbauer isomer shifts and theoretical band-structure calculations for Au to give a description of the valence electronic configuration in these alloys The substantial transfer of electrons to the gold 6s orbital, inferred from the M\"ossbauer results, is partially offset by back transfer of 6p electrons from gold to the partner atom This conclusion is supported by band-structure calculations for AuCs

Variations in enamel thickness and structure in East African hominids.

Abstract: Tooth fragments are an appreciable but neglected proportion of fossil hominid specimens. The present study on 47 naturally fractured enamel surfaces of premolar and molar teeth of Plio-Pleistocene East African hominids measured enamel thickness, slope of incremental lines (striae of Retzius), and the morphology of Hunter Schreger bands (HSBs). Specimens allocated to three categories--"robust" australopithecines (EAFROB), "early Homo" (EAFHOM), and "unknown"--were photographed in ethanol with polarised light. Enamel thickness was measured on the occlusal (OT), cuspal (CT), and lateral (LT) aspects. The angle of intersection of striae of Retzius (D) with the enamel-dentine junction (EDJ) was recorded, together with the degree of curvature and width of Hunter-Schreger bands (HSB). Absolute measurements of enamel thickness were scaled by using two allometry correction factors. Absolute thicknesses of all enamel measurements were significantly greater in the EAFROB (OT 3.1 mm; CT 3.3 mm; LT 2.4 mm) compared with EAFHOM (OT 1.4 mm; CT 1.6 mm; LT 1.6 mm) categories. Correction for size reduces the mean difference between the two taxa, but CT and OT thickness remain significantly different (P less than 0.05). HSBs in EAFROB were relatively straight and narrower (means = 52.8 micron) than in EAFHOM, which are more curved and wider (means = 62.0 micron), suggesting greater enamel prism decussation in early Homo. The slope of striae was less in EAFROB permanent molars (means = 23 degrees) compared with EAFHOM (means = 31 degrees), indicating faster rates of coverage during crown formation in "robust" australopithecines. We conclude that the study of fractured enamel surfaces can contribute to our understanding of the systematic relationships and patterns of enamel growth of early hominids.

Distribution of different fiber types in human skeletal muscles: why is there a difference within a fascicle?

Abstract: The proportions of different fiber types (type 1 and type 2) on the borders of fascicles are shown to differ from the proportions internally This finding is based on the analysis of a total of 245 fascicles from whole cross-sections of the vastus lateralis muscle from 13 men, aged from 26-80 years Generally, the difference is more marked in the young than in the old It is argued that the causes of this difference are likely to be local factors in the muscle

Advantages and disadvantages of egret and heron brood reduction.

Abstract: Data from great egrets and great blue herons were used to test a fundamental assumption of Lack's brood-reduction hypothesis, that mortality is brood-size dependent. This was confirmed for the largest brood sizes (4 and 3), which, in egrets, also have the highest sib-fighting rates. Broods of one, however, experienced paradoxically high mortality, especially early in the season. The hypothesis is advanced that parents desert unprofitably small broods when sufficient time remains for production of a larger brood. A simple game-theory model shows that this parental desertion may hinge primarily on the overall costs of renesting. Egret brood reduction caused by sibling aggression (siblicide) occurred later than less aggressive forms of brood reduction. The inclusive fitness of senior broodmates is maximized by the successful fledging of all sibs, and the physical superiority of seniors (in food-handling for herons; food-handling and aggression for egrets) usually suffices to guarantee their own welfare in brood competitions. Finally, it is shown that the last chick in asynchronously hatching broods represents two kinds of reproductive value (RV) to the parents-"extra RV" (obtained despite the survival of elder sibs) and "insurance RV" (obtained only when at least one elder sib dies first)-which can be distinguished from field data. This approach can be used in comparisons with other asynchronous species for partitioning the fitness contributions of marginal offspring.

The ecology of antibiotic production

Abstract: Over the last 40 years, there has been a steady supply of novel, useful antibiotics produced by microbes isolated from soil and other natural environments. The increased efficiency of screening procedures in the last decade has played a major part in maintaining this supply. However, the selection and sampling of natural environments are still essentially random processes. The main reasons for this are an almost total lack of knowledge of the significance of antibiotics in nature, deficiencies in the taxonomy of antibiotic-producing microbes and its application, and lack of information about the distribution and ecology of known or potential antibiotic producers. The origins of these problems are discussed and some possible solutions are suggested.

Shakespeare and Ovid

Abstract: Shakespeare and the Renaissance Ovid sexual poetry the art of precendent comedy and metamorphosis tragedy and metamorphosis from myth to drama

ATP maintains ATP-inhibited K+ channels in an operational state.

Abstract: In patch-clamp records of K+ ATP channels in an insulin-secreting cell line (RINm5F) inhibition evoked by exposing the internal surface of the membrane to ATP is followed not just by the recovery of K+ ATP channel activity when the ATP is removed but by a marked activation of K+ ATP channels. This phenomenon is not a direct consequence of channel closure as inhibition induced by quinidine and quinine is followed upon the removal of the drug only by the recovery of K+ ATP channel activity and not by post-inhibitory activation. If ATP is applied to the exposed internal surface of a membrane patch when all of its K+ ATP channel have run down subsequent removal of the ATP causes their activation. The magnitude and duration of the reactivation of K+ ATP channels is shown to depend upon both the concentration of ATP and the length of time for which the membrane is exposed to ATP. We therefore have a paradoxical situation in that K+ channels which are inhibited by intracellular ATP require intracellular ATP to retain the ability to open.