Showing papers by "University of Liverpool published in 1992"

Climatic and oceanographic isotopic signals from the carbonate rock record and their preservation

Abstract: Stable isotopic data from marine limestones and their constituent fossils and marine cements can provide quantitative evidence for changes in global climate and ocean circulation. Oxygen isotopic data can indicate changes in temperature and ocean composition whereas stratigraphic variation in carbon isotope ratios may reflect changes in the carbon cycle that can be linked to changes in oceanic productivity and atmospheric greenhouse gases. Terrestrial carbonates–meteoric cements, calcretes and speleothems–similarly offer significant potential for understanding the evolution of terrestrial climates by providing evidence for the composition of rainwater and the nature of vegetative cover.Primary environmental isotopic signals may be obscured by the effects of post-depositional diagenetic alteration. Cementation and replacement reactions can take place in a wide range of diagenetic environments; the diagenetic history of an individual limestone is determined by a combination of its mineralogical diagenetic potential and depositional setting, together with subsequent changes in relative sea-level and burial history. Carbon isotopic values are less prone to alteration during diagenesis than oxygen values but shifts can be significant where organogenic carbon is incorporated. Linear covariation of carbon and oxygen values is not a reliable indicator of diagenetic alteration: water-rock interaction and fluid mixing may produce non-linear distributions.Attempts to determine long-term changes in climatic and oceanographie conditions through isotope stratigraphy of shallow-water limestones must include an assessment of the diagenetic history of the materials analysed. Petrographic examination using conventional microscopy backed up, where appropriate, by cathodoluminescence and scanning electron microscopy together with elemental and strontium isotopic analysis can help to identify the effects of diagenetic alteration. Where material with a range of different degrees of alteration is preserved in the same sediment it may be possible to compare patterns of isotopic and elemental variation and to attempt to unravel the effects of diagenesis in order to determine primary, environmental, isotopic signals. Recent research has shown that these techniques can be successfully employed in both Phanerozoic and Precambrian sediments.

Saliva: its secretion, composition and functions.

Abstract: The secretions of the major and minor salivary glands, together with the gingival crevicular fluid, constitute the oral fluid or whole saliva which provides the chemical milieu of the teeth and oral soft tissues. The crucial role of saliva in the maintenance of dental health is demonstrated by the morbidity associated with loss of salivary gland function. In this article, the physiology of the secretory process, the reflex control of whole saliva flow rate, the composition of the fluid, the factors affecting its composition, and the functions of the organic and inorganic components are described. Finally, the clinical aspects of salivary gland dysfunction are briefly discussed.

Origin and evolution of the genus Homo.

Abstract: It is remarkable that the taxonomy and phylogenetic relationships of the earliest known representatives of our own genus, Homo, remain obscure Advances in techniques for absolute dating and reassessments of the fossils themselves have rendered untenable a simple unilineal model of human evolution, in which Homo habilis succeeded the australopithecines and then evolved via H erectus into H sapiens-but no clear alternative consensus has yet emerged

A reappraisal of ignimbrite emplacement: progressive aggradation and changes from particulate to non-particulate flow during emplacement of high-grade ignimbrite

Abstract: We propose a mechanism by which massive ignimbrite and layered ignimbrite sequences — the latter liable to have been previously interpreted as multiple flow units-form by progressive aggradation during sustained passage of a single particulate flow. In the case of high-temperature eruptive products the mechanism simplifies interpretation of problematic deposits that exhibit pronounced vertical and lateral variations in texture, including between non-welded, eutaxitic, rheomorphic (lineated) and lava-like. Agglutination can occur within the basal part of a hot density-stratified flow. During initial incursion of the flow, agglutinate chills and freezes against the ground. During sustained passage of the flow, agglutination continues so that the non-particulate (agglutinate) layer thickens (aggrades) and becomes mobile, susceptible to both gravity-induced motion and traction-shear imparted by the overriding particulate part of the flow. The particulate to non-particulate (P-NP) transition occurs in and just beneath a depositional boundary layer, where disruptive collisions of hot viscous droplets give way, via sticky grain interactions, to fluidal behavior following adhesion. Because they have different rheologies, the particulate and non-particulate flow components travel at different velocities and respond to topography in different ways. This may cause detachment and formation of two independent flows. The P-NP transition is controlled by factors that influence the rheological properties of individual erupted particles (strain rate, temperature, and composition including volatiles), by cooling and volatile exsolution during transport, and by the particle-size population and concentration characteristics of the depositional boundary layer. At any one location along the flow path one or more of these can change through time (unsteady flow). Thus the P-NP transition can develop momentarily or repeatedly during the passage of an unsteady flow, or it can occur continuously during the passage of a quasi-steady flow supplied by a sustained explosive eruption. Vertical facies successions developed in the deposit (high-grade ignimbrite) reflect temporal changes in flow steadiness and in material supplied at source. The P-NP transition is also influenced by factors that affect flow behaviour, such as topography. It may occur at any location laterally between a proximal site of deflation (e.g. a fountain-fed lava) and a flow's distal limit, but it most commonly occurs throughout a considerable length of the flow path. Up-sequence variations in welding-deformation fabric (between oblate uniaxial to triaxial and prolate) reflect evolving characteristics of the depositional boundary layer (e.g. fluctuations from direct suspension-sedimentation to deposition via traction carpets or traction plugs), as well as possible modifications resulting from subsequent, post-depositional hot loading and slumping. Similar processes can also account for lateral lithofacies gradations in conduits and vents filled with welded tuff. Our consideration of high-grade ignimbrites has implications for ignimbrite emplacement in general, and draws attention to the limitations of the widely accepted models of emplacement involving mainly high-concentration non-turbulent transport and en masse ‘freezing’ of high-yield-strength plug flows.

Curves and singularities : a geometrical introduction to singularity theory

Abstract: 1. Introductory example: a gravitational catastrophe machine 2. Curves, and functions on them 3. More about functions 4. Regular values and smooth manifolds 5. Envelopes 6. Unfoldings 7. Unfoldings: applications 8. Transversality 9. Generic properties of curves 10. More on unfoldings 11. Singular points, several variables and generic surfaces Appendix: Null sets and Sard's theorem.

Alzheimer's disease, other dementias, depression and pseudodementia: prevalence, incidence and three-year outcome in Liverpool.

Abstract: A group of 1070 community-living persons aged 65 and over was assessed using the GMS-AGECAT package and other interviews at years 0 and 3. Year 3 interviewers were 'blind' to the findings at year 0, and the prevalence of organic disorders and depression was very similar in both years. According to the results at year 3, minimum and maximum prevalence figures for dementia at year 0 were 2.4% and 3.8% for moderate to severe and 0.4% and 2.4% for mild or early cases, with a best estimate of 3.5% and 0.8%, or 4.3% overall, divided into: senile, Alzheimer's type 3.3%; vascular 0.7%; and alcohol-related 0.3%. The overall incidence of dementia, clinically confirmed by six-year follow-up, was 9.2/1000 per year (Alzheimer type 6.3, vascular 1.9, alcohol related 1.0). Three years later, 72.0% of those with depressive psychosis and 62.3% of those with depressive neurosis were either dead or had some kind of psychiatric illness. Nearly 60% of milder depressive cases (7.2% of the total sample) had either died or developed a chronic mental illness. The outcome of depressive pseudodementias is equivocal so far. Findings at year 3 provide validation of AGECAT computer diagnosis against outcome; organic and depression diagnoses are seen to have important implications for prognosis.

Amplification of DNA from native populations of soil bacteria by using the polymerase chain reaction.

Abstract: Specific DNA sequences from native bacterial populations present in soil, sediment, and sand samples were amplified by using the polymerase chain reaction with primers for either 'universal' eubacterial 16S rRNA genes or mercury resistance (mer) genes. With standard amplification conditions, 1.5- kb rDNA fragments from all 12 samples examined and from as little as 5 I¼g of soil were reproducibly amplified. A 1-kb mer fragment from one soil sample was also amplified. The identity of these amplified fragments was confirmed by DNA-DNA hybridization.

The evolution of sexual size dimorphism in fish

Abstract: Life history strategy models in which female size depends on fecundity and male size on male-male competition, are used to predict male and female size. Sperm competition alone—without any form of contest competition—cannot readily generate size ratios (male weight/female weight) greater than 1·0, and if sperm competition is very weak, small or even dwarf males are predicted. Increasing sperm competition increases male size, but only with high numbers of competing males can male size approach that of females. Size dimorphism is also affected by the ratio: growth rate/mortality rate in each sex. If this is higher in one sex, its size increases. Two trade-offs in fish could affect this ratio but neither appears likely to yield size ratios above unity under sperm competition. Male-male combat is capable of pushing male size beyond that of females, but male size seems never to exceed female size by more than one order of ten, whilst the reverse can proceed to many orders of ten (dwarf males), a pattern which applies generally in animals. Reasons for this asymmetry in size ratio include buffering effects of reducing growth rate (‘von Bertalanffy buffering’), and an asymmetry in the homeostatic effect of operational sex ratio (‘OSR buffering’). High adult male mortality and weak male-male competition can generate dwarf males. A fundamental problem concerns why the sexes are often so similar in size: this may relate to sperm competition, size buffering effects, and many other features not considered in the present models.

Recruitment and mortality of early post-settlement stages of benthic algae

Abstract: Four transitional life history stages are generally recognized for benthic marine algae. On the basis of differences in size, we propose two more: young germlings and young juveniles. Three of these (spores or zygotes, young germlings, and germlings) are considered early post-settlement (EPS) stages. Many of the available data on recruitment and mortality were not collected with EPS stages specifically in mind, and considerable extrapolation and inference are required to interpret effects on early phases. Data on EPS stages, and grazing in particular, are based on the disappearance of early stages (laboratory or field experiments, including outplantings), on indirect information on mortality from manipulations of grazers or juvenile stages, and combinations of observation and manipulation. We also provide original data on the effects of water motion and canopy sweeping on zygote mortality. The most notable finding is the variability in, and multiplicity of, factors preventing successful recruitment of ear...

Sexual dimorphism and distorted sex ratios in spiders

Abstract: SEXUAL dimorphism in body size is widespread in the animal kingdom. Whereas male giantism has been studied and explained extensively1,2, male dwarfism has not. Yet it is neither rare3–7 nor without theoretical interest8,9. Here we provide experimental and comparative data on spiders to support the theory that dwarf males are associated with high differential adult mortality, with males at much greater risk. Species with sedentary (low-risk) females have dwarf, roving (high-risk) males. Life-history theory could readily explain dwarfing if juvenile, but not adult, male mortality were large. We present a new model in which high mortality of searching mature males reduces the adult sex ratio (males: females), relaxing male–male competition and reducing the importance of male body size to favour dwarfing by early maturation. Early maturity also reduces male juvenile mortality and thus opposes adult mortality. This provides a mechanism that buffers skews in adult sex ratio and which is quite distinct from Fisher's principle10 and allied mechanisms9,11 for the primary sex ratio.

Translation, rotation, and scale invariant pattern recognition by high-order neural networks and moment classifiers

Abstract: The classification and recognition of two-dimensional patterns independently of their position, orientation, and size by using high-order networks are discussed. A method is introduced for reducing and controlling the number of weights of a third-order network used for invariant pattern recognition. The method leads to economical networks that exhibit high recognition rates for translated, rotated, and scaled, as well as locally distorted, patterns. The performance of these networks at recognizing types and handwritten numerals independently of their position, size, and orientation is compared with and found superior to the performance of a layered feedforward network to which image features extracted by the method of moments are presented as input. >

Self-absorption corrections for well-type germanium detectors

Abstract: Corrections for self-absorption are of vital importance to accurate determination by gamma spectroscopy of radionuclides such as 210Pb, 241Am and 234Th which emit low energy gamma radiation. A simple theoretical model for determining the necessary corrections for well-type germanium detectors is presented. In this model, self-absorption factors are expressed in terms of the mass attenuation coefficient of the sample and a parameter characterising the well geometry. Experimental measurements of self-absorption are used to evaluate the model and to determine a semi-empirical algorithm for improved estimates of the geometrical parameter.

Relative expression of cytochrome P450 isoenzymes in human liver and association with the metabolism of drugs and xenobiotics.

Abstract: Cytochrome P450s play a central role in the metabolism and disposition of an extremely wide range of drugs and chemical carcinogens. Individual differences in the expression of these enzymes may be an important determinant in susceptibility to adverse drug reactions, chemical toxins and mutagens. In this paper, we have measured the relative levels of expression of cytochrome P450 isoenzymes from eight gene families or subfamilies in a panel of twelve human liver samples in order to determine the individuality in their expression and whether any forms are co-regulated. Isoenzymes were identified in most cases on Western blots based on the mobility of authentic recombinant human cytochrome P450 standards. The levels of the following P450 proteins correlated with each other: CYP2A6, CYP2B6 and a protein from the CYP2C gene subfamily, CYP2E1 and a member of the CYP2A gene subfamily, CYP2C8, CYP3A3/A4 and total cytochrome P450 content. Also, the levels of two proteins in the CYP4A gene subfamily were highly correlated. These correlations are consistent with the relative regulation of members of these gene families in rats or mice. In addition, the level of expression of specific isoenzymes has also been compared with the rate of metabolism of a panel of drugs, carcinogens and model P450 substrates. These latter studies demonstrate and confirm that the correlations obtained in this manner represent a powerful approach towards the assignment of the metabolism of substrates by specific human P450 isoenzymes.

Rehabilitating the industrial revolution

Abstract: Rehabilitating the industrial revolution. Gradualist perspectives now dominate economic and social histories of the industrial revolution. Analyses of economic change which rely on growth accounting and macroeconomic estimates of productivity indicate continuity with the past; social historians have followed in turning aside from the analysis of new class formations. This article challenges these perspectives. Currently accepted economic indicators and recent social history underplay the extent and uniqueness of economic and social transformation. The article emphasizes change in technology, the use of a female and child labour force, regional specialization, demographic behaviour, and political change.

Risk factors for depression in elderly people: a prospective study

Abstract: In 1982-1983 a random sample of 1486 people aged 65 years and above was generated from general practitioner lists; 1070 were interviewed in the community using the Geriatric Mental State and a Social History questionnaire. The cohort was followed up by interview 3 years later. At year 3 the diagnostic computer program AGECAT diagnosed 44 incident cases of depression. Information from the depressed group's initial and further interviews was compared with a control group (which excluded cases of affective or organic mental illness). Univariate analysis yielded three factors that were significantly associated with the development of depression 3 years later: a lack of satisfaction with life; feelings of loneliness; and smoking. Multivariate analysis confirmed their independent effects and revealed 2 further factors attaining significance: female gender and a trigger factor, bereavement of a close figure within 6 months of the third-year diagnosis. Some other factors traditionally associated with depression, such as poor housing, marital status and living alone, failed to attain significance as risk factors.

Exo1 and Exo2 proteins stimulate calcium-dependent exocytosis in permeabilized adrenal chromaffin cells.

Abstract: IN many cell types an increase in cytosolic calcium is the main signal for the exocytotic release of stored secretory components such as hormones and neurotransmitters. The site of action of calcium in exocytosis is not known, neither are the participating molecules1,2. In the case of the intracellular membrane fusions that occur during transport through early stages of the secretory pathway, several cytosolic and peripheral membrane proteins are necessary3–6. Permeabilized cells have been useful in understanding the requirements for calcium and nucleotides in regulated exocytosis7,8 and under certain conditions there is leakage of soluble protein components and run-down of the exocytotic response9–14. This system can be used to identify the soluble proteins involved in exocytosis, one candidate in chromaffin cells being annexin II (calpactin)9. Here we use this assay to identify two other cytosolic protein factors that regulate exocytosis in permeabilized adrenal chromaffin cells, which we term Exol and Exo2. Exol from brain cytosol resolves on electrophoresis in SDS–polyacrylamide gels as a group of polypeptides of relative molecular mass ˜30,000 and shares sequence homology with the 14–3–3 family of proteins. The ability of Exol to reactivate exocytosis is potentiated by protein kinase C activation and there-fore Exol may influence the protein kinase C-mediated control of Ca2+-dependent exocytosis.

Oncogenes and tumour-suppressor genes in squamous cell carcinoma of the head and neck.

Abstract: Cancer is now considered to be a multi-hit process which involves a number of aberrant genetic events culminating in malignant transformation. In squamous cell carcinoma (SCC) of the head and neck the action of both oncogenes and tumour-suppressor genes has been identified during the course of the disease. Cytogenetic analysis of these carcinomas has demonstrated chromosomal breakpoints, particularly in the regions of 1p22 and 11q13 together with frequent amplification of the proto-oncogenes in the 11q13 amplicon; int-2, hst-1 and bcl-1. Ras mutations have been infrequently identified in the Western World whereas ras over-expression has been a common finding and may be associated with the early development of head and neck cancer. C-myc over-expression appears to correlate with a poor prognosis for these patients. The tumour-suppressor gene p53 is also thought to be involved in the development of SCC in head and neck tumours and its aberrant expression is associated with a history of heavy smoking and heavy drinking. E-cadherin, a putative tumour-suppressor gene is down-regulated in poorly differentiated head and neck SCC and maybe important in nodal metastasis. A recent study has indicated that the Human Papilloma Virus (HPV 16 and 33) has a role in the aetiology of tonsillar carcinomas and HPV has been shown to produce transforming proteins which bind to and inactivate the p53 tumour suppressor gene. This evidence suggests that the possibility of a viral mechanism for the development of SCC in the head and neck should be considered. This paper proposes a series of genetic events to explain the development of SCC of the head and neck.

Rapid assessment of bacterial viability by flow cytometry

Abstract: The ability of a flow cytometer to rapidly assess microbial viability was investigated using three vital stains: rhodamine 123 (Rh123); 3,3'-dihexyloxacarbocyanine iodide [DiOC6(3)] and fluorescein diacetate (FDA). Rh123 was found to clearly differentiate viable from non-viable bacteria. The methodology for staining bacteria with this dye was optimised. Rh123 was shown to stain and discriminate several different species of viable bacteria although this was not universal. Viable cells of Bacillus subtilis were found to stain better with FDAthan with Rh123. The results demonstrate the ability of flow cytometry to rapidly detect and estimate the viability of bacterial populations.