Showing papers by "Durham University published in 1993"

Merger rates in hierarchical models of galaxy formation

Abstract: We present an analytical description of the merging of virialized haloes which is applicable to any hierarchical model in which structure grows via gravitational instability. The formulae are an extension of the Press-Schechter model. The dependence of the merger rate on halo mass, epoch, the spectrum of initial density fluctuations and the density parameter Ω0 is explicitly quantified. We calculate the distribution of halo formation times and survival times. We also describe a Monte Carlo method for constructing representative histories of merger events leading to formation of haloes of a prescribed mass. Applying these results to the age distribution of rich clusters of galaxies, we infer that a high value of the density parameter (Ω0 ≳ 0.5) is required to reproduce the substantial fraction of rich clusters that exhibit significant substructure, if such substructure only persists for a time 0.2t0 after a merger, where t0 is the present age of the universe. We also investigate the rate of infall of satellite galaxies into galactic discs, by combining our Monte Carlo technique for halo mergers with an estimate of the time required for dynamical friction to erode the orbits of the baryonic cores of the accreted galaxies. We find that, even for Ω0 = 1, the infall rate is low (provided that the satellite orbits are not too eccentric), and that we would expect only a modest fraction of stellar discs to be thickened or disrupted by this process.

A framework linking intangible resources and capabilities to sustainable competitive advantage

Abstract: This article is concerned with the role of intangible resources in business strategy. In particular it is concerned with identifying the intangible sources of sustainable competitive advantage. Sustainable competitive advantage results from the possession of relevant capability differentials. Regulatory and positional capabilities are concerned with intangible assets; functional and cultural capabilities are concerned with competencies. A framework linking intangible resources to capabilities has been devised and is used as the basis of a new technique for identifying the relative contribution which the different intangible resources make to competitive advantage. The results of the use of this technique in six case studies are reported.

Binding of human apolipoprotein E to synthetic amyloid beta peptide: isoform-specific effects and implications for late-onset Alzheimer disease

Abstract: Apolipoprotein E (apoE), a plasma apolipoprotein that plays a central role in lipoprotein metabolism, is localized in the senile plaques, congophilic angiopathy, and neurofibrillary tangles of Alzheimer disease. Late-onset familial and sporadic Alzheimer disease patients have an increased frequency of one of the three common apoE alleles, epsilon 4, suggesting apoE4 is associated with increased susceptibility to disease. To follow up on this suggestion, we compared the binding of synthetic amyloid beta (beta/A4) peptide to purified apoE4 and apoE3, the most common isoform. Both isoforms bound synthetic beta/A4 peptide, the primary constituent of the plaque and angiopathy, forming a complex that resisted dissociation by boiling in SDS. Oxygen-mediated complex formation was implicated because binding was increased in oxygenated buffer, reduced in nitrogen-purged buffer, and prevented by reduction with dithiothreitol or 2-mercaptoethanol. Binding of beta/A4 peptide was saturable at 10(-4) M peptide and required residues 12-28. Examination of apoE fragments revealed that residues 244-272 are critical for complex formation. Both oxidized apoE4 and apoE3 bound beta/A4 peptide; however, binding to apoE4 was observed in minutes, whereas binding to apoE3 required hours. In addition, apoE4 did not bind beta/A4 peptide at pH < 6.6, whereas apoE3 bound beta/A4 peptide from pH 7.6 to 4.6. Together these results indicate differences in the two isoforms in complexing with the beta/A4 peptide. Binding of beta/A4 peptide by oxidized apoE may determine the sequestration or targeting of either apoE or beta/A4 peptide, and isoform-specific differences in apoE binding or oxidation may be involved in the pathogenesis of the intra- and extracellular lesions of Alzheimer disease.

The baryon content of galaxy clusters: a challenge to cosmological orthodoxy

Abstract: Baryonic matter constitutes a larger fraction of the total mass of rich galaxy clusters than is predicted by a combination of cosmic nucleosynthesis considerations (light-element formation during the Big Bang) and standard inflationary cosmology. This cannot be accounted for by gravitational and dissipative effects during cluster formation. Either the density of the Universe is less than that required for closure, or there is an error in the standard interpretation of element abundances.

Trace element models for mantle melting: application to volcanic arc petrogenesis

Abstract: Understanding mantle melting above subduction zones requires an evaluation of the behaviour of elements for which the mantle contribution greatly exceeds any subduction contribution. In this paper we present a compilation of partition coefficients for a suite of these elements (Nb, Zr, Y, Yb, Ca, Al, Ga, V, Sc, Fe, Mn, Co, Cr, Mg, Ni) for temperatures of 1200–1300°C, oxygen fugacities of QFM ± 1 and sub-alkaline compositions. These coefficients yield good-fit mantle depletion trends for abyssal, orogenic and trench-wall peridotites. Modelling of pooled melts from mantle melting columns, presented as FMM (fertile MORB mantle) normalized patterns, give signatures of the composition and degree of melting of the mantle wedge that are generally independent of the subduction component. In particular, patterns formed from melting of fertile mantle exhibit normalized element abundances in the order VHI > HI > MI (VHI = very highly incompatible, HI = highly incompatible and MI = moderately incompatible) at low degrees of melting, becoming VHI = HI = MI at high degrees of melting. With derivation from progressively depleted sources, the patterns for moderate degrees of melting change to VHI < HI = MI at moderate degrees of depletion and VHI < HI < MI at high degrees of depletion.

Inserting device for a barbed tissue connector

Abstract: An inserting device is disclosed for positioning a barbed tissue connector in tissue to close a wound. The barbed tissue connector is of a type which includes a generally rigid elongated body having a pointed leading end and a plurality of axially spaced barbs on the elongated body. The inserting device comprises a tubular body which is adapted to receive the connector therein with the pointed leading end of the connector protruding from an open leading end of the tubular body. The inserting device and the connector contained therein are positioned in tissue such that at least one of the barbs on the connector is engaging tissue, and the device is then retracted from the tissue, leaving the connector in place.

The amplitude of mass fluctuations in the universe

Abstract: We investigate how the rms linear fluctuation in the mass distribution on scales of 8 h −1 Mpc 1 (denoted by σ 8 ) is constrained by the masses and abundances of rich clusters of galaxies. The derived value of σ 8 is almost independent of the shape of the fluctuation spectrum, but depends strongly on the cosmological density parameter. We find σ 8 ≃ 0.52-0.62 for a critical density universe, and σ 8 ≃ 1.25-1.58 for a spatially flat universe with Ω 0 = 0.2. Our results conflict with the high amplitude inferred for an Ω = 1 cold dark matter universe from the COBE anisotropy measurements and advocated on other grounds by Couchman & Carlberg

On Explicit and Negative Data Effecting and Affecting Competence and Linguistic Behavior.

Abstract: Psychologically speaking, all linguistic behavior is the overt manifestation of some type of underlying knowledge that is represented in the mind/brain of an individual. Exposure to linguistic data is necessary for growth of the system of knowledge. On the basis of only overt linguistic behavior, how can we ascertain whether the native and nonnative knowledge systems that people have are of distinct or similar types? Is there a (necessary) relationship between type of knowledge and type of linguistic exposure?The hypothesis to be defended is that negative data and explicit data result in a type of knowledge that is not to be equated with linguistic competence. The claim is not that negative and explicit data cannot give rise to knowledge; rather, the specific claim is that only positive data can effect the construction of an interlanguage grammar that is comparable to the knowledge system that characterizes the result of first language acquisition.

Simulations of dissipative galaxy formation in hierarchically clustering universes – I: Tests of the code

Abstract: We present tests of a code designed to simulate the evolution of self-gravitating fluids in three dimensions. The code is based on the smoothed-particle hydrodynamics (SPH) technique for solving the hydrodynamical equations, together with a binary tree method for computing gravitational forces. Our tests are relevant to the evolution of non-linear structure in hierarchically clustering universes. In particular, we study the collapse and merger of quasi-spherical, slowly rotating clumps containing a mixture of gas and collisionless dark matter. For self-similar spherical collapse the detailed solution structure is already known, but we also study more realistic situations for which this is not the case

Cultural Politics of Everyday Life: Social Constructionism, Rhetoric and Knowing of the Third Kind

Abstract: Traditions of argumentation and knowing of the third kind "getting in touch" - the metamethodology of postmodern sciences of mental life power on the margins - a new place for intellectuals to be Vico and the poetics of practical sociality Wittgenstein and psychology - on our "hook up" to reality Rome Harre - realism and the turn to social constructionism Vygotsky, Volosinov and Bakhtin - "thinking" as a boundary phenomenon conversational realities and academic discourses rhetoric and the social construction of cognitivism what is a "personal relationship"? the politics of identity and belonging epilogue - critical "tool-making" and providential eloquence.

Globular cluster systems formed in galaxy mergers

Abstract: We show that current observations support the hypothesis that globular clusters form in galaxy mergers. In a previous paper, we presented a model in which globular cluster formation is a result of interactions and mergers of galaxies. Here, this model is compared with new observations of the globular cluster systems of recent galaxy mergers and normal elliptical galaxies. We find that our model is consistent with the number and luminosity of young globular clusters in currently merging galaxies. If elliptical galaxies form through mergers of spiral galaxies, the model also predicts that the globular cluster systems of normal elliptical galaxies should have at least two peaks in the metallicity distribution

Face perception after brain injury: selective impairments affecting identity and expression.

Abstract: SUMMARY Current theoretical models of face perception postulate separate routes for processing information needed in the recognition of a familiar face, for matching photographs of unfamiliar faces and for the analysis of facial expressions. The present study investigated this claim in a group of ex-servicemen who had sustained unilateral brain injuries affecting posterior areas of the left or right cerebral hemisphere. Care was taken to confirm the nature of impairment by using two different tasks to assess each of the three theoretically defined abilities (leading to a total of six tasks). We adopted a stringent application of the double dissociation methodology to investigate the pattern of performance across tasks of individual ex-servicemen. A selective impairment was defined as a significantly impoverished performance on both tests of a specific ability, while all other tasks were performed within normal limits. In addition, we used both accuracy and response latency measures to substantiate evidence for spared or defective abilities. The results showed selective impairments of all three abilities on accuracy scores. Response latency data confirmed the finding of a selective deficit in the processing of facial expressions, but produced evidence suggesting that impairments affecting familiar face recognition and unfamiliar face matching were not completely independent from each other in this group of ex-servicemen.

Development of Concern for the Environment and Formative Experiences of Educators.

Abstract: This article describes part of a larger research project that uses autobiographical, qualitative analysis to investigate the acquisition and development of environmental subject knowledge and concern during a child's first 3 years of school. The project has also established a longitudinal study to investigate the transition from knowledge to active concern. The author examines the significance of various categories of influence on the development of environmental educators' knowledge and concern and the ways in which this significance may change through time.

Blue light-emitting diode with degenerate junction structure

Abstract: A light emitting diode is disclosed that emits light in the blue region of the visible spectrum with increased brightness and efficiency. The light emitting diode comprises an n-type silicon carbide substrate; an n-type silicon carbide top layer; and a light emitting p-n junction structure between the n-type substrate and the n-type top layer. The p-n junction structure is formed of respective portions of n-type silicon carbide and p-type silicon carbide. The diode further includes means between the n-type top layer and the n-type substrate for coupling the n-type top layer to the light-emitting p-n junction structure while preventing n-p-n behavior between the n-type top layer, the p-type layer in the junction structure, and the n-type substrate.

Hexagonal mesophases between lamellae and cylinders in a diblock copolymer melt

Abstract: Two intermediate phases have been observed upon heating an asymmetric poly(ethylenepropylene)-poly(ethylethylene) diblock copolymer between lamellar and hexagonal cylinder phases near the order-disorder transition. Phase transitions betwen ordered morphologies are indicated by the temperature dependence of the dynamic shear moduli, and SANS experiments are used to identify these structures as hexagonally modulated lamellae and layered hexagonal packed channels. The observed wavevectors associated with the interlayer scattering for these structures are incommensurate, leading to an a periodic structure in which the long range translational order of the layers is destroyed

Evidence for systematic evolution in the properties of galaxies in distant clusters

Abstract: This paper investigates the evolution of galaxies as a function of look-back time, primarily using early-type galaxies in rich cluster environments. We demonstrate that, by selecting distant galaxies in the near-infrared, representative samples containing approximately the same proportion of galaxy classes can be constructed independently of redshift, thus avoiding biases introduced by optical selection criteria. Using this method, we construct a sample of 180 galaxies selected at near-infrared wavelengths in the fields of 10 rich clusters with 0.5 < z < 0.9. Observing and data processing techniques, with infrared arrays yielding the required high-precision photometry of cluster members, are discussed

Isolation of a prokaryotic metallothionein locus and analysis of transcriptional control by trace metal ions

Abstract: In eukaryotes, metallothioneins (MTs) are involved in cellular responses to elevated concentrations of certain metal ions. We report the isolation and analysis of a prokaryotic MT locus from Synechococcus PCC 7942. The MT locus (smt) includes smtA, which encodes a class II MT, and a divergently transcribed gene, smtB. The sites of transcription initiation of both genes have been mapped and features within the smt operator-promoter region identified. Elevated concentrations of the ionic species of Cd, Co, Cr, Cu, Hg, Ni, Pb and Zn elicited an increase in the abundance of smtA transcripts. There was no detectable effect of elevated metal (Cd) on smtA transcript stability. Sequences upstream of smtA, fused to a promoterless lacZ gene, conferred metal-dependent beta-galactosidase activity in Synechococcus PCC 7942 (strain R2-PIM8). At maximum permissive concentrations, Zn was the most potent elicitor in vivo, followed by Cu and Cd with slight induction by Co and Ni. The deduced SmtB polypeptide has similarity to the ArsR and CadC proteins involved in resistance to arsenate/arsenite/antimonite and to Cd, contains a predicted helix-turn-helix DNA-binding motif and is shown to be a repressor of transcription from the smtA operator-promoter.

Predicting complications of carotid endarterectomy.

Abstract: Carotid endarterectomy has been shown to be beneficial in patients with high-grade carotid stenosis and ipsilateral transient ischemic attack or stroke. This benefit will be realized only if the operation is performed safely. We sought to determine the extent to which clinically significant adverse events occurring after carotid endarterectomy can be predicted from clinical data available before surgery. Eleven hundred sixty patients were randomly selected from all patients who underwent carotid endarterectomy and were discharged during the calendar years 1988, 1989, and 1990 in 12 academic medical centers in 10 states. Clinical data abstracted from hospital charts were analyzed retrospectively. A model was developed and validated to predict the occurrence of stroke, myocardial infarction, or death during the postoperative period of hospitalization. Eight patients (6.9%) suffered at least one adverse event. Rates for individual complications were as follows: death, 1.4%; nonfatal stroke, 3.4%; nonfatal myocardial infarction, 2.1%; and nonfatal stroke or death, 4.8%. Significant predictors of adverse events were age 75 years or older, symptom status (ipsilateral symptoms versus asymptomatic or nonipsilateral symptoms), severe hypertension (preoperative diastolic blood pressure of greater than 110 mm Hg), carotid endarterectomy performed in preparation for coronary artery bypass surgery, history of angina, evidence of internal carotid artery thrombus, and internal carotid artery stenosis near the carotid siphon. The presence of two or more of these risk factors was associated with a nearly twofold increase in risk of an adverse event (relative risk, 1.7; 95% confidence interval, 1.0 to 3.0). Clinical data can be used to stratify patients undergoing carotid endarterectomy according to risk of postoperative in-hospital stroke, myocardial infarction, or death.

The ecological context of human ovarian function

Abstract: New methods for monitoring ovarian function have allowed an extension of research venue beyond typical clinical settings to studies of human populations in their natural settings. Such studies have confirmed that patterns of variation in ovarian function with age and energetic factors are general features of human reproductive biology. Age patterns of ovarian function are extremely robust across populations of distinct genetic, ecological and cultural backgrounds. Comparable ovarian responses to energetic stresses are likewise observable in different populations where they arise as correlates of local ecologies rather than as correlates of voluntary patterns of diet or exercise. Maternal age and energetic factors also appear to interact with lactation in the modulation of postpartum, ovarian function. Average levels of ovarian function, however, differ considerably between populations, perhaps correlated with chronic environmental conditions that affect growth, development, and the establishment of adult set-points. Western populations appear to represent an extreme of the spectrum of variation in ovarian function, a fact which may relate to the epidemiology of breast and ovarian cancer.

SUSY in the sky

Abstract: Spinning particles in curved space-time can have fermionic symmetries generated by the square root of bosonic constants of motion other than the Hamiltonian. We present a general analysis of the conditions under which such new supersymmetries appear, and discuss the Poisson-Dirac algebra of the resulting set of charges, including the conditions of closure of the new algebra. An example of a new non-trivial supersymmetry is found in black-hole solutions of the Kerr-Newman type and corresponds to the Killing-Yano tensor, which plays an important role in solving the Dirac equation in these black-hole metrics.

Adorno's Aesthetics of Music

Abstract: 1. Constellations: towards a critical method 2. The development of a theory of musical material 3. The problem of mediation 4. A material theory of form 5. Social content and social function 6. The historical dialectic of musical material 7. The disintegration of musical material.

Antimetabolic effects of plant lectins and plant and fungal enzymes on the nymphal stages of two important rice pests, Nilaparvata lugens and Nephotettix cinciteps

Abstract: Insect feeding trials were carried out to determine the effects of incorporating a range of plant derived proteins into artificial diets fed to leafhopper and planthopper pests of rice. The lectins Galanthus nivalis agglutinin (GNA) and wheat germ agglutinin (WGA), and the enzyme soy bean lipoxygenase (LPO) were shown to exhibit significant antimetabolic effects towards first and third instar nymphs of rice brown planthopper (Nilaparvata lugens Stal) when incorporated into artificial diet at 0.1% (w/v), 0.1% (w/v) and 0.08% (w/v) levels respectively. The lectin GNA was also shown to exhibit a significant antimetabolic effect towards third instar nymphs of the rice green leafhopper (Nephotettix cinciteps Uhler). A number of inert proteins, lectins, protein inhibitors and enzymes also tested showed relatively little or no effect towards both insects.

6H–silicon carbide devices and applications

Abstract: A variety of devices with promising characteristics have recently been demonstrated in 6H-SiC. There are four primary application areas for 6H-SiC devices: (1) optoelectronics, (2) high-temperature electronics, (3) high-power/high- frequency devices, and (4) nonvolatile memories. These applications, and current device results in each area, are discussed below.