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Showing papers by "University of Cambridge published in 1980"


Journal ArticleDOI
TL;DR: In this paper, the Einstein equations with quantum one-loop contributions of conformally covariant matter fields are shown to admit a class of nonsingular isotropic homogeneous solutions that correspond to a picture of the universe being initially in the most symmetric (de Sitter) state.

6,969 citations


Journal ArticleDOI
TL;DR: In this article, a simple analytic model is constructed to elucidate some basic features of the response of the tropical atmosphere to diabatic heating, showing that there is considerable east-west asymmetry which can be illustrated by solutions for heating concentrated in an area of finite extent.
Abstract: A simple analytic model is constructed to elucidate some basic features of the response of the tropical atmosphere to diabatic heating. In particular, there is considerable east-west asymmetry which can be illustrated by solutions for heating concentrated in an area of finite extent. This is of more than academic interest because heating in practice tends to be concentrated in specific areas. For instance, a model with heating symmetric about the equator at Indonesian longitudes produces low-level easterly flow over the Pacific through propagation of Kelvin waves into the region. It also produces low-level westerly inflow over the Indian Ocean (but in a smaller region) because planetary waves propagate there. In the heating region itself the low-level flow is away from the equator as required by the vorticity equation. The return flow toward the equator is farther west because of planetary wave propagation, and so cyclonic flow is obtained around lows which form on the western margins of the heating zone. Another model solution with the heating displaced north of the equator provides a flow similar to the monsoon circulation of July and a simple model solution can also be found for heating concentrated along an inter-tropical convergence line.

3,799 citations


Journal ArticleDOI
17 Jul 1980-Nature
TL;DR: The chemokinetic and aggregating activities released from rat and human PMNs exposed to ionophore A23187 are not due to the release of mono-HETEs but to that of 5,12-di- HETE (leukotriene B), which is active over the concentration range 10 pg ml−1 to 5 ng ml-1.
Abstract: Arachidonic acid is metabolised either by cyclooxygenases to produce prostaglandins and thromboxanes or by lipoxygenases to produce mono-, di- and trihydroxyeicosatetraenoic acids (HETEs). Polymorphonuclear leukocytes (PMNs) release HETEs, including mono- and dihydroxy fatty acids, when exposed to stimuli such as the calcium ionophore A23187 (refs 1, 2). The mono-HETEs are assumed to be of particular importance with respect to effects on leukocyte function because they have been shown to possess both chemotactic and chemokinetic activities towards PMNs and eosinophils. However, we have now shown that the chemokinetic and aggregating activities released from rat and human PMNs exposed to ionophore A23187 (ref. 5) are not due to the release of mono-HETEs but to that of 5, 12-di-HETE (leukotriene B). This compound is active over the concentration range 10 pg ml-1 to 5 ng ml-1.

2,010 citations


Journal ArticleDOI
TL;DR: A model is presented to account for the evolution of FB groups in terms of ecological pressures on female relationships and suggests that relationships in most FB groups are ultimately related to feeding competition.
Abstract: 1. Multi-female groups of primates fall into two main classes, (a) female-bonded (FB) and (b) non-female-bonded (non-FB). A model is presented to account for the evolution of FB groups in terms of ecological pressures on female relationships. 2. The model suggests that FB groups have evolved as a result of competition for high-quality food patches containing a limited number of feeding sites. Groups are viewed as being based on cooperative relationships among females. These relationships are beneficial because cooperators act together to supplant others from preferred food patches. 3. Ecological data support the model for most FB species, but not for Theropithecus gelada or Colobus guereza, whose foods are not found in high-quality patches with limited feeding sites. Non-FB species conform to expectation, either because they do not use high-quality patches, or because feeding competition has disruptive effects during periods of food scarcity. 4. The behaviour of females differs as expected between FB and non-FB species in group movements and in inter-group interactions; in both contexts females are more involved in FB species. 5. Multi-male groups tend to be found in non-territorial FB species. The presence of several males per group is suggested to benefit females by raising the competitive ability of the group in inter-group interactions. 6. Competitive relationships among females are more strongly marked in FB groups than in non-FB groups. The model suggests that relationships in most FB groups are ultimately related to feeding competition.

1,849 citations


Journal ArticleDOI
25 Sep 1980-Nature
TL;DR: In this article, the authors explore the possibility that some active galactic nuclei may contain two massive black holes in orbit about each other, which suggests a new interpretation for the observed bending and apparent precession of radio jets emerging from these objects.
Abstract: Most theoretical discussions of active galactic nuclei (including quasars) attribute their energy production either to an accreting black hole or to a precursor stage—for instance a dense star cluster or a supermassive star—whose inevitable end point is a massive black hole1. We explore here the possibility that some active nuclei may contain two massive black holes in orbit about each other. This hypothesis suggests a new interpretation for the observed bending2 and apparent precession3 of radio jets emerging from these objects and may indeed be verified through detection of the direct consequences of orbital motion.

1,704 citations


Journal ArticleDOI
TL;DR: Phospholipids may be measured colorimetrically (as dipalmitoyl lecithin) without conventional acid digestion and color development procedures by forming a complex with ammonium ferrothiocyanate.

1,673 citations


Journal ArticleDOI
TL;DR: The method determines the asymptotic distribution of the number of short cycles in graphs with a given degree sequence, and gives analogous formulae for hypergraphs.

1,237 citations



Journal ArticleDOI
01 Sep 1980
TL;DR: In this paper, the authors derived the differential-integral equation of motion for the mean wave in a solid material containing embedded cavities or inclusions, which consists of a series of terms of ascending powers of the scattering operator, and is here truncated after the third term.
Abstract: The differential-integral equation of motion for the mean wave in a solid material containing embedded cavities or inclusions is derived. It consists of a series of terms of ascending powers of the scattering operator, and is here truncated after the third term. This implies the second-order interactions between scatterers are included but those of the third order are not.The formulae are specialized to the case of thin cracks, either aligned in a single direction or randomly oriented. Expressions for the overall elastic constants are derived for the case of long wavelengths. These expressions are accurate to the second order in the number density of scatterers.

699 citations


Journal ArticleDOI
TL;DR: In this paper, the authors considered the flow of gas/pyroclast dispersions and high viscosity magma through various magma chamber/conduit/vent geometries.
Abstract: Summary Plinian air-fall deposits and ignimbrites are the principal products of explosive eruptions of high viscosity magma. In this paper, the flow of gas/pyroclast dispersions and high viscosity magma through various magma chamber/conduit/vent geometries is considered. It is argued that after the first few minutes of an eruption magma fragmentation occurs at a shallow depth within the conduit system. Gas pressures at the fragmentation level are related to exsolved gas contents by consideration of the exsolution mechanism. The sizes of blocks found near vents imply that gas velocities of 200 to 600 m s−1 commonly occur. These velocities are greater than the effective speed of sound in an erupting mixture (90-200 m s−1) and the transition from subsonic to supersonic flow is identified as occurring at the depth at which the conduit has its minimum diameter. The range of values of this minimum diameter (∼ 5 to ∼ 100 m) is estimated from observed and theoretically deduced mass-eruption rates. The energy and continuity equations are solved, taking account of friction effects, for numerous geometries during the evolution, by wall erosion, of a conduit. Conduit erosion ceases, near the surface, when an exit pressure of one atmosphere is reached. Eruption velocities are found to depend strongly on exsolved magma gas content and weakly on radius of conduit and friction effects. Assuming water as the main volatile phase, velocities of 400-600 m s−1 for plinian events imply magma water contents of 3-6 per cent by weight. Three scenarios are presented of eruptions in which: (1) conduit radius increases but gas content remains constant; (2) conduit radius increases and gas content decreases with time; and (3) conduit radius remains fixed and gas content decreases. These models demonstrate that the reverse grading commonly observed in plinian air-fall deposits is primarily a consequence of conduit erosion, which always results in increasing eruption intensity and eruption column height with time. The models also show that a decrease in gas content as deeper levels in a magma chamber are tapped or an increasing vent radius as conduit walls are eroded leads to the prediction of a progression from air-fall activity through ignimbrite formation to cessation of eruption and caldera collapse.

633 citations


Book ChapterDOI
TL;DR: This chapter takes a view of biogenic amines in the insect nervous system and to assess critically the evidence for their roles as neurotransmitters, neuromodulators and neurohormones.
Abstract: Publisher Summary This chapter takes a view of biogenic amines in the insect nervous system and to assess critically the evidence for their roles as neurotransmitters, neuromodulators and neurohormones. It attempts to answer several questions such as where biogenic amines are located in the insect nervous system; how are they synthesized and inactivated; and what physiological roles do they perform and how do they bring about their effects. Particular emphasis is placed on the correlation of biochemical, physiological, pharmacological and anatomical information from systems containing identified aminergic neurones. The chapter points out instances where data from one or more of the approaches is either missing or conflicts with that from another and suggests experiments to resolve these points. The function of biogenic amines in the insect nervous system has been compared with that in the vertebrate nervous system. In this context the chapter mentions the role of biogenic amines as chemical messengers in the vertebrate nervous system.

Journal ArticleDOI
TL;DR: There were indications that a diurnal rhythm played a role in establishing cleaving embryos, each of the four pregnancies occurring when the embryos were placed in late evening, and three aborted pregnancies in patients given gonadotrophins to stimulate the maturation of oocytes used for fertilization in vitro.

Journal ArticleDOI
27 Mar 1980-Nature
TL;DR: In this paper, the authors examined the distribution and binding characteristics of opiate receptors on dorsal root and in various regions of the adjacent spinal cord and found that both types of opiates may exist on small-diameter primary afferents.
Abstract: In addition to their actions at supraspinal sites, opiates can act directly at the spinal cord level to produce analgesia1–3. Opiate receptors and enkephalins are found in abundance in the dorsal horn of the spinal cord, in the region of termination of small-diameter primary afferents4–6. Furthermore, there is evidence that exogenously administered opiates or endogenous enkephalins act both on postsynaptic receptors in dorsal horn and presynaptically to block transmitter release from nociceptive primary afferent terminals7–10. The possiblity of these two distinct sites of opiate action in dorsal horn is of particular interest in view of recent evidence for the existence of multiple opiate receptors11–13. On the basis of differences in the rank orders of potency of opiate alkaloids and opoid peptides observed in different tissues, Lord et al.14 have proposed two categories of opiate receptor, μ and δ, and these can be differentiated in binding studies, provided that selective radioglands are used in the appropriate experimental conditions15–18. Here we have used the selective radioligands 3H-morphine (μ sites) and 3H-D-Ala2, D-Leu5-enkephalin (δ sites) to examine directly in rat the distribution and binding characteristics of opiate receptors on dorsal root and in various regions of the adjacent spinal cord. Primary afferent tissue (dorsal root) and dorsal horn were found to contain μ and δ opiate binding sites with a relatively high proportion of μ sites. Partial destruction of small-diameter primary afferents after cutting the sciatic nerve led to a significant reduction in both μ and δ binding sites on dorsal roots, suggesting that both types of opiate receptors may exist on small-diameter primary afferents.

Journal ArticleDOI
TL;DR: It is concluded that SN transplants reinnervation the dorsal part of the neostriatum are able to replace the innate SN in normalizing some aspects of the rats motor behaviour, while their sensorimotor deficits and deficits in consummatory behaviour were unaffected.

Book ChapterDOI
TL;DR: Mechanistic studies of intramolecular reactions play an important part in elucidating the chemistry of the groups involved in enzyme catalysis and in defining the mechanisms available for particular reactions.
Abstract: Publisher Summary The first step toward unravelling the mechanism of an enzyme-catalyzed reaction is to specify the mechanisms available for the reaction concerned. Many of these reactions are not observed when the relevant groups are allowed to come together in bimolecular processes in aqueous solution. For mechanistic work involving intermolecular reactions, it is necessary to use activated substrates. An attractive alternative is to study intramolecular reactions. These are generally faster than the corresponding intermolecular processes. Thus, groups like carboxyl and imidazole are involved at the active sites of many enzymes hydrolyzing aliphatic esters and amides. Therefore, mechanistic studies of intramolecular reactions play an important part in elucidating the chemistry of the groups involved in enzyme catalysis and in defining the mechanisms available for particular reactions.

Journal ArticleDOI
TL;DR: Three categories of dietary adaptation are recognized according to the distinctive structural and biochemical features of animal matter, fruit, and leaves respectively, and the predominance of only one in the diets of most species.
Abstract: Three categories of dietary adaptation are recognized--faunivory, frugivory, and folivory--according to the distinctive structural and biochemical features of animal matter, fruit, and leaves respectively, and the predominance of only one in the diets of most species. Mammals subsisting mainly on animal matter have a simple stomach and colon and a long small intestine, whereas folivorous species have a complex stomach and/or an enlarged caecum and colon; mammals eating mostly fruit have an intermediate morphology, according to the nature of the fruit and their tendency to supplement this diet with either animal matter or leaves. The frugivorous group are mostly primates: 50 of the 78 mammalian species, and 117 of the 180 individuals included in this analysis are primates. Coefficients of gut differentiation, the ratio of stomach and large intestine to small intestine (by area, weight, and volume), are low in faunivores and high in folivores; the continuous spread of coefficients reflects the different degrees of adaptation to these two dietary extremes. Interspecific comparisons are developed by allowing for allometric factors. In faunivores, in which fermentation is minimal, the volume of stomach and large intestine is related to actual body size, whereas these chambers are more voluminous in larger frugivores and mid-gut fermenting folivores; fore-gut fermenters show a marked decrease in capacity with increasing body size. Surface areas for absorption are related to metabolic body size, directly so in frugivores; area for absorption is relatively less in larger faunivores and more in large folivores, especially those with large stomachs. Indices of gut specialization are derived from these regressions by nonlinear transformation, with references to the main functional features of capacity for fermentation and surface area for absorption. These are directly comparable with the dietary index, derived from quantitative feeding data displayed on a three-dimensional graph, with all species within a crescentic path from 100% faunivory through 55--80% frugivory to 100% folivory, perhaps illustrating, at least for primates, the evolutionary path from primitive insectivorous forms through three major ecological grades.

Journal ArticleDOI
TL;DR: In this article, the contribution of photon effective action from one-loop vacuum polarization on a general curved background manifold was calculated, and the corrections to the local propagation of photons were investigated, and it was shown that the quantum corrections introduce tidal gravitational forces on the photons which in general alter the characteristics of propagation, so that in some cases photons travel at speeds greater than unity.
Abstract: We calculate in QED the contribution to the photon effective action from one-loop vacuum polarization on a general curved background manifold, and use it to investigate the corrections to the local propagation of photons. We find that the quantum corrections introduce tidal gravitational forces on the photons which in general alter the characteristics of propagation, so that in some cases photons travel at speeds greater than unity. The effect is nondispersive and gauge invariant. We look at a few examples, including a background Schwarzschild geometry, and we argue that although these results are controversial they do not in fact exhibit any obvious inconsistency.

Journal ArticleDOI
TL;DR: The paper examines systematic relationships among primates between brain size (relative to body size) and differences in ecology and social system and the adaptive significance of these relationships is discussed.
Abstract: The paper examines systematic relationships among primates between brain size (relative to body size) and differences in ecology and social system. Marked differences in relative brain size exist between families. These are correlated with inter-family differences in body size and home range size. Variation in comparative brain size within families is related to diet (folivores have comparatively smaller brains than frugivores), home range size and possibly also to breeding system. The adaptive significance of these relationships is discussed.

Journal ArticleDOI
TL;DR: When a group of dots within a random-dot array is discontinuously displaced, it appears as a moving region perceptually segregated from its stationary surround, illustrating the interaction of relatively stimulus-constrained and relatively autonomous processes invisual perception.
Abstract: When a group of dots within a random-dot array is discontinuously displaced, it appears as a moving region perceptually segregated from its stationary surround. The spatial, temporal and other constraints governing this effect are markedly different from those classically found for the apparent motion of isolated stimulus elements. The random-dot display appears to tap a low-level motion-detecting process, distinct from the more interpretive process elicited by the classical displays. The distinct contributions of these processes can be identified in 'multi-stable' displays which yield alternative percepts of apparent motion depending on which one or both of the processes is activated. Such experiments illustrate the interaction of relatively stimulus-constrained and relatively autonomous processes in visual perception. Two contrasting approaches dominate much recent work on visual perception. One is to explore how properties of the stimulus may be decoded in the patterns of activity of neural channels or detectors, each of which has its own selective tuning (Braddick et al. 1978). The other approach (exemplified by Gregory I970) considers perception as a problem-solving process that must interpret the sensory input as evidence for some external object or event, and has tended to cast its explanations in functional terms rather than as hypothetical neural mechanisms. Generally these two approaches have been adopted to attack rather different problems. However, the perception of smooth continuous motion from discontinuous stimulation (vari

Journal ArticleDOI
TL;DR: In this article, microstructural evidence, together with a thermodynamic analysis, of the bainite reaction in steels are presented in support of a growth mechanism involving the propagation of displacive sub-units.


Journal ArticleDOI
TL;DR: In this article, the authors used the best available diffusion data for metals and ceramics to investigate the relationship between the melting point diffusivity and activation energy of a given crystal structure and bond type.

Journal ArticleDOI
TL;DR: Electrodes showed a Nernstian response to [Ca2+] down to 1 micro M free concentration in 0.1 M KCl, and usually a useful response to below 100 nM Ca2+.

Journal ArticleDOI
TL;DR: The mechanisms responsible for the production of major extrapyramidal side-effects (parkinsonism, akathisia, acute dystonic reactions, chronic tardive dyskinesias) are reviewed in the light of the complex effects of these drugs on cerebral dopamine systems.
Abstract: The mechanisms responsible for the production of major extrapyramidal side-effects (parkinsonism, akathisia, acute dystonic reactions, chronic tardive dyskinesias) are reviewed in the light of the complex effects of these drugs on cerebral dopamine systems.

Journal ArticleDOI
TL;DR: In this paper, the authors describe the flow structure observed over a bell-shaped hill with height h (the profile of which is the reciprocal of a fourth-order polynomial) when it was placed first in a large towing tank containing stratified saline solutions with uniform stable density gradients and second in an unstratified wind tunnel.
Abstract: This paper describes the flow structure observed over a bell-shaped hill with height h (the profile of which is the reciprocal of a fourth-order polynomial) when it was placed first in a large towing tank containing stratified saline solutions with uniform stable density gradients and second in an unstratified wind tunnel. (A similarly shaped model hill was also studied in a small towing tank.) Observations were made at values of the Froude number F (≃ U/Nh) in the range 0·1 to 1·7 and at F = ∞, where U is the towing speed and N is the Brunt-Vaisala frequency, and at values of the Reynolds number from 400 to 275000. For F [lsim ] 0·4, the observations verify Drazin's (1961) theory for low-Froude-number flow over three-dimensional obstacles and establish limits of applicability. For Froude numbers of the order of unity, it is found that a classification of the lee-wave patterns and separated-flow regions observed in two-dimensional flows also appears to apply to three-dimensional hills.Flow-visualization techniques were used extensively in obtaining both qualitative and quantitative information on the flow structure around the hill. Representative photographs of dye tracers, potassium permanganate dye streaks, shadowgraphs, surface dye smears, and hydrogen-bubble patterns are included here. While emphasis is centred on obtaining a basic understanding of the flow around three-dimensional hills, the results are applicable to the estimation of air pollutant dispersion around hills.

Journal ArticleDOI
TL;DR: In this paper, the authors observed wild ostriches while feeding alone or in groups of up to four birds, and their vigilance (proportion of time with the head up) recorded.

Journal ArticleDOI
TL;DR: In this article, a new analytical model for toughening of epoxy-rubber composites is proposed, which predicts the failure strain of the particles in terms of their size and the amount of elastic energy stored in the rubber during stretching.
Abstract: Epoxy resins are toughened significantly by a dispersion of rubber precipitates. Microscopic examinations of propagating cracks in epoxy-rubber composites reveal that the brittle epoxy matrix cracks, leaving ligaments of rubber attached to the two crack surfaces. The rubber particles are stretched as the crack opens and fail by tearing at large, critical extensions. This fracture mechanism is the basis of a new analytical model for toughening. An increase in toughness (ΔGIC) of the composite is identified with the amount of elastic energy stored in the rubber during stretching which is dissipated irreversibly (e.g. as heat) when the particles fail. The model predicts the failure strain of the particles in terms of their size. It also relates the toughness increase to the volume fraction and tearing energy of the rubber particles. Direct measurements of the tearing strains of rubber particles, and toughness data obtained from epoxy-rubber composites, are in good agreement with the model. The particle-stretching model provides a quantitative explanation, in contribution to existing qualitative theories, for the toughening of epoxy-rubber composites.

Journal ArticleDOI
TL;DR: A novel means of measuring and analysing behavioural effects of dopamine agonists is described and illustrated by a comparison of the effects of d-amphetamine and apomorphine in the rat, and may be of importance in elucidating the functions of the forebrain dopamine projections.
Abstract: A novel means of measuring and analysing behavioural effects of dopamine agonists is described and illustrated by a comparison of the effects of d-amphetamine and apomorphine in the rat. d-Amphetamine (0–15 mg/kg IP) produced significant dose- and time-dependent changes in responses such as locomotion, rearing and sniffing, but not in licking or gnawing. In contrast, apomorphine (0–5 mg/kg SC) produced significant increases in licking and gnawing, as well as in locomotion and sniffing, but no changes in rearing. The results are discussed in comparison with those obtained by other methods, such as photocell beam interruptions or stereotypy rating scales, and may be of importance in elucidating the functions of the forebrain dopamine projections.

Journal ArticleDOI
TL;DR: In this article, an approximate set of equations is derived for a compressible liquid of infinite Prandtl number, referred to as the anelastic liquid equations, which are solved in two dimensions and a systematic investigation of compressible convection is presented in which d/HT is varied from 0·1 to 1·5.
Abstract: An approximate set of equations is derived for a compressible liquid of infinite Prandtl number. These are referred to as the anelastic-liquid equations. The approximation requires the product of absolute temperature and volume coefficient of thermal expansion to be small compared to one. A single parameter defined as the ratio of the depth of the convecting layer, d, to the temperature scale height of the liquid, HT, governs the importance of the non-Boussinesq effects of compressibility, viscous dissipation, variable adiabatic temperature gradients and non-hydrostatic pressure gradients. When d/HT [Lt ] 1 the Boussinesq equations result, but when d/HT is O(1) the non-Boussinesq terms become important. Using a time-dependent numerical model, the anelastic-liquid equations are solved in two dimensions and a systematic investigation of compressible convection is presented in which d/HT is varied from 0·1 to 1·5. Both marginal stability and finite-amplitude convection are studied. For d/HT [les ] 1·0 the effect of density variations is primarily geometric; descending parcels of liquid contract and ascending parcels expand, resulting in an increase in vorticity with depth. When d/HT > 1·0 the density stratification significantly stabilizes the lower regions of the marginal state solutions. At all values of d/HT [ges ] 0·25, an adiabatic temperature gradient proportional to temperature has a noticeable stabilizing effect on the lower regions. For d/HT [ges ] 0·5, marginal solutions are completely stabilized at the bottom of the layer and penetrative convection occurs for a finite range of supercritical Rayleigh numbers. In the finite-amplitude solutions adiabatic heating and cooling produces an isentropic central region. Viscous dissipation acts to redistribute buoyancy sources and intense frictional heating influences flow solutions locally in a time-dependent manner. The ratio of the total viscous heating in the convecting system, ϕ, to the heat flux across the upper surface, Fu, has an upper limit equal to d/HT. This limit is achieved at high Rayleigh numbers, when heating is entirely from below, and, for sufficiently large values of d/HT, Φ/Fu is greater than 1·00.

Journal ArticleDOI
TL;DR: In this article, the authors have described the nature of the horseshoe vortex system and measured the pressure distribution under the vortex system, and the variation of the vortex and boundary layer separation position with the flow parameters.