Showing papers by "Imperial College London published in 1979"
TL;DR: Consideration is given to the relation between the ecology and evolution of the transmission processes and the overall dynamics, and to the mechanisms that can produce cyclic patterns, or multiple stable states, in the levels of infection in the host population.
Abstract: If the host population is taken to be a dynamic variable (rather than constant, as conventionally assumed), a wider understanding of the population biology of infectious diseases emerges. In this first part of a two-part article, mathematical models are developed, shown to fit data from laboratory experiments, and used to explore the evolutionary relations among transmission parameters. In the second part of the article, to be published in next week's issue, the models are extended to include indirectly transmitted infections, and the general implications for infectious diseases are considered.
2,652 citations
TL;DR: It is reported here that the T antigen in a line of SV40-transformed mouse cells forms an oligomeric complex with a specific cell coded protein.
Abstract: THE early region of the small DNA tumour virus, simian virus 40 (SV40), is known to code for at least two polypeptides, the t and T antigens (‘small t’ and ‘large T’) Both these polypeptides are expressed in cells transformed by the virus1–4, and the T antigen has been shown to be essential for both the initiation and maintenance of the transformed state5–9 We therefore need to know how this T protein interacts with components of the host cell in order to understand the mechanism of SV40-induced transformation We report here that the T antigen in a line of SV40-transformed mouse cells forms an oligomeric complex with a specific cell coded protein
2,400 citations
TL;DR: The notion that computation = controlled deduction was first proposed by Pay Hayes and more recently by Bibel and Vaughn-Pratt and the thesis that algorithms be regarded as consisting of both logic and control components is explored.
Abstract: The notion that computation = controlled deduction was first proposed by Pay Hayes [19] and more recently by Bibel [2] and Vaughn-Pratt [31]. A similar thesis that database systems should be regarded as consisting of a relational component, which defines the logic of the data, and a control component, which stores and retrieves it, has been successfully argued by Codd [10]. Hewitt's argument [20] for the programming language PLANNER, though generally regarded as an argument against logic, can also be regarded as an argument for the thesis that algorithms be regarded as consisting of both logic and control components. In this paper we shall explore some of the useful consequences of that thesis.
633 citations
TL;DR: Molecules of human erythrocyte spectrin have been examined by electron microscopy after low-angle shadowing and the molecular shape of spectrin is quite distinct from that of myosin, to which it has often been likened.
521 citations
TL;DR: It was found that up to a successional age of 16 months, the taxonomic diversities of plants and insects rose; thereafter the diversity of the plant species declined far more than the insect species diversity.
Abstract: The basic features of an intensive study on the various stages of a secondary succession, from fallow Held to birch woodland, are described. The α-β diversities of the green plants, and two orders of insects, Hetcroptera and adult Coleoptera, are described. For the vegetation, in addition to taxonotnic diversity, structural diversity, with both spatial and architectural components, was recognized. It was found that up to a successional age of 16 months, the taxonomic diversities of plants and insects rose; thereafter the diversity of the plant species declined far more than the insect species diversity. It was concluded that in the later successional stages the maintenance of a high level of taxonomic diversity of these orders of insects is correlated with the rising structural diversity of the green plants, which virtually compensates for their falling taxonomic diversity. The larger fungi appear to show a similar trend to the insects.
465 citations
TL;DR: In this article, the authors investigated the power of edge-correction for spatial point patterns and found that edge correction can substantially reduce the sampling fluctuations of a statistic and so boost the test power based on it.
Abstract: SUMMARY Tests of "randomness" and methods of edge-correction for spatial point patterns are surveyed. The asymptotic distribution theory and power of tests based on the nearest-neighbour distances and estimates of the variance function are investigated. A MAP of small objects is often described as "random" if it is consistent with the null hypothesis of a binomial or Poisson process. The usual first step in the analysis of such a pattern is a test of this null hypothesis; indeed the analysis is often confined to quoting a test statistic or its significance level as a "measure of non-randomness". The aim of this paper is to investigate the power of such tests, particularly tests based on nearest-neighbour distances, interpoint distances and estimators of moment measures, and to assess the efficiency of various corrections for edge-effects. One interesting conclusion is that edge-correction such as applied in the k of Ripley (1977) can substantially reduce the sampling fluctuations of a statistic and so boost the power of a test based on it.
416 citations
TL;DR: In this paper, an approximation to the exact evolution equation for the Fourier coefficients of the disturbance is proposed and it is shown, by an asymptotic analysis valid at large times, that the solution of the approximate equations develops a singularity at a critical time.
Abstract: The evolution of a small amplitude initial disturbance to a straight uniform vortex sheet is described by the Fourier coefficients of the disturbance. An approximation to the exact evolution equation for these coefficients is proposed and it is shown, by an asymptotic analysis valid at large times, that the solution of the approximate equations develops a singularity at a critical time. The critical time is proportional to ln $(\epsilon ^{-1})$, where $\epsilon $ is the initial amplitude of the disturbance and the singularity itself is such that the nth Fourier coefficient decays like $n^{-2.5}$ instead of exponentially. Evidence-not conclusive, however-is present to show that the approximation used is adequate. It is concluded that the class of vortex layer motions correctly modelled by replacing the vortex layer by a vortex sheet is very restricted; the vortex sheet is an inadequate approximation unless it is everywhere undergoing rapid stretching.
389 citations
TL;DR: A combination of flocculation and settling is the mechanism by which metal removal is achieved in activated sludge, and bacterial extracellular polymers appear to play an important role inFlocculation; metal cations may also be involved in this process.
331 citations
TL;DR: In this article, the authors cast quantum mechanics into a classical Hamiltonian form in terms of a symplectic structure, not on the Hilbert space of state-vectors but on the more physically relevant infinite-dimensional manifold of instantaneous pure states.
Abstract: Quantum mechanics is cast into a classical Hamiltonian form in terms of a symplectic structure, not on the Hilbert space of state-vectors but on the more physically relevant infinite-dimensional manifold of instantaneous pure states. This geometrical structure can accommodate generalizations of quantum mechanics, including the nonlinear relativistic models recently proposed. It is shown that any such generalization satisfying a few physically reasonable conditions would reduce to ordinary quantum mechanics for states that are “near” the vacuum. In particular the origin of complex structure is described.
321 citations
TL;DR: Hadron jets produced in e+e− annihilation between 13 GeV and 31.6 GeV in c.m. energy at PETRA are analyzed in this article, showing that the broadening of the jets is not uniform in azimuthal angle around the quark direction but tends to yield planar events with large and growing transverse momenta in the plane and smaller transverse momentsa normal to the plane.
317 citations
TL;DR: In this article, the influence of boundary layer growth on the flow stability of the Blasius boundary layer is analyzed on a rational, large Reynolds number, basis, for small disturbances of fixed frequency.
Abstract: The influence of boundary layer growth on the flow stability of the Blasius boundary layer is analysed on a rational, large Reynolds number, basis, for small disturbances of fixed frequency. The parallel-flow solution forms the leading term and the non-parallel flow effects emerge in a consistent fashion from the asymptotic expansions. Compared with previous, successive approximation, procedures, the theoretical neutral curve obtained here is much more affected by the non-parallel effects and consequently shows somewhat improved agreement with experimental observations, even though the previous and the present approaches (both of which calculate only a finite number of terms) would be identical if taken to infinitely many terms.
TL;DR: Extensive measurements of low-energy positive ions and electrons in the vicinity of Uranus have revealed a fully developed magnetosphere, with the boundary of the hot plasma component at L = 5 associated either with Miranda or with the inner limit of a deeply penetrating, solar wind-driven magnetospheric convection system.
Abstract: Extensive measurements of low-energy positive ions and electrons in the vicinity of Uranus have revealed a fully developed magnetosphere. The magnetospheric plasma has a warm component with a temperature of 4 to 50 electron volts and a peak density of roughly 2 protons per cubic centimeter, and a hot component, with a temperature of a few kiloelectron volts and a peak density of roughly 0.1 proton per cubic centimeter. The warm component is observed both inside and outside of L = 5, whereas the hot component is excluded from the region inside of that L shell. Possible sources of the plasma in the magnetosphere are the extended hydrogen corona, the solar wind, and the ionosphere. The Uranian moons do not appear to be a significant plasma source. The boundary of the hot plasma component at L = 5 may be associated either with Miranda or with the inner limit of a deeply penetrating, solar wind-driven magnetospheric convection system. The Voyager 2 spacecraft repeatedly encountered the plasma sheet in the magnetotail at locations that are consistent with a geometric model for the plasma sheet similar to that at Earth.
TL;DR: In this paper, the limit equilibrium method of stability analysis of embankments and slopes is considered in terms of the indeterminacy of the problem and various ways of making assumptions to make the problem a determinate one are also considered.
Abstract: In this paper the limit equilibrium method of stability analysis of embankments and slopes is considered in terms of the indeterminacy of the problem. At the same time, various ways of making assumptions to make the problem a determinate one are also considered. A method of stability analysis is proposed. It shows that the shear strength on internal shear surfaces has an effect on the computed factor of safety. This method is useful in analyzing actual slips in nature. In the example case it produces results compatible with those arising from the plasticity theory.
TL;DR: The adsorption of water vapor on smooth crystalline quartz at pressures close to saturation has been determined by ellipsometry, particular attention being paid to excluding gel layers and contamination as discussed by the authors.
TL;DR: In this article, an experimental investigation of local lattice rotations at non-deformable second phase particles in the size range 0.02 to 5 μm in aluminium and copper single crystals deformed to tensile strains of up to 0.5 is reported.
TL;DR: In this article, the authors studied the variation in discontinuity frequency as a function of scanline orientation in a plane for rock masses containing sets of discontinuities, and the spacing values between discontinuity intersection points that can occur along such scanlines were considered in order to develop a probability density distribution of block lengths.
TL;DR: In this paper, a detailed investigation of the structure of alloys of the Ti-Mo system containing up to 10wt% Mo, water-quenched from the β-phase region was made.
Abstract: A detailed investigation has been made of the structure of alloys of the Ti-Mo system containing up to 10wt% Mo, water-quenched from theβ-phase region. With increase in molybdenum content, the martensite structure changes from hexagonal (α′) to orthorhombic (α″) at ∼4 wt% Mo, and at 10 wt% Mo, the structure is completely retained β. For alloy compositions <4 wt% Mo, there is a diffusional component in the transformation of the β-phase at the quench rates employed. There is a transition, with increase in molybdenum content, in morphology (from massive to acicular) and in substructure (from dislocations to twins). However, the transitions in crystallography, morphology and sub-structure are not directly related to one another except for an abrupt loss of dislocation substructure at theα′/α″ transition. The α toα″ crystallographic transition has the characteristics of a second order transformation, and evidence has been obtained of the existence of a spinodal within the metastable orthorhombic system. The orthorhombic martensites of Ti-6 and 8 wt% Mo decompose during quenching producing a fine modulated structure within the martensite plates, consistent with a proposed spinodal mode of decomposition.
TL;DR: In this paper, an analysis of the propagation characteristics shows that there is a point below the higher-mode cutoff where the difference in group velocities between the two fundamental modes is zero but where there is large enough difference in the phase velocity to preserve polarisation.
Abstract: Elliptically cored fibres with large index differences have been drawn and shown to hold polarisation well, the modal beat length being less than 1 mm. An analysis of the propagation characteristics shows that there is a point below the higher-mode cutoff where the difference in group velocities between the two fundamental modes is zero but where there is a large enough difference in the phase velocities to preserve polarisation.
TL;DR: In this paper, load relaxation and cross-head displacement rate-change experiments have been used to establish log10 stress intensity factor (K) versus log10 crack velocity (v) diagrams for double torsion specimens, of synthetic quartz cracked on thea plane in liquid water and moist air.
Abstract: Load relaxation and cross-head displacement rate-change experiments have been used to establish log10 stress intensity factor (K) versus log10 crack velocity (v) diagrams for double torsion specimens, of synthetic quartz cracked on thea plane in liquid water and moist air. For crack propagation normal toz and normal tor at 20°C,K
Ic (the critical stress intensity factor) was found to be 0.852±0.045 MN·m−3/2 and 1.002±0.048 MN·m−3/2, respectively. Subcritical crack growth at velocities from 10−3 m·s−1 to 10−9 m·s−1 at temperatures from 20°C to 80°C is believed to be facilitated by chemical reaction between the siloxane bonds of the quartz and the water or water vapour of the environment (stress corrosion). The slopes, of isotherms in theK-v diagrams are dependent upon crystallographic orientation. The isotherms have a slope of 12±0.6 for cracking normal tor and 19.9±1.7 for cracking normal toz. The activation enthalpy for crack propagation in the former orientation in liquid water at temperatures from 20°C to 80°C is 52.5±3.8 kJ·mole−1. A discussion is presented of the characteristics of theK-v diagrams for quartz.
TL;DR: O.C..
TL;DR: It is suggested that the low levels of prevalence within snail populations in endemic areas of schistosomiasis are closely associated with high rates of infected snail mortality and the duration of the latent period of infection within the mollusc.
Abstract: The paper draws together a large and scattered body of empirical evidence concerning the prevalence of snail infection with schistosome parasites in field situations, the duration of the latent period of infection in snails (and its dependence on temperature), and the mortality rates of infected and uninfected snails in field and laboratory conditions. A review and synthesis of quantitative data on the population biology of schistosome infections within the molluscan host is attempted and observed patterns of infection are compared with predictions of a schistosomiasis model developed by May (1977) which incorporates differential snail mortality (between infected and uninfected snails) and latent periods of infection. It is suggested that the low levels of prevalence within snail populations in endemic areas of schistosomiasis are closely associated with high rates of infected snail mortality and the duration of the latent period of infection within the mollusc. In certain instances, the expected life-span of an infected snail may be less than the duration of the latent period of infection. Such patterns generate very low levels of parasite prevalence. A new age prevalence model for schistosome infections within snail populations is developed and its predictions compared with observed patterns.The implications of this study of observed and predicted patterns of snail infection within molluscan populations are discussed in relation to the overall transmission dynamics of schistosomiasis.
TL;DR: In this article, the impulse response of the boundary layer, essentially the decay of structural changes downstream of concave or convex bends with turning angles of 20 or 30 degrees, was investigated.
Abstract: Measurements, including one-point double, triple or quadruple mean products of velocity fluctuations, have been made in low-speed turbulent, boundary layers on flat surfaces downstream of concave or convex bends with turning angles of 20 or 30 degrees, the length of the curved region being at most 6 times the boundary-layer thickness at entry These short bends approximate to ‘impulses’ of curvature, and the object of the work was to investigate the impulse response of the boundary layer, essentially the decay of structural changes downstream of the bends The work can be regarded as a sequel, with much more detailed measurements, to the study by So & Mellor (1972, 1973, 1975) who investigated the response to step increases of curvature: turbulent boundary layers being nonlinear systems, responses to several kinds of curvature history are needed to assemble an adequate description of the flow The most striking feature of the ‘impulse’ response is that the decay of the high turbulent intensity found at exit from the concave bends is not monotonic; the Reynolds stresses in the outer layer collapse to well below the level at entry, and are still falling slowly at the end of the test rig although in principle they must recover eventually On the convex (stabilized) side the flow recovers, monotonically in the main, from a low level of turbulent intensity at the exit The pronounced second-order response on the concave side can be explained qualitatively by interaction between the shear stress and the mean shear and is not peculiar to curved flows, but in the present cases the response is complicated by large changes in the dimensionless structure parameters related to double or triple mean products of velocity fluctuations Strong spanwise variations, due presumably to longitudinal vortices, further complicate the flow in the concave bends, and decay only very slowly downstream
TL;DR: In this paper, the authors discuss the Polymorphisms of Oxidation at Carbon Centers of Drugs and their Clinical Significance, and present a review of these polymorphisms in terms of their clinical significance.
Abstract: (1979). Polymorphisms of Oxidation at Carbon Centers of Drugs and Their Clinical Significance. Drug Metabolism Reviews: Vol. 9, No. 2, pp. 301-317.
TL;DR: In this paper, a self-correcting point process is modelled by making the instantaneous rate of t of the process a suitable function of n −ρ t, n being the number of points in [0, t ].
TL;DR: The complete amino acid sequence of a type I variant of CAT, the variant known to be associated with most F-like plasmids conferring chloramphenicol resistance, is determined by combining the results obtained from manual and automated sequential degradation with those obtained by mass spectrometry of peptides generated by enzymatic digestion.
Abstract: Naturally occurring isolates of chloramphenicol-resistant bacteria commonly synthesise chloramphenicol acetyltransferase (EC 2.3.28; CAT) in amounts which are sufficient to account for the resistance phenotype and often harbour plas-mids which carry the structural gene for CAT1,2. The finding of CAT in such diverse prokaryotes as Proteus mirabilis, Agrobacterium tumefaciens, Streptomyces sp., and a soil Flavobacterium has led to speculation concerning the origin and evolution of the more commonly observed CAT variants specified by plasmids in clinically important bacteria2. To provide a more solid basis for studying the evolution and spread of CAT within prokaryotes we chose to determine the complete amino acid sequence of a type I variant of CAT, the variant known to be associated with most F-like plasmids conferring chloramphenicol resistance. The sequence has been determined by combining the results obtained from manual and automated sequential degradation with those obtained by mass spectrometry of peptides generated by enzymatic digestion. The directly determined primary structure is identical with that predicted by the DNA sequence analysis3 of the chloramphenicol resistance transponson Tn9 known to specify a type I variant of chloramphenicol acetyltransferase.
TL;DR: A hypothesis is presented that competition between ectoparasite species, mediated by host defensive responses, is also important in determining community structure, and it argues that all vertebrate associates have evolved along one of two macroevolutionary pathways which differ only in the sequencing of adaptations facilitating host association and host feeding.
Abstract: The evolution of close vertebrate associations has occurred in seven orders of insects, resulting in a great diversity of interactions which range from commensalism to true parasitism. The evolution of each taxon of vertebrate associates is discussed in turn, some new ideas on the development of certain groups are presented and, on a broader scale, a general model for the evolution of ectoparasitic insects is proposed. It argues that all vertebrate associates have evolved along one of two macroevolutionary pathways which differ only in the sequencing of adaptations facilitating host association and host feeding. These pathways lead to parasite types which differ greatly in their life history and intimacy of host association.
Some microevolutionary processes influencing the diversification of ectoparasites are discussed, in particular the process of insect/vertebrate coevolution and the forms this may take. Host specificity, one consequence of coevolution, is recognised as an important factor influencing the structure of ectoparasite communities, and a hypothesis is presented that competition between ectoparasite species, mediated by host defensive responses, is also important in determining community structure.