Showing papers by "University of Oxford published in 1975"

The Ontogenesis of Speech Acts.

Abstract: A speech act approach to the transition from pre-linguistic to linguistic communication is adopted in order to consider language in relation to behaviour generally and to allow for an emphasis on the USE of language rather than on its form. The structure of language is seen as non-arbitrary in that it reflects both attention structures (via predication) and action structures (via the fundamental case grammatical form of language). Linguistic concepts are first realized in action. A pilot study focusing on the regulation of JOINT attention and JOINT activity within the context of mutuality between mother and infant is discussed, with emphasis on ritualization in mutual play as a vehicle for understanding the development of the formal structures of language.

The capacity for joint visual attention in the infant.

Abstract: LITTLE is known about how visual attention of the mother–infant pair is directed jointly to objects and events in the visual surround during the first year of the child's life. To what extent does the child follow the mother's lead and the mother the child's, and what are the processes involved? The ability of the infant to respond successfully to such signals allows the mother to isolate and highlight a much wider range of environmental features than if the infant ignores her attention-directing efforts. We report a preliminary investigation of the extent of the infant's ability to follow changes in adult gaze direction during the first year of life.

Self-tuning controller

Abstract: A strategy for the design of self-tuning controllers of systems with constant but unknown parameters is presented. A cost function which incorporates system input, output and set-point variations is selected, and a control law for a known system is derived. This control law is shown to comprise a least-squares predictor of a function related to the cost function, and the control input is chosen to make the prediction zero. The parameters of the control law for the unknown system are estimated using a recursive-least-squares algorithm, and the optimal parameters are shown to be a fixed point of the algorithm. Whilst retaining their computational simplicity, the proposed method has several advantages over self-tuning-regulator strategies which attempt to minimise the output variance alone: weighting of control is allowed for; set-point variation may be optimally followed; there is no requirement to choose a system-related parameter to ensure convergence; and, for stable but nonminimum phase systems, there is no need to employ time-consuming methods, such as the solution of a Riccati equation. Several simulated examples are used to demonstrate the potential of the method.

Structure of chicken muscle triose phosphate isomerase determined crystallographically at 2.5 angstrom resolution using amino acid sequence data.

Abstract: Structure of chicken muscle triose phosphate isomerase determined crystallographically at 2.5A resolution: using amino acid sequence data

The Ecology of Serpentine Soils

Abstract: Publisher Summary The chapter provides details of the chemistry of the minerals frequently present in ultramafic rocks, and discusses the ecology of serpentine soil. Serpentine is used by biologists to describe a group of ultramafic rocks and the soils derived from them. Three principal polymorphic forms of serpentine are recognized: chrysotile, antigorite, and lizardite. The processes by which serpentine rocks develop into soils depend on climate, time, relief, and biotic factors along with the chemical composition of the parent material. As a result many types of soil occur on serpentines. The characteristics of serpentine are briefly discussed. Serpentine vegetation has two major characteristics: Physiognomic differences from the vegetation of surrounding rocks, and rare species and combinations of species. The vegetation of serpentines presents a wide range of appearances. Biologists have concentrated on the situations where serpentine vegetation is in sharp contrast with that of the surroundings. Such contrasts do not always occur and when this happens the serpentine vegetation is often not documented. The more closely studied serpentines have many vegetation features in common but the causes of these similarities can be very different. There is much scope for further work in many fields on serpentines.

The contents of adenine nucleotides, phosphagens and some glycolytic intermediates in resting muscles from vertebrates and invertebrates

Abstract: The lowest contents of ATP and the lowest ATP/AMP concentration ratios are observed in the molluscan muscles that have very low rates of energy expenditure during contraction. The highest contents of ATP are observed in the extremely aerobic insect flight muscle and the extremely anaerobic pectoral muscle of the pheasant and domestic fowl. In general, the lowest ATP/AMP concentration ratios are observed for muscle in which the variation in the rate of energy utilization is small (e.g. some molluscan muscles, heart muscle); the highest ratios are observed in muscles in which this variation is large (lobster abdominal muscle, pheasant pectoral muscle, some insect flight muscles). This finding is consistent with the proposed role of AMP and the adenylate kinase reaction in the regulation of glycolysis. However, in the flight muscle of the honey-bee the ATP/AMP ratio is very low, so that glycolysis may be regulated by factors other than the variation in AMP concentration. The variation in the contents of arginine phosphate in muscle from the invertebrates is much larger than the variation in creatine phosphate in muscle from the vertebrates. The contents of hexose monophosphates and pyruvate are, in general, higher in the muscles of vertebrates than in those of the invertebrates. The contents of phosphoenolpyruvate are similar in all the muscles investigated, except for the honey-bee in which it is about 4-10-fold higher. The mass-action ratios for the reactions catalysed by phosphoglucoisomerase and adenylate kinase are very similar to the equilibrium constants for these reactions. Further, the variation in the mass-action ratios between muscles is small. It is concluded that these enzymes catalyse reactions close to equilibrium. However, the mass-action ratios for the reactions catalysed by phosphofructokinase and pyruvate kinase are much smaller than the equilibrium constants. The variation in the ratios between different muscles is large. It is concluded that these enzymes catalyse nonequilibrium reactions. Since the variation in the mass-action ratios for the reactions catalysed by the phosphagen kinases (i.e. creatine and arginine phosphokinases) is small, it is suggested that these reactions are close to equilibrium.

Fate of teratocarcinoma cells injected into early mouse embryos

Abstract: ANALYSIS of early mammalian development is complicated by technical difficulties. The initial processes of cellular determination and differentiation in the mouse embryo take place in small populations of cells1,2, and major embryogenic events occur after uterine implantation when the embryo is largely inaccessible. Recent work, however, suggests that murine teratocarcinomas may provide a convenient model for studying mammalian development3–6. These are transplantable tumours of germ cell or embryonic cell origin3–6, typically consisting of a variety of differentiated tissues and undifferentiated stem cells. The stem cells, called embryonal carcinoma, resemble cells of early embryos in morphological, biochemical and cell surface properties, and in developmental potential3–6. They can be propagated in tissue culture to provide sufficient material for biochemical analysis. After inoculation into histocompatible adult hosts they form differentiated teratocarcinomas. They also differentiate in vitro7,8 where the first stages of their differentiation seem to parallel normal embryonic development. We show here that embryonal carcinoma cells can participate in normal embryogenesis, thus providing further evidence for the validity of the use of these cultures as a model of normal embryonic development.

New method for mapping genes in human chromosomes.

Abstract: If human cells are subjected to large doses of ionising radiation and then fused with rodent cells, hybrid clones are obtained in which linked human genes may be segregated. By measuring the frequency with which pairs of linked genes are cotransferred after irradiation, it is possible to determine the linear order of groups of genes and to estimate the distances between them. This technique offers a new and systematic approach to the mapping problem.

Quantum fields in curved space--times

Abstract: The problem of obtaining a quantum description of the (real) Klein-Gordon system in a given curved space-time is discussed. An algebraic approach is used. The *-algebra of quantum operators is constructed explicitly and the problem of finding its *-representation is reduced to that of selecting a suitable complex structure on the real vector space of the solutions of the (classical) Klein-Gordon equation. Since, in a static space-time, there already exists, a satisfactory quantum field theory, in this case one already knows what the 'correct' complex structure is. A physical characterization of this 'correct' complex structure is obtained. This characterization is used to extend quantum field theory to non-static space-times. Stationary space-times are considered first. In this case, the issue of extension is completely straightforward and the resulting theory is the natural generalization of the one in static space-times. General, non-stationary space-times are then considered. In this case the issue of extension is quite complicated and we only present a plausible extension. Although the resulting framework is well-defined mathematically, the physical interpretation associated with it is rather unconventional. Merits and weaknesses of this framework are discussed.

Cellular kinetics of the intestinal immune response to cholera toxoid in rats.

Abstract: The aims of this study were (a) to find a regime of immunization with cholera toxoid in rats which would establish a high density of antitoxin containing cells (ACC) in the lamina propria of the intestine and (b) to determine the origin of the ACC. The best cellular response was achieved by a single i.p. dose of toxoid in FCA followed by an intraintestinal boost 2 wk later. ACC appeared in the thoracic duct lymph 2 days after boosting, reaching a peak of about 200,000 ACC/h at 3--4 days. This was followed by the appearance of large numbers of ACC in the intestine. The i.p. dose of toxoid by itself gave rise to very few ACC in the gut or thoracic duct lymph, but it had clearly primed the gut immune system for a secondary response. Priming was also achieved by the prolonged oral intake of toxoid. The importance of the intestinal route for boosting was shown by the failure of i.p. challenge to give an ACC response in the intestine after i.p. priming and the small response it provoked after oral priming. ACC among thoracic duct lymphocytes (TDL) and in the lamina propria contained predominantly IgA. Two observations indicated that the major source of the lamina propria ACC was from cells that emerged in the thoracic duct lymph after intraintestinal challenge. Firstly, the establishment of a thoracic duct fistula immediately before challenge prevented the appearance of ACC in the intestine. Secondly, many ACC appeared in the intestine of normal rats after the injection of TDL rich in ACC. Although homing of ACC precursors to the gut was not antigen-dependent, the distribution of ACC in the lamina propria was considerably influenced by the site of the intestinal challenge, the density of ACC being greatest at or distal to the site of injection of toxoid into the lumen of the gut.

A Bayesian approach to inference about a change-point in a sequence of random variables

Abstract: SUMMARY A Bayesian approach is considered to the problem of making inferences about the point in a sequence of random variables at which the underlying distribution changes Inferences are based on the posterior probabilities of the possible change-points Detailed analyses are given for cases in which the distributions are binomial and normal, and numerical illustrations are provided An informal sequential procedure is also noted

Paracoccus denitrificans and the evolutionary origin of the mitochondrion

Abstract: It is demonstrated that Paracoccus denitrificans resembles a mitochondrion more closely than do other bacteria, in that it effectively assembles in a single organism those features of the mitochondrial respiratory chain and oxidative phosphorylation which are otherwise distributed at random among most other aerobic bacteria. A feasible evolutionary transition from the plasma membrane of an ancestral aerobic bacterium resembling P. denitrificans to the inner mitochondrial membrane is suggested.

The expansion of a plasma into a vacuum

Abstract: This paper reports calculations of the collision-free expansion of a semi-infinite plasma It is shown that the ion front is accelerated to velocities comparable with the thermal velocity of the electrons

Wang's paradox

Abstract: This paper bears on three different topics: observational predicates and phenomenal properties; vagueness; and strict finitism as a philosophy of mathematics. Of these three, only the last requires any preliminary comment. Constructivist philosophies of mathematics insist that the meanings of all terms, including logical constants, appearing in mathematical statements must be given in relation to constructions which we are capable of effecting, and of our capacity to recognise such constructions as providing proofs of those statements; and, further, that the principles of reasoning which, in assessing the cogency of such proofs, we acknowledge as valid must be justifiable in terms of the meanings of the logical constants and of other expressions as so given. The most powerful form of argument in favour of such a constructivist view is that which insists that there is no other means by which we can give meaning to mathematical expressions. We learn, and can only learn, their meanings by a training in their use; and that means a training in effecting mathematical constructions, and in recording them within the language of mathematics. There is no means by which we could derive from such a training a grasp of anything transcending it, such as a notion of truth and falsity for mathematical statements independent of our means of recognising their truth-values. Traditional constructivism has allowed that the mathematical constructions by reference to which the meanings of mathematical terms are to be given may be ones which we are capable of effecting only in principle. It makes no difference if they are too complex or, simply, too lengthy for any human being, or even the whole human race in collaboration, to effect in practice. Strict finitism rejects this concession to traditional views, and insists, rather, that the meanings of our terms must be given by reference to constructions which we can in practice carry out, and to criteria of correct proof on which we are in practice prepared to rely: and the strict finitist employs against the old-fashioned constructivist arguments of exactly the same form as the constructivist has been

Critical factors in the design of sensitive high resolution nuclear magnetic resonance spectrometers

Abstract: An analysis is given of the factors which influence the performance of a Fourier transform n.m.r. spectrometer including field homogeneity, probe design, transient circuit behaviour, Johnson noise, non linear analysis, phase sensitive detection in quadrature, and signal processing. The building of a spectrometer based upon the analysis of these factors is described, as is the use of a cyclically ordered phase sequence (CYCLOPS) which renders the use of quadrature Fourier transformation easy. Theoretical deductions are experimentally verified, and the performance of the instrument is demonstrated with spectra obtained from caesium and phosphorus resonances.

The Philosophical Basis of Intuitionistic Logic

Abstract: Publisher Summary This chapter discusses the philosophical basis of intuitionistic logic. The chapter explains that within mathematical reasoning, the canons of classical logic is in favor of those of intuitionistic logic. The chapter also emphasizes the standpoint of the intuitionists themselves that classical mathematics employs forms of reasoning that are not valid on any legitimate construal of mathematical statements. The chapter also discusses the most fundamental feature of intuitionistic mathematics and its underlying logic. However, it does not discuss intuitionistic mathematics with other respects (such as the theory of free choice sequences) in which it differs from classical mathematics. It is, therefore, possible to conduct the discussion wholly at the level of elementary number theory.

The Intrinsic, Association and Commissural Connections of Area 17 of the Visual Cortex

Abstract: An experimental neurohistological study has been made of the intrinsic connections of the cortex of area 17 of the monkey, of the commissural connections of the visual cortex of the cat and monkey and of the association fibres passing into area 17 of the cat. In light microscopic studies the axonal degeneration method of Nauta has been used, and the site and mode of termination of the degenerating fibres has also been determined with the electron microscope. After narrow slit lesions through the depth of the cortex of area 17 degeneration of the intrinsic fibre connections does not extend beyond 5-6 mm: this extent is asymmetrical, being 1-2 mm further on one side of the lesion than on the other. In all layers there is intense fine degeneration in a width of 200 $\mu$ m on each side of the lesion and in layer IV no degeneration extends beyond this distance. In all the other layers there is moderate fibre and terminal degeneration for up to 2 mm on one side and 1 mm on the other; in the stria of Gennari fibre degeneration continues for a further 1-2 mm from the lesion, and these fibres probably terminate within the stria and in the immediately adjoining parts of layer IIIb superficially and in layer IV deeply. After a small focal lesion in layers I and II fine degeneration is found in these layers over a total extent of 2-3 mm, and a few fibres pass down into layer III. When the damage extends into layer III, in addition to the horizontal degeneration in this layer there is a moderate degree of fibre degeneration in the stria, in layers V and VI and a few fibres pass into the underlying white matter. If the lesion extends deep enough to involve the stria dense horizontal fibre degeneration appears in it and this extends to a maximum width of 5-6 mm. Similar degeneration in the stria has been found after small lesions restricted to it or within layer IV, indicating that most of the horizontal fibres in the stria arise within the cortex and probably in layer IV (or V and VI). When the lesion reached down to layer V there was an increase in the density of degeneration in layer V itself, in layers II and III, and more degenerating fibres entered the white matter; these observations suggest that many of the fibres in layer V arise in that layer, that there is a recurrent projection from layer V to layers II and III and that most of the efferent fibres from area 17 arise in the deep layers of the cortex. Degenerating fibres which pass vertically up or down from a small lesion in the cortex were confined to a narrow band lying above or below the lesion. Electron microscopic observations are in good agreement with the light microscopy both with respect to the extent of the degeneration and with the variation in the different laminae. The degenerating axon terminals formed only a small proportion of the total number of terminals present, and there was a marked decrease in their number beyond 1 mm from the lesion. The majority (90%) of the terminals had asymmetrical membrane thickenings and most made contact with dendritic spines; others formed synapses upon dendrites and cell somata of stellate cells. Degenerating terminals with symmetrical membrane thickenings formed 10% of the total and the post-synaptic profiles related to these were complementary to those of the asymmetrical terminals, 78% ending on dendrites of both pyramidal and non-pyramidal cells. A small number ended on cell bodies and on initial segments. The degeneration of commissural fibres was studied only at the boundary of areas 17 and 18. With the light microscope it was found that all layers were affected by degeneration in area 18 but that layer IV was clear in area 17. This was confirmed with the electron microscope and it was found that all of the terminals had asymmetrical membrane thickenings and the majority made synaptic contact with dendritic spines. The association fibre connections passing from area 18 into area 17 of the cat were found to terminate only in the lateral part of area 17 and that layer IV was left clear of fragmentation. These fibres have asymmetrical terminals and the majority end on dendritic spines.

The beta2-microglobulin gene is on chromosome 15 and not in the HL-A region.

Abstract: POSSIBLE evolutionary homology between the genetic regions controlling histocompatibility antigens (such as HL-A in man and H-2 in the mouse) and immunoglobulins has been proposed1,2. Recent studies involving β2-microglobulin (β2m) seem to support this idea. Human β2m was found originally in the urine of patients with renal tubular dysfunction. It is also present in serum and on the surface of most types of cell3,4. It has a molecular weight of about 12,000 and shows substantial sequence homology with the constant region domains of immunoglobulin heavy chains5,6. Partially purified papain7,8 and detergent9 solubilised HL-A molecules, and H-2 molecules10, consist of two chains one of which is invariant and has been identified as β2m11–13. Chance association during the isolation procedure has been shown to be unlikely by the cocapping on the cell surface of β2m with the allogeneic chain of HL-A that carries the usual serologically detected determinants14–16.

Experimental bacterial endocarditis. IV. Structure and evolution of very early lesions.

Abstract: The vegetations of experimental sterile and bacterial endocarditis in rabbits were studied using light, immunofluorescent and electron microscopy. At an early stage, both lesions were composed chiefly of masses of platelets supported in a scaffolding of fibrin strands. In previous studies, this structure has often been described merely as "fibrin". After i.v. injection of Thorotrast, sterile vegetations showed remarkable accumulations of mononuclear phagocytes containing this substance, on surfaces projecting into the bloodstream. Sections fixed 30 min. after i.v. injection of streptococci also showed these phagocytes, which contained large numbers of bacteria. The possibility that BE is initiated by phagocytosis of circulating bacteria has been raised. Smaller numbers of circulating streptococci reached the vegetation by direct adhesion to exposed surfaces. In contrast, a majority of Proteus and Staphylococcus albus adhered directly to vegetations, without phagocytosis. Subsequently, these first settlers multiplied rapidly to form rounded colonies surrounded by capsules of fibrin, which apparently provided protection from phagocytosis. The vegetations grew by accretion of layers of fibrin and platelets, with colonies sandwiched between them. This suggested that a cycle of thrombosis and reseeding by circulating bacteria was a factor in their growth. Colonies showed morphological changes consistent with ageing after two days. Healing occurred by endothelialisation and organisation, and was greatly accelerated by penicillin treatment.

The August Krogh principle: “For many problems there is an animal on which it can be most conveniently studied”

Abstract: The idea stated in the title, first clearly expressed by August Krogh, is illustrated by examples from animal biochemistry, physiology, general cell biology, experimental medicine, ethology and botany. General aspects of the concept are discussed.

A Cross-Cultural Study of the Communication of Extra-Verbal Meaning by Gesture

Abstract: English and Italian encoders were asked to communicate two-dimensional shapes to decoders of their own culture, with and without the use of hand gestures, for materials of high and low verbal codability. The decoders drew what they thought the shapes were and these were rated by English and Italian judges, for similarity to the originals. Higher accuracy scores were obtained by both the English and the Italians, when gestures were allowed, for materials of both high and low codability; but the effect of using gestures was greater for materials of low codability. Improvement in performance when gestures were allowed was greater for the Italians than for the English for both levels of codability. An analysis of the recorded verbal utterances has shown that the detriment in communication accuracy with the elimination of gestures cannot be attributed to disruption of speech performance; rather, changes in speech content occur indicating an increased reliance on verbal means of conveying spatial infor...

General Relativistic Quantum Field Theory-An Exactly Soluble Model

Abstract: The massive scalar and Dirac fields quantized on a de Sitter background geometry prove to be exactly soluble models in general-relativistic field theory. The Feynman Green's function is computed for both the scalar and Dirac fields. A dimensional regularization procedure applied in coordinate space facilitates the calculation of their respective effective Lagrangians, which describe the vacuum corrections due to closed matter loops. The model is found to be renormalizable. There is no creation of real particle pairs.