Showing papers by "University of Oxford published in 1977"

Design and analysis of randomized clinical trials requiring prolonged observation of each patient. II. analysis and examples.

Abstract: Part I of this report appeared in the previous issue (Br. J. Cancer (1976) 34,585), and discussed the design of randomized clinical trials. Part II now describes efficient methods of analysis of randomized clinical trials in which we wish to compare the duration of survival (or the time until some other untoward event first occurs) among different groups of patients. It is intended to enable physicians without statistical training either to analyse such data themselves using life tables, the logrank test and retrospective stratification, or, when such analyses are presented, to appreciate them more critically, but the discussion may also be of interest to statisticians who have not yet specialized in clinical trial analyses.

Imitation of facial and manual gestures by human neonates.

Abstract: Infants between 12 and 21 days of age can imitate both facial and manual gestures; this behavior cannot be explained in terms of either conditioning or innate releasing mechanisms. Such imitation implies that human neonates can equate their own unseen behaviors with gestures they see others perform.

Pyroxene thermometry in simple and complex systems

Abstract: Simple mixing models have been applied to ortho- and clinopyroxene solid solutions and a semi-empirical equation of state extracted from the available experimental data for the diopside-enstatite miscibility gap. This equation successfully reproduces the miscibility gap over a temperature range of 800 °C to 1700 °C and is apparently also applicable to aluminous pyroxenes in the system CaSiO3-MgSiO3-Al2O3. The effect of iron solubility in the pyroxenes has been calibrated empirically using most of the available experimental data for multicomponent pyroxenes. This semi-empirical model reproduces most of the experimental data within 70 °C. Temperatures calculated for naturally equilibrated Mg-rich two-pyroxene assemblages deviate markedly from those estimated using the thermometer of Wood and Banno (1973). These discrepancies can be attributed to large inaccuracies in the thermometer of Wood and Banno (1973) for Mg-rich compositions.

The approach of solutions of nonlinear diffusion equations to travelling front solutions

Abstract: The paper is concerned with the asymptotic behavior as t → ∞ of solutions u(x, t) of the equation ut—uxx—∞;(u)=O, x∈(—∞, ∞) , in the case ∞(0)=∞(1)=0, ∞′(0)<0, ∞′(1)<0. Commonly, a travelling front solution u=U(x-ct), U(-∞)=0, U(∞)=1, exists. The following types of global stability results for fronts and various combinations of them will be given.

Storage of elastic strain energy in muscle and other tissues

Abstract: Storage of strain energy in elastic materials has important roles in mammal running, insect jumping and insect flight. The elastic materials involved include muscle in every case, but only in insect flight is the proportion of the energy stored in the muscle substantial.

Forecasting Economic Time Series

Abstract: This book provides a formal analysis of the models, procedures, and measures of economic forecasting with a view to improving forecasting practice. David Hendry and Michael Clements base the analyses on assumptions pertinent to the economies to be forecast, viz. a non-constant, evolving economic system, and econometric models whose form and structure are unknown a priori. The authors find that conclusions which can be established formally for constant-parameter stationary processes and correctly-specified models often do not hold when unrealistic assumptions are relaxed. Despite the difficulty of proceeding formally when models are mis-specified in unknown ways for non-stationary processes that are subject to structural breaks, Hendry and Clements show that significant insights can be gleaned. For example, a formal taxonomy of forecasting errors can be developed, the role of causal information clarified, intercept corrections re-established as a method for achieving robustness against forms of structural change, and measures of forecast accuracy re-interpreted.

Gonadotrophin-releasing hormone deficiency in a mutant mouse with hypogonadism

Abstract: FAMILIAL hypogonadism in man, due to an isolated deficiency of gonadotrophin secretion, has been well documented1–6, but difficult to investigate because of the lack of a suitable animal model4. We report here the genetic and endocrinological background of a mutant strain of mouse in which the testes and ovaries fail to develop postnatally. The primary cause of this seems to be a deficiency in hypothalamic gonadotrophin-releasing hormone (GnRH) with a consequent reduction in pituitary content and circulating levels of luteinising hormone (LH) and follicle-stimulating hormone (FSH). By analogy with the Brattleboro rat (genetic defect in vasopressin synthesis) this mutant should prove useful for studying the synthesis of hypothalamic releasing hormones as well as the role of the hypothalamic–gonadotrophin system in sexual differentiation, puberty, folliculogenesis and spermatogenesis. The mutant has been named hypogonadal, symbol hpg.

Instantons and algebraic geometry

Abstract: Minimum action solutions for SU(2) Yang-Mills fields in Euclidean 4-space correspond, via the Penrose twistor transform, to algebraic bundles on the complex projective 3-space. These bundles in turn correspond to algebraic curves. The implication of these results for the Yang-Mills fields is described. In particular all solutions are rational and can be constructed from a series of AnsatzeA l forl≧1.

Decision making in animals

Abstract: Animals must make decisions about when to feed, when to court, when to sleep, and so on, in such a way as to maximise as far as possible their chances of survival and reproductive success. It is possible to formulate in mathematical terms the optimal strategy for an animal to pursue. The theoretical optimum behaviour can be compared with the actual behaviour of the animal, and perhaps shed some light on the evolution of behaviour.

Optimal foraging in great tits ( Parus major )

Abstract: OPTIMAL foraging theory1–5 is based on the supposition that animals have been designed, by natural selection, to behave in a way that will maximise their inclusive fitness and that in terms of foraging this goal may be approximated by maximising the net rate of energy intake while feeding1–4. Therefore, given the constraints of any particular situation it is possible to predict how an animal ought to behave while foraging. I have tested an optimal foraging model which predicts how a predator should exploit patchily distributed prey. The results are consistent with the predictions of the model.

What does a man do after he makes an error? an analysis of response programming

Abstract: When people make errors during continuous tasks they temporarily pause and then slow down. One line of explanation has been that they monitor feedback to detect errors, that they may make incidenta...

Motion sickness: an evolutionary hypothesis

Abstract: Since the occurrence of vomiting as a response to motion is both widespread and apparently disadvantageous, it presents a problem for evolutionary theory. An hypothesis is proposed suggesting that motion sickness is triggered by difficulties which arise in the programming of movements of the eyes or head when the relations between the spatial frameworks defined by the visual, vestibular, or proprioceptive inputs are repeatedly and unpredictably perturbed. Such perturbations may be produced by certain types of motion, or by disturbances in sensory input or motor control produced by ingested toxins. The last would be the important cause in nature, the main function of the emesis being to rid the individual of ingested neurotoxins. Its occurrence in response to motion would be an accidental by product of this system.

Drug Effects on Fear and Frustration: Possible Limbic Site of Action of Minor Tranquilizers

Abstract: This chapter attempts to answer the following linked questions: 1 What is the simplest adequate description of the effects of the “minor tranquilizers” on “emotional behavior” (terms I shall define below)? 2 What underlying psychological processes are altered by these drugs to produce these behavioral effects, and in what way are they altered? 3 On what brain structures or systems do these drugs act to produce these behavioral effects?

Computer simulation of a gas–liquid surface. Part 1

Abstract: The gas–liquid surface of a system of Lennard-Jones (12, 6) molecules has been simulated by Monte Carlo and by Molecular Dynamic methods at temperatures which span most of the liquid range. For systems of 255 molecules the two methods lead to similar results and this agreement confirms that the density profile, as a function of height, falls monotonically from the density of the bulk liquid to that of the gas. The thickness of the surface layer is sensitive to the surface area, and appears to approach its thermodynamic limit for surface areas of 400σ2 for a system of 4080 molecules. The density profile can be represented by a hyperbolic tangent of an appropriately scaled height. The thickness of the surface is of the order of two molecular diameters at temperatures near the triple point and increases rapidly as the critical point is approached. The computed surfacetens ions agree well with those calculated by statistical perturbation theory.Monte Carlo and Molecular Dynamic simulation of a binary mixture shows clearly the adsorption of the component of higher vapour pressure; the amount absorbed agrees with that calculated from Gibbs's isotherm.

How to read a film

Abstract: At the beginning of the unit the class will break up into new groups. There are three people per group. Before they leave their previous groups they will evaluate how well their previous group worked and how well they individually worked. The students will be working in this group for the entire unit. The unit will be broken into the three elements outlined in Reel Conversations. The first activity is that I will have the class brainstorm films that they like in groups. For every film that they like they have to give at least three reasons why they liked the film. Every group must agree on three films and the three reasons for each film. After the groups have a chance to brainstorm why they liked the film, they will write their choices on an overhead along with the reasons that they chose those particular films. Each group will share their films with the rest of the class. After each group has a chance to present, I will point out many of the similarities between films and literature. Many of the students will say that they enjoyed the film because of the actor, director, setting, characterization, violence, etc. It is important to look at these elements individually and as a whole when analyzing a film. I will tell the class that we will be studying three aspects of film; literary, dramatic, and cinematic. The students will have a project at the end that requires them to utilize these three elements.

Contraction and recovery of living muscles studied by 31p nuclear magnetic resonance

Abstract: 1. Phosphorus nuclear magnetic resonance ((31)P NMR) can be used to measure the concentrations of phosphorus-containing metabolites within living tissue. We have developed methods for maintaining muscles in physiological condition, stimulating them and recording tension while at the same time accumulating their (31)P NMR spectra. Experiments were performed on frog sartorii and frog and toad gastrocnemii at 4 degrees C.2. The NMR signals from (31)P (the naturally occurring phosphorus) is weak, and signal averaging is required. In order to follow the time course of reactions it is necessary to maintain the muscles in a steady state for many hours while they are undergoing repeated contractions. Signals were accumulated in separate computer bins according to time after initiation of contraction. By these means spectra were obtained which corresponded to the different intervals during the contraction and recovery cycle.3. In the absence of stimulation, the spectra of frog sartorius muscles and of their extracts indicated concentrations of adenosine triphosphate (ATP), phosphoryl creatine (PCr), inorganic orthophosphate (P(i)) and sugar phosphates (sugar P) which are in reasonable agreement with the values obtained by chemical analysis.4. We have confirmed that unidentified resonances representing unknown compounds appear in the spectra of both frog and toad muscle; one of these is much larger in spectra from toad than from frog. We have found an additional small, unidentified resonance which appears to be specific to toad muscle.5. Spectra accumulated during actual contractions (1 s tetani every 2 min) did not differ dramatically from those accumulated throughout the 2 min cycle of contraction and partial recovery.6. Following 25 s tetanii, approximately 20% of the PCr had been hydrolysed; it was then rebuilt exponentially with a half-time of about 10 min. The increase in [P(i)] immediately after contraction and the time course of its disappearance corresponded to the changes in [PCr]. During the later half of the recovery period the concentration of P(i) was reduced to below that in resting muscle. The [sugar P] remained very high ( approximately 4 mmol kg(-1)) throughout the 56 min interval between contractions.7. When frog sartorii were tetanized for 1 s every 2 min, the changes in [PCr] and [P(i)] between contractions could not be observed because too little signal was obtained from these small muscles. However, when toad gastrocnemii were similarly stimulated, the changes in these compounds could be readily detected and were even greater than expected.8. The position of the P(i) resonance can be used to monitor intracellular pH and changes in pH. Under the conditions of our experiments the average intracellular pH in unstimulated frog sartorius muscles was 7.5. After a 25 s tetanus this was observed to move in the acid direction by a few tenths of a pH unit and to return to its pre-stimulation value before the end of the recovery period. After a 1 s contraction of toad gastrocnemius the environment of P(i) became slightly more alkaline for the first few seconds.

Studies of the developmental potential of 4‐ and 8‐cell stage mouse blastomeres

Abstract: The object of this study was to assess the full developmental potential of all the blastomeres in 4-cell and 8-cell stage mouse embryos. Isolated blastomeres at these stages have limited developmental powers, and in order to follow their development into the postimplantation period a method of combining each blastomere into a chimaeric composite was devised. Preliminary experiments indicated the most favourable genetic combinations and blastomere arrangements. For the 4-cell stage embryos each individual donor blastomere was combined with genetically distinct blastomeres at the same stage to make a “Quarted” of composite embryos. The occurrence of the donor cell characters in these composites when they were recovered at the tenth day of pregnancy and at term, indicates that each 4-cell stage blastomere is totipotent and may contribute extensively to a mouse and also to the yolk sac and trophoblast. Eight-cell stage blastomeres were obtained in pairs, each pair being derived from a particular 4-cell stage blastomere. The development of the pairs were followed in chimaeric composites. Each blastomere of a pair was found to have the same range of developmental potential. This indicates a lack of segregation of morphogenetic factors and implies totipotency of the 8-cell stage blastomeres. The relevance of these results to the current theories of blastocyst differentiation is discussed.

Optimal mate selection in the toad Bufo bufo

Abstract: SEXUAL reproduction can no longer be regarded as a cooperative venture in which males and females are selected to achieve the same goals. The optimal reproductive strategy for a male is often very different from that for a female1,2. We report here that, in the wild, toads (Bufo bufo) do not pair up at random, that this comes about through male–male competition probably influenced by the behaviour of the female and that mating involves a compromise between different male and female optima.

HLA restriction of cell-mediated lysis of influenza virus-infected human cells.

Abstract: MURINE T lymphocytes that mediate the lysis of virus-infected cells show specificity both for the viral cell surface antigens and for the H–2K or D antigens of the major histo-compatibility complex1–8. The cytotoxic T lymphocytes and the target cell must share H–2K or D products. The experiments reported here demonstrate that there is a similar requirement for partial HLA identity between human cytotoxic lymphocytes and influenza virus-infected target cells.