Showing papers by "University of Oxford published in 1973"

Anomalous Fading of Thermo-luminescence in Mineral Samples

Abstract: THE use of thermoluminescence (TL) for dating archaeological ceramics is well established1. Recently we have been attempting to use similar techniques to date volcanic lava from geologically recent flows (5,000 to 50,000 yr old), by measuring the TL from the feldspars present. These included rhyolites from near Naples and basalts from Iceland and the Massif Central region of France; the latter were of particular interest because palaeomagnetic and potassium argon age measurements and related radiocarbon dates in the Chaine des Puys region have suggested a geomagnetic polarity excursion of the Earth's magnetic field within the past 50,000 yr (ref. 2). The basalts contained the plagioclase feldspars labradorite, andesine and bytownite, and the rhyolites contained the alkali feldspar sanidine. All of the TL ages obtained were significantly lower than the accepted ages of the lava flows, some by an order of magnitude.

On the heat equation and the index theorem

Abstract: The main error occurs on page 306 where it is implicitly assumed that the coefficients of the two operators A*A and AA* (associated to the signature operator A) are polynomial functions in the gij, their derivatives and (det g)-l . As we shall show later this is not quite t r u e t h e coefficients also involve d ] f ~ and the inverses of the principal minors of the matrix gu" Thus the form m in (5.1) is not a regular invariant of the metric in the sense of w 2, and so the Gilkey Theorem as formulated on p. 284 does not apply. To correct this we shall widen the notion of regularity (so as to include, in particular, the form ~o above) and then check that our proof of Gitkey's Theorem still holds in this wider context. In w regularity was only defined for invariants of a Riemann structure g (i.e. satisfying the naturality or invariance property (2.3)). It will perhaps make for greater clarity if we introduce our new notion of regularity for any function of g, independently of the invariance property. We shall say that f(g) is a regular function of g if, in any coordinate system, we have

On the transport of compact particles through solutions of chain-polymers

Abstract: The problem is discussed of providing a theoretical explanation for the empirical equation of Laurent, Bjork, Pietruszkiewicz & Persson (1963) which relates the relative retardation of the sedimentation of compact particles in solutions of hyaluronic acid to the radius of the particle and the concentration of hyaluronic acid. From published and original data, the same relation is shown to apply also to sedimentation and diffusion in solutions of a number of linear and branched chain-polymers. Of several approaches to the problem, only one, based on the stochastic model of diffusional migration, yields the empirical relationship, and predicts a value of the numerical constant close to that observed. This treatment is shown to apply to other forms of migration, including the case where the chain-polymer is itself migrating. The theory is tested by calculation, from migration data, of the effective radii of the polymer chains. The results are consistent and comparable with values deduced from equilibrium experiments.

Configuration-Spaces and Iterated Loop-Spaces.

Abstract: The object of this paper is to prove a theorem relating "configurationspaces" to iterated loop-spaces. The idea of the connection between them seems to be due to Boardman and Vogt [2]. Part of the theorem has been proved by May [6]; the general case has been announced by Giffen [4], whose method is to deduce it from the work of Milgram [7]. Let C. be the space of finite subsets of ~n. It is topologized as the disjoint union LI C~,k, where C~, k is the space of subsets of cardinal k, k->0 regarded as the orbit-space of the action of the symmetric group 2: k on the space ~n,k of ordered subsets of cardinal k, which is an open subset of R "k. There is a map from C. to O"S ~, the space of base-point preserving maps S"--,S ~, where S" is the n-sphere. One description of it (at least when n> 1) is as follows. Think of a finite subset c of ~ as a set of electrically charged particles, each of charge + 1, and associate to it the electric field E c it generates. This is a map Ec: R ~ c-.n~ ~ which can be extended to a continuous map Ec: RnUOO--,~nU~ by defining Ec(~)=oo if ~ec, and Ec(oo)=0. Then E c can be regarded as a base-point-preserving map S"--,S", where the base-point is oo on the left and 0 on the right. Notice that the map c~-,Ec takes Cn, k into ~"Sntk), the space of maps of degree k. Our object is to prove that C. is an approximation to Q~ S ~, in the sense that the two spaces have composition-laws which are respected by the map C~-, f l 'S ~, and the induced map of classifying-spaces is a homotopy-equivalence. In view of the "group-completion" theorem of Barratt-Priddy-Quillen [1, 8] one can say equivalently that Cn, k--~nsn(k ) induces an isomorphism of integral homology up to a dimension tending to oo with k. But to make precise statements it is convenient to introduce a modification of the space C.. If u<=v in R, let R".,~ denote the open set )u, v( x R "-~ in R ~. Then Cn is homotopy-equivalent to the space

Experimental Survival Curves for Interval‐Censored Data

Abstract: A method is given for calculating from interval‐censored data an estimate of the c.d.f. which is analogous to the estimate derivable from right‐censored data by the life‐table technique. A Fortran implementation has been constructed by the author.

Early Archaean Age for the Isua Iron Formation, West Greenland

Abstract: SOME 150 km north-east of Godthaab, on the edge of the inland ice cap, a refolded syncline of mainly basic rocks containing banded ironstones and other rocks of supracrustal origin is enclosed by granitic gneisses (Fig. 1). These gneisses have yielded an Rb-Sr whole-rock isochron age of 3,700 ± 140 m.y., indistinguishable from that of the Amitsoq gneisses of the Godthaab area1. The present metamorphic grade of both the gneisses and the iron formation is upper greenschist to amphibolite facies. There is no published map of the area, but the following geological details are taken from reports by Keto2. The total succession of supracrustal rocks is 2 to 3 km thick. The lower part of the succession consists of quartzites and meta-greywackes. These are overlain by garnet–chlorite schists and banded iron formation, including both Fe-oxides and carbonates. The top of the succession consists of greenschist facies metabasites, Bridgwater et al.3 suggest that the Isua supracrustals may represent a shallow-water shelf facies.

The Pressure Reversal of General Anesthesia and the Critical Volume Hypothesis

Abstract: The anesthetic potencies (ED50) of four gaseous anesthetics and five liquid anesthetics were first determined in newts, using the abolition of righting reflex measured by the rolling response at 20°. The following results were obtained: N2O, 0.69 atm; N2, 21.5 atm; SF6, 1.82 atm; CF4, 11.0 atm; CHCl3 0.89 mM; butanol, 16.7 mM; pentobarbitone sodium, 0.85 mM; halothane, 0.39 mM; ether, 25 mM. The ability of elevated pressures to antagonize the effect of these anesthetics was then studied. For the liquid anesthetics, a graded response to pressure was observed and the reversibility of the antagonistic effect was demonstrated. Dose-response curves were obtained for the interaction of pressure with the gaseous anesthetics, and, from these, ED50 values at various pressures have been interpolated. The data are used to compare the Meyer-Overton and the critical volume hypotheses; the latter not only is consistent with the data but also provides explanations for the antagonistic phenomenon and the lack of anesthetic effect for helium, neon, and hydrogen. The critical volume hypothesis is developed for three solvent model systems, from which estimates of the compressibility of the site of action are made.

Studies of anaesthesia in relation to hypertension v: adrenergic beta-receptor blockade

Abstract: The effects of intravenous practolol 0.4 mg/kg were studied in 12 hypertensive patients during halothane/nitrous oxide anaesthesia. Practolol decreased heart rate (HR) and cardiac output \( Q ˙ \) from the elevated levels following atropine administration during anaesthesia, but values of arterial pressure (AP), HR and Q ˙ after the combination of atropine and practolol were not significantly different from those during anaesthesia prior to blockade. The effects of a similar anaesthetic sequence were studied in a further 11 treated hypertensive patients given practolol by mouth 1.5 mg/kg/6 hours for at least 48 hours preoperatively in addition to current anti-hypertensive therapy. By comparison with treated hypertensive patients previously studied, those pretreated with practolol had similar AP awake, but higher AP throughout anaesthesia with either spontaneous or artificial ventilation. Cardiac output was higher and systemic vascular resistance was lower both before and during anaesthesia. Both the present groups of patients showed significantly attenuated responses of tachycardia and hypertension following laryngoscopy and intubation compared with previous studies. The incidence of dysrhythmia and e.c.g. evidence of myocardial ischaemia was significantly lower (4%) in beta-blocked patients compared with those who had not received practolol (38%).

A theorem about random fields

Abstract: Averintsev [1] and Spitzer [2] proved that the class of Markov fields is identical to the class of Gibbs ensembles when the domain is a finite subset of the cubic lattice and each site may be in either of two given states. Hammersley and Clifford [3] proved the same result for the more general case when the domain is the set of sites of an arbitrary finite graph and the number of possible states for each site is finite. In order to show this, they extended the notion of a Gibbs ensemble to embrace more complex interactions than occur on the cubic lattice. Their method was circuitous and showed merely the existence of a potential function for a Markov field with little indication of its form. In [4], Preston gives a more direct approach to the two-state problem and presents an explicit formula for the potential. We show here that the equivalence of Markov fields and Gibbs ensembles follows immediately from a very simple application of the Mobius inversion theorem of [5] which allows us to construct a natural expression for the potential function of a Markov field. We confine our attention to the set of sites of an arbitrary finite graph and allow each site to be in any one of a countable set of states. The two-state solution of Preston emerges as a corollary.

Uptake of solutes by multiple root systems from soil

Abstract: A procedure is put forward for calculating the plant uptake of solutes supplied by diffusion and mass flow to the randomly dispersed roots of a developing root system. The model was tested as follows: (a) for a constant root density, and both transport processes—against a more accurate numerical solution of the same system (b) for an increasing root density, and for supply by diffusion only—by electrical simulation using the analog described in Part I. In both cases, results obtained by the two types of calculation were in close agreement.

Mid-plate Tectonics

Abstract: There are many examples of mid-plate tectonics which require an explanation. Oceanic island chains, continental graben and rift valleys, and features which pass from continental areas into oceanic parts of the same plate, are particularly important. We argue that these are the result of crustal extension due to tensional stresses — thermal stresses due to the cooling of the lithosphere, membrane stresses due to changes in the radii of curvature or a complicated combination of both.

A study of interstitial clusters in irradiated alkali halides using direct electron microscopy

Abstract: A direct electron microscope study has been made of defect clusters produced in alkali halides by ionizing radiation. A technique has been developed for preparing foils of alkali halide crystals less than a few hundred nanometres thick for observation in the microscope, and a liquid helium cooled stage allows the study of irradiated crystals down to 5 K. At this temperature it has been possible to analyse in detail clusters produced at other temperatures, without confusion from observable damage produced by the investigating election beam. Irradiations have been performed both in the 100 keV microscope beam and externally using γ rays or 400 keV electrons. In this way irradiation products in KI have been extensively studied. The predominant type of defect cluster produced in several alkali halides by room temperature irradiation has contrast typical of planar dislocation loops. Tilt/contrast experiments performed in KI show conclusively that the loops are interstitial in character, and the numbers of point defects involved and the temperature dependence of their growth indicate that mobile interstitial halogen atoms are required for their formation. The loops have Burgers vectors b ═ 1/2 a (110) where a is the lattice parameter. The habit plane of a loop with b ═ 1/2 a [101] lies between (001) and (101). An unfaulted interstitial dislocation loop with Burgers vector 1/2 a formed by condensation of equal numbers of anion and cation interstitials can account for the observed features of the clusters. However, since there is little evidence for the direct production of cation Frenkel pairs by ionizing radiation in alkali halides, alternative models are presented in which the cluster forms primarily as a result of the initial aggregation of halogen interstitials alone. These models are shown to be consistent with specific features of the radiation damage behaviour of alkali halides.

Structural studies of immunoglobulins.

Abstract: In 1946, when I was starting work as research student under the supervision of Dr F. Sanger, the second edition of Karl Lansteiner's book” The Specificity of Serological Reactions’[I] reached England. In it was summarized the considerable body of information available on the range of antibody specificity and much of it was Landsteiner's own work or by others using his basic technique of preparing antibodies against haptenes and testing their ability to inhibit the precipitation of the antisera and t he conjugated protein. Also described in this book was the work in Uppsala of Tiselius and Pederson in collaboration with Heidelberger and Kabat in which they showed that all rabbit antibodies were in the y globulin fraction of serum proteins and that they had a molecular weight of 150.000. This combination of an apparently infinite range of antibody-combining specificity associated with what appeared to be a nearly homogeneous group of proteins astonished me and indeed still does.

Mapping of Asporogenous Mutations of Bacillus subtilis: a Minimum Estimate of the Number of Sporulation Operons

Abstract: Sporulation-specific mutations in Bacillus subtilis have been mapped by transduction and transformation. The mutations caused blocks at stages 0, II, III, and IV of sporulation; more than one phenotype was found for each of these stages. On the basis of the criteria used to define a sporulation operon, a minimum estimate could be made of the number of operons activated during sporulation. Nine operons were identified for stage 0, eight for stage II, five for stage III, and six for stage IV. It is probable that several of these 28 operons are activated in groups so that the number of steps in the dependent sequence of sporulation events should turn out to be less than the number of operons.

Learning through experience and learning through media

Abstract: This paper is concerned broadly with the consequences of two types of experience which may be designated as direct experience and mediated experience, their partial equivalence and substitutability, and their differing potential roles in the intellectual development and acculturation of children. Our analysis will begin with the problem of the nature of direct experience and its effect on development. A clearer conception of the processes involved in direct experience will permit us better to examine the manner and extent m which mediate experience may complement, elaborate and substitute for that direct experience. Much of a child's experience is formalized through schooling. Whether for reasons of economy or effectiveness, schools have settled upon learning out of context through media which are primarily symbolic. Schooling generally reflects the naive psychology which has been made explicit by Fritz Heider (Baldwin, 1967). 3 The general assumption of such a naive psychology is that the effects of experience can be considered as knowledge, that knowledge is conscious, and that knowledge can be translated into words. Symmetrically, words can be translated into knowledge, hence, one can learn, that is acquire knowledge, from being told. Because learning is cognitive, it is possible, according to naive theory, to substitute instruction for learning through experience. Thus, we can tell children what to do and how to do it, and instil wise and proper behaviour without the actual necessity of rewarding and punishing them. It is a common belief among naive educators, how-

Connections between descending visual interneurons and metathoracic motoneurons in the locust

Abstract: Connections between the four DMD neurons and metathoracic motoneurons in the locustSchistocerca were examined by recording extracellularly from the interneurons in the pro-mesothoracic connectives and intracellularly from seventeen motoneurons. A DIMD or DCMD spike causes an EPSP in the fast extensor tibiae motoneuron, which can be modified by changing the membrane potential. The EPSP always follows spikes at frequencies up to 200 Hz and with a latency of 0.9 ms, suggesting that the connections are monosynaptic and chemically mediated. EPSPs from the DIMD or DCMD arrive at the same time, their axons having the same conduction velocity, and appear simultaneously in the fast extensor tibiae motoneurons on both sides of the ganglion. There is spatial and temporal summation between the inputs but on no occasion did the motoneurons spike. Three inhibitory neurons are depolarized by DMD inputs and may on occasion spike, but it is not known whether these connections are direct. Similarly the slow excitatory motoneuron to the anterior coxal adductor muscle is hyperpolarized by DMD input. Other leg, flight or ventilatory motoneurons examined received no inputs from the DMD neurons. The connections shown are consistent with the hypothesis that the DMD neurons are in some way involved with initiation of a jump, but to achieve this must act synergistically with other inputs.

Acceleration of gluconeogenesis from lactate by lysine (Short Communication).

Abstract: l-Lysine (2mm) causes an increase (mean 60%) in the rate of gluconeogenesis from lactate in isolated liver cells. The effect is of a catalytic nature. No other amino acid has the same effect, though ornithine is slightly active. The effect is additional to the stimulatory effects of oleate and of dibutyryl cyclic AMP.