Showing papers by "University of Cambridge published in 1973"
TL;DR: This article derived expressions for the mass of a stationary axisymmetric solution of the Einstein equations containing a black hole surrounded by matter and for the difference in mass between two neighboring such solutions.
Abstract: Expressions are derived for the mass of a stationary axisymmetric solution of the Einstein equations containing a black hole surrounded by matter and for the difference in mass between two neighboring such solutions. Two of the quantities which appear in these expressions, namely the area A of the event horizon and the “surface gravity” κ of the black hole, have a close analogy with entropy and temperature respectively. This analogy suggests the formulation of four laws of black hole mechanics which correspond to and in some ways transcend the four laws of thermodynamics.
3,494 citations
TL;DR: The core Vema 28-238 as discussed by the authors preserves an excellent oxygen isotope and magnetic stratigraphy and is shown to contain undisturbed sediments deposited continuously through the past 870,000 yr.
2,515 citations
TL;DR: In this paper, the critical value of tensile stress (a) for unstable cleavage fracture to the fracture toughness (K,,) for a high-nitrogen mild steel under plane strain conditions.
Abstract: SUMMARY AN ANALYSIS is presented which relates the critical value of tensile stress (a,) for unstable cleavage fracture to the fracture toughness (K,,) for a high-nitrogen mild steel under plane strain conditions. The correlation is based on (i) the model for cleavage cracking developed by E. Smith and (ii) accurate plastic*lastic solutions for the stress distributions ahead of a sharp crack derived by J. R. Rice and co-workers. Unstable fracture is found to be consistent with the attainment of a stress intensification close to the tip such that the maximum principal stress a,, exceeds a, over a characteristic distance, determined as twice the grain size. The model is seen to predict the experimentally determined variation of K,, with temperature over the range -150 to -75°C from a knowledge of the yield stress and hardening properties. It is further shown that the onset of fibrous fracture ahead of the tip can be deduced from the position of the maximum achievable stress intensiiication. The relationship between the model for fracture ahead of a sharp crack, and that ahead of a rounded notch, is discussed in detail.
1,374 citations
TL;DR: Sibson gives an O(n 2) algorithm for single-linkage clustering, and proves that this algorithm achieves the theoretically optimal lower time bound for obtaining a single- linkage dendrogram.
Abstract: Main point Sibson gives an O(n 2) algorithm for single-linkage clustering, and proves that this algorithm achieves the theoretically optimal lower time bound for obtaining a single-linkage dendrogram. This improves upon the naive O(n 3) implementation of single linkage clustering. A single linkage dendrogram is a tree, where each level of the tree corresponds to a different threshold dissimilarity measure h. The nodes of a dataset are grouped into \" equivalence classes \" c(h) at each level of the dendrogram, where two classes C i and C j are merged if there is a pair of \" OTU's \" (vertices) v i ∈ C i and v j ∈ C j such that the dissimilarity measure between v i and v j is less than h, or D(v i , v j) < h. For example, consider a set of 10 vertices v 1 ,. .. , v 10 for which the dissimilarity matrix D is given below, with D ij equal to the dissimilarity between v i and v j. Suppose we take four cutoff dissimilarity measures h 1 , h 2 , h 3 , h 4 and produce the dendrogram according to these thresholds. An example illustrating how the 10 vertices are grouped into equivalence classes at each level is shown in Figure 1. Since no dissimilarity is at or below 1, each vertex or \" OTU \" is its own equivalence class at the level corresponding to h 1 = 1. At the next level, however, we see that some classes have been merged together because several dissimilarity measures are below h 2 = 2. We can see that c(h 2) consists of 6 equivalence classes, c(h 3) has 3 equivalence classes, and c(h 4 = 4) aggregates all the vertices into one equivalence class. In single linkage clustering, the number of levels in the tree is determined by the nearest-neighbor criterion – at each level, at least one new merge is made between two clusters, and the merge is made for clusters C i and C j if the minimal distance between vertices v i ∈ C i and v j ∈ C j is the smallest such distance across all the clusters. In other words, the nearest neighbors between clusters C j and C i are found, and if these neighbors are closer than all the other nearest-neighbor pairs, then C i and C …
1,208 citations
Book•
01 Jan 1973TL;DR: Two essays on utilitarianism, written from opposite points of view, by J. C. Smart and Bernard Williams as mentioned in this paper, argue that the rightness and wrongness of actions is determined solely by their consequences, and in particular their consequences for the sum total of human happiness.
Abstract: Two essays on utilitarianism, written from opposite points of view, by J. J. C. Smart and Bernard Williams. In the first part of the book Professor Smart advocates a modern and sophisticated version of classical utilitarianism; he tries to formulate a consistent and persuasive elaboration of the doctrine that the rightness and wrongness of actions is determined solely by their consequences, and in particular their consequences for the sum total of human happiness. In Part II Bernard Williams offers a sustained and vigorous critique of utilitarian assumptions, arguments and ideals. He finds inadequate the theory of action implied by utilitarianism, and he argues that utilitarianism fails to engage at a serious level with the real problems of moral and political philosophy, and fails to make sense of notions such as integrity, or even human happiness itself. This book should be of interest to welfare economists, political scientists and decision-theorists.
914 citations
TL;DR: In this article, the authors used fracture mechanics to derive conditions for the propagation of a concentrated shear band in heavily overconsolidated clays and found that the mean resolved shear stress on that surface is markedly less than the peak shear strength.
Abstract: In heavily over-consolidated clays there is a marked peak in the observed relation between shear stress and shear strain. As the strain increases, the stress falls from a peak to a much smaller residual stress. Slopes made from such a clay often fail progressively many years after construction. Sliding occurs on a concentrated slip surface, and it is found that the mean resolved shear stress on that surface is markedly less than the peak shear strength. Concepts from fracture mechanics, and in particular the J -integral, are used to derive conditions for the propagation of a concentrated shear band of this kind. The results indicate the presence of a strong size effect, which has important implications for the use of models in soil mechanics. An elastic analysis makes it possible to determine the size of the end zone in which the shear stress on the shear band falls to its residual value. An attempt is made to assess the possible sources of the time-dependence governing propagation speed of the shear band. They include pore-water diffusion to the dilating tip of the band (which governs the rate at which local strength reductions can occur), viscoelastic deformation of the clay (which allows a gradual build-up of strain concentration at the tip of the band), and the weathering break-down of diagenetic bonds.
883 citations
TL;DR: In this article, an optical interference method is described for measuring thickness and refractive index profiles of thin films trapped between two transparent deformable sheets, which is most suitable for studying very thin films whose thicknesses range from zero to a few thousand angstroms (thickness resolution ∼1 A).
682 citations
TL;DR: In this paper, the conduction of heat through a stationary random suspension of spheres is studied for a volume fraction of the spheres (c) which is small, and the work of Maxwell (1873) is extended to calculate the flux of heat exactly to order c 2 by using the method of Batchelor (1972), which reduces the problem to a consideration of interactions between pairs of spheres while avoiding the usual convergence difficulties.
Abstract: The conduction of heat (or electricity) through a stationary random suspension of spheres is studied for a volume fraction of the spheres (c) which is small. The work of Maxwell (1873) is extended to calculate the flux of heat exactly to order c 2 by using the method of Batchelor (1972), which reduces the problem to a consideration of interactions between pairs of spheres while avoiding the usual convergence difficulties. The result depends on the way in which pairs of spheres are distributed with respect to each other; for the case of all possible pair configurations being equally probable the coefficient of c 2 is found explicitly for all values of the ratio of conductivities of the two phases. The results also apply to permittivities and permeabilities of suspensions.
680 citations
TL;DR: In this article, a simple model is given that describes the response of the upper ocean to an imposed wind stress, which is taken to mix thoroughly a layer of depth h, and to erode the stably stratified fluid below.
Abstract: A simple model is given that describes the response of the upper ocean to an imposed wind stress. The stress drives both mean and turbulent flow near the surface, which is taken to mix thoroughly a layer of depth h, and to erode the stably stratified fluid below. A marginal stability criterion based on a Froude number is used to close the problem, and it is suggested that the mean momentum has a strong role in the mixing process. The initial deepening is predicted to obey where u. is the friction velocity of the imposed stress, N the ambient buoyancy frequency, and t the time. After one-half inertial period the deepening is arrested by rotadeon at a depth h = 22/4 u.{(Nf)+ where f is the Coriolis frequency. The flow is then a “mixed Ekman” layer, with strong inertial oscillations superimposed on it. Three quarters of the mean energy of the deepening layer is found to be kinetic, and only one-quarter potential. Heating and cooling are included in the model, but stress dominates for time-scales of ...
632 citations
01 Jun 1973
TL;DR: In this article, a new theory for multiaxial fatigue is presented that is based on a physical interpretation of the mechanisms of fatigue crack growth, represented graphically by contours of constant life, which are expressed mathematically bywhere e1, e2 and e3 are the principal strains, •e1 ≥ e2 ≥ e3.
Abstract: A new theory for multiaxial fatigue is presented that is based on a physical interpretation of the mechanisms of fatigue crack growth. It may be represented graphically by contours of constant life, which are expressed mathematically bywhere e1, e2 and e3 are the principal strains, •e1 ≥ e2 ≥ e3.This equation underlines the importance of strain parameters in correlating fatigue data. It illustrates the effect of both the shear strain and the tensile strain normal to the plane of maximum shear.The theory is compared with several classical and recent theories, which are briefly reviewed. It is shown that classical theories of fatigue failure cannot correlate experimental data, and may be dangerous if used for design purposes.
588 citations
TL;DR: In this paper, the authors developed the classical and quantum mechanics of a massless relativistic string, the light string, which is characterized by an action proportional to the area of the world sheet swept out by the string in space time.
TL;DR: Twistor theory as mentioned in this paper is a new approach, starting with conformally-invariant concepts, to the synthesis of quantum theory and relativity, and it is represented here in two-component spinor terms.
TL;DR: In this article, six or more distinguishable mechanisms contribute to the sintering of an aggregate of particles, even in the absence of applied stresses, and diagrams can be constructed which identify, at a given temperature, particle size and neck size, the dominant mechanism.
TL;DR: The authors explored the subject of goals and values in the farming occupation as one facet of motivation and suggested that a better understanding of motivation, taken in conjunction with information already available on material resources and constraints, could lead to a more adequate explanation and prediction of farmers' economic behaviour.
Abstract: Economic theory treats motivation as a parameter, explaining variation in economic behaviour in terms of availability of resources. This theory does not provide a wholly convincing account of farmers' actions. It is suggested that a better understanding of motivation, taken in conjunction with information already available on material resources and constraints, could lead to a more adequate explanation and prediction of farmers' economic behaviour. This paper explores the subject of goals and values in the farming occupation as one facet of motivation. Values may refer to instrumental, social, expressive or intrinsic aspects of farming and it is their ordering relative to one another which influences farmers' decisions in situations of choice. Pilot studies suggest that farmers have a predominantly intrinsic orientation to work, valuing the way of life, independence and performance of work tasks above expressive, instrumental or social aspects of their occupation. Comparing value orientations of larger with smaller farmers illustrates some implications and possible uses of this approach.
Resume
BUTS ET VALEURS DANS L'ACTIVITE DE L'EXPLOITANT AGRICOLE
Lu theorie economique traite la motivation comme un parametre, expliquant la variation dans le comportement de l'economie en termes de disponibilite des ressources. Cette theorie ne fournit pas une information entierement convaincante sur l'activite des exploitants agricoles, Une meilleure comprehension de la motivation, utilisee en conjonction avec les donnees deja disponibles sur les ressources et contraintes materielles, pourrait conduire, selon l'argument developpe, a des explications et previsions plus rigoureuses sur le comportement economique des agriculteurs. L'auteur analyse le theme des buts et valeurs dans le metier d'exploitant agricole comme un des aspects de la motivation. Les valeurs peuvent se referer a des aspects professionnels, sociaux, expressifs ou intrinseques de l'exploitation agricole et c'est l'ordre dans lequel elles sont placees relativement les unes aux autres qui influence les decisions des agriculteurs dans les situations de choix. Les etudes pilotes convergent vers la conclusion selon laquelle les exploitants agricoles ont une orientation intrinseque predominante vers le travail, placant le style de vie, l'independance et la qualite des tâches qu'ils accomplissent au-dessus des aspects expressifs, contributifs ou sociaux de leur profession. La comparaison des orientations de valeur entre grands et petits exploitants permet de souligner certaines des implications et des utilisations possibles de cette optique.
Zusammenfassung
ZIELE UND WERTE DER FARMER
Die wirtschaftliche Theorie behandelt die Motivation als einen Parameter, der die Veranderung im wirtschaftlichen Verhalten in Form von verfugbaren Ressourcen erklart. Diese Theorie liefert keine ganz uberzeugende Darstellung der Handlungen von Farmem. Es wird vorgeschlagen, doss ein besseres Verstandnis der Motivation, zusammen mit der Information, die schon uber Materialressourcen und uber die notwendigen Folgerungen bestehen, zu einer angemesseren Erklarung und Vorhersage der wirtschaftlichen Verhaltensweise von Farmern fuhren konnte. Dieser Artikel erforscht das Thema der Ziele und Werte in der Farmtatigkeit als einen Teil der Motivation. Werte konnen sich auf instrumental, soziale, aussere oder innere Aspekte des Farmens beziehen, und es ist ihre Anordung zueinander, die die Entscheidungen der Farmer in einer Entscheidungssituation beeinflussen. Grundstudien lassen den Schluss zu, dass Farmer eine hauptsachlich innere Ausrichtung auf ihre Arbeit haben, wobei sie den Lebensstil, die Unabhangigkeit und die Ausfuhrung ihrer Arbeitsaufgaben hoher einschatzen als ausserliche, instrumental oder soziale Aspekte ihrer Beschaftigung. Der Vergleich der Wertorientierung zwischen grossen und kleinen Farmern veranschaulicht einige Folgerungen und mogliche Anwendungen dieses Ansatzes.
TL;DR: It is suggested that developmental aphasics are incapable of perceiving auditory information at a normal rate, and the possibility is considered that this constraint on the speed of auditory processing may underlie their language impairment.
TL;DR: Hydrodynamical effects appear to be important to obligate schooling species, and the endurance of the fish is found to be increased twice to six times when in schools.
Abstract: VARIOUS explanations for fish schooling have been put forward1, including the rate of predation2,3, social4 and genetic1 factors. Hydrodynamical effects appear to be important to obligate schooling species. They commonly show migratory movements4, and the schools usually consist of individuals of the same size range6,7 (with similar cruising speeds, as these depend on body-length) swimming in synchronization and in regular arrays8. The endurance of the fish is found to be increased twice to six times when in schools16. These factors may have practical significance, as many commercially important species are found in schools and knowledge of their possible speed and stamina can help design efficient fishing gear.
01 Jan 1973
TL;DR: In a follow-up work as mentioned in this paper, the same authors have examined the ambiguity in Smart's defence of act-utilitarianism, as against other sorts, arising from a deep difficulty in the whole subject.
Abstract: If we possess our why of life we can put up with almost any how . – Man does not strive after happiness; only the Englishman does that. Nietzsche, The Twilight of the Idols Introductory This essay is not designed as a reply to Smart's. It has been written after it, in knowledge of it, and from an opposed point of view, but it does not try to answer his arguments point for point, nor to cover just the same ground. Direct criticism of Smart's text is largely confined to parts of section 6, where I have tried to show that a certain ambiguity in Smart's defence of act-utilitarianism, as against other sorts, arises from a deep difficulty in the whole subject. I have not attempted, either, to give an account of all the important issues in the area, still less a critical survey of the major items in the literature; I have pursued those questions which seemed to me the most interesting and have deliberately left out a number of things which are often discussed. Like Smart, I have very largely treated utilitarianism as a system of personal morality rather than as a system of social or political decision, but I have tried to say something, very much in outline, about political aspects in section 7.
TL;DR: Parathyroid hormone, secreted in response to decreasing blood calcium concentration, stimulates formation of the kidney hormone, 1,25-dihydroxy-cholecalciferol.
Abstract: Parathyroid hormone, secreted in response to decreasing blood calcium concentration, stimulates formation of the kidney hormone, 1,25-dihydroxy-cholecalciferol.
TL;DR: In this article, a study of the distribution of temperature and salinity in the Weddell Sea is presented, showing that there is a circulation on the shelf in the vertical plane which carries about 106 m3sec−1 of water off the shelf.
TL;DR: Although areAr mutations prevent utilisation of L-arginine, L-ornithine, and L-α-amino-n-butyrate as nitrogen sources, they do not prevent the metabolism of these compounds necessary for repairing auxotrophies for proline and isoleucine in the appropriate double mutants.
Abstract: In Aspergillus nidulans, mutations, designated areAr, can result in the inability to utilise a wide variety of nitrogen sources including amino acids, purines, amides, nitrate, and nitrite, whilst not affecting growth on ammonium. Other allelic areA mutations, designated areAd, lead to derepression of one or more activities which are ammonium repressible in wild type (areA+) strains, whilst not affecting their inducibility. Various areA mutations exhibit a wide variety of phenotypes: areAr alleles can be temperature sensitive on some nitrogen sources while not on others, and different alleles can be temperature sensitive for utilisation of different nitrogen sources. areAd alleles can be derepressed for one ammonium-repressible activity, be normally repressible for another, and lead to abnormally low levels for a third. Once again each areAd allele has its own highly specific phenotype. The inability of areAr strains to utilise most nitrogen sources is paralleled by low activities of certain ammonium-repressible enzymes. areAr mutations appear to be epistatic to some but not all regulatory mutations leading to constitutive synthesis of inducible enzymes and also epistatic to gdhA mutations which lead both to loss of NADP-linked glutamate dehydrogenase and to derepression of ammonium-repressible activities.
areAr mutations do not interfere with repair of a large number of auxotrophies in double mutants. Furthermore, although areAr mutations prevent utilisation of L-arginine, L-ornithine, and L-α-amino-n-butyrate as nitrogen sources, they do not prevent the metabolism of these compounds necessary for repairing auxotrophies for proline and isoleucine in the appropriate double mutants. Utilisation of acetamide and most amino acids as carbon or carbon and nitrogen sources is unaffected by areAr mutations, and areAr strains are able to utilise acetamide and L-proline (but not other amino acids) as nitrogen sources in the presence of non-catabolite-repressing carbon sources such as L-arabinose, glycerol, melibiose, and lactose. Suppressor mutations, designated creAd, probably leading to loss of carbon catabolite repression, allow utilisation of acetamide and proline as nitrogen sources in areAr double mutants in the presence of carbon catabolite-repressing carbon sources. creAd mutations allow ethanol to serve as a source of acetate for pyruvate dehydrogenaseless (pdhA) strains in the presence of carbon catabolite-repressing carbon sources, whereas pdhA single mutants respond to ethanol as sole carbon source only in the presence of non-carbon catabolite-repressing carbon sources. Specific suppressor mutations, designated amd
d and prn
d, allow utilisation of acetamide or proline, respectively, in areAr double mutants. The areA locus can be interpreted as specifying a protein which is capable of (and in most cases essential for) allowing the synthesis of a number of enzymes of nitrogen metabolism but which cannot function in the presence of ammonium (i.e., as specifying a positive regulatory element which mediates ammonium repression) although the possibility that the areA product also plays a negative regulatory role cannot at present be ruled out.
TL;DR: A double-blind prospective trial of prednisone versus azathioprine in the treatment of forty-seven patients with active chronic hepatitis over a 2-year period showed thatprednisone was superior at improving liver function, preventing the development of œsophageal varices, and prolonging survival.
TL;DR: In this paper, the first-order necessary optimality conditions of an optimal control problem for a distributed parameter system with geometric control were obtained for the minimum-drag problem in Stokes flow (flow at a very low Reynolds number).
Abstract: In this paper, we obtain the first-order necessary optimality conditions of an optimal control problem for a distributed parameter system with geometric control, namely, the minimum-drag problem in Stokes flow (flow at a very low Reynolds number). We find that the unit-volume body with smallest drag must be such that the magnitude of the normal derivative of the velocity of the fluid is constant on the boundary of the body. In a three-dimensional uniform flow, this condition implies that the body with minimum drag has the shape of a pointed body similar in general shape to a prolate spheroid but with some differences including conical front and rear ends of angle 120°.
TL;DR: 6-Hydroxydopamine was administered intraventricularly to neonatal rats in order to rear adults with severe catecholamine depletions, suggesting the probable primacy of dopaminergic systems for the mediation of the locomotor response to amphetamine.
TL;DR: Weis-Fogh as mentioned in this paper proposed a new mechanism of lift generation, which could work even in inviscid two-dimensional motions starting from rest, when Kelvin's theorem states that the total circulation round a body must vanish, but does not exclude the possibility that if the body breaks into two pieces then there may be equal and opposite circulations round them, each suitable for generating the lift required in the pieces' subsequent motions.
Abstract: Weis-Fogh (1973) proposed a new mechanism of lift generation of fundamental interest. Surprisingly, it could work even in inviscid two-dimensional motions starting from rest, when Kelvin's theorem states that the total circulation round a body must vanish, but does not exclude the possibility that if the body breaks into two pieces then there may be equal and opposite circulations round them, each suitable for generating the lift required in the pieces’ subsequent motions! The ‘fling’ of two insect wings of chord c (figure 1) turning with angular velocity Ω generates irrotational motions associated with the sucking of air into the opening gap which are calculated in § 2 as involving circulations −0·69Ωc2 and + 0.69Ωc2 around the wings when their trailing edges, which are stagnation points of those irrotational motions, break apart (position (f)). Viscous modifications to this irrotational flow pattern by shedding of vorticity at the boundary generate (§ 3) a leading-edge separation bubble, and tend to increase slightly the total bound vorticity. Its role in a three-dimensional picture of the Weis-Fogh mechanism of lift generation, involving formation of trailing vortices at the wing tips, and including the case of a hovering insect like Encarsia formosa moving those tips in circular paths, is investigated in § 4. The paper ends with the comment that the far flow field of such very small hovering insects should take the form of the exact solution (Landau 1944; Squire 1951) of the Navier-Stokes equations for the effect of a concentrated force (the weight mg of the animal) acting on a fluid of kinematic viscosity v and density p, whenever the ratio mg/pv2 is small enough for that jet-type induced motion to be stable.
TL;DR: In this article, the authors examined spatially homogeneous cosmological models in which the matter content of space-time is a perfect fluid, and the fluid flow vector is not normal to the surfaces of homogeneity.
Abstract: We examine spatially homogeneous cosmological models in which the matter content of space-time is a perfect fluid, and in which the fluid flow vector is not normal to the surfaces of homogeneity. In such universes, the matter may move with non-zero expansion, rotation and shear; we examine the relation between these kinematic quantities and the Bianchi classification of the symmetry group. Detailed characterizations of some of the simplest such universe models are given.
TL;DR: In this article, the behavior at low temperatures can be described using Mott's variable range hopping arguments, and at high temperatures by non-adiabatic small polaron hopping between nearest neighbours.
Abstract: Dc conductivity measurements have been made between 90 and 520 K on three bulk samples of V 2 O 5 P 2 O 5 glass. Heat treatment is found to result in a reduction of the activation energy at a given temperature and this is most noticeable at low temperatures. The behaviour at low temperatures can be described using Mott's variable range hopping arguments, and at high temperatures by non-adiabatic small polaron hopping between nearest neighbours. At intermediate temperatures a simple model is used in which excitations by optical and acoustic phonons are considered to make independent contributions to the jump frequency. Mott's theory is extended to the polaron case for T> 1 4 ⊖ and is shown to be in good agreement with results. Values for r p (∼2.8 A ) the polaron radius and α(∼3.5 A −1 ) the electron decay constant are shown to be consistent with the model for small polarons. A method is suggested for obtaining α and N ( E F ) from the ac conductivity and the slope of 1nσ versus 1 T 1 4 at low temperatures. Values of N ( E ) are obtained which correlate with those obtained by the previous analysis. This implies that the disorder energy separating adjacent sites Δ 0 is large (∼0.4 eV) in these materials.