Showing papers by "University of Cambridge published in 1974"
TL;DR: In this article, it was shown that any black hole will create and emit particles such as neutrinos or photons at just the rate that one would expect if the black hole was a body with a temperature of (κ/2π) (ħ/2k) ≈ 10−6 (M/M)K where κ is the surface gravity of the body.
Abstract: QUANTUM gravitational effects are usually ignored in calculations of the formation and evolution of black holes. The justification for this is that the radius of curvature of space-time outside the event horizon is very large compared to the Planck length (Għ/c3)1/2 ≈ 10−33 cm, the length scale on which quantum fluctuations of the metric are expected to be of order unity. This means that the energy density of particles created by the gravitational field is small compared to the space-time curvature. Even though quantum effects may be small locally, they may still, however, add up to produce a significant effect over the lifetime of the Universe ≈ 1017 s which is very long compared to the Planck time ≈ 10−43 s. The purpose of this letter is to show that this indeed may be the case: it seems that any black hole will create and emit particles such as neutrinos or photons at just the rate that one would expect if the black hole was a body with a temperature of (κ/2π) (ħ/2k) ≈ 10−6 (M/M)K where κ is the surface gravity of the black hole1. As a black hole emits this thermal radiation one would expect it to lose mass. This in turn would increase the surface gravity and so increase the rate of emission. The black hole would therefore have a finite life of the order of 1071 (M/M)−3 s. For a black hole of solar mass this is much longer than the age of the Universe. There might, however, be much smaller black holes which were formed by fluctuations in the early Universe2. Any such black hole of mass less than 1015 g would have evaporated by now. Near the end of its life the rate of emission would be very high and about 1030 erg would be released in the last 0.1 s. This is a fairly small explosion by astronomical standards but it is equivalent to about 1 million 1 Mton hydrogen bombs. It is often said that nothing can escape from a black hole. But in 1974, Stephen Hawking realized that, owing to quantum effects, black holes should emit particles with a thermal distribution of energies — as if the black hole had a temperature inversely proportional to its mass. In addition to putting black-hole thermodynamics on a firmer footing, this discovery led Hawking to postulate 'black hole explosions', as primordial black holes end their lives in an accelerating release of energy.
4,511 citations
Book•
23 Apr 19742,537 citations
TL;DR: Perceptual segregation in an alternated pair of random-dot patterns was perceived as a segregated, coherently moving shape only if the displacement was small, while classical apparent motion with larger displacements involves a different process.
872 citations
713 citations
TL;DR: In this article, the change in energy dissipation due to a small hump on a body in a uniform steady flow is calculated, and the result is used in conjunction with the variational methods of optimal control to obtain the optimality conditions for four minimum-drag problems of fluid mechanics.
Abstract: In this paper, the change in energy dissipation due to a small hump on a body in a uniform steady flow is calculated. The result is used in conjunction with the variational methods of optimal control to obtain the optimality conditions for four minimum-drag problems of fluid mechanics. These conditions imply that the unit-area profile of smallest drag has a front end shaped like a wedge of angle 90°.
699 citations
TL;DR: In this article, a review of the geophysical information and the fluid dynamics of convection in a Boussinesq fluid of infinite Prandtl number is presented and analyzed in terms of simple physical models.
Abstract: Plate tectonics provides a remarkably accurate kinematic description of the motion of the earth's crust but a fully dynamical theory requires an understanding of convection in the mantle. Thus the properties of plates and of the mantle must be related to a systematic study of convection. This paper reviews both the geophysical information and the fluid dynamics of convection in a Boussinesq fluid of infinite Prandtl number. Numerical experiments have been carried out on several simple two-dimensional models, in which convection is driven by imposed horizontal temperature gradients or else by heating either internally or from below. The results are presented and analysed in terms of simple physical models. Although the computations are highly idealized and omit variation of viscosity and other major features of mantle convection, they can be related to geophysical measurements. In particular, the external gravity field depends on changes in surface elevation; this suggests an observational means of investigating convection in the upper mantle.
662 citations
TL;DR: It is concluded that the retrograde axonal transport of NGF, which was estimated to take place at a rate of about 2.5 mm/h, depends on a colchicine-sensitive mechanism as does the orthograde rapid axonal transports, however, the uptake of N GF may not only take place from the nerve terminals but also from the preterminal parts, as has been shown in other studies with horseradish peroxidase.
569 citations
TL;DR: It is hypothesized that it is the brief duration of formant transitions which results in dysphasics' inability to discriminate consonant stimuli, and this deficit may be sufficient to explain the speech disorder of these children.
551 citations
TL;DR: The mechanisms which have been suggested to explain the deformation of crystalline polymers are reviewed in this article, where emphasis has been placed upon the type of information that can be gained from experimental observations and on the extent to which those observations are consistent with suggested deformation mechanisms and current ideas on polymer structure and morphology.
Abstract: The mechanisms which have been suggested to explain the deformation of crystalline polymers are reviewed. Emphasis has been placed upon the type of information that can be gained from experimental observations and on the extent to which those observations are consistent with suggested deformation mechanisms and current ideas on polymer structure and morphology.
437 citations
TL;DR: It is shown that dopamine antagonists antagonise amphetamine induced behaviour in man and animals and block the stimulating effects of dopamine on cyclic AMP production in homogenates of rat brain striatum or mesolimbic nuclei.
Abstract: ONE unifying hypothesis of the behavioural effects produced by neuroleptic drugs is that they act by blocking dopamine receptors in the central nervous system1–3. Neuroleptic drugs produce increases in dopamine turnover4, increase accumulation of its metabolites5, antagonise amphetamine induced behaviour in man and animals6 and block the stimulating effects of dopamine on cyclic AMP production in homogenates of rat brain striatum or mesolimbic nuclei7–9.
TL;DR: It is postulated that fixed C3 interacting with macrophage and B-cell C3 receptors might enhance or facilitate T-dependent presentation of antigen to B cells.
Abstract: In an in vivo study in mice, suppression by the C3-cleaving protein of cobra venom (CoF), and other C3-reactive agents (zymosan, aggregated IgG, anti-C3 antibodies, and type III pneumococcal polysaccharide) of the thymus-dependent antibody responses to sheep erythrocytes, ovalbumin, and human IgG was demonstrated. The thymus-independent antibody response to polyvinyl-pyrrolidone was however unaffected by CoF. These and other published observations suggest that there may be a requirement for functional C3 in induction of thymus-dependent but not thymus-independent antibody production. A model for the role of C3 in lymphocyte cooperation is proposed based on these data analyzed in the light of existing knowledge of this process. It is postulated that fixed C3 interacting with macrophage See PDF for Structure and B-cell C3 receptors might enhance or facilitate T-dependent presentation of antigen to B cells.
TL;DR: Three families have been described in which diabetes, although usually diagnosed in the teens or early 20s, is mild and does not progress to insulin dependence even over a period of 40 years, which provides evidence of the genetic heterogeneity of diabetes mellitus.
Abstract: Three families have been described in which diabetes, although usually diagnosed in the teens or early 20s, is mild and does not progress to insulin dependence even over a period of 40 years. This syndrome seems to be inherited as a Mendelian dominant because (1) there is direct parent to child inheritance through at least three generations (2) the ratio of affected: unaffected children of diabetic parents is 1:1 and (3) almost all affected individuals have a diabetic parent. Complications are uncommon and mild. Seven out of 12 diabetics diagnosed under the age of 30 and having a mean duration of diabetes of 37 years did not have any retinopathy. No death from diabetes has ever been recorded in any of the families. In two families diabetes is associated with a low renal threshold for glucose. This syndrome is distinct from the more usual type of juvenile diabetes mellitus and provides evidence of the genetic heterogeneity of diabetes mellitus.
TL;DR: High concentrations of dopamine were found in the nucleus accumbens and olfactory tubercle of the rat brain using a radiochemical enzymatic assay technique, and an active uptake system for [3H]dopamine that is temperature sensitive and dependent on external sodium ions is present in synaptosome‐rich homogenates of these two brain areas.
Abstract: — High concentrations of dopamine were found in the nucleus accumbens and olfactory tubercle of the rat brain using a radiochemical enzymatic assay technique. An active uptake system for [3H]dopamine that is temperature sensitive and dependent on external sodium ions is present in synaptosome-rich homogenates of these two brain areas. This uptake process is potently inhibited by benztropine (IC50= 2.0 × 10-7m). Dextroamphetamine d was 4.5 times more potent than 1-amphetamine in inhibiting dopamine uptake in the nucleus accumbens and six times more potent in the olfactory tubercle and corpus striatum. Low concentrations of dopamine caused an increase in adenosine 3′5′-monophosphate (cyclic AMP) formation in homogenates of both the nucleus accembens and olfactory tubercle. This effect was potently blocked by chlorpromazine. The α-adrenoceptor antagonist phentolamine weakly antagonized the stimulation of this adenylate cyclase by dopamine, but the β-adrenoceptor antagonist propranolol did not.
TL;DR: In this paper, the connection between conventional matrix methods for layered media and the reflection and transmission properties of a single layer is established, and an iterative approach to the calculation of reflection coefficients in multilayered media is proposed.
Abstract: The connection is established between conventional matrix methods for layered media and the reflection and transmission properties of a single layer. This interrelation is then used to set up an iterative approach to the calculation of reflection and transmission coefficients in multilayered media. This approach lends itself to a ray interpretation and allows estimates of errors involved in taking truncated partial ray expansions to be made. The special effects due to a free surface are also considered.
TL;DR: The results demonstrate that amphetamine is an indirect sympathomimetic agent and further emphasize the critical role of the dopaminergic nigrostriatal pathway in amphetamine induced stereotypy.
Abstract: The caudate nucleus or the tuberculum olfactorium of the rat was lesioned by bilateral stereotaxic injection of 6-hydroxydopamine. The degree of dopamine depletion was assessed by a sensitive regional dopamine assay and revealed severe depletions in the lesioned areas. The locomotor response to a low dose of d-amphetamine was not modified by either lesion. However, the stereotypy response to a high dose of amphetamine was abolished by the caudate lesion. The stereotypy response was not modified by lesion to the tuberculum olfaotorium. Neither lesion abolished the stereotypy response to apomorphine. The results therefore demonstrate that amphetamine is an indirect sympathomimetic agent and further emphasize the critical role of the dopaminergic nigrostriatal pathway in amphetamine induced stereotypy.
TL;DR: In this article, it was shown that the available potential energy in the large-scale mean ocean circulation, excluding the boundary layers, is of order ( BI a) s times the kinetic energy, where B is the basin dimension and a is the internal radius of deformation (c is the speed of long internal waves andfthe Corinlis parameter).
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TL;DR: In this article, the authors propose a method to generate a subgroup of finite index in the Weil curve of any WeiI curve, which is based on the winding number and complex L-series of Weil curves.
Abstract: w 2. Well Curves . . . . . . . . . . . . . . . . . . . . . . 4 (2.1) Deflmtions . . . . . . . . . . . . . . . . . . . . . 4 (2.2) The Winding Number . . . . . . . . . . . . . . . . 7 (2.3) The Complex L-Series o f a Weil Curve . . . . . . . . . 8 (2.4) Is there a "Geometr ic Method*" of Generating a Subgroup of Finite Index in the Mordell-Weil G r o u p of Any WeiI Curve? . . . . . . . . . . . . . . . . . . . . . . 9
TL;DR: Paediatricians in Copenhagen have shown that, by timely treatment of severe febrile convulsions in infants followed by prophylactic therapy with phenobarbitone, later habitual epilepsy can be avoided and both Ammon's horn sclerosis and its consequent epilepsy are probably preventable.
TL;DR: Synaptic vesicles separated by density-gradient centrifugation from extracts of the cholinergic nerve terminals of the electric organ of Torpedo marmorata were found to contain appreciable amounts of ATP as well as acetylcholine, suggesting some degree of chemical heterogeneity in the vesicle population.
Abstract: 1. Synaptic vesicles separated by density-gradient centrifugation from extracts of the cholinergic nerve terminals of the electric organ of Torpedo marmorata were found to contain appreciable amounts of ATP as well as acetylcholine. 2. Vesicular ATP was stable in the presence of concentrations of apyrase and myokinase that rapidly destroyed equivalent amounts of endogenous or added free ATP; pre-treatment of cytoplasmic extracts of electric tissue with these enzymes destroyed endogenous free ATP, but did not affect the vesicular ATP. 3. When [U-14C]ATP was added to electric tissue at the time of comminution and extraction of the vesicles, all the radioactivity was associated with soluble components in the subsequent fractionation: none was associated with vesicles or membrane fragments; thus it is unlikely that vesicular ATP can be accounted for by the sequestration of endogenous free ATP within any vesicles formed during comminution and extraction of the tissue. 4. When synaptic vesicles were passed through iso-osmotic columns of Bio-Gel A-5m, which separates vesicles from soluble proteins and small molecules, all the recovered ATP and acetylcholine passed through together in the void volume. 5. Regression analysis showed that vesicular ATP content was highly correlated with vesicular acetylcholine content in different experiments, the molar ratio acetylcholine/ATP being 5.32±(s.e.m.) 0.45 (21 expts.) for the peak density-gradient fraction. The ratio varied, however, somewhat across the density-gradient peak suggesting some degree of chemical heterogeneity in the vesicle population.
TL;DR: In this paper, the effect of personal and corporate taxation on both the firm's choice of financial policy and its investment decision is analysed, and the results have implications for the specification of the neoclassical investment model which has come to play such an important part in the econometric study of investment behavior.
Abstract: The way in which taxation affects corporate financial policy, and the level of investment through the structure of the cost of capital, is still a bone of contention. Various specifications of the cost of capital have been used in econometric models (for example, Jorgenson [3]) although in a recent theoretical paper Stiglitz [10] has claimed that, ignoring uncertainty, the cost of capital is simply the rate of interest.3 In this paper we shall analyse the effect of personal and corporate taxation on both the firm's choice of financial policy and its investment decision. We shall see that the latter is influenced by the former because the cost of capital depends upon the optimal financial policy. The results have implications for the specification of the neoclassical investment model which has come to play such an important part in the econometric study of investment behaviour, because the cost of capital is a good deal more complicated than most of this work allows for. Another problem which will be examined is how expectations of future changes in tax rates affect the firm's policy. In recent years governments have often announced tax changes in advance, and increasing attention is being paid to the use of announcements of future tax changes as a policy tool in its own right. These announcement effects can have a significant impact on investment behaviour. To make it easier to see the role of taxation we shall assume a world of perfect certainty. There are three justifications for this neglect of uncertainty. First, when tax changes are announced in advance, expectations that these changes will take place are held with a very high degree of certainty. Secondly, this assumption makes our results directly comparable with those of the neoclassical investment model. Finally, in a world of certainty we know that the firm will, if it is acting in the shareholders' interests, maximize the market value of the stock. But in a world of uncertainty which does not have a complete set of Arrow-Debreu markets it is not clear just what the firm should be trying to maximize. This is because shareholders have different subjective beliefs about what the best policy is, and there are no contingent commodity markets for them to hedge on. If one shareholder believes that the firm would make enormous profits by drilling for oil in the North Sea and nobody else believes that this would be successful, then for this shareholder the optimal policy is to drill even though the market value of the firm's stock would slump in the short run.4 Section 2 discusses a model of the valuation of the company and the way in which this is influenced by taxation. This brings out the interaction between the systems of personal and corporate taxation. In Section 3 we analyse the firm's optimal financial policy where it has a choice between financing investment by using retentions, borrowing, or
TL;DR: The interaction of haemin with human serum albumin has been reexamined, and it is suggested, on the basis of an interaction of albumin with iron-free protoporphyrin IX, that the iron is not implicated in the interaction with the protein.
Abstract: The interaction of haemin with human serum albumin has been reexamined. The absorption spectrum of the bound haem is identical with that of uncomplexed monomeric haemin in solution, and it is suggested, on the basis of an interaction of albumin with iron-free protoporphyrin IX, that the iron is not implicated in the interaction with the protein. A ferric cyanide derivative, and a ferrous haem derivative of methaemalbumin can be recognised, but not azide or fluoride derivatives. The bound haemin gives rise to extrinsic Cotton effects, which are different in detail in the derivatives, and in the complex with protoporphyrin IX Spectrophotometric titrations show that there is one strong binding site for haemin and several weaker sites. The latter are associated with optical activity opposite in sign to that of the strong complex. The binding profiles are little affected by pH over a wide range, by ionic strength or by the presence of 40% (v/v) dimethylsulphoxide/water, in which the free haemin is monomeric. The binding of haemin to albumin has been followed by spectrophotometry, circular dichroism and fluorescence. The binding of haemin quenches the protein fluorescence, which progressively changes in character from tryptophan to tyrosine type. The haem at the primary binding site thus strongly quenches the tryptophan specifically. From fluorescence titrations at a range of protein concentrations, binding isotherms were constructed, and gave an association constant for the strong site of 50 μM−1. From binding isotherms based on absorption measurements we can infer the existence of at least four sites with much lower binding constants. A long-chain fatty acid anion was found to compete with haemin only for the weaker binding sites, so that binding beyond one mole per mole of protein can be essentially eliminated. The open-chain tetrapyrrole, bilirubin, was found, in agreement with earlier work, not to compete with haemin, as regards the strongest binding sites of either ligand. Between the weaker sites, however, evidence of competition was obtained.
TL;DR: In this article, a boundary-layer approximation is made to the equations governing the local response to these forcing systems, and the lowfrequency response can be expressed as a sum of modes (continental shelf waves) and the amplitude of each mode is found to satisfy a first-order wave equation which can readily be solved.
Abstract: Currents [O(0.1 m sec−1)] and sea-level variations [O(0.1 m)] on the continental shelf can be produced when atmospheric disturbances pass by. Since the atmospheric systems have length scales large compared with the width of the shelf, a boundary-layer approximation can be made to the equations governing the local response to these forcing systems. The low-frequency response can be expressed as a sum of modes (continental shelf waves) and the amplitude of each mode is found to satisfy a first-order wave equation which can readily be solved. In a case where some details are worked out, the second mode's contribution to sea-level changes is only 25% of the first mode's and the third mode's contribution only 8%. Thus, given appropriate meteorological information, sea level changes can easily be calculated, and a prediction system is theoretically possible.
TL;DR: In this paper, the problem of coastal and equatorial upwelling induced by changing wind patterns is considered and the solution of the linearized problem can be expressed as a sum of modes, the amplitude of each satisfying a first order wave equation.
TL;DR: The interactions of time and the environment on the growth of animals and of their organs are complex and theories that have been formulated are discussed, but none of those yet put forward explain all the facts that can be demonstrated experimentally.
Abstract: An animal can only achieve its full genetic potential if it has lived its life in an ideal environment. Few environments are ideal; they may be unfavourable for numerous reasons and for different lengths of time. Indeed, variations on these themes are almost infinitely possible, but concrete examples will be selected and their effects on the lives of animals and of man demonstrated. Time comes into all this, but its importance and the difference between chronological and biological time have not been properly appreciated. The interactions of time and the environment on the growth of animals and of their organs are complex, but recent work on malnutrition and growth has given us some insight into the matter. Theories that have been formulated are discussed, but none of those yet put forward explain all the facts that can be demonstrated experimentally, and studies that might provide clues have been neglected.
TL;DR: The progressive liver damage of active chronic hepatitis is due, it is postulated, to an autoimmune reaction directed against an hepatocyte surface lipoprotein which is initiated in most cases by a hepatitis-B-virus infection.
TL;DR: In this paper, it was shown how to construct a set of reduced multipole moments of the charge-current vector for an extended body in arbitrary gravitational and electromagnetic fields, and the uniqueness of the chosen set of moments was investigated, leading to the discovery of properties which are sufficient to characterize them uniquely.
Abstract: A study is made of the motion of an extended body in arbitrary gravitational and electromagnetic fields In a previous paper it was shown how to construct a set of reduced multipole moments of the charge-current vector for such a body This is now extended to a corresponding treatment of the energy-momentum tensor It is shown that, taken together, these two sets of moments have the following three properties First, they provide a full description of the body, in that they determine completely the energy-momentum tensor and charge-current vector from which they are constructed Secondly, they include the total charge, total momentum vector and total angular momentum (spin) tensor of the body Thirdly, the only restrictions on the moments, apart from certain symmetry and orthogonality conditions, are the equations of motion for the total momentum and spin, and the conservation of total charge The time dependence of the higher moments is arbitrary, since the process of reduction used to construct the moments has eliminated those contributions to these moments whose behaviour is determinate The uniqueness of the chosen set of moments is investigated, leading to the discovery of a set of properties which is sufficient to characterize them uniquely The equations of motion are first obtained in an exact form Under certain conditions, the contributions from the moments of sufficiently high order are seen to be negligible It is then convenient to make the multipole approximation, in which these high order terms are omitted When this is done, further simplifications can be made to the equations of motion It is shown that they take an especially simple form if use is made of the extension operator of Veblen & Thomas This is closely related to repeated covariant differentiation, but is more useful than that for present purposes By its use, an explicit form is given for the equations of motion to any desired multipole order It is shown that they agree with the corresponding Newtonian equations in the appropriate limit
TL;DR: Twenty-two patients with fulminant hepatic failure who deteriorated to grade-IV coma despite full supportive therapy were treated by repeated periods of haemoperfusion through columns containing activated charcoal, and follow-up liver biopsies showed restitution of the normal lobular architecture.
TL;DR: The responses of cells in the cat's visual cortex to a moving bar of light have been analysed quantitatively, using an integration of the post-stimulus time histogram, with particular reference to orientation selectivity.
Abstract: The responses of cells in the cat's visual cortex to a moving bar of light have been analysed quantitatively, using an integration of the post-stimulus time histogram, with particular reference to orientation selectivity. The method is assessed as to its reliability and usefulness; it is shown that much precise information about a cell can be derived from its orientational tuning curve.