Showing papers by "Imperial College London published in 1972"

Regression Models and Life-Tables

Abstract: The analysis of censored failure times is considered. It is assumed that on each individual arc available values of one or more explanatory variables. The hazard function (age-specific failure rate) is taken to be a function of the explanatory variables and unknown regression coefficients multiplied by an arbitrary and unknown function of time. A conditional likelihood is obtained, leading to inferences about the unknown regression coefficients. Some generalizations are outlined.

A novel finite difference formulation for differential expressions involving both first and second derivatives

Abstract: It is shown that the upwind difference scheme of formulating differential expressions, in problems involving transport by simultaneous convection and diffusion, is superior to the central differences scheme, when the local Peclet number of the grid is large. Even better schemes are derived and discussed. It is pointed out that the best finite differences analogues are found by approximating differential expressions as a whole, and that simple (e.g. one-dimensional) exact solutions form a useful, legitimate and independent source of these optimum algebraic formulae.

Outliers in Time Series

Abstract: THE detection of outliers has mainly been considered for single random samples, although some recent work deals also with standard linear models; see, for example, Anscombe (1960) and Kruskal (1960). Essentially similar problems arise in time series (Burman, 1965) but there seems no published work taking into account correlations between successive observations. In the past, the search for outliers in time series has been based on the assumption that the observations are independently and identically normally distributed. This assumption leads to analyses which will be called random sample procedures. Two types of outlier that may occur in a time series are considered in this paper. A Type I outlier corresponds to the situation in which a gross error of observation or recording error affects a single observation. A Type II outlier corresponds to the situation in which a single "innovation" is extreme. This will affect not only the particular observation but also subsequent observations. For the development of tests and the interpretation of outliers, it is necessary to distinguish among the types of outlier likely to be contained in the process. The present approach is based on four possible formulations of the problem: the outliers are all of Type I; the outliers are all of Type II; the outliers are all of the same type but whether they are of Type I or of Type II is not known; and the outliers are a mixture of the two types. Since more practical solutions than those given by likelihood ratio methods are often obtained from simplifications of likelihood ratio criteria, some simpler criteria are derived. These criteria are of the form /&2a, where A is the estimated error in the observation tested and ^ is the estimated standard error of A. Throughout this paper, trend and seasonal components are assumed either negligible or to have been eliminated. The method adopted to remove these components might affect the results in some way.

The reattachment and relaxation of a turbulent shear layer

Abstract: Existing experiments on the low-speed flow downstream of steps and fences, and some new measurements downstream of a backward-facing step, are used to demonstrate the complicated nature of the flow in the reattachment region and its effect on the slow non-monotonic return of the shear layer to the ordinary boundary-layer state. A key feature of the flow is found to be the splitting of the shear layer at reattachment, where part of the flow is deflected upstream into the recirculating flow region to supply the entrainment; the part of the flow that continues downstream suffers a pronounced decrease in eddy length scale, evidently because the larger eddies are torn in two. This phenomenon will occur in all cases where a shear layer reattaches after a prolonged region of separation, either at low speed or in supersonic flow. For simplicity, the discussion in the present paper is confined to low-speed flows.

The Analysis of Multivariate Binary Data

Abstract: A brief review is given of the main methods and models for the analysis of multivariate binary data. The relation with standard second‐order techniques is discussed.

Fracture under complex stress — The angled crack problem

Abstract: Experiments are described in which thin plates of polymethylmethacrylate were fractured with cracks set at various angles to an applied uniaxial stress. While there is substantial agreement with previous analytical predictions, it is shown that inclusion of the stress component parallel to the crack can improve the correlation between linear theory and experiment, using a critical stress at a critical distance interpretation of the stress intensity factor criterion.

An Investigation of the Flow around Rectangular Cylinders

Abstract: Measurements are presented of the base pressure coefficient, drag coefficient and Strouhal number of rectangular cylinders. The results confirm a finding in Japan that the drag coefficient rises to nearly 3 when the depth of the section is just over half the width. The flow around the sections is found to be strongly influenced by the presence of the trailing-edge corners.

Solution-transfer, an Important Geological Deformation Mechanism

Abstract: Several features common in sedimentary rocks which have been subjected to gravitational compaction or mountain-building movements can be explained in terms of “solution-transfer”, that is, redistribution of minerals by “pressure-solution” and “crystallization” (sometimes known as “Riecke's principle”). A physical explanation of the process based on non-hydrostatic thermodynamic theory is presented here, drawing attention to examples in tectonically deformed rocks.

The motion of a vortex filament with axial flow

Abstract: Infinitesimal waves on a uniform vortex with axial flow are studied The equation for the frequency of helical waves is obtained, and solved for the case of long waves which leave the internal structure almost unaltered A method is developed to obtain results for vortices of non-uniform structure and for displacements which are not necessarily small compared with the core radius The approach consists of balancing the Kutta—Joukowski lift force, the momentum flux due to the axial motion, and the ‘tension’ of the vortex lines A general equation for the motion of a vortex filament is obtained, valid for arbitrary shape and internal structure, and in the presence of an external irrotational velocity field When the axial flow vanishes, the method is equivalent to using the Biot—Savart law for the self-induced velocity, with a suitable cutoff The impulse of a vortex filament is discussed and its rate of change is given

Metabolism of [14C]methamphetamine in man, the guinea pig and the rat

Abstract: 1. The metabolites of (+/-)-2-methylamino-1-phenyl[1-(14)C]propane ([(14)C]methamphetamine) in urine were examined in man, rat and guinea pig. 2. In two male human subjects receiving the drug orally (20mg per person) about 90% of the (14)C was excreted in the urine in 4 days. The urine of the first day was examined for metabolites, and the main metabolites were the unchanged drug (22% of the dose) and 4-hydroxymethamphetamine (15%). Minor metabolites were hippuric acid, norephedrine, 4-hydroxyamphetamine, 4-hydroxynorephedrine and an acid-labile precursor of benzyl methyl ketone. 3. In the rat some 82% of the dose of (14)C (45mg/kg) was excreted in the urine and 2-3% in the faeces in 3-4 days. In 2 days the main metabolites in the urine were 4-hydroxymethamphetamine (31% of dose), 4-hydroxynorephedrine (16%) and unchanged drug (11%). Minor metabolites were amphetamine, 4-hydroxyamphetamine and benzoic acid. 4. The guinea pig was injected intraperitoneally with the drug at two doses, 10 and 45mg/kg. In both cases nearly 90% of the (14)C was excreted, mainly in the urine after the lower dose, but in the urine (69%) and faeces (18%) after the higher dose. The main metabolites in the guinea pig were benzoic acid and its conjugates. Minor metabolites were unchanged drug, amphetamine, norephedrine, an acid-labile precursor of benzyl methyl ketone and an unknown weakly acidic metabolite. The output of norephedrine was dose-dependent, being about 19% on the higher dose and about 1% on the lower dose. 5. Marked species differences in the metabolism of methamphetamine were observed. The main reaction in the rat was aromatic hydroxylation, in the guinea pig demethylation and deamination, whereas in man much of the drug, possibly one-half, was excreted unchanged.

Fully developed asymmetric flow in a plane channel

Abstract: The paper presents the results of a detailed experimental examination of fully developed asymmetric flow between parallel planes. The asymmetry was introduced by roughening one of the planes while the other was left smooth; the ratio of the shear stresses at the two surfaces was typically about 4:1.The main emphasis of the research has been on establishing the turbulence structure, particularly in the central region of the channel where the two dissimilar wall flows (generated by the smooth and rough surfaces) interact. Measurements have included profiles of all non-zero double and triple velocity correlations; spectra of the same correlations at several positions in the channel; skewness and flatness factors; and lateral two-point space correlations of the streamwise velocity fluctuation.The region of greatest interaction is characterized by strong diffusional transport of turbulent shear stress and kinetic energy from the rough towards the smooth wall region, giving rise, inter alia, to an appreciable separation between the planes of zero shear stress and maximum mean velocity. The profiles of length scales of the larger-scale motion are, in contrast to the turbulent velocity field, nearly symmetric. Moreover, it appears that at high Reynolds numbers the small-scale motion may in many respects be treated as isotropic.

Metabolism of beds of mammalian cortical synaptosomes: response to depolarizing influences.

Abstract: — The metabolic properties of synaptosome beds (deposits positioned between nylon gauzes) were studied. They respired, glycolysed, produced ATP and phosphocreatine, and metabolized [U-14C]glucose to glutamate, aspartate, alanine and GABA at similar rates to synaptosome suspensions. Metabolic inhibitors caused massive loss of amino acids from the beds. Synaptosome beds also responded metabolically to electrical pulses; respiration and lactate production increasing by 40 per cent. Differential release of glutamate, aspartate and GABA occurred during electrical stimulation, maximum release being after 10–15 min of stimulation. This differential release also occurred when medium potassium was increased. Omitting and chelating calcium reduced or abolished this response with both forms of stimulation. Including amino acid analogues (β-aminobutyric acid, α, γ-diaminobutyric acid and N-acetyl glutamic acid) in the incubation medium changed the patterns of amino acids present in the medium, indicating that under normal conditions active amino acid uptake processes are occurring in synaptosomes. Tetrodotoxin and ouabain also interfered with amino acid release without greatly affecting the response to stimulation. Cerebral cortex slices incubated between gauzes also showed a glycolytic response to electrical stimulation. GABA was the only amino acid showing a significant increase in the amount released with both potassium and electrical stimulation of the slices.

The effect of aluminium hydroxide on calcium, phosphorus and aluminium balances, the serum parathyroid hormone concentration and the aluminium content of bone in patients with chronic renal failure.

Abstract: 1. Eight patients with chronic renal failure (creatinine clearance 4·9–22·0 ml/min) were given 75–150 ml of aluminium hydroxide gel (‘Aludrox’) daily for 20–32 days. 2. In all patients there was a decrease in plasma phosphorus. The phosphorus balance became more negative in four and less positive in one, remained unchanged in two, and became positive in one. 3. Patients absorbed 100–568 mg of aluminium daily. In two of three patients the content of aluminium in the iliac bone increased but not above normal values. 4. The concentration of parathyroid hormone was decreased by aluminium hydroxide therapy in three patients in whom there was an increase in plasma calcium and in one other patient in whom plasma calcium did not change.

On the theory of rolling

Abstract: A comprehensive solution to von Karman’s basic equation is developed, with the aid of a digital computer, the linear first-order differential equation being integrated by a fourth-order Runge–Kutta process. An analytical solution for the special case of constant interfacial shear stress т , equal to the yield shear stress k of the material being rolled, is derived and used to test the convergence of the numerical solution. The mixed boundary condition т = μ s or k whichever is smaller is incorporated, and back and front tensions and both elastic arcs of contact are included in all the proposed solutions, as well as variation of the yield stress k through the arc of contact, so that the theory can be applied to both hot and cold rolling situations. Comparisons are made with successively more approximate solutions and with well-known existing theories and it is shown that none of these earlier theories are capable of predicting roll torque with any degree of precision.

The propagation and transfer properties of steady convective overturning in shear

Abstract: A conservative quantity is found as an integral of a component of the vorticity equation and used to formulate a non-linear theory of steady, two-dimensional convection in shear. The steering-level and propagation speed are determined in terms of a Richardson number and a density-scaling parameter. Case studies indicate a favourable agreement between theory and observation, especially where the Richardson number is of order unity. The parcel theory of convection is extended and the importance of the horizontal pressure gradient as a control on the updraught intensity is discussed quantitatively. Heat and momentum transfer laws are obtained in terms of the mean flow parameters, and define a non-Fickian transfer.

An in vivo study of aortic flow disturbances

Abstract: The general nature of flow-disturbances and turbulence in fluid flows, and the special features which may govern their appearance in unsteady flows, are considered. A hot-film anemometer system, modified for use within arteries, has been used to examine flow disturbances in the aorta. Results suggested that the extent of flow-disturbances may be influenced by both peak flow velocity and pulse-rate, expressed in terms of the relevant fluid dynamic parameters. Possible underlying mechanisms are discussed, and power spectra for laminar and highly disturbed aortic velocity waveforms presented.

Principles of action of polymeric flocculants

Abstract: The relationship of flocculation by water-soluble polymers to the classical phenomena of colloid chemistry is pointed out and the contributions of electrostatic and non-electrostatic forces are discussed. Modern flocculants have a high degree of polymerization (e.g. c. 50 000) and an extremely extended configuration when dissolved in a favourable solvent; this factor explains qualitatively some of the peculiarities of flocculation by polymers and indicates the need for rational control of their use if optimum results are to be achieved. It is concluded, however, that a quantitative theory of specific flocculant systems is not possible at present. Future developments in flocculation technology will almost certainly include introduction of cheaper or more selective flocculants, improved control through the use of auxiliary reagents and more sophisticated consideration of the surface chemistry of materials that have to be flocculated.

An experimental study of the velocity distribution and transition to turbulence in the aorta

Abstract: The development and evaluation of a hot-film probe, suitable for use within arteries and operated with a commercial constant-temperature anemometer and linearizcr, is described. The performance of the system in the recording of arterial velocity wave forms is described, and instantaneous and time-averaged velocity profiles constructed from measurements in the thoracic aorta of dogs are presented. The profiles were blunt, with boundary layers estimated to be less than 2 mm thick throughout the cycle, and significant skews were observed, the explanation for which appears to lie in the influence of local geometry on the flow. A preliminary study of flow disturbances in the aorta based on visual observation of instantaneous velocity wave forms and frequency spectrum analysis is reported. The occurrence of flow disturbances and turbulence is shown to be related to peak Reynolds number and the frequency parameter α. The possible roles of free-stream disturbances and boundary-layer transition in generating these disturbances are discussed.

The conjugation of phenylacetic acid in man, sub-human primates and some non-primate species.

Abstract: 14 C-Labelled phenylacetic acid has been administered to man, 14 species of sub-human primates and 11 non-primate species and their urine examined for metabolites. Four amino acid conjugates of this acid have been found in various species, namely, phenacetylglutamine, phenacetylglycine, phenacetyltaurine and diphenacetylornithine, but their occurrence varies with species. In the primates the occurrence of the glutamine and glycine conjugates appears to be correlated with their evolutionary status. Man excretes exclusively the glutamine conjugate, the Old World monkeys the glutamine conjugate and very small amounts of the glycine conjugate, the New World monkeys the glutamine conjugate and significant amounts of the glycine conjugate and the prosimians the glycine conjugate only. The non-primate mammalian species excrete the glycine conjugate and no glutamine conjugate. The two avian species examined also differed, since the pigeon excreted the glycine conjugate, whereas the domestic hen excreted mainly the ornithine conjugate with small amounts of the glycine conjugate. The conjugation of phenylacetic acid with taurine is reported for the first time. It occurs in all the species examined except the vampire bat and domestic hen, but its quantitative occurrence is haphazard amongst the species examined. It was found in significant amounts in the pigeon, ferret, bushbaby, capuchin monkey, squirrel monkey, mona monkey and baboon, but in minor amounts in other species.

Measurement of local entrainment rate in the initial region of axisymmetric turbulent air jets

Abstract: The local entrainment rate in the initial region of axisymmetric turbulent air jets has been measured by a novel method, which is an adaptation of the ‘porous-wall’ technique used by Ricou & Spalding (1961). The local entrainment rate, which is independent of the nozzle Reynolds number for values greater than 6 × 104, is strongly dependent upon the axial distance. At an axial distance of one nozzle diameter the local entrainment rate is only about one-third of that in the fully developed jet; the entrainment rate increases with increasing axial distance to reach the fully developed value at an axial distance of about thirteen nozzle diameters.

Species variations in the threshold molecular-weight factor for the biliary excretion of organic anions.

Abstract: 1. The excretion in the bile and urine after intravenous injection of 16 organic anions having molecular weights between 355 and 752 was studied in female rats, guinea pigs and rabbits. 2. These compounds were mostly excreted unchanged, except for three of them, which were metabolized to a slight extent (<7% of dose). 3. The rat excreted all the compounds extensively (22-90% of dose) in the bile. 4. In guinea pigs four of the compounds with mol.wt. 355-403 were excreted in the bile to the extent of 7-16% of the dose, four with mol.wt. 407-465 to the extent of 25-44% and eight compounds with mol.wt. 479-752 to the extent of 44-100%. 5. In rabbits four compounds with mol.wt. 355-465 were excreted in the bile to the extent of 1-8% of the dose, two compounds with mol.wt. 479 and 495 to the extent of 24 and 22%, and six compounds with mol.wt. 505-752 to the extent of 31-94%. 6. These results, together with those of other investigations from this laboratory, are discussed and the conclusion is reached that there is a threshold molecular weight for appreciable biliary excretion (i.e. more than 10% of dose) of anions, which varies with species: about 325+/-50 for the rat, 400+/-50 for the guinea pig and 475+/-50 for the rabbit. 7. Anions with molecular weights greater than about 500 are extensively excreted in the bile of all three species. 8. That proportion of the dose of these compounds which is not excreted in the bile is excreted in the urine, and in the three species, bile and urine are complementary excretory pathways, urinary excretion being greatest for the compounds of lowest molecular weight and tending to decrease with increasing molecular weight. 9. Some implications of this interspecies variation in the molecular-weight requirement for extensive biliary excretion are discussed.

Crystal concentration in ignimbrites

Abstract: A comparison of the crystal contents of selected sieve grades from 9 ignimbrites, with the yield of crystals from crushed pumice, shows that on average a tenfold concentration of crystals has taken place in the ignimbrites. This is explained by the selective loss of pumice by an amount equal to at least the present bulk of the samples studied. The pumice is thought to have been lost above the vent or the moving pyroclastic flow, though there is a possibility, yet untested, that it may be contained in the distil part of the ignimbrites. This paper also further characterises the relatively well-sorted basal layer, and the pipes (interpreted as due to primary fumaroles) which cut some ignimbrites. Basal layer and pipes show an even greater concentration of crystals than the body of the ignimbrites. One corollary of this study is that doubt is placed on the value of making chemical analyses of ignimbrites, the composition of which is likely to depart appreciably from that of the eruptive magma.