Showing papers by "Imperial College London published in 1973"

Analysis of heart rate variability.

Abstract: Spontaneous variability of heart-rate has been related to three major physiological originating factors: quasi-oscillatory fluctuations thought to arise in blood-pressure control, variable frequency oscillations due to thermal regulation, and respiration; frequency selective analysis of cardiac interbeat interval sequences allows the separate contributions to be isolated. Using this method, a laboratory and field study of the effects of mental work load on the cardiac interval sequence has been carried Out. Results suggest that mean heart rate and variance are unreliable measures, but that consistent changes in interval spectrum occur; these have been traced to alterations mainly in the 0·1 Hz region, perhaps originating with changes in the patterns of respiration which interact with the 0·1 Hz vasomotor activity,

The purification, composition and specificity of wheat-germ agglutinin

Abstract: 1 The purification of wheat-germ agglutinin from commercial wheat germ is described By ion-exchange chromatography three active proteins (isolectins) were separated, one of which was examined in detail 2 The amino acid composition is unusual, as 20% of residues are half-cystine and 21% are glycine Unlike most lectins and contrary to previous reports, this protein is not a glycoprotein 3 The efficiency of various saccharides as inhibitors of the agglutination reaction was investigated and from this the specificity of the binding site was inferred Of monosaccharides, only derivatives of glucose with a 2-acetamido group and a free 3-hydroxyl group are effective inhibitors, and glycosides of either anomeric configuration are bound Oligosaccharides are much more powerful inhibitors of agglutination than are monosaccharides 4 It is proposed that the binding site consists of three or four subsites with differing specificities, in a cleft in the molecule resembling that proposed for hen9s-egg-white lysozyme

Explosive volcanic eruptions — a new classification scheme

Abstract: A classification scheme is proposed based on measurements made on the resulting pyroclastic fall deposits, the significant parameters being the area of dispersal and degree of fragmentation of the material. An empirical measure of the first is the area enclosed by the 0.01 Tmax isopach (where Tmax is the maximum thickness of the deposit), called D, which ranges from less than 10 km2 for deposits of strongly cone-building type to more than 1000 km2 for deposits of strongly sheet-forming type. An empirical measure of the second is the percentage of material finer than 1 mm in the deposit, or more simply at the point where the 0.1 Tmax isopach crosses the dispersal axis. The latter value, called F, varies from less than 20 for deposits in which fragmentation was mainly achieved by the tearing apart of magma, to more than 80 where it was largely due to thermal shock resulting from the quenching of lava by water.

Stability analysis of embankments and slopes

Abstract: A simple but accurate method of stability analysis of embankments and slopes is developed to determine the critical earthquake acceleration that is required to bring a mass of soil, bounded by a slip line of any shape and the free surface, to a state of limiting equilibrium. At the same time, the usual factor of safety can be determined. It is based on the principle of limiting equilibrium and the method of slices. Effective stress strength parameters are used. A distribution of internal body forces is found based on a simple assumption. This depends on the geometry of the dam and the sliding surface as well as on the strength of the material. Though a computer is used for the calculations presented in the Paper, it is not essential. As in any solution, the physical acceptability of the complete solution must be checked before accepting the result. It is suggested to use the critical acceleration as a measure of the factors of safety. On a mis au point une methode simple mais precise pour l'analyse de la ...

Interactions between Temperature and Pore-Fluid Pressure during Earthquake Faulting and a Mechanism for Partial or Total Stress Relief

Abstract: At depths in the crust greater than perhaps 1 km, local melting with production of pseudotachylyte should take place on fault planes during seismic faulting1,2. But, although many ancient fault zones are now exposed at erosion levels which correspond to depths of several kilometres when the faults were active, very few of them contain pseudotachylyte; it has been suggested3,4 that the general absence of this material on fault planes puts an upper limit on the magnitude of shear stresses associated with earthquake faulting. In refs 1–4 earthquake fault models with heat generated by dry frictional sliding on a single plane across which there is a constant normal stress are used. Two other factors are probably dominant in controlling the temperature rise on a fault, and the second has important implications with regard to the seismic source mechanism, and the nature of cataclastic rocks produced by rapid faulting.

Non-precipitating cumulus convection and its parameterization

Abstract: This paper discusses the thermodynamic transports of heat, liquid water and (briefly) water vapour by non-precipitating cumulus convection. It is shown that because of the irreversible mixing between cloud and environment, there is a downward transport of enthalphy in the cumulus layer. A lapse-rate adjustment model relates stratification to the life-cycle of a model cloud parcel. A sub-cloud layer model specifies the lower boundary of the lapse-rate model, and the convective transports through cloud-base. Budget equations together with the lapse-rate model, and its time dependent boundary conditions, predict the time development of the cumulus layer, and show the dependence on large-scale mean vertical motion, cloud-base variations, and the surface sensible heat flux.

The interaction between a pair of circular cylinders normal to a stream

Abstract: This paper describes how the flows around two circular cylinders, displaced in a plane normal to the free stream, interact as the two bodies are brought close together. Surface pressure measurements at a Reynolds number of 2·5 × 104, based on the diameter of a single cylinder, show the presence of a mean repulsive force between the cylinders. An instability of the flow was found when the gap between the cylinders was in the range between one diameter and about 0·1 of a diameter. Correlation measurements of hot-wire outputs indicate how mutual interference influences the formation of vortex streets from the two cylinders. Spanwise correlation measurements show that the correlation length doubles as the cylinders are brought into contact.

Lengths of Lava Flows

Abstract: The principal factor influencing the length of a lava flow is the rate of effusion. With a high rate the lava flows rapidly from the source and tends to form an extensive and far-reaching flow which is simple in character (i.e. made of a single flow unit). With a low rate the lava tends to pile up layer upon layer to form a local accumulation of limited lateral extent near the source, and this accumulation is strongly compound in character (i.e. divisible into flow units). The initial viscosity affects the length indirectly by controlling the thickness of the extrusion, and this thickness control is capable of accounting for the fact that the median length of low-viscosity basaltic extrusions is 3.2 times that of high-viscosity andesite, trachyte and rhyolite ones. Other factors, such as the local topography, are thought to be relatively unimportant, an exception being when lava is ponded in a topographic depression. Measurement of the rate of effusion may be critical in any attempt to predict the distance that a lava flow will travel, such as the one which threatened Fornazzo and other towns and villages on Etna in 1971.

Products of Ignimbrite Eruptions

Abstract: Many ignimbrite flow units show a reverse grading of large pumice clasts and a normal grading of large lithic clasts. Each ignimbrite flow unit has a basal layer finer grained than the body of the ignimbrite, with a ground surge deposit commonly underlying the ignimbrite, and a fine ash-fall deposit commonly overlying it. These two types of deposit, although not an integral part of the ignimbrite, are produced by the same eruptive act, and they and the ignimbrite constitute the several and varied products of a Pelean-phase eruption. Volcanic eruptions in which ignimbrite is generated show the following sequence of events so often that it may be regarded as the normal one: (1) a highly explosive, often Plinian, phase, producing a pumice-fall deposit; (2) a Pelean phase; and (3) an effusive phase, producing a lava flow. This sequence is believed to represent the tapping of progressively deeper levels in the magma chamber and the escape during the eruption of magma of progressively lower gas content.

Two calculation procedures for steady, three-dimensional flows with recirculation

Abstract: Two procedures are described for solving the Navier-Stokes equations for steady, fully three-dimensional flows: both are extensions of earlier methods devised for three-dimensional boundary layers, and have the following common features: (i) the main dependent variables are the velocities and pressure; (ii) the latter are computed on a number of staggered, interlacing grids, each of which is associated with a particular variable; (iii) a hybrid central-upwind difference scheme is employed; and (iv) the solution algorithms are sufficiently implicit to obviate the need to approach the steady state via the time evolution of the flow, as is required by wholly explicit methods

Prediction of free shear flows: A comparison of the performance of six turbulence models

Abstract: The performance is evaluated of three distinct classes of turbulence model. These classes are: (1) Turbulent-viscosity models in which the length scale of turbulence is found by way of algebraic formulas, (2) turbulent-viscosity models in which the length scale of turbulence is found from a partial differential equation of transport, and (3) models in which the shear stress itself is the dependent variable of a partial differential conservation equation. Two models were examined in each class; thus, six different models were tested. A complete mathematical statement of these models is provided and a brief commentary on the models is included.

Experiments on the Motion of Solitary Grains Along the Bed of a Water-Stream

Abstract: Experiments are described in which heavy solid grains are observed as they are propelled one at a time by a water stream over a fixed, plane, bed of grains of the same sort. This is a simplification of a sediment flow in a river, and it allows the motions of a particular grain to be followed. Three modes of movement are observed - rolling, saltating and suspension, characteristics of each mode are described, and multi-exposure photographs of grains are obtained to show the trajectories involved. In the saltation mode, grains follow low, smooth trajectories. Since no random motions are detectable on them, they appear to be governed very largely by ballistic forces; in suspension, grains follow much longer, higher paths which, being wavy, show up the influence of the irregular turbulence in the stream. The change from one mode to the other is readily observed with this technique. The grains spin in all three modes. The mean forward speed of grains $\overline{U}$ has been measured over a wide range of shear stress, shape and size of grain and of water depth. Two possible types of non-dimensional plots are presented, one of which is most appropriate to studies of the rolling mode, and the other for the suspension mode. Both methods satisfactorily correlate $\overline{U}$ with various values of the settling speed $V\_{\text{g}}$ in still water, for particles all of the same shape and size. There is a considerable difference in $\overline{U}$ for different shapes of grains, angular ones always travelling more slowly than rounded ones. Relative to the mean stream speed $\overline{u}$, the grains travel faster at small depths than at large depths, for the same stress and $V\_{\text{g}}$. The trajectories of grains confirm that the change from saltation to suspension occurs near a stage when the vertical components of turbulent velocity are approximately equal to the settling velocity of grains. Multi-exposure photographs of trajectories are analysed to determine the angle of friction applicable to the process whereby the motion of grains is retarded by striking the bed. Some experiments have been done with spheres travelling over a bed consisting of cylinders of the same diameter. These travel faster than any natural grains. Their dynamics, when rolling in contact with the cylinders, have been investigated, and a theoretical model evolved to explain the conditions under which their forward motion just stops. This model is shown to give a useful approximation to the forward speed to all types of grain just before they suddenly stop moving; these grains will not travel at all at lower speeds. Finally, an experiment is described where one marked grain is observed while moving in the company of many other grains. Its speed is then reduced below that which it would have as a solitary grain in the same water stream, thus indicating how the friction of the grain load reacts upon the stream to give smaller speeds close to the bed. Appendix 1 gives details of a demonstration that saltation can occur in a laminar flow, with no turbulence present at all. Appendix 2 gives the experimental data, and appendix 3 gives the algebra of the analysis of rolling motion.

Two Plinian Pumice-Fall Deposits from Somma-Vesuvius, Italy

Abstract: Two of the major pumice-fall deposits of Somma-Vesuvius are described. One, the Pompei Pumice, resulted from the classic eruption of A.D. 79, which is taken as the type example of a Plinian eruption. The Pompei Pumice is dispersed south and southeast of the volcano and has been traced to a distance of 72 km. The other, the Avellino Pumice, is probably a thousand years older. It is dispersed to the east and northeast and has been traced to a distance of 50 km. The two deposits are remarkably similar in character, each consisting of a lower part of white pumice and an upper part of mafic gray pumice having a similar grain-size distribution. The distinction between the two deposits is based on (a) the differing proportions of felsic crystals, mafic crystals, and lithic fragments in selected sieve grades; (b) the abundance of nepheline crystals in the Avellino Pumice and their absence from the Pompei; and (c) the greater abundance of crystals in the Avellino Pumice and of lithic debris in the Pompei. The change in composition of the erupting magmas was accompanied by an increase in the vigor of each eruption, as shown by an increase in the density and size of the pumice, in the content and size of lithic fragments, and in the area of dispersal. This is correlated with an increasing depth of origin in a compositionally zoned magma chamber. Granulometric analyses of some ninety samples show that the deposits are well sorted, the sorting improving slightly with increasing distance from the source. Maps showing the median terminal fall velocity, based on the grain-size data, enable limiting values to be derived for the height of the eruptive column and the wind strength. The volume of each deposit has been estimated from the isopach maps, namely, 2.6 km 3 for the Pompei Pumice and 2.1 km 2 for the Avellino Pumice.

The purification and properties of the lectin from potato tubers, a hydroxyproline-containing glycoprotein

Abstract: 1. Potato lectin has been purified and shown to be a glycoprotein containing about 50% of carbohydrate. Most of the sugar residues (92%) are arabinose; small amounts of galactose, glucose and glucosamine are also present. 2. The most abundant amino acid is hydroxyproline (16% of the residues), 11.5% of the residues are half-cystine and phenylalanine is absent. The lectin also contains about one residue/molecule of a basic amino acid, not usually found in proteins, which has been tentatively identified as ornithine. There is indirect evidence that the components of the glycoprotein are linked through hydroxyproline and arabinose. 3. By gel filtration in 6m-guanidine-HCl on Sepharose 4B, it was found that both the native glycoprotein and its S-carboxymethylated derivative had subunit molecular weights of 46000 (+/-5000). In a non-denaturing solution, two of these units appear to be associated. 4. The lectin is specifically inhibited in its agglutination reaction by oligosaccharides that contain N-acetylglucosamine. Its specificity is similar to, but not identical with, that of wheat-germ agglutinin.

Axial Flow in Laminar Trailing Vortices

Abstract: The structure of laminar trailing vortices behind a lifting wing is considered The inviscid roll up of the trailing vortex sheet is examined, and the nature of the singularity at the centre of the spiral is determined It is shown that viscosity removes the singularity and the structure of the viscous core is obtained The pressure in the viscous core is found and used to calculate the axial velocities produced by streamwise pressure gradients It is found that the perturbation of axial velocity can be either away from the wing or towards the wing depending on the distribution of tip loading on the wing For elliptic loading, the perturbation is towards the wing The axial flow deficit in the core due to the boundary layers on the wing is also estimated A comparison with experiment is made and reasonable agreement is found

Burners Producing Large Excess Enthalpies

Abstract: The principle of heat recirculation in combustion systems is analyzed for the case where no direct mixing of reactants and products occurs. The concept leads to a general treatment, the restriction of associating flame temperature with the initial mixture stoichiometry and fuel heating value being removed in burners which rely on an enthalpy excess over initial and final states. This has important consequences particularly for reactants of very low heat content. Otherwise nonflammable mixtures may be burned by recirculating heat so as to increase the temperature in the reaction zone without generating a high final temperature. Idealized models are used to demonstrate the potential rewards from application of the principle in the areas of power generation (including direct energy conversion) from gases of low heat content, fuel saving, flame stability (flammability limits and maximum mass throughput rates) and pollutant emission. Experimental results from a simple burner incorporating a counterflow heat ex...

Vibration Characteristics of Bladed Disc Assemblies

Abstract: A study is made to establish the basic vibration characteristics of bladed disc assemblies. An analysis is presented and used to predict the natural frequencies and mode shapes of uniform bladed di...

Forecasting the start and severity of the hay fever season.

Abstract: Since the season of summer hay fever may last only 4 weeks and rainfall may produce days with virtually no airborne pollen, the timing of clinical trials is important. To facilitate this a method of forecasting the first possible 100% symptom day, and the severity of the season in terms of light, moderate or severe, is presented. The forecast is based on temperature in April and May, and formulae tested by reference to records of grass pollen concentrations over Central London during 1961–70.

Dimensional regularization, abnormal amplitudes and anomalies

Abstract: Identifying axial vectors and pseudoscalars as antisymmetric 3-component and 4-component tensors in space-time of arbitrary dimensions, we discover a new PCAC law:\(\partial [_{K\bar \psi } \Gamma _L \Gamma _M \Gamma _{N]} = \)\( = 2mi\bar \psi \Gamma _{[K} \Gamma _L \Gamma _M \Gamma _{N]} \psi - \frac{1}{5}i\bar \psi (\overleftrightarrow {i\partial }^J + 2eA^J )\Gamma _{[J} \Gamma _K \Gamma _L \Gamma _M \Gamma _{N]} \psi = \), where the extra term on the right-hand side does not exist in 4 dimensions. However, when we do descend to 4 dimensions after dimensional regularization it is precisely the axial vector anomaly. In a parallel calculation we have also shown how to obtain the anomaly in the matrix elements of the trace of the stress tensor.

The stability of tips and spoil heaps

Abstract: 1 Introduction The problem of the stability of tips and spoil heaps was brought to public attention with dramatic force in 1966 by the disaster at Aberfan, when a slide involving only some 140 000 yd 3 of colliery rubbish resulted in the loss of 144 lives, 116 those of children mostly between the ages of 7 and 10 Not only to the public, but also to most professional engineers and geologists—even to those concerned with mining—it came as a problem to which they had given little, if any, serious attention; though the discussion on Knox9s 1927 paper to the South Wales Institute of Engineers suggests that there was local awareness of the problem of tip stability This lack of attention is perhaps surprising when we look at the scale of the problem of the disposal of waste from mining, from industrial processes and power generation, and from domestic sources (Table 1) The total quantity is about 120 million tons per annum within the United Kingdom, of which the largest contribution, nearly 60 million tons, comes from the mining of coal It is of interest to note that the quantity of colliery waste has risen from 7 million tons in 1930 to 60 million tons in 1970 as a result of mechanization, although the overall quantity of coal produced has decreased† It is also very significant that of the 60 million tons, about 5 million tons are in the form of slurry or tailings If tipped in the form of a

Regional Sedimentation along the Trucial Coast, SE Persian Gulf

Abstract: Sediment composition, surface patterns, and vertical sequences vary laterally along the Trucial Coast depending on three major factors: orientation of the shoreline with respect to the onshore “shamal” winds; proximity to Qatar Peninsula, an up-wind barrier; presence of the Great Pearl Bank coastal barrier.