Showing papers by "Imperial College London published in 1980"

Trace Elements in Soils and Plants

Abstract: Fifteen or more elements present in rocks and soils normally in very small amounts are essential for plant and/or animal nutrition. By the nature of their low abundance in natural uncontaminated earth materials or plants, they are known as trace elements, minor elements or micro-nutrients. Boron, copper, iron, manganese, molybdenum, silicon, vanadium and zinc are required by plants; copper, cobalt, iodine, iron, manganese, molybdenum, selenium and zinc by animals. In addition essential roles of arsenic, fluorine, nickel, silicon, tin and vanadium have in recent years been established in animal nutrition.

Chronic obstructive pulmonary disease

Abstract: Chronic obstructive pulmonary disease (COPD) is a common problem in the elderly. The disease is characterised by intermittent worsening of symptoms and these episodes are called acute exacerbations. The best estimate, based on several lines of evidence, is that approximately half of all exacerbations are caused by bacteria. These lines of evidence include studies of lower respiratory tract bacteriology during exacerbations, correlation of airways’ inflammation with results of sputum cultures during exacerbations, analysis of immune responses to bacterial pathogens, and the observation in randomised, prospective, placebo-controlled trials that antibacterial therapy is of benefit. The most important bacterial causes of exacerbations of COPD are nontypeable Haemophilus influenzae, Moraxella catarrhalis, Streptococcus pneumoniae and Chlamydia pneumoniae.

Empirical Strength Criterion for Rock Masses

Abstract: An empirical strength criterion for rocks and rock masses is proposed. The nonlinear criterion includes the uniaxial compressive strength of the intact rock material and introduces two dimensionless parameters, m and s. The parameter m varies with rock type, the angle of interblock or interparticle friction and the degree of block or particle interlock. The parameter s varies from 1.0 for intact rock material to zero for granular aggregates and depends on the interparticle tensile strength and the degree of interlock within the rock mass. For anisotropic rock, both m and s vary with the orientations of the planes of weakness to the principal stress directions. Approximate relationships between rock type, rock mass quality indices, and the rock mass strength parameters m and s, are presented. These relationships have been found useful in preliminary design calculations for slopes and underground excavations in jointed rock.

The Computation of Equivalent Potential Temperature

Abstract: A simplified procedure is described for computation of equivalent potential temperature which remains valid in situations such as in the tropics where a term which is omitted in the derivation of the conventional formula can lead to an error of several degrees absolute. The procedure involves new empirical formulas which are introduced for the saturated vapor pressure of water, the lifting condensation level temperature and the equivalent potential temperature. Errors are estimated for each of these, and results are compared with those obtained by the similar, but more complicated procedures of Betts and Dugan (1973) and Simpson (1978).

Programs, life cycles, and laws of software evolution

Abstract: By classifying programs according to their relationship to the environment in which they are executed, the paper identifies the sources of evolutionary pressure on computer applications and programs and shows why this results in a process of never ending maintenance activity. The resultant life cycle processes are then briefly discussed. The paper then introduces laws of Program Evolution that have been formulated following quantitative studies of the evolution of a number of different systems. Finally an example is provided of the application of Evolution Dynamics models to program release planning.

Machine-component grouping in production flow analysis: an approach using a rank order clustering algorithm

Abstract: Existing cluster analysis methods are reviewed and a new approach using a rank order clustering algorithm is described which is particularly relevant to the problem of machine-component group formation. A relaxation and regrouping procedure is developed whereby the basic rank order clustering method may be extended to the case where there are bottleneck machines.

Left-handed DNA helices

Abstract: The synthetic DNA polymerpoly d(GC) . poly d(GC) has been studied by X-ray diffraction of orientated fibres in which it has either the well known (A or B) randed conformations have been observed with poly d(AC) . poly d(GT) and with poly d(As4T) . poly d(As4T), demonstrating that the novel structure is accessible to any DNA segment with an alternating purine-pyrimidine base sequence.

Structure of slow-reacting substance of anaphylaxis from guinea-pig lung

Abstract: Slow-reacting substance of anaphylaxis (SRS-A) is a primary mediator of immediate-type hypersensitivity reactions, probably having a major bronchoconstrictor role in asthma. Although it was discovered some 40 years ago1 the structure has remained unknown. Major advances in purification technology2,3 have resulted in the preparation of chemically pure material, and the demonstration that SRS-A has a characteristic UV spectrum2 has enabled a correlation to be made between biological activity and a structural moiety in the molecule. Previous studies have indicated that SRS-A from guinea pig lung is derived from arachidonic acid4; data, based on the chemical and enzymatic destruction of biological activity, have indicated the presence of α-amino, carboxyl and thioether functions3. We now report the first spectroscopic (mass spectrometric) and analytical protein chemical data on intact SRS-A which allows us to define unequivocally the complete covalent structure of this immunologically generated material as the novel peptidolipid 5-hydroxy-6-cysteinyl glycinyl-7, 9, 11, 14-eicosatetraenoic acid. The structure determined is identical to that which we have assigned to the major non-immunologically generated slow-reacting substance (SRS) obtained from rat basophil leukaemia (RBL-1) cells5, but different from that of a recently synthesized chemical with SRS-like activity6 whose structure was modified from an earlier, incorrect structure of the natural product7.

Heat transfer model for cw laser material processing

Abstract: (Received 19 September 1979; accepted for publication 12 October 1979)A three‐dimensional heat transfer model for laser material processing with a moving Gaussian heat source is developed using finite difference numerical techniques. In order to develop the model, the process is physically defined as follows: A laser beam, having a defined power distribution, strikes the surface of an opaque substrate of infinite length but finite width and depth moving with a uniform velocity in the positive x direction (along the length). The incident radiation is partly reflected and partly absorbed according to the value of the reflectivity. The reflectivity is considered to be zero at any surface point where the temperature exceeds the boiling point. This is because a ’’keyhole’’ is considered to have formed which will act as a black body. Some of the absorbed energy is lost by reradiation and convection from both the upper and lower surfaces while the rest is conducted into the substrate. That part of the incident r...

Structure of southern bean mosaic virus at 2.8 A resolution.

Abstract: X-ray diffraction studies reveal that the polypeptide chain of the southern bean mosaic virus protein subunit has a fold closely similar to the shell domain of tomato bushy stunt virus. The protruding domain of tomato bushy stunt virus is absent in southern bean mosaic virus. The tertiary structure observed in these viruses may be particularly suitable f or the formation of the protein coat in small, spherical, RNA-containing, plant viruses.

On irregularities of distribution.

Abstract: §

Comparison of bacterial extracellular polymer extraction methods.

Abstract: Five different bacterial extracellular polymer extraction methods and a combination of two of these methods were compared on cultures of activated sludge, synthetic activated sludge, and Klebsiella aerogenes. High-speed centrifugation was the most effective extraction method for the K. aerogenes culture, based on the comparatively small amount of cell disruption and the relatively high extracellular polymer yield. Steaming treatment was the most effective extraction method for the activated sludges, since it released a significant quantity of extracellular polymers from the flocs and caused less cellular disruption than ethylenediaminetetraacetic acid and sodium hydroxide treatments. Sodium hydroxide treatment caused extensive disruption in all cultures. Ultrasonication released low concentrations of extracellular polymers from all cultures. However, it caused no significant cell disruption and therefore may be useful as a preliminary treatment in conjunction with another extraction method.

Spontaneously broken de Sitter symmetry and the gravitational holonomy group

Abstract: The local geometrical structure of general relativity is analyzed in detail from the standpoint of a formulation of gravity as a gauge theory of the de Sitter group SO(3,2). In order to reproduce the structure of the Einstein-Cartan theory, it is essential that the SO(3,2) gauge symmetry be spontaneously broken down to the Lorentz group. In the geometrical analysis of this spontaneously broken theory, the Goldstone field of the symmetry-breaking mechanism plays a central role, representing the coordinates of a point in an internal anti-de Sitter space where the motions induced by parallel transport across space-time take place. In order to establish the connection between the SO(3,2) gauge theory and the Einstein-Cartan theory, the gravitational vierbein and spin connection are derived from the original SO(3,2) gauge fields by passing over to a set of nonlinearly-transforming fields through a redefinition involving the Goldstone field. The original SO(3,2) gauge fields have a different but equally important role: they generate pseudotranslations and rotations in the internal anti-de Sitter space under a kind of parallel transport across space-time that is called "development." Development maps curves in space-time into image curves in the internal space, and vector fields along the curves in space-time into image vector fields along the image curves. Considering development along infinitesimal closed curves in space-time leads to the proper interpretation of the effects of torsion and of curvature in terms of the nonclosure of image curves and of the rotation of image vectors with respect to their original values.

The theory of the Taylor dispersion technique for liquid diffusivity measurements

Abstract: This paper presents a complete analysis of the theory of an instrument to measure the diffusion coefficients in liquid mixtures based upon the phenomenon of Taylor dispersion. The analysis demonstrates that it is possible to design an instrument that operates very nearly in accordance with the simplest mathematical description of the dispersion of a solute pulse in a fluid in laminar flow within a straight, circular cross-section tube. The small departures of a practical instrument from the ideal are evaluated as corrections by means of a general perturbation treatment that allows them to be examined one at a time. The corrections considered include the effects of the finite volume of the injection pulse, the finite volume of the concentration monitor, the coiling of the tube, and the nonuniformity and noncircularity of the cross section, as well as the variation of the fluid properties with composition. All the equations necessary for the design of an instrument of this type, and for the evaluation of experimental data free from significant systematic errors, are presented.

A Combustion Correlation for Diesel Engine Simulation

Abstract: An apparent heat release rate (AHRR) correlation is presented for direct injection diesel engines. It is based on algebraic expressions describing the fuel burning rate as a function of dominant controlling parameters, such as ignition delay and equivalence ratio. Relating the burning rate to these parameters permits the AHRR at one engine running condition to be linked to the AHRR at another condition. By simulating the combustion process via an analytical expression whose governing parameters are linked to in-cylinder conditions, the AHRR empirical correlation simulates the combustion process (heat release) and enables the effect of many engine design and ambient condition changes to be predicted automatically, such as compressor and turbocharger match, valve and injection timing, compression ratio, aftercooling, and other engine design parameters. The correlation includes the influence of these parameters both on combustion and on the turbocharging process. While the experimental approach can reduce engine development costs, it should not replace fundamental research on diesel engine combustion nor detailed mathematical combustion modeling since it cannot predict the effect of combustion chamber design changes.

The Anaemia of P. falciparum Malaria

Abstract: The haematological changes in a group of young Gambian children with P. falciparum malaria have been analysed. In children with acute infection anaemia was most marked during the period after treatment. Although many of these patients developed a positive direct Coombs test during this period of the illness it is not clear whether the anaemia which occurs after treatment has an immune basis. A second group of children showed quite different haematological findings. They appear to have a more chronic form of P. falciparum malaria infection, were profoundly anaemic at presentation, showed gross dyserythropoietic changes in their bone marrows, and had a full reticulocyte response and rise in haemoglobin after treatment. A third group of children were encountered whose haematological abnormalities were intermediate to those of the acute and chronic groups. These findings indicate that the patho-physiological mechanisms responsible for the anaemia of P. falciparum malaria are different at different stages of the illness.

Malignant mesothelioma in North America

Abstract: Ascertainment, through 7,400 pathologists, of all fatal malignant mesothelial tumors in Canada (1960-75) and the U.S.A. (1972) gave a total of 668 cases (272 in 1972). In Canada, the annual number of male cases rose from about 17 in 1966 to 25 in 1972 but the number of female cases remained fairly steady at a much lower level. The annual incidence in North America in 1972 was estimated at 2.8 per million males and 0.7 per million females aged 15 years and over. Occupational histories were obtained "blind" for 480 of the 557 cases through 1972, and their matched controls; relative risks were as follows: insulation work, 46.0 asbestos production and manufacture, 6.1, heating trades (other than insulation) 4.4. For nearly half the male cases and for about 5% of female cases, the tumor could be attributed to occupational exposure to asbestos, of which a fifth were in shipyards. No indication was found of other possible causes (including man-made mineral fibers, tobacco smoking, or residence near zeolite deposits). Four subjects were men who had been employed in Quebec chrysotile mines and 3 were children of employees, but no other subject had lived in the mining area. The findings remain consistent with a much greater mesothelioma-producing potential for crocidolite and amosite than for chrysotile; however, further studies of factory workers exposed to chrysotile only are needed to confirm this. Mineral fiber analysis of lung tissue from patients and controls is in progress.

A note on the generalized information criterion for choice of a model

Abstract: SUMMARY One way of selecting models is to choose that model for which the maximized log likelihood minus a multiple of the number of parameters estimated is a maximum. This note explores the choice of values for the multiplier, with the value one corresponding to Akaike's information criterion. The relationship with Bayesian procedures is mentioned. Suppose that there are a number of competing models which may be fitted to some data. If the log likelihood of the ith model maximized over q* parameters is Li, the generalized information criterion is to choose the model for which Li - -1cq* is a maximum. In the criterion suggested by Akaike as equals 2. Values of os in the range 1-4 are considered by Bhansali & Downham (1977) for the choice of a time series model. As have many other authors, including Geisser & Eddy (1979) and McClave (1978), Bhansali & Downham assessed their criteria by the frequency of choice of the correct model. One purpose of the present note is to suggest that this. may not be an appropriate basis for choice: the objectives of the analysis need more explicit formulation. A similar point is made by Akaike (1979) who com- pares values of ot on the basis of squared prediction error. His simulation is, however, un- informative about the conditions under which various values of a are optimum. In this note a simple example is simulated to investigate the taxonomy of optimum of values for prediction purposes. For simplicity of structure and ease of simulation we work with linear regression models, for which the information criterion reduces to a generalized Cp statistic. The behaviour of this statistic as a function of ot is investigated in the next section. Significance testing and Bayesian alternatives are discussed in ? 3. Section 4 is concerned with asymptotics. The note closes with some general comments which allude to ridge regression and simulation.

Plasma populations in a simple open model magnetosphere

Abstract: The acceleration of charged particles in the magnetic current sheets downstream from magnetic neutral lines is discussed and related to the plasma populations expected to be formed in a simple open model magnetosphere. A simple model of plasma acceleration in the dayside current sheet is set up, and it is shown that magnetospheric particles may take up a considerable fraction of the electromagnetic energy dissipated in the sheet even though they may represent only a small fraction of the total particle influx. The process should result in energetic ring current and ionospheric particles being found in boundary layers on either side of the magnetopause, and accelerated ionospheric particles in the plasma mantle. Acceleration of magnetosheath plasma in the dayside current sheet should result in enhanced flow speeds in these boundary layers, but the process may amount to little more than a return to the sheath plasma of energy previously extracted from it during its inflow on the dayside and stored in the compressed sheath field, due to the appreciable energy take-up from the current sheet by magnetospheric particles. The energy separation between ionospheric plasma and magnetosheath plasma on cusp field lines is shown to result in a spatial separation of polar wind and plasma mantle populations in the tail, the polar wind ions usually reaching out to only a few tens of R E down-tail such that they usually remain on closed field lines, forming a wedge-shaped region within the mantle shadow-zone. Polar wind ions are then convected back towards the Earth and thus their major sink is via the dayside current sheet rather than outflow into the tail. The major source for the plasmasheet depends upon the location of the neutral line, but mantle ions may usually be dominant. However, with a near-Earth neutral line during disturbed periods ionospheric plasma will be the sole ring-current source. Under usual conditions with a more distant neutral line the spatial separation of the two plasma sources in the tail may result in an energy separation in the inner ring current, with ionospheric particles dominant up to ∼2 to 20 keV and mantle ions dominant at higher energies. Formation of the plasmasheet is discussed, and it is shown that a layer of ions unidirectionally streaming towards the Earth should be formed on its outer boundary, due to current sheet acceleration of lobe particles and inward convection of the field lines. A similar process leads to earthward flows on the inner layer of the dayside cusp. Finally, the region tailward of the nightside neutral line is discussed and it is shown that a thin tailward flowing two-stream plasma band should be formed across the centre plane of the tail. The slow-speed stream corresponds to incoming lobe ions, the faster stream to the current sheet accelerated ions.

Crack blunting mechanisms in polymers

Abstract: A quantitative model has been developed to account for the degree of blunting that occurs at crack tips in epoxy materials prior to the onset of crack propagation. This mechanism controls the subsequent mode of crack growth and, to a large extent, the toughness as defined by the stress intensity factor for crack initiation. From this model a unique fracture criterion is derived which is applicable over all modes of crack propagation.