Showing papers by "City University London published in 1975"

Efficiency of utilization of urea nitrogen for albumin synthesis by chronically uraemic and normal man.

Abstract: 1. The relation between endogenous urea metabolism and albumin synthesis has been studied in ten patients with chronic renal failure and in four normal subjects, after single intravenous injections of [ 14 C]urea, [ 15 N]urea and 125 I-labelled albumin. 2. The rate of urea synthesis was determined from the dynamics of plasma [ 14 C]urea specific radioactivity and the rate of urea metabolism was estimated from the relative rates of urea synthesis and urea appearance in urine and body water. Deconvolution analysis of plasma [ 15 N]albumin enrichment and 125 I-labelled albumin radioactivity yielded the cumulative incorporation of 15 N into total exchangeable albumin and enabled calculation of the absolute rate of urea nitrogen utilization for albumin synthesis. 3. Although the mean absolute rate of urea degradation in uraemic patients (3.7 mmol/h) was higher than in normal subjects (2.3 mmol/h) there was no significant positive correlation between urea degradation and plasma urea concentration. 4. In uraemic subjects, there was a significant positive correlation between urea synthetic rate and urea degradation rate. 5. The rate of utilization of urea nitrogen for albumin synthesis was low, but was very much higher in uraemic subjects (mean 83.8 μmol/h) compared with normal subjects (mean 6.4 μmol/h), as was the provision by urea of the nitrogen required for albumin synthesis in uraemic subjects (2.37%) compared with normal subjects (0.13%). 6. The efficiency of utilization of urea nitrogen for albumin synthesis was higher in the uraemic patients (1.3%) than the normal subjects (0.2%), and was higher in those patients with chronic renal failure who received a 30 g protein diet than those on 70 g of protein. A significant negative correlation was noted between efficiency of urea nitrogen utilization and the rate of synthesis of albumin. 7. These studies suggest the presence of a mechanism for the conservation of urea nitrogen in chronic renal failure which is unrelated to the extent of urea degradation, and which can only be partly explained by the higher proportion of intraluminal gut nitrogen derived from urea.

On the stability of slowly varying flow: the divergent channel

Abstract: The linear stability of a slowly varying flow, the flow in a diverging straight-walled channel, is studied using a modification of the ‘WKB’ or ‘ray’ method. It is shown that ‘quasi-parallel’ theory, the usual method for handling such flows, gives the formally correct lowest-order growth rate; however, this growth rate can be substantially in error if its magnitude is comparable to that of the rate of change of the basic state. The method used clearly demonstrates the dependence of the growth rate, wavenumber, neutral curves, etc., on the cross-stream variable and on the flow quantity under consideration. When applied to the divergent channel, the method yields a much wider ‘unstable’ region and a much lower ‘critical’ Reynolds number (depending on the flow quantity used) than those predicted by quasi-parallel theory. The determination of the downstream development of waves of constant frequency shows that waves of all frequencies eventually decay.

Nerve terminals and epithelial cell variety in the human lacrimal gland.

Abstract: Pieces of tissue taken from three human lacrimal glands were examined electron microscopically. Secretory cells varied according to the electron density and structure of their secretion granules. Secretory cells were arbitrarily categorized as light, medium or dark based on their granule content. Acini were composed of two or all three categories of cells together with myoepithelial cells and lymphocytes.

A reliability model for Markov structured software

Abstract: A system is considered in which switching takes place between sub-systems according to a continuous parameter Markov chain. Failures may occur in Poisson processes in the sub-systems, and in the transitions between sub-systems. All failure processes are independent. The overall failure process is described exactly and asymptotically for highly reliable sub-systems. An application to process-control computer software is suggested.

The Creep Behaviour of Structural Adhesive Joints II

Abstract: The creep behaviour of two structural adhesives (a phenolic resin/polyvinyl formal composite and a modified epoxy novolac) has been studied in their glassy state when used to bond high tensile steel lap joints Curves of adhesive shear creep strain vs In t consisted of delay periods (times after application of load but before creep is discernible) followed by essentially logarithmic creep Creep curves were thus classified by recording delay time, td , extrapolated creep rate at zero strain, γ(t0), and the gradient of the logarithmic creep line, k By comparing these values for different joint geometries, it has been established that the high stress concentrations found in lap joints under elastic conditions become much reduced as creep progresses A model is proposed to account for the transition from delay time to creep behaviour

Higher education in Nigeria

Abstract: The great Greek philosopher Aristotle (384-322 B.C.) once remarked that Africa always brings something new. And today it can truly be said that indeed, the black colossus tends to be new in everything, on a grand scale: independent national states, formation of new nations, rapid growth of its specific weight in international relations, a very high initial rate of scientific and technological progress, etc.etc. F.I.M.A. Professor and Head of Department of Aeronautics. The City University, London.

Agonism and antagonism of gamma-aminobutyric acid.

Abstract: EVIDENCE that (+)bicuculline (BIC) is a competitive antagonist of the central inhibitory transmitter γ-aminobutyric acid (GABA) is based1 mainly on apparent similarities between the molecular structures of BIC, GABA and agonists of GABA. Until recently, there has not been any explanation of the differing potencies of the agonists, or why BIC is an antagonist instead.

Hepatic albumin and urea synthesis: The mathematical modelling of the dynamics of [14C]carbonate-derived guanidine-labelled arginine in the isolated perfused rat liver.

Abstract: A mathematical model was constructed to define the dynamics of incorporation of radioactivity into urea carbon and the guanidine carbon of arginine in plasma albumin after the rapid intraportal-venous administration of Na214CO3 in the isolated perfused rat liver. 2. The model was formulated in terms of compartmental analysis and additional experiments were designed to provide further information on subsystem dynamics and to discriminate between alternative model structures. 3. Evidence for the rapid-time-constant of labelling of intracellular arginine was provided by precursor-product analysis of precursor [14C]carboante and product [14C]urea in the perfusate. 4. Compartmental analysis of the dynamics of newly synthesized urea was based on the fate of exogenous [13C]urea, endogenous [14C]urea and the accumulation of [12C]urea in perfusate water, confirming the early completion of urea carbon labelling, the absence of continuing synthesis of labelled urea, and the presence of a small intrahepatic urea-delay pool. 5. Analysis of the perfusate dynamics of endogenously synthesized and exogenously administered [6-14C]arginine indicated that although the capacity for extrahepatic formation of [14C]-urea exists, little or no arginine formed within the intrahepatic urea cycle was transported out of the liver. However, the presence of a rapidly turning-over intrahepatic arginine pool was confirmed. 6. On the basis of these subsystem analyses it was possible to offer feasible estimations for the parameters of the mathematical model. However, it was not possible to stimulate the form and magnitude of the dynamics of newly synthesized labelled urea and albumin which were simultaneously observed after administration of [14C]carbonate on the basis of a preliminary model which postulated that both products were derived from a single hepatic pool of [16-14C]arginine. On the other hand these observed dynamics could be satisfied to a two-compartment arginine model, which also provided an explanation for discrepancies observed between albumin synthesis measured radioisotopically and immunologically. This was based on a relative overestimation of [14C]urea specific radioactivity resulting from the rapid dynamics of [14C]carbonate and the [14C]urea subsystem relative to the labelled albumin subsystem. The effects of arginine compartmentalization could be minimized in the model by minor slowing of the rate of [14C]carbonate turnover or by constant infusion of [14C]carbonate, both of which permitted valid determination of albumin-synthesis rates.

A reliability model for Markov structured software

Abstract: A system is considered in which switching takes place between sub-systems according to a continuous parameter Markov chain. Failures may occur in Poisson processes in the sub-systems, and in the transitions between sub-systems. All failure processes are independent. The overall failure process is described exactly and asymptotically for highly reliable sub-systems. An application to process-control computer software is suggested.

The stopping power of organic compounds for alpha particles in the range 1.5-8 MeV

Abstract: Range-energy relationships for 8.78 MeV alpha particles in polystyrene, polypropylene and ethyl cellulose have been determined. The stopping powers of CH and CH2 groups are compared in the solid, liquid and vapour phases and significant differences are noted. The experimental results are also compared with theoretical results. The differences indicate that the mechanism of charge-changing in different phases is incompletely understood.

Supersonic Flow about Ducted Bodies with Subsonic Internal Boundaries

Abstract: A transient finite-difference method was developed to compute the transonic flow about blunt lipped ducted bodies in supersonic freest reams. A second-order accurate and explicit method was adapted for the computation of the interior regions and a transient method of characteristics was used at the boundaries. The flow velocity at the internal boundary was subsonic; this boundary was specially treated so as to enable the mass flow ratio and/or the axial velocity component to be specified. Three inlet shapes were investigated for axisymmetric and two-dimensional flows: two circular section inlets and an elliptic section.

Colours experienced in dreams.

Abstract: Colours seen in dreams by six observers were recorded from memory and plotted on a CIE u, v, chromaticity diagram. Only about half the dreams recorded contained colour, and in those in which colour appeared the more saturated purples, blues and blue greens were absent. It is suggested that during achromatic dreams the areas of the visual cortex which seem to respond only to colour may be inoperative. The paucity of blue in dreams could be anatomically related to the small population of blue units in the colour areas of the cortex.

A note on special photographic techniques applicable to photoelasticity

Abstract: Equidensity techniques used increasingly in photoelasticity are based on pseudo-solarization effects. These and related photographic phenomena are defined, the classical procedure and improvements described, basic experimental results and calibration methods demonstrated.

Discrete-Time Synchronization of Communications Networks Having Variable Delays

Abstract: A modification of a discrete-time method of synchronizing the clock frequencies in a digital communications network which makes the system frequency independent of time-varying transmission delays in the links of the network is discussed.

The effects of an electrostatic field and air stream on water jet break‐up length

Abstract: An experimental study of the break-up length of a circular section liquid jet subject to the combined action of a coaxial airstream and an electrostatic field is reported. A high speed photographic technique has been employed and the results have been correlated empirically by the following dimensionless equation: where “b” and “k” are functions of Reynolds number. On presente une etude experimentale de la longueur de rupture d'un jet liquide a section circulaire, lequel est soumis a l'action conjointe d'un courant d'air coaxial et d'un champ electrostatique. On a employe une methode photographique a vitesse elevee et l'on a etabli une correlation empirique entre les resultats au moyen de l'equation non dimensionnelle qui suit: ou “b” et “k” sont des fonctions du nombre de Reynolds.

A World Information System for the social sciences

Abstract: A summary of the report of the Unesco meeting of experts on the problems and strategies of incorporating the social sciences into the world science information system (UNISIST) is given, followed by discussion of the implications for social scientists, as users of information services, of some of the proposals put forward at that meeting. In particular, the problems involved in standardizing terminology for thesauri and other bibliographical facilities, and the advantages which are likely to be derived from common standards of data collection are discussed.

Memory Confusions and Memory Codes: A Simulation of the Acoustic Similarity Effect:

Abstract: It is hypothesized that items are coded for short-term storage in the language of the modality through which the customary responses to these items are normally monitored. This Response Monitoring Modality Hypothesis may account for the acoustic similarity effect in short-term memory for verbal items. The hypothesis was tested using non-verbal material. After paired-associate training subjects were found to confuse, in retention tests, items sharing similar previously trained responses to a greater extent than items that were directly similar to one another. The experiment simulates under controlled conditions the natural phenomenon of acoustical confusions in short-term memory, and provides strong support for the Response Monitoring Modality Hypothesis.

Productive and Circulation Capital

Abstract: It is now necessary to consider the different forms that capital assumes at different moments in its circuit. As it passes through the spheres of production and circulation so capital changes; in one it is productive capital; in the other circulation capital. These two forms are as distinct from each other as the activities to which they correspond: the production of commodities in the one case; the buying and selling of them in the other. But in capitalist society the circuit of capital does not merely embrace the spheres of production and circulation, it unites them: they remain distinct, but they are inseparable. So it is with the two forms of capital that operate within them: while each has its own distinguishing features, they share the common property of being capital and are governed by its general laws.

Separated flow convection

Abstract: Separation is an important characteristic of the type of flow encountered in many modern heat transfer devices. Design requirements of compactness have resulted in the rapid growth of the use of complex geometrical heat transfer surfaces, which have developed from the single tube and tube bank placed across the line of flow. A single tube or cylinder placed in a cross-flow is completely submerged in the fluid and it therefore forms an obstacle around which the fluid must flow. A boundary layer exists on the cylindrical surface with free stream velocity at its extreme and zero velocity at the wall. However, the free stream velocity increases around the front of the cylinder and at low approach velocities flow within the boundary layer also accelerates. Behind the cylinder free stream and boundary layer flow decelerates again in a more or less reverse pattern. At higher approach velocities the increased velocity around the front of the cylinder which is accompanied by a drop in static pressure is not followed by a similar increase in velocity in the boundary layer, due to the increased viscous stress at the higher velocity gradients. Thus, in the boundary layer the fluid has lost velocity before it starts to decelerate behind the cylinder and it is then opposed by a ‘surplus’ of static pressure which forces the boundary layer away from the surface. Separation, or break-away, results in the formation of turbulent eddies which are carried downstream behind the cylinder. Separation occurs nearer the front of the cylinder as the approach velocity increases, and occurs much more readily in flow over blunt ended obstacles.

Industrial Capital and Underdevelopment

Abstract: The collapse of primary commodity prices during the depression of the 1930s brought all the pressures bearing on merchant capital to a head. The savagely reduced prices it was forced to pay producers in a desperate attempt to protect its profits carried the crisis into the underdeveloped world, which responded with nationalist opposition to the whole political and economic order established in the nineteenth century. This marked the beginning of the end for the phase of underdevelopment in which merchant capital had mediated between the capitalist and non-capitalist worlds and productive capital had scarcely strayed from its homelands.

Effect of speed adaptation on performance in a self-paced tracking task.

Abstract: 12 Ss were required to perform a self-paced tracking task designed to simulate 'hazardous' road conditions. Those 6 Ss who had previously been exposed to a simple, high-speed version of the task travelled faster and made more errors on the hazardous task than 6 control Ss who performed the hazardous task throughout the experiment. The findings supplement earlier studies of the effect of speed adaptation on the judgment of speed and suggest that, in addition to perceptual distortions, an acquired motivation for speed may be an important factor in the behaviour of drivers leaving high-speed roads. Language: en

The equations of heat conduction

Abstract: The Fourier equation of heat conduction (1.1) has already been introduced. This equation is for one-dimensional heat flow, and may be written in a more general form: $${Q_n} = - kA{{\partial t} \over {\partial n}}$$ (2.1) where Q n is the rate of heat conduction in the n-direction, and ∂t/∂n is the temperature gradient in that direction. The partial derivative is used since there may exist temperature gradients in other directions. One-dimensional conduction does not often occur in practice since a body would have to be either perfectly insulated at its edges or so large that conduction would be one-dimensional at the centre.

Forced convection: Reynolds analogy and dimensional analysis

Abstract: Consideration of convection has so far been limited to laminar flow. For turbulent flow, it is possible to introduce additional terms into the momentum and energy equations to account for the presence of turbulence, and to obtain numerical solutions to the finite difference forms of the equations.1, 2 However, these methods have only become possible with the use of the more recent and more powerful generations of digital computer, and at an introductory level the more classical approaches will be followed.

The Acceleration of Capital

Abstract: As capital accumulates it increases not only the rate of exploitation but also its rate of turnover. While the former is obscured by rising real wages the effects of the latter are plainly visible and directly experienced by all sections of the society. Their impact on the sphere of consumption has always evoked traditional conservative complaints about a ‘decline in the quality of life’ which in recent years have swollen into a fashionable torrent of radical criticism. Capital is intoxicated with speed just as much as with quantity: the question how much? always implies another, how quickly? The ‘increase in the pace of life’ which so many commentators bemoan and explain in terms of the means by which it is achieved — i.e. in terms of modern technology or some other facile euphemism — is the visible result of increases in the rate of turnover of capital for the sole purpose of increasing surplus value and accumulation.