Showing papers by "University of London published in 1968"

Cardiovascular survey methods.

Abstract: Cardiovascular survey methods , Cardiovascular survey methods , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Acetylene reduction by nitrogen-fixing blue-green algae.

Abstract: Known nitrogen-fixing species of blue-green algae are capable of reducing acetylene to ethylene, but acetylene is not reduced by Anacystis nidulans, which does not fix nitrogen. Cycad root nodules which contain blue-green algae as endophytes reduce acetylene. Acetylene reduction is inhibited by carbon monoxide. Nitrate or ammonium-nitrogen has no immediate effect on algae reducing acetylene, but algae grown on nitrate-nitrogen gradually lose their capacity to reduce acetylene. Nitrate-nitrogen also inhibits heterocyst formation in these algae and there is a fairly direct correlation between the abundance of heterocysts in a particular sample and its capacity to reduce acetylene. Aphanizomenon flosaquae reduces acetylene and fixes nitrogen in unialgal culture and there is strong presumptive evidence that these reductions are carried out by the alga rather than by associated bacteria. The molar ratios of ethylene: ammonia produced vary within the range 1.4–1.8.

Epistemology Without a Knowing Subject

Abstract: Publisher Summary This chapter presents the author's view on epistemology. This chapter introduces the author's various theses, and his explanation of the third world and the world of objective contents of thought, especially of scientific and poetic thoughts and of works of art. A biological approach to the third world is provided in the chapter to defend the existence of an autonomous world by a kind of biological or evolutionary argument. The chapter illustrates the objectivity and the autonomy of this third world. With the evolution of the argumentative function of language, criticism becomes the main instrument of further growth. The autonomous world of the higher functions of language becomes the world of science. The chapter provides an appreciation and criticism of Brouwer's epistemology and discusses the logic and the biology of discovery. It presents the concept of discovery, humanism, and self-transcendence.

Is the Heterocyst the Site of Nitrogen Fixation in Blue-green Algae?

Abstract: MANY blue-green algae produce a characteristic type of cell with rather hyaline contents and a thick, refractive wall (Fig. 1) to which the name heterocyst has been given. Heterocysts are formed from vegetative cells only in filamentous forms. It has been suggested that they are reproductive structures1, are involved in spore formation2,3 or that they are storage cells4, but on the whole the various explanations for their function have been unconvincing, and in reviewing the situation in 1951 Fritsch described them as a “botanical enigma”5.

Changes in the Problem of Inductive Logic

Abstract: Publisher Summary This chapter discusses several changes in the problem of inductive logic. There are two main problems of classical empiricism: inductive justification and inductive method. Classical epistemology in general is characterized by its two main problems: (1) the problem of the foundations of—epistemic, that is, perfect, infallible—knowledge (the logic of justification); and (2) the problem of the growth of—perfect, well-founded—knowledge or the problem of heuristic, or of method (the logic of discovery). The classical twin problems of induction were the justification of theories, and the discovery of theories from facts. Carnap's neoclassical solution provides at best a solution of the problem of weak justification. However, it leaves the problem of discovery, the problem of the growth of knowledge, untouched.

Permeability of articular cartilage.

Abstract: IN 1962, McCutcheon1 first drew attention to a decrease in the permeability of articular cartilage with increasing depth from the surface. This observation has been confirmed2 and the permeability shown to be inversely related to the fixed charge density of the cartilage matrix. In turn the fixed charge density can be shown to be a direct measure of the mucopolysaccharide content of the matrix (unpublished results of A. Maroudas and H. Muir).

The Measurement of Psychoticism: a Study of Factor Stability and Reliability

Abstract: An investigation is reported into the measurement of the personality dimension P (psychoticism), which has emerged from factorial and other empirical studies as a third dimension additional to E (extraversion) and N (neuroticism.) Large groups of normal men and women, and of male and female students, were administered an inventory containing 106 potential P, E and N items, and the results analysed in detail. It emerges that P, E and N factors are found, as predicted, in the factor analysis of the data; that reliable scales can be constructed from the available items for P; and that the factors found are relatively invariant from one sex to the other, and from one sample to others. It appears that N and P are not entirely independent, but correlate to a moderate extent. It is suggested that P might be a personality variable of interest in connexion with many experimental investigations; that it might determine differential performance, either alone or in conjunction with E and/or N; and that experimental studies of P in normal subjects might throw much needed light on the nature and meaning of psychoticism as a personality variable.

Tensile Properties of Articular Cartilage

Abstract: ARTICULAR cartilage consists principally of collagen fibres embedded in a mucopolysaccharide ground substance. Electron microscopy studies1 show that the collagen fibres near the articular surface are predominantly parallel to the surface; viewed perpendicularly to the surface, they also show a dominant orientation which varies systematically over the whole joint surface. In contrast, the fibres in the deeper zones have a more random distribution with a tendency to be perpendicular to the surface. The fibre diameter and distance between adjacent fibres appear to increase with depth from the articular surface. Chemical and physico-chemical studies (unpublished results of H. Muir and A. Maroudas) confirm that the collagen density decreases with depth from the articular surface.

Pathogenesis of oedema of the optic disc.

Abstract: The literature on the subject of pathogenesis of oedema of the optic disc (Papilloedema) in intracranial space-occupying lesions and intracranial hypertension has been reviewed. The subject was investigated experimentally in detail in 77 rhesus monkeys and 26 rabbits. No oedema of the optic disc could be produced by acute intracranial hypertension in monkeys. With progressively growing experimental intracranial space-occupying lesion, situated in different regions of the brain, oedema of the optic disc was produced successfully in monkeys but not in rabbits. The various factors influencing the maximum size attained by the intracranial space-occupying lesion, the cerebrospinal fluid pressure (CSFP), and the fundus changes were investigated and co-related. A rise of CSFP in the cranial sub-arachnoid space and its successful transmission into the sheath of the optic nerve, with a rise of pressure in the latter, was found to be essential for the production of oedema of the optic disc. The degree of communication between the cranial cavity and the sheath of the optic nerve was investigated and was found to be variable in the region of the optic canal. The investigations excluded the role of compression of the central retinal vein, the extension of oedema of the brain, and the forcing of the cerebrospinal fluid from the sheath of the optic nerve along the perivascular space in the optic nerve in the production of oedema of the optic disc. Fluorescein fundus photographic studies revealed an increased capillary permeability in the optic disc in its oedema. The various theories of pathogenesis of oedema of the optic disc described in the literature have been discussed in the light of the new facts that have emerged from the present experimental investigation.

Moments of the statistics kappa and weighted kappa

Abstract: This paper considers the mean and variance of the two statistics, kappa and weighted kappa, which are useful in measuring agreement between two raters, in the situation where they independently allocate a sample of subjects to a prearranged set of categories.

Experimentally-Induced “Sexual Fetishism”: Replication and Development

Abstract: Five Ss were conditioned to give sexual response to a photograph of a pair of knee-length boots (CS) and then the response was extinguished by repeated presentation of the CS alone. Another condition (backward conditioning) was included to control for the possibility of pseudo-conditioning. None of the Ss reached the criterion in this control condition.

Mechanisms of sustained increases of firing rate of neurones in the rat cerebral cortex after polarization: role of protein synthesis.

Abstract: THERE is increasing evidence that some long-term changes in the functioning of the central nervous system, for example, learning and memory, are dependent on protein synthesis1,2. The functioning of individual elements, however, is unaffected for long periods of time (24 h) using actinomycin D (ref. 3), which prevents RNA synthesis and for 7–12 h after puromycin has been given4, which blocks protein synthesis. It has been shown that sustained elevations of neuronal firing rate in the cortex following a 10 min period of polarization are not dependent on the activity of reverberating circuits, but more probably on changes in synaptic conduction (see preceding communication), and so it was decided to investigate the effects of inhibitors of protein synthesis on the establishment of these sustained changes.

Mechanisms of Sustained Increases of Firing Rate of Neurones in the Rat Cerebral Cortex after Polarization: Reverberating Circuits or Modification of Synaptic Conductance?

Abstract: IF a rat is anaesthetized with urethane (1.8 g/kg given intraperitoneally) and prepared for microelectrode recording from the cerebral cortex1, cells discharge in bursts. The mean frequency, that is, total number of spikes/s, of these bursts of firing will stay constant for many hours provided the animal is not stimulated in any way and kept at a steady temperature. The passage of a polarizing current between a wick on the cortical surface and an indifferent electrode in the orbit, so that the cortical surface is positive with respect to the indifferent, will cause the rate of discharge of the cells to be increased. Furthermore, if the current maintains the increased rate of discharge for more than 5 min then, on turning the current off, the discharge rate does not return to the preexisting value but remains at an increased level1. I shall refer to this prolonged increase in activity as an “aftereffect” for convenience. Bindman2 and I and Lippold3 have shown that the after-effect is a result of the increase in neuronal discharge rate during stimulation and not of the specific nature of the stimulus itself.

Irrigation of Submerged Marine Sands through Wave Action

Abstract: PRELIMINARY tests carried out on the permanently submerged amphioxus sands at Le Racou (Roussillon) on the Mediterranean coast of France on August 27, 1968, have shown that turbulence and differences in hydrostatic pressure at the seabed caused by the passage of surface waves produce water movements in permeable deposits. These chiefly quartz sands were at a depth of 3 m and had the approximate grain size distribution, determined from samples taken from the area at this depth, shown in Table 1. Sand ripples ran north to south across the line of approach of the waves of maximum fetch from the east and were approximately parallel to the shore. The crests of the ripples were 75 cm apart and separated by a more or less flat trough 30 cm broad. The height from trough to crest of the ripple was 12–15 cm. The hand could be thrust into the sand without excessive resistance to a depth of about 7.5 cm on the crest of the ripple and 5 cm in the trough, indicating unconsolidated conditions to these depths. It was relatively calm at the time of the test, the wave direction being from the east, that is across the sand ripples, and the wave height from trough to crest about 50 cm.

Analysis of unbalanced polyphase networks by the method of phase co-ordinates. Part 1: System representation in phase frame of reference

Abstract: The analysis of unbalanced-power-system problems depends usually on transformation methods by which the primary or phase quantities are substituted by, for example, symmetrical-component quantities. These transformations have had computational advantages in the past, but with the use of the digital computer, they no longer appear to be necessary. Investigations into system-unbalance problems and their solution using only the actual system phase voltages, currents and impedances show that a major difficulty concerns the representation of transformers. In this paper the principles of transformer models in phase co-ordinates are derived and applied to the development of the phase equivalent circuits of a number of balanced and unbalanced polyphase multiwinding transformers. The basic element of these equivalent circuits is shown to be a symmetrical lattice network that is bilinear in all cases except for quadrature boosting transformers. With these equivalent circuits and with the phase representations of the transmission lines, generators and other system components it is then possible to solve unbalanced polyphase network problems entirely in phase co-ordinates, retaining symmetrical components only as measures of system unbalance.

Human power output.

Abstract: IT has been known for a long time that power output in man increases rapidly with decreasing duration of exercise, but there have been few systematic studies of this problem. Indeed, measurements of the power output of the body during a single movement lasting one-tenth of a second or less have not been made.

Excitatory acidic amino acids and the cation content and sodium ion flux of isolated tissues from the brain

Abstract: 1. Sample from the neocortex and piriform cortex of guinea pigs and rats were incubated in inulin-containing glucose-saline. Their intracellular (non-inulin) space contained 19-27muequiv. of Na(+)/g. of original tissue. These values were stable between 30 and 100min. after incubation commenced, but addition of (22)NaCl to the neocortical samples showed them to be associated with a flux of 400muequiv. of Na(+)/g. of tissue/hr. 2. Addition of 0.5-10mm-l-glutamic acid or 0.1mm-N-methyl-dl-aspartic acid rapidly increased the tissue's Na(+) content; N-acetyl-dl-aspartic acid was without action. 3. During the first 1-1.5min. after the addition of l-glutamic acid to neocortical samples their Na(+) content increased at 600muequiv./g. of tissue/hr., and the rate of (22)Na(+) influx corresponded to 1230muequiv. of Na(+)/g./hr. These rates were calculated to be sufficiently rapid to account for loss of the tissue's normal membrane potential within 1-2sec. of the addition of the acid. 4. In addition, a rapid but more limited loss of K(+) took place after the addition of l-glutamic acid or the methylaspartic acid; on continued incubation tissue K(+) content increased, as also did the intracellular volume of the tissue, from its original 670mul./g. to 1100mul./g. 5. Interpretation of these and of associated changes is offered in terms that involve a cation pump and the permeability changes associated with the nerve impulse.

Deriving coefficients of reliability and agreement for ratings.

Abstract: The paper is concerned with the measurement of internal consistency of rating scales and interviewing schedules, with the assessment of bias between different raters and with coefficients for measuring the degree of agreement between them. Analysis of variance models are first employed, but reference is also made to earlier psychometric techniques and to recent work by Armitage et al. and by Fleiss.

Improved holographic model of temporal recall.

Abstract: THE static model of temporal recall which I recently proposed1 as an alternative to Longuet-Higgins' model2 is unsatisfactory in one respect. From a fragment which is remembered it can recall earlier parts of the whole sequence. This is unlike human memory which can readily recall later parts, but earlier parts only with great difficulty, if at all, especially if the sequence has been memorized by rote. If we want to imitate human memory with models, we must take account of the weaknesses of the nervous system as well as of its powers. Longuet-Higgins' model possesses this property, and so does the modified static system described here.