Showing papers by "Queen's University Belfast published in 1974"

Monitors: an operating system structuring concept

Abstract: This paper develops Brinch-Hansen's concept of a monitor as a method of structuring an operating system. It introduces a form of synchronization, describes a possible method of implementation in terms of semaphores and gives a suitable proof rule. Illustrative examples include a single resource scheduler, a bounded buffer, an alarm clock, a buffer pool, a disk head optimizer, and a version of the problem of readers and writers.

Phospholipids and plant membrane permeability

Abstract: SUMMARY Current views on membrane construction are presented as a basis for discussing certain modifications of structure that may render membranes leaky, allowing solutes to diffuse from them. Biophysical experiments on dehydrated membranes indicate that, when their water content is reduced below 20%, they no longer adopt the lipid bilayer conformation. When dry seeds, spores or lichens are placed in water, soluble cell constituents leak from them for a few seconds or minutes until membrane integrity is re-established; the same may apply also to the liberation of solutes from pollen grains. Moreover, there are indications that ‘dry’ in this context means having less than about 20% water. Some plants are sensitive to chilling, their tissues becoming leaky when exposed to temperatures between 0 and 10°C. This chilling-induced leakage, attributed to a phase change in all the phospholipids of which the membrane is composed occurs at a slightly lower temperature than the change in the activation energy of membrane-bound enzymes. At senescence, leaf tissues become leaky and may eventually dry out. So much phospholipid disappears from senescing cotyledons of cucumber that there is no longer sufficient to fabricate complete and intact membranes around the cells. Treating cucumber cotyledons with iodoacetate also causes a loss of phospholipids, allowing solutes to leak out of the cells. It is possible that exposing seeds or mature plant tissues to oxygen at pressures of 1 or more atm renders them leaky because of lipid peroxidation.

Pulse evolution in mode-locked quasi-continuous lasers

Abstract: Various models of a passively mode-locked quasi-continuous laser are discussed and the evolution of pulses in various cavity configurations is traced. In certain circumstances, the combined action of amplifier and absorber saturation is shown to lead to rapid pulse compression even when the pulse duration is far shorter than the relaxation time of either nonlinear component. The results are in good agreement with recent streak- camera measurements involving the pulsed Rhodamine 6G dye laser and satisfactorily explain the efficient generation of picosecond pulses in CW dye-laser systems. The same pulse-compression mechanism can probably be used to generate ultrashort pulses in other quasi-continuous lasers.

Ultrashort pulse measurements

Abstract: The generation of intense ultrashort light pulses in mode-locked laser systems has made possible a wide range of new experiments designed to study the interaction of light with matter. For the quantitative interpretation of the results, accurate measurement of the optical pulse structure is essential, and it is the purpose of this paper to review all the diagnostic techniques currently available. The recent rapid development of the electron-optical streak camera is highlighted, while considerable space is devoted to an extensive description of the many second- and higher order correlation measurements (including the popular two-photon fluorescence method). A discussion of ultrafast shutter techniques is also included, together with a section on pulse chirping and dynamic spectroscopy.

Consistent and complementary formal theories of the semantics of programming languages

Abstract: This paper presents a comparative study of different methods for formal description of programming languages. These methods have been applied to a simple but realistically usable programming language; the more abstract definitions have been proved to be consistent relative to the more concrete ones.

The growth and division of the single mitochondrion and other organelles during the cell cycle ofChlorella, studied by quantitative stereology and three dimensional reconstruction

Abstract: During the cell cycle ofChlorella fusca var.vacuolata 211-8p, the growth of individual organelles is not restricted and holds their average percentage contribution to total cell volume at levels close to 40% for the chloroplast, 3% for the mitochondrion and 10% for the vacuoles and nucleus throughout the cycle. In contrast pyrenoid growth is restricted to the beginning of the cycle and its volume declines after 10 hours, while starch reaches a maximum at 16 hours and disappears during the ensuing dark period. Consumption of pyrenoid starch begins first as cells enter the S phase. Total tonoplast area is equal to at least half of plasmalemma area and an increase in its area is maintained throughout the cycle, even during the period of cytokinesis because although total vacuole volume falls then, there is at this time an increase in the number of vacuoles. The vacuoles contain polyphosphate bodies, which were examined by energy-dispersive x-ray microanalysis.

Studies on the gill of Mytilus edulis: the eu-latero-frontal cirri.

Abstract: Adjacent eu-latero-frontal cirri beat alternately and alternate cirri exhibit metachronous activity. Each cirrus consists of 22-26 pairs of cilia arranged in two parallel but alternating rows. Individual cilia leave the shaft of the cirrus at regular (0.6 $\mu $m) intervals on each side to extend across the intercirrus space. Each cilium, where it bends to leave the cirrus shaft, contains a stiffening rod which extends 1.5 $\mu $m distally as a tapering, hemispherical rod, lying between peripheral fibril 1 and the paired central fibrils. Distal to the bend, the peripheral fibrils are singlets and lack arms. It is concluded that the disposition of this region of the cilium to the cirrus shaft remains more or less constant during both the effective and recovery strokes of the cirrus and this disposition is such that interference between adjacent cirri is minimal while permitting effective filtering of the space between alternate cirri. The mesh of the filter is 0.6 $\mu $m by either 2.4 $\mu $m or 4.8 $\mu $m, the latter depending on the relative positions of adjacent cirri. The pro-latero-frontal cilia may serve to transfer material from the eu-latero-frontal cirri to the frontal cilia of the gill filament.

Blood levels of practolol after oral and parenteral administration and their relationship to exercise heart rate.

Abstract: Blood levels of practolol after oral and parenteral administration were determined in normal subjects, and the effects of each dose on the heart rate induced by strenuous exercise were measured. Oral practolol was rapidly absorbed and produced peak blood levels in 1 to 3 hours. Between 2 and 7 hours blood levels varied little more than twofold either within or between subjects. The half‐life of practolol in blood was 10 to 11 hours. Practolol100 mg was the minimum dose to produce near maximum blockade at 2 hours; maintenance of this effect for 24 hours reqUired 400 mg. Near maximum blockade was produced as long as a blood practolol level of 1.0 to 1.4 µg per milliliter was maintained. There was a correlation between the logarithm of the blood practolollevel and the percentage reduction of exercise heart rate. Practolol 40 mg and 80 mg intravenously initially achieved near maximum blockade associated with blood practolol levels above 1.0 p.g per milliliter. The effects and blood levels fluctuated during the first 7 hours. Intramuscular doses up to 40 mg failed to produce near maximum blockade; higher doses were precluded by pain at the injection site.

Cyclic stress fatigue and thermal softening failure of a thermoplastic

Abstract: The application of a cyclic stress to a polymeric material causes its temperature to rise with the result that failure may occur by one of two completely different mechanisms. In the first the temperature rises for a time but then stabilizes and allows a conventional crack initiation and propagation process to take place. In the second type of failure the temperature continues to increase and results in a thermal softening failure in the material.

Vitelline cell development in monogenean parasites.

Abstract: Histochemical and electron microscopic studies of the vitellaria of three polyopisthocotylean fish-gill flukes,Diplozoon paradoxum, Diclidophora merlangi andD. denticulata, and one monopisthocotylean fish-skin fluke,Calicotyle kroyeri have shown that, in each case, vitelline cell development is basically similar. Immature vitelline cells are typically embryonic and undifferentiated. InD. paradoxum they display annulate lamellae, and inC. kroyeri they are invested with flat, sheet-like extensions of the parenchyma. Differentiation into maturing vitelline cells involves the development of extensive GER, Golgi complexes and the production of dense droplets of shell-protein. With the onset of maturity, protein synthesis stops and, as the GER disintegrates, the cell develops food-reserves in the form of yolk bodies, glycogen and lipid. It is then released into the vitelline ductlet. These processes occur in all the follicles at the same time, and all stages of development can be found in any one follicle.

Potentially dangerous surges in an Antrim mudslide

Abstract: Summary Measurements of surface movements and pore-water pressures in a mudslide at Minnis North, north-eastern Ireland, are presented. This feature comprises steep feeder mudslides leading down to a more gently inclined accumulation mudslide, from which a steep front slope descends to the coast road. Frequent surges of the mudslide, which discharges considerable quantities of debris on to this road, are described and discussed. In one of these, pore-water pressures and surface movements were monitored up to failure and the surge itself witnessed by one of the authors. It is concluded that the surges generally originate through‘undrained loading’ of the rear of the accumulation slide by the feeder slides. Attention is drawn particularly to the danger inherent in situations where large volumes of underconsolidated and therefore potentially highly mobile material can collect above a steep front slope and to the difficulty, in the case studied, of obtaining warning of failure. Evidence is also presented to show that this danger is increased if surface streams are present on the mudslide.

A questionnaire measure of Sexual Interest

Abstract: A questionnaire measure of Sexual Interest is described; in construction and scoring, the authors have borrowed from the Sexual Orientation Method. Five subscale scores relating to different areas of sexual behavior can be measured, and an overall Sexual Interest score obtained. The measure is fully described, and preliminary data on internal consistency, reliability, and validity are presented. Applications of the scale are described for both clinical and research purposes.

Oblique fold axes in the Dalradian rocks of the Southwest Highlands

Abstract: Synopsis The development of folds with axes oblique to the northwest-southeast stretching-direction during the first two stages in the deformational history of Dalradian rocks in the Southwest Highlands is considered in terms of a quantitative model recently proposed by Sanderson (1973). This model allows the distribution of fold axes within the axial planes of the folds to be related to (1) the initial variability of the individual fold axes about a mean fold axis, (2) the initial attitude of the mean fold axis relative to the stretching-direction and (3) the amount of subsequent deformation within the axial planes of the folds. The various patterns of distribution shown by the fold axes in the Southwest Highlands are related to regional variations in (1) the initial attitude of the mean fold axis relative to the stretching-direction and (2) the amount of deformation within the axial planes of the folds. Measurement of strain indicators such as breccia fragments confirms that the strain ratios determined from the distribution of fold axes provide a reasonable estimate of the strain. Previous ideas concerning the development of these oblique folds are discussed in the light of the present work.

Accumulation of fungi by cellulose exposed in a river

Abstract: When sterile cellulose was placed in a river no evidence was found that cellulolytic ‘soil fungi’ and ‘leaf fungi’ actively colonize or break down the cellulose. The observed increase in numbers of such fungi on the cellulose with time of exposure could be attributable to passive accumulation of inactive propagules. At least some of the fungi that appear to be active in exposed substrata fail to develop on the isolation plates used.

THE ASSESSMENT OF β‐ADRENOCEPTOR BLOCKING DRUGS IN HYPERTHYROIDISM

Abstract: 1 Intravenous propranolol and practolol both reduced resting supine heart rate in patients with hyperthyroidism. Propranolol produced a significantly greater reduction than practolol, which did not have a dose-dependent effect. 2 The effect of these drugs on resting heart rate was much less than their effect on the tachycardias produced both by severe exercise and by standing upright in hyperthyroid patients. Propranolol again produced a significantly greater reduction than practolol in each situation, but practolol did have a dose dependent effect on exercise heart rate. 3 The percentage reduction of standing tachycardia produced by the two drugs appeared to parallel closely the reduction in exercise tachycardia. 4 It is concluded that a simple and convenient way of assessing the activity of β-adrenoceptor blocking drugs in hyperthyroid patients would be to measure their effect on the tachycardia induced by standing. Their effect on resting heart rate should not be used. 5 Practolol may be useful in the management of hyperthyroidism in patients in whom propranolol and similar non-selective β-adrenoceptor blocking drugs are contraindicated.

A histological and histochemical study of the cotyledons of Phaseolus vulgaris L. during germination.

Abstract: The cotyledon ofPhaseolus vulgaris L. comprises four tissues: epidermis, abaxial hypodermis, storage parenchyma, and procambium. A complex intercellular space system is present throughout the storage tissue and comprises about 16% of the cotyledon volume. All the cells contain protein bodies, and the hypodermis and storage parenchyma also contain starch grains. The epidermal cells are at the 2 C level of DNA, those of the hypodermis at the 4 C level, and the storage cells vary from 8 C to 32 C. During germination stomata differentiate in the epidermis. Reserve mobilization begins in the cells furthest from the epidermis and from the vascular tissue. Protein is removed from these cells with little or no coalescence of protein bodies. The DNA content of the nuclei decreases. The cell walls swell and then decrease in thickness as material is removed. Finally the nuclei and cytoplasm disappear and the cells collapse. In the cells near vascular bundles the protein bodies coalesce before losing their protein. The DNA content of the nuclei declines but nuclei and cytoplasm are still present at abscission. These cells do not collapse. Cytoplasmic RNA content is highest near the abaxial surface. Most of the RNA is removed during the first three days of germination.

Studies of drugs given before anaesthesia xxiv: metoclopramide with morphine and pethidine

Abstract: When given with pethidine 100 mg or morphine 10 mg as preanaesthetic medication, 10 and 20 mg of metoclopramide cause a reduction in postoperative nausea and vomiting in women undergoing a standard operation with a standard anaesthetic technique. The preoperative emetic effects of pethidine are almost completely abolished by metoclopramide. An additional 10–20 mg of metoclopramide, given i.m. at the end of the operation markedly reduces the emetic effects of pethidine premedication but has less effect when morphine has been given. The evidence suggests that the ineffectiveness of metoclopramide, relative to other antiemetics, is because of its brevity of action.

Defective interfering particles produced during the replication of measles virus.

Abstract: The RNA species present in purified measles virus preparations after 10−3 diluted passage (DP), three undiluted passages (UP3) and eight undiluted passages (UP8) were analysed by sedimentation on sucrose gradients. The particles contained RNAs sedimenting at 52S and 4S, 52S, 18S and 4S, and 52S, 30S, 18S, 11S and 4S respectively. Measles virus particles produced by UP3 were separated into two homogenous populations by rate zonal centrifugation on sucrose gradients. The rapidly sedimenting population contained encapsidated 52S RNA and was infectious virus. The slowly sedimenting particles contained encapsidated 18S RNA, were non-infectious, and they interfered with the replication of infectious virus.

De subitaneis mortibus. IV. Coronary vessels and conduction system in homocystinuria.

Abstract: Conspicuous abnormalities of the coronary arteries and veins and of the sinus node, atrioventricular (A-V) node and His bundle are described in the heart of a boy dying with congenital homocystinuria. The unproven possibility of transient disturbances of cardiac rhythm or conduction is discussed relative to the pathogenesis of the bouts of unconsciousness with and without convulsions characteristic of the disease. Factual information on the stability or instability of electrical activity of the heart in such patients is particularly needed because of the possibility of treatable aspects of an otherwise seemingly inexorable process.

The First Born Approximation

Abstract: Publisher Summary This chapter discusses the calculations using the first Born approximation and compares the theoretical results with experimental data to derive lower limits to the incident system energy. The evaluation of atom–atom cross sections in the Born approximation requires the same matrix elements as are necessary for electron–atom collisions in the first Born approximation, and errors not already inherent in the Born approximation may be introduced through the use of poor wave functions. Comparison of the Born total ionization cross section with the measured cross section suggests that the Born cross section is too large at a proton energy of 50 keV. Comparison of the differential cross section at 50 keV reveals that at this incident energy, the measured differential cross section lies below the Born differential cross section at almost all energies of ejection. For 2s excitation, comparison of the first Born approximation results with both experiment and more sophisticated calculations indicates that it is a satisfactory approximation for impact energies greater than about 10 keV.

Enzyme studies in a patient with saccharopinuria: a defect of lysine metabolism.

Abstract: Extract: Elevated levels of saecharopine, lysine, and citrulline in urine and plasma were observed in a patient suffering from saccharopinuria. Using radioisotope methods the lysine-degradative enzymes, lysine-oxoglutarate reductase and saecharopine dehyrogenase, were studied in skin fibroblasts grown from this patient and from healthy subjects. The results show that, in contrast to healthy individuals (range 177–320 pmol formed/min/mg protein), the paitent's fibroblasts are completely lacking in saecharopine dehydrogenase activity, which accounts for the presence of the high levels of saccharopine. The patient also has a reduced level of lysine-oxoglutarate reductase activity (333 pmol saccharopine formed/min/mg protein; range 550–1,570 nmol), which may in part explain the hyperlysinemia. A further enzyme saecharopine oxidoreductase which metabolizes saecharopine to lysine was found to be present in the patient's fibroblasts (63 pmol lysine formed/min/mg protein) but absent from those of healthy control subjects. This indicated induction of this enzyme by the patient in an attempt to reduce the high levels of saecharopine in her tissues and body fluid. Speculation: There are two interesting features of this patient with saccharopinuria which the present studies have not clearly defined, namely the presence of high levels of lysine and citrulline found in plasma and urine. There are three possible explanations for the hyperlysinemia which may be operating singly or in combination. Depression in activity of lysine-oxoglutarate reductase (the patient possesses 37% of the normal activity). Inhibitory effect of saecharopine on lysine-oxoglutarate reductase (in vitro studies). Induction by the patient of saccharopine oxidoreductase which metabolizes saccharopine to lysine. No explanation has yet been found for the high levels of citrulline in plasma and urine.

Isopeptide crosslinks--their occurrence and importance in protein structure.

Abstract: Isopeptide links refer to bonds between the ϵ-amino group of lysine and the side-chain carboxyl groups of glutamic or aspartic acid. Covalent crosslinks of this kind, which undoubtedly occur in protein feedstuffs and reduce their nutritional value, also participate In the fibrinogen → fibrin transformation and play a part in stabilizing the structure of keratins. Isopeptide links also arise on heating of both fibrous and globular proteins, the amount formed depending upon the severity of heat treatment. The mode of formation and the significance of these crosslinks require further elucidation.

Drain voltage limitations of MOS transistors

Abstract: A comprehensive investigation has been carried out into the factors which influence the maximum drain voltage of an M.O.S. transistor for normal pentode-like operation. The drain voltage is limited by two principal mechanisms, namely punch-through of the drain depletion region to the source, and breakdown, due to impact ionization in the high field region at the drain edge. A two-dimensional analysis technique for determining the drain voltage at the onset of either punch-through or avalanche breakdown, from a solution of Poisson's equation within the substrate depletion region, is described. The solutions are obtained using finite difference numerical methods which take into account the gate-induced potential profiles at the edge of the source and drain junctions. Boundary conditions of zero effective gate bias and channel current are imposed which simplify the solution of Poisson's equation to an electrostatic one. The punch-through voltage VPT is defined as the drain-to-source voltage at which the longitudinal field at any point along the edge of the source region inverts in sign to permit the drift of minority carriers from source to drain. Breakdown voltage, VBD, however, is determined by the drain voltage at which the maximum field in the device reaches the critical value for avalanche multiplication. Good agreement is achieved between theoretical and practical results for both mechanisms on a wide variety of devices. It is shown that VPT decreases as the channel length and substrate doping concentration decrease and as the oxide thickness and diffusion depth increase. VBD, however, decreases as the channel length, oxide thickness and diffusion depth decrease. Punch-through and breakdown are discussed for gate bias conditions above and below threshold. The sharp fall in breakdown voltage as the gate bias rises above threshold is explained on the basis of injected charge from the channel into the drain depletion region.