Showing papers by "University of Manchester published in 1971"

Studies of tunnel MOS diodes, I. Interface effects in silicon Schottky diodes

Abstract: A theoretical and experimental study has been made of silicon Schottky diodes in which the metal and semiconductor are separated by a thin interfacial film. A generalized approach is taken towards the interface states which considers their communication with both the metal and the semiconductor. Diodes were fabricated with interfacial films ranging from 8 to 26 A in thickness, and their characteristics are related to this model. The effects of reduced transmission coefficients together with fixed charge in the film are investigated. The interpretation of the current-voltage characteristics and the validity of the C−2-V method in the determination of diffusion potentials are discussed.

Undernutrition and the Developing Brain

Abstract: The importance of investigating the effects of undernutrition on the developing brain has become more widely recognized in the past few years. Unfortunately, a neurochemical consideration of the problem has scarcely begun. The aim of this chapter is to summarize the present state of knowledge, and an attempt will be made to interest neurochemical readers in the great need which exists for their participation in the debate.

Corrosion by the Sulphate-reducing Bacteria

Abstract: THERE are several explanations for the aggravation of corrosion of iron and steel in oxygen-free conditions by sulphate-reducing bacteria. These are (a) stimulation of the cathodic part of the corrosion cell by the removal and utilization of the polarizing hydrogen by the bacteria1; (b) stimulation of the cathodic reaction by solid ferrous sulphides formed by the reaction of ferrous ions with sulphide ions produced by bacteria2; (c) stimulation of the anodic reaction, metal dissolution, by bacterially produced sulphide3; (d) local acid cell formation4, and (e) formation of iron phosphide by reaction of the metal with bacterially reduced phosphates5.

Conduction in polythene with strong electric fields and the effect of prestressing on the electric strength

Abstract: There has been speculation in the past about the extent to which space charge formed by the flow of prebreakdown current affects the electric strength of polythene In the present work, conduction and absorption-current measurements up to about half the breakdown field have given clear evidence of space-charge effects Further evidence was obtained from measurements of the apparent ‘intrinsic’ electric strength under various modes of stressing It was found that the electric strength of polythene measured with direct voltage below about 30°C exceeded the corresponding value measured with impulse voltages by up to about 25% The impulse electric strength could be increased to equal the direct voltage by prestressing each specimen for 4min with direct voltage of the same polarity as the impulse voltage However, when the impulse was of opposite polarity to the direct prestressing voltage, the electric strength decreased with increase in the prestressing field The effect was dramatic, for the impulse electric strength changed from the normal value of about 6MV cm−1 to less than 2MV cm−1 as the prestressing field was increased to about 75% of the electric stength measured with direct voltage Experiments in which the breakdown impulse was applied some time after removal of the prestressing field showed that the impulse electric strength at 20°C recovered in about 10−2s to the value obtained with impulses without prestressing Thus the prestressing caused no permanent damage The observed effects are attributed to space-charge injection from the electrodes The observations are not consistent with the concept that breakdown occurs when the field at a point within the specimen exceeds a critical value, the intrinsic electric strength of polythene

Heat Transfer near the Critical Point

Abstract: Publisher Summary This chapter describes the behavior of thermodynamic and transport properties near the critical point. The near-critical region may be thought of as that region, in which boiling and convection merge. When the pressure is sufficiently subcritical or supercritical, the problem tends toward either a boiling problem or a constant property convection problem. Under such conditions, existing theoretical and empirical methods are generally adequate. The chapter concentrates on the region rather close to the critical point where the property variations are severe and where there are very significant heat transfer effects. The equations of continuity, momentum, and energy are examined with a view to revealing the effect of variable properties and deciding whether the same simplifications can be made as are common with a constant property fluid. Various modes of heat transfer are also discussed, particular attention being given to the interaction between forced and free convection.

Temperature relationship in continuous culture

Abstract: The steady-state and transient behavior of a chemostat-type continuous culture of Aerobacter aerogenes was investigated with special reference to temperature. Experimentally determined kinetic parameters of the fitted steady-state model were found to be strong functions of temperature. The transient response of the culture to a step change in temperature exhibited a dynamic lag whose magnitude depended on the nature and direction of step change.

Ab initio molecular orbital calculations of transition metal complexes. I. The electronic structure of nickel tetracarbonyl and chromium hexacarbonyl

Abstract: All electron ab initio SCF-MO calculations in a better-than-minimal basis of the electronic structure of Ni(CO)4 and Cr(CO)6 are reported. The results are compared with the measured ionization potentials, force constants and dissociation energies of these molecules, and with the electronic structures calculated by a number of semi-empirical schemes.

A theoretical interpretation of the bonding, and the photoelectron and ultra-violet spectra of sulphur dioxide

Abstract: Ab initio SCFMO calculations are described for SO2, using Slater-type orbitals expanded in gaussian-type functions. The electronic structures of SO, O3 and O2 are investigated, to facilitate analysis of the nature of sulphur 3d orbital participation in SO2. The theoretical interpretation of the photoelectron and ultra-violet spectra of SO2 is considered.

Studies of tunnel MOS diodes II. Thermal equilibrium considerations

Abstract: The oxide thickness δ of a tunnel MOS diode is varied over the range 10 to 45 A. This is done in an effort to establish the restrictions upon δ for which thermal equilibrium in the semiconductor is a valid approximation under the application of bias. Particular attention is paid to the reverse-bias case, and most of the experimental results are for δ>25 A. A transition is observed from the behaviour of the ideal Schottky barrier to that of the thick-film MOS device. The ac conductance and capacitance together with dc current characteristics are studied as continuous functions of bias. From these results, information is obtained which relates the quasi-Fermi levels for (i) majority carriers, (ii) minority carriers and (iii) electrons in the interface states to δ. Thermal equilibrium statistics are found to be applicable to the semiconductor in the presence of a bias voltage when δgreater, similar30 A, which compares with a theoretical prediction of δgreater, similar13 A.

A study in successful exporting

Abstract: Examines the export activities of a sample of companies which have won the Queen's Award to Industry for export achievement Looks at those criteria employed in order to achieve export success States that not all of the companies practised all of the criteria, with the majority using only two Concludes that the historical background and tradition of an organization, together with the attitudes of its senior management, are the most significant factors in determining the level of its success

A comparison of the oxidation behavior of Fe-Cr-Al, Ni-Cr-Al, and Co-Cr-Al alloys

Abstract: The main modes of isothermal oxidation of Fe-Cr-Al, Ni-Cr-Al, and Co-Cr-Al Alloys, containing 10–15 % or 26–30 % Cr and 0.9–1.3 % or 4.3–5.7% Al, in oxygen at 1000 and 1200° C are summarized. Where protectiveα-Al 2 O 3 scales always predominate, their ease of formation is in the order Fe-Cr-Al > Ni-Cr-Al > Co-Cr-Al. However, where catastrophic breakaway is possible, Ni-Cr-Al gives the most reliably protective scales, whereas Co-Cr-Al produces the most generally distributed breakaway or initially nonprotective scales, and Fe-Cr-Al the most locally catastrophic breakaway. The oxidation behavior is discussed in terms of the pertinent alloy and oxide parameters.

Stoicheiometrical proton and potassium ion movements accompanying the absorption of amino acids by the yeast Saccharomyces carlsbergensis

Abstract: 1. Proton uptake into the yeast Saccharomyces carlsbergensis, was studied at pH4.5–5.5 in the presence of both antimycin and 2-deoxyglucose to inhibit energy metabolism. Previous work had shown that the cells then absorbed about 20nmol of glycine or l-phenylalanine against a considerable amino acid concentration gradient. The addition of the amino acid immediately stimulated the rate of uptake of protons two- to three-fold. About 2 extra equivalents of H+ accompanied a given amount of the amino acids into the yeast preparations exposed to the metabolic inhibitors for 2–4min and about 1.2 equivalents after 20min exposure. 2. Analogous observations were made during serial additions of glycine, l-phenylalanine, l-leucine and l-lysine to preparations lacking the metabolic inhibitors and deficient in substrates needed for energy metabolism. In fresh cellular preparations the influx of glycine was then closely coupled to a stimulated flow of 2.1 equiv. of H+ into the yeast. A similar number of K+ ions left the cells. About 30% of the extra protons was subsequently ejected from the yeast. Deoxyglucose and antimycin together inhibited the ejection of protons. When the yeast had been fed with glucose energy metabolism was stimulated and almost as many protons as were absorbed with the amino acid were apparently ejected again. 3. Yeast preparations containing Na+, instead of K+, as the principal cation absorbed about 1 extra equivalent of H+ after the addition of phenylalanine, glycine or leucine. This response was not observed in the presence of both deoxyglucose and antimycin. 4. The observations show that H+ and, in certain circumstances, K+ are co-substrates in the transport of the amino acids into the yeast. An analogy is drawn with the roles of Na+ and K+ as co-substrates in certain mammalian systems. The results lead to various models relating the physical flow of the co-substrate ions on the amino acid carrier to the transduction of chemical energy in an associated ion pump forming part of the mechanism for transporting amino acids into the yeast.

Undernutrition and the developing brain: the use of animal models ot elucidate the human problem.

Abstract: There is no longer any doubt that growth restriction due to malnutrition at certain ages is associated in many children with an irreversible deficit in higher mental function. The phenomenon is by no means confined to the underprivileged communities of developing countries, but can be found, although on a smaller scale, in similar communities in the most advanced country in the world. It may also be allied to the diminished ultimate potential of some low birth weight babies from even the most privileged homes. A constant feature appears to be the need to maintain a good growth rate at least until the eighteenth month of human postnatal life. By contrast, the effects of growth retardation at later ages can apparently be reversed on restoring good dietary and other conditions.

Schottky barriers on p-type silicon

Abstract: Measurements have been made of the electrical characteristics of Schottky barriers made by evaporating films of various metals (Al, Pb, Ni, Au, Ag, Cu) onto p-type silicon. The barriers were generally lower than on n-type silicon, and in the case of Au the barrier was so low as to provide an effectively ohmic contact at room temperature. The truly exponential portion of the forward I–V characteristic was restricted to a comparatively small voltage range. Within this range ‘n’ values of about 1.10 were obtained. The reverse characteristics could be explained in terms of generation in the depletion region. The variation of barrier height with metal work-function indicates that the surface-state parameters (density of states and position of neutral level) are essentially the same for p-type as for n-type silicon. This is confirmed by the fact that, for a given metal, the sum of the barrier heights on n-type and p-type silicon is approximately equal to the band-gap.

Good, bad, or optimal?

Abstract: -Optimal control with a quadratic performance index has been suggested as a solution to the problem of regulating an industrial plant in the vicinity of a steady state. It is shown that such control is usually not feasible, and if feasible can have serious defects.

Effects of α‐methyl‐p‐tyrosine, p‐chlorophenylalanine, l‐β‐(3,4‐dihydroxyphenyl)alanine, 5‐hydroxytryptophan and diethyldithiocarbamate on the analgesic activity of morphine and methylamphetamine in the mouse

Abstract: 1. The analgesic activity of sympathomimetic drugs does not appear to involve a peripheral component. 2. Drugs causing changes in morphine analgesia have similar effects on the analgesia produced by methylamphetamine. 3. The analgesia produced by morphine and methylamphetamine is increased by drugs which increase the ratio of brain 5-hydroxytryptamine (5-HT) to dopamine. 4. The analgesia is decreased by drugs causing a fall in brain 5-HT or a rise in dopamine relative to 5-HT.

Comparison of the antinociceptive activities of physostigmine, oxotremorine and morphine in the mouse.

Abstract: Summary 1 Morphine, oxotremorine and physostigmine showed antinociceptive activity in mice using the hot plate reaction time test. 2 The action of morphine, but not that of oxotremorine, was antagonized by naloxone and by nalorphine, whereas the effect of physostigmine was unaffected by naloxone and increased by nalorphine. 3 The antinociceptive effects of morphine and of physostigmine were increased by procedures reported to increase the ratio of 5-hydroxytryptamine to dopamine in the brain. It was decreased by procedures reported to cause a fall in brain 5-hydroxytryptamine or a rise in dopamine relative to 5-hydroxytryptamine. 4 The antinociceptive effect of oxotremorine was potentiated by procedures reported to decrease brain noradrenaline and was unaffected by procedures altering brain 5-hydroxytryptamine. 5 The results suggest differences in the mode of action of morphine and physostigmine on the one hand and of oxotremorine on the other.

Non‐linear structural analysis by dynamic relaxation

Abstract: Dynamic relaxation, an iterative method for use with digital computers, is described and is shown to be suitable for the solution of a system of linear equations and in particular for such problems derived from structural frame analysis. It is further shown that the method may be modified to include non-linear equations relating to these problems. Some specific examples of linear and non-linear solutions are given and comparisons are made with another computer method which performs the same tasks.

Diets of large mammals in the woodlands around Lake Kariba, Rhodesia.

Abstract: Large mammals that formerly occupied the Kariba basin of the Middle Zambezi Valley have, since it was flooded, been forced to live in a restricted range of deciduous woodland habitats. Feeding records in a study area on the shore of Lake Kariba showed that most herbivore species were browsers, and that only the tree components of their diets varied significantly between vegetation types. The common species varied a proportion of their diet seasonally. However, each depended upon a small range of food staples which differed from those of other species and acted as food refuges for part of the year. Diets overlapped during the wet season because of diversification, and in the late dry season because of common use of a restricted range of plants remaining green. There was a good correlation between the ability of a species to avoid dietary overlap and its biomass in the study area. The chance of interspecific competition occurring increased in the late dry season when most of the species would formerly have migrated from the study area to the flood plain. Despite the enforced occupation of only part of their former annual range the more common herbivores maintained a considerable degree of ecological separation through utilisation of different foods.

Arc propagation along an electrolyte surface

Abstract: Flashover of wet polluted insulation is caused by the propagation of arcs along the wet surface. The paper describes experimental work which has been carried out with simple models to investigate the conditions under which arc propagation occurs. It has been found that arc propagation can be explained in terms of a new mechanism which may be called ‘elongation by ionisation and successive root formation’. This mechanism depends on the discharge current being shared between the developing portion of the discharge and the electrolyte in front of the discharge tip. The experiments also show that, at all stages in the flashover process, the arc-voltage gradient is close to the value for a static arc in air at the same current.