Showing papers by "University of Bath published in 1970"

The Beta‐Binomial Model for Consumer Purchasing Behaviour

Abstract: A model for consumer purchasing behaviour is proposed which is based on the beta-binomial distribution. The model is tested for several nondurable consumer products, and the results give insight into discrepancies from a previously used model based on the negative binomial distribution (NBD).

The ‘half‐life’ of periodical literature: apparent and real obsolescence

Abstract: The expression ‘half‐life’, borrowed from physics, has appeared quite frequently in the literature on documentation since 1960, when an article by Burton and Kebler on The ‘half‐life’ of some scientific and technical literatures was published, although it had certainly been used previously. Burton and Kebler point out that literature becomes obsolescent rather than disintegrating (as in its original meaning), so that ‘half‐life’ means ‘half the active life’, and this is commonly understood as meaning the time during which one‐half of the currently active literature was published. Numerous studies have been carried out, mainly by the analysis of citations, to establish obsolescence rates of the literature of different subjects. Bourne points out that different studies have given widely different results, so that many of the ‘half‐life’ figures reported are not valid beyond the particular sample of literature or users surveyed; certainly they cannot be used as accurate measures for discriminating between different subject‐fields.

Detoxication of isopropyL N-phenylcarbamate (IPC) and isopropyl N-3-chlorophenylcarbamate (CIPC) in soil, and isolation of IPC-metabolizing bacteria

Abstract: Both the phenylcarbamate herbicides isopropyl N-phenylcarbamate (IPC) and isopropyl N-3-chlorophenylcarbamate (CIPC), at rates exceeding those used in agriculture, were dissipated from soil incubated at 27°C within two or three weeks. At all application rates tested IPC was considerably less persistent in soil than CIPC, and the persistence of each compound increased as applications were raised. Bio-degradation of both compounds was strongly suggested by the fact that they persisted in soil treated by autoclaving or addition of azidc. Arthrobacter and Achromobacter, which utilized IPC as their sole source of carbon, were isolated from soil ‘enriched’ by a percolation technique. The ability to utilize IPC was maintained by the Arthrobacter, but readily lost by the Achromobacter when grown in the absence of the compound. Both organisms detoxified IPC by metabolism via the intermediate aniline. IPC was rapidly dissipated in sterilized soil inoculated with a suspension of the active organisms. The bacterial utilization of IPC particles is apparently not attributable to the action of extracellular enzymes; evidence suggests it is a process of gradual dissolving and diffusion of the herbicide in very small amounts to the organisms.

The Microbiology of the Hen's Egg

Abstract: Publisher Summary Systematic studies on this subject had their genesis in an argument between Donne and Pasteur. The former maintained that vigorous shaking was all that was needed to induce the addling of an egg. Pasteur did not always succeed in producing rots by this method, but, when successful, he noted large numbers of bacteria in the decomposing yolk and white. He was uncertain of their origin but favored the view that they came from the oviduct. Even when the arguments occasioned by the concept of spontaneous generation had lapsed, research in egg microbiology was dominated by two questions: Why do eggs rot? How, during the distribution of those intended for human consumption, can this be prevented? In this discussion of the course of the infection process, emphasis has been given to the integrated workings of a shell, shell membranes, and the albumen in the egg's defense. When the egg is considered as an ecosystem, it can be argued that the albumen plays the principal role in isolating the blastoderm and its food supply from the environment of the hen.

Low Magnesium and Phospholipid Content of Cell Walls of Pseudomonas aeruginosa resistant to Polymyxin

Abstract: THE resistance of the pathogenic bacterium Pseudomonas aeruginosa to chemical inactivation is notorious. P. aeruginosa and related species cause problems in plant pathology1,2, food spoilage3, contamination of pharmaceuticals4,5 and hospital cross-infection6,7. We report here results relating to the mechanism of resistance of this organism which may also have wider significance for Gram-negative bacteria.

A comparison of the metamorphosing and macrophthalmia stages of the lampreys Lampetra fluviatilis and L. planeri

Abstract: Comparisons of metamorphosing and macrophthalmia stages of the closely related species, L. fluviatilis (L.) and L. Planeri (Bloch), have shown that these can be distinguished within a few weeks of the onset of metamorphosis by characteristic differences in colouration and body form. Measurements of several body intervals have disclosed differences between the macrophthalmia stages of the two species. A sharp distinction between the blunt teeth of L. planeri and the supposedly sharp teeth of L. fluviatilis has not been confirmed in these early stages, but significant differences have been found in the numbers of teeth in the anterior field of the oral disk and in the lateral and posterior marginal series. For material from several rivers, the range of length of metamorphosing and macrophthalmia stages of L. fluviatilis is83–119 mm (mean 99.3 mm). Weights varied from 0.71-2.5 g (mean 1.51 g). Regression coefficients for weight on length are much lower in the macrophthalmia of L. fluviatilis than in comparable stages of L. planeri. Total oocyte counts on macrophthalmia of L. fluviatilis gave values from8000–20,000 which are in general agreement with egg counts for adults of this species in the river Severn. Observations on the earliest metamorphosing forms have shown that it is not possible at this stage to distinguish the males of the two species by the structure of the testes. The development of the lumen in the adult foregut of L. fluviatilis has been shown to be variable and in some instances the gut does not become patent until early Spring. The possibility has also been raised that, in exceptional cases, a temporary lumen may also be present for a short period in L. planeri. Observations on the foregut and dentition, together with field data, suggest that the climax of downstream migration and the onset of parastic feeding takes place in late March or April.

Larval growth in the river lamprey, Lampetra fluviatilis

Abstract: A series of 987 ammocoetes from the rivers Towy, Teme, and Taw have been identified as mainly L. fluviatilis (L.) on the basis of oocyte counts on female ammocoetes. The length frequency distributions for this material differs from either L. planeri or P. marinus in showing only three modes in addition to the young of the year and the length distribution of the final mode coincides with the length range for 119 metamorphosing and macrophthalmia stages of L. fluviatilis that have been found at the same sites. These animals measured from 80–117 mm in length and weights varied from 0.76–2.28 g. Metamorphosis is believed to take place in late summer and early autumn when in the majority of cases, the ammocoetes are four and a half years old. The evidence that the non-parasitic L. planeri has a longer larval life than the closely related parasitic L. fluviatilis is thought to have some significance in relation to the evolution of the brook lamprey species.

Degradation of the herbicide isopropyl N-phenylcarbamate by Arthrobacter and Achromobacter spp. from soil

Abstract: Arthrobacter and Achromobacter species from soil degraded isopropyl N-phenylcarbamate (IPC) at similar rates via aniline with concomitant dctoxication. Aniline was readily metabolized, possibly through catechol, and did not accumulate in cultures growing on IPC. Evidence shows that the conversion of phenylcarbamates to the corresponding aniline compound is a mechanism widely used by soil microbes to initiate degradation of these herbicides, and the enzyme system for aniline formation is associated with the ‘cell envelope’. Application of IPC to soil in organic liquid formulations is unlikely to prolong persistence.

Communal spawning of brook and river lampreys,Lampetra planeri Bloch and Lampetra fluviatilis L.

Abstract: A description is given of the spawning of brook lampreys Lampetra planed Bloch and unusually small river lampreys Lampetra fluviatilis L. in the same redd. No successful interspecific copulation was observed, although the possibility of accidental cross fertilization cannot be excluded.

Osmotic Properties of Spheroplasts from Saccharomyces cerevisiae Grown at Different Temperatures

Abstract: Spheroplasts were prepared from cells of Saccharomyces cerevisiae NCYC 366, grown at 30 or 15 C, by incubating cells with snail-gut juice after pretreatment with 2-mercaptoethanol. Walls of cells grown batchwise or in continuous culture at 15 C were more resistant to digestion with snail juice than walls on cells grown under the same conditions as 30 C. Spheroplasts lysed when suspended in hypotonic solutions of mannitol. The resistance of spheroplasts to osmotic lysis tended to increase when the test temperature was lowered below 30 C. The increased resistance was greater with spheroplasts from cells grown at 15 C. Cations, especially Ca2+, protected spheroplasts against osmotic lysis. In general, the protective effects, measured at 30 C, were smaller with spheroplasts from cells grown at 15 C compared with 30 C. Citrate and ethylenediaminetetraacetate (EDTA) decreased the resistance of spheroplasts to osmotic lysis. On the whole, the decrease was greater with spheroplasts from cells grown at 30 C rather than 15 C. In the presence of EDTA, spheroplasts from cells grown at 30 C were less resistant to osmotic lysis at 5 C than at 30 C; when spheroplasts from cells grown at 15 C were similarly examined, they were more resistant to lysis at 5 C than at 30 C. Spheroplast membranes from cells grown at 15 C had slightly but significantly greater contents of Mg2+, Ca2+, K+, and Na+ compared with spheroplast membranes from cells grown at 15 C. Mg2+ and Ca2+ were more easily extracted with EDTA from membranes of 30 C-grown cells than from 15 C-grown cells.

The mitotic chromosomes of the lamprey, Petromyzon marinus L.

Abstract: L'etude des chromosomes somatiques de la lamproie,Petromyzon marinus L. a montre que l'equipment chromosomique diploide de cette espece est compose de 168 chromosomes tres petits, dont queleues-uns des plus grands sont metacentriques. Le chiffre semble representer le plus grand nombre de chromosomes trouve dans une espece de Vertebre. On a compare les chromosomes de P.marinus avec ceux des autres especes de lamproies.

The Dynamic Transfer Characteristics of Reciprocating Engines

Abstract: The methods of sampled data analysis and small perturbation techniques are used to predict the dynamic characteristics of reciprocating engines. Extensive frequency response tests have been carried out on a compression ignition engine to determine the engine dynamic characteristics and the results agree well with the theoretical predictions. A method of plotting the results is suggested which has the advantage of generality and takes into account engine speed changes and load torque-speed characteristics.The experimental methods used involve the use of electro-hydraulic systems. These have great advantages for providing the appropriate input and loading conditions.Whilst the main body of the report is concerned with the theory and testing of compression ignition engines, the methods suggested can be applied equally well to petrol engines.

Theoretical efficiencies of class-D power amplifiers

Abstract: The theoretical efficiencies of class-D amplifiers are compared with those of conventional amplifiers by means of a power balance. As a result of certain similarities, it is suggested that class-AD and class-BD modes of operation should be defined. The class-D amplifier converts the collector dissipation of a conventional amplifier into load power components at a large number of modulation frequencies. When these are removed by filtering, a high overall efficiency results. The analysis presented includes an idealised treatment of the class-D amplifier with an inductive load, and enables constructive comparisons to be made.

Chapter II The Effects and Control of Temperature

Abstract: Publisher Summary This chapter presents a discussion on the effects and control of temperature on micro-organisms and microbiological studies. The pioneer microbiologists realized that the rate of growth of a microbe is affected by the environmental temperature, and several studies on the effect of temperature on growth of pure cultures of microorganisms have been made. In a given medium, a microbe grows most rapidly at a particular temperature (or over a small range of temperatures) that is referred to as the ‘optimum temperature’ for growth. In most studies, the optimum temperature for growth is based upon the rate of growth, although it is occasionally based instead on the size of the crop of micro-organisms produced. It is common practice to store stock cultures of micro-organisms on, or in, solidified nutrient media at a temperature near or below the minimum for growth of the organisms on that medium. Anhydric incubators satisfy the requirements of most microbiological laboratories when the need is often only to incubate static cultures under conditions where variations in temperature are not critical. Temperature-gradient incubators have been used to study the effect of temperature on growth of bacteria, yeasts, and algae. A contact thermometer and electronic relay are now almost universally used for control of bath temperature in apparatus used for manometric work.

Performance of Inward Radial Flow Turbines under Unsteady Flow Conditions with Full and Partial Admission

Abstract: The paper describes the most recent work to be completed in the unsteady flow investigation on radial flow turbines, earlier unsteady flow work for single entry casings having been reported in (1)†and (2), and steady flow work for very high pressure ratios and multiple admission in (3). The present paper combines these analyses to give a coherent treatment of single and multiple admission.

Evidence for a Surface Protein Layer on the Saccharomyces cerevisiae Ascospore

Abstract: Electrophoretic measurements on Saccharomyces cerevisiae ascospores indicated the presence of a surface protein layer which can be removed by papain, chymotrypsin or 8 m urea.

The relationship of gonadal development to the life cycles of the paired species of lamprey, Lampetra fluviatilis (L.) and Lampetru planeri (Bloch)

Abstract: Gonadal developnient has been studied throughout the larval period of Lumpetru fluviatitis and comparisons have been made with conditions in the larvae of the closely relatcd non-parasitic species, L. planeri. The two forms differ in the time of onset or mitotic division in germ cells and in the period when oogenesis is initiated. These phases begin in L. pluneri when the ammocoetes are one year old and in L. fluviatilis at the end of the second year. The course of sex differentiation appears to be sinlilar in both forms. While in the early stages, the oocytes of L. planeri are larger than those of L. fluviatilis. at comparable ages, by the end of the third year they are sinlifar in size in both spccics. It is suggested that in L. planeri, during the extension of the larval period, gonad growth is retarded and during this phase the ammocoete accumulates body reserves which are used to meet the metabolic requirements of the rapidly developing gonads after metamorphosis. The differences observed in early gonadogenesis are believed to account for the reduced fecundity of the L. planeri ammococtc and their adaptive significance is discussed.

Optimum catalyst formulation for the aromatization of methylcyclopentane

Abstract: The formation of benzene from methylcyclopentane over platinum impregnated silica-alumina represents a typical reforming reaction occurring in the presence of a bifunctional catalyst. A detailed experimental investigation enabled a previously established kinetic model of the system to be extended and parameters to be evaluated. By application of the maximum principle the catalyst composition could be formulated so as to maximize the yield of benzene, simultaneously suppressing the formation of undesirable products. For an isothermal reactor operating in a temperature region where chemical reaction is rate controlling, it was found that a constant catalyst composition along the reactor length represents a sub-optimal policy which, nevertheless, closely approximates the optimal solution. The effect of intraparticle diffusion limitation on the optimum profile is also investigated. The model developed is limited to low conversions for the reaction model under dehydrogenative conditions. La formation du benzene a partir de methylcyclopentane sur un catalyseur de silice et alumine impregnees de platine constitue une reaction typique de reformage qu'on rencontre en presence d'un catalyseur a fonction double. Une etude experimentale en detail a permis d'apporter une extension a un modele cinetique du systeme deja etabli et d'evaluer les parametres. En appliquant le principe maximum, on a pu formuler la composition du catalyseur de maniere a obtenir un rendement maximum du benzene, tout en eliminant la formation de produits indesirables. Dans le cas d'un reacteur isothermique qui fonctionne dans une echelle de temperatures ou la reaction chimique regle la vitesse, on a trouve qu'une composition constante du catalyseur a la longueur du reacteur etait bien proche de la solution optimale, bien qu'elle ne l'atteignait pas. On a aussi etudie l'effet de la limitation de la diffusion entre les particules sur le profit optimal. Le modele qu'on a mis au point est limite a de faibles transformations dans le cas ou la reaction se fait dans des conditions ou il se produit une deshydrogenation.

Negative differential conductivity effects in semiconductors

Abstract: The discovery of the Gunn Effect has been heralded as the greatest breakthrough in semiconductor physics since the discovery in 1948 of transistor action in germanium. This article shows the basic physics of the effect and lays emphasis on the physics and applications of devices in which there is a bulk negative differential conductivity. Exciting new possibilities are opened up in the microwave region by a range of devices based on the peculiar properties of high field domains in semiconductors like GaAs.