Showing papers by "University of Bath published in 1983"

Characterization of melanin-concentrating hormone in chum salmon pituitaries.

Abstract: Many lower vertebrates exhibit colour change in response to the background. A dual hormonal control of colour change by two antagonistic pituitary melanophorotropic hormones was first postulated in amphibia by Hogben and Slome. It is well established that the melanotropins alpha- and beta-MSH are responsible for pigment dispersion in the integumentary melanophore of lower vertebrates and that these molecules are derived from a common precursor protein, proopiocortin, by specific processing within the intermediate lobe. No evidence has been found for an antagonistic hormone in amphibia, although the existence of such a molecule in the pituitary gland of teleost fishes has long been recognized and was termed the melanophore-concentrating hormone by Enami. Early attempts to separate the two hormones proved unsuccessful. Recently, Baker and Ball re-invoked the dual hormone concept, and it has been suggested that a melanin-concentrating hormone (MCH) is synthesized in the hypothalamus of teleosts and stored and released by the neurohyphophysis. We have now isolated a novel peptide from the pituitary of the salmon (Oncorhynchus keta) possessing an antagonistic function to MSH, and we describe here its chemical and biological characteristics.

The everyday accountant and researching his reality

Abstract: It is the contention of this paper that accounting researchers have been dominated in thier research methodology by methods supposedly adopted from the natural sciences. It is argued that it is time that attention was paid to the possible use of radically different “naturalistic” (or “interpretive humanistic”) research approaches in order both to focus research more closely on the concerns of practitioners and to give greater insight into everyday effects of accounting and the practices of accountants themselves.

Anomalous conductivity prefactors in fast ion conductors

Abstract: We wish to draw attention to the fact that the conductivity prefactor of arguably the most important fast ion conductor, β″-alumina, is anomalously large at low temperatures and we show here that this is caused by an unexpectedly high ion hopping rate. In addition, similar results are found in the Na/Ag β-alumina system and these may be of significance in contributing to the understanding of the mixed alkali effect in general.

Origins of decay in living deciduous trees: the role of moisture content and a re-appraisal of the expanded concept of tree decay

Abstract: Summary It is argued that the development of decay in living hardwoods can best be explained in terms of the unsuitability of functional sapwood for mycelial establishment owing to its high moisture content and lack of easily assimilable nutrients other than within living cells. Decay occurs when these limitations are removed by any mechanisms which prevent or interfere with the normal functioning of sapwood. Recent concepts of decay in living trees have implied an active host defence against infection. This view is discussed against the alternative that non-specific mechanisms which maintain sapwood function will, by their very nature, prevent establishment of -ycelium of decay and stain fungi. The significance of mixed microbial communities in the development of decay is discussed, particularly in relation to the supposed requirement for specific sequences to overcome host defences.

An ultrastructural study of root invasion in three vascular wilt diseases

Abstract: Transmission electron-microscopy was used to study root invasion in resistant and susceptible cultivars of tomato infected with Fusarium oxysporum f. sp. lycopersici or Verticillium albo-atrum and pea infected with F. oxysporum f. sp. pisi. There were many similarities in invasion by all pathogens of root epidermis and cortex in resistant and susceptible cultivars. Hyphae of tomato pathogens adhered to host root cell walls of susceptible cultivars but remained separated by extracellular electron-opaque material; hyphae of F. oxysporum f. sp. pisi on pea roots were embedded in a mucilaginous sheath. Both forms of adhesion were associated with a localized disruption of adjacent host wall structure. Initial penetration was by intercellular hyphae; subsequent intercellular colonization frequently resulted in the formation of wall appositions and papillae within epidermal and cortical cells. Penetration of host walls was achieved by constricted hyphae and localized wall degradation; continued deposition of material occurred around penetration hyphae with consequent formation of elongated penetration papillae. These were lignified, resistant to enzymic and chemical degradation and apparently effective in preventing further hyphal growth, although the frequency of their formation was similar in both resistant and susceptible cultivars. Papillae did not form in the moribund cells often seen even before penetration by F. oxysporum ff. sp.; in contrast V. albo-atrum was occasionally present within apparently healthy cells surrounded by invaginated host plasmalemma. A differential expression of varietal resistance occurred at the endodermis of both plant species. Accumulation of electron-opaque material in tomato endodermal cells and deposition of suberin and autofluorescent material in pea appeared to limit colonization of the stele. Pathogens circumvented this putative line of resistance either by intercellular growth between endodermal cells or by longitudinal growth from the root tip, which is devoid of mature endodermis. The diffuse and extensive intercellular wall structure of root tip cells is particularly amenable to initial colonization from which longitudinal growth allows entry into immature unlignified xylem elements and subsequently into mature vessels; hyphae were never seen to enter vessels from mature stelar cells.

Straw-reinforced polyester composites

Abstract: Annual crop fibres are rich in cellulose and they are a cheap and rapidly renewable source of fibres with potential for polymer reinforcement. Straw fibres have been incorporated in a polyester resin matrix and the properties of the fibre and composite determined. The fibres have a Young's modulus of approximately 8 GN m−2 and an effective density of 5.1 kN m−3 when combined with resin. Useful composites can be formulated with an optimum fibre volume fraction of about 0.61, resulting in a flexural stiffness of 7.3 GN m−2 and flexural strength of 56 MN m−2. The specific flexural stiffness is about 2.5 times greater than that of polyester resin and about half that of softwoods and GRP. The work of fracture measured in impact is about half that of softwoods. It is envisaged that alternative methods for processing the fibres and the use of a phenolic resin matrix will improve the composite properties further. Straw-based composites are suitable as core material for structural board products.

Theoretical models for solvation and catalysis in carbonyl addition

Abstract: Alternative modes of catalysis of formaldehyde hydration by a single ancillary water molecule are investigated by ab initio calculations at the STO-3G level. A cyclic transition state (FW2 double dagger) involving formaldehyde with two molecules of water is characterized and is only 0.8 kcal mol/sup -1/ higher in energy than the isolated reactants. The results indicate that gas-phase formaldehyde hydration probably proceeds via FW2 double dagger in a concerted mechanism with a Gibbs free energy of activation of 27 kcal mol/sup -1/. Addition of a water dimer to formaldehyde via FW2 double dagger is predicted to occur in water with a Gibbs free energy of activation of 16 kcal mol/sup -1/, in agreement with experiment. Empirical extrapolation to the liquid phase of entropies of activation calculated for reaction of one or two waters in the gas phase suggests that a mechanism involving three water molecules would be consistent with experiments for dioxan solution. Specific solvation by four water molecules is predicted to stabilize the zwitterionic adduct H/sub 2/O/sup +/CH/sub 2/O/sup -/ (an unbound state in the gas phase) by 111 kcal mol/sup -1/ relative to H/sub 2/O/sup +/CH/sub 2/O/sup -/ and 4H/sub 2/O or by 37 kcal mol/sup -1/ relativemore » to (H/sub 2/O)/sub 3/ and CH/sub 2/O.2H/sub 2/O. Thus a stepwise mechanism for formaldehyde hydration also may be feasible, although the energy barrier to formation of a solvated zwitterionic intermediate has not yet been calculated.« less

Effect of temperature and water potential on growth rate of wood-rotting basidiomycetes

Abstract: Radial growth of twelve species of wood-rotting basidiomycetes was examined over a range of temperatures on malt agar: optimum growth rate occurred at between 20 and 30 °C. Variability in growth rate of several different isolates of five of the species was assessed at 10° and 20°. A significant difference in growth rates of different isolates was found in four species at 20° but only in one species at 10°. No significant difference was detected between the Q10 coefficients of different isolates of a species. The effect of water potential on growth rate was investigated for one isolate of each of the twelve species using four different solute systems and two types of agar media. Differences were detected between the solute systems and media although a general trend of decrease in growth rate with decrease in water potential was observed. The limit for growth was about −4.4 MPa (− 45 bars).

Dominance and reproductive success among slave-making worker ants

Abstract: Dominance hierarchies are of great theoretical interest because they result from a compromise between selfish and social behaviour. In a wide variety of vertebrates dominance promotes individual fitness1, but often to the detriment of the group as a whole. For example, in gelada baboons, females at the top of the hierarchy produce more offspring because their ovulations are less frequently inhibited and they have fewer abortions than their more harassed subordinates2. This type of selfish behaviour is perhaps least expected within ant colonies because their workers are exceptionally closely related3 and worker inclusive fitness is largely determined by the productivity of the colony as a whole4. For this reason our discovery of primate-like linear dominance hierarchies within colonies of slave-making ants uniquely demonstrates the importance of individual selection in social evolution. High ranking slave-maker workers receive more food from their slaves, have greater ovarian development and do less foraging than their subordinate sisters. This is also the first demonstration that ant queens can recognize the rank of their workers. Experiments show that the queen solicits food preferentially from the most dominant of her workers, possibly to limit their production of eggs. We explain these phenomena in terms of competition for the production of sons.

An ultrastructural study of vascular colonization in three vascular wilt diseases I. Colonization of susceptible cultivars

Abstract: Transmission electron microscopy was used to study vascular colonization in susceptible cultivars of tomato infected with Fusarium oxysporum f. sp. lycopersici or Verticillium albo-atrum and of pea infected with F. oxysporum fsp. pisi. There were many similarities in colonization by all pathogens. Hyphae were normally in close proximity to vessel walls and aligned approximately parallel to the long axes ofvessels. Vessel to vessel colonization was uncommon but occasionally occurred by penetration of intertracheary pit membranes. Pit penetration was achieved by constricted hyphae and localized membrane degradation. Penetration of xylem parenchyma pit membranes was not observed in either host but colonization of xylem parenchyma cells occurred early in disease development in pea but only when the host plant was moribund in tomato. Fusarium oxysporum f. sp. lycopersici and V. albo-atrum caused extensive erosion of tomato vessel secondary walls, both where hyphae were in direct contact with walls and in areas remote from invading hyphae. Penetration of secondary walls was common but its extent was limited by the primary wall/middle lamella. There was little secondary wall erosion in pea although the primary wall/middle lamella of pit fields was often extensively degraded. Many vessel and xylem parenchyma cell secondary walls in both species contained, irregular electron-opaque areas. Vessel walls and colonizing hyphae were often coated in an amorphous electron-opaque material. The material occluded intertracheary and xylem parenchyma pit cavities and encrusted intertracheary pit membranes. Its appearance varied from smooth to rough and “bubbly”. A distinctive fibrillar coating was found much less frequently. Infection was accompanied by the gradual death of xylem parenchyma cells throughout infected plants. Xylem parenchyma cells adjacent to infected vessels often contained well developed “protective” layers. Some also contained wall appositions but their role was unclear. In young infected tomato plants xylem parenchyma cells apparently underwent uncontrolled division resulting in “whorls” of cells and crushing of vessels. The features observed are discussed in relation to symptom development.

Ecological roles of basidiomycetes forming decay communities in attached oak branches

Abstract: Summary From sites in south-west England attached oak (Quercus robur) branches bearing basidiomycete sporophores were cut down from mature trees, and the three-dimensional structure of their decay communities analysed. Twelve basidiomycetes characterized the decay communities. These fungi varied in their ecology, particularly in relation to their ability to colonize living wood, and their interaction with each other and with animals. Phellinus ferreus, Stereum gausapatum and Vuilleminia comedens were pioneers actively growing in partially living branches and causing extensive white rot but little cambial loosening. Peniophora quercina behaved similarly but was often confined to the ends of branches. Exidia glandulosa appeared principally to cause cambial death and loosening leading to white rot in the wood. Phlebia rufa seemed to act as a pioneer causing white rot but only in obviously weakened branches. Coriolus versicoior and Phlebia radiata were secondary invaders only, readily replacing other fungi. Peniophora lycii and Stereum lursutum were each only obtained once. The roles of Hyphodertna setigerum and Schizopora paradoxa were less clear, but both were closely associated with insect activity.

The persistence and metabolism of isoproturon in soil

Abstract: Summary The persistence of isoproturon in soil in pot experiments was the same whether or not the soil contained growing wheat (Triticum aestivum L.) plants, Panllel) work with radioactive isoproturon showed that the breakdown products were the same in the presence and absence of plants. Persistence in the field was reasonably well predicted by a simulation model using the results of laboratory incubation studies and field meteorological data. Resume Perisiance et metabolfsme de l'isoproturon dans le sol a persistance de l'isoproturon dans le sol etudiee au cours d'une experimentation en pots a ete identique en presence ou en l'absence de plants de ble (Triticum aestivum L.) Un travail parallele mene avec des molecules marques d'isoproturon a montre que les produits de degradation elaicnt les memes dans les deux cas. Cette persistance au champ peut etre valablement predite par un modele utilisant les resultats obtenus au cours d'etudes d'ineubation au laboratoire et les donnees meteorologiques de plein champ. Zusammenfassung Persistenz und Metabolismus von Isoproturon im Boden Die Persistenz von Isoproturon im Boden war in Gefassversuchen unabhangig davon. ob im Boden Weizen (Triticum aestivum L.) wuchs oder nicht. Parallelversuehe mit radioaktiv markiertem Isoproturon ergahen. dass die Abbauprodukte mit bzw. ohne Pflanzen dieselben waren. Die Persistenz im Freilund wurde durch ein Simulationsmodell in brauchbarer Naherung vorhergesagt. Fur die Berechnungen dienten Ergebnisse aus Abbaustudien und meteorologischa Daten.

Some facets of the relationship between consultants and clients in organizations

Abstract: Although frequently represented as a critical aspect of consultancy, the relationship between consultants and their clients and its relevance to the achievement of successful outcomes are subjects to which few writers have devoted serious attention. In an earlier piece of research, the author concluded that an ‘interdependent’ relationship was likely to be an important factor in successful consulting assignments. He identified eight facets of this type of relationship. This paper describes how that theory was tested when three consultants, together with a number of their clients, explained why they thought their work together had been successful. The cases illustrate both the ways in which the relationships were built and the extent to which they were perceived as having been important ingredients in the outcomes achieved. The relationships described were characterized by high levels of mutual trust and interaction as well as contingency on the part of the consultants. In several respects the relationships were seen as interdependent. A feature of this study was that the extent to which the consultants found the research useful in a personal sense seemed to depend on the quality of the relationship between the author and the consultants. In the cases described the exercise seems to have been mutually beneficial. In another example this seems not to have been the case and the explanation seems to lie at least partly in a lack of interdependence.

On asymptotically stabilizing feedback control of bilinear systems

Abstract: Asymptotically stabilizing feedback controls for a class of bilinear systems are discussed; a simple modification which strengthens a result of Slemrod [1] is noted and illustrated by example.

Chronic pain and depression: Universal or personal helplessness?

Abstract: The study investigates beliefs about control and links it to the depression found in those with chronic pain. These beliefs are interpreted within the new model of learned helplessness which distinguishes personal helplessness from universal helplessness on the basis of attributions. Despite higher levels of depressive symptoms in the pain group, this was not reflected by higher levels of self-blame or beliefs in the actions of others, so personal helplessness was discounted. Higher beliefs in chance, lack of self-blame and correlations between chance, depression and pain support the presence of universal helplessness in this group. The reporting behaviour of pain patients is discussed in the light of these findings.

ACTION SPECTRA FOR INACTIVATION OF NORMAL and XERODERMA PIGMENTOSUM HUMAN SKIN FIBROBLASTS BY ULTRAVIOLET RADIATIONS

Abstract: —Action spectra for UV-induced lethality as measured by colony forming ability were determined both for a normal human skin fibroblast strain (lBR) and for an excision deficient xeroderma pigmentosum strain (XP4LO) assigned to complementation group A using 7 monochromatic wavelengths in the range 254-365 nm. The relative sensitivity of the XP strain compared to the normal skin fibroblasts shows a marked decrease at wavelengths longer than 313 nm. changing from a ratio of about 20 at the shorter wavelengths to just greater than 1.0 at the longer wavelengths. The action spectra thus indicate that the influence on cell inactivation of the DNA repair defect associated with XP cells is decreased and almost reaches zero at longer UV wavelengths. This would occur, for example, if the importance of pyrimidine dimers as the lethal lesion decreased with increasing wavelength. In common with other studies both in bacterial and mammalian cells, our results are consistent with pyrimidine dimers induced in DNA being the major lethal lesion in both cell strains over the wavelength range 254-313 nm. However, it is indicated that different mechanisms of inactivation operate at wavelengths longer than 313 nm.

Extent, development and function of mycelial cord systems in soil

Abstract: Mycelial cord systems of Phallus impudicus, Phanerochaete velutina, Steccherinum fimbriatum, Stropharia aeruginosa and Tricholomopsis platyphylla, when excavated in the field, were found to be between 318 m (5. aeruginosa) and 317 m (P. velutina) in overall length. Cord systems of P. impudicus, P. velutina and T. platyphylla increased in length by 0.8, 0.95 and l.0 m respectively over 12–14 months. In all cases extension occurred via the peripheries of the systems, whilst certain more central parts disappeared. Mycelial development from colonized wood-blocks in tubes of non-sterile soil showed similar patterns to that observed in the field. However, in tubes of γ-irradiated soil mycelia were not aggregated into cords to such an extent as in non-sterile soil, and, except for T. platyphylla, had slower extension rates, although sometimes being more luxuriant. Wood-blocks colonized by Hypholoma fasciculate, S. fimbriatum, P. impudicus and P. velutina underwent significantly greater losses in dry weight in sterile soil than did blocks in non-sterile soil, except for those colonized by T. platyphylla. Cord systems of like and unlike mycelial types of P. velutina from wood blocks fused in soil, but whilst fusion of those of like mycelial type gave rise to cords of substantial diameter, fusions between different mycelial types were followed by death of the fine cords in the fused regions and avoidance of such regions thereafter. Cord formation by a coprophilous species occurred in non-sterile but not sterile conditions, and was associated with strong substratum directed growth responses.

A variable structure approach to feedback regulation of uncertain dynamical systems

Abstract: Feedback control of uncertain dynamical systems is considered. Adopting a deterministic approach based on the theory of variable structure systems, a feedback regulator is developed which guarantees global asymptotic stability or global ultimate boundedness under certain hypotheses on the bounded system uncertainties and disturbances.

Movements, abundance, age composition and growth of bass, Dicentrarchus labrax, in the Severn Estuary and inner Bristol Channel

Abstract: The movements, abundance, age composition and growth of bass, Dicentrarchus labrax (L.), in the Severn Estuary and inner Bristol Channel have been described from regular samples offish taken from power-station intake screens between 1972 and 1977. Bass began to move into the estuary during late August or September and reached peak abundance between September and early November. The tendency for fish to move seawards in the late autumn and winter may be related to declining water temperatures in the estuary. Likewise, differences in abundance between years appear to be related to annual differences in temperature. Although the populations were dominated by the 0 + age class, successively decreasing numbers of the next four age classes and occasional 5 + fish were also present. Respective mean standard lengths of bass in the estuary at the end of their first to fifth years of life were approximately 65 mm (≡ 4·5 g), 130 mm (≡ 37·9 g), 190 mm (≡ 121·1 g), 250 mm (≡ 280·4 g) and 290 mm (≡ 441.5 g). Growth occurred predominantly between May and September, with the mean standard length of 1 + fish increasing from approximately 65 mm (≡ 4·5 g) to 130 mm (≡ 37·9 g).

Influence of glyphosate on selected plant processes

Abstract: Summary Biochemical effects of glyphosate have been examined with a variety of plant materials using mostly merislematic or actively growing tissues. The accumulation of chlorophyll was severely retarded and photosynthetic CO2 uptake was inhibited to a lesser extent. These inhibitory effects could not be alleviated by the simultaneous admixture of divalent cations. Glyphosate enhanced the initial substrate-induction of nitrate reductase, but repressed induction of nitrite reductase, in Ihe latter case correlating with both inhibition of chlorophyll accumulation and CO2 uptake. Inhibition of macromolecule synthesis in single node buds of Agropyron repens(L.) Beauv. was due partly to inhibition of 14C-precursor uptake. The specific activity of soluble acid phosphatase was enhanced as was the evolution of ethane. Ethylene production was not greatly affected. A marked decrease in microsomal protein was observed but the specific activities of several microsomal enzymes did not decline. Glyphosate had little inhibitory effect on the activity of microsomal ATPases in vitro. Resume Influence du glyphosate sur certains processus biologiques Les effets biochimiques du glyphosate ont eteetudies sur differents materiels vegetaux en utilisant notamment des tissus meristematiques ou des tissus en croissance active. L'accumulation de chlorophylle est severement retardee et dans une moindre mesure on note une inhibition du CO2 photosynthetique. Ces effets inhibiteurs ne peuvent pas etre attenues par l'addition simultanee de cations divalents. Le glyphosate stimule l'induction initiale de nitrate reductase permettant de mettre en evidence, dans ce dernier cas, une correlation entre l'inhibition de l'accumulation de chlorophylle et l'absorption de CO2 L'inhibition de la synthese de macromolecule dans les bourgeons axilaires isoles d'Agropyron repens (L.) Beauv. est due partiellement a l'inhibition de l'absorption du precurseur 14C. L'activite specifique de la phosphatase acide soluble est stimulee de meme que l'evolution de l'ethane. La production d'ethylene n'est pas notablement modifiee; on note une diminution de la proteine microsomale mais les activites specifiques de diverses enzymes microsomales ne sont pas modifiees. Le glyphosate a un faible effet inhibiteur sur l'activitein vitro des ATPases microsomaux. Zusammenfassung Einfluss von Glyphosat auf verschiedene Prozesse in der Pflanze Die biochemische Wirkung von Glyphosat wurde mit einer Reihe verschiedener Pflanzenmaterialien, insbesondere mit meristematischem Gewebe und mit Gewebe aus rasch wachsenden Pflanzenteilen untersucht. Die Anreicherung von Chlorophyll wurde sehr stark verzogert, wogegen die photosynthetische CO2-Aufnahme weniger gehemmt wurde. Diese Hemmeffekte liessen sich durch die gleichzeitige Zugabe von divalenten Kationen nicht abschwachen. Glyphosat verstarkte die anfungliche Substratinduktion der Nitratreduktase aber unterdruckte die Induktion der Nitritreduktase. Letzteres war mit einer Hem-mung der Chtorophyllakkumulation und der CO:-Aufnahme korreliert. Die gehemnite Syn-these von Makromolekulcninein/elnen Knospen von Agropvron repens (L.) Beauv. wurde teilweise durch eine Hemmung der 14C-Percursorauf-nahme verursacht. Die spe/ifische Aktivitat von losucher saurer Phosphatase wurde genauso gefordert wie die Athanentwicklung. Die Athy-lenproduktion wurde nicht nennenswert beein-truchtigt. Es wurde eine deutuche Abnahme an mikrosomalem Protein beobachtet. die spezi-fischc Aktivitatcn verschiedener mikrosonialer Enzyme sanken aber nicht ab. Glyphosat wirkte auf die Aktivitat mikrosomaler ATPase in vitro nur leicht hemmcnd.