Showing papers by "University of Exeter published in 1998"

The biosynthetic pathway of vitamin C in higher plants

Abstract: Vitamin C (L-ascorbic acid) has important antioxidant and metabolic functions in both plants and animals, but humans, and a few other animal species, have lost the capacity to synthesize it Plant-derived ascorbate is thus the major source of vitamin C in the human diet Although the biosynthetic pathway of L-ascorbic acid in animals is well understood, the plant pathway has remained unknown-one of the few primary plant metabolic pathways for which this is the case L-ascorbate is abundant in plants (found at concentrations of 1-5 mM in leaves and 25 mM in chloroplasts) and may have roles in photosynthesis and transmembrane electron transport We found that D-mannose and L-galactose are efficient precursors for ascorbate synthesis and are interconverted by GDP-D-mannose-3,5-epimerase We have identified an enzyme in pea and Arabidopsis thaliana, L-galactose dehydrogenase, that catalyses oxidation of L-galactose to L-galactono-1,4-lactone We propose an ascorbate biosynthesis pathway involving GDP-D-mannose, GDP-L-galactose, L-galactose and L-galactono-1,4-lactone, and have synthesized ascorbate from GDP-D-mannose by way of these intermediates in vitro The definition of this biosynthetic pathway should allow engineering of plants for increased ascorbate production, thus increasing their nutritional value and stress tolerance

Fluorescence near interfaces: The role of photonic mode density

Abstract: A review of fluorescence near interfaces is presented. Recent work that examines the role of photonic mode density in this process is surveyed and the underlying concepts discussed. The review includes an examination of the role of surface and waveguide modes, as well as non-radiative decay. The importance of textured surfaces in providing large changes in photonic mode density and in coupling non-radiative modes to radiation is highlighted. Indications are given for future areas of research and on how photonic mode density may influence optical processes other than fluorescence.

Mutations in the glucokinase gene of the fetus result in reduced birth weight.

Abstract: Low birth weight and fetal thinness have been associated with non-insulin dependent diabetes mellitus (NIDDM) and insulin resistance in childhood and adulthood. It has been proposed that this association results from fetal programming in response to the intrauterine environment. An alternative explanation is that the same genetic influences alter both intrauterine growth and adult glucose tolerance. Fetal insulin secretion in response to maternal glycaemia plays a key role in fetal growth, and adult insulin secretion is a primary determinant of glucose tolerance. We hypothesized that a defect in the sensing of glucose by the pancreas, caused by a heterozygous mutation in the glucokinase gene, could reduce fetal growth and birth weight in addition to causing hyperglycaemia after birth. In 58 offspring, where one parent has a glucokinase mutation, the inheritance of a glucokinase mutation by the fetus resulted in a mean reduction of birth weight of 533 g (P=0.002). In 19 of 21 sibpairs discordant for the presence of a glucokinase mutation, the child with the mutation had a lower birth weight, with a mean difference of 521 g (P=0.0002). Maternal hyperglycaemia due to a glucokinase mutation resulted in a mean increase in birth weight of 601 g (P=0.001). The effects of maternal and fetal glucokinase mutations on birth weight were additive. We propose that these changes in birth weight reflect changes in fetal insulin secretion which are influenced directly by the fetal genotype and indirectly, through maternal hyperglycaemia, by the maternal genotype. This observation suggests that variation in fetal growth could be used in the assessment of the role of genes which modify either insulin secretion or insulin action.

Innate talents: reality or myth?

Abstract: Talents that selectively facilitate the acquisition of high levels of skill are said to be present in some children but not others. The evidence for this includes biological correlates of specific abilities, certain rare abilities in autistic savants, and the seemingly spontaneous emergence of exceptional abilities in young children, but there is also contrary evidence indicating an absence of early precursors of high skill levels. An analysis of positive and negative evidence and arguments suggests that differences in early experiences, preferences, opportunities, habits, training, and practice are the real determinants of excellence.

Influence of hydrodynamics and nutrients on biofilm structure

Abstract: Hydrodynamic conditions control two interlinked parameters; mass transfer and drag, and will, therefore, significantly influence many of the processes involved in biofilm development. The goal of this research was to determine the effect of flow velocity and nutrients on biofilm structure. Biofilms were grown in square glass capillary flow cells under laminar and turbulent flows. Biofilms were observed microscopically under flow conditions using image analysis. Mixed species bacterial biofilms were grown with glucose (40 mg/l) as the limiting nutrient. Biofilms grown under laminar conditions were patchy and consisted of roughly circular cell clusters separated by interstitial voids. Biofilms in the turbulent flow cell were also patchy but these biofilms consisted of patches of ripples and elongated 'streamers' which oscillated in the flow. To assess the influence of changing nutrient conditions on biofilm structure the glucose concentration was increased from 40 to 400 mg/l on an established 21 day old biofilm growing in turbulent flow. The cell clusters grew rapidly and the thickness of the biofilm increased from 30 μ to 130 μ within 17 h. The ripples disappeared after 10 hours. After 5 d the glucose concentration was reduced back to 40 mg/l. There was a loss of biomass and patches of ripples were re-established within a further 2 d.

Corruption, Extortion and Evasion

Abstract: Corruption, evasion and the abuse of power (and the possibility thereof) are pervasive features of economic activity. A prominent instance is tax collection. This paper examines the implications of corruptibility and the potential abuse of authority for the effects and optimal design of (potentially non-linear) tax collection schemes.

Maturity-onset diabetes of the young: clinical heterogeneity explained by genetic heterogeneity.

Abstract: Maturity-onset diabetes of the young (MODY) can be defined by the clinical characteristics of early-onset Type 2 (non-insulin-dependent) diabetes and autosomal dominant inheritance. Mutations in four genes have been shown to cause MODY: glucokinase, hepatic nuclear factor 1 alpha (HNF1alpha), hepatic nuclear factor 4 alpha (HNF4alpha) and insulin promoter [corrected] factor 1 (IPF1). In white Caucasians it is now possible to define the gene in most patients with a clinical diagnosis of MODY. Each gene involved in MODY has its own specific clinical and physiological characteristics. Patients with mutations of the glucokinase gene have mild fasting hyperglycaemia throughout life, and rarely require medication or develop microvascular complications. The principle pathophysiology is stable beta-cell dysfunction characterized by reduced sensing of glucose by the pancreas. Patients with mutations in HNF1alpha have normal glucose tolerance in early childhood and usually present with symptomatic diabetes in their late teens or early adulthood. They show increasing hyperglycaemia and treatment requirements with frequent microvascular complications. The underlying defect is progressive beta-cell failure, with the early lesion characterized by failure to increase insulin secretion with increasing glucose levels. Patients with HNF4alpha and IPF1 mutations show a similar clinical picture to HNF1alpha although diabetes may be diagnosed later. There are other patients with MODY in whom the genetic defect is still unknown. Molecular genetic testing in patients with diabetes offers the possibility of making a firm diagnosis of MODY and allows prediction of the future clinical course. The role of predictive testing in non-diabetic subjects within families is uncertain at present. Preliminary evidence suggests that maintaining insulin sensitivity by avoiding obesity and regular physical exercise may help delay the onset of diabetes.

International retirement migration in Europe.

Abstract: "This paper presents a review and prospectus of international retirement migration (IRM), dealing mainly with European evidence but also referring to some analogous trends in North America. The paper is in three main parts. It first makes the case for regarding IRM as a significant aspect of population geography and of migration studies; in certain areas of Mediterranean Europe, IRM also has effects on regional economic geography. The second section of the paper discusses some of the early findings from a comparative study of British elderly residents in Tuscany, Malta, the Costa del Sol and the Algarve.... The final part of the article offers further reflections on why IRM is important--for the individual migrants themselves, for the host communities, and for public policy."

Deep acceptors trapped at threading-edge dislocations in gan

Abstract: Local-density-functional methods are used to examine the behavior of the oxygen defect, gallium vacancy, and related defect complexes trapped at threading-edge dislocations in GaN. These defects are found to be particularly stable at the core of the dislocation where oxygen sits twofold coordinated in a bridge position. VGa-ON is found to be a deep double acceptor, VGa-(O,N)2 is a deep single acceptor, and VGa-(ON)3 at the dislocation core is electrically inactive. We suggest that the first two defects are responsible for a deep acceptor level associated with the midgap yellow luminescence band. © 1998 The American Physical Society.

Acupuncture for Back Pain: A Meta-Analysis of Randomized Controlled Trials

Abstract: Background Acupuncture is commonly used to treat back pain, but there is no published meta-analysis of trials of its effectiveness for this condition. Objective To perform a meta-analysis of trials of acupuncture for the treatment of back pain. Methods A systematic literature search was conducted to retrieve all randomized controlled trials of any form of acupuncture for any type of back pain in humans. The adequacy of the acupuncture treatment was assessed by consulting 6 experienced acupuncturists. The main outcome measure for the meta-analysis was numbers of patients whose symptoms were improved at the end of treatment. Results Twelve studies were included, of which 9 presented data suitable for meta-analysis. The odds ratio of improvement with acupuncture compared with control intervention was 2.30 (95% confidence interval, 1.28-4.13). For sham-controlled, evaluator-blinded studies, the odds ratio was 1.37 (95% confidence interval, 0.84-2.25). Conclusion Acupuncture was shown to be superior to various control interventions, although there is insufficient evidence to state whether it is superior to placebo.

Newborn infants prefer attractive faces

Abstract: Several previous experiments have found that infants 2 months of age and older will spend more time looking at attractive faces when these are shown paired with faces judged by adults to be unattractive. Two experiments are described whose aim was to find whether the “attractiveness effect” is present soon after birth. In both, pairings of attractive and unattractive female faces (as judged by adult raters) were shown to newborn infants (in the age range 14–151 hours from birth), and in both the infants looked longer at the attractive faces. These findings can be interpreted either in terms of an innate perceptual mechanism that detects and responds specifically to faces, or in terms of rapid learning about faces soon after birth.

Regression Analysis in Accounting Disclosure Studies

Abstract: A problem that sometimes occurs in undertaking empirical research in accounting and finance is that the theoretically correct form of the relation between the dependent and independent variables is not known, although often thought or assumed to be monotonic. In addition, transformations of disclosure measures and independent variables are proxies for underlying constructs and hence, while theory may specify a functional form for the underlying theoretical construct, it is unlikely to hold for empirical proxies. In order to cope with this problem a number of accounting disclosure studies have transformed variables so that the statistical analysis is more meaningful. One approach that has been advocated in such circumstances is to rank the data and then apply regression techniques, a method that has been used recently in a number of accounting disclosure studies. This paper reviews a number of transformations including the Rank Regression procedure. Because of the inherent properties of ranks and ...

Use of composite fingerprints to determine the provenance of the contemporary suspended sediment load transported by rivers

Abstract: Sediment fingerprinting appears to offer a valuable alternative to direct monitoring for elucidating the provenance of suspended sediment and the relative importance of spatial zones or subcatchments comprising larger ( >500 km 2 ) drainage basins. Against this background, a quantitative composite fingerprinting technique, incorporating both statistically verified multicomponent signatures and a multivariate sediment-mixing model, has been employed to determine the spatial origin of contemporary suspended sediment transported from the upper and middle reaches of the River Exe (601km 2 ) and River Severn (4325 km 2 ) basins, UK. Spatial origin is addressed in terms of the relative contribution from three distinct geological subareas constituting each study basin. The consistency of the composite fingerprinting approach is examined using the estimates for mean and seasonal variations in source area contributions and also a comparison between the results obtained for individual flood events and alternative lines of evidence provided by flood travel times and the spatial distribution of precipitation. It is argued that fingerprinting estimates for sediment provenance are consistent with existing information on suspended sediment yields from different subcatchments within the study basins, although in the Severn, the role of storage and remobilization in producing signature ‘averaging’ may complicate comparison of the fingerprinting data with typical floodwater routing times. Validation represents the greatest problem for the cost‐benefit of fingerprinting and scope still exists for further refinement of the procedures involved. © 1998 John Wiley & Sons, Ltd.

Does Asset Ownership Always Motivate Managers? Outside Options and the Property Rights Theory of the Firm

Abstract: This paper studies the Grossman-Hart-Moore (GHM) "property rights" approach to the theory of the firm under alternating-offers bargaining. When managers can pursue other occupations while negotiating over the division of the gains from cooperation, the GHM results obtain. If taking the best alternative job terminates bargaining, outcomes are very different. Sometimes an agent with an important investment decision should not own the assets he works with; sometimes independent assets should be owned together; sometimes strictly complementary assets should be owned separately.

Different standards for reporting ADRs to herbal remedies and conventional OTC medicines: face-to-face interviews with 515 users of herbal remedies

Abstract: Face-to-face interviews (using a structured questionnaire) with 515 usersof herbal remedies were conducted in six pharmacy stores and six healthfood storesin the UK. The questionnaire focused on the likely course of action taken byherbal-remedy users after experiencing an ADR associated with a conventionalOTC medicine and a herbal remedy.

Athletic Identity: An Achilles' Heel to the Survival of Self

Abstract: To illuminate the complex ways in which a strong athletic identity can act as an Achilles' heel in coming to terms with a disruptive life event, this article presents biographical data of one elite athlete whose career was prematurely terminated by illness. The analysis reveals how, as an individual descends from the heights of the extraordinary into the mundane world of ordinariness, the loss of certain selves enforces a heightened reflexivity and awareness of previously taken-for-granted aspects of the body-self relationship that are no longer attainable. The manner in which certain selves at the apex of an identity hierarchy exert pressure on the individual to seek a restored self rather than opt for more attainable or realistic identities is highlighted. The problems of restorying the self when an individual is constrained by limited narrative resources are also considered. Finally, some implications of the findings for health care professionals are discussed.

The development of the Short Explanatory Model Interview (SEMI) and its use among primary-care attenders with common mental disorders

Abstract: Background. Recent anthropological studies have documented the importance of understanding the relation of culture to the experience of mental illness. The use of interviews that elicit explanatory models has facilitated such research, but currently available interviews are lengthy and impractical for epidemiological studies. This paper is a preliminary report on the development of a brief instrument to elicit explanatory models for use in field work. Method. The development of the SEMI, a short interview to elicit explanatory models is described. The interview explores the subject's cultural background, nature of presenting problem, help-seeking behaviour, interaction with physician/healer and beliefs related to mental illness. Results. The SEMI was employed to study the explanatory models of subjects with common mental disorders among Whites, African-Caribbean and Asians living in London and was also used in Harare, Zimbabwe. Data from its use in four different ethnic groups is presented with the aim of demonstrating its capacity to show up differences in these varied settings. Conclusions. The simplicity and brevity of the SEMI allow for its use in field studies in different cultures, data can be used to provide variables for use in quantitative analysis and provide qualitative descriptions.

The Cognitive Psychology of Lottery Gambling: A Theoretical Review.

Abstract: Despite the current popularity of the UK National, psychologists have tended to neglect lottery play. This review provides a summary of current research findings and outlines the main cognitive theories of gambling as related to non-pathological lottery play. A discussion of various biases and irrational thinking patterns typically found in lottery gambling will be given. These will include the misunderstanding of lottery odds, a susceptibility to the gambler's fallacy and cognitive entrapment, a belief in hot and cold numbers, unrealistic optimism, a belief in personal luck, superstitious thinking, the illusion of control, the erroneous perception of near misses, a susceptibility to prize size and rollover effects, the framing of gambling outcomes and finally, the influence of social factors on lottery play. It is concluded that the psychology of lottery play needs a more unified theory which whilst largely cognitive in emphasis, should also incorporate social motivations such as those inherent in syndicate based lottery play.

Controlled Production of Emulsions Using a Crossflow Membrane: Part I: Droplet Formation from a Single Pore

Abstract: Amethod for manufacturing emulsions based on cross flow membrane emulsification has been studied. This involves the formation of emulsions by breaking up the discontinuous phase into droplets in a controlled manner without the use of turbulent eddies. This is achieved by passing the discontinuous phase through a suitable microporous medium and injecting the droplets so formed directly into a moving continuous phase. This paper summarizes the development of this technology. Experimental data obtained using a single pore (capillary tube) are presented here for the production of model oil-in-water emulsions. A high speed video camera was used to measure droplet growth and detachment processes from the pore as a function of process parameters such as transmembrane pressure drop, continuous phase crossflow velocity etc. A phenomenological model is developed and tested to predict droplet size and production rate.

Complementary Therapies for Asthma: What Patients Use

Abstract: Asthma patients are prime candidates to employ complementary medicine (CM) for their conditions, yet little hard data exist on the prevalence of CM use by these patients. This survey was aimed at generating some information on this and related issues. Members of the UK National Asthma Campaign (17,000) were invited to complete a questionnaire and 4741 responded. Only 41% of the respondents had never tried CM. Breathing techniques, homoeopathy, and herbalism were the three most prevalent treatments. The majority of respondents perceived these therapies as moderately useful with only little difference between various treatments. In general, the money spent on CM was modest. It is concluded that CM is frequently used for asthma. Therefore, this area of healthcare would seem to warrant more rigorous investigation.