Showing papers by "University of Exeter published in 2003"

Surface plasmon subwavelength optics

Abstract: Surface plasmons are waves that propagate along the surface of a conductor. By altering the structure of a metal's surface, the properties of surface plasmons--in particular their interaction with light--can be tailored, which offers the potential for developing new types of photonic device. This could lead to miniaturized photonic circuits with length scales that are much smaller than those currently achieved. Surface plasmons are being explored for their potential in subwavelength optics, data storage, light generation, microscopy and bio-photonics.

Culture, Corporate Governance and Disclosure in Malaysian Corporations

Abstract: Evidence from research conducted on corporate accounting indicates that the interaction of environmental factors influences disclosure practices. The purpose of this study is to examine the importance of various corporate governance and cultural (race and education) characteristics, in addition to firm-specific factors, as possible determinants of voluntary (non-mandatory accounting and non-accounting information) disclosures in the annual reports of Malaysian listed corporations. The results of the regression analysis indicate significant associations (at the 5 percent level) between two corporate governance variables (viz. chair who is a non-executive director and domination of family members on boards) and the extent of voluntary disclosure. This finding has implications for corporate governance policy formulation by the Malaysian Institute of Corporate Governance (MISG). One cultural factor (proportion of Malay directors on the board) is significantly associated (at the 5 percent level) with the extent of voluntary disclosure suggesting that governmental focus on culture may solicit a response to secrecy from those who feel threatened.

Photonic structures in biology

Abstract: Millions of years before we began to manipulate the flow of light using synthetic structures, biological systems were using nanometre-scale architectures to produce striking optical effects. An astonishing variety of natural photonic structures exists: a species of Brittlestar uses photonic elements composed of calcite to collect light, Morpho butterflies use multiple layers of cuticle and air to produce their striking blue colour and some insects use arrays of elements, known as nipple arrays, to reduce reflectivity in their compound eyes. Natural photonic structures are providing inspiration for technological applications.

On the Trail of a Cereal Killer: Exploring the Biology of Magnaporthe grisea

Abstract: The blast fungus Magnaporthe grisea causes a serious disease on a wide variety of grasses including rice, wheat, and barley. Rice blast is the most serious disease of cultivated rice and therefore poses a threat to the world's most important food security crop. Here, I review recent progress toward understanding the molecular biology of plant infection by M. grisea, which involves development of a specialized cell, the appressorium. This dome-shaped cell generates enormous turgor pressure and physical force, allowing the fungus to breach the host cuticle and invade plant tissue. The review also considers the role of avirulence genes in M. grisea and the mechanisms by which resistant rice cultivars are able to perceive the fungus and defend themselves. Finally, the likely mechanisms that promote genetic diversity in M. grisea and our current understanding of the population structure of the blast fungus are evaluated.

The formation of a star cluster: predicting the properties of stars and brown dwarfs

Abstract: We present results from the largest numerical simulation of star formation to resolve the fragmentation process down to the opacity limit. The simulation follows the collapse and fragmentation of a large-scale turbulent molecular cloud to form a stellar cluster and, simultaneously, the formation of circumstellar discs and binary stars. This large range of scales enables us to predict a wide variety of stellar properties for comparison with observations. The calculation clearly demonstrates that star formation is a highly-dynamic and chaotic process. Star formation occurs in localized bursts within the cloud via the fragmentation both of dense molecular cloud cores and of massive circumstellar discs. Star-disc encounters form binaries and truncate discs. Stellar encounters disrupt bound multiple systems. We find that the observed statistical properties of stars are a natural consequence of star formation in such a dynamical environment. The cloud produces roughly equal numbers of stars and brown dwarfs, with masses down to the opacity limit for fragmentation (5 Jupiter masses). The initial mass function is consistent with a Salpeter slope (Γ = -1.35) above 0.5 M O ., a roughly flat distribution (r = 0) in the range 0.006-0.5 M O ., and a sharp cut-off below 0.005 M O .. This is consistent with recent observational surveys. The brown dwarfs form by the dynamical ejection of low-mass fragments from dynamically unstable multiple systems before the fragments have been able to accrete to stellar masses. Close binary systems (with separations ≤10 au) are not formed by fragmentation in situ. Rather, they are produced by hardening of initially wider multiple systems through a combination of dynamical encounters, gas accretion, and/or the interaction with circumbinary and circumtriple discs. Finally, we find that the majority of circumstellar discs have radii less than 20 au due to truncation in dynamical encounters. This is consistent with observations of the Orion Trapezium cluster and implies that most stars and brown dwarfs do not form large planetary systems.

Sulfur and selenium: the role of oxidation state in protein structure and function.

Abstract: Sulfur and selenium occur in proteins as constituents of the amino acids cysteine, methionine, selenocysteine, and selenomethionine. Recent research underscores that these amino acids are truly exceptional. Their redox activity under physiological conditions allows an amazing variety of posttranslational protein modifications, metal free redox pathways, and unusual chalcogen redox states that increasingly attract the attention of biological chemists. Unlike any other amino acid, the "redox chameleon" cysteine can participate in several distinct redox pathways, including exchange and radical reactions, as well as atom-, electron-, and hydride-transfer reactions. It occurs in various oxidation states in the human body, each of which exhibits distinctive chemical properties (e.g. redox activity, metal binding) and biological activity. The position of selenium in the periodic table between the metals and the nonmetals makes selenoproteins ideal catalysts for many biological redox transformations. It is therefore apparent that the chalcogen amino acids cysteine, methionine, selenocysteine, and selenomethionine exhibit a unique biological chemistry that is the source of exciting research opportunities.

Fluoride toothpastes for preventing dental caries in children and adolescents.

Abstract: BACKGROUND: Fluoride toothpastes have been widely used for over three decades and remain a benchmark intervention for the prevention of dental caries OBJECTIVES: To determine the effectiveness and safety of fluoride toothpastes in the prevention of caries in children and to examine factors potentially modifying their effect SEARCH STRATEGY: We searched the Cochrane Oral Health Group's Trials Register (May 2000), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 2, 2000), MEDLINE (1966 to January 2000), plus several other databases We handsearched journals, reference lists of articles and contacted selected authors and manufacturers SELECTION CRITERIA: Randomized or quasi-randomized controlled trials with blind outcome assessment, comparing fluoride toothpaste with placebo in children up to 16 years during at least one year The main outcome was caries increment measured by the change in decayed, missing and filled tooth surfaces (D(M)FS) DATA COLLECTION AND ANALYSIS: Inclusion decisions, quality assessment and data extraction were duplicated in a random sample of one third of studies, and consensus achieved by discussion or a third party Authors were contacted for missing data The primary measure of effect was the prevented fraction (PF) that is the difference in caries increments between the treatment and control groups expressed as a percentage of the increment in the control group Random effects meta-analyses were performed where data could be pooled Potential sources of heterogeneity were examined in random effects meta-regression analyses MAIN RESULTS: Seventy-four studies were included For the 70 that contributed data for meta-analysis (involving 42,300 children) the D(M)FS pooled PF was 24% (95% confidence interval (CI), 21 to 28%; p<00001) This means that 16 children need to brush with a fluoride toothpaste (rather than a non-fluoride toothpaste) over three years to prevent one D(M)FS in populations with caries increment of 26 D(M)FS per year In populations with caries increment of 11 D(M)FS per year, 37 children will need to use a fluoride toothpaste for three years to avoid one D(M)FS There was clear heterogeneity, confirmed statistically (p<00001) The effect of fluoride toothpaste increased with higher baseline levels of D(M)FS, higher fluoride concentration, higher frequency of use, and supervised brushing, but was not influenced by exposure to water fluoridation There is little information concerning the deciduous dentition or adverse effects (fluorosis) REVIEWER'S CONCLUSIONS: Supported by more than half a century of research, the benefits of fluoride toothpastes are firmly established Taken together, the trials are of relatively high quality, and provide clear evidence that fluoride toothpastes are efficacious in preventing caries

The Processes by Which Perceived Autonomy Support in Physical Education Promotes Leisure-Time Physical Activity Intentions and Behavior: A Trans-Contextual Model

Abstract: The trans-contextual model proposes that young people's perceived autonomy support in physical education will affect their perceived locus of causality, intentions, and physical activity behavior in leisure time High school students completed measures of perceived autonomy support and perceived locus of causality in physical education One week later, participants' perceived locus of causality and constructs from the theory of planned behavior were assessed in leisure time Leisure-time physical activity behavior was measured 5 weeks later Perceived autonomy support in physical education affected leisure-time physical activity directly and indirectly through a motivational sequence involving internal perceived locus of causality, attitudes, perceived behavioral control, and intentions Results support the trans-contextual model indicating that perceived autonomy support in an educational context influences motivation in a leisure-time context (PsycINFO Database Record (c) 2008 APA, all rights reserved) (journal abstract)

Forty eclipsing binaries in the Small Magellanic Cloud: fundamental parameters and Cloud distance

Abstract: We have conducted a programme to determine the fundamental parameters of a substantial number of eclipsing binaries of spectral types O and B in the Small Magellanic Cloud (SMC). New spectroscopic data, obtained with the two- degree- field (2dF) multi- object spectrograph on the 3.9- m Anglo- Australian Telescope, have been used in conjunction with photometry from the Optical Gravitational Lens Experiment (OGLE- II) data base of SMC eclipsing binaries. Previously we reported results for 10 systems; in this second and concluding paper we present spectral types, masses, radii, temperatures, surface gravities and luminosities for the components of a further 40 binaries. The uncertainties are typically +/- 10 per cent on masses, +/- 4 per cent on radii and +/- 0.07 on log L. The full sample of 50 OB- type eclipsing systems is the largest single set of fundamental parameters determined for high- mass binaries in any galaxy. We find that 21 of the systems studied are in detached configurations, 28 are in semidetached post- mass- transfer states, and one is a contact binary.The overall properties of the detached systems are consistent with theoretical models for the evolution of single stars with SMC metal abundances (Z similar or equal to 0.004); in particular, observed and evolutionary masses are in excellent agreement. Although there are no directly applicable published models, the overall properties of the semidetached systems are consistent with them being in the slow phase of mass transfer in case A. About 40 per cent of these semidetached systems show photometric evidence of orbital- phase- dependent absorption by a gas stream falling from the inner Lagrangian point on the secondary star towards the primary star. This sample demonstrates that case- A mass transfer is a common occurrence amongst high- mass binaries with initial orbital periods P less than or similar to 5 d, and that this slow phase has a comparable duration to the detached phase preceding it.Each system provides a primary distance indicator. We find a mean distance modulus to the SMC of 18.91 +/- 0.03 +/- 0.1 (internal and external uncertainties; D = 60.6 +/- 1.0 +/- 2.8 kpc). This value represents one of the most precise available determinations of the distance to the SMC.

The hierarchical formation of a stellar cluster

Abstract: Recent surveys of star-forming regions have shown that most stars, and probably all massive stars, are born in dense stellar clusters. The mechanism by which a molecular cloud fragments to form several hundred to thousands of individual stars has remained elusive. Here, we use a numerical simulation to follow the fragmentation of a turbulent molecular cloud, and the subsequent formation and early evolution of a stellar cluster containing more than 400 stars. We show that the stellar cluster forms through the hierarchical fragmentation of a turbulent molecular cloud. This leads to the formation of many small subclusters, which interact and merge to form the final stellar cluster. The hierarchical nature of the cluster formation has serious implications in terms of the properties of the new-born stars. The higher number-density of stars in subclusters, compared to a more uniform distribution arising from a monolithic formation, results in closer and more frequent dynamical interactions. Such close interactions can truncate circumstellar discs, harden existing binaries and potentially liberate a population of planets. We estimate that at least one-third of all stars, and most massive stars, suffer such disruptive interactions.

Quantum scattering calculations on chemical reactions.

Abstract: This review discusses recent quantum scattering calculations on bimolecular chemical reactions in the gas phase. This theory provides detailed and accurate predictions on the dynamics and kinetics of reactions containing three atoms. In addition, the method can now be applied to reactions involving polyatomic molecules. Results obtained with both time-independent and time-dependent quantum dynamical methods are described. The review emphasises the recent development in time-dependent wave packet theories and the applications of reduced dimensionality approaches for treating polyatomic reactions. Calculations on over 40 different reactions are described.

Strategies for sustainability: citizens and responsible environmental behaviour

Abstract: Policymakers are becoming increasingly interested in the means by which individuals can be encouraged to engage in environmental actions around the home. This paper uses evidence from existing empirical research and a large questionnaire survey undertaken by the author to argue that environmental action is open to a range of influences, focusing especially on environmental values, situational characteristics and psychological variables. Accordingly, the paper asserts that strategies for promoting environmentally responsible behaviours (such as energy saving, water conservation and waste recycling) should take account of these factors. The implications for the study of environmental behaviour are considered.

The Limitations of ‘Policy Transfer’ and ‘Lesson Drawing’ for Public Policy Research

Abstract: The concepts of 'lesson drawing' and 'policy transfer' have become increasingly influential ways of understanding public policy, especially in the UK. However, the main proponents of the concepts, Rose for 'lesson drawing' and Dolowitz and Marsh for 'policy transfer', have difficulty in providing convincing answers to three questions that are important for them and those engaged in similar studies. First, can they be defined as distinctive forms of policy- making separate from other, more conventional, forms? 'Lesson drawing' is very similar to conventional accounts of 'rational' policy-making and 'policy transfer' is very difficult to define distinctly from many other forms of policy-making. Second, why does 'lesson drawing' and 'policy transfer' occur rather than some other form of policy-making? The proponents of 'policy transfer' put a set of diverse and conflicting theories under a common framework, obscuring differences between them. Third, what are the effects of 'lesson drawing' and 'policy transfer' on policy-making and how do they compare to other processes? Whilst the effect of more 'lesson drawing' seems to be more 'rational' policy-making, the effect of 'policy transfer' on policy 'success' and 'failure' is less clear. Dolowitz and Marsh redescribe aspects of 'failure' as different forms of 'transfer' rather than giving independent reasons for outcomes based on features of transfer processes. Overall, particularly in the case of 'policy transfer', researchers may be better off selecting from a range of alternative approaches than limiting themselves to these conceptual frameworks.

The ASPIRe model: Actualizing Social and Personal Identity Resources to enhance organizational outcomes.

Abstract: A growing body of research points to the contribution of social identity and self-categorization processes to organizational social capital. In particular, this is because all facets of collective behaviour (e.g., trust, communication, leadership, productivity) are facilitated to the extent that individuals define themselves in terms of higher-order social categories (i.e., as members of a common ingroup). However, very little work has sought to translate these social and cognitive insights into models of organizational practice. In an attempt to do this, the present paper outlines a four-phase model for Actualizing Social and Personal Identity Resources (the ASPIRe model). Within a relevant organizational unit, an initial phase involves ascertaining which social identities employees use collectively to define themselves (AIRing). In intermediate phases, relevant subgroups and then the organizational unit as a whole develop goals that are relevant to those identities (Sub-Casing and Super-Casing). In a final phase, organizational planning and direction are informed by the outcomes of the previous two phases and by the new organic organizational identity they produce (ORGanizing). Points of contact with alternative models are identified and the model's potential to encourage sustainable productivity is discussed.

Self-adaptive fitness formulation for constrained optimization

Abstract: A self-adaptive fitness formulation is presented for solving constrained optimization problems. In this method, the dimensionality of the problem is reduced by representing the constraint violations by a single infeasibility measure. The infeasibility measure is used to form a two-stage penalty that is applied to the infeasible solutions. The performance of the method has been examined by its application to a set of eleven test cases from the specialized literature. The results have been compared with previously published results from the literature. It is shown that the method is able to find the optimum solutions. The proposed method requires no parameter tuning and can be used as a fitness evaluator with any evolutionary algorithm. The approach is also robust in its handling of both linear and nonlinear equality and inequality constraint functions. Furthermore, the method does not require an initial feasible solution.

The five minds of a manager.

Abstract: Managers are told: Be global and be local. Collaborate and compete. Change, perpetually, and maintain order. Make the numbers while nurturing your people. To be effective, managers need to consider the juxtapositions in order to arrive at a deep integration of these seemingly contradictory concerns. That means they must focus not only on what they have to accomplish but also on how they have to think. When the authors, respectively the director of the Centre for Leadership Studies at the University of Exeter in the U.K. and the Cleghorn Professor of Management Studies at McGill University in Montreal, set out to develop a masters program for practicing managers, they saw that they could not rely on the usual MBA educational structure, which divides the management world into discrete business functions such as marketing and accounting. They needed an educational structure that would encourage synthesis rather than separation. Managing, they determined, involves five tasks, each with its own mind-set: managing the self (the reflective mind-set); managing organizations (the analytic mind-set); managing context (the worldly mind-set); managing relationships (the collaborative mind-set); and managing change (the action mind-set). The program is built on the exploration and integration of those five aspects of the managerial mind. The authors say it has proved powerful in the classroom and insightful in practice. Imagine the mind-sets as threads and the manager as weaver. Effective performance means weaving each mind-set over and under the others to create a fine, sturdy cloth.

Water–air temperature relationships in a Devon river system and the role of flow

Abstract: The nature of the water–air temperature relationship, and its moderation by discharge, were investigated for catchments ranging in size from 2·1 to 601 km2 in the Exe basin, Devon, UK and for data relating to hourly, daily and weekly time bases. The sensitivity and explanatory power of simple water–air temperature regression models based on hourly data were improved by incorporation of a lag, which increased with catchment size, although relationships became more sensitive and less scattered as the time base of data increased from hourly to weekly mean values. Significant departures from linearity in water–air temperature relationships were evident for hourly, but not for daily mean or weekly mean, data. A clear tendency for relationships between water and air temperatures to be stronger and more sensitive for flows below median levels was apparent, and multiple regression analysis also revealed water temperature to be inversely related to discharge for all catchments and time-scales. However, discharge had a greater impact in accounting for water temperature variation at shorter time-scales and in larger catchments. Copyright © 2003 John Wiley & Sons, Ltd.

More than a Metaphor: Organizational Identity Makes Organizational Life Possible

Abstract: Recent papers by Cornelissen (2002a, 2002b) and Gioia, Schultz and Corley (2002a, 2002b) have debated the utility of organizational identity as a metaphor for understanding organizational life. In the present paper we argue that this debate is limiting because it frames issues of organizational identity purely in metaphorical terms and fails to explore the social psychological basis and consequences of the discontinuity between personal and organizational identity. Extending this debate, we argue that the power of organizational identity as a theoretical and applied construct derives from the fact that it has the capacity to be both an externally shared and negotiated product and an internalized aspect of the collective self. Consistent with recent research informed by the social identity approach to organizational psychology, we discuss how an appreciation of the identity-based dynamic between the social facts of organizations and the socially-structured psychology of organizational members is essential for both theoretical and practical understanding of organizational life.

Public Finances and Long-Term Growth in Europe - Evidence from a Panel Data Analysis

Abstract: In Lisbon the European Council proclaimed a European growth strategy. It considers an average economic "growth rate of around 3 percent as a realistic prospect for the coming years" and assigns public finances an important role in the process of achieving this goal. This paper addresses the question whether we can find empirical evidence for European countries that public finance reform affects trend growth. Focusing on time series patterns, we investigate whether there have been persistent shifts or trends in economic growth and fiscal variables over the last 40 years. In addition, we estimate a distributed lag model, which 1) indicates that government consumption and transfers negatively affect growth rates of GDP per capita over the business cycle, while public investment has a positive impact, and 2) provides robust evidence that distortionary taxation affects growth in the medium-term through its impact on the accumulation of private physical capital.

Three-dimensional calculations of high- and low-mass planets embedded in protoplanetary discs

Abstract: We analyse the non-linear, three-dimensional response of a gaseous, viscous protoplanetary disc to the presence of a planet of mass ranging from 1 Earth mass (1 M⊕) to 1 Jupiter mass (1 MJ) by using the ZEUS hydrodynamics code. We determine the gas f ow pattern, and the accretion and migration rates of the planet. The planet is assumed to be in a f xed circular orbit about the central star. It is also assumed to be able to accrete gas without expansion on the scale of its Roche radius. Only planets with masses Mp 0.1 MJ produce significan perturbations in the surface density of the disc. The fl w within the Roche lobe of the planet is fullythree-dimensional.GasstreamsgenerallyentertheRochelobeclosetothediscmid-plane, but produce much weaker shocks than the streams in two-dimensional models. The streams supply material to a circumplanetary disc that rotates in the same sense as the orbit of the planet. Much of the mass supply to the circumplanetary disc comes from non-coplanar fl w. The accretion rate peaks with a planet mass of approximately 0.1 MJ and is highly efficient occurring at the local viscous rate. The migration time-scales for planets of mass less than 0.1 MJ, based on torques from disc material outside the Roche lobes of the planets, are in excellent agreement with the linear theory of type I (non-gap) migration for three-dimensional discs.ThetransitionfromtypeItotypeII(gap)migrationissmooth,withchangesinmigration times of about a factor of 2. Starting with a core which can undergo runaway growth, a planet can gain up to a few MJ with little migration. Planets with fina masses of the order of 10 MJ would undergo large migration, which makes formation and survival difficult