Showing papers by "Lancaster University published in 2006"

The new mobilities paradigm.

Abstract: It seems that a new paradigm is being formed within the social sciences, the ‘new mobilities’ paradigm. Some recent contributions to forming and stabilising this new paradigm include work from anthropology, cultural studies, geography, migration studies, science and technology studies, tourism and transport studies, and sociology. In this paper we draw out some characteristics, properties, and implications of this emergent paradigm, especially documenting some novel mobile theories and methods. We reflect on how far this paradigm has developed and thereby to extend and develop the ‘mobility turn’ within the social sciences.

The Ecology of Phytoplankton

Abstract: Communities of microscopic plant life, or phytoplankton, dominate the Earth's aquatic ecosystems. This important new book by Colin Reynolds covers the adaptations, physiology and population dynamics of phytoplankton communities in lakes and rivers and oceans. It provides basic information on composition, morphology and physiology of the main phyletic groups represented in marine and freshwater systems and in addition reviews recent advances in community ecology, developing an appreciation of assembly processes, co-existence and competition, disturbance and diversity. Although focussed on one group of organisms, the book develops many concepts relevant to ecology in the broadest sense, and as such will appeal to graduate students and researchers in ecology, limnology and oceanography.

Unconventional quantum Hall effect and Berry’s phase of 2π in bilayer graphene

Abstract: There are two known distinct types of the integer quantum Hall effect. One is the conventional quantum Hall effect, characteristic of two-dimensional semiconductor systems1,2, and the other is its relativistic counterpart observed in graphene, where charge carriers mimic Dirac fermions characterized by Berry’s phase π, which results in shifted positions of the Hall plateaus3,4,5,6,7,8,9. Here we report a third type of the integer quantum Hall effect. Charge carriers in bilayer graphene have a parabolic energy spectrum but are chiral and show Berry’s phase 2π affecting their quantum dynamics. The Landau quantization of these fermions results in plateaus in Hall conductivity at standard integer positions, but the last (zero-level) plateau is missing. The zero-level anomaly is accompanied by metallic conductivity in the limit of low concentrations and high magnetic fields, in stark contrast to the conventional, insulating behaviour in this regime. The revealed chiral fermions have no known analogues and present an intriguing case for quantum-mechanical studies.

Landau-level degeneracy and quantum Hall effect in a graphite bilayer.

Abstract: We derive an effective two-dimensional Hamiltonian to describe the low-energy electronic excitations of a graphite bilayer, which correspond to chiral quasiparticles with a parabolic dispersion exhibiting Berry phase $2\ensuremath{\pi}$. Its high-magnetic-field Landau-level spectrum consists of almost equidistant groups of fourfold degenerate states at finite energy and eight zero-energy states. This can be translated into the Hall conductivity dependence on carrier density, ${\ensuremath{\sigma}}_{xy}(N)$, which exhibits plateaus at integer values of $4{e}^{2}/h$ and has a double $8{e}^{2}/h$ step between the hole and electron gases across zero density, in contrast to $(4n+2){e}^{2}/h$ sequencing in a monolayer.

Guidance on the conduct of narrative synthesis in sytematic reviews

Abstract: Titles & abstract s Titles & abstracts Include N=54 Include N=121 Include N=89 Exclude N = 0 Exclude N = 1,024 Exclude N = 21

Asymmetry gap in the electronic band structure of bilayer graphene

Abstract: A tight-binding model is used to calculate the band structure of bilayer graphene in the presence of a potential difference between the layers that opens a gap $\ensuremath{\Delta}$ between the conduction and valence bands. In particular, a self-consistent Hartree approximation is used to describe imperfect screening of an external gate, employed primarily to control the density $n$ of electrons on the bilayer, resulting in a potential difference between the layers and a density dependent gap $\ensuremath{\Delta}(n)$. We discuss the influence of a finite asymmetry gap $\ensuremath{\Delta}(0)$ at zero excess density, caused by the screening of an additional transverse electric field, on observations of the quantum Hall effect.

Ethylene-induced stomatal closure in Arabidopsis occurs via AtrbohF-mediated hydrogen peroxide synthesis

Abstract: Ethylene is a plant hormone that regulates many aspects of growth and development. Despite the well-known association between ethylene and stress signalling, its effects on stomatal movements are largely unexplored. Here, genetic and physiological data are provided that position ethylene into the Arabidopsis guard cell signalling network, and demonstrate a functional link between ethylene and hydrogen peroxide (H(2)O(2)). In wild-type leaves, ethylene induces stomatal closure that is dependent on H(2)O(2) production in guard cells, generated by the nicotinamide adenine dinucleotide phosphate hydrogen (NADPH) oxidase AtrbohF. Ethylene-induced closure is inhibited by the ethylene antagonists 1-MCP and silver. The ethylene receptor mutants etr1-1 and etr1-3 are insensitive to ethylene in terms of stomatal closure and H(2)O(2) production. Stomata of the ethylene signalling ein2-1 and arr2 mutants do not close in response to either ethylene or H(2)O(2) but do generate H(2)O(2) following ethylene challenge. Thus, the data indicate that ethylene and H(2)O(2) signalling in guard cells are mediated by ETR1 via EIN2 and ARR2-dependent pathway(s), and identify AtrbohF as a key mediator of stomatal responses to ethylene.

Public Engagement as a Means of Restoring Public Trust in Science – Hitting the Notes, but Missing the Music?

Abstract: This paper analyses the recent widespread moves to 'restore' public trust in science by developing an avowedly two-way, public dialogue with science initiatives. Noting how previously discredited and supposedly abandoned public deficit explanations of 'mistrust' have actually been continually reinvented, it argues that this is a symptom of a continuing failure of scientific and policy institutions to place their own science-policy institutional culture into the frame of dialogue, as possible contributory cause of the public mistrust problem.

Weak-localization magnetoresistance and valley symmetry in graphene.

Abstract: Because of the chiral nature of electrons in a monolayer of graphite (graphene) one can expect weak antilocalization and a positive weak-field magnetoresistance in it. However, trigonal warping (which breaks $\mathbf{p}\ensuremath{\rightarrow}\ensuremath{-}\mathbf{p}$ symmetry of the Fermi line in each valley) suppresses antilocalization, while intervalley scattering due to atomically sharp scatterers in a realistic graphene sheet or by edges in a narrow wire tends to restore conventional negative magnetoresistance. We show this by evaluating the dependence of the magnetoresistance of graphene on relaxation rates associated with various possible ways of breaking a ``hidden'' valley symmetry of the system.

Detection of oligomeric forms of α-synuclein protein in human plasma as a potential biomarker for Parkinson’s disease

Abstract: To date there is no accepted clinical diagnostic test for Parkinson's disease (PD) based on biochemical analysis of blood or cerebrospinal fluid (CSF). alpha-Synuclein (alpha-syn) protein has been linked to the pathogenesis of PD with the discovery of mutations in the gene encoding alpha-syn in familial cases with early-onset PD. Lewy bodies and Lewy neurites, which constitute the main pathological features in the brains of patients with sporadic PD and dementia with Lewy bodies, are formed by the conversion of soluble monomers of alpha-syn into insoluble aggregates. We recently reported the presence of alpha-syn in normal human blood plasma and in postmortem CSF. Here, we investigated whether alpha-syn can be used as a biomarker for PD. We have developed a novel ELISA method that detects only oligomeric "soluble aggregates" of alpha-syn. Using this ELISA, we report the presence of significantly elevated (P=0.002) levels of oligomeric forms of alpha-syn in plasma samples obtained from 34 PD patients compared with 27 controls; 52% (95% confidence intervals 0.353-0.687) of the PD patients displayed signals >0.5 OD with our ELISA assay in comparison to only 14.8% (95% confidence intervals 0.014-0.281) for the control cases. An analysis of the test's diagnostic value revealed a specificity of 0.852 (95% confidence intervals 0.662-0.958), sensitivity of 0.529 (95% confidence intervals 0.351-0.702) and a positive predictive value of 0.818 (95% confidence intervals 0.597-0.948). These observations offer new opportunities for developing diagnostic tests for PD and related diseases and for testing therapeutic agents aimed at preventing or reversing the aggregation of alpha-syn.

Selective transmission of Dirac electrons and ballistic magnetoresistance of n − p junctions in graphene

Abstract: We show that an electrostatically created n-p junction separating the electron and hole gas regions in a graphene monolayer transmits only those quasiparticles that approach it almost perpendicularly to the n-p interface. Such a selective transmission of carriers by a single n-p junction would manifest itself in nonlocal magnetoresistance effect in arrays of such junctions and determines the unusual Fano factor in the current noise universal for the n-p junctions in graphene.

Hyperspectral remote sensing of plant pigments.

Abstract: The dynamics of pigment concentrations are diagnostic of a range of plant physiological properties and processes. This paper appraises the developing technologies and analytical methods for quantifying pigments non-destructively and repeatedly across a range of spatial scales using hyperspectral remote sensing. Progress in deriving predictive relationships between various characteristics and transforms of hyperspectral reflectance data are evaluated and the roles of leaf and canopy radiative transfer models are reviewed. Requirements are identified for more extensive intercomparisons of different approaches and for further work on the strategies for interpreting canopy scale data. The paper examines the prospects for extending research to the wider range of pigments in addition to chlorophyll, testing emerging methods of hyperspectral analysis and exploring the fusion of hyperspectral and LIDAR remote sensing. In spite of these opportunities for further development and the refinement of techniques, current evidence of an expanding range of applications in the ecophysiological, environmental, agricultural, and forestry sciences highlights the growing value of hyperspectral remote sensing of plant pigments.

How approaches to teaching are affected by discipline and teaching context

Abstract: Two related studies are reported in this article. The first aimed to analyse how academic discipline is related to university teachers’ approaches to teaching. The second explored the effects of teaching context on approaches to teaching. The participants of the first study were 204 teachers from the University of Helsinki and the Helsinki School of Economics and Business Administration and 136 teachers from the University of Oxford and Oxford Brookes University who returned university teaching inventories. Thus, altogether there were 340 teachers from a variety of disciplines in Finland and the UK. The second study involved only the Finnish sample. The results showed that there was systematic variation in both student‐ and teacher‐focused dimensions of approaches to teaching across disciplines and across teaching contexts. These results confirm the relational nature of teachers’ approaches to teaching and illustrate the need, in using inventories such as the Approaches to Teaching Inventory, to be explic...

Spin and molecular electronics in atomically generated orbital landscapes

Abstract: Ab initio computational methods for electronic transport in nanoscaled systems are an invaluable tool for the design of quantum devices. We have developed a flexible and efficient algorithm for evaluating I-V characteristics of atomic junctions, which integrates the nonequilibrium Green’s function method with density functional theory. This is currently implemented in the package SMEAGOL. The heart of SMEAGOL is our scheme for constructing the surface Green’s functions describing the current-voltage probes. It consists of a direct summation of both open and closed scattering channels together with a regularization procedure of the Hamiltonian and provides great improvements over standard recursive methods. In particular it allows us to tackle material systems with complicated electronic structures, such as magnetic transition metals. Here we present a detailed description of SMEAGOL together with an extensive range of applications relevant for the two burgeoning fields of spin and molecular electronics.

Flagellar motility is required for the viability of the bloodstream trypanosome

Abstract: There is little hope for a vaccine for African sleeping sickness, and most of the drugs currently used to treat it are old, not particularly effective and difficult to use in the conditions that prevail in sub-Saharan Africa, where the disease is endemic. So the discovery of a new class of molecule that might be targeted by drug intervention could be an important boost to the field. The sleeping sickness parasite Trypanosoma brucei is a protozoon equipped with a whip-like flagellum. RNA interference (RNAi) knock-down experiments show that a functioning flagellum is essential for Trypanosoma's survival in the bloodstream. That makes the flagellum a possible point of therapeutic attack, and proteomic analysis points to a number of trypanosome-specific flagellar proteins that could be targeted. On the cover, monstrous cells of bloodstream-form trypanosomes formed by a failure of cell division in cells with defective flagella. The 9 + 2 microtubule axoneme of flagella and cilia represents one of the most iconic structures built by eukaryotic cells and organisms. Both unity and diversity are present among cilia and flagella on the evolutionary as well as the developmental scale. Some cilia are motile, whereas others function as sensory organelles and can variously possess 9 + 2 and 9 + 0 axonemes and other associated structures1. How such unity and diversity are reflected in molecular repertoires is unclear. The flagellated protozoan parasite Trypanosoma brucei is endemic in sub-Saharan Africa, causing devastating disease in humans and other animals2. There is little hope of a vaccine for African sleeping sickness and a desperate need for modern drug therapies3. Here we present a detailed proteomic analysis of the trypanosome flagellum. RNA interference (RNAi)-based interrogation of this proteome provides functional insights into human ciliary diseases and establishes that flagellar function is essential to the bloodstream-form trypanosome. We show that RNAi-mediated ablation of various proteins identified in the trypanosome flagellar proteome leads to a rapid and marked failure of cytokinesis in bloodstream-form (but not procyclic insect-form) trypanosomes, suggesting that impairment of flagellar function may provide a method of disease control. A postgenomic meta-analysis, comparing the evolutionarily ancient trypanosome with other eukaryotes including humans, identifies numerous trypanosome-specific flagellar proteins, suggesting new avenues for selective intervention.

Search for neutral MSSM Higgs bosons at LEP

Abstract: The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for the neutral Higgs bosons which are predicted by the Minimal Supersymmetric standard model (MSSM). The data of the four collaborations are statistically combined and examined for their consistency with the background hypothesis and with a possible Higgs boson signal. The combined LEP data show no significant excess of events which would indicate the production of Higgs bosons. The search results are used to set upper bounds on the cross-sections of various Higgs-like event topologies. The results are interpreted within the MSSM in a number of “benchmark” models, including CP-conserving and CP-violating scenarios. These interpretations lead in all cases to large exclusions in the MSSM parameter space. Absolute limits are set on the parameter cosβ and, in some scenarios, on the masses of neutral Higgs bosons.

Ignorance is bliss: Or seven reasons not to use uncertainty analysis

Abstract: Uncertainty analysis of models has received increasing attention over the last two decades in water resources research. However, a significant part of the community is still reluctant to embrace the estimation of uncertainty in hydrological and hydraulic modeling. In this paper, we summarize and explore seven common arguments: uncertainty analysis is not necessary given physically realistic models; uncertainty analysis cannot be used in hydrological and hydraulic hypothesis testing; uncertainty (probability) distributions cannot be understood by policy makers and the public; uncertainty analysis cannot be incorporated into the decision-making process; uncertainty analysis is too subjective; uncertainty analysis is too difficult to perform; uncertainty does not really matter in making the final decision. We will argue that none of the arguments against uncertainty analysis rehearsed are, in the end, tenable. Moreover, we suggest that one reason why the application of uncertainty analysis is not normal and expected part of modeling practice is that mature guidance on methods and applications does not exist. The paper concludes with suggesting that a Code of Practice is needed as a way of formalizing such guidance.

The smart phone: a ubiquitous input device

Abstract: We show how modern mobile phones (Weiser's tabs) can interact with their environment, especially large situated displays (Weiser's boards). Smart phones' emerging capabilities are fueling a rise in the use of mobile phones as input devices to such resources as situated displays, vending machines, and home appliances. Mobile phones' prevalence gives them great potential to be the default physical interface for ubiquitous computing applications. We survey interaction techniques that use mobile phones as input devices to ubiquitous computing environments. We use smart phone to describe an enhanced mobile phone. Our analysis blurs the line between smart phones and PDAs such as the Palm Pilot because the feature sets continue to converge.

Exact and efficient Bayesian inference for multiple changepoint problems

Abstract: We demonstrate how to perform direct simulation from the posterior distribution of a class of multiple changepoint models where the number of changepoints is unknown. The class of models assumes independence between the posterior distribution of the parameters associated with segments of data between successive changepoints. This approach is based on the use of recursions, and is related to work on product partition models. The computational complexity of the approach is quadratic in the number of observations, but an approximate version, which introduces negligible error, and whose computational cost is roughly linear in the number of observations, is also possible. Our approach can be useful, for example within an MCMC algorithm, even when the independence assumptions do not hold. We demonstrate our approach on coal-mining disaster data and on well-log data. Our method can cope with a range of models, and exact simulation from the posterior distribution is possible in a matter of minutes.

Ownership and Management Issues Associated With Family Firm Performance and Company Objectives

Abstract: Agency and stewardship theories are used to explore associations between ownership and management profiles and the performance and objectives of family firms. Using data from privately held family firms in the United Kingdom, a range of performance measures and objectives were examined. Multivariate regression analysis detected that closely held family firms did not report superior firm performance. The results show that the management rather than the ownership structure of a family firm was generally associated with selected firm-performance indicators and nonfinancial company objectives. Although family CEOs were associated with lower propensity to export, presented evidence generally fails to suggest that private family firms should avoid employing family members in management roles.

Two Cytosolic Glutamine Synthetase Isoforms of Maize Are Specifically Involved in the Control of Grain Production

Abstract: The roles of two cytosolic maize glutamine synthetase isoenzymes (GS1), products of the Gln1-3 and Gln1-4 genes, were investigated by examining the impact of knockout mutations on kernel yield. In the gln1-3 and gln1-4 single mutants and the gln1-3 gln1-4 double mutant, GS mRNA expression was impaired, resulting in reduced GS1 protein and activity. The gln1-4 phenotype displayed reduced kernel size and gln1-3 reduced kernel number, with both phenotypes displayed in gln1-3 gln1-4. However, at maturity, shoot biomass production was not modified in either the single mutants or double mutants, suggesting a specific impact on grain production in both mutants. Asn increased in the leaves of the mutants during grain filling, indicating that it probably accumulates to circumvent ammonium buildup resulting from lower GS1 activity. Phloem sap analysis revealed that unlike Gln, Asn is not efficiently transported to developing kernels, apparently causing reduced kernel production. When Gln1-3 was overexpressed constitutively in leaves, kernel number increased by 30%, providing further evidence that GS1-3 plays a major role in kernel yield. Cytoimmunochemistry and in situ hybridization revealed that GS1-3 is present in mesophyll cells, whereas GS1-4 is specifically localized in the bundle sheath cells. The two GS1 isoenzymes play nonredundant roles with respect to their tissue-specific localization.

Rethinking followership: a post-structuralist analysis of follower identities

Abstract: A number of recent studies highlight the importance of followership, of identity issues for leadership processes, and of leaders' capacity to shape followers' identity. Reviewing these various contributions, this article outlines the potential value of post-structuralist theories for the study of followership and follower identities. It presents an alternative way of conceiving identity and power and examines a wider repertoire of follower selves, exploring in particular the workplace enactment of conformist, resistant, and dramaturgical identities. Suggesting that leaders' impact on followers' identities may be more complex than previously recognized, the article concludes that studies of leadership need to develop a much deeper understanding of follower identities and of the complex ways that these selves may interact with those of leaders.

The upgraded DØ detector

Abstract: The D0 experiment enjoyed a very successful data-collection run at the Fermilab Tevatron collider between 1992 and 1996. Since then, the detector has been upgraded to take advantage of improvements to the Tevatron and to enhance its physics capabilities. We describe the new elements of the detector, including the silicon microstrip tracker, central fiber tracker, solenoidal magnet, preshower detectors, forward muon detector, and forward proton detector. The uranium/liquid-argon calorimeters and central muon detector, remaining from Run I, are discussed briefly. We also present the associated electronics, triggering, and data acquisition systems, along with the design and implementation of software specific to D0.

Exact and computationally efficient likelihood-based estimation for discretely observed diffusion processes (with discussion)

Abstract: Summary. The objective of the paper is to present a novel methodology for likelihood-based inference for discretely observed diffusions. We propose Monte Carlo methods, which build on recent advances on the exact simulation of diffusions, for performing maximum likelihood and Bayesian estimation.