Showing papers by "Lancaster University published in 2003"

The role of stomata in sensing and driving environmental change.

Abstract: Stomata, the small pores on the surfaces of leaves and stalks, regulate the flow of gases in and out of leaves and thus plants as a whole. They adapt to local and global changes on all timescales from minutes to millennia. Recent data from diverse fields are establishing their central importance to plant physiology, evolution and global ecology. Stomatal morphology, distribution and behaviour respond to a spectrum of signals, from intracellular signalling to global climatic change. Such concerted adaptation results from a web of control systems, reminiscent of a 'scale-free' network, whose untangling requires integrated approaches beyond those currently used.

Herbivore-mediated linkages between aboveground and belowground communities

Abstract: Understanding how terrestrial ecosystems function requires a combined aboveground–belowground approach, because of the importance of feedbacks that occur between herbivores, producers, and the decomposer subsystem. In this paper, we identify several mechanisms by which herbivores can indirectly affect decomposer organisms and soil processes through altering the quantity and quality of resources entering the soil. We show that these mechanisms are broadly similar in nature for both foliar and root herbivory, regardless of whether they operate in the short term as a result of physiological responses of individual plants to herbivore attack or long-term following alteration of plant community structure by herbivores and subsequent changes in the quality of litter inputs to soil. We propose that a variety of possible mechanisms is responsible for the idiosyncratic nature of herbivore effects on soil biota and ecosystem function; positive, negative, or neutral effects of herbivory are possible depending upon the balance of these different mechanisms. However, we predict that positive effects of herbivory on soil biota and soil processes are most common in ecosystems of high soil fertility and high consumption rates, whereas negative effects are most common in unproductive ecosystems with low consumption rates. The significance of multiple-species herbivore communities is also emphasized, and we propose that if resource use complementarity among herbivore species or functional groups leads to greater total consumption of phytomass, and thus greater net herbivory, then both positive and negative consequences of increasing herbivore diversity for belowground properties and processes are theoretically possible. Research priorities are highlighted and include a need for comparative studies of herbivore impacts on above- and belowground processes across ecosystems of varying productivity, as well as a need for experimental testing of the influence of antiherbivore defense compounds on complex multitrophic interactions in the rhizosphere and the significance of multiple herbivore species communities on these plant–soil interactions.

Re-Embedding Situatedness: The Importance of Power Relations in Learning Theory

Abstract: This paper critically addresses the coherence, reception, and dissemination of "situated learning theory" (Lave and Wenger 1991). Situated learning theory commends a conceptualization of the process of learning that, in offering an alternative to cognitive theories, departs radically from the received body of knowledge on learning in organizations. The paper shows how elements of situated learning theory have been selectively adopted to fertilize or extend the established terrain of organizational learning. In this process, we argue, Lave and Wenger's embryonic appreciation of power relations as media of learning is displaced by a managerial preoccupation with harnessing (reified) "communities of practice" to the fulfillment of (reified) corporate objectives. We illustrate our argument by reference to Orr's (1990, 1996) study of photocopier technicians, which is very widely cited as an example of the "new," situated conceptualization of learning in communities of practice. We commend a revitalization of situated learning theory in which learning practices are understood to be enabled and constrained by their embeddedness in relations of power; and, more specifically, by the unstable institutionalization of power relations within capitalist work organizations.

A survey of key management for secure group communication

Abstract: Group communication can benefit from IP multicast to achieve scalable exchange of messages. However, there is a challenge of effectively controlling access to the transmitted data. IP multicast by itself does not provide any mechanisms for preventing nongroup members to have access to the group communication. Although encryption can be used to protect messages exchanged among group members, distributing the cryptographic keys becomes an issue. Researchers have proposed several different approaches to group key management. These approaches can be divided into three main classes: centralized group key management protocols, decentralized architectures and distributed key management protocols. The three classes are described here and an insight given to their features and goals. The area of group key management is then surveyed and proposed solutions are classified according to those characteristics.

In Other (People's) Words: Plagiarism by university students--literature and lessons

Abstract: This paper reviews the literature on plagiarism by students, much of it based on North American experience, to discover what lessons it holds for institutional policy and practice within institutions of higher education in the UK. It explores seven themes: the meaning and context of plagiarism, the nature of plagiarism by students, how do students perceive plagiarism, how big a problem is student plagiarism, why do students cheat, what challenges are posed by digital plagiarism and is there a need to promote academic integrity? It is concluded that plagiarism is doubtless common and getting more so (particularly with increased access to digital sources, including the Internet), that there are multiple reasons why students plagiarise and that students often rationalise their cheating behaviour and downplay the importance of plagiarism by themselves and their peers. It is also concluded that there is a growing need for UK institutions to develop cohesive frameworks for dealing with student plagiarism that a...

Primordial density perturbation in the curvaton scenario

Abstract: We analyze the primordial density perturbation when it is generated by a ``curvaton'' field different from the inflaton. In some cases this perturbation may have large isocurvature components, fully correlated or anticorrelated with the adiabatic component. It may also have a significant non-Gaussian component. All of these effects are calculated in a form which will enable direct comparison with current and forthcoming observational data.

Converging Conventions of Comfort, Cleanliness and Convenience

Abstract: Many commentators analyse green consumption as if it were an expression of individual environmental commitment. Such approaches suppose that the adoption of more sustainable ways of life depends upon the diffusion of "green" beliefs and actions through society. In this article, the author explores the idea that patterns of resource consumption (especially of energy and water) reflect what are generally inconspicuous routines and habits. Are such conventions evolving or standardising in ways that are increasingly resource intensive? In addressing this question with reference to three domains of daily life: comfort, cleanliness, and convenience, four simple models of change are outlined, two of which imply an inexorable escalation of resource consumption, two of which do not. The purpose of this illustrative exercise is to demonstrate the importance of understanding the systemic redefinition of "normal practice." Rather than taking individual behaviour to be the central unit of analysis, the case is made for an approach that concentrates on the construction and transformation of collective convention. This theoretical reorientation opens the way for programmes of research and policy informed by an appreciation of the technological and the commercial as well as the symbolic and cultural dimensions of more and less resource-intensive ways of life.

Prevalence of psychiatric disorders in children and adolescents with and without intellectual disability

Abstract: Background There have been very few population-based studies of the prevalence of psychiatric disorders among children and adolescents with and without intellectual disability (ID). Methods Secondary analysis of the 1999 Office for National Statistics survey of the Mental Health of Children and Adolescents in Great Britain was performed. This survey collected information on a multistage, stratified, random sample of 10 438 children between 5 and 15 years of age across 475 postcode sectors in England, Scotland and Wales. Results The prevalence of any diagnosed ICD-10 disorder, conduct disorder, anxiety disorder, hyperkinesis and pervasive developmental disorders were significantly greater among children with ID than among their non-ID peers. There were no statistically significant differences between children with and without ID with regard to the prevalence of depressive disorders, eating disorders or psychosis. Factors associated with an increased risk of psychopathology among children and adolescents with ID included age, gender, social deprivation, family composition, number of potentially stressful life events, the mental health of the child's primary carer, family functioning and child management practices. Conclusions Children and adolescents with ID are at significantly increased risk of certain forms of psychiatric disorder. Careful consideration of the social and economic adversity facing such families will be necessary to ensure that support services are responsive to both the needs of child as well as the needs of the family in which they are living.

Entrepreneurial Learning and Critical Reflection Discontinuous Events as Triggers for ‘Higher-level’ Learning

Abstract: The importance of ‘learning events’ has become an emergent theme within theorizing on how entrepreneurs learn. This article builds a deeper understanding of the learning outcomes triggered by signi...

Bioavailability of hydrophobic organic contaminants in soils: fundamental concepts and techniques for analysis

Abstract: Soils represent a major sink for organic xenobiotic contaminants in the environment. The degree to which organic chemicals are retained within the soil is controlled by soil properties, such as organic matter, and the physico-chemical properties of the contaminant. Chemicals which display hydrophobic and lipophilic characteristics, as well as a recalcitrant chemical structure, will be retained within the soil, and depending on the `strength' of the association may persist for long periods of time. This review describes the behaviour of hydrophobic organic contaminants in soils, focusing on the mechanisms controlling interactions between soil and contaminants. The bioavailability of contaminants in soil is also discussed, particularly in relation to contact time with the soil. It considers the degradation of organic contaminants in soil and the mechanisms microbes use to access contaminants. Finally, the review discusses the `pros' and `cons' of chemical and biological techniques available for assessing bioavailability of hydrophobic organic chemicals in soils, highlighting the need to quantify bioavailability by chemical techniques. It concludes by highlighting the need for understanding the interactions between the soil, contaminants and biota which is crucial to understanding the bioavailability of contaminants in soils.

α-synuclein implicated in Parkinson's disease is present in extracellular biological fluids, including human plasma

Abstract: Parkinson's disease (PD) and other related disorders are characterized by the accumulation of fibrillar aggregates of alpha-synuclein protein (alpha-syn) inside brain cells. It is likely that the formation of alpha-syn aggregates plays a seminal role in the pathogenesis of at least some of these diseases, because two different mutations in the gene encoding alpha-syn have been found in inherited forms of PD. alpha-Syn is mainly expressed by neuronal cells and is generally considered to exist as a cytoplasmic protein. Here, we report the unexpected identification of alpha-syn in conditioned culture media from untransfected and alpha-syn-transfected human neuroblastoma cells, as well as in human cerebrospinal fluid and blood plasma. The method used was immunocapture by using anti-alpha-syn antibodies coupled to magnetic beads, followed by detection on Western blots. In all cases, alpha-syn was identified as a single 15 kDa band, which co-migrated with a recombinant form of the protein and reacted with five different antibodies to alpha-syn. Our findings suggest that cells normally secrete alpha-syn into their surrounding media, both in vitro and in vivo. The detection of extracellular alpha-syn and/or its modified forms in body fluids, particularly in human plasma, offers new opportunities for the development of diagnostic tests for PD and related diseases.

Global distribution and budget of PCBs and HCB in background surface soils: implications for sources and environmental processes.

Abstract: This paper presents data from a survey of polychlorinated biphenyls (PCBs) and hexachlorobenzene (HCB) concentrations in 191 global background surface (0−5 cm) soils. Differences of up to 4 orders of magnitude were found between sites for PCBs. The lowest and highest PCB concentrations (26 and 97 000 pg/g dw) were found in samples from Greenland and mainland Europe (France, Germany, Poland), respectively. Background soil PCB concentrations were strongly influenced by proximity to source region and soil organic matter (SOM) content. Most (>80%) of the estimated soil PCB burden remains in the “global source region” of the Northern Hemisphere (NH) temperate latitudes (30−60° N) or in the OM-rich soils just north of that. %SOM correlated with PCB and HCB in the global data set, with the correlation coefficients being greater for HCB and the lighter PCBs than for heavier homologues. OM-rich soils in the NH consistently contained the highest burdens; such soils are a key global compartment for these compounds. ...

Social networks, travel and talk.

Abstract: This paper considers the role that physical, corporeal travel plays in social life. There is a large and increasing scale of such travel. This increase has occurred simultaneously with the proliferation of communication devices that in some ways substitute for physical travel. I hypothesize that the bases of such travel are new ways in which social life is 'networked'. Such increasingly extensive networks, hugely extended through the informational revolution, depend for their functioning upon intermittent occasioned meetings. These moments of physical co-presence and face-to-face conversation, are crucial to patterns of social life that occur 'at-a-distance', whether for business, leisure, family life, politics, pleasure or friendship. So life is networked but it also involves specific co-present encounters within specific times and places. 'Meetingness', and thus different forms and modes of travel, are central to much social life, a life involving strange combinations of increasing distance and intermittent co-presence. The paper seeks to examine the place of travel within the emergent pattern of a 'networked sociality'. It seeks to contribute to the emerging 'mobility turn' within the social sciences.

Power line communications: state of the art and future trends

Abstract: This article constitutes an overview of the research, application, and regulatory activities on power line communications. Transmission issues on the power line are investigated and modeling approaches illustrated. Contemporary communication techniques and reliability issues are treated. A description of regulatory activities worldwide is given. Finally, market perspectives and promising applications are covered to assess the viability of this communications environment.

Mothers of children and adolescents with intellectual disability: social and economic situation, mental health status, and the self-assessed social and psychological impact of the child's difficulties.

Abstract: Few large-scale studies with well-constructed samples have compared the socio-economic circumstances and social impact of raising a child with intellectual disability (ID). The aims of the present paper were to: (1) compare the socio-economic situation of mothers raising a child with ID to that of mothers of non-ID children; (2) assess the contribution of raising a child with ID to negative psychological outcomes for mothers; and (3) identify variables associated with negative psychological outcomes among mothers of children with ID. Methods The 1999 Office for National Statistics survey, Mental Health of Children and Adolescents in Great Britain, 1999, collected information on a multistage stratified random sample of 10 438 children between 5 and 15 years of age across 475 postal code sectors in England, Scotland and Wales. Secondary analysis was undertaken of the social and economic circumstances, and stress reported by 245 mothers of sampled children with ID and a comparison group of 9 481 mothers of sampled children who did not have ID. Results The results indicate that: (1) families supporting a child with ID were significantly economically disadvantaged when compared with families supporting a child who did not have ID; (2) when compared with mothers of sampled children who did not have ID, mothers of sampled children with ID reported that their child's difficulties resulted in greater social and psychological impact; (3) having a child with ID marginally reduced the odds of mothers screening positive for having mental health problems (once all other variables were taken into account); and (4) among mothers of children with ID, mental health problems were associated with the child's difficulties having a greater social impact, having a boy, the child experiencing more than one potentially stressful life event, poverty, receipt of means-tested welfare benefits and 'unhealthy' family functioning. Conclusions These results highlight the importance of combating poverty among children with ID and their families, and the need to develop more complex models of understanding and intervention.

Modularisation and composition of aspectual requirements

Abstract: An effective requirements engineering (RE) approach must harmonise the need to achieve separation of concerns with the need to satisfy broadly scoped requirements and constraints. Techniques such as use cases and viewpoints help achieve separation of stakeholders' concerns but ensuring their consistency with global requirements and constraints is largely unsupported. In this paper we propose an approach to modularise and compose such crosscutting, aspectual requirements. The approach is based on separating the specification of aspectual requirements, non-aspectual requirements and composition rules in modules representing coherent abstractions and following welldefined templates. The composition rules employ informal, and often concern-specific, actions and operators to specify how an aspectual requirement influences or constrains the behaviour of a set of non-aspectual requirements. We argue that such modularisation makes it possible to establish early trade-offs between aspectual requirements hence providing support for negotiation and subsequent decision-making among stakeholders. At the same time early separation of crosscutting requirements facilitates determination of their mapping and influence on artefacts at later development stages. A realisation of the proposed approach, based on viewpoints and the eXtensible Markup Language (XML), supported by a tool called ARCaDe and a case study of a toll collection system is presented.

Characterization of heterogeneous near-surface materials by joint 2D inversion of dc resistivity and seismic data

Abstract: [1] We have developed a robust 2D joint inversion scheme incorporating the new concept of cross-gradients of electrical resistivity and seismic velocity as constraints so as to investigate more precisely the resistivity-velocity relationships in complex near-surface environments. The results of joint inversion of dc resistivity and seismic traveltime data from collocated experiments suggest that one can distinguish between different types or facies of unconsolidated and consolidated materials, refining a previously proposed resistivity-velocity interrelationship derived from separate inversions of the respective data sets. A consistent interpretive structural model can be obtained from the joint inversion models.

Fathers’ influences on children’s development: The evidence from two-parent families

Abstract: Although it is often assumed that men have an important influence on their children’s development, the supportive evidence can be difficult to locate and summarize. In this paper, we analyse the evidence with respect to four emergent themes. First, men often appear to interact with their children less sensitively than mothers do, and many children thus appear to form closer attachments to their mothers than to their fathers. Second, the data also indicate that fathers may play specific and important roles, with men in some cultures having clearly defined roles as playmates to their children. Third, paternal play styles predict later socio-emotional development while paternal involvement seems to predict adult adjustment better than maternal involvement does. Such evidence suggests, fourth, that we need appropriate measures of fatherhood that are not simply borrowed from the study of motherhood.

Ecological roles of solar UV radiation: towards an integrated approach

Abstract: Research into the effects of ultraviolet (UV) radiation on terrestrial ecosystems remains a relatively new discipline that is currently split into two broad themes: the effects of increased UV-B radiation resulting from ozone depletion, and the role of UV radiation (largely UV-A) in the vision of many animals. Increases in UV-B radiation can damage many organisms, but the effects of solar UV on many ecological processes also depend on the use of UV-B and UV-A by microbes, plants and animals as a source of information about their environment. With few exceptions, the interface between UV vision and broader UV effects, such as altered plant chemistry and pigmentation, which can influence plant–animal interactions, remain unexplored. By considering the diversity of the effects of solar UV radiation on terrestrial ecosystems, we identify areas of common interest at the interface of the two areas of existing UV research.

Seasick on the Third Wave? Subverting the Hegemony of Propositionalism: Response to Collins & Evans (2002)

Abstract: Harry Collins and Rob Evans (Collins & Evans, 2002) offer a typically forthright normative vision for the 'Third Wave' of science studies, after what they call the earlier waves of post-war rationalism, then the postKuhnian 'cultural revolution' from the 1970s. They propose to redefine the accepted qualifications for expert standing in the countless areas of decision-making in which scientific knowledge has held presumptive sway as exclusive (but relentlessly disputed and increasingly eroded) public authority. Collins & Evans (2002) start from the problem of public legitimacy that has been widely recognized to beset science in recent times (House of Lords, 2000; European Union, 2000). They argue that 'the problem of legitimacy' for science has been mistakenly replaced by 'the problem of extension', in which real distinctions between experts and publics are dissolved and 'technical decision-making rights' (as they call them) are thus extended indiscriminately. Their aim of redefining competences for 'technical decision-making' in the public sphere, so as to include practical experience-based expertise alongside 'certified science', would be more inclusive compared with existing boundaries, but more exclusive compared with the apparent assumptions (of infinite 'extension') of the participation in science 'movements'. They use the case studies of Cumbrian sheep farmers (Wynne, 1992) and HIV-AIDS activists (Epstein, 1996) to illustrate this argument. Significantly, and as issues I take up later, for them the public sphere involves an accumulation of completely unrelated 'decisions' about what they define as exclusively 'propositional' decision-questions, such as whether nuclear power, anti-misting kerosene or UK beef is safe,

Exploratory practice: rethinking practitioner research in language teaching

Abstract: This paper is an introduction to the rest of this Special Issue of Language Teaching Research devoted entirely to Exploratory Practice (EP), a form of practitioner research. It is also an introduction to EP itself, telling the story of the development of its practices and its principles over the last ten or so years. Readers already familiar with EP may wish to go directly to the other seven papers in this issue, for illustrations of EP in practice, for research about EP, and for a more thorough review of the relevant research literature (see especially the papers by Miller and by Perpignan). The case for EP presented below is based on a perceived need for practitioner research to be rethought: to be refocused on understanding, and ultimately on a concern for the quality of life in the language classroom, for both teachers and learners. The paper includes, in Section VII, a brief introduction to the other papers in this volume.

Repeated fracture and healing of silicic magma generate flow banding and earthquakes

Abstract: Textures in an exceptionally preserved effusive rhyolite conduit at Torfajokull, Iceland, indicate that rising magma repeatedly fractured and healed at shallow levels in the conduit (RFH process). Anastomosing tuffisite veins filled by fine-grained juvenile clasts were generated by shear fracture of highly viscous magma in the glass transition interval. Welding of the particulate material during subsequent deformation led to thorough healing of veins, allowing repeated fracture of the same body of magma. We propose that the RFH process is a rechargeable trigger mechanism for hybrid seismicity and show that the time scale of the process and the fractures formed by it are consistent with the repeat time and magnitude of hybrid earthquakes during silicic eruptions. The RFH process may also form the flow banding that is nearly ubiquitous in obsidian.

PAHs, PCBs, PCNs, organochlorine pesticides, synthetic musks, and polychlorinated n-alkanes in U.K. sewage sludge: survey results and implications.

Abstract: A survey of the digested sludge from 14 U.K. wastewater treatment plants was carried out to obtain contemporary U.K. data on the concentrations of certain classes of persistent organic compounds for which data are scarce and to assess whether U.K. sludge was likely to comply with the sludge limits for PCBs and PAHs proposed by the European Union. Total PAH (24 compounds) concentrations ranged from 67 to 370 mg/kg dw, in line with data from other countries; all the samples would exceed the proposed EU limit. Total PCB concentrations were 110−440 μg/kg dw, well below the proposed EU limit. Total PCN concentrations ranged from 50 to 190 μg/kg. Total synthetic musk concentrations ranged from 2.1 to 86 mg/kg dw; there were a few very high concentrations of HHCB and AHTN in the samples. Total concentrations of the short- and medium-chained polychlorinated alkanes ranged between 7 and 200 mg/kg and between 30 and 9700 mg/kg, respectively. These very high concentrations are indicative of chemicals with numerous a...

Mobile Transformations of 'Public' and 'Private' Life.

Abstract: Most conceptions of public and private life within political and social theory do not adequately consider the networks or fluidities involved in contemporary social relations. The distinction of public and private is often conceived of as statically `regional' in character. This article, following an extensive analysis of the multiple meanings of the `public' and `private', criticizes such a static conception and maintains that massive changes are occurring in the nature of both public and private life and especially of the relations between them. We consider flows and networks that enable mobility between and across apparent publics and privates. These mobilities are both physical (in the form of mobile people, objects and hybrids of humans-in-machines) and informational (in the form of electronic communication via data, visual images and texts). We consider the transformations of public and private life that have arisen from `complex' configurations of place and space: the dominant system of car-centred automobility whose spatial fluidities are simultaneously private and public; and various globalizations through the exposure of `private' lives on public screens and the public screening of mediatized events. These mobile, machinic examples demonstrate the limitations of the static, regional conceptualizations of public and private life developed within much social and political theory, and suggest that this divide may need relegation to the dustbin of history.

Soil microbes compete effectively with plants for organic‐nitrogen inputs to temperate grasslands

Abstract: Although agricultural grassland soils have inherently high rates of net nitrogen (N) mineralization, they often have soil concentrations of soluble organic N that are comparable to inorganic N. We set out to examine in situ the significance of organic N for plant nutrition in grasslands of differing management intensity and soil fertility. Using in situ dual-labeling techniques (glycine-2-13C-15N) we measured preferential uptake of amino-acid N vs. inorganic N [(15NH4)2SO4] in early and late season in low-productivity Agrostis capillaris–Festuca ovina grassland and in agriculturally improved, high-productivity Lolium perenne-dominated grassland. The dominant soluble-N form differed greatly between grasslands. Inorganic N (especially nitrate N) dominated the soluble N pool of the highly productive improved grassland whereas amino acid N was the dominant soluble N form in the low-productivity unimproved grassland. There was no difference in the amount of 15N taken up by plants from the two N forms in either grassland. However, our data indicate that amino-acid N was taken up directly by plants of both grasslands and that more N was captured in this way by plants of low-productivity grassland where amino acids were the dominant soluble N form in soil. Our data from both grasslands also indicate significant microbial competition for added 15N from both N sources, but especially in the low-productivity grassland where the bulk of 15N added was sequestered by the microbial biomass. A significantly greater amount of added 15N was captured by the microbial biomass in the unimproved than in the improved grassland, and substantially more 15N was detected in the microbial biomass than in plant tissue in the unimproved grassland. On the basis of our findings, we predict that subsequent microbial turnover and release of this N into the plant–soil system is the major pathway for plant N capture in these temperate grasslands. Microbial sequestration of added N might be an important mechanism of N retention in these grasslands, especially in the low-productivity systems where microbial N sink strength is greater and organic matter slowly accumulates.

Practice Developments in Budgeting: An Overview and Research Perspective

Abstract: Practitioners in Europe and the U.S. recently have proposed two distinct approaches to address what they believe are shortcomings of traditional budgeting practices. One approach advocates improving the budgeting process and primarily focuses on the planning problems with budgeting. The other advocates abandoning the budget and primarily focuses on the performance evaluation problems with budgeting. This paper provides an overview and research perspective on these two recent developments. We discuss why practitioners have become dissatisfied with budgets, describe the two distinct approaches, place them in a research context, suggest insights that may aid the practitioners, and use the practitioner perspectives to identify fruitful areas for research.

Efficient construction of reversible jump Markov chain Monte Carlo proposal distributions

Abstract: The major implementational problem for reversible jump Markov chain Monte Carlo methods is that there is commonly no natural way to choose jump proposals since there is no Euclidean structure in the parameter space to guide our choice We consider mechanisms for guiding the choice of proposal The first group of methods is based on an analysis of acceptance probabilities for jumps Essentially, these methods involve a Taylor series expansion of the acceptance probability around certain canonical jumps and turn out to have close connections to Langevin algorithms The second group of methods generalizes the reversible jump algorithm by using the so-called saturated space approach These allow the chain to retain some degree of memory so that, when proposing to move from a smaller to a larger model, information is borrowed from the last time that the reverse move was performed The main motivation for this paper is that, in complex problems, the probability that the Markov chain moves between such spaces may be prohibitively small, as the probability mass can be very thinly spread across the space Therefore, finding reasonable jump proposals becomes extremely important We illustrate the procedure by using several examples of reversible jump Markov chain Monte Carlo applications including the analysis of autoregressive time series, graphical Gaussian modelling and mixture modelling

A dependence measure for multivariate and spatial extreme values: Properties and inference

Abstract: We present properties of a dependence measure that arises in the study of extreme values in multivariate and spatial problems. For multivariate problems the dependence measure characterises dependence at the bivariate level, for all pairs and all higher orders up to and including the dimension of the variable. Necessary and sufficient conditions are given for subsets of dependence measures to be self‐consistent, that is to guarantee the existence of a distribution with such a subset of values for the dependence measure. For pairwise dependence, these conditions are given in terms of positive semidefinite matrices and non‐differentiable, positive definite functions. We construct new nonparametric estimators for the dependence measure which, unlike all naive nonparametric estimators, impose these self‐consistency properties. As the new estimators provide an improvement on the naive methods, both in terms of the inferential and interpretability properties, their use in exploratory extreme value analyses should aid the identification of appropriate dependence models. The methods are illustrated through an analysis of simulated multivariate data, which shows that a lack of self‐consistency is frequently a problem with the existing estimators, and by a spatial analysis of daily rainfall extremes in south‐west England, which finds a smooth decay in extremal dependence with distance.

Transcriptome analysis of root transporters reveals participation of multiple gene families in the response to cation stress

Abstract: Plant nutrition critically depends on the activity of membrane transporters that translocate minerals from the soil into the plant and are responsible for their intra- and intercellular distribution. Most plant membrane transporters are encoded by multigene families whose members often exhibit overlapping expression patterns and a high degree of sequence homology. Furthermore, many inorganic nutrients are transported by more than one transporter family. These considerations, coupled with a large number of so-far non-annotated putative transporter genes, hamper our progress in understanding how the activity of specific transporters is integrated into a response to fluctuating conditions. We designed an oligonucleotide microarray representing 1096 Arabidopsis transporter genes and analysed the root transporter transcriptome over a 96-h period with respect to 80 mm NaCl, K+ starvation and Ca2+ starvation. Our data show that cation stress led to changes in transcript level of many genes across most transporter gene families. Analysis of transcriptionally modulated genes across all functional groups of transporters revealed families such as V-type ATPases and aquaporins that responded to all treatments, and families – which included putative non-selective cation channels for the NaCl treatment and metal transporters for Ca2+ starvation conditions – that responded to specific ionic environments. Several gene families including primary pumps, antiporters and aquaporins were analysed in detail with respect to the mRNA levels of different isoforms during ion stress. Cluster analysis allowed identification of distinct expression profiles, and several novel putative regulatory motifs were discovered within sets of co-expressed genes.