Showing papers by "University of Sussex published in 1998"

Bacillus thuringiensis and Its Pesticidal Crystal Proteins

Abstract: During the past decade the pesticidal bacterium Bacillus thuringiensis has been the subject of intensive research. These efforts have yielded considerable data about the complex relationships between the structure, mechanism of action, and genetics of the organism’s pesticidal crystal proteins, and a coherent picture of these relationships is beginning to emerge. Other studies have focused on the ecological role of the B. thuringiensis crystal proteins, their performance in agricultural and other natural settings, and the evolution of resistance mechanisms in target pests. Armed with this knowledge base and with the tools of modern biotechnology, researchers are now reporting promising results in engineering more-useful toxins and formulations, in creating transgenic plants that express pesticidal activity, and in constructing integrated management strategies to insure that these products are utilized with maximum efficiency and benefit.

Exponential potentials and cosmological scaling solutions

Abstract: We present a phase-plane analysis of cosmologies containing a baryotropic fluid with an equation of state ${p}_{\ensuremath{\gamma}}=(\ensuremath{\gamma}\ensuremath{-}1){\ensuremath{\rho}}_{\ensuremath{\gamma}},$ plus a scalar field $\ensuremath{\varphi}$ with an exponential potential $V\ensuremath{\propto}\mathrm{exp}(\ensuremath{-}\ensuremath{\lambda}\ensuremath{\kappa}\ensuremath{\varphi})$ where ${\ensuremath{\kappa}}^{2}=8\ensuremath{\pi}G$. In addition to the well-known inflationary solutions for ${\ensuremath{\lambda}}^{2}l2$, there exist scaling solutions when ${\ensuremath{\lambda}}^{2}g3\ensuremath{\gamma}$ in which the scalar field energy density tracks that of the baryotropic fluid (which for example might be radiation or dust). We show that the scaling solutions are the unique late-time attractors whenever they exist. The fluid-dominated solutions, where $V(\ensuremath{\varphi})/{\ensuremath{\rho}}_{\ensuremath{\gamma}}\ensuremath{\rightarrow}0$ at late times, are always unstable (except for the cosmological constant case $\ensuremath{\gamma}=0)$. The relative energy density of the fluid and scalar field depends on the steepness of the exponential potential, which is constrained by nucleosynthesis to ${\ensuremath{\lambda}}^{2}g20$. We show that standard inflation models are unable to solve this ``relic density'' problem.

Revision of the Nomenclature for the Bacillus thuringiensis Pesticidal Crystal Proteins

Abstract: The crystal proteins of Bacillus thuringiensis have been extensively studied because of their pesticidal properties and their high natural levels of production. The increasingly rapid characterization of new crystal protein genes, triggered by an effort to discover proteins with new pesticidal properties, has resulted in a variety of sequences and activities that no longer fit the original nomenclature system proposed in 1989. Bacillus thuringiensis pesticidal crystal protein (Cry and Cyt) nomenclature was initially based on insecticidal activity for the primary ranking criterion. Many exceptions to this systematic arrangement have become apparent, however, making the nomenclature system inconsistent. Additionally, the original nomenclature, with four activity-based primary ranks for 13 genes, did not anticipate the current 73 holotype sequences that form many more than the original four subgroups. A new nomenclature, based on hierarchical clustering using amino acid sequence identity, is proposed. Roman numerals have been exchanged for Arabic numerals in the primary rank (e.g., Cry1Aa) to better accommodate the large number of expected new sequences. In this proposal, 133 crystal proteins comprising 24 primary ranks are systematically arranged.

Receptor noise as a determinant of colour thresholds.

Abstract: Inferences about mechanisms at one particular stage of a visual pathway may be made from psychophysical thresholds only if the noise at the stage in question dominates that in the others. Spectral sensitivities, measured under bright conditions, for di-, tri-, and tetrachromatic eyes from a range of animals can be modelled by assuming that thresholds are set by colour opponency mechanisms whose performance is limited by photoreceptor noise, the achromatic signal being disregarded. Noise in the opponency channels themselves is therefore not statistically independent, and it is not possible to infer anything more about the channels from psychophysical thresholds. As well as giving insight into mechanisms of vision, the model predicts the performance of colour vision in animals where physiological and anatomical data on the eye are available, but there are no direct measurements of perceptual thresholds. The model, therefore, is widely applicable to comparative studies of eye design and visual ecology.

The metabolic cost of neural information

Abstract: We derive experimentally based estimates of the energy used by neural mechanisms to code known quantities of information. Biophysical measurements from cells in the blowfly retina yield estimates of the ATP required to generate graded (analog) electrical signals that transmit known amounts of information. Energy consumption is several orders of magnitude greater than the thermodynamic minimum. It costs 10(4) ATP molecules to transmit a bit at a chemical synapse, and 10(6)-10(7) ATP for graded signals in an interneuron or a photoreceptor, or for spike coding. Therefore, in noise-limited signaling systems, a weak pathway of low capacity transmits information more economically, which promotes the distribution of information among multiple pathways.

Tetrachromacy, oil droplets and bird plumage colours

Abstract: There is a growing body of data on avian eyes, including measurements of visual pigment and oil droplet spectral absorption, and of receptor densities and their distributions across the retina. These data are sufficient to predict psychophysical colour discrimination thresholds for light-adapted eyes, and hence provide a basis for relating eye design to visual needs. We examine the advantages of coloured oil droplets, UV vision and tetrachromacy for discriminating a diverse set of avian plumage spectra under natural illumination. Discriminability is enhanced both by tetrachromacy and coloured oil droplets. Oil droplets may also improve colour constancy. Comparison of the performance of a pigeon's eye, where the shortest wavelength receptor peak is at 410 nm, with that of the passerine Leiothrix, where the ultraviolet-sensitive peak is at 365 nm, generally shows a small advantage to the latter, but this advantage depends critically on the noise level in the sensitivity mechanism and on the set of spectra being viewed.

A touchstone of dissent: Euroscepticism in contemporary Western European party systems

Abstract: With the recent acceleration of the integration process of the European Union there has been a rise in political parties expressing either scepticism or outright criticism of the nature of the integration process. Using a four-fold differentiation between single issue, protest, established parties and factions within parties, the first part of the article presents an overview of Euroscepticism within EU member states and Norway. This reveals the diversity of sources of Euroscepticism both in ideology and in the types of parties that are Eurosceptical but with a preponderance of protest parties taking Eurosceptical positions. The second part of the article is an attempt to map Euroscepticism in West European party systems through a consideration of ideology and party position in the party system. The conclusions are that Euroscepticism is mainly limited to parties on the periphery of their party system and is often there used as an issue that differentiates those parties from the more established parties which are only likely to express Euroscepticism through factions. Party based Euroscepticism is therefore both largely dependent on domestic contextual factors and a useful issue to map emergent domestic political constellations.

A Classification of scalar field potentials with cosmological scaling solutions

Abstract: An attractive method of obtaining an effective cosmological constant at the present epoch is through the potential energy of a scalar field. Considering models with a perfect fluid and a scalar field, we classify all potentials for which the scalar field energy density scales as a power law of the scale factor when the perfect fluid density dominates. There are three possibilities. The first two are well known; the much-investigated exponential potentials have the scalar field mimicking the evolution of the perfect fluid, while for negative power laws, introduced by Ratra and Peebles, the scalar field density grows relative to that of the fluid. The third possibility is a new one, where the potential is a positive power law and the scalar field energy density decays relative to the perfect fluid. We provide a complete analysis of exact solutions and their stability properties, and investigate a range of possible cosmological applications.

Evolution of Structure in Cold Dark Matter Universes

Abstract: We present an analysis of the clustering evolution of dark matter in four cold dark matter (CDM) cosmologies. We use a suite of high-resolution, 17 million particle, N-body simulations that sample volumes large enough to give clustering statistics with unprecedented accuracy. We investigate a flat model with Ω0 = 0.3, an open model also with Ω0 = 0.3, and two models with Ω = 1, one with the standard CDM power spectrum and the other with the same power spectrum as the Ω0 = 0.3 models. In all cases, the amplitude of primordial fluctuations is set so that the models reproduce the observed abundance of rich galaxy clusters by the present day. We compute mass two-point correlation functions and power spectra over 3 orders of magnitude in spatial scale and find that in all of our simulations they differ significantly from those of the observed galaxy distribution, in both shape and amplitude. Thus, for any of these models to provide an acceptable representation of reality, the distribution of galaxies must be biased relative to the mass in a nontrivial, scale-dependent fashion. In the Ω = 1 models, the required bias is always greater than unity, but in the Ω0 = 0.3 models, an "antibias" is required on scales smaller than ~5 h-1 Mpc. The mass correlation functions in the simulations are well fit by recently published analytic models. The velocity fields are remarkably similar in all the models, whether they are characterized as bulk flows, single-particle, or pairwise velocity dispersions. This similarity is a direct consequence of our adopted normalization and runs contrary to the common belief that the amplitude of the observed galaxy velocity fields can be used to constrain the value of Ω0. The small-scale pairwise velocity dispersion of the dark matter is somewhat larger than recent determinations from galaxy redshift surveys, but the bulk flows predicted by our models are broadly in agreement with most available data.

A sequence of object-processing stages revealed by fMRI in the human occipital lobe.

Abstract: r r Abstract: Functional magnetic resonance imaging was used in combined functional selectivity and retinotopic mapping tests to reveal object-related visual areas in the human occpital lobe. Subjects were tested with right, left, up, or down hemivisual field stimuli which were composed of images of natural objects (faces, animals, man-made objects) or highly scrambled (1,024 elements) versions of the same images. In a similar fashion, the horizontal and vertical meridians were mapped to define the borders of these areas. Concurrently, the same cortical sites were tested for their sensitivity to image-scrambling by varying the number of scrambled picture fragments (from 16-1,024) while controlling for the Fourier power spectrum of the pictures and their order of presentation. Our results reveal a stagewise decrease in

Molecular biology of salt tolerance in the context of whole-plant physiology

Abstract: The halobacteria are the only organisms that are tolerant of salinity at the molecular level. All other bacteria, all fungi, all plants, and all animals avoid the need for salt tolerance for most of their macromolecules by maintaining defined and conserved conditions in the cytoplasm. These conditions favour potassium over sodium, the limitation of total inorganic ion activity, and the supplementation of this where necessary with organic solutes which are metabolically neutral osmolytes that may also be osmoprotectant. The salt tolerance of an organism depends upon the range of external salinity over which it is able to sustain these conditions in the cytoplasm. There is substantial and increasing knowledge of the molecular biology and molecular genetics of the processes of ion and organic solute transport, solute synthesis, and compart-mentation that underpin cell-based tolerance. Much of recent research focuses on the identification of genes and gene products that affect cell-based tolerance, commonly derived from single-cell models. There is commonly the implicit or explicit assumption that incorporation of these genes will benefit the salt tolerance of food crop species. While this essential experimental approach is giving enormous insight there should not be rash or premature expectations. The unique and overriding consideration for the salinity tolerance of terrestrial plants is the net flux of water due to transpiration and so resides at a higher level of organization. Processes that are advantageous to a single cell in an aqueous medium may be lethal to a cell in a leaf in the air. The likely impact of single structural-gene changes in ion and solute transport upon co-ordinated plant response is probably overestimated, and recent views consider regulatory processes and multiple gene transfers. While the technical ability for plant transformation increases daily, the practicality of using transgenic plants in complex breeding programmes seems rarely to be given enough thought. If intervention at the molecular level is to lead to salt-tolerant crop plants then it will be essential to view this in the contexts of whole plants and of plant breeding. Recent indications that a relatively small number of quantitative trait loci (QTL) may govern complex physiological characters offer the most hope for the future.

Technologies, Products and Organization in the Innovating Firm: What Adam Smith Tells Us and Joseph Schumpeter Doesn't

Abstract: Adam Smith's insights into the increasingly specialized nature of knowledge production are crucially important in understanding the contemporary problems of managing innovating firms. Products and firms are based on an increasing range of fields of specialized technological understanding. Competition is not based on technological diversity, but on diversity and experimentation in products, etc. Firms rarely fail because of an inability to master a new field of technology, but because they do not succeed in matching the firm's systems of coordination and control to the nature of the available technological opportunities. Copyright 1998 by Oxford University Press.

Democracy and Decentralisation in South Asia and West Africa: Participation, Accountability and Performance

Abstract: This book is an in-depth empirical study of four Asian and African attempts to create democratic, decentralised local governments in the late 1980s and 1990s The case studies of Ghana, Cote d'Ivoire, Karnataka (India) and Bangladesh focus upon the enhancement of participation; accountability between people, politicians and bureaucrats; and, most importantly, on whether governmental performance actually improved in comparison with previous forms of administration The book is systematically comparative, and based upon extensive popular surveys and local field work It makes an important contribution to current debates in the development literature on whether 'good governance' and decentralisation can provide more responsive and effective services for the mass of the population - the poor and disadvantaged who live in the rural areas

P3M‐SPH simulations of the Lyα forest

Abstract: We investigate the importance of several numerical artefacts such as lack of resolution on spectral properties of the Lyα forest as computed from cosmological hydrodynamic simulations in a standard cold dark matter universe. We use a new simulation code which is based on a combination of a hierarchical particle–particle–particle–mesh (P3M) scheme for gravity and smoothed particle hydrodynamics (SPH) for gas dynamics. We have performed extensive comparisons between this new code and a modified version of the HYDRA code of Couchman et al. and find excellent agreement. We have also rerun the TREESPH simulations of Hernquist et al. using our new codes and find very good agreement with their published results. This shows that results from hydrodynamical simulations that include cooling are reproducible with different numerical algorithms. We then use our new code to investigate several numerical effects, such as resolution, on spectral statistics deduced from Voigt profile fitting of lines by running simulations with gas particle masses of 1.4 × 108, 1.8 × 107, 2.2 × 106 and 2.1 × 105 M⊙. When we increase the numerical resolution the mean effective hydrogen optical depth converges and so does the column density distribution. However, higher resolution simulations produce narrower lines and consequently the b parameter (velocity width) distribution has only marginally converged in our highest resolution run. Obtaining numerical convergence for the mean He II transmission is demanding. When progressively smaller haloes are resolved at better resolution, a larger fraction of low-density gas contracts to moderate overdensities in which He ii is already optically thick, and this increases the net transmission, making it difficult to simulate He ii reliably. Our highest resolution simulation gives a mean effective optical depth in He ii 5 per cent lower than the simulation with eight times lower mass resolution, illustrating the degree to which the He ii optical depth has converged. In contrast, the hydrogen mean optical depth for these runs is identical. As many properties of the simulated Lyα forest depend on resolution, one should be careful when deducing physical parameters from a comparison of the simulated forest with the observed one. We compare predictions from our highest resolution simulation in a cold dark matter universe, with a photoionizing background inferred from quasars as computed by Haardt &38; Madau, with observations. The simulation reproduces both the H I column density and b parameter distribution when we assume a high baryon density, ΩB h2 ≳ 0.028. In addition we need to impose a higher intergalactic medium (IGM) temperature than predicted within our basic set of assumptions. We argue that such a higher temperature could be caused by differences between the assumed and true reionization history. The simulated H I optical depth is in good agreement with observations, but the He ii optical depth is lower than observed. Fitting the He ii optical depth requires a larger jump, ∼ 14, between the photon flux at the H I and He ii edge than is present in the Haardt &38; Madau spectrum.

Expression of a potassium current in inner hair cells during development of hearing in mice

Abstract: Excitable cells use ion channels to tailor their biophysical properties to the functional demands made upon them1. During development, these demands may alter considerably, often associated with a change in the cells' complement of ion channels2-4. Here we present evidence for such a change in inner hair cells, the primary sensory receptors in the mammalian cochlea. In mice, responses to sound can first be recorded from the auditory nerve and observed behaviourally from 10-12 days after birth; these responses mature rapidly over the next 4 days5-8. Before this time, mouse inner hair cells have slow voltage responses and fire spontaneous and evoked action potentials. During development of auditory responsiveness a large, fast potassium conductance is expressed, greatly speeding up the membrane time constant and preventing action potentials. This change in potassium channel expression turns the inner hair cell from a regenerative, spiking pacemaker into a high-frequency signal transducer

Older (but not younger) siblings facilitate false belief understanding.

Abstract: Results from 4 experiments and an analysis in which all data from 444 English and Japanese children are pooled show (a) a linear increase in understanding false belief with the number of older siblings, (b) no such effect for children younger than 3 years 2 months, (c) no helpful effect of younger siblings at any age (despite the large sample), (d) no effect of siblings' gender, and (e) no helpful effect of siblings on a task measuring children's understanding of how they know something. Discussion involves speculation about how older siblings may assist children (e.g., through pretend play and mental state language) and how different aspects of a theory of mind may develop through different means.

DNA breakage and repair.

Abstract: For many years it has been evident that mammalian cells differ dramatically from yeast and rejoin the majority of their DNA DSBs by a nonhomologous mechanism, recently termed NHEJ. In the last few years a number of genes and proteins have been identified that operate in the pathway providing insights into the mechanism. These proteins include the three components of DNA-PK, DNA ligase IV, and XRCC4. In yeast Sir2, -3, and -4 proteins are also involved in the process and therefore are likely to play a role in higher organisms. Studies with yeast suggest that NHEJ is an error-free mechanism. Although the process is far from understood, it is likely that the DNA-PK complex or Ku alone acts in a complex with the Sir proteins possibly protecting the ends and preventing random rejoining. Further work is required to establish the details of this mechanism and to determine whether this represents an accurate rejoining process for a complex break induced by ionizing radiation. It will be intriguing to discover how the cell achieves efficient and accurate rejoining without the use of homology. Interactions between the components of DNA-PK and other proteins playing a central role in damage response mechanisms are beginning to emerge. Interestingly, there is evidence that DNA repair and damage response mechanisms overlap in lower organisms. The overlapping defects of the yeast Ku mutants, tell mutants, and AT cell lines in telomere maintenance further suggest overlapping functions or interacting mechanisms. A challenge for the future will be to establish how these different damage response mechanisms overlap and interact.

Trust and inter‐firm relations in developing and transition economies

Abstract: The role of trust in facilitating economic growth has been highlighted in previous contributions to this journal. In order to take this debate forward, this article argues (1) that more attention needs to be given to the relationship between sanctions and trust, and (2) that it is worth distinguishing between the minimal trust for making markets effective and the extended trust required for deeper kinds of inter‐firm co‐operation to work. The article goes on to ask why minimal trust is lacking and so hard to construct in the republics of the former Soviet Union. It then examines how extended trust grows or can be made to grow in industrial supply chains and clusters in developing countries.

On the economics and analysis of diversity

Abstract: A review of the literature reveals that the concept of diversity (and especially technological diversity) is of considerable general significance in economics. Diversity is variously argued to be a major factor in the fostering of innovation and growth, an important strategy for hedging against intractable uncertainty and ignorance, the principal means to mitigate the effects of 'lock-in' under increasing returns and a potentially effective response to some fundamental problems of social choice. Recognition of the countervailing costs and wider disadvantages associated with diversification simply compounds the case for the development of a clear, comprehensive and systematic general operational characterisation of diversity in economics. Perhaps surprisingly, then, it is found that existing approaches to the analysis of technological and wider economic diversity tend either to be rather rudimentary or quite circumscribed in character. Drawing on analytical approaches to the concept of diversity undertaken in a range of disciplines (including economics, ecology, palaeontology, archaeology, psychology and chemistry), this article sets out a formal threefold general characterisation of diversity. A variety of quantitative indices are examined and a novel integrated index of 'multi-criteria diversity' is developed and evaluated under this framework. The potential utility of this index is assessed in a more practical (but still hypothetical) exercise which seeks to illustrate how trade-offs might systematically be explored between diversity and wider economic performance in real portfolios of technologies, such as those employed in the electricity supply industry.

Recombinational exchanges at the capsular polysaccharide biosynthetic locus lead to frequent serotype changes among natural isolates of Streptococcus pneumoniae

Abstract: Summary Serotype 19F variants of the major Spanish multiresistant serotype 23F clone of Streptococcus pneumoniae have been proposed to have arisen by recombinational exchanges at the capsular biosynthetic locus. Members of the Spanish multiresistant serotype 23F clone and the serotype 19F variants were confirmed to be essentially identical in overall genotype, as they were indistinguishable by REP-PCR, and had identical sequences at three polymorphic housekeeping genes. Eight serotype 19F variants were studied and all had large recombinational replacements at the capsular biosynthetic locus. In all cases, one of the recombinational cross-over points appeared to be upstream of dexB, which flanks one end of the capsular locus, and in six of the variants the other cross-over point was downstream of aliA, which flanks the other end of the locus. In two strains a recombinational cross-over point between the introduced serotype 19F capsular region and that of the Spanish serotype 23F clone could be clearly identified, within cpsN in one strain and within cpsM in the other. The differences in the recombinational junctions and sequence polymorphisms within the introduced capsular genes, suggested that the eight serotype 19F variants emerged on at least four separate occasions. Changes in capsular type by recombination may therefore be relatively frequent in pneumococci and this has implications for the long-term efficacy of conjugate pneumococcal vaccines that will protect against only a limited number of serotypes.

Concepts of competence

Abstract: An analysis of everyday use of the term ‘competence' is followed by a literature review. Some authors treat competence as a socially situated concept—the ability to perform tasks and roles to the expected standard—leaving its precise meaning to be negotiated by stakeholders in a macro-or micro-political context. Others treat competence as individually situated, a personal capability or characteristic. This latter concept is labelled ‘capability' and its vital relationship with socially-defined Competence is analysed. The importance for practice of representations of competence and for professional preparation of models of capability is discussed.

Mutations in the human |[alpha]|-tectorin gene cause autosomal dominant non-syndromic hearing impairment

Abstract: The tectorial membrane is an extracellular matrix of the inner ear that contacts the stereocilia bundles of specialized sensory hair cells. Sound induces movement of these hair cells relative to the tectorial membrane, deflects the stereocilia, and leads to fluctuations in hair-cell membrane potential, transducing sound into electrical signals. a-tectorin is one of the major non-collagenous components of the tectorial membrane. Recently, the gene encoding mouse a-tectorin (Tecta) was mapped to a region of mouse chromosome 9, which shows evolutionary conservation with human chromosome 11q (ref. 3), where linkage was found in two families, one Belgian (DFNA12; ref. 4) and the other, Austrian (DFNA8; unpublished data), with autosomal dominant non-syndromic hearing impairment. We determined the complete sequence and the intron-exon structure of the human TECTA gene. In both families, mutation analysis revealed missense mutations which replace conserved amino-acid residues within the zona pellucida domain of TECTA. These findings indicate that mutations in TECTA are responsible for hearing impairment in these families, and implicate a new type of protein in the pathogenesis of hearing impairment.

Evolutionary robotics and the radical envelope-of-noise hypothesis

Abstract: For several years now, various researchers have endeavored to apply artificial evolution to the automatic design of control systems for real robots. One of the major challenges they face concerns the question of how to assess the fitness of evolving controllers when each evolutionary run typically involves hundreds of thousands of such assessments. This article outlines new ways of thinking about and building simulations upon which such assessments can be performed. It puts forward sufficient conditions for the successful transfer of evolved controllers from simulation to reality and develops a potential methodology for building simulations in which evolving controllers are forced to satisfy these conditions if they are to be reliably fit. It is hypothesized that as long as simulations are built according to this methodology, it does not matter how inaccurate or incomplete they are: Controllers that have evolved to be reliably fit in simulation still will transfer into reality. Two sets of experiments are...