Showing papers by "University of Sussex published in 1996"

External cognition: how do graphical representations work?

Abstract: Advances in graphical technology have now made it possible for us to interact with information in innovative ways, most notably by exploring multimedia environments and by manipulating three-dimensional virtual worlds. Many benefits have been claimed for this new kind of interactivity, a general assumption being that learning and cognitive processing are facilitated. We point out, however, that little is known about the cognitive value ofanygraphical representations, be they good old-fashioned (e.g. diagrams) or more advanced (e.g. animations, multimedia, virtual reality). In our paper, we critique the disparate literature on graphical representations, focusing on four representative studies. Our analysis reveals a fragmented and poorly understood account of how graphical representations work, exposing a number of assumptions and fallacies. As an alternative we propose a new agenda for graphical representation research. This builds on the nascent theoretical approach within cognitive science that analyses the role played by external representations in relation to internal mental ones. We outline some of the central properties of this relationship that are necessary for the processing of graphical representations. Finally, we consider how this analysis can inform the selection and design of both traditional and advanced forms of graphical technology.

National Culture and the Values of Organizational Employees A Dimensional Analysis Across 43 Nations

Abstract: The values of 8,841 managers and organization employees from 43 countries were surveyed. The range of nations included paralleled many of those surveyed by Hofstede (1980) but added also substantial samples from ex-communist nations. Questionnaire items focused primarily on measures of universalism-particularism, achievement-ascription, and individualism-collectivism. Multidimensional scaling of country means revealed three interpretable dimensions. The relation of these dimensions to the results of earlier large-scale surveys and to a variety of demographic indexes is explored. It is found that there are continuing substantial differences in modal cultural values of organization employees and that these are largely consistent with differences reported by others. The present results suggest that the dimensions defined by Hofstede as individualism-collectivism and power distance may be better defined as representing varying orientations toward continuity of group membership (loyal involvement/ utilitarian ...

Misreading the African Landscape: Society and Ecology in a Forest-Savanna Mosaic

Abstract: Introduction 1. Convictions of forest loss in policy and ecological science 2. Forest gain: historical evidence of vegetation change 3. Settling a landscape: forest islands in regional social and political history 4. Ecology and society in a Kuranko village 5. Ecology and society in a Kissi village 6. Enriching a landscape: working with ecology and deflecting successions 7. Accounting for forest gain: local land use, regional political economy and demography 8. Reading forest history backwards: a century of environmental policy 9. Sustaining reversed histories: the continual production of views of forest loss 10. Towards a new forest-savanna ecology and history.

Initiation of Protein Synthesis in Eukaryotic Cells

Abstract: It is becoming increasingly apparent that translational control plays an important role in the regulation of gene expression in eukaryotic cells. Most of the known physiological effects on translation are exerted at the level of polypeptide chain initiation. Research on initiation of translation over the past five years has yielded much new information, which can be divided into three main areas: (a) structure and function of initiation factors (including identification by sequencing studies of consensus domains and motifs) and investigation of protein-protein and protein-RNA interactions during initiation; (b) physiological regulation of initiation factor activities and (c) identification of features in the 5′ and 3′ untranslated regions of messenger RNA molecules that regulate the selection of these mRNAs for translation. This review aims to assess recent progress in these three areas and to explore their interrelationships.

Density perturbations and black hole formation in hybrid inflation.

Abstract: We investigate the recently proposed hybrid inflation models with two stages of inflation. We show that quantum fluctuations at the time corresponding to the phase transition between the two inflationary stages can trigger the formation of a large number of inflating topological defects. In order to study density perturbations in these models we further develop a method to calculate density perturbations in a system of two scalar fields. We show that density perturbations in hybrid inflation models of the new type can be very large on the scale corresponding to the phase transition. The resulting density inhomogeneties lead to a copious production of black holes. This could be an argument against hybrid inflation models with two stages of inflation. However, we find a class of models where this problem can be easily avoided. The number of black holes produced in these models can be made extremely small, but in general it could be sufficiently large to have important cosmological and astrophysical implications. In particular, for certain values of parameters these black holes may constitute the dark matter in the Universe. It is also possible to have hybrid models with two stages of inflation where the black hole production is not suppressed, but where the typical masses of the black holes are very small. Such models lead to a completely different thermal history of the Universe, where postinflationary reheating occurs via black hole evaporation.

XRCC1 Polypeptide Interacts with DNA Polymerase β and Possibly Poly (ADP-Ribose) Polymerase, and DNA Ligase III Is a Novel Molecular ‘Nick-Sensor’ In Vitro

Abstract: The DNA repair proteins XRCC1 and DNA ligase III are physically associated in human cells and directly interact in vitro and in vivo. Here, we demonstrate that XRCC1 is additionally associated with DNA polymerase-beta in human cells and that these polypeptides also directly interact. We also present data suggesting that poly (ADP-ribose) polymerase can interact with XRCC1. Finally, we demonstrate that DNA ligase III shares with poly (ADP-ribose) polymerase the novel function of a molecular DNA nick-sensor, and that the DNA ligase can inhibit activity of the latter polypeptide in vitro. Taken together, these data suggest that the activity of the four polypeptides described above may be co-ordinated in human cells within a single multiprotein complex.

Function spaces, entropy numbers, differential operators

Abstract: 1. The abstract background 2. Function spaces 3. Entropy and approximation numbers of embeddings 4. Weighted function spaces and entropy numbers 5. Elliptic operators Bibliography.

Colour Vision as an Adaptation to Frugivory in Primates

Abstract: Most mammals possess two classes of cone, sensitive to short and to long wavelengths of light, but Old World primates (Catarrhini) have distinct medium and long wavelength sensitive classes. The sensitivities of these cones photopigments are alike in all catarrhines with peaks at about 440 nm (\`blue'), 533 nm (\`green') and 565 nm (`red'). One possible reason for the evolution and conservatism of catarrhine trichromacy is that colour vision is a specialization for finding food. A model of retinal coding of natural spectra, based on discrimination thresholds, is used to examine the usefulness of dichromatic and trichromatic vision for finding fruit, and for identifying fruit and leaves by colour. For identification tasks the dichromat's eye is almost as good as a trichromat's, but the trichromat has an advantage for detecting fruit against a background of leaves.

The Schizosaccharomyces pombe rad3 checkpoint gene.

Abstract: The rad3 gene of Schizosaccharomyces pombe is required for checkpoint pathways that respond to DNA damage and replication blocks. We report the complete rad3 gene sequence and show that rad3 is the homologue of Saccharomyces cerevisiae ESR1 (MEC1/SAD3) and Drosophila melanogaster mei-41 checkpoint genes. This establishes Rad3/Mec1 as the only conserved protein which is required for all the DNA structure checkpoints in both yeast model systems. Rad3 is an inessential member of the 'lipid kinase' subclass of kinases which includes the ATM protein defective in ataxia telangiectasia patients. Mutational analysis indicates that the kinase domain is required for Rad3 function, and immunoprecipitation of overexpressed Rad3 demonstrates an associated protein kinase activity. The previous observation that rad3 mutations can be rescued by a truncated clone lacking the kinase domain may be due to intragenic complementation. Consistent with this, biochemical data suggest that Rad3 exists in a complex containing multiple copies of Rad3. We have identified a novel human gene (ATR) whose product is closely related to Rad3/Esr1p/Mei-41. ATR can functionally complement esr1-1 radiation sensitivity in S. cerevisiae. Together, the structural conservation and functional complementation suggest strongly that the mechanisms underlying the DNA structure checkpoints are conserved throughout evolution.

The cluster abundance in flat and open cosmologies

Abstract: We use the galaxy cluster X-ray temperature distribution function to constrain the am­ plitude of the power spectrum of density inhomogeneities on the scale corresponding to clusters. We carry out the analysis for critical-density universes, for low-density universes with a cosmological constant included to restore spatial flatness and for genuinely open universes. That clusters with the same present temperature but different formation times have different virial masses is included. We model cluster mergers using two completely different approaches, and show that the final results from each are extremely similar. We give careful consideration to the uncertainties involved, carrying out a Monte Carlo analysis to determine the cumulative errors. For critical density our result agrees with previous papers, but we believe that the result carries a larger uncertainty. For low­ density universes, either flat or open, the required amplitude of the power spectrum in­ creases as the density is decreased. If all the dark matter is taken to be cold, then the clus­ ter abundance constraint remains compatible with both galaxy correlation data and the COBE measurement of microwave background anisotropies for any reasonable density.

Recent advances in understanding of the evolution and maintenance of sex.

Abstract: The evolution of sex has been the focus of considerable attention during recent years. There is some consensus that the solution to the mystery is that sex either enables the creation and spread of advantageous traits (possibly parasite resistance) or helps to purge the genome of deleterious mutations. Recent experimental work has allowed testing of some of the assumptions underlying the theoretical models, most particularly whether interactions between genes are synergistic and whether the mutation rate is adequately high. However, although a variety of theories point out advantages to sex, most of them predict that a little sex and recombination can go a long way towards improving the fitness of a population, and it remains unclear why obligate sex is so common.

Identification of a nonsense mutation in the carboxyl-terminal region of DNA-dependent protein kinase catalytic subunit in the scid mouse

Abstract: DNA-dependent protein kinase (DNA-PK) consists of a heterodimeric protein (Ku) and a large catalytic subunit (DNA-PKcs) The Ku protein has double-stranded DNA end-binding activity that serves to recruit the complex to DNA ends Despite having serine/threonine protein kinase activity, DNA-PKcs falls into the phosphatidylinositol 3-kinase superfamily DNA-PK functions in DNA double-strand break repair and V(D)J recombination, and recent evidence has shown that mouse scid cells are defective in DNA-PKcs In this study we have cloned the cDNA for the carboxyl-terminal region of DNA-PKcs in rodent cells and identified the existence of two differently spliced products in human cells We show that DNA-PKcs maps to the same chromosomal region as the mouse scid gene scid cells contain approximately wild-type levels of DNA-PKcs transcripts, whereas the V-3 cell line, which is also defective in DNA-PKcs, contains very reduced transcript levels Sequence comparison of the carboxyl-terminal region of scid and wild-type mouse cells enabled us to identify a nonsense mutation within a highly conserved region of the gene in mouse scid cells This represents a strong candidate for the inactivating mutation in DNA-PKcs in the scid mouse

The use of multiple indicators in the assessment of basic research

Abstract: This paper argues that evaluations of basic research are best carried out using a range of indicators. After setting out the reasons why assessments of government-funded basic research are increasingly needed, we examine the multi-dimensional nature of basic research. This is followed by a conceptual analysis of what the different indicators of basic research actually measure. Having discussed the limitations of various indicators, we describe the method of converging partial indicators used in several SPRU evaluations. Yet although most of those who now use science indicators would agree that a combination of indicators is desirable, analysis of a sample ofScientometrics articles suggests that in practice many continue to use just one or two indicators. The paper also reports the results of a survey of academic researchers. They, too, are strongly in favour of research evaluations being based on multiple indicators combined with peer review. The paper ends with a discussion as to why multiple indicators are not used more frequently.

The Asymptotic Distribution of Eigenvalues of Partial Differential Operators

Abstract: Main results Oscillatory integrals Construction of the wave group Singularities of the wave group Proof of main results Mechanical applications Appendix A. Spectral problem on the half-line Appendix B. Fourier Tauberian theorems Appendix C. Stationary phase formula Appendix D. Hamiltonian billiards: proofs Appendix E. Factorization of smooth functions and Taylor-type formulae References Principal notation Index.

An Evolved Circuit, Intrinsic in Silicon, Entwined with Physics

Abstract: ‘Intrinsic’ Hardware Evolution is the use of artificial evolution — such as a Genetic Algorithm — to design an electronic circuit automatically, where each fitness evaluation is the measurement of a circuit's performance when physically instantiated in a real reconfigurable VLSI chip. This paper makes a detailed case-study of the first such application of evolution directly to the configuration of a Field Programmable Gate Array (FPGA). Evolution is allowed to explore beyond the scope of conventional design methods, resulting in a highly efficient circuit with a richer structure and dynamics and a greater respect for the natural properties of the implementation medium than is usual. The application is a simple, but not toy, problem: a tone-discrimination task. Practical details are considered throughout.

The Cahn–Hilliard equation with a concentration dependent mobility: motion by minus the Laplacian of the mean curvature

Abstract: We show by using formal asymptotics that the zero level set of the solution to the Cahn–Hilliard equation with a concentration dependent mobility approximates to lowest order in ɛ an interface evolving according to the geometric motion,(where V is the normal velocity, Δ8 is the surface Laplacian and κ is the mean curvature of the interface), both in the deep quench limit and when the temperature θ is where є2 is the coefficient of gradient energy Equation (01) may be viewed as motion by surface diffusion, and as a higher-order analogue of motion by mean curvature predicted by the bistable reaction-diffusion equation

Pointing and social awareness: declaring and requesting in the second year.

Abstract: The production of pointing and other gestures (e.g. reaching or indicative gestures) by 47 infants aged 1;0 to 1;6 was investigated in two experiments contrasting declarative-referential vs. imperative-instrumental conditions of communication. A further group of seven infants aged 0;10 was examined in order to highlight pre-pointing transitional phenomena. Data analyses concerned gestures and associated vocalizations and visual checking with a social partner. Results show that gestures are produced differentially in the experimental conditions: while reaching is only produced in imperative-instrumental contexts, pointing is characteristic of declarative-referential contexts. The pattern of visual checking with the social partner also differentiates gestures; moreover, it shows developmental changes in the case of pointing. Results suggest that pointing relies on some awareness of 'psychological' processes (e.g. attention and sharing) in the other and the self, and that it is this which may account for the specific relevance of pointing for language development.

Metric perturbations in two field inflation

Abstract: We study the metric perturbations produced during inflation in models with two scalar fields evolving simultaneously. In particular, we emphasize how the large-scale curvature perturbation $\ensuremath{\zeta}$ on fixed energy density hypersurfaces may not be conserved in general for multiple field inflation due to the presence of entropy as well as adiabatic fluctuations. We show that the usual method of solving the linearized perturbation equations is equivalent to the recently proposed analysis of Sasaki and Stewart in terms of the perturbed expansion along neighboring trajectories in field space. In the case of a separable potential it is possible to compute in the slow-roll approximation the spectrum of density perturbations and gravitational waves at the end of inflation. In general there is an inequality between the ratio of tensor to scalar perturbations and the tilt of the gravitational wave spectrum, which becomes an equality when only adiabatic perturbations are possible and $\ensuremath{\zeta}$ is conserved.

The effect of efferent stimulation on basilar membrane displacement in the basal turn of the guinea pig cochlea

Abstract: Tone-evoked basilar membrane (BM) displacements were measured with a laser diode interferometer from the basal turn of the guinea pig cochlea. The olivocochlear bundle (OCB) was electrically stimulated for 60--80 msec periods at rates of < 200 sec-1 via electrodes placed at the point at which the OCB crosses the floor of the fourth ventricle. For tones close to the best or characteristic frequency (CF), OCB stimulation tended to linearize the highly compressive displacement-level functions and to displace the steep, low-level region toward higher intensities along the intensity axis by < 27 dB sound pressure levels. This shift resulted in a desensitization of the tip of the BM displacement tuning curve that was associated sometimes with downward shifts in the tuning curve CF of < 500 Hz. OCB-induced suppression of the BM response was not associated with a consistent broadening of the tuning curve or with major changes in the phase of the BM response. At frequencies in the low-frequency tail of the tuning curve, OCB stimulation had no observable effect on the motion of the BM. The effect of OCB stimulation on the BM response was blocked by perfusing the scala tympani with 1 microM strychnine. Thus, the effect of OCB stimulation on the frequency tuning of the BM is very similar to the effect of OCB stimulation on the sensitivity and frequency tuning of afferent fibers and inner hair cells. The results indicate that the postsynaptic action of the OCB may cause a change in gain of the voltage-dependent outer hair cell motility without observable changes in the stiffness of the cochlear partition or the position of the BM.

The C-terminal domain of eukaryotic protein synthesis initiation factor (eIF) 4G is sufficient to support cap-independent translation in the absence of eIF4E.

Abstract: The foot and mouth disease virus, a picornavirus, encodes two forms of a cysteine proteinase (leader or L protease) that bisects the eIF4G polypeptide of the initiation factor complex eIF4F into N-terminal (N(t)) and C-terminal (C(t)) domains. Previously we showed that, although in vitro cleavage of the translation initiation factor, eIF4G, with L protease decreases cap-dependent translation, the cleavage products themselves may directly promote cap-independent protein synthesis. We now demonstrate that translation of uncapped mRNAs normally exhibits a strong requirement for eIF4E. However, this dependence is abolished when eIF4G is cleaved, with the C(t) domain capable of supporting translation in the absence of the N(t) domain. In contrast, the efficient translation of the second cistron of bicistronic mRNAs, directed by two distinct Internal Ribosome Entry Segments (IRES), exhibits no requirement for eIF4E but is dependent upon either intact eIF4G or the C(t) domain. These results demonstrate that: (i) the apparent requirement for eIF4F for internal initiation on IRES-driven mRNAs can be fulfilled by the C(t) proteolytic cleavage product; (ii) when eIF4G is cleaved, the C(t) domain can also support cap-independent translation of cellular mRNAs not possessing an IRES element, in the absence of eIF4E; and (iii) when eIF4G is intact, translation of cellular mRNAs, whether capped or uncapped, is strictly dependent upon eIF4E. These data complement recent work in other laboratories defining the binding sites for other initiation factors on the eIF4G molecule.

Buried polar residues and structural specificity in the GCN4 leucine zipper.

Abstract: A conserved asparagine (Asn 16) buried in the interface of the GCN4 leucine zipper selectively favours the parallel, dimeric, coiled-coil structure. To test if other polar residues confer oligomerization specificity, the structural effects of Gln and Lys substitutions for Asn 16 were characterized. Like the wild-type peptide, the Asn 16Lys mutant formed exclusively dimers. In contrast, Gln 16, despite its chemical similarity to Asn, allowed the peptide to form both dimers and trimers. The Gln 16 side chain was accommodated by qualitatively different interactions in the dimer and trimer crystal structures. These findings demonstrate that the structural selectivity of polar residues results not only from the burial of polar atoms, but also depends on the complementarity of the side-chain stereochemistry with the surrounding structural environment.