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Showing papers by "University of East Anglia published in 1998"


Journal ArticleDOI
TL;DR: This paper presents a general introduction and discussion of recent applications of the multilayer perceptron, one type of artificial neural network, in the atmospheric sciences.

2,389 citations


Journal ArticleDOI
TL;DR: In this paper, the authors reviewed the recent literature on diversification as a livelihood strategy of rural households in developing countries, with particular reference to sub-Saharan Africa, and concluded that removal of constraints to, and expansion of opportunities for, diversification are desirable policy objectives because they give individuals and households more capabilities to improve livelihood security and to raise living standards.
Abstract: This article reviews the recent literature on diversification as a livelihood strategy of rural households in developing countries, with particular reference to sub‐Saharan Africa. Livelihood diversification is defined as the process by which rural families construct a diverse portfolio of activities and social support capabilities in order to survive and to improve their standards of living. The determinants and effects of diversification in the areas of poverty, income distribution, farm output and gender are examined. Some policy inferences are summarised. The conclusion is reached that removal of constraints to, and expansion of opportunities for, diversification are desirable policy objectives because they give individuals and households more capabilities to improve livelihood security and to raise living standards.

2,298 citations


Journal ArticleDOI
15 May 1998-Science
TL;DR: The coi1 mutation defines an Arabidopsis gene required for response to jasmonates, which regulate defense against insects and pathogens, wound healing, and pollen fertility as mentioned in this paper.
Abstract: The coi1 mutation defines an Arabidopsis gene required for response to jasmonates, which regulate defense against insects and pathogens, wound healing, and pollen fertility. The wild-type allele, COI1, was mapped to a 90-kilobase genomic fragment and located by complementation of coi1-1 mutants. The predicted amino acid sequence of the COI1 protein contains 16 leucine-rich repeats and an F-box motif. It has similarity to the F-box proteins Arabidopsis TIR1, human Skp2, and yeast Grr1, which appear to function by targeting repressor proteins for removal by ubiquitination.

1,551 citations


Book ChapterDOI
TL;DR: In this paper, the effects of fishing on benthic fauna, habitat, diversity, community structure and trophic interactions in tropical, temperate and polar marine environments and consider whether it is possible to predict or manage fishing-induced changes in marine ecosystems.
Abstract: We review the effects of fishing on benthic fauna, habitat, diversity, community structure and trophic interactions in tropical, temperate and polar marine environments and consider whether it is possible to predict or manage fishing-induced changes in marine ecosystems Such considerations are timely given the disillusionment with some fishery management strategies and that policy makers need a scientific basis for deciding whether they should respond to social, economic and political demands for instituting or preventing ecosystem-based management Fishing has significant direct and indirect effects on habitat, and on the diversity, structure and productivity of benthic communities These effects are most readily identified and last longest in those areas that experience infrequent natural disturbance The initiation of fishing in an unfished system leads to dramatic changes in fish community structure As fishing intensity increases the additional effects are more difficult to detect Fishing has accelerated and magnified natural declines in the abundance of many forage fishes and this has lead to reduced reproductive success and abundance in birds and marine mammals However, such donor-controlled dynamics are less apparent in food webs where fishes are the top predators since their feeding strategies are rather more plastic than those of most birds and mammals Fishers tend to target species in sequence as a fishery develops and this leads to changes in the composition of the fished communities with time The dramatic and apparently compensatory shifts in the biomass of different species in many fished ecosystems have often been driven by environmental change rather than the indirect effects of fishing Indeed, in most pelagic systems, species replacements would have occurred, albeit less rapidly, in the absence of fishing pressure In those cases when predator or prey species fill a key role, fishing can have dramatic indirect effects on community structure Thus fishing has shifted some coral reef ecosystems to alternate stable states because there is tight predator–prey coupling between invertebrate feeding fishes and sea urchins Fishing has reduced, and locally extirpated, populations of predatory fishes These reductions do not have a consistent effect on the abundance and diversity of their prey: environmental processes control prey populations in some systems, whereas top-down processes are more important in others By-catch which is discarded during fishing activities may sustain populations of scavenging species, particularly seabirds We conclude by identifying the circumstances in which new research is needed to guide managers and stress the importance of unfished control sites for studies of fishing effects We discuss the advantages and disadvantages of closed area management (marine reserves) and the conditions under which such management is likely to provide benefits for the fishery or ecosystem

1,546 citations


Journal ArticleDOI
29 Jan 1998-Nature
TL;DR: Analysis of the sequence revealed an average gene density of one gene every 4.8 kilobases, and 54% of the predicted genes had significant similarity to known genes, and other interesting features were found, such as the sequence of a disease-resistance gene locus, the distribution of retroelements, and the frequent occurrence of clustered gene families.
Abstract: The plant Arabidopsis thaliana (Arabidopsis) has become an important model species for the study of many aspects of plant biology. The relatively small size of the nuclear genome and the availability of extensive physical maps of the five chromosomes provide a feasible basis for initiating sequencing of the five chromosomes. The YAC (yeast artificial chromosome)-based physical map of chromosome 4 was used to construct a sequence-ready map of cosmid and BAC (bacterial artificial chromosome) clones covering a 1.9-megabase (Mb) contiguous region, and the sequence of this region is reported here. Analysis of the sequence revealed an average gene density of one gene every 4.8 kilobases (kb), and 54% of the predicted genes had significant similarity to known genes. Other interesting features were found, such as the sequence of a disease-resistance gene locus, the distribution of retroelements, the frequent occurrence of clustered gene families, and the sequence of several classes of genes not previously encountered in plants.

832 citations


Journal ArticleDOI
TL;DR: In the last decade, many climatologists have put a great deal of effort into developing techniques to identify inhomogeneities and adjust climatic time series to compensate for the biases produced by the inhomogenities as mentioned in this paper.
Abstract: Long-term in situ observations are widely used in a variety of climate analyses. Unfortunately, most decade- to century-scale time series of atmospheric data have been adversely impacted by inhomogeneities caused by, for example, changes in instrumentation, station moves, changes in the local environment such as urbanization, or the introduction of different observing practices like a new formula for calculating mean daily temperature or different observation times. If these inhomogeneities are not accounted for properly, the results of climate analyses using these data can be erroneous. Over the last decade, many climatologists have put a great deal of effort into developing techniques to identify inhomogeneities and adjust climatic time series to compensate for the biases produced by the inhomogeneities. It is important for users of homogeneity-adjusted data to understand how the data were adjusted and what impacts these adjustments are likely to make on their analyses. And it is important for developers of homogeneity-adjusted data sets to compare readily the different techniques most commonly used today. Therefore, this paper reviews the methods and techniques developed for homogeneity adjustments and describes many different approaches and philosophies involved in adjusting in situ climate data. © 1998 Royal Meteorological Society.

820 citations


Journal ArticleDOI
TL;DR: In this article, a Principal Component Analysis (PCA) is performed on yearly values for the 17 reconstructions over the period AD 1660-1970, all extending back at least to the mid-seventeenth century, to form two annually resolved hemispheric series (NH10 and SH7).
Abstract: Palaeoclimatology provides our only means of assessing climatic variations before the beginning of instrumental records. The various proxy variables used, however, have a number of limitations which must be adequately addressed and understood. Besides their obvious spatial and seasonal limitations, different proxies are also potentially limited in their ability to represent climatic variations over a range of different timescales. Simple correlations with instrumental data over the period since AD 1881 give some guide to which are the better proxies, indicating that coral- and ice-core-based reconstructions are poorer than tree-ring and historical ones. However, the quality of many proxy time series can deteriorate during earlier times. Suggestions are made for assessing proxy quality over longer periods than the last century by intercomparing neighbouring proxies and, by comparisons with less temporally resolved proxies such as borehole temperatures. We have averaged 17 temperature reconstructions (representing various seasons of the year), all extending back at least to the mid-seventeenth century, to form two annually resolved hemispheric series (NH10 and SH7). Over the 1901-91 period, NH10 has 36% variance in common with average NH summer (June to August) temperatures and 70% on decadal timescales. SH7 has 16% variance in common with average SH summer (December to February) temperatures and 49% on decadal timescales, markedly poorer than the reconstructed NH series. The coldest year of the millennium over the NH is AD 1601, the coldest decade 1691-1700 and the seventeenth is the coldest century. A Principal Components Analysis (PCA) is performed on yearly values for the 17 reconstructions over the period AD 1660-1970. The correlation between PC1 and NH10 is 0.92, even though PC1 explains only 13.6% of the total variance of all 17 series. Similar PCA is performed on thousand-year-long General Circulation Model (GCM) data from the Geophysical Fluid Dynamics Laboratory (GFDL) and the Hadley Centre (HADCM2), sampling these for the same locations and seasons as the proxy data. For GFDL, the correlation between its PC1 and its NH10 is 0,89, while for HADCM2 the PCs group markedly differently. Cross-spectral analyses are performed on the proxy data and the GFDL model data at two different frequency bands (0.02 and 0.03 cycles per year). Both analyses suggest that there is no large-scale coherency in the series on these timescales. This implies that if the proxy data are meaningful, it should be relatively straightforward to detect a coherent near-global anthropogenic signal in surface temperature data.

790 citations


Journal ArticleDOI
04 Jun 1998-Nature
TL;DR: The most severe short-term Northern Hemisphere cooling event of the past 600 years occurred in 1601, suggesting that either the effect on climate of the eruption of Huaynaputina, Peru, in 1600 has previously been greatly underestimated, or another, as yet unidentified, eruption occurred at the same time as discussed by the authors.
Abstract: A network of temperature-sensitive tree-ring-density chronologies provides circum-hemisphere information on year-by-year changes in summer warmth in different regions of the northern boreal forest1. Combining these data into a single time-series provides a good summer-temperature proxy for northern high latitudes and the Northern Hemisphere as a whole2. Here we use this well dated, high-resolution composite time-series to suggest that large explosive volcanic eruptions produced different extents of Northern Hemisphere cooling during the past 600 years. The large effect of some recent eruptions is apparent, such as in 1816, 1884 and 1912, but the relative effects of other known, and perhaps some previously unknown, pre-nineteenth-century eruptions are also evaluated. The most severe short-term Northern Hemisphere cooling event of the past 600 years occurred in 1601, suggesting that either the effect on climate of the eruption of Huaynaputina, Peru, in 1600 has previously been greatly underestimated, or another, as yet unidentified, eruption occurred at the same time. Other strong cooling events occurred in 1453, seemingly confirming a 1452 date for the eruption of Kuwae, southwest Pacific, and in 1641/42, 1666, 1695 and 1698.

771 citations


Journal ArticleDOI
TL;DR: A significant positive relation was observed between breeding dispersal distance and long-term population decline among migrants, but not among residents, suggesting that this habitat variable does not impose the same constraint on natal dispersal.
Abstract: 1. Dispersal is of critical ecological and evolutionary importance for several issues of population biology, particularly population synchrony, colonization and range expansion, metapopulation and source–sink dynamics, and population genetic structure, but it has not previously been possible to compare dispersal patterns across a wide range of species or to study movement outside the confines of local study areas. 2. Using resampling methods, we verified that statistically unbiased estimates of average dispersal distance and of intraspecific variance in dispersal distance could be extracted from the bird ringing data of the British Trust for Ornithology. 3. Using data on 75 terrestrial bird species, we tested whether natal and breeding dispersal were influenced by a species’ habitat requirements, diet, geographical range, abundance, morphology, social system, life history or migratory status. We used allometric techniques to ascertain whether these relationships were independent of body size, and used the method of phylogenetically independent contrasts to ascertain whether they were independent of phylogeny. 4. Both natal and breeding dispersal distances were lower among abundant species and among species with large geographical ranges. Dispersal distances and life-history variables were correlated independent of phylogeny, but these relationships did not persist after controlling for body size. All morphometrical variables (wing length, tarsus length and bill length) were not significantly correlated with dispersal distances after correcting for body size or phylogenetic relatedness. 5. Migrant species disperse further than resident ones, this relation was independent of body size but not of phylogeny. A significant positive relation was observed between breeding dispersal distance and long-term population decline among migrants, but not among residents. 6. The species living in wet habitats disperse further than those living in dry habitats, which could be explained by the greater patchiness of wet habitats in space and/or time. This relationship was observed only for breeding dispersal, suggesting that this habitat variable does not impose the same constraint on natal dispersal.

759 citations


Journal ArticleDOI
12 Feb 1998-Nature
TL;DR: In this paper, a large-regional-scale analysis of wood-density/air-temperature relationships using measurements from hundreds of sites at high latitudes in the Northern Hemisphere is presented.
Abstract: Tree-ring chronologies that represent annual changes in the density of wood formed during the late summer can provide a proxy for local summertime air temperature1. Here we undertake an examination of large-regional-scale wood-density/air-temperature relationships using measurements from hundreds of sites at high latitudes in the Northern Hemisphere. When averaged over large areas of northern America and Eurasia, tree-ring density series display a strong coherence with summer temperature measurements averaged over the same areas, demonstrating the ability of this proxy to portray mean temperature changes over sub-continents and even the whole Northern Hemisphere. During the second half of the twentieth century, the decadal-scale trends in wood density and summer temperatures have increasingly diverged as wood density has progressively fallen. The cause of this increasing insensitivity of wood density to temperature changes is not known, but if it is not taken into account in dendroclimatic reconstructions, past temperatures could be overestimated. Moreover, the recent reduction in the response of trees to air-temperature changes would mean that estimates of future atmospheric CO2 concentrations, based on carbon-cycle models that are uniformly sensitive to high-latitude warming, could be too low.

736 citations


Journal ArticleDOI
TL;DR: In this article, the role of magnetic enhancement and dilution in determining soil magnetic properties is investigated for a range of modern soil types, including those of the Chinese Loess Plateau, Tajikistan and the Czech Republic, and the relationship is completely opposite, with susceptibility minima associated with the most developed paleosols.

Journal ArticleDOI
TL;DR: In this paper, a multicomponent mole fraction-based thermodynamic model is used to represent aqueous phase activities, equilibrium partial pressures (of H2O, HNO3, and NH3), and saturation with respect to solid phases.
Abstract: A multicomponent mole-fraction-based thermodynamic model is used to represent aqueous phase activities, equilibrium partial pressures (of H2O, HNO3, and NH3), and saturation with respect to solid phases (H2SO4 and HNO3 hydrates, (NH4)2SO4(cr), (NH4)3H(SO4)2(cr), NH4HSO4(cr), (NH4)2SO4·2NH4NO3(cr), (NH4)2SO4·3NH4NO3(cr), and NH4HSO4·NH4NO3(cr)) in the system H+−NH4+−SO42-−NO3-−H2O. The model is valid from 328 to <200 K, dependent upon liquid-phase composition. Parameters for H2SO4−H2O, HNO3−H2O, and (NH4)2SO4−H2O interactions were adopted from previous studies, and values for NH4NO3−H2O obtained from vapor pressures (including data for supersaturated solutions), enthalpies, and heat capacities. Parameters for ternary interactions were determined from extensive literature data for salt solubilities, electromotive forces (emfs), and vapor pressures with an emphasis upon measurements of supersaturated H2SO4−(NH4)2SO4−H2O solutions. Comparisons suggest that the model satisfactorily represents partial pressures...

Journal ArticleDOI
TL;DR: The data suggest that TIMP2 forms a receptor with MT1 MMP that regulates the concentration and efficient generation of functionally active gelatinase A.

Journal ArticleDOI
TL;DR: Results suggest that TIMP‐3, unlike the other TIMPs, may be important in the modulation of pathological events in which TNF‐α secretion is involved.

Journal ArticleDOI
TL;DR: Two Escherichia coli genes required for the export of cofactor‐containing periplasmic proteins, synthesized with signal peptides containing a twin arginine motif are identified, indicating the involvement of the gene products in a novel export system.
Abstract: We describe the identification of two Escherichia coli genes required for the export of cofactor-containing periplasmic proteins, synthesized with signal peptides containing a twin arginine motif. Both gene products are homologous to the maize HCF106 protein required for the translocation of a subset of lumenal proteins across the thylakoid membrane. Disruption of either gene affects the export of a range of such proteins, and a complete block is observed when both genes are inactivated. The Sec protein export pathway was unaffected, indicating the involvement of the gene products in a novel export system. The accumulation of active cofactor-containing proteins in the cytoplasm of the mutant strains suggests a role for the gene products in the translocation of folded proteins. One of the two HCF106 homologues is encoded by the first gene of a four cistron operon, tatABCD, and the second by an unlinked gene, tatE. A mutation previously assigned to the hcf106 homologue encoded at the tatABCD locus, mttA, lies instead in the tatB gene.

Journal ArticleDOI
10 Jul 1998-Science
TL;DR: The coastal seas are one of the most valuable and vulnerable of Earth's habitats and significant inputs of nutrients to the coastal zone arrive via rivers, groundwater, and the atmosphere, which have been increased by human activity.
Abstract: REVIEW The coastal seas are one of the most valuable and vulnerable of Earth9s habitats. Significant inputs of nutrients to the coastal zone arrive via rivers, groundwater, and the atmosphere. Nutrient fluxes through these routes have been increased by human activity. In addition, the N:P:Si ratios of these inputs have been perturbed, and many coastal management practices exacerbate these perturbations. There is evidence of impacts arising from these changes (in phytoplankton numbers and relative species abundance, and deep-water oxygen declines) in areas of restricted water exchange. Elsewhere, the nutrient fluxes through the coastal zone appear to be still dominated by large inputs from the open ocean, and there is little evidence of anthropogenic perturbations.

Journal ArticleDOI
TL;DR: In this article, a multicomponent mole fraction-based thermodynamic model of the H+−NH4+−Na+−SO42-−NO3-−Cl-−H2O system is used to represent aqueous phase activities.
Abstract: A multicomponent mole-fraction-based thermodynamic model of the H+−NH4+−Na+−SO42-−NO3-−Cl-−H2O system is used to represent aqueous-phase activities, equilibrium partial pressures (of H2O, HNO3, HCl, and NH3), and saturation with respect to 19 solid phases ((NH4)2SO4(cr), (NH4)3H(SO4)2(cr), NH4HSO4(cr), NH4NO3(cr), NH4Cl(cr), Na2SO4·10H2O(cr), Na2SO4(cr), Na3H(SO4)2(cr), NaHSO4·H2O(cr), NaHSO4(cr), NaH3(SO4)2·H2O(cr), NaNO3(cr), NaCl(cr), NH4HSO4·NH4NO3(cr), (NH4)2SO4·2NH4NO3(cr), (NH4)2SO4·3NH4NO3(cr), (NH4)2SO4·Na2SO4·4H2O(cr), Na2SO4·NaNO3·H2O(cr), 2NaNO3·NH4NO3(cr)). The model is valid for concentrations from infinite dilution to saturation (with respect to the solid phases) and to about 40 mol kg-1 for acid sulfate systems which can remain liquid to concentrations approaching the pure acid. Parameters for H2SO4−H2O interactions were adopted from a previous study, and values for other binary (water−electrolyte) and ternary (water and three ions) interactions were determined from extensive literature da...

Journal ArticleDOI
TL;DR: In this paper, the authors use an approach based on phylogenetic comparisons to identify life history correlates of abundance trends in 18 intensively exploited fish stocks from the north-east Atlantic and show that those fishes that have decreased in abundance compared with their nearest relatives mature later, attain a larger maximum size, and exhibit significantly lower potential rates of population increase.
Abstract: We use an approach based on phylogenetic comparisons to identify life history correlates of abundance trends in 18 intensively exploited fish stocks from the north–east Atlantic. After accounting for differences in fishing mortality, we show that those fishes that have decreased in abundance compared with their nearest relatives mature later, attain a larger maximum size, and exhibit significantly lower potential rates of population increase. Such trends were not evident in a more traditional cross–species analysis. This is the first phylogenetically independent evidence to link life histories with abundance trends, and provides a quantitative basis for assessing vulnerability of fish populations to exploitation. Our approach can be applied to the conservation and management of other exploited taxa.

Journal ArticleDOI
TL;DR: 20 subjects in which the study of animal behaviour can make a significant contribution to conservation are listed, and how behavioural ecologists could become more involved in conservation is suggested.

Journal ArticleDOI
TL;DR: This article used a gridded terrestrial precipitation dataset for the period 1900 to 1996 to examine the extent to which observed global and zonal-mean precipitation sensitivities to global warming have been captured by a series of model simulations recently completed by the UK Hadley Centre.
Abstract: Recent century-long experiments performed with global climate models have simulated observed trends in global-mean temperature quite successfully when both greenhouse gas and aerosol forcing has been included. The performance of these same experiments in simulating observed global-scale changes in precipitation has not previously been examined. Here we use a gridded terrestrial precipitation dataset for the period 1900 to 1996 to examine the extent to which observed global and zonal-mean precipitation sensitivities to global warming have been captured by a series of model simulations recently completed by the UK Hadley Centre. There are signs that the model has been able to reproduce at least some of the observed zonal-mean variations in the precipitation sensitivity to warming. Questions remain both about the quality of the observed precipitation data and about the spatial scale at which anthropogenically-forced global climate models can be expected to reproduce observed variations in precipitation.

Journal ArticleDOI
TL;DR: A central role for TatC-type proteins in the translocation of tightly folded proteins across a spectrum of biological membranes is suggested.

Journal ArticleDOI
TL;DR: The use of cost-benefit analysis (CBA) in British environmental policy has gone through several stages as mentioned in this paper, and while the amount of CBA being undertaken has increased, its influence on policy making is open to question.
Abstract: The use of cost-benefit analysis (CBA) in British environmental policy has gone through several stages. Early applications of CBA tended to ignore environmental impacts altogether, leave them for a subsidiary "impact analysis", or provide only a partial monetization of impacts. Currently, CBA is the subject of renewed interest in government departments, in the Environment Agency, and among other agencies providing guidance and advice to government. While the amount of CBA being undertaken has increased, its influence on policy making is open to question. Obstacles remain. Much CBA is expensive and this means that "benefits transfer" is widely regarded as essential. Currently, however, the validity of much benefits transfer is questionable. Other problems arise from misunderstandings about the nature of economic values and the links to individuals' self interest, and from concerns that CBA results will "crowd out" flexibility in decision-making, especially the likely context of multiple political objectives over and above economic efficiency. None the less, CBA has begun to have influence in the setting of environmental taxes and alternative decision rules appear to suffer as many, if not more, shortcomings as those faced by CBA. Copyright 1998 by Oxford University Press.

Journal ArticleDOI
TL;DR: In this paper, the authors used tree-ring records from eastern North America and northwestern Europe to develop the first reconstruction of the winter North Atlantic Oscillation (NAO) and found that the reconstructed series spans the interval AD 1701-1980 and explains 41% of the variance in the NAO over the AD 1874-1980 calibration period.
Abstract: Tree-ring records, six from eastern North America and four from northwestern Europe, are used to develop the first reconstruction of the winter North Atlantic Oscillation (NAO) The reconstructed series spans the interval AD 1701-1980 and explains 41%, of the variance in the NAO over the AD 1874-1980 calibration period The reconstruction also captures the spectral properties of this index, suggesting that the oscillatory character of the NAO is a long-term feature of the North Atlantic climate system

Journal ArticleDOI
TL;DR: The authors compare two frameworks which have been proposed to explain risk perceptions, namely, cultural theory and the psychometric paradigm, and find that cultural biases are associated with concern about distinct types of risks and that the pattern of responses was compatible with that predicted by cultural theory.
Abstract: This paper seeks to compare two frameworks which have been proposed to explain risk perceptions, namely, cultural theory and the psychometric paradigm. A structured questionnaire which incorporated elements from both approaches was administered to 129 residents of Norwich, England. The qualitative risk characteristics generated by the psychometric paradigm explained a far greater proportion of the variance in risk perceptions than cultural biases, though it should be borne in mind that the qualitative characteristics refer directly to risks whereas cultural biases are much more distant variables. Correlations between cultural biases and risk perceptions were very low, but the key point was that each cultural bias was associated with concern about distinct types of risks and that the pattern of responses was compatible with that predicted by cultural theory. The cultural approach also provided indicators for underlying beliefs regarding trust and the environment; beliefs which were consistent within each world view but divergent between them. An important drawback, however, was that the psychometric questionnaire could only allocate 32% of the respondents unequivocally to one of the four cultural types. The rest of the sample expressed several cultural biases simultaneously, or none at all. Cultural biases are therefore probably best interpreted as four extreme world views, and a mixture of qualitative and quantitative research methodologies would generate better insights into who might defend these views in what circumstances, whether there are only four mutually exclusive world views or not, and how these views are related to patterns of social solidarity, and judgments on institutional trust.

Journal ArticleDOI
TL;DR: In this paper, the authors compared responses given to decision tasks which are embedded in random lottery designs with responses in single choice designs in which each subject faces just one task for real.
Abstract: The random lottery incentive system is widely used in experimental economics to motivate subjects. This paper investigates its validity. It reports three experiments which compare responses given to decision tasks which are embedded in random lottery designs with responses in ‘single choice’ designs in which each subject faces just one task for real. The experiments were designed to detect cross-task contamination effects in the random lottery treatment. No significant differences between treatments, and no significant contamination effects, were found. Over the three experiments, observed differences between the treatments are adequately explained as sampling variation.

Journal ArticleDOI
30 Jul 1998-Nature
TL;DR: Evidence indicates that the Earth self-regulates at a state that is tolerated by life, but why should the organisms that leave the most descendants be the ones that contribute to regulating their planetary environment?
Abstract: Evidence indicates that the Earth self-regulates at a state that is tolerated by life, but why should the organisms that leave the most descendants be the ones that contribute to regulating their planetary environment? The evolving Gaia theory focuses on the feedback mechanisms, stemming from naturally selected traits of organisms, that could generate such self-regulation.

Journal ArticleDOI
TL;DR: The annual growth of trees, as represented by a variety of ringwidth, densitometric, or chemical parameters, represents a combined record of different environmental forcings, one of which is climat...
Abstract: The annual growth of trees, as represented by a variety of ringwidth, densitometric, or chemical parameters, represents a combined record of different environmental forcings, one of which is climat...

Journal ArticleDOI
TL;DR: In this paper, stable carbon isotopes and C/N ratios of particulate organic matter (POM) in suspended solids, surficial sediments and sediment cores were used to define the spatial and temporal variability of POM in a poorly flushed, urbanized, eutrophic tropical estuary (Hunts Bay, Kingston Harbour, Jamaica).
Abstract: Stable carbon isotopes and C/N ratios of particulate organic matter (POM) in suspended solids, surficial sediments and sediment cores were used to define the spatial and temporal variability of POM in a poorly flushed, urbanized, eutrophic tropical estuary (Hunts Bay, Kingston Harbour, Jamaica). C/N variation in the sediment surface POM is a function of initial suspended particulate organic matter (SPOM) (or other POM) type and the alteration of C/N ratios in the water column or on the sediment surface. The d13CSPOM(-20 to -25‰) values suggest that this material is a mixture of: (1)in situphytoplankton organic matter; (2) terrestrial river-borne SPOM; (3) terrestrial river-borne bottom sediment POM; and (4) sewage. Downcore variation in organic carbon content, C/N and d13Cis attributed mainly to change in the supply rate and type of organic matter. In the NE of Hunts Bay, down core variation in sedimentology and geochemistry are consistent with a change from fully marine to freshwater runoff-dominated sedimentation with increasing organic matter input from sewage in recent times. Despite large overlaps in the C/N and d13Corg‘ end-members ’ pollutant POM, in this case sewage, was the only source which could account for the amount of POM deposited, the surface sediment C/N and d13Corgvalues and the trajectories of evolution in C/N andd13Corgvalues in cores. The data show that the combinedd13C and C/N successfully identifies the source, fate and history of POM even in a poorly-mixed estuary.

Journal ArticleDOI
TL;DR: The data demonstrate that the activation of MMP-2 by HT1080 cells is regulated by the nature of the extracellular matrix, and that signals via the alpha5beta1 integrin receptor may be involved in the fibronectin induced up-regulation of M MP-2 activation.
Abstract: We have assessed the effect of fibronectin and laminin-1 on the expression of molecules involved in the activation pathway of MMP-2, a key proteinase in tissue remodelling. HT1080 fibrosarcoma cells cultured on fibronectin were shown to activate endogenous MMP-2, to a level comparable with that elicited by treatment with phorbol ester. In contrast, the MMP-2 expressed by HT1080 cells cultured on laminin-1 was mainly in the pro- (inactive form). Culture of the cells on peptide fragments of fibronectin derived from the central cell binding domain also promoted MMP-2 activation, indicating that signals via fibronectin binding to integrin receptors may be involved. HT1080 cells cultured on immobilised antibodies to the alpha5 and beta1 integrin subunits secreted levels of active MMP-2 similar to those observed for full length fibronectin, whereas cells cultured on an antibody to the alpha6 integrin subunit secreted mainly proMMP-2. The data demonstrate that the activation of MMP-2 by HT1080 cells is regulated by the nature of the extracellular matrix, and that signals via the alpha5beta1 integrin receptor may be involved in the fibronectin induced up-regulation of MMP-2 activation. We then assessed the effect of fibronectin on the components of the putative MT1-MMP/TIMP-2 'receptor' complex implicated in MMP-2 activation. Levels of TIMP-2 protein expressed by HT1080 cells did not vary detectably between cells cultured on fibronectin or laminin-1. However, the expression of MT1-MMP protein was up-regulated when the cells were cultured on fibronectin, which could be attributed to an increase in levels of a truncated 45 kDa form. Parallel studies using gelatin zymography demonstrated that the up-regulation of the production of the 45 kDa band was concomitant with MMP-2 activation. Inhibitor studies revealed that the truncation of MT1-MMP to a 45 kDa form is MMP mediated, although not inhibited by TIMP-1. In vitro, the 45 kDa form could be generated by cleavage of membrane-bound native MT1-MMP with several recombinant MMPs, including both active MT1-MMP and MMP-2. The implication that either MMP-2 or MT1-MMP can process MT1-MMP to 45 kDa, raises the possibility that truncation of MT1-MMP represents a self-regulatory end-point in the activation pathway of MMP-2.

Journal ArticleDOI
TL;DR: In this article, the authors set out a disaggregated view of food production in urban areas, emphasizing the analytical and policy importance of rural-urban interactions in resource and output markets as well as in income transfers.