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Showing papers by "University of Reading published in 1994"


Journal ArticleDOI
TL;DR: In this paper, a model combining a multivariate linear model for the underlying response with a logistic regression model was proposed for continuous longitudinal data with non-ignorable or informative dropout.
Abstract: A model is proposed for continuous longitudinal data with non-ignorable or informative drop-out (ID). The model combines a multivariate linear model for the underlying response with a logistic regression model for the drop-out process. The latter incorporates dependence of the probability of drop-out on unobserved, or missing, observations. Parameters in the model are estimated by using maximum likelihood (ML) and inferences drawn through conventional likelihood procedures. In particular, likelihood ratio tests can be used to assess the informativeness of the drop-out process through comparison of the full model with reduced models corresponding to random drop-out (RD) and completely random processes

1,034 citations


Journal ArticleDOI
TL;DR: A data assimilation system has been developed at the UK Meteorological Office to analyze the mix of observations available in the troposphere and stratosphere as discussed by the authors, which is used to supply near real-time analyses of meteorological fields from the Troposphere and Stratosphere to the Upper Atmosphere Research Satellite (UARS) Science Team.
Abstract: A data assimilation system has been developed at the UK Meteorological Office to analyze the mix of observations available in the troposphere and stratosphere. The data assimilation system is based on the analysis correction scheme used at the UK Meteorological Office for operational weather forecasting. The assimilation system is currently being used to supply near real-time analyses of meteorological fields from the troposphere and stratosphere to the Upper Atmosphere Research Satellite (UARS) Science Team. At this stage, these analyses are based on a similar set of observations to the operational analyses, so they provide an independent check of the UARS observations. In the stratosphere they are largely based on soundings from the National Oceanic and Atmospheric Administration polar orbiters. Some results from the assimilation system are presented for periods in January and August 1992. They are compared with equivalent products from the National Meteorological Center. A particular study is ...

653 citations


Journal ArticleDOI
18 Aug 1994-Nature
TL;DR: The amphioxus genome has only one Hox gene cluster, and contains homologues of at least the first ten paralogous groups of vertebrate Hox genes in a collinear array, compatible with that inferred for a direct ancestor of the vertebrates.
Abstract: Organization into gene clusters is an essential and diagnostic feature of Hox genes Insect and nematode genomes possess single Hox gene clusters (split in Drosophila); in mammals, there are 38 Hox genes in four clusters on different chromosomes A collinear relationship between chromosomal position, activation time and anterior expression limit of vertebrate Hox genes suggests that clustering may be important for precise spatiotemporal gene regulation and hence embryonic patterning Hox genes have a wide phylogenetic distribution within the metazoa, and are implicated in the control of regionalization along the anteroposterior body axis It has been suggested that changes in Hox gene number and genomic organization played a role in metazoan body-plan evolution, but identifying significant changes is difficult because Hox gene organization is known from only very few and widely divergent taxa (principally insects, nematodes and vertebrates) Here we analyse the complexity and organization of Hox genes in a cephalochordate, amphioxus, the taxon thought to be the sister group of the vertebrates We find that the amphioxus genome has only one Hox gene cluster It has similar genomic organization to the four mammalian Hox clusters, and contains homologues of at least the first ten paralogous groups of vertebrate Hox genes in a collinear array Remarkably, this organization is compatible with that inferred for a direct ancestor of the vertebrates; we conclude that amphioxus is a living representative of a critical intermediate stage in Hox cluster evolution

552 citations


Journal ArticleDOI
TL;DR: A general method for performing the synoptic identification of phenomena that can be used for an objective analysis of atmospheric, or oceanographic, datasets obtained from numerical models and remote sensing.
Abstract: Recent interest in the validation of general circulation models (GCMS) has been devoted to objective methods. A small number of authors have used the direct synoptic identification of phenomena together with a statistical analysis to perform the objective comparison between various datasets. This paper describes a general method for performing the synoptic identification of phenomena that can be used for an objective analysis of atmospheric, or oceanographic, datasets obtained from numerical models and remote sensing. Methods usually associated with image processing have been used to segment the scene and to identify suitable feature points to represent the phenomena of interest. This is performed for each time level. A technique from dynamic scene analysis is then used to link the feature points to form trajectories. The method is fully automatic and should be applicable to a wide range of geophysical fields. An example will be shown of results obtained from this method using data obtained from ...

430 citations


Journal ArticleDOI
TL;DR: Current work on the characterization of antifungal metabolites in higher plants is reviewed and interesting new structures are discussed and the distributi are discussed.

399 citations


Journal ArticleDOI
TL;DR: It was confirmed that zinc is most likely to be responsible for the absence of earthworms from sites close to the Avonmouth works, since the OECD standard test overestimated the potential effects of metals on populations, since earthworms can be found as close as 1 km from the smelting works.

355 citations


Journal ArticleDOI
TL;DR: Human... is an adjective and its use as a noun is in itself regrettable as discussed by the authors, which is why it should not be used as an adjective as in this paper, either.
Abstract: Human... is an adjective and its use as a noun is in itself regrettable. —William Burroughs

348 citations


Journal ArticleDOI
TL;DR: A range of alumina-supported platinum catalysts have been prepared and investigated for the selective reduction of nitrogen monoxide in the presence of a large excess of oxygen in steady state microreactor experiments.
Abstract: A range of alumina-supported platinum catalysts have been prepared and investigated for the selective reduction of nitrogen monoxide in the presence of a large excess of oxygen. Steady-state microreactor experiments have demonstrated that these catalysts are very active and selective for the reduction of nitrogen monoxide by propene at temperatures as low as 200°C. There does not appear to be a simple correlation between the activity for nitrogen monoxide reduction and the platinum surface area. Instead it is found that there is a very good inverse correlation between the maximum nitrogen monoxide reduction activity and the temperature. The most active catalysts for selective nitrogen monoxide reduction are those that generate activity at the lowest temperature. The technique of temporal analysis of products (TAP) has been used to obtain detailed mechanistic data about the selective nitrogen monoxide reduction reaction on an alumina-supported platinum catalyst. Using carbon monoxide, hydrogen or propene as reductant it has been demonstrated that the predominant mechanism for selective nitrogen monoxide reduction involves the decomposition of nitrogen monoxide on reduced platinum metal sites, followed by the regeneration of the active platinum sites by the reductant. In the decomposition step it has been shown that oxygen from nitrogen monoxide is retained on the surface of the platinum and blocks the surface for further adsorption/reaction of nitrogen monoxide; it has been observed that oxidised platinum catalysts are not active for the nitrogen monoxide reduction reaction. Under typical operating conditions, propene is a far more efficient reductant than either carbon monoxide or hydrogen. The greater efficiency of propene as a reductant is explained on the basis of the additional reducing power of the propene molecule, which can react with as many as nine adsorbed oxygen atoms, ensuring that 'patches' of reduced platinum are available for nitrogen monoxide adsorption/reaction. A small additional activity of reduced platinum in the presence of propene, which is not observed when carbon monoxide or hydrogen is used as reductant, has been explained on the basis of a second mechanism involving the carbon-assisted decomposition of nitrogen monoxide at sites on the reduced platinum adjacent to adsorbed carbon-containing moieties, believed to be fragments from adsorbed propene molecules. A model for the selective reduction of nitrogen monoxide on alumina-supported platinum catalysts is presented which is capable of explaining all the results obtained in this work and in the published literature on this subject.

345 citations


Journal ArticleDOI
TL;DR: It is argued that existing frameworks, emanating separately from the respective disciplines (cognitive, social and organizational) do not present an adequate means of studying the dynamics of collaborative activity in situ, and an alternative framework, advocated in this paper, is distributed cognition.
Abstract: This paper examines the theoretical and practical problems that arise from attempts to develop formal characterizations and explanations of many work activities, in particular, collaborative activities We argue that even seemingly discrete individual activities occur in, and frequently draw upon a complex network of factors: individual, social and organizational Similarly, organizational and social constraints and practices impact upon individual cognitive processes and the realization of these in specific tasks Any adequate characterization of work activities therefore requires the analysis and synthesis of information from these traditionally separate sources We argue that existing frameworks, emanating separately from the respective disciplines (cognitive, social and organizational) do not present an adequate means of studying the dynamics of collaborative activity in situ An alternative framework, advocated in this paper, is distributed cognition Its theoretical basis is outlined together with examples of applied studies of computer-mediated work activities in different organizational settings

313 citations


Journal ArticleDOI
TL;DR: Fermented foods and beverages represent a significant proportion of all diets worldwide, typically about one-third of food intake, providing a major contribution nutritionally and to flavour and interest in the authors' food consumption.

289 citations


Book
25 Mar 1994
TL;DR: In this article, the governing physical laws of the global circulation were studied and the atmospheric heat engine was modeled and the zonal mean meridional circulation was observed and the steady eddies in the mid-latitudes were modeled.
Abstract: 1. The governing physical laws 2. Observing and modelling the global circulation 3. The atmospheric heat engine 4. The zonal mean meridional circulation 5. Transient disturbances in the mid-latitudes 6. Wave propagation and the steady eddies 7. Three dimensional aspects of the global circulation 8. Low frequency variability of the circulation 9. The stratosphere 10. Planetary atmospheres and other fluid systems.

Journal ArticleDOI
TL;DR: In this paper, structural information derived from X-ray and neutron diffraction and small angle scattering investigations of vitreous silica is presented, starting from the classic studies of Warren and co-workers in the 1930s.
Abstract: A quantitative assessment is presented of the structural information derived from X-ray and neutron diffraction and small angle scattering investigations of vitreous silica, starting from the classic studies of Warren and co-workers in the 1930s. Particular points that are addressed include the regularity of the SiO4 tetrahedral structural units, the SiOSi angle distribution, the interpretation of the first peak in the diffraction pattern and the extent of the longer range density fluctuations as revealed by X-ray and neutron measurements at small scattering vectors. The use of structural modelling in the interpretation of the diffraction data is discussed and representative models are compared with experiment. The extent of the (dis)agreement of each model with experiment is compared quantitatively and the paper concludes by identifying the most accurate structural model of vitreous silica known to the author at the present time.

Book
01 Jan 1994
TL;DR: This book brings together most of the work done over the last decade or so which has been stimulated by Miller's original idea, and discusses the interrelationships between the techniques and the established ideas of the method of characteristics, Hamilton's equations, the Legendre transformation, and grid equidistribution.
Abstract: This book is mainly concerned with finite element methods for time-dependent partial differential equations when the grids are allowed to move in time, but also describes grid generation techniques which include grid adjustment. The mechanism for grid movement derives from a generalization of the residual minimization technique which is familiar from the Galerkin finite element method. The book brings together most of the work done over the last decade or so which has been stimulated by Miller's original idea, and discusses the interrelationships between the techniques of the method and the established ideas of the method of characteristics, Hamilton's equations, the Legendre transformation, and grid equidistribution. The book highlights the issues involved and should provide the reader with a clear view of the current state of the subject and prompt further research.

Journal ArticleDOI
TL;DR: The authors described the findings of a 3-year research project on teacher development in which some New Zealand teachers of science were developing their teaching to take into account students' thinking and constructivist views of learning.

Journal ArticleDOI
TL;DR: In this paper, NIMSAD, a Systemic Framework for Understanding and Evaluating Methodologies (NIMSDA), is presented, which is based on the concept of understanding and evaluating methodologies.
Abstract: (1996). Understanding and Evaluating Methodologies: NIMSAD, A Systemic Framework. Journal of the Operational Research Society: Vol. 47, No. 4, pp. 594-595.

Journal ArticleDOI
TL;DR: The results suggested that phonological awareness and complex span tasks make a shared and a unique contribution to the variance in all three cognitive abilities, questioning Daneman and Carpenter's (1980, 1983) domain-specific hypothesis.

Journal ArticleDOI
TL;DR: In this paper, the nitrogen concentrations of a suite of purely type IaA diamonds have been determined by a destructive method involving combustion of the specimens and measurement, by capacitance manometry, of the released nitrogen.
Abstract: The nitrogen concentrations of a suite of thirteen purely type IaA diamonds have been determined by a destructive method involving combustion of the specimens and measurement, by capacitance manometry, of the released nitrogen. These values have been related to measurements of the infrared absorption strength due to nitrogen in the form of A centres, or nitrogen-pair defects, in the specimens. It is found that an absorption coefficient of 1 cm−1, at 1282 wavenumbers, is produced by 16.1 ± 1 at. p.p.m. of nitrogen in this form. This is in good agreement with the values found by inert-gas fusion and by an indirect method described in the previous paper. Application of a statistical analysis to these three consistent sets of results taken collectively suggests that a reliable working value for the absorption strength at 1282 wavenumbers due to the A defect in diamond would be 1cm−1 per 16.5 ±1 at. p.p.m.

Journal ArticleDOI
TL;DR: In this paper, the authors analyse the concept, basic issues and different methods of applying this marketing strategy and propose a strategy to create "safe havens" and business opportunities for many companies.
Abstract: The mass markets of previous decades have splintered into smaller market segments or niches, in which companies could be safer from cut‐throat competition and explore new market opportunities. Although part of a positioning strategy, niche marketing may be used as a deliberate marketing strategy to create “safe havens” and business opportunities for many companies. Aims to analyse the concept, basic issues and different methods of applying this marketing strategy.

Journal ArticleDOI
TL;DR: In this article, it has been shown that a growing normal mode on an African easterly jet is characterized by divergent EP fluxes in the region of the jet, implying both barotropic and baroclinic energy conversions.
Abstract: The linear instability problem of the African easterly jet has been investigated using the primitive equations on a sphere. This has included an examination of the linear growth mechanisms and structure using diagnostics traditionally employed for mid latitudes, such as Eliassen-Palm (EP) fluxes and potential vorticity. It has been shown that a growing normal mode on an African easterly jet is characterized by divergent EP fluxes in the region of the jet, implying both barotropic and baroclinic energy conversions. The linear instability is dominated by the interaction between positive and negative potential vorticity gradients at the level of the jet and, as found in previous studies, the normal modes grow mainly through barotropic energy conversions. Many of the synoptic features associated with the normal modes are in good agreement with those observed, except for the vertical-velocity pattern, which has a ‘checkerboard’ structure in the vertical and is much weaker. Changing the jet latitude while keeping the baroclinicity constant changed the growth rates very little, and although barotropic energy conversions remained dominant, the most unstable modes became more baroclinic when the jet was more poleward. The most unstable modes, which grow on a thinner jet, have a larger growth rate, a smaller wavelength and stronger barotropic energy conversions. The ‘checkerboard’ pattern in the vertical velocity persists with the normal modes which grow on these jets. The effect of including diabatic effects in the linear problem has also been examined. First, a simple boundary-layer scheme was found to have very little effect on the normal modes. With simply parametrized latent heat release however, the growth rates of the most unstable modes were increased slightly and the modes became less dominated by barotropic energy conversions. Also, an asymmetry is found between the ascent and descent regions in the wave, with the length scale of the updraught contracted relative to that of the downdraught. The unrealistic ‘checkerboard’ pattern in the vertical velocity is almost removed and the amplitude is increased. The structure of the normal mode, using a CISK-type scheme for the latent heating, has more in common with the observed structures over west Africa than the structure of the dry modes. It is suggested that African easterly waves may arise through a mixed barotropic/baroclinic instability mechanism where the role of latent heating is important in increasing the baroclinic energy conversions relative to the barotropic energy conversions, and also in determining the synoptic structure.

Journal ArticleDOI
TL;DR: In this article, the authors present an analysis of a two-factor experiment with two treatments and two experiments at different sites in the US and Europe, showing that the regression is linear regression.
Abstract: INTRODUCTION The Need for Statistics Types of Data The Use of Computers in Statistics PROBABILITY AND DISTRIBUTIONS Probability Populations and Samples Means and Variances The Normal Distribution Sampling Distributions ESTIMATION AND HYPOTHESIS TESTING Estimation of the Population Mean Testing Hypotheses about the Population Mean Population Variance Unknown Comparison of Samples A Pooled Estimate of Variance A SIMPLE EXPERIMENT Randomization and Replication Analysis of a Completely Randomized Design with Two Treatments A Completely Randomized Design with Several Treatments Testing Overall Variation Between the Treatments CONTROL OF RANDOM VARIATION BY BLOCKING Local Control of Variation Analysis of a Randomized Block Design Meaning of the Error Mean Square Latin Square Designs Multiple Latin Squares Design The Benefit of Blocking and the Use of Natural Blocks PARTICULAR QUESTIONS ABOUT TREATMENTS Treatment Structure Treatment Contrasts Factorial Treatment Structure Main Effects and Interactions Analysis of Variance for a Two-Factor Experiment Partial Factorial Structure Comparing Treatment Means - Are Multiple Comparison Methods Helpful? MORE ON FACTORIAL TREATMENT STRUCTURE More than Two Factors Factors with Two Levels The Double Benefit of Factorial Structure Many Factors and Small Blocks The Analysis of Confounded Experiments Split Plot Experiments Analysis of a Split Plot Experiment Experiments Repeated at Different Sites THE ASSUMPTIONS BEHIND THE ANALYSIS Our Assumptions Normality Variance Homogeneity Additivity Transformations of Data for Theoretical Reasons A More General Form of Analysis Empirical Detection of the Failure of Assumptions and Selection of Appropriate Transformations Practice and Presentation STUDYING LINEAR RELATIONSHIPS Linear Regression Assessing the Regression Line Inferences about the Slope of a Line Prediction Using a Regression Line Correlation Testing Whether the Regression is Linear Regression Analysis Using Computer Packages MORE COMPLEX RELATIONSHIPS Making the Crooked Straight Two Independent Variables Testing the Components of a Multiple Relationship Multiple Regression Possible Problems in Computer Multiple Regression LINEAR MODELS The Use of Models Models for Factors and Variables Comparison of Regressions Fitting Parallel Lines Covariance Analysis Regression in the Analysis of Treatment Variation NONLINEAR MODELS Advantages of Linear and Nonlinear Models Fitting Nonlinear Models to Data Inferences about Nonlinear Parameters Exponential Models Inverse Polynomial Models Logistic Models for Growth Curves THE ANALYSIS OF PROPORTIONS Data in the Form of Frequencies The 2 ' 2 Contingency Table More than Two Situations or More than Two Outcomes General Contingency Tables Estimation of Proportions Sample Sizes for Estimating Proportions MODELS AND DISTRIBUTIONS FOR FREQUENCY DATA Models for Frequency Data Testing the Agreement of Frequency Data with Simple Models Investigating More Complex Models The Binomial Distribution The Poisson Distribution Generalized Models for Analyzing Experimental Data Log-Linear Models Logit Analysis of Response Data MAKING AND ANALYZING SEVERAL EXPERIMENTAL MEASUREMENTS Different Measurements on the Same Units Interdependence of Different Variables Repeated Measurements Joint (Bivariate) Analysis Indices of Combined Yield Investigating Relationships with Experimental Data ANALYZING AND SUMMARIZING MANY MEASUREMENTS Introduction to Multivariate Data Principal Component Analysis Covariance or Correlation Matrix Cluster Analysis Similarity and Dissimilarity Measures Hierarchical Clustering Comparison of PCA and Cluster Analysis CHOOSING THE MOST APPROPRIATE EXPERIMENTAL DESIGN The Components of Design Units and Treatments Replication and Precision Different Levels of Variation and Within-Unit Replication Variance Components and Split Plot Designs Randomization Managing with Limited Resources Factors with Quantitative Levels Screening and Selection On-Farm Experiments SAMPLING FINITE POPULATIONS Experiments and Sample Surveys Simple Random Sampling Stratified Random Sampling Cluster Sampling, Multistage Sampling and Sampling Proportional to Size Ratio and Regression Estimates REFERENCES APPENDIX INDEX

Journal ArticleDOI
TL;DR: In this article, thermal energy storage in some fatty acids as phase-change materials has been investigated for a domestic water heating system, and the selected fatty acids were myristic acid, palmitic acid and stearic acid.

Journal ArticleDOI
TL;DR: In this paper, the effect of mixed-phase clouds on radiative transfer was investigated using Mie scattering theory, and it was found that, because the radiative properties of ice crystals and liquid droplets are significantly different, the mixed phase clouds cannot be simulated successfully if the ice in clouds is converted into liquid water.
Abstract: Radiative parametrizations for both ice and water clouds are developed in terms of liquid/ice water content, based on Mie scattering theory. For ice crystals the application of Mie theory is guided by the hexagonal-crystal/equivalent-spheres comparison of Takano and Liou. These parametrizations are extensively tested against measurements from aircraft and are shown to perform satisfactorily, although corrections for unobserved small crystals and the effect of crystal shape are large and not currently well defined. The parametrizations are then used to investigate the effect of mixed-phase clouds on radiative transfer. It is found that, because the radiative properties of ice crystals and liquid droplets are significantly different, the radiative properties of mixed-phase clouds cannot be simulated successfully if the ice in clouds is converted into liquid water. Both the albedo and the rate of change of albedo with ice fraction are significantly dependent on the method by which the phases are mixed; these factors may be of especial importance in climate-sensitivity experiments that incorporate mixed-phase clouds. The presence of ice in clouds below the cirrus level is often ignored in climate-model and radiation-budget studies. The calculations presented here indicate that this neglect may lead to a serious bias in cloud albedo for a given path of condensed water.

Journal ArticleDOI
TL;DR: Pt/Al 2 O 3 and Pd/Al O 3 catalysts have been investigated for the combustion of methane under lean, stoichiometric, and rich conditions using dilute mixtures as discussed by the authors.
Abstract: Pt/Al 2 O 3 and Pd/Al 2 O 3 catalysts have been prepared from chlorine-free precursors and investigated for the combustion of methane under lean, stoichiometric, and rich conditions using dilute mixtures. It has been found that under lean conditions, and at low conversions under stoichiometric or rich conditions, Pd/Al 2 O 3 is a more effective catalyst. However, at higher conversions with stoichiometric or rich mixtures Pt/Al 2 O 3 is a more active catalyst. This change over between Pd/Al 2 O 3 and Pt/Al 2 O 3 is associated with a ‘light-off’ effect observed with Pt/Al 2 O 3 catalysts. Various possible explanations for these effects are discussed. With the Pt/Al 2 O 3 catalysts there is no evidence of a particle size effect, which is in contrast to reports in the literature that the methane combustion reaction is structure sensitive. Reasons for these variations, including the possible inhibition of activity by chlorine used in many catalyst preparations, are discussed. It is concluded that platinum can be a more effective catalyst than palladium for methane combustion under real conditions and that, in consequence, platinum may play an important role in multimetallic catalysts for emission control for natural gas vehicles.

Journal ArticleDOI
TL;DR: In this article, a technique is introduced by which high-resolution tracer fields may be constructed from low-resolution satellite observations, relying upon the continual cascade of tracer variance from large to small scales and makes use of wind fields generated by a data assimilation scheme.
Abstract: A technique is introduced by which high-resolution tracer fields may be constructed from low-resolution satellite observations. The technique relies upon the continual cascade of tracer variance from large to small scales and makes use of wind fields generated by a data assimilation scheme. To demonstrate its usefulness, the technique has been applied in a study of isentropic distributions of nitrous oxide in the winter midstratosphere, using measurements made by the Improved Stratospheric and Mesospheric Sounder instrument on the Upper Atmosphere Research Satellite. The results show that the high-resolution fields significantly increase the amount of information that is available from the satellite observations. The fields give insights into the characteristic structure and evolution of tracer distributions at scales that are normally obscured from view. Two results are particularly noteworthy. First, at the interface between low and middle latitudes there is evidence of active mixing. This mixi...

Journal ArticleDOI
TL;DR: In this paper, the authors measured the velocities and attenuations of compressional and shear waves in 29 water-saturated samples of sandstones and shales at a confining pressure of 60 MPa and at frequencies of about 0.85 MHz.
Abstract: The authors have measured the velocities and attenuations of compressional and shear waves in 29 water-saturated samples of sandstones and shales at a confining pressure of 60 MPa and at frequencies of about 0.85 MHz. The measurements were made using a pulse echo method in which the samples (diameter 5 cm, length 1.5 cm to 2.5 cm) were placed between perspex buffer rods inside a high-pressure cell. The velocity of each seismic wave was determined from the travel time difference of equivalent phase points (corrected for diffraction effects) of the signals reflected from the top and from the base of each samples. Attenuation was determined in a similar way by comparison of the diffraction corrected amplitudes of the signals. The attenuation data are presented as quality factors'': Q[sub p] and Q[sub s] for compressional and shear waves respectively and shear waves respectively. The results show that Qs is strongly correlated with V[sub s], that Q[sub p] is weakly correlated with V[sub p], and that Q[sub p] is strongly correlated with Q[sub s] [center dot] Q[sub p] is strongly dependent on the volume percentage of the assemblage of intra-pore minerals, whether they are clays or carbonates. It is concluded that themore » attenuation mechanism is due to the local fluid flow arising from the differential dilation of the solid rock frame and the intra-pore mineral assemblage, which is a results of their very different elastic moduli.« less

Journal ArticleDOI
TL;DR: A diagnostic study of a mid-latitude cyclone has been carried out using routinely available numerical weather-prediction model products and imagery as discussed by the authors, and the results are believed to have some generality.
Abstract: A diagnostic study of a mid-latitude cyclone has been carried out using routinely available numerical weather-prediction model products and imagery. The cyclone was intense but not exceptionally so, and the results are believed to have some generality. The detailed description of the cyclone structure, just before it began to deepen rapidly, integrates concepts from a number of researchers into a common framework. A dominant feature of the cyclone, close to its centre, was the ‘cloud head’: a region of cloud with a sharp convex outer edge, which formed poleward of the main polar-front cloud band. The cloud head was caused by two flows that entered it from the east, ascending and fanning out within it. One flow (the ‘cold conveyor belt’) brought low wet-bulb potential temperature (θw) air back into the cloud head from low levels ahead of the warm front. The other flow was due to high-θw air that peeled off from the base of the main warm-sector airflow (i.e. part of the ‘warm conveyor belt’) and travelled in the boundary layer back towards the cyclone centre, first undercutting dry air that had earlier descended from the upper troposphere (called a ‘dry intrusion’), and then ascending at the upper boundary of the cloud head, above the cold conveyor belt. The transverse circulation that gave the ascent within the cloud head also led to the cold front fracturing along its length into two separate sharp surface cold fronts, with a more diffuse frontal region in between (‘frontal fracture’). The two sharp surface cold fronts were associated with narrow cold-frontal rainbands (‘line convection’), one of the line-convection segments forming the southern edge of the cloud head. The overrunning of the dry intrusion in the region of the frontal fracture led to a structure (known as a ‘split front’) in which an upper-level humidity front began to run ahead of the position of the surface cold front. A feature of the cyclone at this intermediate stage in its evolution was that a large proportion of the precipitation was being generated by ascent of relatively cold air (the cold conveyor belt) in the cloud head as part of the thermally indirect circulation at the left exit of a developing secondary upper-level jet.

Journal ArticleDOI
TL;DR: In this article, the selective reduction of nitric oxide by methane or ethane, in the presence and in the absence of a large excess of oxygen, has been investigated on Cu/ZSM-5, Co/ZM-5 and Pt/Zm-5 catalysts over a wide range of temperatures.
Abstract: The selective reduction of nitric oxide by methane or ethane, in the presence and in the absence of a large excess of oxygen, has been investigated on Cu/ZSM-5, Co/ZSM-5, Rh/ZSM-5 and Pt/ZSM-5 catalysts over a wide range of temperatures. It has been found that the maximum nitric oxide conversion is higher with ethane than with methane and the temperature of this maximum is lower with ethane. In the absence of oxygen the order of activity is Rh/ZSM-5>Pt/ZSM-5>Co/ZSM-5 > Cu/ZSM-5 with the Cu/ZSM-5 being essentially inactive, while in the presence of oxygen the order is: Rh/ZSM-5>Co/ZSM-5>Cu/ZSM-5 > Pt/ZSM-5 when ethane is used as reductant and: Rh/ZSM-5>Co/ZSM-5 > Cu/ZSM-5>Pt/ZSM-5 when methane is used. The effect of the oxygen content has been investigated for the Co/ZSM-5 catalyst. It has been found that with a small quantity of oxygen the catalytic activity decreases markedly; with higher oxygen content the activity of the catalyst rises again. It appears that two different reaction schemes may be operative, one in the absence of oxygen the other in the presence of oxygen. It is concluded that neither carbonaceous deposits, nor nitrogen dioxide formation in the gas phase are important in the reaction mechanism on metal-containing zeolites. It is proposed that the reaction is essentially a redox process in which decomposition of nitric oxide occurs on reduced metallic or metal ion sites (the relative activity of each of these depending on the choice of metal), leading to the formation of gaseous nitrogen and adsorbed oxygen, followed by the removal of the adsorbed oxygen by the hydrocarbon, thus recreating the active centres.

Journal ArticleDOI
TL;DR: Using an anti‐receptor mAb that blocks the attachment of echovirus 7 and related viruses (echoviruses 13, 21, 29 and 33), a complementary DNA clone that encodes the human decay‐accelerating factor (CD55) is isolated.
Abstract: Using an anti-receptor mAb that blocks the attachment of echovirus 7 and related viruses (echoviruses 13, 21, 29 and 33), we have isolated a complementary DNA clone that encodes the human decay-accelerating factor (CD55). Mouse cells transfected with the CD55 clone bind echovirus 7, and this binding is blocked by the anti-receptor mAb. The method used (CELICS) allows rapid and direct cloning of genes encoding cell surface receptors. It is based on episomal replication and high efficiency expression of complementary DNA clones in the vector pCDM8 in COS or WOP cells, in conjunction with a sensitive immuno-focal screen that uses antibody probes linked to beta-galactosidase. Receptor positive cells were identified by a colour change and isolated individually using a micromanipulator. DNA extracted from a small number of cells was then cloned directly in Escherichia coli.

Journal ArticleDOI
TL;DR: In this paper, the UK Meteorological Office diagnose transient eddy activity for the winter season of two ten-year equilibrium GCM integrations carried out at the UK Met Office, one with present-day levels of carbon dioxide concentration (control) and one with doubled carbon dioxide (2CO2).
Abstract: Transient eddy activity has been diagnosed for the winter season of two ten-year equilibrium GCM integrations carried out at the UK Meteorological Office, one with present-day levels of carbon dioxide concentration (control) and one with doubled carbon dioxide (2CO2). On synoptic timescales, indicators of storm-track activity such as eddy kinetic energy are shifted northwards and intensified downstream in the 2CO2 experiment relative to the control. This effect is particularly marked for the Atlantic storm track. These patterns correspond closely to changes in relevant diagnostics of the time mean, such as the Eady growth rate and the diabatic heating. In the latter, the downstream intensification is effected by a decrease in the sensible heating and an increase in the latent heating in a warmer, moister atmosphere. Changes in the jet structure are consistent with changes in baroclinicity and eddy forcing. The total zonal-mean poleward energy transport is only slightly different between the two experiments. However, the component of this transport due to transient eddies has a different character when the carbon dioxide is doubled. In particular, the moist contribution to the transient energy flux is enhanced.

Journal ArticleDOI
TL;DR: In this article, a wide range of macro-and micro-structures are associated with calcretes and profile types and stages in profile development can be defined, which can be used to identify the nature of the prevailing climate, although hydromorphic effects related to marine flooding of the platforms can modify the paleosols.