Home About us Contact
|
Home About us Contact | ||
|
|
||
Single Model (single + model)
Selected AbstractsUse of response functions in selecting lodgepole pine populations for future climatesGLOBAL CHANGE BIOLOGY, Issue 12 2006T. WANG Abstract Although growth response functions have previously been developed for lodgepole pine (Pinus contorta Dougl. ex Loud.) populations in British Columbia, new analyses were conducted: (1) to demonstrate the merit of a new local climate model in genecological analysis; (2) to highlight new methods for deriving response functions; and (3) to evaluate the impacts of management options for existing geographically defined seed planning units (SPUs) for reforestation. Results of this study suggest that new methods for anchoring population response functions, and a multivariate approach for incorporating climate variables into a single model, considerably improve the reliability of these functions. These functions identified a small number of populations in central areas of the species distribution with greater growth potential over a wide range of mean annual temperature (MAT). Average productivity of lodgepole pine is predicted to increase (up to 7%) if moderate warming (,2°C MAT) occurs in the next few decades as predicted, although productivity would substantially decline in some SPUs in southern BC. Severe global warming (>3°C MAT) would result in either a drastic decline in productivity or local populations being extirpated in southern SPUs. New deployment strategies using the best seed sources for future reforestation may not only be able to mitigate the negative impact of global warming, but may even be able to increase productivity in some areas. [source] Global Markets and National Regulation: The Protection of Shareholder Interests in Germany and ItalyGOVERNMENT AND OPPOSITION, Issue 1 2007Dermot McCann Global market integration is widely perceived as presenting a major challenge to the sustainability of many national economic regulatory systems. There is far less agreement, however, about precisely how these pressures feed into the politics of reform and reshape national public policy. This article will seek to cast light on this relationship by identifying four influential ,models of linkage' between global pressures and regulatory change. It will then comparatively assess their capacity to elucidate the progress of shareholder protection reform in Germany and Italy. While no single model proves fully satisfactory, it will be argued that the weaknesses of two of them can be largely overcome through a process of refinement and integration. [source] Bed-sharing practices of initially breastfed infants in the first 6 months of lifeINFANT AND CHILD DEVELOPMENT, Issue 4 2007Helen L. BallArticle first published online: 28 AUG 200 Abstract This paper explores the manner in which bed-sharing is practised by breastfeeding infants in the UK, and examines how alternate definitions and interpretations of breastfeeding and bed-sharing can lead to confusion in understanding what bed-sharing entails. Longitudinal studies on parent,infant bed-sharing practices are scarce, but are vital to our understanding of normative bed-sharing behaviour. We present data from a longitudinal study of sleeping and feeding practices in England involving 97 initially breastfed infants from birth to 6 months of age whose behaviour was monitored weekly for a 6-month period. Results demonstrate that bed-sharing practices covary with breastfeeding practices, and that a single model of bed-sharing behaviour does not adequately reflect the experience of all infants. Our findings have ramifications for the way in which case,control studies attempt to ,measure' bed-sharing, and our understanding and interpretation of bed-sharing risk factors. Copyright © 2007 John Wiley & Sons, Ltd. [source] Do consumption expenditures depend on the household's relative position in the income distribution?INTERNATIONAL JOURNAL OF CONSUMER STUDIES, Issue 1 2002Mohamed Abdel-Ghany Abstract Even though the permanent income and relative income hypotheses have been introduced in past research to explain consumer behaviour, no previous attempt was undertaken to integrate them in one model. In this article, the hypotheses were synthesized into a single model. The model was empirically tested using data from the 1996 Canadian Family Expenditure Survey. The results indicate that household consumption behaviour is generally explained by both hypotheses when integrated into one model, contrary to previously treating them as mutually exclusive hypotheses. [source] Conventional and unconventional approaches to exchange rate modelling and assessmentINTERNATIONAL JOURNAL OF FINANCE & ECONOMICS, Issue 1 2008Ron Alquist Abstract We examine the relative predictive power of the sticky price monetary model, uncovered interest parity, and a transformation of net exports and net foreign assets. In addition to bringing Gourinchas and Rey's new approach and more recent data to bear, we implement the Clark,West procedure for testing the significance of out-of-sample forecasts. The interest rate parity relation holds better at long horizons and the net exports variable does well in predicting exchange rates at short horizons in sample. In out-of-sample forecasts, we find evidence that our proxy for Gourinchas and Rey's measure of external imbalances outperforms a random walk at short horizons as do some of the other models, although no single model uniformly beats the random walk forecast. Copyright © 2007 John Wiley & Sons, Ltd. [source] Introduction of an intensive case management style of delivery for a new mental health serviceINTERNATIONAL JOURNAL OF MENTAL HEALTH NURSING, Issue 3 2006Catherine Hangan ABSTRACT:,Mental health case management emerged in the 1960s in response to the shift in focus from inpatient to community care. Case management per se had been used by other service industries for some time previously, particularly those involved with people with intellectual disability. The term case management describes a range of service approaches and strategies in mental health rather than a single model of care. One method of delivering case management is with an intensive model of care. Intensive case management is differentiated from other forms of case management through factors like a smaller caseload size, team management, outreach emphasis, a decreased brokerage role, and an assertive approach to maintaining contact with clients. Research has demonstrated that case management, in particular, intensive case management, can improve clients' and families' experience of mental health services but only when introduced and used for appropriately targeted client populations and suitably resourced. Determining which model of case management best suits the client population and how to introduce it is a major challenge for any mental health service. With a focus on intensive case management, a review of this process is outlined. [source] Numerical analysis on thermal characteristics for chip scale package by integrating 2D/3D modelsINTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 1 2009Ping Yang Abstract The objective of this paper is to investigate stress and strain of a special scale package-substrate on chip for reliability evaluation or manufacture strategy in deep-seated situation. A two-dimensional model with one-half of cross-section (2D model) and a three-dimensional model with one-fourth of whole package (3D model) were built, respectively, to simulate the thermal stress and strain of CSP-SOC under the condition of the standard industry thermal cycling temperature ,40 to125°C. The different locations can be processed by using the two models, respectively, based on different modeling simplified modes. By using 2D model, the numerical simulation shows that the maximum deformation of the prototype occurs in printed circuit board (PCB), the maximum stress and strain occurs in the outer solder balls. In the meantime, by the results of 3D model, the simulation shows that the maximum elastic strain occurs in the interface between the solder balls and PCB, the minimum strain occurs in the underfill tape, the maximum packaging stress occurs in the edge area of the chip. The result from 3D model maybe more impersonal to reflect the stress and strain characteristics because the third direction is considered in modeling. The analysis by integrating the 2D model and 3D model can get a more comprehensive profile for the thermal investigation of chip scale package (CSP) than by using any single model. The investigation built a basis for improving reliability in engineering design of CSP product. Copyright © 2008 John Wiley & Sons, Ltd. [source] Change in Motor Function and Risk of Mortality in Older PersonsJOURNAL OF AMERICAN GERIATRICS SOCIETY, Issue 1 2007Aron S. Buchman MD OBJECTIVES: To assess the association between change in motor function and mortality. DESIGN: Prospective, observational cohort study. SETTING: Approximately 40 retirement communities across the Chicago metropolitan area participating in the Rush Memory and Aging Project. PARTICIPANTS: Eight hundred thirty-seven community-based older persons without dementia. MEASUREMENTS: Change in composite measures of motor performance and muscle strength. RESULTS: During a mean follow-up of 2.2 years, 81 persons died. In a proportional hazards model adjusted for age, sex, education, and body mass index, each 1-unit increase in the level of baseline motor performance was associated with an approximately 10% decrease in risk of mortality (hazard ratio (HR)=0.901, 95% confidence interval (CI)=0.863,0.941), and each unit of annual increase in motor performance was associated with an approximately 11% decrease in the risk of mortality (HR=0.887, 95% CI=0.835,0.942). In a similar model, each 1-unit increase in the level of baseline strength was associated with an approximately 9% decrease in the risk of mortality (HR=0.906, 95% CI=0.859,0.957), and each 1-unit annual increase in strength was associated with an approximately 10% decrease in the risk of mortality (HR=0.898, 95% CI=0.809,0.996). These results were similar when men and women were analyzed separately and after controlling for physical activity, cognition, and chronic disorders. When motor performance and muscle strength were examined in a single model, only baseline and annual change in motor performance were associated with mortality. CONCLUSION: Level and rate of change in strength and motor performance are associated with mortality. The attenuation of the association between strength and mortality by motor performance suggests that motor function is not a unitary process and that its components may vary in their associations with adverse health consequences in older persons. [source] Estimation of immigration rate using integrated population modelsJOURNAL OF APPLIED ECOLOGY, Issue 2 2010Fitsum Abadi Summary 1.,The dynamics of many populations is strongly affected by immigrants. However, estimating and modelling immigration is a real challenge. In the past, several methods have been developed to estimate immigration rate but they either require strong assumptions or combine in a piecewise manner the results from separate analyses. In most methods the effects of covariates cannot be modelled formally. 2.,We developed a Bayesian integrated population model which combines capture,recapture data, population counts and information on reproductive success into a single model that estimates and models immigration rate, while directly assessing the impact of environmental covariates. 3.,We assessed parameter identifiability by comparing posterior distributions of immigration rates under varying priors, and illustrated the application of the model with long term demographic data of a little owl Athene noctua population from Southern Germany. We further assessed the impact of environmental covariates on immigration. 4.,The resulting posterior distributions were insensitive to different prior distributions and dominated by the observed data, indicating that the immigration rate was identifiable. Average yearly immigration into the little owl population was 0·293 (95% credible interval 0·183,0·418), which means that ca 0·3 female per resident female entered the population every year. Immigration rate tended to increase with increasing abundance of voles, the main prey of little owls. 5.Synthesis and applications. The means to estimate and model immigration is an important step towards a better understanding of the dynamics of geographically open populations. The demographic estimates obtained from the developed integrated population model facilitate population diagnoses and can be used to assess population viability. The structural flexibility of the model should constitute a useful tool for wildlife managers and conservation ecologists. [source] Model uncertainty in cross-country growth regressionsJOURNAL OF APPLIED ECONOMETRICS, Issue 5 2001Carmen Fernández We investigate the issue of model uncertainty in cross-country growth regressions using Bayesian Model Averaging (BMA). We find that the posterior probability is spread widely among many models, suggesting the superiority of BMA over choosing any single model. Out-of-sample predictive results support this claim. In contrast to Levine and Renelt (1992), our results broadly support the more ,optimistic' conclusion of Sala-i-Martin (1997b), namely that some variables are important regressors for explaining cross-country growth patterns. However, care should be taken in the methodology employed. The approach proposed here is firmly grounded in statistical theory and immediately leads to posterior and predictive inference. Copyright © 2001 John Wiley & Sons, Ltd. [source] USE OF NONLINEAR DIFFERENTIAL VISCOELASTIC MODELS TO PREDICT THE RHEOLOGICAL PROPERTIES OF GLUTEN DOUGHJOURNAL OF FOOD PROCESS ENGINEERING, Issue 3 2001M. DHANASEKHARAN ABSTRACT Nonlinear viscoelastic models of the differential type, such as the Phan Thien Tanner model, White-Metzner model and Giesekus model were used to predict the steady shear, oscillatory shear and transient shear properties of gluten dough. The predictions were compared with new data and the experimental results of Wang and Kokini (1995b). The Phan-Thien Tanner model and the Giesekus model were used in eight modes to fit the relaxation modulus accurately. The White-Metzner model gave the best prediction for the steady shear properties as it used a Bird-Carreau dependence for the shear viscosity. The Phan-Thien Tanner model and the Giesekus model predicted the transient shear viscosity and the transient first normal stress coefficient better than the White-Metzner model. A consistent prediction of all the experimental data could not be obtained using a single model. [source] AN EVALUATION OF THE AVAILABLE TECHNIQUES FOR ESTIMATING MISSING FECAL COLIFORM DATA,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 6 2004Ashu Jain ABSTRACT: This paper presents the findings of a study aimed at evaluating the available techniques for estimating missing fecal coliform (FC) data on a temporal basis. The techniques investigated include: linear and nonlinear regression analysis and interpolation functions, and the use of artificial neural networks (ANNs). In all, seven interpolation, two regression, and one ANN model structures were investigated. This paper also investigates the validity of a hypothesis that estimating missing FC data by developing different models using different data corresponding to different dynamics associated with different trends in the FC data may result in a better model performance. The FC data (counts/100 ml) derived from the North Fork of the Kentucky River in Kentucky were employed to calibrate and validate various models. The performance of various models was evaluated using a wide variety of standard statistical measures. The results obtained in this study are able to demonstrate that the ANNs can be preferred over the conventional techniques in estimating missing FC data in a watershed. The regression technique was not found suitable in estimating missing FC data on a temporal basis. Further, it has been found that it is possible to achieve a better model performance by first decomposing the whole data set into different categories corresponding to different dynamics and then developing separate models for separate categories rather than developing a single model for the composite data set. [source] Empirical Modeling of Butyl Acrylate/Vinyl Acetate/Acrylic Acid Emulsion-Based Pressure-Sensitive AdhesivesMACROMOLECULAR MATERIALS & ENGINEERING, Issue 5 2004Renata Jovanovic Abstract Summary: Butyl acrylate/vinyl acetate/acrylic acid (BA/VAc/AA) emulsion latexes were produced in a semi-batch mode. The objective was to generate polymers with properties favoring their application as pressure-sensitive adhesives. The influence of the individual monomer concentrations on final properties such as glass transition temperature (Tg), peel strength, shear strength and tack was investigated. To obtain the maximum amount of information in a reasonable number of runs, a constrained three-component mixture design was used to define the experimental conditions. Latexes were coated onto a polyethylene terephthalate carrier and dried. Different empirical models (e.g. linear, quadratic and cubic mixture models) governing the individual properties (i.e. Tg, peel adhesion, shear resistance and tack) were developed and evaluated. In the given experimental region, no single model was found to fit all of the responses (i.e. the final properties). However, in all models the most significant factor affecting the final properties was the AA concentration, followed by the VAc concentration. Shear strength contour lines over the investigated region. [source] Adaptive neuro-fuzzy inference system for computing patch radius of circular microstrip antennasMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 8 2006Kerim Guney Abstract A new method based on the adaptive neuro-fuzzy inference system (ANFIS) is presented to calculate accurately the patch radius of circular microstrip antennas (MSAs). ANFIS combines the benefits of artificial neural networks (ANNs) and fuzzy inference systems (FISs) in a single model. A hybrid learning algorithm based on the least-squares method (LSM) and the backpropagation algorithm is used to identify the parameters of ANFIS. The results of ANFIS are in very good agreement with the experimental results reported elsewhere. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1606,1610, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21695 [source] The Dalai Lamas and State Power1RELIGION COMPASS (ELECTRONIC), Issue 2 2007Derek F. Maher This article explores the evolving political standing of members of the Dalai Lama incarnation lineage. I survey the history of Tibet since the time of Tsong kha pa, the original inspiration for the dGe lugs School, showing how each Dalai Lama established his own position with an ever evolving set of external circumstances framed by rival schools, patrons, Mongolian khans, Chinese emperors, the nobility, the powerful monasteries, and their own regents. I conclude that there is no single model that captures the nature of the relationship between the Dalai Lamas and state power. [source] Can multi-model combination really enhance the prediction skill of probabilistic ensemble forecasts?THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 630 2008A. P. Weigel Abstract The success of multi-model ensemble combination has been demonstrated in many studies. Given that a multi-model contains information from all participating models, including the less skilful ones, the question remains as to why, and under what conditions, a multi-model can outperform the best participating single model. It is the aim of this paper to resolve this apparent paradox. The study is based on a synthetic forecast generator, allowing the generation of perfectly-calibrated single-model ensembles of any size and skill. Additionally, the degree of ensemble under-dispersion (or overconfidence) can be prescribed. Multi-model ensembles are then constructed from both weighted and unweighted averages of these single-model ensembles. Applying this toy model, we carry out systematic model-combination experiments. We evaluate how multi-model performance depends on the skill and overconfidence of the participating single models. It turns out that multi-model ensembles can indeed locally outperform a ,best-model' approach, but only if the single-model ensembles are overconfident. The reason is that multi-model combination reduces overconfidence, i.e. ensemble spread is widened while average ensemble-mean error is reduced. This implies a net gain in prediction skill, because probabilistic skill scores penalize overconfidence. Under these conditions, even the addition of an objectively-poor model can improve multi-model skill. It seems that simple ensemble inflation methods cannot yield the same skill improvement. Using seasonal near-surface temperature forecasts from the DEMETER dataset, we show that the conclusions drawn from the toy-model experiments hold equally in a real multi-model ensemble prediction system. Copyright © 2008 Royal Meteorological Society [source] Modeling discrete heterogeneity in X-ray diffraction data by fitting multi-conformersACTA CRYSTALLOGRAPHICA SECTION D, Issue 10 2009Henry Van Den Bedem The native state of a protein is regarded to be an ensemble of conformers, which allows association with binding partners. While some of this structural heterogeneity is retained upon crystallization, reliably extracting heterogeneous features from diffraction data has remained a challenge. In this study, a new algorithm for the automatic modelling of discrete heterogeneity is presented. At high resolution, the authors' single multi-conformer model, with correlated structural features to represent heterogeneity, shows improved agreement with the diffraction data compared with a single-conformer model. The model appears to be representative of the set of structures present in the crystal. In contrast, below 2,Å resolution representing ambiguous electron density by correlated multi-conformers in a single model does not yield better agreement with the experimental data. Consistent with previous studies, this suggests that variability in multi-conformer models at lower resolution levels reflects uncertainty more than coordinated motion. [source] Colored timed Petri nets for modeling and analysis of cluser tools,ASIAN JOURNAL OF CONTROL, Issue 3 2010NaiQi Wu Abstract In this paper, a colored timed resource-oriented Petri net (CTROPN) is developed to model the cluster tools in semiconductor fabrication. It is structurally simple and concise, since each module in a cluster tool corresponds to a unique place in CTROPN. It is also powerful in modeling the qualitative and temporal behavior of the cluster tools with a single-blade or dual-blade robot. The initial transient behavior, steady-state behavior and the final transient behavior can all be investigated through a single model. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] Real-Time Control and Identification of a Thermal Process Based on Multiple-Modeling ApproachASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2005A. Aminzadeh This article presents implementation of Real-Time Control and Identification algorithms based on a Multiple-Modeling approach for an experimental thermal process. The thermal process is a nonlinear plant; therefore, based on variations of the input and disturbance, four local operating regimes are defined. The linear local ARMAX models are identified for different regimes and integrated into a NARMAX model by combining them via proper validity and interpolation functions. Results of modeling the plant with a single model and multiple models show superior performance of the Multiple-Modeling technique which is also more flexible. Moreover, the Real-Time Control of the plant with four locally designed controllers is addressed. The platform used for the Real-Time implementation is Matlab/Simulink/Real-Time-Workshop with Visual C++ and Watcom compilers using a DAQ interface. The Real-Time application of the global controller based on the Multiple-Model approach demonstrates excellent performance for this design when compared to a single PID controller. [source] HIERARCHICAL BAYESIAN MODELLING OF SOCIAL VARIATION IN THE AGE DEPENDENCE OF DISABILITY PREVALENCEAUSTRALIAN & NEW ZEALAND JOURNAL OF STATISTICS, Issue 4 2005Patrick Graham Summary Motivated by a study of social variation in the relationship of functional limitation prevalence to age, this paper examines methods for modelling social variation in health outcomes. It is argued that, from a Bayesian perspective, modelling the dependence of functional limitation prevalence on age separately for each social group, corresponds to an implausible prior model, in addition to leading to imprecise estimates for some groups. The alternative strategy of fitting a single model, perhaps including some age-by-group interactions but omitting higher-order interactions, requires a strong prior commitment to the absence of such effects. Hierarchical Bayesian modelling is proposed as a compromise between these two analytical approaches. Under all hierarchical Bayes analyses there is strong evidence for an ethnic group difference in limitation prevalence in early- to mid-adulthood among tertiary-qualified males. In contrast, the single-model approach largely misses this effect, while the group-specific analyses exhibit an unrealistically large degree of heterogeneity in gender-education-specific ethnicity effects. The sensitivity of posterior inferences to prior specifications is studied. [source] Revisiting the concept of lineage in prokaryotes: a phylogenetic perspectiveBIOESSAYS, Issue 5 2009Yan Boucher Abstract Mutation and lateral transfer are two categories of processes generating genetic diversity in prokaryotic genomes. Their relative importance varies between lineages, yet both are complementary rather than independent, separable evolutionary forces. The replication process inevitably merges together their effects on the genome. We develop the concept of "open lineages" to characterize evolutionary lineages that over time accumulate more changes in their genomes by lateral transfer than by mutation. They contrast with "closed lineages," in which most of the changes are caused by mutation. Open and closed lineages are interspersed along the branches of any tree of prokaryotes. This patchy distribution conflicts with the basic assumptions of traditional phylogenetic approaches. As a result, a tree representation including both open and closed lineages is a misrepresentation. The evolution of all prokaryotic lineages cannot be studied under a single model unless new phylogenetic approaches that are more pluralistic about lineage evolution are designed. [source] Critical Aspects of Organizational Learning Research and Proposals for Its MeasurementBRITISH JOURNAL OF MANAGEMENT, Issue 2 2001Satu Lähteenmäki Based on an extensive literature review, this paper reveals several gaps in organizational learning (OL) research that need filling before we can really talk about a theory of organizational learning or verify the traits and very existence of learning organizations (LO) as a phenomenon. The critique, however, is not targeted at any single model or theory of organizational learning, but at theory building, which constantly drifts away with new definitions and approaches that break up rather than construct a theory. Despite the fact that numerous consultation tools for turning organizations into learning models have been developed and applied, the concept of organizational learning itself still remains vague and there is an urgent need for a holistic model of OL. Too much emphasis is put on studying the learning of individuals instead of concentrating on the learning of organizations. Since the theory is highly dispersed and does not really build on earlier findings, rich empirical studies are needed in order to validate measures of organizational learning. Modelling of the organizational learning process and clarification of how learning of individuals is turned into learning of organizations is needed. This paper introduces one set of OL measures developed to study whether organizational learning occurred during the operational and business culture change process of a single case company. Suggestions for further OL research are made on the basis of experiences gained when empirically testing this model. [source] Behind the Screen: The Role of State-TV Relationships in Russia, 1990,2000,CANADIAN REVIEW OF SOCIOLOGY/REVUE CANADIENNE DE SOCIOLOGIE, Issue 2 2006JULIA ROZANOVA Les systèmes de régulation de la production des programmes télévisuels sont aussi importants dans les études des médias que l'analyse du corps d'un texte. l'économie politique rend possible l'étude des programmes télévisuels et des systèmes de régulation de la production télévisuelle dans un seul modèle de même que leurs interconnections. Deux systèmes régulateurs de télévision sont décrits, et les dynamiques de leur transformation sont présentées. Les résultats des entrevues avec les fonctionnaires de l'industrie télévisuelle sont utilisés pour examiner l'influence des relations entre l'État et les entreprises de télévision sur le contenu des programmes produits par la télévision russe entre 1990 et 2000. This paper argues that the content of television programs is influenced by how their production is organized and regulated. The political-economic approach provides a useful framework to link television programs and the regulation of TV production within a single model, and to investigate their interrelationship. Two systems of TV regulation are described in this paper and their evolution is discussed. Data from in-depth qualitative interviews with Russian television industry insiders are used to examine the impact of changes in the regulation of television on the types and content of programs produced between 1990 and 2000. [source] Kinetic Reaction Models for the Selective Reduction of NO by Methane over Multifunctional Zeolite-based Redox CatalystsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 12 2004T. Sowade Abstract Kinetic measurements of the selective catalytic reduction (SCR) of NO by methane were performed over CeO2/H-ZSM-5, In-ZSM-5, and CeO2/In-ZSM-5 catalysts. The parameter space covered NO, CH4, and O2 concentrations varying from 250 to 1000 ppm, from 500 to 2000 ppm, and from 0.5 to 10,vol.-%, respectively, space velocities between 5000 and 90000 h,1 and temperatures between 573 and 873 K depending on the catalyst activities. With CeO2/In-ZSM-5 an additional series of measurements was performed with moistened feed gas (0.5,10,vol.-% H2O). On the basis of a pseudo-homogeneous, one-dimensional fixed-bed reactor model, the data were fitted to a kinetic model that includes power rate laws for the reduction of NO and for the unselective total oxidation of methane. From analyses of isothermal data sets, almost all reaction orders were found to vary significantly with changing temperature, which indicates that the simple kinetic model cannot reflect the complex reaction mechanism correctly. Nevertheless, the data measured with In-ZSM-5 could be modeled with good accuracy over a wide range of reaction temperatures (150 K) while the accuracy was less satisfactory with the remaining data sets, in particular for data with the moist feed over CeO2/In-ZSM-5. With the latter catalyst it was not possible to represent the data measured in dry and in moist feed in a single model even upon confinement to fixed reaction temperatures. A comparison of the separate models established showed strong changes in the reaction orders in the presence of water, which occur apparently already at a very low water content (,,0.5,vol.-%). The kinetic parameters found are in agreement with earlier conclusions about the reaction mechanisms. With In-ZSM-5, both reaction orders and the activation energy show a rate-limiting influence of NO oxidation on the NO reduction path which is removed by the presence of the CeO2 promoter. A difference in the reaction mechanism over CeO2/In-ZSM-5 and CeO2/H-ZSM-5 is reflected in different kinetic parameters. The differences of the kinetic parameters between dry-feed and moist-feed models for CeO2/In-ZSM-5 reflect adsorption competition between the reactants and water. [source] | ||||||||||||||||||||||||||||