Página 1 dos resultados de 747 itens digitais encontrados em 0.033 segundos

‣ Análise crítica da utilização de modelagem matemática na avaliação da dispersão de efluentes leves no litoral da Baixada Santista ( Estado de São Paulo).; The analysis of mathematical models in the assessment of effuents dispersion in Baixada Santista coastline (State of São Paulo).

Baptistelli, Silene Cristina
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 08/09/2008 Português
Relevância na Pesquisa
57.50926%
Prever a hidrodinâmica das águas e a dispersão de contaminantes nos corpos dágua, principalmente em regiões costeiras, tem sido um problema a ser enfrentado por engenheiros, devido ao aumento dos impactos ambientais que envolvem as obras e a gestão da engenharia costeira. O uso de modelagem matemática como ferramenta de avaliação tornou-se imperativo para tais estudos. O principal objetivo desta Tese é fazer uma análise crítica da utilização da ferramenta de modelagem matemática na avaliação da dispersão de efluentes leves. A área de estudo engloba a RMBS, com ênfase no Sistema Estuarino de Santos / São Vicente. Para a efetivação desta análise são utilizados três modelos hidrodinâmicos - MIKE 21, POM e Delft3D. Esta abordagem apresentou significativa contribuição para as principais conclusões desta Tese e demonstrou, na prática, as diferenças na utilização dos modelos numéricos hidrodinâmicos. Os resultados dos três modelos utilizados apresentaram-se satisfatórios, sendo que os coeficientes de correlação encontrados, entre os resultados das simulações e dados de medição de campo, para o período de Verão de 2002 foram para o MIKE 21 de 0,63 (considerado 20 dias de processamento); o Delft3D de 0...

‣ Models and applications for risk assessment and prediction of Asian soybean rust epidemics; Modelos e aplicações de avaliação e previsão de risco de epidemias da ferrugem asiática da soja

Del Ponte, Emerson Medeiros; Godoy, Cláudia Vieira; Canteri, Marcelo Giovanetti; Reis, Erlei Melo; Yang, X.B.
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Artigo de Revista Científica Formato: application/pdf
Português
Relevância na Pesquisa
56.960156%
A ferrugem Asiática da soja Glycine max (L.) Merril] é atualmente uma das mais importantes doenças foliares dessa cultura no mundo. A recente introdução de seu agente causal, o fungo Phakopsora pachyrhizi Syd & P. Syd, nas Américas representa uma grande ameaça à sojicultura nas principais regiões produtoras do mundo, onde perdas significativas foram relatadas. A ferrugem Asiática da soja é uma doença extremamente agressiva sob condições ambientais favoráveis, causando rápida desfolha nas plantas e danos à produção de grãos. O conhecimento epidemiológico sob condições controladas e naturais, os quais visam elucidar os fatores que afetam os processos do ciclo da doença tem sido fundamental para dar base a estudos de modelagem da epidemia. Devido à importância e recente expansão da doença para as principais áreas de produção de soja no mundo, uma nova atenção tem sido dada ao desenvolvimento, avaliação e aplicação de modelos para avaliação de risco e previsão de suas epidemias, valendo-se de avanços recentes no conhecimento epidemiológico, métodos estatísticos e simulação por computador. O conhecimento gerado tem permitido a construção de novos modelos para a previsão e avaliação de risco de doenças...

‣ Models and applications for risk assessment and prediction of Asian soybean rust epidemics

Del Ponte,Emerson M.; Godoy,Cláudia V.; Canteri,Marcelo G.; Reis,Erlei M.; Yang,X.B.
Fonte: Sociedade Brasileira de Fitopatologia Publicador: Sociedade Brasileira de Fitopatologia
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2006 Português
Relevância na Pesquisa
56.960156%
Asian rust of soybean [Glycine max (L.) Merril] is one of the most important fungal diseases of this crop worldwide. The recent introduction of Phakopsora pachyrhizi Syd. & P. Syd in the Americas represents a major threat to soybean production in the main growing regions, and significant losses have already been reported. P. pachyrhizi is extremely aggressive under favorable weather conditions, causing rapid plant defoliation. Epidemiological studies, under both controlled and natural environmental conditions, have been done for several decades with the aim of elucidating factors that affect the disease cycle as a basis for disease modeling. The recent spread of Asian soybean rust to major production regions in the world has promoted new development, testing and application of mathematical models to assess the risk and predict the disease. These efforts have included the integration of new data, epidemiological knowledge, statistical methods, and advances in computer simulation to develop models and systems with different spatial and temporal scales, objectives and audience. In this review, we present a comprehensive discussion on the models and systems that have been tested to predict and assess the risk of Asian soybean rust. Limitations...

‣ Exploiting mathematical models to illuminate electrophysiological variability between individuals

Sarkar, Amrita X; Christini, David J; Sobie, Eric A
Fonte: Blackwell Science Inc Publicador: Blackwell Science Inc
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
57.431353%
Across individuals within a population, several levels of variability are observed, from the differential expression of ion channels at the molecular level, to the various action potential morphologies observed at the cellular level, to divergent responses to drugs at the organismal level. However, the limited ability of experiments to probe complex interactions between components has hitherto hindered our understanding of the factors that cause a range of behaviours within a population. Variability is a challenging issue that is encountered in all physiological disciplines, but recent work suggests that novel methods for analysing mathematical models can assist in illuminating its causes. In this review, we discuss mathematical modelling studies in cardiac electrophysiology and neuroscience that have enhanced our understanding of variability in a number of key areas. Specifically, we discuss parameter sensitivity analysis techniques that may be applied to generate quantitative predictions based on considering behaviours within a population of models, thereby providing novel insight into variability. Our discussion focuses on four issues that have benefited from the utilization of these methods: (1) the comparison of different electrophysiological models of cardiac myocytes...

‣ An examination of the use of probability modeling for the analysis of interfuel substitution in residential fuel demand

Hartman, Raymond Steve; Hollyer, Mark R.
Fonte: MIT Energy Laboratory Publicador: MIT Energy Laboratory
Tipo: Trabalho em Andamento Formato: 4561111 bytes; application/pdf
Português
Relevância na Pesquisa
48.45629%
Research was supported by the Energy Research and Development Administration as part of a contract with Arthur D. Little, inc.

‣ International comparisons of the residential demand for energy

Pindyck, Robert S.
Fonte: MIT Energy Laboratory Publicador: MIT Energy Laboratory
Tipo: Trabalho em Andamento Formato: 5905632 bytes; application/pdf
Português
Relevância na Pesquisa
48.77006%
A revised and updated version of "International comparisons of the residential demand for energy: a preliminary analysis," Working paper #MIT-EL 76-023WP, by the same author.; Supported by the National Science Foundation under Grant #GSF SIA075-00379.

‣ A critical review of single fuel and interfuel substitution residential energy demand models

Hartman, Raymond Steve
Fonte: MIT Energy Laboratory Publicador: MIT Energy Laboratory
Tipo: Relatório Formato: 6729957 bytes; application/pdf
Português
Relevância na Pesquisa
58.41582%
The overall purpose of this paper is to formulate a model of residential energy demand that adequately analyzes all aspects of residential consumer energy demand behavior and properly treats the penetration of new technologies, particularly solar photovoltaics, in an explicit fashion. An adequate treatment of energy demand must take account of the fact that both fuel demand and the demand for fuel-burning equipment are jointly derived from the demand for fuel related services. This requires modelling both demand for fuels and for their related equipment. In order to model the equipment demand and the demand for new technologies, the technological characteristics of the alternative equipment must be explicitly analyzed. The formulated model attempts such explicit analyses. In order to formulate such a model this paper first introduces and reviews 19 existing residential energy demand models to ascertain how well they have dealt with these issues.; Prepared by Massachusetts Institute of Technology, Energy Laboratory Cambridge, Mass., for the United States Department of Energy under contract no. EX-876-A-01-2295, task order 37.

‣ Independent assessment of energy policy models : two case studies

Massachusetts Institute of Technology. Model Assessment Group.
Fonte: MIT Energy Laboratory Publicador: MIT Energy Laboratory
Tipo: Relatório Formato: 13822037 bytes; application/pdf
Português
Relevância na Pesquisa
56.92178%
Energy policy models are playing an increasingly important and visible role in supporting both private and public energy policy research and decision making. As importance has increased so too has the need for model review and assessment to assist in establishing model credibility for users and those affected by model-based policy research. Toward this end EPRI has sponsored the M.I.T. Energy Laboratory in a one-year project to assess two important energy system models, the Baughman-Joskow Regionalized Electricity Model and the Wharton Annual Energy Model, and to identify and analyze organizational and procedural issues in the model assessment process.; Prepared for the Electric Power Research Institute, Palo Alto, CA.

‣ Independent assessment of energy policy models : two case studies

Massachusetts Institute of Technology. Model Assessment Group.
Fonte: MIT Energy Laboratory Publicador: MIT Energy Laboratory
Tipo: Relatório Formato: 13822037 bytes; application/pdf
Português
Relevância na Pesquisa
56.92178%
Energy policy models are playing an increasingly important and visible role in supporting both private and public energy policy research and decision making. As importance has increased so too has the need for model review and assessment to assist in establishing model credibility for users and those affected by model-based policy research. Toward this end EPRI has sponsored the M.I.T. Energy Laboratory in a one-year project to assess two important energy system models, the Baughman-Joskow Regionalized Electricity Model and the Wharton Annual Energy Model, and to identify and analyze organizational and procedural issues in the model assessment process.; Prepared for the Electric Power Research Institute, Palo Alto, CA.

‣ Empirical models of emissions and energy efficiencies of coal-fired fluidized bed power plants

Gruhl, Jim; Teare, J. Derek
Fonte: MIT Energy Laboratory Publicador: MIT Energy Laboratory
Tipo: Relatório Formato: 14242235 bytes; application/pdf
Português
Relevância na Pesquisa
57.472515%
Mass and energy balances of fluidized bed energy technologies are to a significant degree dependent upon the specific design being investigated. It is difficult to make any generally accurate comments. about these balances. This study attempts to solve this difficulty by displaying a large amount of available data, especially on parametric experiments, for the specific designs. To the extent that generalizations about the efficiencies and emissions of these cycles are.possible empirical correlation models have been developed, along with measures of the predictive quality of these models over existing data bases. These empirical correlations consist of probabilistic models that have been fit to published experimental data. In several instances, there have been comparison of these empirical models with available analytic models. In the cases of unavailable experimental data, such as for the potassium topping cycles, models have been fit to analytic data. Although the overall scale of this effort was very small compared to other fluidized bed reviews, such as those performed at Babcock and Wilcox, Burns and Roe, and Battelle-Columbus, the empirical models are new and in the narrow scope of this study some of-the literature reviews are more comprehensive than others available at this time. Extensive bibliographic research and identification-of on-going projects is also included in this report.; Work performed on a subcontract to Exxon Research and Engineering Co....

‣ Robust techniques for developing empirical models of fluidized bed combustors

Gruhl, Jim; Tung, Shao-E.; Schweppe, Frederic C.
Fonte: MIT Energy Laboratory Publicador: MIT Energy Laboratory
Tipo: Relatório Formato: 4222282 bytes; application/pdf
Português
Relevância na Pesquisa
57.4321%
This report is designed to provide a review of those data analysis techniques that are most useful for fitting m-dimensional empirical surfaces to very large sets of data. One issue explored is the improvement of data (1) using estimates of the relative size of measurement errors and (2) using known or assumed theoretical relationships. An apparently new concept is developed, named robust weighting, which facilitates the incorporation of a Driori knowledge, based upon the values of input and response variables, about the relative quality of different experiments. This is a particularly useful technique for obtaining statistical inferences from the most relevant portions of the data base, such as concentrating on important ranges of variables or extrapolating off the leading edge of the frontier of knowledge for an emerging technology. The robust weightings are also useful for forcing a priori known asymptotic behaviors, as well as for fighting biases due to shear size of conflicting data clusters and for formulating separate models for conflicting clusters. Another new development has evolved from the two very different objectives of the empirical modeling in this project. The first objective is the usual requirement for the best possible predictive mechanism...

‣ Residential demand for electricity and gas in the short run : an econometric analysis

Werth, Alix
Fonte: MIT Energy Laboratory Publicador: MIT Energy Laboratory
Tipo: Trabalho em Andamento Formato: 2386403 bytes; application/pdf
Português
Relevância na Pesquisa
48.96832%
Short-run residential demand equations for electricity and gas are estimated in this study. Short-run demand depends on the appliance stock in existence. Use of the appliance stock is a function of the price of fuel, income, and the weather. The major difference between this study and others explicitly using appliance stock data is that appliances are not aggregated into a single stock measure. Demand consists of the sum of the individual demands for energy for each fuel-burning appliance type. Consequently, different price, income, and weather elasticities are estimated for each use of the fuels. The data consist of annual observations for each state for the years 1960-1975. Most of the appliance stock data were developed by Data Resources, Inc. These are supplemented by appliance data developed for use in this study. Two different methods of pooling time-series and cross-section data, the random and fixed effects models, are used, and a specification test is performed to test for consistency of the random effects model estimates. The results are somewhat mixed. However, they do suggest directions for further research. Fairly reasonable estimates in terms of average energy consumption for each type of appliance are obtained. The aggregate price and income elasticities fall in the range found in previous work. Price elasticities appear to vary among the demands for fuel for different end uses...

‣ Models of new product diffusion : current status and research agenda

Kalish, Shlomo; Lilien, Gary Louis
Fonte: MIT Energy Laboratory Publicador: MIT Energy Laboratory
Tipo: Trabalho em Andamento Formato: 1186954 bytes; application/pdf
Português
Relevância na Pesquisa
57.265444%
Diffusion models, mathematical attempts to describe the growth patterns of new products and relate them to variables such as price and population characteristics, have seen major development trends in the past few years. This paper reviews that progress in order to isolate those areas most likely to be fruitful for further development. The paper first reviews some of the behavioral underpinnings of diffusion models: the phenomena being modeled. Next, the major explicit form models are reviewed and classified according to whether they have market-controls or not and according to the number of stages they explicitly consider. These models are related to larger-scale simulation models (especially in the solar energy area) that use explicit-form models as building blocks. The paper concludes with a discussion of some important advances that still need to be made in this important and rapidly-growing area.

‣ Development of models for the sodium version of the two-phase three dimensional thermal hydraulics code THERMIT

Wilson, Gregory James; Kazimi, Mujid S.
Fonte: MIT Energy Laboratory Publicador: MIT Energy Laboratory
Tipo: Relatório Formato: 6959220 bytes; application/pdf
Português
Relevância na Pesquisa
58.54476%
Several different models and correlations were developed and incorporated in the sodium version of THERMIT, a thermal- hydraulics code written at MIT for the purpose of analyzing transients under LMFBR conditions. This includes: a mechanism for the inclusion of radial heat conduction in the sodium coolant as well as radial heat loss to the structure surrounding the test section. The fuel rod conduction scheme was modified to allow for more flexibility in modelling the gas plenum regions and fuel restructuring. The formulas for mass and momentum exchange between the liquid and vapor phases were improved. The single phase and two phase friction factors were replaced by correlations more appropriate to LMFBR assembly geometry. The models incorporated in THERMIT were tested by running the code to simulate the results of the THORS Bundle 6A experiments performed at Oak Ridge National Laboratory. The results demonstrate the increased accuracy provided by the inclusion of these effects.; "Sponsored by U.S Department of Energy, General Electric Co. and Hanford Engineering Development Laboratory."

‣ A two dimensional, two fluid model for sodium boiling in LMFBR fuel assemblies

Granziera, Mario Roberto; Kazimi, Mujid S.
Fonte: MIT Energy Laboratory Publicador: MIT Energy Laboratory
Tipo: Relatório Formato: 11731420 bytes; application/pdf
Português
Relevância na Pesquisa
58.331094%
A two dimensional numerical model for the simulation of sodium boiling transient was developed using the two fluid set of conservation equations. A semiimplicit numerical differencing scheme capable of handling the problems associated with the ill-posedness implied by the complex characteristic roots of the two fluid problems was used, which took advantage of the dumping effect of the exchange terms. Of particular interest in the development of the model was the identi- fication of the numerical problems caused by the strong disparity between the axial and radial dimensions of fuel assemblies. A solution to this problem was found which uses the particular geometry of fuel assemblies to accelerate the convergence of the iterative technique used in the model. The most important feature of the model was its ability to simulate severe conditions of sodium boiling, in particular flow reversal, which was shown in the tests performed with the model. Three sodium boiling experiments were simulated with the model, with good agreement between the experimental results and the model predictions.; "Sponsored by U.S Department of Energy, General Electric Co. and Hanford Engineering Development Laboratory."

‣ Mathematical predictive models for cooling ponds and lakes. Part B, User's manual and applications of MITEMP. Part C. A transient analytical model for shallow cooling ponds

Octavio, Kathleen Ann Hurley; Adams, E. Eric; Koussis, Antonis D.
Fonte: MIT Energy Laboratory Publicador: MIT Energy Laboratory
Tipo: Relatório Formato: 8457389 bytes; application/pdf
Português
Relevância na Pesquisa
57.30862%
In Part B a computer code, '"MITEMP: M.I.T. Transient Temperature Prediction Model for Natural Reservoirs and Cooling Impoundments," is presented as a feasible and efficient tool for the prediction of transient performance of man-made impoundments. Particular emphasis is placed on waste heat dissipation from steam-electric power stations. The code allows the simulation of the physical regime (temperature and flow patterns) of impoundments as a function of design and for long time periods. The code contains the following elements: (1) Natural Deep Lake and Reservoir Model, (2) Deep Stratified Cooling Pond Model, (3) Shallow Vertically Mixed Dispersive Cooling Pond Model, and (4) Shallow, Vertically Mixed Recirculating Cooling Pond Model. The physical and mathematical basis for the present computer code is developed in an earlier report entitled, "Mathematical Predictive Models for Cooling Ponds and Lakes, Part A: Model Development and Design Considerations," by G. Jirka, M. Watanabe, K.H. Octavio, C. Cerco and D.R.F. Harleman, R.M. Parsons Laboratory for Water Resources and Hydrodynamics, Technical Report No. 238, December 1978. The user's manual presented herein gives a detailed description of the computational structure of MITEMP and discusses input and output requirements. The application to several case studies is presented. A complete code listing is given in the appendix...

‣ Qualitative and quantitative reliability analysis of safety systems

Karimi, Roohollah
Fonte: MIT Energy Laboratory Publicador: MIT Energy Laboratory
Tipo: Relatório Formato: 11009616 bytes; application/pdf
Português
Relevância na Pesquisa
57.19636%
A code has been developed for the comprehensive analysis of a fault tree.' The code designated UNRAC (UNReliability Analysis Code) calculates the following characteristics of an Tnput fauTt tree: a) minimal cut sets, b) top event unavailability as point estimate and/or in time dependent form, c) quantitative importance of each component involved, and d) error bound on the top event unavailability UNRAC can analyze fault trees, with any kind of gates (EOR, NAND, NOR, AND, OR), up to a maximum of 250 components and/or gates. For generating minimal cut sets the method of bit manipu- lation is employed. In order to calculate each component's time dependent unavailability, a general and consistent set of mathematical models is developed and the repair time density function is allowed to be represented by constant, exponen- tial, 2nd order erlangian and log-normal distributions. A normally operating component is represented by a three-state model in order to be able to incorporate probabilities for revealed faults, non-revealed faults and false failures in unavailability calculations. For importance analysis, a routine is developed that will rearrange the fault tree to evaluate the importance of each component to system failure...

‣ Fuel cycle optimization of thorium and uranium fueled PWR systems

Garel, Keith Courtnay; Driscoll, Michael J.
Fonte: MIT Energy Laboratory Publicador: MIT Energy Laboratory
Tipo: Relatório Formato: 13486795 bytes; application/pdf
Português
Relevância na Pesquisa
58.559136%
The burnup neutronics of uniform PWR lattices are examined with respect to reduction of uranium ore requirements with an emphasis on variation of the fuel-to-moderator ratio (lattice pitch at constant fuel pin diameter) and the use of thorium. Fuel cycles using all combinations of the major fissile (U-235, U-233, Pu) and fertile (U-238, Th) species are examined. The LEOPARD code and prescriptions developed from a linear reactivity model are used to determine initial core and annual makeup fissile requirements for input into an in-house, simple, systems model, MASFLO-2, which calculates ore (and separative work) requirements per GWeyr for growing, declining, or finite-life nuclear electric systems. For low growth scenarios drier lattices are favored, and the thorium fuel cycle requires as much as 23% less ore than a comparably optimized uranium cycle with full recycle. For unmodified lattices, the thorium fuel cycle with full recycle exhibits long term uranium ore savings of 17% over the comparable uranium cycle with full recycle. For rapidly growing systems, drier lattices, and those using thorium, are less attractive because of their high startup inventories. Thus the introduction of thorium may increase ore and separative work requirements in the short term but will more than repay the ore investment in the very long term. Very little improvement was achieved by varying fuel pin diameter at a given fuel-to-moderator ratio...

‣ Design and fuel management of PWR cores to optimize the once-through fuel cycle

Fujita, Edward Kei; Driscoll, Michael J.; Lanning, David D.
Fonte: MIT Energy Laboratory Publicador: MIT Energy Laboratory
Tipo: Relatório Formato: 11277096 bytes; application/pdf
Português
Relevância na Pesquisa
58.3503%
The once-through fuel cycle has been analyzed to see if there are substantial prospects for improved uranium ore utilization in current light water reactors, with a specific focus on pressurized water reactors. The types of changes which have been examined are: (1) re-optimization of fuel pin diameter and lattice pitch, (2) Axial power shaping by enrichment gradation in fresh fuel, (3) Use of 6-batch cores with semi-annual refueling, (4) Use of 6-batch cores with annual refueling, hence greater extended (.doubled) burnup, (5) Use of radial reflector assemblies, (6) Use of internally heterogeneous cores (simple seed/blanket configurations), (7) Use of power/temperature coastdown at the end of life to extend burnup, (8) Use of metal or diluted oxide fuel, (9) Use of thorium, and (10) Use of isotopically separated low a cladding material. a State-of-the-art LWR computational methods, LEOPARD/PDQ-7/FLARE-G, were used to investigate these modifications. The most effective way found to improve uranium ore utilization is to increase the discharge burnup. Ore savings on the order of 20% can be realized if greatly extended burnup (- double that of current practice) is combined with an increase in the number of batches in the core from 3 to 6. The major conclusion of this study is that cumulative reductions in ore usage of on the order of 30% are fore- seeable relative to a current PWR operating on the once-through fuel cycle...

‣ Modeling and simulation of JP-8 fuel based hybrid solid oxide fuel cell system

Nishtala, Kalyan
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
68.47375%
Solid Oxide Fuel Cells (SOFC) are solid state energy conversion devices that operate at high temperatures (800 to 1000 ±C). Their inherent advantage of fuel flexibility, tolerance to impurities, faster chemical kinetics with non precious catalyst materials and capability of supporting bottoming cycle components make them an attractive proposition for energy generation in comparison to other fuel cell technologies. To assist the advancement of this technology, this work develops dynamic, computer-based, mathematical models of an Auto-thermal reformer (ATR) based SOFC system with Jet Propellant-8 as the fuel to the ATR. Limitations in the existing models of SOFC systems lie in handling of complex hydrocarbon mixtures and also in simulating start up conditions. Although experimental data necessary to model these accurately is currently not available, this work puts forth a structured method for model development and management. Hierarchical libraries are developed herein, allowing easy modification of the models on multiple levels for simulation of various SOFC system configurations, which can help in improving accuracy as and when experimental data is accessible. The comprehensive model consists of submodels for individual components...