Model needed research

The modeling of fluidized beds remains a difficult problem since the usual assumptions made for the heat and mass transfer processes in coal combustion in stagnant air are no longer vaUd. Furthermore, the prediction of bubble behavior, generation, growth, coalescence, stabiUty, and interaction with heat exchange tubes, as well as attrition and elutriation of particles, are not well understood and much more research needs to be done. Good reviews on various aspects of fluidized-bed combustion appear in References 121 and 122 (Table 2). 

Molecularly motivated empiricisms, such as the solubility parameter concept, have been valuable in dealing with mixtures of weakly interacting small molecules where surface forces are small. However, they are completely inadequate for mixtures that involve macromolecules, associating entities like surfactants, and rod-like or plate-like species that can form ordered phases. New theories and models are needed to describe and understand these systems. This is an active research area where advances could lead to better understanding of the dynamics of polymers and colloids in solution, the rheological and mechanical properties of these solutions, and, more generally, the fluid mechaiucs of non-Newtonian liquids. 

The mechanism of TFL can be summarized to the ordered him lubrication, concluded from previous researches. It should be noted that the property and mechanism of TFL are not fully understood to date, and there remains a wide blank area to be covered between experiments and theoretical predictions and it leaves a far cry to achieve predictive ability. Some key problems associated with theoretical modeling which need to be addressed are ... 

In this paper, we first briefly describe both the single-channel 1-D model and the more comprehensive 3-D model, with particular emphasis on the comparison of the features included and their capabilities/limitations. We then discuss some examples of model applications to illustrate how the monolith models can be used to provide guidance in emission control system design and implementation. This will be followed by brief discussion of future research needs and directions in catalytic converter modeling, including the development of elementary reaction step-based kinetic models. 

Future needs in support of model validation and performance testing must continue to be in the area of coordinated, well-designed field data collection programs supplemented with directed research on specific topics. The FAT workshop produced a listing of the field data collection and research needs for the air, streams/lakes/estuaries, and runoff/unsaturated/saturated soil media categories, as follows ... 

Abstract This chapter embodies two sections. In the first section a survey of the state of the art of azo-dye conversion by means of bacteria is presented, with a focus on reactor design and operational issues. The relevance of thorough characterization of reaction kinetics and yields is discussed. The second section is focused on recent results regarding the conversion of an azo-dye by means of bacterial biofilm in an internal loop airlift reactor. Experimental results are analyzed in the light of a comprehensive reactor model. Key issues, research needs and priorities regarding bioprocess development for azo-dye conversion are discussed. 

The conditions in the reaction zone determine the release rate of the N-precursors HCN and NH3 [11], Among these conditions are the properties of the fuel (e.g., N-content and particle size), parameters related to the combustion front (temperature and propagation velocity) and the gas composition in and directly above the combustion front. As the prediction of the mass fractions of the N-precursors is important for the final goal of this research, i.e., the prediction of NO formation of the complete furnace, a model is needed in which all these conditions are represented. 

The most important research needs are related to the determination of the responses of natural ecosystems and agroecosystems to chronic exposure to oxidant pollutants. In particular, chronic-dose-response models are needed to understand the responses of the dominant primary-producer species constituting forest ecosystems in both the eastern and the western United States. The resulting alteration of interactions with other sub ems-—e.g., consumers and decomposers—must also be investigated. 

The review is organized as follows. Section 2 defines a systematic framework for fuel cell modeling research, called computational fuel cell dynamics (CFCD), and outlines its four essential elements. Sections 3—5 review work performed in the past decade on PEFCs, DMFCs, and SOFCs, respectively. Future research needs and directions of the three types of fuel cells are pointed out wherever applicable and summarized separately at the end of each section. 

Effect. There are no specific disease states in humans or animals that have been associated with exposure to 3,3 -dichlorobenzidine. Hemoglobin adducts have been isolated from the blood of 3,3 -dichlorobenzidine-treated animals (Bimer et al. 1990 Joppich-Kuhn et al. 1997). It is not known what relationship exists between adduct levels in the blood and 3,3 -dichlorobenzidine toxicity. Further research in animal models is needed to determine if these adducts could be correlated with effects of 3,3 -dichlorobenzidine exposure. Further studies to identify more sensitive toxic effects (noncancer) that are specific for 3,3 -dichlorobenzidine would be useful in monitoring effects in people living near hazardous waste sites containing 3,3 -dichlorobenzidine. 

Scientific inquiry demands a number of skills. The National Committee on Science Education Standards and Assessment and the National Research Council, in addition to other organizations such as the National Science Teachers Association, have stressed the training and development of these skills. Science students must learn how to raise important questions, design the tools or experiments necessary to answer these questions, apply models in explaining the results and revise the model as needed, be alert to alternative explanations, and construct and analyze arguments for and against competing models. 

Research is needed on various aspects of chemicals mixtures beginning with better reporting from population-based biomonitoring studies on the number and diversity of chemicals found in subjects. New bioassays are needed that explore the health outcomes of environmentally relevant mixtures (that is chemicals and amounts found in human tissues). PBPK models also need to be expanded to better understand chemical-chemical interactions. 

In addition, existing databases where environmental media and biomonitoring data are collected (such as NHEXAS) could be further studied to estimate exposure and explore the relationships between biomarker concentration and exposure. That information can be used to apportion chemical intake into the different exposure pathways to assist in interpreting population variability, to calculate exposure by combining environmental measurements with survey information to verify estimates of exposure from pharmacokinetic models, and to identify research needs on the basis of discrepancies between estimates obtained from the exposure-pathways analysis and biomonitoring results. 

It is hoped that this book will serve not only as an update and expansion on the agricultural and environmental sciences of the triazine herbicides, but also as a model for the discovery, development, and extensive research needed for future classes of agricultural chemicals and technology. Among the topics it covers are ... 

Models. Both empirical and simulation models are needed. (Models can help bridge the gap between experimental conditions and the real world and between actual observations and predictions. Obviously, models can be no better than the data used to construct them, and much of these data will come from the tests described above. The tremendous advantage of models comes as increased experience and better data bases permit their refinement to the degree that they can be used in place of, or to guide some of the more complex testing described above. Well-validated models can be a powerful research and regulatory tool.)... 

A tiered system for mixture extrapolation is proposed. The lowest tier is based on extrapolation using toxicological point-estimate information such as EC50 values. This translates into the use of toxic units, toxic equivalencies, and similar techniques. The use of the entire concentration-response relationships of the separate compounds is recommended for Tier-2, in conjunction with the use of either concentration or response addition as a modeling approach. In Tier-3, a mixed-model approach can be considered, to more specifically address considerations on toxic modes of action. In the latter case, the approach may be extended to allow incorporation of the responses of different ecological receptors (Tier-4). Research needs have been clearly identified in community-level mixture assessments. 

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