Multi-media models

On-line system. Provides support for exposure assessments of toxic substances. Includes chemical properly estimation techniques, siahsiical analysis, multi-media modeling, and graphics display (including models)... 

A variety of modeling approaches may be used to estimate pollutant concentrations in exposure media. These range from qualitative estimates extrapolated from case examples or environmental scenarios, simple analytical equilibrium or transport models, to complex multi-media models. In selecting an approach or approaches, it is important that ... 

Staples, C.A. (2000) A screening level examination of the potential risks of acetone in aquatic and terrestrial environments nsing multi-media modeling. Chemosphere 41, 1529-1533. 

Many types of mathematical models have been developed to evaluate the fate and exposure of chemicals in the environment These models are categorized in various ways, eg, based on the environmental media in concern, ie, single-medium and multi-media models. 

Multi-media models can assess simultaneously the fate of chemicals in the environment consisting of multi-media such as air, water, soil, sediment, etc. Many users are interested in these models, because most of the chemicals released into the environment can transport between the environmental media. 

We have developed a number of multi-media models based on our (Higinal idea, and validated their predictability for evaluating environmental fate and exposure [2-9]. In our models, it is assumed that the environment consists of phases which are composed of several homogenous compartments. Also, the models assume that rates of intraphase transfer processes are faster than those of interphase transfer, transport and transformation processes (local equilibrium). 

In this section, we introduce examples of the application of our multi-media models, MNSEM and MAC for evaluating the environmental fate of organic chemicals under generic and site-specific conditions in Japan. 

Prevedouros K, Palm-Cousins A, Gustafsson C, Cousins IT (2008) Development of a black carbon-inclusive multi-media model application for PAHs in Stockholm. Chemosphere 70 607-615... 

The Champ-Sons model is a most effieient tool allowing quantitative predictions of the field radiated by arbitrary transducers and possibly complex interfaces. It allows one to easily define the complete set of transducer characteristics (shape of the piezoelectric element, planar or focused lens, contact or immersion, single or multi-element), the excitation pulse (possibly an experimentally measured signal), to define the characteristics of the testing configuration (geometry of the piece, transducer position relatively to the piece, characteristics of both the coupling medium and the piece), and finally to define the calculation to run (field-points position, acoustical quantity considered). 

The CPA has proved to be an enormously successful tool in the study of alloys, and has been implemented within various frameworks, such as the TB, linear muffin-tin orbital and Korringa-Kohn-Rostoker (Kumar et al 1992, Turek et al 1996), and is still considered to be the most satisfactory single-site approximation. Efforts to do better than the single-site CPA have focused on multi-site (or cluster) CPA s (see, e.g., Gonis et al 1984, Turek et al 1996), in which a central site and its set of nearest neighbours are embedded in an effective medium. Still, for present purposes, the single-site version of the CPA suffices, and we derive the necessary equations here, within the framework of the TB model. 

For analytical purposes, the fiber composites are conveniently modeled using axisymmetric three-phase (i.e. fiber-interlayer-matrix), four-phase (i.e. fiber-interlayer-matrix-composite medium) cylindrical composites, or in rare cases multi-layer composites (Zhang, 1993). These models are schematically presented in Fig. 7.9. The three-phase uniform interphase model is typified by the work of Nairn (1985) and Beneveniste et al. (1989), while Mitaka and Taya (1985a, b, 1986) were the pioneers in developing four-phase models with interlayer/interphase of varying stiffness and CTE values to characterize the stress fields due to thermo-mechanical loading. The four phase composite models contain another cylinder at the outermost surface as an equivalent composite (Christensen, 1979 Theocaris and Demakos, 1992 Lhotellier and Brinson, 1988). 

As noted earlier, protein structure is stabilised by a series of weak forces which often give rise to the properties which are functionally important (models of active sites and substrate binding are discussed above). On the other hand, because active sites involve a set of subtle molecular interactions involving weak forces, they are vulnerable and can be transformed into less active configurations by small perturbations in environmental conditions. It is therefore not surprising that a multitude of physical and chemical parameters may cause perturbations in native protein-geometry and structure. Thus, enzyme deactivation rates are usually multi-factorial, e.g. enzyme sensitivity to temperature varies with pH and/or ionic strength of the medium. 

This analysis can be applied to enzymatic as well as to simple chemical transformations [9-11], for uni- and multi-substrate [12] reactions according to Eqs. (1) and (2). nNKM denotes the product of Michealis-Menten constants for all substrates. In this analysis one assumes that kinetics follow the Michaelis-Menten model, which is the case for most antibody-catalyzed processes discussed below. The kcat denotes the rate constant for reaction of the antibody-substrate complex, Km its dissociation constant, and kuncat the rate constant for reaction in the medium without catalytic antibody or when the antibody is quantitatively inhibited by addition of its hapten. In several examples given below there is virtually no uncatalyzed reaction. This of course represents the best case. 

The THM formulation presented here is based on the one proposed in Olivella et al. (1994) applied to clays. The formulation uses a multi-phase, multispecies conceptual model. The porous medium is assumed to be made up of three phases solid, liquid and gas. The main part of the solid phase is an inert mineral that does not dissolve but it may contain precipitated species. The liquid phase contains water, dissolved air and dissolved chemical species whereas the gas phase is made up of dry air and water vapour. Note that dry air is considered as a... 

In future work, we wiU extend and validate the different models to other class of diseases. Approximately 1-1.5 % of the French population suffer from dementia and the causes of dementia are neurological disorders such as Alzheimer s disease (which causes 50 %-70 % of aU dementia), blood flow-related (vascular) disorders such as multi-infarct diseases, inherited disorders such as Huntington s disease, and infections such as HIV [15]. In fact, we would like to simulate the patient s progress in order to forecast and to analyze the need for long, medium and short-term care. This allows us to evaluate human, financial and physical resources in the future. 

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