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Modeling factors considered

A thorough analysis of atmospheric transport and deposition to the Great Lakes has been carried out using the HYSPLIT model developed by the US National Atmospheric and Oceanic Administration (NOAA) [28,29]. An emissions inventory of PCDD/Fs for North America in 1996 was used as input to the model. Factors considered in the fate and distribution were meteorological data, vapor-particle partitioning, aerosol characteristics, reaction with hydroxyl radicals, photolysis, and dry and wet deposition. The model was generally satisfactory at estimating fluxes, except for HpCDD and OCDD, which appeared to be underestimated by about a factor of four. The model output was summarized as 2378-TeCDD toxic equivalent concentrations (TEQs) based on the WHO mammalian 2378-TeCDD toxic equivalent factors (TEFs) [30]. Since HpCDD and OCDD were estimated to contribute only 2% of TEQs, the model was considered to be valid for the purpose intended. [Pg.78]

As with continuous processes, the heart of a batch chemical process is its reactor. Idealized reactor models were considered in Chapter 5. In an ideal-batch reactor, all fluid elements have the same residence time. There is thus an analogy between ideal-batch reactors and plug-flow reactors. There are four major factors that effect batch reactor performance ... [Pg.291]

This section is concerned with analyses of simultaneous reaction and mass transfer within porous catalysts under isothermal conditions. Several factors that influence the final equation for the catalyst effectiveness factor are discussed in the various subsections. The factors considered include different mathematical models of the catalyst pore structure, the gross catalyst geometry (i.e., its apparent shape), and the rate expression for the surface reaction. [Pg.439]

It is entirely possible that isomerization may proceed much faster with this catalyst than with the model system considered by Tolman. To test this possibility, reactions were run at reduced ethylene concentrations. This should slow down the insertion reaction (d ) relative to the isomerization reaction (c). No effect on the trans/cis ratio of the product was observed, while the rate of hexadiene formation was reduced over 200-fold (39). So, unlike the Rh systems, the syn-to-anti isomerization appeared too slow to be a controlling factor for the stereoselectivity. [Pg.305]

The rate of dispersion and the values of the dispersion coefficients depend also on terrain and atmospheric conditions. There are prairie grass coefficients and values for forests (Eares etal., 1980). Both are discussed by Elkinton etal. (1984). (In one more complicated equation, the Gaussian model also considers absorption on the ground surface by introducing a factor a.)... [Pg.11]

If sufficient data are available, substance-specific PBPK models should always be given preference over the use of general scaling factors. However, PBPK models were considered not to replace all of the sub-factors in the interspecies comparison and should, by definition, only include toxicokinetic differences. A further extrapolation factor for toxicodynamic differences between the species needs to be discussed. [Pg.239]

In CVD processes, due to the simultaneous presence of gaseous and solid phases, models should consider heterogeneous nucleation (defined as nucleation at an interface) rather than homogeneous nucleation (defined as nucleation in an indefinite point of a fluid matrix). Nevertheless, the complexity of the factors involved in heterogeneous nucleation leads us to first examine the more simple homogeneous nucleation. [Pg.159]

Figure 4.16 Typical example of a PRESS plot to select the model dimensionality (data shown in Figure 4.9, mean centred) (a) overall PRESS and (b) behaviour of each sample for each number of factors considered in the model. Four factors seem to be the optimal choice here as the minimum is clearly defined. [Pg.207]

The friction factor / for the RB model is given by condition III. In order to obtain / for the DTO model we consider the minimum relaxation time given by Eq. (2.2) ... [Pg.108]

Since 1992 the two Italian stations of Rome, urban site (latitude 41.9° N, longitude 12.5° E, altitude 60 m), and Ispra, semi-rural site (latitude 45.8° N, longitude 8.6° E, altitude 240 m), collect regular continuous measurements of spectral UV (290-325 nm) irradiance by means of Brewer Spectrophotometry. The measured data are compared with the output of the STAR model (System for Transfer of Atmospheric Radiation) [1], STAR is a multiple scattering radiative transfer model which considers all atmospheric factors modulating UV radiation at ground (ozone, aerosol, clouds, pollutants, albedo, pressure, temperature, humidity) [2], The model involves combination of a radiative transfer code, an initialisation procedure and an integration scheme. [Pg.187]

In these models the increase in the number of factors considered is clearly observed, as is the respective increasing adequacy that accompanies them. One of the first and sufficiently complete models of the global C02 cycle is the model proposed by Bjorkstrom (1979) which takes into account the dynamic interaction between carbon reservoirs in the biosphere and fluxes between them. For the first time, a unit for the World Ocean was realistically represented. In this unit the ocean is... [Pg.162]

An important point is determining to what extent these results relate to actual biodegradation potential of the compounds concerned. In other words, could the regression models be considered QSBRs. This is of particular significance because a lack of reproducible quantitative data on biodegradation is one of the factors that limits the development of QSBRs (Degner et al., 1991). [Pg.388]

Discrepancies between different researchers derive from the character inter-or intramolecular of the interactions presumably controlling the reactive conformation. Thus, in most of the cases, the population of the different rotamers in the sulfinylated substrate (only governed by intramolecular interactions) is the only factor considered for explaining the observed 7r-facial selectivity. This explanation (static conformational polarization) was formulated by Koizumi and used by many authors to justify the behavior of vinyl sulfoxides acting as dienophiles and dipolarophiles. A second explanation assumes that the interactions of the two reagents in the transition states determine a different reactivity of the rotamers around the C-S bond. This intermolecular factor can become the most important one in the control of the 7r-facial selectivity of the cycloadditions, and therefore the tendency expected from conformational stability criteria was not observed in those cases where the most reactive conformation is not the most populated one. This dynamic conformational polarization has been used just to explain some of the results obtained for sulfinyl quinones and sulfinyl dienes (unexplainable with the above model) but it can be applied to many other cases. [Pg.116]

A conventional approach is to set up a mathematical model linking the response to coefficients of the various factors. Consider the simple linear calibration experiment, of Section 2.2.1 where the response and concentration are linked by the equation... [Pg.24]

The Taylor approximation model is a polynomial in the experimental factors. The rest term, R(x), becomes smaller and smaller the more polynomial terms are included in the model. R(x) accounts for the variation which is not described by the polynomial terms and will thus contain the model error. A model is considered as satisfactory if the model error is significantly less than the experimental error. [Pg.8]

Some important factors cannot be included in the model we consider these separately. [Pg.174]

MO models may be used for molecules that have covalent bonds. Ionic bonds having little orbital overlap between the bonded atoms are less influenced by the stereochemical guidance of the valence orbitals. The geometry of ionic compounds is mainly determined by the electronic repulsion between the nonbonded atoms. A bonding model that considers the latter interaction as the dominant factor for determining molecular geometries is the VSEPR approach, which is discussed further below. [Pg.1243]


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See also in sourсe #XX -- [ Pg.841 ]




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