Compositional constraints

As different regulations have been adopted, the approach to controlling pollution has evolved. Initial regulations controlled solvent composition later regulations were concerned primarily with overall VOC reduction. More recent regulations have combined VOC reduction with composition constraints. 

Reformulating to reduce HAP solvents frequently means that solvent blend costs increase. The newer blends are generally not be as effective. For example, many coatings were usually formulated using ketones as the active solvents with aromatic hydrocarbons as diluents. This combination produced the most cost-effective formulations. However, when MEK, MIBK, toluene, and xylene became HAP compounds, less-effective solvents had to be used for reformulation. Esters are the most common ketone replacements, and aUphatic diluents would replace the aromatic hydrocarbons. In this situation, more strong solvent is required compared to the ketone/aromatic formulation and costs increase. The combination of reduced VOC emissions and composition constraints in the form of HAP restrictions have compHcated the formulator s task. 

Example Optimization of an Eleven Component Glass Formulation. Piepel (6) discussed the generation and analysis of a mixture design consisting of eleven oxides used to prepare glasses for waste vitrification. Although many responses must be considered for the end use of this composition, the intent of Piepel s study was to minimize the response of leachability subject to the compositional constraints of ... 

The modeler can constrain the initial equilibrium state in many ways, depending on the nature of the problem, but the number of pieces of information required is firmly set by the laws of thermodynamics. In general, the modeler sets the temperature and provides one compositional constraint for each chemical component in the system. Useful constraints include... 

In addition to reserved descriptions for these products, the 1964 regulations also defined minimum levels for carbohydrates and imposed various compositional constraints. It is perhaps noteworthy that at the time of writing, the only compositional constraint that is legally imposed in the United Kingdom is that for a quinine content (milligrams/litre) to enable a product to be described as Indian Tonic Water . 

Summation or stoichiometric equations or composition constraints. Heat or enthalpy or energy balance equations. 

The summation equation. The Summation equation or composition constraint simply states that the sum of the mole fractions on each stage is equal to unity. For the liquid phase,... 

The bubble- and dew-point equations. The equilibrium equation (Eq. 4.3) and the composition constraint [Eq. (4.1)] are combined to get the bubble-point equation,... 

Granjeon and Tarroux (1995) studied the compositional constraints in introns and exons by using a three-layer network, a binary sequence representation, and three output units to train for intron, exon, and counter-example separately. They found that an efficient learning required a hidden layer, and demonstrated that neural network can detect introns if the counter-examples are preferentially random sequences, and can detect exons if the counter-examples are defined using the probabilities of the second-order Markov chains computed in junk DNA sequences. 

Granjeon, E. Tarroux, P. (1995). Detection of compositional constraints in nucleic acid sequences using neural networks. Comput Appl Biosci 11,29-37. 

Jochum K. P., McDonough W. F., Pahne H., and Spettel B. (1989) Compositional constraints on the continental lithospheric mantle from trace elements in spinel peridotite xenoliths. Nature 340, 548-550. 

Turner S. P., Sandiford M., and Foden J. (1992b) Some geodynamic and compositional constraints on postoro-genic magmatism. Geology 20, 931-934. 

Outlet composition constraints of the component p for rich streams ... 

Maximal composition constraints of component p for lean streams ... 

A more systematic investigation was done by Katti et al. [3]. Using the competitive Langmuir isotherm model, the equilibrium-dispersive model [24], and the Knox equation [25], these authors optimized the operating parameters of given columns for maximum production rate of either the first or the second component of binary mixtures with various separation factors (1.2 < a < 1.7) and composition. Constraints of purity (98%) and maximum inlet pressure (125 atm) were included, and also, in some cases, a recovery yield (60 or 90%) constraint. The maximum production rates achieved with the two modes are comparable when there is no yield constraint. However, the recovery yield is lower in displacement than in elution, because the maximum production rate is achieved imder non-... 

Both the abundances and the values of acidic functional groups in humic substances are constrained and controlled by the compositional and structural properties of these substances. It is therefore important to be familiar with the principal structural properties that determine the acidities of organic acids. In this section of the chapter, compositional constraints on the abundances of acidic functional groups and a general discussion of statistical, electrostatic, and delocalization effects on the acidities of organic acids are presented. Specific applications to humic substances are given in the following sections of the chapter. 

For the DOF, equations and constraints include the independent material balances for each species or a total flow balance and (N,p - 1) species balances, the energy balance, the phase equilibrium relationships that link the compositions between phases, and the chemical equilibrium relationships. The unit and composition constraints may be explicit (e.g., a given stream fraction is condensing) or implicit (e.g., a species concentration is zero). Flimmelblau (1996) provides the full derivation for the degrees of freedom for the following Examples 16.11-16.14. 

A striking feature of P. falciparum, the unicellular parasite responsible for the most virulent and widespread form of human malaria, is that it hosts the GC-poorest (22% GC) nuclear genome known so far (Poliak et al., 1982, McCutchan et al., 1984). This genome, which only comprises 3 Mb of DNA (Weber, 1988) organized in 14 chromosomes (Kemp et al., 1987 Wellems et al., 1987), is, therefore, an excellent model for studying compositional constraints and their effects. 

In the case of the P. falciparum genes that we analyzed here, we noted that the biases in base composition of different codon positions, amino acid frequencies and codon preferences are almost identical in housekeeping and antigen sequences. If we take into account that both the level of expression and the evolutionary constraints over these sequences are most unlikely to be the same, it is reasonable to conclude (i) that the extremely biased composition of the genome (Poliak et al., 1982 McCutchan et al., 1984) is the major factor in determining codon preferences and amino acid frequencies and (ii) that the compositional constraints (Bernardi and Bernardi, 1986a) operate in the same direction over all the translated sequences and their codon positions (Musto et al., 1995, 1997, 1999). 

Our results further support the hypothesis that among the various factors that certainly influence the architecture of the coding (and non-coding) sequences, the compositional constraints on the genome (or on isochores) are most relevant, as already proposed (Bernard et al., 1985b). 

Other factors do, however, play a role in shaping codon usage, even in the case of vertebrates. Indeed, if multivariate analysis is applied to the coding sequences of Xenopus, which are characterized by a rather average GC3 distribution, with very scarce high values, the results obtained (Musto et ah, 2001) show that codon usage, although mainly determined by compositional constraints, is, in fact, also influenced by translational selection... 

---