Multi-flux analysis

Similar models using a multi-flux analysis of particle absorption and scattering are reported by Radauer, Glatzer and Linzer (1996). 

The classical calibration of NAA methods involves comparison of sample activities with those of co-irradiated standards of the same element. Especially at multi-element analysis, the need for a large number of standards has limited the sample throughput capacity. To circumvent this, alternative calibration techniques have been elaborated. The single comparator method makes multi-element determinations possible, by use of a single element standard (neutron flux monitor). The mass of the analyte is calculated by use of an experimentally determined element-specific factor (k-value), valid for the analytical equipment in question (Girardi et al., 1965 Linekin, 1973 Simonits et al., 1975). Later, a more generalized standardization method, based on accurately determined constants for the active compound nuclei (ko-factors), and applicable to various analytical equipments, has been proposed (Moens et al., 1984 De Code et al., 1987). 

Analysis of the model schemes of the flux diagrams of nitrogen compounds in nature proposed by various experts means we can construct a block diagram like that in Figure 4.6. Here the atmosphere, soil, lithosphere, and hydrosphere are considered as nitrogen reservoirs. The first three reservoirs are described by 2-D models, and the hydrosphere is described by a 3-D multi-layer model. The characteristics of nitrogen fluxes between these reservoirs are given in Table 4.5. The equations of the model are written as... 

The availability of high flux thermal neutron irradiation facilities and high resolution intrinsic Ge and lithium drifted germanium (Ge(Li)) or silicon (Si(Li)) detectors has made neutron activation a very attractive tool for determining trace elemental composition of petroleum and petroleum products. This analytical technique is generally referred to as instrumental neutron activation analysis (INAA) to distinguish it from neutron activation followed by radiochemical separations. INAA can be used as a multi-elemental method with high sensitivity for many trace elements (Table 3.IV), and it has been applied to various petroleum materials in recent years (45-55). In some instances as many as 30 trace elements have been identified and measured in crude oils by this technique (56, 57). 

He et al used a binary mixture-based film model to perform a theoretical analysis on the concentration polarization in a generic membrane. They defined a concentration polarization coefficient for both the two species involved in the separation as the ratio of the actual flux to the ideal one (without polarization), quantifying the polarization effect by means of the ratio of the actual fluxes of the components. Although this is a simplified approach that cannot be generalized to multi-component systems, nevertheless, under some operating conditions, the authors predicted a significant influence of the external mass transfer on the process. 

The analysis in this section was performed in order to better visualize the CHF behavior in the established conditions. Through a multi-linear regression one can evaluate the CHF as a function of temperature, pressure and mass flux. The variables were codified for values between -1.0 and 1.0 so that -1.0 represents the minimum value and -i-l.O represents the maximum one. The coefficients and their standard errors are shown in Table 2, where quadratic terms proved to be non significant based on p-values greater than 0.10. The regression was performed through STATISTICA version 12 (Hill Lewicki 2006). 

Implementation of a control system depends on its structure, which is subject to regulatory processes at work in varied conditions. Two sources of electricity may exist in hybrid systems. Usually one of these sources is to provide the main energy flux while the other plays auxiliary functions. There is therefore a need to identify possible structures for systems analysis of power distribution to the various subsystems. A multi-stage procedure is used to determine the control strategy of SOFC-GT hybrid systems, as follows ... 

These models consider either the thermodynamic or mechanical non-equilibrium between the phases. The number of conservation equations in this case are either four or five. One of the most popular models which considers the mechanical non-equilibrium is the drift flux model. If thermal non-equilibrium between the phases is considered, constitutive laws for interfacial area and evaporation/condensation at the interface must be included. In this case, the number of conservation equations is five, and if thermodynamic equilibrium is assumed the number of equations can be four. Well-assessed models for drift velocity and distribution parameter depending on the flow regimes are required for this model in addition to the heat transfer and pressure drop relationships. The main advantage of the drift flux model is that it simplifies the numerical computation of the momentum equation in comparison to the multi-fluid models. Computer codes based on the four or five equation models are still used for safety and accident analyses in many countries. These models are also found to be useful in the analysis of the stability behaviour of BWRs belonging to both forced and natural circulation type. 

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