Description and characterization of the samples

Twentyfive samples which have been investigated are presented in Table 4-7. These samples were characterized by the usual technical data and by detailed analysis. 

1 Vacuum residue from a crude from Boscan (Venezuela) properties between bitumens B80 and B200 

2 Bitumen B45 (semiblown) from a crude from Safaniya (Saudi Arabia) 

3 Bitumen B80 from a crude from Agha Jari (fran) 

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A microscopic description characterizes the structure of the pores. The objective of a pore-structure analysis is to provide a description that relates to the macroscopic or bulk flow properties. The major bulk properties that need to be correlated with pore description or characterization are the four basic parameters porosity, permeability, tortuosity and connectivity. In studying different samples of the same medium, it becomes apparent that the number of pore sizes, shapes, orientations and interconnections are enormous. Due to this complexity, pore-structure description is most often a statistical distribution of apparent pore sizes. This distribution is apparent because to convert measurements to pore sizes one must resort to models that provide average or model pore sizes. A common approach to defining a characteristic pore size distribution is to model the porous medium as a bundle of straight cylindrical or rectangular capillaries (refer to Figure 2). The diameters of the model capillaries are defined on the basis of a convenient distribution function. 

The unequivocal characterization of the mesophases is quite often very tricky and problematic. Each phase shows typical textures under a polarizing microscope a lot of them are documented in precise photos and pictures, but the formation of a texture depends strongly on the sample preparation, surface treatment, temperature control and other parameters. DSC curves and the phase-transition enthalpies yield important information, but the only unequivocal and suitable tool for the determination of the mesophases is given in the different x-ray methods, and nowadays modern resonance and atomic probe techniques attract more and more notice and acceptance9-11. A general description is given in the next section. 

Numerous methods are required to characterize drug substances and drug products (Chapter 10). Specifications may include description identification assay (of composite sample) tests for organic synthetic process impurities, inorganic impurities, degradation products, residual solvents, and container extractables tests of various physicochemical properties, chiral purity, water content, content uniformity, and antioxidant and antimicrobial preservative content microbial tests dissolution/disintegration tests hardness/friability tests and tests for particle size and polymorphic form. Some of these tests may be precluded, or additional tests may be added as dictated by the chemistry of the pharmaceutical or the dosage form. 

The conclusion from this e-sample is of extreme imponance in reactor analysis The RTD is not a complete description of structure for a particular reactor or system of reactors. The RTD is unique for a particular reactor. However, the reactor or reaction system is not unique for a particular RTD. When analyzing nonideal reactors, the RTD alone is not sufficient to determine its performance, and more information is needed. It will be shown that in addition to the RTD. an adequate model of the nonideal reactor flow patleni and knowledge of the quality of mixing or degree of segregation" are both required to characterize a reactor properly. 

The microscope spectrophotometer system in routine use at the TRL is described in reference (7), so no details of the apparatus and its use are given here. Instead a brief description of the reason for developing and continually refining the microscope spectrophotometer facility will be presented. Historically the way to characterize a solid-state sample of a transplutonium element has been by standard X-ray powder diffraction analysis. When a systematic study of element 99, einsteinium, was undertaken, it was found that obtaining useful diffraction data from Es-containing materials was a very difficult, if not an impossible, task (22). The intensely radioactive Es-253 not only caused rapid blackening of the film used to record the diffraction pattern, but more importantly, it degraded the crystallinity of the sample. 

Characterization of porous media based on the pore (microscopic) level is carried out for the purpose of understanding, modeling, and sometimes controling the macroscopic behavior and properties of the medium. The macroscopic (bulk) properties needed to relate to the pore description are porosity, permeability, tortuosity, and connectivity. When one examines a sample of a porous medium, for example, sandstone, it is obvious that the number of pore sizes, shapes, orientations, and interconnections is enormous. Furthermore, even the identification of a pore is not unique. Because of this complexity, pore structure is often characterized based on an idealized model. A true description is not realistic for a natural porous medium. 

Determination of the unperturbed dimensions of the polymeric pro-cyanidins presents special challenges. Well-characterized samples of high molecular weight are not readily available, and the solubility characteristics of the high polymers are incompatible with the application of the classical techniques for the measurement of the dimensions of a macromolecule. An alternative route to the unperturbed dimensions exploits structural determinations in the solid state (8, 9), spectroscopic studies of well-characterized oligomers in dilute solution (iO, ii), molecular mechanics (MM2 software) (i2) calculations (i3, 14), and rotational isomeric state analysis (15-17) to provide a realistic description of the dimensions of the high polymers. A vital piece of information comes from the time-resolved fluorescence of the monomers and oligomers of well-defined covalent structure. The fluorescence measurements also show promise for the characterization of the com-... 

The last decades have witnessed a growing interest in the search of new tools for food characterization. Any progress in analytical instrumentation is exploited to obtain more advanced description of foodstuff. Often the diffusion of a new methodology is hampered only by the complex sample preparation and the associated costs. Therefore methods that do not require any (or minimal) sample treatment are highly desired. Analysis of food products should require the use of non-invasive techniques because sensorial and safety properties are related to the structural and compositional complexity and heterogeneity of the matrix, which must be preserved as mueh as possible in its original state. 

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