Rheological fluid mechanics is an intellectually interesting and technologically important subject. The reason that this subject has not come into a more central place in fluid mechanics is because of uncertainty about the correct form for the governing equations. Constitutive relations which are general enough to describe the tremendously varied responses open to a Theologically complex fluid are too general to solve many problems. And specific constitutive equations, developed from models, suitable for problem solving, are at best guided guesses which leave open the ultimate question about whether the constitutive relation you give is the right one for the fluid you got. Authors have had to decide between a good treatment of principles, without much problem solving, and a good treatment of fluid models, emphasizing problem solving. In the first category the treatise by Truesdell and Noll (The Nonlinear Field Theories of Mechanics, Springer, 1965) is without peer; in the second category are the books of Lodge (Elastic Liquids, Academic Press, 1964), and Middleman (The

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A research on the preparation of composite samarium-doped ceria (SDC) with yttrium-stabilized zirconia (YSZ) has been conducted at the SDC:YSZ ratio of 0:1; 1:9; 1:1; 9:1 and 1:0. This research aims to investigate the crystal structure and the ionic conductivity of the prepared materials. XRD analysis equipped with Le Bail refinement was used to analyze the crystal structure, space group, cell parameters, and cell volume. Meanwhile, the ionic conductivity was determined by impedance measurement. The result shows that the composites of SDC-YSZ were crystallized in two phases of cubic SDC and cubic YSZ without the presence of secondary phases. It indicates that the mixing and the heating at 1523 K did not change the crystal structure, even though it changed the cell parameters. Composite SDC-YSZ 91 shows a highest ionic conductivity at 873 K without the presence of electrode-bulk interface conductivity. It is a good indication of YSZ role regarding the inhibition of cerium ions auto-reduction.

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Ceria false(CeO2false) doped with divalent or trivalent cations is a mixed conductor; conduction occurs predominantly by the motion of oxygen vacancies or by electrons, depending on the departure from stoichiometry. In order to establish the electrolytic domain false(Tnormalvs.pO2false) at which false(CeO2)0.95false(Y2O3)0.05 behaves primarily as an ionic conductor with transference number tnormali≧0.99 , a careful study was made of the conductivity, σ, as a function of temperature and oxygen partial pressure, covering the pO2 range of 100;–10−22 atm in small steps. From these data the electrolytic domain was determined; it extends to about 10−13 atm at 600°C. When compared to calcia‐stabilized zirconia (CSZ), doped ceria shows a higher conductivity, lower activation energy (0.76 eV) for anion vacancy migration, and absence of polarization effects to lower temperatures. These results indicate that doped ceria may be an attractive candidate for fuel cells and other applications at temperatures below those at which CSZ is useful.