Figure 11 Models of the structures of Ba2YCu3Ox for x = 6.85 (Figure a) and x = 6.15 (Figure b). Both structures are based on a unit cell of parameters 2>/2ac 2y/2ac 3ac where a is the basic perovskite parameter. Also in this case some of the Cu(l) atoms are in three-fold coordination. |

Desig- nation Nominal Size Surface Area (m g) Total Void Fraction Diu X 10 (cm /sec) Average Tortuosity Factor t, Parallel-Path Pore Model r. = 2y.is, (A) r. Based on Avmge Pore -Radius [Pg.565]

The a-helix (3.613) is not the only nonintegral spiral model. At least five others have been proposed 2.2t, 3.6u, 4.3u, 4.4i6 (7r-helix), 5.In (7-helix). Donohue (536) discusses all of these and ranks them in stability order 3.613 (a), 4.4ie ( ) and 2.2y, 5.In (7), 4.3h, 3.6u. The first three are very nearly equivalent in energy. Robinson and Ambrose (1733) carried out a somewhat different comparison, using integral spirals and the a-helix. They find the a-helix and a 2 model to be almost equivalent. [Pg.314]

Thermodynamic consistency requites 5 1 = q 2y but this requirement can cause difficulties when attempts ate made to correlate data for sorbates of very different molecular size. For such systems it is common practice to ignore this requirement, thereby introducing an additional model parameter. This facihtates data fitting but it must be recognized that the equations ate then being used purely as a convenient empirical form with no theoretical foundation. [Pg.256]

M2 layer, the characters 2i,2j+ are replaced by the characters 2j.2j+ or za +i, depending on the parity of T2y and 12/+1, and the displacement character obtained by the PID is simply V2y,2y+i- No indication can be obtained from the PID that the polytype may belong to the hetero-octahedral family. For the meso- and hetero-octahedral family, as well as for the distinction between the two members of an enantiomorphous pair, a complete structure refinement is required, similarly to the case of MDO polytypes. However, only the structural models corresponding to polytypes homomorphic to the homo-octahedral sequence obtained by PID analysis must be considered. [Pg.248]

In Eq.lO the Boltzmann population is assumed. Although the model predictions and experimental data are consistent, it is very difficult to state firmly that the equilibrium population of the states has already been reached. The population depends exponentially on the energy, and this in turn depends on the square of the oid radius, thus it is extremely sensitive to the accepted radius value. The pore radii acting in annihilation processes need not be identical with. say. the hydraulic pore radius. Additional distortion of experimental s. R dependence can be due to the difference in the efficiency of registration of 2y and 3y annihilation events. However, the results presented abo e indicate that the model parameter AR = 0.19 nm allows us to accept the commonly used LN pore radius in annihilation experiments [Pg.562]

Parameter Two distinct definitions for parameter are used. In the first usage (preferred), parameter refers to the constants characterizing the probability density function or cumulative distribution function of a random variable. For example, if the random variable W is known to be normally distributed with mean p and standard deviation o, the constants p and o are called parameters. In the second usage, parameter can be a constant or an independent variable in a mathematical equation or model. For example, in the equation Z = X + 2Y, the independent variables (X, Y) and the constant (2) are all parameters. [Pg.181]

To obtain a rough physical understanding of the mechanism of the instability, attention may be focused first on a planar detonation subjected to a one-dimensional, time-dependent perturbation. Since the instability depends on the wave structure, a model for the steady detonation structure is needed to proceed with a stability analysis. As the simplest structure model, assume that properties remain constant at their Neumann-spike values for an induction distance after which all of the heat of combustion is released instantaneously. If v is the gas velocity with respect to the shock at the Neumann condition, then may be expressed approximately in terms of the explosion time given by equation (B-57) as = vtg. From normal-shock relations for an ideal gas with constant specific heats in the strong-shock limit, the Neumann-state conditions are expressible by v/vq = Polp = (y - l)/(y + ),p = PoMl 2y/(y -I- 1), and T = T Ml 2y(y - l)/(y -I- 1). If 0 is perturbed by an amount 5vq, then is perturbed by an amount 51, where [Pg.206]

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