Homogeneous units

Most battery electrodes are porous stmctures in which an interconnected matrix of soHd particles, consisting of both nonconductive and electronically conductive materials, is filled with electrolyte. When the active mass is nonconducting, conductive materials, usually carbon or metallic powders, are added to provide electronic contact to the active mass. The soHds occupy 50% to 70% of the volume of a typical porous battery electrode. Most battery electrode stmctures do not have a well defined planar surface but have a complex surface extending throughout the volume of the porous electrode. MacroscopicaHy, the porous electrode behaves as a homogeneous unit. 

Coming back to the problem of liquid fraction in the MWPB, we observe that the replacement of Eq. (4.177) by (4.202) imposes homogenizing units because we previously established that the mean residence time of the liquid was calculated considering v =1 in dm/s and, consequently, was used in decimeters. Now considering Hj in meters, relation (4.177) becomes ... 

One-Compartment Open Model In this simple model, the body is treated as a homogenous unit with an entry and an exit (i.e., open model) (Figure 2a). It is assumed that changes occurring in blood concentrations reflect similar changes in tissue levels as the xenobiotic rapidly equilibrates between blood and all the various tissues of the body. 

The TNT model postulates a linear relationship between the mass of fuel and that of TNT in order to express the explosion potential of a gas cloud. This implies that the cloud is regarded as a homogeneous unit. This is normally is not true. Rather we have to expect turbulent zones (caused either by the initial momentum or by obstacles such as structural elements of the plant) and quiet zones. Whilst in turbulent zones an explosion may occur, in the quiet zones slow combustion without notable pressure rise is to be expected. 

For purposes of calculation the Plexiglas walls of the cylinders employed in the experiments were treated as HjO and were mixed in with the solution, giving a concentration of 349 g/U (92.6% U-23S) per liter. The homogenized units were approximated by spheres having a radius of 11.25 cm. The reflectors were all assumed to be HjO, and the effect of thickness was calculated from experimental data expressed as albedos. The material buckling of a unit was calculated to be 0.0306 cm" which, with bare and water reflected extrapolation distances of 2.6 and 5.8 cm, is consistent with experimental data for similar solutions. ... 

W. R. STRATTON, Criticality Date and Factors Affecting Criticality of Single Homogeneous Units, LA-3612, Los Alamos Scientific Laboratory (1967). 

The rate of change of free energy of a homogeneous unit volume of material, which is understood to include a fixed number of lattice sites, is... 

Although the classical concept regarding the body as a more or less homogeneous unit enables us to describe a series of pharmacokinetic phenomena with sufficient accuracy, it is now clear that one may arrive at a better understanding of the dynamics of drug distribution if the body is considered as a system divided into finite number of mutually interconnected compartments. It should be pointed out, however, that the term compartment is utilized only as a purely operational concept and that in this respect it cannot be fully identified with the existence of a particular anatomical or morphological structure. It may in some instances serve as an equivalent for the chemical state if, for example, a drug is transformed in the body into a metabolite, this may be represented by the formation of an additional compartment... 

To rationalize this apparent contradiction, a first step is to look at what happens if the macromolecule is no longer described by an infinitely thin thread (Figure 2). Tlie finite lateral size of the polymer can be describe in a very simple way The backbone and lateral parts of the monom form an homogeneous unit and simple geometrical forms are considered. With a circular cross section e size of the side group, or more accurately their extension in tiie solvent, is the unique parameter. With a rectangular cross section. 

---