Penneability

We now turn to a new kind of boundary for a system, a wall penneable to matter. Molecules that pass tlirough a wall carry energy with them, so equation (A2.1.15) must be generalized to include the change of the energy with a change in the number of moles dn ... 

Here p is the chemical potential just as the pressure is a mechanical potential and the temperature Jis a thennal potential. A difference in chemical potential Ap is a driving force that results in the transfer of molecules tlnough a penneable wall, just as a pressure difference Ap results in a change in position of a movable wall and a temperaPire difference AT produces a transfer of energy in the fonn of heat across a diathennic wall. Similarly equilibrium between two systems separated by a penneable wall must require equality of tire chemical potential on the two sides. For a multicomponent system, the obvious extension of equation (A2.1.22) can be written... 

The grand canonical ensemble is a set of systems each with the same volume V, the same temperature T and the same chemical potential p (or if there is more than one substance present, the same set of p. s). This corresponds to a set of systems separated by diathennic and penneable walls and allowed to equilibrate. In classical thennodynamics, the appropriate fimction for fixed p, V, and Tis the productpV(see equation (A2.1.3 7)1 and statistical mechanics relates pV directly to the grand canonical partition function... 

Small molecules can penetrate and penneate tlirough polymers. Because of this property, polymers have found widespread use in separation teclmology, protection coating, and controlled delivery [53]. The key issue in these applications is the selective penneability of the polymer, which is detennined by the diffusivity and the solubility of a given set of low-molecular-weight compounds. The diffusion of a small penetrant occurs as a series of jumps... 

Noncarcinogenic elTects include all toxicological responses except tumors. Toxicological responses and iiicchanisins vary widely, and e.xamples of these include interference with normal cell processes by displacing elements out of the cell and binding with a cell to reduce membrane penneability. However,... 

A rigorous treatment of dispersion in soils is beyond the scope of this book. However, some qualitative discussion is warranted because of the potential and existing problems already described. Two ntain problems arise bceause dispersion in soil (or land) is anisotropic (i.e., it varies with direction) and the penneability is not only a variable but also att unknown. 

For beds made up of randomly oriented symmetric particles, the penneability may be estimated by... 

PE. See polyethylene (PE) pendulum test method perfonnance of product design affecting predicting process and penneability of plastic PET. See polyethylene terephthalate (PET)... 

In physics, an elastic two-dimensional plate is tenned a membrane (Latin membram = parchment) but in chemistry the tenn denotes a body, usually thin, which serves as a phase separating two other bulk phases. If this body is penneable to the same degree for all components of the adjacent phases and does not affect their mobility, then its only function is to prevent rapid mixing of the two phases. This is then tenned a diaphragm. A real membrane must exhibit a certain selectivity, based on different penneability for the components of the two phases, and is then tenned a semipenneable membrane. Membranes separating two electrolytes that are not penneable to the same degree for all ions are called electrochemical membranes. It is with these that we are concerned here. 

Physiologically Based Pharmacokinetic (PBPK) Model—Comprised of a series of compartments representing organs or tissue groups with realistic weights and blood flows. These models require a variety of physiological information tissue volumes, blood flow rates to tissues, cardiac output, alveolar ventilation rates and, possibly membrane penneabilities. The models also utilize biochemical information such as air/blood partition coefficients, and metabolic parameters. PBPK models are also called biologically based tissue dosimetry models. 

The drug substance for which a waiver is being requested should be highly soluble and highly penneable. Sponsors requesting biowaivers based on the BCS should submit the following information to the Agency for review by the Office... 

Another kind of underground storage reservoir is called an aquifer. An aquifer is an underground rock structure holding large quantities of water. The. iindergiound lock is poious and penneable The. pole, spaces aie filled with w ater, and impermeable rock covers the porous rock. Wells are drilled into such formations, and gas is forced into the pores under pressure. As [he gas pressure increases, the gas pushes the water farther down into the porous rock, making room for the gas. 

Abraham, W. and Downing, D. T. (1990). Factors affecting the formation, morphology and penneability of stratum comeum lipid bilayers in vitro. In Scott, R. C., Guy, R. H, and Hadgraft, J., eds. Prediction of Percutaneous penetration. IBC Technical Services, London, pp. 110-122. 

In the previous discussion of Darcy s Law only homogeneous fluid flow was considered. If the porous medium is only partially saturated with a fluid the permeability of the porous medium to the fluid will be less than the permeability obtained when the medium is 100% saturated. The permeability at less than 100% saturation is known as the effective permeability. Values of the effective penneability range between 0 and K where K represents the permeability at 100% saturation. The symbols Kg, Kg, and are used to represent the effective permeabilities to oil, gas, and water, respectively. 

Abbott NJ (2002) Asti ocyte endotlielial interaction and blood brain bander. Penneability. A Anat 200 629-638. 

Kirkhiezos IG, Heiiiandez D, Bradley WG, Moraes CT (2004) An ALS mouse model widi a penneable blood-brain baiiier benefits ffom systemic cyclosporhie A deatment. J Neui ochem 88 821-826. 

CseiT HF, DePasquale M, Haiiing-Berg CJ, Park JT, Knopf PM (1992b) Afferent and efferent anus of die humoral immune response to CSF-admimstered albumins in a rat model widi normal blood-brain banier penneability. J Neui oimmunol 41 195—202. 

Lum H, Andersen TT, Siflinger-Bimboim A, Tiruppathi C, Goligorsicy MS, Fenton n,J.W., Main AB Thrombin receptor peptide inhibits thiombin-induc increase in endothelial penneability by receptor desensitizaticm. J Cdl Biol 120 1491,1993... 

It is thus said that whether the thermal explosion of a chemical of the TD type, including every gas-penneable oxidatively-heating substance, having an arbitrary shape and an arbitrary size, placed in the atmosphere under isothermal conditions, ultimately occurs or not, or simply the for the chemical, is decided, based on the balance between the rate of heat generation in the chemical and the rate of heat transfer from the chemical to the atmosphere at the critical state for the thermal explosion which exists at the end of the early stages of the self-heating process. 

The PID-SCR temperature control technique is adopted for the adiabatic control. Besides, other devices are also adopted to attain as complete an adiabatic control as possible. To cite an instance, a pre-amplifier is incorporated before the PID controller to amplify the A i.e., the temperature difference between the temperature of 2 cm of a chemical of the TD type, including every gas-penneable oxidatively-heating substance, and the T),. A zero suppression circuit is composed of this amplifier to cancel the slight stray-, or pseudo-, Ihermoelcctromotive force of the differential thermocouple. Such a pscudo-ihcmioclcctromolivc force of a differential thermocouple may still appear even if the temperature of 2 cm of the chemical and the r , . are physically the same, and even if the two thermocouples to make up the differential thermocouple are... 

Glass vent tube 2. Thermocouple to measure the or the temperature of an oxidatively-heating substance 3. Thermocouple to measure the 7, , 4. Gas inlet 5. Gas outlet 6. Safety valve 7. Bellows 8. Draft cell in which a reference material or a gas-permeable oxidatively-heating substance is charged 9. Thin gas-penneable silica fiber sheet 10. Heating wire 11. Glass wool. 

---