Browsing by Author "Wang, C. C."
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Item Cation transport by the ionophores dianemycin, monensin, and nigericin in a simple model membrane system(1977) Harris, David L.; Wang, C. C.The transport of alkali metal cations by the carboxylic lonophores dianemycm, monensin, and nigericin was studied using a model membrane system in which a solution of the ionophore in a dense, water-immiscible solvent fills the bottom of a "U"-shaped glass tube, forming a liquid "membrane" between two aqueous salt solutions. Small samples of the salt solutions were taken over a period of several days and analyzed by flame spectroscopic techniques to measure the relative rates of exchange of two competing cations on one side of the membrane for a third cation on the opposite side. With ortho-dichlorobenzene as the membrane solvent, the "selectivity sequences" obtained from the relative transport rates were similar to published sequences resulting from equilibrium studies with one- and two-phase systems. However, they resemble more closely the sequences obtained from non-equilibrium experiments on biological and non-biological membrane systems. The transport of the alkali metal cations was strongly influenced by both the pH and the buffering capacity of the aqueous phases. Experiments with chloroform and carbon tetrachloride as the membrane solvents indicate that the transport rate is also effected by a change of solvent.Item Inertia effects in consolidation problems(1981) Lockett, Robert R.; Bowen, Ray M.; Wang, C. C.; Wilhoit, James C.The dynamic behavior of a chemically inert, isothermal mixture of an isotropic elastic solid with an elastic fluid is studied. Geometrically, this mixture is assumed to comprise a layer of fixed depth, bounded below by a rigid, impervious surface, and above by a free surface to which loads are applied. The resulting boundary-initial value problem is solved by use of a Green's function. Two different loading conditions are used to demonstrate the effect of including inertia terms in the equations of motion. In the first example of a constant compressive load, our result is found to agree with the inertia-free solution only for very long times. The second example shows that for a harmonically varying compression, resonance displacements occur at certain loading frequencies, whereas the solution obtained by neglecting inertia does not predict this behavior.Item One dimensional shear motions in fluid saturated porous media(1981) Roberson, Kyle R.; Bowen, Ray M.; Wilhoit, James C.; Wang, C. C.An analytic solution is presented for shear motions in a binary mixture of a chemically inert, isothermal, elastic isotropic solid and elastic fluid subject to a sinusoidally varying solid displacement on one boundary and free of tractions on the other. It is demonstrated that the retention of inertial terms, and the resulting resonance phenomenon, can cause solid displacements in the interior of the region orders of magnitude greater than the exciting solid displacement on the boundary. Displacement spectra are presented for certain well known porous media.Item Short range order in lattice dynamics and the feasibility of exafs measurements(1985) Laaksonen, Reima Tapani; Wang, C. C.; Trammell, George T.; Miettinen, Hannu E.We studied theoretically the kinetics of a bcc lattice near the critical temperature. Our motivation is to examine the feasibility of using the recently developed time-resolved EXAFS technique to study the lattice dynamics. We derived the kinetic equations using the quasi-chemical approximation and keeping the number of particles constant and allowing only atom-vacancy exchange process. We solved these equations for a relaxation process following a sudden temperature change. Our calculations show that the long-range order exhibits critical slowing-down, as expected. Also the non-linear coupling between short- and long-range order was observed. Because of this non-linear coupling the relaxation of the short-range also slows down near the critical temperature. Our results put stringent conditions on possible experiments.Item Structure of valinomycin-K+ complex and cryptate-k+ complex in solution by extended x-ray absorption fine structure(1981) Williams, Craig; Wang, C. C.; Rorschach, Harold E.; Hannon, James P.A new tool used to study the structure of molecules is Extended X-ray Absorption Fine Structure (EXAFS). EXAFS is small oscillatory signals added on to the smooth x-ray absorption structure curve produced from the excitation of an inner electron out of its bound inner shell into a free electron state. The oscillations are produced from scattering of the excited electron from surrounding atoms. These oscillations, EXAFS, contain molecular structure information, such as the distances between atoms. Since EXAFS can be used for crystals, amorphous solids, solutions and gases it has a strong advantage over x-ray crystallography in many cases for determining local structural information. I used EXAFS to determine what structural changes occur between the known crystalline states and the unknown solution states of K+ complexed with the ionophores cryptate and valinomycin. Ionophores are organic molecules which have a polar oxygen and nitrogen cage in the center of the molecule and a hydrophobic organic exterior. These ionophores are capable of trapping a potassium ion within the cage. The hydrophobic exterior allows the ionophore to dissolve in organic solvents. For the K+-cryptate complex I found no differences in the structure between the crystalline and acetone solution states. For the K+-valinomycin complex I found the K+- distances increased by .3 ± .2 A in the solutions as compared to the crystalline state.Item Theoretical interpretation of anomalous diffusion coefficient of micellar solutions measured by light scattering(1980) Chen, Fang-Yu; Wang, C. C.; Rorschach, Harold E.; Dodds, Stanley A.A sodium di-2-ethyl hexylsulfosuccinate (AOTj/H2O/ decane (in the weight ratio of 3:5:95) system is believed to be a solution of micelles consisting of AOT coated water droplets dispersed in decane. A recent experiment of light scattering from such a system showed a diffusion coefficient strongly dependent on the scattering wave vector q. We examine several mechanisms which are known to cause q-dependence in diffusion coefficient. These include intermicelle interactions and mode-mode couplings. If the micelles are rigid, theories can not reproduce the data. In order to be consistent with data, the micelles should be deformate and stressless. That means the relative motion between parts of a micelle is hydrodynamic. The theory is tested by comparing the correlation length § determined from the scattering intensity with the § independently determined from the diffusion coefficient. We also found the "bare" diffusion constant to be negative.