Pore structures in an implantable sol-gel titania ceramic device used in controlled drug release applications: A modeling study

Several process variables, which may be helpful in optimizing the rate at which drugs are released from implantable, sol-gel titania devices have been identified in this study. The controlled rate of drug release is compared for two different anticonvulsant drugs, valproic acid and sodic phenytoin. Contrary to what one might expect, when the concentration is increased in the titania reservoir the rate of initial drug delivery decreases. This is a desirable result, because it may reduce the danger of a high initial discharge, which may harm the epileptic rat. The structure of the porous structure within the titania network has been studied using a generalized form of the BET equation which considers only n layers. In general, following an initial discharge, the rate at which the drug is released will increase with the increasing concentration. Pore mouth blocking can present a problem. However, this problem tends to disappear following the initial discharge. The extent of drug loading is a useful variable parameter, which can be adjusted in order to deliver the amount of drug required in a given application.     

Perfluorinated anion exchange membranes: Preparation and preliminary tests of dialysis

Using the preirradiation technique a kinetic study of the grafting of the 4-vinyl pyridine (V₄P) and an aliphatic ammonium monomer (ALAM) onto the copolymer film of ethylene–tetrafluoroethylene (ETFE) has been performed. The influence of dose, temperature, and concentration of monomer, reticular agent, and inhibitor were investigated. The results are discussed on the basis of the interactions between monomer diffusibility and viscosity of the medium. The characteristics of some membranes were determined. Their applicability to the recovery of acid by dialysis is demonstrated.     

Numerical analysis of pattern formation on the surface of transpiring leaves

The process of photosynthesis is facilitated by pores on the leaf surface called stomata. When a particular stoma is open, CO₂ is absorbed through its aperture, but H₂O is also lost due to evaporation. Thus a plant will seek a stomatal aperture that balances its need for CO₂ with its aversion to H₂O loss. In order to visualize a particular leaf’s stomatal aperture distribution and how it changes with time, fluorescence data is collected at regular intervals as digital images, resulting in a video sequence. It has been observed that stomatal apertures are often synchronized into spatially extended patches. In order objectively to analyze this phenomenon we have developed a technique to isolate patches via a three-dimensional PDE-based segmentation method. The resulting segmented data is then collapsed to a vector valued time series of much smaller dimension with a hybrid PCA-Archetypal Analysis approach. This allows for a unique interpretation of the data in terms of statistical measures of the motions of representative patches. The technique is illustrated with a data-set from a particularly complicated regime collected by the Complexity and Stomatal Behavior research lab at Utah State University.     

Fluctuations in a fluid under a stationary heat flux II. Slow part of the correlation matrix

The general formulas, derived in a previous paper, are used to calculate the correlation functions of the hydrodynamic variables in the Rayleigh-Bénard system. The behavior of the correlation functions on a time scale slow compared to that of sound propagation is determined, using systematically nonequilibrium hydrodynamic eigenmodes. These (slow) eigenmodes of the linearized Boussinesq equations in the presence of gravity and a temperature gradient are the viscous and the visco-heat modes. They are determined for ideal heat-conducting plates with stick boundary conditions. The visco-heat modes are found to behave qualitatively different from those obtained with slip boundary conditions. Using these eigenmodes, the slow part of the correlation functions can be determined explicitly. On a small length scale, as probed by light scattering, we recover the same expression for the Rayleigh line as quoted in the literature. On larger length scales, as probed by microwaves, the coupling of gravity to the temperature gradient gives rise to a convective instability (heating form below) or to propagating visco-heat modes (heating from above). The corresponding correlation functions and the Rayleigh line are calculated and discussed.     

Excitation and ionization accompanying the beta decay of T2

The probabilities for shake-up and shake-off excitation accompanying the beta decay of molecular tritium have been computed. The shake-off channels account for 15% of the excitation probability. Roughly 2/3 of the shake-off intensity is concentrated in a band of resonances occuring about 20 eV above threshold.     

Bands on trees

Communicated by D. R. Brown