Hydrotrope Action of Vitamin C (VC) and Its Application in a Sunscreen

The solubility regions of the sunscreen 2-ethyIhexyl p-methoxycinnamate (E557) in the CTAB/ n-CsHnOH/ H₂ O system with and without the hydrotrope agent vitamin C (VC) are determined. E357 was only sohibilized in the bicontinuous microemulsion (BI), the W/ O microemulsion area and the lamellar liquid crystal region (LLC). The addition of VC in the system greatly enlarged the solubility amount of E₅₅₇in the bicontinuous region, but reduced h in the lamellar liquid crystal area. Small angle X-ray diffraction measurement was used to determine the location of E₅₅₇ in the lamellar liquid crystal showing the suncreen molecule penetrating between the hydrocarbon chains in the liquid crystal structure.The UV absorption spectra of E557 in various media was measured, surprisingly showing a dependence on the colloidal structure.     

Finite-Element Methods for a Strongly Damped Wave Equation

Error estimates of optimal order are proved for semidiscreteand completely discrete finite-element methods for a linearwave equation with strong damping, arising in viscoelastic theory.It is demonstrated that the exact solution may be interpretedin terms of an analytic semigroup, and as a result that, althoughthe solution has essentially the spatial regularity of its initialdata, it is infinitely differentiable in time for t>0. Theestimates for the spatially discrete method are derived by energyarguments. Rational approximation of analytic semigroups isdiscussed in a general setting, by means of spectral representation,and the results are used to analyse the completely discreteschemes. Both smooth (and compatible) and less smooth data areconsidered.     

Process Based Reconstruction of Sandstones and Prediction of Transport Properties

We present a process based method for reconstructing the full three-dimensional microstructure of sandstones. The method utilizes petrographical information obtained from two-dimensional thin sections to stochastically model the results of the main sandstone forming processes – sedimentation, compaction, and diagenesis. We apply the method to generate Fontainebleau sandstone and compare quantitatively the reconstructed microstructure with microtomographic images of the actual sandstone. The comparison shows that the process based reconstruction reproduces adequately important intrinsic properties of the actual sandstone, such as the degree of connectivity, the specific internal surface, and the two-point correlation function. A statistical reconstruction of Fontainebleau sandstone that matches the porosity and two-point correlation function of the microtomography data differs strongly from the actual sandstone in its connectivity properties. Transport properties of the samples are determined by solving numerically the local equations governing the transport. Computed permeabilities and formation factors of process based reconstructions of Fontainebleau sandstone compare well with experimental measurements over a wide range of porosity.