The penetration of drugs and other micromolecules through intact human skin can be regarded as a process of dissolution and molecular diffusion through a composite, multilayer membrane, whose principal barrier to transport is localized within the stratum corneum. A mathematical model of the stratum corneum as a two‐phase protein‐lipid heterogeneous membrane (in which the lipid phase is continuous) correlates the permeability of the membrane to a specific penetrant with the water solubility of the penetrant and with its lipid‐protein partition coefficient. Experimentally measured permeabilities of human skin to a variety of drugs have been found to conform to this model. The extraordinarily low permeability of skin to most micromolecules appears to arise from the very low diffusivity of such molecules in the intercellular lipid phase.

We report the finding of new surface treatments that permit to manipulate the niobium resonator nitrogen content in the first few nanometers in a controlled way, and the resonator fundamental Mattis-Bardeen surface resistance and residual resistance accordingly. In particular, we find surface "infusion" conditions that systematically a) increase the quality factor of these 1.3 GHz superconducting radio frequency (SRF) bulk niobium resonators, up to very high gradients; b) increase the achievable accelerating gradient of the cavity compared to its own baseline with state-of-the-art surface processing. Cavities subject to the new surface process have larger than two times the state of the art Q at 2K for accelerating fields > 35 MV/m. Moreover, very high accelerating gradients ~ 45 MV/m are repeatedly reached, which correspond to peak magnetic surface fields of 190 mT, among the highest measured for bulk niobium cavities. These findings open the opportunity to tailor the surface impurity content distribution to maximize performance in Q and gradients, and have therefore very important implications on future performance and cost of SRF based accelerators. They also help deepen the understanding of the physics of the RF niobium cavity surface.

A technique for direct measurement of the differential diffusion coefficients in a ternary system of water, sugar, and a dilute organic species is described. The individual sugars were d-fructose, d-glucose, and sucrose; and ethyl olcohol. ethyl acetote, n-butyl acetate, and n-hexanal individually constituted the dilute organic species. The four ternary diffusivities were obtained over a range of sugar concentrations by the use of horizontal diaphragm cells, a differential interferometer, a flome-ionization gos-liquid chromatograph and postulation of the validity of the Onsager reciprocal relations. The equilibrium partial pressures of the dilute organic species over these solutions have olso been measured, using a vapor head space chromatogrophic technique.Two main approaches have been utilized for the determination of multicomponent liquid diff usivities. Pseudo steady state diffusion through a porous diaphragm has been one method (1 to 4 ) , while unsteady state diffusion from an initially sharp boundary is the second ( 5 to 9 ) .In this study, the existing binary diffusion data for aqueous sugar solutions are used as a partial basis for a diaphragm cell study of diffusion in a ternary mixture of water, sugar, and a dilute organic species. The ternary diffusion data were required for the analysis of the mechanism of volatiles loss during the drying of food liquids; that analysis is reported in the following paper. For the analysis one of the cross-diffusion terms is highly significant; hence it was necessary that cross-diffusion coefficients as well as straight diffusion coefficients be determined for these systems. The individual sugars were two monosaccharides, d-fructose and d-glucose, and one disaccharide, sucrose. Ethyl alcohol, ethyl acetate, n-butyl acetate, and n-hexanal individually constituted the dilute organic species. From a single experiment with a diaphragm cell and two independent experimental measurements, together with known binary diffusion data for aqueous sugar solutions, the three independent ternary diffusion coefficients are determined. The fourth diffusion coefficient is then obtained from these three ternary diffusivities by the use of the Onsager reciprocal relationship. The variation of these diffusion coefficients with sugar concentration is experimentally obtained. The extent of nonideality of the systems is evaluated by measuring the activity coefficients of the dilute organic components as a function of sugar concentration. These data are required for using the Onsager reciprocal relation. THEORYThe description of the diffusion flux in a binary system of species '4 and B requires that the diffusion coefficient DAB be related to the flux J A in a fixed volume frame of reference by Equation ( 1 ) :Correspondence concerning this paper should be addressed to C. J. where C A is the molar concentration of component A. The mutual diffusion coefficients DAB and DBA are equal, but they are concentration dependent. Equation (1) is equivalent to other definitions of the Chapman-Cowling dif...

In the past decade, high Q values have been achieved in high purity Nb superconducting radio frequency (SRF) cavities. Fundamental understanding of the physical metallurgy of Nb that enables these achievements is beginning to reveal what challenges remain to establish reproducible and cost-effective production of high performance SRF cavities. Recent studies of dislocation substructure development and effects of recrystallization arising from welding and heat treatments and their correlations with cavity performance are considered. With better fundamental understanding of the effects of dislocation substructure evolution and recrystallization on electron and phonon conduction, as well as the interior and surface states, it will be possible to design optimal processing paths for cost-effective performance using approaches such as hydroforming, which minimizes or eliminates welds in a cavity.

In this letter, we present the frequency dependence of the vortex surface resistance of bulk niobium accelerating cavities as a function of different state-of-the-art surface treatments. Higher flux surface resistance per amount of trapped magnetic field-sensitivity-is observed for higher frequencies, in agreement with our theoretical model. Higher sensitivity is observed for N-doped cavities, which possess an intermediate value of electron mean-free-path, compared to 120 • C and EP/BCP cavities. Experimental results from our study showed that the sensitivity has a non-monotonic trend as a function of the mean-free-path, including at frequencies other than 1.3 GHz, and that the vortex response to the rf field can be tuned from the pinning regime to flux-flow regime by manipulating the frequency and/or the mean-free-path of the resonator, as reported in our previous studies. The frequency dependence of the trapped flux sensitivity to the amplitude of the accelerating gradient is also highlighted.