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We present a model for multicomponent diffusion in ionic crystals. The model accounts for vacancy-mediated diffusion on a sub-lattice and for diffusion due to binary exchange of different ionic species without involvement of vacancies on the same sub-lattice. The diffusive flux of a specific ionic species depends on the self-diffusion coefficients, on the diffusion coefficients related to the binary exchanges, and on the site fractions of all ionic species. The model delivers explicit expressions for these dependencies, which lead to a set of coupled non-linear diffusion equations. We applied the model to diffusion of 23 Na, 39 K, and 41 K in alkali feldspar. To this end, gem-quality crystals of alkali feldspar were used together with 41 K doped KCl salt as diffusion couples, which were annealed at temperatures between 800 • and 950 • C. Concentration-distance data for 23 Na, 39 K, and 41 K were obtained by Time of Flight Secondary Ion Mass Spectrometry. Over the entire investigated temperature range the Na self-diffusion coefficient is by a factor of ≥ 500 higher than the K self-diffusion coefficient. Diffusion mediated by binary 39 K-41 K exchange is required for obtaining satisfactory fits of the model curves to the experimental data, and the respective kinetic coefficient is well constrained.

Recent technological advances coupled with the collaboration between government and industry will soon make it possible to include IP routers and IP modems on board a commercial geostationary communications satellite. The Internet Protocol Routing in Space (IRIS) Joint Capability Technology Demonstration (JCTD) will introduce a new network capability that is aimed at enhancing military network-centric operations through information access, collaboration and dissemination.This paper describes the IRIS vision and strategy, and the specific goals ofthe JCTD. It describes the network architecture and technology development aspects for deploying a combined router and modem function as part of a hosted payload within a commercial transponded satellite.1-4244-151

<p><span>Alkali feldspar is one of the most common rock forming minerals in magmatic and metamorphic rocks. It forms a solid-solution between the sodium and potassium end members. At temperatures above about 600</span><span>°</span><span>C alkali feldspar shows continuous miscibility. Towards lower temperatures, a miscibility gap exists. When cooled from super-solvus temperatures into the two phase region of the phase diagram, alkali feldspar of intermediate composition exsolves forming coherently intergrown lamellae of Na-rich and K-rich alkali feldspar, a microstructure referred to as perthite. The compositions and the characteristic widths of the exsolution lamellae reflect the cooling history. For a quantitative retrieval of cooling rates the thermodynamics of the solid solution including the effect of coherency strain and Na-K interdiffusion, which determines the coarsening kinetics, must be known. </span></p><p><span>Four alkali feldspars with different degrees of Al-Si ordering were investigated, namely Madagascar Orthoclase, Volkesfeld Sanidine, Zillertal Adular and Zinggenstock Adular. For each feldspar a ther- modynamic mixing model describing the strain free solvus was derived from feldspar-NaCl-KCl salt Na-K partitioning experiments performed at 800</span><span>°</span><span>C, 900</span><span>°</span><span>C and 1000</span><span>°</span><span>C. The models show increasing non-ideality with increasing degree of Al-Si ordering. The corresponding coherent solvi and spinodes were calculated using the strain energy function of Robin (1974). </span></p><p><span>The coarsening kinetics was obtained from exsolution experiments. To this end, each alkali feldspar was shifted to intermediate compositions by exchange with NaCl-KCl melt at 900</span><span>°</span><span>C for 35 days and subsequently tempered at 440</span><span>°</span><span>C, 480</span><span>°</span><span>C, 520</span><span>°</span><span>C and 560</span><span>°</span><span>C for 4, 8, 16, 32, 64, 128 or 256 days. Analyses of the run products by pXRD revealed splitting of reflections of the lattice planes that are subparallel to the lamellae subparallel to (-801), a feature that is diagnostic for coherent exsolution in feldspar. TEM investigation of foils extracted perpendicular to the crystallographic </span><strong><span>b</span></strong><span>-axis revealed fully coherent lamellae and lamellar widths between 8 and 30 nm. Lamellae growth rates were obtained from the time series experiments. For a given annealing time and temperature Madagascar Orthoclase shows relatively sharp and thick lamellae as compared to the other three feldspars. The coherency strain was derived from a comparison of the lattice parameters determined for the Na-rich and the K-rich lamellae by pXRD measurements of the experimental products with those of strain free feldspar as given by Kroll et al. (1986). The strain energy density calculated for the coherent intergrowth is by a factor of two smaller than the one given by Robin (1974).</span></p><p>Kroll, H., Schmiemann, I., and Cölln, G. (1986). <span>Feldspar solid solutions. </span><span>American Mineralogist</span><span>, 71:1–16.</span></p><p><span>Robin, P.-Y. F. (1974). Stress and strain in cryptoperthite lamellae and coherent solvus of alkali feldspars. </span>Am Mineral, 59:1299–1318.</p>