Permeabilities to salts and water of macrocyclic polyether–polyamide membranes

The polyether–polyamide (PC-6) strongly absorbs sodium salts from their aqueous solutions. Membranes based on PC-6 and on its polymeric alloys with poly(vinylpyrrolidone) (PVP) are, however, much more permeable to water than to salts. The membrane permselectivity is due to the low mobility of the absorbed salts. Desorption experiments were conducted to determine the values of the diffusion coefficients of the sodium ions in the investigated membranes. They were found to vary from 5 × 10^-12 cm²/sec in loose PC-6 membranes to 1.7 × 10^-9 cm²/sec in the polymeric alloy containing 30% PVP. Water permeation experiments with the alloy membranes yielded values of the diffusion coefficients in the range of 2–5 × 10^-7 cm²/sec. The apparent “energy of activation of the diffusion” of sodium ions in such membranes was found to be essentially indentical (～12 kcal) with the energy of activation of the decomplexation of the sodium–“crown” complex. The ramifications of the proposed “site to site jump” diffusion mechanism were discussed. The permeability characteristics of PC-6 membranes were found to be strongly affected by their “history.”. The observed phenomenon was explained in terms of reversible changes in the structure of the polymeric network, in the presence and in the absence of the absorbed salts. It has been found that PVP has a stabilizing effect on the permeability characteristics of the membranes. Reverse osmosis experiments indicated that their intrinsic osmotic characteristics seem to be superior to those of the commercially used materials. Their salt rejections are in the range of 95–99.5%, and their permeabilities to water are at least one order of magnitude higher than those of the unmodified aromatic polyamides.     

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Ohne Zusammenfassung VDI     

Fair,biased, and self-balancing merge operators: Their specification and implementation in Concurrent Prolog

The problem of allowing a dynamically changing set of processes fair access to a shared resource is considered, in the context of communication-stream based systems. It is argued that fair binary merge operators alone cannot solve this problem satisfactorily. Two solutions are proposed. One employs binary merge operators with a programmable bias; the other binary and ternary fair merge operators capable of self-balancing, using the concept of 2–3 trees. A Concurrent Prolog implementation of these operators is described. The implementation of the self-balancing merge operators illustrates the expressive power of incomplete messages, a programming technique that supports messages that contain communication channels as arguments. In the course of implementing the self-balancing merge operator, it was necessary to develop a distributed variant of the 2–3 tree deletion algorithm.     

Innovations in the ENHS reactor design and fuel cycle

A number of approaches were explored for improving characteristics of the encapsulated nuclear heat source (ENHS) reactor and its fuel cycle, including: increasing the ENHS module power, power density and the specific power, making the core design insensitive to the actinides composition variation with number of fuel recycling and reducing the positive void coefficient of reactivity. Design innovations examined for power increase include intermediate heat exchanger (IHX) design optimization, riser diameter optimization, introducing a flow partition inside the riser, increasing the cooling time of the LWR discharged TRU, increasing the minor actinides' concentration in the loaded fuel and split-enrichment for power flattening. Another design innovation described utilizes a unique synergism between the use of MA and the design of reduced power ENHS cores.

Also described is a radically different ENHS reactor concept that has a solid core from which heat pipes transport the fission power to a coolant circulating around the reflector. Promising features of this design concept include enhanced decay heat removal capability; no positive void reactivity coefficient; no direct contact between the fuel clad and the coolant; a core that is more robust for transportation; higher coolant temperature potentially offering higher energy conversion efficiency and hydrogen production capability.     

A stable finite element simulation of convective transport

A finite element simulation of the equations of momentum and energy transport in fluids has been implemented with triangular elements. An attempt is made to single out the reasons for numerical instabilities reported by other investigators for convection–diffusion transport operations in fluid mechanics when the ratio of the convective to the diffusive terms, measured by the Reynolds and Peclét numbers, is of the order of a hundred. To this end, the equations are solved for several problems to permit a direct comparison with results of other formulations. It is shown that the appearance of instability can be delayed by a proper choice of boundary conditions, and its intensity can be reduced through the use of triangular finite elements. Results agree very well with theoretical solutions for particular test problems including flows with large convection effects, large dissipation effects and fluids with temperature dependent properties.