Salt elimination reactions of tris(trimethylsilyl)silyl potassium (1), and two 1,4-dipotassiooligosilanes (3, 5) with 2,2,6,6-tetramethylpiperidinodichloroborane and diethylaminodichlorophosphane have generated open (2), cyclic (4) and bicyclic (6) bora- and phosphaoligosilanes. A monosilylated phosphane and the two five-membered cyclosilanes have been subjected to single crystal X-ray diffraction analysis.
The cross-coupling of a variety of terminal alkynes 1 with allenylphosphine oxides 2 catalyzed by a Pd(OAc)(2)-TDMPP system provided conjugated endo-enynes 3 solely, while the TCPC-catalyzed reaction of the same regents led to the exclusive formation of exo-isomers 4. The mechanistic rationale for these selective transformations was proposed. Synthetic usefulness of the prepared exo-enyne 4 was demonstrated in the synthesis of multisubstituted diarylbenzylphosphine oxides 5 via the Pd-catalyzed [4+2]-benzannulation reaction.
Abstract-Published data describing the probability distributions of data communication system reliability parameters such as availability are very sparse. This paper describes a set of data collected in order to model communication line availability by monitoring operational communication systems. Probability distribution functions for single line availabilities and for the durations of failures are given. A heuristic model for estimating availabilities for more complex systems is presented along with computer simulation data validating the accuracy of the model. The results presented make possible more realistic availability predictions for common types of networks than have previously been computable.
Technical innovations such as large-scale integrated circuit technology and distributed operating systems have respectively reduced the cost of computing and provided a basis for large networks within the confines of a single building or cluster of buildings in close proximity to one another. Local area networks can provide a systematic approach for interconnecting personal workstations, control units, and central processing units, thereby providing a means for these machines to pass information from one to the other. This paper describes a local area network based on the fundamental concepts of a token-ring. Two main ideas are presented. The first idea concerns the physical topology of the wiring network and its star-ring organization. Next, the logical data flows are overlaid on the physical network to provide control procedures for exchanging data through the network. The resulting system has unique features that produce a local area network with good performance and reliability characteristics.T he present trend toward distributed data processing, coupled with the increased emphasis on office automation and the widespread use of automated office terminals, displays, and computers, has created a demand for a more comprehensive approach to terminal interconnection systems. Personal workstations can increase overall productivity by allowing the individual office workers, both clerical and professional, to share access to host systems, common data bases, peripheral print-
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