Three-Phase Induction Generator for Single-Phase Line

Hydroelectric generators of less than 20 kilowatts can be in remote areas served only by a single-phase line. For high efficiency and low cost, a three-phase induction generator should be used. This three-phase generator can operate with balanced voltages and currents when the ``phase-splitting' circuit uses two capacitors connetted to two different single-phase voltage sources.     

Electrical characterization of megabit DRAMs. 11. Internal testing

For pt.I. see ibid., vol.8, no.3, p.36-43 (1991). Contactless tools for testing inside dynamic RAMs, including hot-spot detection, emission microscopy, scanning laser microscopy, and submicron electron beam testing, are described. Basic principles and experimental setups are described. The utility of the techniques is assessed     

Something completely different: Informatik und Sport

Ohne Zusammenfassung     

Heat transfer mechanisms in gas fluidized beds. Part 3: Heat transfer in circulating fluidized beds

Part 1 of this contribution reported on the effects of system properties on heat transfer between heating or cooling surfaces and bubbling fluidized beds. This investigation produced four correlations which define the respective maximum heat transfer. Part 2 of this study suggests that the heat transfer between exchanger surfaces and bubbling fluidized beds depends on superficial gas velocity, expressed as dimensionless excess gas velocity. The present paper shows that heat transfer coefficients in circulating fluidized beds can be predicted by evaluation of a state diagram, which combines three dimensionless groups: Nusselt number, Archimedes number and a dimensionless pressure gradient. A comparison of coal combustion experiments with own cold model measurements indicates that the radiative component of heat transfer coefficients is only evident at very low dimensionless pressure gradients.     

On confluence versus strong confluence for one-rule trace-rewriting systems

Examples of one-rule trace-rewriting systems are given that are confluent but not strongly confluent. This contrasts with the situation for one-rule string-rewriting systems as well as with the situation for one-rule commutative string-rewriting systems.     

Head-to-head polymers: 33. Bromination of cis-1,4-polybutadiene to head-to-head poly(vinyl bromide)

Cis-1,4-polybutadiene (PB) in a 0.5% solution of a solvent mixture of dichloromethane and 1,2-dibromoethane or tetrahydrofuran was quantitatively brominated with elemental bromine at 0°C under careful exclusion of oxygen to head-to-head poly(vinyl bromide). Partially brominated PB has a structure of random or block sequences of butadiene units in the polymer depending on the bromination solvent but shows no stereospecificity in the CHBrCHBr-dyads. Partially brominated PB with block structure showed a microphase-separated morphology over a wide range of composition. Microphase separation is less pronounced for the more random structure of butadiene units. I.r and ¹³C n.m.r. spectroscopy of the partially brominated PB was used to follow the progress of the bromination.     

Functional polymers

Summary Polymeric antioxidants prepared from 2,6-di-tertiary-butyl-4-vinyl (4-lsopropenyl)phenol and butadiene or isoprene, and their hydrogenated products (6-8 mol % of phenolic AO in the polymer) were tested by oxygen uptake studies for their effectiveness as antioxidants for polyolefins and polydienes. The polymeric antioxidants seem to be slightly less effective in short-term protection against oxidation at 150° C as compared to low molecular weight antioxidants, but more effective in long-term protection of the polymer samples at a level of 0.1 weight percent.Part 43: P. Grosso, O. Vogl: J. Macromol. Sci. Chem., in pressNow Chemical Company, Midland, MI 48674, USATo whom all correspondence should be addressed: Herman F. Mark Professor of Polymer Science, Polytechnic Institute of New York, Brooklyn, NY 11201, USA     

Throughput of a satellite channel communication

Summary The throughput of a satellite channel communication is depending upon the link protocol. It is well known that the classical HDLC protocol is inadequate when applied to satellite links instead of short terrestrial links. Several modifications have been proposed to overcome this problem. The present paper gives an analysis and evaluation of a new class of protocols called Virtual Subchannel schemes which splits the satellite link into several components; these subchannels are assigned for transmission in cyclic order and are controlled independently of each other by the classical HDLC procedure.     

Catalytic steam gasification of graphite: Effects of calcium,strontium, and barium with and without sulfur

Alkaline earths strongly catalyze steam gasification of graphite. The catalytic effect increases in the order Ca < Sr < Ba. Reaction rates of graphite impregnated with 0.3 at.% Ba are 500 times larger than those of pure graphite. Catalysis is due to the participation of additional reaction sites, not to a lowering of the true activation energy. It follows from kinetic data, electron microscopic observations, and theoretical considerations that the efficiency of the catalysts is closely related to their ability to coat a carbon surface and to continue contact with carbon atoms emerging from the bulk. In the presence of sulfur, severe, but not complete, catalyst deactivation occurs. This poisoning is to a large degree reversible.     

Einfluß von Lösungsmitteln auf den Partikeldurchmesser von Dispersionen anionischer Polyurethanionomerer

Aqueous dispersions of anionic polyurethanes were prepared by reaction of polyethers, 1,6-hexamethylene diisocyanate, 1,2,4-benzenetricarboxylic acid anhydride and triethyl amine. Formation of the dispersion was achieved by phase reversal or by precipitation. Phase reversal occurred when the solution or the melt of the polymer was treated with water, while precipitation took place when the solution was stirred into water. The amount of acetone used has an effect on the mean particle diameter, D?_T, obtained by turbidity measurements. There was an optimal acetone concentration at which D?_T reached a minimum. A similar effect was observed when tetrahydrofuran, 2-butanone or acetonitrile were used as solvents instead of acetone. When the dispersion was formed by precipitation, only adequately diluted acetonic solutions formed colloidal dispersions, while concentrated solutions gave dispersions with a broad particle size distribution.