The catalytic behavior of alkali metal carbonates and oxides in graphite oxidation reactions

The reactions that occur in different gaseous environments between graphite and alkali metal carbonates and oxides have been studied by simultaneous thermogravimetry-differential thermal analysis and hot-stage microscopy. The catalytic effects of these salts during gasification of graphite in oxygen and carbon dioxide are interpreted on the basis of distinct oxidation-reduction cycles, involving the intermediate formation of peroxide in the former case and alkali metal in the latter. The thermodynamic feasibility of the proposed cycles has been discussed in detail.     

Very low sensitivity recursive digital filter structures

A type of realisation of recursive digital filters is proposed here to give very low-magnitude transfer function sensitivity with respect to multiplier coefficients. Simulation results of sensitivity values for a simple 2nd-order filter are presented and compared with some of the existing realisations to show the order of improvements.     

Studies of alkali-silica reaction — part II effect of air-entrainment on expansion

From an extensive petrographic investigation of concrete samples suffering from alkali-silica reaction, it has been hypothesized that a deliberately introduced air-bubble system will reduce expansion due to alkali-silica reaction. The above hypothesis has been tested using mortar bars made from 35 sand types of differing degrees of alkali-silica reactivity. The results show that on the average the introduction of 4% air decreased the expansion by about 40%. A petrographic examination of mortar bars has shown that in the case of reactive sand the air-bubbles tend to get filled up by gel, but the air-bubbles remain empty in the case of unreactive sand. It has also been noted that this filling up of the air-bubbles will decrease their effectiveness in a freezethaw environment.     

The mediator for stringent control, ppGpp, binds to the beta-subunit of Escherichia coli RNA polymerase

OBJECTIVE: Evaluate the behavioral reputation and peer acceptance of children diagnosed and treated for brain tumors. METHOD: Twenty-eight children surviving brain tumors (8-18 years of age) were compared to 28 nonchronically ill, same classroom, same gender comparison peers (COMP). Peer, teacher, and self-report data were collected. RESULTS: Relative to COMP, children who had been diagnosed with brain tumors received fewer friendship nominations from clasmates and were described by peer, teacher, and self-report as socially isolated. Although they were no longer receiving therapy for their disease, peers perceived brain tumor survivors as being sick, more fatigued, and often absent from school. CONCLUSIONS: These data suggest that children surviving brain tumors are at risk for social difficulties even after treatment ends, although the specific cause(s) for this vulnerability were not investigated in the current study.     

CaO/SiO2 mole ratio of calcium silicate hydrate in fully hydrated tricalcium silicate paste

CaO/SiO₂ mole ratio of calcium silicate hydrate in fully hydrated pastes of tricalcium silicate have been determined both directly by the electron beam microanalytical technique and indirectly by extracting Ca(OH)₂. Both techniques yield a CaO/SiO₂ mole ratio of 1.6.