Synthesis of Si3N4 with Emphasis on Si-S-N Chemistry

Industrial production of Si₃N₄ from SiCI₄, is increasing. An element rivaling CI in abundance and cheapness with potentially suitable chemistry for this application is sulfur. Thus, Si–S–N chemistry was investigated to determine its usefulness in producing Si₃N₄. Bifunctionality in S, as opposed to mono-functionality in CI, may allow special routes via polymers to become important.     

Accountability of work activity in high-consequence work systems: human error in context

Organizational context is now accepted as a central concept in attempts to understand error in human–machine systems. However, accounts which emphasize the processes of everyday organizing, such as accountability and work activity, are needed in order to establish organizational requirements for design. In this article, we provide a framework for the consideration of organizational contexts of human error in high-consequence work systems, with a view to integrating empirical insights and supporting practical design work. We draw on computer-supported cooperative work conceptualizations of the process of everyday organizing, particularly the notion of “accountability for work activity” which is pivotal to our organizational account of error. The conceptual framework is characterized here as a set of dimensions which are expressive concerning the relationship between accountability and work activity in different contexts: (1) explicit–implicit; (2) global–local; (3) stable–transient and (4) dependent–independent. The framework is demonstrated with respect to everyday work practices in a radiology department and its analytical utility validated with respect to two documented aviation system failures. Applying the framework has enabled us to identify and define, in terms of the dimensions, a number of contexts for vulnerability in high-consequence systems: contexts for collusion, violation, deference, loss of control, buck passing and complacency. These are discussed in terms of requirements for error-tolerant design. In the final section of the article, links between the various contexts for vulnerability and the design process are explored.     

“BACK THE BID”: THE 2012 SUMMER OLYMPICS AND THE GOVERNANCE OF LONDON

ABSTRACT: The Olympic Park being developed in east London for the 2012 Games is one large urban renewal project among many in the city. The impact of the Games on urban development may be of less significance than the impact on city politics. Bidding for and delivering the Games has contributed to a reassessment of the recent experiment with mayoral government. The article examines these changing representations of the structures of London government that are now seen as a success. Much of the literature on Olympic cities is highly critical of the impact of the games, but the (current) substantial support for London 2012 also needs to be explained. We examine how London has created opportunities for support, and moments and spaces for celebration when political leaders and Londoners can come together around particular representations of themselves and the city.     

Liquid Immiscibility in the Systems X2O-MO-B2O3-SiO2 (X=Na, K; M=Mg, Ca, Ba) and Na2O-MgO-BaO-B2O3-SiO2

The limits of miscibility at 650°C were determined for compositions with the mole ratio SiO₂/B₂O₃=1.07 in the systems X₂O-MO-B₂O₃-SiO₂ (X = Na,K; M = Mg,Ca,Ba) and Na₂O-MgO-BaO-B₂O₃-SiO₂. The form of the miscibility gaps in the quaternary systems is similar to that previously described for the system Na₂O-ZnO-B₂O₃-SiO₂. The topography of miscibility gaps in systems of this type is discussed in detail. The extent of the miscibility gap is correlated with the polarizing power of each cation, X and M (Na > K and Zn ≅ Mg > Ca > Ba) both among the seven quaternary systems and within the single five-component system examined. The possibility of using empirical correlations observed among the quaternary systems to predict the behavior of other compositions, or of more complex systems, is explored.     

On-line Animated Visualization of Huge Graphs using a Modified Spring Algorithm

On-line graph drawing deals with huge graphs which are partially unknown. At any time, a tiny part of the graph is displayed on the screen. Examples include web graphs and graphs of links in distributed file systems. This paper discusses issues arising in the presentation of such graphs. The paper describes a system for dealing with web graphs using on-line graph drawing.     

The histochemical properties of some periodate-reactive mucosubstances of the pregnant Syrian hamster before and after methylation with methanolic thionyl chloride

The mucosubstances secreted in various tissues of pregnant Syrian hamsters exhibit a wide range of histochemical characteristics. When sections of fixed tissues containing these mucosubstances are treated with a methanolic solution of thionyl chloride for four hours at room temperature, nucleic acid phosphate groups, protein and sialomucin carboxyl groups, and the sulphate groups of many sulphomucins are apparently esterified. In sulphomucins believed to contain carboxyl and sulphate groups, only the sulphate is esterified; the carboxyls (uronic acid groups ?) are left free. If such methylated mucins are saponified (to remove their ester methyl groups) some, but not all, of their histochemical reactions for “free” sulphate are restored. Some desulphation, however, usually occurs during the methylation process. A few sulphated mucins, such as those in the goblet cells of the small intestine, are desulphated completely. The ability to esterify many sulphated mucins without either desulphating them completely or extracting them from the tissue distinguishes methanolic thionyl chloride from the hot methanolic solutions of hydrochloric acid usually used for methylating tissue sections. Moreover, methanolic thionyl chloride solutions are much easier to use. The little chemistry that is at present known about the reactions between methanol and thionyl chloride is insufficient to explain how methanolic thionyl chloride solutions actually methylate polyanionic substances in tissue sections.