A QUANTIFIED ASSESSMENT OF THE RELATIONSHIP BETWEEN THE RELIABILITY AND ENTROPY OF WATER DISTRIBUTION SYSTEMS

Several researchers have suggested that it might be possible to use entropy as a general performance indicator for water distribution systems. It has several advantages over other performance and reliability indices, for example, it is extremely rapid and far easier to calculate than other measures, has minimal data requirements and lends itself to direct incorporation into design optimization frameworks.

This paper summarises the first proper attempt to investigate the apparent relationship between the entropy and reliability of water distribution systems. A maximum entropy-constrained approach was used to generate designs for a sample water distribution system which, along with traditional minimum-cost designs, formed the basis of this study. By varying the layout, number of loops and links and reversing the direction of flow in some pipes, it is shown statistically that the correlation between entropy and reliability is strong. Based on the results, a new method for sizing the pipes of water distribution systems is proposed. It is quick, easy to implement, finds optimal pipe sizes, does not require non-linear programming and always guarantees a high level of reliability.     

Prospects for United Kingdom milk producers

Milk producers have been extremely successful since the establishment of the EEC in increasing production and reducing costs. However, this led to overproduction and the imposition of quotas in April 1984. In the area of the Scottish Milk Marketing Board, producers have been able to keep within their quota limits. Costs have been trimmed to meet a cutback in income of about 6%, largely by reducing purchases of feeding stuffs by 15–20%. Nevertheless, farm incomes have fallen sharply, and flexibility and readjustment will be needed to meet the demands of the future.     

Microcrystalline BaTiO3 by Crystallization from Glass

The properties and composition of glasses suitable for crystallization of BaTiO₃ are described. The crystallization of certain glasses results in a nearly complete recovery of BaTiO₃, besides the feldspar BaAl₂SiO₃ as a minor phase. The mechanism of crystallization was investigated by thermal analysis, viscosity, and grainsize measurements as a function of the temperature whereas density data were used for evaluation of the BaTiO₃ content. Within the range 30 to 60% by volume of BaTiO₃ at about 1μ grain size, the measured dielectric constant increased from 100 to 1200. The calculated partial dielectric constant of the Titanate phase at this grain size was about 3500. As the grain size approached 0.1μ, the dielectric constant decreased and became nearly independent of the temperature because of the predominance of surface states. Other effects were attributed to special structural characteristics, such as absence of porosity and clamping of the titanate particles within the microcrystalline matrix. Data are also presented on dielectric constant and loss tangent at different frequencies, dc breakdown strength, dc resistivity, and ferroelectric properties as a function of the grain size of the crystallized material.     

Copper(II)-mediated oxidation of (+)-catechin in a model white wine system

This study was undertaken to establish the role played by copper(II) in enhancing the rate of oxidation of flavanols. A model white wine system consisting of 12% (v/v) aqueous ethanol saturated with potassium hydrogen tartrate and adjusted to pH 3.2 was used to allow experimentation under well-defined conditions. (+)-Catechin was the oxidisable substrate and copper(II) concentrations up to 0.6 mg/L were employed. The model white wines were maintained at 45C to induce the browning process. Under these conditions an increase in absorbance at 440 nm occurred provided the copper(II) concentration was 0.3 mg/L or greater. The coloured species responsible for the increase in absorbance were identified as xanthylium cations, formed by linkage of two (+)-catechin molecules. Glyoxylic acid acted as the bridge between the phloroglucinol-type moiety of the (+)-catechin molecules. The production of the xanthylium cations was inhibited by ethanol and also by mannitol and the implications of these observations for a free-radical induced mechanism are discussed.     

Stability analysis of a class of non-linear distributed parameter systems—tubular chemical reactors†

A sufficient condition for local stability of the spatially discretized model of a class of non-linear distributed parameter systems is derived using the circle criterion for stability and bounded-input, bounded-output stability. As a physical system the catalytic packed-bed tubular reactor is taken to illustrate the application of the theorem to process control systems. The stability condition in the large derived from non-linear system equations is compared with the stability condition in the small derived from linearized system equations. Interpretations of the result are given in terms of physical variables.     

Fighter aircraft lateral directional axes full envelope control law design

A decoupled wide envelope lateral/directional axes control design is presented for a supermanoeuvrable version of an F-18 aircraft. A control structure is developed that separates gain scheduling issues from aircraft performance issues. Flight condition dependent state and control effectiveness variations are accounted for by an inner loop controller designed using eigenstructure assignment. Structured singular value synthesis is used to design an implicit model following outer loop controller that addresses flying qualities performance specifications. A control selector is designed that generates lateral/directional aerodynamic and thrust vectoring commands from generalized control inputs of roll and yaw acceleration. Flying qualities and robustness analyses show that the control system performs well despite neglected dynamics and system uncertainties. Nonlinear simulations are presented showing excellent decoupling of roll and yaw responses.     

Nucleation and Crystallization of NaNbO3 from Glasses in the Na2O-Nb2O5-SiO2 System

Transparent glass-ceramics, in which the major phase was NaNbO₃, were obtained by heat treatment of glasses in the Na₂O-Nb₂O₅-SiO₂ system. The structure of the glass and the changes occurring during crystallization as a function of temperature and heating rate were examined by X-ray diffraction, transmission and replication electron microscopy, density, and other measurements. On heating, a rather abrupt formation of uniformly dispersed particles was observed. In the early stages of crystallization, these particles contained NaNbO₃ as loose, radially grown dendrites of identical crystal orientation which became dense during later stages of crystallization. The particle sizes ranged from 200 to 10,000 A, depending on the SiO₂ content of the glass. Transparency of the crystallized material was dependent on the particle size rather than on the amount of NaNbO₃ formed. The temperature at which crystallization occurred increased with the heating rate whereas the viscosity at crystallization decreased. For a given value of the rate of crystal formation per °C of temperature increase, the product (viscosity)ⁿ× (heating rate) was constant. The nucleation and growth phenomena which occurred in these glasses was attributed to microheterogeneities of higher Nb₂O₅ content which formed part of the glass structure.     

BIG CITY MAYORS: POLITICAL SPECIALIZATION AND BUSINESS DOMINATION IN THE 19TH AND 20TH CENTURIES

ABSTRACT: An examination of mayoral recruitment in 19 major American cities from 1820 to 1995 finds that mayors are now more likely to have prior political experience, serve longer in office, and have previously served on city councils. They are also less likely to come from business backgrounds, and those mayors who are still in business are less likely to have big business and manufacturing backgrounds. A multivariate analysis of mayors serving between 1870 and 1995 indicates that mayors from business backgrounds are less likely to be selected when their cities have partisan elections, when their cities have a large African American population, and when mayors are machine candidates. This analysis also finds that the number of mayors with business backgrounds declines as the number of college graduates increases, even though (after 1896) political machines disappeared and more cities adopted reform (council manager and commission) governments.