Commutation modelling and sparks reduction based on coupled circuit method

The commutating machines have a notable effect on the exchanges in brush–commutator contact area, which is particularly obvious when determining the intensity of sparks located on the brush. With time, higher current density at the descending edge promote sparks excitation, which itself increases intensity of the electrical erosion, brush temperature and thus also the wear. So in order to make an analytical study of commutation phenomenon, the coupled circuit method was developed. Therefore, a generalized mathematical model of the commutation, for brush–commutator, is established and can be extended for any other types of commutation on the basis of electromagnetic field (e.g. transformers and phase shift transformer. This model provides a greater efficiency to explain the impact of the electromagnetic fluxes surrounding brush area (or switch), specially for the current transition of the commutation process. Successful commutation is defined as operation in normal service, with no serious damages to the commutator, brushes or switches due to sparking that might require abnormal maintenance. It is recognized that some visible sparking are not evidence of unsuccessful commutation. The recommendation to improve the commutation (to achieve longer brush life) is the implementation of the proposal (slotted brush), which provides a linear and a sweet transition of currents in the coils of commutation. Copyright © 2012 John Wiley & Sons, Ltd.     

Isolation,Chemical Modification and Rheological Characterization of Leucaena Gum. Part I: Carboxymethylation

Leucaena gum was isolated from leucaena seeds and subjected to chemical modification via carboxymethylation under a variety of conditions. Variables studied include concentration of the etherifying agents and the preparation medium. It was found that the extent of carboxymethylation expressed as DS increases by increasing the concentration of the etherifying agents. Higher DS values were obtained in non-aqueous medium. The carboxymethylated leucaena derivatives are cold water soluble and can be precipitated by ethanol. Their pastes are characterized by non-Newtonian pseudoplastic behaviour regardless of the method of preparation or DS of the products. The apparent viscosity at various rates was thouroughly investigated. The effect of storing of these pastes on the rheological properties was also studied.     

Rate of Starch-Hydrolysis by Bacterial Amylase

The rates of starch-hydrolysis by different bacterial amylases were compared using the digital oscillator densimeter technique. Reaction rates of amylase determined by this method were evaluated using the standard method for amylase activity.     

Heterocyclic azo dyes. II. Azo Dyes Containing the Benzotriazole and/or benzimidazole nucleus

The synthesis, some dyeing, and fastness properties of several new dispersed and acid dyes derived from the amino-benzotriazoles 1 & 3 and the aminobenzimidazoles 2a , 2b & 4 are described. The suitability of the amino derivatives 1 , 2a , 2b , 3 & 4 as bases for azoic dyeing has also been studied. Several interesting observations between the properties of some synthesised dyes and the corresponding benzene or naphthalene analogues are cited.     

Factors Affecting the Catalytic Hydrogenation of D-Glucose Part II. Effect of Pressure and Temperature

The effect of different degrees of pressure and temperature on the rate of the catalytic hydrogenation of glucose has been investigated.     

Factors Affecting the Catalytic Hydrogenation of D-Glucose. Part IV. Effect of Solvent-Catalyst Concentration at High Pressure,Temperature and pH 8 and the Re-use of Catalyst

In ethanolic solution the rate of hydrogenation of glucose was highly increased. When the hydrogenation was carried out in aqueous solution at pH 8, 170 °C and 60 at pressure the time required for complete hydrogenation decreased from 6 to 1 h. The re-use of catalyst was also investigated.