RESUMEN
Different composite propellant mixtures have been prepared using ammonium perchlorate, aluminium powder and hydroxyl terminated polybutadiene by varying the percentage of plasticiser and addition of toluene diisocyanate at different temperatures, and studied their different properties such as viscosity build-up, mechanical and ballistic properties and sensitivity. The data on different plasticiser level indicate that on decreasing the plasticiser content, there is a significant enhancement in end of mix viscosity, tensile strength and modulus while elongation decreases drastically. The data on sensitivity of the studied mixtures reveal that on decreasing the percentage of plasticiser, the sensitivity increases, accordingly. Further, the data on the effect of addition of TDI at different temperatures (35-60 degrees C) infer that on increasing the addition temperature of TDI there is a decrease in end of mix viscosity i.e. 800Pas at 35 degrees C to 448Pas at 60 degrees C. Moreover, there is no effect on mechanical and ballistic properties on higher temperature addition of TDI was observed.
Asunto(s)
Propelentes de Aerosoles/química , Plastificantes/química , 2,4-Diisocianato de Tolueno/química , Fenómenos Mecánicos , Presión , Temperatura , ViscosidadRESUMEN
BACKGROUND: While rising Caesarean section rates have been the subject of much attention and debate worldwide, there is not much information available on this rate and its potential adverse impact in India. METHODS: Our survey was a standard Expanded Programme on Immunization 30-cluster design, carried out in an urban educated, middle/upper class population in Chennai. Mothers of 210 children aged 12-36 months were interviewed and data collected on immunization and breast-feeding practices. Since the mode of delivery was one of the questions, we could generate population-based data on the Caesarean section rate and its influence on breast-feeding. RESULTS: Of the 210 babies, 95 (45%, 95% confidence interval: 39.1-51.3) had been delivered by Caesarean section. Two hundred and six of 210 babies (98%) had been breast-fed at some time. However, babies born by Caesarean section tended to be started late on breast-feeds were given prelacteal feeds more often, and colostrum less often when compared to babies delivered vaginally (all statistically significant). CONCLUSIONS: Our study revealed a very high rate of Caesarean section in the selected metropolitan population. On purely scientific grounds, a rate of 40% to 50% is extremely difficult to justify. Though not conclusive, the data also suggest that Caesarean section may be adversely affecting some aspects of breast-feeding. There is a need for more data and audits on Caesarean section rates in India, and a wider debate on its potential adverse impact on the health of mothers and newborns.