No abstract

Two series of antihail rocket propellant grains failed only 3 months after production, due to the appearance of cracks in the grain channel. Structural integrity analysis demonstrated sufficient reliability at the beginning of service life. Further analysis showed that under temperature loads, cumulative damage during the short period in field stocks caused the grain failure, despite the established opinion that such failure can become significant only after lengthy storage. A linear cumulative damage law is evaluated by exposing a number of hydroxyl-terminated polybutadiene (HTPB) composite propellant specimens to different but constant stress levels. The analysis showed that cumulative damage must not be overlooked at the design stage. Further, a positive correlation between the propellant cumulative damage law and tensile strength is strongly indicated.

The main aim of the animal production is to produce animal proteins of high value in a sustainable manner. However, sustainability is not easy to define. It is a complex phenomenon, which includes integration of economic, social, and environmental dimensions of the certain production, within a given socio-economic context. In this respect, poultry production meets first two dimensions - it provides affordable dietary item for consumers and profit for producers. It additionally generates up and downstream investment opportunities and it contributes to the development of the local economy. However, with the concentration of poultry production and increase in operation size, considerable environmental problems have occurred. During the last several decades, the environmental impact of the poultry production has received an ever-growing attention. Nowadays, producers are under heavy pressure, from different fronts, to minimize the impact of their production on the environment and to adopt welfare friendly practices. The major challenges, which will affect animal production in the future, will likely deal with the environment. In this paper, the environmental impact of poultry production and the differences in this respect between the different production systems are presented.

Composite solid propellants based on ammonium perchlorate/hydroxyterminated polybutadiene/isophorone dyisocyanate including different contents of octogene (HMX) have been represented in this paper. The mass of HMX increased in relation to oxidant, with constant bimodal fraction ratio. Combustion of the propellants has been improved by adding of titanium (IV) oxide powder as stabilizer. Parameters of burning rate laws were determined and compared for the propellants of the same total solid phase. Also, the apparent viscosity, uniaxial mechanical characteristic, density and energetic values were determined for the same formulations.

The economic and political crisis Serbia had to face during the nineties affected the competitive advantages its agricultural sector had in comparison with the other countries of the region. Despite a number of differences related to the specific economic, political and social settings and developments, the reform path Serbia started in 2000 showed a number of similarities, but also some differences in comparison with most of the Central and Eastern European Countries. In this paper the main features of structural changes in the Serbian agricultural sector are analyzed, also in comparison with other countries in the region, the basic factors that contributed to these changes are identified and explained, and the key consequences and implications of this process are examined.