Long-term aging of elastomers: Chemical stress relaxation of fluorosilicone rubber and other studies

Aerospace applications of elastomers are considered, including: propellant binders, bladder materials for liquid propellant expulsion systems, and fuel tank sealants for high-speed aircraft. A comprehensive molecular theory for mechanical properties of these materials has been developed but has only been tested experimentally in cases where chemical degradation processes are excluded. Hence, a study is being conducted to ascertain the nature, extent, and rate of chemical changes that take place in some elastomers of interest. Chemical changes that may take place in the fluorosilicone elastomer, LS 420, which is regarded as a fuel and high-temperature-resistant rubber are investigated. The kinetic analysis of the chemical stress relaxation and gel permeation chromatography studies comprise the major portion of the report

Ribbed Mat Foundation for Aseismic Building

This paper describes the design of a two-way ribbed mat used as the foundation of a tall aseismic building located in a very heavy seismic area of northern Venezuela. The soil description, the structural analysis and some construction provisions are also described

Potential and actual bud fruitfulness: A tool for predicting and managing the yield of table grape varieties

Microscopic bud dissection can be used to assess grapevine bud fruitfulness prior to winter pruning and long before actual bud fruitfulness can be measured in the vineyard the following spring. Bud dissections should be performed by qualified and trained personnel because inflorescence primordia are difficult to distinguish in some varieties. In the Puglia region, Southeastern Italy, in 2018 and 2019, potential fruitfulness using bud dissection and actual fruitfulness observed in the vineyard were compared for seventeen table grape varieties. The percentage of fertile buds, the number of inflorescence primordia (IP) per node, and the incidence of primary bud necrosis (PBN) were detected with bud dissection to be used either for managing winter pruning or for predicting yield during the successive season. The data were successively compared with fertile buds and actual bud fruitfulness observed in the vineyard during spring. The table grape varieties examined had similar values of fertile buds and fruitfulness both with bud dissection and in the vineyard. The application of longitudinal sections in bud dissections can be an alternative approach (or can be integrated into traditional cross sections) to distinguish IP in some difficult varieties, but the two techniques can be used together for more repeatable results. The bud dissection technique (with both cross and longitudinal sections) can provide useful insights for viticulturist to help guide winter pruning (intensity of pruning and number of canes) and to predict potential yield

EVALUATION OF NATURAL AND TRAFFIC-PRODUCING TURBULENCES USING FULL SCALE DATA FROM FOUR STREET CANYONS

In urban areas, high air pollutant concentrations may be observed, mostly within street canyons, where buildings and other obstacles disturb the airflow and turbulence. Air motions inside the street canyons are influenced by aerodynamic and thermal effects and by the movements of the vehicles. Parameters related with natural and traffic produced turbulences are estimated for four street canyons considering all wind directions. Available data used include air pollution concentrations measured in Göttinger Strasse (Hannover, Germany), Schildhornstrasse (Berlin, Germany), Jagtvej (Copenhagen, Denmark) and Hornsgatan (Stockholm, Sweden), and background pollution, wind speed and direction measured on the roof of a nearby building and information of traffic flow. For each street canyon, the variation with traffic density of critical wind speed (that equals the contributions of turbulent motions related to wind and traffic to the effective velocity variance inside the street canyon) is also studied

Liquidity Costs and Stock Price Response to Convertible Security Calls

Firms\u27 announcements to call in-the-money convertible securities for redemption essentially force their conversion into common stock, and such announcements are generally met with significant reductions in the calling firms\u27 equity values. An explanation based on liquidity costs is advanced and tested. The explanation implies that investors who choose to sell their shares early in the conversion period bear liquidity costs by selling at reduced prices. Consistent with the explanation, the average share price decline is short-lived, lasting most of the conversion period. Thus, a component of the call announcement effect appears to be due to liquidity costs