XLII.—Notes on the Racquet-tailed rollers

The sweet spots of a tennis racquet

Measurements are presented on the behaviour of a hand-held tennis racquet when it impacts with a tennis ball. It is shown that an impulse is transmitted through the racquet to the hand in about 1.5 ms, with the result that the hand and the forearm both have a strong in ̄uence on the behaviour of the racquet even while the ball is still in contact with the strings. Regardless of the impact point,...

survey on the rule of the due & hindering relying on the sheikh ansaris ideas

قاعده مقتضی و مانع در متون فقهی کم و بیش مستند احکام قرار گرفته و مورد مناقشه فقهاء و اصولیین می باشد و مشهور معتقند مقتضی و مانع، قاعده نیست بلکه یکی از مسائل ذیل استصحاب است لذا نگارنده بر آن شد تا پیرامون این قاعده پژوهش جامعی انجام دهد. به عقیده ما مقتضی دارای حیثیت مستقلی است و هر گاه می گوییم مقتضی احراز شد یعنی با ماهیت مستقل خودش محرز گشته و قطعا اقتضاء خود را خواهد داشت مانند نکاح که ...

High breeding performance of European Rollers Coracias

Rollers smell the fear of nestlings.

Many animals react to danger by producing chemical cues that can be smelled by others, which is called the smell of fear. Some bird species produce chemical compounds when threatened, such as nestlings of the Eurasian roller Coracias garrulus that vomit an odorous orange liquid when scared in their nests. Here, we experimentally explore the possibility that parents were informed about recent pr...

Measurements of Shallow Water Breaking Wave Rollers

Large scale laboratory experiments concerning breaking wave propagation over a fixed-bed, barred beach were performed. The primary observations of interest were video intensity time series obtained from a set of high-resolution video cameras in order to study the onset of wave breaking in shallow water and wave roller transformation in the surf zone. The approach is new in the sense that the an...