How sails generate forces

We propose a new paradigm of the aerodynamics of sails that reconciles our understanding of the force generation mechanisms of both upwind and downwind sails, and that is applicable to both attached and separated flow conditions. Sail experience significant flow separation. Even when the flow appears to be attached, this is sometimes only in the time averaged sense. In these conditions, the underlining as- sumptions of thin airfoil theory and lifting line theory are violated. There is therefore a need to develop an intuitive understanding of the force generation mechanisms that does not rely on these assumptions. This paper aims to address this issue by proposing a new paradigm based on the impulse theory. The force generation mechanism can be intuitively associated with the vorticity field, which can be gathered with computational fluid dynamics or particle image velocimetry. This paradigm intuitively reconciles key results of traditional wing aerodynamics, and provides sail designers a measurable objective to modify a sail shape also in separated flow conditions. It will hopefully underpin both a deeper understanding of sail aerodynamics and the development of low order models for new design tools

Influence of aeroallergens on bronchial reactivity in children sensitized to grass pollens

Abstract Nine children, sensitized to grass pollens, with seasonal rhinitis and mild asthma underwent bronchial challenge with carbachol and EIA test repeatedly either during a pre-seasonal or in seasonal period. We failed to find any significant difference between pre-seasonal and seasonal values in both tests. We believe that atmospheric conditions are an important determinant of our results. It is our hypothesis that a threshold concentration in atmospheric pollen may exist which must be reached before an allergic reaction is evident

Green alder decline in the Italian Alps

Decline of green alder (Alnus viridis spp. viridis [Chaix] D.C.) has been reported since the 1990s in the Alps. In recent years, this disease has spread all over the Alps and it is now recorded over all Italian alpine regions, with several secondary green alder stands heavily affected. Old damaged stands show dramatic changes both in tree species composition and coverage. Investigations were carried out in Trentino province (northern Italy) to describe the pathological and ecological aspects of this phenomenon. Various fungi and insects were detected on declining trees, but no single agent appeared to be a primary cause; the most common coloniser of declining stems, Cryptodiaporthe oxystoma (Rehm) Urb., had an endophytic behaviour in green healthy tissues but failed to produce symptoms in artificial inoculations. There was a negative relation between altitude and alder decline. Furthermore, reduction in snow cover and trends of increase in winter temperature are possible influencing factors. The spread of the syndrome may be related to climate change, reducing green alder vigour and allowing opportunistic parasites to cause host decline. The disappearance of green alder stands will likely affect soil protection, biodiversity and stand evolution in treeline forests of the Alps. More research is needed to define future management options