We studied the relationship between atmospheric dust deposition, N 2 fixation rates, and the abundance of unicellular diazotrophs and Trichodesmium in weekly or biweekly samplings over 3 months in the Canary Islands. On average, N 2 fixation rates by unicellular diazotrophs and Trichodesmium were low (0.2 nmol N L 21 h 21 and 1.66 3 10 23 nmol N L 21 h 21 , respectively). However, N 2 fixation rates associated with unicellular diazotrophs increased by 86% and 92% after a peak of aerosol concentration in samples incubated in both light and dark, while the rates associated with Trichodesmium diminished by 34% and 92% in the light and in the dark, respectively. The abundance of unicellular diazotrophs ranged from 4 cells L 21 to 54 cells L 21 . After the input of aerosols, 66% of the unicellular diazotrophs observed were attached to putatively organic matter particles. Trichodesmium abundance was low (average of 0.5 trichomes L 21 ), mainly in the form of free trichomes, which might hinder the ability of these organisms to take advantage of the Fe dissolved in the water column after dust deposition events. We also highlight the importance of monitoring short-term variability of N 2 fixation in order to have a better understanding of the nitrogen cycle in the ocean.
In this paper, personal memories of famous scientists and their positions with regard to some problems as world war, disarmement, space race, ... which affect to what is generally known as «the responsibility of the scientist~ are analysed.
The symbols are primarily a creation of human unconcious, and even now they belong to our cerebral background. The concrete symbols have served t o represent the changing mentality about the chemical knowledge. There is a repeted use of determined geometrical figures, especialy triangles and circles. This article rewiews the development of chemical symbolism, its changing role, from the ancient civilization to the modern notationai systems.
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