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The Earth is embedded in the solar wind, this ever-streaming extremely tenuous ionized gas emanating from the Sun. It is the geomagnetic field which inhibits the solar wind plasma to directly impinge upon the terrestrial atmosphere. It is also the geomagnetic field which moderates and controls the entry of energetic particles of cosmic and solar origin into the atmosphere. During geomagnetic polarity transitions the terrestrial magnetic field decays down to about 10% of its current value. Also, the magnetic field topology changes from a dipole dominated structure to a multipole dominated topology. What happens to the Earth system during such a polarity transition, that is, during episodes of a weak transition field? Which modifications of the configuration of the terrestrial magnetosphere can be expected? Is there any influence on the atmosphere from the intensified particle bombardment? What are the possible effects on the biosphere? Is a polarity transition another example of a cosmic cataclysm? A review is provided on the current understanding of the problem. A first, illustrating model is also discussed to outline the complexity of any biospheric reaction on polarity transitions.
Modeling pollen dispersal to predict cross-pollination is of great
importance for the ongoing discussion of adventitious presence of
genetically modified material in food and feed. Two different modeling
approaches for pollen dispersal were used to simulate two years of data for
the rate of cross-pollination of non-GM maize (Zea mays (L.)) fields by pollen from a
central 1 ha transgenic field. The models combine the processes of wind
pollen dispersal (transport) and pollen competition. Both models used for
the simulation of pollen dispersal were Lagrangian approaches: a stochastic
particle Lagrange model and a Lagrangian transfer function model. Both
modeling approaches proved to be appropriate for the simulation of the
cross-pollination rates. However, model performance differed significantly
between years. We considered different complexity in meteorological input
data. Predictions compare well with experimental results for all
simplification steps, except that systematic deviations occurred when only
main wind direction was used. Concluding, it can be pointed out that both
models might be adapted to other pollen dispersal experiments of different
crops and plot sizes, when wind direction statistics are available. However,
calibration of certain model parameters is necessary.
The subject of this paper, is of a nature to find favour with all those chemists who are disposed to recognise in the fast accumulating evidence of a new and remarkable order of chemical phenomena rich and valuable materials for the construction of a sounder and more comprehensive chemical theory. This new order of phenomena appears to me, nevertheless, but imperfectly appreciated and understood, even on the part of our most distinguished experimentalists. Thus, for instance, Monsieur Pasteur, the illustrious French philosopher, and with him a host of other eminent thinkers, is of opinion, that matter is indebted for its chemical and physical properties mainly and exclusively to the peculiar manner in which the atoms are grouped together. In alluding to the probable cause of circular polarisation, Monsieur Pasteur considers, that this singular property ought to be referred to the unsymmetrical disposition of the constituents, and that the restoration of the chemical symmetry must at the same time obliterate every trace of circularly polarising power.
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