2,316 research outputs found
Successfull Blossom Thinning and Crop Load Regulation for Organic Apple Growing with Potassium-bi-carbonate (Armicarb(R)): Results of Field Experiments over 3 Years and with 11 Cultivars
With field trials over 3 years in a commercial organic orchard in Switzerland we have tested the efficacy of Armicarb® (potassium-bi-carbonate) for flower thinning in organic apple production. Over time, Armicarb was tested on 11 cultivars, at different application periods, in different concentrations, and always in comparison to other agents that are already allowed for thinning in organic fruit production in the European Union as e.g. lime sulphur, molasses, mechanical rope-thinner or combinations of methods. Armicarb proved to be an efficient and reliable thinning agent with an efficacy similar to the now recommended methods with rope device, molasses or lime sulphur but has the advantage to be an environmentally very friendly product. On the other hand, the risk for fruit russeting is comparably elevated especially with cultivars ‘Elstar’, ‘Golden Del.’ ’and ‘Gala’. Finally, we have elaborated cultivar-specific recommendations for the use of Armicarb for thinning purposes, which were the basis for the Swiss Federal approval to use Armicarb for thinning in conventional and organic apple production in 2011/2012
Optimal branching asymmetry of hydrodynamic pulsatile trees
Most of the studies on optimal transport are done for steady state regime
conditions. Yet, there exists numerous examples in living systems where supply
tree networks have to deliver products in a limited time due to the pulsatile
character of the flow. This is the case for mammals respiration for which air
has to reach the gas exchange units before the start of expiration. We report
here that introducing a systematic branching asymmetry allows to reduce the
average delivery time of the products. It simultaneously increases its
robustness against the unevitable variability of sizes related to
morphogenesis. We then apply this approach to the human tracheobronchial tree.
We show that in this case all extremities are supplied with fresh air, provided
that the asymmetry is smaller than a critical threshold which happens to fit
with the asymmetry measured in the human lung. This could indicate that the
structure is adjusted at the maximum asymmetry level that allows to feed all
terminal units with fresh air.Comment: 4 pages, 4 figure
Extending Johnson's and Morita's homomorphisms to the mapping class group
We extend certain homomorphisms defined on the higher Torelli subgroups of
the mapping class group to crossed homomorphisms defined on the entire mapping
class group. In particular, for every , we construct a crossed
homomorphism which extends Morita's homomorphism
to the entire mapping class group. From this crossed homomorphism we also
obtain a crossed homomorphism extending the th Johnson homomorphism
to the mapping class group.
D. Johnson and S. Morita obtained their respective homomorphisms by
considering the action of the mapping class group on the nilpotent truncations
of the surface group; our approach is to mimic Morita's construction
topologically by using nilmanifolds associated to these truncations. This
allows us to take the ranges of these crossed homomorphisms to be certain
finite-dimensional real vector spaces associated to these nilmanifolds.Comment: 32 pages; cleaned up and minor corrections to proofs; updated to
agree with version published by Alg. & Geom. Top at:
http://msp.warwick.ac.uk/agt/2007/07/p050.xhtm
Self-buckling and self-writhing of semi-flexible microorganisms
Multi-flagellated microorganisms can buckle and writhe under their own
activity as they swim through a viscous fluid. New equilibrium configurations
and steady-state dynamics then emerge which depend on the organism's mechanical
properties and on the oriented distribution of flagella along its surface.
Modeling the cell body as a semi-flexible Kirchhoff rod and coupling the
mechanics to a dynamically evolving flagellar orientation field, we derive the
Euler-Poincar{\'e} equations governing dynamics of the system, and rationalize
experimental observations of buckling and writhing of elongated swarmer {\it P.
mirabilis} cells. A sequence of bifurcations is identified as the body is made
more compliant, due to both buckling and torsional instabilities. The results
suggest that swarmer cells invest no more resources in maintaining membrane
integrity than is necessary to prevent self-buckling.Comment: 6 pages, 3 figure
Femmes, islam et identité religieuse dans l'immigration turque en Alsace
La difficile recomposition de l'identité des femmes dans l'immigration en Alsace semble prendre la forme, pour beaucoup, d'une « entrée en islam ». Paradoxalement considérée comme un chemin vers l'émancipation, cette voie débouche souvent sur un pouvoir coercitif exercé par les femmes islamistes envers les autres femmes du groupe
Interplay between geometry and flow distribution in an airway tree
Uniform fluid flow distribution in a symmetric volume can be realized through
a symmetric branched tree. It is shown here, however, that the flow
partitioning can be highly sensitive to deviations from exact symmetry if
inertial effects are present. This is found by direct numerical simulation of
the Navier-Stokes equations in a 3D tree geometry. The flow asymmetry is
quantified and found to depend on the Reynolds number. Moreover, for a given
Reynolds number, we show that the flow distribution depends on the aspect ratio
of the branching elements as well as their angular arrangement. Our results
indicate that physiological variability should be severely restricted in order
to ensure uniform fluid distribution in a tree. This study suggests that any
non-uniformity in the air flow distribution in human lungs should be influenced
by the respiratory conditions, rest or hard exercise
Global Dimension of Polynomial Rings in Partially Commuting Variables
For any free partially commutative monoid , we compute the global
dimension of the category of -objects in an Abelian category with exact
coproducts. As a corollary, we generalize Hilbert's Syzygy Theorem to
polynomial rings in partially commuting variables.Comment: 11 pages, 2 figure
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