11,192 research outputs found
Loss of superfluidity by fermions in the boson Hubbard model on an optical lattice
The experimentally observed loss of superfluidity by introducing fermions to
the boson Hubbard system on an optical lattice is explained. We show that the
virtual transitions of the bosons to the higher Bloch bands, coupled with the
contact boson-fermion interactions of either sign, result in an effective
increase of the boson on-site repulsion. If this renormalization of the on-site
potential is dominant over the fermion screening of the boson interactions, the
Mott insulating lobes of the Bose-Hubbard phase diagram will be enhanced for
either sign of the boson-fermion interactions. We discuss implications for cold
atom experiments where the expansion of the Mott lobes by fermions has been
conclusively established.Comment: 4 pages, 1 eps figure, minor change
The evolution of sperm morphometry in pheasants
Postcopulatory sexual selection is thought to be a potent evolutionary force driving the
diversification of sperm shape and function across species. In birds, insemination and
fertilisation are separated in time and sperm storage increases the duration of sperm
female interaction and hence the opportunity for sperm competition and cryptic female
choice. We performed a comparative study of 24 pheasant species (Phasianidae,
Galliformes) to establish the relative importance of sperm competition and the duration of
sperm storage for the evolution of sperm morphometry (i.e. size of different sperm traits).
We found that sperm size traits were negatively associated with the duration of sperm
storage but were independent of the risk of sperm competition estimated from relative
testis mass. Our study emphasises the importance of female reproductive biology for the
evolution of sperm morphometry particularly in sperm storing taxa
Características e manejo de azevém resistente ao glyphosate.
bitstream/CNPT-2010/40677/1/p-do59.pd
Identificação e manejo de plantas daninhas resistentes a herbicidas.
bitstream/CNPT-2010/40678/1/p-do60.pd
Herbicidas e a qualidade química da água usada como diluente.
bitstream/CNPT-2010/40675/1/p-do57.pd
Wrapping an adhesive sphere with a sheet
We study the adhesion of an elastic sheet on a rigid spherical substrate.
Gauss'Theorema Egregium shows that this operation necessarily generates metric
distortions (i.e. stretching) as well as bending. As a result, a large variety
of contact patterns ranging from simple disks to complex branched shapes are
observed as a function of both geometrical and material properties. We describe
these different morphologies as a function of two non-dimensional parameters
comparing respectively bending and stretching energies to adhesion. A complete
configuration diagram is finally proposed
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