2,249 research outputs found
The Gysin sequence for -actions on manifolds
We construct a Gysin sequence associated to any smooth -action
on a smooth manifold.Comment: Accepted for publication in Publicationes Mathematicae Debrecen,
scheduled for 2014 Publicationes Mathematicae Debrecen (2014
Top dimensional group of the basic intersection cohomology for singular riemannian foliations
It is known that, for a regular riemannian foliation on a compact manifold,
the properties of its basic cohomology (non-vanishing of the top-dimensional
group and Poincar\'e Duality) and the tautness of the foliation are closely
related. If we consider singular riemannian foliations, there is little or no
relation between these properties. We present an example of a singular
isometric flow for which the top dimensional basic cohomology group is
non-trivial, but its basic cohomology does not satisfy the Poincar\'e Duality
property. We recover this property in the basic intersection cohomology. It is
not by chance that the top dimensional basic intersection cohomology groups of
the example are isomorphic to either 0 or . We prove in this Note
that this holds for any singular riemannian foliation of a compact connected
manifold. As a Corollary, we get that the tautness of the regular stratum of
the singular riemannian foliation can be detected by the basic intersection
cohomology.Comment: 11 pages. Accepted for publication in the Bulletin of the Polish
Academy of Science
Dielectric confinement of excitons in type-I and type-II semiconductor nanorods
We theoretically study the effect of the dielectric environment on the
exciton ground state of CdSe and CdTe/CdSe/CdTe nanorods. We show that
insulating environments enhance the exciton recombination rate and blueshift
the emission peak by tens of meV. These effects are particularly pronounced for
type-II nanorods. In these structures, the dielectric confinement may even
modify the spatial distribution of electron and hole charges. A critical
electric field is required to separate electrons from holes, whose value
increases with the insulating strength of the surroundings.Comment: Journal of Physics: Condensed Matter (in press
Efficiency, profitability and carbon footprint of different management programs under no-till to control herbicide resistant Papaver rhoeas
The present work examines the effects of different integrated weed management (IWM) programs on multiple herbicide-resistant Papaver rhoeas populations in terms of effectiveness, profitability and carbon footprint. With this aim a trial was established in a winter cereal field under no-till in North-Eastern Spain during three consecutive seasons. Four IWM programs with different intensification levels, from less (crop rotation, mechanical control, and no herbicides) to more intense (wheat monoculture with high chemical inputs), were established. The different strategies integrated in the four programs were efficient in managing the weed after three years, with increased effectiveness after management program intensification. Whereas low input program (which includes fallow season) represented less economic cost than the other programs, on average, no differences were observed on carbon foot print, considered as kg CO2eq kg−1 product, between the different programs, except in the crop rotation program due to the low pea yield obtained. The results from this study show that in the search for a balance between crop profitability and reduction of the carbon footprint while controlling an herbicide resistant population is challenging, and particularly under notill. In this scenario the short term priority should be to reduce the presence of multiple herbicide resistant biotypes integrating the different available chemical, cultural, and physical strategies.This work has been supported by the Agencia Estatal de Investigación (AEI) and the European Regional Development Fund (ERDF) with project AGL2014-52465-C4-2-R. Dr. J. Torra obtained a Ramon y Cajal contract from the Spanish Ministry of Science, Innovation and Universities (RYC2018-023866-I). Mr. F. Valencia-Gredilla obtained a PhD grant from the University of Lleida
Emission spectrum of quasi-resonant laterally coupled quantum dots
We calculate the emission spectrum of neutral and charged excitons in a pair
of laterally coupled InGaAs quantum dots with nearly degenerate energy levels.
As the interdot distance decreases, a number of changes take place in the
emission spectrum which can be used as indications of molecular coupling. These
signatures ensue from the stronger tunnel-coupling of trions as compared to
that of neutral excitons.Comment: 7 pages, 7 figure
Coulomb interaction signatures in self-assembled lateral quantum dot molecules
We use photoluminescence spectroscopy to investigate the ground state of
single self-assembled InGaAs lateral quantum dot molecules. We apply a voltage
along the growth direction that allows us to control the total charge occupancy
of the quantum dot molecule. Using a combination of computational modeling and
experimental analysis, we assign the observed discrete spectral lines to
specific charge distributions. We explain the dynamic processes that lead to
these charge configurations through electrical injection and optical
generation. Our systemic analysis provides evidence of inter-dot tunneling of
electrons as predicted in previous theoretical work.Comment: 9 pages, 4 figure
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