2,465 research outputs found
Excitation, two-center interference and the orbital geometry in laser-induced nonsequential double ionization of diatomic molecules
We address the influence of the molecular orbital geometry and of the
molecular alignment with respect to the laser-field polarization on
laser-induced nonsequential double ionization of diatomic molecules for
different molecular species, namely and . We
focus on the recollision excitation with subsequent tunneling ionization (RESI)
mechanism, in which the first electron, upon return, promotes the second
electron to an excited state, from where it subsequently tunnels. We show that
the electron-momentum distributions exhibit interference maxima and minima due
to the electron emission at spatially separated centers. We provide generalized
analytical expressions for such maxima or minima, which take into account
mixing and the orbital geometry. The patterns caused by the two-center
interference are sharpest for vanishing alignment angle and get washed out as
this parameter increases. Apart from that, there exist features due to the
geometry of the lowest occupied molecular orbital (LUMO), which may be observed
for a wide range of alignment angles. Such features manifest themselves as the
suppression of probability density in specific momentum regions due to the
shape of the LUMO wavefunction, or as an overall decrease in the RESI yield due
to the presence of nodal planes.Comment: 11 pages revtex, 2 figure
Distribuição espacial das necessidades hídricas das culturas do feijão, milho e soja na bacia do rio Tibaji, PR.
bitstream/item/89786/1/BOP-16.pd
Efeito de fosfatos naturais em plantas de melão cultivdas em vasos.
Com o advento da agricultura orgânica no Vale do Submédio São Francisco, surge a demanda por técnicas que atendam aos princípios desse sistema de exploração agrícola. Dessa forma, realizou-se este trabalho com o objetivo de avaliar a eficiência de fosfatos naturais em três solos (argissolo Acinzentado distrófico - PACd, Argissolo Amarelo eutrofico - PAe e Vertissolo - V) da região, cultivados com melão (Cucumis melo) em vasos, na Embrapa Semi-Árido. Os tratmentos constituíram um fatorial (3 x 4) + 1, sendo três doses de P (40, 80 e 160 mg dm-³ de P2O5), quatro fontes de P (superfosfato triplo-ST, termofosfato-TM, fosfato natural de Gafsa-FG e fosfato natural Fosbahia-FB) e uma testemunha sem P, dispostos no delineamento experimental inteiramente casualizado, com três repetições. Cada solo constitui um ensaio. Após 38 dias de cultivo do melão, avaliaram-se a produção de matéria seca (MS) da parte aérea, o P absorvido pela planta e o P do solo extraído pelos métodos de Mehlich-1 e resina de troca aniônica (RTA). No V e PACd, os fosfatos apresentaram-se menos eficientes que no PAe. O TM foi a fonte de P que apresentou maior eficiência para produção de MS do melão nos três solos (56 a 100% em relação ao superfosfato triplo). No PAe, o FG também mostrou boa eficiência, sendo equivalente a 80% do superfosfato triplo). Os extratores Mehlich e RTA foram igualmente eficientes para avaliar a disponibilidade do P
Forward and hybrid path-integral methods in photoelectron holography: sub-barrier corrections, initial sampling and momentum mapping
We construct two strong-field path integral methods with full Coulomb
distortion, in which the quantum pathways are mimicked by interfering electron
orbits: the rate-based CQSFA (R-CQSFA) and the hybrid forward-boundary CQSFA
(H-CQSFA). The methods have the same starting point as the standard Coulomb
quantum-orbit strong-field approximation (CQSFA), but their implementation does
not require pre-knowledge of the orbits' dynamics. These methods are applied to
ultrafast photoelectron holography. In the rate-based method, electron orbits
are forward propagated and we derive a non-adiabatic ionization rate from the
CQSFA, which includes sub-barrier Coulomb corrections and is used to weight the
initial orbit ensemble. In the H-CQSFA, the initial ensemble provides initial
guesses for a subsequent boundary problem and serves to include or exclude
specific momentum regions, but the ionization probabilities associated with
individual trajectories are computed from sub-barrier complex integrals. We
perform comparisons with the standard CQSFA and \textit{ab-initio} methods,
which show that the standard, purely boundary-type implementation of the CQSFA
leaves out whole sets of trajectories. We show that the sub-barrier Coulomb
corrections broaden the resulting photoelectron momentum distributions (PMDs)
and improve the agreement of the R-CQSFA with the H-CQSFA and other approaches.
We probe different initial sampling distributions, uniform and otherwise, and
their influence on the PMDs. We find that initial biased sampling emphasizes
rescattering ridges and interference patterns in high-energy ranges, while an
initial uniform sampling guarantees accurate modeling of the holographic
patterns near the ionization threshold or polarization axis. Our results are
explained using the initial to final momentum mapping for different types of
interfering trajectories.Comment: 25 pages revtex, 14 figures; in the revised version, some
explanations have been extended and some figures have been modifie
Exploring the adoption of precision agriculture for irrigation in the context of agriculture 4.0: The key role of internet of things
In recent years, the concept of Agriculture 4.0 has emerged as an evolution of precision agriculture (PA) through the diffusion of the Internet of things (IoT). There is a perception that the PA adoption is occurring at a slower pace than expected. Little research has been carried out about Agriculture 4.0, as well as to farmer behavior and operations management. This work explores what drives the adoption of PA in the Agriculture 4.0 context, focusing on farmer behavior and operations management. As a result of a multimethod approach, the factors explaining the PA adoption in the Agriculture 4.0 context and a model of irrigation operations management are proposed. Six simulation scenarios are performed to study the relationships among the factors involved in irrigation planning. Empirical findings contribute to a better understanding of what Agriculture 4.0 is and to expand the possibilities of IoT in the PA domain. This work also contributes to the discussion on Agriculture 4.0, thanks to multidisciplinary research bringing together the different perspectives of PA, IoT and operations management. Moreover, this research highlights the key role of IoT, considering the farmer’s possible choice to adopt several IoT sensing technologies for data collection
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