785 research outputs found
Highlights in gibberellin research A tale of the dwarf and the slender
It has been almost a century since biologically active gibberellin (GA) was isolated. Here, we give a historical overview of the early efforts in establishing the GA biosynthesis and catabolism pathway, characterizing the enzymes for GA metabolism, and elucidating their corresponding genes. We then highlight more recent studies that have identified the GA receptors and early GA signaling components (DELLA repressors and F-box activators), determined the molecular mechanism of DELLA-mediated transcription reprograming, and revealed how DELLAs integrate multiple signaling pathways to regulate plant vegetative and reproductive development in response to internal and external cues. Finally, we discuss the GA transporters and their roles in GA-mediated plant development
Does tiny-scale atomic structure exist in the interstellar medium ?
We report on preliminary results from the recent multi-epoch neutral hydrogen
absorption measurements toward three pulsars, B0823+26, B1133+16 and B2016+28,
using the Arecibo telescope. We do not find significant variations in optical
depth profiles over periods of 0.3 and 9--10 yr, or on spatial scales of 10--20
and 70--85 AU. The large number of non detections of the tiny scale atomic
structure suggests that the AU-sized structure is not ubiquitous in the
interstellar medium and could be quite a rare phenomenon.Comment: Accepted by ApJ Letters, 5 pages, 2 figure
Modelo computacional para suporte à decisão em áreas irrigadas. Parte II. Testes e aplicação.
Apresentou-se, na Parte I desta pesquisa, o desenvolvimento de um modelo computacional denominado MCID, para suporte à tomada de decisão quanto ao planejamento e manejo de projetos de irrigação e/ou drenagem. Objetivou-se, na Parte II, testar e aplicar o MCID. No teste comparativo com o programa DRAINMOD, espaçamentos entre drenos, obtidos com o MCID, foram ligeiramente maiores ou idênticos. Os espaçamentos advindos com o MCID e o DRAINMOD foram consideravelmente maiores que os obtidos por meio de metodologias tradicionais de dimensionamento de sistemas de drenagem. A produtividade relativa total, YRT, obtida com o MCID foi, em geral, inferior à conseguida com o DRAINMOD, devido a diferenças de metodologia ao se estimar a produtividade da cultura em resposta ao déficit hídrico. Na comparação com o programa CRO-PWAT, obtiveram-se resultados muito próximos para (YRT) e evapotranspiração real. O modelo desenvolvido foi aplicado para as condições do Projeto Jaíba, MG, para culturas perenes e anuais cultivadas em diferentes épocas. Os resultados dos testes e aplicações indicaram a potencialidade do MClD como ferramenta de apoio à decisão em projetos de irrigação e/ou drenagem
Computational modeling for irrigated agriculture planning. Part I: general description and linear programming.
Linear programming models are effective tools to support initial or periodic planning of agricultural enterprises, requiring, however, technical coefficients that can be determined using computer simulation models. This paper, presented in two parts, deals with the development, application and tests of a methodology and of a computational modeling tool to support planning of irrigated agriculture activities. Part I aimed at the development and application, including sensitivity analysis, of a multiyear linear programming model to optimize the financial return and water use, at farm level for Jaíba irrigation scheme, Minas Gerais State, Brazil, using data on crop irrigation requirement and yield, obtained from previous simulation with MCID model. The linear programming model outputted a crop pattern to which a maximum total net present value of R 372.723,00 para o período de quatro anos. Restrições quanto à disponibilidade mensal de água, mão-de-obra, terra e produção foram críticas na solução ótima. Em relação à otimização de uso da água, verificou-se que expressivas reduções no requerimento de irrigação podem ser obtidas com pequenas reduções no valor presente líquido total máximo
Khovanov homology is an unknot-detector
We prove that a knot is the unknot if and only if its reduced Khovanov
cohomology has rank 1. The proof has two steps. We show first that there is a
spectral sequence beginning with the reduced Khovanov cohomology and abutting
to a knot homology defined using singular instantons. We then show that the
latter homology is isomorphic to the instanton Floer homology of the sutured
knot complement: an invariant that is already known to detect the unknot.Comment: 124 pages, 13 figure
Correlation effects on electronic transport through dots and wires
We investigate how two-particle interactions affect the electronic transport
through meso- and nanoscopic systems of two different types: quantum dots with
local Coulomb correlations and quasi one-dimensional quantum wires of
interacting electrons. A recently developed functional renormalization group
scheme is used that allows to investigate systems of complex geometry.
Considering simple setups we show that the method includes the essential
aspects of Luttinger liquid physics (one-dimensional wires) as well as of the
physics of local correlations, with the Kondo effect being an important
example. For more complex systems of coupled dots and Y-junctions of
interacting wires we find surprising new correlation effects.Comment: to appear in "Advances in Solid State Physics" Volume 46, Ed. R. Haug
(Springer, 2006
Arecibo HI Absorption Measurements of Pulsars and the Electron Density at Intermediate Longitudes in the First Galactic Quadrant
We have used the Arecibo telescope to measure the HI absorption spectra of
eight pulsars. We show how kinematic distance measurements depend upon the
values of the galactic constants R_o and Theta_o, and we select our preferred
current values from the literature. We then derive kinematic distances for the
low-latitude pulsars in our sample and electron densities along their lines of
sight. We combine these measurements with all others in the inner galactic
plane visible from Arecibo to study the electron density in this region. The
electron density in the interarm range 48 degrees < l < 70 degrees is [0.017
(-0.007,+0.012) (68% c.l.)] cm^(-3). This is 0.75 (-0.22,+0.49) (68% c.l.) of
the value calculated by the Cordes & Lazio (2002) galactic electron density
model. The model agrees more closely with electron density measurements toward
Arecibo pulsars lying closer to the galactic center, at 30 degrees<l<48
degrees. Our analysis leads to the best current estimate of the distance of the
relativistic binary pulsar B1913+16: d=(9.0 +/- 3) kpc.
We use the high-latitude pulsars to search for small-scale structure in the
interstellar hydrogen observed in absorption over multiple epochs. PSR B0301+19
exhibited significant changes in its absorption spectrum over 22 yr, indicating
HI structure on a ~500 AU scale.Comment: Accepted by Astrophysical Journal September 200
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