158 research outputs found
Floristic composition of weeds in different winter and summer covers.
The usage of cover crops is an adopted cultural measure that shows positive effects when associated with the no-till system and weed management. During the cycle of the plants there might be competition within them for water, solar radiation and nutrients and effects of allelopathic substances released by leaching, volatilization and/or root exudation in the environment might also coexist. The study aimed to quantify the floristic composition of weed species in an cultivated area with cover crops during winter and summer, for two years, 2011/12 and 2012/13, in an experimental area of UFSM, Campus of Frederico Westphalen ? RS state, Brazil. The treatments consisted of Italian ryegrass, wild radish, black oat, vetch, wheat and uncultivated, in winter, and, sorghum, sunflower, black velvet bean, dwarf velvet bean, gray velvet bean and green velvet bean in the summer. In the first year of the experiment, a diversity of weeds in winter was observed, especially occuring Stellaria media and Bowlesia incana. In summer, the weeds of higher importance were Ipomoea spp. and Bidens spp., both of utter importance in agricultural systems. Winter cover crops of wild radish and Italian ryegrass and summer cover crops of sorghum and sunflower provided a lower weed infestatio
Augmented visualization by computer vision and chromatographic fingerprinting on comprehensive two-dimensional gas chromatographic patterns: Unraveling diagnostic signatures in food volatilome
Exploring the dimming event of RW Aur A through multi-epoch VLT/X-Shooter spectroscopy
RW Aur A is a CTTS that has suddenly undergone three major dimming events
since 2010. We aim to understand the dimming properties, examine accretion
variability, and derive the physical properties of the inner disc traced by the
CO ro-vibrational emission at NIR wavelengths (2.3 mic).
We compared two epochs of X-Shooter observations, during and after the
dimming. We modelled the rarely detected CO bandhead emission in both epochs to
examine whether the inner disc properties had changed. The SED was used to
derive the extinction properties of the dimmed spectrum and compare the
infrared excess between the two epochs. Lines tracing accretion were used to
derive the mass accretion rate in both states. The CO originates from a region
with physical properties of T=3000 K, N=1x10 cm and
vsini=113 km/s. The extinction properties of the dimming layer were derived
with the effective optical depth ranging from teff 2.5-1.5 from the UV to the
NIR. The inferred mass accretion rate Macc is Msun/yr and Msun/yr after and during the dimming respectively. By fitting the
SED, additional emission is observed in the IR during the dimming event from
dust grains with temperatures of 500-700K. The physical conditions traced by
the CO are similar for both epochs, indicating that the inner gaseous disc
properties do not change during the dimming events. The extinction curve is
flatter than that of the ISM, and large grains of a few hundred microns are
thus required. When we correct for the observed extinction, Macc is constant in
the two epochs, suggesting that the accretion is stable and therefore does not
cause the dimming. The additional hot emission in the NIR is located at about
0.5 au from the star. The dimming events could be due to a dust-laden wind, a
severe puffing-up of the inner rim, or a perturbation caused by the recent
star-disc encounter.Comment: Accepted by Astronomy & Astrophysic
Relative yield of wheat in coexistence with concurrent plants as indicator of competitiveness.
One of the factors that limit the yield of wheat is the weed competition, being the competitive potential of plants affected by their morphophysiological characteristics. The objective of this study was to determine the competitiveness of wheat when in coexistence with Italian ryegrass (Lolium multiflorum) and radish (Raphanus sativus) competitive plants or with wheat as simulator competition plant. There were realized four experiments in the greenhouse of the Agricultural Department of Environmental Sciences of the UFSM, Campus of Frederico Westphalen ? RS, during July to September, 2012. The treatments were arranged in a replacement series, in the proportions of 100:00 (wheat monoculture), 75:25, 50:50, 25:75 and 100:00 (competitor plant monoculture) for wheat plants (cv. Fundacep Cristalino) and for Italian ryegrass, radish and wheat (cv. BRS Guamirim) as competitor plants. The wheat is more competitive than Italian ryegrass in initial coexistence, even in the smallest proportion of plants. The radish when intercropped with wheat demonstrates similar competitive potential for environmental resources to the crop. There is mutual beneficial effect when wheat cultivars Fundacep Cristalino and BRS Guamirim coexisted, and each cultivar seems to have mechanism to avoid competition
POISSON project - I - Emission lines as accretion tracers in young stellar objects: results from observations of Chamaeleon I and II sources
We present the results of the analysis of LR optical-NIR spectra (0.6-2.4 um)
of a sample 47 YSOs in the ChaI and II star-forming clouds. These data are part
of the POISSON project (Protostellar Optical-Infrared Spectral Survey on NTT).
The aim is to determine the accretion luminosity (Lacc) and mass accretion rate
(Macc) of the sources through the analysis of the detected emission features.
We also aim at verifying the reliability and consistency of the existing
empirical relationships connecting emission line luminosity and Lacc. We employ
five tracers (OI-6300A, Ha, CaII-8542A, Pab, and Brg) to derive the accretion
luminosity. The tracers provide Lacc values showing different scatters when
plotted as a function of L*. The Brg seems to be the most reliable, because it
gives the minimum Lacc dispersion over the entire range of L*, whereas the
other tracers provide much more scattered Lacc values, which are not expected
for our homogeneous sample. The comparison between Lacc(Brg) and Lacc obtained
from the other tracers also shows systematic differences among the empirical
relationships. These may probably be ascribed to different excitation
mechanisms contributing to the line emission, which may vary between our sample
and those where the relationships were calibrated. Adopting the Lacc derived
from Brg, we find Lacc=0.1L*-1L* for all sources, and Macc of the order of
10^-7-10^-9 Msun/yr. The Macc derived in ChaI are proportional to M*^2, as
found in other low-mass star-forming regions. The discrepancies observed in the
case of Lacc(Brg) and Lacc(Pab) can be related to different intrinsic Pab/Brg,
ratios. The derived ratios show the existence of two different emission
modalities, one that agrees with predictions of both wind and accretion models,
the other suggesting optically thick emission from relatively small regions
(10^21-10^22 cm^-3) with gas at low temperatures (<4000K).Comment: 22 pages, 8 figures, accepted for publication in A&A; institute
affiliations and typos correcte
Ocorrência de capim-annoni no banco de sementes do solo de áreas infestadas.
O objetivo do trabalho foi caracterizar e comparar o banco de sementes do solo de campo nativo infestado por capim-annoni, após anos de adoção do Método Integrado de Recuperação de Pastagens - MIRAPASTO e de sistema de Integração Lavoura-Pecuária ? ILP, através da avaliação da distribuição vertical de sementes da planta indesejável no perfil do solo.bitstream/item/218527/1/BPD-46-online.pd
A highly-collimated SiO jet in the HH212 protostellar outflow
We mapped the HH212 Class 0 outflow in SiO(2--1, 5--4) and continuum using
the PdBI in its extended configurations. The unprecedented angular resolution
(down to 0.34") allows accurate comparison with a new, deep H2 image obtained
at the VLT. The SiO emission is confined to a highly-collimated bipolar jet
(width 0.35") along the outflow axis. The jet can be traced down to within 500
AU of the protostar, in a region that is heavily obscured in H2 images. Where
both species are detected, SiO shows the same overall kinematics and structure
as H2, indicating that both molecules are tracing the same material. We find
that the high-velocity SiO gas near the protostar is not tracing a wide-angle
wind but is already confined to a flow inside a narrow cone of half-opening
angle < 6 deg.Comment: Astronomy and Astrophysics Letter, in pres
Protostellar Outflows at the EarliesT Stages (POETS). II. A possible radio synchrotron jet associated with the EGO G035.02+0.35
Centimeter continuum observations of protostellar jets have revealed the
presence of knots of shocked gas where the flux density decreases with
frequency. This spectrum is characteristic of nonthermal synchrotron radiation
and implies the presence of both magnetic fields and relativistic electrons in
protostellar jets. Here, we report on one of the few detections of nonthermal
jet driven by a young massive star in the star-forming region G035.020.35.
We made use of the NSF's Karl G. Jansky Very Large Array (VLA) to observe this
region at C, Ku, and K bands with the A- and B-array configurations, and
obtained sensitive radio continuum maps down to a rms of 10 Jy
beam. These observations allow for a detailed spectral index analysis of
the radio continuum emission in the region, which we interpret as a
protostellar jet with a number of knots aligned with extended 4.5 m
emission. Two knots clearly emit nonthermal radiation and are found at similar
distances, of approximately 10,000 au, each side of the central young star,
from which they expand at velocities of hundreds km s. We estimate both
the mechanical force and the magnetic field associated with the radio jet, and
infer a lower limit of M yr km s and
values in the range mG, respectively.Comment: 10 pages, 4 figures, 5 tables, accepted by Astronomy & Astrophysic
Competition between the exotic grass Eragrostis plana and forage grass Paspalum nutatum under drought conditions.
Resumo
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