Infection with ectomycorrhizal fungi can increase the ability of plants to resist drought stress through morphophysiological and biochemical mechanisms. However, the metabolism of antioxidative ...enzyme activities in the ectomycorrhizal symbiosis remains poorly understood. This study investigated biomass production, reactive oxygen metabolism (hydrogen peroxide and malondialdehyde concentration) and antioxidant enzyme activity (superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase) in pure cultures of the ectomycorrhizal fungi Descolea antartica Sing. and Pisolithus tinctorius (Pers.) Coker & Couch, and non-mycorrhizal and mycorrhizal roots of Nothofagus dombeyi (Mirb.) roots under well-watered conditions and drought conditions (DC). The studied ectomycorrhizal fungi regulated their antioxidative enzyme metabolism differentially in response to drought, resulting in cellular damage in D. antartica but not in P. tinctorius. Ectomycorrhizal inoculation and water treatment had a significant effect on all parameters studied, including relative water content of the plant. As such, N. dombeyi plants in symbiosis experienced a lower oxidative stress effect than non-mycorrhizal plants under DC. Additionally, ectomycorrhizal N. dombeyi roots showed a greater antioxidant enzyme activity relative to non-mycorrhizal roots, an effect which was further expressed under DC. The association between the non-specific P. tinctorius and N. dombeyi had a more effective reactive oxygen species (ROS) metabolism than the specific D. antartica-N. dombeyi symbiosis. We conclude that the combination of effective ROS prevention and ROS detoxification by ectomycorrhizal plants resulted in reduced cellular damage and increased plant growth relative to non-mycorrhizal plants under drought.
A stellar occultation observed on 3rd June 2013 revealed the presence of two dense and narrow rings separated by a small gap around the Centaur object (10 199) Chariklo. The composition of these ...rings is not known. In this work, we aim to determine if the variability in the absolute magnitude of Chariklo and the temporal variation of the spectral ice feature, even when it disappeared in 2007, can be explained by an icy ring system whose aspect angle changes with time. We showed that absolute photometry of Chariklo from the literature and new photometric data that we obtained in 2013 can be explained by a ring of particles whose opening angle changes as a function of time. Chariklo surface is composed with about 60% of amorphous carbon, 30% of silicates and 10% of organics; no water ice was found on the surface. The ring, on the other hand, contains 20% of water ice, 40-70% of silicates, and 10-30% of tholins and small quantities of amorphous carbon.
Evolution of the TRANSYT model in a developing country Fernandez, Rodrigo; Valenzuela, Eduardo; Casanello, Federico ...
Transportation research. Part A, Policy and practice,
06/2006, Letnik:
40, Številka:
5
Journal Article
Recenzirano
TRANSYT has been used in Chile since the early 1980s for cost–benefit analysis of infrastructure and traffic management projects. It is also the main tool of the Area Traffic Control Unit of Santiago ...de Chile since mid 1990s. As a result of this experience, many methodological improvements to the model have been done in order to take into account local conditions. This paper presents a review of these methodological as well as practical advances on the TRANSYT model made in the Chilean context during the past 15 years. Issues considered are cruise time distributions, the cycle-time selection method, saturation flows and car equivalents, public transport modeling, peak-hour delay calculation, modeling unsignalized intersections and zebra crossings, and fuel-consumption estimation.
Recent stellar occultations have allowed accurate instantaneous size and apparent shape determinations of the large Kuiper belt object (50000)~Quaoar and the detection of two rings with spatially ...variable optical depths. In this paper we present new visible range light curve data of Quaoar from the Kepler/K2 mission, and thermal light curves at 100 and 160 \(\mu\)m obtained with Herschel/PACS. The K2 data provide a single-peaked period of 8.88 h, very close to the previously determined 8.84 h, and it favours an asymmetric double-peaked light curve with a 17.76 h period. We clearly detected a thermal light curve with relative amplitudes of \(\sim\)10% at 100 and at 160 \(\mu\)m. A detailed thermophysical modelling of the system shows that the measurements can be best fit with a triaxial ellipsoid shape, a volume-equivalent diameter of 1090 km, and axis ratios of a/b = 1.19 and b/c = 1.16. This shape matches the published occultation shape}, as well as visual and thermal light curve data. The radiometric size uncertainty remains relatively large (\(\pm\)40 km) as the ring and satellite contributions to the system-integrated flux densities are unknown. In the less likely case of negligible ring or satellite contributions, Quaoar would have a size above 1100 km and a thermal inertia \(\leq\) 10 Jm\(^{-2}\)K\(^{-1}\)s\(^{-1/2}\). A large and dark Weywot in combination with a possible ring contribution would lead to a size below 1080\,km in combination with a thermal inertia \(\gtrsim\) 10 Jm\(^{-2}\)K\(^{-1}\)s\(^{-1/2}\), notably higher than that of smaller Kuiper belt objects with similar albedo and colours. We find that Quaoar's density is in the range 1.67-1.77 g/cm\(^3\), significantly lower than previous estimates. This density value closely matches the relationship observed between the size and density of the largest Kuiper belt objects.
We observed Sedna, Gonggong, and Quaoar with the NIRSpec instrument on the James Webb Space Telescope (JWST). All three bodies were observed in the low-resolution prism mode at wavelengths spanning ...0.7 to 5.2 \(\mu\)m. Quaoar was also observed at 10x higher spectral resolution from 0.97 to 3.16 \(\mu\)m using medium-resolution gratings. Sedna's spectrum shows a large number of absorption features due to ethane (C\(_2\)H\(_6\)), as well as acetylene (C\(_2\)H\(_2\)), ethylene (C\(_2\)H\(_4\)), H\(_2\)O, and possibly minor CO\(_2\). Gonggong's spectrum also shows several, but fewer and weaker, ethane features, along with stronger and cleaner H\(_2\)O features and CO\(_2\) complexed with other molecules. Quaoar's prism spectrum shows even fewer and weaker ethane features, the deepest and cleanest H\(_2\)O features, a feature at 3.2 \(\mu\)m possibly due to HCN, and CO\(_2\) ice. The higher-resolution medium grating spectrum of Quaoar reveals several overtone and combination bands of ethane and methane (CH\(_4\)). Spectra of all three objects show steep red spectral slopes and strong, broad absorptions between 2.7 and 3.6 \(\mu\)m indicative of complex organic molecules. The suite of light hydrocarbons and complex organic molecules are interpreted as the products of irradiation of methane. We infer that the differences in apparent abundances of irradiation products are likely due to their distinctive orbits, which lead to different timescales of methane retention and to different charged particle irradiation environments. In all cases, however, the continued presence of light hydrocarbons implies a resupply of methane to the surface. We suggest that these three bodies have undergone internal melting and geochemical evolution similar to the larger dwarf planets and distinct from all smaller KBOs.
On 12 December 2023, the star \(\alpha\) Orionis (Betelgeuse) will be occulted by the asteroid (319) Leona. This represents an extraordinary and unique opportunity to analyze the diameter and ...brightness distribution of Betelgeuse's photosphere with extreme angular resolution by studying the light curve as the asteroid occults the star from different points on Earth and at different wavelengths. Here we present observations of another occultation by Leona on 13 September 2023 to determine its projected shape and size in preparation for the December 12th event. The occultation observation campaign was highly successful. The effective diameter in projected area derived from the positive detections at 17 sites turned out to be 66 km \(\pm\) 2 km using an elliptical fit to the instantaneous limb. The body is highly elongated, with dimensions of 79.6 \(\pm\) 2.2 km x 54.8 \(\pm\) 1.3 km in its long and short axis, respectively, at the occultation time. Also, an accurate position coming from the occultation, to improve the orbit determination of Leona for December 12 is provided.
Centaurs, distinguished by their volatile-rich compositions, play a pivotal
role in understanding the formation and evolution of the early solar system, as
they represent remnants of the primordial ...material that populated the outer
regions. Stellar occultations offer a means to investigate their physical
properties, including shape, rotational state, or the potential presence of
satellites and rings.
This work aims to conduct a detailed study of the centaur (54598) Bienor
through stellar occultations and rotational light curves from photometric data
collected during recent years.
We successfully predicted three stellar occultations by Bienor, which were
observed from Japan, Eastern Europe, and the USA. In addition, we organized
observational campaigns from Spain to obtain rotational light curves. At the
same time, we develop software to generate synthetic light curves from
three-dimensional shape models, enabling us to validate the outcomes through
computer simulations.
We resolve Bienor's projected ellipse for December 26, 2022, determine a
prograde sense of rotation, and confirm an asymmetric rotational light curve.
We also retrieve the axes of its triaxial ellipsoid shape as a = (127 $\pm$ 5)
km, b = (55 $\pm$ 4) km, and c = (45 $\pm$ 4) km. Moreover, we refine the
rotation period to 9.1736 $\pm$ 0.0002 hours and determine a geometric albedo
of (6.5 $\pm$ 0.5) %, higher than previously determined by other methods.
Finally, by comparing our findings with previous results and simulated
rotational light curves, we analyze whether an irregular or contact-binary
shape, the presence of an additional element such as a satellite, or
significant albedo variations on Bienor's surface, may be present.
We could accurately predict the shadow path and successfully observe an occultation of a bright star by Chiron on 2022 December 15. The Kottamia Astronomical Observatory in Egypt did not detect the ...occultation by the solid body, but we detected three extinction features in the light curve that had symmetrical counterparts with respect to the central time of the occultation. One of the features is broad and shallow, whereas the other two features are sharper with a maximum extinction of \(\sim\)25\(\%\) at the achieved spatial resolution of 19 km per data point. From the Wise observatory in Israel, we detected the occultation caused by the main body and several extinction features surrounding the body. When all the secondary features are plotted in the sky plane we find that they can be caused by a broad \(\sim\)580 km disk with concentrations at radii of 325 \pm 16 km and 423 \pm 11 km surrounding Chiron. At least one of these structures appears to be outside the Roche limit. The ecliptic coordinates of the pole of the disk are \(\lambda\) = 151\(^\circ~\pm\) 8\(^\circ\) and \(\beta\) = 18\(^\circ~\pm\) 11\(^\circ\), in agreement with previous results. We also show our long-term photometry indicating that Chiron had suffered a brightness outburst of at least 0.6 mag between March and September 2021 and that Chiron was still somewhat brighter at the occultation date than at its nominal pre-outburst phase. The outermost extinction features might be consistent with a bound or temporarily bound structure associated with the brightness increase. However, the nature of the brightness outburst is unclear, and it is also unclear whether the dust or ice released in the outburst could be feeding a putative ring structure or if it emanated from it.
Quaoar is a classical Trans-Neptunian Object (TNO) with an area equivalent diameter of 1,100 km and an orbital semi-major axis of 43.3 astronomical units. Based on stellar occultations observed ...between 2018 and 2021, an inhomogeneous ring (Q1R, Quaoar's first ring) was detected around this body. Aims. A new stellar occultation by Quaoar was observed on August 9th, 2022 aiming to improve Quaoar's shape models and the physical parameters of Q1R while searching for additional material around the body. Methods. The occultation provided nine effective chords across Quaoar, pinning down its size, shape, and astrometric position. Large facilities, such as Gemini North and the Canada-France-Hawaii Telescope (CFHT), were used to obtain high acquisition rates and signal-to-noise ratios. The light curves were also used to characterize the Q1R ring (radial profiles and orbital elements). Results. Quaoar's elliptical fit to the occultation chords yields the limb with an apparent semi-major axis of \(579.5\pm4.0\) km, apparent oblateness of \(0.12\pm0.01\), and area-equivalent radius of \(543\pm2\) km. Quaoar's limb orientation is consistent with Q1R and Weywot orbiting in Quaoar's equatorial plane. The orbital radius of Q1R is refined to a value of \(4,057\pm6\) km. The radial opacity profile of the more opaque ring profile follows a Lorentzian shape that extends over 60 km, with a full width at half maximum (FWHM) of \(\sim5\) km and a peak normal optical depth of 0.4. Besides the secondary events related to the already reported rings, new secondary events detected during the August 2022 occultation in three different data sets are consistent with another ring around Quaoar with a radius of \(2,520\pm20\) km, assuming the ring is circular and co-planar with Q1R. This new ring has a typical width of 10 km and a normal optical depth of \(\sim\)0.004. Like Q1R, it also lies outside Quaoar's classical Roche limit.
PDF
