2,977 research outputs found
Orbit determination of Transneptunian objects and Centaurs for the prediction of stellar occultations
The prediction of stellar occultations by Transneptunian objects and Centaurs
is a difficult challenge that requires accuracy both in the occulted star
position as for the object ephemeris. Until now, the most used method of
prediction involving tens of TNOs/Centaurs was to consider a constant offset
for the right ascension and for the declination with respect to a reference
ephemeris. This offset is determined as the difference between the most recent
observations of the TNO and the reference ephemeris. This method can be
successfully applied when the offset remains constant with time. This paper
presents an alternative method of prediction based on a new accurate orbit
determination procedure, which uses all the available positions of the TNO from
the Minor Planet Center database plus sets of new astrometric positions from
unpublished observations. The orbit determination is performed through a
numerical integration procedure (NIMA), in which we develop a specific
weighting scheme. The NIMA method was applied for 51 selected TNOs/Centaurs.
For this purpose, we have performed about 2900 new observations during
2007-2014. Using NIMA, we succeed in predicting the stellar occultations of 10
TNOs and 3 Centaurs between 2013 and 2015. By comparing the NIMA and JPL
ephemerides, we highlighted the variation of the offset between them with time.
Giving examples, we show that the constant offset method could not accurately
predict 6 out of the 13 observed positive occultations successfully predicted
by NIMA. The results indicate that NIMA is capable of efficiently refine the
orbits of these bodies. Finally, we show that the astrometric positions given
by positive occultations can help to further refine the orbit of the TNO and
consequently the future predictions. We also provide the unpublished
observations of the 51 selected TNOs and their ephemeris in a usable format by
the SPICE library.Comment: 12 pages, 9 figures, accepted in A&
How does landscape anthropization affect the myrmecofauna of urban forest fragments?
We evaluate whether landscape variables surrounding urban remnant forest fragments influence ant diversity and its components in urban areas. The study was conducted in six riparian forest fragments in midwestern Minas Gerais State, Brazil, by sampling epigaeic and arboreal ants. Arboreal ants respond to fragmente isolation with changes in alpha, beta and gamma diversities. Isolation likely hinders dispersion and re-colonization such that the more isolated a fragment is, the less likely that new species arrive there. On other hand, epigaeic diversity did not show any response to variables of the surroundings or fragments, probably because natural periodic floods constitute a more severe disturbance for these ants. In addition, throughout the process of urbanization, anthropogenic improvements, such as paving, that prevent the natural percolation of water, increase the flooding of riparian soil. Arboreal ant species composition responds to percentage of urban area, fragment area and distance from the urban center, while epigaeic ants respond only to fragment area and percentage of urban area. We believe that even with the loss of species diversity and anthropogenic influences on fragments within urban centers, these areas are still important for species conservation. We also suggest the development of environmental protection projects for riparian áreas within urban centers, including investments in ecological corridors connecting fragments and public policies seeking to preserve these areas
Estimação de parâmetros genéticos e predição de valores genotípicos para o caráter germinação em leucena pelo procedimento REML/BLUP.
Resumo
Enraizamento de cipó-de-são-joão (Pyrostegia venusta Miers.) pela aplicação de IBA e NAA.
Organizado por Patricia Póvoa de Mattos, Celso Garcia Auer, Rejane Stumpf Sberze, Katia Regina Pichelli e Paulo César Botosso
Rejuvenescimento de Ficus enormis (Mart. ex Miq.) Miq. para o enraizamento de estacas caulinares.
Organizado por Patricia Póvoa de Mattos, Celso Garcia Auer, Rejane Stumpf Sberze, Katia Regina Pichelli e Paulo César Botosso
Astrometry of the main satellites of Uranus: 18 years of observations
We determine accurate positions of the main satellites of Uranus: Miranda,
Ariel, Umbriel, Titania, and Oberon. Positions of Uranus, as derived from those
of these satellites, are also determined. The observational period spans from
1992 to 2011. All runs were made at the Pico dos Dias Observatory, Brazil.
We used the software called Platform for Reduction of Astronomical Images
Automatically (PRAIA) to minimise (digital coronography) the influence of the
scattered light of Uranus on the astrometric measurements and to determine
accurate positions of the main satellites. The positions of Uranus were then
indirectly determined by computing the mean differences between the observed
and ephemeris positions of these satellites. A series of numerical filters was
applied to filter out spurious data. These filters are mostly based on the
comparison between the positions of Oberon with those of the other satellites
and on the offsets as given by the differences between the observed and
ephemeris positions of all satellites.
We have, for the overall offsets of the five satellites, -29 (+/-63) mas in
right ascension and -27 (+/-46) mas in declination. For the overall difference
between the offsets of Oberon and those of the other satellites, we have +3
(+/-30) mas in right ascension and -2 (+/-28) mas in declination. Ephemeris
positions for the satellites were determined from DE432+ura111. Comparisons
using other modern ephemerides for the solar system -INPOP13c- and for the
motion of the satellites -NOE-7-2013- were also made. They confirm that the
largest contribution to the offsets we find comes from the motion of the
barycenter of the Uranus system around the barycenter of the solar system, as
given by the planetary ephemerides. Catalogues with the observed positions are
provided.Comment: 13 pages, 21 figure
Influência do arsênio e fósforo sobre o crescimento de Sesbania exasperata Kunth.
Objetivou-se avaliar o efeito da interação de diferentes doses de fósforo (P) e arsênio sobre o crescimento de plantas de Sesbania exasperata Kunth.Suplemento. Edição dos Resumos do XI Congresso Brasileiro de Fisiologia Vegetal, Gramado, set. 2007
The Distance to the Large Magellanic Cloud from the Eclipsing Binary HV2274
The distance to the Large Magellanic Cloud (LMC) is crucial for the
calibration of the Cosmic Distance Scale. We derive a distance to the LMC based
on an analysis of ground-based photometry and HST-based spectroscopy and
spectrophotometry of the LMC eclipsing binary system HV2274. Analysis of the
optical light curve and HST/GHRS radial velocity curve provides the masses and
radii of the binary components. Analysis of the HST/FOS UV/optical
spectrophotometry provides the temperatures of the component stars and the
interstellar extinction of the system. When combined, these data yield a
distance to the binary system. After correcting for the location of HV2274 with
respect to the center of the LMC, we find d(LMC) = 45.7 +/- 1.6 kpc or DM(LMC)
= 18.30 +/- 0.07 mag. This result, which is immune to the metallicity-induced
zero point uncertainties that have plagued other techniques, lends strong
support to the ``short'' LMC distance scale as derived from a number of
independent methods.Comment: 6 pages, including 2 pages of figures. Newly available optical (B and
V) photometry has revealed -- and allowed the elimination of -- a systematic
error in the previously reported determination of E(B-V) for HV2274. The new
result is E(B-V) = 0.12 mag (as compared to the value of 0.083 reported in
the original submission) and produces a DECREASE in the distance modulus of
HV2274 by 0.12 mag. ApJ Letters, in pres
Efeito da benziladenina na multiplicação de guanandi (Calophyllum brasiliense Cambess.) in vitro.
Heat-induced masculinization in domesticated zebrafish is family-specific and yields a set of different gonadal transcriptomes
Understanding environmental influences on sex ratios is important for the study of the evolution of sex-determining mechanisms and for evaluating the effects of global warming and chemical pollution. Fishes exhibit sexual plasticity, but the underlying mechanisms of environmental effects on their reproduction are unclear even in the well-established teleost research model, the zebrafish. Here we established the conditions to study the effects of elevated temperature on zebrafish sex. We showed that sex ratio response to elevated temperature is family-specific and typically leads to masculinization (female-to-male sex reversal), resulting in neomales. These results uncovered genotype-by-environment interactions that support a polygenic sex determination system in domesticated (laboratory) zebrafish. We found that some heat-treated fish had gene expression profiles similar to untreated controls of the same sex, indicating that they were resistant to thermal effects. Further, most neomales had gonadal transcriptomes similar to that of regular males. Strikingly, we discovered heat-treated females that displayed a normal ovarian phenotype but with a “male-like” gonadal transcriptome. Such major transcriptomic reprogramming with preserved organ structure has never been reported. Juveniles were also found to have a male-like transcriptome shortly after exposure to heat. These findings were validated by analyzing the expression of genes and signaling pathways associated with sex differentiation. Our results revealed a lasting thermal effect on zebrafish gonads, suggesting new avenues for detection of functional consequences of elevated temperature in natural fish populations in a global warming scenario
- …