4,386 research outputs found
Properties of Microlensing Central Perturbations by Planets in Binary Stellar Systems under the Strong Finite-Source Effect
We investigate high-magnification events caused by planets in wide binary
stellar systems under the strong finite-source effect, where the planet orbits
one of the companions. From this, we find that the pattern of central
perturbations in triple lens systems commonly appears as a combination of
individual characteristic patterns of planetary and binary lens systems in a
certain range where the sizes of the caustics induced by a planet and a binary
companion are comparable, and the range changes with the mass ratio of the
planet to the planet-hosting star. Specially, we find that because of this
central perturbation pattern, the characteristic feature of high-magnification
events caused by the triple lens systems appears in the residual from the
single-lensing light curve despite the strong finite-source effect, and it is
discriminated from those of the planetary and binary lensing events and thus
can be used for the identification of the existence of both planet and binary
companion. This characteristic feature is a simultaneous appearance of two
features. First, double negative-spike and single positive-spike features
caused by the binary companion appear together in the residual, where the
double negative spike occurs at both moments when the source enters and exits
the caustic center and the single positive spike occurs at the moment just
before the source enters into or just after the source exits from the caustic
center. Second, the magnification excess before or after the single
positive-spike feature is positive due to the planet, and the positive excess
has a remarkable increasing or decreasing pattern depending on the source
trajectory.Comment: 12 pages, 3 figures, accepted for publication in Ap
A Novel Bias Correction Method for Soil Moisture and Ocean Salinity (SMOS) Soil Moisture: Retrieval Ensembles
Bias correction is a very important pre-processing step in satellite data assimilation analysis, as data assimilation itself cannot circumvent satellite biases. We introduce a retrieval algorithm-specific and spatially heterogeneous Instantaneous Field of View (IFOV) bias correction method for Soil Moisture and Ocean Salinity (SMOS) soil moisture. To the best of our knowledge, this is the first paper to present the probabilistic presentation of SMOS soil moisture using retrieval ensembles. We illustrate that retrieval ensembles effectively mitigated the overestimation problem of SMOS soil moisture arising from brightness temperature errors over West Africa in a computationally efficient way (ensemble size: 12, no time-integration). In contrast, the existing method of Cumulative Distribution Function (CDF) matching considerably increased the SMOS biases, due to the limitations of relying on the imperfect reference data. From the validation at two semi-arid sites, Benin (moderately wet and vegetated area) and Niger (dry and sandy bare soils), it was shown that the SMOS errors arising from rain and vegetation attenuation were appropriately corrected by ensemble approaches. In Benin, the Root Mean Square Errors (RMSEs) decreased from 0.1248 m3/m3 for CDF matching to 0.0678 m3/m3 for the proposed ensemble approach. In Niger, the RMSEs decreased from 0.14 m3/m3 for CDF matching to 0.045 m3/m3 for the ensemble approach.open
A Planetary lensing feature in caustic-crossing high-magnification microlensing events
Current microlensing follow-up observations focus on high-magnification
events because of the high efficiency of planet detection. However, central
perturbations of high-magnification events caused by a planet can also be
produced by a very close or a very wide binary companion, and the two kinds of
central perturbations are not generally distinguished without time consuming
detailed modeling (a planet-binary degeneracy). Hence, it is important to
resolve the planet-binary degeneracy that occurs in high-magnification events.
In this paper, we investigate caustic-crossing high-magnification events caused
by a planet and a wide binary companion. From this study, we find that because
of the different magnification excess patterns inside the central caustics
induced by the planet and the binary companion, the light curves of the
caustic-crossing planetary-lensing events exhibit a feature that is
discriminated from those of the caustic-crossing binary-lensing events, and the
feature can be used to immediately distinguish between the planetary and binary
companions. The planetary-lensing feature appears in the interpeak region
between the two peaks of the caustic-crossings. The structure of the interpeak
region for the planetary-lensing events is smooth and convex or boxy, whereas
the structure for the binary-lensing events is smooth and concave. We also
investigate the effect of a finite background source star on the
planetary-lensing feature in the caustic-crossing high-magnification events.
From this, we find that the convex-shaped interpeak structure appears in a
certain range that changes with the mass ratio of the planet to the
planet-hosting star.Comment: 14 pages, 4 figures. Accepted for publication in Ap
Properties of the Planetary Caustic Perturbation
Just two of 10 extrasolar planets found by microlensing have been detected by
the planetary caustic despite the higher probability of planet detection
relative to the central caustic which has been responsible for four extrasolar
planet detections. This is because the perturbations induced by the planetary
caustic are unpredictable, thus making it difficult to carry out strategic
observations. However, if future high-cadence monitoring surveys are conducted,
the majority of planetary caustic events including the events by free-floating
planets and wide-separation planets would be detected. Hence, understanding the
planetary caustic perturbations becomes important. In this paper, we
investigate in detail the pattern of the planetary caustic perturbations. From
this study, we find three properties of the planetary caustic perturbations.
First, planetary systems with the same star-planet separation (s) basically
produce perturbations of constant strength regardless of the planet/star mass
ratio (q), but the duration of each perturbation scales with sqrt{q}. Second,
close planetary systems with the same separation produce essentially the same
negative perturbations between two triangular-shaped caustics regardless of q,
but the duration of the perturbations scales with sqrt{q}. Third, the positive
perturbations for planetary systems with the same mass ratio become stronger as
the caustic shrinks with the increasing |log s|, while the negative
perturbations become weaker. We estimate the degeneracy in the determination of
q that occurs in planetary caustic events. From this, we find that the mass
ratio can be more precisely determined as q increases and |log s| decreases. We
also find that the degeneracy range of events for which the source star passes
close to the planetary caustic is usually very narrow, and thus it would not
significantly affect the determination of q.Comment: 5 pages, 3 figures, 2 tables, accepted in MNRA
Formation mechanism of SiGe nanorod arrays by combining nanosphere lithography and Au-assisted chemical etching
The formation mechanism of SiGe nanorod (NR) arrays fabricated by combining nanosphere lithography and Au-assisted chemical etching has been investigated. By precisely controlling the etching rate and time, the lengths of SiGe NRs can be tuned from 300 nm to 1
μm. The morphologies of SiGe NRs were found to change dramatically by varying the etching temperatures. We propose a mechanism involving a locally temperature-sensitive redox reaction to explain this strong temperature dependence of the morphologies of SiGe NRs. At a lower etching temperature, both corrosion reaction and Au-assisted etching process were kinetically impeded, whereas at a higher temperature, Au-assisted anisotropic etching dominated the formation of SiGe NRs. With transmission electron microscopy and scanning electron microscopy analyses, this study provides a beneficial scheme to design and fabricate low-dimensional SiGe-based nanostructures for possible applications
Distinguishing central perturbations by binary stellar and planetary systems under the moderately strong finite-source effect
We investigate high-magnification events caused by wide binary stellar and
planetary systems under the moderately strong finite-source effect where the
diameter of the source star is comparable with the caustics induced by a binary
companion and a planet. From this investigation, we find that a characteristic
feature in the central perturbations induced by the binary systems commonly
appears in a constant range where the size of the caustic induced by the binary
companion is between 1.5 and 1.9 times of the diameter of the source, whereas
in the central perturbations induced by the planetary systems the feature
commonly appears in a range where the ratio of the size of the caustic induced
by the planet to the source diameter changes with the planet/primary mass
ratio. High-magnification events caused by the binary and planetary systems
with the characteristic feature produce a distinctive short-duration bump in
the residuals from the single-lensing light curve, where the bump occurs near
the time of peak magnification of the events. Because of a well-known
planet/binary degeneracy, we compare binary- and planetary-lensing events with
the short-duration bump in the residuals. As a result, we find the features of
the binary-lensing events that are discriminated from the planetary-lensing
events despite the moderately strong finite-source effect and thus can be used
to immediately distinguish between the binary and planetary companions. We also
find the feature that appears only in binary-lensing events with a very low
mass ratio or planetary-lensing events. This implies that the lens systems with
the feature have a very low mass binary companion (such as a brown dwarf) or a
planet.Comment: 18 pages, 7 figures, accepted by Ap
Inhibition of Inducible Nitric Oxide Synthase, Cycleooxygenase-2 and Lipid Peroxidation by Methanol Extract of Pericarpium Zanthoxyli
Purpose: To explore the antioxidant properties of the methanol extract of Pericarpium Zanthoxyli and its effect on inducible nitric oxide synthase (iNOS), cycleooxygenase-2 (COX-2) and lipopolysaccharides (LPS)-induced cell damage in macrophage cells.Methods: Anti-oxidant activities were tested by measuring free radical scavenging activity (DPPH, NO) and lipid peroxidation levels. The mechanism of anti-oxidant action of Pericarpium Zanthoxyli extractwas determined by Western blot analysis for iNOS and COX-2 expression in LPS-stimulated RAW 264.7 cells.Results: Pericarpium Zanthoxyli extract contained anti-oxidant components including phenolics (2.456 mg/g), flavonoids (0.127 mg/g) and anthocyanins (20.34 mg/g). The extract exerted significant radicalscavenging activity in a dose-dependent manner. It also inhibited lipid peroxidation and exerted dramatic reducing power (28.9-fold compared with control at a concentration of 1 mg/ml). Production of iNOS induced by LPS was significantly (p < 0.05) inhibited by the extract, suggesting that the extract inhibits nitric oxide (NO) production by suppressing iNOS expression. Strikingly, COX-2 induced by LPS was also significantly (p < 0.05) inhibited by the extract.Conclusion: These results suggest that the methanol extract of Pericarpium Zanthoxyli exerts significant anti-oxidant activity via inhibiting free radicals, iNOS and lipid peroxidation as well as by inhibition of COX-2 enzyme.Keywords: Pericarpium Zanthoxyli, Nitric oxide, iNOS, COX-2, Lipid peroxidation, Antioxidan
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