4,411 research outputs found
The Light and Period Variations of the Eclipsing Binary AA Ursae Majoris
We present new multiband CCD photometry for AA UMa made on 8 nights between
January and March 2009; the light curves are the first ever compiled.
Historical light curves, as well as ours, display partial eclipses and inverse
O'Connell effects with Max I fainter than Max II. Among possible spot models, a
cool spot on either of the component stars and its variability with time permit
good light-curve representations for the system. A total of 194 eclipse timings
over 81 yrs, including our five timings, were used for ephemeris computations.
We found that the orbital period of the system has varied due to a periodic
oscillation overlaid on an upward parabolic variation. The continuous period
increase at a fractional rate of 1.310 is consistent with
that calculated from the W-D code and can be interpreted as a thermal mass
transfer from the less to the more massive secondary star at a rate of
6.610 M yr. The periodic component is in
satisfactory accord with a light-time effect due to an unseen companion with a
period of 28.2 yrs, a semi-amplitude of 0.007 d, and a minimum mass of =0.25 but this period variation could also arise from
magnetic activity.Comment: 23 pages, including 5 figures and 8 tables, accepted for publication
in PAS
Photoreductive Dissolution of Iron Oxides Trapped in Ice and Its Environmental Implications
The availability of iron has been thought to be a main limiting factor for the productivity of phytoplankton and related with the uptake of atmospheric CO_2 and algal blooms in fresh and sea waters. In this work, the formation of bioavailable iron (Fe(II)_(aq)) from the dissolution of iron oxide particles was investigated in the ice phase under both UV and visible light irradiation. The photoreductive dissolution of iron oxides proceeded slowly in aqueous solution (pH 3.5) but was significantly accelerated in polycrystalline ice, subsequently releasing more bioavailable ferrous iron upon thawing. The enhanced photogeneration of Fe(II)_(aq) in ice was confirmed regardless of the type of iron oxides [hematite, maghemite (γ-Fe_2O_3), goethite (α-FeOOH)] and the kind of electron donors. The ice-enhanced dissolution of iron oxides was also observed under visible light irradiation, although the dissolution rate was much slower compared with the case of UV radiation. The iron oxide particles and organic electron donors (if any) in ice are concentrated and aggregated in the liquid-like grain boundary region (freeze concentration effect) where protons are also highly concentrated (lower pH). The enhanced photodissolution of iron oxides should occur in this confined boundary region. We hypothesized that electron hopping through the interconnected grain boundaries of iron oxide particles facilitates the separation of photoinduced charge pairs. The outdoor experiments carried out under ambient solar radiation of Ny-Ålesund (Svalbard, 78°55′N) also showed that the generation of dissolved Fe(II)_(aq) via photoreductive dissolution is enhanced when iron oxides are trapped in ice. Our results imply that the ice(snow)-covered surfaces and ice-cloud particles containing iron-rich mineral dusts in the polar and cold environments provide a source of bioavailable iron when they thaw
Blending in Future Space-based Microlensing Surveys
We investigate the effect of blending in future gravitational microlensing
surveys by carrying out simulation of Galactic bulge microlensing events to be
detected from a proposed space-based lensing survey. From this simulation, we
find that the contribution of the flux from background stars to the total
blended flux will be equivalent to that from the lens itself despite the
greatly improved resolution from space observations, implying that
characterizing lenses from the analysis of the blended flux would not be easy.
As a method to isolate events for which most of the blended flux is
attributable to the lens, we propose to use astrometric information of source
star image centroid motion. For the sample of events obtained by imposing a
criterion that the centroid shift should be less than three times of the
astrometric uncertainty among the events for which blending is noticed with
blended light fractions , we estimate that the contamination of
the blended flux by background stars will be less than 20% for most () of the sample events. The expected rate of these events is
events/yr, which is large enough for the statistical analysis of the lens
populations.Comment: total 6 pages, including 5 figures, ApJ, in pres
Visfatin Induces Sickness Responses in the Brain
BACKGROUND/OBJECTIVE: Visfatin, also known as nicotiamide phosphoribosyltransferase or pre-B cell colony enhancing factor, is a pro-inflammatory cytokine whose serum level is increased in sepsis and cancer as well as in obesity. Here we report a pro-inflammatory role of visfatin in the brain, to mediate sickness responses including anorexia, hyperthermia and hypoactivity. METHODOLOGY: Rats were intracerebroventricularly (ICV) injected with visfatin, and changes in food intake, body weight, body temperature and locomotor activity were monitored. Real-time PCR was applied to determine the expressions of pro-inflammatory cytokines, proopiomelanocortin (POMC) and prostaglandin-synthesizing enzymes in their brain. To determine the roles of cyclooxygenase (COX) and melanocortin in the visfatin action, rats were ICV-injected with visfatin with or without SHU9119, a melanocortin receptor antagonist, or indomethacin, a COX inhibitor, and their sickness behaviors were evaluated. PRINCIPAL FINDINGS: Administration of visfatin decreased food intake, body weight and locomotor activity and increased body temperature. Visfatin evoked significant increases in the levels of pro-inflammatory cytokines, prostaglandin-synthesizing enzymes and POMC, an anorexigenic neuropeptide. Indomethacin attenuated the effects of visfatin on hyperthermia and hypoactivity, but not anorexia. Further, SHU9119 blocked visfatin-induced anorexia but did not affect hyperthermia or hypoactivity. CONCLUSIONS: Visfatin induced sickness responses via regulation of COX and the melanocortin pathway in the brain
Fabrication and characterization of silicon wire solar cells having ZnO nanorod antireflection coating on Al-doped ZnO seed layer
In this study, we have fabricated and characterized the silicon [Si] wire solar cells with conformal ZnO nanorod antireflection coating [ARC] grown on a Al-doped ZnO [AZO] seed layer. Vertically aligned Si wire arrays were fabricated by electrochemical etching and, the pn junction was prepared by spin-on dopant diffusion method. Hydrothermal growth of the ZnO nanorods was followed by AZO film deposition on high aspect ratio Si microwire arrays by atomic layer deposition [ALD]. The introduction of an ALD-deposited AZO film on Si wire arrays not only helps to create the ZnO nanorod arrays, but also has a strong impact on the reduction of surface recombination. The reflectance spectra show that ZnO nanorods were used as an efficient ARC to enhance light absorption by multiple scattering. Also, from the current-voltage results, we found that the combination of the AZO film and ZnO nanorods on Si wire solar cells leads to an increased power conversion efficiency by more than 27% compared to the cells without it. © 2012 Baek et al.1
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