Results 1 - 10 of 51
Results 1 - 10 of 51. Search took: 0.014 seconds
|Sort by: date | relevance|
[en] We present the Kepler photometry of KIC 6048106, which is exhibiting the O’Connell effect and multiperiodic pulsations. Including a starspot on either of the components, light-curve synthesis indicates that this system is a semi-detached Algol with a mass ratio of 0.211, an orbital inclination of 73.°9, and a large temperature difference of 2534 K. To examine in detail both the spot variations and pulsations, we separately analyzed the Kepler time-series data at the interval of an orbital period in an iterative way. The results reveal that the variable asymmetries of the light maxima can be interpreted as the changes with time of a magnetic cool spot on the secondary component. Multiple frequency analyses were performed in the outside-eclipse light residuals after removal of the binarity effects from the observed Kepler data. We detected 30 frequencies with signal to noise amplitude ratios larger than 4.0, of which six ( f 2– f 6 and f 10) can be identified as high-order (17 ≤ n ≤ 25) low-degree ( ℓ = 2) gravity-mode pulsations that were stable during the observing run of 200 days. In contrast, the other frequencies may be harmonic and combination terms. For the six frequencies, the pulsation periods and pulsation constants are in the ranges of 0.352–0.506 days and 0.232–0.333 days, respectively. These values and the position on the Hertzsprung–Russell diagram demonstrate that the primary star is a γ Dor variable. The evolutionary status and the pulsation nature of KIC 6048106 are discussed.
[en] We investigate the scale-free network properties of the bipartite ecological network, in particular, the plant-pollinator network. In plant-pollinator network, the pollinators visit the plant to get the nectars. In contrast to the other complex network, the plant-pollinator network has not only the trophic relationships among the interacting partners but also the complexities of the coevolutionary effects. The interactions between the plant and pollinators are beneficial relations. The plant-pollinator network is a bipartite and weighted network. The networks have two types of the nodes: plant and pollinator. We consider the visiting frequency of a pollinator to a plant as the weighting value of the link. We defined the strength of a node as the sum of the weighting value of the links. We reported the cumulative distribution function (CDF) of the degree and the strength of the plant-pollinator network. The CDF of the plants followed stretched exponential functions for both degree and strength, but the CDF of the pollinators showed the power law for both degree and strength. The average strength of the links showed the nonlinear dependence on the degree of the networks.
[en] Free-form surfaces are widely used in CAD systems to describe the part surface. Today, the most advanced machining of free from surfaces is done in five-axis machining using a flat end mill cutter. However, five-axis machining requires complex algorithms for gouging avoidance, collision detection and powerful computer-aided manufacturing (CAM) systems to support various operations. An accurate and efficient method is proposed for five-axis CNC machining of free-form surfaces. The proposed algorithm selects the best tool and plans the tool path autonomously using curvature matching and integrated inverse kinematics of the machine tool. The new algorithm uses the real cutter contact tool path generated by the inverse kinematics and not the linearized piecewise real cutter location tool path
[en] Potassium copper hexacyanoferrate-cellulose hydrogel composites (HCF-gels) and potassium copper hexacyanoferrate-embedded poly-citric acid hydrogel film (HPC) were synthesized. In Cs+ removal experiments, HCF-gels exhibited exceptional Cs+ adsorption capacities 2.06-2.32 mmol g-1. HPC showed a very high Cs+ uptake of 667 mg/g KCuHCF. The adsorbents revealed stable and high Cs+ removal efficiency across a wide pH range. Notably, the adsorbents could adsorb Cs+ selectively in seawater containing Cs+. The combination of testing and radiation stability results indicated that the performance of the materials are maintained whether irradiated or not. The cost of the HCF-gels and HPC were estimated approximately 13.0055 $/kg and 38.2490 $/kg respectively. This is reasonable cost compared to commercialized Cs+ adsorbents. New pool scrubbing system is designed for engineering system design to apply novel Cs+ adsorbents under severe accident condition. (authors)
[en] In cases of large-scale release or decommissioning, due to their large volume and extremely low cesium concentration, adsorption with ion exchange is suitable for decontamination. A variety of cesium adsorbents such as zeolite, crystalline silicotitanates, aluminum molybdophosphate, chalcogenides have been considered for cesium decontamination from liquid solution. Due to the lack of cost-benefit analysis information, it is difficult to apply cesium adsorbents for specific situations. In order to apply cesium adsorbents during the severe accident, it is necessary to design an engineering system considering the situation at the time of severe accident. The objective of this research is to develop novel cesium adsorbents, and analyze their chemical and radiation stability. Their physical and chemical characteristics were investigated. Preliminary results show two adsorbents can be applied to a wide range of pHs while maintaining a high removal efficiency. The combination of testing and radiation stability results indicated that the performance of the material is maintained whether irradiated or not. The novel adsorbents can be applied for decommissioning radiation environment (0.5Gy/hr).
[en] Nutrients from a flowering plant are shared by its pollinators, giving rise to competition in the latter. Such exploitative competition of pollinators can limit their abundance and affect the global organization of the mutualistic partnership in the plant-pollinator mutualistic community. Here we investigate the effects of the exploitative competition between pollinators on the structure and the species abundance of the mutualistic networks which evolve by changing mutualistic partnership towards higher abundance of species. Simulations show different emergent network characteristics between plants and animals; hub plants connected to many pollinators are very rare while a few super-hub pollinators appear with the exploitative competition included, in contrast to equally many hubs of both types without the exploitative competition. More interestingly, the abundance of plant species increases with increasing the exploitative competition strength. We analyze the inverse of the generalized interaction matrix in the weak-interaction limit to identify the leading structural factors relevant to the species abundance, which are shown to be instrumental in optimizing the network structure to increase the mutualistic benefit and lower the cost of exploitative competition. (paper: biological modelling and information)
[en] In our previous study, we showed that the peculiar globular cluster (GC) M22 contains two distinct stellar populations, namely the Ca - w and Ca - s groups, which have different physical properties, chemical compositions, spatial distributions, and kinematics. We proposed that M22 was most likely formed via a merger of two GCs with heterogeneous metallicities in a dwarf galaxy environment and then later accreted to our Galaxy. In their recent study, Mucciarelli et al. claimed that M22 is a normal monometallic globular cluster without any perceptible metallicity spread among the two groups of stars, which challenges our results and those of others. We devise new strategies for the local thermodynamic equilibrium abundance analysis of red giant branch stars in GCs and show that there exists a spread in the iron abundance distribution in M22.
[en] Using our ingeniously designed new filter systems, we investigate multiple stellar populations of the red giant branch (RGB) and the asymptotic giant branch (AGB) in the globular cluster (GC) M5. Our results are the following. (1) Our index accurately traces nitrogen abundances in M5, while other color indices fail to do so. (2) We find bimodal CN distributions in both RGB and AGB sequences, with number ratios between CN-weak (CN-w) and CN-strong (CN-s) of n(CN-w):n(CN-s) = 29:71 (±2) and 21:79 (±7), respectively. (3) We also find a bimodal photometric [N/Fe] distribution for M5 RGB stars. (4) Our –[O/Fe] and –[Na/Fe] relations show clear discontinuities between the two RGB populations. (5) Although small, the RGB bump of CN-s is slightly brighter, = 0.07 ± 0.04 mag. If real, the difference in the helium abundance becomes = 0.028 ± 0.016, in the sense that CN-s is more helium enhanced. (6) Very similar radial but different spatial distributions with comparable center positions are found for the two RGB populations. The CN-s RGB and AGB stars are more elongated along the NW–SE direction. (7) The CN-s population shows a substantial net projected rotation, while that of the CN-w population is nil. (8) Our results confirm the deficiency of CN-w AGB stars previously noted by others. We show that it is most likely due to stochastic truncation in the outer part of the cluster. Finally, we discuss the formation scenario of M5.
[en] Oscillating Algol-type eclipsing binaries (oEA) are very interesting objects that have three observational features of eclipse, pulsation, and mass transfer. Direct measurement of their masses and radii from the double-lined radial velocity data and photometric light curves would be the most essential for understanding their evolutionary process and for performing the asteroseismological study. We present the physical properties of the oEA star XX Cep from high-resolution time-series spectroscopic data. The effective temperature of the primary star was determined to be 7946 ± 240 K by comparing the observed spectra and the Kurucz models. We detected the absorption lines of the secondary star, which had never been detected in previous studies, and obtained the radial velocities for both components. With the published BVRI light curves, we determined the absolute parameters for the binary via Wilson–Devinney modeling. The masses and radii are , , , and , respectively. The primary star is about more massive and larger than the zero-age main sequence stars with the same effective temperature. It is probably because XX Cep has experienced a very different evolutionary process due to mass transfer, contrasting with the normal main sequence stars. The primary star is located inside the theoretical instability strip of δ Sct-type stars on the HR diagram. We demonstrated that XX Cep is an oEA star, consisting of a δ Sct-type pulsating primary component and an evolved secondary companion.
[en] We present the physical properties of KIC 5621294, showing light and timing variations from the Kepler photometry. Its light curve displays partial eclipses and the O’Connell effect, with Max II fainter than Max I, which was fitted quite well by applying third-body and spot effects to the system. The results indicate that the eclipsing pair is a classical Algol-type system with parameters of q = 0.22, i = 76.°8, and Δ(T1−T2) = 4235 K, in which the detached primary component fills about 77% of its limiting lobe. Striking discrepancies exist between the primary and secondary eclipse times obtained with the method of Kwee and van Woerden. These are mainly caused by surface inhomogeneities due to spot activity detected in our light curve synthesis. The 1253 light curve timings from the Wilson–Devinney code were used for a period study. It was found that the orbital period of KIC 5621294 has varied due to periodic variation overlaid on a downward parabola. The sinusoidal variation with a period of 961 days and a semi-amplitude of 22.5 s most likely arises from a light-time effect due to a third component with a mass of M3sini3 = 46.9 MJup, which is in good agreement with that calculated from the light curve itself. If its orbital inclination is larger than about 40°, the mass of the circumbinary object would possibly match a brown dwarf. The parabolic variation could not be fully explained by either a mass transfer between the binary components or angular momentum via magnetic braking. It is possible that the parabola may be the only observed part of a period modulation caused by the presence of another companion in a wider orbit.