Hiroyasu Ando

Neutron Capture Elements in s -Process-rich, Very Metal-poor Stars

We report abundance estimates for neutron capture elements, including lead (Pb), and nucleosynthesis models for their origin, in two carbon-rich, very metal-poor stars, LP 625-44 and LP 706-7. These stars are subgiants whose surface abundances are likely to have been strongly aUected by mass transfer from companion asymptotic giant branch (AGB) stars that have since evolved to white dwarfs. The detections of Pb, which forms the —nal abundance peak of the s-process, enable a comparison of the abundance patterns from Sr (Z 38) to Pb (Z 82) with predictions of AGB models. The derived chemical compositions provide strong constraints on the AGB stellar models, as well as on s-process nucleosynthesis at low metallicity. The present paper reports details of the abundance analysis for 16 neutron capture elements in LP 625-44, including the eUects of hyper—ne splitting and isotope shifts of spectral lines for some elements. A Pb abundance is also derived for LP 706-7 by a reanalysis of a previously observed spectrum. We investigate the characteristics of the nucleosynthesis pathway that produces the abundance ratios of these objects using a parametric model of the s-process without adopting any speci—c stellar model. The neutron exposure q is estimated to be about 0.7 mbarn~1, signi—cantly larger than that which best —ts solar system material, but consistent with the values predicted by models of moderately metal-poor AGB stars. This value is strictly limited by the Pb abundance, in addition to those of Sr and Ba. We also —nd that the observed abundance pattern can be explained by a few recurrent neutron exposures and that the overlap of the material that is processed in two subsequent exposures is small (the overlap factor r D 0.1).

Synthetic gene networks as potential flexible parallel logic gates

We show how a synthetic gene network can function, in an optimal window of noise, as a robust logic gate. Interestingly, noise enhances the reliability of the logic operation. Further, the noise level can also be used to switch logic functionality, for instance toggle between AND, OR and XOR gates. We also consider a two-dimensional model of a gene network, where we show how two complementary gate operations can be achieved simultaneously. This indicates the flexible parallel processing potential of this biological system.

Instability of a thin magnetic tube in the solar atmosphere

Abstract The static equilibrium of a thin vertical magnetic tube embedded in the solar atmosphere is shown to be dynamically unstable against the fundamental mode of perturbation having no nodes in the vertical displacement. The instability has its origin in the convection zone, and the eigenfunction is extended further up in the stable upper layers by the magnetic field which guides the displacement mainly in the longitudinal direction. It is suggested that the downdraft observed in the solar network structure is a finite amplitude consequence of this instability. The overtone modes are found to be stable.

Chaotic phase synchronization in bursting-neuron models driven by a weak periodic force

We investigate the entrainment of a neuron model exhibiting a chaotic spiking-bursting behavior in response to a weak periodic force. This model exhibits two types of oscillations with different characteristic time scales, namely, long and short time scales. Several types of phase synchronization are observed, such as 1:1 phase locking between a single spike and one period of the force and 1:l phase locking between the period of slow oscillation underlying bursts and l periods of the force. Moreover, spiking-bursting oscillations with chaotic firing patterns can be synchronized with the periodic force. Such a type of phase synchronization is detected from the position of a set of points on a unit circle, which is determined by the phase of the periodic force at each spiking time. We show that this detection method is effective for a system with multiple time scales. Owing to the existence of both the short and the long time scales, two characteristic phenomena are found around the transition point to chaotic phase synchronization. One phenomenon shows that the average time interval between successive phase slips exhibits a power-law scaling against the driving force strength and that the scaling exponent has an unsmooth dependence on the changes in the driving force strength. The other phenomenon shows that Kuramotos order parameter before the transition exhibits stepwise behavior as a function of the driving force strength, contrary to the smooth transition in a model with a single time scale.

Preliminary study of light variations of the eclipsing binary AB Cassiopeiae

Preliminary study of the eclipsing binary AB Cas is presented here by using the photometric observational data. The primary component is one of the δ Sct variables with period of 0d.054, and whether the oscillation is of a radial mode or of a non-radial one is discussed. Two colour indices (B-V andU-B) data and the light curve analysis suggest that this binary system is a typical Algol type binary system, in which the primary component is near the ZAMS with about 2.3M⊙ and the secondary one is a subgiant star with about 0.5M⊙.

State concentration exponent as a measure of quickness in Kauffman-type networks.

We study the dynamics of randomly connected networks composed of binary Boolean elements and those composed of binary majority vote elements. We elucidate their differences in both sparsely and densely connected cases. The quickness of large network dynamics is usually quantified by the length of transient paths, an analytically intractable measure. For discrete-time dynamics of networks of binary elements, we address this dilemma with an alternative unified framework by using a concept termed state concentration, defined as the exponent of the average number of t-step ancestors in state transition graphs. The state transition graph is defined by nodes corresponding to network states and directed links corresponding to transitions. Using this exponent, we interrogate the dynamics of random Boolean and majority vote networks. We find that extremely sparse Boolean networks and majority vote networks with arbitrary density achieve quickness, owing in part to long-tailed in-degree distributions. As a corollary, only relatively dense majority vote networks can achieve both quickness and robustness.

Oscillations in G-Type Giants

The precise radial-velocity measurements of 4 G-type giants, 11Com,

Time-delayed feedback control of diffusion in random walkers

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Adaptive feedback control of chaotic neurodynamics in analog circuits

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Long-term variations of nonradial oscillations in a rapidly rotating early-type star (ζ oph)

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