Coupled Map Modeling for Cloud Dynamics

A coupled map model for cloud dynamics is proposed, which consists of the successive operations of the physical processes; buoyancy, diffusion, viscosity, adiabatic expansion, fall of a droplet by gravity, descent flow dragged by the falling droplet, and advection. Through extensive simulations, the phases corresponding to stratus, cumulus, stratocumulus and cumulonimbus are found, with the change of the ground temperature and the moisture of the air. They are characterized by order parameters such as the cluster number, perimeter-to-area ratio of a cloud, and Kolmogorov-Sinai entropy.Comment: 9 pages, 4 figure, LaTeX, mpeg simulations available at http://aurora.elsip.hokudai.ac.jp

Relation between gamma-ray family and EAS core: Monte-Carlo simulation of EAS core

Preliminary results of Monte-Carlo simulation on Extensive Air Showers (EAS) (Ne=100,000) core is reported. For the first collision at the top of the atmosphere, high multiplicity (high rapidity, density) and a large Pt (1.5GeV average) model is assumed. Most of the simulated cores show a complicated structure

Design of oscillator networks with enhanced synchronization tolerance against noise

Can synchronization properties of a network of identical oscillators in the presence of noise be improved through appropriate rewiring of its connections? What are the optimal network architectures for a given total number of connections? We address these questions by running the optimization process, using the stochastic Markov Chain Monte Carlo method with replica exchange, to design the networks of phase oscillators with the increased tolerance against noise. As we find, the synchronization of a network, characterized by the Kuramoto order parameter, can be increased up to 40 %, as compared to that of the randomly generated networks, when the optimization is applied. Large ensembles of optimized networks are obtained and their statistical properties are investigated.Comment: 9 pages, 8 figure

Slow relaxation to equipartition in spring-chain systems

In this study, one-dimensional systems of masses connected by springs, i.e., spring-chain systems, are investigated numerically. The average kinetic energy of chain-end particles of these systems is larger than that of other particles, which is similar to the behavior observed for systems made of masses connected by rigid links. The energetic motion of the end particles is, however, transient, and the system relaxes to thermal equilibrium after a while, where the average kinetic energy of each particle is the same, that is, equipartition of energy is achieved. This is in contrast to the case of systems made of masses connected by rigid links, where the energetic motion of the end particles is observed in equilibrium. The timescale of relaxation estimated by simulation increases rapidly with increasing spring constant. The timescale is also estimated using the Boltzmann-Jeans theory and is found to be in quite good agreement with that obtained by the simulation

Constraints on Cold Dark Matter in the Gamma-ray Halo of NGC 253

A gamma-ray halo in a nearby starburst galaxy NGC 253 was found by the CANGAROO-II Imaging Atmospheric Cherenkov Telescope (IACT). By fitting the energy spectrum with expected curves from Cold Dark Matter (CDM) annihilations, we constrain the CDM-annihilation rate in the halo of NGC 253. Upper limits for the CDM density were obtained in the wide mass range between 0.5 and 50 TeV. Although these limits are higher than the expected values, it is complementary important to the other experimental techniques, especially considering the energy coverage. We also investigate the next astronomical targets to improve these limits.Comment: 13 pages, 5 figures, aastex.cls, natbib.sty, To appear in ApJ v596n1, Oct. 10, 200

Design of Easily Synchronizable Oscillator Networks Using the Monte Carlo Optimization Method

Starting with an initial random network of oscillators with a heterogeneous frequency distribution, its autonomous synchronization ability can be largely improved by appropriately rewiring the links between the elements. Ensembles of synchronization-optimized networks with different connectivities are generated and their statistical properties are studied

Chaotic pulses for discrete reaction diffusion systems

Existence and dynamics of chaotic pulses on a one-dimensional lattice are discussed. Traveling pulses arise typically in reaction diffusion systems like the FitzHugh-Nagumo equations. Such pulses annihilate when they collide with each other. A new type of traveling pulse has been found recently in many systems where pulses bounce off like elastic balls. We consider the behavior of such a localized pattern on one-dimensional lattice, i.e., an infinite system of ODEs with nearest interaction of diffusive type. Besides the usual standing and traveling pulses, a new type of localized pattern, which moves chaotically on a lattice, is found numerically. Employing the strength of diffusive interaction as a bifurcation parameter, it is found that the route from standing pulse to chaotic pulse is of intermittent type. If two chaotic pulses collide with appropriate timing, they form a periodic oscillating pulse called a molecular pulse. Interaction among many chaotic pulses is also studied numerically

Evidence for TeV gamma-ray emission from the shell type SNR RXJ1713.7-3946

We report the results of TeV gamma-ray observations of the shell type SNR RXJ1713.7-3946 (G347.3-0.5). The discovery of strong non-thermal X-ray emission from the northwest part of the remnant strongly suggests the existence of electrons with energies up to 100 TeV in the remnant, making the SNR a good candidate TeV gamma-ray source. We observed RXJ1713.7-3946 from May to August 1998 with the CANGAROO 3.8m atmospheric imaging Cerenkov telescope and obtained evidence for TeV gamma-ray emission from the NW rim of the remnant with the significance of 5.6 sigma. The observed TeV gamma-ray flux from the NW rim region was estimated to be (5.3 +/- 0.9[statistical] +/- 1.6[systematic]) * 10^{-12} photons cm^{-2} s^{-1} at energies >= 1.8 +/- 0.9 TeV. The data indicate that the emitting region is much broader than the point spread function of our telescope. The extent of the emission is consistent with that of hard X-rays observed by ASCA. This TeV gamma-ray emission can be attributed to the Inverse Compton scattering of the Cosmic Microwave Background Radiation by shock accelerated ultra-relativistic electrons. Under this assumption, a rather low magnetic field of 11 micro gauss is deduced for the remnant from our observation.Comment: Accepted for publication by Astronomy and Astrophysics (5 pages, 2 figures