Stochastic Dynamics Toward the Steady State of Self-Gravitating Systems

We will construct a theory which can explain the dynamics toward the steady state self-gravitating systems (SGSs) where many particles interact via the gravitational force. Real examples of SGS in the universe are globular clusters and galaxies. The idea is to represent an interaction by which a particle of the system is affected from the others by a special random force. That is, we will use a special Langevin equation, just as the normal Langevin equation can unveil the dynamics toward the steady state described by the Maxwell-Boltzmann distribution. However, we cannot introduce the randomness into the system without any evidence. Then, we must confirm that each orbit is random indeed. Of course, it is impossible to understand orbits of stars in globular clusters from observations. Thus we use numerical simulations. From the numerical simulations of SGS, grounds that we use the random noise become clear. The special Langevin equation includes the additive and the multiplicative noise. By using the random process, we derive the non-Maxwellian distribution of SGS especially around the core. The number density can be obtained through the steady state solution of the Fokker-Planck equation corresponding to the random process. We exhibit that the number density becomes equal to the density profiles around the core by adjusting the friction coefficient and the intensity of the multiplicative noise. Moreover, we also show that our model can be applied in the system which has a heavier particle, corresponding to the black hole in a globular cluster

The effect of modified gravity on weak lensing

We study the effect of modified gravity on weak lensing in a class of scalar-tensor theory that includes f(R) gravity as a special case. These models are designed to satisfy local gravity constraints by having a large scalar-field mass in a region of high curvature. Matter density perturbations in these models are enhanced at small redshifts because of the presence of a coupling Q that charac- terizes the strength between dark energy and non-relativistic matter. We compute a convergence power spectrum of weak lensing numerically and show that the spectral index and the amplitude of the spectrum in the linear regime can be significantly modified compared to the CDM model for large values of |Q| of the order of unity. Thus weak lensing provides a powerful tool to constrain such large coupling scalar-tensor models including f(R) gravity

Consensus Algorithm Using Transaction History for Cryptocurrency

Blockchain consensus algorithms for cryptocurrency consist of the proof of work and proof of stake. However, current algorithms have problems, such as huge power consumption and equality issues. We propose a new consensus algorithm that uses transaction history. This algorithm ensures equality by randomly assigning approval votes based on past transaction records. We also incorporate a mechanism for adjusting issuance volume to measure the stability of the currency\u27s value

A Portable Grid-Enabled Computing System for A Nuclear Material Study

We have built a portable grid-enabled computing system specialized for our molecular dynamics (MD) simulation program to study Pu material easily. Experimental approach to reveal properties of Pu materials is often accompanied by some difficulties such as radiotoxicity of actinides. Since a computational approach reveals new aspects to researchers without such radioactive facilities, we address an MD computation. In order to have more realistic results about e.g., melting point or thermal conductivity, we need a large scale of parallel computations. Most of application users who don’t have supercomputers in their institutes should use a remote supercomputer. For such users, we have developed the portable and secured grid-enabled computing system to utilize a grid computing infrastructure provided by ITBL (Information Technology Based Laboratory). This system enables us to access remote supercomputers in the ITBL system seamlessly from a client PC through its graphical user interface (GUI). Typically it enables seamless file accesses on the GUI. Furthermore monitoring of standard output or standard error is available to see progress of an executed program. Since the system provides fruitful functionalities which are useful for parallel computing on a remote supercomputer, researchers can concentrate on their researches

Non-Gaussianity of the density distribution in accelerating universes

According to recent observations, the existence of the dark energy has been considered. Even though we have obtained the constraint of the equation of the state for dark energy ($p = w \rho$) as $-1 \le w \le -0.78$ by combining WMAP data with other astronomical data, in order to pin down $w$, it is necessary to use other independent observational tools. For this purpose, we consider the $w$ dependence of the non-Gaussianity of the density distribution generated by nonlinear dynamics. To extract the non-Gaussianity, we follow a semi-analytic approach based on Lagrangian linear perturbation theory, which provides an accurate value for the quasi-nonlinear region. From our results, the difference of the non-Gaussianity between $w = -1$ and $w= -0.5$ is about 4% while that between $w = -1$ and $w= -0.8$ is about $0.9$. For the highly non-linear region, we estimate the difference by combining this perturbative approach with N-body simulation executed for our previous paper. From this, we can expect the difference to be more enhanced in the low-$z$ region, which suggests that the non-Gaussianity of the density distribution potentially plays an important role for extracting the information of dark energy.Comment: 15 pages, 4 figures, accepted for publication in JCAP; v2: smoothing scale has been change