Molecular dynamics analysis for the brownian motion of nano bubble

The smaller bubble whose diameter is below 1 micrometer is called nanobubble or ultra-fine bubble. The size of nano bubble is so small and invisible that the diameter distribution is generally evaluated as a mean square distance(MSD) of brownian motion that is measured by Dynamic Light Scattering(DLS) method based on the Einstein-Stokes equation. The equation, however, is not clarified for the application to the bubble sizing. In our previous study, the different behavior between solid particle and bubble with the same diameter at sub-micro scale was confirmed. In this study, the Brownian motion of nano bubble as well as the solid Pt particle whose diameter are around a few nano meters were simulated with the Molecular Dynamics(MD) method. The simulation employed Lennard Jones(LJ) potential to estimate the MSD of the bubbles and particles by tracing the trajectories of the center of gravity of them and resulted that the displacement of solid particles in liquid argon was less than the predicted amount by the Einstein-Stokes equation. In order to confirm apparent viscosity caused by periodic boundary conditions, the drop velocity of the particle due to the gravity force is measured and apparent viscosity is obtained using Stokes’ low with this velocity. Considering this apparent viscosity, the diameter of the solid particle is approximated using the Einstein-Stokes equation under its diameter of 4 nm. The bubble diameter obtained by the Brownian motion is lower than the Einstein-Stokes equatio

Lunin-Maldacena backgrounds from the classical Yang-Baxter equation -- Towards the gravity/CYBE correspondence

We consider \gamma-deformations of the AdS_5xS^5 superstring as Yang-Baxter sigma models with classical r-matrices satisfying the classical Yang-Baxter equation (CYBE). An essential point is that the classical r-matrices are composed of Cartan generators only and then generate abelian twists. We present examples of the r-matrices that lead to real \gamma-deformations of the AdS_5xS^5 superstring. Finally we discuss a possible classification of integrable deformations and the corresponding gravity solution in terms of solutions of CYBE. This classification may be called the gravity/CYBE correspondence.Comment: 18 pages, no figure, LaTeX, v2:references and further clarifications adde

Angular Momentum Transport by MHD Turbulence in Accretion Disks: Gas Pressure Dependence of the Saturation Level of the Magnetorotational Instability

The saturation level of the magnetorotational instability (MRI) is investigated using three-dimensional MHD simulations. The shearing box approximation is adopted and the vertical component of gravity is ignored, so that the evolution of the MRI is followed in a small local part of the disk. We focus on the dependence of the saturation level of the stress on the gas pressure, which is a key assumption in the standard alpha disk model. From our numerical experiments it is found that there is a weak power-law relation between the saturation level of the Maxwell stress and the gas pressure in the nonlinear regime; the higher the gas pressure, the larger the stress. Although the power-law index depends slightly on the initial field geometry, the relationship between stress and gas pressure is independent of the initial field strength, and is unaffected by Ohmic dissipation if the magnetic Reynolds number is at least 10. The relationship is the same in adiabatic calculations, where pressure increases over time, and nearly-isothermal calculations, where pressure varies little with time. Our numerical results are qualitatively consistent with an idea that the saturation level of the MRI is determined by a balance between the growth of the MRI and the dissipation of the field through reconnection. The quantitative interpretation of the pressure-stress relation, however, may require advances in the theoretical understanding of non-steady magnetic reconnection.Comment: 45 pages, 5 tables, 17 figures, accepted for publication in Ap

VSOP observation of the quasar PKS 2215+020: a new laboratory for core-jet physics at z=3.572

We report results of a VSOP (VLBI Space Observatory Programme) observation of a high redshift quasar PKS 2215+020 (z=3.572). The ~1 milliarcsecond resolution image of the quasar reveals a prominent `core-jet' structure on linear scales from 5/h to 300/h pc ($H_0=100*h km/(s*Mpc). The brightness temperatures and sizes of bright features identified in the jet are consistent with emission from relativistic shocks dominated by adiabatic energy losses. The jet is powered by the central black hole with estimated mass of ~4*10^9 solar masses. Comparisons with VLA and ROSAT observations indicate a possible presence of an extended radio/X-ray halo surrounding 2215+020.Comment: 15 pages, 6 figures, aastex macros; accepted for publication in The Astrophysical Journal, V.546, N.2 *(January 10 2001

Identification of SH Δv=1\Delta v=1 ro-vibrational lines in R And

We report the identification of SH $\Delta v=1$ ro-vibrational lines in the published high-resolution infrared spectrum of the S-type star, R And. This is the first astronomical detection of this molecule. The lines show inverse P-Cygni profiles, indicating infall motion of the molecular layer due to stellar pulsation. A simple spherical shell model with a constant infall velocity is adopted to determine the condition of the layer. It is found that a single excitation temperature of 2200 K reproduces the observed line intensities satisfactory. SH is located in a layer from 1.0 to ~1.1 stellar radii, which is moving inward with a velocity of 9 km s-1. These results are consistent with the previous measurements of CO $\Delta v=3$ transitions. The estimated molecular abundance SH/H is 1x10^-7, consistent with a thermal equilibrium calculation.Comment: 10 pages, 2 figures. Accepted for publication in ApJ Letter

A variability study of the Seyfert 2 galaxy NGC 6300 with XMM-Newton

We present the results of timing analysis of the XMM-Newton observation of the Seyfert 2 galaxy NGC 6300. The hard X-ray spectrum above 2 keV consists of a Compton-thin-absorbed power law, as is often seen in Seyfert 2 galaxies. We clearly detected rapid time variability on a time scale of about 1000 s from the light curve above 2 keV. The excess variance of the time variability (sigma2_RMS) is calculated to be ~0.12, and the periodogram of the light curve is well represented by a power law function with a slope of 1.75. In contrast with previous results from Seyfert 2 nuclei, these variability characteristics are consistent with those of Seyfert 1 galaxies. This consistency suggests that NGC 6300 has a similar black hole mass and accretion properties as Seyfert 1 galaxies. Using the relation between time variability and central black hole mass by Hayashida et al. (1998), the black hole mass of NGC 6300 is estimated to be ~2.8x10^5 Mo. Taking uncertainty of this method into account, the black hole mass is less than 10^7 Mo. Taking the bolometric luminosity of 3.3x10^43 erg/s into consideration, this yields an accretion rate of > 0.03 of the Eddington value, and comparable with estimates from Seyfert 1 galaxies using this method. The time variability analysis suggests that NGC 6300 actually has a Seyfert 1 nucleus obscured by a thick matter, and more generally provides a new pillar of support for the unified model of Seyfert galaxies based on obscuration.Comment: 11 pages, 6 figures, accepted for publication in Ap

Growth of a smooth CaF 2 layer on NdFeAsO thin film

We studied the method to grow a smooth and flat CaF 2 layer on NdFeAsO thin films since CaF 2 is a promising candidate material for the barrier layer of a superconducting junction. When the CaF 2 layer was grown at 800°C, the surface was very rough because {111} facets had grown preferentially. However, when CaF 2 was grown at lower temperatures and post-annealed in situ at 800°C for 30 min the facets were eliminated and a CaF 2 layer with a smooth surface was obtained. Fluorine diffusing from CaF 2 into NdFeAsO was observed when CaF 2 was grown at high temperatures, but the diffusion was suppressed by lowering the growth temperature to 400°C

Are the jets accelerated from the disk coronas in some active galactic nuclei?

We use a sample of radio-loud active galactic nuclei (AGNs) with estimated central black hole masses to explore their jet formation mechanisms. The jet power of AGNs is estimated from their extended radio luminosity. It is found that the jets in several AGNs of this sample are too powerful to be extracted from the standard thin accretion disks or rapidly spinning black holes surrounded by standard thin disks. If the advection dominated accretion flows (ADAFs) are present in these AGNs, their bright optical continuum luminosity cannot be produced by pure-ADAFs due to their low accretion rates and low radiation efficiency, unless the ADAFs transit to standard thin disks at some radii $R_{\rm tr}$. If this is the case, we find that the dimensionless accretion rates as high as 0.05 and transition from ADAFs to standard thin disks at rather small radii around 20GM/c^2 are required to explain their bright optical continuum emission. We propose that the disk-corona structure is present at least in some AGNs in this sample. The plasmas in the corona are very hot, and the pressure scale-height of the corona H\sim R. Powerful jets with Q_jet \sim L_bol (bolometric luminosity) can form by the large-scale magnetic fields created by dynamo processes in the disk corona of some AGNs. The maximal jet power extractable from the corona Q_jet^max\le 0.6L_c (L_c is the corona luminosity) is expected by this jet formation scenario. The statistic results on the sample of AGNs are consistent with the predictions of this scenario. Finally, the possibility that the jet is driven from a super-Keplerian rotating hot layer located between the corona and the cold disk is discussed. We find that, in principle, this layer can also produce a powerful jet with Q_jet\sim L_bol.Comment: 9 pages, accepted for publication in Ap

Force fluctuation in a driven elastic chain

We study the dynamics of an elastic chain driven on a disordered substrate and analyze numerically the statistics of force fluctuations at the depinning transition. The probability distribution function of the amplitude of the slip events for small velocities is a power law with an exponent $+AFw-tau$ depending on the driving velocity. This result is in qualitative agreement with experimental measurements performed on sliding elastic surfaces with macroscopic asperities. We explore the properties of the depinning transition as a function of the driving mode (i.e. constant force or constant velocity) and compute the force-velocity diagram using finite size scaling methods. The scaling exponents are in excellent agreement with the values expected in interface models and, contrary to previous studies, we found no difference in the exponents for periodic and disordered chains.Comment: 8 page

Statistical Consequences of Devroye Inequality for Processes. Applications to a Class of Non-Uniformly Hyperbolic Dynamical Systems

In this paper, we apply Devroye inequality to study various statistical estimators and fluctuations of observables for processes. Most of these observables are suggested by dynamical systems. These applications concern the co-variance function, the integrated periodogram, the correlation dimension, the kernel density estimator, the speed of convergence of empirical measure, the shadowing property and the almost-sure central limit theorem. We proved in \cite{CCS} that Devroye inequality holds for a class of non-uniformly hyperbolic dynamical systems introduced in \cite{young}. In the second appendix we prove that, if the decay of correlations holds with a common rate for all pairs of functions, then it holds uniformly in the function spaces. In the last appendix we prove that for the subclass of one-dimensional systems studied in \cite{young} the density of the absolutely continuous invariant measure belongs to a Besov space.Comment: 33 pages; companion of the paper math.DS/0412166; corrected version; to appear in Nonlinearit