Dynamical pattern formations in two dimensional fluid and Landau pole bifurcation

A phenomenological theory is proposed to analyze the asymptotic dynamics of perturbed inviscid Kolmogorov shear flows in two dimensions. The phase diagram provided by the theory is in qualitative agreement with numerical observations, which include three phases depending on the aspect ratio of the domain and the size of the perturbation: a steady shear flow, a stationary dipole, and four traveling vortices. The theory is based on a precise study of the inviscid damping of the linearized equation and on an analysis of nonlinear effects. In particular, we show that the dominant Landau pole controlling the inviscid damping undergoes a bifurcation, which has important consequences on the asymptotic fate of the perturbation.Comment: 9 pages, 7 figure

Laser spectroscopy of the antiprotonic helium atom – its energy levels and state lifetimes

The antiprotonic atom is a three-body exotic system consisting of an antiproton, an electron and a helium nucleus. Its surprising longevity was found and has been studied for more than 10 years. In this work, transition energies and lifetimes of this exotic atom were systematically studied by using the antiproton beam of AD(Antiproton Decelerator) facility at CERN, with an RFQ antiproton decelerator, a narrow-bandwidth laser, Cerenkov counters with fast-response photomultiplier tubes, and cryogenic helium target systems. Thirteen transition energies were determined with precisions of better than 200 ppb by a laser spectroscopy method, together with the elimination of the shift effect caused by collisions with surrounding atoms. Fifteen lifetimes (decay rates) of short-lived states were determined from the time distributions of the antiproton-annihilation signals and the resonance widths of the atomic spectral lines. The relation between the magnitude of the decay rates and the transition multipolarity was investigated, and some states were found to have anomalously short lifetimes. The reasons were explained as state-mixing and collisional effects. The experimental transition energies and lifetimes were compared with latest precise three-body variational calculations, and we succeeded in putting an upper limit (CPT limit) of 10 ppb on the proton-antiproton mass and charge differences

Frequency ratios of Sr, Yb and Hg based optical lattice clocks and their applications

This article describes the recent progress of optical lattice clocks with neutral strontium ($^{87}$Sr), ytterbium ($^{171}$Yb) and mercury ($^{199}$Hg) atoms. In particular, we present frequency comparison between the clocks locally via an optical frequency comb and between two Sr clocks at remote sites using a phase-stabilized fibre link. We first review cryogenic Sr optical lattice clocks that reduce the room-temperature blackbody radiation shift by two orders of magnitude and serve as a reference in the following clock comparisons. Similar physical properties of Sr and Yb atoms, such as transition wavelengths and vapour pressure, have allowed our development of a compatible clock for both species. A cryogenic Yb clock is evaluated by referencing a Sr clock. We also report on a Hg clock, which shows one order of magnitude less sensitivity to blackbody radiation, while its large nuclear charge makes the clock sensitive to the variation of fine-structure constant. Connecting all three types of clocks by an optical frequency comb, the ratios of the clock frequencies are determined with uncertainties smaller than possible through absolute frequency measurements. Finally, we describe a synchronous frequency comparison between two Sr-based remote clocks over a distance of 15 km between RIKEN and the University of Tokyo, as a step towards relativistic geodesy.Comment: 11 pages, 5 figures, invited review article in Comptes Rendus de Physique 201

Element Stratification in the Middle-Aged Type Ia Supernova Remnant G344.7-0.1

Despite their importance, a detailed understanding of Type Ia supernovae (SNe Ia) remains elusive. X-ray measurements of the element distributions in supernova remnants (SNRs) offer important clues for understanding the explosion and nucleosynthesis mechanisms for SNe Ia. However, it is challenging to observe the entire ejecta mass in X-rays for young SNRs, because the central ejecta may not have been heated by the reverse shock yet. Here we present over 200 kilosecond Chandra observations of the Type Ia SNR G344.7-0.1, whose age is old enough for the reverse shock to have reached the SNR center, providing an opportunity to investigate the distribution of the entire ejecta mass. We reveal a clear stratification of heavy elements with a centrally peaked distribution of the Fe ejecta surrounded by intermediate-mass elements (IMEs: Si, S, Ar Ca) with an arc-like structure. The centroid energy of the Fe K emission is marginally lower in the central Fe-rich region than in the outer IME-rich regions, suggesting that the Fe ejecta were shock-heated more recently. These results are consistent with the prediction for standard SN Ia models, where the heavier elements are synthesized in the interior of an exploding white dwarf. We find, however, that the peak location of the Fe K emission is slightly offset to the west with respect to the geometric center of the SNR. This apparent asymmetry is likely due to the inhomogeneous density distribution of the ambient medium, consistent with our radio observations of the ambient molecular and neutral gas.Comment: 16 pages, 10 figures, Accepted for publication in Astrophysical Journa

Bovine Myoblast Differentiation

Satellite cells are involved in postnatal myogenesis and in muscle hypertrophy. A better understanding of the mechanisms of myogenesis is useful to improve the muscle production in farm animals. Herein, we show the cytokine effects on the myogenesis in bovine myoblast cultures. Acidic fibroblast growth factors (aFGF) and interleukin 1 (IL-1) stimulated the cell proliferation, and insulin-1ike growth factor-I (IGF-I) stimulated to form multinucleated myotubes. Thus, it was possible to regulate the bovine myoblast differentiation by aFGF, IL-1 and/or IGF-I. Using the culture system, the expression of myosin heavy chain (MyHC) isoforms was detailed in bovine myoblasts during the differentiation. It was immunohistochemically confirmed that bovine myoblasts expressed β/slow-type MyHC (MyHC-slow), fast-type MyHC (MyHC-fast) and developmental-type MyHC (MyHC-dev) isoforms. Furthermore, the expression of fast 2a and β/slow MyHC mRNA was recognized in the cultures of bovine myoblasts. The results support the existence of bovine myoblast phenotypes that express differentially MyHC isoforms