Plectoneme creation reduces the rotational friction of a polymer

The torsional dynamics of a semiflexible polymer with a contour length $L$ larger than its persistence length L_p that is rotated at fixed frequency omega_0 at one end is studied by scaling arguments and hydrodynamic simulations. We find a non-equilibrium transition at a critical frequency omega_*: In the linear regime, omega_0 < omega_*, axial spinning is the dominant dissipation mode. In the non-linear regime, omega_0 > omega_*, the twist-dissipation mode involves the continuous creation of plectonemes close to the driven end and the rotational friction is substantially reduced

Discrete elastic model for stretching-induced flagellar polymorphs

Force-induced reversible transformations between coiled and normal polymorphs of bacterial flagella have been observed in recent optical-tweezer experiment. We introduce a discrete elastic rod model with two competing helical states governed by a fluctuating spin-like variable that represents the underlying conformational states of flagellin monomers. Using hybrid Brownian dynamics Monte-Carlo simulations, we show that a helix undergoes shape transitions dominated by domain wall nucleation and motion in response to externally applied uniaxial tension. A scaling argument for the critical force is presented in good agreement with experimental and simulation results. Stretching rate-dependent elasticity including a buckling instability are found, also consistent with the experiment

Obscuring Material around Seyfert Nuclei with Starbursts

The structure of obscuring matter in the environment of active galactic nuclei with associated nuclear starbursts is investigated using 3-D hydrodynamical simulations. Simple analytical estimates suggest that the obscuring matter with energy feedback from supernovae has a torus-like structure with a radius of several tens of parsecs and a scale height of about 10 pc. These estimates are confirmed by the fully non-linear numerical simulations, in which the multi-phase inhomogeneous interstellar matter and its interaction with the supernovae are consistently followed. The globally stable, torus-like structure is highly inhomogeneous and turbulent. To achieve the high column densities (> 10^{24} cm^{-2}) as suggested by observations of some Seyfert 2 galaxies with nuclear starbursts, the viewing angle should be larger than about 70 degree from the pole-on for a 10^8 solar mass massive black hole. Due to the inhomogeneous internal structure of the torus, the observed column density is sensitive to the line-of-sight, and it fluctuates by a factor of order 100. The covering fraction for N > 10^{23} cm^{-2} is about 0.4. The average accretion rate toward R < 1 pc is 0.4 solar mass/yr, which is boosted to twice that in the model without the energy feedback.Comment: ApJL in press (4 pages, 3 figures) A gziped ps file with high resolution figures is available at http://th.nao.ac.jp/~wada/AGN

On the Interpretation of the l-v Features in the Milky Way Galaxy

We model the gas dynamics of barred galaxies using a three-dimensional, high-resolution, $N$-body+hydrodynamical simulation and apply it to the Milky Way in an attempt to reproduce both the large-scale structure and the clumpy morphology observed in Galactic H\emissiontype{I} and CO $l-v$ diagrams. Owing to including the multi-phase interstellar medium, self-gravity, star-formation and supernovae feedback, the clumpy morphology, as well as the large-scale features, in observed $l-v$ diagrams are naturally reproduced. We identify in our $l-v$ diagrams with a number of not only large-scale peculiar features such as the '3-kpc arm', '135-km s$^{-1}$ arm' and 'Connecting arm' but also clumpy features such as `Bania clumps', and then link these features in a face-on view of our model. We give suggestions on the real structure of the Milky Way and on the fate of gas clumps in the central region.Comment: accepted to PAS

On Phase Transition of NH4H2PO4NH_{4}H_{2}PO_{4}-Type Crystals by Cluster Variation Method

The Cluster Variation Method (CVM) is applied to the Ishibashi model for ammonium dihydrogen phosphate ($\rm NH_{4}H_{2}PO_{4}$) of a typical hydrogen bonded anti-ferroelectric crystal. The staggered and the uniform susceptibility without hysteresis are calculated at equilibrium. On the other hand, by making use of the natural iteration method (NIM) for the CVM, hysteresis phenomena of uniform susceptibility versus temperature observed in experiments is well explained on the basis of local minimum in Landau type variational free energy. The polarization $P$ curves against the uniform field is also calculated.Comment: 14 pages, 10 figure

Nuclear Bar, Star Formation and Gas Fueling in the Active Galaxy NGC 4303

A combination of Hubble Space Telescope (HST) WFPC2 and NICMOS images are used to investigate the gas/dust and stellar structure inside the central 300 pc of the nearby active galaxy NGC 4303. The NICMOS H-band (F160W) image reveals a bright core and a nuclear elongated bar-like structure of 250 pc in diameter. The bar is centered on the bright core, and its major axis is oriented in proyection along the spin axis of the nuclear gaseous rotating disk recently detected (Colina & Arribas 1999). The V-H (F606W - F160W) image reveals a complex gas/dust distribution with a two-arm spiral structure of about 225 pc in radius. The southwestern arm is traced by young star-forming knots while the northeastern arm is detected by the presence of dust lanes. These spirals do not have a smooth structure but rather they are made of smaller flocculent spirals or filament-like structures. The magnitudes and colors of the star-forming knots are typical of clusters of young stars with masses of 0.5 to 1 x $10^5 M_{solar}, and ages of 5 to 25 million years. The overall structure of the nuclear spirals as well as the size, number and masses of the star-forming knots are explained in the context of a massive gaseous nuclear disk subject to self-gravitational instabilities and to the gravitational field created by the nuclear bar. According to the model, the gaseous disk has a mass of about 5 x 10^7 M_{solar} inside a radius of 400 pc, the bar has a radius of 150 pc and a pattern speed of about 0.5 Myr^{-1}, and the average mass accretion rate into the core (R < 8 pc) is about 0.01 M_{solar}$ yr^{-1} for about 80 Myr.Comment: ApJ, in press (February 1, 2000

Investigation of the dc-excited xenon laser final report, 24 mar. 1964 - 24 mar. 1965

Electron energy spectra in gas laser discharges and investigation of new discharge configuration

Non-equilibrium hydrodynamics of a rotating filament

The nonlinear dynamics of an elastic filament that is forced to rotate at its base is studied by hydrodynamic simulation techniques; coupling between stretch, bend, twist elasticity and thermal fluctuations is included. The twirling-overwhirling transition is located and found to be strongly discontinuous. For finite bend and twist persistence length, thermal fluctuations lower the threshold rotational frequency, for infinite persistence length the threshold agrees with previous analytical predictions