574 research outputs found
Evidence of grain growth in the disk of the bipolar proto-planetary nebula M 1--92
We investigate the dust size and dust shell structure of the bipolar
proto-planetary nebula M 1--92 by means of radiative transfer modeling. Our
models consists of a disk and bipolar lobes that are surrounded by an AGB
shell, each component having different dust characteristics. The upper limit of
the grain size in the lobes is estimated to be m from
the polarization value in the bipolar lobe. The value of the
disk is constrained with the disk mass (0.2 M_{\sun}), which was estimated
from a previous CO emission line observation. We find a good model with
m, which provides an approximated disk mass of 0.15
M_{\sun}. Even taking into account uncertainties such as the gas-to-dust mass
ratio, a significantly larger dust of m, comparing to
the dust in the lobe, is expected.
We also estimated the disk inner radius, the disk outer radius, and the
envelope mass to be 30 (=9 AU), 4500 AU, and 4 M_{\sun},
respectively, where is the expansion velocity. If the dust
existing in the lobes in large separations from the central star undergoes
little dust processing, the dust sizes preserves the ones in the dust
formation. Submicron-sized grains are found in many objects besides M 1--92,
suggesting that the size does not depend much on the object properties, such as
initial mass of the central star and chemical composition of the stellar
system. On the other hand, the grain sizes in the disk do. Evidence of large
grains has been reported in many bipolar PPNs, including M 1--92. This result
suggests that disks play an important role in grain growth.Comment: 8 pages with 3 figures. Accepted for publication in A&
Magnetic-field induced competition of two multiferroic orders in a triangular-lattice helimagnet MnI2
Magnetic and dielectric properties with varying magnitude and direction of
magnetic field H have been investigated for a triangular lattice helimagnet
MnI2. The in-plane electric polarization P emerges in the proper screw magnetic
ground state below 3.5 K, showing the rearrangement of six possible
multiferroic domains as controlled by the in-plane H. With every 60-degree
rotation of H around the [001]-axis, discontinuous 120-degree flop of P-vector
is observed as a result of the flop of magnetic modulation vector q. With
increasing the in-plane H above 3 T, however, the stable q-direction changes
from q|| to q||, leading to a change of P-flop patterns under
rotating H. At the critical field region (~3 T), due to the phase competition
and resultant enhanced q-flexibility, P-vector smoothly rotates clockwise twice
while H-vector rotates counter-clockwise once.Comment: 4 pages, 3 figures. Accepted in Physical Review Letter
Assembling strategies in extrinsic evolvable hardware with bi-directional incremental evolution
Bidirectional incremental evolution (BIE) has been proposed as a technique to overcome the ”stalling” effect in evolvable hardware applications. However preliminary results show perceptible dependence of performance of BIE and quality of evaluated circuit on assembling strategy applied during reverse stage of incremental evolution. The purpose of this paper is to develop assembling strategy that will assist BIE to produce relatively optimal solution with minimal computational effort (e.g. the minimal number of generations)
Interplay of Spin-Orbit Interaction and Electron Correlation on the Van Vleck Susceptibility in Transition Metal Compounds
We have studied the effects of electron correlation on Van Vleck
susceptibility () in transition metal compounds. A typical
crossover behavior is found for the correlation effect on as
sweeping spin-orbit interaction, . For a small , orbital
fluctuation plays a dominant role in the correlation enhancement of
; however, the enhancement rate is rather small. In contrast,
for an intermediate , shows a substantial increase,
accompanied by the development of spin fluctuation. We will discuss the
behavior of in association with the results of Knight-shift
experiments on SrRuO and an anomalously large magnetic susceptibility
observed for Ir compounds.Comment: 5 pages, 3 figures, to appear in J. Phys. Soc. Jp
Effect of Spin-Orbit Interaction in Spin-Triplet Superconductor: Structure of -vector and Anomalous O-NQR Relaxation in SrRuO
Supposing the spin-triplet superconducting state of SrRuO, the
spin-orbit (SO) coupling associated with relative motion in Cooper pairs is
calculated by extending the method for the dipole-dipole coupling given by
Leggett in the superfluid He. It is shown that the SO coupling works only
in the equal-spin pairing (ESP) state to make the pair angular momentum
and the pair spin angular momentum parallel with each other. The SO coupling gives rise to the internal
Josephson effect in a chiral ESP state as in superfluid A-phase of He with
a help of an additional anisotropy arising from SO coupling of atomic origin
which works to direct the {\bf d}-vector into -plane. This resolves the
problem of the anomalous relaxation of O-NQR and the structure of {\bf
d}-vector in SrRuO.Comment: Accepted for publication in J. Phys. Soc. Jpn. vol.79 (2010), No.2
(February issue); 18 pages, 2 figure
The Water-ice Feature in Near-infrared Disk-scattered Light around HD 142527:Micron-sized Icy Grains Lifted up to the Disk Surface?
We study the m scattering feature of water ice detected in the outer
disk of HD 142527 by performing radiative transfer simulations. We show that an
ice mass abundance at the outer disk surface of HD 142527 is much lower than
estimated in a previous study. It is even lower than inferred from far-infrared
ice observations, implying ice disruption at the disk surface. Next, we
demonstrate that a polarization fraction of disk-scattered light varies across
the ice-band wavelengths depending on ice grain properties; hence, polarimetric
spectra would be another tool for characterizing water-ice properties. Finally,
we argue that the observed reddish disk-scattered light is due to grains with a
few microns in size. To explain the presence of such grains at the disk
surface, we need a mechanism that can efficiently oppose dust settling. If we
assume turbulent mixing, our estimate requires ,
where is a non-dimensional parameter describing the vertical diffusion
coefficient of grains. Future observations probing gas kinematics would be
helpful to elucidate vertical grain dynamics in the outer disk of HD 142527.Comment: 21 pages, 14 figures, 1 table; Accepted for publication in Ap
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