2,221 research outputs found
Dynamical Effects of CDM Subhalos on a Galactic Disk
We investigate the dynamical interaction between a galactic disk and
surrounding numerous dark subhalos as expected for a galaxy-sized halo in the
cold dark matter (CDM) models. Our particular interest is to what extent
accretion events of subhalos into a disk are allowed in light of the observed
thinness of a disk. Several models of subhalos are considered in terms of their
internal density distribution, mass function, and spatial and velocity
distributions. Based on a series of N-body simulations, we find that the disk
thickening quantified by the change of its scale height, Delta z_d, depends
strongly on the individual mass of an interacting subhalo M_{sub}. This is
described by the relation, Delta z_d / R_d = 8 Sum_{j=1}^N (M_{sub,j}/M_d)**2,
where R_d is a disk scale length, M_d is a disk mass, and N is the total number
of accretion events of subhalos inside a disk region (< 3R_d). Using this
relation, we find that an observed thin disk has not ever interacted with
subhalos with the total mass of more than 15% disk mass. Also, a less massive
disk with smaller circular velocity V_c is more affected by subhalos than a
disk with larger V_c, in agreement with the observation. Further implications
of our results for the origin of a thick disk component are also discussed.Comment: 12 pages, 9 figures, accepted by PAS
Systematic Design of Antireflection Coating for Semi-infinite One-dimensional Photonic Crystals Using Bloch Wave Expansion
We present a systematic method for designing a perfect antireflection coating
(ARC) for a semi-infinite one-dimensional (1D) photonic crystal (PC) with an
arbitrary unit cell. We use Bloch wave expansion and time reversal symmetry,
which leads exactly to analytic formulas of structural parameters for the ARC
and renormalized Fresnel coefficients of the PC. Surface immittance (admittance
and impedance) matching plays an essential role in designing the ARC of 1D
PC's, which is shown together with a practical example.Comment: This article may be downloaded for personal use only. Any other use
requires prior permission of the author and the American Institute of Physic
Chapter 1 Japanese Pirates in an “Information Society” : From 2channeru to Nikoniko Dōga
A Pirate’s View of World History : A Reversed Perception of the Order of Things From a Global Perspective, 2016年4月27-29日, 国際日本文化研究センタ
Strong magnetic field enhancement of spin triplet pairing arising from coexisting spin and charge fluctuations
We study the effect of the magnetic field (Zeeman splitting) on the triplet
pairing. We show generally that the enhancement of spin triplet pairing
mediated by coexisting spin and charge fluctuations can be much
larger than in the case of triplet pairing mediated by ferromagnetic spin
fluctuations. We propose that this may be related to the recent experiment for
(TMTSF)ClO, in which a possibility of singlet to triplet pairing
transition has been suggested.Comment: 5 page
"Pudding Mold"-type Band as an Origin of Large Thermopower in tau-type Organic Conductors
We study the origin of the large thermopower in quasi-two-dimensional a
-type organic conductor, (), from the view point of a "pudding mold"-type band structure. We
calculate the electronic band structure using an \textit{ab initio} band
calculation package, and obtain a tight binding model fit to the \textit{ab
initio} band structure. Using the model and the Boltzmann's equation approach,
we calculate the temperature dependence of the Seebeck coefficient. We conclude
that the peculiar band structure is the origin of the large Seebeck coefficient
and the appearance of the maximum value at a certain temperature.Comment: proceedings of ISCOM 2009 (to be published in Physica B
Realization of Berezinskii's superconductivity in quasi-one-dimensional systems
We revisit the pairing symmetry competition in quasi-one-dimensional systems.
We show that spin-triplet s-wave pairing, where the pair is formed by electrons
with different times and has an odd-frequency symmetry, can be realized in
systems with strong one-dimensionality when the strength of charge fluctuation
dominates over spin fluctuation. The present study provides a novel microscopic
mechanism for this exotic pairing originally proposed by Berezinskii in 1974.Comment: 4 pages, 4 figure
Superconductivity in an Effective Model Derived from Wannier Orbitals for an Organic Conductor (TMTSF)2ClO4
AbstractWe perform first-principles band calculations and derive an effective tight-binding model for a quasi-one-dimensional organic conductor (TMTSF)2ClO4. The first-principles band structures show four bands near the Fermi level. Since four TMTSF molecules are present in the unit cell, we regard a TMTSF molecule as a site and derive an effective tight-binding model exploiting the maximally localized Wannier orbitals. The outer Fermi surface almost contacts the inner one as in the previous studies. We introduce the on-site repulsive interaction and deal with the electron correlation applying the two-particle self-consistent (TPSC) method. The diagonalized spin susceptibility takes large values at the nesting vector between the outer and inner Fermi surfaces. Assuming a pairing mechanism mediated by the spin fluctuations, it is found that the sign of the superconducting gap in the spin-singlet channel changes between the outer and inner Fermi surfaces
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