5,061 research outputs found
Comment on ``Density Matrix Renormalization Group Study of the Haldane Phase in Random One-Dimensional Antiferromagnets"
In a recent Letter (PRL 83, 3297 (1999)), Hida presented numerical results
indicating that the Haldane phase of the Heisenberg antiferromagnetic spin-1
chain is stable against bond randomness, for box distributions of the bond
strength, even when the box distribution stretches to zero bond strength. The
author thus concluded that the Haldane phase is stable against bond randomness
for any distribution of the bond strength, no matter how broad. In this
Comment, we (i) point out that the randomness distributions studied in this
Letter do not represent the broadest possible distributions, and therefore
these numerical results do not lead to the conclusion that the Haldane phase is
stable against any randomness; and (ii) provide a semiquantitative estimate of
the critical randomness beyond which the Haldane phase yields to the Random
Singlet phase, in a specific class of random distribution functions for the
bond strength.Comment: A comment on PRL 83, 3297 (1999). One pag
A Note on the Eigenvalue Problem in the su(1,1)-Algebra
Normalization constant in the eigenstate appearing in the eigenvalue problem
of the su(1,1)-algebra is discussed. This normalization constant is expressed
in terms of the Gauss' hypergeometric series which is not absolutely
convergent. It is proved that this series is obtained as a certain limit of an
absolutely convergent series, which was conjectured in the previous paper.Comment: 9 pages, 2 figure
Direct observation of the effective bending moduli of a fluid membrane: Free-energy cost due to the reference-plane deformations
Effective bending moduli of a fluid membrane are investigated by means of the
transfer-matrix method developed in our preceding paper. This method allows us
to survey various statistical measures for the partition sum. The role of the
statistical measures is arousing much attention, since Pinnow and Helfrich
claimed that under a suitable statistical measure, that is, the local mean
curvature, the fluid membranes are stiffened, rather than softened, by thermal
undulations. In this paper, we propose an efficient method to observe the
effective bending moduli directly: We subjected a fluid membrane to a curved
reference plane, and from the free-energy cost due to the reference-plane
deformations, we read off the effective bending moduli. Accepting the
mean-curvature measure, we found that the effective bending rigidity gains even
in the case of very flexible membrane (small bare rigidity); it has been rather
controversial that for such non-perturbative regime, the analytical prediction
does apply. We also incorporate the Gaussian-curvature modulus, and calculated
its effective rigidity. Thereby, we found that the effective Gaussian-curvature
modulus stays almost scale-invariant. All these features are contrasted with
the results under the normal-displacement measure
On the Eigenvalue Problem of the su(1,1)-Algebra and the Coupling Scheme of Two su(1,1)-Spins
After recapitulating the eigenvalue problem of the su(1,1)-algebra in the
conventional form, the same problem is treated in an unconventional form, in
which the eigenvalue is pure imaginary. Further, the coupling scheme of two
su(1,1)-spins is discussed in the framework of two possibilities, in which
certain new aspects appear. Finally, the coupling scheme developed in this
paper is applied to a concrete example, which will serve boson realization of
the so(4)- and the so(3,1)-algebra presented in the next paper.Comment: 19 pages, No figur
Can the frequency-dependent specific heat be measured by thermal effusion methods?
It has recently been shown that plane-plate heat effusion methods devised for
wide-frequency specific-heat spectroscopy do not give the isobaric specific
heat, but rather the so-called longitudinal specific heat. Here it is shown
that heat effusion in a spherical symmetric geometry also involves the
longitudinal specific heat.Comment: Paper presented at the Fifth International Workshop on Complex
Systems (Sendai, September, 2007), to appear in AIP Conference Proceeding
Nanostructure of cellulose microfibrils in spruce wood
The structure of cellulose microfibrils in wood is not known in detail, despite the abundance of cellulose in woody biomass and its importance for biology, energy, and engineering. The structure of the microfibrils of spruce wood cellulose was investigated using a range of spectroscopic methods coupled to small-angle neutron and wide-angle X-ray scattering. The scattering data were consistent with 24-chain microfibrils and favored a “rectangular” model with both hydrophobic and hydrophilic surfaces exposed. Disorder in chain packing and hydrogen bonding was shown to increase outwards from the microfibril center. The extent of disorder blurred the distinction between the I alpha and I beta allomorphs. Chains at the surface were distinct in conformation, with high levels of conformational disorder at C-6, less intramolecular hydrogen bonding and more outward-directed hydrogen bonding. Axial disorder could be explained in terms of twisting of the microfibrils, with implications for their biosynthesis
Scaling Theory of Antiferromagnetic Heisenberg Ladder Models
The antiferromagnetic Heisenberg model on multi-leg ladders is
investigated. Criticality of the ground-state transition is explored by means
of finite-size scaling. The ladders with an even number of legs and those with
an odd number of legs are distinguished clearly. In the former, the energy gap
opens up as , where is the strength of the
antiferromagnetic inter-chain coupling. In the latter, the critical phase with
the central charge extends over the whole region of .Comment: 12 pages with 9 Postscript figures. To appear in J. Phys. A: Math.
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Quantum-fluctuation-induced collisions and subsequent excitation gap of an elastic string between walls
An elastic string embedded between rigid walls is simulated by means of the
density-matrix renormalization group. The string collides against the walls
owing to the quantum-mechanical zero-point fluctuations. Such ``quantum
entropic'' interaction has come under thorough theoretical investigation in the
context of the stripe phase observed experimentally in doped cuprates. We found
that the excitation gap opens in the form of exponential singularity DeltaE ~
exp(-Ad^sigma) (d: wall spacing) with the exponent sigma =0.6(3), which is
substantially smaller than the meanfield value sigma=2. That is, the excitation
gap is much larger than that anticipated from meanfield, suggesting that the
string is subjected to robust pinning potential due to the quantum collisions.
This feature supports Zaanen's ``order out of disorder'' mechanism which would
be responsible to the stabilization of the stripe phase
Near-Infrared Counterparts to Chandra X-ray Sources toward the Galactic Center. I. Statistics and a Catalog of Candidates
We present a catalog of 5184 candidate infrared counterparts to X-ray sources
detected towards the Galactic center. The X-ray sample contains 9017 point
sources detected in this region by the Chandra X-ray Observatory, including
data from a recent deep survey of the central 2 x 0.8 deg of the Galactic
plane. A total of 6760 of these sources have hard X-ray colors, and the
majority of them lie near the Galactic center, while most of the remaining 2257
soft X-ray sources lie in the foreground. We cross-correlated the X-ray source
positions with the 2MASS and SIRIUS near-infrared catalogs, which collectively
contain stars with a 10-sigma limiting flux of K_s<=15.6 mag. In order to
distinguish absorbed infrared sources near the Galactic center from those in
the foreground, we defined red and blue sources as those which have H-K_s>=0.9
and <=0.9 mag, respectively. We find that 5.8(1.5)% of the hard X-ray sources
have real infrared counterparts, of which 228(99) are red and 166(27) are blue.
The red counterparts are probably comprised of WR/O stars, HMXBs, and
symbiotics near the Galactic center. We also find that 39.4(1.0)% of the soft
X-ray sources have blue infrared counterparts; most of these are probably
coronally active dwarfs in the foreground. There is a noteworthy collection of
~20 red counterparts to hard X-ray sources near the Sagittarius-B H II region,
which are probably massive binaries that have formed within the last several
Myr. For each of the infrared matches to X-ray sources in our catalog we
derived the probability that the association is real, based on the results of
the cross-correlation analysis. The catalog will serve spectroscopic surveys to
identify infrared counterparts to X-ray sources near the Galactic center.Comment: Submitted to ApJ January 16, 2009; accepted July 21, 2009; 30 pages,
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