5,014 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
Hydrogen thermal conductivity at temperatures from 2000 to 4000 deg F Final report
Hydrogen thermal conductivity at temperatures from 2000 to 4600 deg
Additive noise effects in active nonlinear spatially extended systems
We examine the effects of pure additive noise on spatially extended systems
with quadratic nonlinearities. We develop a general multiscale theory for such
systems and apply it to the Kuramoto-Sivashinsky equation as a case study. We
first focus on a regime close to the instability onset (primary bifurcation),
where the system can be described by a single dominant mode. We show
analytically that the resulting noise in the equation describing the amplitude
of the dominant mode largely depends on the nature of the stochastic forcing.
For a highly degenerate noise, in the sense that it is acting on the first
stable mode only, the amplitude equation is dominated by a pure multiplicative
noise, which in turn induces the dominant mode to undergo several critical
state transitions and complex phenomena, including intermittency and
stabilisation, as the noise strength is increased. The intermittent behaviour
is characterised by a power-law probability density and the corresponding
critical exponent is calculated rigorously by making use of the first-passage
properties of the amplitude equation. On the other hand, when the noise is
acting on the whole subspace of stable modes, the multiplicative noise is
corrected by an additive-like term, with the eventual loss of any stabilised
state. We also show that the stochastic forcing has no effect on the dominant
mode dynamics when it is acting on the second stable mode. Finally, in a regime
which is relatively far from the instability onset, so that there are two
unstable modes, we observe numerically that when the noise is acting on the
first stable mode, both dominant modes show noise-induced complex phenomena
similar to the single-mode case
Global unions: chasing the dream or building the reality?
This article takes as its theme the global restructuring of capital and its impact on worker organization. It argues for a reassertion of class in any analysis of global solidarity, and assesses the opportunities and barriers to effective global unionization. Rooted in the UK experience, the article analyzes the impact of the European social dimension on trade unions, before taking the discussion into a global dimension. It concludes by suggesting that there are reasons for cautious optimism in terms of solidarity building, despite difficult historical legacies and the common replacement of action with rhetoric
Percolation Transition in the random antiferromagnetic spin-1 chain
We give a physical description in terms of percolation theory of the phase
transition that occurs when the disorder increases in the random
antiferromagnetic spin-1 chain between a gapless phase with topological order
and a random singlet phase. We study the statistical properties of the
percolation clusters by numerical simulations, and we compute exact exponents
characterizing the transition by a real-space renormalization group
calculation.Comment: 9 pages, 4 encapsulated Postscript figures, REVTeX 3.
Ground State and Magnetization Process of the Mixture of Bond-Alternating and Uniform S=1/2 Antiferromagnetic Heisenberg Chains
The mixture of bond-alternating and uniform S=1/2 antiferromagnetic
Heisenberg chains is investigated by the density matrix renormalization group
method. The ground state magnetization curve is calculated and the exchange
parameters are determined by fitting to the experimentally measured
magnetization curve of \CuClBr(-pic). The low
field behavior of the magnetization curve and low temperature behavior of the
magnetic susceptibility are found to be sensitive to whether the
bond-alternation pattern (parity) is fixed all over the sample or randomly
distributed. The both quantities are compatible with the numerical results for
the random parity model.Comment: 5 pages, 7 figures. Final and enlarged version accepted for
publication in J. Phys. Soc. Jp
Thermal properties of solid and porous tungsten at temperatures to 5000 deg F
Thermal properties of solid and porous tungsten at high temperature
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