10,361 research outputs found
Novel ordering of the pyrochlore Heisenberg antiferromagnet with the ferromagnetic next-nearest-neighbor interaction
The ordering property of the classical pyrochlore Heisenberg antiferromagnet
with the ferromagnetic next-nearest-neighbor interaction is investigated by
means of a Monte Carlo simulation. The model is found to exhibit a first-order
transition at a finite temperature into a peculiar ordered state. While the
spin structure factor, i.e., the thermal average of the squared Fourier
amplitude of the spin, exhibits a finite long-range order characterized by the
commensurate spin order of the period four, the thermal average of the spin
itself almost vanishes. It means that, although the amplitude of the spin
Fourier component is long-range ordered, the associated phase degree of freedom
remains to be fluctuating.Comment: Proceedings of the Highly Frustrated Magnetism (HFM2006) conference.
To appear in a special issue of J. Phys. Condens. Matte
Preparing pseudo-pure states with controlled-transfer gates
The preparation of pseudo-pure states plays a central role in the
implementation of quantum information processing in high temperature ensemble
systems, such as nuclear magnetic resonance. Here we describe a simple approach
based on controlled-transfer gates which permits pseudo-pure states to be
prepared efficiently using spatial averaging techniques.Comment: Significantly revised and extended: now 7 pages including 3 figures;
Phys. Rev. A (in press
Anti-pheromone as a tool for better exploration of search space
Many animals use chemical substances known as pheromones to induce behavioural changes in other members of the same species. The use of pheromones by ants in particular has lead to the development of a number of computational analogues of ant colony behaviour including Ant Colony Optimisation. Although many animals use a range of pheromones in their communication, ant algorithms have typically focused on the use of just one, a substance that encourages succeeding generations of (artificial) ants to follow the same path as previous generations. Ant algorithms for multi-objective optimisation and those employing multiple colonies have made use of more than one pheromone, but the interactions between these different pheromones are largely simple extensions of single criterion, single colony ant algorithms. This paper investigates an alternative form of interaction between normal pheromone and anti-pheromone. Three variations of Ant Colony System that apply the anti-pheromone concept in different ways are described and tested against benchmark travelling salesman problems. The results indicate that the use of anti-pheromone can lead to improved performance. However, if anti-pheromone is allowed too great an influence on ants' decisions, poorer performance may result
Low-dimensional chaos induced by frustration in a non-monotonic system
We report a novel mechanism for the occurrence of chaos at the macroscopic
level induced by the frustration of interaction, namely frustration-induced
chaos, in a non-monotonic sequential associative memory model. We succeed in
deriving exact macroscopic dynamical equations from the microscopic dynamics in
the case of the thermodynamic limit and prove that two order parameters
dominate this large-degree-of-freedom system. Two-parameter bifurcation
diagrams are obtained from the order-parameter equations. Then we analytically
show that the chaos is low-dimensional at the macroscopic level when the system
has some degree of frustration, but that the chaos definitely does not occur
without the frustration.Comment: 2 figure
Ordering of the Heisenberg Spin Glass in High Dimensions
Ordering of the Heisenberg spin glass with the nearest-neighbor Gaussian
coupling is investigated by equilibrium Monte Carlo simulations in four and
five dimensions. Ordering of the mean-field Heisenberg spin-glass is also
studied for comparison. Particular attention is paid to the nature of the
spin-glass and the chiral-glass orderings. Our numerical data suggest that, in
five dimensions, the model exhibits a single spin-glass transition at a finite
temperature, where the spin-glass order accompanying the simultaneous
chiral-glass order sets in. In four dimensions, by contrast, the model exhibits
a chiral-glass transition at a finite temperature, not accompanying the
standard spin-glass order. The critical region associated with the chiral-glass
transition, however, is very narrow, suggesting that dimension four is close to
the marginal dimensionality.Comment: 18 pages, 12 figure
Resonant speed meter for gravitational wave detection
Gravitational-wave detectors have been well developed and operated with high
sensitivity. However, they still suffer from mirror displacement noise. In this
paper, we propose a resonant speed meter, as a displacement noise-canceled
configuration based on a ring-shaped synchronous recycling interferometer. The
remarkable feature of this interferometer is that, at certain frequencies,
gravitational-wave signals are amplified, while displacement noises are not.Comment: 4 pages, 4 figure
Dynamical Critical Phenomena in three-dimensional Heisenberg Spin Glasses
Spin-glass (SG) and chiral-glass (CG) orderings in three dimensional (3D)
Heisenberg spin glass with and without magnetic anisotropy are studied by using
large-scale off-equilibrium Monte Carlo simulations. A characteristic time of
relaxation, which diverges at a transition temperature in the thermodynamic
limit, is obtained as a function of the temperature and the system size. Based
on the finite-size scaling analysis for the relaxation time, it is found that
in the isotropic Heisenberg spin glass, the CG phase transition occurs at a
finite temperature, while the SG transition occurs at a lower temperature,
which is compatible with zero. Our results of the anisotropic case support the
chirality scenario for the phase transitions in the 3D Heisenberg spin glasses.Comment: 9 pages, 19 figure
Ordering of the Heisenberg spin glass in two dimensions
The spin and the chirality orderings of the Heisenberg spin glass in two
dimensions with the nearest-neighbor Gaussian coupling are investigated by
equilibrium Monte Carlo simulations. Particular attention is paid to the
behavior of the spin and the chirality correlation lengths. In order to observe
the true asymptotic behavior, fairly large system size L\gsim 20 (L the linear
dimension of the system) appears to be necessary. It is found that both the
spin and the chirality order only at zero temperature. At high temperatures,
the chiral correlation length stays shorter than spin correlation length,
whereas at lower temperatures below the crossover temperature T_\times, the
chiral correlation length exceeds the spin correlation length. The spin and the
chirality correlation-length exponents are estimated above T_\times to be
\nu_SG=0.9+-0.2 and \nu_CG=2.1+-0.3, respectively. These values are close to
the previous estimates on the basis of the domain-wall-energy calculation.
Discussion is given about the asymptotic critical behavior realized below
T_\times.Comment: to appear in a special issue of J. Phys.
Periodicity and criticality in the Olami-Feder-Christensen model of earthquakes
Characteristic versus critical features of earthquakes are studied on the
basis of the Olami-Feder-Christensen model. It is found that the local
recurrence-time distribution exhibits a sharp -function-like peak
corresponding to rhythmic recurrence of events with a fixed ``period'' uniquely
determined by the transmission parameter of the model, together with a
power-law-like tail corresponding to scale-free recurrence of events. The model
exhibits phenomena closely resembling the asperity known in seismology
Catalogue of 12CO(J=1-0) and 13CO(J=1-0) Molecular Clouds in the Carina Flare Supershell
We present a catalogue of 12CO(J=1-0) and 13CO(J=1-0) molecular clouds in the
spatio-velocity range of the Carina Flare supershell, GSH 287+04-17. The data
cover a region of ~66 square degrees and were taken with the NANTEN 4m
telescope, at spatial and velocity resolutions of 2.6' and 0.1 km/s.
Decomposition of the emission results in the identification of 156 12CO clouds
and 60 13CO clouds, for which we provide observational and physical parameters.
Previous work suggests the majority of the detected mass forms part of a
comoving molecular cloud complex that is physically associated with the
expanding shell. The cloud internal velocity dispersions, degree of
virialization and size-linewidth relations are found to be consistent with
those of other Galactic samples. However, the vertical distribution is heavily
skewed towards high-altitudes. The robust association of high-z molecular
clouds with a known supershell provides some observational backing for the
theory that expanding shells contribute to the support of a high-altitude
molecular layer.Comment: To be published in PASJ Vol. 60, No. 6. (Issued on December 25th
2008). 35 pages (including 13 pages of tables), 7 figures. Please note that
formatting problems with the journal macro result in loss of rightmost data
columns in some long tables. These will be fixed in the final published
issue. In the meantime, please contact the authors for missing dat
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