123 research outputs found
Critical exponents of ferromagnetic Ising model on fractal lattices
We review the value of the critical exponents , , and
of ferromagnetic Ising model on fractal lattices of Hausdorff
dimension between one and three. They are obtained by Monte Carlo simulation
with the help of Wolff algorithm. The results are accurate enough to show that
the hyperscaling law is satisfied in non-integer
dimension. Nevertheless, the discrepancy between the simulation results and the
-expansion studies suggests that the strong universality should be
adapted for the fractal lattices.Comment: 5 pages, 1 figure, 1 table; conference article for the sixth
international school "Symmetry and Structural Properties of Condensed Matter
(SSPCM'2000)" in Polan
Comment on "Critical and slow dynamics in a bulk metallic glass exhibiting strong random magnetic anisotropy" [Appl. Phys. Lett. 92, 011923 (2008)]
In this comment, by using Monte Carlo simulation, we show that the
perpendicular shift of hysteresis loops reported in the commented work is
nothing special but simply due to the fact that the range of field does not
surpass the reversible field beyond which the two branches of the loop merge.
If the reversible field is exceeded, the shift is no longer observed. Moreover,
we point out that even using a small range of field, the shift will not be
observed if the observation time is long enough for the reversible field to
drop within the range.Comment: 2 pages, 2 figures, accepted for publication in Applied Physics
Letters Volume 94, Issue 15, Issue date 13 April 200
Mangetic phase transition for three-dimensional Heisenberg weak random anisotropy model: Monte Carlo study
Magnetic phase transition (MPT) to magnetic quasi-long-range order (QLRO)
phase in a three-dimensional Heisenberg weak (D/J=4) random anisotropy (RA)
model is investigated by Monte Carlo simulation. The isotropic and cubic
distributions of RA axes are considered for simple-cubic-lattice systems.
Finite-size scaling analysis shows that the critical couplings for the former
and latter are K_c= 0.70435(2) and K_c=0.70998(4), respectively. While the
critical exponent 1/\nu =1.40824(0) is the same for both cases. A second-order
MPT to the QLRO phase is therefore evidenced to be possible in favor with the
existence of the QLRO predicted by recent functional renormalization group
theories.Comment: 9 pages, 3 figures. to be appeared in Journal of Applied Physics
Volume 105 Issue 7 on April 1, 200
An ac field probe for the magnetic ordering of magnets with random anisotropy
A Monte Carlo simulation is carried out to investigate the magnetic ordering
in magnets with random anisotropy (RA). Our results show peculiar similarities
to recent experiments that the real part of ac susceptibility presents two
peaks for weak RA and only one for strong RA regardless of glassy critical
dynamics manifested for them. We demonstrate that the thermodynamic nature of
the low-temperature peak is a ferromagnetic-like dynamic phase transition to
quasi-long range order (QLRO) for the former. Our simulation, therefore, is
able to be incorporated with the experiments to help clarify the existence of
the QLRO theoretically predicted so far.Comment: 10 pages, 4 figures, to appear in Appl. Phys. Lett. volume 95, Issue
22, Isue date: 30 November 200
Acoustic coupling between two air bubbles in water
The acoustic coupling between two air bubbles immersed in water is clearly
demonstrated. The system is acoustically forced, and its response is detected.
The experimental results confirm that both theoretically predicted eigenmodes,
respectively symmetrical and antisymmetrical, do exist. Their frequencies,
measured as a function of the bubbles spacing, follow theoretical estimations
within a 10% accuracy.Comment: 14 pages, 6 figures, submitted to European Physical Journal E (2nd
version
Effect of chain stiffness on ion distributions around a polyelectrolyte in multivalent salt solutions
Ion distributions in dilute polyelectrolyte solutions are studied by means of
Langevin dynamics simulations. We show that the distributions depend on the
conformation of a chain while the conformation is determined by the chain
stiffness and the salt concentration. We observe that the monovalent
counterions originally condensed on a chain can be replaced by the multivalent
ones dissociated from the added salt due to strong electrostatic interaction.
These newly condensed ions give an important impact on the chain structure. At
low and at high salt concentrations, the conformation of a semiflexible chain
is rodlike. The ion distributions show similarity to those for a rigid chain,
but difference to those for a flexible chain whose conformation is a coil. In
the mid-salt region, the flexible chain and the semiflexible chain collapse but
the collapsed chain structures are, respectively, disordered and ordered
structures. The ion distributions hence show different profiles for these three
chain stiffness with the curves for the semiflexible chain lying between those
for the flexible and the rigid chains. The number of the condensed multivalent
counterions, as well as the effective chain charge, also shows similar
behavior, demonstrating a direct connection with the chain morphology.
Moreover, we find that the condensed multivalent counterions form triplets with
two adjacent monomers and are localized on the chain axis at intermediate salt
concentration when the chain stiffness is semiflexible or rigid. The
microscopic information obtained here provides valuable insight to the
phenomena of DNA condensation and is very useful for researchers to develop new
models.Comment: 28 pages, 10 figures, accepted for publication in JC
Unfolding Polyelectrolytes in Trivalent Salt Solutions Using DC Electric Fields: A Study by Langevin Dynamics Simulations
We study the behavior of single linear polyelectrolytes condensed by
trivalent salt under the action of electric fields through computer
simulations. The chain is unfolded when the strength of the electric field is
stronger than a critical value. This critical electric field follows a scaling
law against chain length and the exponent of the scaling law is ,
smaller than the theoretical prediction, [Netz, Phys. Rev. Lett. 90
(2003) 128104], and the one obtained by simulations in tetravalent salt
solutions, [Hsiao and Wu, J. Phys. Chem. B 112 (2008) 13179]. It
demonstrates that the scaling exponent depends sensitively on the salt valence.
Hence, it is easier to unfold chains condensed by multivalent salt of smaller
valence. Moreover, the absolute value of chain electrophoretic mobility
increases drastically when the chain is unfolded in an electric field. The
dependence of the mobility on electric field and chain length provides a
plausible way to impart chain-length dependence in free-solution
electrophoresis via chain unfolding transition induced by electric fields.
Finally, we show that, in addition to an elongated structure, a condensed chain
can be unfolded into an U-shaped structure. The formation of this structure in
our study is purely a result of the electric polarization, but not of the
elasto-hydrodynamics dominated in sedimentation of polymers.Comment: 15 pages, 7 figures, accepted for publication in Biomicrofluidic
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