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1.
Hiroshi Koibuchi 《Journal of statistical physics》2007,129(4):605-621
We have studied two types of meshwork models by using the canonical Monte Carlo simulation technique. The first meshwork model
has elastic junctions, which are composed of vertices, bonds, and triangles, while the second model has rigid junctions, which
are hexagonal (or pentagonal) rigid plates. Two-dimensional elasticity is assumed only at the elastic junctions in the first
model, and no two-dimensional bending elasticity is assumed in the second model. Both of the meshworks are of spherical topology.
We find that both models undergo a first-order collapsing transition between the smooth spherical phase and the collapsed
phase. The Hausdorff dimension of the smooth phase is H≃2 in both models as expected. It is also found that H≃2 in the collapsed phase of the second model, and that H is relatively larger than 2 in the collapsed phase of the first model, but it remains in the physical bound, i.e., H<3. Moreover, the first model undergoes a discontinuous surface fluctuations transition at the same transition point as that
of the collapsing transition, while the second model undergoes a continuous transition of surface fluctuation. This indicates
that the phase structure of the meshwork model is weakly dependent on the elasticity at the junctions.
This work was supported in part by a Grant-in-Aid for Scientific Research from Japan Society for the Promotion of Science. 相似文献
2.
I. Endo H. Koibuchi 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(4):467-475
We numerically study the phase structure of two types of triangulated spherical surface models, which includes an in-plane
shear energy in the Hamiltonian, and we found that the phase structure of the models is considerably influenced by the presence
of the in-plane shear elasticity. The models undergo a first-order collapsing transition and a first-order (or second-order)
transition of surface fluctuations; the latter transition was reported to be of second-order in the first model without the
in-plane shear energy. This leads us to conclude that the in-plane elasticity strengthens the transition of surface fluctuations.
We also found that the in-plane elasticity decreases the variety of phases in the second model without the in-plane energy.
The Hamiltonian of the first model is given by a linear combination of the Gaussian bond potential, a one-dimensional bending
energy, and the in-plane shear energy. The second model is obtained from the first model by replacing the Gaussian bond potential
with the Nambu-Goto potential, which is defined by the summation over the area of triangles. 相似文献
3.
H. Koibuchi 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(3):321-330
Two types of surface models have been investigated by Monte Carlo simulations on triangulated spheres with compartmentalized
domains. Both models are found to undergo a first-order collapsing transition and a first-order surface fluctuation transition.
The first model is a fluid surface one. The vertices can freely diffuse only inside the compartments, and they are prohibited
from the free diffusion over the surface due to the domain boundaries. The second is a skeleton model. The surface shape of
the skeleton model is maintained only by the domain boundaries, which are linear chains with rigid junctions. Therefore, we
can conclude that the first-order transitions occur independent of whether the shape of surface is mechanically maintained
by the skeleton (=the domain boundary) or by the surface itself. 相似文献
4.
H. Koibuchi 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(1):85-90
A compartmentalized surface model of Nambu and Goto is studied on triangulated spherical surfaces by using the canonical Monte
Carlo simulation technique. One-dimensional bending energy is defined on the skeletons and at the junctions, and the mechanical
strength of the surface is supplied by the one-dimensional bending energy defined on the skeletons and junctions. The compartment
size is characterized by the total number L′ of bonds between the two-neighboring junctions and is assumed to have values in the range from L′ = 2 to L′ = 8 in the simulations, while that of the previously reported model is characterized by L′ = 1, where all vertices of the triangulated surface are the junctions. Therefore, the model in this paper is considered to
be an extension of the previous model in the sense that the previous model is obtained from the model in this paper in the
limit of L′↦1. The model in this paper is identical to the Nambu-Goto surface model without curvature energies in the limit of L′↦∞ and hence is expected to be ill-defined at sufficiently large L′. One remarkable result obtained in this paper is that the model has a well-defined smooth phase even at relatively large
L′ just as the previous model of L′↦ 1. It is also remarkable that the fluctuations of surface in the smooth phase are crucially dependent on L′; we can see no surface fluctuation when L′≤ 2, while relatively large fluctuations are seen when L′≥ 3. 相似文献
5.
A. J. Stoffel M. Gulácsi 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(1):79-88
We investigate the newly discovered supersolid phase by solving in random-phase approximation the anisotropic Heisenberg model
of the hard-core boson 4He lattice at zero temperature. We include nearest and next-nearest neighbor interactions and calculate exactly all pair correlation
functions in a cumulant decoupling scheme. We demonstrate the importance of vacancies and interstitials in the formation of
the supersolid phase. The supersolid phase is characterised by strong quantum fluctuations which are taken into account rigorously.
Furthermore we confirm that the superfluid to supersolid transition is triggered by a collapsing roton minimum however is
stable against spontaneously induced superflow, i.e. vortex creation. 相似文献
6.
H. Koibuchi 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(1):55-62
Nambu-Goto model is investigated by using the canonical Monte Carlo simulation technique on dynamically triangulated surfaces
of spherical topology. We find that the model has four distinct phases; crumpled, branched-polymer, linear, and tubular. The
linear phase and the tubular phase appear to be separated by a first-order transition. It is also found that there is no long-range
two-dimensional order in the model. In fact, no smooth surface can be seen in the whole region of the curvature modulus α,
which is the coefficient of the deficit angle term in the Hamiltonian. The bending energy, which is not included in the Hamiltonian,
remains large even at sufficiently large α in the tubular phase. On the other hand, the surface is spontaneously compactified
into a one-dimensional smooth curve in the linear phase; one of the two degrees of freedom shrinks, and the other degree of
freedom remains along the curve. Moreover, we find that the rotational symmetry of the model is spontaneously broken in the
tubular phase just as in the same model on the fixed connectivity surfaces. 相似文献
7.
We study the force-induced unfolding of random disordered RNA or single-stranded DNA polymers. The system undergoes a second-order
phase transition from a collapsed globular phase at low forces to an extensive necklace phase with a macroscopic end-to-end
distance at high forces. At low temperatures, the sequence inhomogeneities modify the critical behaviour. We provide numerical
evidence for the universality of the critical exponents which, by extrapolation of the scaling laws to zero force, contain
useful information on the ground-state (f = 0) properties. This provides a good method for quantitative studies of scaling exponents characterizing the collapsed globule.
In order to get rid of the blurring effect of thermal fluctuations, we restrict ourselves to the ground state at fixed external
force. We analyze the statistics of rearrangements, in particular below the critical force, and point out its implications
for force-extension experiments on single molecules.
Received 18 June 2002 and Received in final form 23 September 2002
RID="a"
ID="a"e-mail: muller@ipno.in2p3.fr 相似文献
8.
Deconfinement phase transition is studied in the FL model at finite temperature and chemical potential. At MFT approximation, phase transition can only be first order in the whole μ-T phase plane. Using a Landau expansion, we further study the phase transition order and the possible phase diagram of deconfinement. We discuss the possibilities of second order phase transitions in the FL model. From our analysis, if the cubic term in the Landau expansion could be cancelled by the higher order fluctuations, second order phase transition may occur. By an ansatz of the Landau parameters, we obtain a possible phase diagram with both the first and second order phase transitions, including the tri-critical point which is similar to that of the chiral phase transition. 相似文献
9.
H. Koibuchi 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(2):265-273
A first-order phase transition is found in two types of intrinsic curvature models defined on dynamically triangulated surfaces
of disk topology. The intrinsic curvature energy is included in the Hamiltonian. The smooth phase is separated from a non-smooth
phase by the transition. The crumpled phase, which is different from the non-smooth phase, also appears at sufficiently small
curvature coefficient α. The phase structure of the model on the disk is identical to that of the spherical surface model,
which was investigated by us and reported previously. Thus, we found that the phase structure of the fluid surface model with
intrinsic curvature is independent of whether the surface is closed or open. 相似文献
10.
H. Koibuchi 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(3):405-411
A surface model of Nambu and Goto is studied statistical mechanically by using the canonical Monte Carlo simulation technique
on a spherical meshwork. The model is defined by the area energy term and a one-dimensional bending energy term in the Hamiltonian.
We find that the model has a large variety of phases; the spherical phase, the planar phase, the long linear phase, the short
linear phase, the wormlike phase, and the collapsed phase. Almost all two neighboring phases are separated by discontinuous
transitions. It is also remarkable that no surface fluctuation can be seen in the surfaces both in the spherical phase and
in the planar phase. 相似文献
11.
A. Benyoussef D. Dohmi A. El Kenz L. Peliti 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(4):503-510
Using a replica formalism, a generalization of a recent mean field model corresponding to the observed wrinkling transition
in randomly polymerized membranes is presented. In this model we study the effects of global fluctuations of the surface normals
to the flat membrane, which can be introduced by a random local field. In absence of these global fluctuations, we show that,
the model exhibits both continuous and discontinuous transitions between flat and wrinkled phases, contrary to what has been
predicted by Bensimon et al. and Attal et al. Phase diagrams both in replica symmetry and in breaking of replica symmetry in sense of Almeida and Thouless are given. We
have also investigated the effects of global fluctuations on the replica symmetry phase diagram. We show that, the wrinkled
phase is favored and the flat phase is unstable. For large global fluctuations, the transition between wrinkled and flat phases
becomes first order.
Received: 3 December 1997 / Revised: 31 March 1998 / Accepted: 3 August 1998 相似文献
12.
《Nuclear Physics B》2006,732(3):426-443
We found that three types of tethered surface model undergo a first-order phase transition between the smooth and the crumpled phase. The first and the third are discrete models of Helfrich, Polyakov, and Kleinert, and the second is that of Nambu and Goto. These are curvature models for biological membranes including artificial vesicles. The results obtained in this paper indicate that the first-order phase transition is universal in the sense that the order of the transition is independent of discretization of the Hamiltonian for the tethered surface model. 相似文献
13.
Ruff JP Clancy JP Bourque A White MA Ramazanoglu M Gardner JS Qiu Y Copley JR Johnson MB Dabkowska HA Gaulin BD 《Physical review letters》2008,101(14):147205
We report detailed measurements of the low temperature magnetic phase diagram of Er2Ti2O7. Heat capacity and time-of-flight neutron scattering studies of single crystals reveal unconventional low-energy states. Er3+ magnetic ions reside on a pyrochlore lattice in Er2Ti2O7, where local XY anisotropy and antiferromagnetic interactions give rise to a unique frustrated system. In zero field, the ground state exhibits coexisting short and long-range order, accompanied by soft collective spin excitations previously believed to be absent. The application of finite magnetic fields tunes the ground state continuously through a landscape of noncollinear phases, divided by a zero temperature phase transition at micro{0}H{c} approximately 1.5 T. The characteristic energy scale for spin fluctuations is seen to vanish at the critical point, as expected for a second order quantum phase transition driven by quantum fluctuations. 相似文献
14.
We study the effect of quantum fluctuations in an Ising
spin system on a scale-free network of
degree exponent γ>5 using
a quantum Monte Carlo simulation technique. In our model,
one can adjust the magnitude of the magnetic field perpendicular
to the Ising spin direction and can therefore control the
strength of quantum fluctuations for
each spin. Our numerical analysis
shows that quantum fluctuations reduce the transition
temperature Tc of the ferromagnetic-paramagnetic phase
transition. However, the phase transition belongs to
the same mean-field type universality class both with
and without the quantum fluctuations.
We also study the role of hubs by turning on the
quantum fluctuations exclusively
at the nodes with the most links. When only a small number of hub
spins fluctuate quantum mechanically, Tc
decreases with increasing magnetic field
until it saturates at high fields. This effect
becomes stronger as the number of hub spins increases.
In contrast, quantum fluctuations at the same number of
“non-hub” spins do not affect Tc. This implies
that the hubs play an important role in
maintaining order in the whole network. 相似文献
15.
D. De Martino M. Marsili 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,65(4):595-600
We study how the volatility, node- or link-based, affects the evolution of social networks in simple models. The model describes
the competition betweenorder – promoted by the efforts of agents to coordinate – and disorder induced byvolatility in the
underlying social network.We find that when volatility affects mostly the decay of links, the model exhibit a sharp transition
between an ordered phase with a dense network and a disordered phase with a sparse network. When volatility is mostly node-based,
instead, only the symmetric (disordered) phase existsThese two regimes are separated by a second order phase transition of
unusual type, characterized by an order parameter critical exponent β = 0+.We argue that node volatility has the same effect in a broader class of models, and provide numerical evidence in this direction. 相似文献
16.
We study on a model the role of fluctuations size in the nucleation of a first order phase transition. A bifurcation point exists between metastable and stable equilibrium solutions for a critical value of fluctuations size. 相似文献
17.
《Physics letters. A》1999,260(5):429-435
The critical behavior at phase transitions of two coupled, m-component systems with cubic anisotropy is studied by a simplified model in which the fluctuations are partially considered. The phase transition could be a new fluctuation-induced first order transition into the anisotropic phase, or a new second order phase transition. Unlike in uncoupled systems, the second order phase transition could be into either the anisotropic or isotropic phase. As expected, upon suppression of fluctuations, all results reduce to those of mean field theory. 相似文献
18.
We calculate the correlation functions in the SU(2) gauge-spin system with spin in the fundamental representation. We analyze the result making use of finite size scaling. There is a possibility that there are no second order phase transition lines in this model, contrary to previous assertions. 相似文献
19.
We study the thermodynamic phase transition of a quantum-corrected Schwarzschild black hole. The modified metric affects the critical temperature which is slightly less than the conventional one. The space without black holes is not the hot flat space but the hot curved space due to vacuum fluctuations so that there appears a type of Gross–Perry–Yaffe phase transition even for the very small size of black hole, which is impossible for the thermodynamics of the conventional Schwarzschild black hole. We discuss physical consequences of the new phase transition in this framework. 相似文献
20.
Jonas Johansson 《Physics letters. A》2008,372(42):6301-6304
Finite size effects on the phase transition in the 2D Potts model with open boundary conditions are studied with Wang-Landau Monte Carlo simulations. We show the lattice size dependent cross-over from first order to continuous phase transition and discuss it in terms of surface induced disorder and size dependence of the latent heat. 相似文献