共查询到20条相似文献,搜索用时 15 毫秒
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.
Hiroshi Koibuchi 《Physics letters. A》2007,371(4):278-284
An elastic surface model is investigated by using the canonical Monte Carlo simulation technique on triangulated spherical meshes. The model undergoes a first-order collapsing transition and a continuous surface fluctuation transition. The shape of surfaces is maintained by a one-dimensional bending energy, which is defined on the mesh, and no two-dimensional bending energy is included in the Hamiltonian. 相似文献
3.
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
4.
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
5.
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
6.
Ye-Ning Wang Hui-Min Shen Lin-Hai Sun Xiao-Hua Chen Jin-Song Zhu Jin Wu 《Phase Transitions》2013,86(1-4):9-30
Two broad internal friction (attenuation as well) peaks in YBCO measured at around 120 K and 250 K are found to exhibit the characteristics of a first-order phase transition. X-ray diffraction indicates no symmetry change on cooling from room temperature but only a downward jump of the lattice parameters was observed. This is referred to as a phase-like transition (PLT) and further confirmed by stress-strain, specific heat and Debye-Waller factor measurements. There always occurs a phase-like transition at 10-30 K above T c in YBCO, BSCCO and TBCCO which disappears in the non-superconducting phases. Ultrasonic studies on single-crystal BSCCO reveal a pronounced elastic anisotropy in the c-plane and a velocity minimum associated with PLT. The overall trend of elastic stiffening below room temperature and some discrepancies and questions in elasticity measurements so far observed for high-T c oxides have been explained or clarified in terms of an abnormal fast change of lattice parameters. 相似文献
7.
We have investigated the pressure-induced phase transition of NiO and other structural properties using three-body potential
approach. NiO undergoes phase transition from B1 (rocksalt) to B2 (CsCl) structure associated with a sudden collapse in volume
showing first-order phase transition. A theoretical study of high pressure phase transition and elastic behaviour in transition
metal compounds using a three-body potential caused by the electron shell deformation of the overlapping ion was carried out.
The phase transition pressure and other properties predicted by our model is closer to the phase transition pressure predicted
by Eto et al.
相似文献
8.
Molecular simulation methodologies are employed to study the first-order transition of variable square-well (SW) fluids on a wide range of weak attractive surfaces. Surface phase diagram of SW fluids of attractive well diameter λ ff = 1.5, 1.75, 2.0 on a smooth, structureless surface modelled by a SW potential is reported via grand-canonical transition-matrix Monte Carlo (GC-TMMC) and histogram reweighting techniques. Fluids with λ ff = 1.5 and 1.75 show quasi-2D vapour–liquid phase transition; on the other hand, prewetting transition is visible for a SW fluid with larger well-extent λ ff = 2.0. The prewetting line, its length, and closeness to the bulk saturation curve are found to depend strongly on the nature of the fluid–fluid and fluid–wall interaction potentials. Boundary tension of surface coexistence films is calculated by two methods. First, the finite size scaling approach of Binder is used to evaluate the boundary tension via GC-TMMC. Second, the results of the boundary tension are verified by virtue of its relation to the pressure tensor components, which are calculated using a NVT-Monte Carlo approach. The results from the two methods are in good agreement. Boundary tension is found to increase with the increase in the wall–fluid interaction range for the quasi-2D system; conversely, boundary tension for thin–thick film, at prewetting transition, decreases with the increase in the wall–fluid interaction range. 相似文献
9.
K. Gesi 《Phase Transitions》2013,86(2-3):107-112
Dielectric properties of single-crystal {N(CH3)4}2HgCl4 (structure at room temperature; orthorhombic Pmcn) have been measured in a temperature range from 4 K to about 370 K. The dielectric constant along the a-, b-, and c-axes shows a break at 278 K. No other anomalies are detected in the temperature range studied. The transition temperature increases linearly with increasing hydrostatic pressure at a rate of 0.20 K/MPa. Twin boundaries are observed in the low-temperature phase on b-plate specimens. The results indicate that the phase transition in {N(CH3)4}2HgCl4 is ferroelastic, as in {N(CH3)4}2XBr4 (X: Mn, Co, Zn). 相似文献
10.
We report on specific-heat and resistivity measurements on quench-condensed Si1-xAux films for 0.11 ⩽ x 0.36 in the temperature range 0.35 K ⩽ T ⩽ 6 K. A distinct increase of the specificheat derived electronic density of states at the Fermi level is observed at xb ≈ 0.2, i.e., in the vicinity of the metal-insulator transition occurring for our samples at xc = 0.16. This suggests a different type of bonding between Au and Si for x < xb and x > xb. While resistive transitions to superconductivity are observed for x⩾0.21, the absence of a specific-heat anomaly at the transition points to filamentary superconductivity except for × = 0.35 where a sizable anomaly is seen. The difference in various electronic properties between differently prepared samples of these metastable alloys, in particular the influence of different preparation and annealing temperatures is emphasized. It is suggested that these differences are caused by incipient phase separation in the room-temperature prepared samples. 相似文献
11.
We present a self-assembly phase diagram for the shape of retroviral capsids, based on continuum elasticity theory. The spontaneous curvature of the capsid proteins drives a weakly first-order transition from spherical to spherocylindrical shapes. The conical capsid shape which characterizes the HIV-1 retrovirus is never stable under unconstrained energy minimization. Only under conditions of fixed volume and/or fixed spanning length can the conical shape be a minimum energy structure. Our results indicate that, unlike the capsids of small viruses, retrovirus capsids are not uniquely determined by the molecular structure of the constituent proteins but depend in an essential way on physical constraints present during assembly. 相似文献
12.
Na3Bi(PO4)2 exhibits several phase transitions at about 575, 820 and 905°C. The structure was determined at ambient temperature (α-form) and above the first transition (β-form). The α-form cell is monoclinic with a = 19.86(1), b = 5.353(6), c = 13.96(3) Å, β = 110.64(7)°, Z = 8, space group P21/ c ; the structure was solved from 3769 independent reflections to an R value, calculated on intensities, of 0.069. The β-form cell is orthorhombic with a = 18.71(3), b = 7.18(2), c = 5.429(7) Å, Z = 4, space group Pnam; the structure was solved to an R value, calculated on structure factors, of 0.055 using intensities of 858 unique reflections measured on a single crystal at 650°C. Both structures are related to that of glaserite. At high temperature, one of the PO4 tetrahedra is statistically disordered over two positions related by the m-mirror. Below the transition, ordering of this ion leads to a unit cell of lower symmetry. At the transition, two individuals grow on the two sides of the m-mirror which disappears; thus, at ambient temperature, the crystals are systematically twinned. Above the second transition, the unit cell is hexagonal. 相似文献
13.
Soma Sanyal 《Pramana》2003,61(5):1033-1037
Baryon number inhomogeneities may be generated during the epoch when the baryon asymmetry of the universe is produced, e.g.
at the electroweak phase transition. These lumps will have a lower temperature than the background. Also the value ofT
c
will be different in these regions. Since a first-order quark-hadron (Q–H) transition is susceptible to small changes in
temperature, we investigate the effect of the presence of such baryonic lumps on the dynamics of the Q–H transition. We find
that the phase transition is delayed in these lumps for significant overdensities. Consequently, we argue that baryon concentration
in these regions grows by the end of the transition. We mention some models which may give rise to such high baryon overdensities
before the Q–H transition. 相似文献
14.
Deformation of a spherical shell adhering onto a rigid substrate
due to van der Waals attractive interaction is investigated by
means of numerical minimization (conjugate gradient method) of
the sum of the elastic and adhesion energies.
The conformation of the deformed shell is governed by two
dimensionless parameters, i.e., Cs/epsilon and
Cb/epsilon where Cs and Cb are
respectively the stretching and the bending constants, and
epsilon is the depth of the van der Waals potential between
the shell and substrate.
Four different regimes of deformation are characterized as
these parameters are systematically varied:
(i) small deformation regime, (ii) disk formation regime,
(iii) isotropic buckling regime, and (iv) anisotropic buckling
regime.
By measuring the various quantities of the deformed shells,
we find that both discontinuous and continuous bucking transitions
occur for large and small Cs/epsilon, respectively.
This behavior of the buckling transition is analogous to van der
Waals liquids or gels, and we have numerically determined the
associated critical point.
Scaling arguments are employed to explain the adhesion induced
buckling transition, i.e., from the disk formation regime to
the isotropic buckling regime.
We show that the buckling transition takes place when the
indentation length exceeds the effective shell thickness which
is determined from the elastic constants.
This prediction is in good agreement with our numerical results.
Moreover, the ratio between the indentation length and its
thickness at the transition point provides a constant number
(2–3) independent of the shell size.
This universal number is observed in various experimental systems
ranging from nanoscale to macroscale.
In particular, our results agree well with the recent compression
experiment using microcapsules. 相似文献
15.
Thea–b microtwinning in the 90 K superconductors of the Y(1)Ba(2)Cu(3)O(7–) family of perovscites is studied by transmission electron microscopy betwen 300 and 85 K. Thermally stable twin spacings of order 300 Å are observed in dense polycrystalline material. In grains with free surfaces of sufficiently regular shape, the twin pattern is observed to refine at low temperature, either spontaneously or by low temperature thermal cycling, from a spacing of about 1000 Å to about 300 Å. In grains with free surfaces of less regular shape, the twins can be brought to disappear at low temperature after a sufficient electron dosis, and to reappear reversibly. A correlation between transition temperature and twin spacing is discussed. 相似文献
16.
Effects of the Mn/Co ratio on the magnetic transition and magnetocaloric properties of Mn1+xCo1-xGe alloys 下载免费PDF全文
We have investigated the magnetic transition and magnetocaloric effects of Mn 1+x Co 1 x Ge alloys by tuning the ratio of Mn/Co.With increasing Mn content,a series of first-order magnetostructural transitions from ferromagnetic to paramagnetic states with large changes of magnetization are observed at room temperature.Further increasing the content of Mn (x=0.11) gives rise to a single second-order magnetic transition.Interestingly,large low-field magnetic entropy changes with almost zero magnetic hysteresis are observed in these alloys.The effects of Mn/Co ratio on magnetic transition and magnetocaloric effects are discussed in this paper. 相似文献
17.
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
18.
《Nuclear Physics B》1998,528(3):453-468
We address the problem of “phantom” folding of the tethered membrane modeled by the two-dimensional square lattice, with bonds on the edges and diagonals of each face. Introducing bending rigidities K1 and K2 for respectively long and short bonds, we derive the complete phase diagram of the model, using transfer matrix calculations. The latter displays two transition curves, one corresponding to a first-order (ferromagnetic) folding transition, and the other to a continuous (anti-ferromagnetic) unfolding transition. 相似文献
19.
采用非格点珠簧球链模型, 结合Monte Carlo方法, 研究了半刚性高分子链受限于无限长圆柱体的构象性质. 模拟结果表明: 在圆柱体内表面附近具有吸附能的情况下, 当弯曲能b由小到大变化时, 发现半刚性高分子链由开始时的无规则被吸附在圆柱体内表面, 到逐渐出现螺旋结构, 最后伸展成类似棒状的结构. 同时计算了不同弯曲能b时的半刚性高分子链的平均螺旋数Nt, 平均每条链单体的螺旋百分比Ph和能量涨落. 发现高分子链螺旋结构的形成与转变, 不仅与圆柱体半径R的大小有关, 还与弯曲能b的大小有关. 研究结果能有助于加深对受限生物大分子构象的认识. 相似文献
20.
A. Fujita S. Fujieda K. Fukamichi 《Journal of magnetism and magnetic materials》2009,321(21):3553-3558
The influence of interstitial hydrogen on the electronic structure and the itinerant-electron metamagnetic (IEM) transition in strong magnetocaloric compound La(Fe0.88Si0.12)13H1.6 has been investigated by Mössbauer spectroscopy. A slight change in the average hyperfine field at 4.2 K was observed after hydrogen absorption. In contrast, the thermally induced first-order transition related to the IEM transition for y=1.6 appears at the Curie temperature TC=330 K, much higher than TC=195 K for y=0.0. The increase of isomer shift δIS at 4.2 K indicates that the valence electron transfer from hydrogen to Fe is negligibly small, hence the change in the magnetic state is closely associated with a volume expansion after hydrogen absorption. No change in shape by hydrogenation for the Mössbauer spectra in the paramagnetic state has been observed except for a difference in only δIS, indicating the volume expansion by hydrogenation is isotropic. Accordingly, the significant increase of TC by hydrogen absorption is attributed to the magnetovolume effect associated with characteristic feature in IEM compounds. A discontinuous change of ferromagnetic moment, ΔM, around TC has been observed by Mössbauer spectra, as expected from the magnetization measurement. The value of ΔM is slightly decreased by increase of TC after hydrogenation but its magnitude is almost the same due to the stabilization of ferromagnetic moment. As a result, strong magnetocaloric effect is maintained up to room temperature after hydrogenation. 相似文献