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1.
E. Brézin C. De Dominicis 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(1):71-76
The field theory of a short range spin glass with Gaussian random interactions, is considered near the upper critical dimension
six. In the glassy phase, replica symmetry breaking is accompanied with massless Goldstone modes, generated by the breaking
of reparametrization invariance of a Parisi type solution. Twisted boundary conditions are thus imposed at two opposite ends
of the system in order to study the size dependence of the twist free energy. A loop-expansion is performed to first order
around a twisted background. It is found, as expected but it is non trivial, that the theory does renormalize around such
backgrounds, as well as for the bulk. However two main differences appear, in comparison with simple ferromagnetic transitions:
(i) the loop expansion yields a (negative) anomaly in the size dependence of the free energy, thereby lifting the lower critical
dimension to a value greater than two (ii) the free energy is lowered by twisting the boundary conditions. This situation
is common in spin glasses, reflecting the non-positivity of mode multiplicity in replica symmetry breaking, but its physical
meaning is still unclear.
Received 12 April 2002 / Received in final form 30 July 2002 Published online 19 November 2002 相似文献
2.
The relationship between extended structures, glassy dynamics and an underlying critical point is examined in the context
of a lattice model of fluctuating lines. Monte Carlo simulations are used to construct an effective, coarse-grained dynamics
for the “order parameter” near the critical point. Analysis of the effective dynamics reveals that the critical point is associated
with diverging barriers leading to the observed Vogel-Fulcher divergence of the relaxation times. A direct connection is established
between the presence of extended structures and the activated dynamics.
Received 15 March 2002 相似文献
3.
A. Marucci P. Launois R. Moret A. Pénicaud 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(1):29-34
The phase diagram of the newly synthesized mixed crystal C60-biphenyl is investigated as a function of temperature by single-crystal X-ray scattering. Diffuse scattering investigations
evidencing complex disorder and local order effects are presented. Two phase transitions leading to two different doublings
of the high temperature unit cell are observed, at 212 K and 147 K. The first transition is attributed to the ordering of
twisted biphenyls, which couples to the orientational ordering of the C60 molecules as the temperature decreases. Full ordering of the C60 molecules is achieved below 100 K only, in the low temperature phase. The rich phase diagram of C60-biphenyl is due to the interplay between fullerene and biphenyl ordering phenomena.
Received 31 August 2001 and Received in final form 4 December 2001 相似文献
4.
R.J. Jiménez Riobóo K.-P. Bohn J.K. Krüger 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(4):643-651
High performance Brillouin spectroscopy (BS) has been used to study the elastic properties (static and dynamic) of the orientational
glassy state of Na(CN)xCl1-x samples ). The temperature behaviour of the elastic properties reveals a more complex scenario for the orientational glass transition
than generally believed. The shear elastic constant shows the well-known c
44
(
T
) anomaly, indicated by a minimum, found in other cyanide mixed crystals. The results obtained for the hypersonic attenuation
are in clear contradiction with the dynamic character of the c
44
(
T
)-minimum. The temperature behaviour of the longitudinal elastic constant c11 of very dilute Na(CN)xCl1-x samples shows two striking features: i) Similar to the anomalous temperature behaviour of c
44
(
T
), lowering the temperature c
11
(
T
) first decreases, goes through a minimum and then rises again. The minimum takes place at a temperature above the temperature,
, where c
44
(
T
) reaches its minimum value. ii) A kink-like anomaly of c
11
(
T
) is observed at lower temperatures. This second anomaly is similar to the classical one observed in canonical glasses at their
glass transition temperature .
Received 8 April 1999 and Received in final form 3 June 1999 相似文献
5.
S. Moreno R.G. Rubio G. Luengo F. Ortega M.G. Prolongo 《The European physical journal. E, Soft matter》2001,4(2):173-182
The complex dielectric permittivity has been measured for three poly(ethylenglycol)-b-poly(propylenglycol)-b-poly(ethylenglycol)
copolymers with different content of poly(ethylenglycol) (15%, 33% and 80%), and increasing degree of crystallinity (0%, 10%
and 20%, respectively). Only the non-crystalline sample shows the normal mode relaxation together with the segmental (α-relaxation)
and the Johari-Goldstein (β-relaxation) modes. The crystalline samples show also polarization contributions due to the existence
of interfaces between the crystallites and the amorphous phase. The relaxation times of the (α and normal modes can be described
by a VFT equation with the same value of T0. There is a slowing-down of the segmental mode due to the presence of crystallites. The temperature dependence of the α and
β relaxations in the copolymers is very similar to that found in pure PPG, while there are significant differences in the
case of the normal mode of the non-crystalline sample. The size of the cooperatively rearranging regions CRR, and the width
of the glass transition region increase slightly with the degree of crystallinity. The temperature dependence of the size
of CRRs is compatible with the prediction of fluctuation theory. No systematic effect of the degree of crystallinity on the
β-relaxation has been found. Near T
g the β-relaxation time is close to the primitive time of the coupling model.
Received: 31 May 2000 相似文献
6.
D.K. Yu R.Q. Zhang S.T. Lee 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(1):57-63
The structures and energetics of carbon bridged C60 clusters (C
60
)
n
Cm have been studied by simulated annealing technique within the tight-binding molecular-dynamics. The “sp2 addition” ball-and-chain dimers exhibit odd-even alternations over the number of chain atoms, with the dimers containing
even chain atoms more stable against dissociation than their immediate neighbors containing odd chain atoms. In addition to
the usual “sp2 addition” dimers, a pentagon-linked C121 isomer and a hexagon-linked C122 isomer are also found to be stable. Based on our tight-binding calculations, trimers and larger clusters can be simply regarded
as being made up of independent or weakly interacting dimers, if the C-C60 joints on a single cage are not too close to each other. Large C60 clusters connected by chains each containing only one or two carbon atoms have similar stability to that of constituent dimers,
indicating the possibility to form stable C60-carbon polymers.
Received 17 January 2001 and Received in final form 26 February 2001 相似文献
7.
Several semicrystalline polymers show a recrystallization after melting during a heating scan. We have studied the mechanisms
of such recrystallization processes for two different polymers, namely syndiotactic polypropylene (sPP) and isotactic polystyrene
(iPS). This was done by monitoring the structure evolution during the recrystallization process and its changes during a subsequent
heating scan via time- and temperature-dependent SAXS measurements, respectively. The results of this study showed that the
sPP samples exhibited a recrystallization mechanism similar to the multi-stage route found upon initial crystallization of
semicrystalline polymers from an entangled melt. Meanwhile, a different recrystallization mechanism was shown by the iPS samples.
In this case, the recrystallization process proceeded as a direct growth into the melt in a one-step process. This is the
first time we have observed such a mechanism which resembles the picture presented by the classical models for crystallization
from an entangled polymer melt. The reason for such different mechanisms may be related to the initial melt state prior to
crystallization. It seems as though, when crystallization sets in an entangled polymer melt, it follows the multi-stage route,
whereas if the melt is locally disentangled, it proceeds by a direct growth mechanism.
Received 23 July 2001 and Received in final form 4 October 2001 相似文献
8.
9.
J.M. Carmona J. Richert P. Wagner 《The European Physical Journal A - Hadrons and Nuclei》2001,11(1):87-93
We test the influence of the Coulomb interaction on the thermodynamic and cluster generation properties of a system of classical
particles described by different lattice models. Numerical simulations show that the Coulomb interaction produces essentially
a shift in temperature of quantities like the specific heat but not qualitative changes. We also consider a cellular model.
The thermodynamic properties of the system are qualitatively unaltered.
Received: 7 November 2000 / Accepted: 17 May 2001 相似文献
10.
E. Albayrak M. Keskin 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):505-510
A two-fold Cayley tree graph with fully q-coordinated sites is constructed and the spin-1 Ising Blume-Emery-Griffiths model on the constructed graph is solved exactly
using the exact recursion equations for the coordination number q = 3. The exact phase diagrams in (kT/J, K/J ) and (kT/J, D/J) planes are obtained for various values of constants D/J and K/J, respectively, and the tricritical behavior is found. It is observed that when the negative biquadratic exchange (K) and the positive crystal-field (D) interactions are large enough, the tricritical point disappears in the (kT/J, K/J) plane. On the other hand, the system always exhibits a tricritical behavior in the phase diagram of (kT/J, D/J) plane.
Received 8 June 2001 and Received in final form 28 September 2001 相似文献
11.
Z. Iqbal Y. Zhang H. Grebel S. Vijayalakshmi A. Lahamer G. Benedek M. Bernasconi J. Cariboni I. Spagnolatti R. Sharma F.J. Owens M.E. Kozlov K.V. Rao M. Muhammed 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(4):509-515
Evidence is presented for the formation of a solid phase based on the smallest fullerene, C20, in thin diamond-like carbon films deposited by ultraviolet laser ablation from diamond onto nickel substrates at room temperature
in the presence of 10-4 torr of cyclohexane or benzene. Laser desorption mass spectrometry from the films shows the presence of C20, C21 and C22 species, while micro-Raman spectroscopy and electron diffraction from selected particles together with first principle density-functional
calculations, indicate a cubic solid with dodecahedral C20 cages as building blocks. Unlike solid C60 and fully protonated C20, which are bound by van der Waals forces, the proposed structure is stabilized by linking of the C20 dodecahedra with bridging carbon atoms at interstitial tetrahedral sites to form a face-centered-cubic lattice with 22 carbon
atoms per unit cell.
Received 10 October 2002 / Received in final form 24 December 2002 Published online 6 March 2003
RID="a"
ID="a"e-mail: zafar.iqbal@njit.edu 相似文献
12.
It has been shown over the last few years that the dynamics close to the glass transition is strongly heterogeneous, both
by measuring the diffusion coefficient of tagged particles or by NMR studies. Recent experiments have also demonstrated that
the glass transition temperature of thin polymer films can be shifted as compared to the same polymer in the bulk. We propose
here first a thermodynamical model for van der Waals liquids, which accounts for experimental results regarding the bulk modulus
of polymer melts and the evolution of the density with temperature. This model allows us to describe the density fluctuations
in such van der Waals liquids. Then, by considering the thermally induced density fluctuations in the bulk, we propose that
the 3D glass transition is controlled by the percolation of small domains of slow dynamics, which allows to explain the heterogeneous
dynamics close to T
g. We show then that these domains percolate at a lower temperature in the quasi-2D case of thin suspended polymer films and
we calculate the corresponding glass transition temperature reduction, in quantitative agreement with experimental results
of Jones and co-workers. In the case of strongly adsorbed films, we show that the strong adsorption amounts to enhance the
slow domains percolation. This effect leads to 1) a broadening of the glass transition and 2) an increase of T
g in quantitative agreement with experimental results. For both strongly and weakly adsorbed films, the shift in T
g is given by a power law, the exponent being the inverse of that of the correlation length of 3D percolation.
Received 21 March 2000 and Received in final form 4 December 2000 相似文献
13.
Organic compounds exhibiting the smectic C phase are made of rod-like molecules that have dipolar groups with lateral components. We argue that the off-axis character of the lateral dipolar groups can account for tilt in layered smectics (SmC, SmC*, SmI etc.). We develop a mean-field
theory of the smectic C phase based on a single-particle potential of the form U
C ∝ sin(2θ)cosφ, consistent with the biaxial nature of the phase, where θ and φ are the polar and azimuthal angles, respectively.
The hard-rod interactions that favour the smectic A phase with zero tilt angle are also included. The theoretical phase diagrams
compare favourably with experimental trends. Our theory also leads to the following results: i) a first-order smectic C to
smectic A transition above some value of the McMillan parameter α, leading to a tricritical point on the smectic C to smectic
A transition line and ii) a first-order smectic C to smectic C transition over a very small range of values of the model parameters.
We have also extended the theory to include the next higher-order term in the tilting potential and to include the effect
of different tilt angles for the molecular core and the chain in the SmC phase.
Received 3 August 2002
RID="a"
ID="a"Present address: Department of Physics, Vijaya College, R. V. Road, Bangalore - 560 004, India.
RID="b"
ID="b"e-mail: nvmadhu@rri.res.in 相似文献
14.
15.
Ellison CJ Kim SD Hall DB Torkelson JM 《The European physical journal. E, Soft matter》2002,8(2):155-166
Fluorescence intensity measurements of chromophore-doped or -labeled polymers have been used for the first time to determine
the effects of decreasing film thickness on glass transition temperature, T
g, the relative strength of the glass transition, and the relative rate of physical aging below T
g in supported, ultrathin polymer films. The temperature dependence of fluorescence intensity measured in the glassy state
of thin and ultrathin films of pyrene-doped polystyrene (PS), poly(isobutyl methacrylate) (PiBMA), and poly(2-vinylpyridine)
(P2VP) differs from that in the rubbery state with a transition at T
g. Positive deviations from bulk T
g are observed in ultrathin PiBMA and P2VP films on silica substrates while substantial negative deviations from bulk T
g are observed in ultrathin PS films on silica substrates. The relative difference in the temperature dependences of fluorescence
intensity in the rubbery and glassy states is usually reduced with decreasing film thickness, indicating that the strength
of the glass transition is reduced in thinner films. The temperature dependence of fluorescence intensity also provides useful
information on effects of processing history as well as on the degree of polymer-substrate interaction. In addition, when
used as a polymer label, a mobility-sensitive rotor chromophore is demonstrated to be useful in measuring relative rates of
physical aging in films as thin as 10 nm.
Received 21 August 2001 相似文献
16.
M. Cosentino Lagomarsino B. Bassetti P. Jona 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(1):81-88
We introduce a model system of stochastic entities, called rowers which include some essentials of the behavior of real cilia. We introduce and discuss the problem of symmetry breaking for
these objects and its connection with the onset of macroscopic, directed flow in the fluid. We perform a mean field-like calculation
showing that hydrodynamic interaction may provide for the symmetry breaking mechanism and the onset of fluid flow. Finally,
we discuss the problem of the metachronal wave in a stochastic context through an analytical calculation based on a path integral
representation of our model equation.
Received 12 June 2001 and Received in final form 9 January 2002 相似文献
17.
F. Uhlík Z. Slanina E. Ōsawa 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):349-352
The five isolated-pentagon-rule (IPR) satisfying isomers of C78, labeled 1-5, or according to symmetry as D3, C2v, C'
2v
, D3h, and D'
3h
, are computed. The cage geometries are optimized at the ab initio HF level with the standard 3-21G basis set (HF/3-21G). The separation energetics is then computed using the B3LYP density-functional
treatment in the standard 6-31G* basis set (B3LYP/6-31G*//HF/3-21G). Harmonic vibrational frequencies are calculated by the
SAM1 semiempirical method. The computed energies, structural and vibrational data are employed in the construction of isomeric
partition functions and evaluation of the relative Gibbs free energies. The results are converted into relative concentrations
for a wide temperature interval. The C'
2v
structure is the most populated throughout while the D3h species is negligible at all temperatures. The agreement between theory and experiment is reasonable, though some aspects
are still to be clarified.
Received 28 November 2000 相似文献
18.
M. Abbate J.A. Guevara S.L. Cuffini Y.P. Mascarenhas E. Morikawa 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(2):203-208
We studied the changes in the electronic structure of SrTi1-xRuxO3 across the metal-insulator transition. The parent compound, SrTiO3, is a well known diamagnetic insulator; whereas the doped compound, SrTi1-xRuxO3, becomes a ferromagnetic metal above x
C
= 0.35. The techniques used in the study were photoemission (PES) and O 1
s X-ray absorption (XAS) spectroscopy. The experimental spectra were analyzed in terms of band structure and Hubbard model
calculations. The PES and XAS spectra of SrTi1-xRuxO3 show the Ru 4
d bands growing in the band gap of SrTiO3 . The analysis in terms of the Hubbard model indicates that the Ti 3
d and Ru 4
d bands are mostly decoupled. This suggests that the metal-insulator transition is a percolation transition like that of metals
embedded in a rare gas matrix. Electron correlation effects are present in this system, but they do not seem to play a major
role in the transition.
Received 10 September 2001 相似文献
19.
O.-H. Kwon H. Yoo D.-J. Jang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):69-75
While the intercalation of C60 and the formation of C
60
-
in the supercages of NaX and NaY are confirmed by using 129Xe NMR and ESR, the photophysical properties of C60 and C
60
-
are characterized by monitoring transient reflectance spectra and kinetics, fluorescence kinetics, and diffuse reflectance
spectra. C
60
-
is considerably more abundant in NaY than in NaX. This difference is explained in terms of polarity difference between two
zeolites. Both C60 and C
60
-
have remarkably elongated excited-state lifetimes due to their collision-free environment in zeolitic nanocavities although
C
60
-
has much shorter lifetimes than C60. C
60
-
, in particular, shows intense absorption and emission due to its reduced symmetry in zeolites.
Received 13 July 2001 and Received in final form 8 October 2001 相似文献
20.
F. Honda A.V. Andreev V. Sechovský Y. Homma Y. Shiokawa 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(3):313-318
Single crystals of U(Ni1-xPdx)2Si2 with x = 0.05, 0.09 and 0.135 have been grown. Magnetization and electrical resistivity measurements were performed in a wide range
of temperatures and magnetic fields in order to study stability of magnetic phases in the solid solutions between UNi2Si2 and UPd2Si2 with a special emphasis on the type of ground state. In UPd2Si2 the simple AFI-type antiferromagnetic structure of U moments is observed at low temperatures. UNi2Si2 adopts the uncompensated AF structure (UAF) with the + + - stacking of U moments along the c-axis and consequently this compound exhibits a spontaneous magnetization corresponding to 1/3 of the U moment. The substitution
of Pd for Ni leads to a rapid decay of the spontaneous magnetization. The evolution of magnetization and electrical resistivity
behavior with Pd doping is tentatively attributed to the coexistence of the AF-I and UAF phases in the ground state of U(Ni0.91Pd0.09)2Si2 and U(Ni0.865Pd0.135)2Si2. In this scenario, the volume fraction of the AF-I phase rapidly grows with Pd doping on account of the UAF. At lowest temperatures
an irreversible transition to the UAF phase is observed when a sufficiently high magnetic field is applied along the c-axis.
Received 28 March 2002 / Received in final form 8 August 2002 Published online 19 December 2002
RID="a"
ID="a"e-mail: sech@mag.mff.cuni.cz 相似文献