共查询到20条相似文献,搜索用时 15 毫秒
1.
Y. Luspin D. De Sousa Meneses P. Simon G. Hauret 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(2):215-221
The elastic properties of Cs3H
(
SeO4
)
2
are investigated by Brillouin spectroscopy in the temperature range 20-220 covering the two transitions III II and II I occurring at and , respectively. Phase I is known to be a protonic conductive one. Discontinuities of elastic constants are generally observed
at both transitions, implying first orderness. In phases II and I, a slight broadening of the Brillouin lines is detected.
The results are discussed in comparison with compounds of the families XHSeO4 (X
=
NH4, Rb and Cs) and CsH2BO4 (B
=
As and P) which also undergo a transition to a superionic phase. In the conductive phase, it appears that the lattice anharmonicity
is weaker in Cs3H
(
SeO4
)
2
than in these other compounds.
Received 16 October 1998 相似文献
2.
N. Magneron Y. Luspin G. Hauret E. Philippot 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(1):7-15
Transverse and pseudo-transverse elastic waves have been studied in several scattering geometries in order to investigate
the temperature dependences of C
E
66
and C
E
14
over the range 300-1100 K, including the transitions near 860 K. These results complete those on C
E
44
we have obtained in a previous work. All these constants display discontinuities at the lock-in transition. In the phase, the results are analysed in term of lowest order couplings between strains (e) and the order parameter (Q). The main features are described by the lowest order biquadratic e2Q2 coupling, in particular for C
E
44
in a large temperature range. However, it appears that a contribution of the next coupling term arises for C
E
66
below K and that the first two lowest order terms have to be taken into account even just below the lock-in transition in the case
of C
E
14
. The temperature dependence of Q has been deduced and it can be well described in the framework of Landau's theory.
Received: 2 October 1997 / Received in final form: 3 December 1997 / Accepted: 29 January 1998 相似文献
3.
C. Dreyfus A. Aouadi R.M. Pick T. Berger A. Patkowski W. Steffen 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(3):401-419
We discuss the hydrodynamic equations which describe the shear dynamics of a liquid composed of anisotropic molecules, both
in its normal and its supercooled phases. We use these equations to analyze 90 depolarized light scattering experiments performed in the supercooled phase of a glass forming liquid, metatoluidine, and
show that the information extracted from this analysis is consistent with independent shear viscosity measurements performed
on that liquid in the same temperature range.
Received 28 April 1998 相似文献
4.
G. Pratesi A. Bellosi F. Barocchi 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(2):283-287
The pressure and temperature dependences of the depolarized light scattering spectra of salol have been measured at isobaric
condition P = 1 bar for T between 328 and 393 K, and at isothermal condition T = 343 K for P between 1 and 625 bar, i.e. outside the metastable liquid region. The experimental results for both the α- and β-relaxations can be well described by
the Mode Coupling Theory. The independence of the power-law parameters a, and consequently b and γ, from the thermodynamic variables T and P is demonstrated.The critical temperature T
c at 1 bar and the critical pressure P
c at T = 343 K have been determined from the normal liquid state.
Received 2 May 2000 相似文献
5.
A. Li Bassi C.E. Bottani B.K. Tanner A. Stella P. Tognini P. Cheyssac R. Kofman 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(1):31-38
The abrupt change of velocity in surface acoustic waves in thin films of amorphous SiOx containing nanometre scale -Sn crystals is shown to be directly associated with the size-dependent melting of the nanoparticles, confirming preliminary
experiments. High resolution thin film powder diffraction using synchrotron radiation shows that the abrupt redshift in the
Brillouin spectra satellites occurs at the same temperature as the melting of the nanoparticles, evident for the loss of the
Bragg peaks. Effective medium theory is used to explain the origin of the anomaly. A central peak in the Brillouin spectrum,
the intensity of which shows a maximum at the melting temperature, can be interpreted in terms of overdamped fluctuations
in the dielectric function. The melting temperature as a function of particle size is in agreement with theoretical predictions.
No evidence for strain could be found on the X-ray diffraction profiles; the a- and c-axis thermal expansion coefficients are the same as those in bulk tin.
Received 30 March 2000 and Received in final form 24 July 2000 相似文献
6.
R.M. Pick T. Franosch A. Latz C. Dreyfus 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(2):217-228
We derive expressions for the intensity of the Brillouin polarized spectrum of a molecular liquid formed of axially symmetric
molecules. These expressions take into account both the molecular dielectric anisotropy and the modulation of the local polarisability
by density fluctuations. They also incorporate all the retardation effects which occur in such liquids. We show that the spectrum
splits into a q-independent rotational contribution and q-dependent term, which reflects the propagation of longitudinal acoustic modes. In the latter, the two light scattering mechanisms
enter on an equal footing and generate three scattering channels. We study the influence of the two new channels and show
that they may substantially modify the Brillouin line-shape when the relaxation time of the supercooled liquid and the period
of the acoustic excitation are of the same order of magnitude.
Received 14 August 2002 Published online 4 February 2003
RID="a"
ID="a"e-mail: franosch@hmi.de 相似文献
7.
T. Franosch A. Latz R.M. Pick 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(2):229-246
The constitutive equations for the orientational dynamics of a liquid formed of linear molecules are derived microscopically.
The resulting generalised Langevin equations coincide with the phenomenological approach of Dreyfus et al. [1]. Formally exact expressions are given for the phenomenological coefficients and various constraints are shown to be consequences
of this microscopic approach.
Received 14 August 2002 Published online 4 February 2003
RID="a"
ID="a"e-mail: franosch@hmi.de 相似文献
8.
F. Decremps M. Fischer A. Polian M. Sieskind 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(1):7-13
The sound velocities for longitudinal and transverse waves have been measured in single crystalline BaFCl at room temperature
using ultrasonic pulse echo and Brillouin scattering techniques. The complete set of elastic constants is deduced and lead
to the bulk moduli values of BaFCl at ambiant conditions (, , ) which are compared with those obtained by a shell model. Moreover, using the ultrasonic technique under pressure, the pressure
derivatives of the second order elastic constants at 298 K have been determined up to 0.3 GPa. All moduli increase linearly
with pressure in this pressure range, allowing to determine directly and separately the first derivative of the bulk modulus
B'0 = 5.8. These data are used to calculate a Murnaghan equation of state. A detailed comparison is given between our results
with those recently obtained by X-ray diffraction on powder or calculated using the local density approximation method. Finally,
the anisotropy of BaFCl under pressure is discussed.
Received: 19 March 1998 / Revised: 15 May 1998 /
Accepted: 19 May 1998 相似文献
9.
S. Batzill R. Luxemburger R. Deike R. Weber 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(4):491-501
Results on the structural and dynamical properties of aqueous solutions of NaPSS (HPSS) are reported. Most samples of previous
measurements, including our own, are contaminated by the presence of (temporal) aggregates. The emphasis of this paper lies
on investigations of well purified samples at very low ionic strength where interacting effects are maximum. As previously
reported, this can be achieved by pumping the suspension through ion exchange resin by means of a tube-pump, using filters
of pore size. Information has been extracted from static and dynamic light scattering and viscosity measurements. A second maximum
is observed in the scattering curves versus wavenumber for the first time. It is discussed on the basis of two current models describing the structure of charged macromolecules.
The short time dynamics reflects the measured intensity. Detailed viscosity data in comparison of those of rodlike (TMV),
slightly flexible so-called fd virus particles (length 880 nm) are used to confirm the interpretation of the light scattering results. The recently observed maximum
in the reduced viscosity could be confirmed.
Received: 5 May 1997 / Revised: 1 September 1997 / Accepted: 10 November 1997 相似文献
10.
A. Latz M. Letz 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):323-343
The theory of light scattering for a system of linear molecules with anisotropic polarizabilities is considered. As a starting
point for our theory, we express the result of a scattering experiment in VV and VH symmetry as dynamic correlation functions
of tensorial densities ρ
lm(q) with l = 0 and l = 2. l, m denote indices of spherical harmonics. To account for all observed hydrodynamic singularities, a generalization of the theory
of Schilling and Scheidsteger [1] for these correlation functions is presented, which is capable to describe the light scattering
experiments from the liquid regime to the glassy state. As a microscopic theory it fulfills all sum rules contrary to previous
phenomenological theories. We emphasize the importance of the helicity index m for the microscopic theory by showing, that only the existence of m = 1 components lead to the well known Rytov dip in liquids and to the appearance of transversal sound waves in VH symmetry
in the deeply supercooled liquid and the glass. Exact expressions for the phenomenological frequency dependent rotation translation
coupling coefficients of previous theories are derived.
Received 3 July 2000 and Received in final form 7 November 2000 相似文献
11.
S. Franz T. Garel H. Orland 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(3):463-468
We consider a model of two (fully) compact polymer chains, coupled through an attractive interaction. These compact chains
are represented by Hamiltonian paths (HP), and the coupling favors the existence of common bonds between the chains. We use
a (n=0 component) spin representation for these paths, and we evaluate the resulting partition function within a homogeneous saddle
point approximation. For strong coupling (i.e. at low temperature), one finds a phase transition towards a “frozen” phase where one chain is completely adsorbed onto the
other. By performing a Legendre transform, we obtain the probability distribution of overlaps. The fraction of common bonds
between two HP, i.e. their overlap q, has both lower () and upper () bounds. This means in particular that two HP with overlap greater than coincide. These results may be of interest in (bio)polymers and in optimization problems.
Received 4 December 1998 and Received in final form 10 March 1999 相似文献
12.
F. Baffioni F. Rosati 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(3):439-447
The mean field spin glass model is analyzed by a combination of exact methods and a simple Ansatz. The method exploited is general, and can be applied to others disordered mean field models such as, e.g., neural networks. It is well known that the probability measure of overlaps among replicas carries the whole physical content
of these models. A functional order parameter of Parisi type is introduced by rigorous methods, according to previous works
by F. Guerra. By the Ansatz that the functional order parameter is the correct order parameter of the model, we explicitly find the full overlap distribution.
The physical interpretation of the functional order parameter is obtained, and ultrametricity of overlaps is derived as a
natural consequence of a branching diffusion process. It is shown by explicit construction that ultrametricity of the 3-replicas
overlap distribution together with the Ghirlanda-Guerra relations determines the distribution of overlaps among s replicas, for any s, in terms of the one-overlap distribution.
Received 14 February 2000 相似文献
13.
Erichsen J Shiferaw T Zaporojtchenko V Faupel F 《The European physical journal. E, Soft matter》2007,24(3):243-246
Using the cluster-embedding method of V. Zaporojchenko et al. (Macromolecules 34, 1125 (2000)), we measured the glass transition temperature T
g at the polystyrene/vacuum interface of bimodal mixtures of monodisperse polystyrenes of 3.5k and 1000k. Embedding of ≈ 1
nm Au clusters was monitored in situ by X-ray photoelectron spectroscopy (XPS). The clusters were formed by evaporation of Au onto the polymer surface. Only one
glass transition was observed in the mixtures. The surface glass transition temperatures are correlated to but are below the
bulk values of the mixtures and obey the Gordon-Taylor equation. The results suggest that the earlier reported molecular-weight
dependence of the surface glass transition is not due to segregation of short chains to the surface. 相似文献
14.
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
15.
L. Saviot E. Duval J.F. Jal A.J. Dianoux 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(4):661-666
Relaxations in amorphous bis-phenol A polycarbonate are studied by neutron scattering, as a function of temperature below
the glass transition. Two different processes are observed. One is very fast, with a characteristic time (∼ 0.3 ps), that
is independent of temperature and momentum transfer. Conversely the other is slower, with a time which is dependent on temperature
and momentum transfer. The very fast localized anharmonic motion is interpreted by the overdamping of low-frequency vibrational
modes, by nearby dynamic holes. The slower relaxation is thermally activated and momentum transfer dependent. It corresponds
to molecular group motions and possibly to the short-time regime of the segmental relaxation.
Received 29 February 2000 and Received in final form 13 June 2000 相似文献
16.
Anionic polyacrylate chains (NaPA) form precipitates if alkaline earth cations are added in stoichiometric amounts. Accordingly,
precipitation thresholds were established for three different alkaline earth cations Ca2+, Sr2+ and Ba2+. Close to the precipitation threshold, the NaPA chains significantly decrease in size. This shrinking process was followed
by means of combined static and dynamic light scattering. Intermediates were generated by varying the ratio [MCl2]/[NaPA] with M denoting the respective alkaline earth cation. All experiments were performed at an inert salt level of 0.01M
NaCl. Similar coil-to-sphere transitions could be observed with all three alkaline earth cations Ca2+, Sr2+ and Ba2+. Based on these findings, supplementary conventional and anomalous small-angle X-ray scattering experiments using selected
intermediates close to the precipitation threshold of SrPA were performed. The distribution of Sr counterions around the polyacrylate
chains in aqueous solution provided the desired scattering contrast. Energy-dependent scattering experiments enabled successful
separation of the pure-resonant terms, which solely stem from the counterions. The Sr2+ scattering roughly reflects the monomer distribution of the polyacrylate chains. Different ratios of the concentrations of
[ SrCl2]/[NaPA] revealed dramatic changes in the scattering curves. The scattering curve at the lowest ratio indicated an almost
coil-like behaviour, while at the higher ratios the scattering curves supported the model of highly contracted polymer chains.
Most of X-ray scattering experiments on intermediate states revealed compact structural elements which were significantly
smaller than the respective overall size of the NaPA particles. 相似文献
17.
P. Zieliński W. Schranz D. Havlik A.V. Kityk 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(2):155-165
A four-state pseudospin model is constructed for the isomorphous phase transition hcp-2↦hcp-1 in pure C70 and in C70-rich mixed crystal C
70(1 - x)
C60x. With the specific anisotropic pseudospin interactions adapted to the C70 crystal the model is equivalent to a two-state Ising model in a temperature-dependent field. Replica symmetric state of the
model is shown to approach the critical point when the width of distribution of random fields and/or of random bonds increases.
The temperature of the phase transition and the phase equilibrium temperature then are practically constant, whereas the experiment
shows their strong decrease with x. The main effect of dilution resides in an x-dependence of the model parameters. Dilatometric data on the hexagonal C
70(1 - x)
C60x are used to fit these parameters. A metastable disordered phase subsisting below the phase transition is discovered in a
range of the model parameters and is shown to be responsible for the macroscopic behaviour of the system. A good agreement
with experimental data is obtained for the spontaneous strain and for the x-dependence of the hysteresis.
Received 20 April 2001 and Received in final form 26 September 2001 相似文献
18.
L. Ramos P. Fabre F. Nallet C.-Y.D. Lu 《The European physical journal. E, Soft matter》2000,1(4):285-299
We investigate, using quasi-elastic light scattering, some features of the long-wavelength, low-frequency modes of the hexagonal
phase often encountered in the study of lyotropic (surfactant-solvent) systems. The hexagonal phase is swollen by an oil-based
ferrofluid, allowing magnetically aligned samples to be prepared. We show experimentally the anisotropy of the two lowest-frequency
modes. We develop a model which predicts that these slow modes are associated to particle diffusion and tube motion. With
the help of microscopic as well as phenomenological analyses, we suggest that the latter presumably corresponds to a peristaltic
mode. Confinement effects on the one-dimensional, Brownian diffusion of the colloids along the tube axis together with the
coupling between the two modes are studied experimentally, varying the tube diameter to particle size ratio.
Received 7 July 1999 相似文献
19.
J. Wuttke M. Seidl G. Hinze A. Tölle W. Petry G. Coddens 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(2):169-172
The dynamics of supercooled toluene, studied in a GHz-THz range by incoherent neutron and depolarized light scattering, is
found to be in full accord with mode coupling predictions. Around the susceptibility minimum, neutron spectra are wavenumber
independent and proportional to light scattering data; the fast -relaxation scaling law applies; amplitude and frequency diverge with power laws that extrapolate towards a crossover temperature
K.
Received: 20 June 1997 / Accepted: 3 November 1997 相似文献
20.
Electric field light scattering results on aqueous solutions of linear, flexible NaPSS at minimal ionic strength are reported.
Samples of molecular weights between 356 kg/mol and 2870 kg/mol were investigated. With increasing field strength the intensity
as a function of wavenumber develops a pronounced oscillating behaviour. Besides the well-known first peak a second maximum
is observed at the position at which a weak maximum for some samples already occurs at zero field. The overall intensity strongly
depends on the frequency of the electric field. The electro-optical effect shows a maximum at 300 kHz. Increasing the particle
concentration gives a large increase of the peak maximum, normalized to concentration. If plotted versus scattering angle the relative intensity increase is maximum for samples of medium molecular weight. The results strongly
indicate a stretching and alignment of the chains, thus leading to or enlarging the short range order of the chains.
Received 9 April 1999 and Received in final form 18 August 1999 相似文献