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1.
Shear break-up of reversible fractal clusters is investigated by ultrasound and multiple light scattering in the low shear
regime. We consider a dense suspension of Rayleigh scatterers (particles or clusters) with acoustic properties close to those
of the surrounding liquid so that the attenuation of the ultrasonic coherent field is weak and multiple scattering is negligible.
The concept of variance in local particle volume fraction is used to derive an original expression of the ultrasound scattering
cross-section per unit volume for Rayleigh fractal clusters. On the basis of a scaling law for the shear break-up of aggregates,
then we derive the shear stress dependence of the ultrasound scattered intensity from a suspension of reversible fractal clusters.
In a second part, we present rheo-acoustical experiments to study the shear break-up of hardened red cell aggregates in plane-plane
flow geometry and we examine both the self consistent field approximation and the scaling laws used in microrheological models.
We further compare the ability of acoustical backscattering and optical reflectometry techniques to estimate the critical
disaggregation shear stress and the particle surface adhesive energy. Finally, the microrheological model from Snabre and
Mills [#!ref5!#] based on a fractal approach is shown to describe the non Newtonian behavior of a dense distribution of hardened
red cell aggregates.
Received 12 November 1998 and Received in final form 17 May 1999 相似文献
2.
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
3.
A steady shear flow can drive supercooled liquids into a non-equilibrium state. Using molecular dynamics simulations under
steady shear flow superimposed with oscillatory shear strain for a probe, non-equilibrium mechanical responses are studied
for a model supercooled liquid composed of binary soft spheres. We found that even in the strongly sheared situation, the
supercooled liquid exhibits surprisingly isotropic responses to oscillating shear strains applied in three different components
of the strain tensor. Based on this isotropic feature, we successfully constructed a simple two-mode Maxwell model that can
capture the key features of the storage and loss moduli, even for highly non-equilibrium state. Furthermore, we examined the
correlation functions of the shear stress fluctuations, which also exhibit isotropic relaxation behaviors in the sheared non-equilibrium
situation. In contrast to the isotropic features, the supercooled liquid additionally demonstrates anisotropies in both its
responses and its correlations to the shear stress fluctuations. Using the constitutive equation (a two-mode Maxwell model),
we demonstrated that the anisotropic responses are caused by the coupling between the oscillating strain and the driving shear
flow. Due to these anisotropic responses and fluctuations, the violation of the fluctuation-dissipation theorem (FDT) is distinct
for different components. We measured the magnitude of this violation in terms of the effective temperature. It was demonstrated
that the effective temperature is notably different between different components, which indicates that a simple scalar mapping,
such as the concept of an effective temperature, oversimplifies the true nature of supercooled liquids under shear flow. An
understanding of the mechanism of isotropies and anisotropies in the responses and fluctuations will lead to a better appreciation
of these violations of the FDT, as well as certain consequent modifications to the concept of an effective temperature. 相似文献
4.
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
5.
ABSTRACTLarge-scale molecular dynamics (MD) simulations of systems containing up to 256,000 molecules were performed to investigate the scattering behaviour of the ST2 water model at deeply supercooled conditions. The simulations reveal that ST2 exhibits anomalous scattering, reminiscent of that observed in experiment, which is characterised by an increase in the static structure factor at low wavenumbers. This unusual behaviour in ST2 is linked with coupled fluctuations in density and local tetrahedral order in the liquid. The Ornstein–Zernike correlation length estimated from the anomalous scattering component exhibits power-law growth upon cooling, consistent with the existence of a liquid–liquid critical point (LLCP) in the ST2 model at ca. 245 K. Further, spontaneous liquid–liquid phase separation is observed upon thermally quenching a large system with 256,000 water molecules below the predicted critical temperature into the two-phase region. The large-scale MD simulations therefore confirm the existence of a metastable liquid–liquid phase transition in ST2 and support findings from previous computational studies performed using smaller systems containing only a few hundred molecules. We anticipate that our analysis may prove useful in interpreting recent scattering experiments that have been performed to search for an LLCP in deeply supercooled water. 相似文献
6.
Pulsed dielectric spectroscopy is introduced as a technique for selectively emphasizing specific components of the non-exponential
dielectric response of matter. Samples studied include supercooled liquid propanol, propylene carbonate, and poly(lauryl-methacrylate).
It is shown that particular sequences of pulses can be used to emphasize the fast response regime, to produce a cross-over
or memory effect, or to eliminate the response of selected components. Furthermore, for materials characterized by broad distributions
of relaxation times, the technique facilitates the investigation of a relatively narrow band from that distribution. It is
also shown that the time domain spectroscopy can be combined with conventional frequency domain techniques to provide the
characterization of dielectric response over an extraordinarily broad spectral range. 相似文献
7.
Simulation of the Second Grade Fluid Model for Blood Flow through a Tapered Artery with a Stenosis
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We analyze the blood flow through a tapered artery, assuming the blood to be a second order fluid model. The resulting nonlinear implicit system of partial differential equations is solved by the perturbation method. The expressions for shear stress, velocity, flow rate, wall shear stress and longitudinal impedance are obtained. The physical behavior of different parameters is also discussed, as are trapping phenomena. 相似文献
8.
A. Milchev J.P. Wittmer D.P. Landau 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(2):241-251
We use an off-lattice microscopic model for solutions of equilibrium polymers (EP) in a lamellar shear flow generated by means
of a self-consistent external field between parallel hard walls. The individual conformations of the chains are found to elongate
in flow direction and shrink perpendicular to it while the average polymer length decreases with increasing shear rate. The
Molecular Weight Distribution of the chain lengths retains largely its exponential form in dense solutions whereas in dilute
solutions it changes from a power-exponential Schwartz distribution to a purely exponential one upon an increase of the shear
rate. With growing shear rate the system becomes increasingly inhomogeneous so that a characteristic variation of the total
monomer density, the diffusion coefficient, and the center-of-mass distribution of polymer chains of different contour length
with the velocity of flow is observed. At higher temperature, as the average chain length decreases significantly, the system is shown to undergo an order-disorder transition
into a state of nematic liquid crystalline order with an easy direction parallel to the hard walls. The influence of shear
flow on this state is briefly examined.
Received 22 October 1998 and Received in final form 12 April 1999 相似文献
9.
U. Seifert 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(3):405-415
The dynamics of a single fluid bilayer membrane in an external hydrodynamic flow field is considered. The deterministic equation
of motion for the configuration is derived taking into account both viscous dissipation in the surrounding liquid and local
incompressibility of the membrane. For quasi-spherical vesicles in shear flow, thermal fluctuations can be incorporated in
a Langevin-type equation of motion for the deformation amplitudes. The solution to this equation shows an overdamped oscillatory
approach to a stationary tanktreading shape. Inclination angle and ellipticity of the contour are determined as a function
of excess area and shear rate. Comparisons to numerical results and experiments are discussed.
Received 20 August 1998 相似文献
10.
M. Celli D. Colognesi M. Zoppi 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(2):239-244
TOSCA is a novel inelastic spectrometer operating on the pulsed neutron source ISIS (UK). It covers a wide momentum and energy
range, even though its kinematic region is close to a line in the (k, E) plane. Its use is mainly intended for vibrational spectroscopy. However, taking advantage of its good resolving power, we
have carried out a test experiment aimed to use this instrument to measure the centre of mass kinetic energy of molecular
hydrogen. The experiment was successful and we have obtained the translational kinetic energy of liquid and solid para-hydrogen
improving the overall accuracy by almost an order of magnitude with respect to previous determinations. The data are compared
with the results of a Path Integral Monte-Carlo simulations with almost perfect agreement. We have demonstrated that TOSCA
can be used for measuring the translational kinetic energy of small molecular systems, taking advantage of the intrinsic incoherence
that is introduced in the scattering process by the intra-molecular transitions.
Received 9 June 1999 相似文献
11.
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
12.
13.
Increasing Superplasticity and Strong Dynamic Behaviour of Zr--Cu--Ni--Al Bulk Metallic Glass
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The plasticity and the dynamic fragility of bulk metallic glass of a Zr62 CuxsNiloAllo alloy are studied by three- point beam bending methods. We find that the alloy behaves super plastic not only at room temperature, but also at high temperatures. More importantly, it is found that the superplasticity increases with increasing temperature. In addition, the dynamic fragility parameter m for the supercooled liquid of this alloy is measured to be 34.87 and the supercooled liquid of Zr62 CuxsNixoAlxo alloy behaves as a strong liquid. 相似文献
14.
P. Snabre F. Magnifotcham 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(3):379-386
The recirculation flow induced by the rising motion of a bubble stream in a viscous fluid within an open-top rectangular enclosure
is studied. The three-dimensional volume averaged conservation equations are solved by a control-volume method using a hybrid
finite differencing scheme to describe the liquid phase hydrodynamics. The momentum exhange between the bubbles and the liquid
phase is modeled with a source term equals to the volumetric buoyancy force acting on the gas in the bubble stream. The volumetric
buoyancy force accounts for in line interactions between bubbles through the average gas volume fraction in the gas liquid
column which depends on the size and the rising velocity of bubbles. The fluid flow within an open-top rectangular enclosure
is further investigated by particle image velocimetry for a bubble stream rising in a water-glycerol solution. The measured
fluid velocities in a vertical plane are compared with the predictions of the numerical model over a wide range of fluid viscosity
(43 mPa s-800 mPa s) and gas flow rates. Finally, the recirculation flows resulting from the interaction of two neighbouring
vertical bubble streams are studied.
Received: 23 July 1997 / Revised: 19 December 1997 / Accepted: 11 May 1998 相似文献
15.
A. Martin P. Odier J.-F. Pinton S. Fauve 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(2):337-341
Magnetohydrodynamics studies in laboratory experiments have long been restricted to low magnetic Reynolds number flows, mainly
as a result of the very high magnetic diffusivity λ = 1/μσ of common conducting fluids (μ is the fluid's magnetic permeability
and σ its electrical conductivity). The best conductivities are found in liquid metals which have a unit magnetic permeability,
relative to vacuum. We show experimentally that a suspension of solid particles with a high magnetic permeability in a liquid
metal yields an effective medium that has a high electrical conductivity and an enhanced magnetic permeability. The dispersion
of the beads results from the turbulent fluid motion. The range of accessible magnetic Reynolds number can be increased by
a factor of as much as 4 in our experimental setup.
Received 6 March 2000 and Received in final form 13 July 2000 相似文献
16.
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
17.
Basing on the density functional theory of fermion condensation, we analyze the non-Fermi liquid behavior of strongly correlated Fermi-systems such as heavy-fermion metals. When deriving equations for the effective mass of quasiparticles, we consider solids with a lattice and homogeneous systems. We show that the low-temperature thermodynamic and transport properties are formed by quasiparticles, while the dependence of the effective mass on temperature, number density, magnetic fields, etc., gives rise to the non-Fermi liquid behavior. Our theoretical study of the heat capacity, magnetization, energy scales, the longitudinal magnetoresistance and magnetic entropy are in good agreement with the remarkable recent facts collected on the heavy-fermion metal YbRh2Si2. 相似文献
18.
P. C.R. Rodrigues F. M.S. Silva Fernandes 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,40(1):115-123
Molecular dynamics simulations of the melting, freezing and nucleation are presented for unconstrained nanoclusters of KCl
with a number of ions between 512 and 10648. The maximum extent of the probed liquid supercooling is analysed to the light
of theoretical predictions and compared with experimental data. The fraction of the solid-like ions in the supercooled liquid
is used as an indicator of heterogeneities within the liquid. Induced nucleation by seeding the supercooled liquid indicates
that solid-liquid coexistence is stable, and sustained during the lifetime of the clusters, relatively to the supercooled
liquid. A phenomenological analysis on the relaxation times of the crystal growth process is made. Critical nuclei sizes computed
from the effectiveness of the seeds in the heterogeneous nucleation of the supercooled liquid, and from the residual crystallites
in clusters not totally melted, are presented as a function of the temperature. The behavior of the systems is followed through
various properties such as liquid and solid molar fractions, enthalpies of melting, heat capacities, self-diffusion coefficients
and relaxation times related to the freezing process. The consistency of the simulation results for the heterogeneous nucleation
is assessed by means of a classical nucleation model, from which an estimate of the interfacial surface tension is also worked
out and compared with experimental data. 相似文献
19.
《Current Applied Physics》2014,14(7):965-969
The vitrification process of racemic RS- and enantiomorphic S-ibuprofen was studied by using Brillouin light scattering and modulated differential scanning calorimetry (DSC). The sound velocity and the attenuation coefficient of both compounds were determined for the first time in the glassy, supercooled liquid and liquid states. The sound velocity and the hypersonic damping were similar between the two ibuprofen pharmaceuticals over the whole investigated temperature range including glassy, supercooled liquid and liquid states. The thermal expansion coefficient of the RS-ibuprofen was smaller than that of the S-ibuprofen, which suggests that the intermolecular force of the former is slightly stronger than the latter. The thermal relaxation times derived from the modulated DSC were consistent with the dielectric relaxation times in both RS- and S-ibuprofens. The fragility index of S-ibuprofen just above the glass transition was determined to be 73, which was smaller compared to the value of RS-ibuprofen, 89. This difference in the fragility indicates that the decrease in the fragility of S-ibuprofen compared to the racemic one may improve its stability of the amorphous state below the glass transition temperature against crystallization. 相似文献
20.
Makarov A. S. Goncharova E. V. Qiao J. C. Kobelev N. P. Khonik V. A. 《JETP Letters》2021,113(11):723-727
JETP Letters - A method for calculating the fragility of high-entropy bulk metallic glasses using the data on shear elasticity relaxation in the supercooled liquid range is suggested and verified. 相似文献