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1.
P. Sancho 《Il Nuovo Cimento D》1998,20(2):191-197
Summary We present an analysis of the temperature and concentration of turbulent fluctuations in a binary mixture. The crossed effects
introduce a coupling between temperature and concentration fluctuations that modifies the spectral picture of these passive
scalar fluctuations.
The author of this paper has agreed to not receive the proofs for correction.
This work has been partially supported by the Spanish Ministry of Education and Science under contract n. CLI-95-1867. 相似文献
2.
Discrete simulation methods are efficient tools to investigate the behaviors of complex fluids such as dry granular materials
or dilute suspensions of hard particles. By contrast, materials made of soft and/or concentrated units (emulsions, foams,
vesicles, dense suspensions) can exhibit both significant elastic particle deflections (Hertz-like response) and strong viscous
forces (squeezed liquid). We point out that the gap between two particles is then not determined solely by the positions of
their centers, but rather exhibits its own dynamics. We provide the first ingredients of a new discrete numerical method,
named Soft Dynamics, to simulate the combined dynamics of particles and contacts. As an illustration, we present the results for the approach
of two particles. We recover the scaling behaviors expected in three limits: the Stokes limit for very large gaps, the Poiseuille-lubricated limit for small gaps and even smaller surface deflections, and the Hertz limit for significant surface deflections. We find that for each gap value, an optimal force achieves the fastest approach
velocity. The principle of larger-scale simulations with this new method is provided. They will consitute a promising tool
for investigating the collective behaviors of many complex materials. 相似文献
3.
Persistency of material element deformation in isotropic flows and growth rate of lines and surfaces
J. Duplat E. Villermaux 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(2):353-361
We explore the consequence of isotropy on the growth of material lines and surfaces in complex flows. We show that the key
parameter is the persistency , defined as the product of a typical stretching rate to its associated coherence time . In particular, we derive the dependence of the net growth rate of both lines and surfaces on . Their growth rates increase strongly with increasing persistencies for small , and then saturate for . Making use of measurements of Girimaji and Pope [1], we estimate the persistency to be of order 1 in isotropic turbulence. We then comment on the evolution of the shape of an initially spherical material
blob. While its length increases, one of its tranverse dimension increases slowly and the other one decreases. This quasi-two-dimensional
deformation leads a final ribbon-shape.
Received 10 November 1999 and Received in final form 14 August 2000 相似文献
4.
5.
H. Willaime J. Maurer F. Moisy P. Tabeling 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(2):363-369
Turbulence produced in low temperature helium gas flowing over arrays of rectangular- and triangular-shaped blunt obstacles
is investigated experimentally. The set-up allows both low fluctuation rates (down to 8%), and high microscale Reynolds numbers,
(up to 1 150). The forced Kolmogorov equation is found to apply accurately. Similar to another flow configuration (counter
rotating flow case [1]), the analysis of the flatness factor evolution with the Reynolds number reveals a transitional behavior
around 650.
Received 26 August 1999 and Received in final form 28 August 2000 相似文献
6.
Mesfin Asfaw 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,65(1):109-116
We discuss various properties of a homogeneous random multifractal
process, which are related to the issue of scale correlations. By
design, the process has no built-in scale correlations. However, when
it comes to observables like breakdown coefficients, which are based on
a coarse-graining of the multifractal field, scale correlations do
appear. In the log-normal limit of the model process, the conditional
distributions and moments of breakdown coefficients reproduce the
observations made in fully developed small-scale turbulence. These
findings help to understand several puzzling empirical details, which
have been extracted from turbulent data already some time ago. 相似文献
7.
We study the thermophoretic coefficient DT of a charged colloid. The non-uniform electrolyte is characterized in terms of densities and diffusion currents of mobile
ions. The hydrodynamic treatment in the vicinity of a solute particle relies on the Hückel approximation, which is valid for
particles smaller than the Debye length, a ≪ . To leading order in the parameter a/ , we find that the coefficient DT consists of two contributions, a dielectrophoretic term proportional to the permittivity derivative d/dT , and a Seebeck term, i.e., the macroscopic electric field induced by the thermal gradient in the electrolyte solution. Depending on the particle valency,
these terms may take opposite signs, and their temperature dependence may result in a change of sign of thermophoresis, as
observed in several recent experiments. 相似文献
8.
Underwater excimer laser ablation of polymers 总被引:1,自引:0,他引:1
I. Elaboudi S. Lazare C. Belin D. Talaga C. Labrugère 《Applied Physics A: Materials Science & Processing》2008,92(4):743-748
In this paper, we study the photoablation kinetic of poly (ethylene terephthalate) (PET), polycarbonate (PC), polyimide (PI)
and polystyrene (PS) in both air and water. Compared to the results obtained in air, we highlight the decrease of the ablation
threshold (AT) of polyesters in contact with water as a function of polymer chemical structure. In order to check the expected
hydrolytic reaction of polyesters near the ablation threshold, the chemical modification of the polymer surfaces, as well
the composition of the ablation products, were investigated after irradiation near the fluence of ablation threshold in air
(air-F
t
) by X-ray photoelectron spectroscopy (XPS) and confocal Raman microspectroscopy. The morphology of polymers obtained by underwater
irradiation and near the air-F
t
was also examined using scanning electron microscopy (SEM). To understand the process and its dynamics in contact with water,
we consider the model of temperature at the polymer-water interface based on the semi-analytical solution of the transit heat-diffusion
equation. 相似文献
9.
Moreau P van Effenterre D Navailles L Nallet F Roux D 《The European physical journal. E, Soft matter》2008,26(3):225-234
The dynamic behaviour of three hydrophilic probes (two dyes and one fluorescently-labelled protein) inserted in the water layers of lyotropic lamellar phases has been studied by confocal fluorescence recovery experiments. Two different, ionic (AOT/NaCl/ H(2)O and non-ionic ( C(12)E(5) /hexanol/ H(2)O host systems were studied. The confinement effect has been carefully monitored using the swelling properties of the lamellar phases. In all cases, we measure the evolution of the probe diffusion coefficient in the layer plane D ( perpendicular) versus the separation between the membranes d(w). Depending on the composition of the lamellar phase, this distance can be continuously adjusted from 500A to about 20A. For all systems, we observe a first regime, called dilute regime, where the diffusion coefficient decreases almost linearly with 1/d (w) . In this regime, the Faxén theory for the friction coefficient of a spherical particle symmetrically dragged between two rigid walls can largely explain our results. More unexpectedly, when the membranes are non-ionic, and also quite flexible ( C(12)E(5) /hexanol in water), we observe the existence of a second, concentrated (or confined) regime, where the diffusion coefficient is nearly constant and different from zero for membrane separations smaller than the particle size. This new regime can be heuristically explained by simple arguments taking into account the membrane fluidity. 相似文献
10.
G. Hartung J. Hult R. Balachandran M. R. Mackley C. F. Kaminski 《Applied physics. B, Lasers and optics》2009,96(4):843-862
This paper describes the simultaneous application of time-sequenced laser-induced fluorescence imaging of OH radicals and
stereoscopic particle image velocimetry for measurements of the flame front dynamics in lean and premixed LP turbulent flames.
The studied flames could be acoustically driven, to simulate phenomena important in LP combustion technologies. In combination
with novel image post processing techniques we show how the data obtained can be used to track the flame front contour in
a plane defined by the illuminating laser sheets. We consider effects of chemistry and convective fluid motion on the dynamics
of the observed displacements and analyse the influence of turbulence and acoustic forcing on the observed contour velocity,
a quantity we term as s
d
2D. We show that this quantity is a valuable and sensitive indicator of flame turbulence interactions, as (a) it is measurable
with existing experimental methodologies, and (b) because computational data, e.g. from large eddy simulations, can be post
processed in an identical fashion. s
d
2D is related (to a two-dimensional projection) of the three-dimensional flame displacement speed s
d
, but artifacts due to out of plane convective motion of the flame surface and the uncertainty in the angle of the flame surface
normal have to be carefully considered. Monte Carlo simulations were performed to estimate such effects for several distributions
of flame front angle distributions, and it is shown conclusively that s
d
2D is a sensitive indicator of a quantity related to s
d
in the flames we study. s
d
2D was shown to increase linearly both with turbulent intensity and with the amplitude of acousting forcing for the range of
conditions studied. 相似文献
11.
12.
Previously, we have proposed a direct simulation scheme for colloidal dispersions in a Newtonian solvent (Phys. Rev. E 71, 036707 (2005)). An improved formulation called the “Smoothed Profile (SP) method” is presented here in which simultaneous
time-marching is used for the host fluid and colloids. The SP method is a direct numerical simulation of particulate flows
and provides a coupling scheme between the continuum fluid dynamics and rigid-body dynamics through utilization of a smoothed
profile for the colloidal particles. Moreover, the improved formulation includes an extension to incorporate multi-component
fluids, allowing systems such as charged colloids in electrolyte solutions to be studied. The dynamics of the colloidal dispersions
are solved with the same computational cost as required for solving non-particulate flows. Numerical results which assess
the hydrodynamic interactions of colloidal dispersions are presented to validate the SP method. The SP method is not restricted
to particular constitutive models of the host fluids and can hence be applied to colloidal dispersions in complex fluids. 相似文献
13.
From polymer films to organic nanoparticles suspensions by means of excimer laser ablation in water 总被引:1,自引:0,他引:1
I. Elaboudi S. Lazare C. Belin D. Talaga C. Labrugère 《Applied Physics A: Materials Science & Processing》2008,93(4):827-831
This study highlights the preparation of organic nanoparticles (NP) by laser ablation (LA) of polymeric materials in water.
Experiments focused on poly(ethylene terephtalate) (PET) were carried out with the KrF laser pulse (248 nm). Size distribution
and concentration of nanoparticles were deduced from suspensions turbidity measurements with the aid of Mie model, by Atomic
Force Microscopy (AFM) on the basis of a statistical study and Scanning Electron Microscopy (SEM). The obtained results show
that assemblies of spherical NP with a mean diameter 50 nm were synthesised. Composition and surface chemistry of NP were
investigated using the Confocal Micro-Raman Spectroscopy (CMRS) and X-ray Photoelectron Spectroscopy (XPS). It indicates that
NP are graphitic carbon rich and have a polymeric structure like polyacetylene. The possible mechanisms responsible of NP
synthesis by under water LA of polymers was briefly discussed by investigating other polymers targets. 相似文献
14.
Y. Malécot C. Auriault H. Kahalerras Y. Gagne O. Chanal B. Chabaud B. Castaing 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(3):549-561
The velocity increments statistic in various turbulent flows is analysed through the hypothesis that different scales are
linked by a multiplicative process, of which multiplier is infinitely divisible. This generalisation of the Kolmogorov-Obukhov
theory is compatible with the finite Reynolds number value of real flows, thus ensuring safe extrapolation to the infinite
Reynolds limit. It exhibits a estimator universally depending on the Reynolds number of the flow, with the same law either for Direct Numerical Simulations
or experiments, both for transverse and longitudinal increments. As an application of this result, the inverse dependence
is used to define an unbiased value for a Large Eddy Simulation from the resolved scales velocity statistics. However, the exact shape of the multiplicative
process, though independent of the Reynolds number for a given experimental setup, is found to depend significantly on this
setup and on the nature of the increment, longitudinal or transverse. The asymmetry of longitudinal velocity increments probability
density functions exhibits similarly a dependence with the experimental setup, but also systematically depends on the Reynolds
number.
Received 7 January 2000 and Received in final form 17 March 2000 相似文献
15.
A. Garber H. Kantz 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(3):437-443
The BTW Abelian sandpile model is a prominent example of systems showing self-organised criticality (SOC) in the infinite
size limit. We study finite-size effects with special focus on the statistics of extreme events, i.e., of particularly large
avalanches. Not only the avalanche size probability distribution, but also the mutual independence of large avalanches in
the critical state is affected by finite-size effects. Instead of a Poissonian recurrencetime distribution, in the finite
system we find a repulsion of extreme events that depends on the avalanche size and not on the respective probability. The
dependence of these effects on the system size is investigated and some data collapse is found. Our results imply that SOC
is an unsuitable mechanism for the explanation of extreme events which occur in clusters. 相似文献
16.
V. de la Mota F. Sébille B. Rémaud P. Schuck 《Zeitschrift für Physik A Hadrons and Nuclei》1992,343(4):417-427
Theoretical analyses of heavy-ion reactions are performed in the framework of the semi-classical Landau-Vlasov approach. The incident energies are investigated in the range from intermediate to low energy regimes, where transverse collective motion has been experimentally evidenced. The influence of the equation of state (E.O.S.) parameters on various collective observables is studied in relation with the action of the residual interactions. From the sensitivity to both aspects, and taking into account the experimental biases limitations, our investigation indicates that E.O.S. signatures should be more expected at energies below 100 MeV per nucleon. 相似文献
17.
The binding energy of excitonium negative ion for the ground1,3S-states in bulk semiconductors GaAs and ZnO in the hyperspherical coordinate method was found. Angular and radial correlations
between electrons in gerade and ungerade states were taken into account by channel functions, that are the eigenfunctions
of Hamiltonian on the surface of the sphere in the three-dimensional configuration space. Energy values were calculated using
the adiabatic and Born-Oppenheimer approximations. The obtained energy values are in agreement with those obtained using variational
method. 相似文献
18.
D. Lambrecht T. Blaich T. W. Elze H. Emling H. Freiesleben K. Grimm W. Henning R. Holzmann J. G. Keller H. Klingler J. V. Kratz R. Kulessa S. Lange Y. Leifels E. Lubkiewicz E. F. Moore W. Prokopowicz R. Schmidt C. Schütter H. Spies K. Stelzer J. Stroth E. Wajda W. Waluś M. Zinser E. Zude 《Zeitschrift für Physik A Hadrons and Nuclei》1994,350(2):115-120
We investigate the beam energy dependence of neutron and proton squeeze-out in collisions of197Au+197Au atE/A=400—800 MeV. The azimuthal anisotropy that describes the enhanced emission of mid-rapidity neutrons perpendicular to the reaction plane rises strongly with the transverse momentum of the neutrons. This dependence of the azimuthal anisotropy follows a universal curve — independent of beam energy — if the neutron momenta are measured in fractions of the projectile momentum per mass unit. Analogously, the kinetic energy spectra of mid-rapidity neutrons exhibit a universal behaviour as a function of the kinetic energy of the projectile.
The members of the FOPI-collaboration: J.P. Alard, Z. Basrak, N. Bastid, I.M. Belayev, M. Bini, R. Bock, A. Buta, R. aplar, C. Cerruti, N. Cindro, J.P. Coffin, M. Crouau, P. Dupieux, J. Erö, Z.G. Fan, P. Fintz, Z. Fodor, R. Freifelder, L. Fraysse, S. Frolov, A. Gobbi, Y. Grigorian, G. Guillaume, N. Herrmann, K.D. Hildenbrand, S. Hölbling, O. Houari, S.C. Jeong, M. Jorio, F. Jundt, J. Kecskemeti, P. Koncz, Y. Korchagin, R. Kotte, M. Krämer, C. Kuhn, I. Legrand, A. Lebedev, C. Maguire, V. Manko, T. Matulewicz, G. Mgebrishvili, J. Mösner, D. Moisa, G. Montarou, P. Morel, W. Neubert, A. Olmi, G. Pasquali, D. Pelte, M. Petrovici, G. Poggi, F. Rami, W. Reisdorf, A. Sadchikov, D. Schüll, Z. Seres, B. Sikora, V. Simion, S. Smolyankin, U. Sodan, N. Taccetti, K. Teh, R. Tezkratt, M. Trzaska, M.A. Vasiliev, P. Wagner, J.P. Wessels, T. Wienold, Z. Wilhelmi, D. Wohlfarth, A.V. Zhilin. 相似文献
19.
Takeshi Yasuda Masatoshi Saito Hiroaki Nakamura Tetsuo Tsutsui 《Applied Physics A: Materials Science & Processing》2009,95(1):179-183
We have studied the electronic excitations of fluorinated copper phthalocyanine, CuPcF16, thin films using electron energy-loss spectroscopy in transmission. This allowed for the derivation of the dielectric function
in a wide energy range. Furthermore, we have analyzed the lowest excitation feature using a Lorentz model, which enabled the
determination of the dielectric background in the energy range of the gap excitation, and an analysis of the momentum dependence
of the spectral intensities at low energies. 相似文献
20.
We apply the Bogoliubov compensation principle to the gauge electro-weak interaction to demonstrate the spontaneous generation
of an anomalous three-boson gauge invariant effective interaction. The non-trivial solution of the compensation equations
uniquely defines the values of the parameters of the theory and the form factor of the anomalous interaction. The contribution
of this interaction to the running EW coupling, α
ew(p
2), gives its observable value α
ew(M
W
2)=0.0374, in satisfactory agreement to the experiment. The anomalous three-boson interaction gives a natural explanation of
the well-known discrepancy in the muon g−2. The implications for EW studies at Tevatron and LHC are briefly discussed. 相似文献