共查询到20条相似文献,搜索用时 31 毫秒
1.
K. Esfarjani S.T. Chui V. Kumar Y. Kamazoe 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(2):181-189
We investigate the statics and dynamics of spatial phase segregation process of a mixture of fermion atoms in a harmonic trap
using the density functional theory. The kinetic energy of the fermion gas is written in terms of the density and its gradients.
Several cases have been studied by neglecting the gradient terms (the Thomas-Fermi limit) which are then compared with the
Monte-Carlo results using the full gradient corrected kinetic energy. A linear instability analysis has been performed using
the random-phase approximation. Near the onset of instability, the fastest unstable mode for spinodal decomposition is found
to occur at q = 0. However, in the strong coupling limit, many more modes with q ≈ K
F decay with comparable time scales.
Received 12 September 2001 Published online 24 September 2002
RID="a"
ID="a"e-mail: k1@sharif.edu
RID="b"
ID="b"Permanent address: Dr. Vijay Kumar Foundation, 45 Bazaar Street, K.K. Nagar (West), Chennai 600 078, India. 相似文献
2.
Y. Mao T.C.B. McLeish P.I.C. Teixeira D.J. Read 《The European physical journal. E, Soft matter》2001,6(1):69-77
We address the effect of an asymmetric concentration-dependent mobility on the early stages of spinodal decomposition in polymer
blends and solutions, and characterise it quantitatively. This is particularly important when one of the components has a
slower dynamics than the other, e.g., because it is closer to its glass transition, or is weakly cross-linked. Composition mode coupling is proposed as the underlying
physical mechanism, and then investigated by means of numerical simulations of the Cahn-Hilliard equation in one (1d) and
two (2d) dimensions. In general, this coupling broadens the peak in the structure factor: in 1d an asymmetric concentration
profile is obtained, with sharpened interfaces, whereas in 2d the formation is favoured of sharp peaks of the phase rich in
the more mobile component. It is shown how the changing morphology of this phase-separating system can be described with the
aid of Minkowski functionals.
Received 28 August 2000 and Received in final form 18 July 2001 相似文献
3.
W. Nörenberg G. Papp P. Rozmej 《The European Physical Journal A - Hadrons and Nuclei》2000,9(3):327-343
The diabatic approach to dissipative collective nuclear motion is reformulated in the local-density approximation in order
to treat the normal modes of a spherical nuclear droplet analytically. In a first application the adiabatic isoscalar modes
are studied and results for the eigenvalues of compressional (bulk) and pure surface modes are presented as function of density
and temperature inside the droplet, as well as for different mass numbers and for soft and stiff equations of state. We find
that the region of bulk instabilities (spinodal regime) is substantially smaller for nuclear droplets than for infinite nuclear
matter. For small densities below 30% of normal nuclear matter density and for temperatures below 5 MeV all relevant bulk
modes become unstable with similar growth rates. The surface modes have a larger spinodal region, reaching out to densities
and temperatures way beyond the spinodal line for bulk instabilities. Essential experimental features of multifragmentation,
like fragmentation temperatures and fragment-mass distributions (in particular the power-law behavior) are consistent with
the instability properties of an expanding nuclear droplet, and hence with a dynamical fragmentation process within the spinodal
regime of bulk and surface modes (spinodal decomposition).
Received: 4 September 2000 / Accepted: 14 November 2000 相似文献
4.
W. Nörenberg G. Papp P. Rozmej 《The European Physical Journal A - Hadrons and Nuclei》2002,14(1):43-51
Results on dissipative isoscalar modes of a hot and dilute nuclear droplet are presented. As compared to the adiabatic limit
(part I), realistic dissipation yields a substantial reduction of the growth rates for all unstable modes, while the area
of spinodal instability in the (ϱ,T)-plane remains unchanged. The qualitative features of multifragmentation through spinodal decomposition as obtained in the
adiabatic limit are not significantly affected by dissipation.
Received: 10 January 2002 / Accepted: 10 February 2002 相似文献
5.
Summary A thermodynamic calculation of the Fe−Cr−Ni phase diagram suggests that the composition 30 at.%Cr-5 at.%Ni is expected to
be found inside the spinodal line, whereas 16 at.%Cr-5 at.%Ni is expected outside at 723 K. These two alloys have been thermally
aged for time periods up to 40 minutes at 723K. A significant broadening of the magnetic-hyperfine-field distribution indicates
that Fe-30 at.%Cr-5 at.%Ni undergoes typical spinodal decomposition in agreement with the calculation. Spinodal decomposition
is distinguished from nucleation-growth by a detailed analysis of the magnetic-hyperfine-field distribution.
Paper presented at ICAME-95, Rimini, 10–16 September 1995 相似文献
6.
A. Guarino S. Ciliberto A. Garcimartın M. Zei R. Scorretti 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(2):141-151
The acoustic emission of fracture precursors, and the failure time of samples of heterogeneous materials (wood, fiberglass)
are studied as a function of the load features and geometry. It is shown that in these materials the failure time is predicted
with a good accuracy by a model of microcrack nucleation proposed by Pomeau. We find that the time interval δt between events (precursors) and the energy ɛ are power law distributed and that the exponents of these power laws depend
on the load history and on the material. In contrast, the cumulated acoustic energy E presents a critical divergency near the breaking time τ which is E∼
. The positive exponent γ is independent, within error bars, on all the experimental parameters.
Received 31 July 2001 and Received in final form 17 December 2001 相似文献
7.
J. Rosti L.I. Salminen E.T. Seppälä M.J. Alava K.J. Niskanen 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(2):259-263
We study the statistics of crack pinning in two dimensions by experiments and simulations of directed polymers in random media.
Mode I tensile tests on paper samples show a delocalization phenomenon as the notch length is varied if the fraction of cracks
pinned to the notch is monitored. This is compared with the behavior of directed polymers in the presence of both an energetically
favorable localized pinning center and bulk disorder. An analysis of the crack interface roughness indicates self-affine behavior
with a roughness exponent ζ in the proximity of the minimum energy surface value 2/3.
Received 4 April 2000 and Received in final form 10 October 2000 相似文献
8.
K. Hamada T. Wada C. Guet 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(3):359-368
Stability of highly charged metal clusters in the electric field of an external ion is investigated with the classical liquid
drop model. We study the optimum shape of the cluster which has a local minimum of the total energy, taking account of the
effects of the surface charge polarization on the Coulomb energy and the cluster deformation on the surface energy. We find
that the cluster deformation greatly affects the total energy of the system and that a cluster with a fissility larger than
some critical value 0.7-0.8 can become unstable against deformation. We investigate the local competition between the Coulomb
force and the surface tension at the cluster surface and show that the surface charge polarization which is induced by the
external electric field significantly affects the shape of the cluster and its stability.
Received 5 November 2002 / Received in final form 27 January 2003 Published online 11 March 2003
RID="a"
ID="a"e-mail: hamada@konan-u.ac.jp 相似文献
9.
M. Modarres H.R. Moshfegh A. Sepahvand 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(2):159-166
The free energy of the homogeneous electron fluid at finite temperature is obtained using the lowest order constrained variational
(LOCV) method. In order to test the convergence of cluster expansion series the three-body cluster terms are calculated with
the LOCV correlation functions. The results agree reasonably with those of Monte Carlo, coupled-cluster, perturbational expansion
etc, techniques at zero temperature. The flashing and critical temperatures as well as the critical exponent are found to
be about 0.6, 1.3 eV and 0.384 respectively. A similar liquid-gas phase transition to that of nuclear matter and liquid He3 is observed.
Received 15 April 2002 / Received in final form 19 October 2002 Published online 4 February 2003
RID="a"
ID="a"e-mail: modarres@khayam.ut.ac.ir 相似文献
10.
M. Schnürer S. Ter-Avetisyan H. Stiel U. Vogt W. Radloff M. Kalashnikov W. Sandner P.V. Nickles 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(3):331-335
Using 50 fs ( ∼ 2×1018 W/cm2) and 2 ps ( ∼ 5×1016 W/cm2) pulses from a Ti:Sa multi-TW laser at 800 nm wavelength large Xe-clusters ( 105...106 atoms per cluster) have been excited. Absolute yield measurements of EUV-emission in a wavelength range between 10 nm and
15 nm in combination with cluster target variation were carried out. The ps-laser pulse has resulted in about 30% enhanced
and spatially more uniform EUV-emission compared to fs-laser excitation. Circularly polarized laser light instead of linear
polarization results in enhanced emission which is probably caused by electrons gaining higher energies by the polarization
dependent optical field ionization process. An absolute emission efficiency at 13.4 nm of up to 0.8% in 2π sr and 2.2% bandwidth
has been obtained.
Received 11 January 2001 and Received in final form 27 March 2001 相似文献
11.
Y. Couder L. Pauchard C. Allain M. Adda-Bedia S. Douady 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(2):135-138
The veins of plant leaves exhibit a large variety of morphologies. They are often thought to result from their growth in a
concentration scalar field. It is shown here that the topology of these patterns rather corresponds to what is expected from
growth in a tensorial stress field. This is demonstrated by analogic experiments performed on crack formation in gel films
where many characteristic venation patterns, of both dicotyledons and monocotyledons, were reproduced. This suggests, for
the origin of the veins formation, a set of hypotheses which is new but supported by known physiological data.
Received 11 March 2002 Published online 19 July 2002 相似文献
12.
J. Dunkel W. Ebeling U. Erdmann 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):511-524
We investigate the stochastic dynamics of an one-dimensional ring with N self-driven Brownian particles. In this model neighboring particles interact via conservative Morse potentials. The influence of the surrounding heat bath is modeled by Langevin-forces (white noise) and
a constant viscous friction coefficient γ. The Brownian particles are provided with internal energy depots which may lead to active motions of the particles. The depots
are realized by an additional nonlinearly velocity-dependent friction coefficient γ
1(v) in the equations of motions. In the first part of the paper we study the partition functions of time averages and thermodynamical
quantities (e.g. pressure) characterizing the stationary physical system. Numerically calculated non-equilibrium phase diagrams are represented.
The last part is dedicated to transport phenomena by including a homogeneous external force field that breaks the symmetry
of the model. Here we find enhanced mobility of the particles at low temperatures.
Received 21 July 2001 相似文献
13.
E. Api naniz F. Plazaola J.S. Garitaonandia 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(2):167-177
Tight Binding Linear Muffin-Tin Orbital (TB-LMTO) electronic calculations are presented for the magnetic and structural properties
of ordered and disordered FeAl alloys. The total energy, bulk modulus, lattice parameter and magnetic moments of B2, D03 and
B32 ordered structures and A2 disordered structure were calculated for different compositions. The different structures are
obtained by varying the position of Fe and Al atoms in a BCC superstructure. In this way, we examine the order-disorder transition
that takes place in these alloys. Disordered alloys present both larger Fe magnetic moment and lattice parameter than ordered
ones. In this work comparison of the calculated quantities with available experimental results is provided and it can be concluded
that the results are in quantitative agreement with the experimental trends.
Received 7 May 2002 / Received in final form 20 September 2002 Published online 4 February 2003
RID="a"
ID="a"e-mail: eaf@we.lc.ehu.es 相似文献
14.
By replacing quasiparticles by quasiskyrmions, we calculate the binding energy of the alpha-particle using the cluster expansion
method.
Received: 8 November 2001 / Accepted: 3 April 2002 相似文献
15.
The subject of this paper is inspired by microphase-separated copolymer melts in which a small-scale structure is present
inside one of the phases of a large-scale structure. Such a situation can arise in a diblock copolymer melt, if one of the
blocks of the diblock is in itself a multiblock copolymer or a comb copolymer. Due to the presence of the large-scale structure,
the chains are stretched. The aim of this paper is to investigate the influence of this chain stretching on the formation
of the small-scale structure. To gain insight we study infinite melts of infinitely long copolymer chains that are subjected
to a stretching force. For melts of monodisperse multiblock copolymers we find that the stretching destabilizes the homogeneous
phase. If the stretching is strong, the lamellar structure is the only stable structure. The periodicity increases with the
degree of stretching. For melts of monodisperse comb copolymers the chain stretching has no influence on the stability of
the homogeneous phase. If the stretching is strong, the lamellar structure and the hexagonal structure are the only stable
structures. The periodicity is independent of the degree of stretching. For the multiblock copolymer we investigated the influence
of block length polydispersity. For small polydispersity the period of the structure increases monotonically with the degree
of stretching. For intermediate polydispersity, the period initially decreases before it starts to increase. For large polydispersity, the mean-field period at the spinodal is infinite, becoming finite
once the stretching force exceeds some critical value. For very large polydispersity the mean-field period at the spinodal
remains infinite for any value of the stretching force.
Received: 14 February 2002 / Accepted: 24 March 2003 / Published online: 29 April 2003
RID="a"
ID="a"e-mail: hindrik.angerman@abp.nl 相似文献
16.
A computational model was developed to simulate the spinodal decomposition process of ferromagnetic alloys under an external magnetic field. In this model, the temporal evolution of the modulated structure was described by a phase field method, and the magnetic configuration was solved by using a micromagnetic method. The spinodal decomposition and coarsening processes of a single magnetic particle and an A-B hypothetical system under an external magnetic field were simulated using the proposed model. The simulation results show that the precipitated particles were elongated along the direction of the external magnetic field. The dependence of the modulated structure of an A-B hypothetic system on external magnetic field is much more sensitive than that of the single particle structure. The simulation results also demonstrate that the modulation of the external magnetic field is effective even if the spinodal decomposition has been completed and a stable modulated structure was formed. 相似文献
17.
M. Hyslop A. Wurl S.A. Brown B.D. Hall R. Monot 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):233-236
A beam of Pb clusters is produced with the inert gas aggregation method and probed by electron diffraction. Analysis of the
diffraction patterns indicates that average cluster size can vary between 3 and 7 nm, according to nucleation conditions.
The diffraction patterns from beams with larger average cluster size are very similar to patterns calculated from model decahedron
clusters, while those for smaller cluster size do not appear to have simple geometrical face-centred cubic, decahedral, or
icosahedral structure.
Received 30 November 2000 相似文献
18.
We discuss the stick-slip motion of an elastic block sliding along a rigid substrate. We argue that for a given external shear stress this system shows a discontinuous nonequilibrium transition from a uniform stick state to uniform sliding at some critical stress which is nothing but the Griffith threshold for crack propagation. An inhomogeneous mode of sliding occurs when the driving velocity is prescribed instead of the external stress. A transition to homogeneous sliding occurs at a critical velocity, which is related to the critical stress. We solve the elastic problem for a steady-state motion of a periodic stick-slip pattern and derive equations of motion for the tip and resticking end of the slip pulses. In the slip regions we use the linear friction law and do not assume any intrinsic instabilities even at small sliding velocities. We find that, as in many other pattern forming system, the steady-state analysis itself does not select uniquely all the internal parameters of the pattern, especially the primary wavelength. Using some plausible analogy to first-order phase transitions we discuss a soft selection mechanism. This allows to estimate internal parameters such as crack velocities, primary wavelength and relative fraction of the slip phase as functions of the driving velocity. The relevance of our results to recent experiments is discussed. 相似文献
19.
Ying-Yuan Deng 《中国物理 B》2021,30(8):88101-088101
Grain boundary directed spinodal decomposition has a substantial effect on the microstructure evolution and properties of polycrystalline alloys. The morphological selection mechanism of spinodal decomposition at grain boundaries is a major challenge to reveal, and remains elusive so far. In this work, the effect of grain boundaries on spinodal decomposition is investigated by using the phase-field model. The simulation results indicate that the spinodal morphology at the grain boundary is anisotropic bicontinuous microstructures different from the isotropic continuous microstructures of spinodal decomposition in the bulk phase. Moreover, at grain boundaries with higher energy, the decomposed phases are alternating α/β layers that are parallel to the grain boundary. On the contrary, alternating α/β layers are perpendicular to the grain boundary. 相似文献
20.
P. Poulin J. Bibette D.A. Weitz 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(2):277-281
Aggregation mechanisms of emulsions at high initial volume fractions () is studied using light scattering. We use emulsion droplets which can be made unstable towards aggregation by a temperature
quench. For deep quenches and , the aggregation mechanism is identified as diffusion-limited cluster aggregation (DLCA). An ordering of the clusters, which
is reflected by a peak in the scattering intensity, is shown to result from the intercluster separation, exhibiting different
scaling than that observed at lower volume fractions. This manifests an increasing similarity to spinodal decomposition observed
as is increased. For and shallow quenches, different mechanisms, closer to spinodal decomposition, are observed. These results allow the subtle
boundaries between DLCA and spinodal decomposition to be explored.
Received: 7 April 1998 / Revised: 19 August 1998 / Accepted: 21 August 1998 相似文献