共查询到20条相似文献,搜索用时 703 毫秒
1.
D.H.E. Gross E.V. Votyakov 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(1):115-126
Traditionally, phase transitions are defined in the thermodynamic limit only. We discuss how phase transitions of first order
(with phase separation and surface tension), continuous transitions and (multi)-critical points can be seen and classified
for small systems. “Small” systems are systems where the linear dimension is of the characteristic range of the interaction
between the particles; i.e. also astrophysical systems are “small” in this sense. Boltzmann defines the entropy as the logarithm of the area of the surface in the mechanical N-body phase space at total energy E. The topology of S(E,N) or more precisely, of the curvature determinant allows the classification of phase transitions without taking the thermodynamic limit. Micro-canonical thermo-statistics
and phase transitions will be discussed here for a system coupled by short range forces in another situation where entropy
is not extensive. The first calculation of the entire entropy surface S(E,N) for the diluted Potts model (ordinary (q=3)-Potts model plus vacancies) on a square lattice is shown. The regions in {E,N} where D>0 correspond to pure phases, ordered resp. disordered, and D<0 represent transitions of first order with phase separation and “surface tension”. These regions are bordered by a line
with D=0. A line of continuous transitions starts at the critical point of the ordinary (q=3)-Potts model and runs down to a branching point Pm. Along this line vanishes in the direction of the eigenvector of D with the largest eigen-value . It characterizes a maximum of the largest eigenvalue . This corresponds to a critical line where the transition is continuous and the surface tension disappears. Here the neighboring
phases are indistinguishable. The region where two or more lines with D=0 cross is the region of the (multi)-critical point. The micro-canonical ensemble allows to put these phenomena entirely
on the level of mechanics.
Received 18 October 1999 and received in final form 17 November 1999 相似文献
2.
Consider a map ψ0 of class C
r for large r of a manifold of dimension n greater than or equal to 2 having a Feigenbaum attractor. We prove that any such ψ0 is a point of a local codimension-one manifold of C
r
transformations also exhibiting Feigenbaum attractors. In particular, the attractor persists when perturbing a one-parameter
family transversal to that manifold at ψ0. We also construct such a transversal family for any given ψ0, and apply this construction to prove a conjecture by J. Palis stating that a map exhibiting a Feigenbaum attractor can be
perturbed to obtain homoclinic tangencies.
Received: 4 August 1998 / Accepted: 11 May 1999 相似文献
3.
Virendra Singh 《Pramana》1985,24(1-2):31-37
We propose an analytic perturbative approach for the determination of the Feigenbaum-Cvitanović function and the universal
parameterα occurring in the Feigenbaum scenario of period doubling for approach to chaotic behaviour. We apply the method to the caseZ=2 whereZ is the order of the unique local maximum of the nonlinear map. Our third order approximation givesα=2.5000 as compared to “exact” numerical valueα=2.5029 ... We also obtain a reasonably accurate value of the Feigenbaum-Cvitanović function. 相似文献
4.
R. Tonelli M. Coraddu 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(1-2):355-359
This paper compares three different types of “onset of chaos”
in the logistic and generalized logistic map: the Feigenbaum attractor
at the end of the period doubling bifurcations; the tangent bifurcation at the
border of the period three window; the transition to chaos in the generalized logistic
with inflection 1/2 (xn+1 = 1-μxn1/2), in which
the main bifurcation cascade, as well as
the bifurcations generated by the periodic windows in the chaotic region,
collapse in a single point.
The occupation number and the Tsallis entropy are studied.
The different regimes of convergence to the attractor,
starting from two kinds of far-from-equilibrium initial conditions,
are distinguished by the presence or absence of log-log
oscillations, by different power-law scalings and by a gap in the
saturation levels.
We show that the escort distribution
implicit in the Tsallis entropy may tune
the log-log oscillations or the crossover times. 相似文献
5.
A. Nersessian 《Czechoslovak Journal of Physics》2000,50(11):1309-1315
We propose the model ofD-dimensional massless particle whose Lagrangian is given by theN-th extrinsic curvature of world-line. The system hasN+1 gauge degrees of freedom constitutingW-like algebra; the classical trajectories of the model are space-like curves which obey the conditionsk
N+a=kN−a, k2N
=0,a=1, ...,N−1,N≤[(D−2)/2], while the firstN curvaturesk
i remain arbitrary. We show that the model admits consistent formulation on the anti-DeSitter space. The solutions of the system
are the massless irreducible representations of Poincaré group withN nonzero helicities, which are equal to each other.
Presented at the 9th Colloquium “Quantum Groups and Integrable Systems”, Prague, 22–24 June 2000. 相似文献
6.
The theoretical optimization of the design parametersN
A
,N
D
andW
P
has been done for efficient operation of Au-p-n Si solar cell including thermionic field emission, dependence of lifetime and mobility on impurity concentrations, dependence
of absorption coefficient on wavelength, variation of barrier height and hence the optimum thickness ofp region with illumination. The optimized design parametersN
D
=5×1020 m−3,N
A
=3×1024 m−3 andW
P
=11.8 nm yield efficiencyη=17.1% (AM0) andη=19.6% (AM1). These are reduced to 14.9% and 17.1% respectively if the metal layer series resistance and transmittance with
ZnS antireflection coating are included. A practical value ofW
P
=97.0 nm gives an efficiency of 12.2% (AM1). 相似文献
7.
It is found that a fixed point of the renormalization group equation corresponding to a system of a unimodal map with extremum
of power κ and a map summarizing values of a function of the dynamical variable of the first subsystem, undergoes a bifurcation in the
course of increase of κ. It occurs at κ
c
=1.984396 and results in a birth of the period-2 stationary solution of the RG equation. At κ=2 this period-2 solution corresponds to the universal period-doubling behavior discovered earlier and denoted as the C-type
criticality (Kuznetsov and Sataev in Phys. Lett. A 162:236–242, 1992). By combination of analytical methods and numerical computations we obtain and analyze an asymptotic expansion of the period-2
solution in powers of Δκ=κ−κ
c
. The developed approach resembles the ε-expansion in the phase transition theory, in which a “trivial” stationary point of the RG transformation undergoes a bifurcation
that gives rise to a new fixed point responsible for the critical behavior with nontrivial critical indices. 相似文献
8.
Shaolin Liao Ronald J. Vernon 《International Journal of Infrared and Millimeter Waves》2007,28(6):479-490
The newly developed Taylor-Interpolation-FFT (TI-FFT) algorithm dramatically increases the computational speeds for millimeter
wave propagation from a planar (cylindrical) surface onto a “quasi-planar” (“quasi-cylindrical”) surface. Two different scenarios
are considered in this article: the planar TI-FFT is for the computation of the wave propagation from a plane onto a “quasi-planar” surface and the cylindrical TI-FFT is for the computation of wave propagation from a cylindrical surface onto a “quasi-cylindrical” surface. Due to the
use of the FFT, the TI-FFT algorithm has a computational complexity of O(N
2 log2
N
2) for an N × N computational grid, instead of N
4 for the direct integration method. The TI-FFT algorithm has a low sampling rate according to the Nyquist sampling theorem.
The algorithm has accuracy down to −80 dB and it works particularly well for narrow-band fields and “quasi-planar” (“quasi-cylindrical”)
surfaces. 相似文献
9.
D. I. Dimitrov L. I. Klushin A. Skvortsov A. Milchev K. Binder 《The European physical journal. E, Soft matter》2009,29(1):9-25
A flexible polymer chain under good solvent conditions, end-grafted on a flat repulsive substrate surface and compressed by
a piston of circular cross-section with radius L may undergo the so-called “escape transition” when the height of the piston D above the substrate and the chain length N are in a suitable range. In this transition, the chain conformation changes from a quasi-two-dimensional self-avoiding walk
of “blobs” of diameter D to an inhomogeneous “flower” state, consisting of a “stem” (stretched string of blobs extending from the grafting site to
the piston border) and a “crown” outside of the confining piston. The theory of this transition is developed using a Landau
free-energy approach, based on a suitably defined (global) order parameter and taking also effects due to the finite chain
length N into account. The parameters of the theory are determined in terms of known properties of limiting cases (unconfined mushroom,
chain confined between infinite parallel walls). Due to the non-existence of a local order parameter density, the transition
has very unconventional properties (negative compressibility in equilibrium, non-equivalence between statistical ensembles
in the thermodynamic limit, etc.). The reasons for this very unusual behavior are discussed in detail. Using Molecular Dynamics
(MD) simulation for a simple bead-spring model, with N in the range 50
N
300 , a comprehensive study of both static and dynamic properties of the polymer chain was performed. Even though for the
considered rather short chains the escape transition is still strongly rounded, the order parameter distribution does reveal
the emerging transition clearly. Time autocorrelation functions of the order parameter and first passage times and their distribution
indicate clearly the strong slowing down associated with the chain escape. The theory developed here is in good agreement
with all these simulation results. 相似文献
10.
Summary The structure of water in bis(2-ethylhexyl)sodium sulfosuccinate (AOT) micelles has been studied as a function of the [H2O]/[AOT] ratio (W) by using the absorption IR due to O−H stretching modes in the 3800–3000 cm−1 range. Three systems have been studied: water/AOT/carbon tetrachloride, water/AOT/n-heptane and water/AOT iso-octane. Experimental spectra are presented and discussed for the O−H stretching region both of
H2O and isotopically diluted HDO molecules in D2O. We have restricted ourselves to the region of small amounts of water (0<W<20) where the properties of the systems change strongly with the water content. The results show that IR spectra can be expressed
as sum of contributions from interfacial and bulk-like water. The fraction of water in the two “regions” within the water
pool was evaluated as a function ofW. From the data a continuous variation appears in the water properties inside micellar cores rather than a two-steps hydration
mechanism. The solubilization of water is described in terms of hydration of the AOT head group and Na+ counterions. The maximum hydration number of AOT was found to be 3.5. The same behaviour has been observed in the three solvents
studied. 相似文献
11.
I. G. Gogidze P. B. Kuminov A. V. Sergeev A. I. Elant’ev E. M. Men’shchikov E. M. Gershenzon 《Technical Physics》1998,43(10):1193-1198
A new type of fast detector is proposed. The operation of the detector is based on the change induced in the kinetic inductance
of NbN and YBa2Cu3O7−δ
superconducting films by nonequilibrium quasiparticles produced by electromagnetic radiation. The speed of a NbN detector
is essentially temperature-independent and is less than 1 ps. A model based on the Omen-Scalapino scheme describes well the
experimental dependence of the voltage-power sensitivity of a NbN detector on the modulation frequency of the radiation. A
low equilibrium quasiparticle density and a high quantum yield give detecting power D*=1012W−1 · cm · Hz1/2 at temperature T=4.2 K and D*=1016 W−1 · cm · Hz1/2 at temperature T=1.6 K. The time constant of the low-temperature YBaCuO induction detector is determined only by the electron-phonon interaction
time τ
e-ph
d
in the nodal regions.
Zh. Tekh. Fiz. 68, 63–69 (October 1998) 相似文献
12.
Damir Be?irevi? Benjamin Haas 《The European Physical Journal C - Particles and Fields》2011,71(8):1734
The axial coupling and the magnetic moment of D
∗-meson or, more specifically, the couplings gD*Dpg_{D^{\ast}D\pi} and gD*Dgg_{D^{\ast}D\gamma }, encode the non-perturbative QCD effects describing the decays D
∗→Dπ and D
∗→Dγ. We compute these quantities by means of lattice QCD with N
f=2 dynamical quarks, by employing the Wilson (“clover”) action. On our finer lattice (a≈0.065 fm) we obtain gD*Dp+=20±2g_{D^{\ast}D\pi^{+}}=20\pm2, and gD*0 D0g=2.0±0.6 GeV-1g_{D^{\ast0} D^{0}\gamma}=2.0\pm 0.6~{\rm GeV}^{-1}. This is the first determination of gD*0 D0gg_{D^{\ast0} D^{0}\gamma} on the lattice. We also provide a short phenomenological discussion and the comparison of our result with experiment and
with the results quoted in the literature. 相似文献
13.
J.W. Eerkens 《Applied physics. B, Lasers and optics》2001,72(7):885-892
An approximate closed-form expression is derived for the average wall-reaching rate kW or time τW=kW
-1 of laser-tagged molecules diluted in an inert carrier gas migrating to the wall of a long cylinder where they are removed
with sticking coefficient ηW. The exact equation for the sticky wall problem requires a trial-and-error solution of a transcendental relation with Bessel–functions.
With the aid of the Fermi–Amaldi albedo theory, an explicit “compromise” relation is derived which approximates the exact
diffusion curve of kW versus ηW rather well. The result is applied to obtain curves of kW versus ηW at different gas mix pressures for UF6 diluted in N2.
Received: 5 June 2000 / Revised version: 31 January 2001 / Published online: 27 April 2001 相似文献
14.
M. Welk 《Czechoslovak Journal of Physics》2000,50(11):1379-1384
We study covariant differential calculus on the quantum Euclidean spheres S
q
N−1
which are quantum homogeneous spaces with coactions of the quantum groups O
q
(N). First order differential calculi on the quantum Euclidean spheres satisfying a dimension constraint are found and classified:
ForN≥6, there exist exactly two such calculi one of which is closely related to the classical differential calculus in the commutative
case. Higher order differential forms and symmetry are discussed.
Presented at the 9th Colloquium “Quantum Groups and Integrable Systems”, Prague, 22–24 June 2000. 相似文献
15.
Vilson Tonin-Zanchin Erasmo Recami José A. Roversi Luis A. Brasca-Annes 《Foundations of Physics Letters》1994,7(2):167-179
Within a purely classical formulation of “strong gravity,” we associated hadron constituents (and even hadrons themselves)
with suitable stationary, axisymmetric solutions of certain new Einsteintype equations supposed to describe the strong field
inside hadrons. Such equations are nothing but Einstein equations—with cosmological term—suitably scaled down. As a consequence,
the cosmological constant Λ and the massesM result in our theory to be scaled up, and transformed into a “hadronic constant” and into “strong masses,” respectively.
Due to the unusual range of Λ andM values considered, we met a series of solutions of the Kerr-Newman-de Sitter (KNdS) type with rather interesting properties:
aim of the present work is putting forth such results, while “translating” them into the more popular language of ordinary
gravity.
The requirement that those solutions be stable, i.e., that their temperature (or surface gravity) bevanishingly small, implies the coincidence of at least two of their (in general, three) horizons. Imposing the stability condition of a certain
horizon does yield (once chosen the values ofJ, q and Λ) mass and radius of the associated black hole.
In the case of ordinary Einstein equations and for stable blackholes of the KNdS type, we get in particular Regge-like relations
among massM, angular momentumJ, chargeq and cosmological constant Λ; which did not receive enough attention in the previous literature. For instance, with the standard
definitionsQ
2 = Gq2/(4πε
0
c
4), a ≡ J/(Mc), m ≡GM/c
2, in the case Λ=0 in whichm
2=a2+Q2 and ifq is negligible, we findm
2=J. When considering, for simplicity, Λ>0 andJ=0 (andq still negligible), then we obtainm
2 = 1/(9Λ). In the most general case, the condition, for instance, of “triple coincidence” among the three horizons yields
for |Λa
2|<< 1 the couple of independent relationsm
2 = 2/(9Λ) andm
2 = 8(a
2 + Q2.
Another interesting point is that—with few exceptions—all such relations (amongM, J, q, Λ) lead to solutions that can be regarded as (stable) cosmological models.
Work partially supported by INFN, MURST, and CNR and by CNPq, FAPESP, and CAPES. 相似文献
16.
We study stable “bookshelf” smectic-A structures within a very thin plane-parallel cell of thickness L in which the mismatch between surface preferred (d
s) and intrinsic (d0) smectic layer thicknesses occurs. The Landau-Ginzburg approach based on a complex smectic order parameter is used. For a
weak enough smectic positional anchoring strength W smectic layers adopt the modified bookshelf profile. In a thick enough cell with increasing W a lattice of edge dislocations is continuously formed at the confining surfaces and then depinned from them. The structure
with dislocations is formed when the condition d
0/(
d
0/d
s - 1) ∼ 2 is fulfilled, where is the positional surface anchoring extrapolation length. If the cell is thin enough the dislocations formed at opposite
cell plates annihilate and consequently the smectic layers adopt a locked bookshelf structure. This transition is discontinuous
and takes place when d
0/(L
d
0/d
s - 1) ∼ 5 is realized. To observe these transitions in a cell of thickness L∼ 1μm the conditions W∼ 10-6
J/m
2 and
d
0/d
s - 1∼ 5 . 10-4 have to be fulfilled. All the three qualitatively different structures coexist at the triple point.
Received 21 February 2002 相似文献
17.
We consider a D-dimensional model of gravity with non-linear “scalar fields” as a matter source. The model is defined on the product manifold M, which contains n Einstein factor spaces. General cosmological type solutions to the field equations are obtained when n − 1 factor spaces are Ricci-flat, e.g. when one space M 1 of dimension d 1 > 1 has nonzero scalar curvature. The solutions are defined up to solutions to geodesic equations corresponding to a sigma model target space. Several examples of sigma models are presented. A subclass of spherically symmetric solutions is studied and a restricted version of “no-hair theorem” for black holes is proved. For the case d 1 = 2 a subclass of latent soliton solutions is singled out. 相似文献
18.
The purpose of this contribution, is to initiate a classification of Lie superalgebras (LS) of dimension five, over the base
field ℝ of real numbers. We use the “graded skew-symmetry” and the “graded Jacobi identity” in order to get restrictions for the commutators and anticommutators of an arbitrary five-dimensional Lie superalgebra L = L
0⊕ L
1
PACS 2003: 02.20.Sv 相似文献
19.
N. Yu. Svechnikov 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2011,5(1):21-29
The 2D-photoemission image of the beam spot was obtained for the first time for the W5+ oxidation state on the preliminary irradiated WO3 − x
thin film surface, created by scanning of the SR beam over the film surface. The W5+ beam profile intensity was found to spread up to a distance of 3.2 μm for an amorphous film and 5.5 μm for a polycrystalline
film, it exceeds considerably the beam spot size. The image saturation dose was reached faster for a polycrystalline film.
Among the possible mechanisms explaining this phenomenon, for the case of an almost unchangeable O2s state under irradiation, a choice was made in favor of a photon-generated charge diffusion due to low-energy secondary electrons
from photoemission, which produce the “coloration” effect, e− + W6+ (W5+) W5+ → W5+(W4+). The O512-eV Auger peak was found to degrade at the distance of 1.5–2 mm outside the beam spot under long-time electron
beam irradiation, which is attributed to electron-stimulated oxygen desorption and outdiffusion. 相似文献
20.
K. J. Falconer 《Communications in Mathematical Physics》1999,206(1):235-245
A Laplacian may be defined on self-similar fractal domains in terms of a suitable self-similar Dirichlet form, enabling discussion
of elliptic PDEs on such domains. In this context it is shown that that semilinear equations such as Δu+u
p
= 0, with zero Dirichlet boundary conditions, have non-trivial non-negative solutions if 0<ν≤ 2 and p>1, or if ν >2 and 1<p< (ν+ 2)/(ν− 2), where ν is the “intrinsic dimension” or “spectral dimension” of the system. Thus the intrinsic dimension
takes the r\^{o}le of the Euclidean dimension in the classical case in determining critical exponents of semilinear problems.
Received: 11 December 1998 / Accepted: 22 March 1999 相似文献