共查询到20条相似文献,搜索用时 31 毫秒
1.
Parongama Sen 《Pramana》2008,71(2):313-317
We consider navigation or search schemes on networks which have a degree distribution of the form P(k) ∝ exp(−k
γ). In addition, the linking probability is taken to be dependent on social distances and is governed by a parameter λ. The searches are realistic in the sense that not all search chains can be completed. An estimate of μ = ρ/s
d, where ρ is the success rate and s
d the dynamic path length, shows that for a network of N nodes, μ ∝ N
−δ
in general. Dynamic small world effect, i.e., δ ≃ 0 is shown to exist in a restricted region of the λ−γ plane.
相似文献
2.
L. G. Moyano A. P. Majtey C. Tsallis 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(4):493-500
We introduce, and numerically study, a system of N symplectically and globally coupled
standard maps localized in a d=1 lattice array. The global coupling is modulated
through a factor r-α, being
r the distance between maps. Thus, interactions are long-range (nonintegrable) when
0≤α≤1, and short-range (integrable) when α>1.
We verify that the largest Lyapunov exponent λM scales as λM ∝
N-κ(α), where κ(α) is positive when interactions are
long-range, yielding weak chaos in the thermodynamic
limit N↦∞ (hence λM→0). In the short-range case,
κ(α) appears to vanish,
and the behaviour corresponds to strong chaos. We show that, for certain
values of the control parameters of the system, long-lasting metastable states
can be present. Their duration tc scales as tc ∝Nβ(α),
where β(α) appears to be numerically in agreement with the following
behavior: β>0 for 0 ≤α< 1, and zero for α≥1.
These results are consistent with features typically found in nonextensive statistical mechanics.
Moreover, they exhibit strong similarity between the present
discrete-time system, and the α-XY Hamiltonian ferromagnetic model. 相似文献
3.
I.?Lon?arevi? Z. M.?Jak?i? S. B.?Vrhovac Lj.?Budinski-Petkovi? 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,73(3):439-445
Random sequential adsorption with diffusional relaxation of extended objects
both on a one-dimensional and planar triangular lattice is studied numerically
by means of Monte Carlo simulations. We focus our attention on the behavior of
the coverage θ(t) as a function of time. Our results indicate that the
lattice dimensionality plays an important role in the present model.
For deposition of k-mers on 1D lattice with diffusional relaxation, we found
that the growth of the coverage θ(t) above the jamming limit to the
closest packing limit θCPL is described by the pattern
θCPL-θ(t) ∝Eβ[-(t/τ)β], where Eβ
denotes the Mittag-Leffler function of order β∈(0,1). In the case of
deposition of extended lattice shapes in 2D, we found that after the initial
“jamming", a stretched exponential growth of the coverage θ(t) towards
the closest packing limit θCPL occurs, i.e., θCPL -
θ(t) ∝exp [-(t/τ)β]. For both cases we observe that: (i)
dependence of the relaxation time τ on the diffusion probability Pdif
is consistent with a simple power-law, i.e., τ∝Pdif
-δ;
(ii) parameter β depends on the object size in 1D and on the particle
shape in 2D. 相似文献
4.
A. I. Alekseev 《Journal of Experimental and Theoretical Physics》1997,84(1):35-50
The properties of the density matrix and the multipole moments arising in oriented and aligned atoms with zero nuclear spin
through the interaction with strong resonant ultrashort pulses with wave vector k
0 and circular or linear polarization have been found. Calculations have been made for the time-dependent light-induced magnetization
μ(t′) of a gas of pre-oriented and prealigned atoms following the passage of a weak resonant elliptically polarized pulse with
frequency ω and wave vector k collinear with k
0. It is shown that for oriented atoms, μ(t′) is an even function of the detuning from resonance, ω-ω
ba, and can be split into two terms whose directions are a consequence of symmetry and are determined by the vectors k
0 and k as well as by the direction of rotation of the electric fields corresponding to the pulses. For aligned atoms the vector
μ(t′) is collinear with k, and the first term is an even function of ω-ω
ba. However, the second term is an odd function of ω-ω
ba and reverses direction when the sign of ω-ω
ba changes, as well as when the orientation of the axes of the polarization ellipse is changed. It is shown that if a series
of weak linearly polarized pulses pass through the gas, the light-induced magnetization of the oriented and aligned gas atoms
can be decomposed into three factors: the first determines the direction and is a consequence of the symmetry; the second
(with the dimensions of magnetic moment) depends on the characteristics of the resonant transitions; and the third is a universal
function of t′ and ω-ω
ba that does not depend on the underlying characteristics of the resonant transition. These vector factors and the universal
functions are in principle different for oriented and aligned atoms.
Zh. éksp. Teor. Fiz. 111, 63–92 (January 1997) 相似文献
5.
We derive a type of kinetic equation for Kelvin waves on quantized vortex filaments with random large-scale curvature, that
describes step-by-step (local) energy cascade over scales caused by 4-wave interactions. Resulting new energy spectrum E
LN(k) ∝ k
−5/3 must replace in future theory (e.g., in finding the quantum turbulence decay rate) the previously used spectrum E
KS(k) ∝ k
−7/5, which was recently shown to be inconsistent due to nonlocality of the 6-wave energy cascade. 相似文献
6.
In the framework of a simple spin-boson Hamiltonian we study an interplay between dynamic and spectral roots to stochastic-like
behavior. The Hamiltonian describes an initial vibrational state coupled to discrete dense spectrum reservoir. The reservoir
states are formed by three sequences with rationally independent periodicities 1; 1 ± δ typical for vibrational states in
many nanosize systems (e.g., large molecules containing CH2 fragment chains, or carbon nanotubes). We show that quantum evolution of the system is determined by a dimensionless parameter
δΓ, where Γ is characteristic number of the reservoir states relevant for the initial vibrational level dynamics. When δΓ
> 1 spectral chaos destroys recurrence cycles and the system state evolution is stochastic-like. In the opposite limit δΓ
< 1 dynamics is regular up to the critical recurrence cycle k
c
and for larger k > k
c
dynamic mixing leads to quasi-stochastic time evolution. Our semi-quantitative analytic results are confirmed by numerical
solution of the equation of motion. We anticipate that both kinds of stochastic-like behavior (namely, due to spectral mixing
and recurrence cycle dynamic mixing) can be observed by femtosecond spectroscopy methods in nanosystems in the spectral window
1011–1013 s−1 相似文献
7.
O.V. Bychuk B. O'Shaughnessy N.J. Turro 《The European physical journal. E, Soft matter》2001,4(3):281-291
We propose and theoretically study an experiment designed to measure short-time polymer reaction kinetics in melts or dilute
solutions. The photolysis of groups centrally located along chain backbones, one group per chain, creates pairs of spatially
highly correlated macroradicals. We calculate time-dependent rate coefficients κ(t) governing their first-order recombination kinetics, which are novel on account of the far-from-equilibrium initial conditions.
In dilute solutions (good solvents) reaction kinetics are intrinsically weak, despite the highly reactive radical groups involved.
This leads to a generalised mean-field kinetics in which the rate of radical density decay - ∼S(t), where S(t) ∼t
- (1 + g/3) is the equilibrium return probability for 2 reactive groups, given initial contact. Here g≈ 0.27 is the correlation hole exponent for self-avoiding chain ends. For times beyond the longest coil relaxation time τ,
- ∼S(t) remains true, but center of gravity coil diffusion takes over with rms displacement of reactive groups x(t) ∼t
1/2 and S(t) ∼ 1/x
3(t). At the shortest times ( t
10-6s), recombination is inhibited due to spin selection rules and we find ∼tS(t). In melts, kinetics are intrinsically diffusion-controlled, leading to entirely different rate laws. During the regime limited
by spin selection rules, the density of radicals decays linearly, n(0) - n(t) ∼t. At longer times the standard result - ∼d
3(t)/d (for randomly distributed ends) is replaced by ∼d2x
3(t)/d
2 for these correlated initial conditions. The long-time behavior, t > τ, has the same scaling form in time as for dilute solutions.
Received 18 May 2000 相似文献
8.
Eunghyun Lee 《Journal of statistical physics》2010,140(4):635-647
In this paper we give the distribution of the position of a particle in the asymmetric simple exclusion process (ASEP) with
the alternating initial condition. That is, we find ℙ(X
m
(t)≤x) where X
m
(t) is the position of the particle at time t which was at m=2k−1, k∈ℤ at t=0. As in the ASEP with step initial condition, there arises a new combinatorial identity for the alternating initial condition,
and this identity relates the integrand of the integral formula for ℙ(X
m
(t)≤x) to a determinantal form together with an extra product. 相似文献
9.
V. Bezák 《Czechoslovak Journal of Physics》1998,48(5):529-535
The linear stochastic equation dx
β
/dt+[1+f
β
(t)]x
β
(t)=A sin (Ωt) is discussed. The functionƒ
β
(t) is defined as a Poissonian noise dependent on a parameterβ>0,ƒ
β
(t)=β Σ
j
[δ(t − t
j
+
) −δ (t − t
j
−
)]. The mean frequency of the delta-pulses is chosen asβ-dependent in the formλ(β)=2γ(β
−2 + 1) exp(−β) whereγ is a constant from the interval (0, 0.974). With the stochastic functionƒ
β
(t) defined in this way, attention is paid on the oscillational term of the averaged function 〈x(t)〉, 〈x(t)〉osc=Āsin(Ωt − α). It is found that the dependenceĀ=Ā(β) exhibits one maximum and one minimum. The occurrence of these extrema seems to affirm the presence of stochastic resonance.
This work has been supported by the Slovak Grant Agency VEGA under contract No. 1/4319/97. 相似文献
10.
Theory of non-stationary coherent effects is developed for superconductor-normal-superconductor (SNS) structures with relatively
strong normal scattering on S/N interfaces (interface resistance is large compared to intrinsic resistance of N metal). Analytical
expressions are found for the time-dependent anomalous Green’s functions induced in the N region under the fixed-voltage-bias.
The amplitude of the current oscillations is determined in non-equilibrium conditions. Non-stationary correction to the distribution
function is calculated in high-temperature limit and found to be slowly decreasing with the temperature, leading to the dominance
of the second-harmonic term in the Josephson current, I
s
(t) ∝ sin(4eVt) at high temperatures and low voltage.
The article is published in the original. 相似文献
11.
The rare t-quark decays t → cl
j
+
l
k
−
and t → cṽ
j
k
k
induced by scalar-leptoquark doublets are considered within the minimal model involving four-color quark-lepton symmetry
and the Higgs mechanism of quark and lepton mass splitting. The partial widths with respect to the decays being considered
and the total widths Γ(t → cl
+′l
−) = Σj,k Γ(t → cl
j
+
l
k
−
) and Γ(t → cl
+′l
−) = Σj,kΓ(t → cṽ
j
v
k
) with respect to, respectively, the charged leptonic and neutrino modes are calculated. It is shown that, at scalar-leptoquark
masses higher than the t-quark mass (m
S > m
t), the branching ratios for these modes are Br(t → cl
+′l
−) ≈ (3.5−0.4) × 10−5 and Br(t → cṽ′v) ≈ (7.1−0.8) × 10−5 at m
s
= 180–250 GeV and an appropriate value of the leptoquark-mixing angle (sin β ≈ 0.2) and can increase for m
S < m
t to Br(t → cl
+′l
−) ≈ 0.03−0.002 and Br(t → cl
+′l
−) ≈ 0.46−0.05 for the charged mode at m
S
= 150–170 GeV for sin β ≈ 1 and sin β ≈ 0.2, respectively. In the cases being considered, t-quark decays to pairs of charged leptons can be accessible to detection at LHC. In the last case, these decays could manifest
themselves (for example, in dilepton events) at the Tevatron as well.
Original Russian Text ? P.Yu. Popov, A.D. Smirnov, 2006, published in Yadernaya Fizika, 2006, Vol. 69, No. 6, pp. 1006–1016. 相似文献
12.
L. A. Mel’nikovskii S. A. Kriminskii 《Journal of Experimental and Theoretical Physics》1997,84(4):758-759
An external electric field changes the dispersion law of waves on the surface of a liquid. Besides the usual capillary term
(∝k
3, k is the wave number) and gravitational term (∝k), a term quadratic in the wave vector appears in the expression for the square of the frequency in a homogeneous field. These
excitations are associated with the variation of the coefficient of surface tension of the liquid at low temperatures. In
the case of a large field tangent to the surface, the correction is proportional to T
8/3, unlike the T
7/3 correction in the absence of a field.
Zh. éksp. Teor. Fiz. 111, 1369–1372 (April 1997) 相似文献
13.
Living polymers are formed by reversible association of primary units (unimers). Generally the chain statistical weight involves
a factor σ < 1 suppressing short chains in comparison with free unimers. Living polymerization is a sharp thermodynamic transition
for σ ≪ 1 which is typically the case. We show that this sharpness has an important effect on the kinetics of living polymerization
(one-dimensional association). The kinetic model involves i) the unimer activation step (a transition to an assembly-competent
state); ii) the scission/recombination processes providing growth of polymer chains and relaxation of their length distribution.
Analyzing the polymerization with no chains but unimers at t = 0 , with initial concentration of unimers M ≳ M
* (M* is the critical polymerization concentration), we determine the time evolution of the chain length distribution and find
that: 1) for M
* ≪ M ≪ M
*/σ the kinetics is characterized by 5 distinct time stages demarcated by 4 characteristic times t1, t2, t3 and t*; 2) there are transient regimes (t
1 ≲ t ≲ t
3) when the molecular-weight distribution is strongly non-exponential; 3) the chain scissions are negligible at times shorter
than t2. The chain growth is auto-accelerated for t
1 ≲ t ≲ t
2 : the cut-off chain length (= polymerization degree 〈n〉w
N
1 ∝ t
2 in this regime. 4) For t
2 < t < t
3 the length distribution is characterized by essentially 2 non-linear modes; the shorter cut-off length N1 is decreasing with time in this regime, while the length scale N2 of the second mode is increasing. (5) The terminal relaxation time of the polymer length distribution, t*, shows a sharp maximum in the vicinity of M*; the effective exponent
is as high as ∼ σ-1/3 just above M*. 相似文献
14.
The structure of stationary isotropic, homogeneous turbulence in an incompressible fluid with Re ≫ 1 set into motion by a
force with amplitude f
0 and spatial and temporal time scales of r
0 and τ
0, respectively, is examined. It is found that, depending on the magnitude of the force that sets the fluid into motion, three
fundamentally different turbulent stationary states of the fluid can develop and the dimensionless parameters responsible
for transitions from one state to another, γ=f
0
τ
0
2
/r
0 and Γ=γ
4/3 Re, are determined. It is shown that for γ≪1 and Γ≪1 a Kolmogorov spectrum with E(k)∝1/k
5/3 develops in the inertial range. During the transition to turbulent flows driven by large amplitude forces f
0, i.e., during the transition to a regime with γ≪1 and Γ ≫ 1, a segment of the spectrum with E(k)∝1/k
2 develops near the viscous range and “detaches” the Kolmogorov spectrum from the viscous range. Further increases in the amplitude
f
0 of the force, i.e., approaching the parameter range with γ≫1 and Γ≫1, causes the entire inertial range to be “occupied” by a spectrum E(k)∝1/k
2, and outside the inertial range, large scale structures with a characteristic size extending to γ
2/5
r
0 begin to be generated. In the regime with Γ≪1, the power dissipated per unit mass of fluid is independent of the viscosity,
but on going to turbulent regimes with Γ≫1, the viscous losses begin to depend on the viscosity of the fluid. The “turn-off”
of viscous dissipation for Γ≫1 shows that a drag crisis can occur simply as the source power is increased, without any further
conditions. With this method for the excitation of turbulence, the Loitsyanskii integral diverges for arbitrary values of
γ and Γ. A physical mechanism is proposed to explain the readjustment of the spectrum of the turbulent fluctuations at different
γ and Γ. These results have all been obtained neglecting intermittency.
Zh. éksp. Teor. Fiz. 116, 1630–1647 (November 1999) 相似文献
15.
I. M. Suslov 《Journal of Experimental and Theoretical Physics》2010,111(3):450-465
The previously-obtained analytical asymptotic expressions for the Gell-Mann-Low function β(g) and anomalous dimensions in the ϕ4 theory in the limit g → ∞ are based on the parametric representation of the form g = f(t), β(g) = f
1(t) (where t ∝ g
0−1/2 is the running parameter related to the bare charge g
0), which is simplified in the complex t plane near a zero of one of the functional integrals. In this work, it has been shown that the parametric representation
has a singularity at t → 0; for this reason, similar results can be obtained for real g
0 values. The problem of the correct transition to the strong-coupling regime is simultaneously solved; in particular, the
constancy of the bare or renormalized mass is not a correct condition of this transition. A partial proof has been given for
the theorem of the renormalizability in the strong-coupling region. 相似文献
16.
17.
A. A. Ovchinnikov M. Ya. Ovchinnikova E. A. Plekhanov 《Journal of Experimental and Theoretical Physics》1998,87(3):534-545
It is shown that d-symmetry superconductivity due to valence bond correlations is possible. Valence bond correlations are compatible with antiferromagnetic
spin order. In order to explictly construct a homogeneous state with the valence bond structure in the two-dimensional Hubbard
model for an arbitrary doping, we have used the variational method based on unitary local transformation. Attraction between
holes in the d-channel is due to modulation of hopping by the site population in course of the valence bond formation, and corresponding
parameters have been calculated variationally. An important factor for the gap width is the increase in the density of states
on the Fermi level due to antiferromagnetic splitting of the band. The gap width and its ratio to the T
c are 2Δ≃0.1t and 2Δ/kT
c≃4.5−4 for U/t≃8. The correspondence between the theoretical phase diagram and experimental data is discussed. The dependence of T
c on the doping δ=|n−1| and the Fermi surface shape are highly sensitive to the weak interaction t′ leading to diagonal hoppings. In the case of t′>0 and p-doping, the peak on the curve of T
c(δ) occurs at the doping δ
opt, when the energy of the flattest part of the lower Hubbard subband crosses the Fermi level at k∼(π,0). In underdoped samples with δ<δ
opt, the anisotropic pseudogap in the normal state corresponds to the energy difference |E(π,0)−μ| between this part of the spectrum and the Fermi level.
Zh. éksp. Teor. Fiz. 114, 985–1005 (September 1998) 相似文献
18.
S. Cohen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,55(1):67-74
The systematics of perturbative semiclassical quantum
defect expansions corresponding to a hydrogenic potential plus a perturbing
term of the form -A/2rκ,
k\geqslant 2\kappa \geqslant 2, are studied as a function
of expansion order N. Towards this task the expansions μ
Nare first used
as input for constructing associated N-dependent atomic RKR-QDT potential
curves. Subsequently the coordinate Fisher information for the energy levels
supported by those curves as well as its rate ε with respect to N is
semiclassically computed. Then, the plot of relative quantum defect error
between successive orders, δμ
N+1,N, with respect to ε serves as
convergence indicator for both approximate potentials and quantum defects.
For a given κ and when the quantum defect expansion proves to be of limited
accuracy the plot reveals an A- and N-dependent scatter of points and
“saturation” (the relative error remains almost constant with respect to
ε). More importantly, when ε is equal to or lower than the value of
ε (N=1) for which πμ
1\leqslant 1/2_{1}\leqslant 1/2 the relative error exhibits a κ-, A- and
N-independent power-law dependence, δμ
N+1,N∝ ε
m, clearly
distinguishing the N=1 order (m=1/2) from all other N>1 orders (m=1). These
power-laws may be employed for setting-up confidence level bounds on
perturbative expansions. 相似文献
19.
The high-velocity distribution of a two-dimensional dilute gas of Maxwell molecules under uniform shear flow is studied. First
we analyze the shear-rate dependence of the eigenvalues governing the time evolution of the velocity moments derived from
the Boltzmann equation. As in the three-dimensional case discussed by us previously, all the moments of degreek⩾4 diverge for shear rates larger than a critical valuea
c
(k)
, which behaves for largek asa
c
(k)
∼k
−1. This divergence is consistent with an algebraic tail of the formf(V) ∼V
−4-σ(a), where σ is a decreasing function of the shear rate. This expectation is confirmed by a Monte Carlo simulation of the Boltzmann
equation far from equilibrium. 相似文献
20.
C?t?lin I. Carstea 《Communications in Mathematical Physics》2010,300(2):487-528
The existence of co-rotational finite time blow up solutions to the wave map problem from ${\mathbb{R}^{2+1} \to N}The existence of co-rotational finite time blow up solutions to the wave map problem from
\mathbbR2+1 ? N{\mathbb{R}^{2+1} \to N} , where N is a surface of revolution with metric d
ρ
2 + g(ρ)2
dθ2, g an entire function, is proven. These are of the form u(t,r)=Q(l(t)t)+R(t,r){u(t,r)=Q(\lambda(t)t)+\mathcal{R}(t,r)} , where Q is a time independent solution of the co-rotational wave map equation −u
tt
+ u
rr
+ r
−1
u
r
= r
−2
g(u)g′(u), λ(t) = t
−1-ν, ν > 1/2 is arbitrary, and R{\mathcal{R}} is a term whose local energy goes to zero as t → 0. 相似文献