共查询到19条相似文献,搜索用时 250 毫秒
1.
Stochastic resonance in a time-delayed asymmetric bistable system with mixed periodic signal 下载免费PDF全文
This paper studies the phenomenon of stochastic resonance
in an asymmetric bistable system with time-delayed feedback and
mixed periodic signal by using the theory of signal-to-noise ratio
in the adiabatic limit. A general approximate Fokker--Planck
equation and the expression of the signal-to-noise ratio are derived
through the small time delay approximation at both fundamental
harmonics and mixed harmonics. The effects of the additive noise
intensity $Q$, multiplicative noise intensity $D$, static asymmetry
$r$ and delay time $\tau$ on the signal-to-noise ratio are
discussed. It is found that the higher mixed harmonics and the
static asymmetry $r$ can restrain stochastic resonance, and the
delay time $\tau $ can enhance stochastic resonance. Moreover, the
longer the delay time $\tau $ is, the larger the additive noise
intensity $Q$ and the multiplicative noise intensity $D$ are, when
the stochastic resonance appears. 相似文献
2.
We propose a strategy updating mechanism based on pursuing the highest average payoff to investigate the prisoner's dilemma game and the snowdrift game. We apply the new rule to investigate cooperative behaviours on regular, small-world, scale-free networks, and find spatial structure can maintain cooperation for the prisoner's dilemma game. fn the snowdrift game, spatial structure can inhibit or promote cooperative behaviour which depends on payoff parameter. We further study cooperative behaviour on scale-free network in detail. Interestingly, non-monotonous behaviours observed on scale-free network with middle-degree individuals have the lowest cooperation level. We also find that large-degree individuals change their strategies more frequently for both games. 相似文献
3.
In this paper, we have improved the calculation of the relic
gravitational waves (RGW) in two aspects. First, we investigate the
transfer function by taking into consideration the
redshift-suppression effect, the accelerating expansion effect, the
damping effect of free-streaming relativistic particles, and the
damping effect of cosmic phase transition, and give a simple
approximate analytic expression, which clearly illustrates the
dependence on the cosmological parameters. Second, we develop a
numerical method to calculate the primordial power spectrum of RGW in
a very wide frequency range, where the observed constraints on
$n_{\rm s}$ (the scalar spectral index) and $P_{\rm S}(k_0)$ (the
amplitude of primordial scalar spectrum) and the Hamilton--Jacobi
equation are used. This method is applied to two kinds of
inflationary models, which satisfy the current constraints on $n_{\rm
s}$, $\alpha$ (the running of $n_{\rm s}$) and $r$ (the
tensor--scalar ratio). We plot them in the $r-{\it\Omega}_{\rm g}$
diagram, where ${\it\Omega}_{\rm g}$ is the strength of RGW, and
study their measurements from the cosmic microwave background (CMB)
experiments and laser interferometers. 相似文献
4.
The transfer of the quantum correlation from two-mode nonclassical state field to the supercurrents in two distant SQUID rings 下载免费PDF全文
We have considered two distant mesoscopic superconducting quantum
interference device (SQUID) rings A and B in the presence of two-mode
nonclassical state fields and investigated the correlation of the
supercurrents in the two rings using the normalized correlation
function $C_{\rm AB}$. We show that when the parameter $\alpha$ is
very small for the separable state with the density matrix $\hat
{\rho } = (\left| {\alpha , - \alpha } \right\rangle \left\langle
{\alpha , - \alpha } \right| + \left| { - \alpha ,\alpha }
\right\rangle \left\langle { - \alpha ,\alpha } \right|) / 2$ and
entangled coherent state (ECS) $\left| u \right\rangle = N_1 (\left|
{\alpha , - \alpha } \right\rangle + \left| { - \alpha ,\alpha }
\right\rangle )$ fields, the dynamic behaviours of the normalized
correlation function $C_{\rm AB}$ are similar, but it is quite
different for the entangled coherent state $\left| {u}'
\right\rangle = N_2 (\left| {\alpha , - \alpha } \right\rangle -
\left| { - \alpha ,\alpha } \right\rangle )$ field. When the
parameter $\alpha $ is very large, the dynamic behaviours of $C_{\rm
AB}$ are almost the same for the separable state, entangled coherent
state $\left| u \right\rangle $ and $\left| {u}' \right\rangle $
fields. For the two-mode squeezed vacuum state field the maximum of
$C_{\rm AB}$ increases monotonically with the squeezing parameter
$r$, and as $r \to \infty $, $C_{\rm AB} \to 1$. This means that the
supercurrents in the two rings A and B are quantum mechanically
correlated perfectly. It is concluded that not all the quantum
correlations in the two-mode nonclassical state field can be
transferred to the supercurrents; and the transfer depends on the
state of the two-mode nonclassical state field prepared. 相似文献
5.
Spatial snowdrift game in heterogeneous agent systems with co-evolutionary strategies and updating rules 下载免费PDF全文
We propose an evolutionary snowdrift game model for heterogeneous systems with two types of agents, in which the inner-directed agents adopt the memory-based updating rule while the copycat-like ones take the unconditional imitation rule; moreover, each agent can change his type to adopt another updating rule once the number he sequentially loses the game at is beyond his upper limit of tolerance. The cooperative behaviors of such heterogeneous systems are then investigated by Monte Carlo simulations. The numerical results show the equilibrium cooperation frequency and composition as functions of the cost-to-benefit ratio r are both of plateau structures with discontinuous steplike jumps, and the number of plateaux varies non-monotonically with the upper limit of tolerance vTas well as the initial composition of agents fa0.Besides, the quantities of the cooperation frequency and composition are dependent crucially on the system parameters including vT, fa0, and r. One intriguing observation is that when the upper limit of tolerance is small, the cooperation frequency will be abnormally enhanced with the increase of the cost-to-benefit ratio in the range of 0 < r < 1/4. We then probe into the relative cooperation frequencies of either type of agents, which are also of plateau structures dependent on the system parameters. Our results may be helpful to understand the cooperative behaviors of heterogenous agent systems. 相似文献
6.
Evolutionary prisoner’s dilemma on Newman-Watts social networks with an asymmetric payoff distribution mechanism 下载免费PDF全文
In this paper, we introduce an asymmetric payoff
distribution mechanism into the evolutionary prisoner's dilemma game
(PDG) on Newman--Watts social networks, and study its effects on the
evolution of cooperation. The asymmetric payoff distribution
mechanism can be adjusted by the parameter α: if α>0,
the rich will exploit the poor to get richer; if α<0, the
rich are forced to offer part of their income to the poor.
Numerical results show that the cooperator frequency monotonously
increases with α and is remarkably promoted when α>0.
The effects of updating order and self-interaction are also
investigated. The co-action of random updating and self-interaction
can induce the highest cooperation level. Moreover, we employ the Gini
coefficient to investigate the effect of asymmetric payoff
distribution on the the system's wealth distribution. This work may
be helpful for understanding cooperative behaviour and wealth
inequality in society. 相似文献
7.
In this paper, we have introduced a shell-model of Kraichnan's passive
scalar problem. Different from the original problem, the prescribed
random velocity field is non-Gaussian and $\delta$ correlated in
time, and its introduction is inspired by She and L\'{e}v\^{e}que (Phys. Rev. Lett.
{\bf 72}, 336 (1994)). For comparison, we also give the passive
scalar advected by the Gaussian random velocity field. The
anomalous scaling exponents $H(p)$ of passive scalar advected by
these two kinds of random velocities above are determined for
structure function with values of $p$ up to 15 by Monte Carlo simulations of the
random shell model, with Gear methods used to solve the stochastic
differential equations. We find that the $H(p)$ advected by
the non-Gaussian random velocity is not more anomalous than that
advected by the Gaussian random velocity. Whether the advecting
velocity is non-Gaussian or Gaussian, similar scaling exponents of
passive scalar are obtained with the same molecular diffusivity. 相似文献
8.
Adaptive co-evolution of strategies and network leading to optimal cooperation level in spatial prisoner’s dilemma game 下载免费PDF全文
We study evolutionary prisoner's dilemma game on adaptive
networks where a population of players co-evolves with their
interaction networks. During the co-evolution process, interacted
players with opposite strategies either rewire the link between them
with probability $p$ or update their strategies with probability
$1-p$ depending on their payoffs. Numerical simulation shows that
the final network is either split into some disconnected communities
whose players share the same strategy within each community or forms
a single connected network in which all nodes are in the same
strategy. Interestingly, the density of cooperators in the final
state can be maximised in an intermediate range of $p$ via the
competition between time scale of the network dynamics and that of
the node dynamics. Finally, the mean-field analysis helps to
understand the results of numerical simulation. Our results may
provide some insight into understanding the emergence of cooperation
in the real situation where the individuals' behaviour and their
relationship adaptively co-evolve. 相似文献
9.
A chiral quark-model approach is extended to the study of the
$\bar{K}N$ scattering at low energies. The process of
$K^-p\rightarrow \Sigma^0\pi^0$ at $P_K\lesssim 800$ MeV/c (i.e. the
center mass energy $W\lesssim 1.7$ GeV) is investigated. The
$\Lambda(1405)S_{01}$ dominates the reactions over the energy region
considered here. Around $P_K\simeq 400$ MeV/c, the
$\Lambda(1520)D_{03}$ is responsible for a strong resonant peak in
the cross section. Our analysis suggests that there exist
configuration mixings within the $\Lambda(1405)S_{01}$ and
$\Lambda(1670)S_{01}$ as admixtures of the
$[\textbf{70},^2\textbf{1},1/2]$ and
$[\textbf{70},^2\textbf{8},1/2]$ configurations. The
$\Lambda(1405)S_{01}$ is dominated by
$[\textbf{70},^2\textbf{1},1/2]$, and $\Lambda(1670)S_{01}$ by
$[\textbf{70},^2\textbf{8},1/2]$. The non-resonant background
contributions, i.e. $u$-channel and $t$-channel, also play important
roles in the explanation of the angular distributions due to
amplitude interferences. 相似文献
10.
Prisoner's Dilemma Game on Clustered Scale-Free Networks under Different Initial Distributions 下载免费PDF全文
The evolutionary prisoner's dilemma game is investigated under different initial distributions for cooperators and defectors on scale-free networks with a tunable clustering coefficient. It is found that, on the one hand, cooperation can be enhanced with the increasing clustering coefficient when only the most connected nodes are occupied by cooperators initially. On the other hand, if cooperators just occupy the lowest-degree nodes at the beginning, then the higher the value of the clustering coefficient, the more unfavorable the environment for cooperators to survive for the increment of temptation to defect. Thereafter, we analytically argue these nontrivial phenomena by calculating the cooperation probability of the nodes with different degrees in the steady state, and obtain the critical values of initial frequency of cooperators below which cooperators would vanish finally for the two initial distributions. 相似文献
11.
Using a single-mode approximation, we carry out the entanglement measures, e.g., the negativity and von Neumann entropy when a tetrapartite generalized GHZ state is treated in a noninertial frame, but only uniform acceleration is considered for simplicity. In terms of explicit negativity calculated, we notice that the difference between the algebraic average $\pi_{4}$ and geometric average $\varPi_{4}$ is very small with the increasing accelerated observers and they are totally equal when all four qubits are accelerated simultaneously. The entanglement properties are discussed from one accelerated observer to all four accelerated observers. It is shown that the entanglement still exists even if the acceleration parameter $r$ goes to infinity. It is interesting to discover that all 1-1 tangles are equal to zero, but 1-3 and 2-2 tangles always decrease when the acceleration parameter $r$ increases. We also study the von Neumann entropy and find that it increases with the number of the accelerated observers. In addition, we find that the von Neumann entropy $S_{\text{ABCDI}}$, $S_{\text{ABCIDI}}$, $S_{\text{ABICIDI}}$ and $S_{\text{AIBICIDI}}$ always decrease with the controllable angle $\theta$, while the entropies $S_{3-3~\rm non}$, $S_{3-2~\rm non}$, $S_{3-1~\rm non}$ and $S_{3-0~\rm non}$ first increase with the angle $\theta$ and then decrease with it. 相似文献
12.
Takamichi Terao 《The European Physical Journal B - Condensed Matter and Complex Systems》2016,89(10):209
The hopping electron model on the Kagome lattice was investigated by kinetic Monte Carlo simulations, and the non-equilibrium nature of the system was studied. We have numerically confirmed that aging phenomena are present in the autocorrelation function \hbox{$C \, \left({t,t_{W} } \right)$}C?t,tW)( of the electron system on the Kagome lattice, which is a geometrically frustrated lattice without any disorder. The waiting-time distributions \hbox{$p\left(\tau \right)$}pτ)( of hopping electrons of the system on Kagome lattice has been also studied. It is confirmed that the profile of \hbox{$p\, \left(\tau \right)$}p?τ)( obtained at lower temperatures obeys the power-law behavior, which is a characteristic feature of continuous time random walk of electrons. These features were also compared with the characteristics of the Coulomb glass model, used as a model of disordered thin films and doped semiconductors. This work represents an advance in the understanding of the dynamics of geometrically frustrated systems and will serve as a basis for further studies of these physical systems. 相似文献
13.
A. Kobakhidze L. Mersini-Houghton 《The European Physical Journal C - Particles and Fields》2007,49(3):869-873
We show that a unique, most probable and stable solution for the wavefunction of the universe, with a very small cosmological
constant , can be predicted from the supersymmetric minisuperspace with N vacua of the landscape of string theory without referring
to the anthropic principle. Due to the nearest neighbor tunneling in moduli space lattice, the N-fold degeneracy of the vacua
is lifted and a discrete spectrum of bound state levels over the whole minisuperspace emerges. Supersymmetry is spontaneously
broken by these bound states, with discrete non-zero energy levels , s=1,2,...
PACS 98.80.Qc; 11.25.Wx 相似文献
14.
A straightforward method for calculating the quantum-field functions in terms of the Yang–Mills gauge theory is proposed. The Green functions of a free gluon in the n μ $n_\mu \dot A_\mu = 0{\text{ }}and{\text{ }}\partial _\mu \dot A_\mu = 0$ gauges are calculated using the method. New formulas are derived that have no analogy in the literature. 相似文献
15.
This paper presents a model to describe alternating current (AC) conductivity of DNA sequences, in which DNA is considered as a one-dimensional (1D) disordered system, and electrons transport via hopping between localized states. It finds that AC conductivity in DNA sequences increases as the frequency of the external electric field rises, and it takes the form of σac (ω)~ω 2\ln 2(1/ω). Also AC conductivity of DNA sequences increases with the increase of temperature, this phenomenon presents characteristics of weak temperature-dependence. Meanwhile, the AC conductivity in an off-diagonally correlated case is much larger than that in the uncorrelated case of the Anderson limit in
low temperatures, which indicates that the off-diagonal correlations in DNA sequences have a great effect on the AC conductivity, while at high temperature the off-diagonal correlations no longer play a vital role in electric transport. In addition, the proportion of nucleotide pairs p also plays an important role in AC electron
transport of DNA sequences. For p < 0.5, the conductivity of DNA sequence decreases with the increase of p, while for p ≥ 0.5, the conductivity increases with the increase of p. 相似文献
16.
We prove that AB site percolation occurs on the line graph of the square lattice when $p \in (1 - \sqrt {1 - p_c } ,\sqrt {1 - p_c } )$ , where p c is the critical probability for site percolation in $\mathbb{Z}^2$ . Also, we prove that AB bond percolation does not occur on $\mathbb{Z}^2$ for p = $\frac{1}{2}$ . 相似文献
17.
18.
SUPERCONDUCTING TRANSITION TEMPERATURES AND NORMAL-STATE ELECTRICAL RESISTIVITIES OF Tm1-xPrxBa2Cu3O7-δ 下载免费PDF全文
曹效文 《物理学报(海外版)》1994,3(8):583-588
Superconducting transition temperature Tc and normal-state electrical resistivities ρ of the Tm1-xPrxBa2Cu3O7-δ system have been measured. The results indicate that Tc remains constant for x = 0 to 0.08 before it drops steadily with higher x. Following the Abrikosov-Gor'kov model, a total suppression of superconductivity occurs at a critical Pr concentration xcr≈0.56. It is found for the first time, as far as we know, that the logarithmic resistivity at 270 K increases linearly with increasing x, yielding ρ= ρ0eax. Judging from the relation between dρ/dT and x, a metal to insulator transition occurs just beyond xcr. 相似文献
19.
Theoretical calculation of the quadratic Zeeman shift coefficient of the 3P0o clock state for strontium optical lattice clock 下载免费PDF全文
Benquan Lu 《中国物理 B》2022,31(4):43101-043101
In the weak-magnetic-field approximation, we derived an expression of quadratic Zeeman shift coefficient of $^3P^{\rm o}_0$ clock state for $^{88}$Sr and $^{87}$Sr atoms. By using this formula and the multi-configuration Dirac-Hartree-Fock theory, the quadratic Zeeman shift coefficients were calculated. The calculated values $C_2$ = $-23.38(5)$ MHz/T$^2$ for $^{88}$Sr and the $^3P^{\rm o}_0$, $F = 9/2$, $M_F = \pm9/2$ clock states for $^{87}$Sr agree well with the other available theoretical and experimental values, especially the most accurate measurement recently. In addition, the calculated values of the $^3P^{\rm o}_0$, $F = 9/2$, $M_F = \pm9/2$ clock states were also determined in our $^{87}$Sr optical lattice clock. The consistency with measurements verifies the validation of our calculation model. Our theory is also useful to evaluate the second-order Zeeman shift of the clock transition, for example, the new proposed $^1S_0$, $F = 9/2$, $M_F = \pm5/2$-${}^3P^{\rm o}_0$, $F = 9/2$, $M_F = \pm3/2$ transitions. 相似文献