共查询到20条相似文献,搜索用时 187 毫秒
1.
本文讨论了三分子反应模型在1+k3A2<[1+A((k3D1)/D2)1/2]2情况下的临界行为。由于在临界点附近不稳定模式是空间均匀的,因此可由总粒子数满足的生-灭方程来讨论。我们引入了涨落波的幅度作为描述涨落分布突变的参数。在利用重整化方法迴避了定态解在临界点上涨落发散所引起的困难后,得到了描述平均密度及涨落分布临界行为的广义Landau-Ginzburg方程。解析及数值分析表明,当B增大越过临界点Bm,平均密度达到周期变化的稳态,这和反应扩散方程结果是一致的,涨落二阶矩一般也达到一周期稳态,振幅很大而且主要由平均密度振动的幅度所决定。因此从涨落分布的突变来看,Bm并不与典型的二类相变类似。
关键词: 相似文献
2.
3.
采用一维原子链模型研究了反铁磁耦合的硬磁/软磁/硬磁三层膜体系的反磁化过程. 研究结果表明,当考虑了软磁层的磁晶各向异性能后,软磁层厚度和界面交换耦合强度的改变都有可能导致软磁层的交换弹性反磁化过程由可逆过程转变为不可逆过程. 对软磁层很薄的体系,其反磁化过程是典型的可逆交换弹性反磁化过程. 然而,当软磁层厚度超过某一临界厚度tc时,反磁化过程转变为不可逆的交换弹性反磁化过程. 软磁-硬磁界面交换耦合强度Ash对反磁化行为也有很大的影响. 对于软磁层厚度小于临界厚度tc的体系,也存在一个临界界面交换耦合强度Ashc. 当Ash大于Ashc时,软磁层的反磁化过程是可逆的交换弹性反磁化过程;而当Ash小于Ashc时,这一过程变为不可逆. 给出了体系的可逆与不可逆交换弹性反磁化过程随软磁层厚度和界面交换耦合强度变化的磁相图. 同时还研究了偏转场随软磁层厚度的变化关系.
关键词:
反铁磁耦合三层膜
交换弹性反磁化过程
反磁化机理
磁相图 相似文献
4.
快速算法结合推广的Bethe公式,可以为应用研究提供便于使用的偶极激发碰撞强度和速率系数.用准相对论平面波Born(QRPB)近似计算高能区Au50+离子n0l0→nl偶极激发的碰撞强度,给出Bethe公式中动量转移截断参数k0,从而确定激发过程的高能行为.快速计算方法中采用了Cowan所发展的准相对论方法,用统一的Hartree-Fock-Slater势计算束缚和连续态电子波函数.用准相对论扭曲波(QRDW)近似计算阈值附近的碰撞强度并外推阈值处的碰撞强度Ω0,然后拟合到高能碰撞强度上.对于特殊情况还需增加三倍阈值点a的计算,用三个参数Ω0,Ωa和k0拟合出全能域(出射电子能量εb=0—∞)的碰撞强度.由此可以得到全部温度范围(电子温度Te=0—∞)的速率系数<σv>.这样得到的Ω和<σv>,在相应的感兴趣的能量和温度范围内有合理的精度.
关键词: 相似文献
5.
研究了高位振动态RbH(X1∑+,v″=15~21)与CO2碰撞转移过程.脉冲激光激发RbH至高位态,利用激光感应荧光光谱(LIF)得到RbH(X1∑+,v″)与CO2的猝灭速率系数kv″(CO2),kv″=21(CO2)=2.7kvn=15(CO2).利用激光泛频光谱技术,测量了CO2(000,J)高转动态分布,得到了转动温度,从而获得了平均转动能rot>和转动能的变化<△Erot>,发现<△Erot>v″=21≈2.9<△Erot>v″=15.对于v″=16,证实了振动—振动能量转移的4-1近共振过程.在一次碰撞条件下,通过速率方程分析,得到RH(v″)-CO2振转速率系数.对于v″=15,J=32-48,速率系数在1.25-0.33×10-13cm3s-1.之间;对于v″=21,速率系数在2.47-1.53×10-13cm3s-1之间,其能量相关性是明显的. 相似文献
6.
激发态Na2与H2碰撞,使H2(V=3,J=3)得到布居,在H2和He总气压为800 Pa及温度为700 K的条件下,利用相干反斯托克斯拉曼散射(CARS)光谱技术研究了H2(3,3)与H2(He)间转动能量转移过程.改变CARS激光束与激发Na2的激光之间的延迟时间,测量He不同摩尔配比时H2(3,J)态CARS谱强度的时间演化,得到H2(3,3)的总弛豫速率系数分别为k3,3H2=(21士5)×10-3cm3·s-1和k3,3He=(5.6士1.6)×10-13cm3·s-1.测量H2(3,J)各转动态的相对CARS谱强度,由速率方程分析,得到H2(3,3)+H2→H2(3,J)+H2中,对于J=2,4,转移速率系数分别为(11±4)×10-13cm3·s-1和(8.2±3.1)×10-13cm3·s<sup>-1.在H2(3,3)+He→H2(3,J)+He中,对于J=2,4,转移速率系数分别为(3.1±1.2)×10-13cm3·s-1和(2.1士0.7)×1013cm3·s-1.对于H2(3,3),单量子弛豫|△J|=1约占该态总弛豫率的90%. 相似文献
7.
8.
利用含时量子波包动力学理论在HLi2 基态势能面上研究了H+Li2 → LiH+Li 反应的动力学性质. 计算得到了体系在0-0.4 eV 范围内J = 0 不同振动量子数(v = 0, 1, 2, 3), v = 0 不同转动量子数(J = 0, 5, 10,15) 下的反应概率、积分反应截面和热速率常数, 在此基础上讨论了释能反应的反应阈能随总角动量量子数的变化规律以及振动量子数对反应概率的影响等问题. 研究发现, 随着转动量子数的增大, 反应阈能也在逐渐增大; 然而随着振动量子数的增大, 由于反应为释能反应, 反应发生的概率却在逐渐减小. 分析了碰撞能对积分散射截面的影响以及温度对反应速率常数影响的规律. 相似文献
9.
10.
11.
The possibility of a periodic phase in the ferromagnetic superconductors is pointed out. The critical temperature Tp which is less than Tm0, the magnetic Curie temperature in the normal state, and the wave number kp are estimated. The characteristic nature of this phase is discussed. 相似文献
12.
Surface magnetoelastic Love waves and nonuniform distributions of the magnetization and elastic strains are investigated in
a uniaxial ferromagnetic film on a massive nonmagnetic substrate in a tangential external magnetic field. A new inhomogeneous
phase is predicted having spatial modulation of the order parameter, arising from magnetostrictive coupling of the magnetization
with lattice strains near the interface of the magnetoelastic and elastic media. It is shown that, at some critical magnetic
field H
c, different from the orientational transition field in an isolated sample, a magnetoelastic Love wave propagating parallel
to the magnetization vector in the film plane becomes unstable. The frequency and group velocity of the wave vanish at wave
number k=k
c≠0 and the wave freezes, forming a domain structure localized in the film and adjoining substrate.
Fiz. Tverd. Tela (St. Petersburg) 41, 665–671 (April 1999) 相似文献
13.
《Physica A》1996,229(2):147-165
The spatiotemporal evolution and memory retrieval properties of a Hopfield-like neural network with cycle-stored patterns and finite connectivity are studied. The analytical studies on a mean-field version show that, given the number of stored patterns p, there is a critical connectivity kc such that the retrieval states are stable fixed points if and only if k > kc. The dependence of kc on the number of stored patterns is also present. The numerical simulations are applied to the short-ranged model with local interaction. It is revealed that, given p, the memory retrieval function is kept if the connectivity is high enough while the dynamics of the system is in the frozen phase. However when the connectivity k is less than a critical value kc the system is in the chaotic phase and loses its memory retrieval ability. The critical points of both the dynamical phase transition and memory-loss phase transition are obtained by simulation data. 相似文献
14.
H. Chamati D.M. Dantchev 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(1):89-99
The finite size behavior of the susceptibility, Binder cumulant and some even moments of the magnetization of a fully finite
O(n) cubic system of size L are analyzed and the corresponding scaling functions are derived within a field-theoretic ɛ-expansion scheme under periodic
boundary conditions. We suppose a van der Waals type long-range interaction falling apart with the distance r as r
- (d + σ), where 2 < σ < 4, which does not change the short-range critical exponents of the system. Despite that the system belongs
to the short-range universality class it is shown that above the bulk critical temperature T
c the finite-size corrections decay in a power-in-L, and not in an exponential-in-L law, which is normally believed to be a characteristic feature for such systems.
Received 8 August 2001 相似文献
15.
Fast-time instability for diffusion flames, with Lewis numbers set equal for fuel and oxidizer but greater than unity, is numerically analysed by the activation energy asymptotics and Evans function method. The time and length scales being chosen to be those of the inner reactive–diffusive layer, the problem corresponds to the instability problem for the Liñán's diffusion-flame regime. The instability is primarily oscillatory and emerges prior to reaching the turning point of the characteristic C-curve, usually known as the Liñán's extinction condition. A critical Lewis number, L c , is also found, across which the instability changes its qualitative character. Below L c , the instability possesses primarily a pulsating nature in that the two real branches of the dispersion relation existing for small wave numbers merge at a finite wave number, from which a pair of complex conjugate branches bifurcate. The maximum growth rate is found at the zero wave number. For Lewis numbers greater than L c , the eigensolution branch for small reactant leakages is found to be purely complex with the maximum growth rate found at a finite wave number, thereby exhibiting a travelling nature. As the reactant-leakage parameter is further increased, the instability characteristics turns into a pulsating type, similar to that for 1 < L < L c . The switching between different instability characters is found to correspond to the Bogdanov-Takens bifurcation. 相似文献
16.
Numerical study of the influence of the distribution of pinning centres on the dynamics of a two-dimensional vortex system is performed. The superconductor sample has a periodic structure with a pinned region of length Lp and an unpinned region of length Lx-Lp along the direction of driving force (Lorentz force). Results show that, at zero temperature, the critical force Fc increases with the increase of Lp, indicating that the homogeneity of pinning centres helps to enhance the critical electric current of the superconductor. At large driving forces, vortex static channels form in the pinned region even for Lpx. 相似文献
17.
We investigate quantum dynamics of vibrational excitations in one-dimensional (1D) molecular chain. Our model includes nearest
neighbor interaction between identical molecular sites and one impurity atom placed in the middle (n = 0). We show that upon exciting the impurity site, its excess energy for relatively long for molecular scales time up to
100 ps is not redistributed uniformly among all other degrees of freedom. On the contrary an excitation propagates along the
chain, reflected from the chain ends, and quantum interference of these waves yields to recurrence cycles and echo phenomena.
For a critical cycle number k
c
, echo components of the neighboring cycles start to overlap, and eventually for k ≫ k
c
dynamics looks like chaotic one. The critical cycle number k
c
depends on the coupling strength 0 ≤ C ≤ 1 of the impurity site with its neighbors n = ±1. k
c
achieves the maximum for C
2 = 1/2. Our results are in qualitative agreement with experimental data on vibrational excitations in various (CH2)
n
molecular chains, and besides offer a way for loss-free energy transfer between separated in space reaction centers. 相似文献
18.
The finite-size scaling analysis of the density distribution function of subsystems of a system studied at constant total density is studied by a comparative investigation of two models: (i) the nearest-neighbor lattice gas model on the square lattice, choosing a total lattice size of 64×64 sites. (ii) The two-dimensional off-lattice Lennard-Jones system (truncated at a distance of 2.5 σ, σ being the range parameter of the interaction) withN=4096 particles, applying the NVT ensemble. In both models, the density distribution functionP L (ρ) is obtained forL×L subsystems for a wide range of temperaturesT, subblock linear dimensionsL and average densities <ρ>. Particular attention is paid to the question whether accurate estimates of critical temperatureT c and critical density ρ c can be obtained. In the lattice gas model these critical parameters are known exactly and the limitations of the approach can thus be definitively asserted. The final estimates for the Lennard Jones problem areT c =0.47±0.01 (in units of the Lennard Jones energy ε) and ρ c (in units of σ2), a comparison with previous estimates is made. 相似文献
19.
A quantum dynamical problem has been analytically solved for a two-level system where localized states L
0 and R
0 are strongly coupled with reservoirs of local oscillations {L
n
} and {R
n
}. It is additionally assumed that the spectra of reservoirs are equidistant and the coupling constants are the same. It has
been shown that the evolution of states L
0 and R
0 in recurrence cycles depends on three independent factors, which characterize exchange with the two-level system, exchange
of L
0 with {L
n
} (R
0 with {R
n
}) and the phonon-induced decay of {L
n
} and {R
n
}. In addition to coherent oscillations with the frequency of the two-level system, Δ, and dissipative tunneling with a rate
Δ2/πC
2 (where C is the matrix element of the coupling of L
0 and R
0 with L
n
and R
n
), a new regime appears where L-R transitions are induced by the partial recovery of the populations of L
0 and R
0 in each recurrence cycle due to synchronous transitions from reservoirs. These transitions induce repeating changes in the
populations of the states of the two-level system (Loschmidt echo). The number and width of the echo components increase with
the cycle number. Evolution becomes irregular because of the mixing of the contributions from pulses of the neighboring cycles,
when the cycle number k exceeds the critical value k
c = π2
C
2. Unlike the populations, their cycle-average values remain regular at k ≫ k
c. When Δ ≪ πC
2, the cycle-average populations oscillate with a frequency of ΔΩ/πC
2 irrespective of mixing. The frequency of oscillations of the populations of the states {L
n
} and {R
n
} is approximately nΩ(Δ/2πC
2)2, where Ω is the spacing between the neighboring levels of the reservoir and nΩ is the difference between the energies of the states L
0 and L
n
. The appearance of the mentioned low-frequency oscillations is due to the formation of collective states of the two-level
system that are “dressed” by the reservoir. The predicted oscillations can be detected by femtosecond spectroscopy methods. 相似文献
20.
The energy and the specific heat of the four-dimensional U(1) lattice gauge model is evaluated by Monte Carlo simulations on lattices of size L4, where L = 4, 5 and 6, evidence is presented for the occurence of a second-order phase transition. A finite size scaling analysis of our results gives the critical value of the coupling constant e2c = 0.995 and a correlation length exponent . 相似文献