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本文提出了一种关于一维和二维量子自旋系统的Monte Carlo模拟新算法。具体给出了对于一维和二维Heisenberg模型的计算方案。在s=1/2的铁磁和反铁磁链情况下的计算结果证实了此方法有效地克服了“临界慢化(CSD)”效应和能够达到更低的温度区域进行计算。该方法可推广到各向异性和高自旋(s=1,3/2,…)量子系统、二维经典8-顶角格点模型和低维费密系统。
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三角格点基底上磁性分形团簇形貌演化规律 总被引:1,自引:1,他引:0
在扩散限制凝聚模型基础上引入粒子的自旋自由度,将磁耦合系数扩展为随自旋间距离幂次变化的非常数项J/ra,采用Monte Carlo方法研究在二维三角格点基底上具有幂次相互作用的磁性团簇形貌及其分形维数Df的演化规律.模拟结果表明,对于较大的幂指数α值,即α≥5时,团簇形貌随耦合参数J的变化较小,其分形维数Df在1.50~1.70之间;随着α值的减小,团簇形貌随参数J有一明显的演化过程,在模拟范围内,分形维数Df在1.20~1.90之间. 相似文献
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利用维数正规化方法,通过到单圈的明显计算,证明了包含重轻子的无Adler-Bell-Jackiw(ABJ)反常的SU(2)_L×U(1)_Y模型中的轴矢Ward恒等式的成立性是与γ_5的两个在n维中的定义无关的。它的一个自然的推论是维数正规化方法适用于我们的有轴矢耦合费米子的模型。当把AVV三角形嵌入到轴矢费米子顶角中时,发现在n→4的物理极限下它并不会引起任何新的有限的反常,从而至少到两圈的水平证明了Frampton有关存在新的与质量相关的反常的猜测在我们的非Abel情况下同样是不成立的。 相似文献
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光子数分束攻击对星地量子密钥分配系统安全的影响 总被引:2,自引:1,他引:1
由于仪器设备性能的不完美和信道传输损耗的存在,光子数分束(PNS)攻击对采用弱相干脉冲(WCP)光源的量子密钥分配(QKD)系统的安全性构成重大威胁.以基于WCP光源的星地QKD系统为研究对象,推导了在PNS攻击者采用最佳窃听策略进行窃听时,保证密钥绝对安全的最大天顶角和可采用的平均光子数之间的关系.理论分析和计算结果表明,星地QKD系统的最大安全传输天顶角和可使用的平均光子数等重要系统参数的取值上限均受PNS攻击的限制,最终系统的密钥交换速率和系统容量受到限制.对星地QKD系统的传输容量来说,天顶角和平均光子数是一对矛盾的影响因素.提供了一种对实际星地QKD系统的天顶角和平均光子数参数进行估算的方法. 相似文献
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本文根据含复合场的Wark-Takahashi恒等式所得到的费米子质量谱,利用虚时温度场论计算了准确到1/N阶的费米子和σ介子的顶角修正,并讨论了顶角函数随温度的变化关系和退耦合相变.结果表明:退耦合相变的临界温度随着零下π介子和费米质量的增大而升高,由热涨落对顶角修正所引起的费米子质量的改变不能忽略. 相似文献
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采用πN作用的赝标 (PS)耦合和赝矢 (PV)耦合两种形式 ,计算了J/ ψ→NNπ衰变中核子极点图的贡献 ,并加入各种强子顶角形状因子 ,考察它们的离壳效应。 相似文献
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The critical behaviour of conductivity for some two-dimensional fractals is studied by experiments. The results show that the conductivity exponent is fractal dimensionality dependent with exponential scaling behaviour but is fractal material independent. 相似文献
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B. Widom 《Molecular physics》2013,111(3):657-671
From a study of the liquid-vapour equilibrium at low temperatures in the lattice-gas and penetrable-sphere models it is concluded that the phase transformation can occur as soon as the dimensionality of the fluid exceeds one, even if, formally, by a small, non-integral amount. A hypothetical fluid of dimensionality s only slightly greater than 1 is defined through its cluster integrals, and its thermodynamic properties are deduced. It is found that its behaviour is identical to that of a one-dimensional system for temperatures above some critical temperature T c (with T c →0 as s →1), while for temperatures below T c its behaviour is that of a two-phase system of dimensionality s greater than 1. 相似文献
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Franz Wegner 《Zeitschrift für Physik B Condensed Matter》1979,35(3):207-210
An apparently overlooked symmetry of the disordered electron problem is derived. It yields the well-known Ward-identity connecting the one- and two-particle Green's function. This symmetry and the apparent shortrange behaviour of the averaged one-particle Green's function are used to conjecture that the critical behaviour near the mobility edge coincides with that of interacting matrices which have two different eigenvalues of multiplicity zero (due to replicas). As a consequence the exponents of the d.c. conductivity is expected to approach 1 for real matrices and 1/2 for complex matrices as the dimensionality of the system approaches two from above. In two dimensions no metallic conductivity is expected. 相似文献
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S. Y. Huang J. J. Liang S. Y. Hsu L. K. Lin T. C. Tsai S. F. Lee 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,79(2):153-162
A direct determination of the interfacial transparency on the basis of
current-perpendicular-to-plane (CPP) resistances for Cu0.5Ni0.5/Nb layered system is
presented. This particular realization has substantial significance for understanding the
interfacial transport in such heterostructures. The unexpected large critical thickness for this
weak ferromagnetic containing system can be attributed to the strong pair-breaking effect as a
result of the high interfacial transparency. Besides, the strong pair-breaking also plays a
decisive role in the occurrence of the dimensionality crossover of the temperature dependent upper
critical magnetic field. 相似文献
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The critical behaviour of thin films containing quenched random impurities and inhomogeneities is investigated by the renormalization-group method to the one-loop order within the framework of the n-component φ4-model. The finite-size crossover in impure films has been considered on the basis of the fundamental relationship between the effective dimensionality Deff and the characteristic lengths of the system. The fixed points, their stability properties and the critical exponents are obtained and analyzed, using an
-expansion near the effective spatial dimensionality Deff of the fluctuation modes in D-dimensional hyperslabs with two types of quenched impurities: point-like impurities with short-range random correlations and extended (linear) impurities with infinite-range random correlations along the small-size spatial direction. The difference between the critical properties of infinite systems and films is demonstrated and investigated. A new critical exponent, describing the scaling properties of the thickness of films with extended impurities has been derived and calculated. A special attention is paid to the critical behaviour of real impure films (D=3). 相似文献
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S.N. Dorogovtsev 《Physics letters. A》1980,76(2):169-170
The critical behaviour of magnets with non-zero-dimensional defects is investigated by the renormalization group method. Expansions of the critical exponents in the small parameters ? and ?d are obtained, where ?d is the defect dimensionality. The corresponding renormalization group equations are shown to possess a focus-type fixed point. 相似文献
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In this paper we discuss the nature of the ion conduction pathways in LixRb1−xPO3 glasses. Our investigations are based on a bond valence analysis of reverse Monte Carlo (RMC) produced structural models
in quantitative agreement with neutron and X-ray diffraction data. In a previous letter [11] we have shown that this approach
enables us to reproduce and understand the mixed alkali effect (MAE) directly from the structural models. The results have
shown that the drastic drop of the conductivity for an intermediate composition (x ≈ 0.5) is mainly caused due to the blocking
by immobile unlike cations, which is highly effective since the two types of alkali ions are randomly mixed and have distinctly
different conduction pathways of low dimensionality. Here, we explore the local dimensionality of the pathways and discuss
its implications for the network of pathways and the related ionic conductivity.
Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004. 相似文献
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N. Nishida M. Yamaguchi T. Furubayashi K. Morigaki H. Ishimoto K. Ono 《Solid State Communications》1982,44(2):305-309
Electrical conductivity of metallic amorphous Si1?xAux films was measured down to 10 mK. Superconducting transition was observed in a certain range of Au content. In the normal state, the temperature variation of electrical conductivity showed √T-dependence at higher temperatures and ln T-dependence at lower temperatures. This crossover is interpreted as being due to a change of sample dimensionality. 相似文献
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H. E. Roman 《Phase Transitions》2013,86(2):435-461
Dispersed ionic conductors are random mixtures of a solid salt, e.g. AgI, LiI, with fine particles of an insulating second phase, like Al2O3 or SiO2. These composites can show a dramatic increase in ionic conductivity compared to the pure homogeneous system. Generally, this observation is attributed to an increased conductivity along the internal interface between the conducting salt and the insulating material. In this work a three-component random resistor network (RRN) model for dispersed ionic conductors is reviewed. In the model, the ionic conductor is represented by normally conducting bonds, the insulating material by non-conducting bonds and the interface between the two phases by highly conducting bonds. A special feature of the model is the existence of two critical concentrations of the insulating phase, p′c and p″c , for interface percolation and bulk conduction, respectively, where critical transport properties corresponding to conductor/superconductor and conductor/insulator networks are predicted. The model describes satisfactorily the dependence on composition of the conductivity and activation energy of dispersed ionic conductors. Furthermore, the observed effect on the conductivity of the size of dispersed particles can be described qualitatively well by a generalized version of the RRN model, which in addition predicts a sensitive dependence of the critical thresholds on particle size. Non-universality features in the critical exponents for the conductivity are also discussed within a continuum percolation analog of the model. 相似文献