均匀外场中扩散控制聚集集团标度性质的实验

本文采用无分岔扩散控制聚集(DLA)模型,利用计算机模拟均匀外场中微小颗粒的不可逆生长过程,发现均匀外场的存在将改变生长集团的标度性质。对在均匀外场中生长的DLA,集团的豪斯道夫维数D与均匀外场F之间存在函数关系:D=2.50F^0.37exp(-1.08F)+1。 关键词：     

三维X-Y模型的滞后标度和动态相变行为

采用Monte Carlo方法对3DX-Y模型进行数值模拟计算，研究了在非线性外场驱动下3DX-Y模 型的滞后标度和动态相变.得出了滞后标度关系为Area～h^α₀ωβ(1-T/T_c)^γ， 其中α=0.57，β=0.34，γ=0.90.发现其动态相变行为在一定的临界参数条件下，初始短周 期(周期数PN≤10)内的结果具有与Ising模型类似的对称性破缺；但在长周期内(PN≥200)的 结果则明显区别于Ising模型而与Heisenberg模型相近，也即无稳定动态有序铁磁相的存在. 关键词： X-Y模型 滞后标度 动态相变 Monte Carlo方法     

溶液中向列型液晶有序度以及外场对它们的影响

根据Lebwohl-Lasher模型以及平均场近似得到了存在于外场中的溶液中向列型液晶分子有序度参数的自洽方程.无外场时,溶液中液晶发生一级相变,不同浓度相转变时2>均为0.324,T^N1与浓度成正比,T_φ^N1=T_φ=1^N1φ。而存在外场时,液晶发生二级相变,且都发生于2>=0.40处.液晶分子取向分布曲线为V型,均方偏差随2关键词：     

弱场下熔融织构YBa2Cu3O7-δ样品局域磁通蠕动的实验研究

利用半导体霍尔探头测量法在液氮温度下研究了低场下圆柱状熔融织构YBa₂Cu₃O_7-δ样品的局域磁通蠕动行为.对瞬时加减场样品端面局域磁场的磁弛豫,磁滞回线以及不同扫场速率下局域磁场的变化进行了测量,观察到了对数时间磁弛豫的行为,发现由加场和去场数据所得的激活能U₀有明显的不同.磁滞回线测量中,局域点的磁场随外场几乎同步变化,不同扫场速率下局域磁场随外场变化的差别不大.实验结果表明,外场除对样品侧面外,对端面也有明显的穿 关键词： 局域磁通蠕动 激活能 磁弛豫     

外场存在时界面生长的重整化群研究

用重整化群方法分析了有外场存在时的界面生长行为,得到了非平庸的稳定的固定点,固定点粗糙指数x和动力学标度指数z。结果表明,外场趋于使生长表面平滑并且不破坏伽利略不变性。 关键词：     

交换弹簧磁性多层膜的磁矩取向及磁滞回线的解析研究

本文以界面交换耦合常数Jⁱ和软磁相厚度L^s为主要参变量,研究了易轴与膜面平行情况下的Nd₂Fe₁₄B/α-Fe磁性多层膜的磁矩随外场变化的取向及磁滞回线,并得到了成核场的解析公式.分析发现,Jⁱ对磁矩取向、钉扎场和矫顽力机理有着较大的影响.当L^s较小时,钉扎场等于成核场,随着Jⁱ的减小 关键词： 成核场 钉扎场 矫顽力 磁滞回线     

混合交通流时间序列的去趋势波动分析

应用去趋势波动分析法研究交通流时间序列的复杂性,探讨了混合交通流时间序列演变行为的标度指数.根据标度指数的变化特征,进而揭示交通流时间序列所具有的长程相关性和短程相关性.通过分析发现,存在一密度ρ,当ρ₁<ρ<ρ₂时,交通流时间序列具有长程相关性;而当ρ<ρ₁或ρ>ρ₂时,交通流时间序列具有短程相关性,即密度的变化影响着标度指数的变化.另外分析了在不同慢车比率条件下时间序列的标度指数,发现慢车比率的变化 关键词： 混合交通流 去趋势波动分析 时间序列 长程相关     

向列相液晶电流体不稳定性——偏置电场效应

本文考虑了外电场与液晶盒玻璃片法线成倾角θ₀时,沿面排列的向列相液晶(θ_α<0,σ_α>0)的电流体不稳定性现象。在Dubois-Violette等人的一维理论的基础上,我们获得了直流、正弦波和矩形波三种电场激发下的失稳条件。重要结果包括:(1)电荷弛豫时间随θ₀单调上升。(2)对于MBBA液晶,存在一个临界角θ_c(ω)(ω是外场频率),当θ₀>θ_c(ω) 关键词：     

打结高分子链穿孔行为的研究

以三叶草型结(即3₁结)为例,采用分子动力学(MD)方法,研究打结高分子链在外场力作用下穿越微孔的动力学过程.模拟发现,在拉动打结高分子链的过程中,结的大小呈涨落变化,直至最后散结.定性讨论了结的存在对高分子链穿孔速率的影响.在外场力作用下,打结高分子链平均穿孔时间(τ)与链长(N)满足标度关系τ～N ^α,其中标度系数α随外场力f增大而增大.对于短链,外场力越大,平均穿孔时间越短     

2H-Nb0.9Ta0.1Se2中磁通涡旋输运的标度行为

测量了2H-Nb_0.9Ta_0.1Se₂单晶样品在不同电流下电压随磁场变化的曲线V(H),并从V(H)曲线得到V(I)数据.使用标度关系V=α(I-I_c)^β进行了拟合,得到了临界电流随磁场I_c(H)和微分电阻随磁场R_d的变化关系.在微分电阻随磁场变化的曲线中,电流较大时,靠近上临界磁场H_c2附近出现一个强峰,而在低电流下,该峰消失.同 关键词： 磁通涡旋 标度定律 临界电流峰效应     

Exact phase diagrams for an Ising model on a two-layer Bethe lattice

Using an iteration technique, we obtain exact expressions for the free energy and the magnetization of an Ising model on a two-layer Bethe lattice with intralayer coupling constants J1 and J2 for the first and the second layer, respectively, and interlayer coupling constant J3 between the two layers; the Ising spins also couple with external magnetic fields, which are different in the two layers. We obtain exact phase diagrams for the system and find that when /J3/-->0, DeltaT(c) identical with[T(c)(J3)-T(c)(0)]/T(c)(0) approximately [J3]/J(1)/(1/psi), where T(c)(J3) is the phase-transition temperature for the system with interlayer coupling constant J3 and the shift exponent psi is 1 for J(1)=J(2) and is 0.5 for J1 not equal to J2. Such results are consistent with predictions of a scaling theory. We also derive equations for DeltaT(c) when /J3/ approaches infinity.     

缺陷对滞后标度性的影响

对二维Ising铁磁系统中的非磁杂质，利用Monte Carlo方法，获得不同杂质浓度、不同磁场变化速率下的磁滞(?)线，从而得到滞后(?)线面积与磁场变化速率的关系．结果表明，在温度和缺陷浓度组成的相图上，存在一条相变线．低温和低浓度时，(?)线面积与磁场速率的标度指数约为1/3，只微弱地依赖于温度及杂质浓度；而对高温和高浓度的杂质，指数强烈地依赖于温度和浓度 关键词：     

Diffusion-controlled first-order surface reaction in turbulent flow

The effect of advective diffusion on the rate of reactant consumption by a first-order surface reaction is analyzed in the fast-reaction limit. The decay of reactant concentration is described by the function n(t) ～ exp(?λt). In the limit of well-developed turbulence, the scaling estimates λ ～ L ^?1κ^3/4μ^1/4 and λ ～ fκ^3/4μ^1/4 are obtained, respectively, for a confined flow with characteristic length scale L and in the case when the reactants are contained near the surface by an external field with potential U/T = fx, where κ is molecular diffusivity and μ is the constant parameter in the eddy diffusivity D _adv = μx ⁴ (x is distance to the wall). The coefficients in the scaling laws are evaluated by a variational method and by numerical solution of the governing equations.     

Non-equilibrium phase transition of the fully frustrated square lattice Coulomb gas model

The non-equilibrium phase transitions of the fullyfrustrated (f = 1/2) square lattice Coulomb gas (CG) modeldriven by external electrical fields are studied in the frameworkof the short-time dynamic scaling approach. The criticaltemperature T_c, the static and dynamic critical exponents2β/ν, ν, and z are obtained for several smalldriving fields. The results show that T_c decreases with theincrease of electric field, and 2β/ν and z arestrongly dependent on the external electric field. Interestingly,contrary to the equilibrium case, in the presence of smallelectric field, the calculated exponent ν is close to that inpure 2D Ising model, which provides numerical evidence thatexternal electric field may change the universality class of thef = 1/2 CG system.     

A scaling limit with many noncommutativity parameters

We derive the worldsheet propagator for an open string with different magnetic fields at the two ends, and use it to compute two distinct noncommutativity parameters, one at each end of the string. The usual scaling limit that leads to noncommutative Yang–Mills can be generalized to a scaling limit in which both noncommutativity parameters enter. This corresponds to expanding a theory with U(N) Chan–Paton factors around a background U(1)^N gauge field with different magnetic fields in each U(1).     

Direct gauging of the Poincaré group V. Group scaling,classical gauge theory,and gravitational corrections

Homogeneous scaling of the group space of the Poincaré group,P ₁₀, is shown to induce scalings of all geometric quantities associated with the local action ofP ₁₀. The field equations for both the translation and the Lorentz rotation compensating fields reduce toO(1) equations if the scaling parameter is set equal to the general relativistic gravitational coupling constant 8Gc ^–4. Standard expansions of all field variables in power series in the scaling parameter give the following results. The zeroth-order field equations are exactly the classical field equations for matter fields on Minkowski space subject to local action of an internal symmetry group (classical gauge theory). The expansion process is shown to breakP ₁₀-gauge covariance of the theory, and hence solving the zeroth-order field equations imposes an implicit system ofP ₁₀-gauge conditions. Explicit systems of field equations are obtained for the first- and higher-order approximations. The first-order translation field equations are driven by the momentum-energy tensor of the matter and internal compensating fields in the zeroth order (classical gauge theory), while the first-order Lorentz rotation field equations are driven by the spin currents of the same classical gauge theory. Field equations for the first-order gravitational corrections to the matter fields and the gauge fields for the internal symmetry group are obtained. Direct Poincaré gauge theory is thus shown to satisfy the first two of the three-part acid test of any unified field theory. Satisfaction of the third part of the test, at least for finite neighborhoods, seems probable.     

Phenomenology of asymptotically free theories in deep inelastic scattering: (I). Electron and muon scattering

We calculate the predictions of asymptotically free theories for deep inelasric scattering using a straightforward Mellin transform technique which uses a minimum of theoretical assumptions. Parameterizing the quark and anti-quark distributions functions, we fit all the available μ and e scattering data. We investigate the sensitivity of the theory of the (almost) unknown gluon distributions and the choice of scaling variable. The best fit uses the formalism of Georgi and Politzer for the 1/Q² terms with a quark gluon coupling constant g²/4π ～ 1 at Q² = 1 (GeV/c)². (Equivalently the scale parameter Λ is 500 MeV/c.) Good fits are also found in simpler models using x, x′ or ξ as scaling variables. The best value of Λ depends strongly on the choice of scaling variable.     

Efficient Quantum Algorithms for Simulating Sparse Hamiltonians

We present an efficient quantum algorithm for simulating the evolution of a quantum state for a sparse Hamiltonian H over a given time t in terms of a procedure for computing the matrix entries of H. In particular, when H acts on n qubits, has at most a constant number of nonzero entries in each row/column, and ||H|| is bounded by a constant, we may select any positive integer k such that the simulation requires O((log^* n)t ^1+1/2k ) accesses to matrix entries of H. We also show that the temporal scaling cannot be significantly improved beyond this, because sublinear time scaling is not possible.     

An effective scaling frequency factor method for scaling of harmonic vibrational frequencies: The use of redundant primitive coordinates

A modified effective scaling frequency factor (ESFF) method that takes advantage of the potential energy distribution (PED) coefficients calculated in the basis of redundant primitive internal coordinates is presented. This approach is simpler and more flexible than that based on the natural internal coordinates. The sets of optimal scaling factors for routine 9- and 11-parameter ESFF calculations based on B3LYP/6-311G∗∗ force fields are derived from Baker’s training set of 30 molecules (660 frequencies). The calculated root-mean-square (RMS) deviations for all frequencies are 11.42 and 11.44 cm⁻¹ for 9- and 11-parameter scaling, respectively. They are somewhat lower than in the case of ordinary ESFF calculations. The new sets of factors seem to be particularly well suited for scaling of frequencies in the middle region of the vibrational spectra (1000-2500 cm⁻¹) - the RMS values in this range are 8.37 for 9-, and 9.56 cm⁻¹ for 11-parameter scaling. These values are to be compared with 9.20 and 10.29 cm⁻¹, respectively, calculated within the natural coordinates based ESFF formalism.