Estimate of the core size of a vortex in an extreme type II superconductor

The core size of a single straight vortex in an extreme type II superconductor is estimated at zero temperature. The free energy is expressed as a non-local functional of the order parameter and vector potential associated with the vortex. Profiles for the order parameter and vector potential that depend on the length scales ξ and λ, respectively, are assumed. For an order parameter profile that achieves its bulk value after the finite distance, ξ, the free energy approximately separates into a sum of two contributions, one depending on the order parameter and the other on the magnetic field. Using two different approximation schemes the two parts of the free energy are minimised. For an order parameter profile that, in its region of change, varies linearly with distance from the vortex axis, the length scale ξ is found to be comparable with the zero temperature coherence length, in agreement with the findings of Ullah et al. (Phys. Rev. B 42 (1990), 9950) for a one-parameter fit to the order parameter. The length scale associated with the magnetic field is also estimated.     

胆甾相液晶的相诱导双轴性

采用胆甾相液晶的格胞理论,运用一定的统计方法,导出分布函数,定义序参数张量,由此推导出自由能表达式．在定域坐标系中,对胆甾相的长程取向序参数Ｓ和相诱导双轴序参数Δ进行了数值计算．所得的结果较前人有了不同程度的改善,和实验接近 关键词：     

Theoretical and experimental studies of parameter estimation based on chaos feedback synchronization

In this paper, we perform theoretical and experimental studies of parameter estimation based on chaos feedback synchronization. The Chua chaotic system is applied as the original system, and its time series of a single variable is applied as a feedback variable to drive a simulative system. The simplex method is employed to minimize the synchronization error in the simulative system to iteratively approach the original system parameters. Furthermore, the effects of feedback function, feedback weight, and noise are investigated. The parameter estimation method based on feedback synchronization shows its robustness to noise perturbation. Finally, the circuit experiment of parameter estimation is implemented in order to examine its practical applicability. The original Chua circuit parameters can be well approached from its recorded time series of a single variable. The results show the parameter estimation method based on feedback synchronization may be capable of estimating real system parameters from a chaotic time series.     

Effect of higher harmonics in quarter-filled Su-Schrieffer-Heeger model

The role of the higher harmonics of the order parameter in the ground state of the quarter-filled Su-Schrieffer-Heeger model is investigated. The lowest energy is obtained when the 4k_F order parameter Δ₂ vanishes. Furthermore, as far as the uniform excitations are concerned, the energy of the system has a minimum at a finite value of Δ₂ when the phase of the fundamental (or 2k_F) order parameter deviates from its ground state values.     

The phase-transition order parameter, fluctuations, and nanoclusters in benzil crystals

Bragg and diffuse X-ray reflections from the M points of the Brillouin zone boundary of a benzil crystal paraphrase, the integral intensity of which is associated with the order parameter and its fluctuations, are studied. Original data on the temperature behavior of the order parameter and diffuse scattering are obtained. The relevant critical exponents are determined. A conclusion is drawn as to the proximity of the phase transition in these crystals to the tricritical point. A phase transition model is discussed.     

X-ray and optical studies of an isothiocyanato liquid crystal mixture

In this work, X-ray and optical studies have been carried out on a four-component isothiocyanato liquid crystal mixture with laterally substituted fluorine atoms. Molecular characteristics, such as effective inter molecular distances and apparent molecular length of the average-simulated molecule have been determined from X-ray studies at various temperatures in the liquid crystalline phase. From the nature of molecular alignment as envisaged from X-ray photographs, the orientational order parameter and its variation with temperature have been determined. Optical studies have also been conducted at various temperatures to investigate the thermal variations of birefringence. Macroscopic orientational order parameter and its thermal variation have been determined from these studies. The nature of order parameter variation obtained from the two studies, X-ray and optical have been compared.     

Order parameter and its fluctuations in Hg<Subscript>2</Subscript>Br<Subscript>2</Subscript> model ferroelastics

The Bragg and diffuse reflections from different X points of the Brillouin zone boundary of the Hg₂Br₂ crystal in the paraphase are studied. The intensities of these reflections are related to the order parameter and its fluctuations. The temperature dependence of the order parameter and its fluctuations is analyzed, and the values of the critical exponents indicating closeness of the phase transition in these crystals to the tricritical point are determined.     

Chiral and deconfinement transition from correlation functions: SU(2) vs. SU(3)

We study a gauge-invariant order parameter for deconfinement and the chiral condensate in SU(2) and SU(3) Yang–Mills theory in the vicinity of the deconfinement phase transition using the Landau gauge quark and gluon propagators. We determine the gluon propagator from lattice calculations and the quark propagator from its Dyson–Schwinger equation, using the gluon propagator as input. The critical temperature and a deconfinement order parameter are extracted from the gluon propagator and from the dependency of the quark propagator on the temporal boundary conditions. The chiral transition is determined using the quark condensate as order parameter. We investigate whether and how a difference in the chiral and deconfinement transition between SU(2) and SU(3) is manifest.     

二级相变理论和Lifshitz条件不成立的论证

系统的自由能是序参量的泛函。在二级相变点附近,自由能密度是序参量及其关联项的幂次展式。按本文给定的方法,无论关联项是定域还是非定域的,由对自由能的一级变分等于零,都能求得表示平衡态位形的序参量。在求解过程,必须将序参量进行傅氏变换,这与序参量以系统对称群的基函数展开是一致的,由此对二级相变中对称改变进行了分析。利用变分法中极值的充要条件(或充分条件),我们讨论了二级相变过程中状态的稳定性条件。由于我们对自由能求极值时没有略去关联项,因此不存在Lifshitz的对称改变限制条件。这里强调指出:实质上,Lif     

Irreversible behavior of interacting systems. I. The approach to equilibrium

The Kac ring model is used to test the validity of some conjectures about irreversibility. If the whole system is regarded as the universe, then it is demonstrated that all clocks (subsystems) run in the same direction during those times when the universe is not in equilibrium. In addition, mathematical techniques are introduced by means of which the appropriate order parameter for large, finite Kac ring models can be evaluated asymptotically. It is shown that the relaxation of this order parameter to its equilibrium value of zero is not exponential.     

Segmental order in end-linked polymer networks: A Monte Carlo study

Segmental order in end-linked monomodal and bimodal polymer networks is investigated by means of bond-fluctuation Monte Carlo simulations. The tensor order parameter, which is a central observable in NMR experiments, is not uniquely related to simple vectorial order. The relaxation of NMR-detected tensorial interactions towards their finite long-time limit is best described by a power law and occurs over much longer time scales than the relaxation of vectorial order. The well-known prediction for the segmental order of Gaussian chains as a simple function of the segment number between constraints is not straightforwardly obeyed, neither in dry nor in swollen networks. Excluded-volume interactions tend to significantly reduce the tensorial order, as is clearly observed in single-chain simulations. A distribution extends along the chain, where order is increased in a region of 30-40 bonds around the cross-links in networks. The dominating contribution to the order parameter distribution arises from the frozen-in distribution of end-to-end separations. We find strong deviations from the Gamma distribution, which has so far been implicitly used in most NMR works, as it is a straightforward consequence of a Gaussian distribution of end separations. Specifically, we find narrower distributions, as small values of the tensor order parameter are strongly suppressed, most probably as a result of trapped entanglements. The markedly subaffine behavior of the average order parameter and the changes in its distribution on swelling are assigned to orientation processes of strands which compensate for the non-affine local deformation. Our central observations and interpretations are well supported by our previous experimental and theoretical work.     

X-ray structural investigations of the phase transition in benzyl crystals

The Bragg (fundamental) and diffuse reflections from the M-points of the Brillouin zone boundary of the paraphase of the benzyl crystals, whose integrated intensity is related to the order parameter and its fluctuations, respectively, have been investigated. The original information on the temperature behavior of the order parameter and the diffuse scattering is obtained and the values of the corresponding critical exponents are determined. The temperature behavior of the correlation radius and its anisotropy are analyzed. The conclusion is drawn that the phase transition in these crystals is close to the tricritical point. The mechanism of the phase transition in the benzyl crystals alternative to the “trigger” mechanism is suggested.     

How Phase Transitions Induce Classical Behaviour

We continue the analysis of the onset of classical behaviour in a scalar field after a continuous phase transition, in which the system-field, the long wavelength order parameter of the model, interacts with an environment, of its own short-wavelength modes and other fields, neutral and charged, with which it is expected to interact. We compute the decoherence time for the system-field modes from the master equation and directly from the decoherence functional (with identical results). In simple circumstances the order parameter field is classical by the time the transition is complete.     

Renormalization-group description of nonequilibrium critical short-time relaxation processes: A three-loop approximation

The influence of nonequilibrium initial values of the order parameter on its evolution at a critical point is described using a renormalization group approach of the field theory. The dynamic critical exponent θ of the short time evolution of a system with an n-component order parameter is calculated within a dynamical dissipative model using the method of Σ-expansion in a three-loop approximation. Numerical values of θ for three-dimensional systems are determined using the Padé-Borel method for the summation of asymptotic series.     

A linear polymerized photopolymer orienting a nematic liquid crystal within nonextensive formalism

The distribution function of photogenerated cross-links in thin films of poly(vinyl cinnamate) or poly(vinyl 4-methoxy-cinnamate) is investigated within nonextensive statistics, in terms of the irradiation time of these films with linearly polarized UV light. The scalar order parameter is obtained from the generalized distribution function, and is compared to the measured birefringence for some values of the entropic index q. The exposure time dependence of the nematogen scalar order parameter is plotted, and the effect of the nonextensive formalism on its exposure time dependence is presented.     

基于核各向异性扩散的红外小目标检测

为了减少红外图像中背景边缘对检测的影响,提出了一种具有鲁棒性的弱小目标检测算法,该算法利用核各向异性扩散模型进行背景预测,再与原图像差分实现弱小目标检测。为了提高算法的自适应能力,提出了一种鲁棒性扩散系数,能够根据图像背景的起伏程度自适应调整扩散系数曲线的陡峭程度。实验结果表明,与现有的检测算法相比,该算法能够在不同类型的复杂背景下有效抑制背景及其边缘,保留目标大小,降低虚警率,具有更强的鲁棒性。     

Spin nutation in the quasi-isotropic A-like superfluid phase of 3He

The order parameter of the quasi-isotropic A-like superfluid phase of ³He has been reduced to a simple form. The frequencies of the spatially homogeneous oscillations of the spin and the spin part of the order parameter of this phase have been obtained taking into account the anisotropy of its magnetic susceptibility. It has been shown that the anisotropy of susceptibility strongly affects the low-frequency oscillation mode, which is similar to the nutation of an asymmetric top. The possibility of observing this mode using the NMR method is discussed.     

Higher-order Dirac solitons in binary waveguide arrays

We study optical analogues of higher-order Dirac solitons (HODSs) in binary waveguide arrays. Like higher-order solitons obtained from the well-known nonlinear Schrödinger equation governing the pulse propagation in an optical fiber, these HODSs have amplitude profiles which are numerically shown to be periodic over large propagation distances. At the same time, HODSs possess some unique features. Firstly, the period of a HODS depends on its order parameter. Secondly, the discrete nature in binary waveguide arrays imposes the upper limit on the order parameter of HODSs. Thirdly, the order parameter of HODSs can vary continuously in a certain range.     

Resonating plaquette phase of a quantum six-vertex model

The simplest quantum generalization of the six-vertex model describes fluctuations of the order parameter of the d-density wave (DDW), believed to compete with superconductivity in the high-T(c) superconductors. The ground state of this model undergoes a first order transition from the DDW phase to a resonating plaquette phase as the quantum fluctuations are increased, which is explored with the help of quantum Monte Carlo simulations and analytic considerations involving the n-vector (n = 2) model with cubic anisotropy. In addition to finding a new quantum state, we show that the DDW is robust against a class of quantum fluctuations of its order parameter. The inferred finite temperature phase diagram contains unsuspected multicritical points.     

Superconducting pairing from repulsion: Contact potential approximation

Pairing of repulsive particles with large total momentum results in essential relative-motion momentum dependence of the superconducting order parameter with a nodal line crossing the Fermi contour inside kinematically accessible domains of the momentum space. Repulsive interaction potential resulting in the superconducting pairing is reduced to a stepwise one with a degenerate kernel having two eigenvalues of opposite sign. Using such a kind of contact potential approach the self-consistency equation is transformed into a system of two integral equations determining average values of the order parameter inside the subdomains of its constant sign. The solution of this equation system is obtained in the weak coupling limit.