A New Variational Principle for the Fundamental Equations of Classical Physics

In this paper we introduce a variational principle from which the fundamental equations of classical physics can be deduced. This principle permits a sort of unification of the gravitational and the electromagnetic fields. The basic point of this variational principle is that the world-line of a material point is parametrized by a parameter a which carries some physical information, namely it is related to the rest mass and to the charge. In particular, the (inertial) rest mass will not be a property of a material point, but it will be a constant of the motion which is determined by the initial conditions. In this framework the equality between the inertial and gravitational mass can be deduced.     

Design of a cyclic multiverse

Recently, it has been noticed that the amplification of the amplitude of curvature perturbation cycle by cycle can lead to a cyclic multiverse scenario, in which the number of universes increases cycle by cycle. However, this amplification will also inevitably induce either the ultimate end of corresponding cycle, or the resulting spectrum of perturbations inside corresponding universe is not scale invariant, which baffles the existence of observable universes. In this Letter, we propose a design of a cyclic multiverse, in which the observable universe can emerges naturally. The significance of a long period of dark energy before the turnaround of each cycle for this implementing is shown.     

望远镜干涉阵中光程调制的研究

提出了在单模光纤联接的望远镜干涉阵中通过拉伸红外单模光纤实现光程调制的方法。简要分析了该方法的机理及存在的问题，如偏振效应，色散等，用少模光纤和单模光纤分别代替马赫－陈德尔（Ｍａｃｈ－Ｚｅｈｎｄｅｒ）干涉仪的两个臂，并且其中一臂的光纤缠在直径为６ｃｍ的ＰＺＴ圆柱上，给ＰＺＴ圆柱施加三角皮电压后，首次得到干涉条纹，并证明了方法的可行性。     

On the many-body Van der Waals binding energy of a dense fluid

We consider a dense system of neutral atoms. When the atoms are represented by isotropic oscillators (Drude-Lorentz model) interacting with nonretarded dipole-dipole forces, the binding energy of the system is given exactly by a well-known expression which is written as a sum of two-bond, three-bond, etc., Van der Waals interactions. For a Bravais lattice this expression for the binding energy can be computed numerically to arbitrary accuracy. This has been done for the f.c.c. lattices of the noble-gas solids by Lucas. For a fluid an exact evaluation would require the knowledge of higher-order molecular distribution functions. Various approximations are discussed for this case, the simplest of which is the so-called long-wavelength approximation due to Doniach. When this approximation is checked by comparison with the exact result for a lattice, it turns out that the two-bond contribution leads to a value which is more than twice too large. Some more refined approximations are considered which treat the two-bond contribution exactly. It is pointed out that the model is consistent only if the distance of closest approach between the atoms is not too small.     

Information storage capacity of discrete spin systems

Understanding the limits imposed on information storage capacity of physical systems is a problem of fundamental and practical importance which bridges physics and information science. There is a well-known upper bound on the amount of information that can be stored reliably in a given volume of discrete spin systems which are supported by gapped local Hamiltonians. However, all the previously known systems were far below this theoretical bound, and it remained open whether there exists a gapped spin system that saturates this bound. Here, we present a construction of spin systems which saturate this theoretical limit asymptotically by borrowing an idea from fractal properties arising in the Sierpinski triangle. Our construction provides not only the best classical error-correcting code which is physically realizable as the energy ground space of gapped frustration-free Hamiltonians, but also a new research avenue for correlated spin phases with fractal spin configurations.     

Gravitational Gauge Interactions of Dirac Field

Gravitational interactions of Dirac field are studied in this paper. Based on gauge principle, quantum gauge theory of gravity, which is perturbatively renormalizable, is formulated in the Minkowski space-time. In quantum gauge theory of gravity, gravity is treated as a kind of fundamental interactions, which is transmitted by gravitational gauge field, and Dirac field couples to gravitational field through gravitational gauge covariant derivative. Based on this theory, we can easily explain gravitational phase effect, which has already been detected by COW experiment.     

一种数字控制三相逆变电路的局部振荡行为分析

针对数字控制三相逆变系统, 对其在同步旋转坐标系比例控制下的局部振荡行为进行了分析.通过建立系统各个状态变量离散迭代方程, 针对这个高阶系统提出了各种不稳定行为的解析判别式. 以此为基础,得到了系统产生局部振荡的条件,以及控制参数与局部振荡点的关系. 最后,通过Simulink仿真以及电路实验证明了理论分析的正确性以及有效性. 研究结果揭示了三相逆变系统的运动行为及各相之间的内在耦合关系, 并准确地描述了系统产生的局部振荡现象. 关键词： 三相逆变电路 数字控制 运动行为 局部振荡     

利用定量相衬成像消除X射线同轴轮廓成像中散射的影响

在所有的相衬成像方法中，X射线同轴轮廓成像由于光路简单、不需要任何光学元件而备受关注.其缺点是无法直接消除散射的影响，从而限制了它在生物医学等领域中的应用.利用数字模拟方法研究了引入散射前后轮廓像的质量随样品到探测器距离的变化情况.模拟结果表明直接轮廓成像存在一个最佳成像距离，因而无法通过改变样品到探测器距离来减小散射的影响.利用定量相衬成像不受成像距离限制的特点，研究了远距离成像时散射的影响.结果表明，样品到探测器的距离增大到一个临界值时，散射对重构像的影响可降到一个极值，此时成像质量得到了明显改善. 关键词： 散射 X射线同轴轮廓成像 定量相衬成像     

Improving the signal to noise of FIR polarimetry onconstrained-access plasma experiments

Experimental results are presented that demonstrate the pronounced effects produced on the polarization state of an FIR (far infrared) laser beam when a portion of the beam intersects a metallic tubulation at a glancing angle. The effects produced by this interaction are sufficient to totally obscure the desired measurement of Faraday rotation. A model is developed which qualitatively predicts the observations. A method of suppressing this effect, which is viable for the heterodyne method of measuring Faraday rotation, is presented. It is further shown that reflections off the mechanically vibrating tubulations are the source of a variable effective birefringence, which is perceived as an anomalous Faraday rotation. Minimizing these reflections by threading the inside of the tubulations overcame this problem and allowed measurements to be obtained     

An application of stochastic resonance for energy harvesting in a bistable vibrating system

The application of stochastic resonance to mechanical energy harvesting is currently of topical interest, and this paper concentrates on an analytical and experimental investigation in which stochastic resonance is deliberately exploited within a bistable mechanical system for optimised energy harvesting. The condition for the occurrence of stochastic resonance is defined conventionally by the Kramers rate, and the modelling of a theoretical nonlinear oscillator driven by a small periodic modulating excitation and a harvestable noise source, which, together satisfy this condition, is developed in the paper. A novel experiment is also discussed which validates this particular form of stochastic resonance, showing that the response can indeed be amplified when the frequency of the weak periodic modulating excitation fulfills the correct occurrence condition. The experimental results indicate that the available power generated under this condition of stochastic resonance is noticeably higher than the power that can be collected under other harvesting conditions.     

Thermal quenching of the 1–1.35 eV extrinsic photoconductivity in semi-insulating GaAs (Cr,O)

We report in this work, photoconductivity measurements between 77 and 300 K, in semi-insulating GaAs samples doped with chromium and oxygen. These samples exhibit a striking photoconductivity behaviour, which is characterized by a strong increase of the photoconductivity after long time excitation with photons in the 1–1.35 eV spectral range at 77 K. This increase is thermally quenched at 135 K. We explain this anomalous behaviour by means of a generation of traps by light within this spectral range; these photogenerated traps being annealed at 135 K. To our knowledge this is a phenomenon which has not yet been observed in GaAs.     

Integrability of the Gross-Pitaevskii equation with Feshbach resonance management

In this Letter we study the integrability of a class of Gross-Pitaevskii equations managed by Feshbach resonance in an expulsive parabolic external potential. By using WTC test, we find a condition under which the Gross-Pitaevskii equation is completely integrable. Under the present model, this integrability condition is completely consistent with that proposed by Serkin, Hasegawa, and Belyaeva [V.N. Serkin, A. Hasegawa, T.L. Belyaeva, Phys. Rev. Lett. 98 (2007) 074102]. Furthermore, this integrability can also be explicitly shown by a transformation, which can convert the Gross-Pitaevskii equation into the well-known standard nonlinear Schrödinger equation. By this transformation, each exact solution of the standard nonlinear Schrödinger equation can be converted into that of the Gross-Pitaevskii equation, which builds a systematical connection between the canonical solitons and the so-called nonautonomous ones. The finding of this transformation has a significant contribution to understanding the essential properties of the nonautonomous solitons and the dynamics of the Bose-Einstein condensates by using the Feshbach resonance technique.     

Free vibration analysis of the completely free rectangular plate by the method of superposition

While the subject of free vibration analysis of the completely free rectangular plate has a history which goes back nearly two centuries it remains a fact that most theoretical solutions to this classical problem are considered to be at best approximate in nature. This is because of the difficulties which have been encountered in trying to obtain solutions which satisfy the free edge conditions as well as the governing differential equation. In a new approach to this problem, by using the method of superposition, it is shown that solutions which satisfy identically the differential equation and which satisfy the boundary conditions with any desired degree of accuracy are obtained. Eigenvalues of four digit accuracy are provided for a wide range of plate aspect ratios and modal shapes. Exact delineation is made between the three families of modes which are characteristic of this plate vibration problem. Accurate modal shapes are provided for the response of completely free square plates.     

Particle Size Analysis of Some Difficult Measurable Systems

Knowledge of the granulometric behaviour of dispersed systems is vital for a full and complete characterisation. Despite the variety of methods and devices which have been developed for this purpose, difficulties frequently arise in the practical determination of particle size distribution. In this paper it is shown, by means of examples, how measurements for surface modified and porous particles can be influenced by the behaviour of the material, and which approaches exist to obtain accurate values by taking this into account.     

Reversible maps in two-degrees of freedom Hamiltonian systems

It has been shown that a sub-class of two-degrees of freedom Hamiltonian systems possesses a reversing symmetry discovered by Birkhoff in the restricted problem of three bodies. This mixed space-time reversing symmetry, which is different from the classical time reversal symmetry, can be shared by time-reversible as well as time-irreversible systems. Examples of time-irreversible systems which possess this reversing symmetry are the restricted problem of three bodies as shown by Birkhoff in 1915, and a special case of the motion of a rigid body with a fixed point discussed in this paper. If a Hamiltonian system possesses this Birkhoff reversing symmetry, then there exists a surface of section for which the corresponding Poincare map is Birkhoff-reversible. The Birkhoff-reversibility of this map may be used to study its global dynamics such as the locations and the distribution of the stable and unstable periodic points, the distribution of stable and chaotic regions, and the identification of the scattering regions. (c) 2002 American Institute of Physics.     

The long-range correlations of various Ising lattices

The object of this paper is to determine the long-range order parameter for any Ising lattice whose partition function can be evaluated by existing methods. The partition function of a general class of two-dimensional lattices is evaluated by a technique found byGreek andHurst, and this technique is extended to determine correlation coefficients. In this way the determination of the long-range correlation coefficients is reduced to an eigenvalue problem, which can be solved by algebraic methods. A simple formula is found for the long-range order parameter, which contains, but is considerably more general than the known result for the rectangular lattice.     

Structure of the generalized Friedmann problem

An investigation of those cases of the generalized Friedmann equation which are solvable in terms of elementary or elliptic functions is undertaken together with a study of the time gauges which allow this to occur. This is accomplished by examining the natural choices of independent and dependent variables in this problem using manipulations like those of the Kepler problem, which is shown to be equivalent to a generalized Friedmann problem, thus clarifying the similarities between the simplest solutions of each.     

Theory of the Ising model on a Cayley tree

The Ising model on a Cayley tree is known to exhibit a phase transition of continuous order. In this paper we present a complete and quantitative analysis of the leading singular term in the free energy which is associated with this phase transition. We have been able to solve this problem by considering the distribution of zeros of the partition function. The most interesting new feature in our results is a contribution to the free energy which performs singular oscillations as the magnetic field approaches zero.