Modern Physics Letters B

Using a simple signal processing approach and taking into account the finite linewidth of each longitudinal mode in a mode-locked laser, we investigate the measurement accuracy of the mode-locked laser and analyze the mode-locked pulse train coherence characteristic. Results show that the measurement accuracy in the interference between two mode-locked pulses with the same repetition rate depends on mode-locking stability rather than pulse duration. Mode-locking stability can be achieved by reducing the longitudinal mode linewidth. The mode-locked pulse amplitude is modulated by a modulation envelope function, rather than illimitably continuous pulses because of the finite linewidth of the longitudinal modes. A mode-locked laser emits numerous pulse modulation envelopes one by one and each pulse modulation envelope is described by the same function. Powerful ways are proposed to decrease the linewidth and improve mode-locking stability and measurement accuracy.

This paper investigates the generalized synchronization issue for two different dimensional chaotic systems with unknown parameters. Based on Lyapunov stability theory and adaptive control theory, an adaptive controller is derived to achieve the generalized synchronization whether the dimension of drive system is greater than the one of the response system or not. Meanwhile, corresponding parameter updating laws can be obtained so as to exactly identify uncertain parameters. This technique has been successfully applied to two examples, the generalized synchronization of hyperchaotic Rössler system and chaotic Lorenz system, chaotic Chen system and generalized Lorenz system. Numerical simulations are finally shown to illustrate the effectiveness of the proposed approach.

Based on the Fokker–Planck description of a single-mode laser system and the projection operator method, the mean relaxation time T of a single-mode laser system with correlations between the real and imaginary parts of the quantum noise as well as the pump noise is studied. It is found that the mean relaxation time T increases with the increasing net gain a₀ and decreases with the increasing self-saturation coefficient A. T increases with the increasing pump noise strength Q but decreases with the increasing quantum noise strength D. The mean relaxation time T increases (decreases) with the increasing pump noise self-correlation time τ if a₀ > 0 (a₀ < 0). T decreases with the increasing |λ| (λ is the coefficient of cross-correlation between the real and imaginary parts of the quantum noise).

The levitation force characteristics in a superconducting levitation device are determined not only by the geometry and electromagnetic properties of its components, but also by the initial cooling process of the superconductor. In this paper we present the experimental results of effects of the different initial cooling heights between a superconductor and magnet on the levitation force characteristics including maximum levitation force, relaxation of the levitation force and drift of the levitation force caused by the magnet vibration. It was found that the different cooling heights have large influences on the levitation force characteristics of YBCO bulk.

Nonlinear vibration behaviors of double-walled carbon nanotubes (DWCNTs) with fluid inside the inner tube are investigated based on Donnell's cylindrical shell model and the more refined van der Waals (vdW) interaction formula. The Galerkin method and harmonic balance method are used to study the issue. The results obtained show that the radial vibrational modes of simply supported DWCNTs have twice the dynamical mode transitions as the frequency increases. The transitions correspond to twice the noncoaxial vibrations which play a critical role in electronic and transport properties of CNTs. Moreover, comparisons of the dynamical behaviors of fluid-filled DWCNTs with different wave numbers, radii and aspect ratios demonstrate that the amplitude–frequency curve topological forms are identical. Meanwhile, it is also concluded that the existence of fluid is significant for the value of amplitude ratio corresponding to noncoaxial vibration whereas it does not change the nonlinear vibrating topological pattern of amplitude–frequency curves.

The properties of the even and odd negative binomial states are investigated. Mainly we concentrate on the statistical properties for such states and we consider the squeezing phenomenon by examining the variation in the quadrature variances. Using the Pegg–Barnett formalism of phase operator, the phase probability distributions of the states are discussed, and also the phase and number squeezing with different parameters are studied. The numerical computation results show that the phase probability distributions for the even and odd NBSs can clearly exhibit the different features of quantum effects.

Porous anodized aluminum oxide (AAO) template was combined with sol-gel method in this work for the fabrication of high-ordered NdVO₄ nanotube arrays. The diameter, length, and wall thickness of the nanotubes can be adjusted conveniently. The sample was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), absorption spectra, and photoluminescence spectra. The results show that these uniformly distributed, high-ordered, and parallel nanotubes have great light emission in both the visible region and near-infrared region due to their corresponding energy level transitions. With this method, future application of rare-earth hollow nanostructures will be widely extended.

BiFeO₃-Pb(ZrTi)O₃ [i.e., (Bi_1-xPb_x)(Fe_1-xZr_0.6xTi_0.4x)O₃ (x = 0.15, 0.25, 0.40, 0.50)] nanocomposites were synthesized using mechanical activation followed by a solid-state reaction technique. The dielectric parameters (capacitance, dissipation factor D, impedance Z and phase angle Φ) of all the samples were measured in a wide range of frequencies (1 kHz–1 MHz) and temperatures (300–630 K) in air atmosphere using an impedance analyzer with low signal amplitude of 500 mV. Electrical properties of the compounds were studied using a complex impedance spectroscopy (CIS) technique. The frequency dependence of electrical data was analyzed in the framework of conductivity and modulus formalisms. AC conductivity spectrum obeys Jonscher's universal power law.

Bismuth-based glasses containing ZnO, B₂O₃ and Li₂O are investigated through different physical, polarizability and transport properties. Raman spectroscopy reveals that these glasses are built from [BiO₃] and [BiO₆] units. Zinc in tetrahedral form is also observed. Density and glass transition temperature increase with the bismuth content. The refractive index, oxide ion polarizability and optical basicity also increase with the Bi₂O₃ content, whereas the interaction parameter decreases. The DC electrical conductivity increases and the activation energy decreases with the increase in the Li₂O content.

We investigate theoretically the generation of squeezed states in spontaneous and stimulated five-wave mixing process. It has been found that squeezing occurs in field amplitude, amplitude-squared, amplitude-cubed and fourth-order amplitude states of the fundamental mode in the process. It is found to be dependent on coupling parameter g and phase values of the field amplitude of the fundamental mode. The process involves the absorption of two pump photons each having frequency ω₁, emission of two probe photons of same frequency ω₂ and a signal photon of frequency ω₃. It is shown that squeezing is greater in a stimulated interaction than the corresponding squeezing in the spontaneous process. It is found that the degree of squeezing depends on the photon number in the first and higher orders. We study the statistical behaviour of quantum field in the fundamental mode. It has been found that the field shows sub-Poissonian behavior in this mode.

Nanomanipulation as a new emerging area enables precise manipulation, interaction and control at the nanoscale. Currently, the modeling schemes are based on continuum mechanics approaches. A main consideration in the nanomanipulation process is the fact that surface attraction forces are greater than gravitational forces at the nanoscale. In other words, surface area properties dominate volume properties. Especially at the nanoscale (i.e. the manipulation of fine nanoparticles with size of about 5 nm) the physical phenomena have not been completely understood. Along this line of reasoning, the aim of this paper is to conduct an atomistic investigation of physical interaction analysis of particle–substrate system for manipulation and positioning purposes. In the present paper, 2D molecular dynamics have been conducted to simulate metallic nanoparticle behavior during the pushing process. Dependency of the aforementioned behavior on size, matter, temperature, etc. is investigated.