Dynamics of superradiant medium in resonator

Experimental data and theoretical model describing superradiance from the LaF₃ crystal doped with impurity praseodymium ions are presented in cases of non-resonator and resonator generation. The spiky structure of superradiance is registered and studied. When the crystal is placed inside a resonator, a new channel of energy removal by superradiance related to the resonator mode appears; the old non-resonator channels are preserved, as well. It has been found that the duration of superradiance in each channel decreases, and there arises a modulation independent of the length of resonator. These new peculiarities of superradiance induced by the presence of resonator have been explained on the basis of the developed simple mean-field theory.     

Elimination of Anti-spiral Waves by Local Inhomogeneity in Oscillatory Systems

采用系统中的局部不均匀性消除振荡系统中的反螺旋波. 该不均匀性在系统中成为一个波源,不断产生稳定的相波. 研究结果发现,不均匀性的尺寸大小存在一个临界值,如果低于此临界值,则系统将无法激发任何相波. 根据不均匀性形状的不同,系统分别产生靶波和行波. 此外,实验还发现靶波与反螺旋波之间以及行波与反螺旋波之间存在着不同的动态竞争. 数值计算表明,对于行波,无论是低频行波还是高频行波,都可以成功地消除系统中的反螺旋波;而对于靶波,只有低频靶波才可以消除反螺旋波. 此控制方法简单易行,且同样适用于消除向外传播的螺旋波     

Linearized oscillations in nonlinear delay difference equations

Consider the nonlinear delay difference equation We establish a linearized oscillation result of this equation, which is the extension of the result in the paper [1]. Supported by the National Natural Science Foundation of China     

Rough oscillatory singular integral operators of nonconvolution type

In this paper, we study a classes of oscillatory singular integral operators of nonconvolution type with phases more general than polynomials. We prove that such operators are bounded on Lp provided their kernels satisfy a very weak condition. In addition, we also study the related truncated oscillatory singular integral operators. Moreover, we present a class of unbounded oscillatory singular integral operators.     

Flame behavior in heated porous sand bed

This paper reports experimental and numerical investigations on the combustion characteristics of a lean methane–air mixture in a heated porous sand bed. The porous bed consisted of sand (SiO₂) particles with a mean particle diameter of 0.56 mm. The horizontally placed quartz tube was heated externally to initiate the combustion reaction in the porous bed combustor. The stabilized flame location curve as a function of averaged mixture velocity was obtained for various equivalence ratios. Contrary to the earlier finding of a C-shape flame stabilization behavior, a new S-shape behavior was observed in the present study. This can be divided into three regimes: high, moderate, and low velocity regimes. In the low velocity regime, flame with very weak luminosity was confirmed and the stabilized flame location moved downstream with the increase of the mixture velocity. For the moderate velocity regime, a stable flat flame was observed and the flame location moved upstream with the increase of the mixture velocity. An oscillatory flame behavior was observed in the high velocity regime. In this oscillatory mode, the flame front oscillated with a characteristic time period of the order on 1 h and increased with the increase of the mixture velocity. In order to further understand these experimental results, one-dimensional computational studies with detailed chemistry and heat transfer mechanisms were carried out. The computational results were in good agreement with experimental observations. The computations showed that solid-to-solid radiation played a significant role in the flame stabilized location. From the examination of the flame structure, it was found that the flame behavior in the low velocity regime was similar to that of the flameless combustion mode.     

Aromatic free Fenton process for rapid removal of phenol from refinery wastewater in an oscillatory baffled reactor

The need for clean, safe, and unpolluted water has recently become an important issue. Industrial processes such as petrochemical, pharmaceutical, pulp, and paper industries emit organic products in water, such as phenols, which are extremely toxic to aquatic life. The severe operating conditions, such as high pressure and temperature, of the conventional chemical oxidation processes of phenols cost a lot and limited the extensive application of the process. The present work depicts the development of a highly efficient and rapid oxidation process in an oscillating baffled reactor (OBR) to allow continuous and safe phenol removal under moderate operating conditions. Phenol conversion was studied as a function of initial concentration (300–500 ppm), pH (3–5), residence time (1–5 min), at constant amplitude (A = 4 mm), and frequency (f = 4 Hz) of oscillation and room temperature to achieve up to 94.6%. At 70 °C, 300 ppm starting concentration, pH = 3, 4 Hz frequency, and 4 mm amplitude, an exceptional removal of 99.858% phenol was achieved without additional extraction in just 3 min by optimizing the working parameters. This is a significant improvement over comparable processes at this temperature, and it was done in a reactor that scales up reliably, so this performance can likely be replicated on a large scale. Also, the present process was safe as it produced a nil concentration of the hazardous Fenton intermediate compounds.     

Inertial and coriolis effects on oscillatory flow in a horizontal dendrite layer

Flow instability due to oscillatory modes of disturbances in a horizontal dendrite layer during alloy solidification is investigated under an external constraint of rotation. The flow in the dendrite layer, which is modeled as flow in a porous layer and with the inertial effects included, is assumed to rotate about the vertical axis at a constant angular velocity. The investigation is an extension of the work in Riahi (On stationary and oscillatory modes of flow instablity in a rotating porous layer during alloy solidification. J. Porous Media, 6, 177–187, 2003), which was for the case in the absence of the inertial effects. Results of the stability analyses indicate, in particular, that the Coriolis effect can enhance the physical domain for the oscillatory flow, while the inertial effect tends to reduce such domain. Sufficiently strong inertial effect can eliminate presence of the oscillatory mode only for the rotation rate beyond some value. The effect of interaction between the local volume fraction of solid and the flow associated with the Coriolis term was found to be stabilizing.     

Wave atoms and sparsity of oscillatory patterns

We introduce “wave atoms” as a variant of 2D wavelet packets obeying the parabolic scaling wavelength(diameter)². We prove that warped oscillatory functions, a toy model for texture, have a significantly sparser expansion in wave atoms than in other fixed standard representations like wavelets, Gabor atoms, or curvelets. We propose a novel algorithm for a tight frame of wave atoms with redundancy two, directly in the frequency plane, by the “wrapping” technique. We also propose variants of the basic transform for applications in image processing, including an orthonormal basis, and a shift-invariant tight frame with redundancy four. Sparsity and denoising experiments on both seismic and fingerprint images demonstrate the potential of the tool introduced.     

非线性时滞差分方程的线性化振动性

本文建立了非线性时滞差分方程的线性化振动性的结果,推广了文[1]的工作．