The effects of cubic potentials on discrete breathers in a mixed Klein－Gordon /Fermi－Pasta－Ulam chain

Nonlinearity has a crucial impact on the symmetry properties of dynamical systems. This paper studies a one-dimensional mixed Klein--Gordon/Fermi--Pasta--Ulam diatomic chain using the expanded rotating plane-wave approximation and numerical calculations to determine the effect of cubic potentials on the symmetry properties of discrete breathers in this system. The results will be very useful to researchers in the field of numerical calculations on discrete breathers.     

Stochastic resonance in a time-delayed asymmetric bistable system with mixed periodic signal

This paper studies the phenomenon of stochastic resonance in an asymmetric bistable system with time-delayed feedback and mixed periodic signal by using the theory of signal-to-noise ratio in the adiabatic limit. A general approximate Fokker--Planck equation and the expression of the signal-to-noise ratio are derived through the small time delay approximation at both fundamental harmonics and mixed harmonics. The effects of the additive noise intensity $Q$, multiplicative noise intensity $D$, static asymmetry $r$ and delay time $\tau$ on the signal-to-noise ratio are discussed. It is found that the higher mixed harmonics and the static asymmetry $r$ can restrain stochastic resonance, and the delay time $\tau $ can enhance stochastic resonance. Moreover, the longer the delay time $\tau $ is, the larger the additive noise intensity $Q$ and the multiplicative noise intensity $D$ are, when the stochastic resonance appears.     

基于改进中值滤波和提升小波变换的阈值去噪方法研究

对于实际拍摄的一些图像信噪比低,噪声密度大,且含有混合噪声,而现有算法大多只能去除单一噪声的问题。针对混合噪声中含有的脉冲噪声和高斯噪声,提出基于改进中值滤波和提升小波变换去噪相结合的方法。去噪过程中,使用中值滤波器提取脉冲噪声并采用中值滤波算法滤波后,构造提升小波,采用改进阈值函数提升小波阈值去噪方法去除高斯噪声。实验结果表明,当噪声值(,)=(0.4, 20)时,采用本文去噪方法,峰值信噪比（PSNR）为34.002 1,平均绝对误差（MAE）为2.365 3。     

大挠度弯曲直梁混合变量最小势能原理的应用

应用大挠度弯曲直梁混合变量最小势能原理,求解均载两端固定大挠度柱面弯曲板条的轴向挠度分布和轴向弯矩分布．实例计算表明:该方法简单实用、精度高,是一种计算大挠度柱面弯曲板条变形的有效方法．     

利用浓盐酸脱苯基方法合成混合二烃基二氯化锡

利用RSnPh3(R= Me3SiCH2、EtMe2SiCH2、Bu)和浓盐酸直接混合加热反应,合成了三种混合二烃基二氯化锡,通过IR,1H NMR和MS的测定,对产物的结构进行了表征;并探讨了反应时间、温度和浓盐酸用量对该反应产率的影响.实验结果表明,该方法与其它方法比较,具有操作简单、反应速度快、环境污染小、产率较高等特点;当四烃基锡与浓盐酸的物质的量比为1:8,在97 ℃反应7 min,混合二烃基二氯化锡的产率大于70%.     

混合交通OD分布与随机平衡分配组合模型及算法

基于我国城市混合交通的特点,借助于Logit选择模型,建立了混合交通OD分布与随机平衡分配组合的数学规划模型,证明了模型最优解的等价性与唯一性,同时给出了算法和算例.     

A stabilized mixed method applied to Stokes system with nonhomogeneous source terms: The stationary case Dedicated to Prof. R. Rodríguez,on the occasion of his 65th birthday

This article is concerned with the Stokes system with nonhomogeneous source terms and nonhomogeneous Dirichlet boundary condition. First, we reformulate the problem in its dual mixed form, and then, we study its corresponding well-posedness. Next, in order to circumvent the well-known Babuška-Brezzi condition, we analyze a stabilized formulation of the resulting approach. Additionally, we endow the scheme with an a posteriori error estimator that is reliable and efficient. Finally, we provide numerical experiments that illustrate the performance of the corresponding adaptive algorithm and support its use in practice.     

Permethylated dinuclear Mn(III) coordination nanostructure with stripe-ordered magnetic domains

A di-manganese(III) complex structure was built by an original approach consisting of a two-step procedure. First, the mononuclear complex of the manganese(III) with the Schiff base of the salen-type ligand (H₂L) derived from 1,3-bis(3-aminopropyl)tetramethyldisiloxane and 3,5-di-tert-butyl-2-hydroxybenzaldehyde was prepared. The main feature of note is the 12-membered chelate ring formed upon coordination of the Schiff base to central atom, which adopts a distorted N₂O₄ octahedron environment. In the second step, the acetato co-ligand in this complex is replaced by the carboxylate anion of a dicarboxilic acid, namely adipic acid. This metathesis reaction leads to the formation of dinuclear structure by connecting two manganese centers. The structure, as was determined by X-ray single crystal diffractometry, elemental and spectral analysis, is permethylated dinuclear complex with long aliphatic bridge. Thermal and magnetic properties were studied. In addition, the formation of magnetically induced stripe-ordered domains was highlighted by the magnetic force microscopy (MFM) on films born from diluted solution.     

New 3D metal–organic framework isomer containing trinuclear oxo-centered mixed valence iron

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Positron annihilation lifetime spectroscopy study of polyvinylpyrrolidone-added polyvinylidene fluoride membranes: Investigation of free volume and permeation relationships

Polyvinylidene fluoride (PVDF) membranes were prepared via the phase inversion method from casting solutions containing PVDF, dimethylformamide (DMF), and polyvinylpyrrolidone (PVP) as pore former. PVP was used in the casting solution in a range of 0–5 wt % and extracted. The effect on membranes of using PVP in the casting process was analyzed by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, viscosity, and water permeability techniques. With an increase of PVP from 0 to 5 wt %, the PVDF casting solution viscosities increased from 858 to 1148 cP; the resulting PVDF membrane thickness increased; and the crystallinity of PVDF membranes decreased from 40.0 to 33.3%, which indicates that the addition of PVP inhibits the degree of crystallization in the PVDF membranes. SEM results revealed the shape and size of macropores in the membranes; these macropores changed after PVP addition to the casting solutions. The impact of structural changes on free-volume properties was evaluated using positron annihilation lifetime spectroscopy (PALS) studies. PALS analysis indicated no effect on the average radius (~3.4 Å) of membrane free-volume holes from the addition of PVP to the casting solution. However, the percentage of o-Ps pick-off annihilation intensity, I₃, increased from 1.7 to 5.1% with increased PVP content. Further, increasing the PVP content from 0.5 to 5% resulted in an increased final pure water permeability flux. For instance, the 210 min flux for a 14% PVDF + 0.5% PVP membrane was found to be 3.3 times greater than a control membrane having the same PVDF concentration. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 589–598