低浓度三分子模型差速流动引起的化学不稳定性

建立了低浓度三分子反应模型反应 流动 扩散方程 ,理论分析了出现差速流动化学不稳定的条件 ,得到了临界流动速率c 和扰动波包的群速度vg,讨论了扰动增长率与流速的关系 ,并理论研究了出现不稳定时系统的时、空结构 .研究结果表明 ,化学反应在低浓度条件下也可能出现差速流动引起的化学不稳定 .     

热非局域非线性高阶界面孤子的多种孤子解

讨论了是光束在(1+1)维的热致非局域介质中的传输, 此介质在中心处被分为两部分, 两部分的线性折射率是不同的. 发现在中心处的界面附近存在多阶稳定的界面孤子. 本文研究的是五阶和六阶界面孤子, 它们都存在三种不同的孤子解. 三种孤子解的波形、束宽、光束重心、存在和稳定区间都是不相同的. 五阶孤子的三种解都存在稳定区间, 并且其中两个解存在共同稳定区域. 然而六阶孤子只有其中一种解存在稳定区间.     

周期驱动的一维台球模型的量子扩散特性

经典的一维台球模型(1D-KBM)是一个不连续的哈密顿系统,一种由不连续所导致的新型随机网结构存在于1D-KBM的相空间中,曾对其经典的扩散特性作过深入的探讨.就1D-KBM的量子扩散特性作了进一步的讨论,通过与经典扩散特性的对比,发现了经典扩散特性与量子扩散特性之间存在着一定的联系,而更多的量子系统所特有的特性也被揭示出来,特别是参数α分别处于区间［0,π/2)和［-π/2,0)上时系统所表现出来的完全不同的演化特性. 关键词：     

非局域非线性耦合器中暗孤子的传输

研究了空间暗孤子在非局域非线性耦合器中的新解和传输稳定性.发现非局域非线性耦合器中存在稳定的基态暗孤子和多极暗孤子的束缚态.分析了非局域程度、非线性参数、传播常数和耦合系数变化对基态暗孤子的峰值、束宽和功率的影响.讨论了基态暗孤子和多极暗孤子的传输稳定性,发现基态暗孤子在其存在的区域总是稳定的,偶极以及多极暗孤子存在不稳定区间,稳定区间取决于传播常数和介质的非局域程度,并且多极暗孤子的稳定传输还受孤子间距的影响.     

竖直上升通道RP-3航空煤油不稳定流动换热特性及临界准则

针对空-油换热器的冷却换热问题,对竖直上升圆管内超临界压力RP-3航空煤油的不稳定流动换热开展了实验研究.探究了由稳定流动换热向不稳定流动换热的过渡过程,考察了测量参数的振荡特性和机理,阐述了质量流量、进口压力、进口温度对壁温振荡和不稳定边界的影响.提出了两个无量纲参数,建立了不稳定边界预测准则.结果表明:通道施加高热...     

双层非线性耦合反应扩散系统中复杂Turing斑图

采用双层耦合的Brusselator模型, 研究了两个子系统非线性耦合时Turing 模对斑图的影响, 发现两子系统Turing 模的波数比和耦合系数的大小对斑图的形成起着重要作用. 模拟结果表明: 斑图类型随波数比值的增加, 从简单斑图发展到复杂斑图; 非线性耦合项系数在0–0.1时, 系统1中短波模在系统2失稳模的影响下不仅可形成简单六边形、四边形和条纹斑图, 两模共振耦合还可以形成蜂窝六边形、超六边形和复杂的黑眼斑图等超点阵图形, 首次在一定范围内调整控制参量观察到由简单正四边形向超六边形斑图的转化过程; 耦合系数在0.1–1时, 系统1中短波模与系统2失稳模未发生共振耦合仅观察到与系统2相同形状的简单六边形、四边形和条纹斑图. 关键词： Brusselator模型 非线性耦合 Turing模     

Al表面的"类液"结构及其自扩散通道

应用分子动力学方法,采用嵌入势模型在熔点下和熔点上对Al(001),(110)和(111)表面的原子结构和自扩散现象进行研究.发现这些表面的第一层原子在低于熔点时,Al(110)面在700±10 K,Al(001)面在 860±10 K,Al(111)面在 930±10 K呈现明显自扩散且最终转变为"类液"结构,而其余各层仍保留有序状态.对这种"类液"结构进行均方位移、结构有序参数、径向分布函数和z向粒子密度分析,发现其结构和扩散行为与熔化的Al表面不同,并能在一定温度区间稳定存在.在"类液 关键词： 表面结构 分子动力学 自扩散     

横荡条件下不稳定射流压力振荡主频实验研究

蒸汽浸没射流具有高效的传热传质特性,在核反应堆等相关系统中有重要应用,但其凝结过程会产生压力振荡,危及相关设备的安全稳定运行。本研究对横荡条件下不稳定射流的压力振荡主频进行了实验研究,获得了不同横荡参数对压力振荡主频的影响规律。研究结果表明,横荡条件下不稳定射流的压力振荡主频高于静止条件下,在横荡周期为2 s,横荡幅值为70 mm时,压力振荡主频最大增幅达到102.7%,并且压力振荡主频随着横荡周期和过冷水温度的增加而减小,随着横荡幅值的增加而增加。     

燃料空气供给条件对热声不稳定燃烧影响的研究

对Solar低排放预混燃烧系统的燃烧稳定性进行了数值研究.应用非定常N-S方程、雷诺应力紊流模型及涡团耗散燃烧模型,数值模拟了该类型燃烧器在不同的燃料空气供给条件下的气流流动特性和压力振荡特性,并给出了不稳定发生时压力和速度振荡的幅值和频率.根据供给条件的不同,燃烧可以是稳定的或是不稳定的,取决于燃料到火焰前沿的迟滞时间.采用CFD方法,可精确地获得燃料到火焰前沿的迟滞时间,证实了所采用的模型能够精确预测不稳定燃烧的出现及振荡特性.通过调整燃料与空气的供给条件,可使振荡激励或阻尼.     

α稳定噪声环境下多频微弱信号检测的参数诱导随机共振现象

本文将α稳定噪声与双稳随机共振系统相结合, 研究了不同α稳定噪声环境下高低频(均为多频)微弱信号检测的参数诱导随机共振现象, 探究了α稳定噪声的特征指数α(0 < α ≤ 2)和对称参数β (-1≤ β ≤ 1)及随机共振系统参数a, b对共振输出效应的作用规律. 研究结果表明, 在不同分布的α稳定噪声环境下, 通过调节系统参数a和b均可诱导随机共振来实现多个高、低频微弱信号的检测, 且存在多个a, b参数区间均可诱导随机共振, 这些区间不随α或β的变化而变化; 在高、低频微弱信号检测中, α或β对随机共振输出效应的作用规律相同. 本研究结果将有助于α稳定噪声环境下参数诱导随机共振现象中系统参数的合理选取, 进而可为实现基于随机共振的多频微弱信号检测方法的工程应用奠定基础. 关键词： 随机共振 α稳定噪声')" href="#">α稳定噪声 多频微弱信号检测 平均信噪比增益     

Ordinary Mode Instability in a Cairns Distributed Electron Plasma

Employing the linearized Vlasov-Maxwell equations, a generalized dispersion relation for the ordinary mode is derived by employing the Cairns distribution function. The instability of the mode and its threshold condition is investigated. It is found that the temperature anisotropy χ = T_∥/T_⊥ 1 required to excite the instability varies with density values whereas the growth rate is dependent on various parameters like non-thermality Λ, equilibrium number density n_0 and temperature anisotropy. It is found that with the increase in the values of any of the parameters Λ, n_0 and χ, the growth rate is enhanced and the k-domain is enlarged. The results are applicable for space plasma environments like solar wind.     

离子通道摇摆电子束流激发的纵向慢波不稳定性

考虑相对论电子束入射等离子体所产生的离子通道的具体结构,利用线性电磁流体力学理论对离子通道摇摆电子束激发的纵向慢波电磁不稳定性进行研究.通过对导出的系统色散关系的数值分析,给出了系统中电磁波、空间电荷波以及两者在一定条件下互作用形成的电磁-静电混合模式的传播特性.研究发现系统在慢波区域存在电磁不稳定性,并揭示此慢波不稳定性是由电子束的betatron振荡所导致,且系统的不稳定性程度与betatron振动频率密切相关.对betatron振荡激发的慢波电磁不稳定性物理机理进行了分析,并给出了不稳定性存在的条件 关键词： 离子通道 betatron振荡 电磁不稳定性     

Oscillating two-stream instability of a lower hybrid wave in aninhomogenous plasma

The effect of the density inhomogeneity on the oscillating two-stream instability of a lower hybrid pump wave with a finite wavelength is investigated. The density inhomogeneity introduces dephasing that restricts the interaction region where the matching conditions hold. The loss of energy due to convection from this region introduces a certain convection threshold for the onset of this instability. The coupled differential equations are solved in Fourier space by converting them into an uncoupled eigenvalue equation and then applying a quantization condition. Expressions are obtained for the growth rate and the convective threshold, and the results are applied to the Princeton Large Torus parameters     

Turing instability for a semi-discrete Gierer-Meinhardt system

In this paper, we investigate the spatial patterns of a Gierer-Meinhardt system where the space is discrete in two dimensions with the periodic boundary condition and time is continuous, in contrast to the continuum models. The conditions of Turing instability are obtained by linear analysis and a series of numerical simulations are performed. In the instability region, we have shown that this system can produce a number of different patterns such as stripes and snowflake pattern, other than ubiquitous fix-spotted patterns. As mentioned, the results are substantiated only by means of snapshots of the apatial grid. However, we also give some analysis by using the time series at three random grids and of the average value of states, that is, the stable state patterns can be observed. On the other hand, the effects of varying parameters on pattern formation are also discussed. Moreover, simulations for fixed parameters and special initial conditions indicate that the initial conditions can alter the structure of patterns. The patterns can form as a consequence of cellular interaction. So patterns arising from a semi-discrete model can present simulations on a geometrically accurate representation in biology. As a result, our work is interesting and important in ecology.     

Two-stream instabilities in degenerate quantum plasmas

The quantum effects on the plasma two-stream instability are studied by the dielectric function approach. The analysis suggests that the instability condition in a degenerate dense plasma deviates from the classical theory when the electron drift velocity is comparable to the Fermi velocity. Specifically, for a high wave vector comparable to the Fermi wave vector, a degenerate quantum plasma has larger regime of instability than predicted by the classical theory. A regime is identified, where there are unstable plasma waves with frequency 1.5 times of a normal Langmuir wave.     

Bifurcation analysis and amplitude equations for viscoelastic convective fluids

Summary The possible bifurcations of a convective instability in viscoelastic fluid are studied. The viscoelastic behaviour is modelized by means of the Oldroyd type fluid whose parameters can be adjusted to suit a large class of polymeric fluids. We analyse in some detail bifurcations of codimension one (stationary or oscillatory convection) and codimension two for such kind of fluids. By a weak nonlinear analysis, the coefficients of the amplitude equations corresponding to the different bifurcations are also determined. It has been found that the nature of the convective solution depends crucially on both the viscoelastic parameters and the constitutive equation used to describe the fluid.     

The refined inviscid stability condition and cellular instability of viscous shock waves

Combining the work of Serre and Zumbrun, Benzoni-Gavage, Serre, and Zumbrun, and Texier and Zumbrun, we propose as a mechanism for the onset of cellular instability of viscous shock and detonation waves in a finite-cross-section duct, the violation of the refined planar stability condition of Zumbrun-Serre, a viscous correction of the inviscid planar stability condition of Majda. More precisely, we show for a model problem involving flow in a rectangular duct with artificial periodic boundary conditions that transition to multidimensional instability through violation of the refined stability condition of planar viscous shock waves on the whole space generically implies for a duct of sufficiently large cross-section, a cascade of Hopf bifurcations involving more and more complicated cellular instabilities. The refined condition is numerically calculable as described by Benzoni-Gavage-Serre-Zumbrun.     

Collisional effects on the current-filamentation instability in a dense plasma

The collisional current-filamentation instability (CFI) is studied for a nonrelativistic electron beam penetrating an infinite uniform plasma. It is analytically shown that the CFI is driven by the drift-anisotropy rather than the classical anisotropy of the beam and the background plasma. Therefore, collisional effects can either attenuate or enhance the CFI depending on the drift-anisotropy of the beam-plasma system. Numerical results are given for some typical parameters, which show that collisional effects cannot stabilize but enhance the CFI in a dense plasma. Thus, the CFI may play a dominant role in the fast electron transport and deposition relevant to the fast ignition scenario (FIS).     

Statistical Approach of Modulational Instability in the Class of Derivative Nonlinear Schrödinger Equations

The modulational instability (MI) in the class of NLS equations is discussed using a statistical approach (SAMI). A kinetic equation for the two-point correlation function is studied in a linear approximation, and an integral stability equation is found. The modulational instability is associated with a positive imaginary part of the frequency. The integral equation is solved for different types of initial distributions (δ-function, Lorentzian) and the results are compared with those obtained using a deterministic approach (DAMI). The differences between MI of the normal NLS equation and derivative NLS equations is emphasized. PACS: 05.45.     

航天光学遥感器光机结构尺寸稳定性变化对成像质量的影响

发射过程中的力学环境和在轨运行时的热环境,影响航天光学遥感器的尺寸稳定性,进而影响成像质量。用光学元件相对各自理想位置的变化、光学元件方程参数的变化和光学元件面形质量的变化表示遥感器光机结构尺寸稳定性的变化。结合实际工程项目,利用Zemax软件,分析主、次镜离焦、离轴、倾斜以及非球面方程参数变化对成像质量的影响。结果表明,离焦和非球面方程参数变化对成像质量影响较离轴和倾斜敏感。