条件不稳定性

PIC results show that the occurrence of absolute instability is determined by the operating current.

通过PIC模拟，给出了采用无损耗波导结构，且工作电流为25A和10A条件下的放大器频谱图和功率图，结果表明绝对不稳定性的出现与否主要由工作电流是否超过起振的阈值电流决定，损耗波导是抑制绝对不稳定性的有效手段。

A threshold current which brings about the transition to absolute instability was investigated.

分析表明，绝对不稳定性的起振存在一定阈值，起振电流对电子注参数和电路参数极其敏感，确定起振电流是稳定器件工作的前提条件。

In the second chapter, we investigate propagations of desynchronous disturbances in synchronized chaotic one-way coupled map lattices. It is well known that spatiotemporally chaotic systems with large gradient couplings may show convective instability under the absolute stability condition of chaos synchronization. This convective instability is the key reason for the effective propagation of control signals.

时空混沌在不同的耦合系数情况下会表现出不同的动力学行为，用驱动实现具有强梯度耦合系数的时空混沌同步时，会观察到在绝对稳定条件下被驱动系统表现出对流不稳定性，这种对流不稳定性是在单个信号驱动下实现混沌同步的关键原因。

Based on the work of the first part, we studied the possibility of allyl as a protection group in the synthesis of oligonucleotides consisting in some unstable nucleotide analogues, such as nueleoside carbonate and sulfite.

在寡核苷酸的类似物中，碳酸酯及亚硫酸酯在碱性条件下的不稳定性使其在合成上有一定的困难，这限制了对它们的性质作进一步的研究。

Several common degradation phenomena were summarized from some recent typical research work on the reliability of low-temperature processed poly-silicon thin film transistors, which includes self-heating, hot carriers and negative gate bias temperature instability. Degradation mechanisms and models are presented as well as conclusions of their influences on various device parameters and typical stress conditions.

结合近几年来国际上对于低温多晶硅薄膜晶体管器件可命性开展的一些有代表性的研究工作，对其中几种常见的退化现象：自加热、热载流子和负偏置温度不稳定性做了分析和归纳，介绍了其退化机制及退化模型，并总结了它们在一般情况下对器件性能的影响及各自的典型应力条件。

1Niche construction can lead to stable coexistence of diverse genotypes in spatially structured population, which supports a stable polymorphism even without heterozygote superiority.(2)With habitat deterioration, niche construction accelerates the formation of steady polymorphism and hence impedes the harmful influences of environment on the population, which might embody a life-history strategy of organism under the unfavorable environment.(3)Niche construction results in the coexistence with alternative polymorphism through genotype-environment feedback and limited gene flow.(4)The niche-constructing organism is an active force to alter its environment and hence the direction of natural selection in order to better survival.(5)Spatial dynamics and distribution pattern of metapopulation are profoundly influenced by time-lagged niche construction.(6)Metapopulation size can reach a fixed level in the recency effect and equal weighting of time lag but is statistical stability in primacy effect, which implies the primacy effect is most remarkable.(7)The increment in the relative weightingof each generation\' niche construction and the length of time lag are significant factors for system destabilization.(8)Moderate capacity of positive niche construction benefits the metapopulation persistence.(9)The narrowing of niche breadth can decrease the metapopulation size and thereby increase the extinction risk.(10)The coupled function of time lag and niche construction make the system oscillation and generate the spiral wave, spiral-broken and circular wave in heterogeneous habitat.The spatial distributions of metapopulation and resource content are complementary due to a phase lag of their both frequencies.(12)Metapopulation persistence with niche construction depends not only on the balance between colonization and extinction, but also on the balance between the ability of niche construction and natural dissipation of habitat.(13)Metapopula-tion can survive under certain condition when the percent of suitable patches in habitat is lower than the ration of extinction to colonization.(14)Two thresholds exist in the process of transition of habitat quality dynamics from unsuitable to suitable, which include the intensity of niche construction and the initial condition of system.(15)Metapopulation size is positive correlated with the ability of positive niche construction, which means that organism or population who has strongly positive influences on their environment plays an important role to maintain the available habitat.

通过上述几个方面的研究，主要得出以下15条结论：(1)生态位构建可使空间结构种群，甚至是在没有杂合子优势的条件下，形成多种可能的稳定基因型分布模式；(2)随着环境的破坏与恶化，种群的生态位构建作用加速其较早形成稳定多态以阻碍环境对种群的不利影响，解释了有机体在不利环境下的一种生活史对策；(3)生态位构建作用通过基因型—环境反馈机制及有限的基因交流导致基因型多态的稳定共存；(4)有机体的生态位构建作用是一种积极的动力改变环境进而改变其自然选择的方向；(5)生态位构建的时滞作用对集合种群动态和空间分布产生深刻影响；(6)集合种群大小在时滞的崭新效应和等权重效应下达到一固定值，而在首位效应下达到统计稳定，表明首位效应的影响最显著；(7)首位效应下生态位构建相对权重的增量和时滞的长度是影响系统不稳定性动态的关键因素；(8)适中的生态位构建强度有利于集合种群的续存；(9)生态位宽度变窄会减少集合种群的数量从而增加其灭绝风险；(10)时滞和生态位构建的双重作用使系统产生周期振荡，并在异质性环境中产生稳定的螺旋波，破碎的螺旋波和环形波三种分布模式；(11)集合种群与资源含量的空间分布因为相滞而互补；(12)具有生态位构建的集合种群续存不仅取决于侵占率与灭绝率之间的平衡，而且依赖于生态位构建能力同其生境的自然消耗速率之间的妥协；(13)当生境中适合侵占的斑块比例小于其侵占率与灭绝率之比时，生态位构建作用促使集合种群在一定条件下续存：(14)生境斑块的状态从不适合到适合转变过程中存在生态位构建强度和系统初始条件这两个阈值；(15)集合种群的大小同正生态位构建能力正相关，意味着对环境具有较强正作用的有机体对维持有效生境起积极作用。

Therefore, the moist potential vorticity analysis associated with the mesoscale convective system was researched in the paper, so as to reveal the moist potential characteristics of mesoscale convective system in typhoon circulation. The results showed that, during the generation stage, convective instability characterized by MPV1 was a favorable condition for forming MCS, while the vorticity which was caused by the slantwise isentropic surface and the vertical shear of the horizontal wind characterized by MPV2 was an inspiring mechanism. The specific process was that, the atmosphere exhibited the feature of strong convective instability at the low level of convection areas and the southeast areas, which included plenty of erratic energy. The slantwise ascended the stream transfer the erratic energy to northwest, where the stratification stability was small. As decreased, the cyclonic vorticity increased. On the other hand, the vorticity caused by the slantwise isentropic surface and the vertical shear of the horizontal wind inspired the release of convective instability and as a result that the MCS formed. During the development stage, the cyclonic vorticity increased quickly with the persistent decreasing of . Meanwhile, the inclination of isentropic linewas bigger than the absolute momentum line at middle level, which exhibited the feature of conditional symmetric instability , then the conditional symmetric instability was forced to release by the vorticity resulted from the slantwise isentropic surface and the vertical shear of horizontal wind, and the MCS developed.

结果表明，在对流形成阶段，MPV1即对流不稳定为MCS的形成提供背景不稳定条件，由MPV2即湿等熵面的倾斜和水平风的垂直切变而引起的涡旋发展作为强迫机制：MCS形成的区域及东南区域中低层是强对流不稳定层，蕴含丰富的不稳定能量，倾斜上升运动把对流不稳定区具有强不稳定能量的暖湿空气向西北中层的中性层结区输送，由于的减小，气旋性涡度增强，有利于形成对流，另一方面，由于湿等熵面倾斜和低空急流加强而引起的涡旋发展作为一种强迫机制激发对流不稳定能量得到释放，从而形成对流；在对流系统地发展阶段，由于低层的对流不稳定性进一步减弱，进一步减小，气旋性涡度进一步增强，有利于MCS的增强，中层等θe 线的倾斜度比绝对动量M 等值线的倾斜度大，对应有条件对称不稳定区域，满足条件对称不稳定条件，在湿等熵面倾斜和台风低空急流作用下引起的涡旋发展强迫对称不稳定能量释放，从而使得对流得以维持和加强。

In annular flow, a lower critical flow velocity of shell system is got if steady viscous effects are considered.

二、对固支—简支端部边界条件下的同轴圆柱壳体系统的流致不稳定性进行了系统的参数研究。

Firstly, we simulate the influence of pump waves on two-stream instability occurred at heights of equatorial ionospheric E region. The simulation results show that pump waves can control the two-stream instability, that's to say, pump radio can stabilized or unstabilized this instability.

首先，模拟了加热泵波对赤道电离层E区双流不稳定性的影响，模拟结果定性地表明，在一定条件下，加热泵波对发生在该区域的双流不稳定性有很好的致稳或不稳作用。

The wave propagation and refraction of type "O" irregularities in the counter-electrojet conditions is investigated with a model electrojet in terms of the linear theory of the electrojet instability.

本文分析了反向赤道电射流条件下的不均匀性的对流放大特性。根据电射流不稳定性的线性理论，对一个分层均匀的电射流的模式的数值计算表明：在反向电射流条件下，电射流不均匀性有如下的特性：在波的传播过程中，在上电射流区内，波矢向下旋转，在下电射流区内，波矢向上旋转；在驱动电场E_D数值相同的情况下，反向电射流条件下的射线路径积分增长率r比正常电射流情况的要小得多。

Breath, muscle contraction of the buttocks; arch body, as far as possible to hold his head, right leg straight towards the ceiling (peg-leg knee in order to avoid muscle tension).

呼气，收缩臀部肌肉；拱起身体，尽量抬起头来，右腿伸直朝向天花板（膝微屈，以避免肌肉紧张）。

The cost of moving grain food products was unchanged from May, but year over year are up 8%.

粮食产品的运输费用与5月份相比没有变化，但却比去年同期高8％。