变阈作用

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。

Proceed from the principle of neural networks, the mechanism of mapping between input and output of neural networks was analyzed, and the BP algorithm for training the thresholds of neurons was derived. Based on the study to the distinguishability of input of networks, the effect of neural networks to distinguish-ability of characteristics was studied, and the optimizations of the structure of networks, learning rate, impulse factor, thresholds of neurons and initial weight of networks were completed. Through the experiments under fixed cutting regime and alternative cutting regime, the methods based on neural networks for tool wear monitoring were studied.

本文从神经网络的基本原理出发，研究了神经网络输入输出的映射机理，探讨了神经网络处理方法具有自适应性的原因；推导了神经元阈值学习BP算法；在研究网络输入特征可分性准则和特征敏感性准则的基础上，探讨了神经网络对特征可分性的作用；完成对网络结构参数、网络学习率和冲量因子、神经元阈值以及网络初始权值等参数的优化；并在固定切削用量和变切削用量条件下，对基于神经网络的刀具磨损检测方法进行了实验研究。

Integral transform is employed to acquire response character istic of ner...

从时空两域阐述神经纤维对不同时变磁场诱导作用下的阈下响应行为，对磁刺激仪中刺激线圈的刺激电流的选择和线圈尺寸的设计都具有指导意义。

The results showed that:(1) The characteristic frequency of IC neurons of house mouse was increased with increasing recording depth, and the masker intensity used was positive relevant to the IC neurons\' minimum threshold. When the minimum threshold was high, the masker intensity needed was loud, vice versa.(2) According to the masking rate at MT+10dB of IC neurons to frequency modulation and tone burst, the IC neurons were classified as three types: type I neurons ( 72/113, 63.7%), in which the masking effect of TB was better than frequency modulation ;type II neurons (32/113, 28.3%), in which the masking effects of the two maskers were same; type III neurons( 9/113, 8.0%), in which the masking effect of FM was better than TB.(3) Type I neurons, the minimum threshold of which was low, but the Q_(10) and DR values of which were large; in type III neurons, the minimum threshold was high, the Q_(10) and DR values were narrow; in type III neurons, the MT Q_(10) and DR values were in between.(4) Both FM and TB could make the MT of type I neurons shift upward distinctively, but the effect of TB was more significant than FM.(5) The Q_(10) values of type I neurons became narrower under the influence of TB, were unaffected under the influence of FM.

结果显示：(1)小鼠下丘神经元的特征频率随着记录深度的增加而增高，掩蔽声强度与神经元的最小阈值呈正相关，即对高最小阈值的神经元进行掩蔽时需要的掩蔽声强度高，对低最小阈值神经元进行掩蔽需要的掩蔽声强度低：(2)根据调频声(frequency modulation， FM)和短纯音(tone burst， TB)对下丘神经元阈上10dB处反应的掩蔽，将小鼠IC神经元分为三类：Ⅰ类神经元(72/113，63.7％)，短纯音的掩蔽效果比调频声更好；Ⅱ类神经元(32/113，28.3％)，两者对神经元声反应的掩蔽率相同；Ⅲ类神经元(9/113，8.0％)，调频声的掩蔽效果更好；(3)Ⅰ类神经元的最小阈值低、Q_(10)值和动态范围大，Ⅲ类神经元最小阈值高、Q_(10)值和动态范围小，Ⅱ类神经元的最小阈值、Q_(10)值和动态范围介于Ⅰ和Ⅲ类神经元之间；(4)短纯音和调频声都可以使Ⅰ类神经元声反应的最小阈值明显上移，但短纯音使神经元最小阈值的上移更显著：(5)短纯音使Ⅰ类神经元的Q_(10)值变小，调频声使神经元的Q_(10)值增大不显著，短纯音与调频声对神经元Q_(10)的影响差别显著；(6)短纯音与调频声都使神经元的动态范围减小，并且作用显著，但短纯音的效果更显著：(7)短纯音与调频声都使神经元反应的潜伏期延长，效果显著，但TB的延长作用更为显著；(8)随着探测声强度的升高，短纯音和调频声对Ⅰ类神经元声反应的掩蔽率都降低，但在各个探测声强度短纯音的掩蔽率都比调频声高。

I didn't watch TV last night, because it .

昨晚我没有看电视，因为电视机坏了。

Since this year, in a lot of villages of Beijing, TV of elevator liquid crystal was removed.

今年以来，在北京的很多小区里，电梯液晶电视被撤了下来。