临界频率

南极中山站电离层F2层临界频率变化特征

Variations of the ionospheric F2 layer critical frequency at Zhongshan Station , Antarctica

从非线性傍轴波动方程出发，利用坐标变换，推导出发散光束小尺度扰动的传输方程，进而得到小尺度扰动增长的临界频率、最大增长频率和相应B积分值的变化规律。

Based on the nonlinear paraxial wave equation , the propagation equation of small-scale perturbation of divergent beams has been deduced with a coordinate transformation . The evolvement law of the growth critical frequency of small-scale perturbation , maximum growth frequency and relative B integral is obtained .

主要是在一定的输入功率下，小尺度调制增长的临界频率、最快增长频率及其对应的最大增益（B积分）均随介质增益或传输距离的增大而增大；

For a given input power , the cutoff spatial frequency , the fastest growing frequency and the maximum perturbation growth , in an amplifying medium , increase with the increase of the gain of the medium and propagation distance .

在电离层风暴期，现存的电离层F2层临界频率预测方法不能满足实际应用的要求。

During ionospheric storm periods , the existing prediction methods for the critical frequency of ionospheric F2 layer ( foF2 ) can not satisfy the requirements of the practical applications .

计算结果能较好地反映出E层电子密度峰值（NmE）或E层临界频率（foE）的日变化、季节变化以及随太阳活动的变化趋势。

The diurnal , seasonal and solar variation tendencies of electron peak density ( N m E ) or critical frequency ( f o E ) in E layer are revealed preferably in the computing results .

分析日本4次地震前5个电离层垂测站资料，发现地震前后震中附近夜间电离层偶发E层的临界频率f0ES值多数呈下降趋势，少数呈增加趋势。

The data of 5 ionospheric vertical sounding stations before 4 earthquakes in Japan are analyzed . It is found that most of the critical frequencies of the E sporadic layer tended to decrease and the only few tended to increase around the epicenters before and after the earthquakes .

本文给出了计算中纬E层临界频率（f（0E））和低电离层的电子密度分布与太阳天顶角、太阳黑子数、地方时之间关系的经验公式。

In this paper , experimental formulae of the critical frequencies of the E-layer in mid-latitudes and of the distribution of electron density in the lower ionosphere are found . These formulae are expressed in terms of the sunspots number , the solar zenith angle and the local time .

本文运用FEM将受周期轴向动载荷的铁木辛柯交叉梁系的动力稳定性控制方程化为Mathieu-Hill型方程，然后用谐调平衡方法得到临界频率方程。

In this paper the control equation of the dynamic stability of the Timoshenko cross beams which undergo the periodic axial dynamic load is transformed into Mathieu & Hill type equation by using the finite element method . Then the critical frequency equation is obtained with the harmonic balance method .

利用Lagrange方程推导了在轴向周期压载作用下点弹性支承粘弹性杆的运动微分方程，并由动力稳定理论给出了杆的临界频率方程和动力不稳定边界。

The differential equation of motion for a viscoelastic rod with point elastic supports under the action of axially periodic load is derived by Lagrange ′ s equation . By using dynamic stability theory , the critical frequency equation and dynamic stability boundary of the rod are obtained .

对南极中山站数字式电离层测高仪1995~2002年观测数据的月中值进行了统计分析，揭示了中山站电离层F2层临界频率（foF2）的主要特征：foF2存在明显的日变化和年变化；

With the statistical analysis of the monthly medians from 1995 to 2002 of the DPS-4 ionospheric sounder at Zhongshan Station , Antarctica , main features of the ionospheric critical frequency ( f_oF_2 ) are revealed .

利用人工神经网络重构区域电离层临界频率分布

Reconstruction ionospheric critical frequency using Artificial Neural Network over limited region

参数共振临界频率的分析

Analysis of Critical Frequency of Parameter - Excited Resonance

对某一梯度指数以小的改变，当自然频率超过临界频率，它会有突变。

For some gradient index , the natural frequencies have an abrupt jump when across its critical frequencies .

对某一指数梯度梁，存在一个依赖梯度参数的临界频率。

For certain beams with exponential gradients , there exists a critical frequency depending on the gradient parameter .

指出响应谱峰值中的“临界频率”与“环频率”的重要意义。

The significance of the " critical frequency " and " ring frequency " in response is pointed out .

给出了一种利用仿真估计电路临界频率和电缆（传输线）特性阻抗的方法。

And two examples are given to estimate critical frequency of a car control circuit and the matching impedance of a special wire .

频率超过临界频率的传播波才能激起振动，否则振动不会产生。

Vibration can be only excited by propagating waves with frequencies in excess of the critical frequency , and otherwise vibration is prohibited .

研究表明，当扰动频率低于多壁碳纳米管的临界频率时，振动模态是同轴的；

The analysis shows that when the frequency is lower than the critical frequencies of the shells in MWCNT , the vibration mode is almost coaxial .

并根据天体物理的有关实测数据参数，给出了曲率辐射表达式的具体形式及临界频率与峰频的数值。

According to the measured data and parameters of Astrophysics , the concrete form of curvature radiation expression , the numerical value of critical and peak frequencies are presented here .

电离层临界频率的分形分析得到其相关维为2.7。其次，我们选用5个因子作为网络输入，用电离层观测资料训练网络，建立了我国南海地区电离层模式。

From analyses of the ionospheric critical frequency , their correlation dimensions are about 2 . 7 . Next , five factors are used as the input parameters of this ANN .

采用改进的双线性变换方法&临界频率预翘曲方法，对双线性变换方法引起的偏差进行预补偿，从而减小飞控系统的实时仿真误差。

In order to reduce the flight control system real time simulation error , the critical frequency prewarping approximation is adopted to compensate the error that resulted from the bilinear approximation .

进而提出了一种根据动力设备负载质量，激振频段下限频率值以及临界频率比设计主被动复合隔振系统的方法，完成了主被动复合隔振器主、被动环节的设计工作。

Then , a design method of active-passive composite isolation system based on the quality of power equipment , the lower frequency value of vibration frequency and the critical frequency ratio is derived .

举个例子来说，我们谈论的临界频率是，光从金属表面逐出一个电子，所需的最小频率。

So , for example , we were talking about a threshold frequency as in a minimum frequency of light that you need in order to eject an electron from a metal surface .

通过软件仿真的方法研究了信号完整性问题中的信号反射。以实例的形式给出了一种利用仿真估计电路临界频率的方法。

A method which use an EMC software tool to simulate signal reflection in signal integrality is introduced , and an example is given to estimate critical frequency of a circuit by simulation .

这些表达式建立在对该类表面在不同临界频率范围内弹塑性接触变形方式的分析基础上，是研究多重分形接触表面的有关分形性质所必需的。

Based on the analysis of elastic-plastic deformation 's mechanism of these surfaces in the different ranges of critical frequencies , these equations are necessary to research into some properties concerning fractal of these surfaces .

如果扰动频率至少高于多壁碳纳米管的一个临界频率时，振动模态是非同轴的，并以不同的波速传播，或低或高于单壁连续弹性壳模型的波速。

However , when the frequency is higher than at least one of the critical frequencies , non-coaxial vibration modes emerge and these vibrations propagate at various speeds significantly higher or lower than the speed predicted by the single-elastic-shell model .

求出了非线性色散方程，揭示了非线性s偏振表面波存在一个临界频率，低于这个频率，非线性s偏振波是后向表面波。

The nonlinear dispersion equation was derived . It is found that there is a critical frequency in the nonlinear s polarized surface waves . Below this frequency , the nonlinear s polarized waves on the interface are backward surface waves .

本文实验验证了泡状流压力波色散特性的临界频率现象，即高于临界频率，压力波的色散特性消失。

A new phenomenon about critical disturbed frequency of the pressure wave dispersion in bubbly flow was validated in the present experimental investigation , which the dispersion of pressure wave would disappear under the perturbation frequency greater than a critical value .

放电电流波形表明了放电形式的差异，在一定的高频段会出现均匀的辉光放电，其相应的临界频率还与气体种类等因素有关。

The measured waveforms of discharge current confirm the difference in discharge form . The homogeneous glow discharge will appear in a certain range of high frequency , and the critical frequency is related to some factors , such as gas properties .

当磁场的频率高于一个临界频率后，转子系统的动力特性与无磁场时的动力特性相同，正弦磁场不能够控制磁流变流体阻尼器的动力特性。

The dynamic character of the rotor system is the same as that without magnetic field when the magnetic field frequency is over a critical frequency , and the sinusoidal magnetic field cannot control the dynamic performance of the disk-type MR fluid damper .