群速度

Generally speaking, the high group velocity and low attenuation factor and high Q〓 in the same area, but relatively low group velocity and high attenuation factor and low Q〓 in the same area in China is the general distribution.

在不同周期，面波衰减系数或品质因子在整个中国大陆区域分布是不均匀的；总体表现为高群速度分布的区域呈现高Q〓和低衰减系数、低群速度分布的区域呈现低Q〓和高衰减系数分布的特点。

On the basis of the dispersion relation, we investigated the properties of nonlinear surface waves. It is shown that there exist backward surface waves, with the phase velocity and group velocity opposite in direction. For transverse electric waves, the nonlinear wave equation is transformed into Bernoulli equation, and the exact solutions of magnetic fields are obtained.

在色散关系的基础上研究了非线性旋磁表面波的频率特性，揭示了该系统能激发后向表面波，其群速度与相速度反向；将反铁磁晶体中TE表面波满足的非线性波动方程变形为伯努利方程，用反函数形式给出了表面波磁场的精确解。

In order to solve the problem,starting from the analysis of the simplest plane wave numerical theory,we derived the formula of relative phase velocity and group velocity under the condition of arbitrary high-order finite-difference approximation,and gave the computational method for acquiring the optimum Courant number,and then analyzed the anisotropic effects due to finite difference approximation.

针对此，从最简单的平面波数值理论分析出发，推导了任意高阶有限差分近似条件下相对相速度和相对群速度的计算公式，给出了求解最佳Courant数的计算方法，分析了差分近似造成的各向异性效应。

Phase velocity and group velocity are important characteristics of elastic wave propagation.

相速度、群速度是弹性波传播的重要特征。

The group velocity is the speed at which modulated signals would be transmitted.

群速度就是将调制信号发送出去的速度。

The guided wave group velocity was calculated according to the experiment result, and the location of damage was estimated with the group velocity and time of flight.

通过对实验结果的处理分析，计算出导波的群速度，并根据群速度和飞行时间得到了损伤的位置信息。

Transversely isotropy; phase velocity; group velocity; ray parameter; group-phase deviation

横向各向同性；相速度；群速度；射线参数；群相偏离

Through detailed calculation and analysis of the dispersion characteristic of the noble metals like Au and Ag, we found that the group velocity combined with the group refractive index can change from negative to positive with increase of the photons energy in the visible Drude region and has the spectral property which is in agreement with the experimental results obtained in this work.

通过对贵金属Au和Ag的光学常数的色散特性分析和数值计算，发现在可见光的Drude光谱区，表征光子能量传播方向的群速度和群折射率的值会随光子能量的增大而发生从负到正的改变，这与本论文研究的实验测量和观察结果相符合。

The phase and group velocities of Lamb waves in the aluminum plate related to the frequency and the thickness of the plate because of the material characters. However, for the carbon fiber composite lamina, the situation was of difference, in which the velocities were with regarded to the frequency and thickness as well as the propagational direction and the fiber orientation.

输入铝板和碳纤维板的材料参数，即可得出铝板和碳纤维材料单层板中Lamb波的频散曲线，铝板为各向同性材料，其中的Lamb波相群速度只与频率板厚的乘积相关，碳纤维板为各向异性材料，其中的Lamb波相群速度不仅与频厚积有关，还与Lamb波传播方向、碳纤维的铺层方向相关。

Evidence suggests that 1 under more stable stratification, the basic flow, if moving faster at low and high levels (particularly in the presence of jets there), allows a resulting meso-β unsteady wave to propagate eastward with respect to basic flow and even at greater velocity compared with it; 2 vertical windspeed shear of basic flow causes instabilities of the TWT perturbation; 3 considering the second derivative of basic-flow wind with respect to z (denoted by zz≠ 0 which is simply given as β* hereafter) the expression for the phase velocity of vortex Rossby wave is obtained, which is unidirectional in propagation with respect to basic flow; 4 VRoW has its physical origin from β*, i.e., from z-varying heterogeneities of y-direction averaged vorticity of the basic flow field; 5 VRoW phase velocity is associated with zonal wave number k, its energy is dispersive and the group velocity exists in the x direction; 6 when windspeed meets the condition of β*, TWT disturbance instability may be that of mixed VRoW and gravity wave; 7 if basic flow is subject to linear shear but does not meet the condition of β*, the TWT instability is that of inertia-gravity wave.

在大气层结比较稳定的情况下，如果基本气流在低层和高层较大(有可能存在低空急流和高空急流)，此时产生的β中尺度不稳定扰动相对于基流向东传播，甚至于快速向东传播。基本气流在垂直方向上的风速切变对于中尺度横波型的扰动起着不稳定的作用。如果考虑基流的二次切变，可以得到涡旋Rossby波的相速度表达式，涡旋Rossby波相对于基本气流是单向传播的。涡旋Rossby波产生的物理根源是基本流场的风速二次切变，亦即基本流场y方向的平均涡度在空间z方向上的不均匀所致。涡旋Rossby波的相速度与纬向波数也有关，它的能量是频散的，其在纬向x方向也存在群速度。在基本流场的风速存在二次切变时，横波型不稳定可能是混合的涡旋Rossby重力波的不稳定；而在基本流场的风速仅仅存在线性切变，不存在二次切变时，横波型扰动的不稳定则是重力惯性波的不稳定。

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％。