超声波在液体中相速与群速的测量

简要叙述了相速与群速的定义,并用实验测量了超声波在不同液体中的相速与群速.     

光纤速度干涉仪

本文提出了一种用光纤作为延迟臂的新型速度干涉仪——光纤速度干涉仪,用以测量速度随时间的变化。选取不同长度的光纤,可测不同的速度范围。它扩展了测速范围,提高了测量精度。该系统提供两个相位差为90°的信号,因而提高了分辨率,并可鉴别加速与减速。     

用光学记录速度干涉仪测量自由面速度

建立了一套光学记录速度干涉仪系统(ORVIS),用于测量强激光产生的冲击波状态方程中的自由面速度。该光学记录速度干涉仪系统的时间分辨率为179 ps,可以测量自由面速度随时间变化的整个过程。在天光KrF高功率准分子激光装置上进行激光打靶实验,激光波长248.4 nm,脉冲宽度25 ns,最大输出能量158 J。在激光功率密度为6.24×1011W·cm-2的条件下,测得厚20 μm铁膜的自由面速度可达3.86 km/s;在激光功率密度为7.28×1011W·cm-2条件下,100 μm铝膜（靶前有100 μm的CH膜作为烧蚀层）的自由面速度可以达到2.87 km/s。     

用光学记录速度干涉仪测量自由面速度

 建立了一套光学记录速度干涉仪系统(ORVIS),用于测量强激光产生的冲击波状态方程中的自由面速度。该光学记录速度干涉仪系统的时间分辨率为179 ps,可以测量自由面速度随时间变化的整个过程。在天光KrF高功率准分子激光装置上进行激光打靶实验,激光波长248.4 nm,脉冲宽度25 ns,最大输出能量158 J。在激光功率密度为6.24×10¹¹W·cm^-2的条件下,测得厚20 μm铁膜的自由面速度可达3.86 km/s;在激光功率密度为7.28×10¹¹W·cm^-2条件下,100 μm铝膜（靶前有100 μm的CH膜作为烧蚀层）的自由面速度可以达到2.87 km/s。     

用自相关法测量横向流速

以LabVIEW为平台,搭建了横向流速测量实验系统.流动微粒对探测光起阻挡作用,导致透射信号强弱变化,通过归一化自相关函数可以计算粒子通过探测区域的渡越时间,测量探测区域宽度后,可以计算得到流速.     

Ultrasonic velocity hydration numbers of polyamines

Ultrasonic velocity hydration numbers of diamines, triamines and tetraamines and hydrochlorides of these amines were determined by measuring the maximum velocity of ultrasound in aqueous-ethanolic solutions. The results are interpreted on the basis of the hydrogen-bonded framework model of the water structure.     

瞬时速度的实验研究

研究了高中物理中理解瞬时速度概念的实验.通过理论分析,自制光电门和挡光板,使得测量速度最大程度接近了瞬时速度.     

左手介质中电磁波的传播速度

在同向介质中,电磁波的群速度一般是能量传播的方向,并且电磁波的相速度和群速度在大部分情况下都满足瑞利关系.为了研究左手介质的电磁特性,本文从理论上导出了左手介质中电磁波的相速度、群速度及其关系,得出左手介质中电磁波的群速度为负,并介绍了左手介质的一些应用前景.     

Comments on superoptic group velocity

A recent article, claiming to identify an electromagnetic system with a field whose group velocity is faster than light, is disproved.     

The correlations between the saturated and dry P-wave velocity of rocks

Sometimes engineers need to estimate the wet-rock P-wave velocity from the dry-rock P-wave velocity. An estimation equation embracing all rock classes will be useful for the rock engineers. To investigate the predictability of wet-rock P-wave velocity from the dry-rock P-wave velocity, P-wave velocity measurements were performed on 41 different rock types, 11 of which were igneous, 15 of which were sedimentary and 15 of which was metamorphic. In addition to the dry- and wet-rock P-wave velocity measurements, the P-wave velocity changing as a function of saturation degree was studied. Moreover, dry-rock S-wave velocity measurements were conducted. The test results were modeled using Gassmann’s and Wood’s theory and it was seen that the measured data did not fit the theories. The unconformity is due to the fact that the theories are valid for high-porosity unconsolidated sediments at low frequencies. Gassmann’s equation was modified for the rocks except high-porosity unconsolidated sediments.

The dry- and wet-rock P-wave velocity values were evaluated using regression analysis. A strong linear correlation between the dry- and wet-rock P-wave velocities was found. Regression analyses were repeated for the rock classes and it was shown that correlation coefficients were increased. Concluding remark is that the derived equations can be used for the prediction of wet-rock P-wave velocity from the dry-rock P-wave velocity.     

气垫导轨实验中滑块的等速和定速发射

设计了由改进的弹射架和定位释放器组成的等速发射装置,实现了气垫导轨实验中滑块的等速发射,并可通过控制滑块初始位置使滑块获得预期发射速度.分析表明滑块发射所获得的速度和初始位置间的关系为近似的线性关系,这一结论和实验结果完全符合.     

A new car-following model considering velocity anticipation

The full velocity difference model proposed by Jiang et al. [2001 Phys. Rev. E 64 017101] has been improved by introducing velocity anticipation. Velocity anticipation means the follower estimates the future velocity of the leader. The stability condition of the new model is obtained by using the linear stability theory. Theoretical results show that the stability region increases when we increase the anticipation time interval. The mKdV equation is derived to describe the kink--antikink soliton wave and obtain the coexisting stability line. The delay time of car motion and kinematic wave speed at jam density are obtained in this model. Numerical simulations exhibit that when we increase the anticipation time interval enough, the new model could avoid accidents under urgent braking cases. Also, the traffic jam could be suppressed by considering the anticipation velocity. All results demonstrate that this model is an improvement on the full velocity difference model.     

Oneway Sagnac device to measure absolute velocity

The difference in the intensity of light produced by two independent beams passing in opposite directions through a oneway Sagnac device may be used to measure the absolute velocity of the device and, thus, the solar system.     

用对比法深入认识速度势

介绍了运用对比法深入认识速度势的一种方法,圆满地解决了学生对速度势的深入认识及灵活运用问题.     

一种新的线成像激光干涉测速系统

 设计并搭建了一种新的线成像激光干涉测速系统,用于小样品材料的冲击波诊断或飞片速度测量。系统采用梳状干涉条纹做为信号载体,利用1维光纤阵列＋光电倍增管＋数字示波器替代变像管扫描相机作为记录设备,记录伪推挽四路干涉信号,实现1 ns时间分辨和86 μm空间分辨。用它测量了脉冲激光驱动铝膜飞片的速度场,获得对比度较好的信号,数据处理结果揭示了飞片加速过程将近20 ns,飞片的平面度为14.8 mrad。实验证明,该线成像激光干涉测速系统具有一定实用性。     

Chapman-Enskog velocity distribution for tracer diffusion

The Chapman-Enskog method is used to obtain an approximate velocity distribution function for tracer diffusion in dilute hard-sphere mixtures. Different ratios of the mass of the tracer to that of the excess component (including the well-known limiting cases of the Lorentz and the Rayleigh models) are considered and the corresponding diffusion coefficients are also evaluated. A comparison with the recent results of Tompson and Loyalka for both the diffusion coefficients and the distribution functions provides a perspective on the usefulness and nature of the approximate method.     

水中声速的测量

将空气中声速测量实验拓展至水中声速的测量,将NaCl溶于水中,制成不同浓度的盐水来模拟海水,对不同盐分的"海水"中的声速进行了测量.结果表明,随着海水盐度的增加,声速也增加.     

Sound velocity in water vapour

The effective potential is used to calculate the sound velocity of water vapour. The agreement between theoretical and experimental values confirms the validity of the effective potential.     

电枢膛内高速运动控制仿真与试验

电磁轨道发射的过程中,电枢在膛内高速运动时会受到电磁力、电枢初始正压力、摩擦力、空气阻力、烧蚀阻力等多种因素影响,电枢的出口速度呈现出在一定范围内波动的特征。为了提高电枢的出口速度精度,针对膛内电枢与轨道摩擦不均衡性和烧蚀程度不确定的特性,综合考虑脉冲成形网络的电路模型与电枢的动力学特征,建立了电枢在膛内的运动开环控制仿真模型。通过仿真,得出了脉冲电源模块触发时刻与电枢出口速度之间的关系,提出了电枢出口速度闭环控制模型,探究了电枢出口速度控制可行方案。结果表明：应用闭环控制算法,可实现对电枢出口速度的精确控制。