超声波声速测量方法的探讨

介绍一种测量空气中超声波声速的新方法--改变频率干涉法（也叫改变频率驻波法）.并对实验数据、测量精度进行了分析.     

超声光栅测声速实验方法的探索

对实验室现有的超声光栅测声速实验装置加装反射镜及利用激光光源进行改进,通过对样品纯净水的测试比较,改进后的实验装置对实验测量结果精度有明显提高。测试样品的范围扩大,实现了物理实验技术和方法与石油专业相结合,有利于提高实验教学效果。     

Sound of Speed in Nuclear Matter with Skyrme Forces

An analytical expression for sound of speed in asymmetric nuclear matter is acquired, based on the thermal Fermi-gas model and Skyrme-type nucleon-nucleon interactions. A low temperature high density approximation is adopted to the Fermi-Dirac integrals. The dependence of sound of apeed on the temperature and density bf nuclear matter under consideration ie investigated. For all the cases concerned, the so-called superluminosity is observed, the position of which is found to depend on the force parameters used and the asymmetric parameter of the nuclear matter. A possible way to avoid this causal-constraint violation is suggested.     

Matlab GUI在驻波法测声速实验中的应用

结合教学实际,利用Matlab GUI编写了三个程序,分别用来模拟理想驻波的形成、对比合成声场振幅与声压振幅、模拟驻波法测声速。直观形象的演示,既有助于学生理解实验原理,又可以激发他们的学习兴趣。     

基于手机APP实现驻波法对声速的测量

介绍了一种利用普通智能手机和一根两端开口奶茶管基于声驻波现象来测量声速的方法。这种实验方法所用的实验仪器随手可得,无需学生再到学校的实验室进行实验,激发了学生的学习兴趣,增强了学生的动手能力。     

驻波法测定声速实验的matlab模拟

在驻波法测定声速实验中,根据发射器和接收器之间合成声场的位移波动方程和声压波动方程,用matlab程序模拟了声场和声压的振幅和初相位分布,并对模拟结果进行了分析和讨论。     

基于最小二乘法的声速测定实验数据处理及分析

用振幅极大值法比振幅极小值法测声速的误差小和声波在传播过程中声压按指数函数关系衰减。     

Studies on the Measuring Method of Number Density of Ions in the High Speed Flow Field

At present, the method of using a parallel-plate probe to measure the number density of ions at atmosphere has some limitations such as big size of probe, low velocity of gas flow allowed to measure, and low accuracy. In this paper, a detector with a spherical probe is fabricated and is used to measure the number density of ions. The diameter of probe can be reduced to 6 mm. The highest velocity that can be measured is extended to 28 m/s, and the collecting rate is up to 100%. The spatial distribution diagram of ion number density is also given, with a cross section of 0.36 $hbox{m}^{2}$. Then, an effective method is provided to measure the number density of ions generated from the miniature ion source or in the gas flow with high velocity.      

迈克尔逊干涉仪测波长的一种便捷方法

提出了迈克尔逊干涉仪测波长的一种便捷且精确的测量方法。利用自制的光电计数及电机控制装置,在短时间内无须任何数据处理便可由计数器直接读取待测光源波长值。该方法不仅实现了条纹的全自动计数,又简化了干涉仪繁复的读数环节,更消除了仪器的零点误差。     

逐差法和Origin7．0软件在驻波法测超声波波速的实验数据处理中的比较

本文用逐差法和Origin7．0软件分别对驻波法测超声波波速的实验数据进处理。进行比较后得出用Origin7．0软件对此实验数据处理也是一种很好的选择。     

测量重力加速度的一种新方法

提出了一种测量重力加速度的新方法,结合CCD杨氏模量实验仪给出了重力加速度和杨氏模量的物理关系式,从测量结果可知,所测重力加速度与标准值相比其相对误差甚小,说明该实验方案确实可行,具有一定的应用价值。     

A Simple Method for Measuring Tensile Force with Piezoelectric Patch

We propose a simple method for monitoring the axial tensile and compressive force in a structure by using a piezoelectric patch with the piezoelectric impedance based measurement. A simple approximate equation for estimating the tensile force in two different conditions, which can be calculated easily if the naturM frequencies in two different states are measuredt is explained in detail. On another front, the natural frequency can be very easily measured by a piezoelectric element by bonding it on the measuring subject structure, because its electric impedance of piezoelement is related to the structural mechanical impedance. Furthermore, an experiment for measuring a tensile force in a simple supported beam is carried out for validating the proposed method. The results show a good accuracy in estimating the tensile force variation by the natural frequency change measured from the piezoelement.     

激光诱导纳秒时间分辨荧光猝灭法原位研究菲及烷基菲与腐植酸相互作用

利用激光诱导纳秒时间分辨荧光(laser-induced nanosecond time-resolved fluorescence,LITRF)猝灭法原位研究腐植酸(humic acid,HA)分别与母环多环芳烃(polycyclic aromatic hydrocarbons,PAHs)菲(phenanthrene,Phe)及烷基PAHs 9-乙基菲(9-Ethylphenanthrene,9-EP)和惹稀(retene,Ret)相互作用,考察HA对母环及烷基PAHs结合特性差异与机制,对了解PAHs环境行为及生物有效性有重要意义。结果表明,通过改变延迟时间(50ns)可有效消除HA荧光干扰,实现游离Phe,9-EP及Ret浓度直接测定。利用Freundlich非线性等温吸附模型描述Phe,9-EP和Ret与HA结合特性,LITRF猝灭法与传统荧光法获得的模型拟合参数及单点结合系数结果一致。其中,参数n小于1,表明Phe,9-EP及Ret与HA均以非线性形式结合,且9-EP和Ret非线性程度高于Phe;相同给定平衡浓度下,HA与9-EP和Ret单点结合系数KOC大于Phe,而9-EP和Ret结合能力相近,且PAHs与HA结合系数均随给定浓度增加而降低。疏水性、取代基及与HA疏水空腔适应能力决定特定PAHs与HA结合特性。通过荧光寿命分析,HA存在下Phe,9-EP和Ret寿命分别为36.90,35.34和35.13ns,与未加入HA时的36.36,35.34和35.84ns无明显差异,表明Phe,9-EP和Ret与HA间的荧光猝灭以静态过程为主。LITRF猝灭法可快速有效原位研究PAHs与HA相互作用,有助于实现PAHs生态风险原位评估。     

声速测量实验假象的探讨

应用共振干涉测量法测定空气中的声速,相同条件下多台仪器重复测量实验,对实验结果进行数据处理和误差分析表明：对于某些声速测量仪,当换能器之间的距离小于10毫米时,在移动换能器测量声速的过程中出现了假峰现象,它对实验测量结果造成了很大影响。当使两换能器之间的距离大于10毫米开始测量,可以避免假象对测量结果的影响。     

干涉条纹法测量LD端面泵浦Nd∶YAG热透镜焦距

研究了端面泵浦Nd∶YAG晶体热透镜效应,提出了一种新的测量热透镜的方法-干涉条纹法,并通过理论估算与用此方法所测的热透镜焦距相比较, 表明此方法所测热透镜焦距随着泵浦光功率的增大二者越来越吻合, 验证了该方法的可靠性. 该方法解决了端泵Nd∶YAG时, 由温度梯度, 热应力双折射和端面形变所引起的总的热透镜焦距难以测量的问题.     

测量折射率的两种方法

文章对普通大学物理实验中分光计测量介质折射率实验进行总结,介绍了两种能够依托分光计测量介质折射率的方法。并且通过实验对这两种测量方法进行了验证。     

Efficient evaluation of process stability in milling with Spindle Speed Variation by using the Chebyshev Collocation Method

Chatter is a vibrational problem affecting machining operations, which may cause bad surface quality and damages to the machining system. In recent decades, several techniques for avoiding chatter onset were developed. Among other techniques, the continuous modulation of spindle speed during the cutting process (also called Spindle Speed Variation – SSV) has been demonstrated to be very effective for reducing the chance of chatter onset. However, spindle speed modulation parameters should be adequately chosen before machining, in order to effectively increase the material removal rate. In this perspective, chatter prediction algorithms play a crucial role, since they allow a preventive evaluation of process stability for any given spindle speed regime. State of the art algorithms for chatter prediction in milling with SSV are characterized by extremely long computation times, hindering their practical application in industry. In this paper, an innovative and fast algorithm for chatter prediction in milling with SSV, based on the Chebyshev Collocation Method, is presented. The algorithm was successfully compared with a state of the art algorithm – the Semi Discretization Method – in different experimental configurations and cutting conditions. The results showed that the new method is generally more accurate and from ten to one thousand times faster than the Semi Discretization Method.     

A Novel Hydrophilic Modification of PTFE Membranes Using In Situ Deposited PANI

A new kind of polyaniline/polytetrafluoroethylene (PANI/PTFE) composite membrane has been successfully prepared by in situ deposition of PANI onto PTFE membranes during the aniline's dispersion polymerization. The PTFE membrane was plasma treated before the aniline polymerization; the induced alteration of morphology and surface properties accelerated the polymerization of aniline and increased the number density of the deposited PANI onto the PTFE surface. The surface properties and morphology of the membranes were characterized. The composite PANI/PTFE membrane exhibited an enhanced flux in salt water separation, which is up to 75% higher than the pristine membrane.     

An In Situ Testing Method for Analyzing the Changes of Active Groups in Coal Oxidation at Low Temperatures

This study details an in situ Fourier transform infrared spectroscopy analytical system that was employed to follow chemical variations in the functional groups on coal surface during the oxidation process at low temperatures. In the reported in situ Fourier transform infrared spectroscopy system, a special chamber was used to contain the coal powders, and a gas inlet tube and a programmable heater were used to simulate different reaction atmospheres and temperatures. The comparisons between in situ and ex situ Fourier transform infrared spectroscopy spectra indicate that the in situ Fourier transform infrared spectroscopy data offer a more accurate reflection of changes in the functional groups. The real-time changes of aliphatic hydrocarbon groups and oxygen-containing groups in a lignite coal sample were analyzed from 30°C to 220°C using in situ Fourier transform infrared spectroscopy. The experimental results indicate that the chemical variations in the functional groups are affected by their relative chemical activities. The results show that the presence of aliphatic groups on the coal surface varies with temperature. Over the range of 30–70°C the presence of these groups decreases, but then their abundance increases over the range of 70–180°C and finally decreases again when the temperature is increased to between 180°C and 220°C. With respect to oxygen-containing functional groups, three various trends were observed as the test temperature was varied. Our conclusion was that these variations are a function of the reaction activities of the various oxygen-containing functional groups.