精密扭摆研究

本研究旨在提高扭摆精度。扭摆采用大理石——这取自地球的天然材料作摆盘;通过试验,挑选了Q值高、内耗小、剪切模量温度系数接近于零的恒弹性合金丝作为吊丝。特别是,我们把Saxl类型的每周期吸合一次的间断振荡摆回复到小阻尼情况下的自由振荡摆,减少对摆振动的人为干预;增加真空条件,以减少周围环境干扰,延长了阻尼时间;同时在摆盘中央安放多面反射镜环,增加测量点,变一周期仅测一次时间为同一周期测四次以上。这就提供了用计算机求阻尼振荡方程θi=Ae^-t_i/τsin(ωt_i+φ)数值解的条件,不但可直接测得周期T的变化,而且可望计算得振幅A、阻尼时间τ、初相角φ的变化。另外,在光电接收方面也作了一些改进。通过这些措施,我室的精密扭摆对周期的探测精度已比美国Saxl 1964年发表第一篇文章时的扭摆精度提高100倍;比其运转17年,经一再改进的扭摆精度提高10倍。测量有效数字6位至7位,周期相对误差一般达2×10^-6,最佳状况可达8×10^-7,基本达到预期设计要求,为将来探测引力异常,“区分长期间与短期间内频率起伏”提供了可能性。 关键词：     

Precise Determination of Period of a Torsion Pendulum in Measurement of Gravitational Constant

The period of a torsion pendulum would vary under the disturbances of environmental noise factors. In order to subtract the period of the pendulum from external influence, we employ the correlation method to determine the period with a high precision. Theoretical analysis shows that the relative precision is improved to be proportional to 1/m^3/2 with the number of the period m, compared with the conventional statistical mean that is proportional to 1/m^1/2, which is significant for the determination of gravitational constant with the swing time method.     

Ag-Cd合金贝氏体相变内耗

使用低频倒扭摆测量了Ag-42.3at％Cd合金在室温至250℃范围内等温过程中内耗随时间的变化和不同升温速率下内耗与温度的关系。试验表明,Ag-Cd合金发生贝氏体相变时内耗升高是由于贝氏体相变形核过程中母相基体点阵的不稳定,内耗的升高决定于贝氏体形核率J^*与点阵局部软化区单位体积内耗值Q_s^-1的乘积。 关键词：     

扭摆法测转动惯量的系统误差与实验改进

本文研究分析扭摆法测量转动惯量实验的系统误差来源,在此基础上对实验方法、装置提出改进,改进后实验结果与理论值的百分差可降低一至二个数量级．     

铁在范性形变过程中的低频内耗

在改装了的拉力试验机上测量了纯铁在范性形变过程中的内耗。研究了拉伸速率(在0.73×10^-6-50×10^-6/秒范围内)、测量频率(在0.3—3.6/秒范围内)、应变退火及含碳量等对纯铁范性形变过程中内耗的影响。所得结果表明,在屈服平台上,范性形变过程中内耗基本不变,且其值随范性形变速率的增加和测量频率倒数的增加而线性增加。将实验结果与范性形变过程内耗的位错动力学模型所得出的定量关系式进行了对比,得到了满意的符合。求得了退火纯铁在屈服平台上的位错动力学指数为10 关键词：     

Relaxation during short-range-ordering in Cu-30% Zn alloy

The internal friction measured in a vacuum torsion pendulum has been used to determine the kinetics of short range ordering in an Cu-30% Zn alloy. Curves of relative internal friction (Q^–1/Q ₀ ^–1 ) against annealing time have been determined for various annealing temperatures. Average activation energy of 1·7 eV was found for the ordering process, which equals to that derived for zinc diffusion in coarse grained copper.     

马氏体式相变过程中所引起的内耗变化

用扭摆测量两种跌锰合金(Mn17.5％和12.8％)和一种铜铝合金(Al13％)的内耗,在发生正和反的马氏体相变的温度范围内各出现一个内耗峰。这种内耗峰出现的条件是必须伴随着马氏体式相变过程的进行。用含Mn17.5％的铁锰合金作了系统实验,观察到内耗峰的高度随升温(或降温)速度和应力的增加而增高,随振动频率和含碳量的增加而减低。可以用振动一周内试样中转变量愈多内耗也愈大的关系得到统一的解释。讨论了关于产生内耗峰的机构。认为主要由于马氏体相变是突然间完成,此时扭转的外力可视为常数,从应力和不均匀物质交互作用能的计算,可以证明外力所做的功必须损失一半,因而引起内耗。此外应力感生相变也可以引起很小一部分内耗。     

New measurements with a torsion pendulum during the solar eclipse

During the solar eclipse of 11 July 1991 in Mexico the period of a torsion pendulum was measured in order to reexamine possible anomalies observed in previous experiments of this kind. In our experiment no significant change was found as the relative change in the period associated with the eclipse was less than 2.0×10^–6 (90% confidence). Results were similar to our previous ones made during the eclipse in 1990 in Finland when the Sun was much lower in the horizon. However, two small but distinct shifts were observed in the horizontal position of the pendulum wire which were well correlated with the beginning and the end of the eclipse.     

用扭摆法测定物体转动惯量

本文简要地介绍了我校工科物理实验引进德国实验设备，用扭摆测定物体转动惯量的仪器装置和方法     

Determination of the thermal noise limit in test of weak equivalence principle with a rotating torsion pendulum

Thermal noise is one of the most fundamental limits to the sensitivity in weak equivalence principle test with a rotating torsion pendulum. Velocity damping and internal damping are two of many contributions at the thermal noise, and which one mainly limits the torsion pendulum in low frequency is difficult to be verified by experiment. Based on the conventional method of fast Fourier transform, we propose a developed method to determine the thermal noise limit and then obtain the precise power spectrum density of the pendulum motion signal. The experiment result verifies that the thermal noise is mainly contributed by the internal damping in the fiber in the low frequency torsion pendulum experiment with a high vacuum. Quantitative data analysis shows that the basic noise level in the experiment is about one to two times of the theoretical value of internal damping thermal noise.     

用霍耳传感器测量扭摆周期

本文介绍二种开关型霍耳传感器在扭摆周期测定中的应用 ,给出了部分传感器参数和安装接线图     

黄金分割法在物理实验中的应用--金割效应物理摆

“金割效应物理摆”是应用黄金分割法对物理摆进行研究的自制教学仪器,使用它可以进行物理摆周期极小值的测定等实验内容,实验装置采用计算机实时数据采集和处理等技术手段,教学效果更加理想。     

混沌的解析与e-measure混沌摆实验

阐述了混沌的建模;利用旋转移动传感器对物理摆的相空间轨迹进行了实时测量,记录了混沌产生过程中相空间的角位移和角速度的变化。证实了混沌对初始条件的敏感性,以及混沌中3周期点的存在。     

A torque magnetometer for thin films applications

We describe the development of an automatic torque magnetometer based on a torsion pendulum. The instrument uses the capacitive arrange developed by Randall D. Peters, Rev. Sci. Instr. 60 (8), 2789 (1989), as sample's angular position sensor. The instrument performance is illustrated by measuring the in plane magnetic anisotropy of Co thin films and systems with exchange-bias. It possesses a sensitivity of 10^?10 Nm and is capable to determine anisotropy constants in magnetic films as thin as 3 nm. The instrument design and the measurement procedures are presented.     

利用强迫振动扭摆方法测量液体粘滞系数的原理

研究了利用强迫振动扭摆方法测量液体粘滞系数的原理-由标准滞弹性体的Voigt型三参数模型确定了测量系统的基本参量,从而证明了利用强迫振动扭摆测量液体粘滞系数的四参数模型的正确性- 关键词：     

扭摆法验证平行轴定理实验的改进

转动惯量是物体定轴转动中的重要物理量,物体的转动惯量测量的常用方法有三线摆法与扭摆法。扭摆法通常测量物体通过质心转轴的转动惯量,所以用扭摆法验证平行轴定理一直不怎么直观,本文就是在已有的基础上进行一些改进,已达到更好、更直观验证平行轴定理。     

单摆振动周期随摆角变化实验之讨论

本文就如何选择恰当的计时仪器来测量单摆振动周期随摆角变化的问题进行了讨论。主要说明要根据具体的实验装置和具体的实验内容合理地选择仪器的灵敏度。     

Influence of the colored noise on determining the period of a torsion pendulum

Based on statistical properties, two typical models are considered to calculate the uncertainties for some random noise sequences on the period extraction of a torsion pendulum, which is important and instructive in the measurement of gravitational constant G with the time-of-swing method. An expression of the uncertainty for the period measurement is obtained, which is dependent on the ratio ?t/(1/λ) where ?t is the interval of the sample time and 1/λ is the length of the correlation time. The result of processing experimental data shows that as the interval of the sample time ?t gradually shortens, the uncertainty of the period becomes smaller, and further when the ratio ?t/(1/λ) is less than 1, the uncertainty remains substantially unchanged.     

Concentration dependence of Fe segregation near the surface in V-Fe alloys after V+ ion irradiation

The effect of Fe segregation near the free surface of V model alloys containing 2, 5, or 7 at % Fe is investigated by x-ray photoelectron spectroscopy. Segregation is induced by 50-keV V⁺ ion irradiation at a temperature of 30–40°C with fluences ranging from 10¹⁹ to 10²¹. Young’s moduli in these alloys are measured by the torsion pendulum method. The degree of Fe segregation is estimated, and its dependence on the irradiation dose and iron concentration in these alloys is analyzed. Correlation is found between the behavior of Young’s moduli and the degree of iron surface segregation as functions of the Fe concentration in the alloys.     

DETERMINATION OF THE LIFETIME OF THE 4p1P0 STATE OF CALCIUM BY ELECTRON PHOTON COINCIDENCE

The electron-photon delayed coincidence technique has been used to measure precisely the lifetime for the 4p¹P⁰ state in calcium. The lifetime of this state was obtained by measuring the time correlation spectrum between the inelastically scattered electrons and the corresponding de-excitation photons. By using the least-squares fitting program to fit Gale's equation to the data points, a value of (4.15±0.17) ns was obtained. The result was compared to some of the earlier experimental measurements.