Measurement of Poisson's ratio using Newton's rings

A simple optical method of measuring Poisson's ratio is reported. It is most applicable to polymer spheres in circumstances where conventional nondestructive testing is not possible. The method relies on the use of microscopic investigations of Newton's rings to measure the radius of the Hertzian contact between the test sample and a flat glass plate. Measurement over a range of loads gives an estimate of Poisson's ratio provided that Young's modulus is known for the sample.     

用电子分析天平测量静电力及真空介电常量

介绍了用电子分析天平测量平行板电容器两极板间的静电力和真空介电常量的原理和方法．     

用天平测定电介质的相对介电常量

利用分析天平，测出了带电平行板电容器两金属板间的相互吸引力F，根据F与两极板间电压U的函数关系，对测量数据进行回归计算，得出平行板电容中电介隔片的相对介电常量。     

Test of the equivalence principle using a rotating torsion balance

We used a continuously rotating torsion balance instrument to measure the acceleration difference of beryllium and titanium test bodies towards sources at a variety of distances. Our result Deltaa(N),(Be-Ti)=(0.6+/-3.1)x10(-15) m/s2 improves limits on equivalence-principle violations with ranges from 1 m to infinity by an order of magnitude. The E?tv?s parameter is eta(Earth,Be-Ti)=(0.3+/-1.8)x10(-13). By analyzing our data for accelerations towards the center of the Milky Way we find equal attractions of Be and Ti towards galactic dark matter, yielding eta(DM,Be-Ti)=(-4+/-7)x10(-5). Space-fixed differential accelerations in any direction are limited to less than 8.8x10(-15) m/s2 with 95% confidence.     

Thermal noise limit in measuring the gravitational constant G using the angular acceleration method and the dynamic deflection method

A general comparison is made between two methods of measuring the gravitational constant G. The angular acceleration method can avoid the anelasticity effect since the torsion fiber is not twisted. The dynamic deflection method is similar in principle but it does not use feedback, therefore a major noise introduced by the feedback control system in the angular acceleration method can be avoided. Both methods have their advantages and can be performed with the same device. Based on different expressions of G, we have expressed the signal-to-noise ratio and calculated the thermal noise limit for both methods. In order to get a lower thermal noise limit, the dynamic deflection method should avoid resonance.     

Tuneable vibration absorber using acceleration and displacement feedback

This study is concerned with the analysis and design of a tuneable vibration absorber, which is composed by a flexible beam with a clamping block in the middle and two masses symmetrically mounted at the two ends. The free length of the beam is used to accommodate piezoelectric strain actuators. The two masses at the ends are equipped with inertial accelerometers. This arrangement is used to generate two independent acceleration feedback control loops that produce virtual mass effects, which shift the absorbing frequency of the device. Another arrangement is also studied where the two accelerometer outputs are time-integrated twice in order to implement displacement feedback loops that change the beam stiffness to shift the characteristic frequency of the device. The two feedback approaches are first analysed theoretically, using a mobility-impedance model, and then experimentally on a prototype absorber unit. The stability of the feedback loops is studied using the Nyquist criterion in order to estimate the limits on the tuneable range of frequencies which are set by the maximum stable feedback gains. The study indicates that the stability margins for the acceleration feedback loops substantially depend on the application of an appropriate low-pass filter. On the contrary, the implementation of displacement feedback gives better stability margins.     

Rotation and acceleration as parallel transport in a space-time with torsion

We demonstrate that two simple noninertial motions, namely, uniformly rotating and uniformly accelerated motions, can be described as parallel transports, in a space-time manifold with torsion, of the moving object's reference frame along its world line. On the basis of that, it is conjectured that the electromagnetic field tensor is really only the temporal part of the contortion tensor. The only disturbing feature is that the decrease of the electromagnetic/gravitational coupling ratio with velocity (by the factor ) does not appear in this approach.     

Measurement of remanent magnetic moment using a torsion pendulum with single frequency modulation method

In Tian Qin spaceborne gravitational-wave detectors, the stringent requirements on the magnetic cleanliness of the test masses demand the high resolution ground-based characterization measurement of their magnetic properties. Here we present a single frequency modulation method based on a torsion pendulum to measure the remanent magnetic moment mr of 1.1 kg dummy copper test mass, and the measurement result is(6.45 ± 0.04(stat) ± 0.07(syst)) × 10^-8A · m². The measurement pr...     

Numerical modeling of the motion of a torsion balance in the problem of measuring the Newtonian gravitational constant

The motion of a torsion balance with five degrees of freedom has been numerically simulated. It has been shown that the oscillations along the swing degrees of freedom are excited by the random noise of the seismic origin and their amplitude varies with time. It has been shown also that the nonlinear couplings between the swing and torsion degrees of freedom result in the appearance of combination oscillations. The methods for effectively suppressing these combination oscillations have been considered.     

Determination of the gravitational constant with a beam balance

The Newtonian gravitational constant G was determined by means of a novel beam-balance experiment with an accuracy comparable to that of the most precise torsion-balance experiments. The gravitational force of two stainless steel tanks filled with 13 521 kg mercury on 1.1 kg test masses was measured using a commercial mass comparator. A careful analysis of the data and the experimental error yields G=6.674 07(22)x10(-11) m(3) kg(-1) s(-2). This value is in excellent agreement with most values previously obtained with different methods.     

Test of cosmic spatial isotropy for polarized electrons using a rotatable torsion balance

To test the cosmic spatial isotropy, we use a rotatable torsion balance carrying a transversely spin-polarized ferrimagnetic Dy6Fe23 mass. With a rotation period of 1 h, the period of anisotropy signal is reduced from one sidereal day by about 24 times, and hence the 1/f noise is reduced. Our present experimental results constrain the cosmic anisotropy Hamiltonian H=C(1)sigma(1)+C2sigma(2)+C3sigma(3) (sigma(3) is in the axis of earth rotation) to (C(2)(1)+C(2)(2))(1/2)=(1.1+/-2.0)x10(-20) eV and /C(3)/=(1.1+/-6.0)x10(-19) eV. This improves the previous limits on (C(2)(1)+C(2)(2))(1/2) by 27 times.     

Active vibration control of beam structures using acceleration feedback control with piezoceramic actuators

In this study, the active vibration control of clamped–clamped beams using the acceleration feedback (AF) controller with a sensor/moment pair actuator configuration is investigated. The sensor/moment pair actuator is a non-collocated configuration, and it is the main source of instability in the direct velocity feedback control system. First, the AF controller with non-collocated sensor/moment pair actuator is numerically implemented for a clamped–clamped beam. Then, to characterize and solve the instability problem of the AF controller, a parametric study is conducted. The design parameters (gain and damping ratio) are found to have significant effects on the stability and performance of the AF controller. Next, based on the characteristics of AF controllers, a multimode controllable single-input single-output (SISO) AF controller is considered. Three AF controllers are connected in parallel with the SISO architecture. Each controller is tuned to a different mode (in this case, the second, third and fourth modes). The design parameters are determined on the basis of the parametric study. The multimode AF controller with the selected design parameters has good stability and a high gain margin. Moreover, it reduces the vibration significantly. The vibration levels at the tuned modes are reduced by about 12 dB. Finally, the performance of the AF controller is verified by conducting an experiment. The vibration level of each controlled mode can be reduced by about 12 dB and this value is almost same as the theoretical result.     

New measurements of G using the measurement standards laboratory torsion balance

This Letter presents the results of a series of measurements of the Newtonian gravitational constant G using the compensated torsion balance developed at the Measurement Standards Laboratory. Since our last published result using the torsion balance in the compensated mode of operation [Meas. Sci. Technol. 10, 439 (1999)]], several improvements have been made to reduce the uncertainty in the final result. The new measurements have used both stainless steel and copper large masses. The values of G for the two sets of masses are in good agreement. After combining all of the measurements we get a value of G=6.673 87(0.000 27) x 10(-11) m3 kg(-1) s(-2). This new value is 5 parts in 10(5) smaller than our previous published values.     

集成扭秤放大法测量薄膜的表面张力系数

根据能量守恒定律将薄膜表面张力系数的测量转化为几何量的测量.利用扭秤装置和光路放大测量微小长度,实现了对薄膜表面张力系数的间接测量.