Monitoring of bitumen hardening with a non-destructive ultrasonic shear wave reflection technique

The article presents a possibility of using a non-destructive ultrasonic shear wave reflection technique for monitoring hardening process of bitumen. The technique relies on the use of a new measuring instrument called USWR-4 Hardening meter, which was developed to be applicable directly in situ and has been effectively used for cement-based materials so far. It works on the principle of continuous measurement of change of a shear wave reflection coefficient. Three different types of paving grade and two polymer-modified bitumens were used. Results show that the presented ultrasound technique can effectively track a temperature-dependent hardening process of bitumen.     

Precision submillimeter wave laser reflection measurements of high-temperature superconductors

Submillimeter wave laser reflection measurements of surface resistance can provide improved capability in the combination of sensitivity, spatial resolution, and frequency range. We have made reflectivity measurements on metals at 1630 GHz with an uncertainty of less than 0.3%. This sensitivity corresponds to a measurement sensitivity for surface resistance of 0.3 . Assuming anf ² frequency scaling of high-temperature superconductor surface resistance from the microwave to the terahertz frequency range, this sensitivity corresponds to about 1 ×10^–5 at 10 GHz. Capability for 10^–7 sensitivity could eventually be possible. Preliminary submillimeter wave reflection measurements of a YBCO thin film have been made with a sensitivity of 1%. Submillimeter wave reflectometry can make it possible to determine the spatial dependence of surface resistance in a wide range of material sizes and shapes. The spatial resolution could be on the order of 0.3–0.5 mm.     

Water depercolation of setting cement paste evaluated by diffuse ultrasound

Microstructural evolution during setting of cement-based materials explains its solidification. While various studies have attempted to reveal the microstructural evolution, many questions still remain. The setting process refers to the phase change from a cement suspension to a poroelastic solid. This study proposes a diffuse ultrasound method to investigate microstructural evolution and to determine the setting of cement paste. The diffuse ultrasound refers the propagation of an incoherent component on P-waves through-transmission. Its velocity and attenuation reflect the tortuous paths in early-age cement paste. Closing the tortuous paths by cement hydration and coagulation causes the diffuse ultrasound to combine with the propagated P-wave. The combined time is then an indicator of the setting point. The diffusivity, dissipation, and permeability evaluated by the diffuse ultrasound also shed light on the microstructural evolution of fresh cement paste.     

考虑临空面冲击波反射的复合结构水压爆破

对水压爆破时结构物临空面的冲击波反射情况进行了分析，提出了在不同的冲击波反射强度时的水压爆破药量计算公式，常用的水压爆破药量公式没有反映临空面的影响，所以该公式是对常用的水压爆破药量公式的改进，在实际工程中得到了成功应用。     

Measurement of ultrasonic wave velocity in a solid under gas pressures up to 0·4 GPa

A set-up is described for the measurement of longitudinal and transverse wave velocities in a solid under gas pressures up to 0·4 GPa. To check the performance of the set-up, the elastic constants of Se and As₂Se₃ glasses and their pressure derivatives were obtained from the wave velocity data and compared with the data available in the literature.     

一维声子晶体中弹性波的全反射贯穿效应

为了研究一维声子晶体中弹性波的全反射贯穿效应,利用转移矩阵法计算了弹性波在大于全反射角入射一维声子晶体的透射率。在透射波中发现了两条透射峰带,即出现了全反射贯穿效应。得出了贯穿效应随入射角的变化规律、贯穿效应随介质厚度的变化规律以及贯穿效应随周期数的变化规律。并利用波的量子理论和渐逝波的理论对一维声子晶体的贯穿效应作出了定性的理论解释     

相关函数算法在超声导波计量管道内液体流速中的应用

通过对超声导波技术在充液管道内流量计量的研究,提出了一种新的供热管路中热量表流量计量在线检测方法。试验中,因超声导波在充液管道内传播速度较快,为了准确地测量管道内液体流速对导波传播速度的影响,需要非常准确地提取导波的传播时间。分析了相关函数法在计算导波传播时间的应用原理,并通过理论分析和实验验证了相关函数法的准确性,为采用超声导波测量管道内液体流量提供理论基础。