Effect of diffraction on the ultrasonic velocity measuredby the pulse interference method in VHF range

The effect of diffraction on the ultrasonic velocity measured by the pulse interference method has been investigated in VHF range theoretically and experimentally. Two silicate glasses are taken as the specimens, their frequency dependences of longitudinal velocities are measured in the frequency range of 50-350 MHz, and the phase advances of ultrasonic signals caused by diffraction effect are calculated using A. O. Williams' theoretical expression. For the velocity error due to diffraction effect, the experimental results are in good agreement with the theoretical prediction. It has been shown that the velocity error due to diffraction effect is directly proportional to dθ21 (f)/df, whereθ21 (f) is the phase advances difference between the two partial reflection signals used in velocity measurement and f is the ultrasonic frequency.

A STUDY OF INTERFACES OF COMPOSITES BY MEANS OF OPTICAL FIBRE SENSING TECHNTIQUE

Fibre stress of glass fibre reinforced polymeric copmosites on load is determined by using optical fibre as model fiber and by means of laser interference method. In addition, the origination of fibre stress during moulding process of composites and the relation between fiber stress of loaded composites and external stress are examined. The experiments show that fibre stress is related to molecular structure of inter facial materials and structure of inter facial layers. When stress is transferred from matrix to fibre, each inter facial layer has different stress gradient and deformability. This property can be characterized by introducing an inter facial stress transfer coefficient k to the two-phase model.

Research on underwater acoustic channel estimation and temperature factors based on FBMC

The complexity of underwater environment poses a challenge to underwater acoustic communication.In marine environment,different temperatures,depths and salinities would affect the performance of acoustic communication.The analysis of the underwater acoustic channel under the influence of temperature factors provides a reference for further study of the underwater acoustic channel estimation problem based on filter bank multi-carrier(FBMC).The FBMC based offset quadrature amplitude modulation(OQAM)technology(FBMC/OQAM)was introduced into the underwater acoustic communication.Based on FBMC,the underwater acoustic channel estimation technology was studied.By changing the pilot structure to adapt to the complex and variable underwater acoustic channel,the iterative method was used to obtain the channel information with higher accuracy and further improve the performance of channel estimation.Theoretical analysis and simulation results show that iterative channel estimation algorithm based on the new interference approximation method(IAM)pilot proposed in this paper has better performance in underwater acoustic channel.

A frequency-adapted optimal-weighted method of array interference striations

Considering the filter properties of the long horizontal line array （HLA） to the sound field modes, we established an adaptive optimal method to design HLA weights, which can change the filter pass band with the frequency. Using the normal modes theory and combining with the feature of the sound field HLA beamformer, and analyzing the differences of definition and slope in the LOFAR （Low Frequency Analysis Recording） spectrogram between the single-hydrophone and the beamformer, a frequency-adapted optimal-weighted （FAOW） estimate method was obtained by solving a quadratic optimization model with linear equality constraints. The numerical simulation and the experimental data analysis indicated that we can obtain the beamformer signal with the designed optimal array weight which was made up by the Surface-Reflected Bottom-Reflected modes or Non-Surface-Reflected Bottom-Reflected modes. The slope of striations in the signal spectrogram fitted well with the theoretical analysis.

Simple and cost-effective methods for precise analysis of trace element abundances in geological materials with ICP-MS

Inductively coupled plasma mass spectrometry （ICP-MS） is the most commonly used technique to deter- mine the abundances of trace elements in a wide range of geological materials. However, incomplete sample digestion, isobaric interferences and instrumental drift remain obvious problems that must be overcome in order to obtain precise and accurate results, For this reason, we have done many experi- ments and developed a set of simple, cost-effective and practical methods widely applicable for precise and rapid determination of trace element abundances in geological materials using ICP-MS. Commonly used high-pressure digestion technique is indeed effective in decomposing refractory phases, but this inevitably produces fluoride complexes that create new problems. We demonstrate that the fluoride complexes formed during high-pressure digestion can be readily re-dissolved using high-pressure vessel at 190 ℃ for only 2 h for 50 mg sample. In the case of isobaric interferences, although oxide （e.g., MO^＋/M^＋） and hydroxide （e.g., MO^＋/M^＋） productivity is variable between runs, the （MO^＋/M^＋）/（CeO^＋/Ce^＋） and （MOH^＋/M^＋）/（CeO^＋/Ce^＋） ratios remain constant, making isobaric interference correction for all other elements of interest straightforward, for which we provide an easy-to-use off-line procedure. We also show that mass-time-intensity drift curve is smooth as recognized previously, for which the correction can be readily done by analyzing a quality-control （QC） solution and using off-line Excel VBA procedure without internal standards. With these methods, we can produce data in reasonable agreement with rec- ommended values of international rock reference standards with a relative error of 〈8% and precision generally better than 5%. Importantly, compared to the widely used analytical practice, we can effectively save 〉60% of time （e.g., 〈24 h vs. 〉60 h）.