Extended synthetic aperture focusing technique for ultrasonic imaging of concrete

Quantitative nondestructive characterization of defects and inclusions in portland cement concrete structures are realized in this paper via extended reconstructions for linear array ultrasound systems. This is accomplished through generalization of traditional Kirchhoff-based synthetic aperture focusing technique migration to mitigate the effects of limited aperture and handle multiple scans as a single virtual array with increased effective aperture. Pearson’s correlation is utilized to account for uncertainty in relative position of individual measurement and mitigate the need for robotic precision when placing adjacent scans. The robustness of the method is demonstrated on artificially generated data as well as in-situ measurements for assessment of internal portland cement concrete characteristics such as inclusions and cracks.     

Effect of nanoparticles on clay swelling and migration

Clay migration/swelling has been widely documented as the main reason leading to oil recovery impairment. Interactions of clay particles with the medium surface in the presence of permeating fluid have been recognized as a critical parameter controlling the fate of clay particles. These interactions are strongly functions of the ionic strength of the permeating fluid. It is widely reported that reducing the salinity of the reservoir environment facilitates the challenges induced by clay particles. On the other hand, low salinity reservoir environment has been recognized as a very favorable condition for oil recovery. Accordingly, one should consider the positive effect of reducing salinity on oil recovery and its deteriorative effect on clay particles at the same time to improve oil recovery in a controlled formation damage mode. This experimental work aims to investigate the potential remedial effect of different metal oxide nanoparticles to treat clay swelling. Several core flood experiments and micro-model tests have been conducted to achieve the mentioned goal. Furthermore, swelling tests were quantified in terms of swelling indices to explain the effect of nanoparticles on clay swelling. We concluded that although nanoparticles can be used as a permanent stabilizer to prevent clay migration, they are not able to prevent clay swelling and may also increase the pressure drop due to fitting between clay crystals and blocking pores.     

Experimental Investigation on Micro Deep Drawing of Stainless Steel Foils with Different Microstructural Characteristics

In the present work, austenitic stainless steel(ASS) 304 foils with a thickness of 50 μm were first annealed at temperatures ranging from 700 to 1100℃ for 1 h to obtain different microstructural characteristics.Then the effects of microstructural characteristics on the formability of ASS 304 foils and the quality of drawn cups using micro deep drawing(MDD) were studied, and the mechanism involved was discussed. The results show that the as-received ASS304 foil has a poor formability and cannot be used to form a cup using MDD. Serious wrinkling problem occurs on the drawn cup, and the height profile distribution on the mouth and the symmetry of the drawn cup is quite nonuniform when the annealing temperature is 700 ℃. At annealing temperatures of 900 and 950 ℃, the drawn cups are both characterized with very few wrinkles, and the distribution of height profile, symmetry and mouth thickness are uniform on the mouths of the drawn cups. The wrinkling becomes increasingly significant with a further increase of annealing temperature from 950 to 1100 ℃. The optimal annealing temperatures obtained in this study are 900 and 950 ℃ for reducing the generation of wrinkling, and therefore improving the quality of drawn cups. With nonoptimized microstructure, the distribution of the compressive stress in the circumferential direction of the drawn foils becomes inhomogeneous, which is thought to be the cause of the occurrence of localized deformation till wrinkling during MDD.     

Trend-specific clustering for micro mass production of linked parts

In micro production, small tolerances, as well as size effects increase the requirement for a fast, precise, and reliable methodology that enhances the output of assemblies. In contrast to conventional approaches, a widening of the tolerance field enables an overall improvement of the output of a process chain while assuring functionality of parts. Therefore, the consideration of trends for building sections is essential for increasing the outcome by identifying sections that can be matched. This paper presents the Linked Parts Clustering Algorithm for the identification of trend-specific clusters in linked parts and demonstrates the area of application.     

焊缝结构微区材料力学性能研究

介绍三种对微区材料力学性能进行测试的方法,微拉伸试验、微剪切试验和维氏硬度试验,并分析其各自的优缺点。采用这三种方法对0Cr18Ni10Ti焊接接头不同区域材料进行力学性能测试,并对试验结果进行比较分析。研究指出,采用微小拉伸试样的微拉伸试验方法测定微区材料的力学性能更为准确可靠。     

用于激光测距的高精度时间数字转换电路

针对大容量现场可编程门阵列(FPGA)时间数字转换电路线性度较差的问题,采用小容量FPGA实现了用于激光测距的高精度、高线性度时间数字转换电路。通过对高速计数器、数字插入方法、编码器硬件算法的研究,分析了影响时间数字转换电路精度和非线性误差的因素,提出了一种降低非线性误差的方法。首先,根据所分析的影响因素,解决了高速锁存的问题,在单片小容量FGPA XC2V250上实现了时间数字转换电路;接着,通过USB接口将携带时间信息的计数器值和温度计码转为二进制编码值传给PC机,进行计算和显示;最后,设计了延时测量电路,对所设计的时间数字转换电路进行了测试,得到了各个延时单元延时的大小,并进行了数据分析和处理。测试结果显示:时间数字转换电路单次测时分辨率约为80 ps,校正后可达40 ps左右,微分非线性误差为-0.524LSB~+0.448LSB,积分非线性误差为-1.598LSB~+1.492LSB,可以满足飞行时间法激光测距中高精度测时的要求。     

Characterisation of micro gears produced by micro powder injection moulding

The paper describes the fabrication of micro gears of diameter and height 1 mm by micro powder injection moulding. 316L stainless steel powder of 2.4 µm (d₅₀) is mixed with a multi-component wax-based binder system. The feedstock is then injection-moulded into micro gears followed by debinding and sintering. The microstructure of the micro gear at its tooth and hub is studied by electron backscattered diffraction. The average grain size at the hub is ~ 5 µm. However, a high content of annealing twin and a significant grain growth is found at the tooth.     

Designing coarse-grain reconfigurable architectures by inlining flexibility into custom arithmetic data-paths

This paper introduces a design technique for coarse-grained reconfigurable architectures targeting digital signal processing (DSP) applications. The design procedure is analyzed in detail and an area-time-power efficient reconfigurable kernel architecture is presented. The proposed technique inlines flexibility into custom carry-save (CS) arithmetic datapaths exploiting a stable and canonical interconnection scheme. The canonical interconnection is revealed by a transformation, called uniformity transformation, imposed on the basic architectures of CS-multipliers and CS-chain-adders/subtractors. Experimental results including quantitative and qualitative comparisons with existing reconfigurable arithmetic cores and exploration results of the proposed reconfigurable architecture are provided.     

Computationally efficient underwater acoustic 2-D source localization with arbitrarily spaced vector hydrophones at unknown locations using the propagator method

This paper presents a propagator-based algorithm for underwater acoustic 2-D direction-of-arrival (DOA) estimation with arbitrarily spaced vector hydrophones at unknown locations. The proposed algorithm requires only linear operations but no eigen-decomposition or singular value decomposition into the signal and noise subspaces. Comparing with its ESPRIT counterpart (Wong and Zoltowski, IEEE J Oceanic Eng 22:566–575, 1997a), the proposed propagator algorithm has its computational complexity reduced by this ratio: the number of sources to quadruple the number of vector hydrophones. Simulation results show that at high and medium signal-to-noise ratio, the proposed propagator algorithm’s estimation accuracy is similar to its ESPRIT counterpart.

Thermoelectric Properties of Bismuth Micro/Nanowire Array Elements Pressured into a Quartz Template Mold

A quartz template having a length of several millimeters and with holes having diameters on the order of micro/nanometers was fabricated. Bismuth was injected into the template holes by high-pressure injection. A bismuth micro/nanowire array sample was prepared, and the temperature dependence of the Seebeck coefficient and the resistance were measured in the temperature range of 50 K to 300 K. Although the temperature dependence of the Seebeck coefficient is similar to that of polycrystalline bulk bismuth, the temperature coefficient of the resistance is much less than that of the bulk sample. The magnetic-field dependence of the Seebeck coefficient was also measured. The Umkehr effect was observed, demonstrating that the mixed micro/nanowires are a bundle of single-crystal wires. The magnitude of the absolute value of the Seebeck coefficient was found to be large in high magnetic field and at low temperature.