Nonuniform phase distribution in ultrasound speckle analysis. I. Background and experimental demonstration

In some cases, the statistical properties of the phase of ultrasound speckle in B-scan images differ from the uniform distribution characteristic exhibited by the fully developed speckle. This phenomenon has been noted when examining scattering structures with a somewhat regular spacing using wideband pulse excitation. It is shown by computer simulation and experiments on phantoms that when the mean scatterer spacing is equal to multiples of a half wavelength at the reference frequency of the receiver quadrature demodulator, the center of the echo phase distribution, plotted on the complex plane, will shift away from the origin. When the spacing is equal to an odd multiple of a quarter wavelength, the phase distribution will have a figure ;8' shape. By noticing those noncircular phase distributions while changing the demodulation frequency, the mean scatterer spacing can be estimated.     

Effect of interface on bulk polymer: control of glass transition temperature of rubber

In current paper, we demonstrated that molecular dynamics and glass transition of rubber can be controlled by constructing attractive interface between rubber matrix and fillers. Based on a combination of experiments and molecular simulations, it was revealed that interfacial segmental mobility was reduced and glass transition temperatures (T_gs) of epoxidized natural rubber (ENR) were significantly improved due to in situ polymerization of zinc dimethacrylate (ZDMA). During curing, ZDMA polymerizes in rubber matrix, resulting in the appearance of nanodispersion phases of poly-ZDMA (PZDMA). It was demonstrated that coordination interaction exists between epoxy groups and PZDMA in interfacial regions. Furthermore, using dynamic Monte Carlo simulations, it was observed that the interfacial regions that have highest content of epoxy groups exhibit lowest segmental mobility. Then, the increase of ZDMA content leads to the rise of the fraction of absorbed interfacial segments, and thus the T_gs of filled rubbers are improved.     

Mechanism of internal and external electron donor effects on propylene polymerization with MgCl2‐supported Ziegler–Natta catalyst: New evidences based on active center counting

Two TiCl₄/Di/MgCl₂ type supported Ziegler–Natta catalysts were prepared by loading dibutylphthalate or dicyclopentyldimethoxysilane (DCPDMS) (internal donor, Di) and TiCl₄ on activated δ‐MgCl₂ in sequence, and a blank catalyst was prepared by loading TiCl₄ on the same δ‐MgCl₂ without adding Di. These catalysts have similar specific surface area and pore size distribution, thus form a suitable base for comparative studies. Propylene polymerization with the catalysts was conducted in n‐heptane slurry using triethylaluminum (TEA) as cocatalyst, and the effects of Di as well as De (external donor, in this work it was DCPDMS) on the number of active centers, the distribution of active centers among three polypropylene (PP) fractions (isotactic, medium isotactic, and atactic PP chains), and chain propagation rate constants of the PP fractions were studied by counting the number of active centers in the PP fractions using a method based on selective quench‐labeling of the propagation chains by 2‐thiophenecarbonyl chloride. When De was not added in the polymerization, introducing a phthalate type Di in the catalyst evidently changed the active center distribution by enhancing the proportion of active centers producing isotactic PP (iPP) ( ), but scarcely changed reactivities of the three groups of active centers forming the three fractions. When the De was added in the polymerization system with TiCl₄/phthalate/MgCl₂ catalyst, further shifting of active center distribution in favor of took place, meanwhile reactivities of the three groups of active centers also remarkably changed in favor of . Mutual effects of these changes led to overwhelming dominance of iPP production in the TiCl₄/Di/MgCl₂–TEA/De system (Di = phthalate, De = alkoxysilane). In contrast, though using alkoxysilane as Di also caused shifting of active center distribution in favor of when De was not added, addition of alkoxysilane De caused reverse shifting of active center distribution in favor of those producing PP of lower stereoregularity. This unfavorable change largely counteracted the reactivity changes in favor of caused by the De, rendering the catalytic system rather poor isospecificity. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46605.     

Adaptive Crowd Segmentation Based on Coherent Motion Detection

In order to obtain effective crowd relationships for crowd behavior analysis, an adaptive crowd segmentation method based on coherent motion detection is proposed. This method can improve the accuracy of segmentation results and be adaptively applied to various collective scenes that have different distributions at different scales. Firstly, an orientation clustering algorithm and a spatial joint strategy are proposed to preliminarily profile all agents into several partitions with different motion orientations. Then, the Natural Nearest Neighbor algorithm is introduced to construct the adaptive crowd motion networks combining with the profiling results, which can describe the neighborhood relationships of agents with stronger coherence. Finally, the improved Coherent Neighbor Invariance optimized by fusing motion information of neighbors is proposed to segment crowds with coherent motions from the crowd motion networks. The experiment results on videos depicting real-world crowd scenes indicate that the proposed method is effective and adaptive to various scenes.     

Performance tests of vacuum pumps in small and large dental facilities

A study was conducted to compare and assess the performance of various vacuum pumps in small and large dental clinic operations. A four-chair dental clinic operation was set up at the laboratory to simulate a small dental clinic environment. The performance of two dry and two wet pumps was assessed in the laboratory via extensive performance data acquisition tests. Data were also collected in two small dental clinics of practising dentists. Large dental system performance tests were conducted at the Ellsworth Air Force Base and Minot Air Force Base dental clinics. At each clinic, data were collected with both the existent turbine pump and a rotary vane RAMVAC pump.     

Sb对原位Mg2Si/Al-5Si复合材料显微组织的影响

研究了Sb含量对Mg2Si／Al-5Si复合材料显微组织的影响。结果表明，随着Sb含量的增加，初生Mg2Si颗粒形貌明显发生了细化，Mg2Si形态由变质前的汉字体和枝晶状变为细小的、均匀分布的颗粒状，Mg2Si体积分数也有所增加。当Sb含量为0．4％时，细化效果达到最佳，由变质前的52μm变为25μm。当Sb含量超过0．4％后，Mg2Si颗粒尺寸开始粗化，因此，过量的Sb对Mg2Si颗粒的细化无益。Sb对Mg2Si颗粒的细化主要由于AlSb引起的异质形核作用，Sb使液相线温度和熔体表面张力扩σLV降低，对Mg2Si颗粒的细化也具有一定的作用。     

通过PC-PLC实现的复合离子注入机实时监控

在PLC广泛应用于工业控制的背景下，希望对应用于表面改性处理的复合离子注入机进行实时监控，阐述了控制系统的工作原理以及所实现的监测和控制功能，介绍了采用LG公司的MASTER-K200S系列PLC在该系统中进行的硬件及软件设计方法等，开发出基于PC-PLC的复合离子注入机的实时控制系统。     

智能化仪表在交通管理中的应用

介绍一种采用硅微电容式加速度传感器作为检测部件,应用智能化数据处理技术制成的便携式汽车制动性能测试仪.实践证明该测试仪能满足国标<机动车运行安全技术条件>(GB7258-1997)规定的检验要求,可广泛适用于交通管理部门对车辆进行路检及对事故车辆的勘查.     

桥式起重机机构测试的计算机硬软件分析和研制

起重机微机安全测试系统是将便携式计算机与测试仪器结合起来，实现起重机安全测试智能化的一整套系统。本文介绍该系统中起升机构和运行机构测试的工作原理、硬件组成及计算机软件研制。     

Tb_(0.27)Dy_(0.73)Fe_(1.98)在恒场下磁致伸缩应变──随压力变化曲线的诠释

本文用标准应变片法研究了Ｔｂ０．２７Ｄｙ０．７３Ｆｅ１．９８在压应力下的磁致伸缩特性，由于样品中存在多个晶粒，所以没有发现“巴克豪森跳跃”现象，但是λ－Ｐ曲线却表现出了一定的规律性：在低场下曲线单调下降，当Ｈ＝５０ｋＡ／ｍ时在Ｐ０＝１３．６ＭＰａ处曲线开始出现一峰值，且Ｐｏ不随外场的增加而变化。文中用自由能极小原理对这一现象作了诠释，发现Ｐ０与样品的各向异性场Ｈａ成正比：Ｐ０＝μ０ＭｓＨａ３λ