Mechanical properties of roller compacted concrete containing rice husk ash with original and recycled asphalt pavement material

This study focused on the effects of rice husk ash (RHA) on the mechanical properties of roller compacted concrete (RCC) designed with original and reclaimed asphalt pavement (RAP) materials. The RCC mixes were produced by partial substitution of cement with RHA at varying amounts of 3% and 5%. Four aggregate combinations including the mix with original aggregate, coarse RAP + fine original aggregate, coarse original aggregate + fine RAP and total RAP were considered. The main experimental design consisted of the compressive strength and three points bending tests. Bending test was used to measure the modulus of rupture, material’s energy absorbency and analyse the fatigue response of RCC mixes. All tests were performed after 7, 28 and 120 days curing except the fatigue test that performed on 120 days specimens. Adding RHA resulted in higher optimum moisture content (OMC) and lower maximum dry density. Furthermore, adding RAP with different dimensions reduced the OMC and maximum dry density. The material’s flexibility improved upon replacing 3% cement by RHA. However, the energy absorbency reduced by increasing the RHA content to 5%. The fatigue life of RCC mixes containing RAP material was lower than the conventional one. Furthermore, replacing the coarse aggregate by RAP led to higher fatigue life than the fine aggregate. There was a strong relationship (R² > 0.90) between the energy absorbency and fatigue response of RCC mixes. At higher stress ratios of 0.72, the mix with higher energy absorbency behaved better under repeated loadings. Besides, a reverse relationship was found between the fatigue life and material porosity. Adding 3% RHA reduced the porosity especially after 120 days curing and improved the fatigue resistance. However, the addition of RHA to 5% resulted in higher porosities and lower fatigue lives.     

一种适用于浅海信道的盲均衡算法研究

针对多径衰落浅海水声信道，采用分数间隔判决反馈均衡器，提出了一种非线性结构的盲均衡算法。该算法不仅有效克服了水声通信中普遍存在的码间干扰效应，而且还进一步抑制了浅海信道引入的严重码内干扰现象，获得了更快的收敛速度和更小的剩余误差，提高了浅海水声通信的有效性和可靠性。仿真结果表明，该算法的性能优于通常的波特间隔均衡器，因而具有重要的工程应用价值。     

一种适用于水声信道盲均衡算法及仿真

对于高阶QAM信号,常数模算法的收敛误差不为零,而多模算法的收敛速度慢,提出了一种混合常数模算法,并将该算法应用于水声信道盲均衡。该算法根据均衡器输出信号模值与其判决模值之间的距离,设置一判决域。根据该判决域,算法的迭代过程在常数模和多模算法之间自动切换,且收敛后自动切换到多模算法。该算法收敛速度快,且均方误差小,特别适合高于高阶QAM信号的盲均衡,通过对水声信道均衡的计算机仿真,验证了该算法的优点及对多途干扰抑制的有效性。     

Second generation (low modulus) titanium alloys in total hip arthroplasty

Titanium alloys ‐ type (α+β) ‐ like Ti6Al7Nb or Ti6Al4V are widely used in cementless total hip arthroplasty due to their lower modulus, biocompatibility and enhanced corrosion resistance in comparison to Stainless Steel or Cobalt‐Chromium implant materials. Several articles report about atrophy of the proximal femur in cases where long stems with a big diameter made of (α+β) Titanium alloys with a relatively high value of the Youngs’ Modulus (110 GPa) in comparison to the Youngs’ Modulus of cortical bone (15–25 GPa) have been implanted using a prosthesis design with distal anchorage technique. Meanwhile several implant manufacturers have developed a new group of biocompatible Beta‐Titanium alloys with a lower Youngs’ Modulus around 70 GPa. This article gives an overview of the current status of available low modulus Titanium alloys including their mechanical characteristics and future developments.     

A novel data hiding scheme based on modulus function

Four criteria are generally used to evaluate the performance of data hiding scheme: the embedding capacity, the visual quality of the stego-image, the security, and the complexity of the data-embedding algorithm. However, data hiding schemes seldom take all these factors into consideration. This paper proposes a novel data hiding scheme that uses a simple modulus function to address all the performance criteria listed above. According to the input secret keys, the encoder and decoder use the same set-generation functions H_r() and H_c() to first generate two sets Kr and Kc. A variant Cartesian product is then created using Kr and Kc. Each cover pixel then forms a pixel group with its neighboring pixels by exploiting an efficient modulus function; the secret data are then embedded or extracted via a mapping process between the variant of the Cartesian product and each pixel group. The proposed scheme offers several advantages, namely (1) the embedding capacity can be scaled, (2) a good visual quality of the stego-image can be achieved, (3) the computational cost of embedding or extracting the secret data is low and requires little memory space, (4) secret keys are used to protect the secret data and (5) the problem of overflow or underflow does not occur, regardless of the nature of the cover pixels.We tested the performance of the proposed scheme by comparing it with Mielikainen’s and Zhang and Wang’s schemes for gray-scale images. The experimental results showed that our proposed scheme outperforms Mielikainen’s in three respects, namely scalable embedding capacity, embedding rate, and level of security. Our data hiding scheme also achieved a higher embedding capacity than Zhang and Wang’s. The proposed scheme can easily be applied to both gray-scale and color images. Analyses of its performance showed that our proposed scheme outperforms Tsai and Wang’s in terms of its time complexity and memory space requirement.     

模数法设计金属型铸造铝活塞保温冒口

根据保温冒口的散热特征,引用有效散热系数修正凝固模数,进一步修正金属型铸造的凝固比得出金属型保温胃口方程式.并设计了东风EQ140汽车活塞的保温冒口.浇注实验结果显示:铸造工艺出品率提高到84.9%,显著提高了冒口有效补缩效率.     

MAS小波的钢板表面缺陷边缘检测的研究

针对钢板表面缺陷与背景的对比度差、边缘复杂、采光不均、噪声较大等特点,应用一种基于MAS小波变换进行钢板表面缺陷边缘检测。该方法由Lipschitz指数阐明了图像的边缘几何结构,通过分析图像中不同类型的奇异点,并结合尺度独立算法区分了目标图像中不同类型的边缘,有效的提取了钢板表面缺陷图像的边缘。实验结果表明,基于MAS小波算法可以有效提取图像中阶梯型边界,检测到的缺陷边缘轮廓较为清晰,且去噪能力较强,检测效果优于传统的同类方法。     

氧化铝材料力学性能的分子动力学模拟

基于Al2O3材料在各大领域的重要性,提出了运用分子动力学方法来计算Al2O3材料的力学性能(杨氏模量、体模量、剪切模量、柯西压等),所得的结果与材料的实际值相近。计算结果不仅对Al2O3材料的力学性能进行了预示,还从侧面验证了该方法的准确性与可靠性,为材料的研究提供了一种可靠的理论方法。     

基于遗传算法的水声信道常模类盲均衡算法研究

为了解决CMA盲均衡算法收敛速度缓慢、稳态误差大的问题,考虑到初始化权值对CMA算法的重要影响,利用了遗传算法对CMA算法进行有效改进,引入了小样本重用的思想,给出了一种新的适用于水声信道的常模类盲均衡算法,计算机仿真研究证明,该算法不仅大大加快了收敛速度,而且有效的降低了稳态误差。     

Detection of singularities in the pressure fluctuations of circulating fluidized beds based on wavelet modulus maximum method

Pressure fluctuations are often selected to analyze the dynamic changes in the gas-solid fluidized bed. In this study, the wavelet modulus maximum method is applied to analyze the pressure fluctuations in a circulating fluidized bed. Continuous wavelet transform is put on the pressure signals, then, maxima lines are extracted and the Lipschitz exponent, α, of every maximum line is calculated using the non-linear least-squares method. The mean of the negative α is adopted to describe the hydrodynamic characteristics in the circulating fluidized bed. The value of the mean of the negative α increases with the superficial gas velocity and turns stable when the flow regime is fast fluidization. This method has been tested effective under various operation conditions.