Microstructure stabilization of a novel glass/YSZ composite coating material by adding alumina particles

Glass-based composite coating materials incorporating particles of alumina or YSZ were prepared by reaction sintering. It was revealed that phase evolution played a key role on thermal expansion behavior of the composite coating materials. Both precipitating of t-ZrO₂ crystals and adding YSZ inclusions could raise CTEs of the glass-based matrix, while the formation of zircon produced the reverse effect. Especially, alumina additives retarded the crystallization of the base glass and reduced reaction rates between YSZ and the glass matrix remarkably. Thus, the Al₂O₃/YSZ/glass tri-composites could serve as an environmental barrier coating for intermetallics and superalloys because of the stabilized microstructure.     

The impact of inoculum source,inoculum to substrate ratio and sample preservation on methane potential from different substrates

Batch experiments were conducted to evaluate the impact of inoculum sources, inoculum to substrate (IS) ratio and storage conditions on the potential and production rate of methane (CH₄) from different substrates: wheat straw, whole crop maize, cattle manure, grass and cellulose.The results of the test with four inocula and four substrates indicated that inoculum source could have a significant impact on both CH₄ potential (BMP) and the kinetics parameters of different substrates. The two inocula showing the highest BMP and production rates in each period were those coming from a feeding with more than 70% of animal manure under thermophilic conditions. The impact of the IS ratio in the range 0.25–2.5, in terms of g volatile solids (VS) substrate/g VS inoculum, depended on substrate type. Maize silage was more affected to changes in the IS ratio than wheat straw. The optimal IS ratio range for maize was 1.0–1.5, however, a wider IS range can be used in wheat straw (0.5–2.5). The impact of freezing and drying depended on biomass type. Freezing, drying and ensiling of grass increased the CH₄ yield compared to fresh grass. Drying of maize had no impact while freezing reduced the CH₄ potential. Drying and freezing had no impact on straw.     

An investigation of the mechanical fatigue behavior of low thermal expansion lattice structures

A study of the mechanical fatigue behavior of a Ti–6Al–4V lattice structure designed to exhibit controlled thermal expansion has been performed. Comparison of S–N curves generated under both zero-tension and fully reversed cyclic loading has determined that the fatigue resistance of the lattice is substantially poorer than that of the constituent Ti–6Al–4V material for the same remote applied (macroscopic) stress. In addition, the effect of beta annealing the as-received mill-annealed alloy was also to reduce fatigue life in both the lattices and parent material. This effect is due to significant microstructural changes that occurred during heat treatment. Increasing the stress ratio (σ_min/σ_max) of the cyclic waveform from −1 to 0 had a similar effect. An analytical model has been developed to predict the fatigue life of the lattice structures from the S–N curves of the parent material, by determining the relationship between the macroscopic stresses acting on the lattice structure and the local stresses. The local stresses were then used in a multiaxial fatigue model to determine the fatigue life. The analytical model is able to predict the fatigue life with reasonable accuracy and minimal cost. The Findley multiaxial fatigue parameter for the parent material and lattice structures can be fitted with a power law equation and appears to fall onto a single curve, suggesting the local behavior within the lattice material is similar to the parent material. The analytical tools developed in this study can be hugely beneficial to the design of these lattice structures in the aerospace and communications industries.     

Difference angle quantization index modulation scheme for image watermarking

In this paper, we propose a new angle quantization index modulation (AQIM) method, called the difference AQIM (DAQIM) method. The proposed method aims to improve the watermarking performance against gain attacks. Unlike the original AQIM method (Ourique et al., Angle QIM: a novel watermark embedding scheme robust against amplitude scaling distortions, in: Proceedings of IEEE International Conference on Acoustics, Speech, and Signal Processing, vol. 2, 2005, pp. 797–800), the DAQIM method quantizes the difference of the two angles instead of the angles themselves. The main advantage of the DAQIM method is to disperse the interference to the watermark signal from one angle to more angles. Thus, the watermark has a higher ability to resist attacks. We perform a theoretical analysis of the document-to-watermark ratio (DWR) based on our proposed method. We show that our proposed method can obtain a lower embedding distortion compared to the AQIM and the gradient direction watermarking (GDWM) (Nezhadarya et al., IEEE Trans. Inf. Forensics Secur., 6(4), 2011, 1200–1213), methods under the same robustness and payload conditions. The experimental results demonstrate that our proposed method outperforms common existing methods in terms of the robustness against various attacks such as the JPEG quantization noise, additive white Gaussian noise (AWGN), cropping effect and mean filtering.     

Temperature cycling and its effect on mechanical behaviours of highporosity chalks

Temperature history can have a significant effect on the strength of water-saturated chalk.In this study,hydrostatic stress cycles are applied to understand the mechanical response of chalk samples exposed to temperature cycling between each stress cycle,compared to the samples tested at a constant temperature.The total accumulated strain during a stress cycle and the irreversible strain are reported.Chalk samples from Kansas(USA)and Mons(Belgium),with different degrees of induration(i.e.amount of contact cementation),were used.The samples were saturated with equilibrated water(polar)and nonpolar Isopar H oil to quantify water weakening.All samples tested during 10 stress cycles with varying temperature(i.e.temperature cycled in between each stress cycle)accumulated more strain than those tested at constant temperatures.All the stress cycles were performed at 30℃.The two chalk types behaved similarly when saturated with Isopar H oil,but differently when saturated with water.When saturated with water,the stronger Kansas chalk accumulated more total strain and more irreversible strain within each stress cycle than the weaker Mons chalk.     

Direct strain evaluation method for laboratory-based pillar performance

Pillar stability is one of important aspects for underground mines.Generally,the stability of the pillars is evaluated empirically based on case studies and site-specific rock mass conditions in mines.Nevertheless the empirical approach applicability can sometimes be constrained.The numerical-based approaches are potentially more useful as parametric studies can be undertaken and,if calibrated,can be more representative.Both empirical and numerical approaches are dependent on the strength evaluation of the pillars while the strain developing in the pillars is seldom taken into consideration.In this paper,gypsum and sandstone samples were tested in laboratory with different width-to-height ratios(W/H)to adapt the strain evaluation method to the laboratory-based pillars.A correlation was then developed between the strain and the width-to-height ratio for pillar monitoring purposes.Based on the results,a flowchart was created to conduct back analysis for the existing pillars to evaluate their stability and design new pillars,considering the strain analysis of the existing pillars with the W/H ratios modelled.     

Comfort design and optimization of direct expansion multi-connected radiant air conditioning based on 3D flow field simulation

The air conditioning method based on radiation heat exchange has the characteristics of small vertical temperature gradient, high thermal comfort and energy saving, and has become a hot spot of attention. The Fluent numerical simulation, the experiment in this paper studies the direct expansion multi-line radiant air conditioner under the artificially simulated climate environment in winter heating, summer cooling and dehumidification. The temperature difference of the radiation + fresh air mode at the same time indoors under heating conditions is less than 2.5 °C, and the time to reach the indoor set temperature of 24 °C is about 2–3 h. Under cooling conditions, the temperature difference of the radiation + fresh air mode at the same time in the room is about 0.5–2 °C, and the time to reach the indoor set temperature of 26 °C is about 1–3 h. In the fresh air mode, the indoor temperature difference and response time at the same time are slightly larger than the radiation + fresh air mode. The freezing and dehumidification effect of fresh air is obvious, the moisture content of dehumidifying fresh air is between 6.3 and 10.5 g/kg, and the dehumidification efficiency can reach 50%. Under the same artificial simulated climate environment, the consumption of the three modes is not much different. When the outdoor temperature in heating conditions is higher than 9 °C, the fresh air mode can get better, and the radiation + fresh air mode can achieve better comfort when running indoors under various conditions.     

Adaptive GLR-, Rao- and Wald-based CFAR detectors for a subspace signal embedded in structured Gaussian interference

The problem of detecting a subspace signal embedded in subspace Gaussian interference and thermal noise is studied in this paper. In this problem, both the signal-independent and signal-dependent interferences are assumed to be present, therefore the overall interference subspace covers the signal subspace. The approach of this paper extends previous works involving either of those two kinds of interferences. A set of secondary data containing only interference plus noise is employed to estimate the interference covariance matrix and the noise power. Three new detectors are designed via the generalized likelihood ratio (GLR), Rao and Wald tests, respectively. Their probabilities of false alarms (PFAs) and detections are analytically derived. The PFAs show that the new detectors have the constant false alarm rate (CFAR) property against the interference and noise. Numerical results show that the new detectors outperform their counterparts for the studied problem. Furthermore, the new detectors are less sensitive to the secondary data size and to the mismatched subspace signal than some other detectors, such as the GLR detector (GLRD), the adaptive matched filter (AMF), the adaptive subspace detector (ASD), etc.     

面向文本数据的正则化交叉验证方法

面向文本数据建模时,交叉验证方法是特征选择及模型比较任务中的常用方法。许多研究表明,文本数据模型的性能估计对交叉验证的数据切分方式较为敏感,不合理的切分方式可能会导致不稳定的性能估计值,使得实验结果可复现性差。该文试图论证基于多次重复(m次)的2折交叉验证,通过引入对训练集、验证集分布差异的约束,所构造的正则化m×2交叉验证方法(简记为m×2 BCV)可以改善模型的性能指标的估计,适宜于模型比较。该文首先针对文本数据引入训练集与验证集分布差异的卡方度量,基于该度量构建数据切分的正则化条件,以最大化模型性能指标的信噪比为目标,给出了满足正则化条件的m×2 BCV的数据切分优化算法。最后,以自然语言处理中汉语框架语义角色标注任务为例,验证了基于m×2 BCV方法的有效性。     

少量有机碳对单级自养脱氮工艺性能的影响

采用序批式生物膜反应器(SBBR),经过4个阶段的培养,快速富集好氧氨氧化细菌(AOB)和厌氧氨氧化细菌(AnAOB),并考察不同低碳氮比对工艺脱氮性能的影响。结果表明,NH4^+-N去除率可达到99%以上,TN去除率可达到90%以上。对应C/N=0、1和2时,反应器出水NH4^+-N和TN去除率分别为99.59%、99.5%、98.47%和93.75%、97.22%、98.11%。说明少量COD的存在,可实现同步硝化-厌氧氨氧化-反硝化,且在一定程度上提高脱氮效率。