The averaged periodogram estimator for a power law in coherency

We prove the consistency of the averaged periodogram estimator (APE) in two new cases. First, we prove that the APE is consistent for negative memory parameters, after suitable tapering. Second, we prove that the APE is consistent for a power law in the cross‐spectrum and therefore for a power law in the coherency, provided that sufficiently many frequencies are used in estimation. Simulation evidence suggests that the lower bound on the number of frequencies is a necessary condition for consistency. For a Taylor series approximation to the estimator of the power law in the cross‐spectrum, we consider the rate of convergence and obtain a central limit theorem under suitable regularity conditions.     

Synthesis of Chlorinated and Non-chlorinated Polyols from Model Cross-Metathesis Modified Triacylglycerols

Three pure triacylglycerols (TAG) containing decenoic acid (D), and stearic acid (S), were hydroxylated into chlorinated and non-chlorinated polyols and studied in detail. D is a fatty moiety that can result from the cross metathesis of small olefins with common vegetable oils such as soybean oil. A fundamental understanding relating chemical composition and derived structure, particularly the number and position of the hydroxyl groups, to physical properties was established allowing us to add some perspective to the growing body of knowledge on industrially relevant polyol and polyurethane systems produced with metathesis-modified TAG (MTAG). The hydroxyl value, crystallization and melting behaviors, thermal degradation behavior of the polyols were directly related to their peculiar shortened and primary functionality inherited from the parent MTAG. The effect of regiochemistry on the physical properties of the polyols was investigated with the chromatography fractions of the trichlorinated polyol of propane-1,2,3-triyl tris(dec-9-enoate), giving an unhindered insight into the role of short and terminal functionality of MTAG polyols that will help select the optimal isomer composition for designer polyurethane materials.     

Effect of External Recycle and Double-Pass Barrier Location on Membrane Extraction in Cross-Flow Modules

Abstract

The dispersion free membrane extraction through a cross-flow rectangular membrane module with arbitrary location of an impermeable plate placed for double-pass and external-recycle operations in raffinate phase, has been investigated. Theoretical treatment was analogous to the heat transfer in heat exchangers for the mass transfer in mass exchangers. An experiment was carried out in a cross-flow conduit of stainless steel inserted with a membrane sheet made of microporous polypropylene to extract acetic acid from aqueous solution by methyl iso-butyl ketone. Theoretical predictions are in agreement with the experimental results. Considerable improvement in mass-transfer performance is obtainable if the width of the first-pass subchannel, ΔB decreases, as well as the width of the second-pass subchannel, (1?Δ)B increases. The mass-transfer rate increases also when the reflux ratio increases. Based on the economic point of view, the suitable value of Δ (B is the width of a membrane sheet) may be 0.2.     

综放工作面过小窑破坏区浅析

阐述了新阳煤业207工作面由于小窑破坏,材料巷、运输巷不同程度的受空巷影响,导致回采推进速度减慢,给正常生产带来不良影响。分析了工作面现场实际条件及作业中出现的问题,总结了综采工作面过空巷的经验,提出了应对措施,应用效果良好。     

Quantitative cross impact analysis with latent semantic indexing

Cross impact analysis (CIA) consists of a set of related methodologies that predict the occurrence probability of a specific event and that also predict the conditional probability of a first event given a second event. The conditional probability can be interpreted as the impact of the second event on the first. Most of the CIA methodologies are qualitative that means the occurrence and conditional probabilities are calculated based on estimations of human experts. In recent years, an increased number of quantitative methodologies can be seen that use a large number of data from databases and the internet. Nearly 80% of all data available in the internet are textual information and thus, knowledge structure based approaches on textual information for calculating the conditional probabilities are proposed in literature. In contrast to related methodologies, this work proposes a new quantitative CIA methodology to predict the conditional probability based on the semantic structure of given textual information. Latent semantic indexing is used to identify the hidden semantic patterns standing behind an event and to calculate the impact of the patterns on other semantic textual patterns representing a different event. This enables to calculate the conditional probabilities semantically. A case study shows that this semantic approach can be used to predict the conditional probability of a technology on a different technology.     

Critical heat flux and mass loss rate for extinction of flaming combustion of timber

The critical mass loss rate and critical heat flux for self-extinction of flaming combustion during steady-state burning of timber was measured in this study for a range of timber species. A vertical mass loss calorimeter was used to provide the external heat flux and to measure the mass loss of the timber samples. The results showed that the critical mass loss rate was dependent upon the timber species but did not show a clear dependency with the timber density. Critical mass loss rates and heat fluxes for self-extinction exist for each of the timber species tested for both the solid timber and cross laminated timber (CLT). Debonding of both the char layer and the individual lamella of the CLT caused increased mass loss rates, re-ignition after self-extinction and increased flame lengths. Both char and ply fall-off were observed.     

基于扫描间距调控Inconel 738合金的微观组织和力学性能

采用EBSD技术系统地研究了扫描间距h对选区激光熔化(SLM)成形Inconel 738合金微观组织、动态再结晶行为、织构演变和力学性能的影响。研究表明,随着h的增加,平行于沉积方向的细长柱状晶晶粒长/径比减小,晶粒的形貌由粗大的细长柱状晶向细小的等轴晶转变,晶粒的取向变得更加随机;随着h的增加,动态再结晶体积分数增加,再结晶区域位错密度和应变低于未再结晶区域;随着h的增加,其铸造织构的类型发生变化,织构主要由Rotated-Goss织构{110}110转变为Rotated-Goss织构{110}110+Cube织构{001}100,Cube织构的强度逐渐增强,而Rotated-Goss织构的强度逐渐减弱;此外,通过选择合适的扫描间距(h=70μm),沉积态Inconel 738合金可获得优异室温力学性能(σ_y=933 MPa,σ_(uts)=1209 MPa,ε_f=38%),达到良好的强度与塑性匹配。     

定向穿越管道的挤毁失效及其防护装置的设计

定向穿越敷管技术由于其特殊优势,被越来越多地应用于油气管道敷设,但复杂的地质条件又极易导致穿越管道挤毁失效,对油气输送安全造成严重威胁。为此,针对复杂地层中穿越管道的挤毁失效行为,分析了其失效原因,主要是由孔壁失稳、地层沉降和地下水渗流等所导致的。进而基于管材非线性及管土耦合作用,建立了无缺陷和凹陷穿越管道的挤毁数值计算模型,并对其挤毁行为进行了研究。结果表明:①无缺陷管道与凹陷管道的挤毁失效模式不同,完整穿越管道的挤毁过程可分为6个阶段,管道横截面经历了椭圆形、"新月"形、"葫芦"形及"8"字形变化过程;②而凹陷管道的挤毁过程可分为5个阶段,管道横截面经历了"心"形、"新月"形、"葫芦"形及"8"字形变化过程;③围土压力越大,管道的挤毁失效后果越严重。最后,设计了一种结构简单、易于操作且具有自主知识产权的定向穿越管道用防护装置,可以有效降低管道发生凹陷、挤毁等失效的概率,延长管道使用寿命,可用于穿越危险地层的油气管道防护。     

Evaluation of kinetics and transport mechanism of solvents through natural rubber composites containing organically modified gadolinium oxide

The solvent transport properties of the prepared composites were analysed using solvents of varying cohesive energy density and the effect of both modified as well as unmodified filler on the sorption and diffusion behaviour of NR vulcanisates has been investigated. It is found that the equilibrium uptake decreases with increase in filler content, as anticipated owing to the restrictions offered by the filler for solvents to diffuse into the polymer matrix. The mechanism of transport in natural rubber composites was carefully tracked and it was found to exhibit an anomalous mode of solvent transport where the polymer relaxation is in par with the rate of diffusion. Theoretical modelling of the swelling parameters was done and the results were found to be in agreement with existing models. The excellent swelling resistance coupled with the simultaneous improvement in mechanical properties would definitely pave way for the utilisation of these composites as barrier membranes.     

基于MRSVD与LMD的工业机器人交叉滚子轴承故障特征提取

针对奇异值分解(SVD)优化局部均值分解(LMD)方法提取工业机器人交叉滚子轴承振动信号微弱故障特征分量时出现的模态混淆现象,提出一种基于最大分辨率SVD与LMD的工业机器人交叉滚子轴承故障特征提取方法。以最大奇异值分辨率原则将一维振动信号构造成Hankel矩阵,采用SVD对Hankel矩阵进行分解得到奇异值序列;按照奇异值曲率谱原则及非目标值抑制原则对奇异值序列进行重构,将包含故障突变信息的重构奇异值序列进行SVD逆运算得到重构振动信号;最后利用LMD方法对重构振动信号进行故障特征提取,得到能够表征原始振动信号振动特征的故障特征分量。通过与SVD优化LMD方法对比可知,该方法完整地提取了工业机器人交叉滚子轴承振动信号的微弱故障特征分量,改善了模态混淆现象。