Synthesis of boron-doped diamond/porous Ti composite materials — Effect of carbon concentration

Highly boron-doped diamond films were deposited on porous titanium substrates by hot filament chemical vapor deposition technique.The morphology variation of highly boron-doped diamond films grown on porous titanium substrates was investigated,and the effects of carbon concentration on nucleation density and diamond growth were also studied.The continuous change of surface morphology and structure of diamond film were characterized by scanning electron microscopy.The structures of diamond film and interlayer were analyzed by X-ray diffraction.The quality of boron-doped diamond film was confirmed by visible Raman spectroscopy.The experimental results reveal that surface morphology and quality of boron-doped diamond films are various due to the change of carbon concentration.The thickness of intermediate layer decreases with the carbon concentration increasing.     

Heating process of thermosetting insulation materials for buildings

Polyurethane (PU) and phenolic (PF) foams used for building isolation were analyzed by thermal gravity/differential thermal analysis to determine their pyrolysis behavior, including the decomposition point and the maximum reaction rate point. Besides, the shape deformations of PU and PF foams were observed, and their oxygen index and the calorific value in combustion were also studied. The results showed that the pyrolysis of both PU and PF can be divided into three stages from room temperature to 1 000 ℃ in the atmospheric air, with total mass loss of 94.345% for PF and 88.191% for PU, respectively. The oxygen index of PU and PF decreased with increasing the temperature and the duration of the heat treatment. With the temperature increasing, the calorific values of both materials were reduced remarkably. These results of the PU and PF could provide basic data of the thermal stability and fire safety design in the application of thermosetting insulation materials.     

基于回声状态网络的飞机混沌时间序列预测模型

准确检测飞机即将发生的故障或预测其状态的变化趋势,对于实现飞行安全具有重要意义。文章针对传统基于回声状态网络在故障预测中的不足,构建了基于小波降噪的回声状态网络预测模型。该模型保留了非线性时间序列回声状态网络预测的优势,并采取小波变换对混沌时间序列进行降噪预处理,有效提高了含噪混沌时间序列的预测精度。论文通过对某飞机发动机滑油散热器温度时间序列数据序列进行预测分析,表明文中模型具有较好的预测精度,验证了模型的有效性。     

Stress wave propagation in supporting bolts: A test for bolt support quality

A test method for the non-destructive determination of bolt length, anchoring length, and bolt body force is described. This addresses the problems of low accuracy, limited number of data, and untimely warning signs encountered with existing test methods. Numerical simulations of the bolt, resin, and rock system show that the length accuracy when using the velocity wave is lower than when using the acceleration wave. It is accepted practice to use the acceleration wave for length tests because of improved signal to noise ratios of the waveforms. Laboratory and in situ underground tests showed that the precision of the measurements meets field requirements. Using this method the anchor properties of each single bolt and, thus, the safety of the entire roadway support may be evaluated.     

Acoustic emission generated during the gas sorption–desorption process in coal

An experimental system for monitoring the acoustic signals generated in coal during gas sorption and/or desorption was designed and the acoustic signals were observed under different gas pressures. The experimental results show that signals generated by the coal during gas adsorption are attenuated over time. Also, the signals are not continuous but are impulsive. The intensity of the signals generated during gas desorption is far smaller than that observed during adsorption. The signal seen during desorption remains essentially stable. Cycles of sorption and desorption cause acoustic emission signals that exhibit a memory effect, which depends upon the maximum gas pressure the sample was exposed to in earlier cycles. Lower pressures in subsequent cycles, compared to the maximum adsorption pressure in previous cycles, cause both the energy and impulse frequency to be lower than previously. On the contrary, a gas adsorption pressure that exceeds the maximum pressure seen by the sample during earlier cycles causes both the energy and impulse frequency to be high.     

Evolution and distribution of macroscopic gas channels in an overburden strata

The evolution of gas bearing channels in the roof, and their spatial distribution, was studied. A complete consideration of gas flow changes through the stress–strain changes in the roof near a working face is made. The theoretical abutment pressure distribution using displacement monitors and borehole visual recording instruments allow a theoretical analysis. Field test research determined the conditions for formation of macroscopic gas channels. These appear along the working face roof, normally distributed to it. These results show that the coal rock stratification becomes a macroscopic gas channel boundary if its deformation is less than the lower layer, or greater than the layer above it. At the same time the stability is greater than the distance from the roof for hanging dew conditions. The working face advances and the roof gas channels experience a cycle of development. Microscopic channels dominate the initial stage then macroscopic gas channels form, develop, and close. The evolution of the macroscopic channels depends on the ratio between the distances from the new compaction area in the goaf to the initial stress area in front of the working face. The amount of daily advance of the face also affects channel development. The experimental observations in one mining area showed that the main gas channels are located about 2 and 6.2 m above the lower surface of the roof and that they have an evolution period 7 to 11 days long.     

Design and analysis of a model predictive controller for active queue management

Model predictive (MP) control as a novel active queue management (AQM) algorithm in dynamic computer networks is proposed. According to the predicted future queue length in the data buffer, early packets at the router are dropped reasonably by the MPAQM controller so that the queue length reaches the desired value with minimal tracking error. The drop probability is obtained by optimizing the network performance. Further, randomized algorithms are applied to analyze the robustness of MPAQM successfully, and also to provide the stability domain of systems with uncertain network parameters. The performances of MPAQM are evaluated through a series of simulations in NS2. The simulation results show that the MPAQM algorithm outperforms RED, PI, and REM algorithms in terms of stability, disturbance rejection, and robustness.     

吉沙水电站施工总布置设计

吉沙水电站为长引水式电站,主要由混凝土闸坝、水道系统和地面厂房等组成,根据枢纽布置特点及施工支洞布置方案,结合工程实际情况,并考虑其他因素,施工总布置采用集中与分散相结合的布置方式。经过施工实践检验,设计规划的施工总布置方案满足工程建设的需要。     

蒲石河抽水蓄能电站工程金属结构设计

蒲石河抽水蓄能电站总装机容量为1 200 MW,是我国东北地区在建中的第一座大型纯抽水蓄能电站。主要介绍了电站金属结构设备的布置与选型,并总结了主要设计成果,为今后类似工程的设计提供了可供借鉴的宝贵经验。     

Water and Sediment Quality in Lakes along the Middle and Lower Reaches of the Yangtze River, China

Water and sediment samples were collected from 45 lakes along the middle-lower Yangtze River, China. Each lake was sampled seasonally, over a period of one year. Water quality variables and metals in sediments were measured. Lakes along the lowest part of the river, within the Yangtze River Delta, had highest nutrient concentrations and were eutrophic or hypereutrophic. Lakes displayed a gradient in many water chemistry variables, from the middle to the lower Yangtze River. Lakes of the Delta region had the highest conductivity, sulfate, turbidity, and Chl-a values, and the lowest dissolved oxygen concentrations. A number of lakes near urban areas in the study region also displayed similar conditions. Lakes polluted by heavy metals were found in the upper part of the lower Yangtze River and had high Cu, Cr, and Co concentrations in sediments. The mean I_geo (index of geoaccumulation) values for Cu, Cr, and Co classes ranged from 0 to 4, indicating moderate to heavy contamination, contributed mainly from untreated industrial waste water produced within the lake catchments. Lakes of the middle Yangtze River are generally in relatively better condition, except for those around urban zones, which experience higher nutrient and heavy metal loading. The spatial distribution of lake conditions in the area can be related to the policy of regional economic development. The Delta region in China is developed and includes such cities as Shanghai and Suzhou. Heavy industries have moved into the interior region of China too, and development of modern cities is now occurring under some level of environmental protection. Nevertheless, lakes in the central part are becoming seriously polluted with both heavy metals and nutrients because local authorities promote industrialization and urbanization to improve economic conditions, while often ignoring environmental protection. Pollution is increasingly occurring in upstream reaches, a tendency that will bring more environmental problems. Interior lakes of China require immediate attention to prevent further declines in water quality.