Papers by Keyword: Decomposition

Abstract: Growing demand of machines such as gas turbine, pump, and compressor in power generation, aircraft, and other fields have yielded the transformation of machine maintenance strategy from corrective and preventive to condition-based maintenance. Real-time fault diagnosis has grabbed attention of researchers in looking for a better approach to overcome current limitation. The parameters of health condition in machinery could be monitored thus faults could be detected and diagnosed by using signal analysis approach. Since some fault signals are non-stationary or time dependent in nature, therefore time-frequency signal analysis is crucial for machinery fault diagnosis. Common time-frequency signal analysis methods are such as short time Fourier transform (STFT), wavelets analysis, empirical mode decomposition (EMD), Hilbert-Huang transform (HHT), etc. This review provides a summary of the basic principle of signal analysis, the most recent researches, and some advantages and limitations associated to each types of time-frequency signal analysis method.

Abstract: Health monitoring of the bridge structure has gradually become one of the hot topics. The signal decomposition technology is the key technique of the bridge structural health monitoring. The traditional data analysis and processing methods, which can only be applied to stationary or linear signal processing, have significant limitations. However, the structural response signals tested are mostly non-stationary and nonlinear. So methods that can effectively analyze non-stationary and nonlinear signal are urgently needed. Based on the summarization and analysis of the shortage of wavelet analysis method, the application of local wave method for data processing and analysis in structural health monitoring is put forward. The feasibility and superiority of local wave method is discussed. Experimental simulation results show that the application of local wave method in bridge health monitoring signal decomposition is feasible.

Abstract: In developing software, which are basic developing strategy to be used This is a worthy issue. After studying various software development methods, four basic developing strategies are found. The four basic developing strategies are linear developing strategy, iterative developing strategy, developing strategy of decomposition, developing strategy of assembling. For any a software development method, it may use a type basic developing strategy, it may use also two types or more than two types of basic developing strategies. The content of the basic developing strategies is discussed. People can use the basic developing strategies to build new software development methods, and to build development program of definite issues.

Abstract: There are many thinking method, the thinking method of decomposition and combination is important and widely used. In the category of scholars, "decomposition and combination" belong to "analysis and synthesis". Developing software is a complex mental activity, so it requires the use of a variety of thinking method. Thinking method of decomposition and combination is the use of the most frequent in developing software. Content of thinking method of decomposition and combination is analyzed. Application of thinking method of decomposition and combination has been analyzed from four aspects. Four aspects are the development trend of software, the main content of the structured software development method, the main content of the object-oriented software development method, several commonly used software development tools.

Abstract: Characteristics of litter decomposition and carbon and nitrogen release were comparatively studied under meadow, typical and desert steppe ecosystems. The results showed that litter under meadow ecosystem had the highest decomposition rate constant of biomass, percentage of carbon, nitrogen and cellulose loss than that under typical and desert steppe ecosystems. Analysis of variance showed that there were obvious significant differences in decomposition rate constant of biomass, percentage of carbon, nitrogen and cellulose loss of litter among three grassland ecosystems. Stepwise regression analysis showed that annual average relative humidity played significant or very significant impact on decomposition rate constant of biomass, percentage of cellulose, carbon, nitrogen loss under three grassland ecosystems. Therefore, litter decomposition and nitrogen release was mainly influenced by precipitation under different grassland ecosystems.

Abstract: To provide an important basic knowledge for the biogeochemical cycle of bamboo forest ecosystem, particularly the cycling of global carbon, we studied decomposition dynamics of leaf-litter with different mass accumulation in moso bamboo forest. Our study area located in Miaoshanwu nature reserve, Fuyang, Zhejiang province. Based on the survey, we concluded that: (1) the sequence of remaining mass of leaf-litter with different mass accumulation after 240 days' decomposition from the most to the least was in the following order: 30g (58.53%) > 60g (51.92%) > 90g (48.48%), implying that leaf-litter with more mass accumulation decomposed faster in the unit area. (2)The more accumulated leaf-litter lead to more TOC loss in leaf-litter which will not helpful for TOC increase on surface soil carbon pools. This implying that the faster leaf-litter decomposed, the less TOC increased on surface soil carbon pools in 240 day s' observation. (3)The concentration of N, P, K and Ca showed the similar tendency with initially increasing but decreasing gradually in the following stage and then increasing again in the next stage. And concentration of Mg, Fe, Cu and Zn increased gradually in the period of 0-240 days.

Abstract: Gas emission is basically non-stationary time series, Based on this view, wavelet multi-resolution analysis was applied to the predication of gas emission. Firstly, the gas emission data was decomposed by wavelet multi-resolution analysis. Secondly, the single branch reconstruction of each layer was predicted by establishing AR forecasting model. Synthesized all of the results from every layers, the forecasting result was obtained. The simulation showed that predication for mine gas emission with the method of this paper has much higher accuracy than AR model forecasting model.

Abstract: Volatile organic compounds (VOCs) are organic chemicals mostly emitted from different sources like industrial or domestic having high vapor pressure at room-temperature conditions. Some of these are also anthropogenic in nature and also these are the major contributor for the photochemical ozone. The different methods available for the abatement of VOCs are thermal oxidation, catalytic oxidation, photocatalytic oxidation, adsorption etc. Due to the stringent regulation of VOCs emission in different countries there is a need of efficient abatement technology to preserve the environment. In this context catalytic combustion of organic pollutants offers considerable advantages over the industrially operated thermal combustion process. Generally, oxidative destruction is possible at low temperature in presence of a catalyst. In addition catalytic process is more energy efficient and can operate with very dilute pollutants. A number of catalysts have been used for the complete oxidation of VOCs, among these Pillared clays type porous materials are also useful for the purpose. Pillared clays have high surface area, pore volume, thermal stability and can be tailor made for particular catalytic application compared with the parent clays. In the present review we will summarize the latest developments on the clay based materials including the effect of different controlling parameters for the synthesis of pillared clay based porous materials and its specific application for the low temperature VOCs decomposition. In particular the effect of transition metals like iron and manganese oxide pillared clay on the VOC decomposition is discussed.

Abstract: This work is dedicated to the development of an on-line monitoring system of SF6 decomposition in electrical devices (SF₆DcpMS) in order to evaluate the health condition of the devices in real time. The feature decomposition, SO₂, and SF₆ purity are continuously monitored. Considering the oxidation-reduction reactions of SO₂ electrochemical sensor during detection, the methodology of utilizing the air in the electrical device is proposed based on the tests of serving devices. And it is proved via tests that electrochemical sensors can be applied into SF₆DcpMS. Besides, infrared detector is employed to detect SF₆ purity. Sampling method of SF₆ in electrical devices is described. There are three keys in the sampling device design for the on-line monitoring system: -- Sensor working environment: The rating pressure is one atmospheric pressure for sensor working. Therefore, a gas chamber is constructed, in which the suitable environment for sensor is completed via a pressure regulator and a pressure sensor. At the same time, an appropriate control method is scheduled. Gas in the chamber is continuously replaced with that in the electrical device to ensure detection accuracy within an acceptable range. -- SO₂ adsorption feature: The monitoring accuracy is seriously influenced by the adsorption feature of SO₂. As we known, flowing gas can decrease SO₂ adsorption feature. So, a micro bump is designed in the gas chamber, which can ensure the gas flowing at the speed of 200ml/min. -- Sample gas back into electrical devices: In order to avoid the gas cause harm to humans, the gas leakage is not allowed in the on-line monitoring system, and the sample gas must be sent back to the electrical device after detection is accomplished. Sample gas back into electrical devices is realized via a bump and a check valve with adjustable cracking pressure. The first SF₆DcpMS in China has been successfully put into service in Zunyi substation, and its performance has been proved out.

Abstract: The reaction process between Ti₂AlC and Ag-Cu filler alloy was mentioned in our previous study. However, the reaction mechanism between Ti₂AlC and filler alloy remained uncertain due to the existence of TiAl₂, which was widely distributed in the dual-phase Ti₂AlC substrate and exhibited intense reaction with Cu. In current research, pure-phase Ti₂AlC was brazed to Cu using Ag-Cu filler alloy respectively at 850°C and 900°C for 10 min. First of all, to investigate the influence of TiAl₂ on clarifying the reaction mechanism, Ti₂AlC substrates with different component (single phase and dual phase) were joined to Cu at 850°C for comparison. However, in these joints, it was difficult to find any other reactant except for AlCu₂Ti. Thus, the pure-phase Ti₂AlC was brazed to Cu at 900°C, aiming to intensify the interaction between substrates and filler alloy. For characterizing the microstructure evolution in the joint, the typical region of the joint that contained all the reactants was selected and sliced by focused ion beam technology. Combining with transmission electron microscopy, all the decomposition products (e.g. Ti₃AlC₂ and TiC) in the joint were identified. Then the decomposition mechanism of Ti₂AlC was clearly disclosed.