Papers by Keyword: Trend

Abstract: The characteristics of the macrostructure of expanded clay concretes are compared using the topological and fractal approaches. The sensitivity of concrete strength to the fractal dimensions of a cement-sand matrix, expanded clay gravel, feldspar grains, large fractions of quartz and pores is verified. The trend of the influence of the expanded clay concrete macrostructure on its strength is determined using the fractal approach. Fractal modeling of the macrostructure of expanded clay concrete made it possible to reduce the forecast error in the indices of their strength by 1.18...2.03 times in comparison with the topological approach.

Abstract: Based on the precipitation data observed monthly of 19 weather stations in Hebei province from 1960 to 2011, three methods, linear trend estimation, Mann-Kendall test as well as Morlet wavelet transformation, were adopted to analyze the characteristics of precipitation trend, abrupt change points and cyclical variations under the circumstance of multi-time scales in the past 52 years. Annual precipitation had a decreasing trend, and precipitation in spring increased dramatically, meanwhile precipitation of summer decreased significantly; however, precipitations in autumn and winter were fluctuated in an acceptable range. There were various abrupt change points both in annual precipitation series and in spring as well as in summer, yet any abrupt change points were found in autumn and winter. Multi-scale periodicities were found by wavelet analysis in annual and seasonal precipitations.

Abstract: In order to extract useful information of underwater acoustic signals from noise, preprocessing steps are unavoidable. In view of trend and transient pulse interference exited in the original data inevitability, morphological filter method is applied and analyzed in this paper. Data processing results show that the morphological filter method is superior to the traditional filter method.

Abstract: Reference crop evapotranspiration (ET₀) is a key to estimate crop water requirements, and also an important component of irrigation schedule and water resources planning, sensitivity analysis are crucial in assessing the impact of climate changes in ET₀ estimations. In this study, based on the daily meteorological data of 18 meteorological stations in Shanxi Province from 1961 to 2000, the daily ET₀ values were calculated using Penman-Monteith equation recommended by FAO-56. The trends of climate variables were detected by using Mann-Kendall test. Sensitivity coefficients were employed to predict responses of ET₀ to five climatic variables, combined with annual of meteorological factors quantitative analysis of ET₀ changes. The results show that statistically significant decreasing trends are observed in wind and daily sunshine hours in Guanzhong and southern Shaanxi. Relative humidity has a significant decreasing trend in northern Shaanxi. In general, ET₀ value is on the decline; relative humidity is the most sensitive variable, followed by solar radiation, daily sunshine hour, wind speed and mean temperature. The change of ET₀ is primarily attributed to the significantly decreasing in wind speed and sunshine hour.

Abstract: Exhaust gas temperature (EGT) is an important parameter for aeroengine. By monitoring the change in trend, can effectively predict the engine take-off performance. The characteristics of takeoff EGT were introdeced firstly. Two methods of estimating takeoff performance were analyzed subsequently. According to the statistical data, EGT can be used for takeoff performance prediction.

Abstract: Intelligent greenhouse cultivation and management is one of the most important technologies for continuous production of agricultural products. This article deals with the development history, status, key technologies and trend of greenhouse intelligent monitoring system£¬ makes analysis on the existent problems and developing trend so as to provide reference for the growth of China's facility agriculture intellectualization£®

Abstract: This paper used the Mann-Kendall test, Spearman rank correlation test, Pettitt-Mann-Whitney change-point statistics, and complex Morlet wavelet analysis method to analyze the trend, change-point, and period of the tidal level at Nanjing Station from 1950 to 2012. The results demonstrated that there was a significant increase of annual highest and lowest tidal levels, while the trend of annual average tidal level change was not obvious. Significant mutations existed not only in the term of annual highest tidal level but also in the lowest one: the annual highest tidal level increased by 0.49m after 1972, while the annual lowest one increased by 0.29m after 1982. The period of annual average tidal level, highest one, and lowest one were 10 years, 15 years, and 14 years respectively. The scale of fluctuations in the annual highest tidal level was close to the annual lowest tidal level. The cause analysis of fluctuation indicated that runoff variation was the dominant factor of tidal level change.

Abstract: National Nature Reserve for the Rare and Endemic Fishes in the Upper Reaches of the Yangtze River (RURYR) in China has been established to protect the extraordinarily perfect aquatic ecosystem since 2005. However, four cascade hydropower stations located in the upstream of RURYR will impound and generate electricity gradually, which may change the natural flow regime there. Since flow regime is of great importance to maintaining the healthy and integrity of aquatic ecosystems, it is essential to study the rules of its variation. The flow alteration in RURYR was characterized by Indicators of Hydrologic Alteration (IHA) during 1960-2010, and its trends and the change rules were analyzed for further study on environmental flow and multi-objective optimal operation. The results indicate that in terms of almost no change in total annual runoff, the flow shows a decreasing trend in the flood season, especially in August and October, but an increasing trend in the dry season (from January to June). The variation trend seems reduce the flood risk as a good purpose, however, along with the multi-operation of the cascade reservoirs, the loss of flood peak will increase more significantly, which is harmful to the aquatic ecosystems.

Abstract: With the further development of national economy, people have become more concerned about the environment quality. Especially in recent years, due to the frequent occurrence of hazy weather, there has been a growing demand for clean energy [Fig. 1]. As one kind of non-conventional energy, natural gas hydrate, featured by large reserves and relatively clean products of combustion, is considered by the scientific community to be an alternative energy resource in replacement of coal and petroleum. This paper gives a brief introduction of the research progress of natural gas hydrate both at home and abroad, presents the research results and the obstacles in the next step to be taken for China, and then looks into the future development trend.

Abstract: Microgrid has become one of the most important adjuncts to solve the power system in some developed countries. This article aims to introduce the every country’s definition of Microgrid and its significance, discuss the key technologies in Microgrid research, including control technologies, management techniques and so on; Secondly, I summarize the key problems of Microgrid in current stage; Finally, discuss the trend of Micro-grid in the light of the current development status and problems.