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  • Hindawi Limited  (3)
  • 1
    Online Resource
    Online Resource
    Hindawi Limited ; 2021
    In:  Journal of Mathematics Vol. 2021 ( 2021-7-21), p. 1-11
    In: Journal of Mathematics, Hindawi Limited, Vol. 2021 ( 2021-7-21), p. 1-11
    Abstract: Scientific prediction and accurate grasp of the future trend of population change are conducive to the formulation of different population policies at different stages, so as to alleviate the adverse effects of the aging population on society and provide scientific theoretical reference for controlling the population size and making policy. Considering that the population system is affected by many complex factors and the structural relationship among these factors is complex, it can be regarded as a typical dynamic grey system. In this paper, the fractional-order GM (1, 1) model and the fractional-order Verhulst model are established, respectively, based on the statistical data of China's population indices from 2015 to 2019 to forecast the population size and the change trend of population structure of China from 2015 to 2050 in the short-term and medium- to long-term. The forecast results show that China’s population will grow in an inverse S shape from 2015 to 2050, when the total population will reach 1.43 billion. Moreover, during this period, the birth rate and natural growth rate of population will decrease year by year, and the proportion of aging population and the dependency ratio of population will increase year by year. Besides, the problem of aging population is going to become increasingly serious. The application of grey system method to population prediction can mine the complex information contained in the population number series. Meanwhile, the fractional-order accumulation can weaken the randomness of the original data series and reduce the influence of external disturbance factors, so it is a simple and effective population prediction method.
    Type of Medium: Online Resource
    ISSN: 2314-4785 , 2314-4629
    Language: English
    Publisher: Hindawi Limited
    Publication Date: 2021
    detail.hit.zdb_id: 2717090-1
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  • 2
    Online Resource
    Online Resource
    Hindawi Limited ; 2019
    In:  International Journal of Polymer Science Vol. 2019 ( 2019-01-09), p. 1-7
    In: International Journal of Polymer Science, Hindawi Limited, Vol. 2019 ( 2019-01-09), p. 1-7
    Abstract: In this work, different kinds of ionic liquids and reaction conditions for the extraction of lipid from microalgae biomass were optimized and repeated use of ionic liquids for microalgal lipid extraction was evaluated. Morphological changes of microalgae cells were compared in terms of pre- and post-treatment to understand the mechanisms of ionic liquid treatment. Ionic liquid [BMIM][MeSO 4 ] showed the best lipid extraction efficiency at 70°C and with reaction time of 2 hours. The ratios (ILs : methanol) of 1 : 7 and 1 : 3 were the optimum ratios to complete the extraction of the lipids from microalgae. The initial 50% volume fraction of [BMIM] [MeSO 4 ] was 16.04% of dry weight, which showed the highest five average extraction rates. The loss of ionic liquid in the reaction system and the increase in water content of ionic liquids were considered as the main reasons for the decrease in the extraction rate. It is suggested that the potential of lipid extraction in this IL-methanol co-solvent system is promising due to the high efficiency, low cost, safety, environmental protection, and other characteristics.
    Type of Medium: Online Resource
    ISSN: 1687-9422 , 1687-9430
    Language: English
    Publisher: Hindawi Limited
    Publication Date: 2019
    detail.hit.zdb_id: 2520688-6
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  • 3
    Online Resource
    Online Resource
    Hindawi Limited ; 2022
    In:  Journal of Mathematics Vol. 2022 ( 2022-2-18), p. 1-10
    In: Journal of Mathematics, Hindawi Limited, Vol. 2022 ( 2022-2-18), p. 1-10
    Abstract: In view of the inaccuracy of rock movement observation data and the inaccuracy of mining subsidence prediction parameters, a prediction model of mining subsidence parameters based on fuzzy clustering is proposed. Through the analysis of the main geological and mineral characteristics of mining subsidence, the geological and mineral characteristics are simplified according to the third similar theorem. The feature equation is obtained by using the equation analysis method and dimension analysis method. The original fuzzy clustering method is improved, and the IWFCM_CCS algorithm based on competitive merger strategy is obtained. The data of rock movement observation are analyzed by fuzzy clustering. The membership matrix and clustering center of observation station data are obtained, and the regression model based on the weight of membership degree is established. The accuracy and feasibility of the parameter prediction model are verified by analyzing and comparing the actual measurement data and the predicted results of the model. The method reduces the error of the predicted parameters caused by the observation data and provides a method for the future calculation of the predicted parameters.
    Type of Medium: Online Resource
    ISSN: 2314-4785 , 2314-4629
    Language: English
    Publisher: Hindawi Limited
    Publication Date: 2022
    detail.hit.zdb_id: 2717090-1
    Location Call Number Limitation Availability
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