Cd accumulation in paddy soils and its subsequent transfer to the food chain are widespread environmental issues, which has been extensively investigated in China. However, most studies focused on ...regional scales and these results may not be applicable to present the Cd contamination status in soil-rice ecosystems at a national scale. Therefore, based on collected data from China’s rice cultivation dominated regions, this study provides the Cd pollution level of paddy soils and rice grains in China. Results indicates that the Yangtze River basin, especially Hunan, required more attention due to the elevated Cd concentrations in soil-rice ecosystems. Moreover, this review summarizes the significant natural and anthropogenic sources, transport and accumulation mechanism as well as the influencing factors of Cd in soil-rice ecosystems. The wide occurrence of Cd contamination in paddy soils derived primarily from mining activities, intensive application of phosphates fertilizers and e-waste. Physicochemical characteristics of soil, soil microorganisms, temperature as well as the physiological features of rice plants all contribute to Cd accumulation in rice grains, which can be controlled to mitigate Cd accumulation in rice grains. This review will provide a scientific reference for Cd pollution control and management with respect to paddy field ecosystems in China and other countries.
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•We explored Cd pollution of soil-rice ecosystems in China on the national scale.•Cd in soils and grains in Hunan (China) are significantly higher than in other regions.•The concentration of Cd in paddy soil and grain have increasing trend.•Cd pollution in paddy soil mainly derived from mining activity and excessive phosphate fertilizer.
This study will be helpful for Cd pollution control and management of paddy field ecosystems at national level.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
For reducing the steady state speed ripple, especially in high performance speed servo system applications, the steady state precision is more and more important for real servo systems. This paper ...investigates the steady state speed ripple periodic disturbance problem for a permanent magnet synchronous motor (PMSM) servo system; a fuzzy adaptive repetitive controller is designed in the speed loop based on repetitive control and fuzzy information theory for reducing periodic disturbance. Firstly, the various sources of the PMSM speed ripple problem are described and analyzed. Then, the mathematical model of PMSM is given. Subsequently, a fuzzy adaptive repetitive controller based on repetitive control and fuzzy logic control is designed for the PMSM speed servo system. In addition, the system stability analysis is also deduced. Finally, the simulation and experiment implementation are respectively based on the MATLAB/Simulink and TMS320F2808 of Texas instrument company, DSP (digital signal processor) hardware platform. Comparing to the proportional integral (PI) controller, simulation and experimental results show that the proposed fuzzy adaptive repetitive controller has better periodic disturbance rejection ability and higher steady state precision.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Southwestern China contains the largest and most well-developed karst region in the world, and the potentially toxic elements (PTEs) content in the soils of the region is remarkably high. To explore ...the internal and external control factors and sources of soil PTEs enrichment in this area and to provide a basis for the treatment of PTE pollution, 113 soil samples were collected from Hengxian County, a karst region in Guangxi Province, southwestern China. The importance of eighteen influencing factors including parent material, weathering, physicochemical properties, topography and human activities were quantitatively analyzed by (partial) redundancy analysis. The sources of PTEs were identified using the Pb isotope ratio and absolute principal component score/multiple linear regression (APCS-MLR) model. The contents of all soil PTEs were higher than the corresponding background values of Guangxi soils. The contents in Cu, Zn, Cd, Hg and Pb were the highest in the soil from carbonate rock. The factor group of geological background and weathering explained 26.5% for the accumulation and distribution of soil PTEs and the influence of physicochemical properties was less than 2% but increased to 25.6% through interaction with weathering. Fe (47.1%), Al (42.1%), Mn (22%), chemical index of alteration (12.8%) and clay (11.9%) were the key factors affecting the soil PTEs, while the influence of human activities was weak. Pb isotope ratio and APCS-MLR classified 62.8–74% of soil PTEs as derived from natural sources, whereas 18.23% and 18.95% were derived from industrial activities and agricultural practice/traffic emissions, respectively. The Pb isotope ratio showed that the natural sources account for up to 90% of the Pb in the soil from carbonate rock, the highest contribution among the studied soils. The results of the study can provide background information on the soil PTEs contamination in the karst areas of China and other areas worldwide.
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•PRDA was used to assess the effect of influence factor groups on soil PTE content.•PTE content in the soil from carbonate rock were higher than other soils.•IRA of Pb point out the soil background is the major source of Pb content in soil.•Weathering and soil background were the key factors affecting PTE content.
This study is of great significance for providing a background information on potentially toxic elements contamination in the karst areas of China and other areas worldwide.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Effects of lake evaporation (EW) on basin evapotranspiration (ETB) and lake water storage change (LWSC) at lake‐basin scale have never been reported for most basins on the inner Tibetan Plateau (IB). ...In this study, EW of 118 large lakes in 95 closed lake‐basins were estimated, and its effects on ETB and LWSC over 2001–2018 were examined using a derivative‐guided framework from the aspects of EW amount, rate, trend slope and inter‐annual variability. We found that EW amount has a high effect (17%) on regional ETB amount compared to the average lake area ratio (α) (∼5%), and the effect has increased significantly (2%/10 a). The spatial pattern of the effect is mainly controlled by α, and the increasing trend of α (0.6%/10 a) also dominated the increasing trend in regional ETB rate (0.30 mm/a) though with large spatial heterogeneity. Variance in α and EW rate have a minor effect (∼3%) on ETB variance, especially for the basins with lower α. The combination of quasi lake inflow (RL, 41%) and lake surface precipitation (PW, 16%) offset the depletion of EW (−43%), resulting in the surplus of regional lake water (LWSC > 0). The increase in EW mount, which is mainly from lake area expansion (90%), caused a decreasing trend in LWSC (i.e., slower growth rate) with a contribution of −59%. This suggests a negative feedback between lake area expansion and EW amount in the IB, and the feedback may continue with the predicted area increases.
Key Points
Amount of evaporation for 118 lakes was estimated using two open water evaporation algorithms with annual lake area
A new derivative‐guided framework was presented to examine lake effects on basin evapotranspiration and lake water storage change
Basin scale lake inflow of 95 ungauged lake‐basins was estimated based on lake water balance
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
In this article, a low-cost multistep finite control set model predictive current control (FCS-MPCC) using a dc link single current sensor is proposed for permanent magnet synchronous motor (PMSM). ...In order to reduce the system cost, the single dc link current sensor is used to reconstruct the three-phase current. Different from the current reconstruction technology of field-orientated control strategy, there are some problems of the existed current reconstruction technology applied for finite control set model predictive control (FCS-MPC). First, the optimal switching state of FCS-MPC in each cycle is not fixed, and only contains at most one phase current information for reconstruction, which will cause the reconstruction failure. Therefore, a multiperiod sampling method is proposed to obtain the different two-phase current information to reconstruction. Second, the uncertainty of the two-phase reconstruction current interval will lead to current error, so this article proposes a variable period compensation method to solve this problem. Moreover, in order to improve the system closed-loop performance without significantly increasing the computational cost and enhance the system reliability, a low-cost multistep FCS-MPCC strategy based on the reconstructed three-phase current is proposed for PMSM. Finally, simulation and experimental results validate the effectiveness of the low-cost multistep FCS-MPCC method using a dc link single current sensor reconstruction for PMSM.
This paper investigates the finite-time output feedback control problem for dc-dc buck switched power converters of the current sensorless mode. A finite-time state-feedback controller is first built ...by using a recursive design method, and then a novel reduced-order observer, rather than the conventional full-order observer, is derived to estimate the unmeasurable state of the dc-dc buck system with a finite-time convergence rate. The output feedback control law built by combining the state-feedback control law and the measured system state from the observer is proved to be effective with an explicit stability analysis. Compared with the asymptotic stability control method, not only a faster convergence rate around the equilibrium is obtained but also a better suppression ability against resistance, inductance, and input voltage variation can be achieved for the closed-loop system. Moreover, the sensorless control strategy will be more reliable and cost reducible than its state-feedback control counter-case. Simulations and experimental comparison results verify the effectiveness of the proposed control method.
Finite control set model predictive control techniques have been emerged as good alternatives in particularly for multilevel and multiphase power converters, for which switching vectors with multiple ...magnitudes/directions are available but the modulator or switching table design becomes complex. In this paper, a finite-control-set model predictive direct torque and power control (FCS-DTC-DPC) for grid-tied three-level neutral-point clamped back-to-back power converters in permanent-magnet synchronous generator wind turbine systems is presented and experimentally compared with its counterpart: switching table-based direct torque and power control (ST-DTC-DPC). Both methods have been implemented and verified at a lab-constructed setup with a fully FPGA-based real-time controller. Experimental results confirm that both achieve (equivalently) good control dynamics, whereas FCS-DTC-DPC outperforms ST-DTC-DPC in terms of steady-state control performances at similar switching frequencies but has a higher computational demanding and is more sensitive to system parameter variations.
Long-term trends of sediment compositions are important for assessing the impact of human activities on the sediment and protecting the sediment environment. In this study, based on the contents of ...heavy metals and the Pb isotope ratios in lake sediments, atmospheric dustfall and soil in Yixing, China, the representative heavy metals (Zn, Pb, Cr and Cd) in lake sediments from western Taihu Lake were studied. The evolution history of heavy metals in the local environment was constructed for the past 100 years. From 1892 to the 1990s, the anthropogenic fluxes of the representative heavy metals were negligible, indicating minimal anthropogenic emissions of heavy metals. Since the 1990s, anthropogenic fluxes of the representative heavy metals began to increase, concurrent with the economic growth and development in the western Taihu Lake Basin after the Chinese economic reform. The maximum flux percentage of the heavy metals in the sediments, caused by human activities, is 23.0% for Zn, 31.6% for Pb, 39.5% for Cr and 85.3% for Cd, indicating that most of the Cd comes from human activities. The Cd content in the western Taihu Lake Basin was significantly higher than that in the other areas, and the rapid development of the industry in the western Taihu Lake Basin and ceramics in Yixing led to the enrichment of heavy metals in local sediments. Since the 21st century, measures have been taken to control the pollution of heavy metals, including the increase in local government attention and the deployment of environmental monitoring technology. However, heavy metal content remains high, and the Pb content is still increasing. The ratios of Pb isotopes show that the main sources of heavy metals in the western Taihu Lake sediments, the local soil of Yixing and the atmospheric dustfall are coal combustion, leaded gasoline combustion, industrial wastewater and domestic sewage.
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•High-resolution anthropogenic fluxes of heavy metals are recorded.•Coal combustion, leaded gasoline combustion, etc., have lead to lead pollution.•Serious pollution of Cd in western Taihu Lake was caused by ceramics industry.
In the 21st century, the content of heavy metals produced during the industrial development in the western basin of Taihu Lake has declined, but it is still high.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
In order to reduce the influence of time-varying disturbances for magnetic levitation system, we propose a reduced-order generalized proportional integral observer (RGPIO) based continuous dynamic ...sliding mode control scheme for magnetic levitation system in this paper. Unlike the popular extended state observer (ESO), it could deal with constant or slowing varying disturbances from theoretical point of view, the reduced-order generalized proportional integral observer (RGPIO) is designed to estimate the time-varying disturbances and system states, then the dynamic sliding mode surface is developed and deduce a continuous sliding mode controller (CSMC) for magnetic levitation system. Compared with ESO based continuous sliding mode controller, the proposed method not only ensures the position tracking accuracy, but also obtain better time-varying disturbance reject ability. Simulation and experimental results are also given to verify the effectiveness.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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