In order to reduce the negative influence of wind speed randomness and prediction error on frequency modulation, the reliability of the wind storage system was assessed effectively. In the wind ...storage frequency modulation system, a state of charge (SOC) adaptive adjustment method for wind speed randomness is proposed. Firstly, through the correlation analysis between the standby capacity of frequency modulation and the output power of wind turbine, the uncertainty of its frequency modulation capacity is revealed. Secondly, in view of the uncertainty of wind turbine frequency modulation, the output power of energy storage frequency modulation is optimized with the goal of minimizing the frequency modulation power deviation of the wind storage front under the framework of model predictive control, and the improved whale optimization algorithm (WOA) is used to solve the problem. Finally, the simulation results show that, under the given 5 min continuous disturbance, the root mean square of frequency regulation of the proposed restoration method is reduced by 56.65% compared to the SOC recovery base point set to 0.5. Under continuous large perturbations, the maximum frequency deviation is reduced by 0.0455 Hz. This effectively shows that this method can not only improve the frequency modulation reliability of wind power system but also improve the continuous frequency modulation capability of energy storage system.
• The daily minimum temperature was the dominant limited factor to corn production. • Corn yield was positively correlated with the minimum temperatures in May and September. • 1°C increase of ...minimum temperature in May or September may lead to an average increment of 303kgha−1 or 284kgha−1 in corn yield.
Recent crop model projections have shown that crop production may benefit from warming, especially in the high latitudes, but hard evidence is limited. In this study we conducted correlation and regression analyses of climate records of seventy-two meteorological stations and records of corn yield over the period 1965–2008 in Northeast China. It was found that over these forty-four years, the diurnal mean, minimum and maximum temperatures during corn growing season increased on average by 0.31°C, 0.42°C and 0.23°C every ten years, respectively. No significant change in precipitation was found, although differences between years were large. The daily minimum temperature was the dominant factor to corn production. Corn yield was significantly correlated with the daily minimum temperature in May and September. According to a regression analysis of the anomalies of corn yield and air temperature, a 1.0°C increase in daily minimum temperature in May or September will lead to an increment of 303kgha−1 or 284kgha−1 in corn yield, respectively. Corn varieties with longer growth duration will profit most from the climatic changes but agronomic practices may have to be modified to address expected weather extremes such as droughts and periods with heavy rainfall.
High‐quality epitaxy consisting of Al1−xGaxN/Al1−yGayN multiple quantum wells (MQWs) with sharp interfaces and emitting at ≈280 nm is successfully grown on sapphire with a misorientation angle as ...large as 4°. Wavy MQWs are observed due to step bunching formed at the step edges. A thicker QW width accompanied by a greater accumulation of gallium near the macrostep edge than that on the flat‐terrace is observed on 4° misoriented sapphire, leading to the generation of potential minima with respect to their neighboring QWs. Consequently, a significantly enhanced photoluminescence intensity (at least ten times higher), improved internal quantum efficiency (six times higher at low excitation laser power), and a much longer carrier lifetime are achieved. Importantly, the wafer‐level output‐power of the ultraviolet light emitting diodes on 4° misoriented substrate is nearly increased by 2–3 times. This gain is attributed to the introduction of compositional inhomogeneities in AlGaN alloys induced by gallium accumulation at the step‐bunched region thus forming a lateral potential well for carrier localization. The experimental results are further confirmed by a numerical modeling in which a 3D carrier confinement mechanism is proposed. Herein, the compositional modulation in active region arising from the substrate misorientation provides a promising approach in the pursuit of high‐efficient ultraviolet emitters.
Enhanced ultraviolet luminescence of AlGaN wavy‐quantum‐wells grown on large misoriented sapphires is demonstrated, enabled by the successful introduction of compositional inhomogeneities in AlGaN alloys induced by gallium accumulation and thus forming a 3D carrier confinement for radiative recombination. Herein, the compositional modulation in active region arising from large misoriented‐substrate offers a promising approach in the pursuit of high‐efficient ultraviolet emitters.
The early identification of rotten potatoes is one of the most important challenges in a storage facility because of the inconspicuous symptoms of rot, the high density of storage, and environmental ...factors (such as temperature, humidity, and ambient gases). An electronic nose system based on an ensemble convolutional neural network (ECNN, a powerful feature extraction method) was developed to detect potatoes with different degrees of rot. Three types of potatoes were detected: normal samples, slightly rotten samples, and totally rotten samples. A feature discretization method was proposed to optimize the impact of ambient gases on electronic nose signals by eliminating redundant information from the features. The ECNN based on original features presented good results for the prediction of rotten potatoes in both laboratory and storage environments, and the accuracy of the prediction results was 94.70% and 90.76%, respectively. Moreover, the application of the feature discretization method significantly improved the prediction results, and the accuracy of prediction results improved by 1.59% and 3.73%, respectively. Above all, the electronic nose system performed well in the identification of three types of potatoes by using the ECNN, and the proposed feature discretization method was helpful in reducing the interference of ambient gases.
This paper proposes a Configuration method for energy storage (ES), in which the ES inertia of ES is equal to an equal capacity synchronous generator. The purpose is to enhance the frequency ...modulation capability of double-fed induction generator (DFIG) and wind power consumption. Through the proposed method, the system inertia can remain unchanged after the DFIGs replacing the conventional turbines. During the DFIG rotor speed recovery, the ES releases energy to compensate for sudden changes in active power. On this basis, the DFIG and ES structure model is created, and the ES control strategy is optimized, thereby effectively improving the DFIG frequency modulation capability. Besides, in the non-frequency modulation period, the ES is used to suppress wind power fluctuations, thereby improving system wind power consumption and ES utilization. Simulation results indicate, in the ES-embedded wind turbine structure model, the combination of the ES Configuration method and multi-functional strategy significantly improves the frequency modulation ability and anti-interference performance of a single DFIG. Moreover, the wind power consumption and ES utilization are improved, and the ES achieves additional value.
The band structures of two locally resonant phononic crystals (LRPCs) with periodic multilayered cylindrical inclusions embedded in an elastic matrix are investigated by the finite-element method. ...The inclusions consist of electroactive polymer layer(s). Tunability of the band gaps of the phononic crystals by applying electric field upon the electroactive layer is demonstrated. A simple analytical expression is presented on the relationship between the stop band boundaries and the electric field. Good agreement between the analytical and numerical predictions is obtained. The effects of initial stress on the band structures are explored. It is found that tensile initial stress shifts up the band gaps while compressive initial stress shifts down or even closes them.
Neurological symptoms are increasingly being noted among COVID-19 patients. Currently, there is little data on the mental health of neurological healthcare workers. The aim of this study was to ...identify the prevalence and influencing factors on anxiety and depression in neurological healthcare workers in Hunan Province, China during the early stage of the Coronavirus Disease 2019 (COVID-19) outbreak.
An online cross-sectional study was conducted among neurological doctors and nurses in early February 2020 in Hunan Province. Symptoms of anxiety and depression were assessed by the Chinese version of the Self-Rating Anxiety Scale (SAS) (defined as a total score ≥ 50) and Self-Rating Depression Scale (SDS) (defined as a total score ≥ 53). The prevalences of probable anxiety and depression were compared between different groups, and multivariate logistic regression analysis was used to understand the independent influencing factors on anxiety and depression.
The prevalence of probable anxiety and depression in neurological nurses (20.3 and 30.2%, respectively) was higher than that in doctors (12.6 and 20.2%, respectively). Female healthcare workers (18.4%) had a higher proportion of anxiety than males (10.8%). Probable anxiety and depression were more prevalent among nurses, younger workers (≤ 40 years), and medical staff with junior titles. Logistic regression analysis showed that a shortage of protective equipment was independently associated with probable anxiety (OR = 1.980, 95% CI: 1.241-3.160, P = 0.004), while young age was a risk factor for probable depression (OR = 2.293, 95% CI: 1.137-4.623, P = 0.020) among neurological healthcare workers.
Probable anxiety and depression were more prevalent among neurological nurses than doctors in Hunan Province. The shortage of protective equipment led to probable anxiety, and young age led to probable depression in healthcare workers in neurology departments, which merits attention during the battle against COVID-19.
► Warming led to annually increments of 16.6kgha−1, 15.5kgha−1 and 3.2kgha−1 in rice, corn and soybean yields, respectively in Northeast China. ► Growth durations of new varieties of rice, corn and ...soybean have respectively prolonged by 14.0 days, 7.0 days and 2.7 days since the 1950s. ► Actual growing periods of rice and corn have respectively prolonged by 6 days and 4 days since 1990s. ► Existing spatial distribution of rice cropping area has been extended northward about 80 kilometers compared to the 1970. ► Actual responses of cropping system are consistent with the theoretical calculation based on the historical warming level.
To learn the historical response of cropping system to climate change will benefit the strategy decision of future cropping adaptation. In this paper, we conducted an integrated analysis of the climate records of seventy-two meteorological stations and the records of crop yields over the period 1970–2009 in Northeast China. It was found that over these forty years, the daily mean, maximum and minimum temperatures during crop growing season increased on average by 0.34°C, 0.28°C, 0.43°C every ten years, respectively. No significant change in the precipitation was found, although the differences between years were large. After de-trending the agronomic technique contributions to the increments of crop yields, the historical warming had led to great annually increments of 16.6kgha−1, 15.5kgha−1 and 3.2kgha−1 in rice, corn and soybean yields, respectively. According to the historical warming level, present cropping boundaries can be theoretically extended northward about 80km with a prolonged growing period by 10 days compared to the 1970s. Actually, the growth durations of newly approved varieties of rice, corn and soybean have really prolonged by 14.0 days, 7.0 days and 2.7 days since the 1950s, respectively. The actual growing periods of rice and corn have also respectively prolonged by 6 days and 4 days due to the adjustment of sown and harvest dates by the farmer since 1990s. The existing rice cropping region has been extended northward 80km in the 2006 compared to the 1970. These actual responses were consistent with the theoretical calculation according to the historical warming trends. Our results demonstrate that cropping system owns the potential to progressively and actively adapt to the global warming for high yield through a comprehensive strategy.
To obtain high-precision for focal length fitting and improve the visible-light camera autofocusing speed, simultaneously, the backlash caused by gear gaps is eliminated. We propose an improved RBF ...(Radical Basis Function) adaptive neural network (ANN) FUZZY PID (Proportional Integral Derivative) position closed-loop control algorithm to achieve the precise positioning of zoom and focus lens groups. Thus, the Levenberg-Marquardt iterative algorithm is used to fit the focal length, and the improved area search algorithm is applied to achieve autofocusing and eliminate backlash. In this paper, we initially adopt an improved RBF ANN fuzzy PID control algorithm in the position closed-loop in the visible-light camera position and velocity double closed-loop control system. Second, a similar triangle method is used to calibrate the focal length of the visible-light camera system, and the Levenberg-Marquardt iterative algorithm is used to fit the relation of the zoom potentiometer code values and the focal length to achieve the zoom position closed-loop control. Finally, the improved area search algorithm is used to achieve fast autofocusing and acquire clear images. The experimental results show that the ITAE (integrated time and absolute error) performance index of the improved RBF ANN fuzzy PID control algorithm is improved by more than two orders of magnitude as compared with the traditional fuzzy PID control algorithm, and the settling time is 6.4 s faster than that of the traditional fuzzy PID control. Then, the Levenberg-Marquardt iterative algorithm has a fast convergence speed, and the fitting precision is high. The quintic polynomial fitting results are basically consistent with the sixth-degree polynomial. The fitting accuracy is much better than that of the quadratic polynomial and exponential. Autofocusing requires less than 2 s and is improved by more than double that of the traditional method. The improved area search algorithm can quickly obtain clear images and solve the backlash problem.
Mercury-free semiconductor deep ultraviolet light-emitting diodes (DUV-LEDs) still suffer from low power efficiencies due to extremely poor light extraction efficiency. In this paper, a ...high-reflective electrode is proposed and carefully optimized for making an ohmic contact with the n-type AlGaN layer in the DUV-LEDs (~280 nm). The electrode is made of Cr/120-nm Al metal stack with a different thickness of the Cr layer in a range of 1-20 nm followed by the complete LED fabrication process. We found that the DUV-LED with a 1-nm Cr/120-nm Al electrode obtains maximum light output power and the highest external quantum efficiency, showing an enhancement factor of 40.9% and 25.4%, respectively, in comparison to a conventional LED with an electrode made of 20-nm Cr/120-nm Al. This enhancement is mainly attributed to a higher UV reflectivity of the 1-nm Cr/120-nm Al electrode. Furthermore, a better ohmic contact was achieved in such electrode due to the formation of higher quality Al-Cr and Cr-N alloys in such metal/n-AlGaN junction.
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