Background: Smartphones are becoming increasingly indispensable in everyday life for most undergraduates in China, and this has been associated with problematic use or addiction. The aim of the current study was to investigate the prevalence of smartphone addiction and the associated factors in male and female undergraduates. Methods: This cross-sectional study was conducted in 2016 and included 1441 undergraduate students at Wannan Medical College, China. The Smartphone Addiction Scale short version (SAS-SV) was used to assess smartphone addiction among the students, using accepted cut-offs. Participants' demographic, smartphone usage, and psycho-behavioral data were collected. Multivariate logistic regression models were used to seek associations between smartphone addiction and independent variables among the males and females, separately. Results: The prevalence of smartphone addiction among participants was 29.8% (30.3% in males and 29.3% in females). Factors associated with smartphone addiction in male students were use of game apps, anxiety, and poor sleep quality. Significant factors for female undergraduates were use of multimedia applications, use of social networking services, depression, anxiety, and poor sleep quality. Conclusions: Smartphone addiction was common among the medical college students investigated. This study identified associations between smartphone usage, psycho-behavioral factors, and smartphone addiction, and the associations differed between males and females. These results suggest the need for interventions to reduce smartphone addiction among undergraduate students.

No abstract

No abstract

No abstract

No abstract

No abstract

Photovoltaic (PV) inverter is the most important part for energy conversion, and the current research focus for PV inverter is high efficiency, high reliability, and low-output accurrent distortion. With considerable grid-connected PV installation in last few years, high penetration PV system is desired, which requires integrating PV inverter into grid regulation. New code in Germany already requires PV inverter providing system regulation and service for low voltage distribution system. One of obvious impact on PV inverter is reactive power generation requirement. Most state-of-the-art high-efficiency PV inverters that adopt single-stage topology only allow unity power generation but none of them are able to generate reactive power. This paper proposes a high-efficiency dual-buck full-bridge PV inverter for a wide range power factor operation. Additionally, a novel hybrid bipolar PWM method is proposed to achieve low ground leakage current and low output current distortion in the PV system. At last, simulation and experiment demonstrate that the proposed PV inverter system can provide a wide-range power factor operation with high efficiency, low ground leakage current, and low output current distortion.

Parabolic current control is an attractive current control method with fast transient response and constant switching frequency. Due to the good dynamics of parabolic current control, it can be employed in voltage source inverters to improve the system performance such as minimizing the distortion of current waveforms or voltage waveforms. To implement parabolic current control, a current sensor is required, associated with the current conditioning circuit and parabolic carrier generators. Since parabolic current control is based on the real-time information of the inductor current, any phase delay or propagation delay of the sensor itself and the conditioning circuitry, or limited resolution of parabolic carrier generators, could impact the current control performance.Since the parabolic current control compares analog signals to generate the required control signals, noise from the control board impacts the control precision as well. This paper will explore solutions to these problems. First, the inductor current of voltage source inverter is analyzed and the parabolic current control strategy is studied, then a sensorless parabolic current control method is proposed. The new sensorless parabolic control method utilizes a current emulator to rebuild the inductor current on a micro-controller. To avoid a dc offset on the ac-side output voltage caused by the current emulator, an additional control loop in the current emulator is added. The effectiveness of the proposed methods are experimentally verified by the use of an H-bridge voltage source inverter. INDEX TERMSParabolic current control, sensorless current control, current tracking error, voltage source inverters, hysteresis current control, non-linear current control 0885-8993 (c) Furthermore, since the parabolic carriers are generated digitally in a micro-controller, it is more flexible to adjust the magnitude and frequency of the carriers.4) The causes of a dc offset on the ac-side output voltage are analyzed. To eliminate this dc offset, an additional control loop is introduced to the current emulator. An implementation method and control loop design are illustrated.The performance of the proposed sensorless PCC method is verified by experimental results.A hardware prototype employing the proposed sensorless method achieves good transient performance under the operating conditions of both a resistor load and a nonlinear load such as a rectifier load. The dc offset on the ac-side voltage is eliminated by the proposed control strategy.Constant switching frequency is achieved and current tracking error remains in the parabolic band.