Yanshan University

About: Yanshan University is a education organization based out in Qinhuangdao, China. It is known for research contribution in the topics: Microstructure & Control theory. The organization has 19544 authors who have published 16904 publications receiving 184378 citations. The organization is also known as: Yānshān dàxué.

Microwave-absorbing properties of shape-optimized carbonyl iron particles with maximum microwave permeability

Abstract: The microwave-absorbing properties for different shapes of carbonyl-iron particles prepared by the high-energy planetary ball milling with 40 vol% in epoxy resin matrix have been investigated. Higher value of magnetic permeability and permittivity can be obtained in the composites for thin flake carbonyl iron than spherical powders. The results are attributed to reduction of eddy current loss, orientation of magnetic moment and space–charge polarization with the shape change from spherical powders to thin flake particles. As the iron flakes with 0.4 μm in thickness as the absorbent fillers, the minimum RL value of −6.20 dB was observed at 4.57 GHz with thickness of 1 mm. The minimum reflection loss (RL) shifts to lower frequency and the value declines with change from spherical powders to thin flakes. It results from the considerable dielectric loss in the absorbing materials.

A PWM and PFM Hybrid Modulated Three-Port Converter for a Standalone PV/Battery Power System

Abstract: A pulsewidth modulation (PWM) and pulse frequency modulation (PFM) hybrid modulated three-port converter (TPC) interfacing a photovoltaic (PV) source, a storage battery, and a load is proposed for a standalone PV/battery power system. The TPC is derived by integrating a two-phase interleaved boost circuit and a full-bridge $LLC$ resonant circuit. Hence, it features a reduced number of switches, lower cost, and single-stage power conversion between any two of the three ports. With the PWM and PFM hybrid modulation strategy, the dc voltage gain from the PV to the load is wide, the input current ripple is small, and flexible power management among three ports can be easily achieved. Moreover, all primary switches turn ON with zero-voltage switching (ZVS), while all secondary diodes operate with zero-current switching over full operating range, which is beneficial for reducing switching losses, switch voltage stress, and electromagnetic interference. The topology derivation and power transfer analysis are presented. Depending on the resonant states, two different operation modes are identified and explored. Then, main characteristics, including the gain, input current ripple, and ZVS, are analyzed and compared. Furthermore, guidelines for parameter design and optimization are given as well. Finally, a 500-W laboratory prototype is built and tested to verify the effectiveness and advantages of all proposals.

College students' stress and health in the COVID-19 pandemic: The role of academic workload, separation from school, and fears of contagion.

Abstract: The COVID-19 pandemic has unhinged the lives of people across the globe. In particular, more than 30 million Chinese college students are home-schooling, yet there is little understanding of how academic workload, separation from school, and fears of contagion lead to a decrease in their health. This study examined the relationships between Chinese college students' three critical stressors and two types of health in the COVID-19 pandemic context. We used a three-wave lagged design with a one-week interval. All the constructs were assessed by self-report in anonymous surveys during the COVID-19 pandemic. College students were asked to report their demographic information, academic workload, separation from school, fears of contagion, perceived stress, and health. The results of this study showed that academic workload, separation from school, and fears of contagion had negative effects on college students' health via perceived stress. In the COVID-19 crisis, multiple prevention and control measures focusing on college students may lead them to have different degrees of stress and health problems. Our results enrich the literature on stress and health and offer novel practical implications for all circles of the society to ensure students' health under the context of the COVID-19 epidemic.