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Abstract: Based on PHOENICS software, the suitability of the outdoor wind environment at pedestrian heights of a low-carbon building under different operating conditions was quantitatively analysed using a κ-ε numerical model of low-speed turbulence. Three simulated conditions for the outdoor wind environment of low carbon buildings were determined by typical annual meteorological parameters for Shijiazhuang in cold regions. Combining the information on the full domain flow field obtained from the numerical simulations, the appropriate wind environment parameters were determined. The analysis of the wind environment indicators revealed that the low carbon buildings studied had clear year-round wind flow lines, with no dead zones and no obvious vortex areas. The wind speed at the pedestrian height of the low carbon building under different working conditions was less than 5 m/s (Wind speed in winter, summer and transitional season were 2.95 m/s, 2.54 m/s, and 3.3 m/s respectively), which meets the requirements of human comfort and standard regulations. The surface pressure difference between the different operating conditions (winter, summer and transitional seasons) of the low carbon building is not higher than 5 Pa, which meets the requirements for wind protection in winter in the area and contributes to the comfort level required for ventilation in summer. The study of the building wind environment can effectively identify the gap between the design and the actual use process, providing effective reference and guidance for the actual construction.Abstract: Based on PHOENICS software, the suitability of the outdoor wind environment at pedestrian heights of a low-carbon building under different operating conditions was quantitatively analysed using a κ-ε numerical model of low-speed turbulence. Three simulated conditions for the outdoor wind environment of low carbon buildings were determined by typica...Learn More
Abstract: Stealth measure is a key index to measure radar signal stealth capability. However, current radar signal stealth measure is mostly a single evaluation index, which is difficult to comprehensively evaluate radar signal stealth capability. Based on this, this paper improves the evaluation factor on the basis of previous LPI evaluation factor, relative entropy and interception factor, and eliminates the factors that have no influence on the power spectrum distribution. A new spectral distribution factor is constructed and the spectral distribution factor of ideal LPI signal is used to normalize the spectral distribution factor. The final calculation formula of relative entropy is simplified to reduce the dependence on the calculation process. The relative entropy can be calculated only by the beginning and end of the empirical distribution function of random variable after integral transformation. The interception factors are sorted out again to extract the power, time width, bandwidth and other factors that affect the stealth performance of radar signal. A new comprehensive stealth measure was constructed from the above three stealth evaluation indexes by means of equal weight product. The comprehensive stealth measure is used to simulate common LPI radar signals, and the effectiveness of the comprehensive stealth measure is proved by simulation analysis.Abstract: Stealth measure is a key index to measure radar signal stealth capability. However, current radar signal stealth measure is mostly a single evaluation index, which is difficult to comprehensively evaluate radar signal stealth capability. Based on this, this paper improves the evaluation factor on the basis of previous LPI evaluation factor, relativ...Learn More
Abstract: The process of bone mineralization is affected by piezoelectricity. As biomedical materials, titanium and titanium alloys are widely used as implant materials due to their excellent mechanical and biological properties. They do not have piezoelectric properties. The preparation of a layer of zinc oxide film with good piezoelectric properties on the surface of titanium is conducive to enhancing the ability of bone mineralization. In this paper, the effect of the piezoelectricity of zinc oxide on the deposition of CaP on the surface of titanium alloy excited by sound waves in vitro was studied, providing a new idea for improving the surface bioactivity of titanium alloy. A dense nano ZnO film was prepared on TC4 sheet by hydrothermal synthesis using zinc chloride and sodium hydroxide as raw materials. The piezoelectric constant d33 of zinc oxide thin film was measured by quasi-static method. The piezoelectric property of zinc oxide thin film was stimulated by acoustic vibration generated by a flat motor vibrator. The biomimetic mineralization experiment was carried out to study the piezoelectric property of zinc oxide and the effect of different vibration time of the motor on CaP deposition. The results show that the ZnO thin films prepared by this method have good crystallinity, high purity and are mostly hexagonal sheets, with the length ranging from 200nm to 300nm, and the longitudinal piezoelectric constant d33 is 2.13-3.68pC•N-1. More CaP was deposited on the vibrating sample surface than on the non vibrating surface, and CaHPO4 and Ca3(PO4)2 were mostly used as the deposition products. The immersion sample that vibrated for 30s within 1h (12h in total) had the best deposition effect.Abstract: The process of bone mineralization is affected by piezoelectricity. As biomedical materials, titanium and titanium alloys are widely used as implant materials due to their excellent mechanical and biological properties. They do not have piezoelectric properties. The preparation of a layer of zinc oxide film with good piezoelectric properties on the...Learn More
Abstract: With the continuous development of power electronics technology, the third-generation semiconductor materials represented by SiC and GaN have significant advantages in the band gap width, breakdown electric field, thermal conductivity, electron saturation rate and other key parameters, which meet the needs of modern industry for high power, high voltage and high frequency. When the SiC MOSFET plays its high frequency advantage, with the increase of switching frequency, the voltage change rate and current change rate of the device will be larger in the process of turning on and off. This paper mainly analyzes the characteristics of SiC MOSFET devices, and modifies the model based on the model provided by the manufacturer. By establishing static and dynamic test circuits, the static characteristic curves of the model were observed, and the drain voltage and current waveforms of the original model and the optimized model were compared during the switching process. The results show that the switching time of the optimized model is improved, and the oscillation waveform is greatly improved. Then, the accuracy of the optimized model is verified by the double-pulse circuit, and the drain source voltage and the drain source current are studied and observed under different temperature and drive resistance conditions. This paper provides data support for improving the switching characteristics of SiC MOSFET in practical applications.Abstract: With the continuous development of power electronics technology, the third-generation semiconductor materials represented by SiC and GaN have significant advantages in the band gap width, breakdown electric field, thermal conductivity, electron saturation rate and other key parameters, which meet the needs of modern industry for high power, high vo...Learn More
Abstract: The attention mechanism is derived from the study of human vision, which improves the accuracy of the model by increasing the weight of the noteworthy parts, and the existing attention is channel attention, spatial attention, and hybrid models. The development of attention in improving the accuracy of the model is sufficient, but under the influence of adversarial attacks, the influence of attention on the adversarial robustness of the model has not been fully studied. The purpose of this paper is to explore the effect of attention on model robustness. In this paper, the commonly used attention SENet, CBAM, ECAnet, SGE, SKNet, etc. are combined with the commonly used classification model ResNet to train the weights of the model from scratch, and compare the robustness of the combined model against confrontation. In addition, the influence of attention on ordinary noise is also reflected by comparison with Gaussian and salt and pepper noise. Based on the robustness formula of the predecessors, this paper proposes an adversarial robustness formula to uniformly evaluate the adversarial samples with different disturbance parameters of different networks. It is proved that the structure of attention has an impact on the robustness of the model, and SKNet, SGE, and CBAM will improve the robustness of the model in the 18-layer model, with the deepening of the model, attention has a negative improvement on the robustness of the model. Attention has a good robustness to Gaussian and salt and pepper noise, but also reflects a negative improvement with the deepening of the network.Abstract: The attention mechanism is derived from the study of human vision, which improves the accuracy of the model by increasing the weight of the noteworthy parts, and the existing attention is channel attention, spatial attention, and hybrid models. The development of attention in improving the accuracy of the model is sufficient, but under the influenc...Learn More
Abstract: When the distribution network is disturbed or fails, the microgrid connected to it will suddenly leave the distribution network and cause some serious consequences. Aiming at the low voltage ride through (LVRT) capability of the microgrid when the voltage of the distribution network drops, a control strategy of LVRT for the optical storage microgrid based on Quasi-resonant control (QPR) is proposed. During the voltage sag period of the optical storage microgrid, the active power at the DC side is absorbed by the energy-storage device to maintain the voltage stability of the DC bus, and the injection power of the converter is reduced to avoid over-current; The photovoltaic inverter collects the voltage and current at the junction point in the two-phase static coordinate system as the outer loop feedback and the filtered capacitor current as the inner loop feedback to provide the internal equivalent virtual impedance, thus providing the required damping for the filter circuit, and modulates it into a PWM wave to directly control the AC quantity to reduce the impact of the harmonic component on the optical storage microgrid. Finally, the simulation model is built in Matlab/Simulink, The research shows that the control strategy proposed in this paper can effectively maintain the stability of the DC bus voltage and limit the current of the junction point, which confirms the rationality of the LVRT control strategy.Abstract: When the distribution network is disturbed or fails, the microgrid connected to it will suddenly leave the distribution network and cause some serious consequences. Aiming at the low voltage ride through (LVRT) capability of the microgrid when the voltage of the distribution network drops, a control strategy of LVRT for the optical storage microgri...Learn More
