激光陀螺数字机抖电路优化

针对实际功率放大电路中存在的反向充电的问题,提出了双向放电的优化解决方案;针对电路中耦合电容器件导致驱动信号占空比调节范围窄的问题,提出了去除耦合电容器件,增加防共态导通保护电路的解决方案,并对优化后的电路进行了仿真和试验。结果表明,优化后的驱动电路可以解决目前存在的问题,获得更优的机抖驱动信号。     

Effect of initial microstructure on performance and corrosion behavior of GH4169 superalloy joint produced by linear friction welding

The pre-weld heat treatment was carried out to obtain different initial microstructures of the GH4169 superalloy, and then Linear Friction Welding（LFW） was performed. The effect of the pre-weld heat treatment on the microstructure evolution and mechanical properties of the joint was analyzed, and the joint electrochemical corrosion behavior as well as the hot corrosion behavior was studied. The results show that the joint hardness of Base Metal（BM） increases after pre-weld heat treatment, and the strengthening phases γ'and γ'further precipitate. However, the precipitation phases dissolve significantly in the Weld Zone（WZ） due to the thermal process of LFW. The corrosion resistance in BM is reduced after the pre-weld heat treatment, while it is similar in WZ with a slight decrease. The surface morphology of the BM and WZ can be generally divided into a loose and porous matrix and a scattered oxide particle layer after hot corrosion. The joint cross section exhibits a Cr-depleted zone with the diffusion of Cr to form an oxide film. The corrosion product mainly consists of Fe₂O₃/Fe₃O₄ as the outer layer and Cr₂O₃ as the inner layer.     

Effect of fiber breakage defect and waviness defect on compressive fatigue behavior and damage evolution of 3D multiaxial braided composites

This paper reports the effects of fiber breakage defects and waviness defects on the compressive fatigue behavior and the progressive damage evolution process of 3D Multiaxial Braided Composites(3DMBCs). Combined with finite element compression simulation and ultra-depth microscope, the internal defect content of composites with different braiding angles was determined.The results demonstrate that the weakening effect of waviness and fiber breakage defects is greater than the strengthening effect of the braiding angle. This causes the fatigue resistance of 3DMBCs with the 31° braiding angle being better in both directions of 0° and 90°. The increase of 4° waviness and 10% fiber breakage defect results in the average fatigue life of composites being shortened by 48% and the energy consumption rate increased by 10% at 85% stress level in 90° compression direction. The alteration in loading direction modifies the included angle corresponding to the stress component. The stress component parallel to the fiber direction under compressive fatigue load leads to interfacial debonding in the composites, whereas the stress component perpendicular to the fiber direction results in pronounced shear failure.     

A critical review on oxidation behavior of Co-based superalloys

The novel Co-based superalloys are extensively used in gas-powered and jet engine turbines due to their excellent high-temperature performance, achieved by strengthening the L1₂-γ'ordered phase. This review presents an overview of the research progress on oxidation behavior of Co-based superalloys, including oxidation kinetics, oxides morphology, the formation and spallation of oxide layers, and importantly, the synergistic effects of alloying elements on oxidation resistance-a critical area considering the complex interactions with multiple alloying elements.Additionally, this review compares the oxidation resistance of single crystal versus polycrystalline alloys. The effect of phase interface and dislocations on oxidation behavior is also discussed. While significant progress has been achieved, areas necessitating further investigation include optimizing alloy compositions for enhanced oxidation resistance and understanding the long-term stability of oxide layers. The future prospects for Co-based superalloys are promising as ongoing research aims to address the existing challenges and unlock new applications at even higher operating temperatures.     

Robust pre-departure scheduling for a nation-wide air traffic flow management

Air traffic flow management has been a major means for balancing air traffic demandand airport or airspace capacity to reduce congestion and flight delays. However, unpredictable fac-tors, such as weather and equipment malfunctions, can cause dynamic changes in airport and sectorcapacity, resulting in significant alterations to optimized flight schedules and the calculated pre-departure slots. Therefore, taking into account capacity uncertainties is essential to create a moreresilient flight schedule. This paper addresses the flight pre-departure sequencing issue and intro-duces a capacity uncertainty model for optimizing flight schedule at the airport network level.The goal of the model is to reduce the total cost of flight delays while increasing the robustnessof the optimized schedule. A chance-constrained model is developed to address the capacity uncer-tainty of airports and sectors, and the significance of airports and sectors in the airport network isconsidered when setting the violation probability. The performance of the model is evaluated usingreal flight data by comparing them with the results of the deterministic model. The development ofthe model based on the characteristics of this special optimization mechanism can significantlyenhance its performance in addressing the pre-departure flight scheduling problem at the airportnetwork level.     

Femtosecond laser rotary drilling for SiC_f/SiC composites

SiC_f/SiC ceramic matrix composites（SiC_f/SiC composites） are difficult to drill small holes due to their heterogeneity, high hardness, and low electrical conductivity. In order to solve the difficulties of poor quality and low efficiency when drilling small holes, a novel femtosecond laser rotary drilling（FLRD） technique is proposed. Beam kinematic paths and experimental studies were carried out to analyze the effects of processing parameters on the drilling results in the twostep drilling process. In the through-hole drilling stage, the material removal rate increases with increasing laser power, decreasing feed speed and decreasing pitch. As for the finishing stage of drilling, the exit diameter increased with increasing laser power and decreasing feed speed. The drilling parameters were selected by taking the processing efficiency of through-hole and the quality of finished hole as the constraint criteria. Holes with a diameter of 500 μm were drilled using FLRD in 3 mm thick SiC_f/SiC composites with a drilling time < 150 s. The hole aspect ratio was 6, the taper < 0.2°, and there was no significant thermal damage at the orifice or the wall of the hole.The FLRD provides a solution for precision machining of small holes in difficult-to-machine materials by offering the advantages of high processing quality and short drilling times.     

Progress of 2014—2016 China's Earth Observation and Earth Science

The support given by Earth observation data and Earth system science play an increasingly important role in global change, regional sustainable development, extreme events, and the development of social and economic needs. This field is also moving towards systematization, platforms, and standardized development. In December 2015, nearly 200 parties of the United Nations Framework Convention on Climate Change agreed in Paris to make arrangements for global action in response to climate change by 2020. China jointly issued a climate change adaptation strategy for cities in 2016 and then elevated national action to respond to climate change. China's Earth Observation and Earth Science development is facing new challenges as it supports the national civil space infrastructure and high-resolution Earth observation system.     

A reply from Earth?

An approach is proposed to developing a message from Humankind to extraterrestrial intelligence if we detect it.     

光传导信号同步传输系统

介绍了光传导信号同步传输系统。该系统由信号发送部分、光纤光电耦合部分、信号接收部分等组成。系统采用数字编码的方式，具有良好的抗干扰性能，同时由于用光纤进行传导，有效地解决了绝缘问题。该系统可用于光纤电流互感器（OCT）。