晚中新世-上新世黄土高原佳县红粘土剖面碳同位素记录与C4植被演化

新生代C4植被开始扩张的年代、过程和驱动机制是全球古气候变化研究的焦点问题.中国黄土高原的黄土-红粘土剖面保存了连续的古生态演化记录,是研究这一关键科学问题的理想载体.本文选择黄土高原北部佳县厚达64m的红粘土剖面(8.2～2.7Ma),对190个层位的次生方解石矿物进行了无机碳同位素测试,由此分析了晚中新世-上新世末的C4植被扩张和演化过程.C4植被持续增长与全球冰盖的扩张基本一致,表明气候变冷很可能导致了黄土高原区域气候的干旱化与降雨季节性的增强.C4植被的扩张存在明显的3个阶段,分别以6.6Ma和3.6Ma为界限,每一次扩张增加10％左右,暗示了全球性的构造事件对黄土高原植被演化的控制.此外,佳县红粘土剖面呈现10次持续时间为10 ～ 20万年的碳同位素正漂移事件,平均每40万年发生一次,说明40万年轨道周期也控制着C4植被的演化.     

一种结合四元数与直方图的多光谱图像自适应边缘检测方法

针对图像自适应边缘检测的难点和传统多光谱遥感图像边缘检测方法的局限性,提出了一种结合四元数与直方图的自适应边缘检测方法。该方法在四元数空间,利用矢量旋转完成了多光谱图像的边缘检测,并通过直方图统计的方法获取自适应阈值,实现了边缘图像的检测。利用陆地多光谱遥感图像和水域多光谱遥感图像分别进行实验,验证了方法的有效性。     

The population structural transition effect on rising per capita CO2 emissions: evidence from China

ABSTRACT

The per capita CO₂ emissions (PCCE) of many developing countries like China have been rising faster than total CO₂ emissions, and display spatial divergence. Such temporal growth and spatial divergence will have a significant influence on efforts to mitigate CO₂ emissions. Given the research gap on the impact of the structural transition in population on PCCE, we constructed an econometric model using the dynamic panel method. The results reveal that the population structural transition has a significant nonlinear impact on PCCE, as the rate of population growth in China decelerates. Both demographic ageing and urban-rural migration have a stronger impact on PCCE than other factors. This effect, however, decreases beyond a certain threshold. An increase in the number of households due to urbanization and family downsizing has resulted in a positive effect on PCCE, without a threshold turning point. The research also finds that an increased share of the service sector in employment can reduce PCCE only if the sector employs more than 31.56% of the total employed population. Overall, these findings indicate that policymakers should pay attention to the prominence of the demographic structural transition for effective climate policy.

Key policy insights

• Policymakers should address rising per capita carbon emissions (PCCE) and their spatial divergence in future climate policies, not just total CO₂ emissions.

• The transitioning demographics of ageing and urbanization in China show a nonlinear, inverted U-shaped effect on PCCE instead of a continuously positive effect.

• Based on the nonlinear effect of employment structure on PCCE, policymakers should focus on the relationship between the structural transition of the economy and PCCE in future climate mitigation policies.

     

天气雷达Z I关系本地化及RPG降水产品改进

利用2004—2008年5—9月大连新一代天气雷达和自动站资料,在进行回波分型、多次采用最优化Z I关系,结合系统误差消除的技术方法,得到适用于实际业务需要的整体本地化Z I关系。以大连地区2008年全部5次大暴雨过程为例,经RPG数据处理系统中的降水估计产品检验,较沿用 WSR 88D 默认值生成值准确率提高40%以上,经2009—2011年使用,估算准确率稳定在75%以上,提高了天气雷达数据处理的质量。     

Artificial Martian frozen orbits and Sun-Synchronous orbits using continuous low-thrust control

This paper analyses three types of artificial orbits around Mars pushed by continuous low-thrust control: artificial frozen orbits, artificial Sun-Synchronous orbits and artificial Sun-Synchronous frozen orbits. These artificial orbits have similar characteristics to natural frozen orbits and Sun-Synchronous orbits, and their orbital parameters can be selected arbitrarily by using continuous low-thrust control. One control strategy to achieve the artificial frozen orbit is using both the transverse and radial continuous low-thrust control, and another to achieve the artificial Sun-Synchronous orbit is using the normal continuous low-thrust control. These continuous low-thrust control strategies consider J ₂, J ₃, and J ₄ perturbations of Mars. It is proved that both control strategies can minimize characteristic velocity. Relevant formulas are derived, and numerical results are presented. Given the same initial orbital parameters, the control acceleration and characteristic velocity taking into account J ₂, J ₃, and J ₄ perturbations are similar to those taking into account J ₂ perturbations for both Mars and the Earth. The control thrust of the orbit around Mars is smaller than that around the Earth. The magnitude of the control acceleration of ASFOM-4 (named as Artificial Sun-Synchronous Frozen Orbit Method 4) is the lowest among these strategies and the characteristic velocity within one orbital period is only 0.5219 m/s for the artificial Sun-Synchronous frozen orbit around Mars. It is evident that the relationship among the control thrusts and the primary orbital parameters of Martian artificial orbits is always similar to that of the Earth. Simulation shows that the control scheme extends the orbital parameters’ selection range of three types of orbits around Mars, compared with the natural frozen orbit and Sun-Synchronous orbit.     

浅析油气卸放时静电的成因和预防措施

通过某油库卸油时发生燃烧爆炸的原因分析,指出静电形成的原因和危害,根据静电形成的原因,指出在装卸油气时应注意控制装卸速度、做好防静电接地并留足静电泄放时间,保证工作安全。     

Formation flying solar-sail gravity tractors in displaced orbit for towing near-Earth asteroids

Several methods of asteroid deflection have been proposed in literature and the gravitational tractor is a new method using gravitational coupling for near-Earth object orbit modification. One weak point of gravitational tractor is that the deflection capability is limited by the mass and propellant of the spacecraft. To enhance the deflection capability, formation flying solar sail gravitational tractor is proposed and its deflection capability is compared with that of a single solar sail gravitational tractor. The results show that the orbital deflection can be greatly increased by increasing the number of the sails. The formation flying solar sail gravitational tractor requires several sails to evolve on a small displaced orbit above the asteroid. Therefore, a proper control should be applied to guarantee that the gravitational tractor is stable and free of collisions. Two control strategies are investigated in this paper: a loose formation flying realized by a simple controller with only thrust modulation and a tight formation realized by the sliding-mode controller and equilibrium shaping method. The merits of the loose and tight formations are the simplicity and robustness of their controllers, respectively.     

Periodic orbits based on geometric structure of center manifold around Lagrange points

This study proposes an analytical method that determines the center manifold and identifies the reduced system on the center manifold. The proposed method expresses the center manifold through general equations containing only state variables, and not functions with respect to time. This is the so-called geometric structure of the center manifold. The location of periodic or quasi-periodic orbits is identified after the geometric structure of the center manifold is determined. The reduced system on the center manifold is described using ordinary differential equations, so that periodic or quasi-periodic orbits can be computed by numerically integrating the reduced system. The results indicate that the analytical method proposed in this study has higher precision compared with the Lindstedt-Poincaré method of the same order.     

地震安评中天然地震波选取方法研究

近年来工程场地地震安全性评价工作日趋规范化,安评相关方法与技术也在不断的发展与完善.而超高、超限等复杂结构类型越来越成为城市建筑建设重点,根据《建筑抗震设计规范》要求,此类建筑在抗震设计工作中需要进行时程分析,时程分析输入地震动的选用需考虑与规范反应谱在"统计意义上相符".在总结常用选择方法的基础上,提出一种新的选波思路,即按照安评结果反应谱作为目标反应谱,基于强震记录数据库,利用PEER强震记录数据库及搜索平台,寻找最优匹配天然地震波,作为结构时程分析输入地震波,通过实例对比分析,该方法选取的地震波在结构时程分析中具有良好的适用性.