Design and on-orbit status of the trigger system for the DAMPE mission

DArk Matter Particle Explorer(DAMPE), the first Chinese astronomical satellite, was successfully launched at the Jiuquan Satellite Launch Center on 2015 Dec. 17. DAMPE consists of four subdetectors: Plastic Scintillator array Detector(PSD), Silicon-Tungsten tracKer-converter(STK), Bismuth Germanium Oxide(BGO) imaging calorimeter and NeUtron Detector(NUD). The global hardware trigger signal, which is generated by hits from the BGO calorimeter and the trigger logic board in the data acquisition system(DAQ), is responsible for event selection and DAQ synchronization of DAMPE. On orbit,to improve the detection efficiency, different trigger logics are used for event selection in different regions of latitude. The DAMPE trigger system compresses the average on-orbit trigger rate to 60 Hz and reduces science data mass to less than 13 GB per day to meet the requirement for the satellite's data link. The whole trigger system has run stably up to now, ensuring excellent on-orbit operation of DAMPE.     

1957~2016年中国农业界限温度时空变化研究

利用中国830个气象站点1957~2016年地面气象观测资料,采用五日滑动平均法和GIS方法确定了近60 a农业界限温度（0℃、5℃、10℃）的初终日期和持续日数,并比较分析1957~1986年和1987~2016年2个时段的≥0℃、≥5℃和≥10℃农业界限温度的初终日期和持续日数的变化情况。结果表明：与1957~1986年相比,1987~2016年中国农业界限温度（0℃、5℃、10℃）的总体变化规律基本一致,即初日提前、终日推迟、持续日数增加,各地区变化幅度不同,东北、华北和青藏高原地区变化幅度最大。中国各界限温度的终日变化幅度均较小,初日和持续日数变化较大。≥0℃初日在东北北部和青藏高原地区分别提前3~9 d和3~15 d,持续日数在东北和华北部分地区分别增加3~15 d和2~18 d,青藏高原部分地区增加4~16 d;≥5℃初日在东北和华中地区分别提前4~9 d和6~13 d,持续日数在东北、华北部分地区分别增加4~13 d和2~14 d,青藏高原地区增加2~23 d;≥10℃初日在东北和青藏高原地区分别提前2~9 d和2~13 d,持续日数在东北和青藏高原地区变化最为显著,分别增加3~15 d和5~25 d。农业界限温度的初终日期和持续日数变化,使作物生育期延长和种植界线北移。     

Free-surface evolution and wave kinematics for nonlinear uni-directional focused wave groups

This paper concerns the propagation of transient wave groups, focused at a point in time and space to produce locally large waves having a range of steepness. The experimental study was carried out in a wave flume at Dalian University of Technology. The numerical simulations were based on a nonlinear boundary integral equation solved by a higher-order boundary element method (HOBEM). Rather than simulate the whole experimental tank, local surface elevation measurements were used to drive the numerical solution from a point less than two wavelengths upstream of the focus position, leading to significant savings in computational time. Excellent agreement is achieved between the water surface elevations and the water particle kinematics measured in the experiments and those predicted numerically at wave group focus, even for near-breaking waves up to a steepness of kA=0.405 for which even locally matched 2nd-order theory is inadequate. Results based on the linear and 2nd-order theory are also presented in the comparisons. When compared with the first- and 2nd-order solutions, the fully nonlinear wave–wave interactions produce a steeper wave envelope in which the central wave crest is higher and narrower, while the adjacent wave troughs are broader and less deep.     

沉积白云石形成条件的试验研究

经过大量试验研究工作，总结出在常温常压条件下，全成碳酸盐矿物的控制因素和形成条件，合成出原白云石（无序白云）等一系列碳酸盐矿物.原白云石经加温加压，在100℃或150℃转化为白云石（有序白云石）.     

Effect of brittle fracture on the rheological structure of the lithosphere and its application in the Ordos

An empirical formula for the fracture strength of the principal rock type in the lithosphere is obtained based on the experimental data from previous studies, in which the effects of the confining pressure, size of the rock sample, temperature, strain rate and the pore pressure are taken into account, the empirical formulae for the effects of them are also presented. By comparing the frictional strength to the fracture strength calculated using the new empirical formula, it is shown that frictional sliding is dominant in the upper crust but brittle fracture is dominant in the lower part of the crust and the lithosphere beneath the crust. Therefore the fracture mechanism must be taken into account in the study of the rheological structure of the lithosphere. The empirical formula for the fracture strength is applied to study the rheological structure of the lithosphere in the Ordos block. Brittle regime in the rheological structure can be divided into two sub-regions, in one of which brittle fracture and in the other frictional sliding are dominant, respectively, unlike previous conventional studies in which frictional sliding is assumed to be the only factor; the magnitude of the rheological strength of the lithosphere calculated by the empirical formula is also lower than that obtained in previous conventional studies.     

THE LANDSCAPE ECOLOGICAL ，ASSESSMENT AND PLANNING IN THE CONTOL WATERSHED BY RESERVOIR OF ERLKONG MOUNTAIN

Based on the theories of landscape ecology,landscape eco-environment in the coutrol watershed by reser-voir of Erlong Mountain in Heilogjiang Province was analyzed and assessed by using GIS technique and statistical model of Principal Component Analysis and Spatial Cluster Analysis.It is found that 100.08km^2(36%) of the total area is in the state of kilter,85.73km^2(31%) of the total area is in the state of general,and 47.26km^2(17%) and 15.48km^2(16%) is in the relatively poor state and ideal state.According to landscape ecological structure,there are three land-scape function areas being planned and designed.1) Agricultural landscape function area:its developmental direction is tour agriculture and high-benefit agriculture.2)Eco-environment protected function area:the direction of development and utilization of this region is to develop vigorously forest for soil and water conservation ,and try to increase the rate of vegetation cover.3)Forest landscape function area:rational cut and utilization of forest resources,space optimization disposal of category of forest ,foster of forest and protection of wildwood will become the main development directions for this region.This study trys to provide scientific foundation for ecological restoration of the whole valley and its sustain-able development.     

Method of Separating Cosmic-Ray Positrons from Electrons in the DAMPE Experiment

A method of identifying positron/electron species from the cosmic rays was studied in the DArk Matter Particle Explorer(DAMPE)experiment.As there is no onboard ...     

Water conservancy projects in China: Achievements,challenges and way forward

China's water policies in the past decades have relied heavily on the construction of massive water conservancy projects in the form of dams and reservoirs, water transfer projects, and irrigation infrastructure. These facilities have brought tremendous economic and social benefits but also posed many adverse impacts on the eco-environment and society. With the intensification of water scarcity, China's future water conservancy development is facing tremendous challenge of supporting the continuous economic development while protecting the water resources and the dependent ecosystems. This paper provides an overview of China's water conservancy development, and illustrates the socioeconomic, environmental and ecological impacts. A narrative of attitude changes of the central government towards water conservancy, as well as key measures since the 1950s is presented. The strategic water resources management plan set by the central government in its Document No. 1 of 2011 is elaborated with focus on the three stringent controlling “redlines” concerning national water use, water use efficiency and water pollution and the huge investments poised to finance their implementation. We emphasize that realizing the goals set in the strategic plan requires paradigm shifts of the water conservancy development towards maximizing economic and natural capitals, prioritizing investment to preserve intact ecosystems and to restore degraded ecosystems, adapting climate change, balancing construction of new water projects and rejuvenation of existing projects, and managing both “blue” (surface/groundwater) and “green” water (soil water).     

Simulation of frozen ground distribution in northeast China based on a surface frost number model

Journal of Geographical Sciences - Against the background of global warming, environmental and ecological problems caused by frozen ground degradation have become a focus of attention for the...     

Source parameters of bohai earthquake, July 18, 1969 and yongshan earthquake, May 11, 1974 determined by synthetic seismograms of teleseismic P waves

The source parameters of the Bohai Sea earthquake, July 18, 1969 and Yongshan, Yunnan earthquake, May 11, 1974 were determined by full — wave theory synthetic seismograms of teleseismic P waves. P+pP+sP wereform were calculated with WKBJ approximation and real integral paths. One — dimensional unilateral, finite propagation source was also considered. By trail — and — error in comparing the theoretical seismograms with the observational ones of WWSSN stations, the source parameters were obtained as follow: for Bohai earthquake, φ=195°, δ=85°, λ=65°,M _o=0.9×10¹⁹Nm,L=59.9km.V _R=3.5km/s, ∧ _R =160°; for Yongshan earthquake, φ=240°, δ=80°, ∧=150°,M _o=1.3×10¹⁸Nm,L=48.8km,V _R=3km/s, ∧ _R =−10°, where φ is strike, δ dip angle, λ slip angle,M _o seismic moment,L rupture length,V _R rupture propagation speed. As III type fractures the faulting propagated along the fault planes, and ∧ _R is the angle from the strike to the propagation direction. Yongshan earthquake showed complexity in its focal process, having four sub—ruptures during the first 60 seconds. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 1–8, 1991.