短脉冲激光在实验室天体物理方面的研究进展     

孙嘉宁  袁大伟  王菲鹿 《天文研究与技术》2021,(2):248-254

随着啁啾脉冲放大技术(Chirped Pulse Amplification,CPA)的飞速发展,激光功率密度实现了飞跃式的提升,利用短脉冲激光开展实验室天体物理研究的条件日趋成熟。短脉冲激光与靶相互作用可以产生相对论粒子(正负电子、质子、中子等)和高能电磁辐射(X射线、γ射线),这些粒子和辐射的产生过程与天体中的某些物理现象相对应。介绍了利用短脉冲激光开展实验室天体物理的研究进展,重点介绍了核天体物理、空心离子光谱学、相对论无碰撞冲击波以及等离子体状态诊断等。  相似文献   

南海风暴潮对风场和外围海水敏感性研究     

李健  刘清容  阮成卿  訚忠辉  冀承振 《海洋科学》2018,42(2):99-107

为探索来自西北太平洋台风风暴潮与南海局地生成台风风暴潮不同,本研究在假设两种台风气象条件相同情况下,研究随台风而来外围海水所形成增水对南海沿岸的影响。以0814"黑格比"强台风风暴潮为基础,使用ROMS(regional ocean modeling system)模式进行数值模拟并通过设计对比试验方法进行研究,研究发现在台风登陆时引起的增水最大,最大增水出现在台风路径右侧,其中在沿岸区域,外围海水形成增水约占总增水10%,且大约3 h后出现增水回震现象。同时,设计对比试验,研究来自西北太平洋台风风暴潮对台风路径、台风强度、台风移动速度和流入角等气象条件敏感性,并获得与前人一致的结果。  相似文献   

Bibliometric Analysis of Global Research Progress on Coastal Flooding 1995–2016     

Chao Gao  Tian Ruan 《中国地理科学(英文版)》2018,28(6):998-1008

Global research progress on coastal flooding was studied using a bibliometric evaluation of publications listed in the Web of Science extended scientific citation index. There was substantial growth in coastal flooding research output, with increasing publications, a higher collaboration index, and more references during the 1995–2016 period. The USA has taken a dominant position in coastal flooding research, with the US Geological Survey leading the publications ranking. Research collaborations at institutional scales have become more important than those at global scales. International collaborative publications consistently drew more citations than those from a single country. Furthermore, coastal flooding research included combinations of multi-disciplinary categories, including ‘Geology' and ‘Environmental Sciences Ecology'. The most important coastal flooding research sites were wetlands and estuaries. While numerical modeling and 3 S(Remote sensing, RS; Geography information systems, GIS; Global positioning systems, GPS) technology were the most commonly used methods for studying coastal flooding, Lidar gained in popularity. The vulnerability and adaptation of coastal environments, their resilience after flooding, and ecosystem services function showed increases in interest.  相似文献   

Estimating the properties of weathered bedrock and pilerock interaction from the geological strength index     

Chun-mei Zhou  Wei Shao  Kun-long Yin  Zong-ji Yang 《山地科学学报》2018,15(8):1757-1776

The effect of variable rock mass properties on pile-rock interaction poses a great challenge to the design of stabilizing piles and numerical analysis of pile-rock interaction. The paper presents a novel method to estimate the properties of weathered bedrock, which can be applied to routine design of landslide-stabilizing piles for collivial landslides. The Ercengyan landslide located in the Three Gorges Reservoir, China, is the area of interest for this study. A geological investigation and triaxial tests were conducted to estimate the basic parameters, including Geological Strength Index(GSI), uniaxial compressive strength σ_(ci) and Hoek-Brown constant m_i of intact bedrock in the study area. Hoek-Brown criterion was used to estimate mechanical properties of the weathered rock, including elastic modulus E_m, cohesion c, friction angle Φ, and normal ultimate lateral resistance p_(max). A parametric study was performed to evaluate the effect of parameterizations of GSI, σ_(ci) and m_i on the bedrock properties and p-y curves. The estimated rock mass properties were used with PLAXIS 2D software to simulate pile-rock interaction. Effect of GSI on stress at the pile-rock interface and in the rock, pile bending moment, pile shear force, and p-y curve were analysed.  相似文献   

Secular dynamics of multiplanetary circumbinary systems: stationary solutions and binary-planet secular resonance     

Eduardo Andrade-Ines  Philippe Robutel 《Celestial Mechanics and Dynamical Astronomy》2018,130(1):6

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Hydrological management strategies for the control of algal blooms in regulated lowland rivers     

Jian Li  Wei Yin  Haiyan Jia  Xiaokang Xin 《水文研究》2021,35(6):e14171

Reservoirs of lowland floodplain rivers with eutrophic backgrounds cause variations in the hydrological and hydraulic conditions of estuaries and low-dam reservoir areas, which can promote planktonic algae to proliferate and algal bloom outbreaks. Understanding the ecological effects of variations in hydrological and hydraulic processes in lowland rivers is important for algal bloom control. In this study, the middle and lower reaches of the Han River, China, a typical regulated lowland river with a eutrophic background, are selected. Based on the effect of hydrological and hydraulic variability on algal blooms, a hydrological management strategy for river algal bloom control is proposed. The results showed that (a) differences in river morphology and background nutrient levels cause significant differences in the critical threshold flow velocities for algal bloom outbreaks between natural river and low-dam reservoir sections; there is no uniform threshold flow velocity for algal bloom control. (b) There are significant differences in the river hydrological/hydraulic conditions between years with and without algal blooms. The average river flow, water level and velocity in years with algal blooms are significantly lower than those in years without algal blooms. (c) For different river sections where algal blooms occur and to meet the threshold flow velocities, the joint operation of cascade reservoirs and diversion projects is an effective method to prevent and control algal blooms in regulated lowland rivers. This study is expected to deepen our understanding of the ecological significance of special hydrological processes and guide algal bloom management in regulated lowland rivers.  相似文献   

Analytical study of the swing-by maneuver in an elliptical system     

Alessandra F. S. Ferreira  Antônio F. B. A. Prado  Othon C. Winter  Denilson P. S. Santos 《Astrophysics and Space Science》2018,363(2):24

The objective of the present paper is to derive a set of analytical equations that describe a swing-by maneuver realized in a system of primaries that are in elliptical orbits. The goal is to calculate the variations of energy, velocity and angular momentum as a function of the usual basic parameters that describe the swing-by maneuver, as done before for the case of circular orbits. In elliptical orbits the velocity of the secondary body is no longer constant, as in the circular case, but it varies with the position of the secondary body in its orbit. As a consequence, the variations of energy, velocity and angular momentum become functions of the magnitude and the angle between the velocity vector of the secondary body and the line connecting the primaries. The “patched-conics” approach is used to obtain these equations. The configurations that result in maximum gains and losses of energy for the spacecraft are shown next, and a comparison between the results obtained using the analytical equations and numerical simulations are made to validate the method developed here.  相似文献   

Fine-resolution analysis of exoplanetary distributions by wavelets: hints of an overshooting iceline accumulation     

Roman V. Baluev  Vakhit S. Shaidulin 《Astrophysics and Space Science》2018,363(9):192

We investigate 1D exoplanetary distributions using a novel analysis algorithm based on the continuous wavelet transform. The analysis pipeline includes an estimation of the wavelet transform of the probability density function (p.d.f.) without pre-binning, use of optimized wavelets, a rigorous significance testing of the patterns revealed in the p.d.f., and an optimized minimum-noise reconstruction of the p.d.f. via matching pursuit iterations.In the distribution of orbital periods, \(P\), our analysis revealed a narrow subfamily of exoplanets within the broad family of “warm Jupiters”, or massive giants with \(P\gtrsim 300~\mbox{d}\), which are often deemed to be related with the iceline accumulation in a protoplanetary disk. We detected a p.d.f. pattern that represents an upturn followed by an overshooting peak spanning \(P\sim 300\mbox{--}600~\mbox{d}\), right beyond the “period valley”. It is separated from the other planets by p.d.f. concavities from both sides. It has at least 2-sigma significance.In the distribution of planet radii, \(R\), and using the California Kepler Survey sample properly cleaned, we confirm the hints of a bimodality with two peaks about \(R=1.3R_{\oplus }\) and \(R=2.4R_{ \oplus }\), and the “evaporation valley” between them. However, we obtain just a modest significance for this pattern, 2-sigma only at the best. Besides, our follow-up application of the Hartigan and Hartigan dip test for unimodality returns 3 per cent false alarm probability (merely 2.2-sigma significance), contrary to 0.14 per cent (or 3.2-sigma), as claimed by Fulton et al. (2017).  相似文献   

Understanding the Role of Mass-Unloading in a Filament Eruption     

J. M. Jenkins  D. M. Long  L. van Driel-Gesztelyi  J. Carlyle 《Solar physics》2018,293(1):7

We describe a partial filament eruption on 11 December 2011 that demonstrates that the inclusion of mass is an important next step for understanding solar eruptions. Observations from the Solar Terrestrial Relations Observatory-Behind (STEREO-B) and the Solar Dynamics Observatory (SDO) spacecraft were used to remove line-of-sight projection effects in filament motion and correlate the effect of plasma dynamics with the evolution of the filament height. Flux cancellation and nearby flux emergence are shown to have played a role in increasing the height of the filament prior to eruption. The two viewpoints allow the quantitative estimation of a large mass-unloading, the subsequent radial expansion, and the eruption of the filament to be investigated. A 1.8 to 4.1 lower-limit ratio between gravitational and magnetic-tension forces was found. We therefore conclude that following the loss-of-equilibrium of the flux-rope, the radial expansion of the flux-rope was restrained by the filamentary material until 70% of the mass had evacuated the structure through mass-unloading.  相似文献   

Influence of periodic orbits on the formation of giant planetary systems     

Anne-Sophie Libert  Sotiris Sotiriadis  Kyriaki I. Antoniadou 《Celestial Mechanics and Dynamical Astronomy》2018,130(2):19

The late-stage formation of giant planetary systems is rich in interesting dynamical mechanisms. Previous simulations of three giant planets initially on quasi-circular and quasi-coplanar orbits in the gas disc have shown that highly mutually inclined configurations can be formed, despite the strong eccentricity and inclination damping exerted by the disc. Much attention has been directed to inclination-type resonance, asking for large eccentricities to be acquired during the migration of the planets. Here we show that inclination excitation is also present at small to moderate eccentricities in two-planet systems that have previously experienced an ejection or a merging and are close to resonant commensurabilities at the end of the gas phase. We perform a dynamical analysis of these planetary systems, guided by the computation of planar families of periodic orbits and the bifurcation of families of spatial periodic orbits. We show that inclination excitation at small to moderate eccentricities can be produced by (temporary) capture in inclination-type resonance and the possible proximity of the non-coplanar systems to spatial periodic orbits contributes to maintaining their mutual inclination over long periods of time.  相似文献