How useful is the 'mean stream' in discussing meteoroid stream evolution?     

I. P. Williams  D. C. Jones 《Monthly notices of the Royal Astronomical Society》2007,375(2):595-603

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SOFTWARE REVIEWS     

《The Professional geographer》1988,40(1):106-116

software reviews are in this article BMDP/PC CONCEPTS COMPUTERIZED ATLAS EVALUATION OF ALTERNATE PROPOSALS (EAP) EXTRA: EXPRESS TRANSIT ANALYSIS MATC CAD MOTORS TRANSPORTATION PACKAGE PCMAP: Thematic Mapping Software for the IBM Personal Computer, Version 2.3 PLACE TRANPLAN . US-ATLAS  相似文献   

Three-dimensional numerical simulation of a nonstationary gravitating <Emphasis Type="Italic">N</Emphasis>-body system with gas     

V. N. Snytnikov  V. A. Vshivkov  E. A. Kuksheva  E. V. Neupokoev  S. A. Nikitin  A. V. Snytnikov 《Astronomy Letters》2004,30(2):124-137

We developed a three-dimensional numerical model to investigate nonstationary processes in gravitating N-body systems with gas. We used efficient algorithms for solving the Vlasov and Poisson equations that included the evolutionary processes under consideration, which ensures rapid convergence at high accuracy. We give examples of the numerical solution of the problem on the growth of physical instability in the model of a flat rotating disk with a gaseous component and its three-dimensional dynamics under various initial conditions including a nonzero velocity dispersion along the rotation axis.  相似文献   

SRG剖分编码与地理坐标的转换算法研究     

张玉梅  聂洪山  谢启友  孙兆林  徐欣 《地理与地理信息科学》2012,28(2):40-43

提出一种基于SRG剖分方法的剖分编码与经纬度坐标之间的转换算法,不涉及任何投影变换,计算过程只需加、减、乘、除简单算术运算,计算速度快,且SRG剖分编码本身就具有固定的方向性,利于邻近搜索。算法中采用坐标系辅助区分一些难以区分的菱形块,降低了转化误码率,进而提高了转换的精度。  相似文献   

二维能量平衡模式中大气温度对二氧化碳增温效应的响应     

巢纪平  李耀锟 《气象学报》2010,68(2):147-152

利用一个考虑了辐射能传输的二维能量平衡气候模式,解析地分析了二氧化碳浓度改变后冰界纬度的变化,得到了冰界纬度随CO2浓度变化的关系以及全球平均温度的变化曲线.结果表明,当CO2浓度由工业革命前的280×10-6增加到700×10-6时,冰界仅后退(北半球向北)几个纬度;当CO2的浓度继续增加时,冰界纬度会加速向极地退缩,直至出现全球无极冰覆盖的现象.同样地,当CO2浓度由280×10-6增加到700×10-6时,全球地表平均温度虽然在增加,但增加的速率很小,并且增加的速率在减小,而当大于700×10-6之后,温度增加的速率会快速增大,温度将加速上升.对不同反照率进行敏感性试验,发现当反照率从0.1到0.32时,结果并没有显著地改变,即结果对反照率的变化并不敏感.这一计算结果表明,在目前的状态下,由CO2引起的增温作用似乎处于变化很小的准饱和状态,即目前气候不会因为CO2浓度的增加而迅速变暖.较为实际的情形可能是大气温度在缓慢增加到一定程度后才会迅速升高.这并不意味着可以忽视CO2的增温效应,因为根据计算结果,这个临界值大概在700×10-6左右,当CO2浓度增加到超过临界值之后,气温会剧烈上升,气候将会处在一个非常温暖的阶段.  相似文献   

北太平洋的年代际振荡与全球变暖   总被引：3，自引：2，他引：1  

刘秦玉  李春  胡瑞金 《气候与环境研究》2010,15(2):217-224

通过回顾和总结前人工作,特别是有关北太平洋年代际振荡的研究,针对近50年来北太平洋中纬度海温变冷的现象进行了分析与讨论。从全球气候变化的角度,总结了影响北太平洋中纬度海温变冷现象的几种可能机制,推测了全球气温变暖可能会对北太平洋的直接或间接影响,归纳指出了研究该问题的复杂性与目前面临的困难。  相似文献   

Galactic Sun's motion in the cold dark matter,MOdified Newtonian Dynamics and modified gravity scenarios     

L. Iorio 《Astronomische Nachrichten》2009,330(8):857-862

We numerically integrate the equations of motion of the Sun in Galactocentric Cartesian rectangular coordinates for –4.5 Gyr ≤ t ≤ 0 in Newtonian mechanics with two different models for the Cold Dark Matter (CDM) halo, in MOdified Newtonian Dynamics (MOND) and in MOdified Gravity (MOG) without resorting to CDM. The initial conditions used come from the latest kinematical determination of the 3D Sun's motion in the Milky Way (MW) by assuming for the rotation speed of the Local Standard of Rest (LSR) the recent value Θ₀ = 268 km s^–1 and the IAU recommended value Θ₀ = 220 km s^–1; the Sun is assumed located at 8.5 kpc from the Galactic Center (GC). For Θ₀ = 268 km s^–1 the birth of the Sun, 4.5 Gyr ago, would have occurred at large Galactocentric distances (12–27 kpc depending on the model used), while for Θ₀ = 220 km s^–1 it would have occurred at about 8.8–9.3 kpc for almost all the models used. The integrated trajectories are far from being circular, especially for Θ₀ = 268 km s^–1, and differ each other with the CDM models yielding the widest spatial extensions for the Sun's orbital path (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Two-component galaxies with flat rotation curve     

Luca Ciotti  Lucia Morganti †  P. T. de Zeeuw 《Monthly notices of the Royal Astronomical Society》2009,393(2):491-500

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On the habitability of the OGLE-2006-BLG-109L planetary system     

Cezary Migaszewski  Krzysztof Go&#;dziewski  Tobias C. Hinse 《Monthly notices of the Royal Astronomical Society》2009,395(3):1204-1212

We investigate the dynamics of putative Earth-mass planets in the habitable zone (HZ) of the extrasolar planetary system OGLE-2006-BLG-109L, a close analogue of the Solar system. Our work is inspired by the work of Malhotra & Minton. Using the linear Laplace–Lagrange theory, they identified a strong secular resonance that may excite large eccentricity of orbits in the HZ. However, due to uncertain or unconstrained orbital parameters, the subsystem of Jupiters may be found in a dynamically active region of the phase space spanned by low-order mean-motion resonances. To generalize this secular model, we construct a semi-analytical averaging method in terms of the restricted problem. The secular orbits of large planets are approximated by numerically averaged osculating elements. They are used to calculate the mean orbits of terrestrial planets by means of a high-order analytic secular theory developed in our previous works. We found regions in the parameter space of the problem in which stable, quasi-circular orbits in the HZ are permitted. The excitation of eccentricity in the HZ strongly depends on the apsidal angle of jovian orbits. For some combinations of that angle, eccentricities and semimajor axes consistent with the observations, a terrestrial planet may survive in low eccentric orbits. We also study the effect of post-Newtonian gravity correction on the innermost secular resonance.  相似文献   

The Data Depth-weight-kernel Estimation of the Model Error of Satellite Orbit Determination     

Xiao-Gang Pan  Hai-Yin Zhou 《Chinese Astronomy and Astrophysics》2009,33(3):293-304

It is an objective fact that there exists error in the satellite dynamic model and it will be transferred to satellite orbit determination algorithm, forming a part of the connotative model error. Mixed with the systematic error and random error of the measurements, they form the unitive model error and badly restrict the precision of the orbit determination. We deduce in detail the equations of orbit improvement for a system with dynamic model error, construct the parametric model for the explicit part of the model and nonparametric model for the error that can not be explicitly described. We also construct the partially linear orbit determination model, estimate and fit the model error using a two-stage estimation and a kernel function estimation, and finally make the corresponding compensation in the orbit determination. Beginning from the data depth theory, a data depth weight kernel estimator for model error is proposed for the sake of promoting the steadiness of model error estimation. Simulation experiments of SBSS are performed. The results show clearly that the model error is one of the most important effects that will influence the precision of the orbit determination. The kernel function method can effectively estimate the model error, with the window width as a major restrict parameter. A data depth-weight-kernel estimation, however, can improve largely the robustness of the kernel function and therefore improve the precision of orbit determination.  相似文献