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通过结构函数可以测量湍流的能量级联速率.在实际观测中,无法测量分子云中气体的3维速度,这使得其湍流结构函数难以测量.对垂直于视线方向的薄分子云的情形,结构函数Stt2可以通过云核速度弥散(core velocity dispersion,CVD)进行测量,CVD2=1/2Stt2.对此进行推广,对于不垂直于视线方向的薄分子云,CVD2=1/2Stt2(1-1/8cos2θ)R2/3,其中,θ是视线方向与投影方向的夹角,平均投影距离与3维距离之比R可以用第2类椭圆积分E(k,φ)表示为R=2/πE(cosθ,π/2). 相似文献
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2.扁平地球解:假设扁平地球单侧面积为A。太阳与扁平地球中心轴的夹角为θ,θ的初始值为0°。由于太阳光是平行光,所以在地球上任意给定点。 相似文献
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《中国科学院上海天文台年刊》2015,(0)
利用高精度大样本Λ冷暗物质(Λcold dark matter,ΛCDM)宇宙学数值模拟的结果,对暗物质主晕与其子晕的自旋方向相关性进行了研究。本文用两者自旋方向夹角的余弦值〈 cosθ〉作为指标,观察〈 cosθ〉随两者之间距离以及红移的变化。若暗物质晕的自旋方向在空间随机分布,则按统计理论可得〈 cosθ〉应为0;若〈 cosθ〉大于0,则表示暗晕之间自旋方向正相关;若〈 cosθ〉小于0,则表示暗晕之间自旋方向反相关。主要得到三个结果:第一,子晕自旋方向在空间的分布非随机,越靠近主晕内部,〈 cosθ〉越大且为正值,与主晕的自旋方向相关性越强烈。当子晕与主晕质量相当时,在主晕的百分之一个维里半径(virial radius)距离处,耦合信号非常强烈,〈 cosθ〉高达约0.8;而在主晕的维里半径距离处,相关性几乎不存在。第二,子晕与主晕的质量比越大,相关性越强烈。当子晕与主晕质量比相同时,对于不同质量主晕,如10~(11±0.5)h~(-1)M,10~(12±0.5)h~(-1)M,10~(13±0.5)h~(-1)M,10~(14±0.5)h~(-1)M(其中M为太阳质量,h为无量纲哈勃常数),相关性曲线几乎重合。第三,该相关性不依赖于红移。但高红移处仍需更高精度模拟进一步验证。这是首次对暗物质主晕与其子晕自旋方向相关性进行的系统性研究,且相关强度较类似物理量的相关更强。末尾简要讨论了产生该相关性的可能原因和可深入进行的后续研究。 相似文献
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本文根据矢量引力子场度规场理论,讨论了旋转带电天体外引力场的某些性质,得出如下结果:1.黑洞不可能具有角动量和电荷,即转动的天体(无论带电与否)不可能是黑洞。Kerr黑洞及Kerr-Newman黑洞是不存在的。2.对于一个旋转的带电的轴对称天体而言,存在着一个与θ有关的“临界径向(坐标)距离”r_k(θ),当r>r_k(θ)时,天体的引力场表现为通常的吸引作用;而当R(天体半径)相似文献
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用单油垫的油膜刚度值来表示柱面和球面轴颈两种极轴静压支承系统三个方向的刚度。由此确立了支承系统的刚度与油垫中心夹角θ、地理纬度φ之间的定量关系,得到了各种φ值下的最佳θ值。为大型天文光学望远镜赤道装置极轴静压支承系统的设计提供了一些初步的理论根据。 相似文献
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用直接数值积分方法通过模拟不同的行星构型探讨了HD82943行星系统(由两颗共振的巨行星组成)的长期动力演化,同时,还研究了在相空间的轨道运动.在对系统长达107年数值积分中,发现所有的稳定轨道均与2:1共振相关联.典型地,在相同的时标内,两个共振幅角θ1和θ2同时(或其中之一)存在秤动.由于共振幅角在一定范围内的秤动,因而使两颗行星轨道半长径被约束而表现为规则运动模式.另外,利用分析模型(包含了外行星偏心率e2的因素),还讨论了对于不同取值的e2和相对近星点经度θ时,内行星在相空间的运动,并发现2:1轨道共振对于相对较小的e2以及当θ=0°时易于保持.此外,适中的e2将导致系统的两颗行星进入深度共振状态.再者,分析模型和数值计算的结果吻合得很好,两者都揭示了行星系统的2:1共振结构. 相似文献
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Solar System Research - Finding and studying possible collisions of asteroids approaching the Earth requires a significant amount of computation. This paper describes the R0 program created to... 相似文献
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In the text-books of astronomy, sections generally related to the Moon deal with the orbital elements of the Earth-Moon system such asa, e, i, ,
and the time of perigee passage. While the MEAN of the first of the three elements do not vary, mean longitude of the ascending node-mean longitude of the lunar perigee and the time of perigee passage undergoes secular as well as periodic changes due predominantly to the action of the Sun's gravitational attraction. While to a certain degree, explanations related to the calculation of the lunar orbit parameters are given, not a single graphical representation of these short- or long-periodic changes are presented. We allow the number of data related to these periodic changes must cover a large span of time; and if regression of the line of nodes or advances of the line of apses are to be graphically seen, data covering 18.61 and 8.85 yr, respectively, are needed. In this work we particularly aim at the graphical representation of the periodic changes of the line of nodes. 相似文献
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Many asteroids with a semimajor axis close to that of Mars have been discovered in the last several years. Potentially some of these could be in 1:1 resonance with Mars, much as are the classic Trojan asteroids with Jupiter, and its lesser-known horseshoe companions with Earth. In the 1990s, two Trojan companions of Mars, 5261 Eureka and 1998 VF31, were discovered, librating about the L5 Lagrange point, 60° behind Mars in its orbit. Although several other potential Mars Trojans have been identified, our orbital calculations show only one other known asteroid, 1999 UJ7, to be a Trojan, associated with the L4 Lagrange point, 60° ahead of Mars in its orbit. We further find that asteroid 36017 (1999 ND43) is a horseshoe librator, alternating with periods of Trojan motion. This asteroid makes repeated close approaches to Earth and has a chaotic orbit whose behavior can be confidently predicted for less than 3000 years. We identify two objects, 2001 HW15 and 2000 TG2, within the resonant region capable of undergoing what we designate “circulation transition”, in which objects can pass between circulation outside the orbit of Mars and circulation inside it, or vice versa. The eccentricity of the orbit of Mars appears to play an important role in circulation transition and in horseshoe motion. Based on the orbits and on spectroscopic data, the Trojan asteroids of Mars may be primordial bodies, while some co-orbital bodies may be in a temporary state of motion. 相似文献
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P. Maltby 《Solar physics》1972,26(1):76-82
Observations of the penumbral intensity of sunspots in 13 wavelength regions are presented. In 4 wavelength regions 54 sunspots are measured. In the other wavelength regions the number of sunspots considered ranges from 3–19.The penumbral intensity alters with position within the spot. This intensity variation is found to be comparable with the change in intensity from one spot to another. The penumbral intensity is found to be independent of spot size in the sample considered.The penumbra model of Kjeldseth Moe and Maltby (1969) with = 0.055 is supported by the measurements. 相似文献
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Magnetars are the neutron stars with the highest magnetic fields up to 1015–1016 G. It has been proposed that they are also responsible for a variety of extra-galactic phenomena, ranging from giant flares in nearby galaxies to fast radio bursts. Utilizing a relativistic mean field model and a variable magnetic field configuration, we investigate the effects of strong magnetic fields on the equation of state and anisotropy of pressure of magnetars. It is found that the mass and radius of low-mass magnetars are weakly enhanced under the action of the strong magnetic field, and the anisotropy of pressure can be ignored. Unlike other previous investigations, the magnetic field is unable to violate the mass limit of the neutron stars. 相似文献