GAME-TIBET青藏高原云和降水综合观测概况及初步结果   总被引：13，自引：7，他引：6  

刘黎平  楚荣忠  宋新民  周筠君  冯锦明  陈成品  张彤  S.Shimizu  K.Ueno  T.Koike  H.Fujii  H.Yamada  Y.Aoi  T.Ueno  J.Horikomi  M.Kajikawa  R Shirooka  J.Teshima 《高原气象》1999,18(3):441-450

对中日合作青藏高原能量水分循环试验项目中云和降水的多普勒雷达观测使用的气象观测仪器和获取的资料等情况进行了总结,并给出了那曲地区水的日变化,不同 雨量计测量降水的对比分析,风速对测量降水影响,多普勒雷达资料的个例分析及云的数值模拟的等初步结果。  相似文献   

On the X-ray image of the Crab nebula: comparison with Chandra observations     

Shinpei Shibata  Haruhiko Tomatsuri  Makiko Shimanuki  Kazuyuki Saito  Koji Mori 《Monthly notices of the Royal Astronomical Society》2003,346(3):841-845

An axisymmetric model for the Crab nebula is constructed to examine the flow dynamics in the nebula. The model is based on that of Kennel & Coroniti, although we assume that the kinetic-energy-dominant wind is confined to an equatorial region. The evolution of the distribution function of the electron–positron plasma flowing out in the nebula is calculated. Given viewing angles, we reproduce an image of the nebula and compare it with the Chandra observation.
The reproduced image is not ring-like, but is rather 'lip-shaped'. It is found that the assumption of a toroidal field does not reproduce the Chandra image. We must assume that there is a disordered magnetic field with an amplitude as large as the mean toroidal field. In addition, the brightness contrast between the front and back sides of the ring cannot be reproduced if we assume that the magnetization parameter σ is as small as ∼10⁻³. The brightness profile along the semimajor axis of the torus is also examined. The non-dissipative, ideal-magnetohydrodynamic approximation in the nebula appears to break down.
We speculate that if the magnetic energy is released by some process that produces a turbulent field in the nebula flow and causes heating and acceleration – for example, by magnetic reconnection – then the present difficulties may be resolved (i.e. we can reproduce a ring image and a higher brightness contrast). Thus, the magnetization parameter σ can be larger than previously expected.  相似文献   

On the Formation of Massive Primordial Stars     

Kazuyuki Omukai  Francesco Palla 《Astrophysics and Space Science》2002,281(1-2):71-74

We investigate the formation by accretion of massive primordial protostars in the range 10 to 300 M _⊙. The high accretion rate used in the models (M _⊙ = 4.4 x 10^-3 M_⊙ yr^-1) causes the structure and evolution to differ significantly from those of both present-day protostars and primordial zero-age main sequence stars. The stellar surface is not visible throughout most of the main accretion phase, since a photosphere is formed in the in falling envelope. Significant nuclear burning does not take place until a protostellar mass of about 80 M _⊙. As the interior luminosity approaches the Eddington luminosity, the protostellar radius rapidly expands owing to the radiation pressure. Eventually, a final swelling occurs when the stellar mass reaches about 300 M _⊙. This expansion is likely to signal the end of the main accretion phase, thus setting an upper limit to the protostellar mass formed in these conditions. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

Sun-perturbed earth-to-moon transfers with low energy and moderate flight time   总被引：1，自引：1，他引：0  

Kazuyuki Yagasaki 《Celestial Mechanics and Dynamical Astronomy》2004,90(3-4):197-212

We construct a spacecraft transfer with low cost and moderate flight time from the Earth to the Moon. The motion of the spacecraft is modeled by the planar circular restricted three-body problem including a perturbation due to the solar gravitation. Our approach is to reduce computation of optimal transfers to a non-linear boundary value problem. Using a computer software called AUTO, we solve it and continue its solutions numerically to obtain the optimal transfers. Our result also shows that the use of the solar gravitation can further lower the transfer cost drastically.  相似文献   

Families of symmetric relative periodic orbits originating from the circular Euler solution in the isosceles three-body problem     

Mitsuru Shibayama  Kazuyuki Yagasaki 《Celestial Mechanics and Dynamical Astronomy》2011,110(1):53-70

We study symmetric relative periodic orbits in the isosceles three-body problem using theoretical and numerical approaches. We first prove that another family of symmetric relative periodic orbits is born from the circular Euler solution besides the elliptic Euler solutions. Previous studies also showed that there exist infinitely many families of symmetric relative periodic orbits which are born from heteroclinic connections between triple collisions as well as planar periodic orbits with binary collisions. We carry out numerical continuation analyses of symmetric relative periodic orbits, and observe abundant families of symmetric relative periodic orbits bifurcating from the two families born from the circular Euler solution. As the angular momentum tends to zero, many of the numerically observed families converge to heteroclinic connections between triple collisions or planar periodic orbits with binary collisions described in the previous results, while some of them converge to “previously unknown” periodic orbits in the planar problem.  相似文献   

Dust coagulation in star formation with different metallicities     

Hiroyuki Hirashita  Kazuyuki Omukai 《Monthly notices of the Royal Astronomical Society》2009,399(4):1795-1801

Dust grains coagulate into larger aggregates in dense gas. This changes their size distribution and possibly affects the thermal evolution of star-forming clouds. We here investigate dust coagulation in collapsing pre-stellar cores with different metallicities by considering the thermal motions of grains. We show that coagulation does occur even at low metallicity  ∼10⁻⁶ Z_⊙  . However, we also find (i) that the H₂ formation rate on dust grains is reduced only after the majority of H₂ is formed and (ii) that the dust opacity is modified only after the core becomes optically thick. Therefore, we conclude that the effects of dust coagulation can safely be neglected in discussing the temperature evolution of the pre-stellar cores for any metallicity as long as the grain motions are thermal.  相似文献   

Empirical formula to relate the auroral electrojet intensity with interplanetary parameters     

Takashi Murayama  Takao Aoki  Hitoshi Nakai  Kazuyuki Hakamada 《Planetary and Space Science》1980,28(8):803-813

An empirical formula has been constructed using the results of correlative analyses to determine in what form the AL index, as a measure of the intensity of the westward auroral electrojet, depends on interplanetary parameters. The formula thus obtained shows that AL is mainly determined by B_sV² where B_s is the southward component of the IMF and V is the solar wind velocity, and is modulated in a characteristic way by the combined effect of the east-west component of the IMF and the tilt angle of the Earth's dipole axis toward the Sun-Earth line. In contrast, effects of the solar wind density and the IMF variability were found to be insignificant.Implications of the empirical formula are discussed mainly in relation to the problem of the location in the dayside magnetosphere of the region where the reconnection process to initiate the substorm takes place.  相似文献   

Formation of Population III stars in fossil H ii regions: significance of HD     

Takanori Nagakura  Kazuyuki Omukai 《Monthly notices of the Royal Astronomical Society》2005,364(4):1378-1386

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A simple method to compute spherical harmonic coefficients for the potential model of the coronal magnetic field     

Kazuyuki Hakamada 《Solar physics》1995,159(1):89-96

It is impossible to make a direct measurement of the coronal magnetic field from the ground. The coronal magnetic field is, then, usually inferred by extrapolation of the observed photospheric magnetic field. The so-called potential model has been used for this extrapolation. We have to solve the Laplacian equation of the magnetic scalar potential. This magnetic scalar potential can be expanded into a spherical harmonic series. In this paper, new simple recursion formulae are proposed to solve the Laplacian equation; that is, to determine the spherical harmonic coefficients.  相似文献   

Estimation of spectral refractive index of colloidal sulfur at 20°C     

Tsuyoshi Samukawa  Masamitsu Onitsuka  Kazuyuki Ohta  Mamoru Tominaga  Hidenori Yoshiyama 《Journal of Oceanography》1992,48(2):129-138

In the marine environment, colloidal sulfurs often occur due to the redox reaction of sulfide ions and oxygen molecules. It is important to know the spectral refractive index of colloidal sulfurs for the discussion of the light scattering in the region where colloidal sulfurs are formed. We presented new methods to estimate the refractive index from the wave length of maximum absorbance (turbidity) of a nearly mono-dispersed colloidal solution. In these methods, the ripples in a first main maximum of the scattering efficiency,Q _sca , were taken into consideration. By virtue of these methods, we obtained the spectral refractive index of colloidal sulfurs,m _s (), at 20°C. The Cauchy's expression of it was given by

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