Observations of Multiple Blobs in Homologous Solar Coronal Jets in Closed Loop     

Q. M. Zhang  H. S. Ji  Y. N. Su 《Solar physics》2016,291(3):859-876

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Emission Measure and Temperature Analysis of the Upper Coronal Source of a Solar Flare     

Z. Ning  D. Li  Q. M. Zhang 《Solar physics》2016,291(6):1783-1798

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Turnover Frequency in Solar Microwave Bursts with an Extremely Flat Optically Thin Spectrum     

Q. W. Song  H. Nakajima  G. L. Huang  B. L. Tan  Y. Huang  Z. Wu 《Solar physics》2016,291(12):3619-3635

Four microwave bursts have been selected from the Nobeyama Radio Polarimeter (NoRP) observations with an extremely flat spectrum in the optically thin part and a very hard spectral index between 0 and ?1 in the maximum phase of all bursts. It is found that the time evolution of the turnover frequency is inversely proportional to the time profiles of the radio flux in all bursts. Based on the nonthermal gyrosynchrotron theory of Ramaty (Astrophys. J. 158, 753, 1969), the local magnetic field strength and the electron spectral index are calculated uniquely from the observed radio spectral index and the turnover frequency. We found that the electron energy spectrum is very hard (spectral index 1?–?2), and the time variation of the magnetic field strength is also inversely proportional to the radio flux as a function of time in all bursts. Hence, the time evolution of the turnover frequency can be explained directly by its dependence on the local magnetic field strength. The high turnover frequency (several tens of GHz) is mainly caused by a strong magnetic field of up to several hundred gauss, and probably by the Razin effect under a high plasma density over \(10^{10}~\mbox{cm}^{-3}\) in the maximum phase of these bursts. Therefore, the extremely flat microwave spectrum can be well understood by the observed high turnover frequency and the calculated hard electron spectral index.  相似文献   

Symplectic adaptive algorithm for solving nonlinear two-point boundary value problems in Astrodynamics     

H. J. Peng  Q. Gao  Z. G. Wu  W. X. Zhong 《Celestial Mechanics and Dynamical Astronomy》2011,110(4):319-342

In this paper, from a Hamiltonian point of view, the nonlinear optimal control problems are transformed into nonlinear two-point boundary value problems, and a symplectic adaptive algorithm based on the dual variational principle is proposed for solving the nonlinear two-point boundary value problem. The state and the costate variables within a time interval are approximated by using the Lagrange polynomial and the costate variables at two ends of the time interval are taken as independent variables. Then, based on the dual variational principle, the nonlinear two-point boundary value problems are replaced by a system of nonlinear equations which can preserve the symplectic structure of the nonlinear optimal control problem. Furthermore, the computational efficiency of the proposed symplectic algorithm is improved by using the adaptive multi-level iteration idea. The performance of the proposed algorithm is tested by the problems of Astrodynamics, such as the optimal orbital rendezvous problem and the optimal orbit transfer between halo orbits.  相似文献   

The Landau level-superfluid modified factor and the overal soft X/<Emphasis Type="Italic">γ</Emphasis>-ray efficiency coefficient of a magnetar     

Z. F. Gao  Q. H. Peng  N. Wang  C. K. Chou  W. S. Huo 《Astrophysics and Space Science》2011,336(2):427-439

As soon as the energies of electrons near the Fermi surface exceed Q, the threshold energy of inverse β-decay, electron capture (EC) dominates inside a neutron star. The high-energy neutrons released by EC will destroy anisotropic ³ P ₂ neutron Cooper pairs in the degenerate superfluid. By colliding with the neutrons produced in the process n+(n↑n↓)→n+n+n, the kinetic energies of the neutrons released by EC will be transformed into thermal energy. A portion of this thermal energy will be transported from the star interior to the star surface by conduction, then converted to a thermal spectrum of soft X-rays and γ-rays. By introducing two important parameters: the Landau level-superfluid modified factor and the overal soft X/γ-ray efficiency coefficient, we compute the theoretical luminosity L _X of a magnetar under our model and plot a diagram of L _X as a function of magnetic field strength B. Numerical calculations based on our model agree well with the observed properties of magnetar candidates.  相似文献   

On Integrated Hard X-Ray Broken-Up Spectra of Solar Flares     

Y. P. Li  W. Q. Gan 《Solar physics》2011,269(1):59-66

The summation of two single power-law spectra with a rather big difference of the spectral indices and with comparable intensities looks like a broken-up spectrum. The spatially integrated hard X-rays contain contributions from different sources, like footpoint and looptop sources. Within the standard scenario of solar flares, the power-law index difference between the footpoints and looptop should be two. Taking the M7.6 flare on 24 October 2003 as an example, we showed that the hard X-ray spectrum itself for footpoints and looptop is a single power-law, but the spatially integrated spectrum presents a broken-up form. It is also shown that the time-integrated spectrum could present a broken-up form, although the spectrum in further refined intervals presents a single power-law. It is concluded that the integrated broken-up spectrum observed here is produced either by the summation of individual sources or by the temporal variation of a single source, not by the acceleration itself.  相似文献   

The evolution of the z distribution of normal neutron stars in the Galaxy     

Y.‐C. Wei  C.‐M. Zhang  Y.‐H. Zhao  Q.‐H. Peng  X.‐J. Wu  J. Wang  Y.‐Y. Pan  H.‐X. Yin  Y. Yan  T.‐S. Yan  H.‐J. Tian  A. Esamdin  A.L. Luo  Y. Cai  A. Taani 《Astronomische Nachrichten》2010,331(8):817-831

Under the two initial 1‐D one parameter velocity distribution forms (one is normal, the other is exponential), the z direction scale height evolution of normal neutron stars in the Galaxy is studied by numerical simulation. We do statistics for the cases at different time segments, also do statistics for the cumulative cases made of each time segment. The results show in the cumulative cases the evolution curves of the scale heights are smoother than in the each time segment, i.e., the cumulation improve the signal‐to‐noise ratio. Certainly the evolution cases are different at different Galactic disk locations, which also have very large difference from the average cases in the whole disk. In the initial stages of z evolution of normal neutron stars, after the beginning transient states, the cumulative scale heights increase linearly with time, and the cumulative scale height increasing rates have linear relationship with the initial velocity distribution parameters, which have larger fluctuation in the vicinity of the Sun than in the whole disk. We utilize the linear relationship of the cumulative scale height increasing rates vs. the initial velocity distribution parameters in the vicinity of the Sun to make comparison with the observation near the Sun. The results show if there is no magnetic decay, then the deserved initial velocity parameters are obvious lower than the present well known results from some authors; whereas if introducing magnetic decay, for the 1‐D normal case we can make consistence among concerning results using magnetic decay time values which are supported by some authors, while for the 1‐D exponential case the results show the lackness of young pulsar samples in the larger z in the vicinity of the Sun (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Elevated concentrations of formate, acetate and dissolved organic carbon found at the Lost City hydrothermal field   总被引：1，自引：0，他引：1  

Susan Q. Lang  David A. Butterfield  Deborah S. Kelley 《Geochimica et cosmochimica acta》2010,74(3):941-5748

Fluids from the ultramafic-hosted Lost City hydrothermal field were analyzed for total dissolved organic carbon and dissolved organic acids. Formate (36-158 μmol/kg) and acetate (1-35 μmol/kg) concentrations are higher than in other fluids from unsedimented hydrothermal vents, and are a higher ratio of the total dissolved organic carbon than has been found in most marine geothermal systems. Isotopic evidence is consistent with an abiotic formation mechanism for formate, perhaps during serpentinization processes in the sub-surface. Further support comes from previous studies where the abiological formation of low molecular weight organic acids has been shown to be thermodynamically favorable during hydrothermal alteration of olivine, and laboratory studies in which the reduction of carbon dioxide to formate has been confirmed. As the second most prevalent carbon species after methane, formate may be an important substrate to microbial communities in an environment where dissolved inorganic carbon is limited. Acetate is found in locations where sulfate reduction is believed to be important and is likely to be a microbial by-product, formed either directly by autotrophic metabolic activity or indirectly during the fermentative degradation of larger organic molecules. Given the common occurrence of exposed ultramafic rocks and active serpentinization within the worlds ocean basins, the abiotic formation of formate may be an important process supporting life in these high pH environments and may have critical implications to understanding the organic precursors from which life evolved.  相似文献   

Modeling Strain Rate Effect of Heterogeneous Materials Using SPH Method     

G. W. Ma  X. J. Wang  Q. M. Li 《Rock Mechanics and Rock Engineering》2010,43(6):763-776

The strain rate effect on the dynamic compressive failure of heterogeneous material based on the smoothed particle hydrodynamics (SPH) method is studied. The SPH method employs a rate-insensitive elasto-plastic damage model incorporated with a Weibull distribution law to reflect the mechanical behavior of heterogeneous rock-like materials. A series of simulations are performed for heterogeneous specimens by applying axial velocity conditions, which induce different strain-rate loadings to the specimen. A detailed failure process of the specimens in terms of microscopic crack-activities and the macro-mechanical response are discussed. Failure mechanisms between the low and high strain rate cases are compared. The result shows that the strain-rate effects on the rock strength are mainly caused by the changing internal pressure due to the inertial effects as well as the material heterogeneity. It also demonstrates that the inertial effect becomes significant only when the induced strain rate exceeds a threshold, below which, the dynamic strength enhancement can be explained due to the heterogeneities in the material. It also shows that the dynamic strength is affected more significantly for a relatively more heterogeneous specimen, which coincides with the experimental results showing that the poor quality specimen had a relatively larger increase in the dynamic strength.  相似文献   

Subtropical montane evergreen broad-leaved forests of Yunnan, China: diversity, succession dynamics, human influence     

Cindy Q. Tang 《Frontiers of Earth Science》2010,4(1):22-32

This paper integrates studies on the natural subtropical montane evergreen broad-leaved forests (EBLFs) and secondary succession of the forests and plantations in Yunnan, to provide a basis for evaluating the sustainability of the forests in the mountain ecosystems of Yunnan, China. The EBLFs include mid-montane moist, monsoon, and semi-humid categories. The monsoon EBLF yielded the highest indices of the Shannon-Wiener H, Equitability J, Simpson D and Fisher’s alpha, followed by the mid-montane moist EBLF, then by the semi-humid forest. Since human uses have varied widely, the plant communities ranged from pioneer deciduous broad-leaved and/or pioneer coniferous stands to late-successional evergreen broad-leaved stands. The secondary succession pathways were from pioneer deciduous stands of Alnus accompanied by stands of pioneer coniferous Pinus and Keteleeria, through broad-leaved and coniferous mixed stands, to late-successional evergreen broad-leaved forests of Cyclobalanopsis and Castanopsis. In Yunnan, the EBLF is commonly replaced by plantations of exotic fast-growing Eucalyptus to produce industrial wood, oil, pulp and fuel. The result has been reduced plant diversity, and great loss of soil nutrients by erosion and runoff, as compared to the EBLF. Seventy-six plant species in the area have been ranked as critically endangered, endangered, or vulnerable. Their condition is seen as largely attributable to habitat loss or degradation. A clear understanding of ecological features and succession pathways of the EBLF can lead to more effective conservation and management of these fragile forests and the mountain ecosystems.  相似文献