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411.
M. Fouka S. Ouichaoui 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
We have analysed a sample of 328 time-integrated GRB prompt emission spectra taken via the Konus instrument on board the US GGS-Wind spacecraft between 2002 and 2004 using a couple of two-components models, Cut-off Power Law (CPL) + Power Law (PL) and blackbody (BB) + PL. The spectra show clear deviation from the Band function. The PL term is interpreted as the low energy tail of a nonthermal emission mechanism. The distributions of corresponding index β give values β < −2/3 consistent with synchrotron and synchrotron self-Compton mechanisms. The distribution of low energy index α associated with the CPL term shows clear discordance with synchrotron models for 31.4% of the analysed GRBs with values exceeding that for the line of death, α = −2/3. Then, a set of nonthermal radiation mechanisms producing harder slopes, i.e., α > −2/3, are presented and discussed. For the remaining majority (68.6%) of GRBs with CPL index α < −2/3, we show that optically thin synchrotron produced by a power law electron distribution of type, N(γ) ∼ γ−p, γ1 < γ < γ2, for finite energy range (γ2 ≠ ∞) is a likely emission mechanism with α ∼−(p + 1)/2 in the frequency range ν1 ? ν ? ν2 (where ν2 = η2ν1 with η = γ2/γ1), such that for p > 1/3, one gets α < −2/3. We also show that corresponding spectra in terms of Fν and νFν functions are peaked around frequency ν2 instead of ν1, respectively for p < 1 and p < 3. Besides, thermal emission is examined taking a single Planck function for fitting the low energy range. It can be interpreted as an early emission from the GRB fireball photosphere with observed mean temperature, kT′ ∼ 16.8 keV. Furthermore, we have performed a statistical comparison between the CPL + PL and BB + PL models finding comparable χ2-values for an important fraction of GRBs, which makes it difficult to distinguish which model and specific radiation mechanism (possible thermal or nonthermal γ-ray emissions) are best suitable for describing the reported data. Therefore, additional information for those bursts, such as γ-ray polarization, would be highly desirable in future determinations of GRBs observational data. 相似文献
412.
非额定条件下变压器损耗测量研究 总被引:1,自引:0,他引:1
任仁良 《中国民航学院学报》1996,(6):44-50
讨论了利用单片机技术测量变压器损耗的基本方法.推导了在非额定电压下测量变压器空载损耗的数学模型及其软件结构.最后给出实践结果. 相似文献
413.
对搞好天津高校健康教育的初探 总被引:2,自引:0,他引:2
郝力行 《中国民航学院学报》1997,15(2):76-78
通过不同侧面说明在高校开展健康教育的意义,简要介绍了我市高校开展健康教育的现状,提出了促进我市高校开展健康教育的看法。 相似文献
414.
The Local Interstellar Cloud (LIC) surrounds the Solar System and sets the boundary conditions for the heliosphere. Using
both in situ and absorption line data towards ε CMa we are able to constrain both the ionization and the gas phase abundances of the LIC gas at the Solar Location. We find
that the abundances are consistent with all of the carbonaceous dust grains having been destroyed, and in fact with a supersolar
abundance of C. The constituents of silicate grains, Si, Mg, and Fe, appear to be sub-solar, indicating that silicate dust
is present in the LIC. N, O and S are close to the solar values. 相似文献
415.
贺东梅 《华北航天工业学院学报》2001,(1)
本文从电信网、广播电视网和因特网三种网络的不同特点入手,说明了三网合一的必要性和可行性,重点探讨了三网合一中关键的接入网技术。 相似文献
416.
The differences between the composition of Galactic cosmic rays and that of the interstellar medium are manifold, and they
contain a wealth of information about the varying processes that created them. These differences reveal much about the initial
mixing of freshly synthesized matter, the chemistry and differentiation of the interstellar medium, and the mechanisms and
environment of ion injection and acceleration. Here we briefly explore these processes and show how they combine to create
the peculiar, but potentially universal, composition of the cosmic rays and how measurements of the composition can provide
a unique measure of the mixing ratio of the fresh supernova ejecta and the old interstellar medium in this initial phase of
interstellar mixing.
In particular, we show that the major abundance differences between the cosmic rays and the average interstellar medium can
all result from cosmic ray ion injection by sputtering and scattering from fast refractory oxide grains in a mix of fresh
supernova ejecta and old interstellar material. Since the bulk of the Galactic supernovae occur in the cores of superbubbles,
the bulk of the cosmic rays are accelerated there out of such a mix. We show that the major abundance differences all imply
a mixing ratio of the total masses of fresh supernova ejecta and old interstellar material in such cores is roughly 1 to 4.
That means that the metallicity of ∼3 times solar, since the ejecta has a metallicity of ∼8 times that of the present interstellar
medium. 相似文献
417.
刘思俊 《西安航空技术高等专科学校学报》2005,23(4):17-18
正确地指导好高职高专在校生的专升本,是每位老师应尽的责任和义务。笔从近几年高职高专在校生专升本的实际出发,分析探讨了高职高专在校生专升本可能遇到的困难和问题,以及如何正确引导学生克服困难,找出解决这些问题的思路和方法。 相似文献
418.
J. S. Kaastra A. M. Bykov S. Schindler J. A. M. Bleeker S. Borgani A. Diaferio K. Dolag F. Durret J. Nevalainen T. Ohashi F. B. S. Paerels V. Petrosian Y. Rephaeli P. Richter J. Schaye N. Werner 《Space Science Reviews》2008,134(1-4):1-6
We present the work of an international team at the International Space Science Institute (ISSI) in Bern that worked together
to review the current observational and theoretical status of the non-virialised X-ray emission components in clusters of
galaxies. The subject is important for the study of large-scale hierarchical structure formation and to shed light on the
“missing baryon” problem. The topics of the team work include thermal emission and absorption from the warm-hot intergalactic
medium, non-thermal X-ray emission in clusters of galaxies, physical processes and chemical enrichment of this medium and
clusters of galaxies, and the relationship between all these processes. One of the main goals of the team is to write and
discuss a series of review papers on this subject. These reviews are intended as introductory text and reference for scientists
wishing to work actively in this field. The team consists of sixteen experts in observations, theory and numerical simulations. 相似文献
419.
Yanxia Zhang Yongheng Zhao Dan Gao 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(12):1949-1954
With the availability of multi-wavelength, multi-scale and multi-epoch astronomical catalogues, the number of features to describe astronomical objects has increases. The better features we select to classify objects, the higher the classification accuracy is. In this paper, we have used data sets of stars and quasars from near-infrared band and radio band. Then best-first search method was applied to select features. For the data with selected features, the algorithm of decision table was implemented. The classification accuracy is more than 95.9%. As a result, the feature selection method improves the effectiveness and efficiency of the classification method. Moreover the result shows that decision table is robust and effective for discrimination of celestial objects and used for preselecting quasar candidates for large survey projects. 相似文献
420.
当前万维网服务发现机制并没有考虑消费者对服务质量的需求,消费者需要花很多时间来选择满足自己服务质量的服务.采取了一个QoS (Quality of Service)过滤器,采用服务质量属性量化方法和一个服务质量匹配算法来选取符合消费者服务质量要求的服务,并把服务存储在本地缓存中.这种方法考虑到消费者对服务质量的要求,减少访问远程发现服务器的次数,加快了服务发现速度.通过对本地服务添加标注和关键字来支持消费者服务的个性化. 相似文献