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891.
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Giuseppe Pucacco 《Celestial Mechanics and Dynamical Astronomy》2004,90(1-2):109-123
We study strongly and weakly integrable 2-dimensional Hamiltonian systems with velocity dependent potentials. We determine
the set of conditions which must be satisfied in order to allow the existence of an independent second invariant polynomial
in the momenta. We then investigate the linear case for which a complete solution of the problem can be obtained. We recover
the classical set of linear strongly integrable systems and provide several new examples of weakly integrable systems whose
equations of motion can be explicitly solved at a fixed value of the energy. 相似文献
895.
896.
We analyze the possibility of observational identification of white dwarfs in the state of an ejector. Among the distinctive features of this class of objects are a high rate of rotational energy loss comparable to or higher than the observed luminosity of the object and nonthermal gamma-ray and/or radio spectra. The manifestations of the white dwarf in the close binary system AE Aquarii closely match these criteria. We show that most of the peculiar manifestations of this object in the hard spectral range and the observed pattern of mass transfer in the system can be explained in terms of a model in which the state of the white dwarf is classified as an ejector. 相似文献
897.
V. P. Grinin O. Yu. Barsunova S. G. Sergeev N. Ya. Sotnikova T. V. Demidova 《Astronomy Letters》2006,32(12):827-831
We present our photometric observations of the T Tauri star H 187. They confirm our conclusion that a new extended eclipse has begun in this young object. By the end of 2005, H 187 reached its minimum light following which its brightness began to slowly increase. Comparison with the previous ~3.5-yr-long eclipse observed by Cohen et al. shows that the new eclipse follows the previous eclipse fairly closely and, hence, it was caused by a second passage of the same extended dust or gas-dust cloud around the object. We have estimated the period between these events to be 4.7 yr. The object reddened during the eclipse, suggesting that the extinction was produced by small grains ~0.1μm in size. Possible mechanisms of such unusual eclipses are discussed. We draw an analogy between these eclipses and the cycles of photometric activity observed in UX Ori stars. Light curves similar to those observed for H 187 are shown to be obtained in the model of a young binary system with a low-mass companion accreting matter from the remnants of a protostellar cloud at a rate of ~10?9 M ⊙ yr?1. 相似文献
898.
C. Polymilis G. Rowlands A. N. Yannacopoulos 《Celestial Mechanics and Dynamical Astronomy》1997,68(4):273-281
A simple method for the determination of the position of singularities in the complex time domain for dynamical systems which
are described by ordinary differential equations is presented. The method is designed for integrable separable systems whose
solutions are not expressible in closed form. A direct consequence of this method is that it ‘closes’ the phase space. Simple
physical meaning is given to the singularity position.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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For analytical, inventory, and a variety of other basic types of geological data the main functions of an information management
system can adequately be accommodated by simple systems in which comprehensiveness is compromised in favor of practicality
and ease of implementation. Albeit possessing some shortcomings, such a strategy is likely to prove profitable particularly
to geologists in developing nations who are confronted with the task of self-developing much needed geological data systems
in the face of limited electronic data processing resources. Based on the experience of the Geological Survey of Israel, several
considerations and practical guidelines for the design and implementation of such systems can be outlined. Data bases should
be limited in their scope to specific subjects or projects, be designed to serve existing and only the more realistic foreseeable
needs, and include provisions for merger and intelligent communication with related files. Such data bases typically contain
logically simple-structured information and are small in size. Revision, deletion, and update transactions are infrequent;
the search criteria for retrieval are for the most part predictable and a fast response time is not essential. These attributes
prescribe a preference for simple fixed- or semi-free-format sequential files which, in turn, simplify appreciably the programming
of the supporting software. Input forms should be meticulously planned with due consideration given to aspects of software
compatibility, user convenience and acceptance, and efficiency in data gathering. The use of standard forms should be integrated
into the institution's routine to facilitate direct data entry by each contributor, thereby improving and economizing the
data collection process, and to secure data capture at its acquisition level (field, laboratory). The user's more immediate
retrieval needs are adequately satisfied by a master list, documenting the entire data base and a number of external inverted
index directories cross-referencing the master list according to the attributes by which the file is most likely to be searched.
Further development of output capabilities should be directed to provide for flexible retrieval by multikey query functions
and base map posting. For data files storing raw chemical analyses of rocks and water samples, the incorporation of processing
capabilities to compute interpretative geochemical parameters as an integral part of the system's output is particularly useful.
Paper presented at the 25th International Geological Congress, Section 16A, Sydney, Australia, August 1976. 相似文献