Earth rotation in the hipparcos reference frame     

J. Vondrak  C. Ron  I. Pešek 《Celestial Mechanics and Dynamical Astronomy》1996,66(1):115-122

New determination of the Earth orientation parameters (EOP), based on optical astrometry observations since the beginning of the century, is now under preparation by the Working group established by Commission 19 of the IAU. The Hipparcos catalog is to define the celestial reference frame in which the new series of EOP are to be described, The novelties of the prepared solution are the higher resolution (5 days) and more parameters estimated from the solution (celestial pole offsets, rheological parameters of the Earth, certain instrumental constants). The mathematical model of the solution is described, and the results based on the observations made with 46 instruments at 29 observatories and a preliminary Hipparcos catalog are presented.  相似文献   

Biaxial test simulations using a packing of polygonal particles   总被引：1，自引：0，他引：1  

A. A. Peña  A. Lizcano  F. Alonso‐Marroquin  H. J. Herrmann 《国际地质力学数值与分析法杂志》2008,32(2):143-160

The mechanical response of cohesionless granular materials under monotonic loading is studied by performing molecular dynamic simulations. The diversity of shapes of soil grains is modelled by using randomly generated convex polygons as granular particles. Results of the biaxial test obtained for dense and loose media show that samples achieve the same void ratio at large strains independent of their initial density state. This limit state resembles the so‐called critical state of soil mechanics, except for some stress fluctuations, which remain for large deformations. These fluctuations are studied at the micro‐mechanical level, by following the evolution of the co‐ordination number, force chains and the fraction of the sliding contacts of the sample. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

海带膳食纤维的提取与功能性试验   总被引：2，自引：1，他引：2  

李来好  陈培基  李刘冬  杨贤庆  吴燕燕  刁石强  薛长湖 《中国海洋大学学报(自然科学版)》2003,33(5):687-694

采用酶技术和化学处理相结合的方法 ,研究了海带膳食纤维的工艺技术 ,筛选出海带膳食纤维提取和漂白的最佳工艺条件 ,提取出海带膳食纤维产品 ,并进行人体的功能性试验。结果表明 ,海带膳食纤维的产率达 2 7.3% ,颜色为类白色 ,膳食纤维含量达 73.3% ,钙含量 7.5% ,膨胀力为55m L/ g,持水力为 2 650 % ;海带膳食纤维的功能性优于小麦麸皮膳食纤维 ,对便秘患者具有良好的疗效。  相似文献   

Plankton size classes, functional groups and ecosystem dynamics: an introduction     

M. Angelica Pea 《Progress in Oceanography》2003,57(3-4):239

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Daily Meteorological Observations in Cádiz – San Fernando. Analysis of the Documentary Sources and the Instrumental Data Content (1786–1996)     

Mariano Barriendos  Javier Martín-Vide  Juan Carlos Peña  Roberto Rodríguez 《Climatic change》2002,53(1-3):151-170

Meteorological observations in the city of Cádiz are acknowledged as having been made from the middle of the 18th century onwards although they were only recorded and preserved in documentary form from 1789 onwards. Data readings were taken at the new Naval Observatory in San Fernando, ten kilometres from Cádiz, from 1797 onwards. Continuous series for temperature and atmospheric pressure at a daily resolution have been compiled and constructed from 1817 until 1996. The data series is composed of thrice daily observations made at Cádiz (1821–1880) by local observers and hourly data from Naval Observatory at San Fernando (1870–1996).  相似文献   

Analysis of extreme rainfall in the Ebre Observatory (Spain)     

Núria Pérez-Zanón  M. Carmen Casas-Castillo  Raúl Rodríguez-Solà  Juan Carlos Peña  Anna Rius  J. Germán Solé  Ángel Redaño 《Theoretical and Applied Climatology》2016,124(3-4):935-944

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Younger Dryas to mid-Holocene environmental history of the lowlands of NW Transylvania, Romania   总被引：2，自引：1，他引：2  

Angelica Feurdean  Volker Mosbrugger  Bogdan P. Onac  Victor Polyak  Daniel Veres   《Quaternary Research》2007,68(3):364-378

Pollen, micro-charcoal and total carbon analyses on sediments from the Turbuta palaeolake, in the Transylvanian Basin of NW Romania, reveal Younger Dryas to mid-Holocene environmental changes. The chronostratigraphy relies on AMS ¹⁴C measurements on organic matter and U/Th TIMS datings of snail shells. Results indicate the presence of Pinus and Betula open woodlands with small populations of Picea, Ulmus, Alnus and Salix before 12,000 cal yr BP. A fairly abrupt replacement of Pinus and Betula by Ulmus-dominated woodlands at ca. 11,900 cal. yr BP likely represents competition effects of vegetation driven by climate warming at the onset of the Holocene. By 11,000 cal yr BP, the woodlands were increasingly diverse and dense with the expansion of Quercus, Fraxinus and Tilia, the establishment of Corylus and the decline of upland herbaceous and shrubs taxa. The marked expansion of Quercus accompanied by Tilia between 10,500 and 8000 cal yr BP could be the result of low effective moisture associated with both low elevation of the site and with regional change towards a drier climate. At 10,000 cal yr BP, Corylus spread across the region, and by 8000 cal yr BP it replaced Quercus as a dominant forest constituent, with only little representation of Picea abies. Carpinus became established around 5500 cal yr BP, but it was only a minor constituent in local woodlands until ca. 5000 cal yr BP. Results from this study also indicate that the woodlands in the lowlands of Turbuta were never closed.  相似文献   

Character of the O–C Variation of Four W UMa Type Stars: AW UMa, AP Leo, AG Vir and AH Vir     

M.A. Hobart  J.H. Peña  C. de la Cruz 《Astrophysics and Space Science》1998,260(3):375-388

An analysis was carried out of the secular period variation of four WU Ma type stars (AW UMa, AP Leo, AG Vir and AH Vir) using some newly determined times of minima as well as others reported in the literature. It was found that two stars show period increases, one a period decrease and the remaining shows no variation in period. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Gravimetric studies of Taal Volcano,philippines     

I. Yokoyama  A. Alcaraz  O. Peña 《Bulletin of Volcanology》1975,39(3):479-489

Taal Volcano is peculiar in its violent explosivity in spite of its low altitude. The surrounding topographies suggest that the origin of Taal Volcano is either a caldera or a graben structure. To confirm the caldera origin one must search for a vast quantity of caldera ejecta balancing with the depression. As a first step, a gravity survey was carried out on and around Taal Volcano, and high gravity anomalies were lound on Volcano Island. The distribution of the gravities may suggest a graben structure overlying a denser layer of igneous material.  相似文献   

Strontium isotope ratios in volcanic rocks from the south-eastern part of the Hellenic arc     

G.G. Pe  A. Gledhill 《Lithos》1975,8(3):209-214

Isotopic ratios of strontium in 9 volcanic rocks from the south-eastern part of the Hellenic arc range from 0.7037 to 0.7075. Within individual series of differentiation, there seems to be a correlation between Sr⁸⁷/Sr⁸⁶ and K₂O/SiO₂.All strontium isotope data for the Hellenic arc are reviewed. Comparable (but slightly smaller) ranges of Sr isotope ratios are found in other island arcs with continental basement. To explain the high values of Sr⁸⁷/Sr⁸⁶ ratio for the Hellenic arc, a selective addition of Sr⁸⁷ from the wall rock, and a process of assimilation involving water, perhaps from subducted sediments, are suggested. Since closely-spaced individual volcanic centres of similar ages have very different Sr isotope ratios, and since the range of Sr isotopic composition in individual centres is quite large, the variation is unlikely to be due to primary variation in mantle composition.  相似文献