On the Ionization Structure of Circumstellar Disks Around Be Type Stars     

J.M. Torrejón  G. Bernabeu  J. Fabregat 《Astrophysics and Space Science》1998,263(1-4):243-246

We present some insight on the ionization structure of the circumstellar disks around Be type stars based on the study of Balmer decrements for absorption-corrected emission lines. Owing to this analysis, three different ionization zones in the envelope are proposed: the inner one, completely ionized, of about ∼ 5R_*, an intermediate recombination zone extending up to ∼ [10 - 20]R_*, and an outer extended zone of neutral H. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

The Role of Cooling Flows in the Star Formation History of Central Cluster Galaxies     

N. Cardiel  J. Gorgas  A. Aragón-Salamanca 《Astrophysics and Space Science》1998,263(1-4):83-86

Using a recent determination of the X-ray luminosity function of galaxy clusters, accurate mass deposition rates and L_X in cooling flow clusters from the literature, and reliable constraints on the star fomation episodes in cooling flows obtained by our group, we quantify the relevance of such star formation in comparison with the SFR in the local universe. We conclude that the SFR density in CF is ≲ 0.1% the total local reference. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Resonant Absorption of Nonlinear Slow MHD Waves in Isotropic Steady Plasmas - I. Theory     

Ballai  István  Erdélyi  Róbert 《Solar physics》1998,180(1-2):65-79

This paper considers driven resonant nonlinear slow magnetohydrodynamic (MHD) waves in dissipative steady plasmas. A theory developed by Ruderman, Hollweg, and Goossens (1997) is used and extended to study the effect of steady flows on the nonlinear resonant behaviour of slow MHD waves in slow dissipative layers. The method of matched asymptotic expansions is used to describe the behaviour of the wave variables in the slow dissipative layer. The nonlinear analogue of the connection formulae for slow MHD waves obtained previously by Goossens, Hollweg, and Sakurai (1992) and Erdélyi (1997) in linear MHD, are derived. The effect of an equilibrium flow results partly in a Doppler shift of the available frequency for slow resonance and partly in the modification of the width of the dissipative layer.  相似文献   

Women, gender, feminisms: visiting physical geography     

Anna Bee  Clare Madge  Jane Wellens 《Area》1998,30(3):195-196

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D型菌解无定形体的形成及其生烃模式   总被引：1，自引：0，他引：1  

丁安娜  惠荣耀 《地质科学》1997,32(2):221-228

通过对准噶尔盆地部分油藏烃源岩的电子显微镜研究,在大量样品中检出D型菌解无定形体,其母质来源具有二元混合性,形成在弱还原─原环境中,生烃门限R_o值为0.4%,生烃期大约为0.4%-0.7%,是轻质油(或凝析油)和天然气形成的重要组分之一。在低演化阶段,由于细菌参加了对有机质的改造,使Ⅱ_B-Ⅲ类烃源岩中富集氢,生烃能力变好。文章还初步探讨了芳烃化合物含量与菌解无定形体D形成的关系,指出当沉积体系中的硫和硫化氢与铁结合,形成稳定的黄铁矿物后,才有可能在Ⅲ型有机质中形成高含量的D型菌解无定形体。  相似文献   

A model study of the temporal behaviour of the emission intensity and rotational temperature of the OH Meinel bands for high-latitude summer conditions     

M. J. López-González  D. P. Murtagh  P. J. Espy  J. J. López-Moreno  R. Rodrigo  G. Witt 《Annales Geophysicae》1996,14(1):59-67

The temporal variation of OH* emission and weighted rotational temperature has been studied for high-latitude summer conditions. Observations for 60°N latitude show OH weighted temperatures that always exceed 145 K even during periods of noctilucent clouds. Using a one-dimensional model the effects in excited OH concentration produced by changes in temperature, eddy diffusion, and water concentration have been analysed. We are forced to conclude that there remains a discrepancy between the OH temperatures predicted by the model and that obtained from OH^* measurements. An increase in OH^* concentration from June to the beginning of August, followed by a slow decrease during August has been obtained in agreement with the measurements. The 16-day modulation present in the measurements was simulated in a simple manner by varying the temperature in the mesopause region. This variation produces periodic modulations in both OH^* concentration and weighted temperature of 16 days. The results show the temperature leading the OH^* column concentration by three days. This phase shift is also present in the observations.  相似文献   

Enhancing Safety Of Nuclear Waste Disposal By Exploiting Regional Groundwater Flow: The Recharge Area Concept     

József Tóth  Grant Sheng 《Hydrogeology Journal》1996,4(4):4-25

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Poets and narrators from Mendoza and their local perceptions     

Prof.  Dr. María E. de Civit Furlani  Prof.  Dr. María J. de Manchón Gutiérrez 《GeoJournal》1996,38(1):109-118

This article outlines three modalities of relation between literature and geography: the literary work as demonstrative element, the literary work as collective image, and the literary work as analogous process. The verification of the three modalities takes place through an approachment to the local literature using a geographical concept, namely region, and a particular area: the province of Mendoza, in western Argentina. Ten literary works of different genre were selected to which content analysis was applied. First the relevance of these representations at the initiation of geographical research is verified and then the way in which they stimulate the definition of problems and the formulation of hypotheses is addressed.  相似文献   

Nd and Sr isotopic systematics of central Australian granulites: chronology of crustal development and constraints on the evolution of lower continental crust     

Dónal P. Windrim  Malcolm T. McCulloch 《Contributions to Mineralogy and Petrology》1986,94(3):289-303

Nd and Sr isotopic data are reported for a granulite terrain in the Proterozoic Arunta Block of Central Australia. Sm-Nd data from a wide range of rock types define a crust formation age of 2,070±125 Ma and provide further evidence for voluminous crustal growth in the Proterozoic. An _Nd value of +1.5±0.8 indicates a depleted mantle source for this crustal segment and there is no evidence for a large component of significantly older sialic crust. Field relationships, geochemistry and Rb-Sr data for mafic and felsic granulites indicate that intracrustal differentiation and polyphase deformation were followed by granulite facies metamorphism (Rb depletion) at 1,800 Ma. Rb-Sr data for strongly retrogressed granulites define an age of 1,700 Ma which is interpreted as the time of retrograde biotite growth. Partial melting at the presently exposed crustal level and anatexis at deeper crustal levels were broadly coeval with the retrograde metamorphism. Sm-Nd and Rb-Sr isotopic systematics of minerals indicate that the terrain cooled slowly, did not experience significant uplift until 1,000 Ma and remained at temperatures above 320° C until the late Palaeozoic. The mineral data are consistent with geological relationships and petrological evidence for a prolonged period of isobaric cooling followed by uplift late in the metamorphic evolution of the terrain. The granulite protoliths appear to have formed in a rift which closed within 280 Ma of initial separation. Deformation and granulite facies metamorphism at 1,800 Ma are interpreted to be a consequence of collision between the continental blocks which defined the rift. Regional retrogression and granitoid magmatism at 1,700 Ma are attributed to underthrusting of the granulites by lower grade rocks in the final stages of collision. Subsequent events in the cooling and uplift history appear to have been controlled by the presence of long-lived major faults in the crust and a prolonged history of episodic compression in the continental lithosphere. The results of this study suggest that granulite terrains, in general, cannot be equated with lower continental crust but instead represent assemblages of (mainly) supracrustal rocks which in some instances have been involved in major collision events.Abbreviations Opx orthopyroxene - Cpx clinopyroxene - Plag plagioclase - Hb hornblende - Ox opaque oxide - Bi biotite - Ap apatite - Zir zircon - Gt garnet - 2°CA secondary clinoamphibole - Qtz quartz - Ol olivine - Sp spinel - Se serpentine - Ep epidote - Kf alkali feldspar - Mz monazite - Sph sphene - Sill sillimanite - Rut rutile - Cd cordierite - Sphal sphalerite - Ms muscovite - Act actinolite - Cc calcite - Scap scapolite - Cor corundum - Xen xenotime - Sapph sapphirine - Ged gedrite - All allanite - Clh clinohumite - Dol dolomite - Mt magnetite - Ghn gahnite - Gal galena  相似文献   

Petrology of a new basalt occurrence in Hungary     

Dr. A. Embey-Isztin  G. Dobosi  Dr. G. Noske-Fazekas  E. Árva-Sós 《Mineralogy and Petrology》1989,40(3):183-196

Summary A new occurrence of basalt (minimum K/Ar age 57.9 ± 2.2 m.y.) is reported from Budaliget, near Budapest. Major and minor element concentrations show that the basalts are alkaline and potassic in nature ranging from olivine tholeiite to moderately undersaturated basanite. High mg-values and concentrations of Ni and Cr indicate that some of the samples may represent primary compositions. High pressure accidental xenoliths, xenocrysts and cognate megacrysts are frequent and the chemical zoning patterns of olivine and pyroxene phenocrysts indicate a complex evolution and polibaric conditions for the crystallization. The discovery of the new basalt occurrence is important from a geodynamical point of view: prior to the last two major geodynamical events (Plio-Pleistocene rifting with associated alkali basaltic volcanism and collision of microplates with associated Miocene calk-alkaline volcanism) the continental lithosphere below NE Transdanubia may have experienced another rifting period in the Paleocene or Upper Cretaceous.With 7 Figures  相似文献