Double starbursts triggered by mergers in hierarchical clustering scenarios     

P. B. Tissera  R. Domínguez-Tenreiro  C. Scannapieco  A. Sáiz 《Monthly notices of the Royal Astronomical Society》2002,333(2):327-338

We use cosmological smooth particle hydrodynamical (SPH) simulations to study the effects of mergers in the star formation history of galactic objects in hierarchical clustering scenarios. We find that during some merger events, gaseous discs can experience two starbursts: the first one during the orbital decay phase, owing to gas inflows driven as the satellite approaches, and the second one when the two baryonic clumps collide. A trend for these first induced starbursts to be more efficient at transforming the gas into stars is also found. We detect that systems that do not experience early gas inflows have well-formed stellar bulges and more concentrated potential wells, which seem to be responsible for preventing further gas inward transport triggered by tidal forces. The potential wells concentrate owing to the accumulation of baryons in the central regions and of dark matter as the result of the pulling in by baryons. The coupled evolution of the dark matter and baryons would lead to an evolutionary sequence during which systems with shallower total potential wells suffer early gas inflows during the orbital decay phase that help to feed their central mass concentration, pulling in dark matter and contributing to build up more stable systems. Within this scenario, starbursts triggered by early gas inflows are more likely to occur at early stages of evolution of the systems and to be an important contributor to the formation of stellar bulges. Our results constitute the first proof that bulges can form as the product of collapse, collisions and secular evolution in a cosmological framework, and they are consistent with a rejuvenation of the stellar population in bulges at intermediate z with, at least, 50 per cent of the stars (in SCDM) being formed at high z .  相似文献   

ISO Observations of Isolated Herbig AE/BE Stars     

C. Waelkens  K. Malfait  L.B.F.M. Waters 《Astrophysics and Space Science》1997,255(1-2):25-33

We report on SWS and LWS observations of the circumstellar disks of young stars of a few solar masses. The ISO spectra of these objects present a diversity of emission features of carbon-rich and oxygen-rich grains. The similarity of the forsterite spectra observed for Comet Hale-Bopp and the Haebe star HD100546 is particularly striking and provides a new argument that huge comet swarms are formed in the disks surrounding young stars. While the data suggest that the formation of crystalline silicates in the dust disks essentially occurs when a Haebe star has already reached the main sequence, no clear correlation with stellar age only is apparent. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Geology on stamps: mountains of fire     

ANDREW C. SCOTT 《Geology Today》1991,7(1):28-29

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The influence of a non‐associated flow rule on the calculation of the factor of safety of soil slopes     

Yu‐Jie Wang  Jian‐Hua Yin  C. F. Lee 《国际地质力学数值与分析法杂志》2001,25(13):1351-1359

This paper presents a method that incorporates a non‐associated flow rule into the limit analysis to investigate the influence of the dilatancy angle on the factor of safety for the slope stability analysis. The proposed method retain's the advantage of the upper bound method, which is simple and has no stress involvement in the calculation of the energy dissipation and the factor of safety. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Why Mt Etna?     

C. Doglioni  F. Innocenti  & G. Mariotti 《地学学报》2001,13(1):25-31

The Etna volcano is located in an apparently anomalous position on the hinge zone of the Apennines subduction and its Na-alkaline geochemistry does not favour a magma source from the deep slab as indicated for the Aeolian K-alkaline magmatism. The steeper dip of the regional foreland monocline at the front of the Apennines in the Ionian Sea than in Sicily, implies a larger rollback of the subduction hinge in the Ionian Sea. Moreover, the lengthening of the Apennines arc needs extension parallel to the arc. Therefore, the larger southeastward subduction rollback of the Ionian lithosphere with respect to the Hyblean plateau in Sicily, should kinematically produce right-lateral transtension and a sort of vertical 'slab window' which might explain (i) the Plio-Pleistocene alkaline magmatism of eastern Sicily (e.g. the Etna volcano) and (ii) the late Pliocene to present right lateral transtensional tectonics and seismicity of eastern Sicily. The area of transfer of different dip and rollback occurs along the inherited Mesozoic passive continental margin between Sicily and the oceanic Ionian Sea, i.e. the Malta escarpment.  相似文献   

Perspectives of the ROT 54/32/2.6 in astronomy     

J. M. Martin  C. Rosolen 《Astrophysics》1995,38(4):361-363

Perspectives for the Radio-Optical Telescope 54/32/2.6 are given for scientific research in radioastronomy. Its characteristics and potential scientific fields are summarized in the frame of the present French-Armenian collaboration. A 3-phase upgrade plan including a detailed technical evaluation of the antenna is presented.Published in Astrofizika, Vol. 38, No. 4, pp. 645–648, October–December, 1995.  相似文献   

Radar observations of the Geminid meteoroid stream     

G. Cevolani  G. Bortolotti  L. Foschini  C. Franceschi  G. Grassi  G. Trivellone  A. Hajduk  V. Porubčan 《Earth, Moon, and Planets》1995,68(1-3):247-255

Continuous radio-wave monitoring of the Geminid activity in December 1992 and 1993 by using a forward scatter (FS) bistatic radar over the Bologna-Lecce baseline (700 km) in Italy, reveals peculiar structural aspects of the stream in terms of signal amplitude-rate and duration-rate dependence. The observational results of the Geminid display obtained in the two consecutive years with differentiated peak levels of transmitted power, exhibit different time distributions of underdense meteors against the signal received power. Both sets of the data relative to the peak activity in December 12–14, show reflection properties of Geminids which are atypical if compared with echoes from cometary-type showers, with really high echo counts at mid-upper levels of the peak received power. An assymmetric curve of activity of the Geminids complex is evidenced, with the peak flux of smaller particles occurring earlier than that of larger ones.  相似文献   

Geophysical investigations over a segment of the Central Indian Ridge, Indian Ocean     

K. A. Kamesh Raju  T. Ramprasad  C. Subrahmanyam 《Geo-Marine Letters》1997,17(3):195-201

 Swath bathymetric, gravity, and magnetic studies were carried out over a 55 km long segment of the Central Indian Ridge. The ridge is characterized by 12 to 15 km wide rift valley bounded by steep walls and prominent volcanic constructional ridges on either side of the central rift valley. A transform fault at 7°45′S displaces the ridge axis. A mantle Bouguer anomaly low of −14 mGals and shallowing of rift valley over the middle of the ridge segment indicate along axis crustal thickness variations. A poorly developed neovolcanic zone on the inner rift valley floor indicate dominance of tectonic extension. The off-axis volcanic ridgs suggest enhanced magmatic activity during the recent past. Received: 24 May 1996 / Rivision received: 13 January 1997  相似文献   

BRIGHTNESS VARIATIONS OF Mg Ib BRIGHT FEATURES     

Dara  H.C.  Koutchmy  S.  Zachariadis  Th.G.  Alissandrakis  C.E. 《Solar physics》2001,198(2):313-324

We study the temporal intensity variations of Mgib bright features and investigate the corresponding Hα velocity pattern. The network bright features are well visible in the continuum, in images averaged over the duration of the observations (130 min). We detected `flashing' bright features, which appear and disappear within two to five minutes, while the rest of the bright features undergo small variations of either their shape and/or their intensity. A power spectrum analysis reveals a 10-min oscillation for approximately half of the stable bright features. The 5-min oscillations are detected mainly at the network boundaries, where stable bright features are located, while 3-min oscillations coincide with few bright features, but are also quite intense inside the network cells. The majority of bright features are associated with Hα downflows. The downflow is very intense at the location of `flashing' bright features.  相似文献   

Trigger conditions and effective areas of imaging air Cherenkov telescopes (Astroparticle Physics 6 (1996) 77)     

C. Khler  G. Hermann  W. Hofmann  A. Konopelko  A. Plyasheshnikov 《Astroparticle Physics》1997,6(3-4):423

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