On the solar rotation and activity     

R. Brajša  H. Wöhl  D. Ruždjak  B. Vršnak  G. Verbanac  L. Svalgaard  J.-F. Hochedez 《Astronomische Nachrichten》2007,328(10):1013-1015

The interaction between differential rotation and magnetic fields in the solar convection zone was recently modelled by Brun (2004). One consequence of that model is that the Maxwell stresses can oppose the Reynolds stresses, and thus contribute to the transport of the angular momentum towards the solar poles, leading to a reduced differential rotation. So, when magnetic fields are weaker, a more pronounced differential rotation can be expected, yielding a higher rotation velocity at low latitudes taken on the average. This hypothesis is consistent with the behaviour of the solar rotation during the Maunder minimum. In this work we search for similar signatures of the relationship between the solar activity and rotation determined tracing sunspot groups and coronal bright points. We use the extended Greenwich data set (1878–1981) and a series of full-disc solar images taken at 28.4 nm with the EIT instrument on the SOHO spacecraft (1998–2000). We investigate the dependence of the solar rotation on the solar activity (described by the relative sunspot number) and the interplanetary magnetic field (calculated from the interdiurnal variability index). Possible rotational signatures of two weak solar activity cycles at the beginning of the 20th century (Gleissberg minimum) are discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Possible detection of an old bipolar shell associated with η Carinae     

Joaquín Bohigas  Mauricio Tapia  María Teresa Ruiz †  Miguel Roth 《Monthly notices of the Royal Astronomical Society》2000,312(2):295-300

Continuum-subtracted dereddened images in the light of several atomic lines show the presence of an extended bipolar nebula surrounding η Carinae with size ∼100×45 arcsec² (1.3×0.5 pc²). This feature is best delineated in [O  iii ] 5007. The geometrical disposition and mass of the shell suggest that it was formed by mass ejections from η Carinae. The dynamic age of the nebula is ∼13 000/ V ₇ yr, where V ₇ is the mean expansion velocity in 100 km s⁻¹, and its mass is between 5 and 10 M_⊙. The nebula is photoionized and composed of unprocessed material. The major axes of the nebula and of the Homunculus are nearly perpendicular. We also report the discovery of elongated emission knots prominent in [N  ii ] located 64 to 100 arcsec away from η Carinae, which implies that they were ejected either centuries ago or at a more recent date but with extremely large velocities.  相似文献   

Astrophysical Molecules AlD and CaH: Transition Probabilities and Dissociation Energy     

F. Partal Ureña  M. Fernández Gómez  J.J. López González  N. Rajamanickam 《Astrophysics and Space Science》2000,272(4):345-352

The Franck-Condon (FC) factors and r-centroids for the bands systemC ¹ Σ ⁺ → X ¹ Σ ⁺ of AlD and E ² Π → X ² Σ ⁺ of CaH have been evaluated by means of a reliable numerical integration procedure by using a suitable potential. The dissociation energy, D _e, for the electronic ground states of AlD and CaH have been estimated by the curve fitting method to the RKRV experimental potential curve turning out to be 3.01 eV and 2.32 eV, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Changes in the Structure of a Coastal Fish Assemblage Exploited by a Small Scale Gillnet Fishery During an El Niño–La Niña Event     

E. Godínez-Domínguez  J. Rojo-Vzquez  V. Galvn-Pia  B. Aguilar-Palomino 《Estuarine, Coastal and Shelf Science》2000,51(6):773

During 1998 an experimental gillnet fishing survey was carried out in a Mexican Central Pacific inshore zone. One-hundred and thirty fish species belonging to 51 families and 18 orders were identified. The most abundant species wereMicrolepidotus brevipinnis (29·0% of the total abundance) and Caranx caninus (19·2%), followed by C. caballus (6·3%), Kyphosus analogus (4·3%) and C. sexfasciatus (3·4%). Thermal SST anomalies showed the existence of two periods. The first, from January to April with positive anomalies, defines the end of an El Niño episode. The second period, from May to December, constitutes the beginning of the La Niña episode. The typical seasonality in a non-anomalous year continued for a large percentage of the inshore fish community, and the effects of the anomalous event consisted of changes in seasonality of occurrence in some individual species and the unusual abundance of some uncommon species. The species richness was higher during the El Niño–La Niña event than in a non-anomalous year, and therefore the event could be considered an interannual environmental mechanism that favours fish diversity in inshore waters.  相似文献   

Chemical abundances and ionizing clusters of H ii regions in the LINER galaxy NGC 4258     

Angeles I. Díaz  Marcelo Castellanos  Elena Terlevich †  María Luisa García-Vargas 《Monthly notices of the Royal Astronomical Society》2000,318(2):462-474

We present long-slit observations in the optical and near-infrared of eight H  ii regions in the spiral galaxy NGC 4258. Six of the observed regions are located in the south-east inner spiral arms, and the other two are isolated in the northern outer arms. A detailed analysis of the physical conditions of the gas has been performed. For two of the regions, an electron temperature has been derived from the [S  iii ] λ 6312 line. For the rest, an empirical calibration based on the red and near-infrared sulphur lines has been used. The oxygen abundances derived by both methods are found to be significantly lower (by a factor of 2) than previously derived by using empirical calibrations based on the optical oxygen lines.
In the brightest region, 74C, the observation of a prominent feature caused by Wolf–Rayet (WR) stars provides an excellent constraint over some properties of the ionizing clusters. In the light of the current evolutionary synthesis models, no consistent solution is found to explain at the same time both the WR feature characteristics and the emission-line spectrum of this region. In principle, the presence of WR stars could lead to large temperature fluctuations and also to a hardening of the ionizing radiation. None of these effects is found in region 74C, for which the electron temperatures found from the [S  iii ] λ 6312 line and the Paschen discontinuity at 8200 Å are equal within the errors, and the effective temperature of the ionizing radiation is estimated at around 35 300 K.
Both more observations of confirmed high-metallicity regions and a finer metallicity grid for the evolutionary synthesis models are needed in order to understand the ionizing populations of H  ii regions.  相似文献   

LiH formation by radiative association in Li⁺+H⁻ collisions     

A. S. Dickinson †  F. X. Gadéa 《Monthly notices of the Royal Astronomical Society》2000,318(4):1227-1231

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Bronze Age ceramics in southwest Spain: An exploratory archaeometric study of technology and function     

Angel Polvorinos del Río  Leonardo García Sanjun  Víctor Hurtado Prez  M. Jesús Hernndez Arnedo 《Geoarchaeology》2005,20(3):263-284

Pottery from the Bronze Age of southwest Spain has traditionally been approached from a “typological” stand seeking the establishment of chronological sequences. This article examines ceramics from two different Bronze Age sites, a settlement (El Trastejón) and a necropolis (La Traviesa), from an archaeometric viewpoint. The methodology involved includes mineralogical characterization by XRD and optical microscopy, chemical analysis by XRF, and morphometric analysis through digital processing of thin sections. The analytical results are contextualized within the general framework of our current archaeological knowledge of both sites and their general background, and then a preliminary interpretation is proposed in terms of the prehistoric technology of pottery manufacture and functionality. © 2005 Wiley Periodicals, Inc.  相似文献   

Stability Assessment of the Gökgöl Karstic Cave (Zonguldak,Turkey) by Analytical and Numerical Methods     

Melih Geniş  Berdan Çolak 《Rock Mechanics and Rock Engineering》2015,48(6):2383-2403

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The effects of biological geotextiles on gully stabilization in São Luís,Brazil     

A. J. T. Guerra  J. F. R. Bezerra  M. A. Fullen  J. K. S. Mendonça  M. C. O. Jorge 《Natural Hazards》2015,75(3):2625-2636

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Erratum to: The effects of biological geotextiles on gully stabilization in São Luís,Brazil     

A. J. T. Guerra  J. F. R. Bezerra  M. A. Fullen  J. K. S. Mendonҫa  M. C. O. Jorge 《Natural Hazards》2015,77(2):1417-1417

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