On the local magnetorotational instability of astrophysical jets     

M. Hanasz  H. Sol  C. Sauty 《Monthly notices of the Royal Astronomical Society》2000,316(3):494-506

We present the local linear stability analysis of rotating jets confined by a toroidal magnetic field. Under the thin flux tube approximation, we derive the equation of motion for slender magnetic flux tubes. In addition to the terms responsible for the conventional instability of the toroidal magnetic field, a term related to the magnetic buoyancy and a term corresponding to the differential rotation become relevant for the stability properties. We find that the rigid rotation stabilizes while the differential rotational destabilizes the jet in a way similar to the Balbus–Hawley instability. Within the frame of our local analysis, we find that if the azimuthal velocity is of the order of or higher than the Alfvén azimuthal speed, the rigidly rotating part of the jet interior can be completely stabilized, while the strong shearing instability operates in the transition layer between the rotating jet interior and the external medium. This can explain the limb-brightening effect observed in several jets. However, it is still possible to find jet equilibria that are stable all across the jet, even in the presence of differential rotation. We discuss observational consequences of these results.  相似文献   

Recent surface marine sediments of Cocos Island in Costa Rica     

Jeffrey A.SIBAJA-CORDERO  Jesús S.TRONCOSO  Eddy GóMEZ-RAMíREZ 《国际泥沙研究》2014,29(1):59-72

Subtidal sediments of Isla del Coco(Cocos Island),Costa Rica were described in their grain size,sorting,organic matter,and carbonates from 27 dredge samples(3-75 m),collected in April 2010.The organic matter range between 1.37-3.31%and carbonates presented a mean of 74±17%.The sorting was moderately or poorly.The grain size ranged between 0.1-1.1mm.The pattern is that sediment change from inner to mouth of bays.Carbonates and gravel fractions increased offshore and organic matter have high values inner the bays.Input of vegetal debris and mud was from the rivers of this island covered with rain and cloud forest.  相似文献   

Inorganic As speciation and bioavailability in estuarine sediments of Todos os Santos Bay, BA, Brazil     

V. Hatje  S.M. Macedo  R.M. de Jesus  G. Cotrim  K.S. Garcia  A.F. de Queiroz  S.L.C. Ferreira 《Marine pollution bulletin》2010,60(12):2225-2232

The spatial distribution of As (total As, As (III) and As (V)) in estuarine sediments from the main tributaries of Todos os Santos Bay, BA, Brazil, was evaluated under high and low flow conditions. The concentrations of As were determined using a slurry sampling procedure with hydride generation atomic absorption spectrometry (HG-AAS). The highest concentrations were observed at estuary mouths, and exceeded conservative lower threshold value (Threshold Effects Level; TEL). Due to the oxic conditions and abundance of Mn and Fe (oxyhydr)oxides in the sediments, most inorganic arsenic in the Subaé and Paraguaçu estuaries was present as As (V). Nevertheless, the concentration of As (III) at several locations along the Jaguaripe River were also above the TEL value, suggesting that As may be toxic to biota. In the Subaé estuary, antropogenic activities are the main source of As. At the Jaguaripe and at Paraguaçu estuaries, nevertheless, natural sources of As need to be considered to explain the distribution patterns.  相似文献   

Non-Fickian mixing: Temporal evolution of the scalar dissipation rate in heterogeneous porous media     

Tanguy Le Borgne  Marco Dentz  Diogo Bolster  Jesus Carrera  Jean-Raynald de Dreuzy  Philippe Davy 《Advances in water resources》2010

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Die Stagoskopie in der Mineralogie     

Alphons Solé 《Mineralogy and Petrology》1955,5(3):162-169

Ohne ZusammenfassungMit 10 Textabbildungen  相似文献   

Early Cambrian granitoids of North Gondwana margin in the transition from a convergent setting to intra-continental rifting (Ossa-Morena Zone,SW Iberia)     

T. Sánchez-García  M. F. Pereira  F. Bellido  M. Chichorro  J. B. Silva  P. Valverde-Vaquero  Ch. Pin  A. R. Solá 《International Journal of Earth Sciences》2014,103(5):1203-1218

Two distinct Cambrian magmatic pulses are recognized in the Ossa-Morena Zone (SW Iberia): an early rift-(ER) and a main rift-related event. This Cambrian magmatism is related to intra-continental rifting of North Gondwana that is thought to have culminated in the opening of the Rheic Ocean in Lower Ordovician times. New data of whole-rock geochemistry (19 samples), Sm–Nd–Sr isotopes (4 samples) and ID–TIMS U–Pb zircon geochronology (1 sample) of the Early Cambrian ER plutonic rocks of the Ossa-Morena Zone are presented in this contribution. The ER granitoids (Barreiros, Barquete, Calera, Salvatierra de los Barros and Tablada granitoid Massifs) are mostly peraluminous granites. The Sm–Nd isotopic data show moderate negative εNdt values ranging from ?3.5 to +0.1 and TDM ages greatly in excess of emplacement ages. Most ER granitoids are crustal melts. However, a subset of samples shows a transitional anorogenic alkaline tendency, together with more primitive isotopic signatures, documenting the participation of lower crust or mantle-derived sources and suggesting a local transient advanced stage of rifting. The Barreiros granitoid is intrusive into the Ediacaran basement of the Ossa-Morena Zone (Série Negra succession) and has yielded a crystallization age of 524.7 ± 0.8 Ma consistent with other ages of ER magmatic pulse. This age: (1) constrains the age of the metamorphism developed in the Ediacaran back-arc basins before the intrusion of granites and (2) defines the time of the transition from the Ediacaran convergent setting to the Lower Cambrian intra-continental rifting in North Gondwana.  相似文献   

Orientation of extragalactic radio sources relative to the elliptical galaxies associated with them     

R. R. Andreasyan  H. Sol 《Astrophysics》1999,42(3):275-279

The relative orientations of the optical and radio axes of radio galaxies are analyzed using data for 271 objects. It is found that the radio axes correlate with the minor axes of the optical galaxies for more elongated radio galaxies (K > 2.5, where K is the ratio of the lengths of the major and minor axes of the radio image) and for radio galaxies of the class FRII, whereas for less elongated radio galaxies (K < 2.5) and radio galaxies of the class FRI the radio axes correlate with the major axes of the optical galaxy. In both cases the correlation turns out to be more significant when the radio galaxies are classified in terms of their elongation than when they are classified in terms of the Fanaroff-Riley criterion. The classification in terms of elongation of the radio image can therefore be of interest for understanding overall problems associated with the mechanism of formation and evolution of radio galaxies. A theoretical foundation for such a classification may be the alternative mechanism of formation of radio galaxies from relativistic plasma ejected from the central part of the optical galaxy and moving in its large-scale, dipole magnetic field. Translated from Astrofizika, Vol. 42, No. 3, pp. 365–371, July–September, 1999.  相似文献   

An integrated magnetic,geochemical and archeointensity investigation of casting debris from ancient metallurgical sites of Michoacán,Western Mesoamerica     

Juan Morales  María del Sol Hernández-Bernal  Avto Goguitchaichvili  José Luis Punzo-Díaz 《Studia Geophysica et Geodaetica》2017,61(2):290-309

The ability of baked clay-elaborated objects to record the temporal variations of both direction and intensity of the geomagnetic field at the time of their elaboration or last use has been widely used during the last decades to fill the gaps left by available time-discrete volcanic-rock logs for a better knowledge of the evolution of the geomagnetic field. Further refinement of the secular variation curves has motivated the search for alternative non-conventional materials as attractive targets for archeomagnetic studies. Both clay and copper have been used since pre-Hispanic times for the elaboration of a wide variety of ornamental and utilitarian objects in Mesoamerica. Previous studies carried out in Europe and Israel have shown the usefulness of copper slags as one of these non-conventional materials. We present the results of an integrated study carried out on ten copper slags from seven ancient metallurgical sites of Michoacán. The analysis included a series of rock magnetism experiments, scanning electron microscope analysis, archeointensity determinations following the Thellier-Coe method and their corresponding dating. Based on the results obtained the slag-set analyzed can be divided in two main groups: low Fe concentrations (associated with high Cu concentrations) for slags comprising the first group, and high Fe concentrations (associated with low Cu concentrations) for slags from second group. Slags from the first group are characterized by almost reversible thermomagnetic curves, while those corresponding to the second group show a quite irreversible behavior. A crystalline (vitreous) structure within the massive surface of the slags is observed for those coming from the second (first) group. These striking features could reflect significant differences in the metallurgical process followed at these sites, which according to archeological and historical evidences correspond to Colonial and pre-Hispanic usage metallurgical sites; first and second group, respectively. The good experimental behavior exhibited by these materials demonstrates the suitability of copper slag to obtaining absolute archeointensity data which can be used to improve the existing Mesoamerican archeomagnetic record. This in turn, can be used both for geomagnetic field modelling purposes and archeomagnetic dating.  相似文献   

Improving the descendant relationship of cluster galaxies at z < 1     

Cleivison Souza de Jesus  Andre Luis Batista Ribeiro  Christine Cordula Dantas 《Astronomische Nachrichten》2024,345(1):e220081

In this work, we study how to improve well-known techniques for detecting progenitors/descendants of galaxies, such as the NDpredict program, when applied to galaxies in clusters. The improvement of this particular method is based on the use of the red sequence of galaxies in those environments. Objects close to the red sequence in the color and magnitude diagram are more likely to belong to the cluster. This defines a probability scale which is then combined with the one generated by NDpredict. This procedure is optimized for the study of galaxies in clusters over different epochs. Our main result is that, for a sample composed of $120$ clusters, with masses greater than ${10}^{13.25}{M}_{\odot }$, selected from the IllustrisTNG simulations (namely, the TNG100 runs). In $99\%$ of the cases (i.e., $119$ systems), we obtain better performance with the red sequence method in comparison to the original NDpredict, and the average gain obtained is $28\%$ in the identification of descendants for this sample of cluster galaxies.  相似文献