Dynamics of Saturn's magnetodisk near Titan's orbit: Comparison of Cassini magnetometer observations from real and virtual Titan flybys     

Sven Simon  Alexandre Wennmacher  Cesar L. Bertucci  Hendrik Kriegel  Michele K. Dougherty 《Planetary and Space Science》2010,58(12):1625-1635

We analyze the variability of the ambient magnetospheric field along Titan's orbit at 20.3 Saturn radii. However, while our preceding study (Simon et al., 2010) focused on Cassini magnetometer observations from the 62 Titan flybys (TA-T62) between October 2004 and October 2009, the present work discusses magnetic field data that were collected near Titan's orbit when the moon was far away. In analogy to the observations during TA-T62, the magnetospheric fields detected during these 79 “virtual” Titan flybys are strongly affected by the presence of Saturn's bowl-shaped and highly dynamic magnetodisk current sheet. We therefore provide a systematic classification of the magnetic field observations as magnetodisk current sheet or lobe-type scenarios. Among the 141 (62 real+79 virtual) crossings of Titan's orbit between July 2004 and December 2009, only 17 encounters (9 real+8 virtual) took place within quiet, magnetodisk lobe-type fields. During another 50 encounters (21 real+29 virtual), rapid transitions between current sheet and lobe fields were observed around the moon's orbital plane. Most of the encounters (54=22 real+32 virtual) occurred when Titan's orbit was embedded in highly distorted current sheet fields, thereby invalidating the frequently applied idealized picture of Titan interacting with a homogeneous and stationary magnetospheric background field. The locations of real and virtual Titan flybys are correlated to each other. Each of the 62 real Titan flybys possesses at least one virtual counterpart that occurred shortly before or after the real encounter and at nearly the same orbital position. A systematic comparison between Cassini magnetometer observations from the real Titan flybys and their virtual companions suggests that there is no clear evidence of Titan exerting a significant level of control on the vertical oscillatory motion of the magnetodisk near its orbit.  相似文献   

Viscous Newtonian laminar flow in a rectangular channel: application to Etna lava flows     

Andrea Tallarico  Michele Dragoni 《Bulletin of Volcanology》1999,61(1-2):40-47

 We introduce a 3D model for near-vent channelized lava flows. We assume the lava to be an isothermal Newtonian liquid flowing in a rectangular channel down a constant slope. The flow velocity is calculated with an analytical steady-state solution of the Navier-Stokes equation. The surface velocity and the flow rate are calculated as functions of the flow thickness for different flow widths, and the results are compared with those of a 2D model. For typical Etna lava flow parameters, the influence of levees on the flow dynamics is significant when the flow width is less than 25 m. The model predicts the volume flow rate corresponding to the surface velocity, taking into account that both depend on flow thickness. The effusion rate is a critical parameter to evaluate lava flow hazard. We propose a model to calculate the effusion rate given the lava flow width, the topograhic slope, the lava density, the surface flow velocity, and either the lava viscosity or the flow thickness. Received: 20 January 1998 / Accepted: 8 January 1999  相似文献   

Debris flow and slide deposits at the top of the Internal Liguride ophiolitic sequence, Northern Apennines, Italy: A record of frontal tectonic erosion in a fossil accretionary wedge     

Michele Marroni  Luca Pandolfi 《Island Arc》2001,10(1):9-21

Abstract In the Northern Apennines, the Internal Liguride units are characterized by an ophiolite sequence that represents the stratigraphic base of a late Jurassic–early Paleocene sedimentary cover. The Bocco Shale represents the youngest deposit recognized in the sedimentary cover of the ophiolite and can be subdivided into two different groups of deep sea sediments. The first group is represented by slide, debris flow and high density turbidity current-derived deposits, whereas the second group consists of thin-bedded turbidites. Facies analysis and provenance studies indicate, for the former group, small and scarcely evoluted flows that rework an oceanic lithosphere and its sedimentary cover. We interpret the Bocco Shale as an ancient example of a deposit related to the frontal tectonic erosion of the accretionary wedge slope. The frontal tectonic erosion resulted in a large removal of materials, from the accretionary wedge front, that was reworked as debris flows and slide deposits sedimented on the lower plate above the trench deposits. The frontal tectonic erosion was probably connected with subduction of oceanic crust characterized by positive topographic relief. This interpretation can be also applied for the origin of analogous deposits of Western Alps and Corsica.  相似文献   

Predation impact on the meiobenthic harpacticoidCanuella perplexa in a lagoon of the Po River Delta,Italy     

Victor Ugo Ceccherelli  Michele Mistri  Piero Franzoi 《Estuaries and Coasts》1994,17(1):283-287

The impact of predation by juvenile marbled gobies,Pomatoschistus marmoratus, on the meiobenthic harpacticoid copepodCanuella perplexa was investigated at a subtidal station located in a shallow-water, brackish embayment of the Po River delta, northern Italy, in summer and fall 1978. In august, predation mainly centered on adults, with a very large number of prey for each predator; the energy supplied by the harpacticoid is high enough to sustain, almost entirely, the gobies’ daily energy requirement. The situation is different in September and October, when the adult copepod population declines dramatically and predation is shifted to less energy-providing copepodites and marbled gobies sensibly widen their prey spectrum.C. perplexa showed alterations of biological parameters, such as clutch size and average brood size, to cope with such a heavy predation pressure.  相似文献   

The lattice energy of forsterite. Charge distribution and formation enthalpy of the SiO 4 4− ion     

Michele Catti 《Physics and Chemistry of Minerals》1981,7(1):20-25

In the lattice energy expression of forsterite, based on a Born-Mayer (electrostatic+repulsive+dispersive) potential, the oxygen charge z _o, the hardness parameter ρ and the repulsive radii r _Mg and r _Si appear as unknown parameters. These were determined by calculating the first and second partial derivatives of the energy with respect to the cell edges, and equalizing them to quantities related to the crystal elastic constants; the overdetermined system of equations was solved numerically, minimizing the root-mean-square deviation. To test the results obtained, the SiO ₄ ^4? ion was assumed to move in the unit-cell, and the least-energy configuration was sought and compared with the experimental one. By combining the two methods, the optimum set of parameters was: z _o=?1.34, ρ=0.27 Å, r _Mg=0.72 Å, r _Si=0.64 Å. The values ?8565.12 and ?8927.28 kJ mol^?1 were obtained, respectively, for the lattice energy E _Land for its ionic component E _L ⁰ ,which accounts for interactions between Mg²⁺ and SiO ₄ ^4? ions only. The charge distribution calculated on the SiO ₄ ^4? ion was discussed and compared with other results. Using appropriate thermochemical cycles, the formation enthalpy and the binding energy of SiO ₄ ^4? were estimated to be: ΔH _f(SiO ₄ ^4? )=2117.6 and E(SiO ₄ ^4? )=708.6 kJ mol^?1, respectively.  相似文献   

Generalized Regularization Techniques with Constraints for the Analysis of Solar Bremsstrahlung X-ray Spectra     

Eduard?P.?KontarEmail author  Michele?Piana  Anna?Maria?Massone  A.?Gordon?Emslie  John?C.?Brown 《Solar physics》2004,225(2):293-309

Hard X-ray spectra in solar flares provide knowledge of the electron spectrum that results from acceleration and propagation in the solar atmosphere. However, the inference of the electron spectra from solar X-ray spectra is an ill-posed inverse problem. Here, we develop and apply an enhanced regularization algorithm for this process making use of physical constraints on the form of the electron spectrum. The algorithm incorporates various features not heretofore employed in the solar flare context: Generalized Singular Value Decomposition (GSVD) to deal with different orders of constraints; rectangular form of the cross-section matrix to extend the solution energy range; regularization with various forms of the smoothing operator; and preconditioning of the problem. We show by simulations that this technique yields electron spectra with considerably more information and higher quality than previous algorithms.  相似文献   

Mesozoic to Tertiary tectonic history of the Mirdita ophiolites, northern Albania   总被引：3，自引：0，他引：3  

Valerio  Bortolotti  Michele  Marroni  Luca  Pandolfi  Gianfranco  Principi 《Island Arc》2005,14(4):471-493

Abstract In this paper, a summary of the tectonic history of the Mirdita ophiolitic nappe, northern Albania, is proposed by geological and structural data. The Mirdita ophiolitic nappe includes a subophiolite mélange, the Rubik complex, overlain by two ophiolite units, referred to as the Western and Eastern units. Its history started in the Early Triassic with a rifting stage followed by a Middle to Late Triassic oceanic opening between the Adria and Eurasia continental margins. Subsequently, in Early Jurassic time, the oceanic basin was affected by convergence with the development of a subduction zone. The existence of this subduction zone is provided by the occurrence of the supra‐subduction‐zone‐related magmatic sequences found in both the Western and Eastern units of the Mirdita ophiolitic nappe. During the Middle Jurassic, continuous convergence resulted in the obduction of the oceanic lithosphere, in two different stages – the intraoceanic and marginal stages. The intraoceanic stage is characterized by the westward thrusting of a young and still hot section of oceanic lithosphere leading to the development of a metamorphic sole. In the Late Jurassic, the marginal stage developed by the emplacement of the ophiolitic nappe onto the continental margin. During this second stage, the emplacement of the ophiolites resulted in the development of the Rubik complex. In the Early Cretaceous, the final emplacement of the ophiolites was followed by the unconformable sedimentation of the Barremian–Senonian platform carbonate. From the Late Cretaceous to the Middle Miocene, the Mirdita ophiolitic nappe was translated westward during the progressive migration of the deformation front toward the Adria Plate. In the Middle to Late Miocene, a thinning of the whole nappe pile was achieved by extensional tectonics, while the compression was still active in the westernmost areas of the Adria Plate. On the whole, the Miocene deformations resulted in the uplift and exposition of the Mirdita ophiolites as observed today.  相似文献   

Effect of Overstrength on the Seismic Behaviour of Multi-Storey Regularly Asymmetric Buildings     

Mario de Stefano  Edoardo Michele Marino  Pier Paolo Rossi 《Bulletin of Earthquake Engineering》2006,4(1):23-42

In past years, seismic response of asymmetric structures has been frequently analysed by means of single-storey models, because of their simplicity and low computational cost. However, it is widely believed that use of more realistic multi-storey models is needed in order to investigate effects of some system characteristics (such as overstrength, higher modes of vibration, etc.) that make behaviour of multi-storey schemes different from that of single-storey systems. This paper examines effects of the overstrength in element cross-sections on the seismic behaviour of multi-storey asymmetric buildings. It is shown that in actual buildings this characteristic, which is sometimes very variable both in plan and along the height of the building, may lead to distributions of ductility demands different from those expected according to the results from single-storey models. Consequently, torsional provisions, which aim at reducing ductility demands of single-storey asymmetric systems to those of the corresponding torsionally balanced systems, should be re-checked in light of the behaviour of realistic multi-storey buildings.  相似文献   

Origin and depositional environment of Ordovician stratiform iron mineralization from Zamora (NW Iberian Peninsula)     

A. Fernández  M. C. Moro 《Mineralium Deposita》1998,33(6):606-619

The Ordovician stratiform iron deposits at Zamora (NW Iberia) are arranged in several levels ranging between 0.2 and 1.5 m in thickness, which are interstratified in the upper member of the “Pielgo” Quartzites Formation (Arenig). The sandy nature, and trace-fossils corresponding to the ichnogenus Cruziana and Daedalus, together with major and trace element contents of this formation suggest an inter and subtidal, shallow marine depositional environment, which on a global scale formed part of a broad shelf situated in the northern margin of the Gondwana continent. The iron mineralization displays a foliated and banded structure due to the alternation of quartzitic, phosphatic (apatite), chamositic, chamositic-biotitic and ferriferous (magnetite and hematite) beds. They have high TiO₂, Ta, Sc, V, Nb, Co, Zn and Y contents. The magnetite contains unusually large amounts of TiO₂, V, Cr and Ni; there is also a clear depletion in Eu and the (Eu/Sm)_CN ratio is <1 and the (Sm/Yb)_CN ratio is >1. The chamosite contains high concentrations of Cr and V. These results suggest that iron was supplied from the weathering of a continental source, in combination with volcanic activity, such as within-basin basic volcanism or the presence of basic volcanic rocks in the exposed land. The physicochemical conditions of iron mineral crystallization calculated from chamosite compositions are the following: log f O₂: −38.8 to −30.7, log f S₂: −13.2 to −9.5 and T: 200 to 330 °C. These results together with the δ¹⁸O value (∼2‰) of the magnetite suggest that chamosite and magnetite were crystallized during later diagenesis and early low-grade metamorphism under redox conditions below the magnetite-hematite buffer. Received: 25 September 1996 / Accepted: 2 February 1998  相似文献   

Tectonic structure and post-Hercynian evolution of the Serre, Calabrian Arc, southern Italy: Geological, petrological and radiometric evidences     

Aldo Del Moro  Antonio Paglionico  Giuseppe Piccarreta  Alessandro Rottura 《Tectonophysics》1986,124(3-4)

Conflicting opinions exist concerning the structure and the post-Hercynian evolution of the Serre. The present paper deals with these topics on the basis of new geological, petrological and radiometric evidence. The composition of the so-called Stilo and Polia-Copanello units has been redefined. The above domains—former sections of upper and lower Palaeozoic continental crust respectively—came into contact, due to transcurrent movements 130–140 Ma ago. A significant vertical component during the transcurrent movements, probably, exhumed the former section of lower crust. The above domains, juxtaposed, were successively involved as a single kinematic body in the Alpine orogenesis. The results enable us to make inferences for the Calabrian Arc evolution and call attention to similarities between an Austro-Alpine element (Stilo + Polia-Copanello) of the Calabrian chain and a South-Alpine sector of the Alps (Ivrea + Ceneri zones).  相似文献