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311.
Rosati P. Basa S. Blain A. W. Bozzo E. Branchesi M. Christensen L. Ferrara A. Gomboc A. O’Brien P. T. Osborne J. P. Rossi A. Schüssler F. Spurio M. Stergioulas N. Stratta G. Amati L. Casewell S. Ciolfi R. Ghirlanda G. Grimm S. Guetta D. Harms J. Le Floc’h E. Longo F. Maggiore M. Mereghetti S. Oganesyan G. Salvaterra R. Tanvir N. R. Turriziani S. Vergani S. D. Balman S. Caruana J. Erkut M. H. Guidorzi G. Frontera F. Martin-Carrillo A. Paltani S. Porquet D. Sergijenko O. 《Experimental Astronomy》2021,52(3):407-437
Experimental Astronomy - The proposed THESEUS mission will vastly expand the capabilities to monitor the high-energy sky. It will specifically exploit large samples of gamma-ray bursts to probe the... 相似文献
312.
Numerical experiments are performed on the determination of the fundamental frequency of transverse vibration of simply supported rectangular plates having rectangular holes with free edges. This constitutes a rather common technological situation since holes are present in plates or slabs due to operational conditions, namely passage of conduits or ducts, electric conductors, etc., Satisfying exactly the governing natural boundary conditions at the hole edges is practically an impossible task. This study reviews numerical experiments where the displacement function is expanded into a double Fourier series which constitutes the exact solution when the plate is simply connected. Satisfactory convergence is achieved when the plate is doubly connected. 相似文献
313.
Giovanni Pratesi Marco Morelli Angelo Pio Rossi Gian Gabriele Ori 《Meteoritics & planetary science》2005,40(11):1653-1672
Abstract— The impact melt breccias from the Tenoumer crater (consisting of a fine‐grained intergrowth of plagioclase laths, pyroxene crystals, oxides, and glass) display a wide range of porosity and contain a large amount of target rock clasts. Analyses of major elements in impact melt rocks show lower contents of SiO2, Al2O3, and Na2O, and higher contents of MgO, Fe2O3, and CaO, than the felsic rocks (i.e., granites and gneisses) of the basement. In comparison with the bulk analyses of the impact melt, the glass is strongly enriched in Si‐Al, whereas it is depleted both in Mg and Fe; moreover, the impact melt rocks are variably enriched or depleted in some REE with respect to the felsic and mafic bedrock types. Gold is slightly enriched in the impact melt, and Co, Cr, and Ni abundances are possibly due to a contribution from mafic bedrock. Evidences of silicate‐carbonate liquid immiscibility, mainly as spherules and globules of calcite within the silicate glass, have been highlighted. HMX mixing calculation confirm that the impact melt rocks are derived from a mixing of at least six different target lithologies outcropping in the area of the crater. A large contribution is derived from granitoids (50%) and mica schist (17–19%), although amphibolites (?15%), cherty limestones (?10%), and ultrabasites (?6%) components are also present. The very low abundances of PGE in the melt rock seem to come mainly from some ultrabasic target rocks; therefore, the contamination from the meteoritic projectile appears to have been negligible. 相似文献
314.
Hazel Rymer Corinne A. Locke rea Borgia Maria Martinez Jorge Brenes Rodolfo Van der Laat Glyn Williams-Jones 《地学学报》2009,21(4):304-309
Acidic crater lakes at persistently active volcanoes act as both an index and a moderator of volcanic processes. A catastrophic drop in lake level can therefore lead to serious local environmental damage. In the early 1990s, the crater lake at Poás volcano, Costa Rica diminished, and acid aerosols erupted with devastating consequences for local health, environment and economy. The first indications of this event can be retrospectively identified to have started from 1985, on the basis of our unique 20-year data time series, which provides evidence for the shallow intrusion of magma. New data presented in this article show similar trends and we conclude that Poás has now entered another active period with renewed intrusion. Severe environmental damage in this region is expected within the next few years if the current trend continues. 相似文献
315.
Stratigraphic and palaeontologic data from the Lower Cretaceous of Venezuela and the critical revision of the previous results on the whole Caribbean Lower Aptian, show that the South Caribbean region is characterized by an endemic Rudist fauna while some micropalaeontological components have an african affinity. Consequently a South Caribbean palaeobiogeographic province is to be distinguished from a Northern one known to have some European characters. These results fit well with palaeogeographic and palaeotectonic reconstructions concerning both the Caribbean as well as the Central Atlantic areas. New palaeogeographic and palaeoceanographic implications are considered. 相似文献
316.
Summary The chemical characteristics of coexisting biotites and hornblendes and host rocks are examined and discussed. The field data indicate that biotite derives from hornblende at decreasing metamorphism. A chemical equilibrium has been reached for Fe2+, Mg and Mn and approached, but not reached, for tetrahedral ions, Fe3+, Alvi and Ti. The disequilibrium is mainly dependent on biotite and is tentatively ascribed to the oxidizing conditions of the environment, at the time of biotite crystallization. The composition of biotite is thus partly related to that of hornblende and partly to the environment, while intracrystalline variations of hornblende are related to the chemical composition of the host rock and to varying metamorphic grade.
With 7 Figures 相似文献
Amphibole und Biotite der Hornblendegneise in einem Gebiet nordöstlich des Qagssit-Fjordes, Frederikshåb-Distrikt, Südwest-Grönland
Zusammenfassung Der Chemismus koexistierender Biotite und Hornblenden sowie von deren Muttergesteinen wird untersucht und diskutiert. Die Felddaten weisen darauf hin, daß der Biotit aus Hornblende bei abnehmender Metamorphose entsteht. Ein chemisches Gleichgewicht wurde für Fe2+, Mg und Mn erreicht; für die tetraedrisch koordinierten Ionen sowie Fe3+, Alvi und Ti fand eine Annäherung in seine Richtung statt, es wurde aber nicht erreicht. Das Ungleichgewicht hängt im wesentlichen mit dem Biotitgehalt zusammen, und es wird versuchsweise den Oxidationsbedingungen der Umgebung bei der Biotitkristallisation zugeschrieben. Die Zusammensetzung des Biotits hängt folglich teilweise mit jener der Hornblende und teilweise mit der Umgebung zusammen, während die intrakristallinen Variationen der Hornblende von der chemischen Zusammensetzung des Muttergesteins und dem variierenden Metamorphosegrad abhängen.
With 7 Figures 相似文献
317.
F. Barberi F. Innocenti P. Landi U. Rossi M. Saitta R. Santacroce I. M. Villa 《Bulletin of Volcanology》1984,47(1):125-141
Subsurface geothermal exploration has considerably added to our knowledge of the Latera volcanic complex. A syenitic body is located about 2 km below the present-day surface; K-Ar data point a 0.9 Ma age. The primary magma was a silica-saturated trachyte; undersaturated, hauyne-bearing products are found near the carbonatic wall-rocks and have been interpreted as reaction products. Subsurface data from deep drilling and geophysical surveys suggest that the Latera caldera resulted from three main successive collapse phases: (i) formation of an old caldera, now buried, related to the eruption of ignimbrites from the syenitic magma chamber; (ii) sinking of the eastern sector as a consequence of the formation of the nearby Bolsena caldera (0.3 Ma); (iii) multistage formation of the present Latera caldera (0.16 Ma). 相似文献
318.
Analysis of wind profiles at the Boulder Tower (BAO) leads to these conclusions:
- The variation of roughness with wind direction found earlier is confirmed. Roughness lengths measured on the tower are larger than those measured close to the surface.
- The profiles and measurements of Reynolds stress are consistent with a von-Karman constant of 0.35.
- The form φm=(1?15z/L)-1/3 fits best in the range -0.6 < z/L < 0. In the range 0 < z/L < 0.5, θ m ~ 1 + 4.7z/L provides a good fit to the observations. For z/L < 0.1, φ m also depends on h, the thickness of the PBL. For z/L < -0.6, Φ m approaches the constant 0.5, in contrast to all previous suggestions. For larger stabilities, the upper level is usually not in the surface layer, and wind ratios become independent of z/L.
- With snow cover, the effective roughness diminishes to about 1 cm, even for directions for which the roughness length without snow is large.
- Estimation of winds at 100 or 150 m from information near the surface is best for similarity theory provided that the ratio of height to Monin-Obukhov L is less than 0.1. For larger z/L, simple power laws seem more appropriate.
319.
M. J. Rossi 《Bulletin of Volcanology》1996,57(7):530-540
Postglacial Icelandic shield volcanoes were formed in monogenetic eruptions mainly in the early Holocene epoch. Shield volcanoes vary in their cone morphology and in the areal extent of the associated lava flows. This paper presents the results of a study of 24 olivine tholeiite and 7 picrite basaltic shield volcanoes. For the olivine tholeiitic shields the median slope is 2.7°, the median height 60 m, the median diameter 3.6 km, the median aspect ratio (height against diameter) 0.019, and the median cone volume 0.2 km3. The picritic shield volcanoes are considerably steeper and smaller. A shield-volcano cone forms from successive lava lake overflows which are of shelly-type pahoehoe. A widespread apron surrounding the cone forms from tube-fed P-type pahoehoe. The slopes of the cones have (a) a planar or slightly convex form, (b) a concave form, or (c) a convex-concave form. A successive stage of a shield volcano is determined on the basis of cone morphology and lava assemblages. A shield-producing eruption has alternating episodes of lava lake overflows and tube-fed delivery to the distal parts of the flow field. In the late stages of eruption, the cone volume increases in response to the increased amount of rootless outpouring on the cone flanks. Normally, only a small percentage of the total erupted volume of a shield volcano, sometimes as little as 1–3%, is in the shield volcano cone itself, the main volume being in the apron of the shield. 相似文献
320.