We study the possibility to detect extrasolar planets in M31 through pixel-lensing observations. Using a Monte Carlo approach, we select the physical parameters of the binary lens system, a star hosting a planet, and we calculate the pixel-lensing light curve taking into account the finite source effects. Indeed, their inclusion is crucial since the sources in M31 microlensing events are mainly giant stars. Light curves with detectable planetary features are selected by looking for significant deviations from the corresponding Paczyński shapes. We find that the time-scale of planetary deviations in light curves increase (up to 3–4 d) as the source size increases. This means that only few exposures per day, depending also on the required accuracy, may be sufficient to reveal in the light curve a planetary companion. Although the mean planet mass for the selected events is about , even small mass planets ( M P < 20 M⊕) can cause significant deviations, at least in the observations with large telescopes. However, even in the former case, the probability to find detectable planetary features in pixel-lensing light curves is at most a few per cent of the detectable events, and therefore many events have to be collected in order to detect an extrasolar planet in M31. Our analysis also supports the claim that the anomaly found in the candidate event PA-99-N2 towards M31 can be explained by a companion object orbiting the lens star. 相似文献
The ophiolitic mélange of the Sabzevar Range (northern Iran) is a remnant of the Mesozoic oceanic basins on the northern margin of the Neotethys that were consumed during the Arabia–Eurasia convergence history. Occurrence of km-scale, dismembered mafic HP granulitic slices is reported in this study. Granulites record an episode of amphibole-dehydratation melting and felsic (tonalite/throndhjemite) melt segregation at c. 1.1 GPa and 800 °C. In situ U(-Th)–Pb geochronology of zircon and titanite grains hosted in melt segregations points to an Early Cretaceous (Albian) age for the metamorphic climax. Results of this study (i) impose reconsideration of the current palaeotectonic models of the Neothetyan convergent margin during the Early Cretaceous and (ii) argue that punctuated events of subduction of short-lived back-arc oceanic basins accompanied the long-lasting history of the Neotethyan subduction in the region. 相似文献
Germanate garnets are often used as isostructural analogues of silicate garnets to provide insight into the crystal chemistry and symmetry of the less accessible natural garnet solid solutions. We synthesised two series of germanate garnets at 3 GPa along the joinVIIICa3VI(CaGe)IVGe3O12–VIIICa3VIFe2IVGe3O12 at 900 °C and 1,100 °C. Samples with compositions close to the CaGeO3 end-member consist of tetragonal garnet with a small amount of triclinic CaGe2O5. Samples with nominal compositions between XFe=0.4 and 1.0 consist of a mixture of tetragonal and cubic garnets; whereas, single-phase cubic garnets were obtained for compositions with XFe>1.2 (XFe gives the iron content expressed in atoms per formula unit, and varies between 0 and 2 along the join). Run products which were primarily single-phase garnet were investigated using Mössbauer spectroscopy. Spectra from samples synthesised at 1,100°C consist of one well-resolved doublet that can be assigned to Fe3+ in the octahedral site of the garnet structure. A second doublet, present primarily in samples synthesised at 900°C, can be assigned to Fe2+ at the octahedral sites of the garnet structure. The relative abundance of Fe2+ decreases with increasing iron content. Transmission electron microscopy analyses confirm this tendency and show that the garnets are essentially defect-free. The unit-cell parameters of tetragonal VIIICa3VI(CaGe)IVGe3O3 garnet decrease with increasing synthesis temperature, and the deviation from cubic symmetry becomes smaller. Cubic garnets show a linear decrease of unit-cell parameter with increasing iron content. The results are discussed in the context of iron incorporation into VIIIMg3VI(MgSi)IVSi3O3 majorite. 相似文献
Marine terrace flights resulting from the interaction of Quaternary glacio-eustatic fluctuations and tectonic uplift are a typical feature of the Tyrrhenian coast of Calabria in Southern Italy; in particular a térrace flight with four orders of terraces is evident in the Diamante area. The lowest terrace levels (fourth order: Diamante-Cirella terrace) are typified by a calcarenitic deposit with Cladocora caespitosa which give a Th/U age > 300,000 years. The third order terrace has a sedimentary cover formed of a basal discontinuous level of well rounded pebbles which underlies a deeply weathered coarse-grained sand horizon. The deposit ends with a paleosol locally cut by erosional scours filled by yellowish tuff deposits. The formation of this terrace dates from the Middle Pleistocene. The second order terrace presents a sedimentary cover composed of two generations of soils and is attributed to Middle Pleistocene age. The first order terrace (M. Carpinoso terrace) presents a wave-cut platform covered by a clastic deposit of marine and continental origin; this deposit consists of superimposed depositional events separated by unconformities, bounded by two diachronous surfaces. The formation of the wave-cut platform could be related to several sea-level stands during a long-lasting slow subsidence phase of the coastal area during the Lower Pleistocene. The uplift following terrace formation displaced the first order terrace most markedly; tectonic lineations controlled the hydrographic pattern and erosion of the surfaces. 相似文献
The risk management of rainfall-induced landslides requires reliable rainfall thresholds to issue early warning alerts. The practical application of these thresholds often leads to misclassifications, either false negative or false positive, which induce costs for the society. Since missed-alarm (false negative) and false-alarm (false positive) cost may be significantly different, it is necessary to find an optimal threshold that accounts for and minimises such costs, tuning the false-alarm and missed-alarm rates. In this paper, we propose a new methodology to develop cost-sensitive rainfall thresholds, and we also analyse several factors that produce uncertainty, such as the accuracy of rainfall intensity values at landslide location, the time of occurrence, the minimum rainfall amount to define the non-triggering event, and the variability of cost scenarios. Starting from a detailed mapping of landslides that occurred during five large-scale rainfall events in the Italian Central Alps, we first developed rainfall threshold curves with a ROC-based approach by using both rain gauge and bias-adjusted weather radar data. Then, based on a reference cost scenario in which we quantified several cost items for both missed alarms and false alarms, we developed cost-sensitive rainfall threshold curves by using cost-curve approach (Drummond and Holte 2000). Finally, we studied the sensitivity of cost items. The study confirms how important is the information regarding rainfall intensity at the landslide site for the development of rainfall thresholds. Although the use of bias-corrected radar strongly improves these values, a large uncertainty related to the exact time of landslide occurrence still remains, negatively affecting the analysis. Accounting for the different missed-alarm and false-alarm misclassification costs is important because different combinations of these costs make an increase or decrease of the rainfall thresholds convenient. In our reference cost scenario, the most convenient threshold is lower than ROC-based thresholds because it seeks to minimise the number of missed alarms, whereas the missed-alarm costs are almost seven times greater than false-alarm costs. However, for different cost scenarios, threshold may vary significantly, as much as half an order of magnitude.
Stromboli is an Italian volcanic island known for its persistent state of activity, which leads to frequent mass failures and consequently to frequent tsunamis ranging from large (and rare) catastrophic events involving the entire southern Tyrrhenian Sea to smaller events with, however, extremely strong local impact. Most of tsunamigenic landslides occur in the Sciara del Fuoco (SdF) zone, which is a deep scar in the NW flank of the volcano, that was produced by a Holocene massive flank collapse and that is the accumulation area of all the eruptive ejecta from the craters. Shallow-water bathymetric surveys around the island help one to identify submarine canyons and detachment scars giving evidence of mass instabilities and failures that may have produced and might produce tsunamis. The main purpose of this paper is to call attention to tsunami sources in Stromboli that are located outside the SdF area. Further, we do not touch on tsunami scenarios associated with gigantic sector collapses that have repeat times in the order of several thousands of years, but rather concentrate on intermediate size tsunamis, such as the ones that occurred in December 2002. Though we cannot omit tsunamis from the zone of the SdF, the main emphasis is on the elaboration of preliminary scenarios for three more possible source areas around Stromboli, namely Punta Lena Sud, Forgia Vecchia and Strombolicchio, with the aim of purposeful contributing to the evaluation of the hazard associated with such events and to increase the knowledge of potential threats affecting Stromboli and the nearby islands of the Aeolian archipelago. The simulations show that tsunami sources outside of the SdF can produce disastrous effects. As a consequence, we recommend that the monitoring system that is presently operating in Stromboli and that is focussed on the SdF source area be extended in order to cover even the other sources. Moreover, a synoptic analysis of the results from all the considered tsunami scenarios leads to a very interesting relation between the tsunami total energy and the landslide potential energy, that could be used as a very effective tool to evaluate the expected tsunami size from estimates of the landslide size. 相似文献