The seismic events occurred in recent years highlighted the extreme vulnerability of large part of the existing constructed facilities and the need to adopt innovative solutions to improve their seismic performance. With this purpose, the possible exploitation of a seismic early warning system (SEWS) in the framework of semi-active structural control using magnetorheological (MR) dampers is herein investigated. The main idea consists in the use of these time-varying properties devices to control an hosting structure by changing their behaviour according to an anticipate estimate, provided by the SEWS, of the peak ground acceleration (PGA) of the incoming earthquake. In this way, the dampers are able to adapt their mechanical characteristics to the specific earthquake obtaining the optimal seismic response. The present paper describes the application of this protection technique to a case-study problem, a highway bridge located in Southern California. The seismic response of the benchmark bridge is investigated by nonlinear time-history analyses by adopting 16 real earthquake ground excitations. These accelerograms cover a wide variety of magnitudes, distances to fault and soil types. Possible errors on estimation of PGA provided by SEWS and their effects on the proposed control system are also considered. The results obtained confirm that unavoidable errors in the PGA estimates provided by the SEWS do not propagate to the seismic response. Conversely, the proposed strategy turns out to damp these errors, resulting in a robust seismic behaviour of the protected structure. 相似文献
Selecting the future site for a large Turkish radio telescope is a key issue. The National Radio Astronomy Observatory is now in the stage of construction at a site near Karaman City, in Turkey. A single-dish parabolic radio antenna of 30?C40 m will be installed near a building that will contain offices, laboratories, and living accommodations. After a systematic survey of atmospheric, meteorological, and radio frequency interference (RFI) analyses, site selection studies were performed in a predetermined location in Turkey during 2007 and 2008. In this paper, we described the experimental procedure and the RFI measurements on our potential candidate??s sites in Turkey, covering the frequency band from 1 to 40 GHz. 相似文献
Benford’s analysis is applied to the recurrence times of approximately 17,000 seismic events in different geological contexts
of Italy over the last 6 years, including the Mt. Etna volcanic area and the seismic series associated with the destructive
Mw 6.3, 2009 L’Aquila earthquake. A close conformity to Benford’s law and a power-law probability distribution for the recurrence
times of consecutive events is found, as typical of random multiplicative processes. The application of Benford’s law to the
recurrence event times in seismic series of specific seismogenic regions represents a novel approach, which enlarges the occurrence
and relevance of Benford-like asymmetries, with implications on the physics of natural systems approaching a power law behaviour.
Moreover, we propose that the shift from a close conformity of Benford’s law to Brownian dynamics, observed for time separations
among non-consecutive events in the study seismic series, may be ruled by a periodical noise factor, such as the effects of
Earth tides on seismicity tuning. 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.