Monitoring of structural systems by using frequency data     

Danilo Capecchi  Fabrizio Vestroni 《地震工程与结构动力学》1999,28(5):447-461

The present work evaluates the possibility of using dynamic data to assess structural integrity. It addresses the problem of understanding when it is sufficient to measure and use only natural frequencies, thus avoiding the need to measure modal shapes. The classic problem of detecting damage in beams, or beam assemblies, due to concentrated cracks, or damage spread over a structural member is dealt with. Damage is represented as a decrease in stiffness and linear behaviour before and after the event assumed to have caused damage is considered. Damage is restricted to a few unknown sections or elements, so that only the modification of few parameters of the system need to be determined. This study thus rejects assumptions unrelated to the physical aspects of the problem, in contrast to many papers on the subject. The amount of data to locate and quantify damage correctly is discussed; general considerations lead to the conclusion that a unique and reliable estimate of the damage can be obtained using only few additional frequency data with respect to the number of damaged zones. Continuous and discrete (finite element) models are examined. Finally the paper considers the applications to both analytical and experimental data of the procedure developed, which takes account of the peculiar characteristics of damage detection problem. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Northwest Africa 6232: Visible–near infrared reflectance spectra variability of an olivine diogenite     

Cristian Carli  Giovanni Pratesi  Vanni Moggi-Cecchi  Francesca Zambon  Fabrizio Capaccioni  Simone Santoro 《Meteoritics & planetary science》2018,53(10):2228-2242

Visible and near-infrared (VNIR) reflectance is an important spectroscopic technique to identify minerals, and their associations, on planetary body surfaces. Howardites, eucrites, and diogenites (HED) are a class of igneous-like meteorites whose genetic connection with asteroid 4 Vesta has since long been inferred and recently confirmed by Dawn mission results. Pyroxene and olivine are the two major mafic minerals present in HED which can be identified with VNIR reflectance measurements. Thus, studying the compositional variability of those phases and their mixtures by means of laboratory spectroscopic measurements on different diogenitic or eucritic samples is one of the prime methods to better understand the evolution of 4 Vesta's crust. Here, we report the VNIR reflectance spectral analysis of a harzburgitic olivine diogenite, Northwest Africa 6232 (probably paired with Northwest Africa 5480), containing variable amounts of olivine as small grains or aggregates. We found that the olivine diogenite spectral parameters (e.g., band position) of powdered samples and polished slabs are in agreement. Moreover, the olivine diogenite band position shifts from synthetic orthopyroxene in accordance with the presence of olivine and chromite. In particular, the presence of a large olivine clast permits us to determine a linear variation of the band position from synthetic orthopyroxene and olivine, but underestimates the presence of olivine in the olivine diogenite spot.  相似文献   

Effects of urban wastewater on crab and mollusc assemblages in equatorial and subtropical mangroves of East Africa     

Stefano Cannicci  Fabrizio Bartolini  Farid Dahdouh-Guebas  Sara Fratini  Carlos Litulo  Adriano Macia  Elisha J. Mrabu  Gil Penha-Lopes  Jos Paula 《Estuarine, Coastal and Shelf Science》2009,84(3):305

Mangrove forests are known to accomplish crucial ecosystem functions and services. They are nursery areas for fish, prawns and crabs, which provide coastal communities with a variety of food, timber and chemicals, and protect coasts from catastrophic events, such as tsunamis. Recently, a novel ecological service has been proposed for mangrove systems, namely natural wastewater treatment wetlands. This hypothesis was based on experimental data collected mainly in Chinese mangrove systems, which proved that mangrove soils were efficient in absorbing nutrients. Moreover, sewage loading seemed harmless to both plants and benthic communities in these systems. However, before promoting the use of natural mangroves as pollution buffers, or constructed mangrove wetlands as sewage treatment facilities, more data are needed on their overall tolerance to organic loading. Differences in macrobenthos patterns were thus investigated between peri-urban mangroves and sites not affected by sewage disposal in East Africa. We assessed differences in epifaunal assemblages, comprising crabs and molluscs, employing multivariate ACI unbalanced analyses to compare peri-urban mangrove swamps with those characteristic of non-urban mangroves with similar ecological traits. The sampling design was spatially nested, replicates being assessed at equatorial (southern Kenya) and subtropical (southern Mozambique) sites. The results manifested a consistent increase in crab biomass at the peri-urban sites in both Kenya and Mozambique. Moreover, the peri-urban systems were richer than the non-urban mangroves, both in terms of fiddler crabs (Uca spp.) which feed on benthic microalgae and bacteria, and sesarmids, such as Perisesarma guttatum and Neosarmatium meinerti, which feed on both substratum and leaf litter. The abundance of gastropods, in contrast, decreased significantly, especially in Kenya, mainly due to the disappearance of the mud whelk Terebralia palustris. The results thus indicate that, in East African mangrove systems, domestic wastewater has detectable effects on crabs and molluscs, suggesting their usefulness as bioindicators of its effects in mangroves. Transformed benthic patterns at the peri-urban sites indicated the need for further study of the actual potential of natural mangrove forests to absorb pollution in sewage treatment.  相似文献   

Changes in biomass structure and trophic status of the plankton communities in a highly dynamic ecosystem (Gulf of Venice,Northern Adriatic Sea)     

Alessandra Pugnetti  Anna Maria Bazzoni  Alfred Beran  Fabrizio Bernardi Aubry  Elisa Camatti  Mauro Celussi  Joan Coppola  Erica Crevatin  Paola Del Negro  Alessandro Paoli 《Marine Ecology》2008,29(3):367-374

The changes in the plankton biomass structure in relation to nutrient inputs were studied in the Gulf of Venice (Northern Adriatic Sea), an area characterized by a very marked trophic state variability. The investigation was carried out at two stations, in March, May and July 2005 and 2006, considering the whole water column. The size structure (from picoplankton to mesozooplankton) of both autotrophs and heterotrophs was analysed. Signals of diluted waters and nutrient inputs were more marked in 2005 than in 2006. In 2005, the total plankton biomass was almost double (87 ± 37 μg·C·l^?1) that in 2006 (44 ± 26 μg·C·l^?1). The variations were determined mainly by phytoplankton, with a 70% decrease, and a shift from a community dominated by microphytoplankton (49 ± 12%) in 2005 to one dominated by bacteria (43 ± 11%) in 2006 was observed. The relationship between the heterotrophic (H) and autotrophic (A) biomass indicated a rapid decline of the H/A ratio with increasing phytoplankton biomass. This study, although temporally limited, is consistent with the results reported for other marine environments and it seems to confirm the importance of nutrient inputs in structuring the biomass of plankton community.  相似文献   

Cold subduction zone in northern Calabria (Italy) revealed by lawsonite–clinopyroxene blueschists     

Fabrizio Tursi  Caterina Bianco  Andrea Brogi  Alfredo Caggianelli  Giacomo Prosser  Giovanni Ruggieri  Eleonora Braschi 《Journal of Metamorphic Geology》2020,38(5):451-469

Lawsonite blueschists are important markers of cold subduction zones, subjected to intense fluid circulation. This is because lawsonite preservation in exhumed blueschists and eclogites is typically linked to cold exhumation paths, accompanied by hydration. In the Catena Costiera (Calabria, southern Italy), lawsonite–clinopyroxene blueschists of the Diamante–Terranova Unit, affected by ductile shearing and retrogression, are exposed. Blueschists contain zoned clinopyroxene crystals, showing core–rim compositional variation from diopside to omphacite and hosting primary inclusions of lawsonite and titanite. Thermodynamic modelling of phase equilibria in the NCKFMASHTO system revealed peak metamorphic conditions of 2.0–2.1 GPa and 475–490°C for the Alpine subduction in Calabria. The subsequent post-peak metamorphic evolution mainly proceeded along a decompression and cooling path up to ~1.1 GPa and ~380°C. The final exhumation stages are recorded in the sheared blueschists where a mylonitic to ultramylonitic foliation developed at ~0.7 GPa and 290–315°C. Therefore, the P–T evolution of the Diamante–Terranova blueschists mostly occurred in the stability field of lawsonite, sustained by H₂O-saturated conditions during the exhumation path. The results of this study indicate that the blueschists underwent peak metamorphic conditions higher than previously thought, reaching a maximum depth of ~70 km under a very cold geothermal gradient (~6.6°C/km), during the Eocene subduction of the Ligurian Tethys oceanic crust in Calabria.  相似文献   

GRIDA3—a shared resources manager for environmental data analysis and applications     

Fabrizio Murgia  Riccardo Biddau  Alessandro Concas  Roberto Demontis  Luca Fanfani  Zeno Heilmann  Cristian Lai  Giuditta Lecca  Eva Lorrai  Marino Marrocu  Vittorio Alessandro Marrone  Laura Muscas  Elisaveta Peneva  Andrea Piras  Massimo Pisu  Gabriella Pusceddu  Guido Satta  Daniela Theis  Andrea Vacca  Paolo Valera  Ana Melina Vallenilla Ferrara  Ernesto Bonomi 《Earth Science Informatics》2009,2(1-2):5-21

GRIDA3 (Shared Resources Manager for Environmental Data Analysis and Applications) is a multidisciplinary project designed to deliver an integrated system to forge solutions to some environmental challenges such as the constant increase of polluted sites, the sustainability of natural resources usage and the forecast of extreme meteorological events. The GRIDA3 portal is mainly based on Web 2.0 technologies and EnginFrame framework. The portal, now at an advanced stage of development, provides end-users with intuitive Web-interfaces and tools that simplify job submission to the underneath computing resources. The framework manages the user authentication and authorization, then controls the action and job execution into the grid computing environment, collects the results and transforms them into an useful format on the client side. The GRIDA3 Portal framework will provide a problem-solving platform allowing, through appropriate access policies, the integration and the sharing of skills, resources and tools located at multiple sites across federated domains.  相似文献   

Synthesis,TEM characterization and thermal behaviour of LiNiSi<Subscript>2</Subscript>O<Subscript>6</Subscript> pyroxene     

Mario Tribaudino  Geoffrey Bromiley  Haruo Ohashi  Fabrizio Nestola 《Physics and Chemistry of Minerals》2009,36(9):527-536

A pyroxene with composition LiNiSi₂O₆ was synthesized at T = 1,473 K and P = 2.0 GPa; the cell parameters at T = 298 K are a = 9.4169(6) Å, b = 8.4465(7) Å, c = 5.2464(3) Å, β = 110.534(6)°, V = 390.78(3) Å³. TEM examination of the LiNiSi₂O₆ pyroxene showed the presence of h + k odd reflections indicative of a primitive lattice, and of antiphase domains obtained by dark field imaging of the h + k odd reflections. A HT in situ investigation was performed by examining TEM selected area diffraction patterns collected at high temperature and synchrotron radiation powder diffraction. In HTTEM the LiNiSi₂O₆ was examined together with LiCrSi₂O₆ pyroxene. In LiCrSi₂O₆ the h + k odd critical reflections disappear at about 340 K; they are sharp up to the transition temperature and do not change their shape until they disappear. In LiNiSi₂O₆ the h + k odd reflections are present up to sample deterioration at 650 K. A high temperature synchrotron radiation powder diffraction investigation was performed on LiNiSi₂O₆ between 298 and 773 K. The analysis of critical reflections and of changes in cell parameters shows that the space group is P-centred up to the highest temperature. The comparative analysis of the thermal and spontaneous strain contributions in P2₁/c and C2/c pyroxenes indicates that the high temperature strain in P-LiNiSi₂O₆ is very similar to that due to thermal strain only in C2/c spodumene and that a spontaneous strain contribution related to pre-transition features is not apparent in LiNiSi₂O₆. A different high-temperature behaviour in LiNiSi₂O₆ with respect to other pyroxenes is suggested, possibly in relation with the presence of Jahn–Teller distortion of the M1 polyhedron centred by low-spin Ni³⁺.  相似文献   

Mantle degassing on a near shore volcano,SE Tyrrhenian Sea          下载免费PDF全文

Maria F. Loreto  Francesco Italiano  Davide Deponte  Lorenzo Facchin  Fabrizio Zgur 《地学学报》2015,27(3):195-205

The presence of a seamount‐like structure, located a few nautical miles offshore the Capo Vaticano Promontory (western Calabria, S Italy), was revealed by combined geophysical and geochemical investigation. The edifice covers ~55 km², with a top located at a depth of about 70 m below sea level, and consists mainly of a NW‐trending structure orthogonally interrupted by minor ridges, the largest of which is affected by extensional faults. The top of the edifice hosts active vents, injected fluids that have been investigated for dissolved volatiles. Gas analyses revealed high CO₂ and CH₄ contents, several orders of magnitude above the atmospheric‐type values expected for shallow, coastal marine waters, and a noteworthy enrichment in mantle‐derived ³He, which is an unambiguous indicator of the mantle origin of the fluids. Our results, combined with available data from the literature, suggest that the edifice is a tectonically controlled volcanic system, which presence near the Calabria region changes the role played by faults in the frame of the subduction process.  相似文献   

Melting and cataclastic features in shatter cones in basalt from the Vista Alegre impact structure,Brazil          下载免费PDF全文

Lidia Pittarello  Fabrizio Nestola  Cecilia Viti  Alvaro Penteado Crósta  Christian Koeberl 《Meteoritics & planetary science》2015,50(7):1228-1243

Shatter cones are one of the most widely recognized pieces of evidence for meteorite impact events on Earth, but the process responsible for their formation is still debated. Evidence of melting on shatter cone surfaces has been rarely reported in the literature from terrestrial impact craters but has been recently observed in impact experiments. Although several models for shatter cones formation have been proposed, so far, no one can explain all the observed features. Shatter cones' from the Vista Alegre impact structure, Brazil, formed in fine‐grained basalt of the Jurassic‐Cretaceous Serra Geral Formation (Paraná large igneous province). A continuous quenched melt film, consisting of a crystalline phase, mica, and amorphous material, decorates the striated surface. Ultracataclasites, containing subrounded pyroxene clasts in an ultrafine‐grained matrix, occur subparallel to the striated surface. Several techniques were applied to characterize the crystalline phase in the melt, including Raman spectroscopy and transmission electron microscopy. Results are not consistent with any known mineral, but they do suggest a possible rare or new type of clinopyroxene. This peculiar evidence of melting and cataclasis in relation with shatter cone surfaces is interpreted as the result of tensile fracturing at the tip of a fast propagating shock‐induced rupture, which led to the formation of shatter cones at the tail of the shock front, likely during the early stage of the impact events.  相似文献   

Joint analysis of Rayleigh- and Love-wave dispersion: Issues, criteria and improvements     

Giancarlo Dal Moro  Fabrizio Ferigo 《Journal of Applied Geophysics》2011,75(3):573-589

Joint analysis of Rayleigh- and Love-wave dispersion is performed with the aim of evaluating how their joint use can improve retrieved vertical V_S profiles. In fact, non-uniqueness of the solution and complex energy distribution among different modes represent problems which, if not properly considered, can eventually lead to ambiguous or erroneous subsurface models.Some tests performed on synthetic datasets show that for the deepest layers the improvements obtained by the joint inversion cannot be considered as fully decisive in terms of ultimate solution of non-uniqueness. Nevertheless joint analysis of dispersive properties of Rayleigh and Love waves reveals as a highly valuable tool able to clarify possible interpretation issues of the single components. Under some stratigraphical circumstances, velocity spectra of Rayleigh waves can in fact be extremely complex in terms of energy distribution among different modes and erroneous interpretations of dispersion curves can thus occur. Beneficial aspects of the joint analysis is shown in the light of possible inconsistencies of the Pareto front, since major interpretative errors can be revealed in the outcomes of the proposed inversion procedure. Two field datasets are analysed also suggesting some improvements in the field acquisition procedures aimed at the acquisition of both Rayleigh and Love waves.  相似文献