Al Huwaysah 010: The most reduced brachinite,so far     

Cristian Carli  Anna Barbaro  Mara Murri  Maria Chiara Domeneghetti  Antonio Langone  Enrico Bruschini  Alice Stephant  Matteo Alvaro  Stefania Stefani  Tiberio Cuppone  Martina Casalini  Alessandra Migliorini  Ted L. Roush  Giovanni Pratesi 《Meteoritics & planetary science》2023,58(6):855-874

Al Huwaysah 010 is an ungrouped achondrite meteorite, recently referred to as a brachinite-like meteorite. This meteorite, showing a fine-grained assemblage of low-Ca pyroxene and opaque phases, is strongly reduced in comparison to other reduced brachinites. The occurrence of some tiny plates of graphite and oldhamite in this meteorite suggests that a partial melt residue has experienced a further reduction process. Olivine, the most abundant phase, is compositionally homogeneous (Fo_83.3) as well as the clinopyroxene (En_45.5Fs_10.8Wo_43.7) and the plagioclase (Ab_69.5). Orthopyroxene (En_85.4Fs_13.9Wo_0.7) also occurs but only in a fine intergrowth. Other accessory phases are Fe metal grains (Ni-free or Cr-bearing Fe-Ni alloy), troilite, chlorapatite, pentlandite (as inclusions in chromite). The sample shows two different closure temperatures: the highest (≈900°C) is determined via the olivine–chromite intercrystalline geothermometer and the lowest temperature (≈520°C) is determined via the pyroxene-based intracrystalline geothermometer. These temperatures may represent, respectively, the closure temperature associated with the formation and a subsequent impact event excavating the sample from the parental body. The visible to near-infrared (VNIR) reflectance spectra of Al Huwaysah 010 exhibit low reflectance, consistent with the presence of darkening components, and weak absorptions indicative of olivine and pyroxene. Comparing the spectral parameters of Al Huwaysah 010 to potential parent bodies characterized by olivine–pyroxene mineralogy, we find that it falls within the field previously attributed to the SIII type asteroids. These results lead us to classify the Al Huwaysah 010 meteorite as the most reduced brachinite, whose VNIR spectral features show strong affinities with those of SIII asteroids.  相似文献   

Editorial     

Alessandra Celletti  Sylvio Ferraz-Mello 《Celestial Mechanics and Dynamical Astronomy》2014,119(3-4):219-219

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Seismic response prediction of reinforced concrete buildings through nonlinear combinations of intensity measures     

Alessandra Fiore  Fabrizio Mollaioli  Giuseppe Quaranta  Giuseppe C. Marano 《Bulletin of Earthquake Engineering》2018,16(12):6047-6076

A widespread approach for the prediction of the structural response as function of the ground motion intensity is based on the Cloud Analysis: once a set of points representing the engineering demand parameter (EDP) values is obtained as function of the selected seismic intensity measure (IM) for a collection of unscaled earthquake records, a regression analysis is performed by assuming a specific functional form to correlate these variables. Within this framework, many studies have been devoted so far to evaluate the effectiveness of several IMs in estimating the EDPs through intrinsically linear functional forms, but it is still unknown to what extent the use of the linear regression analysis affects the quality of the final results. This paper is intended to provide an answer to such question by means of the calibration of suitable nonlinear combinations of scalar IMs, whose statistical performances are compared with those obtained by using the functional form usually adopted for linear regression-based calibrations. Specifically, the Evolutionary Polynomial Regression technique is adopted to calibrate nonlinear regression models for the prediction of maximum inter-story drift ratio and maximum floor acceleration. The comparative analysis is performed for fixed-base and base-isolated reinforced concrete buildings subjected to ordinary or pulse-like ground motion taking into account accuracy, complexity, efficiency and sufficiency. Final results demonstrate that the linear regression analysis is suitable for fixed-base reinforced concrete buildings, but nonlinear regression models provide better estimates. On the other hand, the linear regression analysis can introduce a significant bias in the seismic response prediction of base-isolated buildings, and nonlinear regression models are deemed more appropriate.  相似文献   

Distinct patterns of bank erosion in a navigable regulated river     

Gonzalo Duró  Alessandra Crosato  Maarten G. Kleinhans  Timotheus G. Winkels  Hessel A.G. Woolderink  Wim S.J. Uijttewaal 《地球表面变化过程与地形》2020,45(2):361-374

Distinct bankline patterns appeared after the removal of protection works along a navigable reach of the Meuse River. A series of oblique embayments now dominate the riverine landscape after ten years of bank erosion, but their location and asymmetry cannot be explained yet. This work analyses and integrates field measurements of flow, ship waves, bank composition, bed topography and historical maps to explain the observed patterns along two reaches of the river. An extraordinary low-water-level event generated by a ship accident provided the unique opportunity to also analyse the subaqueous bank topography. The results indicate that the formation of oblique embayments arises from the combination of floodplain heterogeneity, structured by scroll-bar deposits, and the regulation of water levels, resulting in ship-wave attack at a narrow range of bank elevation for 70% of the time. Substrate erodibility acts on the effectiveness of trees to slow down local bank erosion rates, which is possibly enhanced by a positive feedback between woody roots and cohesive soil. The strong regulation of water levels and the waves generated by the intense ship traffic produce an increasingly long mildly-sloping terrace at the bank toe and progressively dominate the bank erosion process. This study demonstrates the important role of floodplain and scroll bar formation in shaping later bank erosion, which has implications for predictive numerical models, restoration strategies, and understanding the role of vegetation in bank erosion processes. © 2019 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd  相似文献   

X‐ray computed tomography: Morphological and porosity characterization of giant Antarctic micrometeorites     

Zelia Dionnet  Martin D. Suttle  Andrea Longobardo  Alessandra Rotundi  Luigi Folco  Vincenzo Della Corte  Andrew King 《Meteoritics & planetary science》2020,55(7):1581-1599

Giant micrometeorites (MMs; 400–2000 µm) are exceedingly rare and scientifically valuable. Three‐dimensional nondestructive characterization by X‐ray computed tomography (X‐CT) provides information on the petrography and thus petrogenesis of MMs and serves as a guide to maximize subsequent multi‐analytical studies on such precious planetary materials. Here, we discuss the results obtained by X‐CT on 22 giant MMs and the classification based on their 3‐D density contrast images. Scoriaceous and unmelted MMs have distinct porosity ranges (10–40 vol% versus 0–25 vol%, respectively). We observe a porosity variation inside scoriaceous MMs, which allows their atmospheric entry flight history to be resolved. For the first time, spinning entry is explicitly demonstrated for four partially melted MMs. Furthermore, we are able to resolve the thermal gradient in a single particle, based on porosity variation (seen as a progressive increase in pore abundance and size with higher peak temperatures). Moreover, we explore parent body alteration through the 3‐D analysis of pores distribution, showing that shock fabrics are either absent or weakly developed in our data set. Finally, owing to the detection of pseudomorphic chondrules, we estimate that the intensively aqueously altered C1 or CI‐like material could represent 18% of the MM flux at this size fraction (400–1000 µm).  相似文献   

New coring study in Augusta Bay expands understanding of offshore tsunami deposits (Eastern Sicily,Italy)     

Alessandra Smedile  Flavia Molisso  Catherine Chagué  Marina Iorio  Paolo Marco De Martini  Stefania Pinzi  Philip E. F. Collins  Leonardo Sagnotti  Daniela Pantosti 《Sedimentology》2020,67(3):1553-1576

Tsunami deposits present an important archive for understanding tsunami histories and dynamics. Most research in this field has focused on onshore preserved remains, while the offshore deposits have received less attention. In 2009, during a coring campaign with the Italian Navy Magnaghi, four 1 m long gravity cores (MG cores) were sampled from the northern part of Augusta Bay, along a transect in 60 to 110 m water depth. These cores were taken in the same area where a core (MS06) was collected in 2007 about 2·3 km offshore Augusta at a water depth of 72 m below sea level. Core MS06 consisted of a 6·7 m long sequence that included 12 anomalous intervals interpreted as the primary effect of tsunami backwash waves in the last 4500 years. In this study, tsunami deposits were identified, based on sedimentology and displaced benthic foraminifera (as for core MS06) reinforced by X-ray fluorescence data. Two erosional surfaces (L1 and L2) were recognized coupled with grain-size increase, abundant Posidonia oceanica seagrass remains and a significant amount of Nubecularia lucifuga, an epiphytic sessile benthic foraminifera considered to be transported from the inner shelf. The occurrence of Ti/Ca and Ti/Sr increments, coinciding with peaks in organic matter (Mo incoherent/coherent) suggests terrestrial run-off coupled with an input of organic matter. The L1 and L2 horizons were attributed to two distinct historical tsunamis (ad 1542 and ad 1693) by indirect age-estimation methods using ²¹⁰Pb profiles and the comparison of Volume Magnetic Susceptibility data between MG cores and MS06 cores. One most recent bioturbated horizon (Bh), despite not matching the above listed interpretative features, recorded an important palaeoenvironmental change that may correspond to the ad 1908 tsunami. These findings reinforce the value of offshore sediment records as an underutilized resource for the identification of past tsunamis.  相似文献   

Analytical study of the powered Swing-By maneuver for elliptical systems and analysis of its efficiency     

Alessandra F. S. Ferreira  Antônio F. B. A. Prado  Othon C. Winter  Denilson P. S. Santos 《Astrophysics and Space Science》2018,363(7):145

Analytical equations describing the velocity and energy variation of a spacecraft in a Powered Swing-By maneuver in an elliptic system are presented. The spacecraft motion is limited to the orbital plane of the primaries. In addition to gravity, the spacecraft suffers the effect of an impulsive maneuver applied when it passes by the periapsis of its orbit around the secondary body of the system. This impulsive maneuver is defined by its magnitude \(\delta V\) and the angle that defines the direction of the impulse with respect to the velocity of the spacecraft (\(\alpha\)). The maneuver occurs in a system of main bodies that are in elliptical orbits, where the velocity of the secondary body varies according to its position in the orbit following the rules of an elliptical orbit. The equations are dependent on this velocity. The study is done using the “patched-conics approximation”, which is a method of simplifying the calculations of the trajectory of a spacecraft traveling around more than one celestial body. Solutions for the velocity and energy variations as a function of the parameters that define the maneuver are presented. An analysis of the efficiency of the powered Swing-By maneuver is also made, comparing it with the pure gravity Swing-by maneuver with the addition of an impulse applied outside the sphere of influence of the secondary body. After a general study, the techniques developed here are applied to the systems Sun-Mercury and Sun-Mars, which are real and important systems with large eccentricity. This problem is highly nonlinear and the dynamics very complex, but very reach in applications.  相似文献   

The dynamics of the de Sitter resonance     

Alessandra Celletti  Fabrizio Paita  Giuseppe Pucacco 《Celestial Mechanics and Dynamical Astronomy》2018,130(2):15

We study the dynamics of the de Sitter resonance, namely the stable equilibrium configuration of the first three Galilean satellites. We clarify the relation between this family of configurations and the more general Laplace resonant states. In order to describe the dynamics around the de Sitter stable equilibrium, a one-degree-of-freedom Hamiltonian normal form is constructed and exploited to identify initial conditions leading to the two families. The normal form Hamiltonian is used to check the accuracy in the location of the equilibrium positions. Besides, it gives a measure of how sensitive it is with respect to the different perturbations acting on the system. By looking at the phase plane of the normal form, we can identify a Laplace-like configuration, which highlights many substantial aspects of the observed one.  相似文献   

An ecotoxicological protocol with caged mussels, Mytilus galloprovincialis, for monitoring the impact of an offshore platform in the Adriatic Sea     

Gorbi S  Virno Lamberti C  Notti A  Benedetti M  Fattorini D  Moltedo G  Regoli F 《Marine environmental research》2008,65(1):34-49

An ecotoxicological protocol with caged mussels, Mytilus galloprovincialis, was developed to evaluate the potential impact of an offshore gas platform in the central Adriatic Sea. Reference organisms were collected on a seasonal basis from an unpolluted site and transplanted for four weeks in both the sampling area and to the investigated platform. Chemical analyses of trace metals in mussel tissues were integrated with a multi-biomarker approach for the early detection of biological responses at several cellular targets. Induction of metallothioneins, peroxisomal proliferation and activity of acetylcholinesterase were measured as markers for specific classes of chemicals. Special attention was given to oxyradical metabolism and appearance of oxidative-mediated toxicity to reveal a more general onset of cellular disturbance. In addition to individual antioxidants (superoxide dismutase, catalase, glutathione S-transferases, glutathione reductase, Se-dependent and Se-independent glutathione peroxidases, and levels of total glutathione), the total oxyradical scavenging capacity (TOSC) allowed a quantification of the overall capability to neutralize specific forms of intracellular reactive oxygen species (ROS; i.e. peroxyl and hydroxyl radicals). Cellular damages were evaluated as lysosomal destabilization (membrane stability, accumulation of lipofuscin and neutral lipids), lipid peroxidation products (malondialdehyde) and DNA integrity (strand breaks and micronuclei); the air survival test was finally applied to evaluate the overall physiological condition of mussels. Concentration of trace metals (As, Ba, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Zn) revealed only limited variations in transplanted mussels during various experimental periods and such changes appeared partly related to natural fluctuations. Among biological responses, variations of antioxidants and lysosomal stability were confirmed as sensitive early warning signals for biological disturbance of both natural and anthropogenic origin. The presented protocol with caged mussels allowed marked biological effects caused by the investigated platform to be excluded, and represented a useful approach that is easy to extend for monitoring the impact of offshore activities in the Adriatic sea.  相似文献   

Annual dynamics of the mesozooplankton communities in a highly variable ecosystem (North Adriatic Sea,Italy)     

Elisa Camatti  Alessandra Comaschi  Alessandra De Olazabal  Serena Fonda Umani 《Marine Ecology》2008,29(3):387-398

Mesozooplankton community composition at the species/taxa level was investigated from January to December 2001, at eight stations in the northern Adriatic Sea. Annual dynamics, taxonomic composition and spatial diversity in relation to different trophic conditions are discussed as related to previous studies and to different conditions, such as the presence of mucilage events. Zooplankton communities all over the northern sub‐basin were dominated by the cladoceran Penilia avirostris in summer, and by the calanoids Paracalanus parvus, Acartia clausi and the poecilostomatoids Oncaea spp. during the rest of the year. Whereas coastal communities were more variable with time and location, we were able to identify a group of offshore stations with a similar species/taxa composition and annual dynamics. Comparing the present results with previous studies, we observed significant changes in community composition in the time scale of 20 years, mostly due to a general decrease of A. clausi as the dominant species, being replaced by P. parvus. Also, P. avirostris swarms appear to have extended their temporal occurrence, and were present for longer periods of time when compared to past records. These changes might be related to the observed general increase of the average sea water temperature in the northern Adriatic Sea.  相似文献