Polarization light curves and position angle variation of beamed gamma-ray bursts     

Gabriele Ghisellini  Davide Lazzati 《Monthly notices of the Royal Astronomical Society》1999,309(1):L7-L11

The recently detected linear polarization in the optical light curve of GRB 990510 renewed interest in how polarization can be produced in gamma-ray burst fireballs. Here we present a model based on the assumption that we are seeing a collimated fireball, observed slightly off-axis. This introduces some degree of anisotropy, and makes it possible to observe a linearly polarized flux even if the magnetic field is completely tangled in the plane orthogonal to the line of sight. We construct the light curve of the polarization flux, showing that it is always characterized by two maxima, with the polarization position angle changing by 90° between the first and the second maximum. The very same geometry as assumed here implies that the total flux initially decays in time as a power law, but gradually steepens as the bulk Lorentz factor of the fireball decreases.  相似文献   

Zn-Al-rich chlorite in interleaved phyllosilicate grains from the low-temperature metamorphic Ordovician terrane of Iglesiente,south-west Sardinia,Italy     

Gabriele Cruciani  Marcello Franceschelli  Stefano Battaglia  Sandro Pasci  Mariano Puxeddu 《Mineralogy and Petrology》2015,109(6):713-718

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Improved evaluation of inelastic displacement demands for short‐period masonry structures          下载免费PDF全文

Gabriele Guerrini  Francesco Graziotti  Andrea Penna  Guido Magenes 《地震工程与结构动力学》2017,46(9):1411-1430

This work discusses the simplified estimation of earthquake‐induced nonlinear displacement demands as required by nonlinear static procedures, with particular attention on short‐period masonry structures. The study focuses on systems with fundamental periods between 0.1 and 0.5 s, for which inelastic amplification of the elastic displacement demand is more pronounced; hysteretic force‐displacement relationships characteristic of masonry structures are adopted, because these structures are more commonly found within the considered period range. Referring to the results of nonlinear dynamic analyses of single‐degree‐of‐freedom oscillators, some limitations of the Eurocode 8 and Italian Building Code formulations are first discussed, then an improved equation is calibrated that relates inelastic and elastic displacement demands. Numerical values of the equation parameters are obtained, considering the amount of hysteretic energy dissipation associated with various damage mechanisms observed in masonry structures. Safety factors are also calculated to determine several percentiles of the displacement demand. It is shown that the proposed equation can be extended to more dissipative systems. Finally, the same formulation is adapted to the estimation of seismic displacements when elastic analysis procedures are employed. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Detrital zircon multi‐chronology,provenance, and low‐grade metamorphism of the Cretaceous Shimanto accretionary complex,eastern Shikoku,Southwest Japan: Tectonic evolution in response to igneous activity within a subduction zone          下载免费PDF全文

Hidetoshi Hara  Yoshihiro Nakamura  Kousuke Hara  Toshiyuki Kurihara  Hiroshi Mori  Hideki Iwano  Tohru Danhara  Shuhei Sakata  Takafumi Hirata 《Island Arc》2017,26(6)

Detrital zircon multi‐chronology combined with provenance and low‐grade metamorphism analyses enables the reinterpretation of the tectonic evolution of the Cretaceous Shimanto accretionary complex in Southwest Japan. Detrital zircon U–Pb ages and provenance analysis defines the depositional age of trench‐fill turbidites associated with igneous activity in provenance. Periods of low igneous activity are recorded by youngest single grain zircon U–Pb ages (YSG) that approximate or are older than the depositional ages obtained from radiolarian fossil‐bearing mudstone. Periods of intensive igneous activity recorded by youngest cluster U–Pb ages (YC1σ) that correspond to the younger limits of radiolarian ages. The YC1σ U–Pb ages obtained from sandstones within mélange units provide more accurate younger depositional ages than radiolarian ages derived from mudstone. Determining true depositional ages requires a combination of fossil data, detrital zircon ages, and provenance information. Fission‐track ages using zircons estimated YC1σ U–Pb ages are useful for assessing depositional and annealing ages for the low‐grade metamorphosed accretionary complex. These new dating presented here indicates the following tectonic history of the accretionary wedge. Evolution of the Shimanto accretionary complex from the Albian to the Turonian was caused by the subduction of the Izanagi plate, a process that supplied sediments via the erosion of Permian and Triassic to Early Jurassic granitic rocks and the eruption of minor amounts of Early Cretaceous intermediate volcanic rocks. The complex subsequently underwent intensive igneous activity from the Coniacian to the early Paleocene as a result of the subduction of a hot and young oceanic slab, such as the Kula–Pacific plate. Finally, the major out‐of‐sequence thrusts of the Fukase Fault and the Aki Tectonic Line formed after the middle Eocene, and this reactivation of the Shimanto accretionary complex as a result of the subduction of the Pacific plate.  相似文献   

The importance of heating duration for Raman CM thermometry: evidence from contact metamorphism around the Great Whin Sill intrusion,UK          下载免费PDF全文

H. Mori  N. Mori  S. Wallis  R. Westaway  C. Annen 《Journal of Metamorphic Geology》2017,35(2):165-180

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Grain-size influence on the mid-infrared spectra of the minerals     

Gabriele Arnold  Christoph Wagner 《Earth, Moon, and Planets》1988,41(2):163-171

Measurements of spectral emittance at wavelengths from 5 to 25 m were carried out for various particulate rocks and minerals (granite, calcite, talk) in dependence on particle size. The experimentally found variation of spectral features with particle size is discussed in terms of photon's mean free path and its dependence on particle size in the wavelength regions characterized by normal and anomalous dispersion, respectively. Moreover, a sample consisting of fine- and coarse-grained material was investigated in order to estimate the chance for mineral identification at conditions relevant to remote sensing of planetary objects. The mixture spectrum comprises characteristic features of both grain size fractions. This implies that the mineralogical composition of the fine-grained fraction also should be accessible by use of high-sensitive spectrometers.  相似文献   

Is the Linné impact crater morphology influenced by the rheological layering on the Moon's surface? Insights from numerical modeling          下载免费PDF全文

Elena Martellato  Valerio Vivaldi  Matteo Massironi  Gabriele Cremonese  Francesco Marzari  Andrea Ninfo  Junichi Haruyama 《Meteoritics & planetary science》2017,52(7):1388-1411

Linné is a simple crater, with a diameter of 2.23 km and a depth of 0.52 km, located in northwestern Mare Serenitatis. Recent high‐resolution data acquired by the Lunar Reconnaissance Orbiter Camera revealed that the shape of this impact structure is best described by an inverted truncated‐cone. We perform morphometric measurements, including slope and profile curvature, on the Digital Terrain Model of Linné, finding the possible presence of three subtle topographic steps, at the elevation of +20, ?100, and ?200 m relative to the target surface. The kink at ?100 m might be related to the interface between two different rheological layers. Using the iSALE shock physics code, we numerically model the formation of Linné crater to derive hints on the possible impact conditions and target physical properties. In the initial setup, we adopt a basaltic projectile impacting the Moon with a speed of 18 km s^?1. For the local surface, we consider either one or two layers, in order to test the influence of material properties or composite rheologies on the final crater morphology. The one‐layer model shows that the largest variations in the crater shape take place when either the cohesion or the friction coefficient is varied. In particular, a cohesion of 10 kPa marks the threshold between conical‐ and parabolic‐shaped craters. The two‐layer model shows that the interface between the two layers would be exposed at the observed depth of 100 m when an intermediate value (~200 m) for the upper fractured layer is set. We have also found that the truncated‐cone morphology of Linné might originate from an incomplete collapse of the crater wall, as the breccia lens remains clustered along the crater walls, while the high‐albedo deposit on the crater floor can be interpreted as a very shallow lens of fallout breccia. The modeling analysis allows us to derive important clues on the impactor size (under the assumption of a vertical impact and collision velocity equal to the mean value), and on the approximate, large‐scale preimpact target properties. Observations suggest that these large‐scale material properties likely include some important smaller scale variations, disclosed as subtle morphological steps in the crater walls. Furthermore, the modeling results allow advancing some hypotheses on the geological evolution of the Mare Serenitatis region where Linné crater is located (unit S14). We suggest that unit S14 has a thickness of at least a few hundreds of meters up to about 400 m.  相似文献   

Assessing space–time variations of denudation processes and related soil loss from 1955 to 2016 in southern Italy (Calabria region)     

Massimo Conforti  Gabriele Buttafuoco 《Environmental Earth Sciences》2017,76(13):457

Studies on denudation processes and soil loss rates can provide insight into the landscape evolution, climate change, and human activities, as well as on land degradation risk. The aims of this study were to analyze the space–time distribution of denudation processes and evaluate the soil loss changes occurred during the period 1955–2016 by using an approach integrating geomorphological, geospatial and modeling analysis. The study area is a representative stream catchment of the Crati Valley (Calabria, southern Italy), which is affected by severe erosion processes. The combined use of aerial photographs interpretation, field survey, geostatistics, and GIS processing has allowed to characterize the types of denudation processes and land use change in space and time. Revised universal soil loss equation implemented in GIS environment was used to estimate the space–time pattern of soil loss and the soil erosion rates for each investigated year. The results showed that from 1955 to 2016, the study area was highly affected by denudation processes, mainly related to landslides and water erosion (slope wash erosion and gully erosion). Comparison of denudation processes maps showed that the total area affected by erosion processes has increased by about 31% and the distribution of geomorphic processes and their space–time evolution resulted from the complex interrelation between geoenvironmental features and human activities. The main land use changes concerned a decrease in areas covered by woodland, scrubland and pasture and an increase in croplands and barren lands that favored erosion processes. The most susceptible areas to soil loss in both years were mapped, and the mean soil loss rates for the study area were 6.33 Mg ha^?1 y^?1 in 1955 and 10.38 Mg ha^?1 y^?1 in 2016. Furthermore, the soil loss in 2016 has increased by about 64% compared to 1955. Finally, the results showed that integrating multi-temporal analysis of denudation processes, land use changes and soil loss rates might provide significant information on landscape evolution which supports decision makers in defining soil management and conservation practices.  相似文献   

A geostatistical approach for mapping and uncertainty assessment of geogenic radon gas in soil in an area of southern Italy   总被引：2，自引：2，他引：0  

Gabriele Buttafuoco  Adalisa Tallarico  Giovanni Falcone  Ilaria Guagliardi 《Environmental Earth Sciences》2010,61(3):491-505

Spatial distribution of concentrations of radon gas in the soil is important for defining high risk areas because geogenic radon is the major potential source of indoor radon concentrations regardless of the construction features of buildings. An area of southern Italy (Catanzaro-Lamezia plain) was surveyed to study the relationship between radon gas concentrations in the soil, geology and structural patterns. Moreover, the uncertainty associated with the mapping of geogenic radon in soil gas was assessed. Multi-Gaussian kriging was used to map the geogenic soil gas radon concentration, while conditional sequential Gaussian simulation was used to yield a series of stochastic images representing equally probable spatial distributions of soil radon across the study area. The stochastic images generated by the sequential Gaussian simulation were used to assess the uncertainty associated with the mapping of geogenic radon in the soil and they were combined to calculate the probability of exceeding a specified critical threshold that might cause concern for human health. The study showed that emanation of radon gas radon was also dependent on geological structure and lithology. The results have provided insight into the influence of basement geochemistry on the spatial distribution of radon levels at the soil/atmosphere interface and suggested that knowledge of the geology of the area may be helpful in understanding the distribution pattern of radon near the earth’s surface.  相似文献   

Biogeochemical processes involving dissolved CO2 and CH4 at Albano, Averno, and Monticchio meromictic volcanic lakes (Central–Southern Italy)     

Jacopo Cabassi  Franco Tassi  Orlando Vaselli  Jens Fiebig  Matteo Nocentini  Francesco Capecchiacci  Dmitri Rouwet  Gabriele Bicocchi 《Bulletin of Volcanology》2013,75(1):1-19

This paper focuses on the chemical and isotopic features of dissolved gases (CH₄ and CO₂) from four meromictic lakes hosted in volcanic systems of Central–Southern Italy: Lake Albano (Alban Hills), Lake Averno (Phlegrean Fields), and Monticchio Grande and Piccolo lakes (Mt. Vulture). Deep waters in these lakes are characterized by the presence of a significant reservoir of extra-atmospheric dissolved gases mainly consisting of CH₄ and CO₂. The δ¹³C-CH₄ and δD-CH₄ values of dissolved gas samples from the maximum depths of the investigated lakes (from ?66.8 to ?55.6?‰ V-PDB and from ?279 to ?195?‰ V-SMOW, respectively) suggest that CH₄ is mainly produced by microbial activity. The δ¹³C-CO₂ values of Lake Grande, Lake Piccolo, and Lake Albano (ranging from ?5.8 to ?0.4?‰ V-PDB) indicate a significant CO₂ contribution from sublacustrine vents originating from (1) mantle degassing and (2) thermometamorphic reactions involving limestone, i.e., the same CO₂ source feeding the regional thermal and cold CO₂-rich fluid emissions. In contrast, the relatively low δ¹³C-CO₂ values (from ?13.4 to ?8.2?‰ V-PDB) of Lake Averno indicate a prevalent organic CO₂. Chemical and isotopic compositions of dissolved CO₂ and CH₄ at different depths are mainly depending on (1) CO₂ inputs from external sources (hydrothermal and/or anthropogenic); (2) CO₂–CH₄ isotopic exchange; and (3) methanogenic and methanotrophic activity. In the epilimnion, vertical water mixing, free oxygen availability, and photosynthesis cause the dramatic decrease of both CO₂ and CH₄ concentrations. In the hypolimnion, where the δ¹³C-CO₂ values progressively increase with depth and the δ¹³C-CH₄ values show an opposite trend, biogenic CO₂ production from CH₄ using different electron donor species, such as sulfate, tend to counteract the methanogenesis process whose efficiency achieves its climax at the water–bottom sediment interface. Theoretical values, calculated on the basis of δ¹³C-CO₂ values, and measured δ¹³C_TDIC values are not consistent, indicating that CO₂ and the main carbon-bearing ion species (HCO₃ ^?) are not in isotopic equilibrium, likely due to the fast kinetics of biochemical processes involving both CO₂ and CH₄. This study demonstrates that the vertical patterns of the CO₂/CH₄ ratio and of δ¹³C-CO₂ and δ¹³C-CH₄ are to be regarded as promising tools to detect perturbations, related to different causes, such as changes in the CO₂ input from sublacustrine springs, that may affect aerobic and anaerobic layers of meromictic volcanic lakes.  相似文献