Gamma-ray source stacking analysis at low galactic latitudes     

Analía N. Cillis  Olaf Reimer  Diego F. Torres 《Astrophysics and Space Science》2007,309(1-4):51-55

We studied the problematic of uncertainties in the diffuse gamma radiation apparent in stacking analysis of EGRET data at low Galactic latitudes. Subsequently, we co-added maps of counts, exposure and diffuse background, and residuals, in varying numbers for different sub-categories of putatively and known source populations (like PSRs). Finally we tested for gamma-ray excess emission in those maps and attempt to quantify the systematic biases in such approach. Such kind of an analysis will help the classification processes of sources and source populations in the GLAST era.  相似文献   

Galaxy pairs in the 2dF survey – II. Effects of interactions on star formation in groups and clusters     

M. Sol Alonso  Patricia B. Tissera  Georgina Coldwell  Diego G. Lambas 《Monthly notices of the Royal Astronomical Society》2004,352(3):1081-1088

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Gravitational microlensing of γ-ray blazars     

Diego F. Torres  Gustavo E. Romero  Ernesto F. Eiroa  Joachim Wambsganss  Martín E. Pessah 《Monthly notices of the Royal Astronomical Society》2003,339(2):335-352

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Star formation in quasar and active galaxy environments     

Georgina V. Coldwell  Diego G. Lambas† 《Monthly notices of the Royal Astronomical Society》2003,344(1):156-160

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Filtering techniques for the detection of Sunyaev–Zel'dovich clusters in multifrequency maps     

D. Herranz  J. L. Sanz  M. P. Hobson  R. B. Barreiro  †  J. M. Diego  E. Martínez-González  A. N. Lasenby 《Monthly notices of the Royal Astronomical Society》2002,336(4):1057-1068

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Imaging the Seismic Crustal Structure of the Western Mexican Margin between 19°N and 21°N     

Rafael Bartolomé  Juanjo Dañobeitia  François Michaud  Diego Córdoba  Luis A. Delgado-Argote 《Pure and Applied Geophysics》2011,168(8-9):1373-1389

Three thousand kilometres of multichannel (MCS) and wide-angle seismic profiles, gravity and magnetic, multibeam bathymetry and backscatter data were recorded in the offshore area of the west coast of Mexico and the Gulf of California during the spring 1996 (CORTES survey). The seismic images obtained off Puerto Vallarta, Mexico, in the Jalisco subduction zone extend from the oceanic domain up to the continental shelf, and significantly improve the knowledge of the internal crustal structure of the subduction zone between the Rivera and North American (NA) Plates. Analyzing the crustal images, we differentiate: (1) An oceanic domain with an important variation in sediment thickness ranging from 2.5 to 1 km southwards; (2) an accretionary prism comprised of highly deformed sediments, extending for a maximum width of 15 km; (3) a deformed forearc basin domain which is 25 km wide in the northern section, and is not seen towards the south where the continental slope connects directly with the accretionary prism and trench, thus suggesting a different deformational process; and (4) a continental domain consisting of a continental slope and a mid slope terrace, with a bottom simulating reflector (BSR) identified in the first second of the MCS profiles. The existence of a developed accretionary prism suggests a subduction–accretion type tectonic regime. Detailed analysis of the seismic reflection data in the oceanic domain reveals high amplitude reflections at around 6 s [two way travel time (twtt)] that clearly define the subduction plane. At 2 s (twtt) depth we identify a strong reflection which we interpret as the Moho discontinuity. We have measured a mean dip angle of 7° ± 1° at the subduction zone where the Rivera Plate begins to subduct, with the dip angle gently increasing towards the south. The oceanic crust has a mean crustal thickness of 6.0–6.5 km. We also find evidence indicating that the Rivera Plate possibly subducts at very low angles beneath the Tres Marias Islands.  相似文献   

Plastic ingestion in Franciscana dolphins, Pontoporia blainvillei (Gervais and d'Orbigny, 1844), from Argentina     

Denuncio P  Bastida R  Dassis M  Giardino G  Gerpe M  Rodríguez D 《Marine pollution bulletin》2011,62(8):1836-1841

Plastic debris (PD) ingestion was examined in 106 Franciscana dolphins (Pontoporia blainvillei) incidentally captured in artisanal fisheries of the northern coast of Argentina. Twenty-eight percent of the dolphins presented PD in their stomach, but no ulcerations or obstructions were recorded in the digestive tracts. PD ingestion was more frequent in estuarine (34.6%) than in marine (19.2%) environments, but the type of debris was similar. Packaging debris (cellophane, bags, and bands) was found in 64.3% of the dolphins, with a lesser proportion (35.7%) ingesting fishery gear fragments (monofilament lines, ropes, and nets) or of unknown sources (25.0%). PD ingestion correlated with ontogenetic changes in feeding regimes, reaching maximum values in recently weaned dolphins. Because a simultaneous increase in gillnet entanglement and the bioaccumulation of heavy metals take place at this stage, the first months after trophic independence should be considered as a key phase for the conservation of Franciscana dolphin stocks in northern Argentina.  相似文献   

Enhancement of magma mixing efficiency by chaotic dynamics: an experimental study   总被引：2，自引：0，他引：2  

Cristina P. De Campos  Diego Perugini  Werner Ertel-Ingrisch  Donald B. Dingwell  Giampiero Poli 《Contributions to Mineralogy and Petrology》2011,161(6):863-881

Magma mixing is common in the Earth. Understanding the dynamics of the mixing process is necessary for dealing with the likely consequences of mixing events in the petrogenesis of igneous rocks and the physics of volcanic eruptive triggers. Here, a new apparatus has been developed in order to perform chaotic mixing experiments in systems of melts with high viscosity contrast. The apparatus consists of an outer and an inner cylinder, which can be independently rotated at finite strains to generate chaotic streamlines. The two cylinder axes are offset. Experiments have been performed for ca. 2 h, at 1,400°C under laminar fluid dynamic conditions (Re ~ 10⁻⁷). Two end-member silicate melt compositions were synthesized: (1) a peralkaline haplogranite and (2) a haplobasalt. The viscosity ratio between these two melts was of the order of 10³. Optical analysis of post-experimental samples reveals a complex pattern of mingled filaments forming a scale-invariant (i.e. fractal) distribution down to the μm-scale, as commonly observed in natural samples. This is due to the development in space and time of stretching and folding of the two melts. Chemical analysis shows strong non-linear correlations in inter-elemental plots. The original end-member compositions have nearly entirely disappeared from the filaments. The generation of thin layers of widely compositionally contrasting interfaces strongly enhances chemical diffusion producing a remarkable modulation of compositional fields over a short-length scale. Notably, diffusive fractionation generates highly heterogeneous pockets of melt, in which depletion or enrichment of chemical elements occur, depending on their potential to spread via chemical diffusion within the magma mixing system. Results presented in this work offer new insights into the complexity of processes expected to be operating during magma mixing and may have important petrological implications. In particular: (1) it is shown that, in contrast with current thinking, rheologically contrasting magmas can mix (i.e. with large proportions of felsic magmas and high viscosity ratios), thus extending significantly the spectrum of geological conditions under which magma mixing processes can occur efficiently; (2) the mixing process cannot be modeled using the classical linear two-end-member mixing model; and (3) the chemical compositions on short-length scales represent snapshots within the process of mixing and therefore may not reflect the final composition of the magmatic system. This study implies that microanalysis on short-length scales may provide misleading information on the parental composition of magmas.  相似文献   

Palaeoenvironmental forcing during the Middle-Upper Palaeolithic transition in central-western Portugal     

Thierry Aubry  Miguel Almeida  Diego E. Angelucci 《Quaternary Research》2011,75(1):66-79

Geoarchaeological analysis of the Middle and Upper Palaeolithic record preserved in cave, rock-shelter and open-air sites in the northern sector of the Meso-Cenozoic of the Western Iberian Peninsula margin (Portugal) reveals several disconformities (erosive unconformities), hiatuses and surface stabilization phases. A recurrent disconformity, dated to ca. 29,500-32,000 cal yr BP, in the time range of Heinrich event 3, must correspond to a main erosive event related to the impacts of climate change on the landscape, including a reduction in vegetation cover and altered precipitation patterns, with the consequent accelerated down-cutting by stream systems, slope reactivation and endokarstic reorganisation, causing the erosion of sediments and soils accumulated in cave, rock-shelter and open-air sites. These processes create a preservation bias that may explain why Early Upper Palaeolithic finds in primary deposition context remains exceptional in the carbonate areas of central-western Portugal, and possibly elsewhere in the other places of Iberia. The impact of such site formation processes must therefore be duly considered in interpretations of the current patchy and scarce archaeological record of the Middle-Upper Palaeolithic transition in south-western Iberia.  相似文献   

Thermo-elastic behaviour of Be2BO3OH (hambergite) up to 7 GPa and 1,100 K     

G. Diego Gatta  Paolo Lotti  Fabrizio Nestola  Marco Merlini  Daria Pasqual  Andrea Lausi 《Physics and Chemistry of Minerals》2013,40(5):401-409

The thermo-elastic behaviour of Be₂BO₃(OH)_0.96F_0.04 (i.e. natural hambergite, Z = 8, a = 9.7564(1), b = 12.1980(2), c = 4.4300(1) Å, V = 527.21(1) ų, space group Pbca) has been investigated up to 7 GPa (at 298 K) and up to 1,100 K (at 0.0001 GPa) by means of in situ single-crystal X-ray diffraction and synchrotron powder diffraction, respectively. No phase transition or anomalous elastic behaviour has been observed within the pressure range investigated. P?V data fitted to a third-order Birch–Murnaghan equation of state give: V ₀ = 528.89(4) ų, K _T0 = 67.0(4) GPa and K′ = 5.4(1). The evolution of the lattice parameters with pressure is significantly anisotropic, being: K _T0(a):K _T0(b):K _T0(c) = 1:1.13:3.67. The high-temperature experiment shows evidence of structure breakdown at T > 973 K, with a significant increase in the full-width-at-half-maximum of all the Bragg peaks and an anomalous increase in the background of the diffraction pattern. The diffraction pattern was indexable up to 1,098 K. No new crystalline phase was observed up to 1,270 K. The diffraction data collected at room-T after the high-temperature experiment showed that the crystallinity was irreversibly compromised. The evolution of axial and volume thermal expansion coefficient, α, with T was described by the polynomial function: α(T) = α ₀ + α ₁ T ^?1/2. The refined parameters for Be₂BO₃(OH)_0.96F_0.04 are: α ₀ = 7.1(1) × 10^?5 K^?1 and α ₁ = ?8.9(2) × 10^?4 K ^?1/2 for the unit-cell volume, α ₀(a) = 1.52(9) × 10^?5 K^?1 and α ₁(a) = ?1.4(2) × 10^?4 K ^?1/2 for the a-axis, α ₀(b) = 4.4(1) × 10^?5 K^?1 and α ₁(b) = ?5.9(3) × 10^?4 K ^?1/2 for the b-axis, α ₀(c) = 1.07(8) × 10^?5 K^?1 and α ₁(c) = ?1.5(2) × 10^?4 K ^?1/2 for the c-axis. The thermo-elastic anisotropy can be described, at a first approximation, by α ₀(a):α ₀(b):α ₀(c) = 1.42:4.11:1. The main deformation mechanisms in response to the applied temperature, based on Rietveld structure refinement, are discussed.  相似文献