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221.
Roberto Bruno Raffaella DAmicis Bruno Bavassano Vincenzo Carbone Luca Sorriso-Valvo 《Planetary and Space Science》2007,55(15):2233-2238
The interplanetary medium is characterized by a very high Reynolds number and is pervaded by fluctuations providing information on a wide range of scales, from fractions of second up to the solar rotation period. In the past decade or so, turbulence in the solar wind has been used as a large wind tunnel to investigate scaling laws of turbulent fluctuations and multifractal models. Moreover, new interesting insights in the theory of turbulence have been derived from the point of view which considers a turbulent flow as a complex system, a sort of benchmark for the theory of dynamical systems. Important finding like the lack of a strict self-similarity of the fluctuations with the consequent nonapplicability of strict scale invariance, the strong anisotropy of velocity and magnetic field fluctuations, the clear lack of equipartition between magnetic and kinetic fluctuations all contributed to suggest the idea that interplanetary fluctuations could possibly be due to a mixture of propagating waves and static structures convected by the wind. In this paper we further discuss this point and bring new evidence about the fact that the presence of a background magnetic field introduces not only a symmetry breaking in interplanetary space but also organizes fluctuations about its large scale orientation. 相似文献
222.
Jaime E. Forero-Romero Jérémy Blaizot Julien Devriendt Ludovic Van Waerbeke Bruno Guiderdoni 《Monthly notices of the Royal Astronomical Society》2007,379(4):1507-1518
We present the Lensed Mock Map Facility ( lemomaf ), a tool designed to perform mock weak-lensing measurements on numerically simulated chunks of the Universe. Coupling N -body simulations to a semi-analytical model of galaxy formation, lemomaf can create realistic lensed images and mock catalogues of galaxies, at wavelengths ranging from the ultraviolet to the submillimetre. To demonstrate the power of such a tool, we compute predictions of the source–lens clustering (SLC) effect on the convergence statistics, and quantify the impact of weak lensing on galaxy counts in two different filters. We find that the SLC effect skews the probability density function of the convergence towards low values, with an intensity which strongly depends on the redshift distribution of galaxies. On the other hand, the degree of enhancement or depletion in galaxy counts due to weak lensing is independent of the SLC effect. We discuss the impact on the two-point shear statistics to be measured by future missions like SNAP and LSST . The SLC effect would bias the estimation of σ8 from two-point statistics up to 5 per cent for a narrow redshift distribution of mean z ∼ 0.5 , and up to 2 per cent in small angular scales for a redshift distribution of mean z ∼ 1.5 . We conclude that accurate photometric redshifts for individual galaxies are necessary in order to quantify and isolate the SLC effect. 相似文献
223.
Equilibration Scales in Silicic to Intermediate Magmas Implications for Experimental Studies 总被引:5,自引:0,他引:5
Pichavant Michel; Costa Fidel; Burgisser Alain; Scaillet Bruno; Martel Caroline; Poussineau Stephane 《Journal of Petrology》2007,48(10):1955-1972
Experimental phase equilibrium studies are increasingly beingused for the determination of intensive variables (P, T, fH2O,fO2 ) in silicic to intermediate magmas. In contrast, silicicigneous bodies are now perceived as open, periodically recharged,systems involving only limited chemical equilibration. Thus,the use of laboratory-determined crystal–liquid equilibriumdata needs clarification. Here we review the field, petrologicaland geochemical evidence concerning states and scales of chemicalequilibrium in silicic magma bodies. It is concluded that totalchemical equilibrium is generally not the rule. However, a subsystemin local equilibrium (the reactive magma) can be identified.Equilibration scales in silicic magmas are rate-limited eitherby diffusive flux in crystals (DICL regime) or by diffusiveflux in the melt (MD regime). The recognition that equilibriumin magmas is limited to a reactive subsystem requires phaseequilibrium studies to be chemically scaled. Experiments, eitherof total or partial equilibrium type, should aim at a closereproduction of equilibrium states specific to natural systems.The laboratory reconstruction of the natural equilibrium statesguarantees a precise determination of the pre-eruptive parametersand a reliable application of the experimental data to activevolcanic systems. KEY WORDS: silicic magmas; chemical equilibrium; timescales; experimental studies 相似文献
224.
Oxygen isotope systematics of gem corundum deposits in Madagascar: relevance for their geological origin 总被引:1,自引:1,他引:1
Gaston Giuliani Anthony Fallick Michel Rakotondrazafy Daniel Ohnenstetter Alfred Andriamamonjy Théogène Ralantoarison Saholy Rakotosamizanany Marie Razanatseheno Yohann Offant Virginie Garnier Christian Dunaigre Dietmar Schwarz Alain Mercier Voahangy Ratrimo Bruno Ralison 《Mineralium Deposita》2007,42(3):251-270
The oxygen isotopic composition of gem corundum was measured from 22 deposits and occurrences in Madagascar to provide a gemstone
geological identification and characterization. Primary corundum deposits in Madagascar are hosted in magmatic (syenite and
alkali basalt) and metamorphic rocks (gneiss, cordieritite, mafic and ultramafic rocks, marble, and calc-silicate rocks).
In both domains the circulation of fluids, especially along shear zones for metamorphic deposits, provoked in situ transformation
of the corundum host rocks with the formation of metasomatites such as phlogopite, sakenite, and corundumite. Secondary deposits
(placers) are the most important economically and are contained in detrital basins and karsts. The oxygen isotopic ratios
(18O/16O) of ruby and sapphire from primary deposits are a good indicator of their geological origin and reveal a wide range of δ18O (Vienna Standard Mean Ocean Water) between 1.3 and 15.6‰. Metamorphic rubies are defined by two groups of δ18O values in the range of 1.7 to 2.9‰ (cordieritite) and 3.8 to 6.1‰ (amphibolite). “Magmatic” rubies from pyroxenitic xenoliths
contained in the alkali basalt of Soamiakatra have δ18O values ranging between 1.3 and 4.7‰. Sapphires are classified into two main groups with δ18O in the range of 4.7 to 9.0‰ (pyroxenite and feldspathic gneiss) and 10.7 to 15.6‰ (skarn in marble from Andranondambo).
The δ18O values for gem corundum from secondary deposits have a wide spread between −0.3 and 16.5‰. The ruby and sapphire found in
placers linked to alkali basalt environments in the northern and central regions of Madagascar have consistent δ18O values between 3.5 and 6.9‰. Ruby from the placers of Vatomandry and Andilamena has δ18O values of 5.9‰, and between 0.5 and 4.0‰, respectively. The placers of the Ilakaka area are characterized by a huge variety
of colored sapphires and rubies, with δ18O values between −0.3 and 16.5‰, and their origin is debated. A comparison with oxygen isotope data obtained on gem corundum
from Eastern Africa, India, and Sri Lanka is presented. Giant placer deposits from Sri Lanka, Madagascar, and Tanzania have
a large variety of colored sapphires and rubies with a large variation in δ18O due to mingling of corundum of different origin: mafic and ultramafic rocks for ruby, desilicated pegmatites for blue sapphire,
syenite for yellow, green, and blue sapphire, and skarn in marbles for blue sapphire. 相似文献
225.
226.
Bruno Pavoni Elena Centanni Sara Valcanover Marco Fasolato Silvia Ceccato Davide Tagliapietra 《Marine pollution bulletin》2007,55(10-12):505
Specimens of Nassarius nitidus were collected in seven stations of the Venice Lagoon to assess the levels of tributyltin (TBT) and its metabolites monobutyltin and dibutyltin in the tissues and monitor their effect on organisms, in particular the phenomenon of imposex (superimposition of male sexual characteristics on females). The following values of population indices were found: vas deferens sequence: 1.2 ± 0.7–4.0 ± 0.5; relative penis length: 6–47%. The least impacted station was situated in the northern part of the Lagoon, where females without imposex were found and Butyltin (BuTs) concentrations in the organisms (average sum of BuTs = 43 ± 14 ng Sn g−1 w.) were significantly lower than in the other stations (range of average sum of BuTs: 101 ± 22–217 ± 27 ng Sn g−1 d.w.). Population indices were found to be related to the TBT content in the tissues. In particular VDSI had a significant logarithmic correlation: r = 0.95, n = 8, p < 0.05. 相似文献
227.
M. Tribaudino P. Benna F. Nestola C. Meneghini E. Bruno 《Physics and Chemistry of Minerals》2005,32(4):314-321
In situ high-temperature synchrotron radiation powder diffraction patterns were taken from room temperature to T = 740°C from synthetic feldspars along the join CaAl2Si2O8–SrAl2Si2O8 (An–SrF). Three samples of composition An95SrF5, An90SrF10 and An85SrF15 were investigated, and the evolution of cell parameters with T was determined by Rietveld analysis of powder X-ray diffraction patterns. The high-temperature $P\bar 1{\text{-}}I\bar 1$ phase transition, previously observed with T c = 241°C in anorthite, was found in An95SrF5, An90SrF10 and An85SrF15 feldspars at T c = 233(5)°, 195(2)° and 174(2)°C respectively. The transition was revealed by the disappearance of critical reflections and variations in the rate of change of cell parameters with temperature. A significant, although small (between 0.0025 and 0.0012 at room temperature), spontaneous strain could be measured, allowing the thermodynamic behaviour of the transition to be modelled. A second-order trend for An90SrF10 and An85SrF15 [β = 0.504(7) and 0.505(7) respectively] or nearly second-order for An95SrF5[β = 0.458(4)] was observed in contrast with tricritical behaviour of end member anorthite. An extrapolation of the T c versus composition to room temperature indicates that the critical composition for the $P\bar 1$ phase is An60SrF40. 相似文献
228.
Measurements of the vertical and latitudinal variations of temperature and C2H2 and C2H6 abundances in the stratosphere of Saturn can be used as stringent constraints on seasonal climate models, photochemical models, and dynamics. The summertime photochemical loss timescale for C2H6 in Saturn's middle and lower stratosphere (∼40-10,000 years, depending on altitude and latitude) is much greater than the atmospheric transport timescale; ethane observations may therefore be used to trace stratospheric dynamics. The shorter chemical lifetime for C2H2 (∼1-7 years depending on altitude and latitude) makes the acetylene abundance less sensitive to transport effects and more sensitive to insolation and seasonal effects. To obtain information on the temperature and hydrocarbon abundance distributions in Saturn's stratosphere, high-resolution spectral observations were obtained on September 13-14, 2002 UT at NASA's IRTF using the mid-infrared TEXES grating spectrograph. At the time of the observations, Saturn was at a LS≈270°, corresponding to Saturn's southern summer solstice. The observed spectra exhibit a strong increase in the strength of methane emission at 1230 cm−1 with increasing southern latitude. Line-by-line radiative transfer calculations indicate that a temperature increase in the stratosphere of ≈10 K from the equator to the south pole between 10 and 0.01 mbar is implied. Similar observations of acetylene and ethane were also recorded. We find the 1.16 mbar mixing ratio of C2H2 at −1° and −83° planetocentric latitude to be and , respectively. The C2H2 mixing ratio at 0.12 mbar is found to be at −1° planetocentric latitude and at −83° planetocentric latitude. The 2.3 mbar mixing ratio of C2H6 inferred from the data is and at −1° and −83° planetocentric latitude, respectively. Further observations, creating a time baseline, will be required to completely resolve the question of how much the latitudinal variations of C2H2 and C2H6 are affected by seasonal forcing and/or stratospheric circulation. 相似文献
229.
230.
Bruno Cordani 《Celestial Mechanics and Dynamical Astronomy》2004,89(2):165-179
A method for the expansion of the perturbative Hamiltonian in the planetary problem is presented, which allows one to immediately
detect the terms vanishing under the averaging process. The method bases itself on a geometrical analysis, through the groups
SO(3) and SU(2), of the Poincaré canonical variables or of the similar Laplace variables. As an outcome, one obtains a MAPLE
program, which calculates the first averaged terms of the perturbative Hamiltonian.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献