Analysis of the impulsive phase of a solar flare at submillimeter wavelengths     

Raulin  Jean Pierre  Makhmutov  Vladimir S.  Kaufmann  Pierre  Pacini  Alessandra Abe  Lüthi  Thomas  Hudson  Hugh S.  Gary  Dale E. 《Solar physics》2004,223(1-2):181-199

We present a report on the strong X5.3 solar flare which occurred on 25 August 2001, producing high-level γ-ray activity, nuclear lines and a dramatic long-duration white-light continuum. The bulk of millimeter radio fluxes reached a peak of ∼100 000 solar flux units at 89.4 GHz, and a few thousands of solar flux units were detected in the submillimeter range during the impulsive phase. In this paper we focus on and discuss (i) the implications inferred from high frequency radio observations during the impulsive phase; (ii) the dynamics of the low corona active region during the impulsive phase. In particular we found that 4–5 × 10³⁶ accelerated (>20 keV) electrons s⁻¹ radiating in a 1000–1100 G region, are needed to explain the millimeter to submillimeter-wave emissions. We present evidence that the magnetic field in the active region was very dynamic, and that strong non-thermal processes were triggered by the appearance of new, compact, low-lying (few thousand kilometers) loop systems, suggesting the acceleration site(s) were also located in the low solar atmosphere.  相似文献   

Analysis of the impulsive phase of a solar flare at submillimeter wavelengths     

Jean Pierre Raulin  Vladimir S. Makhmutov  Pierre Kaufmann  Alessandra Abe Pacini  Thomas Lüthi  Hugh S. Hudson  Dale E. Gary 《Solar physics》2004,223(1):181-199

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Explosion craters associated with shallow submarine gas venting off Panarea island, Italy     

Thomas Monecke  Sven Petersen  Mark D. Hannington  Marco Anzidei  Alessandra Esposito  Guido Giordano  Dieter Garbe-Sch?nberg  Nico Augustin  Bernd Melchert  Mike Hocking 《Bulletin of Volcanology》2012,74(9):1937-1944

Explosions of hot water, steam, and gas are common periodic events of subaerial geothermal systems. These highly destructive events may cause loss of life and substantial damage to infrastructure, especially in densely populated areas and where geothermal systems are actively exploited for energy. We report on the occurrence of a large number of explosion craters associated with the offshore venting of gas and thermal waters at the volcanic island of Panarea, Italy, demonstrating that violent explosions similar to those observed on land also are common in the shallow submarine environment. With diameters ranging from 5 to over 100?m, the observed circular seafloor depressions record a history of major gas explosions caused by frequent perturbation of the submarine geothermal system over the past 10,000?years. Estimates of the total gas flux indicate that the Panarea geothermal system released over 70?Mt of CO₂ over this period of time, suggesting that CO₂ venting at submerged arc volcanoes contributes significantly to the global atmospheric budget of this greenhouse gas. The findings at Panarea highlight that shallow submarine gas explosions represent a previously unrecognized volcanic hazard around populated volcanic islands that needs to be taken into account in the development of risk management strategies.  相似文献   

Seismic reliability of V‐braced frames: Influence of design methodologies     

Alessandra Longo  Rosario Montuori  Vincenzo Piluso 《地震工程与结构动力学》2009,38(14):1587-1608

According to the most modern trend, performance‐based seismic design is aimed at the evaluation of the seismic structural reliability defined as the mean annual frequency (MAF) of exceeding a threshold level of damage, i.e. a limit state. The methodology for the evaluation of the MAF of exceeding a limit state is herein applied with reference to concentrically ‘V’‐braced steel frames designed according to different criteria. In particular, two design approaches are examined. The first approach corresponds to the provisions suggested by Eurocode 8 (prEN 1998—Eurocode 8: design of structures for earthquake resistance. Part 1: general rules, seismic actions and rules for buildings), while the second approach is based on a rigorous application of capacity design criteria aiming at the control of the failure mode (J. Earthquake Eng. 2008; 12 :1246–1266; J. Earthquake Eng. 2008; 12 :728–759). The aim of the presented work is to focus on the seismic reliability obtained through these design methodologies. The probabilistic performance evaluation is based on an appropriate combination of probabilistic seismic hazard analysis, probabilistic seismic demand analysis (PSDA) and probabilistic seismic capacity analysis. Regarding PSDA, nonlinear dynamic analyses have been carried out in order to obtain the parameters describing the probability distribution laws of demand, conditioned to given values of the earthquake intensity measure. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Empirical prediction of the Pitzer’s interaction parameters for cationic Al species with both SiO_2(aq) and CO_2(aq): Implications for the geochemical modelling of very saline solutions     

Marina Accornero  Luigi Marini 《Applied Geochemistry》2009

The Pitzer’s interaction parameters, λ_N–M, involving the Mth cationic Al species Al³⁺ or AlOH²⁺ or AlO⁺ and the Nth neutral species SiO_2(aq) (at temperatures of 25–300 °C) or CO_2(aq) (at temperatures of 25–150 °C), have been evaluated through empirical linear relationships between λ_N–M and the surface electrostatic field of the ionic species of interest. These relationships have been obtained starting from the known λ_N–M for both SiO_2(aq) and CO_2(aq) with the main dissolved cations. The Pitzer’s interaction parameter thus estimated for the pair CO_2(aq)–Al³⁺ at 25 °C, 0.327, is 20–40% higher than the corresponding values obtained from CO₂ solubilities in concentrated solutions of AlCl₃, 0.272 ± 0.010 (2σ), and Al₂(SO₄)₃, 0.232 ± 0.002 (2σ), partly corroborating the empirical approach adopted in this study. To test the Pitzer’s interaction coefficients for cationic Al species with aqueous SiO₂, the log K values of the kaolinite dissolution reaction have been computed starting from available experimental data at 23–25 °C and ionic strengths of 0.0001–0.12 mol/kg adopting, alternatively, the Pitzer’s equations and the Debye–Hückel equation. A satisfactory agreement has been found between the log K values obtained through these two approaches, with maximum deviations of 0.11–0.12 log units. This good convergence of results is encouraging as it represents a necessary condition to prove the reliability of the Pitzer’s interaction coefficients estimated in this work. These results are a first step to take into account specific interactions among solutes in concentrated electrolyte solutions, such as those hosted in sedimentary basins or geothermal waters, for instance through the Pitzer’s equations. However, experimental or field data at higher ionic strengths are absolutely necessary to validate the reliability of the Pitzer’s interaction coefficients determined in this study.  相似文献   

The impact of dolomite and plagioclase weathering on the chemistry of shallow groundwaters circulating in a granodiorite-dominated catchment of the Sila Massif (Calabria,Southern Italy)     

Carmine Apollaro  Marina Accornero  Luigi Marini  Donatella Barca  Rosanna De Rosa 《Applied Geochemistry》2009

This work is aimed at investigating the weathering processes of the granodiorites cropping out in a small catchment of the Sila Massif. The mineral constituents in this granodiorite are plagioclase, often zoned with a Ca-rich core and a Na-rich rim, quartz, chlorite, K-feldspar, white mica and epidote. During this study, dolomite was discovered in local stream sediments, as separate monomineralic grains, probably resulting from erosion of veins cutting the crystalline rocks. Prevailing dissolution of foreign dolomite and a Ca-rich plagioclase is suggested by the Ca–Mg–HCO₃ chemical composition of local groundwaters and stream waters, which is rather unexpected for waters interacting with granitoid rocks. These qualitative observations are quantitatively confirmed by reaction path modelling of the weathering processes occurring in the study area, which was carried out using the EQ3/6 software package, version 8.0, and the Double Solid Reactant Method. Indeed, it was possible to ascertain that the release of both major dissolved constituents and several trace elements (Ba, Co, Cr, Fe, Mn, Ni, Pb, Sr, V and Zn), from rocks to waters, is chiefly controlled by the dissolution of foreign dolomite and the Ca-rich core of zoned plagioclases.  相似文献   

Effects of vegetation on flow and sediment transport: comparative analyses and validation of predicting models   总被引：1，自引：0，他引：1       下载免费PDF全文

Andrés Vargas‐Luna  Alessandra Crosato  Wim S.J. Uijttewaal 《地球表面变化过程与地形》2015,40(2):157-176

The presence of vegetation modifies flow and sediment transport in alluvial channels and hence the morphological evolution of river systems. Plants increase the local roughness, modify flow patterns and provide additional drag, decreasing the bed‐shear stress and enhancing local sediment deposition. For this, it is important to take into account the presence of vegetation in morphodynamic modelling. Models describing the effects of vegetation on water flow and sediment transport already exist, but comparative analyses and validations on extensive datasets are still lacking. In order to provide practical information for modelling purposes, we analysed the performance of a large number of models on flow resistance, vegetation drag, vertical velocity profiles and bed‐shear stresses in vegetated channels. Their assessments and applicability ranges are derived by comparing their predictions with measured values from a large dataset for different types of submerged and emergent vegetation gathered from the literature. The work includes assessing the performance of the sediment transport capacity formulae of Engelund and Hansen and van Rijn in the case of vegetated beds, as well as the value of the drag coefficient to be used for different types of vegetation and hydraulic conditions. The results provide a unique comparative overview of existing models for the assessment of the effects of vegetation on morphodynamics, highlighting their performances and applicability ranges. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Linear time history analysis for the out-of-plane seismic demand of infill walls in RC framed buildings     

Alessandra De Angelis  Marisa Pecce  Fernando Rossi 《Bulletin of Earthquake Engineering》2015,13(11):3325-3352

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Thermal segmentation along the N. Ecuador–S. Colombia margin (1–4°N): Prominent influence of sedimentation rate in the trench     

Boris Marcaillou  George Spence  Kelin Wang  Jean-Yves Collot  Alessandra Ribodetti 《Earth and Planetary Science Letters》2008,272(1-2):296-308

Along the deformation front of the North Ecuador–South Colombia (NESC) margin, both surface heat flow and trench sediment thickness show prominent along-strike variations, indicating significant spatial variations in sedimentation rate. Investigating these variations helps us address the important question of how trench sedimentation influences the temperature distribution along the interplate contact and the extent of the megathrust seismogenic zone. We examine this issue by analysing 1/ a new dense reflection data set, 2/ pre-stack depth migration of selected multichannel seismic reflection lines, 3/ numerous newly-identified bottom-simulating reflectors and 4/ the first heat probe measurements in the region. We develop thermal models that include sediment deposition and compaction on the cooling oceanic plate as well as viscous corner flow in the mantle wedge. We estimate that the temperature from 60–150 °C to 350–450 °C, commonly associated with the updip and downdip limits of the seismogenic zone, extends along the plate interface over a downdip distance of 160 to 190 ± 20 km. We conclude that the updip limit of the seismogenic zone for the great megathrust earthquake of 1979 is associated with low-temperature (60–70 °C) processes. Our models also suggest that 60–70% of the two-fold decrease in measured heat flow from 3°N to 2.8°N is related to an abrupt southward increase in sedimentation rate in the trench. Such a change may potentially induce a landward shift of the 60–150 °C isotherms, and thus the updip limit of the seismogenic zone, by 10 to 20 km.  相似文献   

Charge States of Krypton and Xenon in the Solar Wind     

Peter Bochsler  Andrzej Fludra  Alessandra Giunta 《Solar physics》2017,292(9):128

We calculate charge state distributions of Kr and Xe in a model for two different types of solar wind using the effective ionization and recombination rates provided from the OPEN_ADAS data base. The charge states of heavy elements in the solar wind are essential for estimating the efficiency of Coulomb drag in the inner corona. We find that xenon ions experience particularly low Coulomb drag from protons in the inner corona, comparable to the notoriously weak drag of protons on helium ions. It has been found long ago that helium in the solar wind can be strongly depleted near interplanetary current sheets, whereas coronal mass ejecta are sometimes strongly enriched in helium. We argue that if the extraordinary variability of the helium abundance in the solar wind is due to inefficient Coulomb drag, the xenon abundance must vary strongly. In fact, a secular decrease of the solar wind xenon abundance relative to the other heavier noble gases (Ne, Ar, Kr) has been postulated based on a comparison of noble gases in recently irradiated and ancient samples of ilmenite in the lunar regolith. We conclude that decreasing solar activity and decreasing frequency of coronal mass ejections over the solar lifetime might be responsible for a secularly decreasing abundance of xenon in the solar wind.  相似文献