Coronal magnetic fields from microwave polarization observations     

C. E. Alissandrakis  F. Borgioli  F. Chiuderi Drago  M. Hagyard  K. Shibasaki 《Solar physics》1996,167(1-2):167-179

The solar active region (AR) 7530 was observed at 6 cm on July 3 and 4, 1993 with the Westerbork Synthesis Radio Telescope, using a multi-channel receiver with very narrow bandwidth. We compare the radio data with Yohkoh SXT observations and with the magnetic field extrapolated from the Marshall vector magnetograms in the force-free and current-free approximations. The comparison with soft X-rays shows that, although a general agreement exists between the shape of the radio intensity map and the X-ray loops, the brightness temperature, T _b, obtained using the parameters derived from the SXT is much lower than that observed. The comparison with the extrapolated photospheric fields shows instead that they account very well for the observed T _b above the main sunspots, if gyroresonance emission is assumed. In the observation of July 4 an inversion and strong suppression of the circular polarization was clearly present above different portions of the AR, which indicates that particular relationships exist between the electron density and the magnetic field in the region where the corresponding lines of sight cross the field quasi-perpendicularly. The extrapolated magnetic field at a much higher level ( 10¹⁰ cm), satisfies the constraints required by the wave propagation theory all over the AR. However, a rather low electron density is derived.  相似文献   

Cacti–shrub interactions in the coastal desert of northern Sinaloa, Mexico     

Alvaro Reyes-Olivas  Edmundo García-Moya  Lauro Lpez&#x;Mata 《Journal of Arid Environments》2002,52(4):431

Spatial patterns and replacement in ten cacti were studied on an island of the coastal desert of Sinaloa, México. Four platyopuntias had 74–92% of their individuals beneath shrub canopies, whereas three globose cacti, one columnar cactus and two cylindropuntias had similar or higher percentages of individuals in open spaces. This study advances the idea that open-space colonization is enhanced by less harsh physical and biotic conditions in coastal deserts, and by certain morphological and physiological adaptations of cacti. The absence of nurse-shrub replacement is understood as a result of induced co-existence by physical damage from cyclones in the coastal zone.  相似文献   

Integrated geophysical and geochemical study on AMD generation at the Haveri Au–Cu mine tailings,SW Finland     

Edmundo Placencia-Gómez  Annika Parviainen  Tero Hokkanen  Kirsti Loukola-Ruskeeniemi 《Environmental Earth Sciences》2010,61(7):1435-1447

The Haveri tailings area contains 1.5 Mt of sulfide-bearing waste from the Au–Cu mine that operated during 1942–1961. Geophysical and geochemical methods were used to evaluate and characterize the generation of acid mine drainage (AMD). Correlations were examined among the electrical resistivity tomography (ERT) data, the total sulfide content and concentrations of sulfide-bound metals (Cu, Co, Fe, Mn, Ni, Pb and Zn) of tailings samples, and the resistivity and geochemistry of surface water. The resulting geophysical–geochemical model defines an area in the vadose tailings, where a low resistivity anomaly (<10 Ohm m) is correlated with the highest sulfide content, extensive sulfide oxidation and low pH (average 3.1). The physical and geochemical conditions, resulting from the oxidation of the sulfide minerals, suggest that the low resistivity anomaly is associated with acidic and metal-rich porewater (i.e., AMD). The lower resistivity values in the saturated zone of the central impoundment suggest the formation of a plume of AMD. The natural subsoil layer (silt and clay) and the bedrock surface below the tailings area were well mapped from the ERT data. The detected fracture zones of the bedrock that could work as leakage pathways for AMD were consistent with previous geological studies. The integrated methodology of the study offers a promising approach to fast and reliable monitoring of areas of potential AMD generation and its subsurface movement over large areas (ca. 9 ha). This methodology could be helpful in planning drill core sampling locations for geochemical and mineralogical analysis, groundwater sampling, and choosing and monitoring remedial programs.  相似文献   

Stability of Hamiltonian Systems with Three Degrees of Freedom and the Three Body-Problem     

José Edmundo Mansilla 《Celestial Mechanics and Dynamical Astronomy》2006,94(3):249-269

Results are obtained about formal stability and instability of Hamiltonian systems with three degrees of freedom, two equal frequencies and the matrix of the linear part is not diagonalizable, in terms of the coefficients of the development in Taylor series of the Hamiltonian of the system. The results are applied to the study of stability of the Lagrangian solutions of the Three Body-Problem in the case in which the center of mass is over the curve ρ_*, on the border of the region of linear stability of Routh. The curve ρ_* is divided symmetrically in three arcs in such a way that if the center of mass of the three particles lies on the central arc, the Lagrangian solution is unstable in the sense of Liapunov (in finite order), while if the center of mass determines one point that lies on one of the other two arcs of ρ_*, then the Lagrangian solution is formally stable.  相似文献   

Energy balance in the prominence-corona transition region     

C. Chiuderi  F. Chiuderi Drago 《Solar physics》1991,132(1):81-94

The prominence-corona transition region can be observed both at UV and radio wavelengths. The physical parameters needed to explain one set of observations are, however, in disagreement with those consistent with the other one. A solution of the problem is proposed, based on the proper consideration of the dependence of the thermal conduction on the angle between the magnetic field and the direction of the local temperature gradient.  相似文献   

Brightness distribution at λ = 3 and 21 cm near the solar north pole     

Chiuderi Drago  Franca  Patriarchi  Patrizio 《Solar physics》1974,37(2):403-408

The brightness distribution of the Sun near the north pole at = 3 and 21 cm is obtained using the results of the partial eclipse of February 25, 1971. The solution obtained by expanding B (r) in orthogonal polynomials does not show any brightening at either frequency, but a sensible darkening. If this result is explained by the presence of spicules, the coronal emission must be negligible with respect to the emission coming from the transition region. This is possible, at = 21 cm, only if we assume the presence of a coronal hole near the pole.  相似文献   

On the radio optical depth of the layer where the temperature equals the brightness temperature     

Franca Chiuderi Drago 《Solar physics》1972,27(1):132-136

It is usually believed that the radio optical depth of the layer h* where the temperature equals the brightness temperature is independent of the frequency. This assumption is criticized from the theoretical point of view and the behaviour of (h*) as a function of the frequency v is computed for two different solar models.  相似文献   

Morphology,structure and kinematics of a rainfall controlled slow‐moving Andean landslide,Peru          下载免费PDF全文

Swann Zerathe  Pascal Lacroix  Denis Jongmans  Jersy Marino  Edu Taipe  Marc Wathelet  Walter Pari  Lionel Fidel Smoll  Edmundo Norabuena  Bertrand Guillier  Lucile Tatard 《地球表面变化过程与地形》2016,41(11):1477-1493

The large slow‐moving landslide of Maca is located in the upper Colca valley (southern Peru), a region characterized by a well pronounced rainy period, and intense and recurrent sustained seismicity. The landslide, developed in deep lacustrine deposits, has recently accelerated, threatening the Maca village. This work aims at understanding the rupture mechanism and the causes of the recent landslide reactivation/acceleration. We present a multidisciplinary characterization of the Maca landslide that includes: (i) geological and morphological mapping in the field; (ii) remote sensing analysis using an historical aerial photograph of 1955 and the Pléiades satellite images (2013); (iii) global positioning system (GPS) including time‐series of surveys over 13 years, and continuous measurements over 14 months; (iv) a geophysical campaign with deep electrical resistivity tomography profiles acquired across the landslide mass. Our study shows that this 60 Mm³ landslide, which can be classified as a clay/silt compound landslide, moved by 15 m between 2001 and 2014 with a large inter‐annual velocity variation (up to a factor of 500) depending on the rainfall intensity. We suggest that these dramatic changes in velocity are the result of the combination of a threshold mechanism and the short intense rainy season in Peru. This study reveals three main driving factors acting at different timescales: (i) over several decades, the river course has significantly changed, causing the Maca landslide reactivation in the 1980s due to the erosion of its toe; (ii) at the year scale, a minimum amount of rainfall is required to trigger the motion and this amount controls the landslide velocity; (iii) transient changes in slide velocity may occur anytime due to earthquakes. This study particularly highlights the non‐linear behaviour of the motion with rainfall. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

σ-Coordinates hydrodynamic numerical model for coastal and ocean three-dimensional circulation     

M. Drago  L. Iovenitti 《Ocean Engineering》2000,27(10):607

A three-dimensional finite-difference hydrodynamic model has been developed using σ-coordinate for the vertical dimension. An explicit scheme for temporal integration and a staggered grid for spatial discretization have been adopted. The model has been tested against analytical or literature cases for wind and tide induced circulation. Results are in good agreement both with analytical solutions under idealised conditions and with results from the model of Shankar et al. (1996).  相似文献   

Quiescent radio emission of RS CVn binary systems     

F. Chiuderi Drago  K. -L. Klein 《Astrophysics and Space Science》1990,170(1-2):81-84

It is shown that the quiescent radio emission observed in some RS Vc binary systems cannot be ascribed to the same thermal electrons population responsible for the X-ray emission. An alternative explanation to account for the observed correlation between X-ray and radio luminosity is suggested.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.  相似文献