The structure of coronal magnetic loops     

Claudio Chiuderi  Riccardo Giachetti  Gerard Van Hoven 《Solar physics》1977,54(1):107-122

We present here a model, based on observations, for the magnetic-field equilibrium of a cool coronal loop. The pressure structure, taken from the Harvard/Skylab EUV data, is used to modify the usual force-free-field form in quasi-cylindrical symmetry. The resulting field, which has the same direction but different strength, is calculated and its variation displayed. Finally, localized interchange stability is evaluated and discussed, as the first step in a subsequent complete magnetohydrodynamic-stability analysis.  相似文献   

Contents of Volume 53     

Dario Camuffo  Claudio Cocheo  Giovanni Sturaro 《Climatic change》2002,53(4):531-533

Volume Contents

Contents of Volume 53  相似文献   

The Analysis of the Seasonal,Spatial, and Compositional Distribution of Humic Substances in a Subtropical Shallow Lake     

Stefania Mazzuoli  Steven Loiselle  Vincent Hull  Luca Bracchini  Claudio Rossi 《洁净——土壤、空气、水》2003,31(6):461-468

The spatial and temporal distribution of humic substances in aquatic ecosystems can have important effects on ecosystem productivity, negatively impacting primary productivity while positively impacting secondary productivity. In the present investigation, a large shallow lake ecosystem was studied to determine the spatial and seasonal variation of the composition and concentration of humic substances. Concentrations of total dissolved organic matter, humic acid, and fulvic acid were found to display significant spatial distributions (1.3…13.5 mg/L, DOM; 0.1…5.4 mg/L, HA). The distribution is described by using mapping techniques and the analysis of the spatial distribution of the lake. An analysis of the seasonal variations also indicated the dependence of the occurrence of these compounds on meteorological and hydrological conditions. To identify the potential sources of these organic materials, an analysis was made of the ratio of humic and fulvic acid fractions and total DOM. It was found that areas of high DOM concentration coincided with the areas of highest HA percentage of total DOM. Furthermore using the ratio of the normalised concentrations of HA, FA, and residual DOM (< 5000 g/mol) it was found that areas dominated by each are spatially distinct. This confirms the hypothesis that in these shallow lakes, photodegradation and bacterioplankton activity will create a residence time dependent zonation of each component of the total DOM.  相似文献   

Cloud cover classification through simultaneous ground-based measurements of solar and infrared radiation     

Antonio Orsini  Claudio Tomasi  Francescopiero Calzolari  Marianna Nardino  Alessandra Cacciari  Teodoro Georgiadis   《Atmospheric Research》2002,61(4)

Simultaneous measurements of downwelling short-wave solar irradiance and incoming total radiation flux were performed at the Reeves Nevè glacier station (1200 m MSL) in Antarctica on 41 days from late November 1994 to early January 1995, employing the upward sensors of an albedometer and a pyrradiometer. The downwelling short-wave radiation measurements were analysed following the Duchon and O'Malley [J. Appl. Meteorol. 38 (1999) 132] procedure for classifying clouds, using the 50-min running mean values of standard deviation and the ratio of scaled observed to scaled clear-sky irradiance. Comparing these measurements with the Duchon and O'Malley rectangular boundaries and the local human observations of clouds collected on 17 days of the campaign, we found that the Duchon and O'Malley classification method obtained a success rate of 93% for cirrus and only 25% for cumulus. New decision criteria were established for some polar cloud classes providing success rates of 94% for cirrus, 67% for cirrostratus and altostratus, and 33% for cumulus and altocumulus.The ratios of the downwelling short-wave irradiance measured for cloudy-sky conditions to that calculated for clear-sky conditions were analysed in terms of the Kasten and Czeplak [Sol. Energy 24 (1980) 177] formula together with simultaneous human observations of cloudiness, to determine the empirical relationship curves providing reliable estimates of cloudiness for each of the three above-mentioned cloud classes. Using these cloudiness estimates, the downwelling long-wave radiation measurements (obtained as differences between the downward fluxes of total and short-wave radiation) were examined to evaluate the downwelling long-wave radiation flux normalised to totally overcast sky conditions. Calculations of the long-wave radiation flux were performed with the MODTRAN 3.7 code [Kneizys, F.X., Abreu, L.W., Anderson, G.P., Chetwynd, J.H., Shettle, E.P., Berk, A., Bernstein, L.S., Robertson, D.C., Acharya, P., Rothman, L.S., Selby, J.E.A., Gallery, W.O., Clough, S.A., 1996. In: Abreu, L.W., Anderson, G.P. (Eds.), The MODTRAN 2/3 Report and LOWTRAN 7 MODEL. Contract F19628-91-C.0132, Phillips Laboratory, Geophysics Directorate, PL/GPOS, Hanscom AFB, MA, 261 pp.] for both clear-sky and cloudy-sky conditions, considering various cloud types characterised by different cloud base altitudes and vertical thicknesses. From these evaluations, best-fit curves of the downwelling long-wave radiation flux were defined as a function of the cloud base height for the three polar cloud classes. Using these relationship curves, average estimates of the cloud base height were obtained from the three corresponding sub-sets of long-wave radiation measurements. The relative frequency histograms of the cloud base height defined by examining these three sub-sets were found to present median values of 4.7, 1.7 and 3.6 km for cirrus, cirrostratus/altostratus and cumulus/altocumulus, respectively, while median values of 6.5, 1.8 and 2.9 km were correspondingly determined by analysing only the measurements taken together with simultaneous cloud observations.  相似文献   

Seismic response of multi‐span simply supported bridges to a spatially varying earthquake ground motion     

Giovanna Zanardo  Hong Hao  Claudio Modena 《地震工程与结构动力学》2002,31(6):1325-1345

This paper carries out a parametrical study of the pounding phenomenon associated with the seismic response of multi‐span simply supported bridges with base isolation devices. In particular, the analyses focus on the causal relationship between pounding and the properties of a spatially varying earthquake ground motion. In order to include the effect of the torsional component of pounding forces on the seismic response of the whole structure, a three‐dimensional (3D) finite element model has been defined and 3D non‐linear time‐history analyses have been performed. A parametrical study on the size of the gaps between adjacent bridge decks has highlighted that the pounding effects are amplified when the spatially varying ground motion time histories at each support are considered. Because of a spatially varying input, the pounding forces can assume values 3–4 times larger than those derived by a conventional seismic analysis with uniform input or with spatial input but considering ground motion wave passage effect only. The numerical results show that in order to achieve an acceptably safe structural performance during seismic events, a correct design of the isolation devices should take into account the relative displacements calculated by means of a non‐linear time‐history analysis with multi‐support excitation. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Temperature dependence of goethite dissolution promoted by trihydroxamate siderophores     

Claudio CocozzaCalvin C.G. Tsao  Sing-Foong CheahStephan M. Kraemer  Kenneth N. RaymondTeodoro M. Miano  Garrison Sposito 《Geochimica et cosmochimica acta》2002,66(3):431-438

This article reports an investigation of the temperature dependence of goethite dissolution kinetics in the presence of desferrioxamine B (DFO-B), a trihydroxamate siderophore, and its acetyl derivative, desferrioxamine D1 (DFO-D1). At 25 and 40°C, DFO-D1 dissolved goethite at twice the rate of DFO-B, whereas at 55°C, the behavior of the two ligands was almost the same. Increasing the temperature from 25 to 55°C caused little or no significant change in DFO-B or DFO-D1 adsorption by goethite. A pseudo-first-order rate coefficient for dissolution, calculated as the ratio of the mass-normalized dissolution rate coefficient to the surface excess of siderophore, was approximately the same at 25 and 40°C for both siderophores. At 55°C, however, this rate coefficient for DFO-D1 was about half that for DFO-B. Analysis of the temperature dependence of the mass-normalized dissolution rate coefficient via the Arrhenius equation led to an apparent activation energy that was larger for DFO-B than for DFO-D1, but much smaller than that reported for the proton-promoted dissolution of goethite. A compensation law was found to relate the pre-exponential factor to the apparent activation energy in the Arrhenius equation, in agreement with what has been noted for the proton-promoted dissolution of oxide minerals and for the complexation of Fe³⁺ by DFO-B and simple hydroxamate ligands in aqueous solution. Analysis of these results suggested that the siderophores adsorb on goethite with a only single hydroxamate group in bidentate ligation with an Fe(III) center.  相似文献   

Mechanical stratigraphy as a factor controlling the development of a sandbox transfer zone: a three-dimensional analysis   总被引：3，自引：0，他引：3  

Antonio Ravaglia  Claudio Turrini  Silvio Seno 《Journal of Structural Geology》2004,26(12):2269-2283

In thrust belts, fold–fault terminations are common features of the structural architecture and can pose complicated problems to unravel, in particular when two or more terminations are in close proximity. Such terminations usually reflect pre-existing attributes. Amongst the many factors, lateral variations in the mechanical stratigraphy can control along-strike geometry and kinematics of fault-related folds.A displacement transfer zone was produced in a compressional sandbox model by means of two adjacent, mechanically different stratigraphic domains. The experiment allowed two discrete chains to develop in the different domains, so that a complex structural setting occurred in the connecting area. Periclinal folds, oblique thrust fronts and oblique ramps developed in the resulting transfer zone. The interaction between periclines in the transfer zone produced lateral culminations in the folded structures. The analysis of displacement across the structural domains revealed that a significant loss of slip along the faults occurred in the relay zone. In this area, imbricate faulting was partially replaced by layer-parallel shortening. A linear relationship appears to exist between the bed length of the thrust sheet and the related fault slip.  相似文献   

Landslides triggered by the 23 November 2000 rainfall event in the Imperia Province, Western Liguria, Italy   总被引：1，自引：0，他引：1  

Fausto Guzzetti  Mauro Cardinali  Paola Reichenbach  Francesco Cipolla  Claudio Sebastiani  Mirco Galli  Paola Salvati 《Engineering Geology》2004,73(3-4):229-245

From mid-October to 22 November 2000, the western Liguria Region of Italy experienced prolonged and intense rainfall, with cumulative values exceeding 1000 mm in 45 days. The severe rainfall sequence ended on November 23 with a high-intensity storm that dumped more than 180 mm of rain in 24 h. The high-intensity event caused flooding and triggered more than 1000 soils slips and debris flows and a few large, complex landslides. Slope failures caused three fatalities and severe damage to roads, private homes, and agriculture. Large (1:13,000) and very large (1:5000) scale colour aerial photographs were taken 45 days after the event over the areas most affected by the landslides. Through the interpretation of the 334 photographs covering an area of 500 km², we prepared a landslide inventory map that shows 1204 landslides, for a total landslide area of 1.6 km². We identified the rainfall conditions that triggered landslides in the Armea valley using cumulative- and continuous-rainfall data, combined with detailed information on the time of landslide occurrence. Landslide activity initiated 8 to 10 h after the beginning of the storm, and the most abundant activity occurred in response to rainfall intensities of 8 to 10 mm per hour. For the Ceriana Municipality, an area where the landslides were numerous in November 2000, we also collected information about a historical event that occurred on 8–11 December 1910 and triggered abundant landslides resulting in severe economic damage. A comparison of the damage caused by the historical and the recent landslide events indicated that damage caused by the 1910 historical event was more diffused but less costly than the damage caused by the 2000 event.  相似文献   

Acoustoelasticity in cracked solids     

Claudio Pecorari 《Geophysical Journal International》1997,129(1):169-175

A new model that accounts for the stress dependence of the phase velocity of elastodynamic waves propagating in a cracked solid under compression is presented. The phase velocities of longitudinal and shear waves are derived from the effective elastic properties of a cracked solid, which are evaluated within the framework of Kachanov's approach. Following Kachanov, the extra-compliance tensor of the cracked solid is related to the crack compliances, which display a marked non-linear behaviour when subjected to a compressive load. Such non-linear behaviour is shown to be derived from the elastic interaction between the contacting crack faces under compression. This work does not address the effect of mutual interaction among cracks and the generation of higher harmonics due to the medium non-linearity. Numerical examples are presented that illustrate the phase velocity changes occurring in a solid with a random distribution of parallel cracks as a function of an external compressive load. A distinctive feature of the acoustoelastic effect in solids with large parallel fractures and in solids with distributions of aligned microcracks is also illustrated.  相似文献   

Instrumental seismological data since 1900 for northeastern Italy     

Claudio Margottini  Guido Martini  Dario Slejko 《地震工程与结构动力学》1993,22(12):1017-1030

Statistical analyses on a catalogue of instrumental data for earthquakes in northeastern Italy since 1900 are presented. The different types of magnitude, which are the main parameters under study, have been evaluated so as to be as homogeneous as possible. Comparisons of the different magnitude values show linear dependence, at least in the medium magnitude range represented by the available data set. Correlations between the magnitude most significant for this region and chosen macroseismic data indicate a methodology for assessing the macroseismic magnitude of historical earthquakes which seems to be stable.  相似文献