Emergence and evolution of active and ephemeral regions: Comparison between observations and models     

Francesca Zuccarello  Salvatore L. Guglielmino  Viviana Battiato  Lidia Contarino  Daniele Spadaro  Pado Romano 《Acta Geophysica》2009,57(1):15-23

This work aims to describe some aspects relevant to the emergence of magnetic structures on the solar surface. Using high resolution photospheric and chromospheric data, besides than EUV images acquired by space telescopes, the dynamics of rising flux tubes is studied. It is shown that, for both long-lived and short-lived magnetic regions, the flux tubes are initially characterized by a high rising velocity, which eventually decreases as the region develops. Other results concern the timeline of the active regions appearance in the atmospheric layers and the asymmetries in plasma downflows between preceding and following legs of the flux tubes. These results are briefly discussed in the light of most recent models.  相似文献   

Giant gas bubbles in a rheomorphic vent fill at the Las Cañadas caldera,Tenerife (Canary Islands)     

Carles Soriano  Daniele Giordano  Inés Galindo  Marcel Hürlimann  Paola Ardia 《Bulletin of Volcanology》2009,71(8):919-932

During rheomorphism subsequent to fallout deposition, a portion of the densely welded fallout of the La Grieta Member flowed back into the vent from where it was erupted, while the rest of it flowed down the outer slopes of the Las Cañadas caldera in Tenerife. The welded fallout and conduit-vent structure are physically connected and constitute a rare example of this type of deposits rooted to its feeder conduit and exposed in the caldera wall. The lower part of the vent-filling rheomorphic rocks shows gas bubbles and cavities that increase in size (up to 4 m) down vent. Bubbles are deformed against other bubbles, against the steep vent walls, flattened parallel to the flow foliation planes, and elongated parallel to the flow lineation and flow fold axes. The preservation of such giant bubbles, rather than their formation, seems to be a pretty unique feature of the phonolitic products investigated here and it is likely the result of the combination of factors that acted to preserve, in the surrounding of the glass transition interval, the sealing and the late stage cooling of a pressurized system. In addition, strain drop at the base of the vent-filling rheomorphic flow caused by flow stopping against vertical vent walls may have promoted rapid gas exsolution and the formation of large bubbles.  相似文献   

Physical infrastructure interdependency and regional resilience index after the 2011 Tohoku Earthquake in Japan          下载免费PDF全文

Gian Paolo Cimellaro  Daniele Solari  Michel Bruneau 《地震工程与结构动力学》2014,43(12):1763-1784

A resilience index is used to quantify preventive measures, emergency measures, and restoration measures of complex systems, such as physical infrastructures, when they are subjected to natural disasters like earthquakes, hurricanes, floods, etc. Interdependencies among these systems can generate cascading failures or amplification effects, which can also affect the restoration measures right after an extreme event and generate a reduction of the resilience index. In this article, a method is proposed to evaluate the physical infrastructure resilience of a region affected by a disaster considering infrastructure interdependency. It is illustrated using available restoration curves from the March 11 2011 Tohoku Earthquake in Japan. The weights assigned to each infrastructure, which are used to determine resilience, are evaluated using the degree of interdependency indices which are obtain by time series analysis. Results show that the weight coefficients thus obtained do not influence the resilience index significantly; however, the methodology proposed is unbiased from subjective judgment and is able to identify the critical lifelines. Furthermore, the results of the case study presented here suggest that to obtain meaningful estimation of the weight coefficients, it is necessary to consider the period range between two perturbations (e.g., main shock and aftershock). Future infrastructure disruption data (from this and other earthquakes) would be needed to generalize this finding that will allow also to quantify the changes in the restoration curves caused by the magnitude and distance of the shocks from the epicenter, as well as the intrinsic properties of the physical infrastructures. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Sand transport measurements in Chioggia inlet,Venice lagoon: Theory versus observations     

Monique M. Villatoro  Carl L. Amos  Georg Umgiesser  Christian Ferrarin  Luca Zaggia  Charlotte E.L. Thompson  Daniele Are 《Continental Shelf Research》2010

This paper presents results of recent measurements of sand transport made in Chioggia inlet as part of an extensive monitoring programme in the Venetian inlets. Measurements were made in order: (1) to define a relationship between sand transport magnitude and tidal flow; (2) to derive the thresholds for sand transport; (3) to identify the dominant modes of transport; (4) to evaluate the concentration profiles of sand within the benthic boundary layer; (5) to compare bedload transport observations with model predictions using existent bedload formulae; and (6) to produce yearly estimates of bedload transport across the inlet. The vertical distribution of sand in the water column was sampled using modified Helley–Smith bedload samplers at three sites. Transport was found to vary according to the flow and bed grain size, with considerable temporal and spatial variability. A difference of up to three orders of magnitude in transport was observed through the inlet, with higher transport rates measured on the seaward part. The dominant mode of transport in the central inlet was suspension, while bedload was dominant in the mouths. The measured profiles of sand concentration varied with the tidal stage and seabed grain size according to the Rouse parameter (R). R was high at the inlet mouths (1<R<2), indicative of a well-developed bedload layer. The inverse movability number (W_s/U_*) was also higher at these sites and appeared to be grain size dependant. Formulae for bedload transport were tested against field data; stochastic methods such as Einstein–Brown, Engelund–Hansen and Van Rijn produce the best fits. The coupled model SHYFEM-Sedtrans05 appears to simulate well observed transport for most conditions of flow. Long-term bedload predictions indicate a dominant export of sand, with a yearly average of 4500 m³.  相似文献   

A Smart Sensor System for Detecting Hydrocarbon Volatile Organic Compounds in Sea Water          下载免费PDF全文

Alessandro Tonacci  Daniele Corda  Gennaro Tartarisco  Giovanni Pioggia  Claudio Domenici 《洁净——土壤、空气、水》2015,43(1):147-152

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Depth and morphology of reflectors from the non-linear inversion of arrival times and waveform semblance data. Part II: modelling and interpretation of real data acquired in Southern Apennines, Italy     

M. Corciulo  A. Zollo  M. Vassallo  P. Dell'Aversana  S. Morandi 《Geophysical Prospecting》2008,56(4):541-553

In order to retrieve a 2D background velocity model and to retrieve the geometry and depth of shallow crustal reflectors in the Southern Apennines thrust belt a separate inversion of first arrival traveltimes and reflected waveforms was performed. Data were collected during an active seismic experiment in 1999 by Enterprise Oil Italiana and Eni-Agip using a global offset acquisition geometry. A total of 284 on-land shots were recorded by 201 receivers deployed on an 18 km line oriented SW–NE in the Val D'Agri region (Southern Apennines, Italy).
The two-step procedure allows for the retrieval of a reliable velocity model by using a non-linear tomographic inversion and reflected waveform semblance data inversion. The tomographic model shows that the P wave velocity field varies vertically from approximately 3 km/s to 6 km/s within 4 km from the Earth's surface. Moreover, at a distance of approximately 11 km along the profile, there is an abrupt increase in the velocity field. In this zone indeed, an ascent from 2 km depth to 0 km above sea level of the 5.2 km/s iso-velocity contour can be noted. The retrieved velocity can be associated with Plio-Pleistocene clastic deposits outcropping in the basin zone and with Mesozoic limestone deposits. The inversion of waveform semblance data shows that a P-to-P reflector is retrieved at a depth of approximately 2 km. This interface is deeper in the north-eastern part of the profile, where it reaches 3 km depth and can be associated with a limestone horizon.  相似文献   

Effects of pore-scale dispersion,degree of heterogeneity,sampling size,and source volume on the concentration moments of conservative solutes in heterogeneous formations     

Daniele Tonina  Alberto Bellin 《Advances in water resources》2008

Pore-scale dispersion (PSD), aquifer heterogeneity, sampling volume, and source size influence solute concentrations of conservative tracers transported in heterogeneous porous formations. In this work, we developed a new set of analytical solutions for the concentration ensemble mean, variance, and coefficient of variation (CV), which consider the effects of all these factors. We developed these models as generalizations of the first-order solutions in the log-conductivity variance of point concentration proposed by [Fiori A, Dagan G. Concentration fluctuations in aquifer transport: a rigorous first-order solution and applications. J Contam Hydrol 2000;45(1–2):139–163]. Our first-order solutions compare well with numerical simulations for small and moderate formation heterogeneity and from small to large sampling and source volumes. However, their performance deteriorates for highly heterogeneous formations. Successively, we used our models to study the interplay among sampler size, source volume, and PSD. Our analysis shows a complex and important interaction among these factors. Additionally, we show that the relative importance of these factors is also a function of plume age, of aquifer heterogeneity, and of the measurement location with respect to the mean plume center of gravity. We found that the concentration moments are chiefly controlled by the sampling volume with pore-scale dispersion playing a minor role at short times and for small source volumes. However, the effect of the source volume cannot be neglected when it is larger than the sampling volume. A different behavior occurs for long periods, which may be relevant for old contaminations, or for small injection volumes. In these cases, PSD causes a significant dilution, which is reflected in the concentration statistics. Additionally, at the center of the mean plume, where high concentrations are most likely to occur, we found that sampling volume and PSD are attenuating mechanisms for both concentration ensemble mean and coefficient of variation, except at very large source and sampler sizes, where the coefficient of variation increases with sampler size and PSD. Formation heterogeneity causes a faster reduction of the ensemble mean concentrations and a larger uncertainty at the center of the mean plume. Therefore, our results highlight the importance of considering the combined effect of formation heterogeneity, exposure volume, PSD, source size, and measurement location in performing risk assessment.  相似文献   

Trajectory Studies of Polar Stratospheric Cloud Lidar Observations at Sodankylä (Finland) During SESAME: Comparison with Box Model Results of Particle Evolution     

V. Rizi  G. Redaelli  G. Visconti  F. Masci  C. Wedekind  B. Stein  F. Immler  B. Mielke  P. Rairoux  L. Woste  M. Del Guasta  M. Morandi  F. Castagnoli  S. Balestri  L. Stefanutti  R. Matthey  V. Mitev  M. Douard  J.P. Wolf  E. Kyro  M. Rummukainen  R. Kivi 《Journal of Atmospheric Chemistry》1999,32(1):165-181

Polar stratospheric clouds (PSC) were observed with the multi-wavelength lidar of the MOANA project (Modelling and Observations of Aerosols in the Northern Atmosphere) during SESAME (Second European Stratospheric Arctic and Mid-latitude Experiment). The physical state, liquid or solid, of the cloud particles can be inferred from the lidar data. Using isentropic back-trajectories to obtain the thermal history of the sampled air masses, it is possible to reconcile most of the observations with current ideas on PSC formation and evolution. When the cloud particles were identified as liquid, changes in the size distribution of the droplets along the trajectory were calculated using a micro-physical box model. Backscatter ratios calculated from the size distributions are in broad agreement with the lidar data, giving confidence in current understanding of the evolution of ternary solution (H2SO4, HNO3 and H2O) droplets.Results from two soundings are shown which bear on the problem of the formation of solid particles. In the first, solid particles were detected. The air mass had cooled to the frost point 12 hours earlier. In the second no solid particles were detected although the air temperature was below the nitric acid trihydrate existence point, and had decreased by 12K in the previous 14 hours.  相似文献   

Subsurface mass redistributions at Mount Etna (Italy) during the 1995–1996 explosive activity detected by microgravity studies     

Gennaro Budetta  Daniele Carbone  & Filippo Greco 《Geophysical Journal International》1999,138(1):77-88

Gravity changes are presented from a series of field microgravity surveys conducted at Mt Etna between August 1994 and November 1996, a period including the 1995–1996 explosive summit activity. Data were collected along a microgravity network of 69 stations at a monthly to annual sampling rate, depending on each subarray of the network.
  Results show that seasonal changes in water level within the volcano may induce gravity changes of up to 20  μgal on Etna's southern slope, and indicate that significant magma movement occurred within and below Etna's edifice between 1994 and 1996. In particular, between September 1994 and October 1995, a mass increase of 2 × 10¹⁰  kg occurred 2000  m beneath the summit craters. Between October 1995 and July 1996 this mass was lost, while another 2 × 10¹⁰  kg was injected at about 1000  m  a.s.l. into the 1989 fracture system. From the gravity data alone, it is not possible to distinguish whether the first shallow intrusion (1994–1995) was then injected laterally into the 1989 fracture, or summit activity was fed by the first shallow intrusion, while new magma entered the 1989 fracture system.
  While magma was being redistributed within the volcanic edifice, measurements along an E–W-trending profile on the southern slope of the volcano detected some 1.5 × 10¹¹  kg of magma accumulating 2–3  km below sea level between October 1995 and November 1996.  相似文献   

Single-point position estimation in interplanetary trajectories using star trackers     

Daniele Mortari  Dylan Conway 《Celestial Mechanics and Dynamical Astronomy》2017,128(1):115-130

This study provides a single-point position estimation technique for interplanetary missions by observing visible planets using star trackers. Closed-form least-squares solution is obtained by minimizing the sum of the expected object-space squared distance errors. A weighted least-squares solution is provided by an iterative procedure. The weights are evaluated using the distances to the planets estimated by the least-squares solution. It is shown that the weighted approach only requires one iteration to converge and results in significant accuracy gains compared to simple least squares approach. The light-time correction is taken into account while the star-light aberration cannot be implemented in single-point estimation as it requires knowledge of the observer velocity. The proposed method is numerically validated through a statistical scenario as follows. A three-dimensional grid of test cases is generated: two dimensions sweep through the ecliptic plane and the third dimension sweeps through time from January 1, 2018 to January 1, 2043 in 5-year increments. The observer position is estimated at each test case and the estimate error is recorded. The results obtained show that a large majority of positions are well suited to position estimation by using star trackers pointing to visible planets, and reliable and accurate single-point position estimations can be provided in interplanetary missions. The proposed approach is suitable to be used to initiate a filtering technique to increase the estimation accuracy.  相似文献