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1.
Alessandro Comunian Leonardo De Micheli Claudio Lazzati Fabrizio Felletti Francesca Giacobbo Mauro Giudici Riccardo Bersezio 《Hydrogeology Journal》2016,24(2):319-334
The fine-scale heterogeneity of porous media affects the large-scale transport of solutes and contaminants in groundwater and it can be reproduced by means of several geostatistical simulation tools. However, including the available geological information in these tools is often cumbersome. A hierarchical simulation procedure based on a binary tree is proposed and tested on two real-world blocks of alluvial sediments, of a few cubic meters volume, that represent small-scale aquifer analogs. The procedure is implemented using the sequential indicator simulation, but it is so general that it can be adapted to various geostatistical simulation tools, improving their capability to incorporate geological information, i.e., the sedimentological and architectural characterization of heterogeneity. When compared with a standard sequential indicator approach on bi-dimensional simulations, in terms of proportions and connectivity indicators, the proposed procedure yields reliable results, closer to the reference observations. Different ensembles of three-dimensional simulations based on different hierarchical sequences are used to perform numerical experiments of conservative solute transport and to obtain ensembles of equivalent pore velocity and dispersion coefficient at the scale length of the blocks (meter). Their statistics are used to estimate the impact of the variability of the transport properties of the simulated blocks on contaminant transport modeled on bigger domains (hectometer). This is investigated with a one-dimensional transport modeling based on the Kolmogorov-Dmitriev theory of branching stochastic processes. Applying the proposed approach with diverse binary trees and different simulation settings provides a great flexibility, which is revealed by the differences in the breakthrough curves. 相似文献
2.
Melissa M. Foley Benjamin S. Halpern Fiorenza Micheli Matthew H. Armsby Margaret R. Caldwell Caitlin M. Crain Erin Prahler Nicole Rohr Deborah Sivas Michael W. Beck Mark H. Carr Larry B. Crowder J. Emmett Duffy Sally D. Hacker Karen L. McLeod Stephen R. Palumbi Charles H. Peterson Helen M. Regan Mary H. Ruckelshaus Paul A. Sandifer Robert S. Steneck 《Marine Policy》2010
The declining health of marine ecosystems around the world is evidence that current piecemeal governance is inadequate to successfully support healthy coastal and ocean ecosystems and sustain human uses of the ocean. One proposed solution to this problem is ecosystem-based marine spatial planning (MSP), which is a process that informs the spatial distribution of activities in the ocean so that existing and emerging uses can be maintained, use conflicts reduced, and ecosystem health and services protected and sustained for future generations. Because a key goal of ecosystem-based MSP is to maintain the delivery of ecosystem services that humans want and need, it must be based on ecological principles that articulate the scientifically recognized attributes of healthy, functioning ecosystems. These principles should be incorporated into a decision-making framework with clearly defined targets for these ecological attributes. This paper identifies ecological principles for MSP based on a synthesis of previously suggested and/or operationalized principles, along with recommendations generated by a group of twenty ecologists and marine scientists with diverse backgrounds and perspectives on MSP. The proposed four main ecological principles to guide MSP—maintaining or restoring: native species diversity, habitat diversity and heterogeneity, key species, and connectivity—and two additional guidelines, the need to account for context and uncertainty, must be explicitly taken into account in the planning process. When applied in concert with social, economic, and governance principles, these ecological principles can inform the designation and siting of ocean uses and the management of activities in the ocean to maintain or restore healthy ecosystems, allow delivery of marine ecosystem services, and ensure sustainable economic and social benefits. 相似文献
3.
Marco Micheli Detlef Koschny Gerhard Drolshagen Olivier Hainaut Fabrizio Bernardi 《Earth, Moon, and Planets》2014,113(1-4):1-13
In this work we summarize the initial results of a targeted effort of the ESA NEO Coordination Centre to obtain additional observational data in order to eliminate or reduce the impact probability estimate of a subset of the known near-Earth objects representing the highest fraction of the total known impact risk, as measured by the Palermo Scale. 相似文献
4.
D. Farnocchia S. R. Chesley D. J. Tholen M. Micheli 《Celestial Mechanics and Dynamical Astronomy》2014,119(3-4):301-312
In November 2004 radar delay measurements of near-Earth asteroid (3908) Nyx obtained at the Arecibo radio telescope turned out to be \(7.5\sigma \) away from the orbital prediction. We prove that this discrepancy was caused by a poor astrometric treatment and an incomplete dynamical model, which did not account for nongravitational perturbations. To improve the astrometric treatment, we remove known star catalog biases, apply suitable weights to the observations, and use an aggressive outlier rejection scheme. The main issue related to the dynamical model is having not accounted for the Yarkovsky effect. Including the Yarkovsky perturbation in the model makes the orbital prediction and the radar measurements statistically consistent by both reducing the offset and increasing the prediction uncertainty to a more realistic level. This analysis shows the sensitivity of high precision predictions to the astrometric treatment and the Yarkovsky effect. By using the full observational dataset we obtain a \(5\sigma \) detection of the Yarkovsky effect acting on Nyx corresponding to an orbital drift \(da/dt = (142 \pm 29)\) m/year. In turn, we derive constraints on thermal inertia and bulk density. In particular, we find that the bulk density of Nyx is around 1 g/cm \(^3\) , possibly less. To make sure that our results are not corrupted by an asteroid impact or a close approach with a perturbing asteroid not included in our dynamical model, we show that the astrometry provides no convincing evidence of an impulsive variation of Nyx’s velocity while crossing the main belt region. 相似文献
5.
D. Grassi C. Fiorenza N.I. Ignatiev A. Maturilli V. Formisano 《Planetary and Space Science》2005,53(10):1053-1064
This work reports the first observations of the Martian atmosphere returned by the planetary Fourier spectrometer (PFS) on board of Mars express (MEX) satellite in the vicinity of the greatest volcanic domes of the planet. Two of the early MEX orbits have already covered the region of Olympus Mons and Ascraeus Mons. These measurements are very similar in terms of local time (14LT) and season (LS=337 and 342, respectively).The long wavelength channel (LWC) of the instrument works in the thermal IR (300-1500 cm−1); its data allow the simultaneous retrieval of surface temperature, integrated content of water ice and dust suspended in the atmosphere and air thermal field up to an altitude of about 50 km. Results of the code described in the companion paper by Grassi et al. for the two orbits are presented and compared with the state expected by the European Martian climate dataset v3.1. The parent global circulation model LMD-Oxford-AAS is able to take into account a wide number of physical phenomena, but the results included in EMCD are affected by a relatively coarse spatial resolution, that does not properly describe the great volcanic domes. The comparison demonstrated that observed data follow quite strictly the trends foreseen by the model in low altitude regions, while the behavior shows remarkable differences above the relief, where orography likely plays an important role. Namely, extended mid-altitude minima in air temperature fields above the summit of volcanic domes are observed.The integrated content of dust shows a minima above Olympus, as expected for a dust particle concentration that decays with height. Measurements are consistent with an exponential decay characterized by a scale height of ∼10 km. Consistently, the surface temperature presents a maxima over the dome, as expected for conditions of clearer sky. Water ice clouds are clearly detected around Ascreus Mons, with a strong asymmetry in latitude.Further comparison with the results of the thermal emission spectrometer (TES) on board of Mars global surveyor (MGS) is also provided, partially supporting our observations of air temperature fields.Possible explanation of these trends is represented by thermal circulation, driven by air heating close to the surface. If confirmed by future observations, these data can represent important constraint by PFS data to mesospheric simulation, with possible implications on the Global Circulation Models. 相似文献
6.
Benedetti-Cecchi L Bertocci I Micheli F Maggi E Fosella T Vaselli S 《Marine environmental research》2003,55(5):95-458
Marine protected areas (MPAs) are increasingly used as a management tool to preserve species and habitats. Testing hypotheses about the effectiveness of MPAs is important for their implementation and to identify informative criteria to support management decisions. This study tested the general proposition that MPAs affected assemblages of algae and invertebrates between 0.0 and 0.5 m above the mean low water level of rocky coasts on two islands in the Tuscan Archipelago (northwest Mediterranean). Protection was concentrated mainly on the west coasts of the islands, raising the possibility that neither the full range of assemblages nor the relevant scales of variation were properly represented within MPAs. This motivated the comparison of assemblages on opposite sides of islands (habitats). The effects of MPAs and habitat were assessed with a multifactorial sampling design; hypotheses were tested about differences in structure of assemblages, in mean abundance of common taxa and in univariate and multivariate measures of spatial variation. The design consisted of three replicate shores for each condition of protected and reference areas on the west side of each island and three unprotected shores on the eastern side. Assemblages were sampled independently four times on each island between June 1999 and January 2001. At each time of sampling two sites were selected randomly at each of two tidal heights to represent midshore and lowshore assemblages on each shore. Estimates of abundance were obtained using non-destructive sampling methods from five replicate 20x20 cm quadrats at each site. Results indicated differences among habitats in structure of assemblages, in mean abundance of common taxa and in univariate and multivariate measures of spatial variation at the scale of shores. Most of these patterns were inconsistent with the predicted effect of management through MPAs. The data suggest that designation of MPAs in the Tuscan Archipelago should proceed through management of multiple shores and types of habitat selected to guarantee protection to a representative sample of assemblages and to the processes responsible for maintenance of spatial patchiness at different scales. This study also shows that considerations of spatial heterogeneity are important to underpin management decisions about the number, size and location of MPAs. 相似文献
7.
M. Cortese E. Perozzi M. Micheli B. Borgia E. Dotto E. Mazzotta Epifani S. Ieva M. A. Barucci D. Perna 《Meteoritics & planetary science》2017,52(3):522-531
The present near‐Earth asteroids (NEA) discovery rate has surpassed 1500 objects per year, thus calling for extensive observation campaigns devoted to physical characterization in order to define successful mitigation strategies in case of possible impactors. A tool is presented which, through a prioritization algorithm, aims to optimize the planning and the execution of NEA physical observations. Two ranking criteria are introduced, Importance and Urgency, accounting for the need of satisfying the two basic observational modes for physical characterization, that is, rapid response and large observing programs, aimed at selecting targets for exploration and mitigation space missions. The resulting tool generates a daily table of observable targets and it can also be run as a stand‐alone tool in order to provide future observing opportunities at a specific date of interest. It has been developed and implemented within the framework of the NEOShield‐2 EU/HORIZON 2020 Project; the output of the prioritization algorithm is publicly available, in tabular format, on the NEOShield‐2 NEO Properties Portal ( http://www.neoshield.net/the-neoshield-project/project-activities/neo-properties-portal ), reachable from the main page of the Project website ( http://www.neoshield.eu ). 相似文献
8.
We quantified how rates of stream channel migration in a montane meadow vary as a function of the riparian vegetation community. The South Fork of the Kern River at Monache Meadow, located in California's southern Sierra Nevada range, supports two distinct types of vegetation: a dry meadow community dominated by sagebrush and non‐native grasses (xeric scrub and meadow), and a wet meadow community dominated by rushes and sedges (hydric graminoids). We measured rates of lateral stream migration for dry versus wet meadow reaches from aerial photographs spanning a 40‐year period (1955–1995). While stream migration rates averaged only 0·24 ± 0·02 m a?1 in the wet meadow, the dry meadow channel migrated an average of 1·4 ± 0·3 m a?1. We used a linear model of meander migration to calculate coefficients that characterize bank migration potential, or bank erodibility, independent of channel curvature. These calculations demonstrate that, at Monache Meadow, banks without wet meadow vegetation are roughly ten times more susceptible to erosion than banks with wet meadow vegetation. Where stream bank heights consistently exceed 1 m, low water availability creates riparian habitats dominated by dry meadow vegetation. Thus, channel incision may reduce bank stability not only by increasing bank height, but also by converting banks from wet meadow to dry meadow vegetation. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
9.
A measured calibrated solar radiance in the range 1.2-, with the spectral sampling of does not exist. When studying the measured Planetary Fourier Spectrometer (PFS) spectra of the Earth's or Mars's atmosphere we discover that the most used solar spectrum contains several important errors. Here we present a “calibrated” solar radiance in the wavelength range 1.2-, with the spectral resolution of PFS , which we are going to use for studying Martian spectra. This spectrum has been assembled using measurements from Kitt Peak and from ATMOS Spacelab experiment (uncalibrated high resolution) and theoretical results, together with low resolution calibrated continuum. This is the best we can have in this moment to be used with PFS, while waiting to have good solar calibrated radiances. Examples of solar lines at Mars are given. 相似文献
10.
Paulo Lojkasek‐Lima Ramon Aravena Orfan Shouakar‐Stash Shaun K. Frape Massimo Marchesi Stephanie Fiorenza John Vogan 《Ground Water Monitoring & Remediation》2012,32(4):53-62
A pilot‐scale zero valent iron (ZVI) Permeable Reactive Barrier (PRB) was installed using an azimuth‐controlled ‐vertical hydrofracturing at an industrial facility to treat a chlorinated Volatile Organic Compound (VOC) plume. Following ZVI injection, no significant reduction in concentration was observed to occur with the exception of some multilevel monitoring wells, which also showed high levels of total organic carbon (TOC). These patterns suggested that the zero valent iron was not well distributed in the PRB creating leaky conditions. The geochemical data indicated reducing conditions in these areas where VOC reduction was observed, suggesting that biotic processes, associated to the guar used in the injection of the iron, could be a major mechanism of VOC degradation. Compound‐Specific Isotope Analysis (CSIA) using both carbon and chlorine stable isotopes were used as a complementary tool for evaluating the contribution of abiotic and biotic processes to VOC trends in the vicinity of the PRB. The isotopic data showed enriched isotope values around the PRB compared to the isotope composition of the VOC source confirming that VOC degradation is occurring along the PRB. A batch experiment using site groundwater collected near the VOC source and the ZVI used in the PRB was performed to evaluate the site‐specific abiotic isotopic fractionation patterns. Field isotopic trends, typical of biodegradations were observed at the site and were different from those obtained during the batch abiotic experiment. These differences in isotopic trends combined with changes in VOC concentrations and redox parameters suggested that biotic processes are the predominant pathways involved in the degradation of VOCs in the vicinity of the PRB. 相似文献