Accurate analytical approximation of asteroid deflection with constant tangential thrust

We present analytical formulas to estimate the variation of achieved deflection for an Earth-impacting asteroid following a continuous tangential low-thrust deflection strategy. Relatively simple analytical expressions are obtained with the aid of asymptotic theory and the use of Peláez orbital elements set, an approach that is particularly suitable to the asteroid deflection problem and is not limited to small eccentricities. The accuracy of the proposed formulas is evaluated numerically showing negligible error for both early and late deflection campaigns. The results will be of aid in planning future low-thrust asteroid deflection missions.     

A watershed-scale study of climate change impacts on groundwater recharge (Annapolis Valley,Nova Scotia,Canada)

Abstract

The potential impacts of future climate change on the evolution of groundwater recharge are examined at a local scale for a 546-km² watershed in eastern Canada. Recharge is estimated using the infiltration model Hydrologic Evaluation of Landfill Performance (HELP), with inputs derived from five climate runs generated by a regional climate model in combination with the A2 greenhouse gas emissions scenario. The model runs project an increase in annual recharge over the 2041–2070 period. On a seasonal basis, however, a marked decrease in recharge during the summer and a marked increase during the winter are observed. The results suggest that increased evapotranspiration resulting from higher temperatures does not offset the large increase in winter infiltration. In terms of individual water budget components, clear differences are obtained for the different climate change scenarios. Monthly recharge values are also found to be quite variable, even for a given climate scenario. These findings are compared with results from two regional-scale studies.

Editor D. Koutsoyiannis; Associate editor M. Besbes     

Environmental suitability of ceramic raw materials: a geochemical approach to volatile emissions and leaching potentials

Growing environmental concern is promoting the necessity of additional ceramic tests. The use of unknown materials with potential contamination conditions requires further studies to demonstrate that the piece encapsulates the pollutant and that during its firing it does not produce the emission of harmful volatile elements. The objective of this work was to perform both tests in a ceramic paste made with slip-casting wastes and electro-plating residues. The leaching methods for determining the encapsulation of potential harmful elements were performed following the TCLP, EP-Tox norm. Having precise chemical analysis of both crude and fired brick, the problem of emissions losses during the firing can be solved by the gain/loss techniques used in geological studies. In particular, the Isocon method that permits a quick visualization of the lost elements is useful. Once the volatile elements were determined, their amount was calculated considering a constant element and the chemical concentrations normalized by the loss of ignition, or using the crude/fired brick ratio densities. The leaching tests indicate that the ceramic brick does not produce harmful leachates according to Argentinean specifications. The leachates of B and Ca are high. Ca does not seem to be a problem while the B content is beyond the permitted limits. During the firing, volatilized elements are Ag, Br, Cl, F, Hg, S, Se, and H₂O. The loss of Ag, Br, and Se are negligible. For F and Cl the potential emission rate is very low (100 mg/kg) while in the case of S, the 2,600 mg/kg rate is high. However, extrapolated emission rates at the chimney assuming an air-to-brick ratio of 2.5 N m³/kg, are approximately 1,040 mg/N m³ for S and 40 mg/N m³ for F and Cl, falling inside environmentally acceptable values. The geochemical procedures proved to be useful tools to assess the element mobilization during firing of ceramic wares and in the analyzed case, the results indicate that the paste is environmentally acceptable.     

Spatially distributed rainfall thresholds for the initiation of shallow landslides

The evaluation of the combined influence of rainfall patterns (in terms of mean intensity and duration) and the geomorphological and mechanical characteristics of hillslopes on their stability conditions is a major goal in the assessment of the shallow landslide triggering processes. Geographic Information Systems (GIS) represent an important tool to develop models that combine hydrological and geomechanical analyses for the evaluation of slope stability, as they allow to combine information concerning rainfall characteristics with topographic and mechanical properties of the slopes over wide areas. In this paper, a GIS-based code is developed to determine physically based intensity/duration rainfall thresholds at the local scale. Given the rainfall duration and the local geometric, hydrological and mechanical characteristics of the slopes, the code evaluates the spatial distribution of the minimum rainfall intensity that triggers shallow landslides and debris flows over a given area. The key feature of the code is the capability of evaluating the time t _p required to reach the peak pore pressure head on the failure surface and computing the corresponding critical intensity/duration thresholds based on post-event peak pore pressures. The reliability of the model is tested using a set of one-dimensional analyses, comparing the physically based thresholds obtained for three different slopes with some empirical rainfall thresholds. In a log–log scale, the thresholds provided by the model decrease linearly with increased rainfall duration and they are bracketed by the empirical thresholds considered. Finally, an example of application to a study area of the Umbria region in central Italy is presented, describing the capability of the model of providing site-specific thresholds for different rainfall scenarios.     

Legal and institutional tools to mitigate marine turtle bycatch: Argentina as a case study

This paper explores conservation policy pertinent to three species of marine turtles affected by fisheries, while crossing jurisdictions in their seasonal migrations through the SW Atlantic, particularly the Argentine waters. This case study reviews local legal and institutional frameworks for Argentina and concludes that tools are in place to monitor and mitigate the negative impact of bycatch on the populations. Argentina is signatory of the most relevant international treaties aimed at protecting transboundary species (e.g. Inter-American Convention for the Protection and Conservation of Sea Turtles, Convention on the Conservation of Migratory Species of Wild Animals). Legislation also exists at the federal and provincial levels. Yet, accidental captures continue to occur due to weaknesses in enforcement and the low priority that conservation has in fisheries management decisions. Some urgent practical actions supported by policy are suggested: (a) placement of on-board observers in coastal fishing fleets, (b) application of existing mitigation measures to reduce bycatch, (c) design of a national plan of action for marine turtles in Argentina, and (d) development of a regional plan between Argentina, Brazil and Uruguay. Stakeholder involvement, especially the fishing sector but also the civil society, would be important to energize practical and effective conservation decisions. The example of Argentina is typical for the region and may apply to other countries as well. The conservation community requires investing more in the application of policy, concomitant with perfecting legal tools.     

An overview of laboratory apparatuses to measure seismic attenuation in reservoir rocks

Intrinsic wave attenuation at seismic frequencies is strongly dependent on rock permeability, fluid properties, and saturation. However, in order to use attenuation as an attribute to extract information on rock/fluid properties from seismic data, experimental studies on attenuation are necessary for a better understanding of physical mechanisms that are dominant at those frequencies. An appropriate laboratory methodology to measure attenuation at seismic frequencies is the forced oscillation method, but technical challenges kept this technique from being widely used. There is a need for the standardization of devices employing this method, and a comparison of existing setups is a step towards it. Here we summarize the apparatuses based on the forced oscillation method that were built in the last 30 years and were used to measure frequency‐dependent attenuation in fluid‐saturated and/or dry reservoir rocks under small strains (10^?8–10^?5). We list and discuss important technical aspects to be taken into account when working with these devices or in the course of designing a new one. We also present a summary of the attenuation measurements in reservoir rock samples performed with these apparatuses so far.     

Model‐based attenuation for scattered dispersive waves

Coherent noise in land seismic data primarily consists in source‐generated surface‐wave modes. The component that is traditionally considered most relevant is the so‐called ground roll, consisting in surface‐wave modes propagating directly from sources to receivers. In many geological situations, near?surface heterogeneities and discontinuities, as well as topography irregularities, diffract the surface waves and generate secondary events, which can heavily contaminate records. The diffracted and converted surface waves are often called scattered noise and can be a severe problem particularly in areas with shallow or outcropping hard lithological formations. Conventional noise attenuation techniques are not effective with scattering: they can usually address the tails but not the apices of the scattered events. Large source and receiver arrays can attenuate scattering but only in exchange for a compromise to signal fidelity and resolution. We present a model?based technique for the scattering attenuation, based on the estimation of surface‐wave properties and on the prediction of surface waves with a complex path involving diffractions. The properties are estimated first, to produce surface?consistent volumes of the propagation properties. Then, for all gathers to filter, we integrate the contributions of all possible diffractors, building a scattering model. The estimated scattered wavefield is then subtracted from the data. The method can work in different domains and copes with aliased surface waves. The benefits of the method are demonstrated with synthetic and real data.     

A unified framework for earthquake risk assessment of transportation networks and gross regional product

Natural threats like earthquakes, hurricanes or tsunamis have had serious impacts on communities. In the past, major earthquakes in the United States like Loma Prieta 1989, Northridge 1994, or recent events in Italy like L’Aquila 2009 or Emilia 2012 emphasized the importance of preparedness and awareness to reduce social impacts. In addition to that, earthquake damaged businesses dramatically reduced the gross regional product. Generating scenario earthquakes in a proper way is important to suitably assess the risk in bridge networks and social losses in terms of gross regional product reduction. Seismic hazard is traditionally assessed by means of probabilistic seismic hazard analysis (PSHA). Although PSHA well represents the hazard at a specific location it is not suitable for spatially distributed systems. Scenario earthquakes can overcome this problem; they represent the actual distribution of ground shaking for a spatially distributed system while being hazard consistent. In this work a methodology to generate scenario earthquakes has been proposed using a novel approach with the aim of being the basic step for investigating possible earthquake consequences in seismic areas and contributing to reduce losses.     

DEM assessment of impact forces of dry granular masses on rigid barriers

In the design of sheltering structures/embankments for the mitigation of the risk due to rapid and long spreading landslides, a crucial role is generally played by the assessment of the impact force exerted by the flowing mass on the artificial obstacle. This paper is focused on this issue and in particular on the evaluation of the maximum impact force on the basis of the results obtained by performing an extensive numerical campaign by means of a 3D discrete element code, in which a dry granular mass is schematised as a random distribution of rigid spherical particles. The granular mass is generated just in front of the obstacle: its initial volume, velocity distribution, height, length and porosity are arbitrarily assigned, and the impact process is exclusively analysed. The initial conditions are varied to take a large variety of geometrical/mechanical factors, such as the initial front inclination, its height, the initial void ratio, the length of the impacting mass and the inter-particle friction angle, into consideration. A design formula is also proposed on the base of the obtained results and critically compared with the literature data.