1,721,071 research outputs found
Majorana/Andreev crossover and the fate of the topological phase transition in inhomogeneous nanowires
No full textMajorana bound states (MBS) and Andreev bound states (ABS) in realistic Majorana nanowires setups have similar experimental signatures which make them hard to distinguishing one from the other. Here, we characterize the continuous Majorana/Andreev crossover interpolating between fully-separated, partially-separated, and fully-overlapping Majorana modes, in terms of global and local topological invariants, fermion parity, quasiparticle densities, Majorana pseudospin and spin polarizations, density overlaps and transition probabilities between opposite Majorana components. We found that in inhomogeneous wires, the transition between fully-overlapping trivial ABS and nontrivial MBS does not necessarily mandate the closing of the bulk gap of quasiparticle excitations, but a simple parity crossing of partially-separated Majorana modes (ps-MM) from trivial to nontrivial regimes. We demonstrate that fully-separated and fully-overlapping Majorana modes correspond to the two limiting cases at the opposite sides of a continuous crossover: the only distinction between the two can be obtained by estimating the degree of separations of the Majorana components. This result does not contradict the bulk-edge correspondence: indeed, the field inhomogeneities driving the Majorana/Andreev crossover have a length scale comparable with the nanowire length, and therefore correspond to a nonlocal perturbation which breaks the topological protection of the MBS
Applicazione di metodi geochimici in aree a intensa pressione antropica. Il caso di studio delle discariche RSU
No full textIn order to identify new survey methods for environmental characterization of areas affected by anthropogenic pressure, several geochemical investigations were conducted in two municipal solid waste landfills of Central Italy: Cerratina landfill and Cerreto landfill.
Cerratina landfill is located in an alluvial plain of the lower Sangro river. The area is characterized by a substrate of marine origin formed by clay and sand at the base and coarse sands upwards to sands and conglomerates at the top of the formation. In this area were conducted geochemical investigations on groundwater beneath the landfill. The results of chemical analyses indicate that the samples collected from boreholes located downgradient from the landfill are contaminated. The principal contaminants are Cl-, NH4+, Fe, As, Cr, B, Hg and Zn, which exceed the limit provided by Dlgs 152/2006 during different monitoring campaigns. The boron, tritium and strontium isotopic composition of the collected water samples was analysed to evaluate the principal water-rock interaction processes and source of contamination. The results indicate that contaminated groundwater show highest tritium data and lower δ11B and 87Sr/86Sr ratio. Boron isotopes show that there are two boron sources in the study area, which are geogenic and anthropogenic sources. Sr isotope results show that sample located upgradient from the site presents lower Sr concentration and highest Sr isotopic values, which reflects weathered bedrock, while boreholes located downgradient from the site show lowest Sr values and 87Sr/86Sr ratio, probably due to pollution by landfill leachate.
Another important result was obtained by rare earths elements analyses. A positive Gadolinium anomaly was reported for one sample of studied area which reflects the anthropogenic input of the REEs in groundwater.
Cerreto landfill is located in an alluvial plain of Lazio, central Italy. The area is characterized by a substrate of continental deposits formed by clay and sand, and alluvial deposits associated with different depositional events of the main rivers presents in the area. Were conducted geochemical investigation on groundwater and soils located in the landfill site. The results show that major and trace elements for soil are below the limit provided by Italian law. Rare earths elements pattern of soils were used to evaluate possible anomalies presence and to investigate soil parent material for identifying background values of study area. The geochemical investigations show that some elements, in topsoil, present higher concentration respect to background values. Geoaccumulation index and enrichment factor show possible contamination phenomena of Ni, Cu, Cd e Pb. The results obtained for groundwater show that Fe, Mn and As exceed the limit provided by Dlgs 152/2006, but according to results obtained for soil, these elements naturally occur in the area so their principal source is geological substrate
Soil contamination evaluation by Enrichment Factor (EF) and Geoaccumulation Index (Igeo)
Full text linkHeavy metals are natural constituents of soils and their concentration varies depending on parental materials. The soils were formed by. In the last years, the content of heavy metal in soils has increased due to human activities as: distribution of fertilizers, pesticides, industries, waste disposal and air pollution. Due to these activities the life capacity of soils decreased; especially where the natural background is already high because of natural parental material richness in heavy metal. As a matter of fact it is very important to distinguish between the natural background values and anthropogenic inputs, and to understand that the background values change from area to area and with the scale of the area investigated. To evaluate the soil contamination rate different indexes like Enrichment Factor (EF) and geoaccumulation index (Igeo) can be applied. These indexes are used to assess the presence and intensity of anthropogenic contaminant deposition on surface soil
Hydrogeochemical characterization of Municipal Solid Waste landfill
No full textIn Italy landfills are the main method of waste disposal. Poor
management of these areas can result in significant pollution load in
the different environmental matrices, which, on the other hand, may
naturally contain high amounts of some contaminants. The aim of this
work is to determine the geochemical characteristics of the water
circulating in the vicinity of two Municipal solid waste landfills and to
evaluate their quality status considering the geological characteristics
of the sites. The results show exceedances of threshold concentrations
of contamination provided by Legislative Decree 152/2006 for both
sites, particularly the trace elements present as contaminants are iron
manganese and arseni
Rare earth elements and Heavy metals in soils of an open landfill
No full textFive soils samples and four clay samples have been collected during December 2014 in a landfill of Central Italy to
evaluate the environmental status in the area. The main objective of this study is the characterization of soil samples in
relation to heavy metals values and to critically assess the measured values with respect to anthropogenic input vs
lithogenic background. Heavy metals in soils can be associated with several reactive materials and may exist in various
forms that reflect their solubility and availability. To evaluate the various chemical forms present in the soils, steps I
(exchangeable) and V (residual) of the sequential extraction procedures established by Tessier et al. (1979) and
optimised by Frankowski et al. (2010) have been used. Elements investigates are V, Cr, Fe, Ni, Cu, Zn, As, Rb, Cd, Sb,
Tl and Pb. The results of analyses have been used for statistical analyses and to determine enrichment factor (EF) and
geoaccumulation index (Igeo). These index have been calculated using average crustal values, lithosphere values and
clay values of the study area, for determining differences between values.Furthermore, have been determined the rare
earth elements in samples. The Rare earths elements abundance in soils usually exhibit the typical distribution pattern
reported in geological samples, although fractionation is possible, controlled by pedogenic factors such as pH, redox
condition and organic matter content. Have been determined the REE in clay samples representative of geologic pattern
of the area sampled in different deep
The human impact on the natural environment: Elemental geochemistry of a msw landfill as a tool to trace changes in ecosystem processes
No full textIn Italy landfills are the most common method of organized solid waste disposal as it is simplest and cheapest one. About 60% of total waste produced is disposed in landfills. Landfills continue to serve a key function in the waste management system in the less developed countries, although the general trend is to minimize the use of them by new policies of reducing, reusing, recycling, and the development of technologies for composting and residues incineration. The aim of this study is to assess the impact of a MSW on the environment using some simple geochemical tools as tracer of anthropogenic contamination in the environments surrounding a municipal solid waste (MSW) landfill. The landfill studied here is located in central Italy and it has been working since 1995. It's divided in 3 lots, and it has a capacity more than 2,000,000 cubic meters. The geology of the area is characterized by a Plio-Pleistocene substrate of marine origin formed at the base by clayey-sandy deposits that in the upper part of the formation to pass sands and conglomerates. The oldest deposits are represented by grayblue clays. The aim of this study is to identify the cause(s) of changes in downgrading groundwater quality. To assess the possible impact of the landfill on the environment the groundwater chemical composition (physicochemical parameters, major constituents and trace elements) of 13 wells was taken into account. The wells are located hydraulically downgradient of the site. The results are compared to both background and baseline groundwater quality. The aim of this study is to assess the impact of a MSW on the environment using some simple geochemical tools as tracer of anthropogenic contamination
Strontium Isotope as Tracers of Groundwater Contamination
Full text linkGroundwater flowing under a municipal solid waste landfill has been studied to identify potential contamination phenomenon
and to test strontium isotopic composition as a natural tracer of contamination. The study was carried on in June 2014 in central Italy. Five selected boreholes were selected and analysed according to their location related to the site. Samples taken from boreholes placed upward to the site were considered as uncontaminated groundwater. One borehole located downward from the site and with major contaminant values has been considered as potentially contaminated end-member. Sr isotope results show that samples located upward from the site present lower Sr concentration and highest Sr isotopic values, which reflects weathered bedrock, while borehole located downward from the site show lowest Sr values and 87Sr/86Sr ratio, probably due to pollution by landfill leachate. The mixing calculation highlights the possible mixing phenomenon for the other samples located downward from the site
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