How alternative food networks work in a metropolitan area? An analysis of Solidarity Purchase Groups in Northern Italy

Our paper focuses on Solidarity Purchase Group (SPG) participants located in a highly urbanized area, with the aim to investigate the main motivations underlining their participation in a SPG and provide a characterization of them. To this end, we carried out a survey of 795 participants involved in 125 SPGs in the metropolitan area of Milan (Italy). Taking advantage of a questionnaire with 39 questions, we run a factor analysis and a two-step cluster analysis to identify different profiles of SPG participants. Our results show that the system of values animating metropolitan SPG practitioners does not fully conform to that traditionally attributed to an alternative food network (AFN). In fact, considerations linked to food safety and healthiness prevail on altruistic motives such as environmental sustainability and solidarity toward small producers. Furthermore, metropolitan SPGs do not consider particularly desirable periurban and local food products. Observing the SPGs from this perspective, it emerges as such initiatives can flourish also in those places where the lack of connection with the surrounding territory is counterbalanced by the high motivation to buy products from trusted suppliers who are able to guarantee genuine and safe products, not necessarily located nearby

Carrier-carrier entanglement and transport resonances in semiconductor quantum dots

We study theoretically the entanglement created in a scattering between an electron, incoming from a source lead, and another electron bound in the ground state of a quantum dot, connected to two leads. We analyze the role played by the different kinds of resonances in the transmission spectra and by the number of scattering channels, into the amount of quantum correlations between the two identical carriers. It is shown that the entanglement between their energy states is not sensitive to the presence of Breit-Wigner resonances, while it presents a peculiar behavior in correspondence of Fano peaks: two close maxima separated by a minimum, for a two-channel scattering, a single maximum for a multi-channel scattering. Such a behavior is ascribed to the different mechanisms characterizing the two types of resonances. Our results suggest that the production and detection of entanglement in quantum dot structures may be controlled by the manipulation of Fano resonances through external fields.Comment: 8 pages, 6 figures, RevTex4 two-column format, submitte

Grain size characterization of modern and ancient dunes within a dune field along the Pisan coast (Tuscany, Italy)

In this paper, grain size analysis on a large number of samples from a dune field within the Migliarino – San Rossore – Massaciuccoli Regional Park has been carried out in order to define the textural characterization of modern and ancient dune ridges. More than 200 samples along five transects have been collected from the backshore, the active dunes and the steady dunes up to the last recognizable dune ridge. The samples have been dry-sieved and the obtained data have been processed electronically to achieve textural parameters such as mean diameter and sorting. The results showed similar trends of the transects throughout the entire dune field. In particular, the grain size tends to decrease towards the most ancient dune ridges, showing a significant drop at the transition between active and inactive areas. The drastic decrease might be related to a possible variation of River Arno sediment discharge occurred after the XVIII century

Quantum teleportation of electrons in quantum wires with surface acoustic waves

We propose and numerically simulate a semiconductor device based on coupled quantum wires, suitable for deterministic quantum teleportation of electrons trapped in the minima of surface acoustic waves.We exploit a network of interacting semiconductor quantum wires able to provide the universal set of gates for quantum information processing, with the qubit defined by the localization of a single electron in one of two coupled channels.The numerical approach is based on a time-dependent solution of the three-particle Schr\"odinger equation. First, a maximally entangled pair of electrons is obtained via Coulomb interaction between carriers in different channels. Then, a complete Bell-state measurement involving one electron from this pair and a third electron is performed. Finally, the teleported state is reconstructed by means of local one-qubit operations. The large estimated fidelity explicitely suggests that an efficient teleportation process could be reached in an experimental setup.Comment: 7 pages,4 figures, 1 tabl

Linear entropy as an entanglement measure in two-fermion systems

We describe an efficient theoretical criterion, suitable for indistinguishable particles to quantify the quantum correlations of any pure two-fermion state, based on the Slater rank concept. It represents the natural generalization of the linear entropy used to treat quantum entanglement in systems of non-identical particles. Such a criterion is here applied to an electron-electron scattering in a two-dimensional system in order to perform a quantitative evaluation of the entanglement dynamics for various spin configurations and to compare the linear entropy with alternative approaches. Our numerical results show the dependence of the entanglement evolution upon the initial state of the system and its spin components. The differences with previous analyses accomplished by using the von Neumann entropy are discussed. The evaluation of the entanglement dynamics in terms of the linear entropy results to be much less demanding from the computational point of view, not requiring the diagonalization of the density matrix.Comment: 16 pages. Added references in section 1 Corrected typo

Entanglement dynamics of electron-electron scattering in low-dimensional semiconductor systems

We perform the quantitative evaluation of the entanglement dynamics in scattering events between two insistinguishable electrons interacting via Coulomb potential in 1D and 2D semiconductor nanostructures. We apply a criterion based on the von Neumann entropy and the Schmidt decomposition of the global state vector suitable for systems of identical particles. From the timedependent numerical solution of the two-particle wavefunction of the scattering carriers we compute their entanglement evolution for different spin configurations: two electrons with the same spin, with different spin, singlet, and triplet spin state. The procedure allows to evaluate the mechanisms that govern entanglement creation and their connection with the characteristic physical parameters and initial conditions of the system. The cases in which the evolution of entanglement is similar to the one obtained for distinguishable particles are discussed.Comment: 22 pages, 7 figures, submitted to Physical Review

Effect of electron-electron interaction on the phonon-mediated spin relaxation in quantum dots

We estimate the spin relaxation rate due to spin-orbit coupling and acoustic phonon scattering in weakly-confined quantum dots with up to five interacting electrons. The Full Configuration Interaction approach is used to account for the inter-electron repulsion, and Rashba and Dresselhaus spin-orbit couplings are exactly diagonalized. We show that electron-electron interaction strongly affects spin-orbit admixture in the sample. Consequently, relaxation rates strongly depend on the number of carriers confined in the dot. We identify the mechanisms which may lead to improved spin stability in few electron (>2) quantum dots as compared to the usual one and two electron devices. Finally, we discuss recent experiments on triplet-singlet transitions in GaAs dots subject to external magnetic fields. Our simulations are in good agreement with the experimental findings, and support the interpretation of the observed spin relaxation as being due to spin-orbit coupling assisted by acoustic phonon emission.Comment: 12 pages, 10 figures. Revised version. Changes in section V (simulation of PRL 98, 126601 experiment

Litho-sedimentological and morphodynamic characterization of the Pisa Province coastal area (northern Tuscany, Italy)

In this paper litho-sedimentological and morphodynamic maps of the coastal sector belonging to the Pisa Province are presented as an example of how increasing the accessibility to data on lithology, sedimentology, and morphodynamics may lead to a better approach to coastal management. The database used to build the maps includes an original rendering of remote sensing data (aerial imagery) and new field data (geologic survey), as well as data retrieved from the scientific literature (grain-size and past coastline positions). The maps show that the geometry of beach ridges is an indication of the evolution of the Arno River delta in the last 3000 years, highlighting the relationships between geological aspects and morphodynamic features. The maps represent the synthesis of different data available in the database, and they may be a useful support to coastal management as they are more easily understandable and straightforward than the database from which are created

On demand entanglement in double quantum dots via coherent carrier scattering

We show how two qubits encoded in the orbital states of two quantum dots can be entangled or disentangled in a controlled way through their interaction with a weak electron current. The transmission/reflection spectrum of each scattered electron, acting as an entanglement mediator between the dots, shows a signature of the dot-dot entangled state. Strikingly, while few scattered carriers produce decoherence of the whole two-dots system, a larger number of electrons injected from one lead with proper energy is able to recover its quantum coherence. Our numerical simulations are based on a real-space solution of the three-particle Schroedinger equation with open boundaries. The computed transmission amplitudes are inserted in the analytical expression of the system density matrix in order to evaluate the entanglement.Comment: 20 pages, 5 figure

Farm succession, occupational choice and farm adaptation at the rural-urban interface : The case of Italian horticultural farms

The survival of family farming in Europe is a crucial issue, as it assures landscape maintenance in marginal areas and provides transmission and accumulation of site-specific knowledge in agricultural activity. Using data from a sample of Italian horticultural farms, we explored the multiple forces driving farm succession in a high value added sector. In addition to the traditional factors examined in the literature (farm, farmer and family features), we treated the farm transfer choice as the complement of the decision to migrate out of the agricultural sector, testing the effects of local labour market conditions (employment, income gap between farm and non-farm sector) and population density around the farm, as a proxy of rural-urban interface relationships. It has been shown that both traditional factors and territorial and labour market conditions influence the probability of farm succession. Interestingly labour market conditions exerted an effect in line with occupational choice theory only in less inhabited areas; in more densely populated regions a rural-urban linkage effect seems to prevail, creating an environment that fosters succession of young horticultural farmers. Peri-urban areas may thus be a favourable location for professional and specialised horticultural farms, as well as multifunctional and de-specialised ones, if their assets are properly protected against farmland subtraction. More generally, these findings confirm the validity of a more comprehensive approach toward farm succession, which takes occupational choice theory and rural-urban farm adaptation strategies into account