What Is New about the Exposome? Exploring Scientific Change in Contemporary Epidemiology

In this commentary, I discuss the scientific changes brought by the exposome, asking what is new about this approach and line of research. I place the exposome in a historical perspective, by analyzing the conditions under which the exposome has been conceived, developed and established in the context of contemporary epidemiological research. I argue that the exposome has been developed by transferring approaches, methods and conceptualizations from other lines of research in the life and health sciences. I thus discuss the conceptual and methodological innovations of the exposome as a result of the merging and adaptation of these elements for new uses and purposes. On this basis, I argue that the novelty of the exposome should be seen in incremental rather than revolutionary terms and, in this sense, the exposome shares significant elements with other projects and repertoires in postgenomics. I conclude by discussing the consequences of this analysis for the potential limitations and future development of exposome research

Probing the wavefunction of the surface states in Bi2_2Se3_3 topological insulator: a realistic tight-binding approach

We report on microscopic tight-binding modeling of surface states in Bi$_2$Se$_3$ three-dimensional topological insulator, based on a sp$^3$ Slater-Koster Hamiltonian, with parameters calculated from density functional theory. The effect of spin-orbit interaction on the electronic structure of the bulk and of a slab with finite thickness is investigated. In particular, a phenomenological criterion of band inversion is formulated for both bulk and slab, based on the calculated atomic- and orbital-projections of the wavefunctions, associated with valence and conduction band extrema at the center of the Brillouin zone. We carry out a thorough analysis of the calculated bandstructures of slabs with varying thickness, where surface states are identified using a quantitative criterion according to their spatial distribution. The thickness-dependent energy gap, attributed to inter-surface interaction, and the emergence of gapless surface states for slabs above a critical thickness are investigated. We map out the transition to the infinite-thickness limit by calculating explicitly the modifications in the spatial distribution and spin-character of the surface states wavefunction with increasing the slab thickness. Our numerical analysis shows that the system must be approximately forty quintuple-layers thick to exhibit completely decoupled surface states, localized on the opposite surfaces. These results have implications on the effect of external perturbations on the surface states near the Dirac point.Comment: 11 pages, 11 figure

Midterm press release

project press release issued after the first year of researc

Effects of short-range electron-electron interactions in doped graphene

We study theoretically the effects of short-range electron-electron interactions on the electronic structure of graphene, in the presence of single substitutional impurities. Our computational approach is based on the $\pi$ orbital tight-binding approximation for graphene, with the electron-electron interactions treated self-consistently at the level of the mean-field Hubbard model. We compare explicitly non-interacting and interacting cases with varying interaction strength and impurity potential strength. We focus in particular on the interaction-induced modifications in the local density of states around the impurity, which is a quantity that can be directly probed by scanning tunneling spectroscopy of doped graphene. We find that the resonant character of the impurity states near the Fermi level is enhanced by the interactions. Furthermore, the size of the energy gap, which opens at high-symmetry points of the Brillouin zone of the supercell upon doping, is significantly affected by the interactions. The details of this effect depend subtly on the supercell geometry. We use a perturbative model to explain these features and find quantitative agreement with numerical results.Comment: 10 pages, 5 figure

THE ROLE OF “INTEGRATED PRODUCTION” SCHEME IN THE NEW FRUIT AND VEGETABLE CMO: A TOOL FOR COMPETITIVENESS, SUSTAINABILITY OR OLIGOPSONY BY LARGE RETAIL CHAINS?

The new Common Market Organization (CMO) for the fruit and vegetable sector approved in 2007, continues to include sustainability and competitiveness of the sector among its most important goals. The key role of the new (as well as the old) CMO is still played by Producers Organizations (POs): among other things, they should help farmers to organize and to concentrate supply in order to satisfy the old and new requests by large retailers in Europe as well as in other foreign markets. On the other side POs should also help farmers to apply the best available growing, preserving and packaging technologies, in order to become more competitive but also sustainable from an environmental point of view. In order to satisfy these requests POs have been traditional supporters of new production systems like “Integrated Pest Management” (IPM) and later “Integrated Production” (IP); they have generally offered to their farmers technical assistance for its application in the fruit and vegetable sectors. The main stated objective of IP schemes is to reduce the use of pesticides, and therefore to increase the environmental sustainability of these productions. However differently from the case of organic products, in the case of IP no EU regulation or standard exists. The absence of this common standard has allowed regional authorities to introduce different definitions of IP. Moreover large retail chains, the most important buyers for these products, apply chain-specific requirements, again based on the “idea” of IP and perhaps also on regional IP scheme, to some extent, but always with differences quite important. The actual result is that farmers producing vegetables and fruits must often apply, for the same product grown on the same farm, different technologies in order to obtain different certifications (i.e. regional IP scheme and possibly few different retailers’ scheme) all of them theoretically based on the “common idea” of IP but with quite different interpretations. These different certifications schemes imply, at the farm level, a relevant increase in costs of production and commercialization, without generating any positive economic effect, on one side, and with a large degree of uncertainty in terms of effect on environmental sustainability of these production technologies. The paper starting from the case of fruit production in Emilia-Romagna region, discusses these negative implications together with the possibility for large retail chains to exercise some oligopsony power with respect to POs also using IP schemes. Few implications are drawn with respect to the potential benefits of a common IP scheme defined by EU regulation, and few considerations are made about the main characteristics that this certification should have in order to be (at least theoretically) efficient.Agricultural and Food Policy, Industrial Organization,

Non-Abelian off-diagonal geometric phases in nano-engineered four-qubit systems

The concept of off-diagonal geometric phase (GP) has been introduced in order to recover interference information about the geometry of quantal evolution where the standard GPs are not well-defined. In this Letter, we propose a physical setting for realizing non-Abelian off-diagonal GPs. The proposed non-Abelian off-diagonal GPs can be implemented in a cyclic chain of four qubits with controllable nearest-neighbor interactions. Our proposal seems to be within reach in various nano-engineered systems and therefore opens up for first experimental test of the non-Abelian off-diagonal GP.Comment: Some changes, journal reference adde

The N\'eel order for a frustrated antiferromagnetic Heisenberg model: beyond linear spin-wave theory

Within Dyson-Maleev (DM) transformation and self-consistent mean-field treatment, the N\'eel order/disorder transition is studied for an antiferromagnetic Heisenberg model which is defined on a square lattice with a nearest neighbour exchange $J_1$ and a next-nearest neighbour exchange $J_2$ along only one of the diagonals. It is found that the N\'eel order may exist up to $J_2/J_1=0.572$, beyond its classically stable regime. This result qualitatively improves that from linear spin-wave theory based on Holstein-Primakoff transformation.Comment: 10 pages, 4 eps figure

Trend of the magnetic anisotropy for individual Mn dopants near the (110) GaAs surface

Using a microscopic finite-cluster tight-binding model, we investigate the trend of the magnetic anisotropy energy as a function of the cluster size for an individual Mn impurity positioned in the vicinity of the (110) GaAs surface,We present results of calculations for large cluster sizes, containing approximately 104 atoms, which have not been investigated so far. Our calculations demonstrate that the anisotropy energy of a Mn dopant in bulk GaAs found to be non-zero in previous tight-binding calculations, is purely a finite size effect, and it vanishes as the inverse cluster size. In contrast to this, we find that the splitting of the three in-gap Mn acceptor energy levels converges to a finite value in the limit of infinite cluster size. For a Mn in bulk GaAs this feature is related to the nature of the mean-field treatment of the coupling between the impurity and its nearest neighbors atoms. Moreover, we calculate the trend of the anisotropy energy in the sublayers, as the Mn dopant is moved away from the surface towards the center of the cluster. Here the use of large cluster sizes allows us to position the impurity in deeper sublayers below the surface, compared to previous calculations. In particular, we show that the anisotropy energy increases up to the fifth sublayer and then decreases as the impurity is moved further away from the surface, approaching its bulk value. The present study provides important insight for experimental control and manipulation of the electronic and magnetic properties of individual Mn dopants at the semiconductor surface by means of advanced scanning tunneling microscopy techniques.Comment: 18 pages, 8 figures, Journal. arXiv admin note: text overlap with arXiv:1401.070

Thin films of a three-dimensional topological insulator in a strong magnetic field: a microscopic study

The response of thin films of Bi$_2$Se$_3$ to a strong perpendicular magnetic field is investigated by performing magnetic bandstructure calculations for a realistic multi-band tight-binding model. Several crucial features of Landau quantization in a realistic three-dimensional topological insulator are revealed. The $n=0$ Landau level is absent in ultra-thin films, in agreement with experiment. In films with a crossover thickness of five quintuple layers, there is a signature of the $n=0$ level, whose overall trend as a function of magnetic field matches the established low-energy effective-model result. Importantly, we find a field-dependent splitting and a strong spin-polarization of the $n=0$ level which can be measured experimentally at reasonable field strengths. Our calculations show mixing between the surface and bulk Landau levels which causes the character of levels to evolve with magnetic field.Comment: 5 pages, 4 figure