Beyond time-dependent exact-exchange: the need for long-range correlation

In the description of the interaction between electrons beyond the classical Hartree picture, bare exchange often yields a leading contribution. Here we discuss its effect on optical spectra of solids, comparing three different frameworks: time-dependent Hartree-Fock, a recently introduced combined density-functional and Green's functions approach applied to the bare exchange self-energy, and time-dependent exact-exchange within time-dependent density-functional theory (TD-EXX). We show that these three approximations give rise to identical excitonic effects in solids; these effects are drastically overestimated for semiconductors. They are partially compensated by the usual overestimation of the quasiparticle band gap within Hartree-Fock. The physics that lacks in these approaches can be formulated as screening. We show that the introduction of screening in TD-EXX indeed leads to a formulation that is equivalent to previously proposed functionals derived from Many-Body Perturbation Theory. It can be simulated by reducing the long-range part of the Coulomb interaction: this produces absorption spectra of semiconductors in good agreement with experiment.Comment: 12 pages, 3 figures, 1 tabl

Smart traffic management protocol based on VANET architecture

Nowadays one of the hottest theme in wireless environments research is the application of the newest technologies to road safety problems and traffic management exploiting the (VANET) architecture. In this work, a novel protocol that aims to achieve a better traffic management is proposed. The overal system is able to reduce traffic level inside the city exploiting inter-communication among vehicles and support infrastructures also known as (V2V) and (V2I) communications. We design a network protocol called (STMP) that takes advantages of IEEE 802.11p standard. On each road several sensors system are placed and they are responsible of monitoring. Gathered data are spread in the network exploiting ad-hoc protocol messages. The increasing knowledge about environment conditions make possible to take preventive actions. Moreover, having a realtime monitoring of the lanes it is possible to reveal roads and city blocks congestions in a shorter time. An external entity to the (VANET) is responsible to manage traffic and rearrange traffic along the lanes of the city avoiding huge traffic levels

Quality indicators for modified atmosphere packaging (MAP) storage of high-quality european plum (Prunus domestica L.) cultivars

The use of quality indicators is crucial in selling plums in more distant markets and the evaluation of freshness through multiple index is fundamental to evaluate the goodness of the storage technique. In this study we evaluated the quality of two european plums cultivars ('Ramasin' and 'Ariddo di Core' with purple and yellow flesh colour respectively) after modified atmosphere packaging (MAP) storage, through the selection of the most appropriate indicators. The headspace gas composition, the flesh fruit firmness (FFF), the soluble solid content (SSC), the titratable acidity (TA), the colour and the chlorophyll content of plums wrapped with 5 different films (F1, F2, F3, F4 and F5) were evaluated for up 21 days of storage (at 1±1°C and 90-95% relative humidity). For both cultivars, the multilayered films (F1 and F2, 90 and 65 μm respectively) offered better effectiveness over other films. The total chlorophyll concentration, showing a good correlation with the colorimetric parameters of luminance (L∗) and chroma (respectively R2=0.92 and R2= 0.96) confirmed, in the case of the Ariddo di Core cultivar, the results obtained by monitoring other parameters thus highlighting the usefulness of integrating multiple indexes in evaluating the performance of the storage methods used

Evidence for anisotropic dielectric properties of monoclinic hafnia using high-resolution TEM valence electron energy-loss spectroscopy and ab initio time-dependent density-functional theory

The effect of nanocrystal orientation on the energy loss spectra of monoclinic hafnia (m-HfO$_2$) is measured by high resolution transmission electron microscopy (HRTEM) and valence energy loss spectroscopy (VEELS) on high quality samples. For the same momentum-transfer directions, the dielectric properties are also calculated ab initio by time-dependent density-functional theory (TDDFT). Experiments and simulations evidence anisotropy in the dielectric properties of m-HfO$_2$, most notably with the direction-dependent oscillator strength of the main bulk plasmon. The anisotropic nature of m-HfO$_2$ may contribute to the differences among VEELS spectra reported in literature. The good agreement between the complex dielectric permittivity extracted from VEELS with nanometer spatial resolution, TDDFT modeling, and past literature demonstrates that the present HRTEM-VEELS device-oriented methodology is a possible solution to the difficult nanocharacterization challenges given in the International Technology Roadmap for Semiconductors.Comment: 5 pages, 3 figure

Ecological and economic indicators for the evaluation of almond (Prunus dulcis l.) orchard renewal in sicily

Globally, almond production is experiencing a growing trend thanks to a strong interest in the health, gastronomic, and industrial properties that are linked to the fruits and their derivatives. After a constant and marked decline in the second half of the last century, the Mediterranean Basin is thoroughly reassessing this crop, which provides significant results with a modern orchard management. The opportunity determined by the transition from traditional to modern systems have increased the interest in evaluating the different environmental impacts of the two cultivation models that still coexist today. In this work, through the application of the Life Cycle Assessment (LCA) and an economic assessment approach with an in-depth analysis related to the cultivation cycle and the use of resources, the role played by each factor involved in production was determined. Overall, the Greenhouses Gases (GHG) emissions in modern farms are higher (Global Warming Potential (GWP) 0.224 kg CO2 eq.) than those in traditional farms (GWP 0.182 kg CO2 eq.). Regarding the economic assessment, it appears relevant that the modern almond model in the full production phase guarantees significantly higher margins (+84%).The perception of the importance attributed to evaluating economic and environmental aspects by different stakeholders shows relevant differences in the approach coming from growers, dealers, and governmental institutions allows the investigators to positively underline the current innovation in almond orchard systems considering the balance between fruit production and the conservation of environmental resources

Excitation Pathways in Resonant Inelastic X-Ray Scattering of Solids

We present a novel derivation of resonant inelastic x-ray scattering (RIXS) which yields an expression for the RIXS cross section in terms of emission pathways between intermediate and final many-body states. Thereby electron-hole interactions are accounted for, as obtained from full diagonalization of the Bethe-Salpeter equation within an all-electron first-principles framework. We demonstrate our approach with the emission spectra of the fluorine K edge in LiF, and provide an in-depth analysis of the pathways that determine the spectral shape. Excitoninc effects are shown to play a crucial role in both the valence and core regime

Connection between inelastic x-ray scattering and complementary x-ray spectroscopies: probing excitons at Al K and L1 edges of α\alpha-Al2_2O3_3

We present an ab initio study of core excitations at the aluminum K and L1 edges in ${\alpha}$-Al2O3 within an all-electron many-body perturbation theory (MBPT) framework. Calculated XAS reveals excellent agreement with experiments, highlighting the dipole-forbidden nature of the pre-peak, which in experiments is enabled by sp mixing due to atomic vibrations. Non-resonant inelastic X-ray scattering (NRIXS) is employed to go beyond the dipole approximation and probe transition channels with s, p, and d character, enhancing multipole transitions that contribute to the pre-peak. The RIXS spectra at K and L1 edges are remarkably similar, opening the way to soft X-ray RIXS experiments to probe semi-core s states. The RIXS calculations reveal two distinct regimes based on the behavior with incoming photon energy ($\omega_1$). For $\omega_1$ in resonance with the XAS threshold, we observe Raman-like behavior, where the RIXS spectra show significant dependence on $\omega_1$ , reflecting the coupling between absorption and emission processes. For higher $\omega_1$ , above the XAS threshold, the study reveals fluorescence features that appear at constant emission energy, and can be explained via X-ray emission spectroscopy (XES)

The Italian Almond Industry: New Perspectives and Ancient Tradition

The almond industry in Italy presents a high degree of structural variability that is determined by the jeopardized coexistence of old, traditional orchards and new plantations that differ each other not only in terms of age but also mainly in terms of orchard system. Apulia and Sicily still remain the most important production areas where the 90% of the almond orchards are concentrated. In this southern part of Italy, almond and its derivatives still remain really important. In the last two decades, the Italian almond industry did not show a regular trend, neither with respect to production nor to acreage. An innovative almond industry revealed its consistency year after year since 2000: self-fertile cultivars, clonal rootstocks and new planting design ideal for mechanization were the most important technical aspects which revealed a new way to set up almond orchards. As a matter of fact, the Italian almond industry is still characterized by two strongly different structures: a traditional one, which is based upon old cultivars and orchard systems, with unsatisfactory yields indeed, and an innovative one which is really interesting and appears to be able to partially renew the sector. Technical aspects on this new way to obtain innovative almond orchards and their perspectives are here reported mostly in terms of technical choices

Efficient ab initio calculations of bound and continuum excitons

International audienceWe present calculations of the absorption spectrum of semiconductors and insulators comparing various approaches: (i) the two-particle Bethe-Salpeter equation of Many-Body Perturbation Theory; (ii) time-dependent density-functional theory using a recently developed kernel that was derived from the Bethe-Salpeter equation; (iii) a scheme that we propose in the present work and that allows one to derive different parameter-free approximations to (ii). We show that all methods reproduce the series of bound excitons in the gap of solid argon, as well as continuum excitons in semiconductors. This is even true for the simplest static approximation, which allows us to reformulate the equations in a way such that the scaling of the calculations with number of atoms equals the one of the Random Phase Approximation