Excitonic Effects in Quantum Wires

We review the effects of Coulomb correlation on the linear and non-linear optical properties of semiconductor quantum wires, with emphasis on recent results for the bound excitonic states. Our theoretical approach is based on generalized semiconductor Bloch equations, and allows full three-dimensional multisubband description of electron-hole correlation for arbitrary confinement profiles. In particular, we consider V- and T-shaped structures for which significant experimental advances were obtained recently. Above band gap, a very general result obtained by this approach is that electron-hole Coulomb correlation removes the inverse-square-root single-particle singularity in the optical spectra at band edge, in agreement with previous reports from purely one-dimensional models. Strong correlation effects on transitions in the continuum are found to persist also at high densities of photoexcited carriers. Below bandgap, we find that the same potential- (Coulomb) to kinetic-energy ratio holds for quite different wire cross sections and compositions. As a consequence, we identify a shape- and barrier-independent parameter that governs a universal scaling law for exciton binding energy with size. Previous indications that the shape of the wire cross-section may have important effects on exciton binding are discussed in the light of the present results.Comment: Proc. OECS-5 Conference, G\"ottingen, 1997 (To appear in Phys. Stat. Sol. (b)

Self-consistent model for ambipolar tunneling in quantum-well systems

We present a self-consistent approach to describe ambipolar tunneling in asymmetrical double quantum wells under steady-state excitation and extend the results to the case of tunneling from a near-surface quantum well to surface states. The results of the model compare very well with the behavior observed in photoluminescence experiments in $InGaAs/InP$ asymmetric double quantum wells and in near-surface $AlGaAs/GaAs$ single quantum wells.Comment: 10 pages, REVTeX 3.

Exciton formation and relaxation in GaAs epilayers

Exciton formation and relaxation in GaAs bulk epilayers have been studied by means of time-resolved photoluminescence techniques. It is found that the time evolution of the free exciton luminescence, nonresonantly excited at low temperature and low intensity, is extremely slow, with a rise time of the order of 1 ns and a decay time of several ns. Simulations based on Monte Carlo solution of the set of coupled Boltzmann-like equations for free carriers and excitons show a nice agreement with the experimental data, and suggest a dominant role played by acoustic phonons in the exciton relaxation

Modelling disaster risk reduction: decoding social-ecological interactions to foster transformative adaptation

Questa ricerca intende contribuire alla discussione sulla riduzione del rischio disastri (DRR), esplorando come le comunità locali dovrebbero adattarsi ai pericoli che le circondano. La prima parte riporta la teoria della panarchia alle dinamiche del rischio. Il modello teorico che ne deriva, la Panarchia Sociale-Ecologica, descrive le condizioni di rischio e permette di riconoscere i nuclei del DRR: la resilienza ai disastri e la sostenibilità ambientale. Il modello fornisce le basi per lo sviluppo di una Valutazione Combinata di Resilienza e Sostenibilità, concentrata sul rischio inondazione alla scala comunale. La seconda parte svolge un’analisi quantitativa attraverso indicatori, che identificano e caratterizzano i livelli di resilienza e sostenibilità. La terza parte impiega strumenti qualitativi (questionari) per raccogliere le percezioni delle comunità locali sui rischi presenti nei loro Comuni. L’analisi è stata applicata a due casi studio, la Regione Marche (Italia) e l’Hokkaidō (Giappone). I risultati mostrano il ruolo delle inondazioni nel determinare la resilienza locale, e degli impatti antropici per la sostenibilità. Le criticità maggiori sono concentrate nelle aree montane/collinari. Allo stesso tempo, aspetti di welfare e sicurezza sociale risultano fondamentali per formare la resilienza, così come la presenza di vegetazione lo è per la sostenibilità. Inoltre, emerge una sostanziale differenza fra misurazione e percezione di resilienza e sostenibilità, generalmente in senso peggiorativo. In generale, ulteriori sforzi dovrebbero essere diretti alle aree interne, benché la regione intera gioverebbe del consolidamento della resilienza locale. Inoltre, le comunità sembrano molto sensibili ai temi ambientali, per cui potrebbero appoggiare sforzi per aumentare la sostenibilità. Infine, questi studi possono contribuire alle strategie DRR, per promuovere l’adattamento trasformativo delle comunità locali, reso urgente dall’esasperazione degli eventi estremi.This research intends to contribute to the discussion on disaster risk reduction (DRR), investigating the question of how local communities should adjust to the surrounding threats. The first part adapted the panarchy heuristics to risk dynamics. The drawn theoretical model, the Social-Ecological Panarchy, could describe the conditions of risk and allow to recognise the two cores of DRR: disaster resilience and environmental sustainability. The model supported the development of a Combined Assessment of Resilience and Sustainability, focused on flood risk at the Municipal scale. The second part of the research performed a quantitative analysis through numerical indicators, that identified and characterised the levels of resilience and sustainability. The third part of the research employed qualitative tools (questionnaires) to gather the thoughts of local communities on the risks affecting their Municipalities. The analysis was applied to two case studies, Marche Region (Italy) and Hokkaidō (Japan). Results evidenced the role of flood events in determining the resilience capacities of local communities, and of the anthropic impacts for defining their sustainability. Most critical issues lied in the mountainous/hill areas. At the same time, social welfare and protection appeared pivotal in building local resilience, while the presence of vegetation shaped sustainability. Besides, a substantial mismatch emerged between assessed and perceived conditions of resilience and sustainability, generally in negative terms. Overall, it appeared that further efforts should be tailored to the innermost areas, though the overall region might benefit from consolidated resilience. At the same time, local populations seemed highly responsive to environmental issues, possibly endorsing the enhancement of sustainability. Eventually, these insights might inform risk reduction strategies, to foster a transformative adaptation of local communities, urged by exacerbating disruptive threats

Blockchain for traceability : real use cases from agri-food industry

LAUREA MAGISTRALEDal 2008 la blockchain ha ricevuto una maggiore attenzione, poiché le sue capacità si sono dimostrate promettenti non solo per il mondo finanziario, ma anche per molti altri settori. Una delle applicazioni più importanti al di là della finanza, è quella la trasparenza sulla catena di approvvigionamento. Un numero crescente di aziende sta implementando blockchain per la tracciabilità delle merci, specialmente nel settore agroalimentare, dove i clienti premono le aziende per avere maggiori informazioni sui prodotti che consumano. Tuttavia, sono pochi i casi d'uso reali della blockchain per la tracciabilità e questa mancanza di prove empiriche previene e aziende dall’ adottarla: quest’ ultime sono frenate dal realizzare una blockchain per loro sistemi di tracciabilità a causa dei dubbi su come trarne vantaggio. L'implementazione di una Blockchain comporta costi elevati e le aziende vogliono avere un quadro chiaro prima di coinvolgersi in questi progetti . Pertanto, lo scopo di questo lavoro è indagare su casi d'uso reali al fine di comprendere i motivi per l'implementazione di una blockchain per la tracciabilità e come trarne vantaggio.Since 2008 blockchain received an increased attention, because its capabilities were promising not only for the financial world, but also for many other industries. One of the he most prominent application beyond finance, is to pursue transparency on the supply chain. An increasing number of companies are implementing blockchain for traceability of goods, especially in the agri-food domain where customers press companies to have more information on products they consume. However, there are few real use cases of blockchain for the traceability and this lack of empirical evidence is a barrier of adoption: companies are worried to realize a blockchain in their traceability systems due to the doubts on how to benefit from it. Implementing a Blockchain for traceability of product comes with high costs and firms want to see a clear pictures before engaging in it. Thus, the aim of this work is investigating on real use cases in order to understand the reasons to a blockchain for the traceability of goods and how to benefit from it

INFN What Next: Ultra-relativistic Heavy-Ion Collisions

This document was prepared by the community that is active in Italy, within INFN (Istituto Nazionale di Fisica Nucleare), in the field of ultra-relativistic heavy-ion collisions. The experimental study of the phase diagram of strongly-interacting matter and of the Quark-Gluon Plasma (QGP) deconfined state will proceed, in the next 10-15 years, along two directions: the high-energy regime at RHIC and at the LHC, and the low-energy regime at FAIR, NICA, SPS and RHIC. The Italian community is strongly involved in the present and future programme of the ALICE experiment, the upgrade of which will open, in the 2020s, a new phase of high-precision characterisation of the QGP properties at the LHC. As a complement of this main activity, there is a growing interest in a possible future experiment at the SPS, which would target the search for the onset of deconfinement using dimuon measurements. On a longer timescale, the community looks with interest at the ongoing studies and discussions on a possible fixed-target programme using the LHC ion beams and on the Future Circular Collider.Comment: 99 pages, 56 figure

Multiplicity dependence of jet-like two-particle correlations in p-Pb collisions at sNN\sqrt{s_{NN}} = 5.02 TeV

Two-particle angular correlations between unidentified charged trigger and associated particles are measured by the ALICE detector in p-Pb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV. The transverse-momentum range 0.7 $< p_{\rm{T}, assoc} < p_{\rm{T}, trig} <$ 5.0 GeV/$c$ is examined, to include correlations induced by jets originating from low momen\-tum-transfer scatterings (minijets). The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range $|\eta|<0.9$. The near-side long-range pseudorapidity correlations observed in high-multiplicity p-Pb collisions are subtracted from both near-side short-range and away-side correlations in order to remove the non-jet-like components. The yields in the jet-like peaks are found to be invariant with event multiplicity with the exception of events with low multiplicity. This invariance is consistent with the particles being produced via the incoherent fragmentation of multiple parton--parton scatterings, while the yield related to the previously observed ridge structures is not jet-related. The number of uncorrelated sources of particle production is found to increase linearly with multiplicity, suggesting no saturation of the number of multi-parton interactions even in the highest multiplicity p-Pb collisions. Further, the number scales in the intermediate multiplicity region with the number of binary nucleon-nucleon collisions estimated with a Glauber Monte-Carlo simulation.Comment: 23 pages, 6 captioned figures, 1 table, authors from page 17, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/161

Exploring the formal development of regional policies and their potential to drive local change: Insights on climate change adaptation in Italy.

The growing impacts of climate change are urging effective countermeasures in terms of adaptation, particularly through appropriate policy tools integrated across levels of governance. Local governments, often at the forefront of climate action, play a critical role. The regional level can become a key element in the adaptation chain, connecting higher-level perspectives to local implementation. The present study aimed to investigate, first, the formal development of regional adaptation policies and, second, their potential to drive local change, focusing on the case study of Italian regions. This study proposed a twofold, qualitative-quantitative assessment methodology based on the European Regional Adaptation Support Tool framework and a novel approach built on six main factors. Our analysis revealed the underdevelopment of regional adaptation policies, highlighting a critical interruption in the adaptation chain interconnecting European, national and local levels. Furthermore, even when formally issued, regional policies exhibited several significant weaknesses, severely hampering their potential to foster local change. This was especially evident in the generally limited efforts to engage internal and external climate agents through structured mechanisms. In this context, it would be beneficial for regions to embrace the role of coordinating local efforts and actions. Providing actionable solutions, along with related monitoring and evaluation tools, could enhance local climate action and inform the revision of policies across governance levels. Adaptation policies should envisage actions that progressively involve and promote change comprehensively across the territory. We conclude that further efforts should focus on strengthening local climate resilience, not only by developing formal adaptation policies but also by fostering local change

Instabilities in crystal growth by atomic or molecular beams

The planar front of a growing a crystal is often destroyed by instabilities. In the case of growth from a condensed phase, the most frequent ones are diffusion instabilities, which will be but briefly discussed in simple terms in chapter II. The present review is mainly devoted to instabilities which arise in ballistic growth, especially Molecular Beam Epitaxy (MBE). The reasons of the instabilities can be geometric (shadowing effect), but they are mostly kinetic or thermodynamic. The kinetic instabilities which will be studied in detail in chapters IV and V result from the fact that adatoms diffusing on a surface do not easily cross steps (Ehrlich-Schwoebel or ES effect). When the growth front is a high symmetry surface, the ES effect produces mounds which often coarsen in time according to power laws. When the growth front is a stepped surface, the ES effect initially produces a meandering of the steps, which eventually may also give rise to mounds. Kinetic instabilities can usually be avoided by raising the temperature, but this favours thermodynamic instabilities. Concerning these ones, the attention will be focussed on the instabilities resulting from slightly different lattice constants of the substrate and the adsorbate. They can take the following forms. i) Formation of misfit dislocations (chapter VIII). ii) Formation of isolated epitaxial clusters which, at least in their earliest form, are `coherent' with the substrate, i.e. dislocation-free (chapter X). iii) Wavy deformation of the surface, which is presumably the incipient stage of (ii) (chapter IX). The theories and the experiments are critically reviewed and their comparison is qualitatively satisfactory although some important questions have not yet received a complete answer.Comment: 90 pages in revtex, 45 figures mainly in gif format. Review paper to be published in Physics Reports. Postscript versions for all the figures can be found at http://www.theo-phys.uni-essen.de/tp/u/politi

Multi-particle azimuthal correlations in p-Pb and Pb-Pb collisions at the CERN Large Hadron Collider

Measurements of multi-particle azimuthal correlations (cumulants) for charged particles in p-Pb and Pb-Pb collisions are presented. They help address the question of whether there is evidence for global, flow-like, azimuthal correlations in the p-Pb system. Comparisons are made to measurements from the larger Pb-Pb system, where such evidence is established. In particular, the second harmonic two-particle cumulants are found to decrease with multiplicity, characteristic of a dominance of few-particle correlations in p-Pb collisions. However, when a $|\Delta \eta|$ gap is placed to suppress such correlations, the two-particle cumulants begin to rise at high-multiplicity, indicating the presence of global azimuthal correlations. The Pb-Pb values are higher than the p-Pb values at similar multiplicities. In both systems, the second harmonic four-particle cumulants exhibit a transition from positive to negative values when the multiplicity increases. The negative values allow for a measurement of $v_{2}\{4\}$ to be made, which is found to be higher in Pb-Pb collisions at similar multiplicities. The second harmonic six-particle cumulants are also found to be higher in Pb-Pb collisions. In Pb-Pb collisions, we generally find $v_{2}\{4\} \simeq v_{2}\{6\}\neq 0$ which is indicative of a Bessel-Gaussian function for the $v_{2}$ distribution. For very high-multiplicity Pb-Pb collisions, we observe that the four- and six-particle cumulants become consistent with 0. Finally, third harmonic two-particle cumulants in p-Pb and Pb-Pb are measured. These are found to be similar for overlapping multiplicities, when a $|\Delta\eta| > 1.4$ gap is placed.Comment: 25 pages, 11 captioned figures, 3 tables, authors from page 20, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/87