Quantum Phase Transitions

We give a general introduction to quantum phase transitions in strongly-correlated electron systems. These transitions which occur at zero temperature when a non-thermal parameter $g$ like pressure, chemical composition or magnetic field is tuned to a critical value are characterized by a dynamic exponent $z$ related to the energy and length scales $\Delta$ and $\xi$. Simple arguments based on an expansion to first order in the effective interaction allow to define an upper-critical dimension $D_{C}=4$ (where $D=d+z$ and $d$ is the spatial dimension) below which mean-field description is no longer valid. We emphasize the role of pertubative renormalization group (RG) approaches and self-consistent renormalized spin fluctuation (SCR-SF) theories to understand the quantum-classical crossover in the vicinity of the quantum critical point with generalization to the Kondo effect in heavy-fermion systems. Finally we quote some recent inelastic neutron scattering experiments performed on heavy-fermions which lead to unusual scaling law in $\omega /T$ for the dynamical spin susceptibility revealing critical local modes beyond the itinerant magnetism scheme and mention new attempts to describe this local quantum critical point.Comment: 13 pages, 4 figure

Supersymmetric Approach to Heavy-Fermion Systems

We present a new supersymmetric approach to the Kondo lattice model in order to describe simultaneously the quasiparticle excitations and the low-energy magnetic fluctuations in heavy-Fermion systems. This approach mixes the fermionic and the bosonic representation of the spin following the standard rules of superalgebra. Our results show the formation of a bosonic band within the hybridization gap reflecting the spin collective modes. The density of states at the Fermi level is strongly renormalized while the Fermi surface sum rule includes $n_{c}+1$ states. The dynamical susceptibility is made of a Fermi liquid superimposed on a localized magnetism contribution.Comment: 5 pages, 2 figure

Tessuti in laterizio e tecnologie avanzate

Un tessuto di laterizio riveste gli edifici del nuovo complesso residenziale di Locarno, con una trama aperta e ondulata che lo rende leggero e flessibile. Risultato linguistico ottenuto dalla sperimentazione avanzata di moduli preassemblati in maniera robotizzata, frutto della collaborazione dei progettisti con il mondo della ricerca e dell’industri

Critical phenomena near the antiferromagnetic quantum critical point of Heavy-Fermions

We present a study of the critical phenomena around the quantum critical point in heavy-fermion systems. In the framework of the S=1/2 Kondo lattice model, we introduce an extended decoupling scheme of the Kondo interaction which allows one to treat the spin fluctuations and the Kondo effect on an equal footing. The calculations, developed in a self-consistent one-loop approximation, lead to the formation of a damped collective mode with a dynamic exponent z=2 in the case of an antiferromagnetic instability. The system displays a quantum-classical crossover at finite temperature depending how the energy of the mode, on the scale of the magnetic correlation length, compares to k_B T. The low temperature behavior, in the different regimes separated by the crossover temperatures, is then discussed for both 2- and 3-dimensional systems.Comment: 24 pages, 5 figures, added reference

Vision-Based Hazard Detection with Artificial Neural Networks for Autonomous Planetary Landing

In this paper a hazard detection and landing site selection algorithm, based on a single, visible light, camera acquisition, processed by Artificial Neural Networks (ANNs), is presented. The system is sufficiently light to run onboard a spacecraft during the landing phase of a planetary exploration mission. Unsafe terrain items are detected and arranged in a hazard map, exploited to select the best place to land, in terms of safety, guidance constraints and scientific interest. A set of statistical indexes is extracted from the raw frame, progressively at different scales in order to characterize features of different size and depth. Then, a set of feed-forward ANNs interprets these parameters to produce a hazard map, exploited to select a new target landing site. Validation is carried out by the application of the algorithm to images not considered during the training phase. Landing sites maps are compared to ground-truth solution, and performances are assessed in terms of false positives ratio, false negatives ratio and final selected target safety. Results for different scenarios are shown and discussed, in order to highlight the effectiveness of the proposed system

LCA benchmarks in building's environmental certification systems

The paper deals with the definition of reference values (benchmarks) referred to the Life Cycle Assessment (LCA) indicators used in the environmental certification systems of buildings (Green Building Rating Systems, energy-environmental certifications and environmental labels) highlighting their potentiality and criticality. The environmental certification systems more and more often consider the use of indicators based on LCA methodology which allow to draw attention to environmental performances of building in terms of impacts during the whole life cycle, from the raw materials extraction to the disposal. Today, the environmental impact measure obtained, could be interpreted through the comparison between similar solutions, due to the absence of thresholds which indicate the eco-efficiency of buildings: the benchmark applied to the LCA indicators becomes the threshold value through which measure the real environmental performance of the object analysed. It is a variable value because it depends on the evolution of technologies and construction practices. The environmental certification systems are the first ones which develop a process to define benchmarks because they have to assign a rating score to the indicators in order to obtain the certification. Through the analysis of principal certification systems, characterized by the use of LCA methodology within the score criteria, the different benchmarks methodologies (related to the LCA indicators) are identified and explained. Benchmarks are typically developed through linear interpolation systems, statistical analysis or the modelling of a reference building. In particular the analysis refers to the Green Building Rating Systems (GBRSs), such as DGNB, LEED, and BREEAM, and the energy-environmental certifications (Minergie-Eco). It is showed how the benchmark, into the certification systems, assumes different meanings: it could be the starting standard value (reference value), or the improvement value (target value) or the minimum value to obtain the certification. Starting from these differences and peculiarities, the paper demonstrates potentiality and criticality of the methodological approaches used, in order to understand the role of benchmark in the development of new policies and environmental strategies