Versatile Electro-Dynamic Tethers Dynamics Simulator for Debris Mitigation Tools Design

As far as the space debris mitigation is concerned, the electro-dynamic tethers (EDTs) represent a valuable alternative for de-orbiting. The paper presents a high accuracy numerical simulator developed to support the design and verify the effectiveness of such systems: accurate models are exploited for the mechanical, electrodynamical and environmental representation. Results confirmed the known instabilities of EDTs; to cope with them a control strategy is here proposed, traded off among different laws. The selected control relies on varying either the load resistance or the cathodic emitter voltage drop, at the system cathode, being the current profile the controlled variable. The sensitivity analysis, run on several design parameters, is presented and the interdependencies with stability and performance are discussed

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

Change management and new expertise in AEC firms: improvement in environmental competence

The aim of the paper is to provide an overview of the change management inherent Architecture, Engineering and Construction firms, focusing the attention on the transformation made by environmental issues and their related drivers. Over the last years, building sector has become increasingly complex, due to the heavy demand of a wide range of requirements and to the globalization of the market. This leads on one side the innovation of digital tools, as a result of the development of Information and Communication Technology – ICT, and on the other the division of labour in AEC firms, that is socially spread with an even more highly specialization. The fragmentation can take place in two directions: along what is conventionally defined as the vertical dimension of the process (i.e. the sequence of operations that proceed from inception to implementation phase) as well as along the horizontal dimension (i.e. operations occurring at any given stage). The paper shows the results of the analysis carried out on some of the AEC firms established at international level, highlighting the inner structure, organization, competences and tools used in practice. The configuration of the process structure and the consequent division of labour turn out to be established by a set of internal conditions, generated by the project itself as well as the available technology. Furthermore, the decision to structure internal firm hierarchies or to have external equipment (both experts and tools) depends on the cost that the firms should undertake in order to acquire knowledge, services or products that are external to their sphere of governance. The overview gives an evidence that the explosion of product/service options and the connected specialized systems for the whole building, from exterior cladding to computer-controlled HVAC, require even more a highly amount of knowledge and skills and the demand of new competences and expertise. In particular, the study shows the increasingly request in AEC firms of experts and tools, to deal with the challenging environmental topics. Firms themselves are taking advantage by the integration of environmental topics and goals, as proven by the fact that in the top ten global AEC firms seven of them are considered environmentally friendly (source: ENR). The paper highlights that many drivers are pushing effort in that direction: on one hand, policy and legislation at international and national level, incentive programs and also voluntary certification such as Green Building Rating System; and on the other hand design firms themselves, stimulated by competiveness or, in few case, by their philosophy

Benchmark LCA e uso di EPD nei Green Building Rating System

Lo studio indaga l’utilizzo di valori soglia di riferimento (benchmark) relativi all’analisi Life Cycle Assessment (LCA) e all’uso di certificazioni EPD all’interno dei Green Building Rating Systems (GBRSs). La domanda di certificazioni inerenti alla sostenibilità ambientale in edilizia è in aumento, ma la non comparabilità dei risultati LCA dovuta alle differenti richieste dei sistemi multicriteri costituisce un problema. La scelta di includere nell’analisi LCA diverse parti dell’edificio e di adottare differenti confini di sistema porta ad un’inconfrontabilità delle valutazioni LCA. Lo studio mette in luce potenzialità e criticità dell’uso del Life Cycle Assessment e di EPD nei GBRSs, mostrando come un’uniformità delle scelte legate all’intero ciclo di vita e l’adozione di valori soglia comuni possa portare ad una confrontabilità delle informazioni ambientali degli edifici certificati

Anderson Model out of equilibrium: decoherence effects in transport through a quantum dot

The paper deals with the nonequilibrium two-lead Anderson model, considered as an adequate description for transport through a d-c biased quantum dot. Using a self-consistent equation-of-motion method generalized out of equilibrium, we calculate a fourth-order decoherence rate $\gamma^{(4)}$ induced by a bias voltage $V$. This decoherence rate provides a cut-off to the infrared divergences of the self-energy showing up in the Kondo regime. At low temperature, the Kondo peak in the density of states is split into two peaks pinned at the chemical potential of the two leads. The height of these peaks is controlled by $\gamma^{(4)}$. The voltage dependence of the differential conductance exhibits a zero-bias peak followed by a broad Coulomb peak at large $V$, reflecting charge fluctuations inside the dot. The low-bias differential conductance is found to be a universal function of the normalized bias voltage $V/T_K$, where $T_K$ is the Kondo temperature. The universal scaling with a single energy scale $T_K$ at low bias voltages is also observed for the renormalized decoherence rate $\gamma^{(4)}/T_K$. We discuss the effect of $\gamma^{(4)}$ on the crossover from strong to weak coupling regime when either the temperature or the bias voltage is increased.Comment: 23 pages, 10 figure

Fano factor, ΔT\Delta T-noise and cross-correlations in double quantum dots

We present a theoretical study of electrical current fluctuations and finite-frequency noise in a double quantum dot connected to two electron reservoirs with the aim of deriving the Fano factor, the $\Delta T$-noise and the cross-correlations. This allows one to highlight several interesting features. Firstly the possibility of getting a significant reduction of current noise and Fano factor either when the system is placed in a given operating regime, or when a temperature gradient is applied between the two reservoirs, resulting from the fact that a negative $\Delta T$-noise is generated. The second feature is the sign change found in the cross-correlator between the two reservoirs with increasing frequencies. This study clarifies the understanding of the results obtained experimentally in such systems.Comment: 5 pages, 6 figure

Level anticrossing effect in single-level or multilevel double quantum dots: Electrical conductance, zero-frequency charge susceptibility and Seebeck coefficient

We study electrical and thermoelectrical properties for a double quantum dot system. We consider the cases of both single-level and multilevel quantum dots whatever the way they are coupled, either in a series or in a parallel arrangement. The calculations are performed by using the nonequilibrium Green function theory. In the case of a single-level double quantum dot, the problem is exactly solvable whereas for a multilevel double quantum dot, an analytical solution is obtained in the limit of energy-independent hopping integrals. { We present a detailed discussion about} the dependences of electrical conductance, zero-frequency charge susceptibility and Seebeck coefficient on the gate voltages applied to the dots, allowing us to derive the charge stability diagram. The findings are in agreement with the experimental observations notably with the occurrence of successive sign changes of the Seebeck coefficient when varying the gate voltages. We interpret the results in terms of the bonding and antibonding states produced by the level anticrossing effect which occurs in the presence of a finite interdot coupling. We show that at equilibrium the boundary lines between the domains with different dot occupancies in the charge stability diagram, take place when the bonding and antibonding state levels are aligned with the chemical potentials in the leads. Finally the total dot occupancy is found to be considerably reduced in the case in parallel compared with the case in series, { whenever} the level energies in each dot are equal. We interpret this dip as a direct manifestation of the interference effects occurring in the presence of the two electronic transmission paths provided by each dot.Comment: 18 pages, 13 figure