Three-dimensional Topological Insulators and Bosonization

Massless excitations at the surface of three-dimensional time-reversal invariant topological insulators possess both fermionic and bosonic descriptions, originating from band theory and hydrodynamic BF gauge theory, respectively. We analyze the corresponding field theories of the Dirac fermion and compactified boson and compute their partition functions on the three-dimensional torus geometry. We then find some non-dynamic exact properties of bosonization in (2+1) dimensions, regarding fermion parity and spin sectors. Using these results, we extend the Fu-Kane-Mele stability argument to fractional topological insulators in three dimensions.Comment: 54 pages, 11 figure

modelling and control of a free cooling system for data centers

Abstract Data centers are facilities hosting a large number of servers dedicated to data storage and management. In recent years, their power consumption has increased significantly due to the power density of the IT equipment. In particular, cooling represents approximately one third of the total electricity consumption, therefore efficiently cooling data centers has become a challenging problem and it represents an opportunity to reduce both IT energy costs and emissions environmental impact. The efficiency of computers room air conditioning (CRAC) systems can be increased using both advanced control techniques and new free cooling technologies, such as the indirect adiabatic cooling (IAC), that is the humidification of air under adiabatic conditions. Water sprinkled by spray nozzles humidifies and cools down the air taken from the outside, which then cools down the computers room air by means of a crossflow heat exchanger. In this way, the process air temperature is economically reduced and the cooling process is effective even when the outside temperature is warmer than that desired in the computers room. Beside the traditional approach, that improves energy efficiency of CRAC systems through advanced hardware design, nowadays advanced control systems offer the opportunity to improve both efficiency and performance by mostly acting on software components. In particular, a model-based paradigm can result very useful in the design of the controller. This approach involves three main steps: plant modelling, controller design, and simulations. In this paper, First-Principle Data-Driven (FPDD) techniques have been considered in the modelling phase, in order to obtain a model as simple as possible but accurate enough. All the main components of the plant, such as fans, spray nozzles, heat exchanger, and the computers room have been taken into account and they have been calibrated exploiting real data. The dynamics of the computers room variables (e.g. temperature) are slower than those of the components of the cooling system, due to higher thermal inertias of the computers room. Therefore, fans, heat exchanger, and spray nozzles are described by static models, whereas the computers room is described by a LTI dynamic model. Once obtained a model of the plant, a simulation environment based on Matlab/Simulink is designed accordingly. The developed control system is hierarchical: a supervisor determines the best combination of CRAC water and process air flows which minimizes the total power consumption, while satisfying the cooling demand. This system energy management problem is formulated as a non-linear optimization problem, subject to internal air condition requirements and system operating constraints. The optimization problem is repeatedly solved at each supervision period by using a population based stochastic optimization technique (Particle Swarm Optimization). Results of simulations show that the proposed control system is effective and minimizes the input electric power while satisfying both the data center thermal load and system operating constraints

Promuovere la mediazione culturale in Piemonte : la valutazione di una politica regionale per diffondere la mediazione culturale nelle amministrazioni pubbliche piemontesi

Contributi di ricerca ; n.197/2006- Indice #5- Introduzione #7- Le finalità della valutazione e il metodo di lavoro #11- Il disegno della politica #19- L'iter amministrativo per la realizzazione dei progetti di valutazione #33- Le esperienze di mediazione culturale #41- La formazione per gli operatori pubblici #63- Conclusioni #83- Appendici #8

Abdominal drainage after elective colorectal surgery: propensity score-matched retrospective analysis of an Italian cohort

background: In italy, surgeons continue to drain the abdominal cavity in more than 50 per cent of patients after colorectal resection. the aim of this study was to evaluate the impact of abdominal drain placement on early adverse events in patients undergoing elective colorectal surgery. methods: a database was retrospectively analysed through a 1:1 propensity score-matching model including 21 covariates. the primary endpoint was the postoperative duration of stay, and the secondary endpoints were surgical site infections, infectious morbidity rate defined as surgical site infections plus pulmonary infections plus urinary infections, anastomotic leakage, overall morbidity rate, major morbidity rate, reoperation and mortality rates. the results of multiple logistic regression analyses were presented as odds ratios (OR) and 95 per cent c.i. results: a total of 6157 patients were analysed to produce two well-balanced groups of 1802 patients: group (A), no abdominal drain(s) and group (B), abdominal drain(s). group a versus group B showed a significantly lower risk of postoperative duration of stay >6 days (OR 0.60; 95 per cent c.i. 0.51-0.70; P < 0.001). a mean postoperative duration of stay difference of 0.86 days was detected between groups. no difference was recorded between the two groups for all the other endpoints. conclusion: this study confirms that placement of abdominal drain(s) after elective colorectal surgery is associated with a non-clinically significant longer (0.86 days) postoperative duration of stay but has no impact on any other secondary outcomes, confirming that abdominal drains should not be used routinely in colorectal surgery

Study of an intrinsically safe infrastructure for training and research on nuclear technologies

Within European Partitioning & Transmutation research programs, infrastructures specifically dedicated to the study of fundamental reactor physics and engineering parameters of future fast-neutron-based reactors are very important, being some of these features not available in present zero-power prototypes. This presentation will illustrate the conceptual design of an Accelerator-Driven System with high safety standards, but ample flexibility for measurements. The design assumes as base option a 70MeV, 0.75mA proton cyclotron, as the one which will be installed at the INFN National Laboratory in Legnaro, Italy and a Beryllium target, with Helium gas as core coolant. Safety is guaranteed by limiting the thermal power to 200 kW, with a neutron multiplication coefficient around 0.94, loading the core with fuel containing Uranium enriched at 20% inserted in a solid-lead diffuser. The small decay heat can be passively removed by thermal radiation from the vessel. Such a system could be used to study, among others, some specific aspects of neutron diffusion in lead, beam-core coupling, target cooling and could serve as a training facility

Modellizzazione di un sistema di raffreddamento adiabatico indiretto per applicazioni di risparmio energetico nei centri di elaborazione dati

I centri di Centri di Elaborazione Dati (CED) sono sempre più diffusi e la loro gestione energetica è cruciale.In un CED, il sistema di condizionamento rappresenta più di un terzo dell'energia totale consumata e offre spessoconsistenti opportunità per ridurre i costi energetici e per aumentare l'efficienza. In questa tesi si è sviluppato un modello, in ambiente Matlab/Simulink, di un sistema di raffreddamento adiabatico indiretto per applicazioni di risparmio energetico nei CE

Global Sensitivity Analysis applied to a dynamic energy simulation model: the case study of UniZEB prototype building

Nowadays, due to the growing interest in improving building energy performance, energy models and simulation tools offer new chances to manage the increasing complexity of environments such as nearly Zero- Energy Buildings and Smart Buildings. These tools enable the acceleration of innovation cycles, rapidly exploring new solutions that range from the use of ground source to air source heat pumps, photovoltaic systems, and controlled mechanical ventilation to building automation and HVAC system control. In this scenario, it becomes relevant to define the importance of model inputs and their interactions with respect to the outputs of the model. This paper presents a Global Sensitivity Analysis (GSA) of the TRNSYS-based dynamic model of an nZEB Living-Lab at the University of Padova (Italy). GSA, and in particular the application of the Morris method, provides an overall view of the influence of inputs on outputs, as all the model input factors are varied simultaneously, and the sensitivity is evaluated over the entire range of each input factor