Atomic decoration for improving the efficiency of field electron emission of carbon nanotubes

The field electron emission from the single-walled carbon nanotubes with their open ends terminated by -BH, -NH, and -O has been simulated. The apex-vacuum barrier and the emission current have been calculated. It has been found that -BH and -NH suppress the apex-vacuum barrier significantly and lead to higher emission current in contrast to the -O terminated structure in the same applied field. The calculated binding energy implies that the carbon nanotubes terminated with -BH and -NH are more stable than those saturated by oxygen atoms or by hydrogen atoms.Comment: 8 pages, 9 figures, LaTeX; content changed, typos corrected, references adde

Scheduling and control of systems subject to random faults

LAUREA MAGISTRALEIn questa tesi presentiamo l’applicazione di alcuni recenti risultati teorici sui sistemi lineari a commutazione Markoviana (MJLS) al controllo di sistemi soggetti a guasti. Precisamente, consideriamo un sistema di controllo in retroazione in cui il segnale di attuazione è intermittente a causa della presenza di guasti. Il modello dei guasti è descritto da una catena di Markov a tempo discreto, mentre le dinamiche dell’impianto e del controllore sono lineari. Come ingresso di controllo aggiuntivo si considera un segnale deterministico di schedulazione capace di commutare all’interno di un insieme di possibili controllori. In tal caso il modello diventa un sistema lineare a duplice commutazione (Dual Switching Linear System). Il principale problema trattato in questo lavoro è il progetto di opportune strategie di commutazione in retroazione capaci di assicurare la stabilità in media quadratica e di ottenere un livello garantito di prestazioni in termini di una funzione di costo quadratica. Il progetto è realizzato mediante il Matlab LMI-Toolbox formulando diverse ipotesi sullo schema di controllo (impianto singolo/doppio, controllore singolo/doppio) e sui parametri della sottostante catena di Markov. Sono state condotte varie simulazioni allo scopo di convalidare i risultati teorici, valutare il grado di conservativismo dei risultati di prestazione e confrontare diverse strategie per calcolare l’ingresso all’impianto quando l’attuatore è in condizioni di guasto.In this thesis we present an application of recent theoretical results regarding Markov Jump Linear Systems to the control of systems affected by random faults. More precisely, we consider a feedback control system where the actuation signal is intermittent, due to the occurrence of faults. The model of faults is described by a discrete-time Markov chain, while the dynamics of the plant and the controller is linear. As an additional control input, a deterministic scheduling signal is considered that can switch among a set of possible controllers. In that case, the model becomes a Dual Switching Linear System. The main problem addressed in this work is the design of suitable switching feedback strategies able to ensure mean-square stability and the attainment of some guaranteed level of performance in terms of a quadratic cost function. The design is carried out by using the Matlab LMI-Toolbox under different assumptions on the control scheme (single/multi plant, single/multi controller) and the parameters of the underlying Markov chain. Several simulations are carried out in order to validate the theoretical results, to assess the degree of conservatism of the results on the performance, and to compare different strategies for computing the input applied to the plant when the actuator is faulty (zero-input vs. input-hold)

Sustainability Disclosure and Financial Performance:The Case of Private and Public Real Estate

The built environment carries an outsized environmental footprint, and aspects such as energy consumption impact the bottom line of commercial real estate (CRE) investors. A large portion of CRE assets are owned and operated by both private equity real estate (PERE) funds and listed property companies (REITs). Therefore, the extent to which these public and private entities integrate sustainability considerations into their investment and operating decisions may impact both the environmental and financial performance for the organizations as well as the environmental performance of the broader market. We provide a comprehensive analysis comparing the sustainability performance of REIT and PERE firms/funds, as well as an analysis of the relationship between sustainability and the financial performance of REITs. Results indicate that private and public CRE entities now seem on par in their integration of sustainability into firm/fund management and policies. However, the performance aspect of sustainability is stronger for REITs. Examination of REIT financial performance indicates that higher levels of sustainability disclosure are associated with enhanced operating performance and firm valuation, as well as a higher propensity for holding environmentally certified buildings

A Learning Curve of the Market: Chasing Alpha of Socially Responsible Firms

This paper explores stock market reactions to corporate social performance. We find that a value-weighted portfolio based on the list of “100 Best CSR companies in the world”, published by Reputation Institute, yields statistically significant annual abnormal returns of 1.63% and 1.26%, by controlling for Carhart four factors and Fama-French five factors, respectively (2.39% and 1.84% respectively for an equal-weighted portfolio). Moreover, such abnormal returns decrease as time goes, especially after the inaugural publication of the CSR lists in 2013. The paper also indicates that companies with better social performance are more likely to have positive earnings surprises, and that their returns are more sensitive to earnings surprises. The results of this paper have three implications: firstly, CSR reputation contributes positively to a firm’s short-term superior equity performance; secondly, the CSR lists facilitate market correction of mispricing intangibles such as CSR reputation - abnormal returns decrease as the market gradually learns about the value of firms’ social performance; lastly, the paper contributes to the socially responsible investing (SRI) screens and provides guidance for investors who would like to do well financially by doing good socially

Dynamic Restoration of Active Distribution Networks by Coordinated Repair Crew Dispatch and Cold Load Pickup

This article presents a dynamic restoration strategy for active distribution networks (ADNs) by coordinating repair crew dispatch and frequency-constrained cold load pickup. To incorporate the stochastic repair time, the repair crew dispatch is formulated as “event-driven” with the implementation of model predictive control (MPC). The stochastic repair time is estimated, convexified, and updated dynamically with each MPC execution. The finish of a repair task triggers the subsequent cold load pickup model, where the frequency dynamics are computed and linearly constrained with the help of a uniform frequency response model for low-inertia systems. Next, a co-optimization framework of the two models is developed to coordinate the repair crew dispatch and cold load pickup under a unified time scale. Numerical results on a modified IEEE 33-node test feeder and a real-world 136-node distribution system have verified the effectiveness of the proposed model.©2024 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.fi=vertaisarvioitu|en=peerReviewed

Cyber-physical interdependent restoration scheduling for active distribution network via ad hoc wireless communication

This paper proposes a post-disaster cyber-physical interdependent restoration scheduling (CPIRS) framework for active distribution networks (ADN) where the simultaneous damages on cyber and physical networks are considered. The ad hoc wireless device-to-device (D2D) communication is leveraged, for the first time, to establish cyber networks instantly after the disaster to support ADN restoration. The repair and operation crew dispatching, the remote-controlled network reconfiguration and the system operation with DERs can be effectively coordinated under the cyber-physical interactions. The uncertain outputs of renewable energy resources (RESs) are represented by budget-constrained polyhedral uncertainty sets. Through implementing linearization techniques on disjunctive expressions, a monolithic mixed-integer linear programming (MILP) based two-stage robust optimization model is formulated and subsequently solved by a customized column-and-constraint generation (C&CG) algorithm. Numerical results on the IEEE 123-node distribution system demonstrate the effectiveness and superiorities of the proposed CPIRS method for ADN