Bernardetta Addis - Academia.edu (original) (raw)

Papers by Bernardetta Addis

Operations Research Letters, 2009

We improve the best known lower bounds on the distance between two points of a Morse cluster in R... more We improve the best known lower bounds on the distance between two points of a Morse cluster in R 3 , with ρ ∈ [4.967, 15]. Our method is a generalization of the one applied to the Lennard-Jones potential in [2], and it also leads to improvements of lower bounds for the energy of a Morse cluster. Some of the numerical results have been announced in [1].

Computational Optimization and Applications, 2008

We improve lower bounds on the minimal distance between two points of a minimum energy configurat... more We improve lower bounds on the minimal distance between two points of a minimum energy configuration w.r.t. the Morse potential. This is achieved by generalizing a method that was already applied to the Lennard-Jones potential in Schachinger et al. (Comput. Optim. Appl. 38:329-349, 2007), resulting in improvements of the currently best bounds known for ρ ∈ [4.967, 15] both for minimal distance and for energy of optimal configurations.

In many telecommunication network architectures a given set of client nodes must be served by dif... more In many telecommunication network architectures a given set of client nodes must be served by different kinds of facility, which provide different services and have different capabilities. Such facilities must be located and dimensioned in the design phase. We tackle a particular location problem in which two sets of facilities, mid level and high level, have to be located. Different devices can be installed in each mid level facility, providing different capacities at different costs. The assignment of clients to facilities and of facilities to higher level entities must be optimized, as well. We propose a heuristic approach, based on very large scale neighborhood search, to tackle the problem, in which both ad-hoc algorithms and general purpose solvers are applied to explore the search space. We report on experimental results using datasets of instances from the literature. These experiments show that the approach is promising and that Integer Linear Programming based neighborhoods are significantly effective.

Membrane gas separation processes are considered as one of the most attractive separation technol... more Membrane gas separation processes are considered as one of the most attractive separation technologies for the development of sustainable industries. The process architecture can be complex and the identification of the optimal design addresses a formidable computational challenge. The main objective of this paper is to study the effectiveness of MBH algorithm to find efficient configurations for the problem of the separation of acid gases from crude natural gas. The comparison with a state of the art paper is used to valide our method.

Chemical Engineering Science, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Electronic Notes in Discrete Mathematics, 2018

The demand for network services, such as proxy or firewall, is ever increasing due to the massive... more The demand for network services, such as proxy or firewall, is ever increasing due to the massive diffusion of applications, both on computers and mobile devices. Virtual Network Functions allow to instantiate network services on clouds in a software based manner, thus allowing to dynamically provide services at a reasonable cost. In this work we consider the problem of placing Virtual Network Function instances (services) and routing the demands so as to guarantee that demands can reach the requested services. We discuss the complexity of a particular version of the Virtual Network Function placement and routing problem and the impact of the network topology on the problem complexity.

Networks, 2016

This article focuses on the problem of minimizing the energy consumption in a resilient telecommu... more This article focuses on the problem of minimizing the energy consumption in a resilient telecommunications network. For each demand, an edge-disjoint pair of paths (primary and backup) must be provided and the shared protection scheme is used. The energy consumption is due only to edges used in the no-fault scenario, but both primary and backup paths contribute to capacity consumption. We propose a projected formulation for the problem and show its effectiveness by comparing it with the complete formulation. We propose valid inequalities for both formulations. We evaluate the performances of the proposed formulations and valid inequalities through computational tests. Furthermore, we investigate the relationship between the shared and the dedicated protection version of the problem.

Electronic Notes in Discrete Mathematics, 2016

Computer Networks, 2014

Despite the growing concern for the energy consumption of the Internet, green strategies for netw... more Despite the growing concern for the energy consumption of the Internet, green strategies for network and traffic management cannot undermine the quality and the functional level normally expected from carrier networks. In particular, two very important issues that may be affected by green networking techniques are resilience to node and link failures, and robustness to traffic variations. In this paper, we study how strategies aiming at achieving different levels of resiliency and robustness impact the efficiency of energy-aware network management approaches in saving energy. We propose novel optimization models to minimize the energy consumption of IP networks that explicitly guarantee network survivability to failures and robustness to traffic variations. Network consumption is reduced by putting in sleep mode idle line cards and nodes according to daily traffic variations that are modeled by dividing a single day into multiple time intervals. To guarantee network survivability we consider two different schemes, dedicated and shared protection, which assign a backup path to each traffic demand and some spare capacity on the links along the path. Robustness to traffic variations is provided through an approach that allows to tune the capacity margin on active links in order to accommodate load variations of different magnitude. Furthermore, we impose some inter-period constraints necessary to guarantee network stability and preserve device lifetime. Both exact and heuristic methods are proposed. Experimentations carried out on realistic networks operated with flow-based routing protocols (like MPLS) allow us to quantitatively analyze the trade-off between energy cost and level of protection and robustness. Results show that with optimal strategies significant savings, up to 30%, can be achieved even when both survivability and robustness are fully guaranteed.

2013 International Conference on Computing, Networking and Communications (ICNC), 2013

ABSTRACT A robust multi-period model is proposed to minimize the energy consumption of IP network... more ABSTRACT A robust multi-period model is proposed to minimize the energy consumption of IP networks, while guaranteeing the satisfaction of uncertain traffic demands. Energy savings are achieved by putting into sleep mode cards and chassis. The study of the solution robustness shows that there is a trade-off between energy consumption and the solutions conservatism degree. The model allows this trade-off to be tuned by simply modifying a single parameter per link. The multi-period optimization is constrained by inter-period limitations necessary to guarantee network stability. Both, exact and heuristic methods are proposed. Results show that up to 60% of the energy savings can be achieved for realistic test scenarios in networks operated with flow-based routing protocols (i.e. MPLS) and with a good level of robustness to traffic variations.

Research Report Series of Iasi Cnr Rome Italy, 2013

This paper describes the methodologies used to tackle the problem of the 5th Global Trajectory Op... more This paper describes the methodologies used to tackle the problem of the 5th Global Trajectory Optimization Competition within the team composed by the Advanced Concepts Team of the European Space Agency and the Global Optimization Laboratory of the University of Florence. The method pursued is powered by two innovative approaches: a linearized model of the 'self fly-by' aiding a first broad tree search of chemical propulsion options and the use of global optimization techniques (Monotonic Basin Hopping, in this case) applied directly to the low-thrust trajectory model.

The main target of advanced medical workforce management is to guarantee the efficiency and fairn... more The main target of advanced medical workforce management is to guarantee the efficiency and fairness of the service delivered. To this aim the development of accurate performance models and the management based on forecasted demand are key issues to deal with. In this paper, we report some solution approaches mainly based on Optimization and Petri Nets models

International Series in Operations Research & Management Science, 2012

The use of general descriptive names, registered names, trademarks, service marks, etc. in this p... more The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use.

We consider the Advanced Scheduling Problem (ASP) assuming a block scheduling strategy. A set of ... more We consider the Advanced Scheduling Problem (ASP) assuming a block scheduling strategy. A set of patients and the related surgery waiting list are given, together with a set of Operating Room (OR) blocks and a planning horizon. The problem asks to determine the subset of patients to be scheduled and their assignment to the available OR blocks. We consider a so-called rolling horizon approach in order to solve the ASP over a planning horizon of several weeks. The approach is iterative and readjusts the schedule each week: at each iteration the mid-term schedule over the next n weeks is generated by solving an optimization problem, minimizing a penalty function based on patients' delay and tardiness; the first week schedule is then implemented. Unpredictable extensions of surgeries and new arrivals may disrupt the schedule. The schedule is then repaired in the next week iteration, again optimizing over n weeks the penalty function while limiting the number of disruptions from the previously computed plan. The total delay and tardiness minimization problem is formulated as an ILP model and solved with a commercial solver. A deterministic formulation and a robust one are proposed and compared over different stochastic realization of surgery times.

This work focuses on the problem of managing an energy aware resilient network. A network and a s... more This work focuses on the problem of managing an energy aware resilient network. A network and a set of available links are given. A set of demands have to be routed and must be protected against single edge failure. Share protection mechanism is considered: for each demand, a primary and a edge-disjoint backup path are provided. Backup paths are used only when a failure occurs. As failures are quickly restored, edges used only by backup paths are active for short periods. Energy consumption is due only to edges used by primary paths, but both primary and backup path contribute to link capacity consumption. The problems asks to route all the demands with the aim of minimizing the overall link device energy consumption. We model the problem with two formulations: a formulation including primary and backup routing variables, and a projected formulation including only primary paths, and we propose valid inequalities for both. We compare three solution strategies: complete formulation solved by CPLEX used as stand-alone solver, complete formulation and projected formulation, both with cut generation. We tested the strategies on two sets of instances. Results show that the projected formulation outperforms the others on both sets of instances.

2012 IEEE Online Conference on Green Communications (GreenCom), 2012

ABSTRACT In this paper we consider the problem of minimizing the energy consumption of IP network... more ABSTRACT In this paper we consider the problem of minimizing the energy consumption of IP networks, exploiting the traffic variations over a set of time intervals, while guaranteeing the network QoS and survivability. Energy savings are achieved by putting into sleep mode cards and chassis, when they are not necessary. Network survivability is based on a dedicated protection scheme, wherein a dedicated backup path is assigned to each demand. The multi-period optimization is constrained by inter-period limitations necessary for guaranteeing network stability. Both exact and heuristic methods are proposed. Results obtained with realistic networks operated with flow-based routing protocols (i.e. MPLS) show that up to 60% of the energy savings can be achieved without negatively affecting network resiliency.