Network conduciveness with application to the graph-coloring and independent-set optimization transitions

We introduce the notion of a network's conduciveness, a probabilistically interpretable measure of how the network's structure allows it to be conducive to roaming agents, in certain conditions, from one portion of the network to another. We exemplify its use through an application to the two problems in combinatorial optimization that, given an undirected graph, ask that its so-called chromatic and independence numbers be found. Though NP-hard, when solved on sequences of expanding random graphs there appear marked transitions at which optimal solutions can be obtained substantially more easily than right before them. We demonstrate that these phenomena can be understood by resorting to the network that represents the solution space of the problems for each graph and examining its conduciveness between the non-optimal solutions and the optimal ones. At the said transitions, this network becomes strikingly more conducive in the direction of the optimal solutions than it was just before them, while at the same time becoming less conducive in the opposite direction. We believe that, besides becoming useful also in other areas in which network theory has a role to play, network conduciveness may become instrumental in helping clarify further issues related to NP-hardness that remain poorly understood

The combinatorics of resource sharing

We discuss general models of resource-sharing computations, with emphasis on the combinatorial structures and concepts that underlie the various deadlock models that have been proposed, the design of algorithms and deadlock-handling policies, and concurrency issues. These structures are mostly graph-theoretic in nature, or partially ordered sets for the establishment of priorities among processes and acquisition orders on resources. We also discuss graph-coloring concepts as they relate to resource sharing.Comment: R. Correa et alii (eds.), Models for Parallel and Distributed Computation, pp. 27-52. Kluwer Academic Publishers, Dordrecht, The Netherlands, 200

Optimization of supply diversity for the self-assembly of simple objects in two and three dimensions

The field of algorithmic self-assembly is concerned with the design and analysis of self-assembly systems from a computational perspective, that is, from the perspective of mathematical problems whose study may give insight into the natural processes through which elementary objects self-assemble into more complex ones. One of the main problems of algorithmic self-assembly is the minimum tile set problem (MTSP), which asks for a collection of types of elementary objects (called tiles) to be found for the self-assembly of an object having a pre-established shape. Such a collection is to be as concise as possible, thus minimizing supply diversity, while satisfying a set of stringent constraints having to do with the termination and other properties of the self-assembly process from its tile types. We present a study of what we think is the first practical approach to MTSP. Our study starts with the introduction of an evolutionary heuristic to tackle MTSP and includes results from extensive experimentation with the heuristic on the self-assembly of simple objects in two and three dimensions. The heuristic we introduce combines classic elements from the field of evolutionary computation with a problem-specific variant of Pareto dominance into a multi-objective approach to MTSP.Comment: Minor typos correcte

Development of an Actuator for an Airdropped Platform Landing System

This work presents an actuation system that aims at improving the maneuvering capability during the landing phase of the LAICAnSat platform. The LAICAnSat is a low-cost, modular platform for high altitude applications, such as remote sensing, telecommunications, research, development and innovation within the aerospace field. The landing system uses a ram-air parachute that is actuated by servo motors located on a pseudo 2U CubeSat platform. This platform differs from the actual CubeSat standard due to the actuation mechanisms on the outside of a 2U standard module. A brake lines actuator is responsible for the directional, speed and glide ratio control. The paper provides details of the design, realization and testing of the actuation system, which represent a first attempt in the development of an autonomous landing system for the LAICAnSat

Enumerating Cyclic Orientations of a Graph

Acyclic and cyclic orientations of an undirected graph have been widely studied for their importance: an orientation is acyclic if it assigns a direction to each edge so as to obtain a directed acyclic graph (DAG) with the same vertex set; it is cyclic otherwise. As far as we know, only the enumeration of acyclic orientations has been addressed in the literature. In this paper, we pose the problem of efficiently enumerating all the \emph{cyclic} orientations of an undirected connected graph with $n$ vertices and $m$ edges, observing that it cannot be solved using algorithmic techniques previously employed for enumerating acyclic orientations.We show that the problem is of independent interest from both combinatorial and algorithmic points of view, and that each cyclic orientation can be listed with $\tilde{O}(m)$ delay time. Space usage is $O(m)$ with an additional setup cost of $O(n^2)$ time before the enumeration begins, or $O(mn)$ with a setup cost of $\tilde{O}(m)$ time

Advanced load-shift system: an experimental validation of the ac-dc converter as shunt active power filter

This paper presents a load-shift system with advanced functionalities to interface the power grid (PG). When compared with the conventional approach, an advanced load-shift system (aLSS) permits the compensation of power quality (PQ) problems for the grid-side, namely problems related to current harmonics, current imbalance, and power factor. The proposed aLSS is composed by a bidirectional ac-dc converter to interface the PG and by a bidirectional dc-dc converter to interface an energy storage system (ESS). Since the main innovation is related with the PG interface, the focus of this work is on the analysis of the ac-dc converter, which is based on a three-phase four-leg converter. A theoretical study and the details concerning the control algorithm are presented and discussed along the paper. A laboratory prototype of the proposed aLSS was developed and the details of implementation are described in the paper. Experimental results obtained with the developed prototype prove that the aLSS contributes for the technology progress in this area, validating a new concept of operation concerning the PQ on the PG side.This work has been supported by FCT – Fundação para a Ciência e Tecnologia with-in the Project Scope: UID/CEC/00319/2019. This work has been supported by the FCT Project QUALITY4POWER PTDC/EEI-EEE/28813/2017, and by the FCT Project newERA4GRIDs PTDC/EEI-EEE/30283/2017