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Publications

2010

Dynamics of Epidemiological Models

Authors
Pinto, A; Aguiar, M; Martins, J; Stollenwerk, N;

Publication
ACTA BIOTHEORETICA

Abstract
We study the SIS and SIRI epidemic models discussing different approaches to compute the thresholds that determine the appearance of an epidemic disease. The stochastic SIS model is a well known mathematical model, studied in several contexts. Here, we present recursively derivations of the dynamic equations for all the moments and we derive the stationary states of the state variables using the moment closure method. We observe that the steady states give a good approximation of the quasi-stationary states of the SIS model. We present the relation between the SIS stochastic model and the contact process introducing creation and annihilation operators. For the spatial stochastic epidemic reinfection model SIRI, where susceptibles S can become infected I, then recover and remain only partial immune against reinfection R, we present the phase transition lines using the mean field and the pair approximation for the moments. We use a scaling argument that allow us to determine analytically an explicit formula for the phase transition lines in pair approximation.

2010

Towards the introduction of QoS information in a component model

Authors
Meng, S; Barbosa, LS;

Publication
Proceedings of the ACM Symposium on Applied Computing

Abstract
Assuring Quality of Service (QoS) properties is critical in the development of component-based distributed systems. This paper presents an approach to introduce QoS constraints into a coalgebraic model of software components. Such constraints are formally captured through the concept of a Q-algebra which, in its turn, can be smoothly integrated in the definition of component combinators. © 2010 ACM.

2010

Flexible internal logistics based on AGV system's: A case study

Authors
Rocha, LF; Moreira, AP; Azevedo, A;

Publication
IFAC Proceedings Volumes (IFAC-PapersOnline)

Abstract
Automated Guided Vehicles (AGV) are self-driven vehicles used to transport material between workstations in the shop floor without the help of an operator, although they can also be applied in security and exploration. They are widely used in material handling systems and flexible manufacturing systems, where production orders are constantly changing. Today, and due to the constant development of technology, sophisticated machinery is increasingly available, thus enabling manufacturing firms to achieve significant process and setup time reductions. With this development, enterprises are encouraged to leave mass production approaches and start adopting small productions lot sizes, leading to constant changes in the production operation's sequences as well as changes in the factory layout. As a consequence of the development of technology, products started to spend a big percentage of time in the queue line or being transported from one workstation/storage to another. With the introduction of AGVs production process flexibility may increase, which, in many productions processes, is still below the expectations due to the used transportation system (ex: conveyors). At the same time, with the AGVs it is possible, to decrease transportations times and costs. In this article, we will study by means of simulation, the impact of the use of an AGV transportation based system in an industrial coating application. The AGV will be responsible for transporting the parts from the system's entrance to the workstations. With this, flexibility in the production process will increase, which will be reflected in system's productivity. © 2010 IFAC.

2010

Research issues on customer-oriented and eco-friendly networks for healthy fashionable goods

Authors
Fornasiero, R; Chiodi, A; Carpanzano, E; Carneiro, L;

Publication
IFIP Advances in Information and Communication Technology

Abstract
Needs and expectations of specific target groups - such as elderly, obese, disabled, or diabetic persons- are arising as challenging opportunities for European companies which are asked to supply small series of functional and fashionable goods of high quality, affordable price and eco-compatible. In order to design, develop, produce and distribute such products, a new framework and related components of collaborative networking need to be developed, enabling the product to stay as long as digital to produce on-demand. Research is necessary in many topics like: a) consumer integrated collaborative eco-oriented design, b) radical renewal by the adoption of Rapid Manufacturing technologies; and c) the overall integration and co-ordination of business processes and information exchange by a set of new (web)services for network design and adhoc (re-)configuration, for real-time planning, forecasting and replenishment, d) tracking and tracing of ecology and quality. © IFIP International Federation for Information Processing 2010.

2010

Godel's system T revisited

Authors
Alves, S; Fernandez, M; Florido, M; Mackie, I;

Publication
THEORETICAL COMPUTER SCIENCE

Abstract
The linear lambda calculus, where variables are restricted to occur in terms exactly once, has a very weak expressive power: in particular, all functions terminate in linear time. In this paper we consider a simple extension with natural numbers and a restricted iterator: only closed linear functions can be iterated. We show properties of this linear version of Godel's T using a closed reduction strategy, and study the class of functions that can be represented. Surprisingly, this linear calculus offers a huge increase in expressive power over previous linear versions of T, which are 'closed at construction' rather than 'closed at reduction'. We show that a linear T with closed reduction is as powerful as T.

2010

Assertion-based slicing and slice graphs

Authors
Barros, JB; Da Cruz, D; Henriques, PR; Pinto, JS;

Publication
Proceedings - Software Engineering and Formal Methods, SEFM 2010

Abstract
This paper revisits the idea of slicing programs based on their axiomatic semantics, rather than using criteria based on control/data dependencies. We show how the forward propagation of preconditions and the backward propagation of post conditions can be combined in a new slicing algorithm that is more precise than the existing specification-based algorithms. The algorithm is based on (i) a precise test for removable statements, and (ii) the construction of a slice graph, a program control flow graph extended with semantic labels. It improves on previous approaches in two aspects: it does not fail to identify removable commands; and it produces the smallest possible slice that can be obtained (in a sense that will be made precise). The paper also reviews in detail, through examples, the ideas behind the use of preconditions and post conditions for slicing programs. © 2010 IEEE.

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