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Biblioteca Digital do IPB (53.442 recursos)

A Biblioteca Digital do IPB, tem por objectivo divulgar e permitir o livre acesso à produção científica produzida pela comunidade académica, promovendo a integração, partilha e a visibilidade da informação científica e garantindo a preservação da memória intelectual do Instituto Politécnico de Bragança.

IC - Artigos em Revistas Indexadas ao ISI

Mostrando recursos 1 - 20 de 33

  1. A GRASP approach to the container-loading problem

    Moura, Ana; Oliveira, J.F.
    The GRMODGRASP, a new algorithm for the container-loading problem (CLP) based on the greedy randomized adaptive search procedure (GRASP) approach, is discussed. Based on a wall-building, constructive heuristic, it can achieve high levels of cargo stability without compromising the container's volume use. The algorithm builds a solution, and then it improves the solution with a local-search algorithm. If it finds a better solution, this new solution replaces the old and a new neighborhood is built around it. The algorithm uses a first better strategy when more than one better solution exists

  2. Profiling and framing structures for pervasive information systems development

    Fernandes, José Eduardo; Machado, Ricardo J.; Carvalho, João Álvaro
    Pervasive computing is a research field of computing technology that aims to achieve a new computing paradigm. Software engineering has been, since its existence, subject of research and improvement in several areas of interest. Model-Based/Driven Development (MDD) constitutes an approach to software design and development that potentially contributes to: concepts closer to domain and reduction of semantic gaps; automation and less sensitivity to technological changes; capture of expert knowledge and reuse. This paper presents a profiling and framing structure approach for the development of Pervasive Information Systems (PIS). This profiling and framing structure allows the organization of the functionality that can be assigned to computational devices in a system and...

  3. A DSL for PIM specifications: design and attribute grammar based implementation

    Lukovic, Ivan; Pereira, Maria João; Oliveira, Nuno; Cruz, Daniela; Henriques, Pedro
    IIS*Case is a model driven software tool that provides information system modeling and prototype generation. It comprises visual and repository based tools for creating various platform independent model (PIM) specifications that are latter transformed into the other, platform specific specifications, and finally to executable programs. Apart from having PIMs stored as repository definitions, we need to have their equivalent representation in the form of a domain specific language. One of the main reasons for this is to allow for checking the formal correctness of PIMs being created. In the paper, we present such a meta-language, named IIS*CDesLang. IIS*CDesLang is specified...

  4. An effective algorithm for obtaining the whole set of minimal cost pairs of disjoint paths with dual arc costs

    Gomes, Teresa; Craveirinha, José; Jorge, Luísa
    In telecommunication networks design the problem of obtaining optimal (arc or node) disjoint paths, for increasing network reliability, is extremely important. The problem of calculating kc disjoint paths from s to t (two distinct nodes), in a network with kc different (arbitrary) costs on every arc such that the total cost of the paths is minimised, is NP-complete even for kc = 2. When kc = 2 these networks are usually designated as dual arc cost networks. In this paper we propose an exact algorithm for finding the whole set of arc-disjoint path pairs, with minimal cost in a network with...

  5. An effective algorithm for obtaining the minimal cost pair of disjoint paths with dual arc costs

    Gomes, Teresa; Craveirinha, José; Jorge, Luísa
    Routing optimisation in some types of networks requires the calculation of the minimal cost pair of disjoint paths such that the cost functions associated with the arcs in the two paths are different. An exact algorithm for solving this NP-complete problem is proposed, based on a condition which guarantees that the optimal path pair cost has been obtained. This optimality condition is based on the calculation of upper and lower bounds on the optimal cost. A formal proof of the correctness of the algorithm is described. Extensive experimentation is presented to show the effectiveness of the algorithm, including a comparison...

  6. Using CIM extensions to model managed entities in heterogeneous networks

    Dziunikowski, W.; Wszolek, J.; Gonçalves, P.; Rasmussen, S.; Cuevas, A.; Lopes, Rui Pedro; Roque, Vitor; Oliveira, José Luís
    This paper is devoted to the definition of management information which models specific functionality of the entities that build Daidalos European Project. This management information will be used in policy–based management system (PBNMS) to manage QoS aspects of the network functionality.

  7. Executable graphics for PBNM

    Lopes, Rui Pedro; Raimundo, Nuno; Pereira, Maria João; Oliveira, José Luís; Roque, Vitor
    The specification of a policy is performed in a policy language, usually following a textual representation. However, humans process images faster than text and they are prepared to process information presented in two or more dimensions: sometimes it is easier to explain things using figures and their graphical relations than writing textual representations. This paper describes a visual language, in the form of graphics that are executed in a networking environment, to define a network management policy. This approach allows to map visual tokens and corresponding arrangements into other languages to which a mapping is defined.

  8. Spinning rough disc moving in a rarefied medium

    Plakhov, Alexander; Tchemisova, Tatiana; Gouveia, Paulo D.F.
    We study the Magnus effect: deflection of the trajectory of a spinning body moving in a gas. It is well known that in rarefied gases, the inverse Magnus effect takes place, which means that the transversal component of the force acting on the body has opposite signs in sparse and relatively dense gases. The existing works derive the inverse effect from nonelastic interaction of gas particles with the body. We propose another (complementary) mechanism of creating the transversal force owing to multiple collisions of particles in cavities of the body surface. We limit ourselves to the two-dimensional case of a...

  9. VisualLISA: a visual environment to develop attribute grammars

    Oliveira, Nuno; Pereira, Maria João; Henriques, Pedro; Cruz, Daniela; Cramer, Bastian
    The focus of this paper is on crafting a new visual language for attribute grammars (AGs), and on the development of the associated programming environment. We present a solution for rapid development of VisualLISA editor using DEViL. DEViL uses traditional attribute grammars, to specify the language’s syntax and semantics, extended by visual representations to be associated with grammar symbols. From these specifications a visual programming environment is automatically generated. In our case, the environment allows us to edit a visual description of an AG that is automatically translated into textual notations, including an XML-based representation for attribute grammars (XAGra), and is intended to...

  10. Comparing general-purpose and domain-specific languages: an empirical study

    Kosar, Tomaz; Oliveira, Nuno; Mernik, Marjan; Pereira, Maria João; Crepinsek, Matej; Cruz, Daniela; Henriques, Pedro
    Many domain-specific languages, that try to bring feasible alternatives for existing solutions while simplifying programming work, have come up in recent years. Although, these little languages seem to be easy to use, there is an open issue whether they bring advantages in comparison to the application libraries, which are the most commonly used implementation approach. In this work, we present an experiment, which was carried out to compare such a domain-specific language with a comparable application library. The experiment was conducted with 36 programmers, who have answered a questionnaire on both implementation approaches. The questionnaire is more than 100 pages long....

  11. Computation of conservation laws in optimal control

    Gouveia, Paulo D.F.; Torres, Delfim F.M.
    Making use of a computer algebra system, we define computational tools to identify symmetries and conservation laws in optimal control.

  12. Computing ODE symmetries from a variational point of view

    Gouveia, Paulo D.F.; Torres, Delfim F.M.

  13. Symbolic computation of variational symmetries in optimal control

    Gouveia, Paulo D.F.; Torres, Delfim F.M.; Rocha, Eugénio A.M.
    We use a computer algebra system to compute, in an efficient way, optimal control variational symmetries up to a gauge term. The symmetries are then used to obtain families of Noether’s first integrals, possibly in the presence of nonconservative external forces. As an application, we obtain eight independent first integrals for the sub-Riemannian nilpotent problem (2, 3, 5, 8).

  14. Problems of maximal mean resistance on the plane

    Plakhov, Alexander; Gouveia, Paulo D.F.
    A two-dimensional body moves through a rarefied medium; the collisions of the medium particles with the body are absolutely elastic.The body performs both translational and slow rotational motion. It is required to select the body, from a given class of bodies, such that the average force of resistance of the medium to its motion is maximal. There are presented numerical and analytical results concerning this problem. In particular, the maximum resistance in the class of bodies contained in a convex body K is proved to be 1.5 times resistance of K. The maximum is attained on a sequence of bodies with...

  15. Computing ODE symmetries as abnormal variational symmetries

    Gouveia, Paulo D.F.; Torres, Delfim F.M.
    We give a new computational method to obtain symmetries of ordinary differential equations. The proposed approach appears as an extension of a recent algorithm to compute variational symmetries of optimal control problems [P.D.F. Gouveia, D.F.M. Torres, Automatic computation of conservation laws in the calculus of variations and optimal control, Comput. Methods Appl. Math. 5 (4) (2005) 387 409], and is based on the resolution of a first order linear PDE that arises as a necessary and sufficient condition of invariance for abnormal optimal control problems. A computer algebra procedure is developed, which permits one to obtain ODE symmetries by the...

  16. Two-dimensional body of maximum mean resistance

    Gouveia, Paulo D.F.; Plakhov, Alexander; Torres, Delfim F.M.
    A two-dimensional body, exhibiting a slight rotational movement, moves in a rarefied medium of particles which collide with it in a perfectly elastic way. In previously realized investigations by the first two authors, [Alexander Yu. Plakhov, Paulo D.F. Gouveia, Problems of maximal mean resistance on the plane, Nonlinearity, 20 (2007), 2271–2287], shapes of nonconvex bodies were sought which would maximize the braking force of the medium on their movement. Giving continuity to this study, new investigations have been undertaken which culminate in an outcome which represents a large qualitative advance relative to that which was achieved earlier. This result, now...

  17. Deploying applications in multi-SAN SMP Clusters (extended version)

    Alves, Albano; Pina, António; Rufino, José; Exposto, José
    The effective exploitation of multi-SAN SMP clusters and the use of generic clusters to support complex information systems require new approaches; multi-SAN SMP clusters introduce new levels of parallelism and traditional environments are mainly used to run scientific computations. In this paper we present a novel approach to the exploitation of clusters that allows integrating in a unique metaphor: the representation of physical resources, the modelling of applications and the mapping of application into physical resources. The proposed abstractions favoured the development of an API that allows combining and benefiting from the shared memory, message passing and global memory paradigms.

  18. Visualization of domain-specific programs’ behavior

    Oliveira, Nuno; Pereira, Maria João; Cruz, Daniela; Henriques, Pedro
    Program domain concepts are rather complex and low level for a fast assimilation. On the other hand, problem domain concepts are closer to human’s mind, hence they are easier to perceive. Based on Brook’s theory, a full comprehension of a program is only achieved if both domains are connected and visualized in synchronization, resulting on an action-effect visualization. Domain-specific languages, as languages tailored for a specific class of problems, raise the abstraction of the program domain concepts and approximate them to the problem domain’s. This way, a systematic approach can be used to perform the action-effect visualization of a program written in a domain-specific...

  19. RoCL: a resource oriented communication library

    Alves, Albano; Pina, António; Rufino, José; Exposto, José
    RoCL is a communication library that aims to exploit the low-level communication facilities of today’s cluster networking hardware and to merge, via the resource oriented paradigm, those facilities and the high-level degree of parallelism achieved on SMP systems through multi-threading. The communication model defines three major entities – contexts, resources and buffers – which permit the design of high-level solutions. A low-level distributed directory is used to support resource registering and discovering. The usefulness and applicability of RoCL is briefly addressed through a basic modelling example – the implementation of TPVM over RoCL. Performance results for Myrinet and Gigabit Ethernet, currently supported...

  20. Delegation of expressions for distributed SNMP information processing

    Lopes, Rui Pedro; Oliveira, José
    Due to the scalability problems of SNMP, management distribution has been an important topic during the last years. The DISMAN workgroup propose a set of MIB modules to address this matter. One of the DISMAN modules has the capability of using expressions to perform decentralized processing of management information - the Expression MIB. Although it is essential to network management, the Expression MIB is not as well known as other DISMAN modules, such as the Script MIB, and not as available in terms of implementations. This paper focuses on the Expression MIB features, its implementation details and it also discusses, from...

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