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Kaslik E.,Institute e Austria Timisoara | Kaslik E.,West University of Timișoara | Radulescu I.R.,Institute e Austria Timisoara | Radulescu I.R.,Polytechnic University of Bucharest
Neural Networks | Year: 2017

The dynamics of complex-valued fractional-order neuronal networks are investigated, focusing on stability, instability and Hopf bifurcations. Sufficient conditions for the asymptotic stability and instability of a steady state of the network are derived, based on the complex system parameters and the fractional order of the system, considering simplified neuronal connectivity structures (hub and ring). In some specific cases, it is possible to identify the critical values of the fractional order for which Hopf bifurcations may occur. Numerical simulations are presented to illustrate the theoretical findings and to investigate the stability of the limit cycles which appear due to Hopf bifurcations. © 2017 Elsevier Ltd


Fortis T.-F.,West University of Timișoara | Fortis T.-F.,Institute e Austria Timisoara | Munteanu V.I.,Institute e Austria Timisoara
Future Generation Computer Systems | Year: 2016

Continuous advancement of cloud technologies, alongside their ever increasing stability, adoption, and ease of use, has led to a rise in native cloud applications, possibly over a larger pool of heterogeneous resources or in multi-cloud approaches. This, in turn, brought unprecedented levels of complexity in the context of cloud computing. Such complexity may cause a series of events and incidents that are difficult to be intercepted or managed on time, in a manner that also ensures the overall Quality of Services and existing Service-Level Agreements.Our special issue presents advances in several key areas that are highly relevant for automated cloud incident management: a 'continuous approach' for reliable cloud native applications, novel approaches for Metal-as-a-Service, centered around an advanced reservation system, or development of a framework based on the concept of secure SLA, in order to deal with specific cloud security issues. © 2016.


Rak M.,The Second University of Naples | Suri N.,TU Darmstadt | Luna J.,TU Darmstadt | Petcu D.,Institute E Austria Timisoara | And 2 more authors.
Proceedings of the International Conference on Cloud Computing Technology and Science, CloudCom | Year: 2013

The cloud offers attractive options to migrate corporate applications, without any implication for the corporate security manager to manage or to secure physical resources. While this ease of migration is appealing, several security issues arise: can the validity of corporate legal compliance regulations still be ensured for remote data storage? How is it possible to assess the Cloud Service Provider (CSP) ability to meet corporate security requirements? Can one monitor and enforce the agreed cloud security levels? Unfortunately, no comprehensive solutions exist for these issues. In this context, we introduce a new approach, named SPECS. It aims to offer mechanisms to specify cloud security requirements and to assess the security features offered by CSPs, and to integrate the desired security services (e.g., credential and access management) into cloud services with a Security-as-a-Service approach. Furthermore, SPECS intends to provide systematic approaches to negotiate, to monitor and to enforce the security parameters specified in Service Level Agreements (SLA), to develop and to deploy security services that are cloud SLA-aware and are implemented as an open-source Platform-as-a-Service (PaaS). This paper introduces the main concepts of SPECS. © 2013 IEEE.


Kaslik E.,Institute e Austria Timisoara | Kaslik E.,West University of Timișoara | Sivasundaram Seenith S.,Embry - Riddle Aeronautical University
Neural Networks | Year: 2012

Several topics related to the dynamics of fractional-order neural networks of Hopfield type are investigated, such as stability and multi-stability (coexistence of several different stable states), bifurcations and chaos. The stability domain of a steady state is completely characterized with respect to some characteristic parameters of the system, in the case of a neural network with ring or hub structure. These simplified connectivity structures play an important role in characterizing the network's dynamical behavior, allowing us to gain insight into the mechanisms underlying the behavior of recurrent networks. Based on the stability analysis, we are able to identify the critical values of the fractional order for which Hopf bifurcations may occur. Simulation results are presented to illustrate the theoretical findings and to show potential routes towards the onset of chaotic behavior when the fractional order of the system increases. © 2012 Elsevier Ltd.


Kaslik E.,Institute E Austria Timisoara | Kaslik E.,West University of Timișoara | Sivasundaram S.,Embry - Riddle Aeronautical University
Nonlinear Analysis: Real World Applications | Year: 2012

Using the Mellin transform approach, it is shown that, in contrast with integer-order derivatives, the fractional-order derivative of a periodic function cannot be a function with the same period. The three most widely used definitions of fractional-order derivatives are taken into account, namely, the Caputo, RiemannLiouville and GrunwaldLetnikov definitions. As a consequence, the non-existence of exact periodic solutions in a wide class of fractional-order dynamical systems is obtained. As an application, it is emphasized that the limit cycle observed in numerical simulations of a simple fractional-order neural network cannot be an exact periodic solution of the system. © 2011 Elsevier Ltd. All rights reserved.


Petcu D.,Institute e Austria Timisoara | Petcu D.,West University of Timișoara | Macariu G.,Institute e Austria Timisoara | Macariu G.,Polytechnic University of Timişoara | And 4 more authors.
Future Generation Computer Systems | Year: 2013

The adoption of the Cloud computing concept and its market development are nowadays hindered by the problem of application, data and service portability between Clouds. Open application programming interfaces, standards and protocols, as well as their early integration in the software stack of the new technological offers, are the key elements towards a widely accepted solution and the basic requirements for the further development of Cloud applications. An approach for a new set of APIs for Cloud application development is discussed in this paper from the point of view of portability. The first available, proof-of-the-concept, prototype implementation of the proposed API is integrated in a new open-source deployable Cloudware, namely mOSAIC, designed to deal with multiple Cloud usage scenarios and providing further solutions for portability beyond the API. © 2012 Elsevier B.V. All rights reserved.


Erascu M.,West University of Timișoara | Erascu M.,Institute e Austria Timisoara
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2016

This paper presents efficient simplification techniques tailored for sign semi-definite conditions (SsDCs). The SsDCs for a polynomial f ∈ ℝ[y] with parametric coefficients are written as (Formula Present) f(y) ≥ 0 and (Formula Present) f(y) ≤ 0. We give sufficient conditions for the simplification techniques to be sound for linear and quadratic polynomials. We show their effectiveness compared to state of the art quantifier elimination tools for input formulae occurring in the optimal numerical algorithms synthesis problem by an implementation on top of Reduce command of Mathematica. © Springer International Publishing AG 2016.


Di Martino B.,The Second University of Naples | Petcu D.,Institute E Austria Timisoara | Cossu R.,European Space Agency | Goncalves P.,Terradue SRL | And 2 more authors.
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2011

The current diversity of Cloud computing services, benefic for the fast development of a new IT market, hinders the easy development, portability and inter-operability of Cloud oriented applications. Developing an application oriented view of Cloud services instead the current provider ones can lead to a step forward in the adoption of Cloud computing on a larger scale than the actual one. In this context, we present a position paper exposing the concepts behind a recent proposal for an open-source application programming interface and platform for dealing with multiple Cloud computing offers. © 2011 Springer-Verlag Berlin Heidelberg.


Venticinque S.,The Second University of Naples | Aversa R.,The Second University of Naples | Di Martino B.,The Second University of Naples | Rak M.,The Second University of Naples | Petcu D.,Institute E Austria Timisoara
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2011

Resources management facilities, based on service level agreements, are needed in the Cloud in order to negotiate a collection of inter-connected and virtualized computers between resource providers and consumers. In this paper we present the architectural design of a system named Cloud Agency which aims to respond to this need and to offer added value to the existing Cloud services. This system is in charge to broker the collection of Cloud resources from different providers that fulfills at the best the requirements of user's applications. The user is able to delegate to the Agency the necessary checks of the agreement fulfilment, the monitoring of resource utilization and eventually necessary re-negotiations. © 2011 Springer-Verlag Berlin Heidelberg.


Petcu D.,Institute E Austria Timisoara | Craciun C.,Institute E Austria Timisoara | Neagul M.,Institute E Austria Timisoara | Lazcanotegui I.,Tecnalia | Rak M.,The Second University of Naples
Proceedings of the 2011 International Conference on High Performance Computing and Simulation, HPCS 2011 | Year: 2011

The federation of Cloud resources can be treated at different levels of abstractions. In this paper we focus on application programming interfaces for building Cloud-based applications using services from multiple Cloud providers. A full stack of APIs is proposed to decouple the development of a Cloud-based application from its deployment and execution. A particular attention is paid to the design of the interoperability API aiming to provide programming language interoperability and protocol syntax or semantic enforcements. © 2011 IEEE.

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