Centralized and distributed algorithms for on-line synthesis of maximal control policies under partial observation

This paper deals with the on-line control of partially observed discrete event systems (DES). The goal is to restrict the behavior of the system within a prefix-closed legal language while accounting for the presence of uncontrollable and unobservable events. In the spirit of recent work on the on-line control of partially observed DES (Heymann and Lin 1994) and on variable lookahead control of fully observed DES (Ben Hadj-Alouane et al. 1994c), we propose an approach where, following each observable event, a control action is computed on-line using an algorithm of linear worst-case complexity. This algorithm, called VLP-PO , has the following additional properties: (i) the resulting behavior is guaranteed to be a maximal controllable and observable sublanguage of the legal language; (ii) different maximals may be generated by varying the priorities assigned to the controllable events, a parameter of VLP-PO ; (iii) a maximal containing the supremal controllable and normal sublanguage of the legal language can be generated by a proper selection of controllable event priorities; and (iv) no off-line calculations are necessary. We also present a parallel/distributed version of the VLP-PO algorithm called DI-VLP-PO . This version uses several communicating agents that simultaneously run (on-line) identical versions of the algorithm but on possibly different parts of the system model and the legal language, according to the structural properties of the system and the specifications. While achieving the same behavior as VLO-PO, DI-VLP-PO runs at a total complexity (for computation and communication) that is significantly lower than its sequential counterpart.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45126/1/10626_2005_Article_BF01797138.pd

Provision, protection or participation? Approaches to regulating children’s television in Arab countries

One notable feature of Arab broadcasting has been the belated emergence of free-to-air channels for children. Today, with children’s channels a still-expanding feature of the Arab satellite television landscape, the region is witnessing growth in the local animation industry alongside intensified competition for child audiences through imported content and a selective squeeze on state funds. In this context the policies and rationales that inform production and acquisition of children’s content remain far from transparent, beyond occasional public rhetoric about protecting children from material that ‘breaches cultural boundaries and values’ and providing programmes that revere a perceived ‘Arab-Islamic’ heritage and preserve literary forms of the Arabic language. Attempts at promoting children’s genuine participation in Arab television have been rare. Drawing on theoretical literature that links protection and participation in the sense that children’s safety depends on their agency, this paper explores emerging guidelines developed by Arab regulators, broadcasters and others in relation to television content for children

PSPACE-completeness of Modular Supervisory Control Problems*

In this paper we investigate computational issues associated with the supervision of concurrent processes modeled as modular discrete-event systems. Here, modular discrete-event systems are sets of deterministic finite-state automata whose interaction is modeled by the parallel composition operation. Even with such a simple model process model, we show that in general many problems related to the supervision of these systems are PSPACE-complete. This shows that although there may be space-efficient methods for avoiding the state-explosion problem inherent to concurrent processes, there are most likely no time-efficient solutions that would aid in the study of such “large-scale” systems. We show our results using a reduction from a special class of automata intersection problem introduced here where behavior is assumed to be prefix-closed. We find that deciding if there exists a supervisor for a modular system to achieve a global specification is PSPACE-complete. We also show many verification problems for system supervision are PSPACE-complete, even for prefix-closed cases. Supervisor admissibility and online supervision operations are also discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45090/1/10626_2004_Article_6210.pd

Secure Performance of AF and DF Relaying in Cooperative Noma Systems

In this paper, we study the secrecy outage probability (SOP)and the strictly positive secrecy capacity (SPSC)of cooperative non-orthogonal multiple access (NOMA)system with a single antenna over Rayleigh fading channel in which there are a source, a relay node, two destinations and one eavesdropper. The relay adopts amplify-and-forward (AF)and decode-and-forward (DF)relaying schemes. The SOP and SPSC performance are analyzed to evaluate the level of security granted to legitimate users for both AF and DF protocols. The effects of the optimal power allocation value on system performance are also discussed and provided through numerical results.This publication was made possible by NPRP grant #10-0102-170094 from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors.Scopu

Secure Performance Analysis for Full-Duplex Cooperative NOMA System in the Presence of Multiple Eavesdroppers

This paper investigates the physical layer security of a full-duplex (FD) Decode-and-Forward (DF) NOMA network assumed to undergo independent and identically distributed Nakagami-m fading. Herein, we provide a secrecy performance analysis for the case of multiple external eavesdroppers in both colluding and non-colluding wiretap scenario. Our analysis introduces novel expressions of the secrecy outage probability (SOP) as well as the strictly positive secrecy capacity (SPSC) for the proposed network. Finally, numerical analysis with simulations are given to illustrate the validity of the obtained theoretical results and to highlight the impact of multiple eavesdroppers on FD NOMA systems.Scopu

Alacrymie congénitale révélant un syndrome d’Allgrove: à propos de trois cas

Le syndrome d'Allgrove ou triple A syndrome est une affection autosomique récessive constatée chez la population pédiatrique, associant dans sa forme complète: Achalasie œsophagienne, Alacrymie, maladie d'Addison  (insuffisance surrénale), une dégénérescence neurologique et  occasionnellement une instabilité du système autonome. Nous rapportons les cas de 3 enfants issus de mariages consanguins, chez qui l'examen  ophtalmologique a révélé une sécheresse sévère avec dans deux cas une kératite envahissant l'axe visuel, ainsi qu'une paresse du reflexe  photomoteur. Le bilan radiologique: transit œsogastroduodénal (TOGD) et fibroscopie œsogastroduodénale (FOGD) a révélé un mégaoesophage associé dans un cas à une œsophagite. Un traitement à base de larmes artificielles est instauré aussitôt, ainsi qu'un traitement chirurgical par voie  laparoscopique. La connaissance de cette pathologie permettra une prise de conscience de la gravité de cette maladie en plus de suggérer sa prise en charge

Secrecy performance of AF relaying in cooperative NOMA over rician channel

In this paper, we investigate the secrecy performance of an Amplify-and-Forward (AF) relay in a cooperative NOMA system. The AF relay ensures the transmission of the signal in the presence of one passive eavesdropper where all channels are assumed to undergo a Rician fading. In this context, analytical and asymptotic expressions for Secrecy Outage Probability (SOP) are derived. To verify our theoretical analysis, numerical results are presented, showing the effect of different Rician factors on secrecy performance.Scopu