Comprehensive evaluation of the IEEE 802.15.4 MAC layer performance with retransmissions

Supported by IEEE 802.15.4 standardization activities, embedded networks have been gaining popularity in recent years. The focus of this paper is to quantify the behavior of key networking metrics of IEEE 802.15.4 beacon-enabled nodes under typical operating conditions, with the inclusion of packet retransmissions. We corrected and extended previous analyses by scrutinizing the assumptions on which the prevalent Markovian modeling is generally based. By means of a comparative study, we singled out which of the assumptions impact each of the performance metrics (throughput, delay, power consumption, collision probability, and packet-discard probability). In particular, we showed that - unlike what is usually assumed - the probability that a node senses the channel busy is not constant for all the stages of the backoff procedure and that these differences have a noticeable impact on backoff delay, packet-discard probability, and power consumption. Similarly, we showed that - again contrary to common assumption - the probability of obtaining transmission access to the channel depends on the number of nodes that is simultaneously sensing it. We evidenced that ignoring this dependence has a significant impact on the calculated values of throughput and collision probability. Circumventing these and other assumptions, we rigorously characterize, through a semianalytical approach, the key metrics in a beacon-enabled IEEE 802.15.4 system with retransmissions.

Bit loading for MIMO with statistical channel information at the transmitter and ZF receivers

For single-user MIMO communication with uncoded and coded QAM signals, we propose bit and power loading schemes that rely only on channel distribution information at the transmitter. To that end, we develop the relationship between the average bit error probability at the output of a ZF linear receiver and the bit rates and powers allocated at the transmitter. This relationship, and the fact that a ZF receiver decouples the MIMO parallel channels, allow leveraging bit loading algorithms already existing in the literature. We solve dual bit rate maximization and power minimization problems and present performance resultsthat illustrate the gains of the proposed scheme with respect toa non-optimized transmission.

Discourse, knowledge, power and politics: towards critical epistemic discourse analysis

Although both are fundamental terms in the humanities and social sciences, discourse and knowledge have seldom been explicitly related, and even less so in critical discourse studies. After a brief summary of what we know about these relationships in linguistics, psychology, epistemology and the social sciences, with special emphasis on the role of knowledge in the formation of mental models as a basis for discourse, I examine in more detail how a critical study of discourse and knowledge may be articulated in critical discourse studies. Thus, several areas of critical epistemic discourse analysis are identified, and then applied in a study of Tony Blair’s Iraq speech on March 18, 2003, in which he sought to legitimatize his decision to go to war in Iraq with George Bush. The analysis shows the various modes of how knowledge is managed and manipulated of all levels of discourse of this speech.

Digital storytelling: un’applicazione didattica per ripensare ai media attraverso i media

El presente trabajo de investigación propone un proyecto de investigación centrado en los pre-adolescentes para estudiar, a través deautobiografías digitales (digital storytelling, DST) producidas por ellos, laspracticas cultural-medial y las representaciones que ellos han construido sobre los medios, en relación con los contextos de uso significativos, como el hogar, la escuela o su grupo de par. Los medios forman parte de las actividades cotidianas de los niños quien los emplean en prácticas de socialización, aprendizaje, juego y de construcción de la identidad y del conocimiento. Los digital storytelling,insertados en el contexto escolar, serán empleados como metodología didácticapara la adquisición de competencias tecnológicas y como instrumento de lainvestigación. Los DST, como practica cultural de los chicos, constituirán nuestrocampo para la observación de las modalidades de uso de los medios por parte delos jóvenes y sus capacidad de recombinar lenguajes y construir contenidos. LosDST proporcionaran, además, la posibilidad de acceder al universo simbólicoinfantil para comprender el significado que las tecnologías tienen en sus cotidianidad

Reference intervals for common carotid intima-media thickness measured with echotracking: relation with risk factors.

AIMS: Common carotid artery intima-media thickness (CCIMT) is widely used as a surrogate marker of atherosclerosis, given its predictive association with cardiovascular disease (CVD). The interpretation of CCIMT values has been hampered by the absence of reference values, however. We therefore aimed to establish reference intervals of CCIMT, obtained using the probably most accurate method at present (i.e. echotracking), to help interpretation of these measures. METHODS AND RESULTS: We combined CCIMT data obtained by echotracking on 24 871 individuals (53% men; age range 15-101 years) from 24 research centres worldwide. Individuals without CVD, cardiovascular risk factors (CV-RFs), and BP-, lipid-, and/or glucose-lowering medication constituted a healthy sub-population (n = 4234) used to establish sex-specific equations for percentiles of CCIMT across age. With these equations, we generated CCIMT Z-scores in different reference sub-populations, thereby allowing for a standardized comparison between observed and predicted ('normal') values from individuals of the same age and sex. In the sub-population without CVD and treatment (n = 14 609), and in men and women, respectively, CCIMT Z-scores were independently associated with systolic blood pressure [standardized βs 0.19 (95% CI: 0.16-0.22) and 0.18 (0.15-0.21)], smoking [0.25 (0.19-0.31) and 0.11 (0.04-0.18)], diabetes [0.19 (0.05-0.33) and 0.19 (0.02-0.36)], total-to-HDL cholesterol ratio [0.07 (0.04-0.10) and 0.05 (0.02-0.09)], and body mass index [0.14 (0.12-0.17) and 0.07 (0.04-0.10)]. CONCLUSION: We estimated age- and sex-specific percentiles of CCIMT in a healthy population and assessed the association of CV-RFs with CCIMT Z-scores, which enables comparison of IMT values for (patient) groups with different cardiovascular risk profiles, helping interpretation of such measures obtained both in research and clinical settings.

A Dethroned King? The Limits of State Infrastructural Power in France

Since the 1980s in Western Europe, centralized states' control over subnational territories has been deeply affected by processes of Europeanization and regionalization. These changes have raised the issue of state territorial restructuring in a particular fashion: what capacity have formerly centralized states retained to steer and control subnational territories? The article draws on Mann's concept of infrastructural power, which refers to the state's capacity to exercise control and implement political decisions over the national territory. The article applies the two main operationalizations of the concept, namely the capability of the state to exercise control and the weight of the state in the subnational territories. Empirically, the article focuses on the French state in two policy sectors (education and housing). Although France is a most likely case, this article challenges this expectation, and shows the limits of the French state's infrastructural power over the subnational territories since the late 1980s.

Premissas historicas do surgimento e desenvolvimento dos mass-media nos paises lusofonos

A nossa investigacao esta dedicada a paises que falam essencialmente a lingua portuguesa, nao sera de admirar que a maioria dos livros por nos usados sejam de autores e ediccao portuguesa. No decorrer deste trabalho recorremos a livros e trabalhos academicos de autores como: Carvalho, Arons de: A Censura À Imprensa Na Época Marcelista; Minerva,Coimbra, 1999; Evora, Silvino Lopes: As fontes jornalísticas na televisão caboverdiana, ediccoes FCC, Universidade do Minho,2004; Fontcuberta: Mar de, A Notícia – Pistas para compreender o mundo; Editorial Notícias “Tradução de Fernando Cascais”,Lisboa, 1999; Mata, Maria José: A Autocrítica no Jornalismo – O ombudsman na imprensa nacional e estrangeira; Minerva Editora,Coimbra, 2002; Pigeat, Henri: Médias et Déontologie – Règles du jeu ou jeu sans règles; Presses Universitaires Francaises, Paris, 1997; Sodré, Nelson Werneck. História da imprensa no Brasil. 2ª ed., Rio de Janeiro: Graal, 1977; Sousa, Jorge Pedro: As Notícias e os seus Efeitos; Minerva Editora,Coimbra, 2000; Veiga Manuel: Cabo Verde insularidade e Literatura, editions Karthala, Paris, 1998; Bem como, um conjunto de leis e projectos de lei ligados a comunicacao social, e algumas entrevistas. Estrutura do trabalho: Esta tese e constituida de: introducao, tres capitulos, conclusao, bibliografia e alguns anexos num total de . Na introducao explica-se a escolha do tema, a sua actualidade, o objecto de investigacao e claro a sua inovacao. No primeiro capitulo estudamos o context do aparecimento dos media nos paises lusofonos nos exemplos de Cabo Verde, Brasil, e Portugal. No Segundo cappitulo, analizamos as leis, os processos de controlo e financiamento dos mass-media e a regulacao dos conteudos dos programas de radio e televisao. No terceiro capitulo, a situacao actual dos meios de comunicacao social e do Jornalismo na CPLP, nele esta tambem exposta a parte practica do trabalho ou seja a analize da relacao do publico com os media e o nivel de confianca do publico na informacao por eles veiculada.

Stoneley wave modeling in heterogeneous porous media with viscous pore fluids

We implemented Biot-type porous wave equations in a pseudo-spectral numerical modeling algorithm for the simulation of Stoneley waves in porous media. Fourier and Chebyshev methods are used to compute the spatial derivatives along the horizontal and vertical directions, respectively. To prevent from overly short time steps due to the small grid spacing at the top and bottom of the model as a consequence of the Chebyshev operator, the mesh is stretched in the vertical direction. As a large benefit, the Chebyshev operator allows for an explicit treatment of interfaces. Boundary conditions can be implemented with a characteristics approach. The characteristic variables are evaluated at zero viscosity. We use this approach to model seismic wave propagation at the interface between a fluid and a porous medium. Each medium is represented by a different mesh and the two meshes are connected through the above described characteristics domain-decomposition method. We show an experiment for sealed pore boundary conditions, where we first compare the numerical solution to an analytical solution. We then show the influence of heterogeneity and viscosity of the pore fluid on the propagation of the Stoneley wave and surface waves in general.

En busca del ciudadano Kane : los dueños de medios de comunicación y su utilización política

Aquesta recerca té com a objecte d'estudi la utilització dels mitjans de comunicació per a finalitats polítiques i intenta analitzar la relació que els polítics professionals mantenen amb els mitjans i com aquests poden ser importants dins d'un procés polític-electoral i per a la formació de l'opinió pública. El nostre objectiu general és, entre d’altres, analitzar l'estructura d’aquests mitjans i grups polítics i descriure com estan situats, utilitzant com a exemple l'estat del Rio Grande do Norte (RN), al Nord-est de Brasil. Partint de les preguntes, ¿a qui pertanyen els mitjans de comunicació i qui té el poder d'informar en l'aquest Estat? anem construïm el marc teòric, analitzant el monopoli i oligopoli en la comunicació a Brasil, especialment a la radiodifusió, en la qual hi ha una gran concentració de concessions públiques en propietat dels polítics professionals amb mandats electius i/o de grups partidaris, què pot ser anomenat de ‘coronelismo electrònic’

On commercial media bias

Within the spokes model of Chen and Riordan (2007) that allowsfor non-localized competition among arbitrary numbers of media outlets, we quantify the effect of concentration of ownership on qualityand bias of media content. A main result shows that too few commercial outlets, or better, too few separate owners of commercial outlets can lead to substantial bias in equilibrium. Increasing the number of outlets (commercial and non-commercial) tends to bring down this bias; but the strongest effect occurs when the number of owners is increased. Allowing for free entry provides lower bounds on fixed costs above which substantial commercial bias occurs in equilibrium.

Power of Attorney Handbook, January 2006

This booklet is designed to assist those who have been appointed as an attorney-in-fact, those who are considering the need for a power of attorney, or those who have an interest in the subject. This is a general overview.