Negative index and mode coupling in all-dielectric metamaterials at terahertz frequencies

We report on the role of the coupling of the modes of Mie resonances in all-dielectric metamaterials to ensure negative effective index at terahertz frequencies. We study this role according to the lattice period and according to the frequency overlapping of the modes of resonance. We show that negative effective refractive index requires sufficiently strong mode coupling and that for even more strong mode coupling, the first two modes of Mie resonances are degenerated; the effective refractive index is then undeterminded. We also show that adjusting the mode coupling leads to near-zero effective index, or even null effective index. Further, we compare the mode coupling effect with hybridization in metamaterials.Comment: 17pages, 10 figure

Two-Bit Bit Flipping Decoding of LDPC Codes

In this paper, we propose a new class of bit flipping algorithms for low-density parity-check (LDPC) codes over the binary symmetric channel (BSC). Compared to the regular (parallel or serial) bit flipping algorithms, the proposed algorithms employ one additional bit at a variable node to represent its "strength." The introduction of this additional bit increases the guaranteed error correction capability by a factor of at least 2. An additional bit can also be employed at a check node to capture information which is beneficial to decoding. A framework for failure analysis of the proposed algorithms is described. These algorithms outperform the Gallager A/B algorithm and the min-sum algorithm at much lower complexity. Concatenation of two-bit bit flipping algorithms show a potential to approach the performance of belief propagation (BP) decoding in the error floor region, also at lower complexity.Comment: 6 pages. Submitted to IEEE International Symposium on Information Theory 201

Convergence test in the presence of structural changes: an empirical procedure based on panel data with cross-sectional dependence

This paper presents an essay on empirical testing procedure for economic convergence. Referring to the unit root test proposed by Moon and Perron (2004), we proposed a modified Evans (1996)testing procedure of the convergence hypothesis. The advantage of this modified procedure is that it makes possible to take into account cross-sectional dependences that affect GDP per capita. It also allows to take into account structural instabilities in these aggregates. The application of the procedure on OECD member countries and CFA zone member countries leads to accept the hypothesis of economic convergence for these two groups of countries, and it shows that the convergence rate is significantly lower in the OECD sample. However, the results of the tests applied to the Global sample composed by all countries in these two samples conclude a rejection of the convergence hypothesis.β-convergence; Unit root; Panel data; Factor model; Cross-sectional dependence; Structural change

Le « bien vieillir » : concepts et modèles

Depuis quelques années, l’image associée au phénomène du vieillissement est plus positive : on parle de « bien vieillir », de « vieillissement réussi » ou de « vieillir en santé ». Aucun consensus ne se dégage encore sur ce concept provocateur et stimulant. Dans cette synthèse des principaux écrits, nous présentons un point de vue sur les acceptions et modèles du « bien vieillir ». Ainsi, il apparaît que le contenu du concept varie en fonction du contexte culturel, de la perspective des acteurs et selon les approches. Plusieurs modèles sont aussi identifiés : les uns, unidimensionnels, envisagent le bien vieillir sous l’angle d’un domaine scientifique particulier ; les autres, multicritères, adoptent une perspective plus large. Les déterminants les plus souvent évoqués par ces modèles sont les facteurs psychosociaux, c’est-à-dire les traits de personnalité, les ressources personnelles et sociales. Il demeure toutefois qu’aucun modèle n’intègre encore toutes les dimensions et tous les déterminants potentiels du « bien vieillir ».For a few years, the image associated with the ageing process has been more positive : expressions such as « successful aging », « well aging » or « healthy aging » are more frequently used in relation to aging. However, there is still a lack of consensus on this appealing and challenging concept. Therefore, we present an overview of its definition, psychosocial determinants and conceptual models. We report that the meaning of the concept varies according to the cultural context (individualistic/relational societies), to the actors’ perspectives (researcher/elderly) and according to the dominant approach (biomedical/holistic). Several models have also been identified : some are specific to a scientific domain and rely on a unique marker of well aging ; others are multicriterion and embrace a broader field. Psychosocial factors are the most frequent determinants addressed by models. Among these factors, social and personal resources can be mobilized and learned, contrarily to the less modifiable personality traits. In summary, the « well aging » framework offers a unique opportunity to identify and to reinforce positive aspects in the aging process. However, the integration of the various models, more complementary than opposite, into only one meta-model remains a task to be done by researchers for a better effectiveness of « well aging » promotion programs