Superconductivity-Induced Anderson Localisation

We have studied the effect of a random superconducting order parameter on the localization of quasi-particles, by numerical finite size scaling of the Bogoliubov-de Gennes tight-binding Hamiltonian. Anderson localization is obtained in d=2 and a mobility edge where the states localize is observed in d=3. The critical behavior and localization exponent are universal within error bars both for real and complex random order parameter. Experimentally these results imply a suppression of the electronic contribution to thermal transport from states above the bulk energy gap.Comment: 4 pages, revtex file, 3 postscript figure

Les Mystères de Paris et la mondialisation d’un genre « populaire » ? Lecteurs de « mystères » en France, en Grèce et en Grande-Bretagne au XIXe siècle

Le phénomène de mode littéraire inauguré par la publication du roman d’Eugène Sue Les Mystères de Paris en 1842-3, a souvent été analysé par le recours à la notion de « littérature populaire » qui, dans la majorité des cas, se rapporte davantage à une poétique textuelle particulière qu’à une réalité sociale: les innombrables « mystères » écrits en imitation de ceux de Sue seraient « populaires » parce qu’ils appartiendraient à la « paralittérature », cet ensemble d’oeuvres considéré comme ayant une moindre valeur esthétique et dont les auteurs auraient abandonné la quête d’originalité en choisissant une écriture fondée sur la reprise et le remaniement de divers clichés narratifs. Or qu’en est-il de la « popularité » des mystères au sens strictement sociologique du terme ? Cet article propose d’étudier les lectorats des mystères dans trois pays qui ne connaissent pas les mêmes évolutions dans leurs systèmes éditoriaux respectifs : la France, la Grèce et la Grande-Bretagne. Nous essaierons de montrer que les mystères en tant que genre littéraire pérenne ne peuvent en aucun cas être étudiés à partir d’une hypothèse sociologique unique. Ni proprement « bourgeois » ni « populaires », ils épousent les évolutions complexes des contextes socio-culturels des différents pays en s’adaptant avec souplesse à leurs spécificités ainsi qu’aux diverses situations de communication

Identification of transcription factor targets, gene expression profiles and accessible chromatin regions in the Caenorhabditis elegans epidermis using targeted DamID

Development is an exceptionally complex process that is performed with exquisite control. A series of developmental programmes allow the orchestrated and tightly-regulated deployment of the genomic information, governing events like cell division, cell fate maintenance and differentiation. Understanding the complete regulatory states that instruct a selective decoding of the genome capable of bringing about morphogenetic events is central to developmental biology. Among all cells, stem cells maintain the potential to produce cells that undergo transitions in developmental trajectories and thus are particularly interesting. In this study, I have used the postembryonic development of the Caenorhabditis elegans epidermis driven by the stem cell-like seam cells, to begin exploring the gene regulatory network, transcriptional states and epigenomic regulation involved in cell fate patterning. To that end, I have adapted and present here the first application of the targeted DamID (TaDa) methodology in C. elegans, for assaying protein-DNA interactions, to use as a single technique in approaching all of the above objectives. I show that TaDa requires little starting material, is reproducible and tissue-specific. Using TaDa I identify targets for the transcription factors LIN-22 and NHR-25 that propose new biological functions for these regulators in epidermal development. I acquire gene expression profiles for the seam cells and hypodermis that lead to the discovery of novel transcription and chromatin factors, as well as new miRNAs. Finally, I produce the first cell-type-specific chromatin accessibility maps in C. elegans for the seam cells and hypodermis and use them to identify tissue-specific enhancers. These findings expand our knowledge of the mechanisms underlying fate decisions in epidermal patterning and provide a proof-of-concept for the application of TaDa in C. elegans.Open Acces

Level-spacing distribution of a fractal matrix

We diagonalize numerically a Fibonacci matrix with fractal Hilbert space structure of dimension $d_{f}=1.8316...$ We show that the density of states is logarithmically normal while the corresponding level-statistics can be described as critical since the nearest-neighbor distribution function approaches the intermediate semi-Poisson curve. We find that the eigenvector amplitudes of this matrix are also critical lying between extended and localized.Comment: 6 pages, Latex file, 4 postscript files, published in Phys. Lett. A289 pp 183-7 (2001

Targeted DamID in C. elegans reveals a direct role for LIN-22 and NHR-25 in antagonising the epidermal stem cell fate

Transcription factors are key players in gene networks controlling cell fate specification during development. In multicellular organisms, they often display complex patterns of expression and binding to their targets, hence tissue-specificity is required in the characterisation of transcription factor-target interactions. We introduce here Targeted DamID (TaDa) as a method for tissue-specific transcription factor target identification in intact C. elegans animals. We employ TaDa to recover targets in the epidermis for two key transcription factors, the HES1 homologue LIN-22 and the NR5A1/2 nuclear hormone receptor NHR-25. We demonstrate a direct link between LIN-22 and the Wnt signalling pathway through repression of the Frizzled receptor lin-17. We also find a direct role for NHR-25 in promoting cell differentiation via repressing the expression of stem cell-promoting GATA factors. Our results expand our understanding of the epidermal gene network and highlight the potential of TaDa to dissect the architecture of tissue-specific gene regulatory networks

Selection of earthquake ground motions for multiple objectives using genetic algorithms

Existing earthquake ground motion (GM) selection methods for the seismic assessment of structural systems focus on spectral compatibility in terms of either only central values or both central values and variability. In this way, important selection criteria related to the seismology of the region, local soil conditions, strong GM intensity and duration as well as the magnitude of scale factors are considered only indirectly by setting them as constraints in the pre-processing phase in the form of permissible ranges. In this study, a novel framework for the optimum selection of earthquake GMs is presented, where the aforementioned criteria are treated explicitly as selection objectives. The framework is based on the principles of multi-objective optimization that is addressed with the aid of the Weighted Sum Method, which supports decision making both in the pre-processing and post-processing phase of the GM selection procedure. The solution of the derived equivalent single-objective optimization problem is performed by the application of a mixed-integer Genetic Algorithm and the effects of its parameters on the efficiency of the selection procedure are investigated. Application of the proposed framework shows that it is able to track GM sets that not only provide excellent spectral matching but they are also able to simultaneously consider more explicitly a set of additional criteria