Topological Surface States Protected From Backscattering by Chiral Spin Texture

Topological insulators are a new class of insulators in which a bulk gap for electronic excitations is generated by strong spin orbit coupling. These novel materials are distinguished from ordinary insulators by the presence of gapless metallic boundary states, akin to the chiral edge modes in quantum Hall systems, but with unconventional spin textures. Recently, experiments and theoretical efforts have provided strong evidence for both two- and three-dimensional topological insulators and their novel edge and surface states in semiconductor quantum well structures and several Bi-based compounds. A key characteristic of these spin-textured boundary states is their insensitivity to spin-independent scattering, which protects them from backscattering and localization. These chiral states are potentially useful for spin-based electronics, in which long spin coherence is critical, and also for quantum computing applications, where topological protection can enable fault-tolerant information processing. Here we use a scanning tunneling microscope (STM) to visualize the gapless surface states of the three-dimensional topological insulator BiSb and to examine their scattering behavior from disorder caused by random alloying in this compound. Combining STM and angle-resolved photoemission spectroscopy, we show that despite strong atomic scale disorder, backscattering between states of opposite momentum and opposite spin is absent. Our observation of spin-selective scattering demonstrates that the chiral nature of these states protects the spin of the carriers; they therefore have the potential to be used for coherent spin transport in spintronic devices.Comment: to be appear in Nature on August 9, 200

Deposition of Carbon Nanotubes Onto Aramid Fibers Using as-received and Chemically Modified Fibers

Multiwall carbon nanotubes (MWCNTs) oxidized by an acid treatment were deposited on the surface of as-received commercial aramid fibers containing a surface coating (“sizing”), and fibers modified by either a chlorosulfonic treatment or a mixture of nitric and sulfuric acids. The surface of the aramid fiber activated by the chemical treatments presents increasing density of CO, COOH and OH functional groups. However, these chemical treatments reduced the tensile mechanical properties of the fibers, especially when the nitric and sulfuric acid mixture was used. Characterization of the MWCNTs deposited on the fiber surface was conducted by scanning electron microscopy, Raman spectroscopy mapping and X-ray photoelectron spectroscopy. These characterizations showed higher areal concentration and more homogeneous distribution of MWCNTs over the aramid fibers for as-received fibers and for those modified with chlorosulfonic acid, suggesting the existence of interaction between the oxidized MWCNTs and the fiber coating. The electrical resistance of the MWCNT-modified aramid yarns comprising ∼1000 individual fibers was in the order of MΩ/cm, which renders multifunctional properties

A3CRank: an adaptive ranking method based on connectivity, content and click-through data

Due to the proliferation and abundance of information on the web, ranking algorithms play an important role in web search. Currently, there are some ranking algorithms based on content and connectivity such as PageRank and BM25. Unfortunately, these algorithms have low precision and are not always satisfying for users. In this paper, we propose an adaptive method based on the content, connectivity and click-through data triple, called A3CRank. The aggregation idea of meta search engines has been used to aggregate ranking algorithms such as PageRank, BM25, TF-IDF. We have used reinforcement learning to incorporate user behavior and find a measure of user satisfaction for each ranking algorithm. Furthermore, OWA, an aggregation operator is used for merging the results of the various ranking algorithms. A3CRank adapts itself with user needs and makes use of user clicks to aggregate the results of ranking algorithms. A3Crank is designed to overcome some of the shortcomings of existing ranking algorithms by combining them together and producing an overall better ranking criterion. Experimental results indicate that A3CRank outperforms all other single ranking algorithms in P@n and NDCG measures. We have used 130 queries on University of California at Berkeley’s web to train and evaluate our method

Marqueurs auto-immuns au cours de la drépanocytose

Nous avons évalué de façon prospective la fréquence des anticorps antinucléaires et d'anticorps aniphospholipides sur une cohorte de 18 patients porteurs d'un syndrome drépanocytaire majeur, et effectué une revue de littérature. Nous avons retrouvé une fréquence élevée d'anticorps antinucléaires sans spécificité et sans association à des signes cliniques d'auto-immunité. Quatre études de la littérature retrouvent des taux d'anticorps antinucléaires dans une population drépanocytaire plus élevés que dans une population saine.Ce n'est pas corrélé à l'activité de la drépanocytose. Il en est de même pour les anticorps antiphopholipides. Vingt-et-un cas de lupus associé à la drépanocytose ont été décrits. Il n'y a pas d'association évidente entre ces deux pathologiesAIX-MARSEILLE2-BU Méd/Odontol. (130552103) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF