1,720,964 research outputs found
Geometry as a novel source for topological bound states
No full textTopological phases of matter represent a relatively new and highly active branch of condensed matter. Evading the usual Landau classification, topological insulators and superconductors manifest robust states at their boundaries, whose existence is related to a non trivial topology of the bulk bands.
The interest in these systems is both fundamental and technological. Indeed, they are regarded as promising assets for the development of resilient quantum technologies. Their potential applications include low-power electronic devices and fault-tolerant quantum computation, with 0-dimensional topological bound states being prime candidates for robust qubits due to their topological protection.
This thesis addresses some conceptual aspects, so far partially overlooked, that are expected to assume crucial relevance as the nanostructuration of topological materials progresses towards the realization of topologically protected quantum technologies. Specifically, it investigates the interplay between geometry and topology, examining the effects of geometric confinement and lattice specifics on topological bound states in three different scenarios: finite size Chern insulating phases, finite size nodal superconducting topological phases, and higher-order topological phases. The analysis is carried out on honeycomb lattice based topological phases, which are attracting renewed interest due to the recent experimental results on bismuthene and germanene.
Overall, the reported findings emphasize the need for effective theories that account for lattice geometry in topological systems. Moreover, they imply that geometric confinement can be a general mechanism for engineering effectively 1-dimensional topological phases- and thus topologically protected bound states -through the nanostructuration of 2-dimensional topological counterparts
Emerging topological bound states in Haldane model zigzag nanoribbons
No full textZigzag nanoribbons hosting the Haldane Chern insulator model are considered. In this context, a reentrant topological phase, characterized by the emergence of quasi zero dimensional in-gap states, is discussed. The bound states, which reside in the gap opened by the hybridization of the counter-propagating edge modes of the Haldane phase, are localized at the ends of the strip and are found to be robust against on-site disorder. These findings are supported by the behavior of the Zak phase over the parameter space, which exhibits jumps of π in correspondence to the phase transitions between the trivial and the non-trivial phases. The effective mass inversion leading to the jumps in the Zak phase is interpreted in a low energy framework. Setups with non-uniform parameters also show topological bound states via the Jackiw-Rebbi mechanism. All the properties reported are shown to be extremely sensitive to the strip width
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Anomalous supercurrent and diode effect in locally perturbed topological Josephson junctions
No full textThe simultaneous breaking of time-reversal and inversion symmetry can lead to peculiar effects in Josephson junctions, such as the anomalous Josephson effect or supercurrent rectification, which is a dissipationless analog of the diode effect. Due to their impact in new quantum technologies, it is important to find robust platforms and external means to manipulate the above-mentioned effects in a controlled way. Here, we theoretically consider a Josephson junction based on a quantum spin Hall system as the normal channel, subjected to a magnetic field in the direction defined by spin-momentum locking, and in the presence of a local tip in close proximity to one of the metallic edges in the normal region. We consider different local perturbations, model normal and magnetic tips, and study how they affect the Josephson response of the device. In particular, we argue that magnetic tips are a useful tool that allows for tunability of both phi(0) response and supercurrent rectification
Development of a high backdrivable partially powered Swing assistive actuator knee design: a multiobjective optimization framework
Full text linkThis manuscript presents a multiobjective optimization framework for high backdrivable partially powered swing assistive actuator knee design. The research exploits a Serial Elastic Actuator (SEA), in parallel with a motor valves controlled hydraulic cylinder, with the purpose of expanding the prosthesis capabilities into the power quadrants of the power plane, without sacrificing the benefits relative to existing microprocessorcontrolled-knee prostheses (MPKs), able to allow a strictlypassive ballistic swing-phase. The mechatronic design parameters are optimized by exploiting the multi-objective evolutionary genetic algorithm and validated by means of a knee prosthesis multibody model. The backdrive torque found with the described model corresponds to a relatively low value of 2.56 Nm at the knee joint, allowing the pursued high backdrivability of the system
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