1,721,000 research outputs found
Mutual 3:1 subharmonic synchronization in a micromachined silicon disk resonator
Get PDFWe demonstrate synchronization between two intrinsically coupled oscillators that are created from two distinct vibration modes of a single micromachined disk resonator. The modes have a 3:1 subharmonic frequency relationship and cubic, non-dissipative electromechanical coupling between the modes enables their two frequencies to synchronize. Our experimental implementation allows the frequency of the lower frequency oscillator to be independently controlled from that of the higher frequency oscillator, enabling study of the synchronization dynamics. We find close quantitative agreement between the experimental behavior and an analytical coupled-oscillator model as a function of the energy in the two oscillators. We demonstrate that the synchronization range increases when the lower frequency oscillator is strongly driven and when the higher frequency oscillator is weakly driven. This result suggests that synchronization can be applied to the frequency-selective detection of weak signals and other mechanical signal processing functions
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Chaos in micro-mechanics: towards MEMS-based secured communications
No full textInternational audienc
Dynamique non-linéaire dans les systèmes nano-électromécanique à basses températures
Get PDFThe investigation of non-linear dynamics intrinsically opens access to a broad field of researches, and Nano-Electro-Mechanical Systems (NEMS) are valuable tools for this purpose. In the present manuscript, we emphasize the fundamental applications of non-linear nano-resonators for condensed matter. After a careful calibration of our peculiar experimental set-up, we characterize the relevant parameters associated to the resonance of our devices, notably the Duffing non-linearity which is the essence of coupling mechanisms between distinct modes of the system. We present a new scheme emerging from the mode-coupling technique, using a two-tone drive but actuating a single flexural mode: a high precision detection procedure of the initial resonator's response. The Duffing regime also opens an hysteresis within the resonance line of the NEMS, and the device is then employed as a model system for the associated bifurcation process. We explored numerically and experimentally this physical phenomenon and found that both the non-linear behaviour and the universal power laws described in the general theory are still valid far beyond any analytical predictions. We finally describe different techniques using NEMS as sensors to measure fundamental features of condensed matter physics, like signatures of two level systems within the resonator's material or slippage in a rarefied gas.L'étude des systèmes non-linéaires ouvre un large champ d'investigation en recherche fondamentale, dans cette optique les Systèmes Nano-Electro-Mécanique (NEMS) sont des outils de premier choix. Ce manuscrit met en avant l'utilisation des propriétés non-linéaires de nano-résonateurs pour la physique fondamentale. À la suite d'une calibration rigoureuse de notre dispositif expérimental, nous avons caractérisé les principaux paramètres associés à la résonance de nos structures avec, en particulier, la non-linéarité de Duffing qui est à la source des mécanismes de couplage entre les différents modes de notre système. Une nouvelle procédure expérimentale utilisant une excitation à deux tons est présentée, émergeant du couplage entre modes mais en stimulant un seul mode résonant : un système de détection à haute précision de la résonance de la structure. Le régime de Duffing engendre également l'ouverture d'une hystérésis au sein de la courbe de résonance du NEMS, configuration qui est alors utilisée comme système modèle pour le phénomène de bifurcation. Nous démontrons, numériquement et expérimentalement, que le comportement non-linéaire et les lois de puissances universelles décrites par la théorie sont valides au-delà des prédictions attendues. Différentes techniques expérimentales sont finalement présentées, utilisant les NEMS afin de détecter des caractéristiques fondamentales de la matière condensée, comme les signatures des systèmes à deux niveaux présents au sein des nano-résonateurs ou les propriétés de glissement dans un gaz raréfié
Chaotic MEMS-based TRNG
No full textNational audienceMicro electromechanical systems (MEMS) are hardware tools present in most modern technologies, in the form of accelerometers, microphones, gyroscopes or even clocks [1]. These types of devices present two especially relevant source of stochasticity, Brownian and 1/f noises, which are traditionally difficult to exploit as they are quite low compare to the signal of interest. However, by putting vibrating MEMS in a chaotic regime, the dynamics of these mechanical structures becomes exponentially sensitive to fluctuations, enabling to amplify their source of entropy and to use them as TRNGs. [2]. In this presentation, I will first introduce the concept of chaotic MEMS, and then discuss their figures of merit in the context of TRNGs. </p
Chaos in micro-mechanics: towards MEMS-based secured communications
No full textInternational audienc
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
- …
