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Transporte eletrônico por estados topológicos em grafeno bicamada dobrado: uma plataforma para a valetrônica
No full textValetronics is an emergent field on electronics that manipulates the valley number, a degree
of freedom similar to the electron spin, to develop faster and more efficient devices with
low power consumption. The development of valleytronics demands long-range electronic
transport with preserved valley index. A promising structure to this end is a topological
one-dimensional (1D) channel formed in bilayer graphene (BLG) called domain wall (DW).
In these 1D channels, the valley-index defines the propagation direction of the charge
carriers and the chiral edge states (kink states) are robust over many kinds of disorder.
However, the fabrication of DWs is challenging, requiring the design of complex multi-gate
structures with nanometer alignment or have been producing on rough substrates, showing
a limited mean free path.
In our work, we create a new structure to form a high-quality domain walls. Such structure
is formed along the curved boundary of a folded bilayer graphene. Our investigation
of the ballistic transport at such nano-width channel with two terminal measurements
reveal the resistance quantization by the quantum value of R = h
4e2 at zero-magnetic
fields. The four probe experiments show a collapse of the longitudinal resistance, the
expected resistance of a ballistic channel. We also demonstrate the metallic behavior of the
topologically protected one dimensional states by performing measurements as function
of the temperature and we showed that the ballistic transmission of valley protected
states was achieved for long mean-free paths. At the bulk, we measure an semiconducting
behavior with tunable bandgap. We envision that such new valleytronic platform could
either be exploited for studies of Luttinger liquids behaviors or for the development of
dissipationless electronic quantum wires and development of electronic valley valves.A valetrônica é uma nova área da eletrônica que baseia-se no controle e manipulação do
número quântico de vale, um grau de liberdade similar ao spin. Assim como em spintrônica,
pretende-se criar dispositivos mais rápidos, mais eficientes e com menos consumo energético.
O desenvolvimento da valetrônica necessita de um transporte eletrônico de longo alcance
no qual o índice de vale seja preservado. Uma estrutura promissora para essa finalidade é
um canal topológico unidimensional (1D) formado num grafeno bicamada, chamado de
domain wall (DW). Nesses canais 1D, o índice de vale define a direção de propagação dos
portadores de carga e os estados de borda chirais (kink states) são robustos a diversos tipos
de desordem. Contudo, a fabricação de um DW é desafiadora. Isso requer a fabricação
de dispositivos complexos que necessitam de contatos elétricos alinhados com precisão
nanométrica ou a produção de DW em grafeno depositado sobre substratos rugosos, que
limitam consideravelmente o livre caminho médio.
Nesse trabalho criamos um novo tipo de DW de alta qualidade ao longo da borda curvada
de um grafeno bicamada dobrado. Nessa nova estrutura, fabricamos dispositivos valetrônicos
e investigamos as propriedades do transporte de carga com medidas eletrônicas de dois
e quatro terminais. As medidas com dois terminais ao longo desse canal com espessura
nanométrica revelaram que a resistência é quantizada próxima da resistência quântica
R = h
4e2 em campos magnéticos nulos. Os experimentos com quatro terminais mostraram
um colapso da resistência longitudinal, consistente com a resistência de um canal
balístico. Também demonstramos o comportamento metálico dos estados 1D protegidos
topologicamente conduzindo medidas em função da temperatura. Finalmente, mostramos
que a transmissão balística dos estados protegidos de vale alcançam longos livres caminhos
médios. Nas demais bordas e na região em que o grafeno bicamada estava empilhado, isto
é, no bulk, medimos um comportamento de semicondutor com gap controlável através da
aplicação de campos elétricos transversais. Acreditamos que essa nova plataforma possibilitará
estudos dos comportamentos de líquidos de Luttinger e levará ao desenvolvimento
de dispositivos baseados em linhas quânticas não dissipativas e válvulas de vale.CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológic
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
INVESTIGAÇÃO DA COMPOSIÇÃO DE PRÓPOLIS COM ESPECTROSCOPIA DE ABSORBÂNCIA NO UV-VIS
Full text linkA geoprópolis, é produzida comumente por abelhas-sem-ferrão tendo como destaque a abelha africana sem ferrão. A sua confecção além de ter as características da própolis produzida por abelhas com ferrão, nesse temos ainda a presença intencional de barro e vegetais, para que dessa forma seja mais “reforçada” (DUTRA et al., 2008)
ESTUDO DA FLUORESCÊNCIA DA BSA ASSOCIADA A QUERCETINA
Full text linkDesde o início do século XX a sociedade sofreu grandes avanços tecnológicos que, com o passar dos anos, tais avanços, possibilitou o surgimento de novos ramos de pesquisa
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
SINTESE DE NANOPARTICULAS DE PRATA POR DA ROTA QUÍMICA UTILIZANDO O CITRATO DE SÓDIO
Full text linkAs nanopartículas de prata são nanoestruturas organizadas entre 1 a 100 nm (E. Abbasi et al 2014). Por causa de seu tamanho, formato, morfologia e composição nanométrica estas adquirem propriedades ópticas, elétricas e magnéticas particulares, o que possibilita sua aplicação em diversos campo, pois possui uma alta eficiência como agente antimicrobiano, assim podendo ser utilizado na medicina, odontologia e farmácia (K. N. Thakkar, S. S. Mhatre, and R. Y. Parikh 2010)
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
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