1,721,017 research outputs found
Mesoscopic diode
No full textHere we discuss the possibility of an alternative rectifying structure which operates in the world of mesoscopic devices. A simple quantum constriction (wide–narrow geometry) is found to act as a rectifier in the coherent transport regime if Fermi energy is between the propagation thresholds of the wide and narrow parts. Also a quantum structure is proposed which is predicted to operate as a rectifier at room temperatures. This diode for the nanostructures is a quantum wire with an asymmetric quantum constriction (AQC) which works in the coherent transport regime. Structurally imperfect mesoscopic diodes retain rectifying features, although the actual I–V characteristics are different in comparison to the perfect devices
Electronic transport in quantum waveguide systems with attached stubs
No full textSingle-mode quantum transmission properties of a quantum waveguide system with attached stubs are studied in the ballistic regime. The formation of energy bands is achieved in the case of periodic structure mainly around the energies where a single stub possesses antiresonances. A single defect in the otherwise periodic structure introduces a resonant (or an antiresonant) state. We find that this state is not an exponentially localized state, and is not a Fano-type resonance (although it originates from it), but more a well-known Lorentzian-shaped Breit-Wigner transmission resonance. When this state falls in the energy band, then it forms an antiresonance. A strong magnetic field creates additional quasibound states
Magnetotransport in the quantum interference resonator
No full textWe examine quantum-mechanical transmission in the T-shape quantum interference resonator. The system is interesting as a potential quantum transistor. The modulation of the transmission as electron energy is varied is almost 100% irrespective of disorder. However, in the magnetic field, transmission modulation reduces, and for strong magnetic fields completely disappears
Quantum-constriction rectifier
No full textA simple quantum constriction (wide-narrow geometry) is found to act as a rectifier in the coherent transport regime if Fermi energy is between the propagation thresholds of the wide and narrow parts. Therefore a simple diode could consist of only two identical leads of different widths. The current-voltage characteristics of this structure are calculated for several temperatures and lead widths, and generalized to other cases by appropriate scaling rules. The rectification properties disappear as the temperature or the size of the system increase. This structure also exhibits regions of negative-differential resistanc
The nonlinear transport regime of a T‐shaped quantum interference transistor
No full textWe present the current–voltage characteristics of a T‐shaped semiconductor electron waveguide structure in the nonlinear regime. This system is interesting as a potential quantum interference transistor. Calculated zero‐temperature I–V characteristics are with multiple peaks and exhibit regions of negative‐differential resistance. The peak‐to‐valley ratio has maximum value of 3:1. The calculated values of the transconductance and the differential drain conductance are small, which suggests limited abilities for conventional applications of the transistor
Conductance of quantum interference transistors in parallel and in series
No full textWe theoretically study the electronic conductance G and the current–voltage characteristics of two quantum interference transistors in parallel and in series. We use two different definitions of conductance, G ~ T and G ~ T / R. Neither can reproduce the classical additivity law in the case of coherent transport due to quantum interference for the elements in series and quasibound states when elements are in parallel. In the case of two transistors in series, we find that the quantityT / R only qualitatively better represents the additivity law, which is probably expected because this model avoids counting the contact resistance twice. However, for the parallel configuration of transistors, the conductance is almost additive for the majority of energies when G ~ T, except for the single-mode regime. Possible use of these configurations in digital electronics for basic logic functions is discussed
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
- …
