1,721,030 research outputs found
Decoherence induced by hyperfine interactions with nuclearspins in antiferromagnetic molecular rings
No full textDecoherence induced by hyperfine interactions with nuclearspins in antiferromagnetic molecular ringsMolecular magnets are effective few-level spin systems that allow for the observation of coherent dynamics. Electronic coherence is mainly limited by hyperfine interactions with nuclear spins. Here, we theoretically investigate the resulting inhomogeneous broadening and electron-nuclear entanglement: They take place on the nanosecond and microsecond time scales, respectively. Our microscopic description allows us to clarify the role played by the different chemical elements. The effect of spin echo and the dependence of decoherence on the magnetic field are also estimated. © 2008 The American Physical Society
Semiconductor quantum tubes: Dielectric modulation and excitonic response
Full text linkWe study theoretically the optical properties of quantum tubes, one-dimensional semiconductor nanostructureswhere electrons and holes are confined to a cylindrical shell. In these structures, which bridge betweentwo-dimensional and one-dimensional systems, the electron-hole interaction may be modulated by a dielectricsubstance outside the quantum tube and possibly inside its core. We use the exact Green’s function for theappropriate dielectric configuration and exact diagonalization of the electron-hole interaction within aneffective-mass description to predict the evolution of the exciton binding energy and oscillator strength.Contrary to the homogeneous case, in dielectrically modulated tubes, the exciton binding is a function of thetube diameter and can be tuned to a large extent by structure design and proper choice of the dielectric media
Molecular Spins for Quantum Information Technologies
No full textTechnological challenges for quantum information technologies lead us to consider aspectsof molecular magnetism in a radically new perspective. The design of new derivatives and recentexperimental results on molecular nanomagnets are covered in this tutorial review through thekeyhole of basic concepts of quantum information, such as the control of decoherence andentanglement at the (supra-)molecular level
Solve separation units by combining sure and fast models
No full textProblems met in countercurrent separation units have been solved by means of a proper combination of two different models, referred to as sure and fast, to describe the whole set of theoretical stages. The "sure" model is employed for trays showing particular features, or disturbances, i.e. feed trays, partial condensers, reboilers, side cuts, intercoolers, etc. as well as for trays adjacent to the previous ones. This model is written in terms of single theoretical tray equations. The "fast" model is applied to multitray sections, provided that no "disturbance" exists, with an assumption that molar flowrates and temperatures vary according to prefixed laws. The adoption of effective K-values allows one to use formally the same operating equations for the multitray sections as for single theroretical trays. A Newton-Raphson procedure, combined with a B. P. method, is employed to converge the set of equations describing the problem. © 1982
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
Optimal generation of indistinguishable photons from non-identical artificial molecules
Full text linkWe show theoretically that nearly indistinguishable photons can be generated with non-identical semiconductor-based sources. The use of virtual Raman transitions and the optimization of the external driving fields increases the tolerance to spectral inhomogeneity to the meV energy range. A trade-off emerges between photon indistinguishability and efficiency in the photon-generation process. Linear (quadratic) dependence of the coincidence probability within the Hong-Ou-Mandel setup is found with respect to the dephasing (relaxation) rate in the semiconductor sources
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