1,721,149 research outputs found
Quantum subspace controllability implying full controllability
Full text linkIn the analysis of controllability of finite dimensional quantum systems, subspace controllability refers to the situation where the underlying Hilbert space splits into the direct sum of invariant subspaces, and, on each of such invariant subspaces, it is possible to generate any arbitrary unitary operation using appropriate control functions. This is a typical situation in the presence of symmetries for the dynamics. We investigate whether and when if subspace controllability is verified, the addition of an extra Hamiltonian to the dynamics implies full controllability of the system. Under the natural (and necessary) condition that the new Hamiltonian connects all the invariant subspaces, we show that this is always the case, except for a very specific case we shall describe. Even in this specific case, a weaker notion of controllability, controllability of the state (Pure State Controllability) is verified
Glass foams from dismantled cathode ray tubes
No full textGlasses from dismantled cathode ray tubes (CRTs) represent a pressing environmental problem, since their direct reutilization in manufacturing the original glass components is very difficult. The most hardly recycled glass, panel glass, has been employed for the manufacturing of glass foams, intended for thermal and acoustic insulation, by sintering of a mixture of glass and calcium carbonate powder mixture. In this work we illustrate the effects of the heating rate, the holding time and the concentration of carbonate, employed as foaming agent, in the same sintering process, on the relation between density and crushing strength. Due to the observed mechanical properties and the results of preliminary thermal conductivity tests the obtained materials were found to approach commercial glass foams
SYMMETRIC STATES AND DYNAMICS OF THREE QUANTUM BITS
Full text linkThe unitary group acting on the Hilbert space H:= (C2 )⊗3 of three quantum bits admits a Lie subgroup, US3 (8), of elements which permute with the symmetric group of permutations of three objects. Under the action of such a Lie subgroup, the Hilbert space H splits into three invariant subspaces of dimensions 4, 2 and 2 respectively, each corresponding to an irreducible representation of su(2). The subspace of dimension 4 is uniquely determined and corresponds to states that are themselves invariant under the action of the symmetric group. This is the so called symmetric sector. The subspaces of dimension two are not uniquely determined and we parametrize them all. We provide an analysis of pure states that are in the subspaces invariant under US3 (8). This concerns their entanglement properties, separability criteria and dynamics under the Lie subgroup US3 (8). As a physical motivation for the states and dynamics we study, we propose a physical set-up which consists of a symmetric netw..
Sub-Riemannian geodesics in SU(n)/S(U(n-1)xU(1)) and optimal control of three level quantum systems
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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
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