1,721,868 research outputs found
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
WAVEPACKET APPROACHES TO DISSIPATIVE QUANTUM DYNAMICS
No full textMany processes arising in Chemistry, Physics and Biology show quantum effects. Representative examples are
chemical reactions involving light atoms, energy transfer in complex environments, electronic and
geometrical properties of complex and bulk systems, tunneling phenomena etc. Theoretical Chemistry deals with such kind
of problems with the help of numerical solutions of the Time Dependent Schrodinger Equation (TDSE). On the other
hand, when classical effects are most relevant as, for example, in large dynamical systems like proteins at room temperature,
Theoretical Chemistry deals with this problems with the help of numerical solution of the Newton's equations.
Solving numerically the TDSE is much more expansive than solving the classical Newton's equations of motion.
Thus, often mixed descriptions are used treating the system at the exact -quantum- level and the environment
at the approximated classical level.
When a full quantum approach is needed both for the system and for the environment (as, for example, in
processes involving quantum objects, such as light atoms, energy transfer in small molecules interacting with
a thermal bath at low temperature, and so on), one faces with so called Open Quantum Systems,
and the corresponding dynamics is generally dissipative.
In open quantum systems the wavefunction description fails because of a lack of the complete knowledge of the
state. It is then necessary to switch to the density matrix description, which contains all the information.
The system dynamics is affected by the presence of the bath depending on the interactions between them.
If the coupling is small, than the system evolves in time without been affected by the environment. If the system
is initially prepared as a pure state, then the dynamics is coherent. On the other hand if system and
bath are strongly interacting, than the system dynamics is modified by the presence of the bath and described by
a mixture of states. Under the condition of strong coupling, the modified dynamics is incoherent,
also if the initial state of the system is pure.
Based on the Multi Configuration Time Dependent
Hartree (MCTDH) approach, which writes the wavefunction as linear combination of Hartree products,
the MCTDH program has been developed. This program is the only one allowing
to deal with large, dissipative problems (up to 100 degrees of freedom). Recently, variants of the MCTDH approach
have been developed in order to increase the number of degrees of freedom which can be considered. The GMCTDH
approach treats part of the MCTDH wavefunction as Gaussian functions, which are analytically known; the
LCSA approach, on the other hand, can be viewed as a GMCTDH approach with selected configurations.
In our project we have studied the effect of the environment on quantum systems. In particular, we have studied
the influence of the environment in simple chemical process both from a theoretical and from a computational point of view.
Specifically, we have developed a model to study excitoninc energy transfer in dissipative media,
performed numerical simulations
using the MCTDH approach, and obtained analytical expressions for the equations of motion in the so called
mixed quantum-classical hydrodynamics picture
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
Special Issue on Turbomachinery. Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 2009
No full textIl volume colleziona i migliori articoli della 8th European Turbomachinery Conference che a seguito del processo di revisione internazionale sono stati valutati come eccellenti (valutazione complesiva sopra l'80%) e pubblicati dall'IMechE.
Gli autori, i titoli dgli articoli, e gli abstracts possono essere visionati seguento il link: http://pia.sagepub.com/content/223/6.toc
Lo special Issue non ha un ISBN, ma un ISSN, uno per la parte hardcopy (0957-6509) ed uno per la parte on-line (2041-2967)
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