1,720,966 research outputs found
Competition between inter- and intra- molecular energy exchange in a simple quantistic model of a dimer
No full textCompetition between inter- and intra-molecular energy exchanges in a simple quantum model of a dimer
No full textWe propose a fully quantum model to describe the dynamics of a possible radiationless energy transfer process between identical and nearly localized molecules or monomers coupled through a dipole–dipole term. The system is studied as an environmentally isolated dimeric pair and we find that its dynamics exhibits a competition between the process ruling out the transfer of energy among different degrees of freedom of a given monomer and the one steering the intermolecular passage of excitations from a monomer to the other one. Such a competition is quantitatively characterized investigating on the temporal behaviour of quantum covariances of some couples of appropriate observables having a clear physical meanin
Photodynamics of azobenzene in a hindering environment
No full textWe have run trajectory surface hopping simulations of the trans-cis photoisomerization of azobenzene, subject to a pulling force. The model mimics two situations: a trans-azobenzene derivative with bulky substituents that may not be easily displaced, and a recent experiment by Gaub’s group [T. Hugel, N.B. Holland, A. Cattani, L. Moroder, M. Seitz, H.E. Gaub, Science 296 (2002) 1103; N.B. Holland, T. Hugel, G. Neuert, A. Cattani-Scholz, C. Renner, D. Oesterhelt, L. Moroder, M. Seitz, H.E. Gaub, Macromolecules 36 (2003) 2015; G. Neuert, T. Hugel, R.R. Netz, H.E. Gaub, Macromolecules 39 (2005) 789], in which a polymer with azobenzene units was stretched in an atomic force microscope. In both cases, the shortening of the azobenzene moiety in going from the trans to the cis form is opposed by a pulling force. Our simulations show that the trans-cis photoconversion is only partially suppressed by con- siderably large forces (500 pN or more). However, the cis isomer reverts to trans in the ground state, with the help of the pulling force and using the vibrational energy that is available in the first 1–2 ps. The lowering of the quantum yields is therefore the combined result of hindering of the excited state process and of the hot ground state back reaction
Quantum signatures in the dynamics of two dipole-dipole interacting soft dimers
No full textThe quantum covariances of physically transparent pairs of observables relative to two dimers hosted in a solid matrix are exactly investigated in the temporal domain. Both dimers possess fermionic and bosonic degrees of freedom and are dipolarly coupled. We find out and describe clear signatures traceable back to the presence and persistence of quantum coherence in the time evolution of the system. Manifestations of a competition between intramolecular and intermolecular energy migration mechanisms are brought to light. The experimental relevance of our results is briefly commented. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 200603.65.Ud Entanglement and quantum nonlocality, 61.72.Yx Interaction between different crystal defects; gettering effect, 34.30.+h Intramolecular energy transfer; intramolecular dynamics; dynamics of van der Waals molecules,
Oscillator strength and polarization of the forbidden n-->pi* band of trans-azobenzene. A computational study
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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
Exact decoupling of two dipole-dipole interacting dimers
No full textIt is today possible to test many quantum mechanical predictions, even the most puzzling ones, setting up sophisticated experiments on exemplary "textbook" physical systems like a single atom or molecule or a single material quantum harmonic oscillator. It is therefore conceptually highly exciting to conceive simple but not trivial physical situations representable by exactly solvable hamiltonian models, in the grasp of the experimentalists. In this paper we study a physical system consisting of two coupled identical dimers. Each molecule possesses both fermionic and bosonic degrees of freedom and its internal non adiabatic dynamics is governed by a bilinear term conserving the total excitation number. The two molecules are assumed to interact by a dipole like term. Our main result is that the hamiltonian model representing such a composite system may be unitarily put in a form describing two fictitious uncoupled JC dimers provided the initial excitation number is less than two. The advantage of these canonical transformations is that it makes the restricted dynamical problem exactly tractable. In this way we may successfully study the time evolution of quantum correlation effects get established in the dimer-dimer system due to dipolar like coupling
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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