2,589 research outputs found
Dynamics of quantum correlations and linear entropy in a multi-qubit-cavity system
We present a theoretical study of the relationship between entanglement and
entropy in multi-qubit quantum optical systems. Specifically we investigate
quantitative relations between the concurrence and linear entropy for a
two-qubit mixed system, implemented as two two-level atoms interacting with a
single-mode cavity field. The dynamical evolutions of the entanglement and
entropy, are controlled via time-dependent cavity-atom couplings. Our
theoretical findings lead us to propose an alternative measure of entanglement,
which could be used to develop a much needed correlation measure for more
general multi-partite quantum systems.Comment: New discussions on the generality of entanglement-entropy
relationship, one new reference, and other minor changes. 10 pages, 6
figures, accepted for publication in J.Opt. B: "Special Issue on Fluctuations
& Noise in Photonics & Quantum Optics.
Ultra High Energy Cosmic Ray, Neutrino, and Photon Propagation and the Multi-Messenger Approach
The propagation of UHECR nuclei for A=1 (protons) to A=56 (iron) from
cosmological sources through extragalactic space is discussed in the first
lecture. This is followed in the second and third lectures by a consideration
of the generation and propagation of secondary particles produced via the UHECR
loss interactions. In the second lecture we focus on the generation of the
diffuse cosmogenic UHE-neutrino flux. In the third lecture we investigate the
arriving flux of UHE-photon flux at Earth. In the final lecture the results of
the previous lectures are put together in order to provide new insights into
UHECR sources. The first of these providing a means with which to investigate
the local population of UHECR sources through the measurement of the UHECR
spectrum and their photon fraction at Earth. The second of these providing
contraints on the UHECR source radiation fields through the possible
observation at Earth of UHECR nuclei.Comment: 21 pages, 9 figures, to appear in A.I.P. Conf. Proceedings, 3rd Latin
American School on Cosmic Rays, Arequipa, Peru, September, 200
QSPR modeling aqueous solubility of polychlorinated biphenyls by optimization of correlation weights of local and global graph invariants
Aqueous solubilities of polychlorinated biphenyls have been correlated with topological molecular descriptors which are functions of local and global invariants of labeled hydrogen filled graphs. Morgan extended connectivity and nearest neighboring codes have been used as local graph invariants. The number of chlorine atoms in biphenyls has been employed as a global graph invariant. Present results show that taking into account correlation weights of global invariants gives quite reasonable improvement of statistical characteristics for the prediction of aqueous solubilities of polychlorinated biphenyls.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta
Efficiency of energy transfer in a light-harvesting system under quantum coherence
We investigate the role of quantum coherence in the efficiency of excitation
transfer in a ring-hub arrangement of interacting two-level systems, mimicking
a light-harvesting antenna connected to a reaction center as it is found in
natural photosynthetic systems. By using a quantum jump approach, we
demonstrate that in the presence of quantum coherent energy transfer and
energetic disorder, the efficiency of excitation transfer from the antenna to
the reaction center depends intimately on the quantum superposition properties
of the initial state. In particular, we find that efficiency is sensitive to
symmetric and asymmetric superposition of states in the basis of localized
excitations, indicating that initial state properties can be used as a
efficiency control parameter at low temperatures.Comment: Extended version of original paper. 7 pages, 2 figure
Electronic excitation dynamics in multichromophoric systems described via a polaron-representation master equation
We derive a many-site version of the non-Markovian time-convolutionless
polaron master equation [S. Jang et al., J. Chem Phys. 129, 101104 (2008)] to
describe electronic excitation dynamics in multichromophoric systems. By
treating electronic and vibrational degrees of freedom in a combined frame
(polaron frame), this theory is capable of interpolating between weak and
strong exciton-phonon coupling and is able to account for initial
non-equilibrium bath states and spatially correlated environments. Besides
outlining a general expression for the expected value of any electronic system
observable in the original frame, we also discuss implications of the Markovian
and secular approximations highlighting that they need not hold in the
untransformed frame despite being strictly satisfied in the polaron frame. The
key features of the theory are illustrated using as an example a four-site
subsystem of the Fenna-Mathew-Olson light-harvesting complex. For a spectral
density including a localised high-energy mode, we show that oscillations of
site populations may only be observed when non-equilibrium bath effects are
taken into account. Furthermore, we illustrate how this formalism allows us to
identify the electronic or vibrational origin of the oscillatory dynamics.Comment: 13 pages, 6 figures; minor corrections made; accepted for publication
in Journal of Chemical Physic
QSPR modeling aqueous solubility of polychlorinated biphenyls by optimization of correlation weights of local and global graph invariants
Aqueous solubilities of polychlorinated biphenyls have been correlated with topological molecular descriptors which are functions of local and global invariants of labeled hydrogen filled graphs. Morgan extended connectivity and nearest neighboring codes have been used as local graph invariants. The number of chlorine atoms in biphenyls has been employed as a global graph invariant. Present results show that taking into account correlation weights of global invariants gives quite reasonable improvement of statistical characteristics for the prediction of aqueous solubilities of polychlorinated biphenyls.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta
Chiral analysis of pesticides and drugs of environmental concern: biodegradation and enantiomeric fraction
The importance of stereochemistry for medicinal chemistry and pharmacology is well recognized and the dissimilar behavior of enantiomers is fully documented. Regarding the environment, the significance is equivalent since enantiomers of chiral organic pollutants can also differ in biodegradation processes and fate, as well as in ecotoxicity. This review comprises designed biodegradation studies of several chiral drugs and pesticides followed by enantioselective analytical methodologies to accurately measure the enantiomeric fraction (EF). The enantioselective monitoring of microcosms and laboratory-scale experiments with different environmental matrices is herein reported. Thus, this review focuses on the importance of evaluating the EF variation during biodegradation studies of chiral pharmaceuticals, drugs of abuse, and agrochemicals and has implications for the understanding of the environmental fate of chiral pollutants.info:eu-repo/semantics/publishedVersio
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