959 research outputs found
Transfer of Vibrational Coherence Through Incoherent Energy Transfer Process in F\"{o}rster Limi
We study transfer of coherent nuclear oscillations between an excitation
energy donor and an acceptor in a simple dimeric electronic system coupled to
an unstructured thermodynamic bath and some pronounced vibrational
intramolecular mode. Our focus is on the non-linear optical response of such a
system, i.e. we study both excited state energy transfer and the compensation
of the so-called ground state bleach signal. The response function formalism
enables us to investigate a heterodimer with monomers coupled strongly to the
bath and by a weak resonance coupling to each other (F\"{o}rster rate limit).
Our work is motivated by recent observation of various vibrational signatures
in 2D coherent spectra of energy transferring systems including large
structures with a fast energy diffusion. We find that the vibrational coherence
can be transferred from donor to acceptor molecules provided the transfer rate
is sufficiently fast. The ground state bleach signal of the acceptor molecules
does not show any oscillatory signatures, and oscillations in ground state
bleaching signal of the donor prevail with the amplitude which is not
decreasing with the relaxation rate.Comment: 11 pages, 9 figure
Deep Learning for Short-Term Prediction of Available Bikes on Bike-Sharing Stations
Bike-sharing is adopted as a valid option replacing traditional public transports since they are eco-friendly, prevent traffic congestions, reduce any possible risk of social contacts which happen mostly on public means. However, some problems may occur such as the irregular distribution of bikes on related stations/racks/areas, and the difficulty of knowing in advance what the rack status will be like, or predicting if there will be bikes available in a specific bike-station at a certain time of the day, or if there will be a free slot to leave the rented bike. Thus, providing predictions can be useful to improve the service quality, especially in those cases where bike racks are used for e-bikes, which need to be recharged. This paper compares the state-of-the-art techniques to predict the number of available bikes and free bike-slots in bike-sharing stations (i.e., bike racks). To this end, a set of features and predictive models were compared to identify the best models and predictors for short-term predictions, namely of 15, 30, 45, and 60 minutes. The study has demonstrated that deep learning and in particular Bidirectional Long Short-Term Memory networks (Bi-LSTM) offers a robust approach for the implementation of reliable and fast predictions of available bikes, even with a limited amount of historical data. This paper has also reported an analysis of feature relevance based on SHAP that demonstrated the validity of the model for different cluster behaviours. Both solution and its validation were derived by using data collected in bike-stations in the cities of Siena and Pisa (Italy), in the context of Sii-Mobility National Research Project on Mobility and Transport and Snap4City Smart City IoT infrastructure
Coherent Dynamics in Solutions of Colloidal Plexcitonic Nanohybrids at Room Temperature
The increasing ability to prepare systems with nanoscale resolution and address their optical properties with ultrashort time precision is revealing quantum phenomena with tremendous potential in quantum nanotechnologies. Colloidal plexcitonic materials promise to play a pivotal role in this scenario. Plexcitons are hybrid states originating from the mixing of the plasmon resonances of metal nanostructures with molecular excitons. They allow nanoscale confinement of electromagnetic fields and the establishment of strong couplings between light and matter, potentially giving rise to controllable and tunable coherent phenomena. However, the characterization of the ultrafast coherent and incoherent dynamics of colloidal plexciton nanohybrids remains highly unexplored. Here, two dimensional electronic spectroscopy (2DES) is employed to study the quantum coherent interactions active after the photoexcitation of these systems. By comparing the response of the nanohybrids with the one of the uncoupled systems, the nonlinear photophysical processes at the base of the coherent dynamics are identified, allowing a step forward toward the effective understanding and exploitation of these nanomaterials
Forecasting volcanic ash dispersal and coeval resuspension during the April-May 2015 Calbuco eruption
Atmospheric dispersion of volcanic ash from explosive eruptions or from subsequent fallout deposit resuspension causes a range of impacts and disruptions on human activities and ecosystems. The April-May 2015 Calbuco eruption in Chile involved eruption and resuspension activities. We overview the chronology, effects, and products resulting from these events, in order to validate an operational forecast strategy for tephra dispersal. The modelling strategy builds on coupling the meteorological Weather Research and Forecasting (WRF/ARW) model with the FALL3D dispersal model for eruptive and resuspension processes. The eruption modelling considers two distinct particle granulometries, a preliminary first guess distribution used operationally when no field data was available yet, and a refined distribution based on field measurements. Volcanological inputs were inferred from eruption reports and results from an Argentina-Chilean ash sample data network, which performed in-situ sampling during the eruption. In order to validate the modelling strategy, results were compared with satellite retrievals and ground deposit measurements. Results indicate that the WRF-FALL3D modelling system can provide reasonable forecasts in both eruption and resuspension modes, particularly when the adjusted granulometry is considered. The study also highlights the importance of having dedicated datasets of active volcanoes furnishing first-guess model inputs during the early stages of an eruption.Fil: Reckziegel, Florencia Mabel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Salta. Instituto de Investigaciones en EnergĂa no Convencional. Universidad Nacional de Salta. Facultad de Ciencias Exactas. Departamento de FĂsica. Instituto de Investigaciones en EnergĂa no Convencional; ArgentinaFil: Bustos, Emilce. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Salta. Instituto de Investigaciones en EnergĂa no Convencional. Universidad Nacional de Salta. Facultad de Ciencias Exactas. Departamento de FĂsica. Instituto de Investigaciones en EnergĂa no Convencional; ArgentinaFil: Leonardo, Mingari. Ministerio de Defensa. Secretaria de Planeamiento. Servicio MeteorolĂłgico Nacional; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Baez, Walter Ariel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Salta. Instituto de Investigaciones en EnergĂa no Convencional. Universidad Nacional de Salta. Facultad de Ciencias Exactas. Departamento de FĂsica. Instituto de Investigaciones en EnergĂa no Convencional; ArgentinaFil: Villarosa, Gustavo. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Folch Duran, Arnau. Barcelona Supercomputing Center - Centro Nacional de Supercomputacion; EspañaFil: Collini, E.. Ministerio de Defensa. Secretaria de Planeamiento. Servicio MeteorolĂłgico Nacional; Argentina. Ministerio de Defensa. Armada Argentina. Servicio de HidrografĂa Naval; ArgentinaFil: Viramonte, Jose German. Universidad Nacional de Salta; ArgentinaFil: Romero, J.. Centro de InvestigaciĂłn y DifusiĂłn de Volcanes de Chile; Chile. Universidad de Atacama; ChileFil: Osores, MarĂa Soledad. Comision Nacional de Actividades Espaciales; Argentina. Ministerio de Defensa. Secretaria de Planeamiento. Servicio MeteorolĂłgico Nacional; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentin
Long-lived quantum coherence in photosynthetic complexes at physiological temperature
Photosynthetic antenna complexes capture and concentrate solar radiation by
transferring the excitation to the reaction center which stores energy from the
photon in chemical bonds. This process occurs with near-perfect quantum
efficiency. Recent experiments at cryogenic temperatures have revealed that
coherent energy transfer - a wavelike transfer mechanism - occurs in many
photosynthetic pigment-protein complexes (1-4). Using the Fenna-Matthews-Olson
antenna complex (FMO) as a model system, theoretical studies incorporating both
incoherent and coherent transfer as well as thermal dephasing predict that
environmentally assisted quantum transfer efficiency peaks near physiological
temperature; these studies further show that this process is equivalent to a
quantum random walk algorithm (5-8). This theory requires long-lived quantum
coherence at room temperature, which never has been observed in FMO. Here we
present the first evidence that quantum coherence survives in FMO at
physiological temperature for at least 300 fs, long enough to perform a
rudimentary quantum computational operation. This data proves that the
wave-like energy transfer process discovered at 77 K is directly relevant to
biological function. Microscopically, we attribute this long coherence lifetime
to correlated motions within the protein matrix encapsulating the chromophores,
and we find that the degree of protection afforded by the protein appears
constant between 77 K and 277 K. The protein shapes the energy landscape and
mediates an efficient energy transfer despite thermal fluctuations. The
persistence of quantum coherence in a dynamic, disordered system under these
conditions suggests a new biomimetic strategy for designing dedicated quantum
computational devices that can operate at high temperature.Comment: PDF files, 15 pages, 3 figures (included in the PDF file
How water-mediated hydrogen bonds affect chlorophyll a/b selectivity in Water-Soluble Chlorophyll Protein
The Water-Soluble Chlorophyll Protein (WSCP) of Brassicaceae is a remarkably stable tetrapyrrole- binding protein that, by virtue of its simple design, is an exceptional model to investigate the interactions taking place between pigments and their protein scaffold and how they affect the photophysical properties and the functionality of the complexes. We investigated variants of WSCP from Lepidium virginicum (Lv) and Brassica oleracea (Bo), reconstituted with Chlorophyll (Chl) b, to determine the mechanisms by which the different Chl binding sites control their Chl a/b specificities. A combined Raman and crystallographic investigation has been employed, aimed to characterize in detail the hydrogen-bond network involving the formyl group of Chl b. The study revealed a variable degree of conformational freedom of the hydrogen bond networks among the WSCP variants, and an unexpected mixed presence of hydrogen-bonded and not hydrogen-bonded Chls b in the case of the L91P mutant of Lv WSCP. These findings helped to refine the description of the mechanisms underlying the different Chl a/b specificities of WSCP versions, highlighting the importance of the structural rigidity of the Chl binding site in the vicinity of the Chl b formyl group in granting a strong selectivity to binding sites
Microcavity controlled coupling of excitonic qubits
Controlled non-local energy and coherence transfer enables light harvesting
in photosynthesis and non-local logical operations in quantum computing. The
most relevant mechanism of coherent coupling of distant qubits is coupling via
the electromagnetic field. Here, we demonstrate the controlled coherent
coupling of spatially separated excitonic qubits via the photon mode of a solid
state microresonator. This is revealed by two-dimensional spectroscopy of the
sample's coherent response, a sensitive and selective probe of the coherent
coupling. The experimental results are quantitatively described by a rigorous
theory of the cavity mediated coupling within a cluster of quantum dots
excitons. Having demonstrated this mechanism, it can be used in extended
coupling channels - sculptured, for instance, in photonic crystal cavities - to
enable a long-range, non-local wiring up of individual emitters in solids
Quantum Mechanical Aspects of Cell Microtubules: Science Fiction or Realistic Possibility?
Recent experimental research with marine algae points towards quantum
entanglement at ambient temperature, with correlations between essential
biological units separated by distances as long as 20 Angstr\"oms. The
associated decoherence times, due to environmental influences, are found to be
of order 400 fs. This prompted some authors to connect such findings with the
possibility of some kind of quantum computation taking place in these
biological entities: within the decoherence time scales, the cell "quantum
calculates" the optimal "path" along which energy and signal would be
transported more efficiently. Prompted by these experimental results, in this
talk I remind the audience of a related topic proposed several years ago in
connection with the possible r\^ole of quantum mechanics and/or field theory on
dissipation-free energy transfer in microtubules (MT), which constitute
fundamental cell substructures. Quantum entanglement between tubulin dimers was
argued to be possible, provided there exists sufficient isolation from other
environmental cell effects. The model was based on certain ferroelectric
aspects of MT. In the talk I review the model and the associated experimental
tests so far and discuss future directions, especially in view of the algae
photo-experiments.Comment: 31 pages latex, 11 pdf figures, uses special macros, Invited Plenary
Talk at DICE2010, Castello Pasquini, Castiglioncello (Italy), September 13-18
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Educating consent? A conversation with Noam Chomsky on the university and business school education
In what follows, we present a conversation with Professor Noam Chomsky on the topic of whether the business school might be a site for progressive political change. The conversation covers a number of key issues related to pedagogy, corporate social responsibility and working conditions in the contemporary business school. We hope the conversion will contribute to the ongoing discussion about the role of the business school in neoliberal societies
An enhanced platform for cell electroporation: controlled delivery and electrodes functionalization
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