385 research outputs found
Photo-excitation of a light-harvesting supra-molecular triad: a Time-Dependent DFT study
We present the first time-dependent density-functional theory (TDDFT)
calculation on a light harvesting triad carotenoid-diaryl-porphyrin-C60.
Besides the numerical challenge that the ab initio study of the electronic
structure of such a large system presents, we show that TDDFT is able to
provide an accurate description of the excited state properties of the system.
In particular we calculate the photo-absorption spectrum of the supra-molecular
assembly, and we provide an interpretation of the photo-excitation mechanism in
terms of the properties of the component moieties. The spectrum is in good
agreement with experimental data, and provides useful insight on the
photo-induced charge transfer mechanism which characterizes the system.Comment: Accepted for publication on JPC, March 09th 200
Quantum coherence controls the charge separation in a prototypical artificial light harvesting system
In artificial light harvesting systems the conversion of light into charges or chemical energy happens on the femtosecond time scale and is thought to involve the incoherent jump of an electron from the optical absorber to an electron acceptor. Here we investigate the primary process of electronic charge transfer dynamics in a carotene-porphyrin-fullerene triad, a prototypical elementary component for an artificial light harvesting system combining coherent femtosecond spectroscopy and first-principles quantum dynamics simulations. Our experimental and theoretical results provide strong evidence that the driving mechanism of the photoinduced current generation cycle is a quantum-correlated wavelike motion of electrons and nuclei on a timescale of few tens of femtoseconds. We furthermore highlight the fundamental role played by the interface between the light-absorbing chromophore and the charge acceptor in triggering the coherent wavelike electron-hole splitting. © 2013 IEEE
Mouthiers-sur-Boëme, Chez les Rois
Chez les Rois est un gisement de référence de l'Aurignacien charentais et un des rares gisements aurignaciens européens à avoir livré des restes humains en place. Fouillé entre 1930 et 1939 par Potut et entre 1948 et 1952 par Mouton et Joffroy (1958), ce gisement a fait l'objet d'un sondage en 2005 et d'une fouille programmée entre 2006 et 2008 (d'Errico et Vanhaeren 2005, 2006, 2007, 2008). Cette opération de terrain a fait suite à la reprise de l'étude des restes humains et du matériel archéologique issus des fouilles Mouton et Joffroy ainsi qu'à sa datation (Ramirez Rozzi et al. sous presse). L'objectif des nouvelles fouilles était de préciser l'attribution culturelle des assemblages, la chronologie et nature de l'occupation aurignacienne ainsi que l'affiliation taxinomique des groupes humains qui ont fréquenté le site
Embedded, micro-interdigitated flow fields in high areal-loading intercalation electrodes towards seawater desalination and beyond
Faradaic deionization (FDI) is a promising technology for energy-efficient
water desalination using porous electrodes containing redox-active materials.
Herein, we demonstrate for the first time the capability of a symmetric FDI
flow cell to produce freshwater (<17.1 mM NaCl) from concentrated brackish
water (118mM), to produce effluent near freshwater salinity (19.1 mM) from
influent with seawater-level salinity (496 mM), and to reduce the salinity of
hypersaline brine from 781 mM to 227 mM. These remarkable salt-removal levels
were enabled by using flow-through electrodes with high areal-loading of nickel
hexacyanoferrate (NiHCF) Prussian Blue analogue intercalation material. The
pumping energy consumption due to flow-through electrodes was mitigated by
embedding an interdigitated array of <100 m wide channels in the
electrodes using laser micromachining. The micron-scale dimensions of the
resulting embedded, micro-interdigitated flow fields (e-IDFFs) facilitate
flow-through electrodes with high apparent permeability while minimizing
active-material loss. Our modeling shows that these e-IDFFs are more
suitable for our intercalation electrodes because they have >100X lower
permeability compared to common redox-flow battery electrodes, for which
millimetric flow-channel widths were used exclusively in the past. Total
desalination thermodynamic energy efficiency (TEE) was improved by more than
ten-fold relative to unpatterned electrodes: 40.0% TEE for brackish water,
11.7% TEE for hypersaline brine, and 7.4% TEE for seawater-salinity feeds.
Water transport between diluate and brine streams and charge efficiency losses
resulting from (electro)chemical effects are implicated as limiting energy
efficiency and water recovery, motivating their investigation for enhancing
future FDI performance.Comment: 70 pages, 23 figures. Energy Environ. Sci. (2023
Electron-Electron Interactions in Artificial Graphene
Recent advances in the creation and modulation of graphene-like systems are
introducing a science of "designer Dirac materials". In its original
definition, artificial graphene is a man-made nanostructure that consists of
identical potential wells (quantum dots) arranged in a adjustable honeycomb
lattice in the two-dimensional electron gas. As our ability to control the
quality of artificial graphene samples improves, so grows the need for an
accurate theory of its electronic properties, including the effects of
electron-electron interactions. Here we determine those effects on the band
structure and on the emergence of Dirac points
A taxonomical framework of socio-cultural hazards in transport hubs
This article presents a taxonomical framework that supports the considerations of socio-cultural hazards that may affect crowd management in transport hubs, i.e. airports, ports, underground and train stations, both in normal and emergency situations. Such hazards include communication breakdowns with passengers due, for instance, to language barriers; increased potential for revolts, as in stranded passenger situations; misreporting of security threats; and uncooperative behaviour in case of emergencies. Such socio-cultural hazards are not normally considered from the integrated perspective of transport hub operators, e.g. security staff, first responders and service assistants as well as safety and security managers. The present study provides an integrated perspective of these hazards as a means to increase the performance of transport staff members that interact with the public and with passengers on a daily basis. The methodology used to develop the framework comprises: (i) a focus group with relevant experts, (ii) semi-structured interviews at operational facilities with front-end practitioners, and (iii) a review of academic literature and media reports. The framework has also been qualitatively corroborated with transport operators in dedicated interviews and a focus group session. The study identified 10 socio-cultural hazards that were combined into a single framework comprising three high-level sub-categories: (i) crowd–staff interactions, (ii) crowd–crowd interactions, and (iii) crowd–environment interactions. The framework of socio-cultural factors can increase staff’s awareness of relevant socio-cultural hazards, their potential consequences in both normal and emergency situations, and the associated mitigation strategies. In turn, this can increase the quality and continuity of service, safety and security in the management of members of the public and passengers in transport hubs
Modal Analysis and Coupling in Metal-Insulator-Metal Waveguides
This paper shows how to analyze plasmonic metal-insulator-metal waveguides
using the full modal structure of these guides. The analysis applies to all
frequencies, particularly including the near infrared and visible spectrum, and
to a wide range of sizes, including nanometallic structures. We use the
approach here specifically to analyze waveguide junctions. We show that the
full modal structure of the metal-insulator-metal (MIM) waveguides--which
consists of real and complex discrete eigenvalue spectra, as well as the
continuous spectrum--forms a complete basis set. We provide the derivation of
these modes using the techniques developed for Sturm-Liouville and generalized
eigenvalue equations. We demonstrate the need to include all parts of the
spectrum to have a complete set of basis vectors to describe scattering within
MIM waveguides with the mode-matching technique. We numerically compare the
mode-matching formulation with finite-difference frequency-domain analysis and
find very good agreement between the two for modal scattering at symmetric MIM
waveguide junctions. We touch upon the similarities between the underlying
mathematical structure of the MIM waveguide and the PT symmetric quantum
mechanical pseudo-Hermitian Hamiltonians. The rich set of modes that the MIM
waveguide supports forms a canonical example against which other more
complicated geometries can be compared. Our work here encompasses the microwave
results, but extends also to waveguides with real metals even at infrared and
optical frequencies.Comment: 17 pages, 13 figures, 2 tables, references expanded, typos fixed,
figures slightly modifie
fMRI evidence of ‘mirror’ responses to geometric shapes
Mirror neurons may be a genetic adaptation for social interaction [1]. Alternatively, the associative hypothesis [2], [3] proposes that the development of mirror neurons is driven by sensorimotor learning, and that, given suitable experience, mirror neurons will respond to any stimulus. This hypothesis was tested using fMRI adaptation to index populations of cells with mirror properties. After sensorimotor training, where geometric shapes were paired with hand actions, BOLD response was measured while human participants experienced runs of events in which shape observation alternated with action execution or observation. Adaptation from shapes to action execution, and critically, observation, occurred in ventral premotor cortex (PMv) and inferior parietal lobule (IPL). Adaptation from shapes to execution indicates that neuronal populations responding to the shapes had motor properties, while adaptation to observation demonstrates that these populations had mirror properties. These results indicate that sensorimotor training induced populations of cells with mirror properties in PMv and IPL to respond to the observation of arbitrary shapes. They suggest that the mirror system has not been shaped by evolution to respond in a mirror fashion to biological actions; instead, its development is mediated by stimulus-general processes of learning within a system adapted for visuomotor control
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