1,483 research outputs found

    Statistics of low-energy levels of a one-dimensional weakly localized Frenkel exciton: A numerical study

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    Numerical study of the one-dimensional Frenkel Hamiltonian with on-site randomness is carried out. We focus on the statistics of the energy levels near the lower exciton band edge, i. e. those determining optical response. We found that the distribution of the energy spacing between the states that are well localized at the same segment is characterized by non-zero mean, i.e. these states undergo repulsion. This repulsion results in a local discrete energy structure of a localized Frenkel exciton. On the contrary, the energy spacing distribution for weakly overlapping local ground states (the states with no nodes within their localization segments) that are localized at different segments has zero mean and shows almost no repulsion. The typical width of the latter distribution is of the same order as the typical spacing in the local discrete energy structure, so that this local structure is hidden; it does not reveal itself neither in the density of states nor in the linear absorption spectra. However, this structure affects the two-exciton transitions involving the states of the same segment and can be observed by the pump-probe spectroscopy. We analyze also the disorder degree scaling of the first and second momenta of the distributions.Comment: 10 pages, 6 figure

    Positron Emission Particle Tracking (PEPT) for the analysis of water motion in a domestic dishwasher

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    AbstractMotion of water inside a household dishwasher has been characterised via Positron Emission Particle Tracking (PEPT). The technique enables the visualisation of the motion of a radioactive tracer in three-dimensional and opaque systems. Results showed a periodic sequence of the water over time, encompassing the following steps: movement inside internal equipment and spray arm, ejection via jets, impact over walls and crockery, downfall (either over walls, crockery or free falling) and recirculation of the bulk water from the bottom of the dishwasher. This sequence was shown to occur within a few seconds and the highest velocities, and therefore, the highest kinetic energies, were found upon ejection. Jet paths were observed to follow a straight line. Increased pump speeds increased velocity ejection profiles, but the effect over the downfall step was negligible. In fully loaded dishwasher (with crockery), the tracer moved slower in these high packing zones, showing low velocity profile areas with higher residence times. Other stagnant areas were found at the edges of the bulk of water remaining at the bottom of the dishwasher. Use of detergent did not seem to affect water motion. Finally, data generated via CFD was compared with equivalent PEPT data, showing good agreement for the spray arm and ejection steps but disagreement in the free falling step. The divergences in the results can be explained by a combination of PEPT data processing and CFD model constraints. Information gathered is helping the development of more sustainable and efficient dishwashing systems

    Supramolecular interactions in clusters of polar and polarizable molecules

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    We present a model for molecular materials made up of polar and polarizable molecular units. A simple two state model is adopted for each molecular site and only classical intermolecular interactions are accounted for, neglecting any intermolecular overlap. The complex and interesting physics driven by interactions among polar and polarizable molecules becomes fairly transparent in the adopted model. Collective effects are recognized in the large variation of the molecular polarity with supramolecular interactions, and cooperative behavior shows up with the appearance, in attractive lattices, of discontinuous charge crossovers. The mean-field approximation proves fairly accurate in the description of the gs properties of MM, including static linear and non-linear optical susceptibilities, apart from the region in the close proximity of the discontinuous charge crossover. Sizeable deviations from the excitonic description are recognized both in the excitation spectrum and in linear and non-linear optical responses. New and interesting phenomena are recognized near the discontinuous charge crossover for non-centrosymmetric clusters, where the primary photoexcitation event corresponds to a multielectron transfer.Comment: 14 pages, including 11 figure

    Measurement of the cross-section and charge asymmetry of WW bosons produced in proton-proton collisions at s=8\sqrt{s}=8 TeV with the ATLAS detector

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    This paper presents measurements of the W+→Ό+ÎœW^+ \rightarrow \mu^+\nu and W−→Ό−ΜW^- \rightarrow \mu^-\nu cross-sections and the associated charge asymmetry as a function of the absolute pseudorapidity of the decay muon. The data were collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with the ATLAS experiment at the LHC and correspond to a total integrated luminosity of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the 1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured with an uncertainty between 0.002 and 0.003. The results are compared with predictions based on next-to-next-to-leading-order calculations with various parton distribution functions and have the sensitivity to discriminate between them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables, submitted to EPJC. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13

    Search for chargino-neutralino production with mass splittings near the electroweak scale in three-lepton final states in √s=13 TeV pp collisions with the ATLAS detector