Non-Markovian quantum state diffusion for absorption spectra of molecular aggregates

In many molecular systems one encounters the situation where electronic excitations couple to a quasi-continuum of phonon modes. That continuum may be highly structured e.g. due to some weakly damped high frequency modes. To handle such a situation, an approach combining the non-Markovian quantum state diffusion (NMQSD) description of open quantum systems with an efficient but abstract approximation was recently applied to calculate energy transfer and absorption spectra of molecular aggregates [Roden, Eisfeld, Wolff, Strunz, PRL 103 (2009) 058301]. To explore the validity of the used approximation for such complicated systems, in the present work we compare the calculated (approximative) absorption spectra with exact results. These are obtained from the method of pseudomodes, which we show to be capable of determining the exact spectra for small aggregates and a few pseudomodes. It turns out that in the cases considered, the results of the two approaches mostly agree quite well. The advantages and disadvantages of the two approaches are discussed

Modification of emission properties of ZnO layers due to plasmonic near-field coupling to Ag nanoislands

A simple fabrication method of Ag nanoislands on ZnO films is presented. Continuous wave and time-resolved photoluminescence and transmission are employed to investigate modifications of visible and UV emissions of ZnO brought about by coupling to localized surface plasmons residing on Ag nanoislands. The size of the nanoislands, determining their absorption and scattering efficiencies, is found to be an important factor governing plasmonic modification of optical response of ZnO films. The presence of the Ag nanoislands of appropriate dimensions causes a strong (threefold) increase in emission intensity and up to 1.5 times faster recombination. The experimental results are successfully described by model calculations within the Mie theory.Comment: 14 pages, 5 figure

A decision-making framework for restoring riparian zones degraded by invasive alien plants in South Africa

Riparian habitats in many parts of South Africa are severely degraded by invasive alien plants, especially trees. These invasions reduce water yields from catchments and affect riverine functioning and biodiversity. Initiatives are under way countrywide to clear alien plants from watercourses and surrounding catchments. Current understanding of key processes that regulate riparian functioning and define options for restoration is rudimentary. We review the impacts of riparian invasions and identify factors limiting the recovery of natural vegetation following alien clearance. We propose a framework of strategic interventions for optimizing restoration success. The framework identifies abiotic and biotic barriers to restoration at the scales of catchments and local reaches. In highly transformed catchments, interventions at the reach scale may fail if important barriers at the catchment scale are not addressed. The extent to which propagule supply and microsite conditions inhibit vegetation recovery is unknown. We also know little of the relative importance of dispersing vegetative propagules, dispersing seeds and soil-stored seed banks in vegetation dynamics, particularly after severe disturbances such as dense invasion by alien plants. The importance of geomorphological and hydrological factors in mediating recovery of riparian vegetation has not been adequately explored for all climatic areas in South Africa. More research is needed to determine the influence of different alien species and clearing treatments on the recovery of riparian vegetation. The literature strongly suggests that in highly alien-transformed catchments, the re-introduction of riparian species is required to promote recovery and suppress re-invasion. However, such interventions are unlikely to be widely implemented unless the cost: benefit ratios are favourable

A decision-making framework for restoring riparian zones degraded by invasive alien plants in South Africa

The original publication is available at http://www.sabinet.co.za/?page=open-access-journalsRiparian habitats in many parts of South Africa are severely degraded by invasive alien plants, especially trees. These invasions reduce water yields from catchments and affect riverine functioning and biodiversity. Initiatives are under way countrywide to clear alien plants from watercourses and surrounding catchments. Current understanding of key processes that regulate riparian functioning and define options for restoration is rudimentary. We review the impacts of riparian invasions and identify factors limiting the recovery of natural vegetation following alien clearance. We propose a framework of strategic interventions for optimizing restoration success. The framework identifies abiotic and biotic barriers to restoration at the scales of catchments and local reaches. In highly transformed catchments, interventions at the reach scale may fail if important barriers at the catchment scale are not addressed. The extent to which propagule supply and microsite conditions inhibit vegetation recovery is unknown. We also know little of the relative importance of dispersing vegetative propagules, dispersing seeds and soil-stored seed banks in vegetation dynamics, particularly after severe disturbances such as dense invasion by alien plants. The importance of geomorphological and hydrological factors in mediating recovery of riparian vegetation has not been adequately explored for all climatic areas in South Africa. More research is needed to determine the influence of different alien species and clearing treatments on the recovery of riparian vegetation. The literature strongly suggests that in highly alien-transformed catchments, the re-introduction of riparian species is required to promote recovery and suppress re-invasion. However, such interventions are unlikely to be widely implemented unless the cost:benefit ratios are favourable.Publishers' Versio

Determination of the map of efficiency of the J-PET detector with the GATE package

A novel PET detector consisting of strips of polymer scintillators is being developed by the J-PET Collaboration. The map of efficiency and the map of geometrical acceptance of the 2-strip J-PET scanner are presented. Map of efficiency was determined using the Monte Carlo simulation software GATE based on GEANT4. Both maps were compared using method based on the chi2 test.Comment: 14 pages, 9 figures, proceeding from conference Symposium on Positron Emission Tomography: http://koza.if.uj.edu.pl/pet-symposium-2013