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Harvesting Efficiency (harvesting + efficiency)
Selected AbstractsLight partitioning among species and species replacement in early successional grasslandsJOURNAL OF VEGETATION SCIENCE, Issue 5 2002Marinus J.A. Werger Makino (1962); Ohwi (1965) Abstract. We studied canopy structure, shoot architecture and light harvesting efficiencies of the species (photon flux captured per unit above-ground plant mass) in a series of exclosures of different age (up to 4.5 yr) in originally heavily grazed grassland in N Japan.Vegetation height and Leaf Area Index (LAI) increased in the series and Zoysia japonica, the dominant in the beginning, was replaced by the much taller Miscanthus sinensis. We showed how this displacement in dominance can be explained by inherent constraints on the above-ground architecture of these two species. In all stands light capture of plants increased with their above-ground biomass but taller species were not necessarily more efficient in light harvesting. Some subordinate species grew disproportionally large leaf areas and persisted in the shady undergrowth. Some other species first grew taller and managed to stay in the better-lit parts of the canopy, but ultimately failed to match the height growth of their neighbours in this early successional series. Their light harvesting efficiencies declined and this probably led to their exclusion. By contrast, species that maintained their position high in the canopy managed to persist in the vegetation despite their relatively low light harvesting efficiencies. In the tallest stands ,later successional' species had higher light harvesting efficiencies for the same plant height than ,early successional' species which was mostly the result of the greater area to mass ratio (specific leaf area, SLA) of their leaves. This shows how plant stature, plasticity in above-ground biomass partitioning, and architectural constraints determine the ability of plants to efficiently capture light, which helps to explain species replacement in this early successional series. [source] Ultrafast Hole-Transfer Dynamics in Polymer/PCBM Bulk HeterojunctionsADVANCED FUNCTIONAL MATERIALS, Issue 10 2010Artem A. Bakulin Abstract Ultrafast dynamics of the hole-transfer process from methanofullerene to a polymer in a polymer/PCBM bulk heterojunction are directly resolved. Injection of holes into MDMO-PPV is markedly delayed with respect to [60]PCBM excitation. The fastest component of the delayed response is attributed to the PCBM,polymer hole-transfer process (30,±,10,fs), while the slower component (,150,fs) is provisionally assigned to energy transfer and/or relaxation inside PCBM nanoclusters. The charge generation through the hole transfer is therefore as fast and efficient as through the electron-transfer process. Exciton harvesting efficiency after PCBM excitation crucially depends on the concentration of the methanofullerene in the blend, which is related to changes in the blend morphology. Ultrafast charge generation is most efficient when the characteristic scale of phase separation in the blend does not exceed ,20,nm. At larger-scale phase separation, the exciton harvesting dramatically declines. The obtained results on the time scales of the ultrafast charge generation after PCBM excitation and their dependence on blend composition and morphology are instrumental for the future design of fullerene-derivative-based photovoltaic devices. [source] Symmetric Versus Unsymmetric Platinum(II) Bis(aryleneethynylene)s with Distinct Electronic Structures for Optical Power Limiting/Optical Transparency Trade-off OptimizationADVANCED FUNCTIONAL MATERIALS, Issue 4 2009Guijiang Zhou Abstract A new series of symmetric and unsymmetric Pt(II) bis(acetylide) complexes of the type DC,CPt(PBu3)2C,CD (DPtD), AC,CPt(PBu3)2C,CA (APtA) and DC,CPt(PBu3)2C,CA (DPtA) (D, donor groups; A, acceptor groups) are synthesized, and show superior optical power limiting (OPL)/optical transparency trade-offs. By tailoring the electronic properties of the aryleneethynylene group, distinct electronic structures for these metalated complexes can be obtained, which significantly affect their photophysical behavior and OPL properties for a nanosecond laser pulse at 532,nm. Electronic influence of the ligand type and the molecular symmetry of metal group on the optical transparency/nonlinearity optimization is thoroughly elucidated. Generally, aryleneethynylene ligands with , electron-accepting nature will effectively enhance the harvesting efficiency of the triplet excited states. The ligand variation to the OPL strength of these Pt(II) compounds follows the order: DPtD,>,DPtA,>,APtA. These results could be attributed to the distinctive excited state character induced by their different electronic structures, on the basis of the data from both photophysical studies and theoretical calculations. All of the complexes show very good optical transparencies in the visible-light region and exhibit excellent OPL responses with very impressive figure of merit ,ex/,o values (up to 17), which remarkably outweigh those of state-of-the-art reverse saturable absorption dyes such as C60 and metallophthalocyanines with very poor transparencies. Their lower optical-limiting thresholds (0.05,J,cm,2 at 92% linear transmittance) compared with that of the best materials (ca. 0.07,J,cm,2 for InPc and PbPc dyes) currently in use will render these highly transparent materials promising candidates for practical OPL devices for the protection of human eyes and other delicate electro-optic sensors. [source] A High-Light-Harvesting-Efficiency Coumarin Dye for Stable Dye-Sensitized Solar Cells,ADVANCED MATERIALS, Issue 8 2007Z.-S. Wang A new coumarin dye (see figure) for use in dye-sensitized solar cells (DSSCs) is reported. It exhibits near-unity light harvesting efficiency and incident photon-to-electron conversion efficiency (see figure) over a wide spectral region in 6,,m transparent TiO2 films. DSSCs based on this metal-free organic dye show long-term stability and power-conversion efficiencies of around 6,% under continuous light-soaking stress for up to 1000,h. [source] Shallow-water habitats as sources of fallback foods for homininsAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 4 2009Richard Wrangham Abstract Underground storage organs (USOs) have been proposed as critical fallback foods for early hominins in savanna, but there has been little discussion as to which habitats would have been important sources of USOs. USOs consumed by hominins could have included both underwater and underground storage organs, i.e., from both aquatic and terrestrial habitats. Shallow aquatic habitats tend to offer high plant growth rates, high USO densities, and relatively continuous USO availability throughout the year. Baboons in the Okavango delta use aquatic USOs as a fallback food, and aquatic or semiaquatic USOs support high-density human populations in various parts of the world. As expected given fossilization requisites, the African early- to mid-Pleistocene shows an association of Homo and Paranthropus fossils with shallow-water and flooded habitats where high densities of plant-bearing USOs are likely to have occurred. Given that early hominins in the tropics lived in relatively dry habitats, while others occupied temperate latitudes, ripe, fleshy fruits of the type preferred by African apes would not normally have been available year round. We therefore suggest that water-associated USOs were likely to have been key fallback foods, and that dry-season access to aquatic habitats would have been an important predictor of hominin home range quality. This study differs from traditional savanna chimpanzee models of hominin origins by proposing that access to aquatic habitats was a necessary condition for adaptation to savanna habitats. It also raises the possibility that harvesting efficiency in shallow water promoted adaptations for habitual bipedality in early hominins. Am J Phys Anthropol 140:630,642, 2009. © 2009 Wiley-Liss, Inc. [source] Energy scavenging for energy efficiency in networks and applicationsBELL LABS TECHNICAL JOURNAL, Issue 2 2010Kyoung Joon Kim Telecommunication networks will play a huge part in enabling eco-sustainability of human activity; one of the first steps towards this is to dramatically increase network energy efficiency. In this paper we present two novel approaches for energy scavenging in networks. One involves thermal energy scavenging for improving wireless base station energy efficiency, and the other involves mechanical energy scavenging for powering sensors in sensor networks, for machine-to-machine (M2M) communications, and for smart grid applications. Power amplifier (PA) transistors in base stations waste 30 percent of the total energy used in a wireless access network (WAN) as heat to the environment. We propose a thermoelectric energy recovery module (TERM) to recover electricity from the waste heat of PA transistors. A fully coupled thermoelectric (TE) model, combining thermoelectricity and heat transfer physics, is developed to explore the power generation performance and efficiency as well as the thermal performance of the TERM. The TE model is comprehensively used to determine optimized pellet geometries for power generation and efficiency as a function of PA transistor heat dissipation, heat sink performance, and load resistance. Maximum power generation and efficiency for various parametric conditions are also explored. Untapped kinetic energy is almost everywhere in the form of vibrations. This energy can be converted into electrical energy by means of transducers to power wireless sensors and mobile electronics in the range of microwatts to a few milliwatts. However, many problems limit the efficiency of current harvesting generators: narrow bandwidth, low power density, micro-electro-mechanical system (MEMS) scaling, and inconsistency of vibrating sources. We explore energy scavenger designs based on multiple-mass systems to increase harvesting efficiency. A theoretical and experimental study of two degrees-of-freedom (2-DOF) vibration-powered generators is presented. Both electromagnetic and piezoelectric conversion methods are modeled by using a general approach. Experimental results for the multi-resonant system are in agreement with the analytical predictions and demonstrate significantly better performance in terms of maximum power density per total mass and a wider bandwidth compared to single DOF (1-DOF) generators. © 2010 Alcatel-Lucent. [source] | ||||||||||