| 1. |
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- 2019
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Mantzouki, Evanthia, et al.
(författare)
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Temperature Effects Explain Continental Scale Distribution of Cyanobacterial Toxins
- 2018
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Ingår i: Toxins. - : MDPI. - 2072-6651. ; 10:4
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Tidskriftsartikel (refereegranskat)abstract
- Insight into how environmental change determines the production and distribution of cyanobacterial toxins is necessary for risk assessment. Management guidelines currently focus on hepatotoxins (microcystins). Increasing attention is given to other classes, such as neurotoxins (e.g., anatoxin-a) and cytotoxins (e.g., cylindrospermopsin) due to their potency. Most studies examine the relationship between individual toxin variants and environmental factors, such as nutrients, temperature and light. In summer 2015, we collected samples across Europe to investigate the effect of nutrient and temperature gradients on the variability of toxin production at a continental scale. Direct and indirect effects of temperature were the main drivers of the spatial distribution in the toxins produced by the cyanobacterial community, the toxin concentrations and toxin quota. Generalized linear models showed that a Toxin Diversity Index (TDI) increased with latitude, while it decreased with water stability. Increases in TDI were explained through a significant increase in toxin variants such as MC-YR, anatoxin and cylindrospermopsin, accompanied by a decreasing presence of MC-LR. While global warming continues, the direct and indirect effects of increased lake temperatures will drive changes in the distribution of cyanobacterial toxins in Europe, potentially promoting selection of a few highly toxic species or strains.
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| 3. |
- Fang, Yurui, 1983, et al.
(författare)
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Plasmon Enhanced Internal Photoemission in Antenna-Spacer-Mirror Based Au/TiO2 Nanostructures
- 2015
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 15:6, s. 4059-4065
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Tidskriftsartikel (refereegranskat)abstract
- Emission of photoexcited hot electrons from plasmonic metal nanostructures to semiconductors is key to a number of proposed nanophotonics technologies for Solar harvesting, water splitting, photocatalysis, and a variety of optical sensing and photodetector applications. Favorable materials and catalytic properties make systems based on gold and TiO2 particularly interesting, but the internal photo emission efficiency for visible light is low because of the wide bandgap of the semiconductor. We investigated the incident photon-to-electron conversion efficiency of thin TiO2 films decorated with Au nanodisk antennas in an electrochemical circuit and found that incorporation of a Au mirror beneath the semiconductor amplified the photoresponse for light with wavelength lambda = 500-950 nm by a factor 2-10 compared to identical structures lacking the mirror component. Classical electrodynamics simulations showed that the enhancement effect is caused by a favorable interplay between localized surface plasmon excitations and cavity modes that together amplify the light absorption in the Au/TiO2 interface. The experimentally determined internal quantum efficiency for hot electron transfer decreases monotonically with wavelength, similar to the probability for interband excitations with energy higher than the Schottky barrier obtained from a density functional theory band structure simulation of a thin Au/TiO2 slab.
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| 4. |
- Mehta, Ankit Nalin, et al.
(författare)
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Understanding noninvasive charge transfer doping of graphene: a comparative study
- 2018
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Ingår i: Journal of Materials Science: Materials in Electronics. - : Springer Science and Business Media LLC. - 1573-482X .- 0957-4522. ; 29:7, s. 5239-5252
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we systematically investigate and compare noninvasive doping of chemical vapor deposition graphene with three molecule dopants through spectroscopy and electrical conductivity techniques. Thionyl chloride shows the smallest improvement in conductivity with poor temporal and thermal stability and nitric acid induces the biggest sheet resistance reduction with modified stability. Molybdenum trioxide doping stands out, after thermal annealing, with both causing a significant sheet-resistance reduction and having superior temporal and thermal stability. These properties make it ideal for applications in advanced electronics. Theoretical studies based on the van der Waals density functional method suggest that cluster formation of molybdenum trioxide underpins the significant reduction in sheet resistance, and the stability, that arises after thermal annealing. Our comparative study clarifies charge transfer doping of graphene and brings understanding of the weak-interaction nature of such non-destructive doping of graphene. Our work also shows that we can use weak chemisorption to tailor the electronic properties of graphene, for example, to improve conductivity. This ability open up possibilities for further use of graphene in electronic interconnects, field effect transistors and other systems.
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| 5. |
- Meyer, H.F., et al.
(författare)
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Overview of physics studies on ASDEX Upgrade
- 2019
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:11
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Forskningsöversikt (refereegranskat)abstract
- The ASDEX Upgrade (AUG) programme, jointly run with the EUROfusion MST1 task force, continues to significantly enhance the physics base of ITER and DEMO. Here, the full tungsten wall is a key asset for extrapolating to future devices. The high overall heating power, flexible heating mix and comprehensive diagnostic set allows studies ranging from mimicking the scrape-off-layer and divertor conditions of ITER and DEMO at high density to fully non-inductive operation (q 95 = 5.5, ) at low density. Higher installed electron cyclotron resonance heating power 6 MW, new diagnostics and improved analysis techniques have further enhanced the capabilities of AUG. Stable high-density H-modes with MW m-1 with fully detached strike-points have been demonstrated. The ballooning instability close to the separatrix has been identified as a potential cause leading to the H-mode density limit and is also found to play an important role for the access to small edge-localized modes (ELMs). Density limit disruptions have been successfully avoided using a path-oriented approach to disruption handling and progress has been made in understanding the dissipation and avoidance of runaway electron beams. ELM suppression with resonant magnetic perturbations is now routinely achieved reaching transiently . This gives new insight into the field penetration physics, in particular with respect to plasma flows. Modelling agrees well with plasma response measurements and a helically localised ballooning structure observed prior to the ELM is evidence for the changed edge stability due to the magnetic perturbations. The impact of 3D perturbations on heat load patterns and fast-ion losses have been further elaborated. Progress has also been made in understanding the ELM cycle itself. Here, new fast measurements of and E r allow for inter ELM transport analysis confirming that E r is dominated by the diamagnetic term even for fast timescales. New analysis techniques allow detailed comparison of the ELM crash and are in good agreement with nonlinear MHD modelling. The observation of accelerated ions during the ELM crash can be seen as evidence for the reconnection during the ELM. As type-I ELMs (even mitigated) are likely not a viable operational regime in DEMO studies of 'natural' no ELM regimes have been extended. Stable I-modes up to have been characterised using -feedback. Core physics has been advanced by more detailed characterisation of the turbulence with new measurements such as the eddy tilt angle - measured for the first time - or the cross-phase angle of and fluctuations. These new data put strong constraints on gyro-kinetic turbulence modelling. In addition, carefully executed studies in different main species (H, D and He) and with different heating mixes highlight the importance of the collisional energy exchange for interpreting energy confinement. A new regime with a hollow profile now gives access to regimes mimicking aspects of burning plasma conditions and lead to nonlinear interactions of energetic particle modes despite the sub-Alfvénic beam energy. This will help to validate the fast-ion codes for predicting ITER and DEMO.
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| 6. |
- Tao, Jianmin, et al.
(författare)
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First-principles study of the binding energy between nanostructures and its scaling with system size
- 2018
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 97:15
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Tidskriftsartikel (refereegranskat)abstract
- The equilibrium van der Waals binding energy is an important factor in the design of materials and devices. However, it presents great computational challenges for materials built up from nanostructures. Here we investigate the binding-energy scaling behavior from first-principles calculations. We show that the equilibrium binding energy per atom between identical nanostructures can scale up or down with nanostructure size, but can be parametrized for large N with an analytical formula (in meV/atom), Eb/N=a+b/N+c/N2+d/N3, where N is the number of atoms in a nanostructure and a, b, c, and d are fitting parameters, depending on the properties of a nanostructure. The formula is consistent with a finite large-size limit of binding energy per atom. We find that there are two competing factors in the determination of the binding energy: Nonadditivities of van der Waals coefficients and center-to-center distance between nanostructures. To decode the detail, the nonadditivity of the static multipole polarizability is investigated from an accurate spherical-shell model. We find that the higher-order multipole polarizability displays ultrastrong intrinsic nonadditivity, no matter if the dipole polarizability is additive or not.
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| 7. |
- Yang, Hengyan, et al.
(författare)
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New Understanding on Photocatalytic Mechanism of Nitrogen-Doped Graphene Quantum Dots-Decorated BiVO4 Nanojunction Photocatalysts
- 2017
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 2:7, s. 3766-3773
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Tidskriftsartikel (refereegranskat)abstract
- Bismuth vanadate (BiVO4) is a promising candidate as a visible-light-driven photocatalyst in the aspect of practical applications. To investigate the origin of active species from BiVO4 and understand the influence of the variations of the photocatalytic process, comparative studies on zero-dimensional nitrogen-doped graphene quantum dot (NGQD)-decorated BiVO4 have been carried out for methylene blue photodegradation. It was found that the hydroxyl group-rich NGQD surface and the established heterojunction structure between NGQDs and BiVO4 were greatly beneficial for the conversion of the MOH radical. With NGQD decoration, the dominant oxidant species for NGQDs/BiVO4 were confirmed to be MOH and H2O2, rather than holes originating from the valence band of unmodified BiVO4. The synergistic photocatalytic mechanism with respect to the interfacial charge transport and the conversion of active species was proposed. The achievement of the controllable active species significantly altering the activity may be applied for different photocatalytic reactions.
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| 8. |
- Yang, Yang, 1985-
(författare)
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Phytoplankton and Physical Disturbance : Seasonal dynamics in temperate Lake Erken, Sweden
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Phytoplankton mirrors changes in the environment and plays an important role in biogeochemical processes. Phytoplankton dynamics is the outcome of both autogenic succession and external disturbances. This thesis focused on the seasonal variation of water column stability and its effects on phytoplankton, particularly considering the influence of mixing events on phytoplankton development. Lake Erken is a dimictic lake with weak and often interrupted summer stratification, which represents an intermediate case between a polymictic lake and a lake with strong summer stratification.There are two diatom phases annually. The spring bloom is caused by pioneer centric diatoms, and the autumn diatom phase is dominated by meroplanktonic diatoms induced by turnover. A summer Cyanobacteria bloom – mainly Gloeotrichia echinulata, depended on the length and stability of stratification.Winter and spring air temperature is found to play an important role in the annual succession of phytoplankton by initiating changes in ice/snow-cover and lake thermal stability and setting the basic status. Instead of starting from zero, the vernal phytoplankton piles up on the overwintering community, this trans-annual ecological memory influences both the composition and diversity and taxonomic distinctness of spring phytoplankton.Water column stability during summer in Lake Erken is mainly influenced by wind-induced turbulence and internal seiches. As thermal stratification develops from early until late summer, variations in stability and gradual deepening of the thermocline depth influence phytoplankton dynamics directly by changing its distribution, and also indirectly by altering the nutrient and light availability. A new disturbance index (DI) was defined to quantify environmental stability/disturbance and tested well to indicate phytoplankton equilibrium status in two summer stratification periods. The concept of species and functional groups was generally used in this study. However, a next generation sequencing based approach was also tested and proved to provide an excellent candidate for revealing distribution patterns of phytoplankton in inland waters.
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| 9. |
- Yang, Yang, 1985-, et al.
(författare)
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Repetitive baselines of phytoplankton succession in an unstably stratified temperate lake (Lake Erken, Sweden) : a long-term analysis
- 2016
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Ingår i: Hydrobiologia. - : Springer Science and Business Media LLC. - 0018-8158 .- 1573-5117. ; 764:1, s. 211-227
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Tidskriftsartikel (refereegranskat)abstract
- The seasonal development of phytoplankton is a sequence of consecutive events with waxes and wanes of biomass and compositional shifts. This study analyzed 16 years data in Lake Erken, Sweden and revealed four baselines of phytoplankton succession with their underlying drivers. Results showed that there were two diatom-dominated phases annually. The vernal community was dominated by centric diatoms larger than 15 A mu m (functional groups B and C) which were fast-growing diatoms being highly efficient in the use of nutrients. The autumn community was comprised mainly meroplanktonic mixing-dependent Aulacoseira granulata and Fragilaria sp. (MP and P) or/and large centric diatoms (B). Between the two mixing-phases with diatoms, a Gloeotrichia echinulata (H 2) bloom occurred due to its preference for a stratified water column with elevated water temperatures and high light availability. The summer stratification in Lake Erken was weak and short, thus, favoring meroplanktonic diatoms to peak once the lake turned over in early autumn. Lake Erken represents an intermediate case between a highly mixed polymictic lake and a lake with strong summer stratification, where the observed stratification patterns allowed the development of an autumn diatom phase similar, by extent, to the vernal one and mainly dominated by meroplanktonic diatoms.
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| 10. |
- Yang, Yang, 1985-, et al.
(författare)
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Water column stability and summer phytoplankton dynamics in a temperate lake (Lake Erken, Sweden)
- 2016
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Ingår i: Inland Waters. - 2044-2041 .- 2044-205X. ; 6:4, s. 499-508
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Tidskriftsartikel (refereegranskat)abstract
- Phytoplankton development in aquatic ecosystems is caused by interactions among multiple environmental factors. Physical processes, particularly development of thermal stratification, have been proposed to be important factors for regulating phytoplankton composition and abundance during summer. This study examined the temporal pattern of thermal stratification during summer in Lake Erken, Sweden, based on 21 years of historical data spanning 23 years and investigated the role played by water stability on phytoplankton development. Water column stability indexes were calculated from high frequency measurements during periods of summer thermal stratification. Clustering and ordination analyzed the dissimilarities between communities during different periods and extracted the significant environmental gradients controlling phytoplankton succession. Wind introduced the major external disturbance to Lake Erken during summer and played an important role for the progression of thermocline depth. Species-specific thermal stability preference or tolerance determined the response of individual species to the stratification and constitutes a mechanism of species selection in phytoplankton dynamics. Lake Erken is an unstably stratified lake during summer, caused by wind-induced turbulence and internal seiches. Adaptation to these unstable conditions is the major determinant of phytoplankton dynamics. Hydrodynamic variability, characterized by different stability indexes in early, mid, and late summer, was the key factor regulating phytoplankton dynamics, directly by changing phytoplankton distribution and indirectly by altering both the light and nutrient availability in the epilimnion.
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