3,420 research outputs found
Luminescence and x-ray absorption measurements of persistent SrAl2O4:Eu,Dy powders: evidence for valence state changes
The development of new efficient afterglow phosphors is currently hampered by a limited understanding of the persistent luminescence mechanism. Radioluminescence and x-ray absorption measurements on the persistent phosphor SrAl2O4:Eu,Dy were combined to reveal possible valence state changes for the rare earth (co)dopants. Traps in the phosphor material are quickly filled when exposing thermally emptied SrAl2O4:Eu,Dy powder to x-rays. On the same time scale, a partial oxidation of Eu2+ to Eu3+ is observed by XANES (x-ray absorption near-edge spectroscopy), while for the trivalent dysprosium the valence state remains unchanged. The impact of these observations on the recently proposed models for persistent luminescence is discussed
The microscopic nature of localization in the quantum Hall effect
The quantum Hall effect arises from the interplay between localized and
extended states that form when electrons, confined to two dimensions, are
subject to a perpendicular magnetic field. The effect involves exact
quantization of all the electronic transport properties due to particle
localization. In the conventional theory of the quantum Hall effect,
strong-field localization is associated with a single-particle drift motion of
electrons along contours of constant disorder potential. Transport experiments
that probe the extended states in the transition regions between quantum Hall
phases have been used to test both the theory and its implications for quantum
Hall phase transitions. Although several experiments on highly disordered
samples have affirmed the validity of the single-particle picture, other
experiments and some recent theories have found deviations from the predicted
universal behaviour. Here we use a scanning single-electron transistor to probe
the individual localized states, which we find to be strikingly different from
the predictions of single-particle theory. The states are mainly determined by
Coulomb interactions, and appear only when quantization of kinetic energy
limits the screening ability of electrons. We conclude that the quantum Hall
effect has a greater diversity of regimes and phase transitions than predicted
by the single-particle framework. Our experiments suggest a unified picture of
localization in which the single-particle model is valid only in the limit of
strong disorder
Influence of an Sb doping layer in CIGS thin-film solar cells: a photoluminescence study
Sb doping of Cu(In,Ga)Se2 (CIGS) solar cells has been reported to exhibit a positive effect on the morphology of the absorber layer, offering a possibility to lower manufacturing cost by lowering the annealing temperatures during the CIGS deposition. In this work electron microscopy, energy-dispersive x-ray spectroscopy and photoluminescence experiments have been performed on cells deposited on soda-lime glass substrates, adding a thin Sb layer onto the Mo back contact prior to the CIGS absorber deposition. The defect structure of CIGS solar cells doped with Sb in this way has been investigated and is compared with that of undoped reference cells. The influence of substrate temperature during absorber growth has also been evaluated. For all samples the photoluminescence results can be explained by considering three donor–acceptor pair recombination processes involving the same defect pairs
Efficient Duration-Based Workload Balancing for Interdependent Vehicle Routes
Vehicle routing and scheduling problems with interdependent routes arise when some services must be performed by at least two vehicles and temporal synchronization is thus required between the starting times of these services. These problems are often coupled with time window constraints in order to model various real-world applications such as pickup and delivery with transfers, cross-docking and home care scheduling. Interdependent routes in these applications can lead to large idle times for some drivers, unnecessarily lengthening their working hours. To remedy this unfairness, it is necessary to balance the duration of the drivers\u27 routes. However, quickly evaluating duration-based equity functions for interdependent vehicle routes with time windows poses a significant computational challenge, particularly when the departure time of routes is flexible. This paper introduces models and algorithms to compute two well-known equity functions in flexible departure time settings: min-max and range minimization. We explore the challenges and algorithmic complexities of evaluating these functions both from a theoretical and an experimental viewpoint. The results of this paper enable the development of new heuristic methods to balance the workload of interdependent vehicle routes with time windows
Domain Formation in v=2/3 Fractional Quantum Hall Systems
We study the domain formation in the v=2/3 fractional quantum Hall systems
basing on the density matrix renormalization group (DMRG) analysis. The
ground-state energy and the pair correlation functions are calculated for
various spin polarizations. The results confirm the domain formation in
partially spin polarized states, but the presence of the domain wall increases
the energy of partially spin polarized states and the ground state is either
spin unpolarized state or fully spin polarized state depending on the Zeeman
energy. We expect coupling with external degrees of freedom such as nuclear
spins is important to reduce the energy of partially spin polarized state.Comment: 7 pages, submitted to J. Phys. Soc. Jp
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