13,219 research outputs found

    Cation mono- and co-doped anatase TiO2_2 nanotubes: An {\em ab initio} investigation of electronic and optical properties

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    The structural, electronic, and optical properties of metal (Si, Ge, Sn, and Pb) mono- and co-doped anatase TiO2_{2} nanotubes are investigated, in order to elucidate their potential for photocatalytic applications. It is found that Si doped TiO2_{2} nanotubes are more stable than those doped with Ge, Sn, or Pb. All dopants lower the band gap, except the (Ge, Sn) co-doped structure, the decrease depending on the concentration and the type of dopant. Correspondingly, a redshift in the optical properties for all kinds of dopings is obtained. Even though a Pb mono- and co-doped TiO2_{2} nanotube has the lowest band gap, these systems are not suitable for water splitting, due to the location of the conduction band edges, in contrast to Si, Ge, and Sn mono-doped TiO2_{2} nanotubes. On the other hand, co-doping of TiO2_{2} does not improve its photocatalytic properties. Our findings are consistent with recent experiments which show an enhancement of light absorption for Si and Sn doped TiO2_{2} nanotubes.Comment: revised and updated, 23 pages (preprint style), 7 figures, 5 table

    MANAGEMENT OF SERVICE INNOVATION QUALITY

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    Bossink, B.A.G. [Promotor]Vinig, G.T. [Copromotor

    Modeling of Water Explicitly in the Replica-Exchange Simulation Method for Protein Folding

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    A Telescoping method for Double Summations

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    We present a method to prove hypergeometric double summation identities. Given a hypergeometric term F(n,i,j)F(n,i,j), we aim to find a difference operator L=a0(n)N0+a1(n)N1+...+ar(n)Nr L=a_0(n) N^0 + a_1(n) N^1 +...+a_r(n) N^r and rational functions R1(n,i,j),R2(n,i,j)R_1(n,i,j),R_2(n,i,j) such that LF=Δi(R1F)+Δj(R2F) L F = \Delta_i (R_1 F) + \Delta_j (R_2 F). Based on simple divisibility considerations, we show that the denominators of R1R_1 and R2R_2 must possess certain factors which can be computed from F(n,i,j)F(n, i,j). Using these factors as estimates, we may find the numerators of R1R_1 and R2R_2 by guessing the upper bounds of the degrees and solving systems of linear equations. Our method is valid for the Andrews-Paule identity, Carlitz's identities, the Ap\'ery-Schmidt-Strehl identity, the Graham-Knuth-Patashnik identity, and the Petkov\v{s}ek-Wilf-Zeilberger identity.Comment: 22 pages. to appear in J. Computational and Applied Mathematic

    Applicability of the qq-Analogue of Zeilberger's Algorithm

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    The applicability or terminating condition for the ordinary case of Zeilberger's algorithm was recently obtained by Abramov. For the qq-analogue, the question of whether a bivariate qq-hypergeometric term has a qZqZ-pair remains open. Le has found a solution to this problem when the given bivariate qq-hypergeometric term is a rational function in certain powers of qq. We solve the problem for the general case by giving a characterization of bivariate qq-hypergeometric terms for which the qq-analogue of Zeilberger's algorithm terminates. Moreover, we give an algorithm to determine whether a bivariate qq-hypergeometric term has a qZqZ-pair.Comment: 15 page

    Modeling the AgInSbTe Memristor

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    The AgInSbTe memristor shows gradual resistance tuning characteristics, which makes it a potential candidate to emulate biological plastic synapses. The working mechanism of the device is complex, and both intrinsic charge-trapping mechanism and extrinsic electrochemical metallization effect are confirmed in the AgInSbTe memristor. Mathematical model of the AgInSbTe memristor has not been given before. We propose the flux-voltage controlled memristor model. With piecewise linear approximation technique, we deliver the flux-voltage controlled memristor model of the AgInSbTe memristor based on the experiment data. Our model fits the data well. The flux-voltage controlled memristor model and the piecewise linear approximation method are also suitable for modeling other kinds of memristor devices based on experiment data

    Challenges of Primary Frequency Control and Benefits of Primary Frequency Response Support from Electric Vehicles

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    As the integration of wind generation displaces conventional plants, system inertia provided by rotating mass declines, causing concerns over system frequency stability. This paper implements an advanced stochastic scheduling model with inertia-dependent fast frequency response requirements to investigate the challenges on the primary frequency control in the future Great Britain electricity system. The results suggest that the required volume and the associated cost of primary frequency response increase significantly along with the increased capacity of wind plants. Alternative measures (e.g. electric vehicles) have been proposed to alleviate these concerns. Therefore, this paper also analyses the benefits of primary frequency response support from electric vehicles in reducing system operation cost, wind curtailment and carbon emissions

    Visualizing Convolutional Networks for MRI-based Diagnosis of Alzheimer's Disease

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    Visualizing and interpreting convolutional neural networks (CNNs) is an important task to increase trust in automatic medical decision making systems. In this study, we train a 3D CNN to detect Alzheimer's disease based on structural MRI scans of the brain. Then, we apply four different gradient-based and occlusion-based visualization methods that explain the network's classification decisions by highlighting relevant areas in the input image. We compare the methods qualitatively and quantitatively. We find that all four methods focus on brain regions known to be involved in Alzheimer's disease, such as inferior and middle temporal gyrus. While the occlusion-based methods focus more on specific regions, the gradient-based methods pick up distributed relevance patterns. Additionally, we find that the distribution of relevance varies across patients, with some having a stronger focus on the temporal lobe, whereas for others more cortical areas are relevant. In summary, we show that applying different visualization methods is important to understand the decisions of a CNN, a step that is crucial to increase clinical impact and trust in computer-based decision support systems.Comment: MLCN 201
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