15,781 research outputs found
Doping dependent charge injection and band alignment in organic field-effect transistors
We have studied metal/organic semiconductor charge injection in
poly(3-hexylthiophene) (P3HT) field-effect transistors with Pt and Au
electrodes as a function of annealing in vacuum. At low impurity dopant
densities, Au/P3HT contact resistances increase and become nonohmic. In
contrast, Pt/P3HT contacts remain ohmic even at far lower doping. Ultraviolet
photoemission spectroscopy (UPS) reveals that metal/P3HT band alignment shifts
dramatically as samples are dedoped, leading to an increased injection barrier
for holes, with a greater shift for Au/P3HT. These results demonstrate that
doping can drastically alter band alignment and the charge injection process at
metal/organic interfaces.Comment: 5 pages, 4 figure
Topology optimized all-dielectric cloak: design, performances and modal picture of the invisibility effect
This work was funded by the Engineering and Physical Sciences Research Council (EPSRC), UK under a Programme Grant ( EP/I034548/1) “The Quest for Ultimate Electromagnetics using Spatial Transformations (QUEST
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Operando STM study of the interaction of imidazolium-based ionic liquid with graphite
Understanding interactions at the interfaces of carbon with ionic liquids (ILs) is crucially beneficial for the diagnostics and performance improvement of electrochemical devices containing carbon as active materials or conductive additives in electrodes and ILs as solvents or additives in electrolytes. The interfacial interactions of three typical imidazolium-based ILs, 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (AMImTFSI) ILs having ethyl (C2), butyl (C4) and octyl (C8) chains in their cations, with highly oriented pyrolytic graphite (HOPG) were studied in-situ by electrochemical scanning tunneling microscopy (EC-STM). The etching of HOPG surface and the exfoliation of graphite/graphene flakes as well as cation intercalation were observed at the HOPG/C2MImTFSI interface. The etching also takes place in C4MImTFSI at −1.5 V vs Pt but only at step edges with a much slower rate, whereas C8MIm+ cations adsorbs strongly on the HOPG surface under similar conditions with no observable etching or intercalation. The EC-STM observations can be explained by the increase in van der Waals interaction between the cations and the graphite surface with increasing length of alkyl chains
Accurate Modelling of Left-Handed Metamaterials Using Finite-Difference Time-Domain Method with Spatial Averaging at the Boundaries
The accuracy of finite-difference time-domain (FDTD) modelling of left-handed
metamaterials (LHMs) is dramatically improved by using an averaging technique
along the boundaries of LHM slabs. The material frequency dispersion of LHMs is
taken into account using auxiliary differential equation (ADE) based dispersive
FDTD methods. The dispersive FDTD method with averaged permittivity along the
material boundaries is implemented for a two-dimensional (2-D) transverse
electric (TE) case. A mismatch between analytical and numerical material
parameters (e.g. permittivity and permeability) introduced by the time
discretisation in FDTD is demonstrated. The expression of numerical
permittivity is formulated and it is suggested to use corrected permittivity in
FDTD simulations in order to model LHM slabs with their desired parameters. The
influence of switching time of source on the oscillation of field intensity is
analysed. It is shown that there exists an optimum value which leads to fast
convergence in simulations.Comment: 17 pages, 7 figures, submitted to Journal of Optics A Nanometa
special issu
Opposition-based Memetic Search for the Maximum Diversity Problem
As a usual model for a variety of practical applications, the maximum diversity problem (MDP) is computational challenging. In this paper, we present an opposition-based memetic algorithm (OBMA) for solving MDP, which integrates the concept of opposition-based learning (OBL) into the wellknown memetic search framework. OBMA explores both candidate solutions and their opposite solutions during its initialization and evolution processes. Combined with a powerful local optimization procedure and a rank-based quality-and-distance pool updating strategy, OBMA establishes a suitable balance between exploration and exploitation of its search process. Computational results on 80 popular MDP benchmark instances show that the proposed algorithm matches the best-known solutions for most of instances, and finds improved best solutions (new lower bounds) for 22 instances. We provide experimental evidences to highlight the beneficial effect of opposition-based learning for solving MDP
Simulating aerosol–radiation–cloud feedbacks on meteorology and air quality over eastern China under severe haze conditionsin winter
The aerosol-radiation-cloud feedbacks on meteorology and air quality over
eastern China under severe winter haze conditions in January 2013 are
simulated using the fully coupled online Weather Research and
Forecasting/Chemistry (WRF-Chem) model. Three simulation scenarios including
different aerosol configurations are undertaken to distinguish the aerosol's
radiative (direct and semi-direct) and indirect effects. Simulated spatial
and temporal variations of PM2.5 are generally consistent with surface
observations, with a mean bias of −18.9 μg m−3 (−15.0%)
averaged over 71 big cities in China. Comparisons between different
scenarios reveal that aerosol radiative effects (direct effect and
semi-direct effects) result in reductions of downward shortwave flux at the
surface, 2 m temperature, 10 m wind speed and planetary boundary layer (PBL)
height by up to 84.0 W m−2, 3.2°C, 0.8 m s−1, and 268 m,
respectively. The simulated impact of the aerosol indirect effects is
comparatively smaller. Through reducing the PBL height and stabilizing lower
atmosphere, the aerosol effects lead to increases in surface concentrations
of primary pollutants (CO and SO2). Surface O3 mixing ratio is
reduced by up to 6.9 ppb (parts per billion) due to reduced incoming solar radiation and lower
temperature, while the aerosol feedbacks on PM2.5 mass concentrations
show some spatial variations. Comparisons of model results with observations
show that inclusion of aerosol feedbacks in the model significantly improves
model performance in simulating meteorological variables and improves
simulations of PM2.5 temporal distributions over the North China Plain,
the Yangtze River delta, the Pearl River delta, and central China. Although
the aerosol–radiation–cloud feedbacks on aerosol mass concentrations are
subject to uncertainties, this work demonstrates the significance of
aerosol–radiation–cloud feedbacks for real-time air quality forecasting
under haze conditions
Improving probability learning based local search for graph coloring
This paper presents an improved probability learning based local search algorithm for the well-known graph coloring problem. The algorithm iterates through three distinct phases: a starting coloring generation phase based on a probability matrix, a heuristic coloring improvement phase and a learning based probability updating phase. The method maintains a dynamically updated probability matrix which specifies the chance for a vertex to belong to each color group. To explore the specific feature of the graph coloring problem where color groups are interchangeable and to avoid the difficulty posed by symmetric solutions, a group matching procedure is used to find the group-to-group correspondence between a starting coloring and its improved coloring. Additionally, by considering the optimization phase as a black box, we adopt the popular tabu search coloring procedure for the coloring improvement phase. We show extensive computational results on the well-known DIMACS benchmark instances and comparisons with state-of-the-art coloring algorithms
Dynamic Provable Data Possession Protocols with Public Verifiability and Data Privacy
Cloud storage services have become accessible and used by everyone.
Nevertheless, stored data are dependable on the behavior of the cloud servers,
and losses and damages often occur. One solution is to regularly audit the
cloud servers in order to check the integrity of the stored data. The Dynamic
Provable Data Possession scheme with Public Verifiability and Data Privacy
presented in ACISP'15 is a straightforward design of such solution. However,
this scheme is threatened by several attacks. In this paper, we carefully
recall the definition of this scheme as well as explain how its security is
dramatically menaced. Moreover, we proposed two new constructions for Dynamic
Provable Data Possession scheme with Public Verifiability and Data Privacy
based on the scheme presented in ACISP'15, one using Index Hash Tables and one
based on Merkle Hash Trees. We show that the two schemes are secure and
privacy-preserving in the random oracle model.Comment: ISPEC 201
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