31,988 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
Performance analysis with network-enhanced complexities: On fading measurements, event-triggered mechanisms, and cyber attacks
Copyright © 2014 Derui Ding et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Nowadays, the real-world systems are usually subject to various complexities such as parameter uncertainties, time-delays, and nonlinear disturbances. For networked systems, especially large-scale systems such as multiagent systems and systems over sensor networks, the complexities are inevitably enhanced in terms of their degrees or intensities because of the usage of the communication networks. Therefore, it would be interesting to (1) examine how this kind of network-enhanced complexities affects the control or filtering performance; and (2) develop some suitable approaches for controller/filter design problems. In this paper, we aim to survey some recent advances on the performance analysis and synthesis with three sorts of fashionable network-enhanced complexities, namely, fading measurements, event-triggered mechanisms, and attack behaviors of adversaries. First, these three kinds of complexities are introduced in detail according to their engineering backgrounds, dynamical characteristic, and modelling techniques. Then, the developments of the performance analysis and synthesis issues for various networked systems are systematically reviewed. Furthermore, some challenges are illustrated by using a thorough literature review and some possible future research directions are highlighted.This work was supported in part by the National Natural Science Foundation of China under Grants 61134009, 61329301, 61203139, 61374127, and 61374010, the Royal Society of the UK, and the Alexander von Humboldt Foundation of Germany
Structural System Identification with Extended Kalman Filter and Orthogonal Decomposition of Excitation
Both the structural parameter and external excitation have coupling influence on structural response. A new system identification method in time domain is proposed to simultaneously evaluate structural parameter and external excitation. The method can be used for linear and hysteresis nonlinear structural condition assessment based on incomplete structural responses. In this method, the structural excitation is decomposed by orthogonal approximation. With this approximation, the strongly time-variant excitation identification is transformed to gentle time-variant, even constant parameters identification. Then the extended Kalman filter is applied to simultaneously identify state vector including the structural parameters and excitation orthogonal parameters in state space based on incomplete measurements. The proposed method is validated numerically with the simulation of three-story linear and nonlinear structures subject to external force. The external force on the top floor and the structural parameters are simultaneously identified with the proposed system identification method. Results from both simulations indicate that the proposed method is capable of identifing the dynamic load and structural parameters fairly accurately with contaminated incomplete measurement for both of the linear and nonlinear structural systems
Recurrent Coronal Jets Induced by Repetitively Accumulated Electric Currents
Three extreme-ultraviolet (EUV) jets recurred in about one hour on 2010
September 17 in the following magnetic polarity of active region 11106. The EUV
jets were observed by the Atmospheric Imaging Assembly (AIA) on board the Solar
Dynamics Observatory (SDO). The Helioseismic and Magnetic Imager (HMI) on board
SDO measured the vector magnetic field, from which we derive the magnetic flux
evolution, the photospheric velocity field, and the vertical electric current
evolution. The magnetic configuration before the jets is derived by the
nonlinear force-free field (NLFFF) extrapolation.
We derive that the jets are above a pair of parasitic magnetic bipoles which
are continuously driven by photospheric diverging flows. The interaction drove
the build up of electric currents that we indeed observed as elongated patterns
at the photospheric level. For the first time, the high temporal cadence of HMI
allows to follow the evolution of such small currents. In the jet region, we
found that the integrated absolute current peaks repetitively in phase with the
171 A flux evolution. The current build up and its decay are both fast, about
10 minutes each, and the current maximum precedes the 171 A by also about 10
minutes. Then, HMI temporal cadence is marginally fast enough to detect such
changes.
The photospheric current pattern of the jets is found associated to the
quasi-separatrix layers deduced from the magnetic extrapolation. From previous
theoretical results, the observed diverging flows are expected to build
continuously such currents. We conclude that magnetic reconnection occurs
periodically, in the current layer created between the emerging bipoles and the
large scale active region field. It induced the observed recurrent coronal jets
and the decrease of the vertical electric current magnitude.Comment: 10 pages, 7 figures, accepted for publication in A&
Angle-resolved photoemission studies of the superconducting gap symmetry in Fe-based superconductors
The superconducting gap is the fundamental parameter that characterizes the
superconducting state, and its symmetry is a direct consequence of the
mechanism responsible for Cooper pairing. Here we discuss about angle-resolved
photoemission spectroscopy measurements of the superconducting gap in the
Fe-based high-temperature superconductors. We show that the superconducting gap
is Fermi surface dependent and nodeless with small anisotropy, or more
precisely, a function of momentum. We show that while this observation is
inconsistent with weak coupling approaches for superconductivity in these
materials, it is well supported by strong coupling models and global
superconducting gaps. We also suggest that the strong anisotropies measured by
other probes sensitive to the residual density of states are not related to the
pairing interaction itself, but rather emerge naturally from the smaller
lifetime of the superconducting Cooper pairs that is a direct consequence of
the momentum dependent interband scattering inherent to these materials.Comment: 7 pages, 5 figure
Dual Ginzburg-Landau Theory for Nonperturbative QCD
Nonperturbative QCD is studied with the dual Ginzburg-Landau theory, where
color confinement is realized through the dual Higgs mechanism by QCD-monopole
condensation. We obtain a general analytic formula for the string tension. A
compact formula is derived for the screened inter-quark potential in the
presence of light dynamical quarks. The QCD phase transition at finite
temperature is studied using the effective potential formalism. The string
tension and the QCD-monopole mass are largely reduced near the critical
temperature, . The surface tension is estimated from the effective
potential at . We propose also a new scenario of the quark-gluon-plasma
creation through the color-electric flux-tube annihilation. Finally, we discuss
a close relation between instantons and QCD-monopoles.Comment: Talk presented by H. Suganuma at the Int. Conf. ``CONFINEMENT95'',
March 22-24, 1995, Osaka, Japan, 12 pages, uses PHYZZ
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