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

Guided-wave-based method for concrete de-bonding damage identification using DISC

Guided-wave-based structural damage identification techniques have received more and more attention in the civil engineering community. They not only have the capability of detecting smaller damages on a structure than vibration-based methods, but also can cover a relatively larger magnitude, compared with other traditional non-destructive evaluation techniques. To realize damage identification, features usually need to be extracted from the time domain responses. This is achievable for homogeneous materials, including steel and aluminum. But for composite materials, such as concrete, the features are usually very difficult to be extracted, because of the existence of small aggregates and the nature of uneven material properties which generate multiple reflections. It is very difficult to simulate the time domain responses and to identify damages by using time domain responses directly for such random material. Recently, a new damage identification scheme is proposed, named as DISC (Damage Identification based on Sparse Coding). This method is essentially a pattern recognition technique, which avoids the traditional fixed transform process but takes advantage of the existing data by dictionary learning techniques. This paper will review the DISC method and then apply it to identification of de-bonding damage in concrete beam using guided wave test data. The results will demonstrate the effectiveness of the DISC methodology

Drastic change in transport of entropy with quadrupolar ordering in PrFe4_{4}P12_{12}

The antiferroquadrupolar ordering of PrFe$_{4}$P$_{12}$ is explored by probing thermal and thermoelectric transport. The lattice thermal conductivity drastically increases with the ordering, as a consequence of a large drop in carrier concentration and a strong electron-phonon coupling. The low level of carrier density in the ordered state is confirmed by the anomalously large values of the Seebeck and Nernst coefficients. The results are reminiscent of URu$_{2}$Si$_{2}$ and suggest that both belong to the same class of aborted metal-insulator transitions. The magnitude of the Nernst coefficient, larger than in any other metal, indicates a new route for Ettingshaussen cooling at Kelvin temperatures.Comment: final published versio

Bidirectional optimization of the melting spinning process

This is the author's accepted manuscript (under the provisional title "Bi-directional optimization of the melting spinning process with an immune-enhanced neural network"). The final published article is available from the link below. Copyright 2014 @ IEEE.A bidirectional optimizing approach for the melting spinning process based on an immune-enhanced neural network is proposed. The proposed bidirectional model can not only reveal the internal nonlinear relationship between the process configuration and the quality indices of the fibers as final product, but also provide a tool for engineers to develop new fiber products with expected quality specifications. A neural network is taken as the basis for the bidirectional model, and an immune component is introduced to enlarge the searching scope of the solution field so that the neural network has a larger possibility to find the appropriate and reasonable solution, and the error of prediction can therefore be eliminated. The proposed intelligent model can also help to determine what kind of process configuration should be made in order to produce satisfactory fiber products. To make the proposed model practical to the manufacturing, a software platform is developed. Simulation results show that the proposed model can eliminate the approximation error raised by the neural network-based optimizing model, which is due to the extension of focusing scope by the artificial immune mechanism. Meanwhile, the proposed model with the corresponding software can conduct optimization in two directions, namely, the process optimization and category development, and the corresponding results outperform those with an ordinary neural network-based intelligent model. It is also proved that the proposed model has the potential to act as a valuable tool from which the engineers and decision makers of the spinning process could benefit.National Nature Science Foundation of China, Ministry of Education of China, the Shanghai Committee of Science and Technology), and the Fundamental Research Funds for the Central Universities

Damage Assessment of Two-Way RC Slab Subjected to Blast Load using Mode Approximation Approach

Significant research efforts have been invested on studying the response and damage of structures subjected to blast loads for better life and property protections. The single-degree-of-freedom (SDOF) approach has been widely adopted to simplify the structural response analysis for engineering design purpose. However, such an approach under certain circumstances oversimplifies the structural behavior and might not give reliable predictions of structural responses to blast loads. On the other hand, although detailed high fidelity finite element (FE) approach is able to give relatively accurate predictions of structural response, it is unfortunately not straightforward for application and very time-consuming, which impedes its application among engineers. Therefore, a method that can assure not only reliability but also efficiency is highly needed for design practice. In the present study, mode approximation method with Pressure–Impulse (P-I) diagrams is applied to analyze response and damage of RC slab due to blast load. Slab under analysis is assumed rigid-plastic and simply supported. Shear failure, bending failure and combined failure modes are considered based on different failure modes. Critical equations for structural shear and bending failures are derived respectively with appropriate failure criteria. P–I diagrams are then developed for quick damage assessments. The analytical results are verified by comparing with high fidelity numerical simulations. The reliability and efficiency of using this approach for design and analyzing RC slab response under blast loads are demonstrated

Are Relational Contracting Approaches Applicable to Public Projects in China?

Rising complexities in construction projects management has boosted the importance of relational contracting (RC) in the field. RC is based on recognition of mutual benefits and win-win scenarios gained through more cooperative relationships between contracting parties. There have been a range of RC initiatives across many countries towards deeper collaborative relationships; however, such formal RC approaches are not yet well established in China. In this paper, the feasibility of implementing RC in the China’s public construction projects is investigated. The results indicate that RC is highly feasible for implementation in China due to its theoretical benefits, its alignment to Chinese culture, and its behaviors in past public construction projects. Three strategies for facilitating the implementation of RC in China are proposed

Time-domain structural damage identification: from a dictionary learning perspective

Structures inevitably deteriorate during their service lives. To accurately evaluate their structural condition, the methods capable of identifying and assessing damage in a structure timely and accurately have drawn increasing attention. Compared to widely-used frequency-domain methods, the processing of time-domain data is more efficient, but remains difficult since it is usually hard to discern signals from different conditions. In fact, the signal processing fields have observed the evolution of techniques, from such traditional fixed transforms as Fourier, to dictionary learning (DL). DL leads to better representation and hence can provide improved results in many practical applications. In this paper, an innovative time-domain damage identification algorithm is proposed from a DL perspective, using D-KSVD algorithm. The numerical simulated soil-pipe system is used for verifying the performance of the proposed method. The results demonstrate that this damage identification scheme is a promising tool for structural health monitoring

Damage spectral element for condition assessment of one-dimensional waveguide

The stress waves generated with piezoelectric actuators can propagate along a path defined by the material boundaries of a structure. If there are damages or discontinuities in the path, the received wave will be greatly affected. The changes of the waveform can provide enormous characteristics which will indicate the conditions of damage in the structure. Based on this theory, the guided wave (GW)-based methods are developed to detect local damages in a structure. In order to investigate wave propagation in damaged waveguides, many numerical modelling methods have been developed. Among them, spectral element method (SEM) solves the governing partial differential equation of wave propagation problem in the frequency domain using fast Fourier transformation (FFT). It is not only efficient for computation but also accurate for analysis in comparison with the conventional finite element formulation. In this paper, a damage spectral element is developed to model local discontinuity by using reflection and transmission coefficients. Numerical simulations show that the method is efficient to simulate local damage in one-dimensional waveguides

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