Polymeric carbon nanocomposites from multiwalled carbon nanotubes functionalized with segmented polyurethane

Multiwalled carbon nanotubes (MWNT) were functionalized with segmented polyurethanes (PU) by the “grafting to” approach. Raman and X‐ray photoelectron spectroscopy (XPS) spectra show that the sidewalls of MWNTs have been functionalized with acid treatment, and the amount of COOH increases with increasing acid treatment time. FTIR and X‐ray diffraction (XRD) spectra confirm that PU is covalently attached to the sidewalls of MWNTs by esterification reaction. Similar to the parent PU, the functionalized carbon nanotube samples are soluble in highly polar solvents, such as dimethyl sulfoxide (DMSO) and N,N‐dimethylformamide (DMF). The functionalized acid amount and the grafted PU amount were determined by thermogravimetric analyses (TGA). Comparative studies, based on SEM images between the PU‐functionalized and chemically defunctionalized MWNT samples, also reveal the covalent coating character. Dynamic mechanical analysis (DMA) of nanocomposite films prepared from PU and PU‐functionalized MWNTs show enhanced mechanical properties and increased soft segment T_g. Tensile properties indicate that PU‐functionalized MWNTs are effective reinforcing fillers for the polyurethane matrix. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Hybrid Subset Simulation method for reliability estimation of dynamical systems subject to stochastic excitation

A hybrid Subset Simulation approach is proposed for reliability estimation for general dynamical systems subject to stochastic excitation. This new stochastic simulation approach combines the advantages of the two previously proposed Subset Simulation methods, Subset Simulation with Markov Chain Monte Carlo (MCMC) algorithm and Subset Simulation with splitting. The new method employs the MCMC algorithm before reaching an intermediate failure level and splitting after reaching the level to exploit the causality of dynamical systems. The statistical properties of the failure probability estimators are derived. Two examples are presented to demonstrate the effectiveness of the new approach and to compare with the previous two Subset Simulation methods. The results show that the new method is robust to the choice of proposal distribution for the MCMC algorithm and to the intermediate failure events selected for Subset Simulation.     

Image reconstruction of a buried perfectly conducting cylinder illuminated by transverse electric waves

This article presents a computational approach to the image reconstruction of a perfectly conducting cylinder illuminated by transverse electric waves. A perfectly conducting cylinder of unknown shape buried in one half‐space and scatters the incident wave from another half‐space where the scattered field is recorded. Based on the boundary condition and the measured scattered field, a set of nonlinear integral equations is derived, and the imaging problem is reformulated into an optimization problem. The steady state genetic algorithm is then employed to find out the global extreme solution of the cost function. Numerical results demonstrated that, even when the initial guess is far away from the exact one, good reconstruction can be obtained. In such a case, the gradient‐based methods often get trapped in a local extreme. In addition, the effect of different noise on the reconstruction is investigated. © 2006 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 15, 261–265, 2005     

Multi-Scale Spoken Document Retrieval for Cantonese Broadcast News

This paper presents the application of a multi-scale paradigm to Chinese spoken document retrieval (SDR) for improving retrieval performance. Multi-scale refers to the use of both words and subwords for retrieval. Words are basic units in a language that carry lexical meaning, and subword units (such as phonemes, syllables or characters) are building components for words. Retrieval using subword indexing units is better than retrieval using words because of the robustness of subword units to out-of-vocabulary (OOV) words during speech recognition and ambiguities in word segmentation. Experimental results have demonstrated that subword bigrams can bring improvement in retrieval performance over words (～9.56%). Application of multi-scale fusion to SDR aims at combining the lexical information of words and the robustness of subwords. This work presents the first detailed investigation for a Cantonese broadcast news retrieval task using two different multi-scale fusion approaches: pre-retrieval fusion and post-retrieval fusion. Multi-scale retrieval using both words and syllable bigrams achieves improvement in retrieval performance (～1.90%) over retrieval on the composite scales.     

Performance comparison between the training method and the numerical method of the orthogonal neural network in function approximation

The orthogonal neural network is a recently developed neural network based on the properties of orthogonal functions. It can avoid the drawbacks of traditional feedforward neural networks such as initial values of weights, number of processing elements, and slow convergence speed. Nevertheless, it needs many processing elements if a small training error is desired. Therefore, numerous data sets are required to train the orthogonal neural network. In the article, a least‐squares method is proposed to determine the exact weights by applying limited data sets. By using the Lagrange interpolation method, the desired data sets required to solve for the exact weights can be calculated. An experiment in approximating typical continuous and discrete functions is given. The Chebyshev polynomial is chosen to generate the processing elements of the orthogonal neural network. The experimental results show that the numerical method in determining the weights gives as good performance in approximation error as the known training method and the former has less convergence time. © 2004 Wiley Periodicals, Inc. Int J Int Syst 19: 1257–1275, 2004.     

Robust CMAC control schemes for dynamic trajectory following

Abstract

Improved robust CMAC control schemes are proposed for tracing dynamic trajectories in this paper. There are two main structures in the proposed control schemes: one is the robust controller and the other is the improved CMAC network. The robust controller technique can achieve a certain goal without concern for instability of the controlled system in the presence of significant plant uncertainties if the nominal parameter is roughly estimated. Next, in order to reduce the tracing error, a suitable nominal parameter needs to be chosen. Thus, the improved CMAC learning approach under the robust control structure, using the concept of credit assignment, will be employed to determine control variables that can trace other states repeatedly during control processes. Finally, simulation results demonstrate the capability of the proposed control schemes to trace dynamic trajectories.     

Accurate rotor flux orientation technique for indirect rotor flux oriented control of induction motor drives

Abstract

In this paper, a novel detuning index is first proposed for indicating the proper timing required to correct the rotor time constant of indirect rotor flux oriented controlled single‐cage induction motor drives. This index can faithfully reflect the influence of rotor resistance changes as well as rotor flux changes. It also reduces greatly the number of rotor time constant estimations in practical applications. The theoretical basis of the index and the physical meaning are described in the paper in detail. Based on the proposed index, an on‐line rotor time constant estimator is also proposed to make corrections. Only existing available quantities of the closed loop controller are used for calculating the estimated rotor time constant accurately. Both simulation and experimental results verify the effectiveness of the proposed rotor flux orientation technique. It is seen that the proposed rotor flux orientation technique is suitable for practical applications.     

A microprocessor‐based electrohydraulic servo system

Abstract

A microprocessor‐based electrohydraulic servo system has been constructed and tested. It is implemented with an 8‐bit single‐chip microcomputer to control a hydraulic motor. The control algorithm is based on variable structure control principles. The experimental results show that the system is under good control and possesses a great potential for electrohydraulic servo control.     

Continuous photodetection of resonance fluorescence

Abstract

The concept of photodetection as a continuous quantum measurement introduced by Srinivas and Davies is extended to the detection of resonance fluorescence. This is a new approach to an old subject. This is also a new development in continuous photodetection in the sense that a fermion rather than the traditional boson field is the subject of monitoring. The superoperators for the no-count and the one-count processes are postulated, following the examples of Srinivas and Davies. The probability for the m-count process is then derived on the basis of these postulates. The first two factorial moments of the photon-number distribution are calculated, which are then used to evaluate the non-classical effects in resonance fluorescence. A parameter slightly different from Mandel's is found to be more suitable indicator of photon antibunching in the transient state.     

Stress singularity analysis in the restorations of premolar class ii cavities

Abstract

This paper presents the singular stress analysis near the apex of a structure formed during dental restoration of a premolar class II cavity. Based on the elasticity theory, the stresses may go to infinity at the junctions of different materials (e.g. dentine, enamel, restoration materials). Tensions will cause material separation and then material fracture. In order to reduce the failure probability, the degree of stress concentration has to be reduced. The stress singularity order and the stress intensity factor are two parameters, which are often used in fracture analysis. The objective of this paper is to find conditions such that non‐singular stress fields are possible. Three critical positions in the restoration structure are discussed.

They are the tips of interface between (1) enamel and restoration; (2) dentine and restoration; and (3) enamel, dentine and restoration. In the last two cases, the restoration may be bonded or debonded to enamel or dentine. After employing Kolosov‐Muskhelishvili complex functions together with the eigenfunction expansion method, the singularity orders are computed theoretically. Weak stress singularity conditions can be sought by properly selecting cutting angles or restoration materials.