Showing papers by "South China University of Technology published in 2003"

Resistance distance and Laplacian spectrum

Abstract: The resistance distance r ij between two vertices v i and v j of a (connected, molecular) graph G is equal to the resistance between the respective two points of an electrical network, constructed so as to correspond to G, such that the resistance of any two adjacent points is unity. We show how the matrix elements r ij can be expressed in terms of the Laplacian eigenvalues and eigenvectors of G. In addition, we determine certain properties of the resistance matrix R=||r ij ||.

Stabilization of semiconducting polymers with silsesquioxane

Abstract: Polyhedral oligomeric silsesquioxanes (POSS) anchored to poly(2-methoxy-5-(2-ethylhexyloxy)-1.4-phenylenevinylene) (MEH-PPV) (MEH-PPV–POSS), and to poly(9,9-dihexylfluorenyl-2,7-diyl) (PFO) (PFO–POSS) were synthesized. Compared with the corresponding parent polymers, MEH-PPV and PFO, MEH-PPV–POSS and PFO–POSS have better thermal stability. MEH-PPV–POSS and MEH-PPV have identical absorption and photoluminescent (PL) spectra, both in solution and as thin films. They also have identical electroluminescent (EL) spectra. Devices made from MEH-PPV–POSS exhibit higher brightness (1320 cd m–2 at 3.5 V) and higher external quantum efficiency (ηext = 2.2 % photons per electron) compared to MEH-PPV (230 cd m–2 at 3.5 V and ηext = 1.5 % ph el–1). Compared with PFO in the same device configuration, PFO–POSS has improved blue EL emission and higher ηext.

Synthesis and Optical and Electroluminescent Properties of Novel Conjugated Copolymers Derived from Fluorene and Benzoselenadiazole

Abstract: A novel series of light-emitting copolymers derived from 9,9-dioctylfluorene (DOF) and 2,1,3-benzoselenadiazole (BSeD) is prepared by means of palladium-catalyzed Suzuki coupling reaction. The feed ratios of DOF to BSeD were 50:50, 85:15, 92:8, and 98:2, respectively. All of the copolymers are soluble in common organic solvents and highly fluorescent in solid state. Devices from such copolymers emit orange-red light with λmax = 570−600 nm. The maximal EL emissions of the devices slightly red-shifted gradually with increasing BSeD's contents. The maximal external quantum efficiency of the polymer light-emitting devices (PLED) reaches 1.0%, which indicates that this new seleno-containing EL polymer based on fluorene and benzoselenadiazole is a promising candidate for fabricating PLEDs.

A novel detection method of motor broken rotor bars based on wavelet ridge

Abstract: Detection of cage motor broken rotor bars has long been an important but difficult job in the detection area of motor faults. The characteristic frequency component of faulted rotor (CFCFR) is very close to the power frequency component but by far less in amplitude, which brings about great difficulty for accurate detection. A new detection method based on wavelet ridge is presented in this paper. Aiming at the motor's starting period during which the motor accelerates progressively and CFCFR approaches the power frequency gradually in frequency spectrum, the wavelet ridge-based method is adopted to analyze this transient procedure and the CFCFR is extracted. The influence of power frequency can be effectively eliminated, and detection accuracy can be greatly improved by using the approach presented in this paper. Also, this is indeed a novel but excellent approach for the detection domain of cage induction motor broken rotor bars.

Semiglobal stabilization and output regulation of singular linear systems with input saturation

Abstract: The semi-global stabilization problem and output regulation problem of singular linear systems subject to input saturation are addressed. A reduced-order normal system is obtained by a standard coordinate transformation. It is further shown that the controller that solves the stabilization (output regulation) problem of the reduced-order normal systems also solves the stabilization (output regulation) problem of the original singular systems.

Torsional buckling of a double-walled carbon nanotube embedded in an elastic medium

Abstract: The torsional buckling of a double-walled carbon nanotube embedded in an elastic medium is studied in this paper The effects of surrounding elastic medium and van der Waals forces between the inner and outer nanotubes are taken into account Using continuum mechanics, an elastic double-shell model is presented for the torsional buckling of a double-walled carbon nanotube Based on the model, a condition is derived in terms of the buckling modes of the shell and the parameters describing the effect of van der Waals interaction and surrounding elastic medium A simplified analysis is also carried out estimate the critical torque for torsional buckling of the double-walled carbon nanotube

Applying resonant parametric perturbation to control chaos in the buck dc/dc converter with phase shift and frequency mismatch considerations

Abstract: The buck converter has been known to exhibit chaotic behavior in a wide parameter range. In this paper, the resonant parametric perturbation method is applied to control chaos in a voltage-mode controlled buck converter. In particular, the effects of phase shift and frequency mismatch in the perturbing signal are studied. It is shown that the control power can be significantly reduced if the perturbation is applied with an appropriate phase shift. Moreover, when frequency mismatch is inevitable, intermittent chaos occurs, but effective control can still be accomplished at the expense of raising the control power. Analysis, simulations and experimental measurements are presented to provide theoretical and practical evidences for the proposed control method.

Improvement of color purity in blue-emitting polyfluorene by copolymerization with dibenzothiophene

Abstract: High molecular weight, readily soluble copolymers of 9,9-dioctylfluorene and dibenzothiophene (DBTh) comonomer (less than or equal to 50 mol%) are synthesized by Suzuki polycondensation. PL efficiencies and EL external quantum efficiencies of random copolymers decrease with increasing DBTh content. For the alternating copolymer, a PL efficiency of 62% and an EL external quantum efficiency of 0.42% are obtained. Excimer emission is effectively depressed when the DBTh content is greater than 20 mol%. It is indicated that the meta-linkages of 2,8-substitution of DBTh are effective in enhancing blue emission of polyfluorene.

An expert system for real-time fault diagnosis of complex chemical processes

Abstract: This paper presents the development and implementation of an expert system for real-time fault diagnosis of chemical processes. The expert system is applied as a real-time computer aided decision support system, providing operation suggestions to help field operators when abnormal situations occur. The knowledge base structure, representation of knowledge, and access to expertise are technically considered. Industrial applications to the fluid catalystic cracking process in refinery indicate that the expert system diagnoses abnormal events efficiently and promptly.

Acceleration of Levenberg-Marquardt training of neural networks with variable decay rate

Abstract: In the application of the standard Levenberg-Marquardt training process of neural networks, error oscillations are frequently observed and they usually aggravate on approaching the required accuracy. In this paper, a modified Levenberg-Marquardt method based on variable decay rate in each iteration is proposed in order to reduce such error oscillations. Through a certain variation of the decay rate, the time required for training of neural networks is cut down to less than half of that required in the standard Levenberg-Marquardt method. Several numerical examples are given to show the effectiveness of the proposed method.

Dynamic Response of Suspension Bridge to High Wind and Running Train

Abstract: A framework is presented for predicting the dynamic response of long suspension bridges to high winds and running trains. A three-dimensional finite-element model is used to represent a suspension bridge. Wind forces acting on the bridge, including both buffeting and self-excited forces, are generated in the time domain using a fast spectral representation method and measured aerodynamic coefficients and flutter derivatives. Each 4-axle vehicle in a train is modeled by a 27-degrees-of-freedom dynamic system. The dynamic interaction between the bridge and train is realized through the contact forces between the wheels and track. By applying a mode superposition technique to the bridge only and taking the measured track irregularities as known quantities, the number of degrees of freedom of the bridge-train system is significantly reduced and the coupled equations of motion are efficiently solved. The proposed formulation is then applied to a real wind-excited long suspension bridge carrying a railway inside the bridge deck of a closed cross section. The results show that the formulation presented in this paper can predict the dynamic response of the coupled bridge-train systems under fluctuating winds. The extent of interaction between the bridge and train depends on wind speed and train speed.

A convenient acetylation of sugarcane bagasse using NBS as a catalyst for the preparation of oil sorption-active materials

Abstract: The esterification of sugarcane bagasse with acetic anhydride using N-bromosuccinimide (NBS) as a catalyst under mild conditions in a solvent free system has been investigated. The extent of acetylation was measured by weight percent gain, which increased with an increment of reaction temperature (30–120°C) and time (0.5–72.0 h) and NBS concentration from 0.5 to 1.5%. In comparison with four tertiary amine catalysts (4-dimethylamino pyridine, pyridine, N-methyl pyrrolidine, and N-methyl pyrrolidinone) and one acidic catalyst (0.5% H2SO4), N-Bromosuccinimide was found to be the most effective and inexpensive catalyst for acetylation of hydroxyl groups in the cell walls of bagasse under mild reaction conditions. At a concentration of 1.5% of the NBS catalyst in acetic anhydride, a weight percent gain of 22.3% was achieved at 80°C for 2 h. FT-IR and CP-MAS 13C-NMR studies produced evidence for acetylation. More importantly, the acetylation substantially increased hydrophobic properties of the bagasse. The oil sorption capacity of the acetylated bagasse (18.8 g machine oil/g of bagasse fibre at room temperature), obtained at 80°C for 2 h, was approximately 1.9 times higher than those of the commercial synthetic oil sorbents such as polypropylene fibres. Cyclic sorption/desorption studies showed that a simple squeezing operation was sufficient to remove most of the oil absorbed on the fibre and the sorbents can be used several times. These novel oil sorption-active materials could be used to substitute those of non-biodegradable materials in oil spill cleanup.

Large acoustic band gaps created by rotating square rods in two-dimensional periodic composites

Abstract: Effects of orientations of square rods on the acoustic band gaps in two-dimensional periodic arrays of rigid solid rods embedded in air are studied. The acoustic band gaps will be opened and enlarged greatly by increasing the rotation angle. For any filling fraction F, the maximum acoustic band gaps appear at the same rotation angle θ = 45° for the cases of F≤0.50, otherwise they will appear at different limit values θc and the largest band gap is achieved at a filling fraction of about F = 0.85. This gap-tuning effect will be stronger with increase in filling fraction. This tuning mechanism of band gap suggests a new way to design band gaps of two-dimensional phononic crystals.

On generalized synchronization of spatial chaos

Abstract: Consider the following two spatially generalized Logistic systems with two different real parameters: x m+1,n +ωx m,n+1 =1−μ 1 [(1+ω)x mn ] 2 and y m+1,n +ωy m,n+1 =1−μ 2 [(1+ω)y mn ] 2 , where ω is a constant. We introduce an analytical method for generalized synchronization of these two spatially chaotic systems. We specify a range of the coupling constant in the generalized synchronization, and characterize a nonlinear function for synchronization stability.

Synthesis of new iridium complexes and their electrophosphorescent properties in polymer light-emitting diodes

Abstract: Several new iridium complexes with p-substituted 2-phenylpyridine (R-PPy) ligands have been synthesized and characterized. The complexes were incorporated into phosphorescent polymer light-emitting devices using soluble poly[1,4-bis(6′-cyano-6′-methylheptyloxy)phenylene] (CNPPP) as the host and the resultant materials compared with Ir(PPy)3-doped devices. Green electrophosphorescence was observed, with peak emission at about 495 and 515 nm. Among the devices fabricated, highly efficient polymer light-emitting diodes were obtained with CNPPP doped with fac-tris[2-(4-tert-butylphenyl)pyridinato]iridium. An external quantum efficiency of 4.4% (photoluminescence/electroluminescence) and a luminous efficiency of 10 cd A−1 were obtained at 120 cd m−2. These values remain at 4.2% and 10 cd A−1, respectively, at 2500 cd m−2. The improvement is attributed to improved interaction between the guest and host, and to better and more complete energy transfer from the host singlet to the guest triplet state. These results demonstrate that efficient electrophosphorescence is not limited to small molecule organic light-emitting diodes, it can also be achieved in devices made with polymer hosts.

Multi-objective and MGG evolutionary algorithm for constrained optimization

Abstract: This paper presents a new approach to handle constrained optimization using evolutionary algorithms. The new technique converts constrained optimization to a two-objective optimization: one is the original objective function, the other is the degree function violating the constraints. By using Pareto-dominance in the multi-objective optimization, individual's Pareto strength is defined. Based on Pareto strength and minimal generation gap (MGG) model, a new real-coded genetic algorithm is designed. The new approach is compared with some other evolutionary optimization techniques on several benchmark functions. The results show that the new approach outperforms those existing techniques in feasibility, effectiveness and generality. Especially for some complicated optimization problems with inequality and equality constraints, the proposed method provides better numerical accuracy.