Showing papers by "Donghua University published in 2007"

Spatial and seasonal distributions of carbonaceous aerosols over China

Abstract: [1] Simultaneous measurements of atmospheric organic and elemental carbon (OC and EC) were taken during winter and summer seasons at 2003 in 14 cities in China. Daily PM2.5 samples were analyzed for OC and EC by the Interagency Monitoring of Protected Visual Environments (IMPROVE) thermal/optical reflectance protocol. Average PM2.5 OC concentrations in the 14 cities were 38.1 μg m−3 and 13.8 μg m−3 for winter and summer periods, and the corresponding EC were 9.9 μg m−3 and 3.6 μg m−3, respectively. OC and EC concentrations had summer minima and winter maxima in all the cities. Carbonaceous matter (CM), the sum of organic matter (OM = 1.6 × OC) and EC, contributed 44.2% to PM2.5 in winter and 38.8% in summer. OC was correlated with EC (R2: 0.56–0.99) in winter, but correlation coefficients were lower in summer (R2: 0.003–0.90). Using OC/EC enrichment factors, the primary OC, secondary OC and EC accounted for 47.5%, 31.7% and 20.8%, respectively, of total carbon in Chinese urban environments. More than two thirds of China's urban carbon is derived from directly emitted particles. Average OC/EC ratios ranged from 2.0 to 4.7 among 14 cities during winter and from 2.1 to 5.9 during summer. OC/EC ratios in this study were consistent with a possible cooling effect of carbonaceous aerosols over China.

Variational iteration method: New development and applications

Abstract: Variational iteration method has been favourably applied to various kinds of nonlinear problems. The main property of the method is in its flexibility and ability to solve nonlinear equations accurately and conveniently. In this paper recent trends and developments in the use of the method are reviewed. Major applications to nonlinear wave equation, nonlinear fractional differential equations, nonlinear oscillations and nonlinear problems arising in various engineering applications are surveyed. The confluence of modern mathematics and symbol computation has posed a challenge to developing technologies capable of handling strongly nonlinear equations which cannot be successfully dealt with by classical methods. Variational iteration method is uniquely qualified to address this challenge. The flexibility and adaptation provided by the method have made the method a strong candidate for approximate analytical solutions. This paper outlines the basic conceptual framework of variational iteration technique with application to nonlinear problems. Both achievements and limitations are discussed with direct reference to approximate solutions for nonlinear equations. A new iteration formulation is suggested to overcome the shortcoming. A very useful formulation for determining approximately the period of a nonlinear oscillator is suggested. Examples are given to illustrate the solution procedure.

New periodic solutions for nonlinear evolution equations using Exp-function method

Abstract: The Exp-function method is used to obtain generalized solitonary solutions and periodic solutions for nonlinear evolution equations arising in mathematical physics using symbolic computation. The method is straightforward and concise, and its applications are promising.

Variational approach for nonlinear oscillators

Abstract: We propose a novel variational approach for limit cycles of a kind of nonlinear oscillators Some examples are given to illustrate the effectiveness and convenience of the method The obtained results are valid for the whole solution domain with high accuracy

Solitary solutions, periodic solutions and compacton-like solutions using the Exp-function method

Abstract: In this paper, the Exp-function method is used for seeking solitary solutions, periodic solutions, and compacton-like solutions of nonlinear differential equations. The combined KdV-MKdV equation and the Liouville equation are chosen to illustrate the effectiveness and convenience of the proposed method.

Exponential stability of uncertain stochastic neural networks with mixed time-delays

Abstract: This paper is concerned with the global exponential stability analysis problem for a class of stochastic neural networks with mixed time-delays and parameter uncertainties. The mixed delays comprise discrete and distributed time-delays, the parameter uncertainties are norm-bounded, and the neural networks are subjected to stochastic disturbances described in terms of a Brownian motion. The purpose of the stability analysis problem is to derive easy-to-test criteria under which the delayed stochastic neural network is globally, robustly, exponentially stable in the mean square for all admissible parameter uncertainties. By resorting to the Lyapunov–Krasovskii stability theory and the stochastic analysis tools, sufficient stability conditions are established by using an efficient linear matrix inequality (LMI) approach. The proposed criteria can be checked readily by using recently developed numerical packages, where no tuning of parameters is required. An example is provided to demonstrate the usefulness of the proposed criteria.

Application of parameter-expanding method to strongly nonlinear oscillators

Abstract: The parameter-expanding method is applied to a strongly nonlinear oscillator. The obtained frequency is of high accuracy which is valid for the whole solution domain. Comparison of the obtained solution with exact solution is also given.

Delay-dependent robust H/sub /spl infin// control for uncertain singular time-delay systems

Abstract: The problem of delay-dependent robust H∞ control for uncertain singular systems with time delay has been investigated. The considered systems are not assumed to be necessarily regular and impulse free. In terms of linear matrix inequality approach, a delay-dependent stability criterion is given to ensure the nominal system to be regular, impulse-free and stable. Based on the criterion, the problem is solved via state feedback controller, which guarantees that, for all admissible uncertainties, the closed-loop system is not only regular, impulse-free and stable, but also satisfies a prescribed H∞ performance condition. Some numerical examples are provided to demonstrate the efficiency of the proposed methods.

Nano-effects, quantum-like properties in electrospun nanofibers

Abstract: Electrospun nanofiber technology bridges the gap between deterministic laws (Newton mechanics) and probabilistic laws (quantum mechanics). Our research reveals that fascinating phenomena arise when the diameter of the electrospun nanofibers is less than 100 nm. The nano-effect has been demonstrated for unusual strength, high surface energy, surface reactivity, high thermal and electric conductivity. Dragline silk is made of many nano-fibers with diameter of about 20 nm, thus it can make full use of nano-effects. It is a challenge to developing technologies capable of preparing for nanofibers within 100 nm. Vibration-melt-electrospinning is uniquely qualified to address this challenge. The flexibility and adaptation provided by the method have made the method a strong candidate for producing nanofibers on such a scale. The application of Sirofil technology to strengthen nanofibers is also addressed, E-infinity theory is emphasized as a challenging theory for nano-scale technology and science.

Effect of different salts on electrospinning of polyacrylonitrile (PAN) polymer solution

Abstract: Electrospinning is a relatively simple method to produce submicron fibers from solutions of different polymers and polymer blends. If the solution is absolutely insulating, or the applied voltage is not high enough that electrostatic force cannot overcome the surface tension, then no fiber can be produced by electrospinning; however, if some salt is added in the solution, the problem can be overcome. The effect of different salts on electrospinning of polyacrlonitrile (PAN) polymer solution was investigated in this article. The various inorganic salts used in this work include LiCl, NaNO3, NaCl, and CaCl2.The results show that when the salts were added, respectively, into different concentrations of PAN solution, the order of conductant was LiCl > NaNO3 > CaCl2 > NaCl > no salt added. Viscosity and shearing strength of electrospinning solutions are slightly affected by the adding of salts and mainly affected by the changes in concentration of PAN electrospinning solutions. The diameter of nanofibers electrospun by solutions with different salts size down as follows: LiCl > NaNO3 > CaCl2 > NaCl. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3865–3870, 2007

Preparation, Tg improvement, and thermal stability enhancement mechanism of soluble poly(methyl methacrylate) nanocomposites by incorporating octavinyl polyhedral oligomeric silsesquioxanes

Abstract: The soluble poly(methyl methacrylate-co-octavinyl-polyhedral oligomeric silsesquioxane) (PMMA–POSS) hybrid nanocomposites with improved Tg and high thermal stability were synthesized by common free radical polymerization and characterized using FTIR, high-resolution 1H NMR, 29Si NMR, GPC, DSC, and TGA. The POSS contents in the nanocomposites were determined based on FTIR spectrum, revealing that it can be effectively adjusted by varying the feed ratio of POSS in the hybrid composites. On the basis of the 1H NMR analysis, the number of the reacted vinyl groups on each POSS molecules was determined to be about 6–8. The DSC and TGA measurements indicated that the hybrid nanocomposites had higher Tg and better thermal properties than the pure PMMA homopolymer. The Tg increase mechanism was investigated using FTIR, displaying that the dipole–dipole interaction between PMMA and POSS also plays very important role to the Tg improvement besides the molecular motion hindrance from the hybrid structure. The thermal stability enhances with increase of POSS content, which is mainly attributed to the incorporation of nanoscale inorganic POSS uniformly dispersed at molecular level. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5308–5317, 2007

He's homotopy perturbation method for a boundary layer equation in unbounded domain

Abstract: By means of He's homotopy perturbation method (HPM) an approximate solution of a boundary layer equation in unbounded domain is obtained. Comparison is made between the obtained results and those in open literature. The results show that the method is very effective and simple.

Durability of nano ZnO antibacterial cotton fabric to sweat

Abstract: In this article, an innovative method was put forward to evaluate the endurance of nano ZnO finished fabrics to sweat. The atomic absorption spectrophotometer was used to determine the concentration of zinc in immersion liquor, and at the same time, SEM experiments and biocidal tests were chosen to characterize the antibacterial performance. Half-life time (t(1/2)) of zinc concentration on the fabric was introduced to evaluate the durability to sweat. The results indicated that nano ZnO antibacterial cotton fabric was relatively sensitive to acid artificial sweat while durable in saline or alkaline solution, the t(1/2) exceeded 3000 min in them. SEM characterization and biocidal tests showed the same behavior. (c) 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 412416, 2007

Photocatalytic degradation of Acid Blue 62 over CuO-SnO2 nanocomposite photocatalyst under simulated sunlight.

Abstract: The novel CuO-SnO2 nanocomposite oxide photocatalysts were prepared by simple co-precipitation method, and characterized by X-ray diffraction, transmission electron microscopy, N2 adsorption-desorption measurement and UV-Vis diffuse reflectance spectroscopy. The photocatalytic activities of CuO-SnO2, evaluated using the photodegradation of Acid Blue 62 as a probe reaction under the irradiation of Xenon light, were also found to be related to the calcination temperature and the molar ratio of Cu to Sn. The maximum photocatalytic activity of the CuO-SnO2 photocatalyst was observed to be calcined at 500°C for 3 h (the molar ratio of Cu to Sn was 1:1) due to the sample with good crystallization and high surface area. It also showed much higher photocatalytic activity in treatment dye wastewater under simulated sunlight irradiation compared to Degussa P25 TiO2.

Two sided modification of wool fabrics by atmospheric pressure plasma jet: Influence of processing parameters on plasma penetration

Abstract: Atmospheric pressure plasma jet can treat fabrics from one side and therefore the penetration of the plasmas to the other side of the fabric is critical for the successful treatment of the fabric which needs to be treated on both sides. In this study a wool fabric was treated under various treatment conditions such as different output power, different nozzle to substrate distance, different substrate moving speed and different treatment time to see how these processing parameters influenced the penetration of plasma through the fabric. After the plasma treatments, scanning electron microscopy analysis showed that the fiber surface morphological change occurred on both sides of the fabric; Fourier transform infrared spectrometry analysis showed an increase in number of polar groups on the fiber surface for both sides; the water absorption time was also greatly reduced. The treatment effects were enhanced when the output power and the treatment time were increased. When the fabric was too close (≤ 1 mm) or too far (≥ 6 mm) from the nozzle, the treatment was not effective to either side of the fabric. The treatment on both sides was most effective when the fabric was 2–3 mm away from the nozzle. The substrate moving speed did not affect the treatment results. Therefore adequate plasma processing parameters have to be carefully selected for the best results for treating both sides of the fabric.