Showing papers by "Shanghai University published in 1999"

Variational iteration method – a kind of non-linear analytical technique: some examples

Abstract: In this paper, a new kind of analytical technique for a non-linear problem called the variational iteration method is described and used to give approximate solutions for some well-known non-linear problems. In this method, the problems are initially approximated with possible unknowns. Then a correction functional is constructed by a general Lagrange multiplier, which can be identified optimally via the variational theory. Being different from the other non-linear analytical methods, such as perturbation methods, this method does not depend on small parameters, such that it can find wide application in non-linear problems without linearization or small perturbations. Comparison with Adomian’s decomposition method reveals that the approximate solutions obtained by the proposed method converge to its exact solution faster than those of Adomian’s method.

A comparison of power density for axial flux machines based on general purpose sizing equations

Abstract: Based on the concept of the converter fed machine (CFM), an optimal machine design can be considered as the best match of the machine topology, the power electronic converter and the performance specification. To compare power production potential of axial flux machines with various topologies, different waveforms of back EMF and current, general purpose sizing and power density equations for such machines are needed. In this paper, a general approach is presented to develop and to interpret these equations. Sample applications of the sizing and power density equations are the axial flux toroidal permanent magnet utilized to compare the axial flux toroidal permanent magnet (AFTPM) machine and the axial flux two-stator permanent magnet (AF2SPM) machine.

Error estimation of Hermite spectral method for nonlinear partial differential equations

Abstract: Hermite approximation is investigated. Some inverse inequalities, imbedding inequalities and approximation results are obtained. A Hermite spectral scheme is constructed for Burgers equation. The stability and convergence of the proposed scheme are proved strictly. The techniques used in this paper are also applicable to other nonlinear problems in unbounded domains.

Selective detection of ethanol vapor and hydrogen using Cd-doped SnO2-based sensors

Abstract: The effect of CdO doping on microstructure, conductance and gas-sensing properties of SnO 2 -based sensors has been presented in this study. Precursor powders with Cd/Sn molar ratios ranging from 0 to 0.5 were prepared by chemical coprecipitation. X-ray diffraction (XRD) analysis indicates that the solid-state reaction in the CdO–SnO 2 system occurs and α-CdSnO 3 with pervoskite structure is formed between 600 and 650°C. CdO doping suppresses SnO 2 crystallite growth effectively which has been confirmed by means of XRD, transmission electron microscopy (TEM) and BET method. The 10 mol% Cd-doped SnO 2 -based sensor shows an excellent ethanol-sensing performance, such as high sensitivity (275 for 100 ppm C 2 H 5 OH), rapid response rate (12 s for 90% response time) and high selectivity over CO, H 2 and i-C 4 H 10 . On the other hand, this sensor has good H 2 -sensing properties in the absence of ethanol vapor. The sensor operates at 300°C, the sensitivity to 1000 ppm H 2 is up to 98, but only 16 and 7 for 1000 ppm CO and i-C 4 H 10 , respectively.

An (s, S) model for inventory with exponential lifetimes and renewal demands

Abstract: Inventory control of products with finite lifetimes is important in many modern business organizations. It has been an important and difficult research subject. Here, we study the (s, S) continuous review model for items with an exponential random lifetime and a general renewal demand process through a Markov process. We derive a fundamental rate conservation theorem and show that all the other system performance measures can be obtained easily through the expected reorder cycle length. This leads to a simple expression for the total expected long run cost rate function in terms of the expected reorder cycle length. Subsequently, we derive formulas for computing the expected cycle lengths for the general renewal demand as well as for a large class of demands characterized by the phase type interdemand time distribution. We show analytically when the cost as a function of the reorder level is monotone, concave, or convex. We also show analytically that, depending on the behavior of the expected reorder cycle, the cost as a function of the order-up level is either monotone increasing or unimodal. These analytical properties enable us to understand the problem and make the subsequent numerical optimization much easier. Numerical studies confirm and illustrate some of the analytical properties. The results also demonstrate the impact of various parameters on the optimal policy and the cost. © 1999 John Wiley & Sons, Inc. Naval Research Logistics 46: 39–56, 1999

Phantom cosmology with a nonlinear born–infeld type scalar field

Abstract: Recent many physicists suggest that the dark energy in the universe might result from the Born–Infeld (B–I) type scalar field of string theory. The universe of B–I type scalar field with potential can undergo a phase of accelerating expansion. The corresponding equation of state parameter lies in the range of -1<ω<-⅓. The equation of state parameter of B–I type scalar field without potential lies in the range of 0≤ω≤1. We find that weak energy condition and strong energy condition are violated for phantom B–I type scalar field. The equation of state parameter lies in the range of ω<-1.

The effect of acupuncture in chronic intractable epilepsy

Abstract: We examined the effect of acupuncture on epileptic seizures in humans in a controlled clinical setting. Treatment was administered by two Chinese professors of acupuncture. Effect was measured by change in seizure frequency. Twenty-nine patients with chronic intractable epilepsy completed the study. They were randomized in two groups; 15 were given classical acupuncture and 14 were given sham acupuncture. There was a reduction in seizure frequency in both groups, which did not reach a level of statistical significance. There was also an increase in the number of seizure-free weeks in both groups, which reached a level of significance in the sham group. Thus, we have not been able to prove a beneficial effect of acupuncture in chronic intractable epilepsy.

On a diophantine inequality involving prime numbers (III)

Abstract: Let 1 0 such that for each real numberN>N(c) the inequality $$|p_1^c + p_2^c + p_3^c - N|< N^{ - \tfrac{1}{c}(\tfrac{{11}}{{10}} - c)} \log ^{c_1 } N$$ is solvable in prime numbersp 1,p 2,p 3, wherec 1 is some absolute positive constant.

The quantum behavior of an electron in a uniform magnetic field

Abstract: The total probability current of an electron in a uniform magnetic field is calculated in the symmetric gauge. Even though the eigen motion of the electron in this gauge is similar to the classical orbit motion, the total probability current is found to be equal to zero when the canonical angular momentum is less than zero. The reason is that in this case, the origin of the coordinate system lies outside the circular orbit of corresponding classical motion, in addition to the absence of radial component of the probability current density because of the indeterminacy of the location of the orbit center.

Humidity Dependence of Apparent Dielectric Constant for DSP Cement Materials at High Frequencies

Abstract: The relationship between humidity and dielectric constant for cement densified with small particles (DSP) has been studied in the relative humidity range 0%-93% and the frequency range 1 MHz to 1 GHz. The calculated dielectric constant appears to increase with increasing humidity as a linear relation at fixed frequency. According to experimental data and basic principles for dielectrics, two experimental expressions are suggested for heterogeneous dielectric materials to describe the observed behavior of the dielectric constant. The expressions fit the experimental data well in the frequency range studied. Apparent dielectric constant decreases with increasing frequency. Polarization of DSP cement is also discussed.

Value-estimation function method for constrained global optimization

Abstract: A novel value-estimation function method for global optimization problems with inequality constraints is proposed in this paper. The value-estimation function formulation is an auxiliary unconstrained optimization problem with a univariate parameter that represents an estimated optimal value of the objective function of the original optimization problem. A solution is optimal to the original problem if and only if it is also optimal to the auxiliary unconstrained optimization with the parameter set at the optimal objective value of the original problem, which turns out to be the unique root of a basic value-estimation function. A logarithmic-exponential value-estimation function formulation is further developed to acquire computational tractability and efficiency. The optimal objective value of the original problem as well as the optimal solution are sought iteratively by applying either a generalized Newton method or a bisection method to the logarithmic-exponential value-estimation function formulation. The convergence properties of the solution algorithms guarantee the identification of an approximate optimal solution of the original problem, up to any predetermined degree of accuracy, within a finite number of iterations.

Analysis and design of dual-polarized microstrip antenna array

Abstract: A new dual-polarized microstrip antenna array is presented. Diagonal feeding of the square patch with two ports is proposed to obtain dual linear polarization. A novel coplanar feedline network is also presented for the dual-polarized array. For engineering purposes, a CAD-oriented method of analysis is developed. The measured results demonstrate high isolation between the two input ports. The array has simple structure and is easy to further combine to form larger coplanar arrays. ©1999 John Wiley & Sons, Inc. Int J RF and Microwave CAE 9: 42–48, 1999.

Hybrid problems of determining unknown shape of bladings in compressible S2‐flow in mixed‐flow turbomachinery via variational technique

Abstract: Using the semi‐inverse method proposed by the present author, a family of variational principle for direct problem of S2‐flow in mixed‐flow turbomachinery is obtained; then, applying the functional variation with variable domain, two families of variational principles are established for the hybrid problems of determining the unknown shape of bladings, where pressure or velocity is over‐specified. The present variational models are well posed for redundant data at boundaries. The theory provides both rational ways for best contouring the hub/casing walls to meet various practical design requirements and a theoretical basis for introducing the finite element method into computational aerodynamics of turbomachinery.

Reduction of copper oxide with graphite by mechanical alloying

Abstract: The reduction of CuO with different amounts of C (CuO:C = 2:1, 2:1.5, and 2:2 molar ratios) driven by mechanical alloying was examined by x-ray diffraction and transmission electron microscopy. It was found that reduction behaviors are closely related to the carbon content. The reduction of CuO for the mixture with 1 mol of carbon follows a two-step process; i.e., CuO → Cu → Cu2O. However, the CuO can be completely converted to Cu for the mixtures with higher carbon content. A tentative model in terms of solid-state reactions at the interfaces is proposed to explain the effect of carbon content. Additionally, the thermal responses of the premilled mixtures were investigated by thermogravity and differential thermal analysis followed by x-ray identification. Contrary to mechanical alloying, reduction of CuO during thermal treatment follows a transition sequence of CuO → Cu2O → Cu. The preferential formation of Cu2O at the early annealing stage is probably due to the involvement of gaseous reduction.

Effect of the interdiffusion reaction on the compatibility in PZT/PNN functionally gradient piezoelectric materials

Abstract: The interfacial diffusion reaction Pb(Ni/sub 1/3/Nb/sub 2/3/)O/sub 3/ (PNN) and Pb(Zr,Ti)O/sub 3/ in functionally gradient materials (FGM) has been investigated as a function of sintering temperature and time, respectively. The compositional distribution profiles of the interaction region were examined by electron probe microbeam analysis (EPMA). According to the diffusion model, the concentration distribution profiles were simulated by way of numerical approaches. The diffusivity and activation energy for Ni/sup 2+/, Nb/sup 5+/, Ti/sup 4+/ and Zr/sup 4+/ ions have been estimated. The results were discussed.

Hamiltonian formulation of nonlinear water waves in a two-fluid system

Abstract: In this paper, it is dealt with that the Hamiltonian formulation of nonlinear water waves in a two-fluid system, which consists of two layers of constant-density incompressible inviscid fluid with a horizontal bottom, an interface and a free surface. The velocity potentials are expanded in power series of the vertical coordinate. By taking the kinetic thickness of lower fluid-layer and the reduced kinetic thickness of upper fluid-layer as the generalized displacements, choosing the velocity potentials at the interface and free surface as the generalized momenta and using Hamilton's principle, the Hamiltonian canonical equations for the system are derived with the Legendre transformation under the shallow water assumption. Hence the results for single-layer fluid are extended to the case of stratified fluid.