Showing papers by "Xi'an Jiaotong University published in 1991"
TL;DR: In this paper, it was shown that X is uniformly convex if and only if there is a φ ϵ A such that ∥ x + y ∥ p ⩾ ∥ X √ p + p 〈 j p x, y 〉 + σ φ ( x, y ) ∀ x,y ϵ X and X is uniform smooth if, for given function f, σ f (x,y) is defined by σ p t f t ∥ y √ √ x+ ty �
302 citations
TL;DR: In this paper, a two-dimensional predator-prey system with a finite number of discrete delays is studied and it is shown that the time delays are harmless for uniform persistence of the solutions of the system.
163 citations
TL;DR: The effects of toxicants on naturally stable two-species communities are studied and persistence-extinction thresholds are given for populations in the toxicant stressed Lotka-Volterra model of two interacting species.
Abstract: The effects of toxicants on naturally stable two-species communities are studied. Persistence-extinction thresholds are given for populations in the toxicant stressed Lotka-Volterra model of two interacting species. The threshold results are expressed in terms of relationships involving the population intrinsic growth rates, dose-response parameters, and interaction rates.
117 citations
TL;DR: The Wigner distribution can be interpreted as a distribution of signal energy in both frequency and time domains, which can be applied to the description of machine conditions and is an effective method in machinery fault diagnosis as discussed by the authors.
102 citations
TL;DR: In this paper, the authors used a laser-Doppler velocimeter to obtain information on the distributions of transverse mean velocity and RMS velocity for flow through a sixteen-rod bundle with the mixing blades on grid spacer(mixing promoter).
72 citations
TL;DR: In this paper, a continuum damage model for Isotropie ductile fracture is derived from a new dissipation potential chosen by the author and a comparison between the damage model and experimental results is presented and a good agreement is found.
71 citations
TL;DR: In this article, the micro-mechanisms of void coalescence at different stress triaxiality levels were investigated employing axisymmetrical smooth and notched tension specimens of spheroidized 37Mn5 steel.
31 citations
TL;DR: In this paper, the microstructures of the laser-hardened layer on gray cast iron were examined by optical microscopy, transmission electron microscopy (TEM) and scanning electron microscope (SEM).
28 citations
TL;DR: In this paper, the sliding wear and fretting fatigue resistance of amorphous Ni-P coatings are investigated, and it is shown that Ni-p coatings significantly increase the slide wear resistance of chilled cast iron and decrease the fretting fatigues of high strength steel.
21 citations
TL;DR: In this paper, a new numerical method for solving the nonstationary Stokes equations in an unbounded domain is presented, which consists in coupling the boundary integral and finite element methods, and the variational formulation and well posedness of the coupling method are obtained.
21 citations
TL;DR: A synthesis method of coordination control is developed for the maximally permissive concurrent control of discrete event systems, it is computationally efficient.
TL;DR: In this article, the results of an experimental study of laminar natural convection heat transfer and fluid flow in horizontal annuli between a cylindrical envelope and its inner concentric octagonal heated cylinder are presented.
Abstract: In this paper, the results of an experimental study of laminar natural convection heat transfer and fluid flow in horizontal annuli between a cylindrical envelope and its inner concentric octagonal heated cylinder are presented. Two octagonal cylinders are investigated: one with a complete surface and the other with two horizontal slots on the top and bottom surfaces. The ratio of the slot width W to H is 0.072. Air is used as the working fluid. The range of Rayleigh number is 2.1 {times} 10{sup 2}-1.58 {times} 10{sup 6} for the unslotted case and 1.2 {times} 10{sup 2} - 1.5 {times} 10{sup 6} for the slotted case. The average heat transfer correlations for the two cases are provided. The results show that the heat transfer intensity of the unslotted octagon is slightly weaker than that in a cylindrical annulus, while for the slotted case, the overall heat transfer enhancement may be as high as 74%. The smoke technique is used to visualize the flow patterns. A series of photographs of the flow patterns are provided, which enhances the authors understanding of the mechanism of heat transfer enhancement for the slotted octagonal case.
TL;DR: In this article, the effect of slip amplitude on the fretting fatigue behavior of several alloy steels was investigated, and the results showed that with increasing slip amplitude, the depth of wear scars increases and wear damage becomes more severe.
TL;DR: In this paper, a detailed investigation of analytical and experimental findings for contact melting in a rectangular cavity with phase change materials (PCM) of it-heptadecane and /i-eicosane (research grade purity).
Abstract: This paper reports on a detailed investigation of analytical and experimental findings for contact melting in a rectangular cavity with phase change materials (PCM) of it-heptadecane and /i-eicosane (research grade purity). Specifically, consideration is given to the rectangular cavity with inside dimensions of 100 x 60 x 50 mm. The temperature of the two side walls and bottom surface of the cavity are maintained constant by circulating water through a highly sensitive thermostat. The other surfaces are subjected to adiabatic conditions. The timedependent solid-liquid interface contour is measured photographically during the melting process. According to the shadowgraph technique, the maximum displacement on the screen represents the temperature gradient. This temperature gradient on the wall is measured by the shadowgraph method, which results in calculation of the local Nusselt number. This local Nusselt number is used to show the difference between contact melting and fixed melting in the rectangular cavity at the same boundary conditions. Based on observation of the melting phenomena and data obtained, a theoretical model is developed and its solution is derived analytically. For the purpose of data reduction, a scale analysis method is used to find the functional dependence of the dimensionless parameters. The theoretical prediction is compared with experimental data and an excellent agreement is obtained. It is concluded that heat conduction in the melting phase is the controlling effect in the rectangular cavity.
TL;DR: In this article, the cutoff frequency of TE and TM modes in transmission lines with circular outer conductors and eccentric circular inner conductors is evaluated. But the cutoff values obtained lie outside Kuttler's bounds and some of the modes could not be found in the work of A. Vishen et al.
Abstract: The cutoff wavenumbers of TE and TM modes (higher order modes) in transmission lines with circular outer conductors and eccentric circular inner conductors are carefully evaluated. The correctness of Kuttler's bounds is confirmed and the reason why some of the values obtained lie outside the bounds and why some of the modes could not be found in the work of A. Vishen et al. (1986) is given. A reliable technique for accurately determining the roots of an analytical function is proposed for finding cutoff wavenumbers in such a way as to avoid missing any modes. >
TL;DR: The behavior of void growth in the crack tip regions of four specimen geometries with different stress triaxiality levels have been investigated by the FEM method and experimental observations in plane strain and plane stress cases respectively as mentioned in this paper.
TL;DR: In this article, a previously published work which contains some solutions which are identical to those found in the above-titled work was referred to as the reference work, and the authors agreed that the solutions are identical and express appreciation for having the previously published works called to their attention.
Abstract: For the original article see ibid., vol.MTT-34, no.1, p.161-7 (1986). The commenters cite a previously published work which contains some solutions which are identical to those found in the above-titled work. In replying, the authors agree that the solutions are identical and express appreciation for having the previously published work called to their attention. >
TL;DR: In this paper, a computationally uncoupled numerical scheme for the equations of nonlinear one-dimensional thermoelasticity by using the finite-element method for the spatial variables and an uncouple difference scheme for time variable is presented.
TL;DR: In this paper, a method was developed to size the particles of contaminants in insulation of HV crosslinked polyethylene cable by using a Fraunhofer far-field in-line holographic technique with no need to cut the insulation into thin slices.
Abstract: A method is developed to size the particles of contaminants in insulation of HV crosslinked polyethylene cable by using a Fraunhofer far-field in-line holographic technique with no need to cut the insulation into thin slices The maximum thickness of the sample is 40 cm, when a resolution of 50 mu m is obtained The accuracy of measurement is approximately 10% for particles >20 mu m diameter >
TL;DR: In this article, the role of carbothermic reduction in making low oxygen CuCr contact materials with high oxygen Cr powder is summarized and the influence of residual carbon in the CuCr alloys on their dielectric strength and antiwelding property is studied.
Abstract: The role of carbothermic reduction in making low oxygen CuCr contact materials with high oxygen Cr powder is summarized. Experimental results show that with the help of carbothermic reduction, the total oxygen in Cu50/Cr50 alloys made from high oxygen Cr powder (up to 5000 p.p.m.) is less than 100 p.p.m.. The influence of residual carbon in the CuCr alloys on their dielectric strength and antiwelding property is studied. It is concluded that: (1) carbothermic reduction is a very useful method to make low oxygen CuCr contact materials with high oxygen Cr powder; (2) the effect of carbothermic reduction depends mainly on sintering temperature and Cr particle size; (3) carbon exists as Cr/sub 23/C/sub 6/ carbide in CuCr; (4) 1.8-wt.% C in CuCr alloys will increase dielectric strength of the alloys at high temperature; (5) 1 .8-wt.% C in CuCr alloys will much improve the antiwelding property of the alloys. >
TL;DR: In this paper, the inertia effect in Charpy impact tests has been analyzed theoretically and experimentally, and a solution of the inertia force, which is in a good agreement with experiments, has been obtained.
08 Jul 1991
TL;DR: In this paper, the effects of ferrocene derivatives on dielectric properties of PE and XLPE (cross-linked polyethylene) are investigated in detail, and the results show that the initiation voltage of treeing and the breakdown strength of PE are enhanced by 61% and 10%, respectively, when the content of the derivative B is 1%.
Abstract: In order to improve the stabilization of ferrocene, two kinds of ferrocene derivatives have been synthesized. The effects of ferrocene and its derivatives on dielectric properties of PE and XLPE (cross-linked polyethylene) are investigated in detail. The test results show that the initiation voltage of treeing and the breakdown strength of PE are enhanced by 61% and 10%, respectively, when the content of ferrocene derivative B is 1%. Using the ferrocene derivative B not only increases the treeing initiation voltage and inhibits the growth of treeing, but also increases the breakdown strength in PE and XLPE. The dielectric loss of PE and XLPE blended with ferrocene derivative B is permissible for HV plastic cable. The thermal stability of ferrocene derivative blended in PE is much better than that of ferrocene. Through measurements of the TSC (thermally stimulated current) of the samples and the relation between electric conduction and electrical stress, the mechanism of treeing inhibition by additives is investigated. >
08 Jul 1991
TL;DR: In this paper, a measurement principle which may be used to measure the 2-dimensional electric field distributions in dielectric liquids was proposed by applying a pulse voltage to an optical phase modulator, which can change the incident light from linearly polarized light into elliptically polarized light.
Abstract: On the basis of the Kerr electrooptic effect, a novel measurement principle, which may be used to measure the 2-dimensional electric field distributions in dielectric liquids, was proposed. By applying a pulse voltage to an optical phase modulator, it is possible to change the incident light from linearly polarized light into elliptically polarized light. Modulating both states of polarization of the elliptically polarized light and the DC electric field in a specimen with an AC electric field whose direction is different from that of the DC field, one can measure the magnitudes and angles of both AC and DC electric field intensity (the sensitivity is better than 100 V/cm) in liquids with small Kerr constants (about 10/sup -15/ m/V/sup 2/) using a short electrode length (about 5 cm). >
05 Nov 1991
TL;DR: In this paper, the performance of phase-comparison pilot relays using fault superimposed components of current under different conditions is analyzed, and the results show that phase-compensated pilot relay using fault-superimposed positive sequence current or phase currents are more sensitive and reliable then traditional relays with composite sequence current and phase currents.
Abstract: The performance of phase-comparison pilot relays using fault superimposed components of current under different conditions is analyzed. The results show that phase-comparison pilot relays using fault superimposed positive sequence current or phase currents are more sensitive and reliable then traditional relays using composite sequence current or phase currents, and the relays based on fault superimposed current can overcome many drawbacks of traditional relays.
01 Mar 1991
TL;DR: A novel approach, that makes full use of dynamic and steady- state information on the process when solving steady-state optimising control problems with output dependent constraints, is presented.
Abstract: A stochastic formulation for steady-state optimising control problems with output dependent constraints is proposed and analysed. In this formulation, the output dependent inequality constraints, which become stochastic due to the randomness of the output vector, are characterised by their mean values. A novel approach, that makes full use of dynamic and steady-state information on the process when solving such problems is presented. In this approach, the uncertainty of the performance index is removed, without affecting the true optimum, by use of a fixed steady-state model and a modifier in the model-based optimisation. To tackle the problem of having unknown constraints in the modelbased optimisation, an adaptive linear model is adopted to approximate the output dependent constraints. The parameters of the model are updated because of an extended steady-state identification technique each time the controller set point is changed. A penalty-relaxation technique is employed to ensure the existence of an optimum solution to the model-based optimisation problem in each iteration and the feasibility of the algorithmic solution towards the end of iteration. Since there are no additional perturbations to the process involved in the steady-state identification, the new approach has reduced to one the required number of controller set point changes in each iteration and increased its robustness significantly. Optimality of the algorithm is examined, sufficient conditions for global convergence are provided, and, moreover, an upper bound for the convergence rate is also derived. Practical aspects concerning the implementation of the new approach are discussed, and computer simulations are presented to demonstrate the behaviour of the approach.
TL;DR: In this article, the global stability of the positive steady state in Volterra models with discrete and distributed time delays is shown to be robust to time delays, and conditions for the stability of positive steady states are obtained.
08 Jul 1991
TL;DR: In this paper, the electrical strength of polypropylene (PP) was investigated and two necessary conditions for electrical breakdown were proposed based on the morphology and electronic structure of PP and the energy required for electrons to break chemical bonds in electrical breakdown was the band gap of the polymer instead of the bond energy.
Abstract: The morphology and electrical breakdown of polypropylene (PP) are investigated. Experimental results show that electrical strength depends on the size of microvoids and their distribution in PP instead of the macrostructure parameters such as crystallinity and density, and the microvoids with diameters of 100-1000 AA affect electrical strength remarkably. On the basis of the morphology and electronic structure of PP, two necessary conditions for electrical breakdown are proposed. The energy required for electrons to break chemical bonds in electrical breakdown is the band gap of the polymer instead of the bond energy. >
TL;DR: In this paper, finite element analyses are performed to model quasi-static crack growth under mode I plane stress in a compact tension specimen and a centre-cracked plain, and it is found that the triaxial constraint and stress-field defined by HRR solution in crack-tip regions for a stationary crack have been better met by those presented in the propagating crack tip for two different thin specimens, namely, Jdominance is continuously valid.