scispace - formally typeset
Search or ask a question

Showing papers by "Tsinghua University published in 1991"


Journal Article
Huang Yumin1
01 Jan 1991-Robot
TL;DR: An algorithm of color image understanding which segments the image after analyzing sur-faces with color variations due to lighting condition and object colors and gives forth a physical des-cription of imaging process, including intrinsic images, segmented image, the color of light and objects.
Abstract: We present an algorithm of color image understanding which segments the image after analyzing sur-faces with color variations due to lighting condition and object colors. The work is based on dichromaticreflection model according to the strategy of hypothesis plus test, following the continuity of image and thefeature of color clusters, the algorithm completes the image segmentation and gives forth a physical des-cription of imaging process, including intrinsic images, segmented image, the color of light and objects. Re-flecting respectively the propertics of light condition and every objects, both matte image and highlight im-age compose the intrinsic images.

183 citations


Journal ArticleDOI
TL;DR: Singular fields around a crack running dynamically along the interface between two anisotropic substrates are examined in this article, where the authors extend an established framework for interface fracture mechanics to include rapidly applied loads, fast crack propagation and strain rate dependent material response.
Abstract: Singular fields around a crack running dynamically along the interface between two anisotropic substrates are examined Emphasis is placed on extending an established framework for interface fracture mechanics to include rapidly applied loads, fast crack propagation and strain rate dependent material response For a crack running at non-uniform speed, the crack tip behaviour is governed by an instantaneous steady-state, two-dimensional singularity This simplifies the problem, rendering the Stroh techniques applicable In general, the singularity oscillates, similar to quasistatic cracks The oscillation index is infinite when the crack runs at the Rayleigh wave speed of the more compliant material, suggesting a large contact zone may exist behind the crack tip at high speeds In contrast to a crack in homogeneous materials, an interface crack has a finite energy factor at the lower Rayleigh wave speed Singular fields are presented for isotropic bimaterials, so are the key quantities for orthotropic bimaterials Implications on crack branching and substrate cracking are discussed Dynamic stress intensity factors for anisotropic bimaterials are solved for several basic steady state configurations, including the Yoffe, Gol'dshtein and Dugdale problems Under time-independent loading, the dynamic stress intensity factor can be factorized into its equilibrium counterpart and the universal functions of crack speed

169 citations


Journal ArticleDOI
TL;DR: It is suggested that some specially designed biological aerated filter (BAF), instead of a BAC bed reactor, may be used in advanced wastewater treatment and supported the authors' suggestion that the mechanism of the BAC process is basically a simple combination of biodegradation and carbon adsorption.

136 citations


Journal ArticleDOI
TL;DR: In this paper, a micromechanics constitutive model which takes into account both the dilatation and shear effects of the transformation is proposed to describe the plastic, pseudoelastic and shape memory behaviors of structural ceramics during transformation under different temperatures.
Abstract: B ased on micromechanics, thermodynamics and microscale t → m transformation mechanism considerations a micromechanics constitutive model which takes into account both the dilatation and shear effects of the transformation is proposed to describe the plastic, pseudoelastic and shape memory behaviors of structural ceramics during transformation under different temperatures. In the derivation, a constitutive element (representative material sample) was used which contains many of the transformed m-ZrO2 grains or precipitates as the second phase inclusions embedded in an elastic matrix. Under some basic assumptions, analytic expressions for the Helmholtz and complementary free energy of the constitutive element are derived in a self-consistent manner by using the Mori-Tanaka method which takes into account the interaction between the transformed inclusions. The derived free energy is a function of externally applied macroscopic stress (or strain), temperature, volume fraction of transformed phase and the averaged stressfree transformation strain (eigenstrain) of all the transformed inclusions in the constitutive element, the latter two quantities being considered to be the internal variables describing the micro-structural rearrangement in the constitutive element. In the framework of the Hill-Rice internal variable constitutive theory, the transformation yield function and incremental stress strain relations, in analogy to the theory of metal plasticity, for proportional and non-proportional loading histories are derived, respectively. The theoretical predictions are compared with the available experimental data of Mg-PSZ and Ce-TZP polycrystalline toughening ceramics.

117 citations


Journal ArticleDOI
TL;DR: Analysis of R1 regenerated seedlings showed that both kanamycin resistance and GUS behaved as typical linked dominant genes.
Abstract: We report a simple, direct gene transfer technique based on sonication. Transient expression of a β–glucoronidase (GUS) gene was detected in 86 percent of treated leaf segments of Nicotiana tabacum, and the area of transformed tissue on these segments reached 60–70 percent. GUS activity in the leaves of regenerated, kanamycin resistant plantlets was found at a frequency of 22 percent, and analysis of R1 regenerated seedlings showed that both kanamycin resistance and GUS behaved as typical linked dominant genes.

104 citations


Journal ArticleDOI
TL;DR: In this article, an extended UNIQUAC equation was proposed for the correlation of equilibrium data and the Fowler-Guggenheim equation was used to calculate the long-range electrostatic interaction of the ions.

102 citations


Journal ArticleDOI
TL;DR: Based on an order-disorder transition model and the calculation of coulombic electrostatic interaction of B-site ions, an "ordering structure factor"F0 is introduced in this paper.
Abstract: Based on an order–disorder transition model and the calculation of coulombic electrostatic interaction of B-site ions, an “ordering structure factor”F0 is introduced. Consequently, an available criterion and diagram to predict the order–disorder transition of A(B′B″)O3 is presented quantitatively. The theoretical results compare satisfactorily with experimental data collected from the literature for different kinds of A(B′B″)O3 ferroelectrics and antiferroelectrics. Permittivity ɛ′ is a sensitive parameter and plays an important role in order–disorder transition. The reason for conflicting arguments from different references for the ordering of some compounds is discussed.

89 citations


Journal ArticleDOI
01 Feb 1991-Wear
TL;DR: In this paper, a forward iterative numerical procedure is used to investigate the pure squeeze action in an isothermal elastohydrodynamically lubricated spherical conjunction, and the squeeze velocity resulting from the local deformation of the surfaces, as well as the compressibility of the lubricant, is taken into account.

72 citations


Journal ArticleDOI
TL;DR: The comparison of one-phase and two-phase anaerobic digestion processes in the characteristics of substrate degradation and the bacterial population levels was investigated by using the chemostat-type reactors to which starch was fed as substrate when both processes were operated under the same experimental conditions.

71 citations




Journal ArticleDOI
TL;DR: In this paper, an apparatus for the quantitative experimental investigation of the transient EHL problem for both line and point contacts is described, which can produce many types of dynamic load applied to the EHL contact zone.

Proceedings ArticleDOI
Xueyin Lin1, S. Chen1
09 Apr 1991
TL;DR: A novel method for outdoor natural color image segmentation for road following is presented and it can be seen that the hue, saturation, and intensity (HSI) system should be used rather than the red, green, blue (RGB) system.
Abstract: A novel method for outdoor natural color image segmentation for road following is presented. From the results of experiments it can be seen that the hue, saturation, and intensity (HSI) system should be used rather than the red, green, blue (RGB) system, and segmentation can be done in S-I space with good performance. An automatic adaptive threshold selection method is developed. The preliminary results indicate the effectiveness and efficiency of this method. >

Proceedings ArticleDOI
01 Sep 1991
TL;DR: A new global software pipelining algorithm GURPR* is applied in the URPR-1 optimtilng compiler which has good time efficiency as well as good space efficiency which is quite important for a single-chip VLIW machine with limited capacity of onchip sxmtrol memory.
Abstract: Software pipclining as an effective loop optimization technique has been widefy used in various optimizing compilers. Afthough some software pipefining algorithms can optimize complicated loops globally, they are still not satisfied both in time efficiency and space efficiency simultaneously. In this paper, we present a new global software pipelining algorithm GURPR* which is applied in the URPR-1 optimtilng compiler. Preliminary experiments show that GURPR* has good time efficiency as well as good space efficiency which is quite important for a single-chip VLIW machine with limited capacity of onchip sxmtrol memory.

Journal ArticleDOI
TL;DR: In this article, a coaxially fed hemispherical dielectric resonator antenna is investigated theoretically and the input impedance of the lowest order TE 111 mode that radiates efficiently in the broadside direction is calculated using the reaction formula.
Abstract: A coaxially fed hemispherical dielectric resonator antenna is investigated theoretically. The input impedance of the lowest order TE 111 mode that radiates efficiently in the broadside direction is calculated using the reaction formula. The result is compared with experimental data available in the literature. The erects of the probe length, feed position and dielectric constant on the input impedance are studied

Journal ArticleDOI
TL;DR: In this paper, an extended UNIFAC equation is proposed for the correlation and prediction of liquid-liquid equilibrium data for ammonium sulfate-polyethylene glycol (PEG) aqueous two-phase systems.

Journal ArticleDOI
TL;DR: The real-time operational experience of the RMEEI method in the northeast China power system is outlined and a set of linear recursive formulas, state variables, residuals, and their variances are updated after the removal of a measurement from a suspected data set to the remaining data set, or in the reverse direction.
Abstract: A fast and efficient algorithm, the recursive measurement error estimation identification (RMEEI) method, for bad data (BD) analysis is further developed. By using a set of linear recursive formulas, state variables, residuals, and their variances are updated after the removal of a measurement from a suspected data set to the remaining data set, or in the reverse direction. Neither a re-estimation nor a residual sensitivity matrix are needed in the identification process, which increases the computational speed greatly. Digital tests have been done to compare the RMEEI method with other conventional BD identification methods in terms of identification performance and computational speed. The real-time operational experience of the RMEEI method in the northeast China power system is outlined. >

Journal ArticleDOI
TL;DR: In this paper, a recursive measurement error estimation identification algorithm is proposed for identifying multiple interacting bad data in power system static state estimation, and a set of linearized formulae are developed and used to recursively calculate normalized residuals and normalized measurement error estimates.
Abstract: A recursive measurement error estimation identification algorithm is proposed for identifying multiple interacting bad data in power system static state estimation A set of linearized formulae are developed and used to recursively calculate normalized residuals and normalized measurement error estimates upon which the bad data identification method is based Sparse vector and partial factor modification techniques are used in the recursive identification calculations Neither the submatrix of the residual sensitivity matrix, W/sub ss/, nor state reestimation is needed in the whole identification process Digital tests on various power systems, including a 171 bus real system, are done to show the validity and efficiency of the proposed bad data identification method >

Journal ArticleDOI
TL;DR: In this article, a new procedure for solving 3D dynamic problems of unbounded foundations in the frequency domain by using BEM is studied, and a type of infinite boundary element (IBEM) is presented for modelling a 3D regular or irregular half space.
Abstract: In this paper, a new procedure for solving 3-D dynamic problems of unbounded foundations in the frequency domain by using BEM is studied. For simulations of wave propagations due to far field effects, a type of infinite boundary element (IBEM) is presented for modelling a 3-D regular or irregular half space. The wave type considered could be compressional, shear or a combination of the two. Through the analysis of the asymptotic behaviour of 3-D fundamental solutions for elasto dynamics, a rather feasible technique for obtaining singular integral coefficients for dynamic problems has been developed. Through the analysis of the dynamic response for a 3-D square foundation under a uniform load distribution, excellent accuracy has been achieved in agreement with previous numerical solutions. Another example–analysis of the dynamic compliance of a rigid square plate on a half space–has also shown very good results. The development of this infinite boundary element provides a powerful tool for dealing with 3-D structure foundation interaction or wave propagation problems for irregular foundations such as arch dam canyons.

Journal ArticleDOI
TL;DR: In this paper, a mathematical programming finite element formula for determining the upper bound load multiplier has been established, and an iteration algorithm has been proposed accordingly, where the plastic and rigid zones are distinguished for every iteration step and the goal function is modified gradually.
Abstract: This paper deals with the limit analyses of perfect rigid-plastic continua. Based on the kinematic theorem of the limit analysis theory, a mathematical programming finite element formula for determining the upper bound load multiplier has been established, and an iteration algorithm proposed accordingly. In this algorithm the plastic and rigid zones are distinguished for every iteration step, and the goal function is modified gradually. The difficulties caused by the nonsmoothness of the goal function are overcome. Some examples solved by this algorithm are presented.

Journal ArticleDOI
TL;DR: In this article, a numerical procedure for evaluation of the fracture process of gravity dams during strong earthquakes is presented, where the BEM is used to discretize the dam reservoir system including the crack surfaces and stress intensity factors at the crack tip.
Abstract: A numerical procedure for evaluation of the fracture process of gravity dams during strong earthquakes is presented. The BEM is used to discretize the dam reservoir system including the crack surfaces, and stress intensity factors at the crack tip are employed in a stage by stage procedure which simulates the crack extension. For each stage of constant crack length the mode superposition technique is applied; this is made possible by simulating the impact process of crack closing by a load pulse applied at the contact points which permits the structural stiffness to be assumed unchanged. To verify the proposed procedure, a cantilever beam model structure made of gypsum was tested on a shaking table

Journal ArticleDOI
TL;DR: The unitarized quark model based on the {sup 3}{ital P}{sub 0} quark-pair-creation mechanism is adopted as the coupled-channel model and the emitted pions can now be produced both from the conventional Okubo-Zweig-Iizuka- (OZI) forbidden process described by QCD multipole-gluon emissions and from the light-quark loop through an OZI-allowed process.
Abstract: A systematic calculation of the coupled-channel effects in hadronic transitions in the cc\ifmmode\bar\else\textasciimacron\fi{} and bb\ifmmode\bar\else\textasciimacron\fi{} systems is given. The unitarized quark model based on the $^{3}$${\mathit{P}}_{0}$ quark-pair-creation mechanism is adopted as the coupled-channel model. The emitted pions can now be produced both from the conventional Okubo-Zweig-Iizuka- (OZI) forbidden process described by QCD multipole-gluon emissions and from the light-quark loop through an OZI-allowed process described by the quark-pair-creation model. There is interference between the two kinds of transition amplitudes. Taking the experimental values of \ensuremath{\Gamma}(\ensuremath{\psi}'\ensuremath{\rightarrow}J/\ensuremath{\psi} \ensuremath{\pi}\ensuremath{\pi}) and d\ensuremath{\Gamma}(\ensuremath{\psi}'\ensuremath{\rightarrow}J/\ensuremath{\psi} \ensuremath{\pi}\ensuremath{\pi})/${\mathit{dM}}_{\mathrm{\ensuremath{\pi}}\mathrm{\ensuremath{\pi}}}$ as inputs to determine the two unknown parameters in the theory, we predict the transition rates and ${\mathit{M}}_{\mathrm{\ensuremath{\pi}}\mathrm{\ensuremath{\pi}}}$ distributions in the bb\ifmmode\bar\else\textasciimacron\fi{} system. The obtained rates for \ensuremath{\Upsilon}'\ensuremath{\rightarrow}\ensuremath{\Upsilon}\ensuremath{\pi}\ensuremath{\pi}, \ensuremath{\Upsilon}''\ensuremath{\rightarrow}\ensuremath{\Upsilon}\ensuremath{\pi}\ensuremath{\pi}, \ensuremath{\Upsilon}''\ensuremath{\rightarrow}\ensuremath{\Upsilon}'\ensuremath{\pi}\ensuremath{\pi} and the distribution d\ensuremath{\Gamma}(\ensuremath{\Upsilon}'\ensuremath{\rightarrow}\ensuremath{\Upsilon}\ensuremath{\pi}\ensuremath{\pi})/${\mathit{dM}}_{\mathrm{\ensuremath{\pi}}\mathrm{\ensuremath{\pi}}}$ are in good agreement with the experiments. For d\ensuremath{\Gamma}(\ensuremath{\Upsilon}''\ensuremath{\rightarrow}\ensuremath{\Upsilon}\ensuremath{\pi}\ensuremath{\pi})/${\mathit{dM}}_{\mathrm{\ensuremath{\pi}}\mathrm{\ensuremath{\pi}}}$, the present theory does give a bigger low-${\mathit{M}}_{\mathrm{\ensuremath{\pi}}\mathrm{\ensuremath{\pi}}}$ distribution than the pure QCD multipole expansion does, but it is still too small to fit the CLEO data.

Journal ArticleDOI
01 Feb 1991-Wear
TL;DR: In this article, the Hertzian pressure is used as the initial condition to solve numerically the transient Reynolds' equation; the load is assumed to be constant during the approach.

Journal ArticleDOI
TL;DR: In this article, a rapid method for alpha counting with liquid scintillation is presented, where the interference of beta and gamma radiation with the determination of alpha emitting nuclides by liquid SCINTillation counting was examined.
Abstract: A rapid method for alpha counting with liquid scintillation is presented. The interference of beta and gamma radiation with the determination of alpha emitting nuclides by liquid scintillation counting was examined. In extractive scintillator cocktail, TOPO-PPO-naphthalene-toluene has been developed for transferring actinide elements into organic scintillator and separating the undesirable materials as well as most beta emitters. Pulse Shape Analysis (PSA) was applied for the discrimination of beta radiation. The influence of cocktail composition on PSA has been studied and compared with that of the commercial cocktail. An analytical procedure was suggested for the rapid determination of actinide elements U, Pu, Am and Cm in the nuclear fuel cycle or in environmental samples.

Journal ArticleDOI
TL;DR: Asymptotic solutions of the equations representing the free vibration of thin shells of revolution with a first-order turning point are developed in this paper, and these solutions are uniform and fully approximate.

Journal ArticleDOI
TL;DR: In this article, low and high-Rayleigh number convections induced by internal heat generation in a vertical porous cylinder are studied in different ways according to their flow structures, and the results can be applied to any other enclosures with non-circular boundaries.

Journal ArticleDOI
01 Apr 1991-Zeolites
TL;DR: In this article, the Rietveld method was used to determine the location and the occupancy of the exchangeable cations in hydrated and dehydrated CsZSM-5 structures.

Journal ArticleDOI
10 Mar 1991-Wear
TL;DR: In this article, the behavior of dry sliding wear of pearlitic structures in eutectoid steel was studied with the aid of scanning and transmission electron microscopy and it was suggested that the difference in wear resistance between various pearlitic structure was caused by the difference of energy consumption in these layers during wearing.

Journal ArticleDOI
TL;DR: In this paper, a piezoresistive bridge pressure sensor and a pressure-sensitive MOS oscillator were fabricated and tested on a fully MOS-compatible technology, high-grade performance, intrinsically low temperature coefficient, and feasibility of fabrication are described to show the advantages of the new structure for production of discrete and, in particular, integrated pressure sensors and large-area sensor arrays.
Abstract: A structure for discrete and integrated pressure sensors is proposed. A piezoresistive bridge pressure sensor and a pressure-sensitive MOS oscillator on this structure were fabricated and tested. The fully MOS-compatible technology, high-grade performance, intrinsically low temperature coefficient, and feasibility of fabrication are described to show the advantages of the new structure for production of discrete and, in particular, integrated pressure sensors and large-area sensor arrays. >

Journal ArticleDOI
30 Jul 1991-Wear
TL;DR: In this article, a CVD TiC-TIN multilayer composite coating was used to investigate the tribological behavior of a chemical vapor deposition (CVD) TiC -TIN composite coating, a systematic experiment was carried out.