Showing papers by "Tsinghua University published in 1993"
TL;DR: In this article, a micromechanics constitutive model has been proposed to describe the pseudoelastic and shape memory behavior of polycrystalline shape memory alloys under various temperatures.
Abstract: A MICROMECHANICS constitutive model has been proposed in this paper to describe the pseudoelastic and shape memory behavior of polycrystalline shape memory alloys under various temperatures The derivation of the model is based on the thermodynamics, micromechanics and microstructural physical mechanism analysis of the material during deformation and it is shown that the inelastic deformation of the material in the mechanical and/or thermal loading processes is associated with some temperature, stress state and loading history dependent yielding surfaces which microscopically correspond to the forward and reverse transformation (or reorientation) processes, respectively
414 citations
TL;DR: In this paper, the authors investigated the single-phase forced-flow convection and boiling characteristics of subcooled liquid flowing through microchannels with a cross-section of 0.6 × 0.7 mm, machined on the stainless steel plate 2 mm thick.
322 citations
TL;DR: In this paper, the transient stability and voltage regulation of a single-machine-infinite-bus power system under the effects of a symmetrical three-phase short-circuit fault is detailed.
Abstract: Improvement of the transient stability and voltage regulation of a single-machine-infinite-bus power system under the effects of a symmetrical three-phase short-circuit fault is detailed. The dynamical model of the system is described. A design strategy for nonlinear controllers is considered, and the design of a nonlinear variable-structure excitation controller is described. Simulation results obtained using the nonlinear excitation controller are given, and a new nonlinear coordinated controller is proposed. Simulation results obtained by using the nonlinear coordinated controller are presented. >
310 citations
TL;DR: This deformation of particle image patterns by strong velocity gradients and out-of-pattern motions is investigated and its effect on conventional PIV techniques is quantified for 2D flows.
Abstract: In this second part of the paper, the Particle Image Distortion (PID) technique is described. It is proposed to overcome the limitations of conventional PIV due to the local deformations ∂u/∂x, ∂u/∂y, ∂v/∂x and ∂v/∂y in two-dimensional flows. Both simulation and experiment demonstrate that high accuracy and high spatial resolution are possible with this technique. The large time required to compute the cross-correlations, however, limits its wide applications at present.
267 citations
TL;DR: The Chinese National Improved Stove Program introduced some 129 million improved stoves into rural areas during 1982-1992, mostly biomass cookstove, but also including coal and spaceheating stoves in some areas as mentioned in this paper.
214 citations
TL;DR: In this paper, the constitutive relation for various phenomena of SMA (superelasticity, rubber-like elasticity, ferroelasticity and elastic anomaly) is studied in detail and compared with the available experimental data.
Abstract: T he constitutive relation for various phenomena of SMA ( superelasticity, rubber-like elasticity, ferroelasticity, elastic anomaly, shape memory effect ) is studied in detail and compared with the available experimental data. It is shown that the micromechanical model developed in Part I can satisfactorily describe the main peculiarities of the macroscopic thermomechanical constitutive behavior in the course of uniaxial mchanical and/or thermal loadings and that the existing phenomenological models are special cases of the proposed theory under proportional loading conditions. Some theoretical predictions and discussions for complex loading paths are also given which are yet subject to experimental verification.
211 citations
TL;DR: In this paper, a hemispherical dielectric resonator antenna fed by a coaxial probe is studied both theoretically and experimentally, and the Green's function for the evaluation of the input impedance is derived rigorously and expressed in a form convenient for numerical computations.
Abstract: A hemispherical dielectric resonator antenna fed by a coaxial probe is studied both theoretically and experimentally. The Green's function for the evaluation of the input impedance is derived rigorously and expressed in a form convenient for numerical computations. The method of moments is used to obtain the probe current from which the input impedance of the DR antenna is calculated. Both delta gap and magnetic frill source models are considered. Moreover, the results using a reduced kernel as well as the exact kernel are presented. Both entire basis (EB) and piecewise sinusoidal (PWS) expansion modes are used and the results are compared. The effects of the probe length, feed position, and dielectric constant on the input impedance are discussed. Finally, the theoretical radiation patterns for the first three resonant modes (TE/sub 111/, TM/sub 101/, and TE/sub 221/) of the DR antenna are presented. >
189 citations
TL;DR: In this paper, a non-monotonic trust region method for unconstrained optimization problems is presented, which allows the sequence of values of the objective function to be nonmonotone.
Abstract: A nonmonotonic trust region method for unconstrained optimization problems is presented. Although the method allows the sequence of values of the objective function to be nonmonotonic, convergence properties similar to those for the usual trust region method are proved under certain conditions, including conditions on the approximate solutions to the subproblem. To make the solution satisfy these conditions, an algorithm to solve the subproblem is also established. Finally, some numerical results are reported which show that the nonmonotonic trust region method is superior to the usual trust region method according to both the number of gradient evaluations and the number of function evaluations.
165 citations
TL;DR: The operation of a diode-pumped monolithic self-Q-switched Cr,Nd:YAG laser in which the codoped ions create saturable absorption for Nd(3+) laser emission at 1064 nm is reported.
Abstract: We report the operation of a diode-pumped monolithic self-Q-switched Cr,Nd:YAG laser in which the codoped ions create saturable absorption for Nd3+ laser emission at 1064 nm. With a 70-μm beam diameter in the gain medium, the Q-switched pulse has a duration of 3.5 ns and a peak power of 2 kW. The output is linearly polarized with an extinction ratio of 600:1. The pulse-to-pulse intensity fluctuation is less than the instrument resolution of 0.25%. A 5-mm-long KTP crystal butted against the monolithic cavity produces 2-ns-long pulses at 532 nm with a peak power-conversion efficiency of 30%.
111 citations
20 Jun 1993
TL;DR: In this paper, the authors investigated the control strategy for parallel operation of multiple converters and the advantages of load-current sharing for the parallel system and the superiority of current-balance control.
Abstract: The control strategy for parallel operation of multiple converters is investigated. Analysis and design considerations of load-current sharing for the parallel system are presented and the superiority of current-balance control is discussed. The prominent features of the load-current sharing and analytical results are confirmed experimentally for a three-paralleled forward-converter system. >
93 citations
TL;DR: LuLu et al. as mentioned in this paper improved the mean spherical approximation (MSA) method by the introduction of the effective diameter of the cation, which is mainly attributed to the solvation effect.
TL;DR: In this study, the thiol and amino groups at or near the active site of creatine kinase are labelled with o-phthalaldehyde to form a fluorescent probe and the rate of exposure of the probe is comparable with that of inactivation and is several orders of magnitude faster than that for the unfolding of the molecule as a whole.
Abstract: It has been previously reported that, during denaturation of creatine kinase by guanidinium chloride (GdmCl) or urea [Tsou (1986), Trends Biochem. Sci. 11, 427-429], inactivation occurs before noticeable conformational change can be detected, and it is suggested that the conformation at the active site is more easily perturbed and hence more flexible than the molecule as a whole. In this study, the thiol and amino groups at or near the active site of creatine kinase are labelled with o-phthalaldehyde to form a fluorescent probe. Both the emission intensity and anisotropy decrease during denaturation indicating exposure of this probe and increased mobility of the active site. The above conformational changes take place together with enzyme inactivation at lower GdmCl concentrations than required to bring about intrinsic fluorescence changes of the enzyme. At the same GdmCl concentration, the rate of exposure of the probe is comparable with that of inactivation and is several orders of magnitude faster than that for the unfolding of the molecule as a whole.
TL;DR: The results show that the magnetic moment of the cobalt cluster converges to that of the bulk, and the average moments of the cluster is in agreement with the experiment.
Abstract: The electric structure and magnetic properties of small cobalt clusters (4\ensuremath{\le}n\ensuremath{\le}19) have been studied using the spin-polarized discrete variational method within the local-density-functional theory The results show that the magnetic moment of the ${\mathrm{Co}}_{13}$ cluster converges to that of the bulk, the average moment of the cluster is in agreement with the experiment The ${\mathrm{Co}}_{13}$ cluster with icosahedral symmetry has the highest magnetic moment among the 13-atom isomers The atomic magnetic moments of cobalt clusters have been discussed, in particular, with reference to changing cluster size and interatomic distances The cluster symmetry is an important factor for determining the magnetic moments of the clusters
25 Oct 1993
TL;DR: An application of self-organizing maps as a method of clustering and data analysis, called SOM Analysis, which has some advantages over the traditional clustering algorithms in that it suits more general data distributions and needs less a priori knowledge.
Abstract: Presents an application of self-organizing maps as a method of clustering and data analysis. It is called SOM Analysis. It has some advantages over the traditional clustering algorithms in that it suits more general data distributions and needs less a priori knowledge. It can also be used as a general tool for analysing high-dimensional data relations. Some experimental results are also given in this paper.
TL;DR: In this paper, the complete and irreducible representations with respect to every kind of material symmetry for scalar-, vector-, and second-order tensor-valued functions in two-dimensional space of any finite number of vectors and secondorder tensors were established.
Abstract: All kinds of physically possible material symmetry in two-dimensional space were investigated in a recent work of Q.-S. Zheng and J. P. Boehler. In this paper, we establish the complete and irreducible representations with respect to every kind of material symmetry for scalar-, vector-, and second-order tensor-valued functions in two-dimensional space of any finite number of vectors and second-order tensors. These representations allow general invariant forms of physical and constitutive laws of anisotropic materials to be developed in plane problems.
TL;DR: In this paper, a hemispherical dielectric resonator (DR) antenna fed by a microstripline through an aperture on the ground plane is investigated both theoretically and experimentally.
Abstract: A hemispherical dielectric resonator (DR) antenna fed by a microstripline through an aperture on the ground plane is investigated both theoretically and experimentally. The broadside TE111 mode input impedance of the antenna configuration is evaluated, and reasonable agreement between theory and experiment is obtained. The effects of the slot length and the slot width on the input impedance are studied and discussed.
TL;DR: In this paper, a transient model for micro-elastohydrodynamic lubrication with three-dimensional asperities in line contacts is presented, where the numerical solution of this model is based on an implicit finite difference scheme with under relaxation.
Abstract: A transient model for micro-elastohydrodynamic lubrication with three-dimensional asperities in line contacts is presented in this paper. To take into account the effect of non-Newtonian behavior of lubricant, the Ree-Eyring viscous constitutive equation is employed in deriving Reynolds equation. The numerical solution of this model is based on an implicit finite difference scheme with under relaxation. Numerical simulation results show that the pressure bump caused by an asperity or asperities depends not only on asperity height and orientation but also on asperity dimension. The increase in asperity dimension decreases the pressure bump. The decrease in load and increase in sliding speed increases pressure bump. 14 refs.
01 Jan 1993
TL;DR: The overall structural forms and motions of elephant trunks and squid tentacles are reviewed and some of their biological characteristics are incorporated in the design of a flexible arm manipulator with open loop control and a flexible, two-fingered gripper with closed loop control.
Abstract: Elephants and squids have continuously flexible appendages that are well adapted for manipulating and gripping. In this paper we briefly review the overall structural forms and motions of elephant trunks and squid tentacles. We then discuss how we incorporated some of their biological characteristics in the design of a flexible arm manipulator with open loop control (Part 1) and in the design of a flexible, two-fingered gripper with closed loop control (Part 2).
TL;DR: The results showed that adsorbed protein molecules lose their ordered native structure in the initial stage of adsorption and the structure appears to be a random or disordered conformation, indicating that for certain proteins, the β structure may be a more stable secondary structure than α helix on the hydrophobic surface.
Abstract: Circular dichroism, ellipsometry and radiolabeling techniques were employed to study the induction of changes in the secondary structure of BSA, myoglobin and cytochrome C by a hydrophobic surface. The results showed that adsorbed protein molecules lose their ordered native structure in the initial stage of adsorption and the structure appears to be a random or disordered conformation. Protein molecules adsorbed in later stages adopt a more ordered secondary structure (alpha helix and beta structure). The changes of secondary structure of globular proteins induced by a hydrophobic surface can be explained by the steric interaction between adsorbed proteins as well as by hydrophobic interactions during the adsorption process. In addition, there is obviously an intermediate stage in which the protein molecules are mainly in the beta structure, indicating that for certain proteins, the beta structure may be a more stable secondary structure than alpha helix on the hydrophobic surface.
TL;DR: In this paper, a practical definition of the circulating fluidized bed (CFB) regime has been proposed based on a comprehensive hydrodynamic analysis, and two flow regimes are involved in a CFB: fast fluidization and dense phase conveying.
Abstract: Based on a comprehensive hydrodynamic analysis, a practical definition of the circulating fluidized bed (CFB) regime has been proposed. It was established that two flow regimes are involved in a CFB: fast fluidization and dense phase conveying. By demonstrating the variation of pressure gradient in both the lower and the upper section of the bed versus superficial gas velocity, the criteria for the determination of transition velocities have been obtained. Literature data which over wider operating conditions, particle properties and bed diameters from the basis of the obtained generalized correlations of transition velocities. A quantitative flow diagram is presented.
TL;DR: A leak detection method based on autoregressive modeling that requires only four pressure measurements, two at each end of the pipeline, and can be easily implemented because the computational expenditure is small is proposed.
Abstract: A leak detection method based on autoregressive modeling is proposed. It requires only four pressure measurements, two at each end of the pipeline. A leak above 0.5% can be reliably and quickly detected by analyzing the time sequences of the pressure gradient at the inlet and outlet of the pipeline. It can be easily implemented because the computational expenditure is small. Its effectiveness has been verified by tests on a 10-mm-diameter, 120-m-long experimental water pipeline. >
TL;DR: In this paper, a new type of hysteresis, termed temperature deviation (TD), is described and the physical mechanisms for both TOS and TD are analyzed in detail using thermodynamic nucleation.
TL;DR: In this paper, the longitudinal turbulent intensity measurements of flow in a gravel open-channel have been conducted with a highly accurate one-dimensional LDA-system, where the channel bed was roughened with uniform and non-uniform diameters respectively, and a wide range of H /Ks were considered.
Abstract: In this paper, the systematic longitudinal turbulent intensity measurements of flow in a gravel open-channel have been conducted with a highly accurate one-dimensional LDA-system. The channel bed was roughened with gravels of uniform and non-uniform diameters respectively, and a wide range of H /Ks were considered. In comparison with the smooth bed results, it was found that the bed roughness makes the flow turbulence become well-distributed in the region near the bed and in the case of small H jK% values. With regard to the flow over a non-uniform gravel bed, only the flow region below the maximum gravels is affected by the rough bed, and outside this region, the turbulent intensity distributions could collapse on to a single curve.
01 Dec 1993
TL;DR: The authors show that the static program analysis heuristics identify execution sequences without hazardous conditions that tend to prohibit compiler optimizations that makes a strong case for usingstatic program analysis with or without profile information to facilitate aggressive compiler optimization and scheduling.
Abstract: To achieve higher instruction-level parallelism, the constraint imposed by a single control flow must be relaxed. Control operations should execute in parallel just like data operations. We present a new software pipelining method called GPMB (Global Pipelining with Multiple Branches) which is based on architectures supporting multi-way branching and multiple control flows. Preliminary experimental results show that, for IFless loops, GPMB performs as well as modulo scheduling, and for branch-intensive loops, GPMB performs much better than software pipelining assuming the constraint of one two-way branch per cycle. >
TL;DR: In this article, the authors generalized the fast Fourier transform (FFT) to the three-dimensional and anisotropic case and showed that the proposed procedure converges quite rapidly, whereas the conventional using the conjugate gradient method approach fails to converge.
Abstract: It has been known for a long time that the accuracy of solving the scattering by a dielectric body using the electric field integral equation (EFIE) is poor when the permittivity of the scatterer becomes large. Recently, this problem has been settled by using a procedure involving face-centered node points. Such a procedure is efficient, since it preserves the convolution property in the EFIE and, hence, the applicability of the fast Fourier transform (FFT). This procedure is generalized to the three-dimensional and anisotropic case. The generalization is quite straightforward in both the formulation and the programming. A calculation for a scatterer with a relative permittivity as high as 100 indicates that the proposed procedure converges quite rapidly, whereas the conventional using the conjugate gradient method approach fails to converge. >
TL;DR: The 200 MWt Nuclear Heating Reactor (NHR-200) is an integrated vessel type light water reactor, which will be built in Northern China as a new energy source for district heating as discussed by the authors.
TL;DR: In this paper, variable property effects on vertical channel natural convection in air are studied systematically, and numerical solutions of the governing equations show that both the mass flow rate and heat transfer in the channel are not only lower than the constant property results, but also show a non-monotonic variation with increasing wall temperature or wall heat flux.
Abstract: Variable property effects on vertical channel natural convection in air are studied systematically. Numerical solutions of the governing equations show that both the mass flow rate and heat transfer in the channel are not only lower than the constant property results, but also show a nonmonotonic variation with increasing wall temperature or wall heat flux. This phenomenon, which seemingly conflicts with the conventional knowledge, has also been identified by experiments. For a vertical channel with a uniform heat flux boundary condition, the wall may experience a sharp rise in temperature up to damage of the channel if the wall heat flux is greater than the critical heat flux. This implies that the crisis phenomenon (or burnout) may occur in channel natural convection in gas as well as in the boiling process.
TL;DR: In this article, an iterative algorithm for the square root of a squared Hamiltonian matrix, which is obtained from the S + − 1 transformation of the symplectic pencil associated with the Riccati equation, is presented.
TL;DR: In this article, the authors focus on liquid laminar free convection along an isothermal vertical flat plate with consideration of variable fluid thermophysical properties, and propose a method to predict accurately the heat transfer of LFA by means of numerical solution of the temperature gradient.
TL;DR: The theoretical analysis shows that an inverse relationship exists between the frequency-domain signal-to-noise ratio and the group delay moving standard deviation and/or group delaymoving entropy, so an adaptive Wiener filter can be realized without a priori knowledge of the signal and noise spectra.
Abstract: Several techniques are demonstrated for Wiener filter realization based on group delay statistics. The theoretical analysis shows that an inverse relationship exists between the frequency-domain signal-to-noise ratio and the group delay moving standard deviation and/or group delay moving entropy. Therefore, an adaptive Wiener filter can be realized without a priori knowledge of the signal and noise spectra. Group delay statistics estimation algorithms are proposed and evaluated by simulation. Experimental data from ultrasonic flaw detection are presented to support the effectiveness of the techniques. >