Showing papers by "Tsinghua University published in 1983"

Ordering of Walsh Functions

Abstract: The construction of Walsh functions is derived by means of the concepts of "symmetric copy" and "shift copy." Recursive relations based on the Kronecker product of matrices are also deduced from these concepts. There is a fourth useful ordering of the Walsh functions, called here X-ordering, in addition to the three known orderings usually referred to as Walsh-, Paley-, and Hadamardordering. An X-ordering function has the following features: lower order numbers of X-ordering correspond to even functions; higher order numbers of X-ordering correspond to odd functions; even order numbers of X-ordering correspond to lower sequencies; odd number of X-ordering correspond to higher sequencies. Finally, relations between the four orderings are given.

The asymptotic near-tip solution for mode-III crack in steady growth in power hardening media

Abstract: Two local solutions, one perpendicular and one parallel to the direction of solar gravitational field, are discussed. The influence of gravity on the gas-dynamical process driven by the piston is discussed in terms of characteristic theory, and the flow field is given quantitatively. For a typical piston trajectory similar to the one for an eruptive prominence, the velocity of the shock front which locates ahead the transient front is nearly constant or slightly accelerated, and the width of the compressed flow region may be kept nearly constant or increased linearly, depending on the velocity distribution of the piston. Based on these results, the major features of the transient may be explained. Some of the fine structure of the transient is also shown, which may be compared in detail with observations.

Introduction to Bridge Functions

Abstract: In this paper, a bridge function system is introduced, where bridge functions make up a three-valued function system, only taking the values +1, -1, and 0, and they are orthogonal. It is constructed with the concepts of sequence shift and sequence copying. The notation, waveforms, and recursive relation of the bridge functions are given. Walsh functions are a special case of the bridge functions. Block pulses are another special case. The bridge functions connect the Walsh functions and the block pulse functions. The bridge functions have the property of modulo 2 sum.

Investigation of Errors Related to the Measured Virtual Front Time T 1 of Lightning Impulses

Abstract: Present IEC as well as National Standards define rules for the measurement of lightning impulse voltages by specifying requirements for the accuracy of impulse shape parameters as well as requirements related to the step response of a measuring system used for recording the impulse voltage. For full 1.2/50 lightning impulses without superimposed oscillations the response requirements are only given by the Response Time T of a unit step response. This figure, however, is not sufficient to detect virtual front times T/sub 1/ of the original, true impulse wave shapes which are not any more within the tolerances provided for a standard lightning impulse. Based upon a great number of computations using the convolution integral, a thorough investigation of the measuring errors and the relationship between virtual front time T/sub 1/ and relevant response parameters is made. As a result, the partial response time T..cap alpha.. and the overshoot delta of the step response of the measuring system are considered to be the main parameters determining the errors in the measurement of T/sub 1/. These three values can be interlinked to propose new recommendations for ensuring the measuring accuracy for T/sub 1/.

The nonlinear characteristics of u-shaped bellows——calculations by the method of perturbation

Abstract: In this paper, the linear exact solution and nonlinear solution for U-shaped bellows have been obtained by using the general solution of circular ring shell[1] and the method of perturbation.

Arrival time determination using iterative signal reconstruction from the phase of the cross spectrum

Abstract: A situation encountered in such applications as seismics, ocean acoustics, radar, sonar and others, is that of an unknown wavelet propagating nondispersively in a reverberatory or multipath environment. Two receivers placed in such an environment will each record the arrival of this wavelet numerous times and each time with a different attenuation factor. In this paper, we demonstrate that if 1) there is no noise, 2) the interreceiver delays are distinct, and 3) the arrival sequence at each receiver has no zero phase convolutional component, then the arrival times and attenuation factors at each receiver can be determined as well as the wavelet itself. We show this via the construction of a finite length sequence whose phase equals that of the cross spectrum of the two received signals. This reconstructed signal, under the conditions above, can then be "inverted" to recover the desired arrival time and attenuation information at each receiver. An example using synthetically generated data is provided.

Relaxation Behavior of Metastable as and P Concentrations in Si After Pulsed and CW Laser Annealing

Abstract: Metastable solid solutions of arsenic and phosphorus atoms were created by high-dose ion implantation in silicon, followed by annealing either with pulsed (Nd:YAG) or CW (CO 2 ;) laser irradiation. The relaxation of these supersaturated layers was investigated by thermal post-treatment at temperatures between 600 and 1000°C. By measuring the time dependence of the sheet carrier concentration, the time constant and the activation energies for the relaxation of the electrically-active As and P atoms were investigated. In addition, the equilibrium carrier concentrations at different temperatures were obtained by Halleffect measurements in connection with a layer-removal technique.

Induced Smectic Phase in Binary Systems Containing Alkyl Cyano Phenylcyclohexane

Abstract: The experimental investigation of the induced smectic phase (ISP) phenomenon in the binary system of the homologous series of alkyl cyano phenylcyclohexane (PCH) and 4-n-hexyloxyphenyl 4'-pentyl benzoate ester (5.0.6) is reported. The phase transition temperatures were determined by differential scanning calorimetry and the optical textures were observed through a polarizing microscope in conjunction with a hot-stage. We found that the ISP-effect on equimole mixture of PCH and 5.0.6 increased sharply with the increasing of the length of terminal alkyl chain. By comparing PCH with Cyanobiphenyl (CBP) we also found that the ISP-effect was influenced by molecular framework.

The perturbation finite element method for solving problems with nonlinear materials

Abstract: The perturbation method is one of the effective methods for solving problems in nonlinear continuum mechanics. It has been developed on the basis of the linear analytical solutions for the original problems. If a simple analytical solution cannot be obtained, we would encounter difficulties in applying this method to solving certain complicated nonlinear problems. The finite element method appears to be in its turn a very useful means for solving nonlinear problems, but generally it takes too much time in computation. In the present paper a mixed approach, namely, the perturbation finite element method, is introduced, which incorporates the advantages of the two above-mentioned methods and enables us to solve more complicated nonlinear problems with great saving in computing time.

Subregion generalized variational principles for elastic thick plates

Abstract: In this paper, the subregion generalized variational principle for elastic thick plates is proposed. Its main points may be stated as follows: 1. Each subregion may be assigned arbitrarily as a potential region or complementary region. The subregion variational principles of potential energy, complementary energy and mixed energy represent three special forms of this principle. 2. The number of independent variational variables in each subregion may be assigned arbitrarily. Any one of the subregions may be assigned, as a one-variable-region, two-variable-region or three-variable-region. 3. The conjunction conditions of displacements and stresses on each interline of neighbouring subregions may be relaxed. On the basis of this principle the finite element analysis of non-conforming elements for thick plates can be formulated.

A new method on computation of the characteristic polynomial for a class of square matrices

Abstract: In this correspondence, a new method is proposed to construct the characteristic polynomial for a class of square matrices with some restrictions. An algorithm is also given. The proposed method and algorithm have recursive forms and are therefore suitable for calculation by computer.

Extended bounding theorems of limit analysis

Abstract: This paper studies the bounding problems of the complete solution of limit analysis for a rigid-perfectly plastic medium, allowing for the discontinuity of plastic flow. A generalized variational principle involving conditions of the rigid-plastic interface and the discontinuous surface of a velocity field has been advanced for the mixed-boundary value problem. Based on this principle, a set of variational formulae of limit analysis is established. The safety factors obtained by these formulae lie between the upper and lower bounds obtained by the classical bounding theorems with the same kinematically and statically admissible field.

Dynamic analysis of nonlinear systems by modal synthesis techniques

Abstract: Different kinds of modal synthesis method have been used widely in dynamic analysis of linear structure systems, but, in general, they are not suitable for nonlinear systems.

Dynamic Ship Positioning Control Systems Design Including Nonlinear Thrusters and Dynamics

Abstract: The control systems for dynamically positioned oil-rig drill ships, support vessels and survey vessels include filter to remove the wave motion signal. This is necessary because the thrust devices are not intended and are not rated to suppress the wave induced motions of the vessel. A combined self-tuning filter and Kalman filter scheme is proposed for this role and an optimal state estimate feedback control scheme is described. The ship dynamic equations are nonlinear and significant nonlinearities are present in the thrust devices. The self-tuning filter has the advantage of maintaining optimum performance in different weather conditions and of compensating for the modelling errors introduced by the nonlinearities.

Electric Field Effects on the Elastic Constants of Nematics. I

Abstract: The free energy density expression for nematics in an external electric field is derived both from a quasi-molecular approach similar to that used by Nehring and Saupe and a macroscopic approach based entirely on the symmetry properties of nematics. Under the special model assumed in the quasi-molecular theory the expressions of the elastic constants obtained from the two different methods agree with each other when one makes a proper choice of the material parameters introduced in the macroscopic theory.

The asymptotic analyeical solution of the strain-hardening elasto-plastic plate containing A circular hole under simple tension

Abstract: In this paper the general asymptotic analytical solution of plane problem of elasto-plasticity with strain-hardening[2] is used in solving the problem of an infinitely large plate containing a circular hole under simple tension, and the analytical expressions of stress components of the first two approximations are given These results are compared with the numerical and the experimental results given by other authors[4, 5], and a good agreement is obtained At the end of this paper the authors inspect the correctness of Neuber's formula[9] for this problem

The statistical inference method in heuristic search techniques

Abstract: In this paper we present a new heuristic searching algorithm by introducing statistical inference method on the basic of algorithm A*. It's called algorithm SA*. The following results have been proved. (1) Algorithm SA* in superior to algorithm A*. (2) The mean complexity of SA* is CN2, but in some case A* exhibits exponential complexity (eN). (3) In a (N,d,F)- game tree, the mean complexity of SA* is CN2, but the complexity of other known game-searching algoritham (α-β , SSS* etc.) is at least dN. (4) The maximal storage-space required by SA* is C,N. This shows that under a given significance level SA* is superior to other known algorithm (e.g. A*, B*, α-β, SSS* etc.).

The wavelet reconstructed with phase-only and a study of its uniqueness

Abstract: In this paper, what can the phass function do in wavelet estimation is mainly concerned, the concept of wave-form unigueness in deconvolution of seismic traces has been discussed. Under this conception, mixed-phase wavelets can be classified into three types. Based on the theorem of uniqueness of a sequence with a phase function by M.H.Hayes et al. and with some extensions, two types of wavelets have been reconstructed from its phase using zero-perturbation relaxed iterative algorithm. A new criterion function S p which judges the convergence of iteration and a new criterion of classification are also presented. Several examples of mixed-phase wavelet reconstruction from its phase are provided.

In Situ Electrophoresis of Cancer Cell Membrane Components

Abstract: Biomembranes show some properties of liquid crystal. The molecules of the membrane can diffuse along the membrane plane. ISE (In Situ Electrophoresis) is one of the new techniques to measure the lateral diffusion of the molecules. By this technique, we studied the membrane fluidity of Ehrlich ascitic cancer cell of a mouse, and obtained the diffusion coefficient D = 3.2 × 10−10 cm2/sec and the electrophoretic mobility m = 1.3 × 10−4 (μ/sec)/(v/cm) of the Con A receptors of the membrane at 22°C. A larger dispersion of the diffusion coefficient was noticed. We suggest that this is probably one of the characteristics of cancer cells.

Implementation and performance evaluation of a distributed splitted-bus multiple computer system

Abstract: A simple scheme of implementation of one-dimensional splitted-bus structure is proposed. Insertion of routing switches into the bus enables a distributed multiple-computer system to transmit variable-length messages simultaneously between several distinct processor-node pairs so long as the data links used for them do not conflict with one another. The interconnection topology and the mode of control for such an experimental system are described. Its characteristic performance values, such as data-line utilization, mean total message transmission time, etc. are given as results of simulation. These values are compared with similar results for other wellknown loop networks found in the literature.