Showing papers by "Shanghai Jiao Tong University published in 1986"

Devil's staircase route to chaos in a non-linear circuit

Abstract: A driven second-order negative-resistance oscillator circuit has been observed experimentally to exhibit infinitely many distinct chaotic states in addition to infinitely many subharmonic responses of all orders. Each chaotic state is found to be born out of a devil's staircase whose steps are spaced in accordance with a definite period-adding law. Each devil's staircase emerges at some level of frequency-tuning resolution, where each level is embedded within an outer level, ad infinitum. The global bifurcation structure is self-similar in the sense that upon rescaling, the devil's staircases appear to be clones of each other.

Quantitative measurements of ambient radiation, emissivity, and truth temperature of a greybody: methods and experimental results

Abstract: By regarding the total ambient radiation falling on a greybody as an equivalent radiation of a blackbody at temperature TB and by using two standard reference plates, we are able to measure accurately the ambient radiation. In addition to the ambient radiation, there are two factors still affecting the self-radiation of a greybody, i.e., the emissivity ɛ and the truth temperature T. We point out theoretically that the emissivity could be determined by changing the ambient radiation. In this paper two simple methods are proposed for measuring the emissivity and good results are obtained for a variety of greybodies. These methods are not only practical in the laboratory but also in the field. The experimental results agree well with the data published by other investigators. After TB and ɛ are measured, the truth temperature T of the greybody can be obtained. Based on the theory presented here, we designed and produced a new infrared thermometer which can directly read out the truth temperature.

Application of electro-optic frequency shifters in heterodyne interferometric systems

Abstract: The application of electro-optic frequency shifters in heterodyne interferometric systems is proposed and demonstrated experimentally for the first time. It provides an effective phase measurement configuration for heterodyne interferometric sensing systems.

Analysis of the degree of polarization of optical waves in a single-mode optical fiber with random coupling

Abstract: A single-mode optical fiber model is proposed with discrete mode-coupling centers having random coupling coefficients at regular intervals. The degree of polarization in a single-mode fiber with random-mode coupling does not approach zero with increasing fiber length. Numerical results show that the ensemble average of the degree of polarization approaches a nonzero value the magnitude of which depends on the coupling intensity, the light source spectrum, the fiber birefringence, and the spatial frequency of coupling centers, The theoretical and numerical results clarify the limitation of the perturbation iteration method for long optical fibers.

Cationic polymerization of tetrahydrofuran initiated by multifunctional initiators

Abstract: A series of multifunctional cationic initiators was synthesized from 1,5,9-cyclododecatriene and from methylbenzenes by the Wohl-Ziegler reaction with N-bromosuccinimid. The initiators were treated with silver perchlorate to prepare star-shaped polytetrahydrofurans with three to six arms.

Mode excitation theory and experiment of single-mode fiber directional coupler with strong coupling

Abstract: The mode excitation theory is presented to analyze single-mode optical fiber directional couplers with transverse strong coupling, which either the weakly coupling theory or the ray theory fails to expound. By using the equivalence between the waveguides with square and circular cross sections, regarding the coupling zone of the coupler as a single waveguide, the excitation coefficients of the propagation modes in the coupling zone excited by the modes in the input waveguide have been evaluated. The theoretical coupling amount and insertion loss have been studied. Using a special monitoring technique to control the coupling length, several couplers with various coupling amounts have been made by the polishing method. The spectral characteristic of the coupling amount has been measured and compared with the theoretically inferred result. The two are found to agree with each other. The offset effect on the coupling amount has also been measured and it is different from that of the weak coupling device-the Stanford coupler.

Observation and analysis of noise due to birefringence modulation in a fibre-optic gyroscope

Abstract: The noise due to the birefringence modulation of a nonideal phase modulator in a fibre-optic gyroscope is investigated. Theoretical analysis and experimental observation show that there is a definite ?/2 phase difference between this noise and the Sagnac signal at the modulation frequency.

Influence of termination and transfer on molecular weight distribution of polymers, 6. Chain transfer to monomer and spontaneous termination†

Abstract: In the previous parts of this series, a mathematical procedure was developed for the derivation of molecular size distribution functions of polymers generated in several ionic polymerizations. This paper follows this mathematical procedure to treat theoretically the kinetics of cationic and anionic polymerizations with instantaneous initiation, chain transfer to monomer, and spontaneous termination. The expressions of molecular size distribution functions and other molecular parameters are derived rigorously. Moreover, the simultaneous influence of chain transfer to monomer and spontaneous termination on molecular size distribution is illustrated by means of several numerical examples.

Influence of termination and transfer on molecular weight distribution of polymers, 2†. Radical-radical termination and monomer chain transfer

Abstract: A non-steady state kinetic treatment is rigorously performed for the free radical polymerization with instantaneous initiation, monomer chain transfer and radical-radical termination. An explicit derivation of the molecular weight distribution function is given, and the expressions for other molecular parameters are provided. By means of the formulae given in this paper, the values of the molecular parameters of the polymer generated can be calculated from the initial conditions of polymerization and monomer conversion or reaction time.

Study of Material Dispersion in Amorphous Silica Optical Fibers

Abstract: A study is made of the material dispersion in a-SiO2 optical fiber material over the infrared region. A model of two series of independent oscillators is proposed to describe phonon and electron contributions to material dispersion, and linear response theory is used to analyze the interactions of light with matter. Expressions and curves are obtained for the dispersion of a-SiO2 including the zero dispersion wavelength, which is proved to be related to the intrinsic structures of both, phonons and electrons. The important physical content of empirical formulae most in use for the dispersion is also given. Es wird die Materialdispersion in optischem a-SiO2-Fasermaterial im Infrarotbereich untersucht. Ein Modell von zwei Serien von unabhangigen Oszillatoren wird zur Beschreibung der Beitrage der Phononen und Elektronen zur Materialdispersion vorgeschlagen und eine lineare Response-theorie wird benutzt, um die Wechselwirkungen von Licht mit Materie zu analysieren. Ausdrucke und Kurven fur die Dispersion von a-SiO2, die die Null-Dispersionswellenlange einsehliesen, wer-den erhalten und es wird bestatigt, das sie mit der intrinsischen Struktur der Phononen und Elektroneu verknupft ist. Der wesentliche physikalische Gehalt der am haufigsten benutzten empirischen Formeln fur die Dispersion wird ebenfalls angegeben.

Influence of Termination and Transfer on Molecular Weight Distribution of Polymers. IV. Impurity Termination

Abstract: The effect of impurity termination on molecular size distribution for anionic polymerization with instantaneous initiation is discussed. In order to derive rigorous expressions for the molecular size distribution function and other molecular parameters, this paper follows a mathematical procedure which has proved to be useful for the theoretical treatment of the kinetics of polymerizations in the previous parts of this series. The variation of all molecular parameters with the extent of polymerization is illustrated.

Frequency-doubling PFM system to prolong the distance of optical fibre TV programme transmission

Abstract: In the square-wave PFM system for transmission of TV programmes through optical fibres, square-wave PFM pulses are generated at the transmitter with a relatively low centre frequency, whereas double-frequency equal-width narrow pulses are produced in the receiver before the demodulating low-pass filter, at both the rising and falling edges of the transmitted pulses. The use of the frequency-doubling technique in such a system results in narrow transmission bandwidth and high receiver sensitivity, thus prolonging the transmission distance significantly as compared with ordinary PFM. In the experiment, the system is operated at 1.3 μm with multimode fibre having bandwidth 700 MHz km, a laser diode as optical source and a PIN/FET as detector. It can effectively transmit the high-quality broadcast TV programme with accompanying sound channel to a distance of 50.7 km. Experimental results are: receiver sensitivity −40 dB m, weighted SNR for video 59.3 dB, differential gain and differential phase less than 1% and 1°, respectively.

A new approach to the restoration of an image blurred by a linear uniform motion

Abstract: The limited size of a picture prevents us from realizing the advantage of the Fourier transform of its gray scale function. So Wiener filtering and the related restoration conclusions are invalid in principle. The restoration problem must be accomplished by using the boundary condition which is constructed by the point spread function. Introducing a statistical method to recover the boundary condition, we can restore the linear uniform motion blurred picture with satisfaction. In this case a parameter estimation based on maximizing the likelihood function is used in an endeavor to recapture the lost information. The complexity due to boundedness of picture size is hard to treat when we want to determine some facts about the parameters of the moved picture.

Optical measurement of velocity and acceleration with colour coding

Abstract: By using a white light source and based on the self correlation effect of a group of moving particles, a method is proposed for measuring the velocity and acceleration of the particles. This velocity can be colour coded. A simple theoretical analysis is given and a simulation experiment is presented. The method is simple and economic.

The C.L.m-δ equation of superplasticity

Abstract: In the fundamental equation of superplastic flow, σ = kέm, έ is the strain rate, σ is the flow stress,m is the strain-rate sensitivity index of flow stress, andk is a material constant. Bothm andk vary with increase in strain (δ). Therefore, we can have m0 (≠0), mI (mI1,m,I2,mI3,....), mF; k0 (≠0), kI (kI1,kI2,kI3,.... ), kF values corresponding to the initial strain δ0 (= 0.00 pct), the strain at any instant during stretching, δI (δI1, δI2, 8δI3,....), and the total elongation, δF, at fracture, respectively. The curves expressing the dependence ofm andk on δ can be called them-k- δ orm-C- δ or simply them- δ curves. All these curves can be classified into types and can be expressed by the C. L.m- δ equation derived by the present author: δ(pct) = [Cέ(m- m0 - 1] × 100 whereC = k0+ dk0/k0,m = m0 andC = k0/k0= 1, when δ = δ0;m = mI, andC = CI= kI/k0 when δ= δI;m = mF andC = CF= kF/k0, when δ = δF. By means of this equation, not only the total elongation at fracture but also the strains at any instant during stretching of a material can be predicted, if the correspondingm values are known.

Dependence of total elongations of superplastic materials onm

Abstract: The uniform stretching and thus the high total elongation of superplastic materials have been considered as the result of their highm values in the fundamental equation, σ = kέm, of superplastic flow. The relationships between them values and the total elongations including the experimental curves and the equations obtained for expressing them have been reviewed. The incorrect consideration ofim as a constant in the derivation of these equations and the illogical use ofm value corresponding to the strain of 30 to 50 pct (i.e., m30to50pct) for establishing these curves and for the confirmation of these equations have been analyzed and criticized.

Existence and uniqueness of global strong solutions of two models in atmospheric dynamics

Abstract: In this paper, the author proves by the methods of energy estimates the existence and uniqueness of global strong solutions of barotropic nondivergent model and baroclinic quasi-geostrophic quasi-nondivergent model. The two models are fundamental ones in atmospheric dynamics. The results here generalize the outcome given by the author in [3]–[5] and verify a conjecture posed by Zeng Qing-cun in [1].

A new approach to decentralized control of job scheduling

Abstract: This paper proposes a new approach to improve the existing techniques and algorithms for decentralized control of a multiprocessor system Each processor in the model proposed can either be a controller or a controllee and resides in one of the following statuses: User, System, Blocked and Idle, similar to a process in an operating system Job scheduling strategies are based on the concept of confliction vectors stored in a shared memory Conventional task scheduling strategies such as that with MINIMAX criterion can still be employed to achieve both interprocessor communication minimization and processor load balancing The new approach combines the idea concerning distributed processing and pipelining It has extensibility and strong fault-tolerant capacity, and shows to be of practical use

A Technique for Estimating Wave-induced Motion Responses of a Crane Barge Semisubmersible

Abstract: As an extension of the current twin-hull semisubmersible, a mono-hull crane barge semisubmersible has been developed based on a concept [1] of increasing the displacement together with an increase in waterplane area and a reduction of the width in order to maintain both the motion behaviour and the operation property.