Showing papers by "Jilin University published in 1991"

Sensitivity Analysis Methods for Coupled Acoustic-Structural Systems Part I: Modal Sensitivities

Abstract: An analytical method is proposed for calculating the sensitivities of the eigenvalues and eigenvectors of coupled acoustic-structural systems for the purpose of reducing vehicle interior noise. The concept of the left and right eigenvectors with regard to the eigenvalue problems of coupled systems is presented first, and four propositions concerning this concept are then proved. Based on these propositions, the formulations for the eigenvalue and eigenvector sensitivity analysis of coupled systems are obtained. It is shown that the new method provides better convergence than the "modal method" and "modified modal method" (extensions of these methods to coupled systems), and it achieves better calculation efficiency than the extended Nelson's method when more than one eigenvector is being considered. The theoretical results and computation equations are verified through application of the method to a coupled acoustic-box structure and an actual vehicle interior noise problem.

Theoretical model for the tensile work hardening behaviour of dual-phase steel

Abstract: The modified Crussard-Jaoul analysis was employed to describe the work hardening behaviour (the ln(dσ/dϵ) vs. ln σ curves) of a 1020 dual-phase steel with quenching and quenching plus tempering treatments and with various volume fractions of martensite ( V m ), which demonsrated that this dual-phase steel exhibits two stages of work hardening in the range of plastic deformation. The modified law of mixture was used to simulate the tensile stress-strain and the ln(dσ/dϵ) vs. ln σ curves for the steel. The simulations were divided in different ways in terms of the deformation state of martensite. For the steel with quenching treatment and with V m V m > 50% and the steel with quenching plus tempering treatments and with V m over the whole test range (33–85%), the work hardening behaviour in the first stage of deformation was well simulated with the assumption that martensite deforms elastically and then deforms partly elastically and partly plastically while ferrite deforms plastically. For the steel in all the above-mentioned cases, the work hardening behaviour in the second stage of plastic deformation was simulated with a model in which both phases deform plastically.

Improved mode-superposition technique for modal frequency response analysis of coupled acoustic-structural systems

Abstract: A new formulation is derived by using an orthogonality condition of a coupled system. An improved compensation technique is then proposed for compensating for the effect of truncated modes, which are the lower and/or higher modes beyond the frequency domain of an MFR analysis

Modelling and kinetic study on radical polymerization of methyl methacrylate in bulk, 1. Propagation and termination rate coefficients and initiation efficiency

Abstract: In this work the exact data of the rate coefficients of propagation kp and termination kt, and initiator efficiency f as well as their variations with conversion during the whole processes of the polymerization of methyl methacrylate in bulk have been measured using electron paramagnetic resonance (ESR) without any assumptions and approximations. kp was calculated directly from the synchronously measured data of the concentration of radicals and polymerization rate. kt was determined under nonsteady-state conditions by using the after-effect technique in the ESR measurement. f for the initiation with dimethyl 2,2′-azoisobutyrate was evaluated from the initiation and termination rates. The ESR spectra show that the polymerization system is in a micro-heterogeneous state and there exist inactive radicals. A model of a diffusion-controlled reaction is proposed.

Sensitivity Analysis Methods for Coupled Acoustic-Structural Systems Part II: Direct Frequency Response and Its Sensitivities

Abstract: An iteration method is proposed here that does not employ an inverse matrix (or triangular resolution) of the impedance matrix of coupled system. An algorithm is then derived for calculating the corresponding freqnency response sensitivity

Development of biosensors for the simultaneous determination of sucrose and glucose, lactose and glucose, and starch and glucose.

Abstract: Sensors for the simultaneous determinations of sucrose and glucose, lactose and glucose, and starch and glucose were prepared by a combination of the enzyme system shown below and an oxygen electrode: The mechanism for separating the substrates with the proposed sensors is based on the time lag arising from reaction and diffusion. Invertase, beta-galactosidase, amyloglucosidase, mutarotase, and glucose oxidase were covalently immobilized on triacetyl cellulose membranes containing 1,8-diamino-4-aminomethyloctane. A glucose oxidase membrane, mutarotase membrane, three sheets of triacetyl cellulose membranes, and invertase, or beta-galactosidase or amyloglucosidase membrane were placed in that order on the tip of the oxygen electrode. Calibration curves for sucrose, lactose, and starch were linear up to 40 mM, 60-180 mM, and 10%, respectively. The simultaneous determination of sucrose and glucose, lactose and glucose, and starch and glucose was possible when the amount of glucose coexised was in the range of 2-16% sucrose, 2.8-8.3% lactose, or 0.1-1% starch. The relative errors were +/-4% for sucrose and +/-3% for lactose in 100 assays. The starch sensor was reused only five times. Each enzyme membrane was fairly stable for more than 10 days.

New Families of M(III)X(V)O4-Type Microporous Crystals and Inclusion Compounds

Abstract: Three new M(III)X(V)O 4 -type families, designated GaPO's, AlAsO's and GaAsO's respectively, with microporous or layered framework structures have been synthesized hydrothermally using various amines and quaternary ammoniums as templates. Unlike AlPO's, almost all known structures of these families possess M(III) bonded to more than four O atoms. The micropores of the 3D frameworks are comparable in diameter to the intermediate and small ones of AlPO's. The templates capable of entering the MXO 4 framework contain not more than 8 carbon atoms for GaPO's and not more than 4 for AlAsO's and GaAsO's. Larger primary amines lead to the formation of layered structures of AlAsO's and GaAsO's.

Quantum chemical calculations on buckminsterfullerene and related structures. II. The electronic structure and spectra of some Cn and CnCa2+ cages

Abstract: In this paper, we will examine the electronic structure and spectroscopy of C 24 ,C 50 ,C 60 , and C 70 . In addition, we will examine C n Ca +2 species, examples of C n M +2 structures that have been discovered experimentally, with M=Ca,Sr,Ba, and La. The fact that C n species bind to but one metal atom has also been taken as strong support for the presence of high-symmetry cage clusters. During this study, we used the INDO/CI spectroscopic model

Convergence rates of law of iterated logarithm for b-valued random variables

Abstract: Let {X, X_n; n≥1} be i.i.d.r.v.'s taking values in a separable Banach space (B,||·||)such that EX=0 and Ef~2(X)+∞, ?∈6B~*, and S_n=X_1+…+X_n for n≥1. The purposeof this paper is to study the rates of convergence to zero of P(inf||Sn/(2nloglogn)~(1/2)-x||≥e) and P(sup inf||S_k/(2kloglogk)~(1/2)-x||≥e) (?e0) under precisely necessary and sufficientconditions. We also give new necessary and sufficient conditions for X to satisfy the boundand compact law of the iterated logarithm, respectively. Our results improve some resultsof Darling and Robbins (1967) as well as Davis (1968) even in the case B=R.

Solving deficient polynomial systems with homotopies which keep the subschemes at infinity invariant

Abstract: By a deficient polynomial system of n polynomial equations in n unknowns we mean a system that has fewer solutions than that predicted by the total degree, or the Bézout number, of the system. If the system is mhomogeneous, the Bézout number can be considerably reduced. In this paper, we introduce a homotopy for numerically determining all isolated solutions of deficient m-homogeneous systems. The initial polynomial system Q is chosen which keeps the subschemes of H(x, t) = (1 t)aQ(x) + tP(x) at infinity invariant when / varies in [0, 1 ).

Performance analysis of cross-spectral density estimator and its applications

Abstract: Because of the noise and zero-drift in a preamplifier, it is difficult to measure a weak signal using the conventional spectral analysis method (a pre-amplifier in series with an FFT analyser). A new approach using a cross-spectral density estimator has been developed and the theoretical analysis demonstrates that the expectation of cross-spectral density is not coherent with the noise and zero-drift of the pre-amplifier; consequently, this method can ensure accurate measurement, even if the measured signal is very weak. Also, the noise in the pre-amplifier may increase the variance of cross-spectral estimation, so that the average periodogram using windowing procedures and a low noise pre-amplifier is necessary. Finally, the thermal noise of a small resistance and a nanovolt sinusoidal signal have been measured; the results are in good agreement with the theoretical values, which means that the method is feasible and accurate for measuring weak signals.

Isotropic polycrystal yield surfaces of b.c.c. and f.c.c. metals: crystallographic and continuum mechanics approaches

Abstract: For the crystallographic approach, isotropic yield surfaces of bcc metals with the ratio of critical shear stress on {112}〈111〉 slip systems to that on {110}〈111〉 slip systems in the range of ( √ 3 2 , 2 √3 ) have been simulated with the Taylor model Isotropic yield surface fcc metals is included as a special case where {112}〈111〉 slip systems are all removed out All the yield surfaces considered are located between the Mises and Tresca criteria; and linear variations of the average size and the “shape” of the isotropic yield surface with the critical shear stress ratio were found For the continuum mechanics approach, using a series of stress transformation functions proposed in the present work, the Hill and the Hershey, Hosford and Hill (HHH) yield function shave been developed to be new yield functions expressed in 6-dimensional stress space The new yield function based on the HHH expression can include the Mises and the Tresca criteria, as well as the isotropic form of the Barlat and Lian (BL) yield function as special cases By comparison of the new yield function with the isotropic yield behaviours of both bcc and fcc metals simulated with the Taylor model, very good agreements are obtained and the parameters in the new yield function are determined in the sense of crystallographic plasticity theory

Stress intensity determination by an experimental−numerical hybrid technique

Abstract: Stress intensity factors are obtained from displacement-prescribed boundary conditions on a subregion containing the crack. The subregion, whose boundary can be any arbitrary contour within the physical structure, is analysed numerically using structural finite elements. Nodal boundary displacements of this subregion are obtained photomechanically using a smoothing finite element representation. The technique requires little experimental information and is unaffected by rigid body motions. It is numerically stable and accurate - even in the presence of significant experimental scatter - and the measured data need not come from the immediate vicinity of the crack. The method's practicality is demonstrated by determining the stress intensity factors in a compact tension specimen from moire-measured displacements at locations away from the crack tip.

Current noise due to generation and recombination of carriers in forward-biased p-n junctions

Abstract: The noise associated with generation and recombination of carriers in p-n junction transition regions was first considered in detail by Lauritzen and by K.M. van Vliet. Their theory is used to explain the g-r noise in the recombination current. They pointed that the noise from generation-recombination centers appears not to be particularly significant in BJTs. However, in this study, we have demonstrated that the g-r noise, caused by generation and recombination of carriers in a p-n junction, exists in both recombination current and diffusion current. By noise measurement and theoretical analysis, in the forward-biased junction we find that the g-r noise in the diffusion current may be much greater than the g-r noise in the recombination current. This is particularly significant for evaluating defects in p-n junctions and for reliability screening of BJTs. However, in the low-biased or reverse-biased junction the g-r noise in the recombination current becomes dominate. Consequently, the Lauritzen and K.M. van Vliet theory is satisfactory.