Showing papers by "Sichuan University published in 1996"

Generalized contraction mapping principle and differential equations in probabilistic metric spaces

Abstract: A new generalized contraction mapping principle in probabilistic metric spaces is obtained. As an application, we utilize this principle to prove the existence theorems of solutions to differential equations in probabilistic metric spaces. All the results presented in this paper are new.

Investigations of the temperature dependence of the electron paramagnetic resonance g-factor for the MgO: crystal

Abstract: Detailed theoretical studies of the temperature dependence of EPR g-factor for the MgO:Cr3+ crystal have been made by considering both the static contribution due to the thermal expansion of crystal and the vibrational contributions due to the electron-phonon (including the acoustic and optical phonons) interaction. The static contribution is calculated from the macroscopic thermodynamic method and the microscopic crystal-field method. The results from both methods are close to each other, suggesting that the two methods are applicable to studies of temperature dependence of the g-factor. The vibrational contribution due to acoustic phonons is obtained by using a Debye model for the lattice vibrations, and that due to optical phonons is calculated by use of a single-frequency model. The calculated results show that, for the g(T)-factors at various temperatures, the static contribution is dominant; however, for the temperature dependence of the g-factor, i.e. dg/dT, the vibrational contributions are large and should be taken into account.

Quark delocalization, color screening, and N-N intermediate range attraction: P waves.

Abstract: The quark delocalization and color screening model is used to study the {ital N}-{ital N} interaction of spin-isospin (00) and (11) channels The predicted {sup 1}{ital p}{sub 1} phase shifts qualitatively fit the phase shift analysis of scattering data The {sup 3}{ital p}{sub {ital ls}} phase shifts are enhanced by the quark delocalization effect, but the {sup 3}{ital p}{sub {ital c}} is too strongly repulsive {copyright} {ital 1996 The American Physical Society}

Correction of substrate effect in the measurement of 8-25-keV electron-impact K-shell ionization cross sections of Cu and Co elements.

Abstract: The experimental measurement of electron-impact K-shell ionization cross sections of Cu and Co elements within the energy region 8--25 keV was reported. The influence of a substrate of thin targets on ionization cross sections has been corrected by a method based upon a bipartition model of electron transport [Z. M. Luo, Phys. Rev. B 32, 812 (1985); 32, 824 (1985)]. The measured cross sections are in good agreement with existing data and are well reproduced by the empirical formula of Green and Cosslett [Proc. Phys. Soc. London 78, 1206 (1961)]. \textcopyright{} 1996 The American Physical Society.

Preferred orientation of plasma sprayed hydroxyapatite coatings

Abstract: The long-term stability of hydroxyapatite (HA) coatings has been under investigation for a long time. The evaluation of crystallinity is important since a relationship exists between the degree of crystallinity and the degradation by in vitro cellular reaction. However, the choice of a representative peak to calculate the crystallinity is the subject of some controversy with the (2 1 1) peak and the (0 0 2) peak being the most commonly analysed peaks. Thus the determination of the degree of crystallinity may be biased due to preferred orientation (texture) in the coatings. Therefore, the dependence of texture on thickness during plasma spraying was investigated by the calculation of a texture coefficient (TC). Experiment results showed that the TC value of the (0 0 2) and (0 0 4) peaks increased with thickness and that the TC value in the (2 1 1) peak decreased. This was caused by a high temperature gradient during spraying and also the growth direction for a hexagonal system. It was observed that appropriately controlled temperature increases during annealing did not bring about notable texture to the recrystallized crystallites. However, if the temperature gradient was high during annealing, notable (0 0 2) texture can exist. The effect of particle size on the texture was also investigated.

Temperature-programmed FT-IR study of the adsorption of CO and co-adsorption of CO and H2 on NiAl2O3

Abstract: The adsorption of CO and co-adsorption of CO and H 2 on Ni Al 2 O 3 catalyst prepared by a distinct procedure were studied by means of FT-IR technique. The study shows that only one kind of CO adsorption site — the linear CO adsorption site — exists on the Ni Al 2 O 3 catalyst used in present work. Temperature-programmed heating of CO adspecies in CO atmosphere reveals that the disproportionation of linearly adsorbed CO may occur at above 473 K. In H 2 + CO atmosphere, a new IR band centered near 1910 cm −1 emerges, the intensity of which increases and decreases concomitantly with that of the band centered about 2050 cm −1 with increasing temperature, indicating the occurrence of a new adspecies in the dynamic process of CO hydrogenation under reaction conditions. This new adspecies is tentatively ascribed to nickel carbonyl hydride species. The methanation of CO on Ni Al 2 O 3 may occur via a mechanism involving the formation of nickel carbonyl hydride species.

Phase unwrapping techniques for 3D shape measurement

Abstract: This paper gives an overview of phase unwrapping techniques for complex shape measurement. These techniques include phase unwrapping based on binary control mask, phase unwrapping based on ordering reliability, 2D filtering in Fourier transform profilometry, two-frequency grating phase unwrapping, et al.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Adaptive document segmentation and geometric relation labeling: algorithms and experimental results

Abstract: This paper describes a generic document segmentation and geometric relation labeling method with applications to document analysis. Unlike the previous document segmentation methods where text spacing, border lines, and/or a priori layout models based template processing are performed, the present method begins with a hierarchy of partitioned image layers where inhomogeneous higher-level regions are recursively positioned into lower-level rectangular subregions and at the same time lower-level smaller homogeneous regions are merged into larger homogeneous regions. The present method differs from the traditional split-and-merge segmentation method in that it orthogonally splits regions using thresholds adaptively computed from projection profiles.

Toeplitz operators on the polydisk

Abstract: In this paper it is shown that two analytic Toeplitz operators essentially doubly commute if and only if they doubly commute on the Bergman space of the polydisk. Let D be the open unit disk in C. Its boundary is the circle T. The polydisk Dn and the torus T' are the subsets of C' which are cartesian products of n copies D and T, respectively. Let dA(z) be the normalized volume measure on Dn. The Bergman space L 2(Din) is the subspace of L2(Dnn, dA) whose functions are holomorphic in Dn. There is an orthogonal projection P from L2 (D , dA) onto L2(Dn). The Toeplitz operator with symbol f in L'(D n) is defined by Tf(h) = P(f h), for all h E L 2(D n). Two analytic Toeplitz operators Tf and Tg are said to be essentially doubly commuting if TTg TgTf is compact. They are said to be doubly commuting if TTg TgT; = 0. The function theory on the polydisk Dn is quite different from the function theory on the unit disk [R]. One may expect that there should exist some differences in operator theory on the Bergman spaces between on the polydisk and on the disk. In this paper we will show that two analytic Toeplitz operators essentially doubly commute if and only if they doubly commute on the polydisk. But this is false on the disk [AG], [Z]. Observe that T' is only a small part of the boundary of DTn if n > 1. But it is an important part and is called the distinguished boundary of D n. Tn is also a compact group (with componentwise multiplication as group operation) and as such carries a Haar measure. Its dual group is Zn where Z is the integer group. As in [SW] we consider multiple Fourier series on the n-torus Tn. The multiple Fourier series on the n-torus Tn can be viewed as the Fourier transformation on L1 (Tn). For f in L1 (Tin) the Fourier transformation is given by f(m) = j f (x,... , Xn)e%(7 x) da(xi ) ... du(xn) Tn where m' = (ml,... , mn) E zn and (mf, x) = =l mixi and ui(xi) is the normalized Haar measure on T for i = 1,...,n. By Theorem 1.7 in [SW], the Fourier transformation is injective, i.e. if f E Ll(Tn) and f(m) = 0 for all m E Zn, then f 0_ . The main result in this paper is the following theorem. Received by the editors October 6, 1994 and, in revised form, April 21, 1995. 1991 Mathematics Subject Classification. Primary 47B35.

Enantioselective reduction of aromatic ketones with borane catalyzed by (R) -4-thiazolidinecar☐ylic acids or (R) -4-thiazolidine methanol

Abstract: (R) -4-Thiazolidinecar☐ylic acid. (R) -2. 2-dimethyl-4-thiazolidinecar☐ylic acid. S-ethyl- (L) -cysteine and L-methionine as chiral auxiliaries in the enantioselective catalytic reduction of aromatic ketones with borane have been investigated. When (R) -cyclic sulfur-containing α-amino acids were used as auxiliaries. the products secondary alcohols possess the (S) -configuration in contrast to Martens' (R) -2-Amino-1. 1-diphenyl-3- (isopropylmercapto) -1-propanol.

On a fixed point problem of Reich

Abstract: In this paper, we give an affirmative answer to a fixed point problem of S. Reich.

Three-dimensional intensity distribution of focused Bessel-Gauss beams

Abstract: The focusing properties of Bessel-Gauss beams in the apertured case are studied on the basis of the generalized Huygens-Fresnel diffraction integral. Detailed numerical calculation results including the three-dimensional intensity distribution and isophotes (contours of equal intensity) have been given for different Fresnel numbers and truncation parameter of the system.

A refined potential energy function for the electronic ground state of NO2

Abstract: The potential energy surface for the electronic ground state of the NO2 molecule is optimized by means of a variational procedure using the exact vibrational Hamiltonian in the bond length-bond angle coordinates. In the optimization, the potential energy function of S. A. Tashkun and P. Jensen (1994, J. molec. Spectrosc., 165, 173) is taken as the starting point and the observed band origins given by A. Delon and R. Jost (1991, J. chem. Phys., 95, 5686) are involved. The standard deviation of this fitting for the 142 vibrational levels below 9000 cm−1 is 2·08 cm−1, and that of Tashkun and Jensen is 14·28 cm−1 obtained using an exact Hamiltonian. The refined potential is a reasonable approximation to the true potential at energies below the conical intersection.

Nonlinear optimal-variable-aim strategy for improving multimachine power system transient stability

Abstract: The paper presents an integrated excitation and fast valving controller for improving multimachine power system transient stability. The controller is based on an improved optimal-variable-aim strategy. To avoid transferring measurement information around the system, an ‘observation decoupled’ state space model for multimachine power systems, which include a fast valve and an excitation system, is adopted. Simulation studies employed to test the controller have been performed on a four-machine six-bus system. The results show that the controller is effective for transient stability enhancement.

Improved method for HgI2 crystal growth and detector fabrication

Abstract: Instead of the temperature oscillation method (TOM), a modified vapor growth method was applied in this paper to grow large HgI 2 crystals with fewer lattice defects by providing a relatively stable temperature field during growth. And a new processing technique of HgI 2 crystals was developed for detector fabrication by merging solution string-sawing and hand-cleaving. The lattice deformations caused during cleaving were reduced greatly by eliminating passivated layers on the sawed crystal platelets before cleaving.