Showing papers by "Southeast University published in 1995"

Dynamic learning rate optimization of the backpropagation algorithm

Abstract: It has been observed by many authors that the backpropagation (BP) error surfaces usually consist of a large amount of flat regions as well as extremely steep regions. As such, the BP algorithm with a fixed learning rate will have low efficiency. This paper considers dynamic learning rate optimization of the BP algorithm using derivative information. An efficient method of deriving the first and second derivatives of the objective function with respect to the learning rate is explored, which does not involve explicit calculation of second-order derivatives in weight space, but rather uses the information gathered from the forward and backward propagation, Several learning rate optimization approaches are subsequently established based on linear expansion of the actual outputs and line searches with acceptable descent value and Newton-like methods, respectively. Simultaneous determination of the optimal learning rate and momentum is also introduced by showing the equivalence between the momentum version BP and the conjugate gradient method. Since these approaches are constructed by simple manipulations of the obtained derivatives, the computational and storage burden scale with the network size exactly like the standard BP algorithm, and the convergence of the BP algorithm is accelerated with in a remarkable reduction (typically by factor 10 to 50, depending upon network architectures and applications) in the running time for the overall learning process. Numerous computer simulation results are provided to support the present approaches. >

Second-order elastic analysis of frames using single imperfect element per member

Abstract: In practical stability design and analysis of steel members and structures, one must allow for member imperfection. Various national design codes impose different values of initial imperfection for member-strength determination, such as 0.001 of the member length in the 1986 Load and Resistance Factor Design Specification for Structural Steel Buildings . This paper presents a new method of including the effects of initial imperfection in the element stiffness without needing to adopt a curved-element formulation, which is deficient for members under high axial load, or to divide a member into two or more straight elements in order to simulate member imperfection. A very considerable savings and convenience in data-manipulation effort and computer time can be achieved when using the proposed element.

On the local minima free condition of backpropagation learning

Abstract: It is shown that if there are P noncoincident input patterns to learn and a two-layered feedforward neural network having P-1 sigmoidal hidden neuron and one dummy hidden neuron is used for the learning, then any suboptimal equilibrium point of the corresponding error surface is unstable in the sense of Lyapunov. This result leads to a sufficient local minima free condition for the backpropagation learning. >

The synthesis and characterization of HgBa2Ca2Cu3O8+δ superconductors with substitution of Hg by Pb

Abstract: We have successfully fabricated ceramic superconductors of Hg-1223 with substitution of Pb for Hg, i.e. Hg1−xPbxBa2Ca2Cu3Oy, by using encapsulation and short time annealing techniques. Samples fabricated in this manner may have nearly single phase structure and some enhancement of Tc can be achieved through this method. The materials of this ceramic with x ranging from 0 to 0.5 exhibit high-temperature superconductivity at temperatures falling in the range from 103 to 135 K. The sample with optimum doping of Pb of x = 0.34 and ° = 0.40 has a highest Tc of 135 K, and its diamagnetic onset temperature Tcdia = 143 K. The composition of this sample has been found experimentally and is specified by a formula of Hg0.66Pb0.34Ba2Ca1.98O8.4. The valence number for the copper constituent is given by V Cu = 2.30 . X-ray diffraction (XRD), transmission electron microscope (TEM) and electron probe microanalyzer (EPMA) analyses have been carried out for detailed investigation. Results indicate that the critical temperature for samples which were post-annealed with either oxygen flow or in high pressure of oxygen gas was increased, while that for those annealed in argon flow was decreased. Furthermore, the as-prepared samples were slightly in the under-doped state with respect to the vacancy. It was shown that Tc parabolically depends on the valence state of copper.

Circular groove guide for short millimeter and submillimeter waves

Abstract: A new type of groove guide, circular groove guide, has been designed for use as a low losses, high power handling, low dispersion and single mode transmission medium in the short millimetric and submillimetric waves ranges. The characteristic equations of TE modes and TM modes have been developed and the propagation characteristics of the fundamental mode have been discussed. Experimental measurements are in good agreement with theoretical results. >

Mechanical properties of Fe3Al-based alloys with cerium addition

Abstract: Small amount of cerium addition to Fe3Al-based alloys results in enhancement of ductility and strength at ambient temperature. The improvements of tensile properties and creep resistance at high temperature of 600 °C can also be achieved by combined addition of cerium with molybdenum, zirconium or niobium. Cerium addition changes the fracture mode of Fe3Al-based alloys from transgranular cleavage or mixed transgranular cleavage and intergranular fracture to one of transgranular cleavage with portions of dimple fracture.

Folded waveguide circuit for broadband MM wave TWTs

Abstract: In millimeter wave band, the folded waveguide circuit exists some advantages such as wide operating frequency band, high mechanism strength, better heat disspation, easy fabrication and lower cost. It is expected that contradictory between broadband and high power in millimeter wave range can be solved by using the folded waveguide circuit. Computational results of dispersion character and coupling impedance of the folded waveguide are given. It is shown that the folded waveguide has wide bandwidth character in millimeter wave band.

Analysis and synthesis of fuzzy closed-loop control systems

Abstract: In this paper, the sufficient and necessary conditions on stability of fuzzy closed-loop control systems are formulated. Based on the sufficient condition of stability, an algorithm is presented to synthesize stable fuzzy controllers. An example for synthesizing a fuzzy control system is given to show that the method is available. >

Self-Equilibrating Element for Second-Order Analysis of Semirigid Jointed Frames

Abstract: An accurate pointwise equilibrating polynomial element with springs connected to its ends to model semirigid connections is derived. The formulated element and coded computer program for second-order nonlinear analysis of flexibly jointed steel frames is employed to study a variety of problems using one element per member, which is not possible by the conventional cubic Hermitian function and most of the currently available elements. When incorporated into a nonlinear-analysis computer program, the versatility of the program is greatly improved as the convergence rate is increased, and the modeling effort for accurate solution is reduced considerably because the element stiffness remains accurate under high axial load. The capability of the proposed element in handling a harsh benchmark problem is also verified in one of the examples.

TEM observation of intergrowth structures in the HgBa2Ca2Cu3Oy ceramic superconductor

Abstract: Intergrowth structures, which occur in the HgBa 2 Ca 2 Cu 3 O y ceramic superconductor, were observed by means of transmission electron microscopy (TEM). There are at least two types of intergrowth structure: Hg-1212/Hg-1223 and Hg-1223/Hg-1234. The congruence relationships for these intergrowth structures are respectively: 〈1 1 0〉 Hg-1212 |〈1 1 0〉 Hg-1223 , {0 0 1} Hg-1212 |{0 0 1} Hg-1223 ; and 〈1 1 0〉 Hg-1223 |〈1 1 0〉 Hg-1234 , {0 0 1} Hg-1223 |{0 0 1} Hg-1234 . For a stable intergrowth structure, the total strain energy density should have a minimum value. The strain energy density consists of two parts: the tensile strain energy density U t and the shear strain energy density U s . The tensile strain energy density U t stored in the crystal can be expressed in terms of the ratio between the numbers of matching slabs, i.e. f i = N i / N , where N i is the number of slabs corresponding to Hg-12( n i −1) n i , and N is the number of slabs corresponding to the matrix, i.e. Hg-12( n −1) n . The plots of U t vs. f i = 1.2498 and f i = 0.8272 for intergrowth structures of Hg-1212/Hg-1223 and Hg-1234/Hg-1223, respectively. As was observed from the TEM micrograph, two immobile dislocations can be created by an appropriate combination of intergrowth structures of Hg-1212/Hg-1223 and Hg-1223/Hg-1234. A model for the formation of these immobile dislocations is presented.

A study of interlayer coupling in Co/Cu multilayers

Abstract: Co(22 A)/Cu multilayers with Cu thicknesses varying from 6 to 40 A are studied by vibrating‐sample magnetometry and ferromagnetic‐resonance spectroscopy (FMR). The magnetization was found to increase with decreasing Cu thickness, whereas the linewidth of the uniform mode of the FMR was found to decrease. This is attributed to the spin polarization of the Cu layers due to interlayer coupling and its effect on the lowered dimensionality of the Co layers. We also observed a peak on the high‐field side of the uniform FMR mode, which we attribute to antiparallel coupling of adjacent ferromagnetic layers producing an ‘‘optical’’ mode.

Ray tracing on extended hemispherical and elliptical silicon dielectric lenses

Abstract: In this paper, extended hemispherical and elliptical silicon dielectric lenses are compared by means of ray tracing. It is shown that the optical focuses of two lenses are not at same position though the elliptical lens is synthesized from an extended hemispherical lens by carefully choosing a particular extension length as stated in ref[1]. It may be used to explain why the best compromise between alignment, directivity and Gaussian-coupling effciency will be obtained if the feed antenna is placed at the region between 2.2 mm and 2.4 mm of extension length (for 13.7 mm diameter lens, dielectric contant = 11.7).

Scattering of electromagnetic waves from a chiral cylinder of arbitrary cross section — GMT approach

Abstract: In this article the generalized multipole technique (GMT) is formulated to obtain the scattering response of a chiral cylinder of arbitrary cross section. The convergence of GMT was verified, and the accuracy of GMT was recognized by comparing with the eigenfunction expansion method. © 1995 John Wiley & Sons, Inc.

Effect of niobium addition on the mechanical properties of Fe3Al-based alloys

Abstract: Alloys based on Fe{sub 3}Al are of interest because of their excellent oxidation resistance and low cost. However, low strength above 600 C and a lack of ductility at room temperature limit their use as structural materials. The purpose of the present paper is to investigate the effect of variations of niobium concentration in the polynery alloy of Fe-28Al-5Cr-0.5Mo-0.05B-0.05Zr- (up to 0.8Nb) on mechanical properties at room temperature (RT) and high temperature of 600 C. It was found that small amounts (0.5--0.8at%) of niobium addition to the polynery alloys based on Fe{sub 3}Al (Fe-28Al-5Cr-0.5Mo-0.05Zr-0.05B) increases the yield strength and creep resistance greatly but is not beneficial to room temperature ductility. Results of microanalysis indicate that the addition of niobium causes the formation of a lot of precipitates with complex compositions which strengthen both matrix and grain boundaries.

A new multilayer planar PVDF standard hydrophone and its applications

Abstract: A new type of PVDF hydrophone, the multilayer planar PVDF hydrophone, is described. The hydrophone disturbs measured acoustic fields very little and has a high sensitivity. The noise-equivalent pressure of the hydrophone is 45 dB re 1 /spl mu/ Pa per Hz bandwidth. The working frequency range of the hydrophone is 20 kHz/spl sim/4 MHz. In the range 100 kHz/spl sim/1 MHz, the hydrophone has a flat frequency response with sensitivity -205 dB /spl plusmn/1.5 dB (0 dB=1 V//spl mu/Pa). In this range, the hydrophone has been used for five years as a standard one. Two other applications (measurements of noise spectra and ultrasonic imaging) are also reported. >

Extended SSH model approach to dopyballsC 58 B 2 andC 58 N 2

Abstract: The Su-Schrieffer-Heeger (SSH) model has been extended to study electronic properties of DopyballsC 58 B 2 andC 58 N 2. It is proposed that self-consistent solutions for electronic wave functions should satisfy some symmetry conditions even though the icosahedral symmetryC 60 has lost by doping. The present numerical results are compared with those obtained from a selfconsistent-field molecular-orbital (SCF-MO) method, most of them being in good agreement with each other. However, for aC 58 B 2 isomer in which twoB atoms are on opposite sides of the cage, our result for electronic energy levels differs quite from the SCF-MO result. We discuss this difference from a viewpoint of the symmetry requirement.

Deformation Properties of TiNi Shape Memory Alloy

Abstract: In order to describe the deformation properties due to the martensitic transformation and the R-phase transformation of TiNi shape memory alloy, a thermomechanical constitutive equation considering the volume fractions of induced phases associated with both transformations is developed. The proposed constitutive equation expresses well the properties of the shape memory effect, pseudoelasticity and recovery stress

Stability of CNN with opposite-sign templates and nonunity gain output functions

Abstract: The stability of a cellular neural network (CNN) with opposite-sign templates and a non-unity gain or cyclic voltammogram output function is studied. In the CNN's stable states, new connected component detection structures 1 and 2 (NCCD-1 and NCCD-2) and two thinning-like structures (TL-1 and TL-2) have been discovered. >