Interfacial effects on stress distribution in model composites

Raman mechanical spectroscopy was used to examine interfacial effects on the stress distribution in model polydiacetylene fiber/epoxy composites. Epoxy release agents were coated on fiber surfaces to modify the interfacial adhesion properties. The modified fiber surfaces were then characterized by scanning electron microscopy and x-ray photoelectron spectroscopy as well as optical microscopy. No difference in the maximum stress value or stress distribution was observed for the two types of fibers, coated or uncoated, used in composites. This suggests that adhesion properties at the composite interface do not affect tensile stress transfer efficiency nor, therefore, the composite tensile modulus along the fiber axis direction in uniaxial composites. Experimental data were also compared with theoretical calculations assuming perfect bonding between fiber and matrix, and idealized frictional force transfer mechanism at the fiber–matrix interface.     

The Sheffer group and the Riordan group

We define the Sheffer group of all Sheffer-type polynomials and prove the isomorphism between the Sheffer group and the Riordan group. An equivalence of the Riordan array pair and generalized Stirling number pair is also presented. Finally, we discuss a higher dimensional extension of Riordan array pairs.     

Low-temperature property investigation of the lead indium-niobate-lead nickel-niobate solid solution

The complex perovskite solid solution (1−x) Pb(In_1/2Nb_1/2)O₃-(x) Pb(Ni_1/3Nb_2/3)O₃ has been successfully prepared by the Columbite precursor method. The temperature dependencies of the dielectric constant and pyroelectric coefficient were measured between −261 and 200 °C. Relaxor ferroelectric behavior has been noticed in all compositions across the solid solution. The room-temperature electrostrictive coefficient, Q₃₃, was 1.83×10⁻² C²/m⁴ for x=0.10. No room-temperature piezoelectric activity was detected; however, upon cooling to −261 °C the maximum coupling coefficients k_p=29%, k_t=11%, and k₃₃=31% were observed for the composition x=1.00.     

Pythagorean euclidean four point properties

Characterizations of real inner product spaces among a class of metric spaces have been obtained based on homogeneity of metric pythagorean orthogonality, a metrization of the concept of pythagorean orthogonality as defined in normed linear spaces. In the present paper a considerable weakening of this hypothesis is shown to characterize real inner product spaces among complete, convex, externally convex metric spaces, generalizing a result of Kapoor and Prasad [9], and providing a connection with the many characterizations of such spaces using euclidean four point properties.     

The Recognition of Double Euler Trails in Series-Parallel Networks

Given a series-parallel network (network, for short)N, its dual networkN′ is given by interchanging the series connection and the parallel connection of networkN. We usually use a series-parallel graph to represent a network. LetG[N] andG[N′] be graph representations ofNandN′, respectively. A sequence of edgese₁, e₂,…,e_kis said to form a common trail on (G[N], G[N′]) if it is a trail on bothG[N] andG[N′]. If a common trail covers all of the edges inG[N] andG[N′], it is called adouble Euler trail.However, there are many different graph representations for a network. We say that a networkNhas a double Euler trail (DET) if there is a common Euler trail for someG[N] and someG[N′]. Finding a DET in a network is essential for optimizing the layout area of a complementary CMOS functional cell. Maziasz and Hayes (IEEE Trans. Computer-Aided Design9(1990), 708–719) gave a linear time algorithm for solving the layout problem in fixedG[N] andG[N′] and an exponential algorithm for finding the optimal cover in a network without fixing graph representations. In this paper, we study properties of subnetworks of a DET network. According to these properties, we propose an algorithm that automatically generates the rules for composition of trail cover classes. On the basis of these rules, a linear time algorithm for recognizing DET networks is presented. Furthermore, we also give a necessary and sufficient condition for the existence of a double Euler circuit in a network.     

Stirling渐进公式的一个新的构造证明

本文用简易的分析工具，对ｎ！给出了一个精确等式，从而导出Ｓｔｉｒｌｉｎｇ渐近公式（２）的一个新的简短证明.     

Very high coercivities of top-layer diffusion Au/FePt thin films

The Au/FePt samples were prepared by depositing a gold cap layer at room temperature onto a fully ordered FePt layer, followed by an annealing at 800 °C for the purpose of interlayer diffusion. After the deposition of the gold layer and the high-temperature annealing, the gold atoms do not dissolve into the FePt Ll₀ lattice. Compared with the continuous FePt film, the TEM photos of the bilayer Au(60 nm)/FePt(60 nm) show a granular structure with FePt particles embedded in Au matrix. The coercivity of Au(60 nm)/FePt(60 nm) sample is 23.5 kOe, which is 85% larger than that of the FePt film without Au top layer. The enhancement in coercivity can be attributed to the formation of isolated structure of FePt ordered phase.