Thermal properties,adhesive strength,and optical transparency of cyclolinear poly(aryloxycyclotriphosphazenes)

Four cyclolinear poly(aryloxycyclotriphosphazenes) derived from poly[4,4′‐(isopropoylidene)diphenoxytetrachlorocyclotriphosphazene] and poly[4,4′‐(hexafluoroisopropylidene)diphenoxytetrachlorocyclotriphosphazene] were synthesized from the reaction of hexachlorocyclotriphosphazene (HCP) with 4,4′‐(isopropylidene)diphenol (bisphenol A) or 4,4′‐(hexafluoroisopropylidene)diphenol (bisphenol AF) in molar ratio 1 : 1 via a one‐step condensation polymerization. Subsequent reaction of the resulted chlorine‐bound polymers with adequate amount of the sodium salts of 4‐methoxycarbonylphenoxide or 4‐propoxycarbonylphenoxide yielded the corresponding chlorine‐free polymers, [poly(tetra‐4‐methoxycarbonylphenoxy)‐4,4′‐(isopropoylidene)diphenoxy cyclotriphosphazene] (MBACP), [poly(tetra‐4‐propoxycarbonylphenoxy)‐4,4′‐(isopropoylidene)diphenoxycyclotriphosphazene] (PBACP), [poly(tetra‐4‐methoxycarbonylphenoxy)‐4,4′‐(hexafluoroisopropylidene)diphenoxycyclotriphosphazene] (MBAFCP), [poly(tetra‐4‐propoxycarbonylphenoxy)‐4,4′‐(hexafluoroisopropylidene)diphenoxycyclotriphosphazene] (PBAFCP), respectively. The chemical structures were characterized by Fourier transformer infrared, ¹H, and ¹³C‐NMR. Thermal properties of polymers were investigated using DSC and TGA analysis. The obtained polymers were thermoplastic, having moderate T_g values in the range of 26–78°C and good thermal stability up to 350°C in N₂ and O₂ gases. The thermal decomposition of the isopropylidene‐containing polymers is a one‐step process, while that of hexafluoroisopropylidene‐containing polymers is a two‐step process. However, presence of the latter group in the polymers backbone showed negligible effects on the thermo‐oxidative stability. The adhesive strength was measured by lap‐shear strength test on glass–glass bonded joint and found to be in the range of 1.78–2.62 MPa, this property may be attributed to the physical interactions between glass–glass interfaces and the polar‐pendant units present at the polymers backbone. The products showed high optical transparency when they applied between two glass surfaces, the adhesive layers were colorless, with the UV cut‐off wavelength of 300–302 nm, and the maximum transparency of about 90% was observed within the wavelengths range of 400–700 nm. Because of their properties, the cyclolinear poly(aryloxycyclotriphosphazenes) synthesized in this study are recommended as potential candidates for high thermally stable, transparent adhesives required in industrial applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Small-angle coherent gamma-ray scattering at 662 keV for Pb and Sn

Discrepancies between theory and experiment have been reported in the small-momentum-transfer region x < 10 Å⁻¹ for the coherent scattering of moderate-energy photons. In the present experiment an investigation has been made of the performance of each of the primary components of an annular target setup, arranged for 662 keV photon scattering at angles in the range 5°–15°. The conventional double-cone primary-beam stop is found to significantly degrade the full-energy peak-to-valley ratio compared to that obtained with a parallel-sided arrangement. Asymmetry has been found in the response of the detector to an auxiliary point source radially distributed over the scattering plane. Appropriate experimental procedures and corrections have been adopted in obtaining differential cross sections of reduced uncertainty. Results obtained on the basis of present measurements are found to be in accordance with theory. A reanalysis of an earlier set of experimentally determined differential cross sections has been produced.     

Application profile for ISDN

The authors examine some key data processing applications to be used in conjunction with the voice and facsimile services as a platform for deploying ISDN (integrated services digital network) in North America. Special emphasis is placed on the emerging standards of both Accredited Standards Committees (ACS) T1 and X3 in an attempt to harmonize the computer and telecommunication industries towards providing the user with an integrated platform that is vendor-transparent and ubiquitous. This generic platform, which spans a large spectrum of businesses, is presented as a base context for defining user-specific needs and incubating the applications that directly relate to businesses. Distributed transaction processing, electronic data interchange, information retrieval, electronic mail, and file transfer together with seven supplementary services for voice and G4 facsimile are proposed for ISDN deployment in the marketplace. The authors describe how the relevant standards may be exercised through the various ISDN channels and emphasize the value of the North American ISDN User's Forum for commercializing this platform     

Robust Recursive Inverse Adaptive Algorithm in Impulsive Noise

The recently proposed Recursive Inverse (RI) algorithm has shown a significant performance improvement compared to that of the Recursive Least Squares (RLS) algorithm, in various noise environments. However, both algorithms fail to converge in certain impulsive noise environments, especially if the Signal-to-Noise Ratio (SNR) is low. In this paper, a Robust RI algorithm is proposed. Analytical results show that robustness against impulsive noise is achieved by choosing the weights on the basis of the L ₁ norms of the autocorrelation matrix and the cross-correlation vector. Simulation results confirm that the proposed algorithm provides an improved performance, with a reduction in computational complexity, compared to those of the RLS and the Robust RLS in white and correlated impulsive noise.     

Varistor Behavior at Twin Boundaries in ZnO

The electrical behavior of commercial ZnO varistor devices has been examined with voltage contrast microscopy and point contact dc electrical measurements. Nonlinear voltage-dependent behavior has been observed across both of the major crystalline boundary types present in the system: Bi₂O₃ layer containing ZnO grain boundaries (or grain boundaries) and antimony spinel layer internal ZnO inversion twin boundaries (or twin boundaries). Twin boundaries, which bisect practically every grain in a typical commercial device, possess potential barriers with higher average breakdown voltages than do grain boundaries. Certain zinc antimonate spinel (Zn₇Sb₂O₁₂) grains are electrically isolated from the matrix, whereas others are conductive within the matrix.     

Parametric study for concrete cover separation failure of retrofitted SNSM strengthened RC beams

ABSTRACT

The side near-surface mounted (SNSM) method is a new flexural strengthening method for reinforced concrete (RC) beams which was proposed to allow near-surface mounted (NSM) strengthening to be applied on beams with small width. As a relatively new strengthening method, further studies are needed to determine the effects of strengthening parameters on the flexural performance of RC beams. In response to that, this paper presents a parametric study on the concrete cover separation failure of SNSM strengthened beams using a simulation method based on the moment-rotation (M/θ) approach.     

Sparse leaky‐LMS algorithm for system identification and its convergence analysis

In this paper, a novel adaptive filter for sparse systems is proposed. The proposed algorithm incorporates a log‐sum penalty into the cost function of the standard leaky least mean square (LMS) algorithm, which results in a shrinkage in the update equation. This shrinkage, in turn, enhances the performance of the adaptive filter, especially, when the majority of unknown system coefficients are zero. Convergence analysis of the proposed algorithm is presented, and a stability criterion for the algorithm is derived. This algorithm is given a name of zero‐attracting leaky‐LMS (ZA‐LLMS) algorithm. The performance of the proposed ZA‐LLMS algorithm is compared to those of the standard leaky‐LMS and ZA‐LMS algorithms in sparse system identification settings, and it shows superior performance compared to the aforementioned algorithms. Copyright © 2013 John Wiley & Sons, Ltd.