2,6‐Diamino‐4‐phenylphenol (DAPP) copolymerized polyimides: synthesis and characterization

Novel soluble copolyimides containing phenyl and hydroxyl pendant groups were synthesized from pyromellitic dianhydride (PMDA) and two diamines, 2,6‐diamino‐4‐phenylphenol (DAPP) and 4,4′‐oxydianiline (ODA), in various ratios via thermal imidization. The structures and physical properties of the copolyimides were characterized by FTIR, elemental analysis, DSC, dynamic mechanical analysis (DMA), TGA, a universal testing machine for stress–strain behaviour, and a dielectric analyzer to study the effect of DAPP on the physical properties of the modified polymers. Copolyimides containing more than 40 mol% DAPP were soluble in hot N‐methyl‐2‐pyrrolidone (NMP), dimethylacetamide (DMAc) and dimethylformamide (DMF), and possessed a high glass transition temperature (358 °C) and a high modulus (3.9 GPa). Introduction of the diamine DAPP could also reduce the dielectric constant. A segment of imide linkages could convert to benzoxazole linkages by decarboxylation at temperatures higher than 420 °C under vacuum. Although the heat‐treated polybenzoxazoles (PBOs) exhibited many good properties, they were found to be too rigid and brittle to be processable for microelectronic applications. Copyright © 2005 Society of Chemical Industry     

The impact of the concept of post-industrial society and information society: A citation analysis study

A detailed quantitative, citation study is made on the concepts of Bell, Machlup, and Drucker related to the economic and social effects of the growth of information-based industries.     

Characterization of low-light-level cameras for digitized video microscopy

The use of low-light-level video cameras and solid-state image detectors in conjunction with image digitizers for optical microscopy is increasing dramatically as more people learn about such systems, and as they become more powerful, less expensive, and easier to use. However, there is currently little information available allowing comparison between cameras, or for determining camera suitability for a given experiment. In this paper, we describe a series of tests designed to characterize the performance of low-light-level cameras. The results of these tests should assist in the selection of appropriate cameras for given video microscopy applications.     

Error correction techniques for high-performance differential A/Dconverters

Error correction techniques that overcome several error mechanism that can affect the accuracy of charge-redistribution analog-to-digital converters (ADCs) are described. A correction circuit and a self-calibration algorithm are used to improve the common-mode rejection of the differential ADC. A modified technique is used to self-calibrate the capacitor ratio errors and obtain higher linearity. The residual error of the ADC due to capacitor voltage dependence is minimized using a quadratic voltage coefficient (QVC) self-calibration scheme. A dual-comparator topology with digital error correction circuitry is used to avoid errors due to comparator threshold hysteresis. A fully differential charge-redistribution ADC implemented with these techniques was fabricated in a 5-V 1-μm CMOS process using metal-to-polysilicide capacitors. The successive-approximation converter achieves 16-b accuracy with more than 90 dB of common-mode rejection while converting at a 200-kHz rate     

Mathematical model and tooth surfaces of recess action worm gears with double-depth teeth

In this study, the surface equations of recess action (RA) worm gears with double-depth teeth, generated by a ZN worm-type hob cutter, are proposed. Based on the generation mechanism and the theory of gearing, a mathematical model of a series of worm gears, semi RA, full RA and standard proportional tooth types, with double-depth teeth is developed as the function of design parameters of the ZN worm-type hob cutter. According to the derived tooth surface equations, computer graphs of a series of worm gears with double-depth teeth are plotted. Tooth surface variations of the generated RA worm gears due to the varying pitch line, pressure angle and tooth height of the hob cutter are also investigated.     

Characteristics of heat dissipation from photovoltaic cells on the bottom wall of a horizontal cabinet to ambient natural convective air stream

This study proposes a model to investigate the behaviors of natural convective cooling of photovoltaic cells mounted discretely on the bottom wall of a horizontal cabinet. The effects of Rayleigh number (Ra), dimensionless length of cabinet (C_x), ratio of cabinet wall to air thermal conductivities (K_ef), number of photovoltaic cells (N), emissivity of metal wall (ε_e), and emissivity of glass lens (ε_g) are explored. Furthermore, the importance of thermal interaction between air streams inside and outside the cabinet through conducting wall are examined. The numerical computation domain covers the cabinet and surrounding area, so that the temperature and velocity fields of the combined regions are solved simultaneously. Results show that temperature differences among the photovoltaic cells can be up to 28% for all the investigated cases when 10⁶ ≦ Ra ≦ 10⁸, 5 ≦ C_x ≦ 12.5, 4 ≦ N ≦ 10, 1000 ≦ K_ef ≦ 6300, 0 ≦ ε_e ≦ 0.5 and 0 ≦ ε_g ≦ 0.94. The maximum difference in hot spot temperatures of photovoltaic cells is about 26% among the cases with various K_ef. In addition, the temperatures are rather low for the situation without consideration of thermal interaction between the air streams inside and outside the cabinet. Therefore, without the consideration of the thermal interaction would cause serious under-prediction for the hot spot temperatures of photovoltaic cells in engineering applications.     

A bibliometric analysis and comparison on three information science journals: JASIST,IPM, JOD, 1998–2008

Employing a citation analysis, this study explored and compared the bibliometric characteristics and the subject relationship with other disciplines of and among the three leading information science journals, Journal of the American Society for Information Science and Technology (JASIST), Information Processing and Management and Journal of Documentation. The citation data were drawn from references of each article of the three journals during 1998 and 2008. The Ulrich’s Periodical Directory, Library of Congress Subject Heading, retrieved from the WorldCat, and LISA database were used to identify the main class, subclass and subject of cited journals and books. Quantitative results on the number of JASIST, IPM and JOD literature references, average number of references cited per paper, document type of cited literature and the journal self-citation rate are reported. Moreover, the highly cited journals and books, the main classes and subclasses of cited journals and books in papers of the three journals, the highly cited subjects in journals and books of library and information science were identified and analyzed. Comparison on the characteristics of cited journals and books confirmed that all the three journals under study are information science oriented, except JOD which is library science orientation. JASIST and IPM are very much in common and diffuse to other disciplines more deeply than JOD.     

IDENTIFYING MULTIVARIATE TIME SERIES MODELS

Abstract. This paper is concerned with how canonical variate analysis can be used to identify the structure of a linear multivariate time series model. The procedure used is based on that of Akaike and Cooper and Wood. A correction and a refinement are made, however. The correction is on the testing statistic and the refinement on the allowed order ( p, q ). Appropriate asymptotic distributions for testing zero canonical correlations are also given.