Synthesis and Characterization of New Polyimides Based on 3,6-Bis(4-aminophenoxy)benzonorbornane

A novel benzonorbornane-based dietheramine monomer, 3,6-bis(4-aminophenoxy)benzonorbornane (BAPBN), was prepared in two steps from aromatic nucleophilic chloro-displacement reaction of p-chloronitrobenzene with the potassium phenolate of 3,6-dihydroxybenzonorbornane, followed by hydrazine catalytic reduction of the intermediate dinitro compound. A series of benzonorbornane-based polyimides were prepared from the diamine BAPBN with various aromatic dianhydrides via a conventional two-stage synthesis in which the poly(amic acid)s obtained in the first stage were heated stage-by-stage at 150300°C to give the polyimides. The intermediate poly(amic acid)s had inherent viscosities between 0.58 and 2.03 dL/g. Almost all the solution-cast poly(amic acid) films could be thermally converted into flexible and tough polyimide films with good tensile properties. Some polyimides with more flexible backbones exhibited good solubility in polar organic solvents. Depending on the structures of the dianhydrides, the glass-transition temperatures (T _g) of these polyimides were recorded between 209 and 327°C by differential scanning calorimetry (DSC) or dynamic mechanical analysis (DMA), and the softening temperatures (T _s) determined by thermomechanical analysis (TMA) stayed in the 197320°C range. Decomposition temperatures for 10% weight loss all occurred above 480°C in both air and nitrogen atmospheres. The polyimides also showed low dielectric constants (2.62–3.53 at 1 MHz). For the comparative purpose, a series of corresponding polyimides based on l,4-bis(4-aminophenoxy)benzene (BAPB) was also prepared and characterized.     

Design of piecewise constant gains for optimal control via Walsh functions

This paper presents a technique for determinating time-varying feedback gains of linear systems with quadratic performance criteria. The gains are approximated by the piecewise constants which axe naturally determined by Walsh functions. After introducing Walsh functions in the beginning we develop an operational matrix for solving state equations. Then using the operational matrix we solve the piecewise constant gains problem.     

Analysis of licking responses in rats: Effects of cholecystokinin and bombesin.

Compared the effects of cholecystokinin (CCK) and bombesin (BBS) on the consummatory response in male albino rats in 3 experiments. The normal licking response pattern did not change as the meal progressed; no predictor was found to indicate when the meal would terminate. Licks normally occurred at about 6/sec, but there were a few licks that occurred at about 3/sec with no licking occurring in the intermediate range; thus, a distinctive bimodal frequency distribution of the interlick interval was formed. CCK reduced the intake of milk and the related licking indices as expected, but it also induced an unusual licking pattern: The contact duration was shortened, the interlick interval was lengthened, and there was an increase in the proportion of licks with long interlick intervals, the effects that accentuated the bimodality of the distribution of interlick intervals. BBS reduced the intake and the related licking indices. The CCK effect may be mediated partially by a change in the motor aspect of the consummatory response; however, BBS reduced intake by simply decreasing the number of licks and shortening the intake duration. BBS may be a candidate for a natural satiety hormone. (37 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Studies of the mesophase development in polymeric fibers during deformation by synchrotron SAXS/WAXD

On-line structural and morphological studies on Kevlar 49 and isotactic polypropylene (iPP) fibers during deformation were carried out using synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD). A novel image analysis method was used to extract quantitative fractions of the crystal phase, the amorphous phase and a mesomorphic (intermediate) phase from two-dimensional (2D) WAXD patterns. Results showed that about 20 wt% in the Kevlar 49 fiber had an intermediate mesophase morphology. The transitions between crystal phase, amorphous phase and mesophase were not obvious during deformation of Kevlar 49 fiber at room temperatures. 2D SAXS patterns indicated that the superstructure of the Kevlar 49 fiber was fibril in nature. 2D WAXD results of iPP fibers showed that the -form crystals were quite defective in the initial state and were converted to the well-known mesomorphic form by drawing at room temperatures. The mesophase in Kevlar 49 fibers was then compared with that in iPP fibers. The shape of one-dimensional equatorial peak of the mesophase in the iPP fiber was similar to that in the Kevlar fiber, indicating that the mesophase in both iPP and Kevlar fibers could be similar in some aspects of molecular arrangement. Corresponding 2D SAXS patterns showed that there was no obvious long period in the mesophase of the drawn iPP fiber. We speculate that the constituents of the mesomorphic fraction extracted in the drawn iPP fibers may consist of partially oriented bundles of helical chains with random helical hands as well as oriented chains with no helical structures (consisting of stereo/tacticity defects). The latter is similar to the mesophase of rigid chains in Kevlar fibers, consisting of only oriented chains with no helical structures.     

Mobile Learning

Works in progress from selected papers presented at the 2006 IADIS International Conference on Mobile Learning provide an overview of the diverse research being conducted in this field.     

Investigation of the Phase Equilibria of Sn-Cu-Au Ternary and Ag-Sn-Cu-Au Quaternary Systems and Interfacial Reactions in Sn-Cu/Au Couples

The phase equilibria of the Sn-Cu-Au ternary, Ag-Sn-Cu-Au quaternary systems and interfacial reactions between Sn-Cu alloys and Au were experimentally investigated at specific temperatures in this study. The experimental results indicated that there existed three ternary intermetallic compounds (IMCs) and a complete solid solubility between AuSn and Cu₆Sn₅ phases in the Sn-Cu-Au ternary system at 200°C. No quaternary IMC was found in the isoplethal section of the Ag-Sn-Cu-Au quaternary system. Three IMCs, AuSn, AuSn₂, and AuSn₄, were found in all couples. The same three IMCs and (Au,Cu)Sn/(Cu,Au)₆Sn₅ phases were found in all Sn-Cu/Au couples. The thickness of these reaction layers increased with increasing temperature and time. The mechanism of IMC growth can be described by using the parabolic law. In addition, when the reaction time was extended and the Cu content of the alloy was increased, the AuSn₄ phase disappeared gradually. The (Au, Cu)Sn and (Cu_,Au)₆Sn₅ layers played roles as diffusion barriers against Sn in Sn-Cu/Au reaction couple systems.     

Efficient algorithms for mining closed itemsets and their lattice structure

The set of frequent closed itemsets uniquely determines the exact frequency of all itemsets, yet it can be orders of magnitude smaller than the set of all frequent itemsets. In this paper, we present CHARM, an efficient algorithm for mining all frequent closed itemsets. It enumerates closed sets using a dual itemset-tidset search tree, using an efficient hybrid search that skips many levels. It also uses a technique called diffsets to reduce the memory footprint of intermediate computations. Finally, it uses a fast hash-based approach to remove any "nonclosed" sets found during computation. We also present CHARM-L, an algorithm that outputs the closed itemset lattice, which is very useful for rule generation and visualization. An extensive experimental evaluation on a number of real and synthetic databases shows that CHARM is a state-of-the-art algorithm that outperforms previous methods. Further, CHARM-L explicitly generates the frequent closed itemset lattice.     

Implementing a diffusion model optimized by a hybrid evolutionary algorithm to forecast notebook shipments

Taiwan computer firms need to forecast trends in notebook shipments. The Bass diffusion model has been successfully applied to describe the empirical adoption curve for many new products and technological innovations. In order to improve the parameter estimates, a hybrid evolutionary algorithm, which couples genetic algorithms (GAs) with particle swarm optimization (PSO), is proposed. This hybrid approach can produce more accurate estimates of the parameters for the Bass diffusion model. In addition, the price index plays an important role in the notebook market. Thus, the modified diffusion model is proposed to investigate the forecasting performance for notebook shipments. The results illustrate that a hybrid approach outperforms other methods such as nonlinear algorithm, GA and PSO in terms of mean absolute percentage error.