Protonation of polyaniline by surface-functionalized polymer substrates

The protonation of solution-coated emeraldine (EM) base by sulfonic and carboxylic acid groups on surface-functionalized low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), poly(ethylene terephthalate) (PET), and polytetrafluoroethylene (PTFE) films were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, and conductivity measurements. Surface functionalizations were achieved by sulfonation (for LDPE, HDPE, PP, and PET), by hydrolysis (for PET), and by near-UV-light-induced surface graft copolymerization with the Na salt of styrene sulfonic acid and acrylic acid (for all substrates). The efficiency of surface functionalization by graft copolymerization is substantially enhanced for substrates pretreated with O₃ or Ar plasma. Protonation levels of 50% can be readily achieved for EM coated on sulfonic acid, but not carboxylic acid, functionalized surfaces. The extent of protonation, however, is also dependent on the microstructures of the modified substrate surfaces. In all cases, charge transfer interactions between the EM layer and the functionalized substrates readily result in good adhesion of the electroactive polymer on the polymer substrates to give rise to conductive surface structures. © 1995 John Wiley & Sons, Inc.     

RF sputtered PLZT thin film on Pt/Ti electrode

PLZT (7.5/65/35) thin films were deposited by rf magnetron sputtering on single crystal Si substrates using an oxide sintered target with excess PbO. The effects of postannealing and bottom Pt/Ti electrodes on the thin film crystal structures and ferroelectric properties were studied. Film deposited at 200°C or below crystallizes to a perovskite phase after annealing treatment at 550°C or above, and the crystal structure depends on the annealing treatment. The best crystal structures and electronic properties were obtained when the thin films were annealed at 600°C to 650°C for 1 h in O₂. For the Pt/Ti two-layer bottom electrode, the thickness of the Ti layer has a dominant effect. When the Ti layer was too thick or too thin, the PLZT thin film structures consist mainly of pyrochlore phases. However, using an appropriate Ti layer thickness, PLZT thin films having good crystal structures and ferroelectric properties can be obtained, with typical remanent polarization value of 220 mC/m² and coercive field strength of 6.5 MV/m     

The effect of variation of rake angle on wearland stress in metal cutting

This paper presents an experimental relationship between tool rake angle and wear land stress inorthogonal machining. Results indicated that contrary to general expectation, increasing the rake angle did not result in a continuous decrease in wear land stress. For small rake angles, elastic recovery and swelling of the machined surface seemed to be the major causes of wear land stress. For larger rake angles, however, tool flank swelling appeared to be the dominating cause of the stress on the wear land.     

A Speech Recognition IC Using Hidden Markov Models with Continuous Observation Densities

This paper presents the design of a speech recognition IC using hidden Markov models (HMMs) with continuous observation densities. Results of offline and live recognition tests are also given. Our design employs a table look-up method to simplify the computation and hence the architecture of the circuit. Currently each state of the HMMs is represented by a double-mixture Gaussian distribution. With minor modifications, the proposed architecture can be extended to implement a recognizer in which models with higher order multi-mixture Gaussian distribution are used for more precise acoustic modeling. The test chip is fabricated with a 0.35 μm CMOS technology. The maximum operating frequency is 62.5 MHz at 3.3 V. For a 50-word vocabulary, the estimated recognition time is about 0.16 s. Using noise-corrupted utterances, the recognition accuracy is 93.8% for isolated English digits. Such a performance is comparable to the software implementation with the same algorithm. Live recognition test was also run for a vocabulary of 11 Chinese words. The accuracy is 91.8% for five male and five female speakers.

Controlling a supplier’s subcontracting decisions through contractual enforcement or economic incentives

Suppliers often subcontract part of their workload to other suppliers, and manufacturers might suffer severe consequences if they do not anticipate their suppliers’ incentives to subcontract. In this paper, we study the case where a manufacturer outsources two tasks to a top-tier supplier. The manufacturer must decide whether it should design a contract that enforces that the different tasks are completed by the appropriate suppliers, and when it is preferable to use economic incentives to manipulate the top-tier supplier’s subcontracting behaviour. We find that when the cost difference between suppliers of different tiers is small and the correlation between the risks associated with the two tasks is minimal, the manufacturer can benefit from designing a contract that ensures the preferred subcontracting behaviour, if the cost of enforcing such a contract is not too high. However, when such enforcement cost is substantial, the manufacturer might be better off manipulating the top-tier supplier’s economic incentives.     

Light-induced diffraction in thermally reduced congruent and near-stoichiometric Er:LiNbO3 crystals

A polarization-isotropic two-colour light-induced diffraction (LID) phenomenon from thermally reduced congruent and near-stoichiometric Er:LiNbO₃ crystals was observed when these crystals were exposed to superposed 632.8?nm probe and 488?nm pump beams. The LID is characterized by expansion of the probe beam spot and the appearance of alternate bright and dark diffraction rings at higher pump light intensities. This phenomenon is absent not only in all other Er-doped crystals which either were as grown or had experienced other post-growth treatments such as vapour transport equilibration (VTE), oxidation and strong annealing but also in a pure VTE-treated crystal even though the crystal was subjected to the same reduction procedure. The LID characteristics of five reduced crystals, which have different Li-to-Nb ratios and different doping levels of Er³⁺, were studied in detail by changing the light intensity, polarization state and wave vector direction of both the pump and the probe beams. The origin of the LID was investigated from the viewpoints of the red fluorescence of Er³⁺ excited by a 488?nm pump beam, light-induced scattering and light-induced thermal nonlinearity. The results have shown that the thermal nonlinearity mechanism is preferred as it can reasonably explain almost all the observed experimental phenomena.     

Application of living free radical polymerization for nucleic acid delivery

Therapeutic gene delivery can alter protein function either through the replacement of nonfunctional genes to restore cellular health or through RNA interference (RNAi) to mask mutated and harmful genes. Researchers have investigated a range of nucleic acid-based therapeutics as potential treatments for hereditary, acquired, and infectious diseases. Candidate drugs include plasmids that induce gene expression and small, interfering RNAs (siRNAs) that silence target genes. Because of their self-assembly with nucleic acids into virus-sized nanoparticles and high transfection efficiency in vitro, cationic polymers have been extensively studied for nucleic acid delivery applications, but toxicity and particle stability have limited the clinical applications of these systems. The advent of living free radical polymerization has improved the quality, control, and reproducibility of these synthesized materials. This process yields well-defined, narrowly disperse materials with designed architectures and molecular weights. As a result, researchers can study the effects of polymer architecture and molecular weight on transfection efficiency and cytotoxicity, which will improve the design of next-generation vectors. In this Account, we review findings from structure-function studies that have elucidated key design motifs necessary for the development of effective nucleic acid vectors. Researchers have used robust methods such as atom transfer radical polymerization (ATRP), reverse addition-fragmentation chain transfer polymerization (RAFT), and ring-opening metastasis polymerization (ROMP) to engineer materials that enhance extracellular stability and cellular specificity and decrease toxicity. In addition, we discuss polymers that are biodegradable, form supramolecular structures, target specific cells, or facilitate endosomal release. Finally, we describe promising materials with a range of in vivo applications from pulmonary gene delivery to DNA vaccines.     

Vernier parallel delay-line based time-to-digital converter

This letter proposes a new parallel delay-line time-to-digital converter (TDC) architecture based on the Vernier principle. Two parallel delay-line stages with slightly different incremental step sizes are cascaded, resulting in a finer resolution compared to the traditional parallel delay line. A 2-bit TDC fabricated in a 0.18 μm CMOS technology demonstrates the principle with a time resolution of 2.5 ps and a differential nonlinearity of 0.13 LSB.     

Nonnegative class-specific entropy component analysis with adaptive step search criterion

Nonnegative learning aims to learn the part-based representation of nonnegative data and receives much attention in recent years. Nonnegative matrix factorization has been popular to make nonnegative learning applicable, which can also be explained as an optimization problem with bound constraints. In order to exploit the informative components hidden in nonnegative patterns, a novel nonnegative learning method, termed nonnegative class-specific entropy component analysis, is developed in this work. Distinguish from the existing methods, the proposed method aims to conduct the general objective functions, and the conjugate gradient technique is applied to enhance the iterative optimization. In view of the development, a general nonnegative learning framework is presented to deal with the nonnegative optimization problem with general objective costs. Owing to the general objective costs and the nonnegative bound constraints, the diseased nonnegative learning problem usually occurs. To address this limitation, a modified line search criterion is proposed, which prevents the null trap with insured conditions while keeping the feasible step descendent. In addition, the numerical stopping rule is employed to achieve optimized efficiency, instead of the popular gradient-based one. Experiments on face recognition with varieties of conditions reveal that the proposed method possesses better performance over other methods.