Stability enhancement of polypyrrole thin film ammonia sensor by camphor sulfonic acid dopant

Journal of Materials Science: Materials in Electronics - The main weakness of polymer gas sensors is its stability. Here, we report stability enhancement of a 100 nm polypyrrole (PPy) thin...     

Control of free-radical emulsion polymerization of methyl methacrylate by oxygen injection. II. Experimental study

Oxygen injection has been proposed and experimentally demonstrated as an effective control measure for limiting the rate of heat release and altering the rate of polymerization in emulsion processes. A detailed mathematical model has been previously developed to describe the system behavior with and without oxygen injection. A simple lab scale apparatus was constructed and run extensively. Only trace quantities of oxygen are needed to inhibit the reaction completely. The facile response makes this method attractive for fast temperature control. However, because of the rapid penetration of dissolved oxygen into the polymer particles, growing radical chains are terminated prematurely, lowering product molecular weights. To minimize this detrimental effect, pulsed oxygen control is used and extensive experimental work was performed to determine the effects of controller set points on molecular weight. Moderate oxygen flows and moderate set point temperatures are found to give the optimal response without significant lowering of the final molecular weight. Injected quantities agree well with the order-of-magnitude sparging calculations needed to completely stop initiation. However, complete agreement between model simulations and experimental results was not reached due to an unmeasured loss of monomer from the reactor. Chain transfer to monomer is found to be important in modeling the polymer molecular weight. It has, however, a negligible effect on the reaction rate.     

An Approximate Model of Multistage Automatic Transfer Lines with Possible Scrapping Of Workpieces

We consider multistage automatic transfer lines with unreliable stages, finite interstage buffer storages, and possible scrapping of workpieces. It is assumed that the first stage never idles and the last stage never becomes blocked. Assuming that uptimes and downtimes of a stage are geometrically distributed, an approximate model is developed to compute different performance measures of the transfer line. The results obtained through the approximate model are compared to the exact results for three-stage transfer lines and to simulation results for longer transfer lines. It is observed that the approximate results are good in almost all cases considered.     

Signature analysis and defect detection in layered manufacturing of ceramic sensors and actuators

This paper presents the concept of a process signature for the use of online signature analysis and defect detection in the layered manufacturing (LM) of ceramic sensors and actuators. To achieve the high quality of parts built by the fused deposition of ceramics (FDC), an online process-monitoring system is implemented to detect the processing defects. Using a process signature extracted from the image of a layer captured by the monitoring system, an ideal image is created that is then compared to the original image to detect and identify the defects. Some results of signature analysis and defect detection for single-material and multi-material parts are also presented.Received: 22 July 1999, Accepted: 21 October 2001, Published online: 29 October 2003 Correspondence to: Mohsen A. JafariThis work was supported by the Office of Naval Research under grant # N-0014-96-1-1175. Ref. US Patent # S-5738817, April 14, 1998.     

Thermal modeling in cylindrical coordinates using effective conductivity

Predictive thermometry, utilizing minimally invasive sampling techniques, is an essential ingredient in the development of hyperthermia treatment planning capabilities. The authors demonstrate a powerful, but simple approach toward predicting temperature distributions in tissues, based on analytic solution, using in cylindrical symmetry, of the heat diffusion equation. Conduction and localized perfusion effects are combined as an effective conductivity term, readily measurable, and parametrized in a general exponential form. The proposed approach allows a first-order approximation to modeling three typical situations: hypoxic or necrotic tumor core with homogeneously perfused periphery; highly perfused periphery (in rapidly growing tumors); or perfused central cover with a less well-supplied periphery (such as for some invasive tumors). The utility and strength of this approach is that it provides a rapid, accurate model of directly observing the technical quality to be expected for different heating methods, making it possible to optimally configure source distributions in a treatment planning setting.     

Compatibilizing Effects on the Phase Morphology and Thermal Properties of Polymer Blends Based on PTT and m-LLDPE

Summary Morphology and thermal characteristics of poly (trimethylene terephthalate) (PTT)/ metallocene linear low-density polyethylene (m-LLDPE) blends with different amounts of a terpolymer based on glycidyl methacrylate (GMA), employed as a possible compatibilizer, were systematically examined. DMTA results show two distinct peaks for all neat blends associated with each phase. Melt crystallization degree of both phases in all the blends was observed to be reduced compared to pure components, except for that of PTT-rich phase in those blends with PTT as the matrix which slightly increases. Addition of the terpolymer to the system is found to effectively reduce the droplet size of the dispersed phase and increase phase adhesion. Also it increases the crystallinity of PTT in the system with PTT as the matrix. The influence of the compatibilizer is ascribed to the chemical interaction of PTT functional end groups with GMA functionalities. The efficiency of the terpolymer as a compatibilizer beyond 5 wt% content decreases which can be ascribed to the interface saturation and formation of micelles in the bulk phases.     

Improvement of cyclodextrin glucanotransferase as an antistaling enzyme by error-prone PCR

In an effort to improve the properties of cyclodextrin glucanotransferase (CGTase) as an antistaling enzyme, error-prone PCR was used to introduce random mutations into a CGTase cloned from alkalophilic Bacillus sp. I-5 (CGTase I-5). A mutant CGTase[3-18] with the three mutations M234T, F259I and V591A was selected by agar plate assay. Sequence alignment of various CGTases indicated that M234 and F259 are located in the vicinity of the catalytic sites of the enzyme and V591 in the starch binding domain E. The cyclization activity of CGTase[3-18] was dramatically decreased by 10-fold, while the hydrolyzing activity was increased by up to 15-fold. These mutations near subsite +1 (M234T) and at subsite +2 (F259I) are likely to alter the enzyme activity in a concerted manner, promoting hydrolysis of substrate while retarding cyclization. The addition of CGTase[3-18] reduced the retrogradation rate of bread by as much as did the commercial antistaling enzyme Novamyl during 7-day storage at 4 degrees C. No cyclodextrin (CD) was detected in bread treated with CGTase[3-18], whereas 21 mg of CD per 10 g of bread was produced in bread treated with wild-type CGTase.     

Torrefied agro-industrial residue as filler in natural rubber compounds

This study explored the feasibility of using torrefied biomass as a reinforcing filler in natural rubber compounds. Carbon black was then replaced with the torrefied biomass in elastomer formulations for concentrations varying from 0% to 100% (60 parts per hundred rubber or phr total). Their influence on the curing process, dynamic properties, and mechanical properties was investigated. Results were compared with the properties of vulcanizates containing solely carbon black fillers. Time to cure (t₉₀) for compounds with torrefied biomass fillers increased, while filler-filler interactions (ΔG') decreased, compared to carbon black controls. At low strains, the tan δ values of the torrefied fillers vulcanizates were similar to the controls. Incorporation of torrefied biomass into natural rubber decreased compound tensile strength and modulus but increased elongation. Replacement with torrefied fillers resulted in a weaker filler network in the matrix. Still, results showed that moderate substitution concentrations (~20 phr) could be feasible for some natural rubber applications.     

Hypermedia Support for Software Development: A Retrospective Assessment

Hypermedia technologies have been available for about a decade. Beginning with Douglas Engelbart, researchers have become interested in applying hypermedia concepts and technologies to software development. This paper assesses this symbiosis between hypermedia and software development as described by research contributions; by our count, more than one hundred articles. To date, no collection of, or guide to, this literature has been published. A number of significant contributions are classified, described, and appraised — providing a guide into what has been a rich but perhaps under-reported research area. Hypermedia has made significant contributions to software development in three primary areas: coping with massive amounts of information associated with software development projects; establishing and maintaining linkages between various types of software engineering documents; and enabling development engineers to record, document, and preserve knowledge about development thoughts, processes and rationale. These contributions may help direct the focus of future research towards building on, combining and assessing the resulting contributions. A research agenda is proposed along these lines.     

Autobiographical Accounts of Students' Experiences Learning Mathematics: A Review

ABSTRACT

In this article, we review published literature that draws on autobiographical accounts of students' experiences learning mathematics. We summarize the main findings of the target literature and present recommendations for further research that will extend this field. Our review indicates that autobiographical and narrative methodological approaches have the potential to occasion important advances in our knowledge of students' experiences learning mathematics. However, relative to accounts of preservice teacher learning, there is a paucity of published research that documents the mathematics learning experiences of kindergarten to Grade 12 students.