High char‐yielding poly[acrylonitrile‐co‐(itaconic acid)‐co‐(methyl acrylate)]: synthesis and properties

Polyacrylonitrile terpolymers of various compositions consisting of acrylonitrile (AN), itaconic acid (IA) and methyl acrylate (MA) were synthesized by solution polymerization in dimethylsulfoxide. Increase in concentration of either IA or MA retarded the overall polymerization rate and the polymer molecular weight. The system consisting of AN + MA and varying IA concentration was more prone to retardation in comparison with the system composed of AN + IA with variable MA concentration. The retardation factors were quantified. Minor quantities of MA boost the reactivity of IA in the terpolymer system. The terpolymer was richer in MA vis‐à‐vis the feed. The thermal characteristics of the terpolymer were examined as a function of its composition. In contrast to the copolymer of AN and IA requiring 1–1.5 mol% IA, the terpolymer required an IA content of approximately 2.5 mol% for optimum thermal stability. The polymer with 90 mol% AN, 2.5 mol% IA and 7.5 mol% MA exhibited reasonably good char‐forming characteristics and thermal stability. The overall crystallinity and crystallite size of the polymers were found to decrease on incorporation of the comonomers. The ‘aromatization index’ of the copolymer increased with the temperature of pyrolysis through re‐organization of the tetrahydropyridine ladder structure. Copyright © 2005 Society of Chemical Industry     

Development of Anticandidal Delivery Systems: (I) Anticandidal Activities of Antifungal Agents and Synergistic Combination with Other Drugs

Susceptibility testing with antifungal agents, e. g., minimum inhibitory concentration (MIC) determination, is performed to obtain reliable data that permit selection of the most suitable agents for treatment of an infective condition. To determine the drugs that provide maximum effectiveness against oral candidiasis, the MICs of various antifungal agents were determined. Also, synergism between two chosen antifungal agents was evaluated, and the effect of benzocaine, an anesthetic, and hydrocortisone, an antiinflammatory agent, on their MICs was examined. It was observed that among all the drugs tested, clotrimazole was the most promising candidate for use as an oral local antifungal. The combination of clotrimazole and chlorhexidine resulted in a decrease in the MIC. While the addition of hydrocortisone to this combination resulted in a slight increase in the MIC, the inclusion of benzocaine resulted in a substantial decrease in the MIC of the antifungal agent combination.     

Oxidation and Fracture Strength of High-Purity Reaction-Bonded Silicon Nitride

Reaction-bonded Si₃N₄ (RBSN) made from high-purity Si powder is unusually resistant to degradation caused by exposures to air for up to 50 h at temperatures up to 1400°C. The weight gain during oxidation of this SiH₄-originating RBSN is approximately 10 times less than conventional RBSN. Contrary to normally observed strength degradations, room-temperature strengths of this high-purity, oxidized RBSN (avg = 435 MPa, max. = 668 MPa) remained at their unusually high, as-processed levels after 1000° and 1400°C oxidizing exposures. Fracture toughness values were unaffected by oxidation ( K _IC= 2.3 to 2.4 MPa · m^1/2). This superior oxidation resistance results from the high purity and the small diameter pore channels (0.01 to 0.06 μm) achieved in this SiH₄-originating RBSN.     

On quasi-degeneracies in plate vibration problems

In plotting the variation of frequencies with geometric parameters such as side ratio, skew angle, thickness taper, etc. in detailed studies of the vibration characteristics of plates, situations are encountered such as crossing of the frequency curves or the tendency of these curves to come close together and veer away from each other. These have been generally referred to as “frequency crossings” and “transitions” respectively. The latter may preferably be referred to as “quasi-degeneracies”. In the literature there appears to be some ambiguity in the analysis and interpretation of these features. In this paper, a clarification of some of these questions as regards rectangular and skew plates is presented by making use of concepts from physics dealing with molecular vibrations.     

On the validity of unintentional doping densities extracted using Mott–Schottky analysis for thin film organic devices

The organic electronic devices are often understood invoking the concept of ‘unintentional doping’. However, the applicability and usefulness of this controversial concept is not very clear and is under much recent debate. In this work, we revaluate the validity of this concept through careful experiments and detailed numerical simulations. Specifically, we use the Capacitance Voltage (CV) measurement of pentacene devices as a testbed to unravel the role of injecting electrodes and unintentional doping (if any). Indeed, our results indicate that the CV of pentacene capacitors can be solely understood in terms of properties of the contact electrodes. The unintentional doping, if present, has an inconsequential role in device performance. Our conclusions indicate that, often, an incorrect interpretation of CV results would lead to unphysical values of unintentional doping and have obvious implications towards the fundamental understanding of organic semiconductor device physics, modeling, and characterization; thus resolving many ambiguities in literature by providing a consistent interpretation through a coherent conceptual framework.     

Identifying technology horizons for strategic investment decisions

Technology investment models usually assume that a known number of technologies will appear in the future, though their appearance, cost, and revenue parameters may be uncertain. In practice, however, it is not always clear how many future technologies or periods need to be considered. We introduce the concept of a technology horizon, which we define as the minimum number of future technologies and future periods that need to be considered to guarantee that the optimal decision would not change even if additional technologies or periods worth of data were to be considered. We also allow the costs and revenue of existing technologies in our model to vary depending on the latest technology introduced. Further, we allow for implementation costs, which enables us to model situations where it may cost more to leapfrog technologies than if one were to buy intervening technologies. We then provide a fast algorithm to identify such technology horizons     

Dual frequency miniature microstrip antenna

A single-feed dual frequency compact microstrip antenna with a shorting pin is described. This new antenna configuration gives a large variation in frequency ratio of the two operating frequencies, without increasing the overall size of the antenna     

A precise sensor fault detection technique using statistical techniques for wireless body area networks

One of the major challenges in wireless body area networks (WBANs) is sensor fault detection. This paper reports a method for the precise identification of faulty sensors, which should help users identify true medical conditions and reduce the rate of false alarms, thereby improving the quality of services offered by WBANs. The proposed sensor fault detection (SFD) algorithm is based on Pearson correlation coefficients and simple statistical methods. The proposed method identifies strongly correlated parameters using Pearson correlation coefficients, and the proposed SFD algorithm detects faulty sensors. We validated the proposed SFD algorithm using two datasets from the Multiparameter Intelligent Monitoring in Intensive Care database and compared the results to those of existing methods. The time complexity of the proposed algorithm was also compared to that of existing methods. The proposed algorithm achieved high detection rates and low false alarm rates with accuracies of 97.23% and 93.99% for Dataset 1 and Dataset 2, respectively.     

Compact Models of Spreading Resistances for Electrical/Thermal Design of Devices and ICs

Building upon our recent work (IEEE Electron Device Lett., vol. 26, pp. 909-912, Dec, 2005), we present simple and continuous closed-form models for several rectangular and circular spreading resistance geometries encountered in electrical/thermal design of devices and integrated circuits. The resistance geometries considered involve current/heat flow between parallel contacts of rectangular or circular shape and concentric or eccentric nature, between a horizontal and a vertical stripe, and between a horizontal circular contact and a surrounding vertical cylindrical contact. The modeling procedure involves normalization of the spreading resistance with respect to its value under 1D flow conditions, followed by a curve-fit of the variation of this normalized resistance with contact area in terms of physical parameters. The resistance models may also be used to estimate the reciprocal of capacitance of similar insulator-electrode geometries, by replacing the resistivity by the reciprocal of the insulator permittivity.     

2,2′-OXO-1, 1 ′-azobenzene A microbially transformed allelochemical from 2,3-Benzoxazolinone: I

2,2-Oxo-1,1 -azobenzene (AZOB), a compound with strong herbicidal activity, was isolated and characterized from a soil supplemented with 2,3-benzoxazolinone (BOA). A parallel experiment with 6-methoxy-2,3-benzoxazolinone (MBOA) yielded AZOB as well as its mono-(MAZOB) and dimethoxy-(DIMAZOB) derivatives. These compounds were produced only in the presence of soil microorganisms, via possible intermediates, I and II, which may dimerize or react with the parent molecule to form the final products. In the case of MBOA, it was shown that demethoxylation precedes the oxidation step. Although BOA and 2,4-dihydroxy-1,4(2H)-benzoxazin-3-one (DIBOA) were leached out of rye residues, there were no detectable amounts of the biotransformation products in the soil. When BOA was mixed with soil and rye residue, either under field conditions or in vitro, AZOB was detected. Levels of free BOA in the soil were greatly reduced by incubation with rye residue. AZOB was more toxic to curly cress (Lepidium sativum L.) and barnyardgrass (Echinochloa crusgatti L.) than either DIBOA or BOA.Journal Article No. 12943 of the Michigan Agricultural Experiment Station.