Transport properties of conducting amorphous carbon-poly(vinyl chloride) composite

The dc electrical conductivity of composites of poly(vinyl chloride) filled with amorphous carbon (a-C) flakes has been studied from room temperature to 1.2 K. The dc conductivity shows percolative behavior and as a function of a-C content, follows the scaling law σα(p − p_c)^t where p_c is percolation threshold and t the critical exponent with values 0.0165 and 3.1, respectively. The value of t shows evidence for non-universal value of critical exponent. In the temperature range 1.2 K to 50 K-60 K all the samples show the thermal fluctuation induced tunneling of the charge carriers through the insulating layer of polymer separating amorphous carbon aggregates. At high temperatures the differential thermal expansion of PVC and amorphous carbon plays a crucial role in conduction mechanism that leads to positive temperature coefficient of resistivity near to room temperature.     

Ferroelectric Thin Films-Based Technology for Frequency- and Phase-Agile Microwave Communication Applications

This paper deals with the current status of thin film ferroelectric-based frequency and phase agile microwave devices for communication applications. Researchers around the world have been active in this area for several years, and their results have been very relevant in determining the advantages and limitations of this technology when contrast with technology currently in use. The aforementioned results will be discussed in terms of device parameters such as RF losses, tunability, phase shift, frequency of operation, ease of fabrication, and projected cost, amongst others. Although the presentation will emphasize a NASA perspective, the information provided should offer a perspective of the attributes of this technology for other government agencies' electronically steerable electronics requirements, and for commercial communication applications.     

Diversity and antibiotic resistance of enterococci associated with stored-product insects collected from feed mills

Diversity and antibiotic resistance of enterococci associated with stored-product insects were assessed by screening 298 live adults from nine insect species collected from six feed mills in the midwestern United States. The eight antibiotics tested were tetracycline, ampicillin, erythromycin, vancomycin, chloramphenicol, ciprofloxacin, streptomycin, and neomycin. Enterococci were isolated from seven out of nine insect species collected. A majority of enterococci and aerococci were isolated from the red flour beetle, Tribolium castaneum (Herbst). Approximately 18% of the insects tested positive for bacteria on mEnterococcus agar, and the mean colony forming units ranged from 2×10¹ to 1.3×10⁵ per insect. Bacteria isolated on mEnterococcus agar included Enterococcus faecium, Enterococcus gallinarum, and Aerococcus viridans 3. Isolates of E. faecium displayed complete or intermediate resistance, most frequently to neomycin, tetracycline, and erythromycin. In addition, many E. faecium isolates exhibited intermediate resistance to vancomycin. The majority of A. viridans 3 isolates were susceptible to all antibiotics, while isolates of E. gallinarum displayed resistance to neomycin. Enterococci and aerococci are nosocomial human pathogens and are implicated in secondary infections, mainly in immuno-compromised individuals. Additionally, enterococci are considered an important reservoir of antibiotic resistance genes that can be horizontally transferred to other bacteria, including serious human pathogens. Our data reinforce the need for pest management to reduce the availability of vectors (insects) for dissemination of microorganisms carrying antibiotic resistance genes in the feed mill environment.     

Performance and emission characteristics of biofuel in a small-scale gas turbine engine

Performance and emissions characteristics of a 30 kW gas turbine engine burning Jet A, soy methyl ester, canola methyl ester, recycled rapeseed methyl ester, hog-fat biofuel, and their 50% (volume) blends in Jet A were studied over a range of throttle settings. The addition of biofuel resulted in a reduction in static thrust and thrust-specific fuel consumption, and increased thermal efficiency. The CO and NO emissions from the turbine were reduced with the biofuel blends. The results suggest that an optimum mixture may be found that reduces pollutant emissions while producing the desired thrust. This study demonstrates that biofuels may serve as viable supplements to petroleum-based fuels.     

Structural morphology of amorphous conducting carbon film

Amorphous conducting carbon films deposited over quartz substrates were analysed using X-ray diffraction and AFM technique. X-ray diffraction data reveal disorder and roughness in the plane of graphene sheet as compared to that of graphite. This roughness increases with decrease in preparation temperature. The AFM data shows surface roughness of carbon films depending on preparation temperatures. The surface roughness increases with decrease in preparation temperature. Also some nucleating islands were seen on the samples prepared at 900°C, which are not present on the films prepared at 700°C. Detailed analysis of these islands reveals distorted graphitic lattice arrangement. So we believe these islands to be nucleating graphitic. Power spectrum density (PSD) analysis of the carbon surface indicates a transition from the nonlinear growth mode to linear surface-diffusion dominated growth mode resulting in a relatively smoother surface as one moves from low preparation temperature to high preparation temperature. The amorphous carbon films deposited over a rough quartz substrate reveal nucleating diamond like structures. The density of these nucleating diamond like structures was found to be independent of substrate temperature (700–900° C).     

Redox polymerisation—kinetics of polymerisation of acrylamide initiated by the Mn3+-citric acid redox system

The kinetics and mechanism of polymerisation of acrylamide initiated by manganese(III) acetate-citric acid (CA) redox system in aqueous acetic acid and sulphuric acid medium were studied over the temperature range 30-50° C. The overall rates of polymerisation (R_p), disappearance of manganic ion (—R_m), and degree of polymerisation (X?_n) were measured with variation in [monomer], [Mn³⁺], [CA], [H⁺], μ and temperature. The polymerisation is initiated by the organic free radical arising from the Mn³⁺-CA reaction and the termination is by metal ions. The various rate parameters were evaluated and discussed.     

Management of pulmonary tuberculosis suspects with negative sputum smears and normal or minimally abnormal chest radiographs in resource-poor settings

SETTING: Queen Elizabeth Central Hospital, Blantyre, Malawi. OBJECTIVES: 1) To determine the proportion of pulmonary tuberculosis (PTB) suspects with negative sputum smears and a normal/minimally abnormal chest radiograph (CXR) who are culture-positive for Mycobacterium tuberculosis, and 2) to determine how many develop smear or radiographic evidence of PTB (TB CXR) during follow-up. METHODS: PTB suspects with negative sputum smears and a normal/minimally abnormal CXR were given a second course of antibiotics and followed up at 3-week intervals over 3 months with repeat sputum smears and chest radiography. RESULTS: Of 79 patients (38 men and 41 women, mean age 33 years) with negative smears and a normal/minimally abnormal CXR, 16 (21%) were culture-positive for M. tuberculosis. Of 15 culture-positive patients who were alive and attended follow-up, seven (47%) developed a TB-CXR by 3 months. Of 41 culture-negative patients who were alive and attended follow-up, 13 (32%) developed a TB-CXR, including one patient who became sputum smear-positive. TB-CXRs were found only in patients with a cough. CONCLUSION: TB suspects with negative smears and normal/minimally abnormal CXRs in high human immunodeficiency virus (HIV) prevalent countries should be given a second course of antibiotics. If cough improves, patients can be advised not to return for further follow-up. If cough continues, patients should return for further follow-up with sputum smear examination and chest radiography. Approximately 50% of those who have culture-positive PTB will develop a TB-CXR by 3 months and can be identified if radiographic facilities are available.     

A study of the structure of poly(hexene-1) prepared by nickel(α-diimine)/MAO catalyst using high resolution NMR spectroscopy

Homopolymerization of hexene-1 with nickel(α-diimine) catalyst forms poly(hexene-1) containing different types of branches and varying number of methylene units in the backbone. Types of branches identified by NMR spectroscopy include, butyl (C₄), longer than butyl (>C₄) and methyl (isolated and meso and racemic head-to-head). Formation of ethyl (C₂) and propyl (C₃) branches were not observed. The migration of the nickel during polymerization not only causes the formation of branches other than C₄, but also the runs of methylene units in the backbone due to complete 1,6-enchainment (chain running). The formation of regio-irregular methyl branches required an insertion of hexene-1 in the nickel-secondary carbon. Formation of methyl branches and (1, ω) enchainment has also been observed during the polymerization of octene-1, decene-1, tetradecene-1 using the same catalyst system. The extent formation of these subunits in the polymer depends on polymerization temperature. A plausible explanation for the formation of different branches is discussed.