Monitoring the packet gap of real-time packet traffic

Real-time packet traffic is characterized by a strict deadline on the end-to-end time delay and an upper bound on the information loss. Due to the high correlation among consecutive packets, the individual packet loss does not well characterize the performance of real-time packet sessions. An additional measure of packet loss is necessary to adequately assess the quality of each real-time connection. The additional measure considered here is the average number of consecutively lost packets, also called the average packet gap. We derive a closed form for the average packet gap for the multiclassG/G/m/B queueing system in equilibrium and show that it only depends on the loss behavior of two consecutive packets. This result considerably simplifies the monitoring process of real-time packet traffic sessions. If the packet loss process is markovian, the consecutive packet loss has a geometric distribution.     

Matrix effects in the determination of butyltin compounds in environmental samples by GC AA after hydride generation

Experiments for the determination of mono-, di and tri-butyltin (MBT, DBT and TBT) by hydride generation/gas chromatography/atomic absorption spectrometry in various matrices (sediment, suspended matter, mussel, algae and water) have revealed that poor butyltin recoveries are obtained in sediments displaying high sulphur and hydrocarbon contents; very poor recoveries were also observed for TBT in sediments with high chlorophyll pigment contents as well as in algal samples. It was however not clear whether the hydride generatin was inhibited by these infering compounds, as was previously assumed in the case of hydrocarbons, or whether interferences affected the atomization rate. Further studies were performed to solve this problem in order to validate this method in the case of analyses of, for example, oil-contaminated sediment and algae. This paper presents the results obtained. It is concluded here that the poor recoveries were due to an inhibition of hydride generation rather than to interference at the atomization stage.     

Breakage of λ-DNA by inorganic tin and organotin compounds as environmental pollutants

In proportion to the environmental pollution problems caused by organotin compounds, the genotoxicities of tin compounds in the environments have become of interest so as to estimate their safety in recent years. In this work, isolated λ-DNA (double-strand DNA) was incubated with inorganic tin(II) and tin(IV) and five organotin compounds [n-butyltin trichloride, di(n-butyltin) dichloride, methyltin trichloride, dimethyltin dichloride and trimethyltin chloride] in reaction systems both with and without hydrogen peroxide (H₂O₂) content. The tin compounds tested in this study did not induce DNA breakage in the absence of hydrogen peroxide. Divalent inorganic tin (SnCl₂) and tetravalent inorganic tin (SnCl₄) caused DNA breakage in the presence of hydrogen peroxide (10 mM), and the DNA damage activity of inorganic tin was much more potent in divalent inorganic tin (SnCl₂) than in tetravalent inorganic tin (SnCl₄). Divalent inorganic tin (SnCl₂) induced DNA breakage in a concentration-dependent fashion at concentrations greater than 0.1 mM of SnCl₂ in the presence of hydrogen peroxide (10 mM). DNA breakage was not caused by n-butyltin compounds and methyltin compounds either in the presence or in the absence of hydrogen peroxide.     

In‐line monitoring of UV photopolymerization with a quartz crystal resonator

An in‐line monitoring device using a quartz crystal resonator for thin film polymerization was proposed, and its performance has been evaluated by implementing in the UV polymerization of 2‐hydroxyethyl methacrylate with a photoinitiator of 1‐chloroanthraquinone. Because the variation of resonant resistance of the resonator is proportional to the square root of viscosity change that is closely related to the polymerization degree, the resistance can be used as a measure of the polymerization degree. The resistance measurements were compared with the outcome of instrumental analyses of polymerization degree using an FTIR spectrometer and a gel permeation chromatograph. The experimental results showed that the resistance measurements were consistent with the experimental outcome of the instrumental analyses, and this indicates the effectiveness of the proposed device. Owing to the simplicity and availability of the resonator system, its wide utilization in the monitoring of a variety of film polymerization processes, including photoresistor application, is expected. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2428–2439, 2006     

Communication Roles, Perceived Effectiveness, and Satisfaction in an Environmental Management Program

Earlier research has shown a relationship between various forms of structural centrality and perceived leadership and role satisfaction in small experimental groups. The limited amount of research on this topic in naturally occurring social networks has yielded results that often conflict with one another. Different results have generally been attributed to possible differences in task environments. This paper examines the relationship between two types of structural centrality and perceived influence, role satisfaction, and perceived effectiveness in an environmental resource management program. Findings in this paper suggest that the observed differences in relationships between the network and other variables is partly a function of global network properties (e.g., marginality of subgroups) and related task environments. This revised version was published online in August 2006 with corrections to the Cover Date.     

The ICP-MS approach to environmental studies

The certification of marine materials for trace metals is a process which challenges every technique involved, especially if a technique is as recent as inductively coupled plasma mass spectrometry (ICP-MS), Developmental work was required for several materials (natural waters, biological materials, marine sediments). It is reviewed here, in an attempt to show how one can take full advantage of ICP-MS. This includes a review of the digestion procedures developed for the multielement analysis of biological materials and marine sediments in order to minimize spectroscopic interferences. The multielement analysis of natural waters is also reviewed, in particular that of saline waters which requires a separation of the analytes from the alkali and alkaline earths elements and a preconcentration of the analytes on a column of silicaimmobilized 8-hydroxyquinoline. The potential of performing this separation/preconcentration procedure on-line is showed using both published and original results. Finally, the application of ICP-MS to speciation is illustrated by the determination of methylmercury in biological materials after extraction, and by the determination of arsenic species by high performance liquid chromatography coupled to ICP-MS.Presented in part at the 1989 European Winter Conference on Plasma Spectrochemistry, Reutte, AustriaThe work described was carried out while the author was a Research Associate at the Analytical Chemistry Section, Chemistry Division, National Research Council of Canada, Ottawa, K1A OR9, Canada     

Hydrogen Oxidation on a Platinum Microelectrode: Effect of Carbon Monoxide Impurities

The kinetics of the hydrogen oxidation and the CO adsorption on a Pt (ultra)microelectrode is studied in a 0.5 M H₂SO₄ solution saturated with a mixture of gaseous H₂ and CO at partial CO pressures p _CO = 10–500 ppm. The balance between rates of diffusion and adsorption of CO at different adsorption times is studied. Studied is the effect of CO impurities in H₂ on steady-state polarization curves for the hydrogen ionization and nonsteady-state curves of the oxidation current decay with time at 0.02–0.05 V. Conditions under which in a certain time interval and at a certain CO concentration the slope of an I vs. t curve is proportional to p _CO are determined. The obtained dependence may be used when designing a technique for monitoring CO impurities in technical hydrogen.     

A scratch-resistant single-layer antireflective coating by a low temperature sol-gel route

A novel quarterwave-thick narrow-bandwidth antireflective coating has been developed for both plastic and vitreous substrates by a sol-gel route. This coating has revealed pronounced scratch- and climatic-resistance under adverse conditions. The single-layer coating consists basically of a composite material made of silica as the discontinuous phase and of a polytetrafluoroethylene-derived (Teflon¹) organic polymer as the continuous phase. This leads to fluorine-containing colloidal silica product, or a so-called Flucosil coating. The coating is applied by spinning or dipping from specific solutions at room temperature followed by a mild and short heat treatment. In addition to remarkable abrasion and environmental resistance properties, such coatings have displayed excellent laser-induced damage threshold levels, surpassing uncoated substrates.We hope such a product might open new perspectives concerning household articles, architectural optical thin-films, ophthalmic uses, and so on.     

环境和生物样品中铂族金属的分析研究进展

评述了近年来环境和生物样品中痕量铂族金属的分析研究进展，重点介绍了样品的预处理和分离富集技术以及检测手段等。     

Identification of a chemical indicator of the rupture of 1,4-β-glycosidic bonds of cellulose in an oil-impregnated insulating paper system

In this study, headspace gas chromatography/mass spectrometry has been used to assess the volatile by-products generated by the ageing of oil-impregnated paper insulation of power transformers. Sealed-glass ampoules were used to age under oxidative conditions 0.5-g specimens of insulating paper in 9 mL of inhibited mineral oil in a temperature range of 60–120 °C and moisture of 0.5, 1 and 2% (w/w). A linear relationship between one of the oil-soluble degradation by-products, i.e. methanol, and the number of ruptured 1,4-β-glycosidic bonds of cellulose, regardless of the type of paper (ordinary Kraft or thermally-upgraded (TU) Kraft paper), was established for the first time in this field. Ageing at 130 °C of model compounds of the Kraft paper constituents (α-cellulose, hemicellulose and lignin) and two cellulosic breakdown by-products (D-(+)-glucose and 1,6-anhydro-β-d-glucopyranose) confirmed that the α-cellulose degradation was mostly responsible for the presence of this molecule in the system. Furthermore, additional 130 °C-tests with six different papers and pressboard samples under a tight control of initial moisture indicated that at least one molecule of methanol is formed for each rupture of 1,4-β-glucosidic bond of the molecular chains. Stability tests showed that the ageing indicator is stable under the oxygen and temperature conditions of open-breathing transformers. The presence of methanol was detected in 94% of oil samples collected from over than 900 in-service pieces of equipment, confirming the potential for this application. Lastly, the tests have shown that oil-oxidation by-products and TU-nitrogenous agents modify the methanol partitioning coefficients in the paper/oil/air system, which makes their study essential over a range of field conditions encountered by power transformers. Results are presented and discussed in comparison with 2-furfuraldehyde, which is the current reference in the domain.