Charge motion in solid argon

The measurement of currents induced in solid argon by a radioactive source is described. The results show evidence of negative and positive charge motion. In one sample small bubbles were observed at the interface between solid and anode at a threshold field. The movement of these bubbles shows the possibility of mass transport through solid argon.     

Understanding Performance for Two 802.11 Competing Flows

It is well known that 802.11 suffers from both inefficiency and unfairness in the face of competition and interference.This paper provides a detailed analysis of the impact of topology and traffic type on network performance when two flows compete with each other for airspace.We consider both TCP and UDP flows and a comprehensive set of node topologies.We vary these topologies to consider all combinations of the following four node-to-node interactions:(1) nodes unable to read or sense each other,(2)nodes able to sense each other but not able to read each other's packets and nodes able to communicate with(3)weak and with(4)strong signal.We evaluate all possible cases through simulation and show that the cases can be reduced to 9 UDP and 10 TCP 802.11g models with similar efficiency/fairness characteristics. We also validate our simulation results with extensive experiments conducted in a laboratory testbed.These more detailed models improve on previous work such as hidden-/exposed-terminal categorization and are thus better suited as a basis for adaptive techniques to improve performance in 802.11 multi-hop WLAN or Mesh Networks.     

In situ high temperature FTIR studies of NOx reduction with propylene over Cu/ZSM-5 catalysts

High temperature in situ FTIR has been used to investigate the surface species present on Cu/ZSM-5 during the reduction of NO_x with propylene in a lean environment. Parallels have been observed between adsorbed surface species and catalytic activity for this reaction. Species detected at low temperatures are not representative of those detected at high temperatures where the catalyst is active. An oxidized nitrogen-containing species has been observed at 2580 cm^–1 on Cu during reaction conditions (400°C). In contrast, at low temperatures, where the catalyst is less active, coke and Cu⁺-CO predominated. The effects of Cu weight loading, C/NO ratio, reaction temperature, and catalyst deactivation by steaming have been investigated with IR.     

Selective isotopic oxygen incorporation into C5 and C6 ethers via solid acid-catalyzed reaction of methanol and ethanol with isobutanol

Reaction of CH₃ ¹⁸OH with¹⁶O-containing isobutanol (2-methylpropan-1-ol) over strong acid Nafion-H and Amberlyst-H 35 resin catalysts gave the two distinctly labelled C₅ ethers 1-methoxy(¹⁶O)-2-methylpropane (also designated as methyl isobutyl ether,¹⁶O-MIBE) and 2-methoxy(¹⁸O)-2-methylpropane (also designated as methyl tertiary-butyl ether,¹⁸O-MTBE). Reaction of CH₃CH₂ ¹⁸OH with isobutanol gave the analogously labelled C₆ ethers,¹⁶O-EIBE and¹⁸O-ETBE. These results show that the isobutyl and tertiary-butyl ethers are formed from the alcohols by distinctly different mechanistic pathways, i.e. the former are produced bysurface-catalyzed S_N2 reactions that follow Langmuir-Hinshelwood kinetics involving competitive adsorption while the latter arise via carbenium or olefinic intermediates. There is no pathway for isomerization of the two ethers, MIBE and MTBE, under the reaction conditions employed.     

Environmental contaminants and human health in the Canadian Arctic

The third Canadian Arctic Human Health Assessment conducted under the Canadian Northern Contaminants Program (NCP), in association with the circumpolar Arctic Monitoring and Assessment Programme (AMAP), addresses concerns about possible adverse health effects in individuals exposed to environmental contaminants through a diet containing country foods. The objectives here are to: 1) provide data on changes in human contaminant concentrations and exposure among Canadian Arctic peoples; 2) identify new contaminants of concern; 3) discuss possible health effects; 4) outline risk communication about contaminants in country food; and 5) identify knowledge gaps for future contaminant research and monitoring. The nutritional and cultural benefits of country foods are substantial; however, some dietary studies suggest declines in the amount of country foods being consumed. Significant declines were found for most contaminants in maternal blood over the last 10 years within all three Arctic regions studied. Inuit continue to have the highest levels of almost all persistent organic pollutants (POPs) and metals among the ethnic groups studied. A greater proportion of people in the East exceed Health Canada's guidelines for PCBs and mercury, although the proportion of mothers exceeding these guidelines has decreased since the previous assessment. Further monitoring and research are required to assess trends and health effects of emerging contaminants. Infant development studies have shown possible subtle effects of prenatal exposure to heavy metals and some POPs on immune system function and neurodevelopment. New data suggest important beneficial effects on brain development for Inuit infants from some country food nutrients. The most successful risk communication processes balance the risks and benefits of a diet of country food through input from a variety of regional experts and the community, to incorporate the many socio-cultural and economic factors to arrive at a risk management decision that will be the most beneficial in Arctic communities.     

Numerical approaches for collaborative data processing

We present an approach to uncertainty propagation in dynamic systems, exploiting information provided by related experimental results along with their models. The approach relies on a solution mapping technique to approximate mathematical models by polynomial surrogate models. We use these surrogate models to formulate prediction bounds in terms of polynomial optimizations. Recent results on polynomial optimizations are then applied to solve the prediction problem. Two examples which illustrate the key aspects of the proposed algorithm are given. The proposed algorithm offers a framework for collaborative data processing among researchers. This work was supported by the National Science Foundation, Information Technology Research Program, Grant No. CTS-0113985.     

Toxic equivalency factors (TEFs) for PCBs, PCDDs, PCDFs for humans and wildlife

An expert meeting was organized by the World Health Organization (WHO) and held in Stockholm on 15-18 June 1997. The objective of this meeting was to derive consensus toxic equivalency factors (TEFs) for polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) and dioxinlike polychlorinated biphenyls (PCBs) for both human, fish, and wildlife risk assessment. Based on existing literature data, TEFs were (re)evaluated and either revised (mammals) or established (fish and birds). A few mammalian WHO-TEFs were revised, including 1,2,3,7,8-pentachlorinated DD, octachlorinated DD, octachlorinated DF, and PCB 77. These mammalian TEFs are also considered applicable for humans and wild mammalian species. Furthermore, it was concluded that there was insufficient in vivo evidence to continue the use of TEFs for some di-ortho PCBs, as suggested earlier by Ahlborg et al. [Chemosphere 28:1049-1067 (1994)]. In addition, TEFs for fish and birds were determined. The WHO working group attempted to harmonize TEFs across different taxa to the extent possible. However, total synchronization of TEFs was not feasible, as there were orders of a magnitude difference in TEFs between taxa for some compounds. In this respect, the absent or very low response of fish to mono-ortho PCBs is most noticeable compared to mammals and birds. Uncertainties that could compromise the TEF concept were also reviewed, including nonadditive interactions, differences in shape of the dose-response curve, and species responsiveness. In spite of these uncertainties, it was concluded that the TEF concept is still the most plausible and feasible approach for risk assessment of halogenated aromatic hydrocarbons with dioxinlike properties.     

Lead contamination in mining areas in western Ireland. II. Survey of animals, pastures, foods and waters

The determination of detectable amounts of lead contamination in blood, foods and biological materials has been a recent problem in relation to the operation of lead mining in the West of Ireland. Following the mining activities, the incidence of lead contamination was investigated in the following ways: (i) lead values in viscera, blood and faeces of dead animals and control of lead contamination in blood, faeces and milk of live animals in mining areas; (ii) examination of pastures in areas adjoining mining operations and road dust; (iii) analysis of foods, milks and waters in the mine vicinity; and (iv) lead content in workers blood due to exposure in mines. Investigations under (i), (ii) and (iii) are dealt with in this paper. As a result of the toxicity results found in the laboratory, the mining authorities instituted precautionary steps in the mining operations to eliminate lead ‘fallout’.     

Subchronic toxicity of PCB 105 (2,3,3'',4,4''-pentachlorobiphenyl) in rats

Increases in the intracellular free calcium concentration are of great importance to the initiation of development in deuterostomes. Their involvement has not yet been clearly defined in protostomes. We used endogenous ligands (IP3, cADPR, ryanodine and NAADP) and pharmacological agents (thapsigargin [Tg], thimerosal, caffeine and heparin) to study smooth endoplasmic reticulum Ca2+ pump and release mechanisms in eggs of an annelid, Chaetopterus. Oocyte homogenates effectively sequestered Ca2+ and released it in response to IP3 in a concentration-dependent manner. Repeated additions of IP3 were unable to cause further release. Heparin inhibited Ca2+ release in response to IP3. The homogenates also released Ca2+ in response to thimerosal, and this release was sensitive to heparin. Two antibodies to IP3 receptors recognized an appropriate band in Chaetopterus egg lysates. These results indicate that the oocytes possess type-1 IP3-gated Ca2+ channels. Neither calcium itself, nor strontium, cADPR, ryanodine, caffeine nor NAADP released appreciable Ca2+. At low concentrations, Tg caused a slow release of Ca2+; at higher concentrations, it elicited a rapid release. Release of Ca2+ by Tg activated development. Since one theory of fertilization invokes the introduction of a Ca2+ releasing soluble protein into the egg upon sperm-egg fusion, we also tested whether soluble extracts of Chaetopterus sperm could stimulate Ca2+ release in Chaetopterus egg homogenates. There was no Ca2+ release when the sperm extract was added to the homogenate; however, homogenates exposed to sperm extract became refractory to IP3. Thus, Ca2+ release at fertilization in these oocytes occurs through IP3-gated channels.