Gas sensing properties of nanocrystalline metal oxide powders produced by thermal decomposition and mechanochemical processing

The objective of this research, was the synthesis of LaFeO3 and SnO2 fine powders for the subsequent preparation of thick film gas sensors. On producing fine metal oxide powders, often it is not possible to ensure separation of the particles during the synthesis, resulting in the formation of highly agglomerated material. In addition, there are often high synthetic costs associated with the powders obtained by these methods. Thermal decomposition and mechanochemical processing methods were selected to produce fine metal oxide powders. Thermal decomposition of a heteronuclear complex is a simple and relatively cheap method. Heat treatment of La[Fe(CN)6] · 4H2O leads to single-phase perovskite-type LaFeO3 fine powders. Heating in the temperature range 600-750 °C causes fast crystallite growth of slightly agglomerated particles and X-ray diffraction analysis showed only the pattern of orthorhombic transition phase of LaFeO3 particles. A paste for the preparation of the LaFeO3 thick film coating was obtained by mixing of polyvinyl alcohol solution and decomposed powder in a ball mill for 1 h. It was determined that there are two factors important for gas sensing, concentration of surface metal ions [Fe3+], and the concentration of oxygen adsorptive sites [Vo(..)]. LaFeO3−δ thick film with small crystallites, promotes a more rapid NO2 gas reaction at the surface and allows an equilibrium state to be obtained at 350 °C. Mechanochemical processing (MCP) is selected as the second, low cost method of manufacturing of fine powders in a conventional ball mill. During milling, deformation, fracture, and welding of powder particles continuously occur. The chemical reactions are activated by the repeated ball-powder collisions. Most of the reports on MCP that have appeared to date, concern the use of high-energy mills. It is shown that it may be possible to produce fine powder particles using a centrifugal mill of the conventional type instead of high-energy one. Nanocrystalline SnO2 powder was produced by two different chemical reactions. The first reaction, initiated by ball milling, produces water and the second reaction does not produce water. It should be noted that water, produced by the chemical reaction during milling, has a considerable influence on the reactivity of surface. Milling of predetermined stoichiometric amounts of SnCl2 with Ca(OH)2 and K2CO3 in an excess of CaCl2 and KCl respectively, resulted in the formation of the desired mass of SnO. After heat treatment and removal of the salt, slightly agglomerated SnO2 particles were produced with a tetragonal phase, confirmed by X-ray diffraction pattern. A very narrow particle size distribution of the powder is observed. The response of the LaFeO3 thick film to NO2 gas is investigated in the temperature range 250-350 °C, where the surface reactions are moderately fast. On exposure to low concentrations of H2S gas in air in the range 20-50 ppm the SnO2 film, prepared from anhydrous powder has higher gas response than the film prepared from hydrated powder.reviewe

A Computational Study Of The Influence Of Cortical Processes On The Olfactory Bulb

The olfactory bulb sits at the crossroads of input from an animal’s external and internal world. In this neural structure, chemical information from the environment interacts with contextual information emanating from higher cortical regions to shape mental representations of odor. Nevertheless, the factors influencing this interaction, and how the cortex manipulates these factors to the advantage of the animal, remain a mystery. To investigate this question, we have developed a large-scale computational model of the olfactory bulb. This model consists of a new algorithm to determine connectivity between mitral cells and granule cells, based in known anatomical constraints, combined with a dynamical systems approach utilizing the Izhikevich equations to simulate the network’s behavior. Using this model, we first examine connectivity and activity patterns of our network to demonstrate the strong relationship between structure and function in the olfactory bulb. We then further employ this model to analyze the effects of centrifugal feedback to the olfactory bulb on cortical odor representations; through this analysis, we are able to show that stochastic feedback patterns can evoke distinct trends in convergence and divergence between these representations depending on cortical excitability. Finally, we take advantage of the ease of incorporating new neurons into the model to study neurogenesis in the olfactory bulb, in particular to elucidate possible rules governing the placement of new cells. Through these experiments, our model provides new insight into the olfactory bulb and its role in the greater olfactory system

Nanocrystalline SnO2:F Thin Films for Liquid Petroleum Gas Sensors

This paper reports the improvement in the sensing performance of nanocrystalline SnO2-based liquid petroleum gas (LPG) sensors by doping with fluorine (F). Un-doped and F-doped tin oxide films were prepared on glass substrates by the dip-coating technique using a layer-by-layer deposition cycle (alternating between dip-coating a thin layer followed by a drying in air after each new layer). The results showed that this technique is superior to the conventional technique for both improving the film thickness uniformity and film transparency. The effect of F concentration on the structural, surface morphological and LPG sensing properties of the SnO2 films was investigated. Atomic Force Microscopy (AFM) and X-ray diffraction pattern measurements showed that the obtained thin films are nanocrystalline SnO2 with nanoscale-textured surfaces. Gas sensing characteristics (sensor response and response/recovery time) of the SnO2:F sensors based on a planar interdigital structure were investigated at different operating temperatures and at different LPG concentrations. The addition of fluorine to SnO2 was found to be advantageous for efficient detection of LPG gases, e.g., F-doped sensors are more stable at a low operating temperature (300 °C) with higher sensor response and faster response/recovery time, compared to un-doped sensor materials. The sensors based on SnO2:F films could detect LPG even at a low level of 25% LEL, showing the possibility of using this transparent material for LPG leak detection

MultimediaN E-Culture demonstrator

The main objective of the MultimediaN E-Culture project is to demonstrate how novel semantic-web and presentation technologies can be deployed to provide better indexing and search support within large virtual collections of cultural-heritage resources. The architecture is fully based on open web standards, in particular XML, SVG, RDF/OWL and SPARQL. One basic hypothesis underlying this work is that the use of explicit background knowledge in the form of ontologies/vocabularies/thesauri is in particular useful in information retrieval in knowledge-rich domains

Ethanol oxidation activity and structure of carbon-supported Pt-modified PdSn-SnO2 influenced by different stabilizers

PdSn-SnO2 nanoparticles supported on Vulcan XC-72 carbon were synthesized by chemical reduction in the presence of three different stabilizing agents: ethylene diamine tetra-acetic acid (EDTA), sodium citrate (Nacitrate) and hexamethylenetetramine (HMTA). TEM analysis showed that PdSn-SnO2 /C catalyst made using the HMTA stabilizer produced the smallest particle size. XRD analysis detected the presence of PdSn alloy and the SnO2 phase in all three PdSn-SnO2 /C samples, and showed that PdSn-SnO2 (HMTA) had the smallest lattice parameter. After PdSn-SnO2 samples were modified by Pt, the particle size distribution and average size of nanoparticles of Pt-PdSn-SnO2 did not obviously change, and the fcc structure of PdSn in all three samples was retained. XPS measurement showed a higher upshift of Pt 4f binding energy occurred for Pt/PdSn-SnO2 /C (HMTA) compared to those of Pt/PdSn-SnO2 /C (EDTA) and Pt/PdSn-SnO2 /C (Nacitrate). Pt/PdSn-SnO2 /C (HMTA) was also found to have the highest CO and ethanol oxidation activity among the three catalysts.Web of Scienc

Residential exposure to microbial emissions from livestock farms: Implementation and evaluation of land use regression and random forest spatial models

Adverse health effects have been linked with exposure to livestock farms, likely due to airborne microbial agents. Accurate exposure assessment is crucial in epidemiological studies, however limited studies have modelled bioaerosols. This study used measured concentrations in air of livestock commensals (Escherichia coli (E. coli) and Staphylococcus species (spp.)), and antimicrobial resistance genes (tetW and mecA) at 61 residential sites in a livestock-dense region in the Netherlands. For each microbial agent, land use regression (LUR) and random forest (RF) models were developed using Geographic Information System (GIS)-derived livestock-related characteristics as predictors. The mean and standard deviation of annual average concentrations (gene copies/m3) of E. coli, Staphylococcus spp., tetW and mecA were as follows: 38.9 (±1.98), 2574 (±3.29), 20991 (±2.11), and 15.9 (±2.58). Validated through 10-fold cross-validation (CV), the models moderately explained spatial variation of all microbial agents. The best performing model per agent explained respectively 38.4%, 20.9%, 33.3% and 27.4% of the spatial variation of E. coli, Staphylococcus spp., tetW and mecA. RF models had somewhat better performance than LUR models. Livestock predictors related to poultry and pig farms dominated all models. To conclude, the models developed enable enhanced estimates of airborne livestock-related microbial exposure in future epidemiological studies. Consequently, this will provide valuable insights into the public health implications of exposure to specific microbial agents