Nitrogen Trace Research Articles

Thermometry in noble gas dielectric barrier discharges at atmospheric pressure using optical emission spectroscopy

We measure the temperature, T, of dielectric barrier discharges (DBD), in noble gases using optical emission spectroscopy (OES), by analysing rotational bands in the emission spectra of the first negative system (FNS) of N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> . This has the advantage that rotational structure can be fully resolved even with a spectrograph of average performance, and that the rotational temperature, T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rot</sub> (~ T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gas</sub> ) can then be determined from a conventional Boltzmann plot. Ionization of N2 occurs mainly via Penning transfer from metastable excited states of He (ca. 20 eV) or Ne (ca. 16.6 eV). Using two glass-walled DBD chambers of very different volumes (0.1 and 20 liters), we have studied atmospheric-pressure discharges in flowing helium (He) or neon (Ne) containing traces of nitrogen. Discharges were excited by audio-frequency (10 kHz) high voltage (HV) using a needle as the HV electrode and a dielectric (alumina)-covered planar grounded counter-electrode. OE spectra were acquired with a 0.5 m focal length spectrograph, coupled to an intensified charge coupled device (ICCD) detector. Using the (0-0) R-branch of the FNS N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> (B <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> Σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> - X <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> Σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ) bands near a wavelength of 391.4 nm, we have measured axial (inter-electrode) distributions of T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rot</sub> for the two different reactor volumes in both He and Ne. T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rot</sub> values were found to be highest at the needle electrode, of about 450 K and 740 K for He and Ne, respectively; in He, T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rot</sub> dropped to a minimum of about 405 K at the mid-gap position in the small chamber, and ~ 360 K near the planar electrode in the large chamber. We conclude that temperatures in noble gas discharges depend critically on thermal conductivities of the particular gases (K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">He</sub> = 1.9; K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ne</sub> = 0.6, both in mW.cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> .K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ) and on other experimental factors that influence heat transfer.

Characterization of Household Solid Waste in the Town of Abomey - Calavi in Benin

Identification of waste characteristics is an important step towards improving waste recovery. The aim of this research was to determine the physical and physico-chemical characteristics of waste of Abomey–Calavi city and to study the relationship between standard of living and average ratio of daily waste generated by each person. In this study the methodology used French standards to characterize particle size and typology of solid waste generated by the population of Calavi City in Benin, West Africa. According to home criteria, the study area was stratified into three distinct levels of standard of living called: high standing, medium standing and low standing; Waste from 60 households was weighed daily. The total waste produced by each household was collected seven (7) days a week, for a period of three weeks. Waste characterization was performed using ratio, size granulometry and typological composition. Physico- Chemical analysis including organic mater, pH, Total Organic Carbon, total Kjeldahl nitrogen and metal trace element were also performed. To better assess waste compostability, water extractable organic matter was quantified and qualitative identification was made with XAD8 and XAD4 resins. Results show that the amount of waste increases with the standard of living; the average ratio of daily waste generated is 0.89 kg day-1 person-1. Independently of the standard of living, fermentable compounds represent the largest proportion of waste materials (45%). Qualitative difference of waste content in organic matter is shown as a function of the population’s living standards. These results could be explained by a higher consumption of meat in the households with a higher standard of living, reflecting a greater proportion of transphilic (TPI), and hydrophilic (HPI) fractions. The C/N ratio is lower in the high standing households than in low ones. Metal trace element analysis showed a low but still significant pollution, whereas high iron and alu minum concentrations were found in all standings. In conclusion we propose a strategy for waste management in Abomey-Calavi based on sorting at the source to eliminate plastic waste and valorization of wastes via composting.

Experimental investigation on micro-hollow cathode sustained discharge

Based on micro-hollow cathode discharge (MHCD) as a plasma cathode, a second anode was added to the device for obtaining large volume and uniform plasma at high pressure. The discharge producing condition of MCSD was investigated in the experiments. And the rotational structures of the N2 first positive bands were analyzed with traces of nitrogen added in argon for the measurements of the gas temperature in the MCSD plume. The experimental results show that when the current of the plasma cathode exceeds the threshold, the large volume stable plasma is generated. The gas temperature in the plume is increased a little with increasing the current (0.5-4 mA) and is about 500 K at the pressure of 50 Torr.

Measured density of copper atoms in the ground and metastable states in argon magnetron discharge correlated with the deposition rate

In a dc-magnetron discharge with argon feed gas, densities of copper atoms in the ground state Cu(2S1/2) and metastable state Cu*(2D5/2) were measured by the resonance absorption technique, using a commercial hollow cathode lamp as light source. The operating conditions were 0.3–14 µbar argon pressure and 10–200 W magnetron discharge power. The deposition rate of copper in a substrate positioned at 18 cm from the target was also measured with a quartz microbalance. The gas temperature, in the range 300–380 K, was deduced from the emission spectral profile of N2(C 3Πu − B 3Πg) 0–0 band at 337 nm when trace of nitrogen was added to the argon feed gas. The isotope-shifts and hyperfine structures of electronic states of Cu have been taken into account to deduce the emission and absorption line profiles, and hence for the determination of atoms' densities from the measured absorption rates. To prevent error in the evaluation of Cu density, attributed to the line profile distortion by auto-absorption inside the lamp, the lamp current was limited to 5 mA. Density of Cu(2S1/2) atoms and deposition rate both increased with the enhanced magnetron discharge power. But at fixed power, the copper density augmented with argon pressure whereas the deposition rate followed the opposite trend. Whatever the gas pressure, the density of Cu*(2D5/2) metastable atoms remained below the detection limit of 1 × 1010 cm−3 for magnetron discharge powers below 50 W and hence increased much more rapidly than the density of Cu(2S1/2) atoms, over passing this later at some discharge power, whose value decreases with increasing argon pressure. This behaviour is believed to result from the enhancement of plasma density with increasing discharge power and argon pressure, which would increase the excitation rate of copper into metastable states. At fixed pressure, the deposition rate followed the same trend as the total density of copper atoms in the ground and metastable states. Two important conclusions of this work are (i) copper atoms sputtered from the target under ion bombardment are almost all in the ground state Cu(2S1/2) and hence in the plasma volume they can be excited into the metastable states; (ii) all atoms in the long-lived ground and metastable states contribute to the deposition of copper layer on the substrate.

Assessment of trace gases, carbon and nitrogen emissions from field burning of agricultural residues in India

Field burning of crop residue (FBCR) is becoming a growing environmental concern in developing countries. In this instance, a comprehensive crop-wise and spatially distributed study on the FBCR emissions from India for the period 1980 through 2010 have been undertaken, that covers: residue generation, its types, use pattern, and estimates of carbon, nitrogen, CH4, CO, N2O and NOX emissions; along with associated uncertainties. FBCR contributed about 44 and 14% of the non-biofuel biomass and total biomass burning, respectively in India in the year 2000. The total dry residue generated are estimated as 217, 239 and 253 Tg, of which 45, 60 and 63 Tg of dry biomass are estimated to be subjected to FBCR in the years 1994, 2005 and 2010, respectively. Wheat and rice crops together accounted for about 76% of this. Burning of such huge amount of biomass is estimated to emit 22.4, 24.4 and 26.1 Tg of carbon; 0.30, 0.33 and 0.35 Tg of nitrogen; 4.18, 4.59 and 4.86 Tg carbon dioxide equivalent of greenhouse gases (GHG, viz., CH4 and N2O; which is over 1% of the Indian agriculture sector GHG emissions); 2951, 3,240 and 3,431 Gg of CO; and 120.8, 132.9 and 140.6 Gg NOx emissions in 1994, 2005 and 2010, respectively. Further, the Indian states of U.P, Punjab, Haryana, M.P, Maharashtra, T.N, Karnataka, Andhra Pradesh, Bihar and W.B have been found to contribute maximum to the Indian FBCR emissions. FBCR avoidance and optimum utilization of crop-residue resource is urgently required for agro-ecosystem sustainability in the region.

Effects of Gray-tailed Vole Activity on Soil Properties

Voles are well-known crop pests, especially when peak populations are present, but their role in soil fertility and impacts on agricultural sustainability are not well understood. Five months after the abrupt disappearance of a peak in a gray-tailed vole (Microtus canicaudus) population, we examined burrow structure, determined concentrations of trace elements, carbon and nitrogen in the soil immediately surrounding vole burrows, and compared soil chemical properties to a depth of 90 cm between areas with prior vole activity and areas of no activity. Vole tunneling activity was confined to the top 10 cm of the soil profile and was coincident with the majority of root biomass. Soil NH4 , NO3-, extractable organic carbon, and soil organic matter were greater below vole tunnels than above; however, due to small sample sizes, differences were not significant. There were no differences in trace elements with respect to position around vole tunnels. Vole activity was associated with increased soil nitrate concentrations and decreased soil pH to a depth of 90 cm, indicating that nitrification might be enhanced by vole activity, and that this effect continues after vole populations crash. Greater inorganic nitrogen could have long-term effects on ecosystem productivity. The effects voles have on soil processes that influence carbon and nutrient cycle requires further investigation.

Estuarine sediment quality assessment by Fourier-transform infrared spectroscopy

Partial least squares Fourier-transform infrared (PLS-FTIR) models were developed for the quality assessment of estuarine sediments through the evaluation of several physico-chemical parameters. Models were based on the chemometric treatment of attenuated total reflection (ATR) spectra directly obtained from samples previously lyophilized and sieved through a lower than 63 μm grid. Spectra were scanned from 3997 to 523 cm −1, averaging 36 scans per spectrum with a nominal resolution of 8 cm −1. Models were built using reference data obtained for sediment samples collected from Ria de Arousa estuary. Hierarchical cluster classification of sediment ATR spectra was employed for the establishment of the independent calibration and validation sample sets. Several parameters, like trace element content (Sn, Pb, Cd, As, Sb and total Cr and also acid soluble, reducible and oxidizable Cr fractions), elemental composition (carbon (C), nitrogen (N) and hydrogen (H) content), pH, redox potential (Eh), together with the amount of fulvic and humic acids, were evaluated. Residual predictive deviation (RPD) values ranging from 1.79 to 2.28 were obtained for all trace elements with the exception of Pb, which exhibited a RPD value of 1.5, similar to those obtained for the different extractable fractions of Cr. Regarding the elemental analysis, excellent RPD values were also obtained for C and N, but for H only adequate values for screening purposes were achieved. Prediction errors for pH and Eh were 0.13 units and 30 mV, respectively, thus indicating the good prediction capabilities of the method. For humic substances, excellent results were obtained for humic acids when compared with fulvic ones. In short, direct ART-FTIR measurements on solid sediments allow a rapid screening of many components of sediments and quantitative data of the main physico-chemical parameters.

Gas temperature and electron density profiles in an argon dc microdischarge measured by optical emission spectroscopy

Optical emisssion spectroscopy was employed to study a high pressure (100 s of Torr), slot-type (600 μm interelectrode gap), argon dc microdischarge, with added traces of nitrogen. Spatially resolved gas temperature profiles were obtained by analyzing rovibrational bands of the N2 first positive system. The gas temperature peaked near the cathode and increased with current. The contribution of Stark broadening to the hydrogen Hβ emission lineshape was used to extract the electron density. The axial distribution of electron density as well as visual observation revealed that the microdischarge positive column was highly constricted. The electron density near the sheath edge increased with both pressure and current.

Impact of trace elements on biocompatibility of titanium scaffolds

A titanium oxide scaffold has recently been reported with high compressive strength (>2 MPa) which may allow its use in bone. However, would it be possible to enhance the scaffolds’ performance by selecting a titanium oxide raw material without elemental contamination? Elements in implant surfaces have been reported to provoke implant failure. Thus, this study aims to compare different commercial titanium dioxide powders in order to choose the appropriate powder for scaffold making. The x-ray photoelectron spectroscopy (XPS) analysis identified the trace elements, mainly Al, Si, C, Ca and P. Cellular response was measured by cytotoxic effect, cell growth and cytokine secretion from murine preosteoblasts (MC3T3-E1) in vitro. The XPS data showed that traces of carbon-based molecules, silicon, nitrogen and aluminium in the powder were greatly reduced after cleaning in 1 M NaOH. As a result, reduction in cytotoxicity and inflammatory response was observed. Carbon contamination seemed to have a minor effect on the cellular response. Strong correlations were found between Al and Si contamination levels and the inflammatory response and cytotoxic effect. Thus, it is suggested that the concentration of these elements should be reduced in order to enhance the scaffolds’ biocompatibility.

Experimental Investigation of Microhollow Cathode Discharge for the Application to Microplasma Thrusters

As to microhollow cathode discharge (MHCD) in argon, the discharge characteristic was analyzed, the gas temperature was determined from the emission spectroscopy with traces of nitrogen added, and the electron density was also evaluated through the Stark broadening of the Balmer H β line from hydrogen as trace impurity in the gas. The electron density is in the order of 10 14 cm −3 and increases with the increasing gas pressure and discharge current. The gas temperature also increases with the increasing pressure and current, and can reach 1000 K in the stable glow regime. The results show that the extremely small dimensions of the MHCD combining with relative intense and controllable gas heating can be applied as a new micro electro-thermal thruster for micro-satellite propulsion. Due to the heating of the propellant gas in the microdischarge plasma and its expansion through the micro-nozzle, the performance of specific impulse and thrust of the microplasma thruster using the MHCD will be higher than the conventional cold gas microthrusters.

A biogeochemical model of contaminant fate and transport in river waters and sediments

A quasi-two-dimensional model is presented for simulating transport and transformation of contaminant species in river waters and sediments, taking into account the effect of both biotic and abiotic geochemical reactions on the contaminant fate and mobility. The model considers the downstream transport of dissolved and sediment-associated species, and the mass transfer with bed sediments due to erosion and resuspension, using linked advection–dispersion–reaction equations. The model also couples both equations to the reactive transport within bed sediment phases. This is done by the use of a set of vertical one-dimensional columns representing sediment layers that take into account the reactive transport of chemicals, burial, sorption/desorption to/from the solid phase, and the diffusive transport of aqueous species. Kinetically-controlled reversible solid-water mass exchange models are adopted to simulate interactions between suspended sediments and bulk water, as well as the mass exchange between bed sediments and pore water. An innovative multi-time step approach is used to model the fully kinetic nonlinear reaction terms using a non-iterative explicit method. This approach enables the model to handle fast and near-equilibrium reactions without a significant increase in computational burden. At the end, two demonstration cases are simulated using the model, including transport of a sorbing, non-reactive trace metal and nitrogen cycling, both in the Colusa Basin Drain in the Central Valley of California.

Flexible laser diode trace gas sensor based on cavity ringdown spectroscopy with an optical fiber-coupled high-finesse external-cavity diode laser

A flexible and portable trace nitrogen dioxide sensor based on cavity ringdown spectroscopy using an optical fiber-coupled high-finesse cavity was successfully demonstrated. Tailoring the spatial mode matching condition of the core of an optical fiber and high-finesse external cavity allows for effective optical feedback into an antireflection-coated laser diode for stable resonant enhancement of the external cavity. The external cavity, which works as a ringdown cavity, could be remotely located from the light source and receiver section by only a single mode optical fiber. The sensitivity was found to be 1.0×10−7 cm−1 in a compact 1-cm3 ringdown cavity volume.

N 2O and NO fluxes between a Norway spruce forest soil and atmosphere as affected by prolonged summer drought

Global change scenarios predict an increasing frequency and duration of summer drought periods in Central Europe especially for higher elevation areas. Our current knowledge about the effects of soil drought on nitrogen trace gas fluxes from temperate forest soils is scarce. In this study, the effects of experimentally induced drought on soil N 2O and NO emissions were investigated in a mature Norway spruce forest in the Fichtelgebirge (northeastern Bavaria, Germany) in two consecutive years. Drought was induced by roof constructions over a period of 46 days. The experiment was run in three replicates and three non-manipulated plots served as controls. Additionally to the N 2O and NO flux measurements in weekly to monthly intervals, soil gas samples from six different soil depths were analysed in time series for N 2O concentration as well as isotope abundances to investigate N 2O dynamics within the soil. N 2O fluxes from soil to the atmosphere at the experimental plots decreased gradually during the drought period from 0.2 to −0.0 μmol m −2 h −1, respectively, and mean cumulative N 2O emissions from the manipulated plots were reduced by 43% during experimental drought compared to the controls in 2007. N 2O concentration as well as isotope abundance analysis along the soil profiles revealed that a major part of the soil acted as a net sink for N 2O, even during drought. This N 2O sink, together with diminished N 2O production in the organic layers, resulted in successively decreased N 2O fluxes during drought, and may even turn this forest soil into a net sink of atmospheric N 2O as observed in the first year of the experiment. Enhanced N 2O fluxes observed after rewetting up to 0.1 μmol m −2 h −1 were not able to compensate for the preceding drought effect. During the experiment in 2006, with soil matric potentials in 20 cm depth down to −630 hPa, cumulative NO emissions from the throughfall exclusion plots were reduced by 69% compared to the controls, whereas cumulative NO emissions from the experimental plots in 2007, with minimum soil matric potentials of −210 hPa, were 180% of those of the controls. Following wetting, the soil of the throughfall exclusion plots showed significantly larger NO fluxes compared to the controls (up to 9 μmol m −2 h −1 versus 2 μmol m −2 h −1). These fluxes were responsible for 44% of the total emission of NO throughout the whole course of the experiment. NO emissions from this forest soil usually exceeded N 2O emissions by one order of magnitude or more except during wintertime.

Recovery of Nitrogen Pools and Processes in Degraded Riparian Zones in the Southern Appalachians

Establishment of riparian buffers is an effective method for reducing nutrient input to streams. However, the underlying biogeochemical processes are not fully understood. The objective of this 4-yr study was to examine the effects of riparian zone restoration on soil N cycling mechanisms in a mountain pasture previously degraded by cattle. Soil inorganic N pools, fluxes, and transformation mechanisms were compared across the following experimental treatments: (i) a restored area with vegetation regrowth; (ii) a degraded riparian area with simulated effects of continued grazing by compaction, vegetation removal, and nutrient addition (+N); and (iii) a degraded riparian area with simulated compaction and vegetation removal only (-N). Soil solution NO(3)(-) concentrations and fluxes of inorganic N in overland flow were >90% lower in the restored treatment relative to the degraded (+N) treatment. Soil solution NO(3)(-) concentrations decreased more rapidly in the restored treatment relative to the degraded (-N) following cattle (Bos taurus) exclusion. Mineralization and nitrification rates in the restored treatment were similar to the degraded (-N) treatment and, on average, 75% lower than in the degraded (+N) treatment. Nitrogen trace gas fluxes indicated that restoration increased the relative importance of denitrification, relative to nitrification, as a pathway by which N is diverted from the receiving stream to the atmosphere. Changes in soil nutrient cycling mechanisms following restoration of the degraded riparian zone were primarily driven by cessation of N inputs. The recovery rate, however, was influenced by the rate of vegetation regrowth.

Nitrogen stabilized reactive sputtering of optimized TiO2−x photocatalysts with visible light reactivity

Photoreactive and visible light responsive nonstoichiometric mixed-phase titania was prepared by reactive direct current magnetron sputtering. Trace amounts of nitrogen were added for process stabilization without being incorporated into the films. Based on the CO2 photoreduction tests and structural and optical characterization, the influence of the trace nitrogen on the sputtered nonstoichiometric TiO2 was studied and was compared to nitrogen-doped titania.

Neutron attenuation coefficients for non-invasive quantification of wood properties

Abstract Attenuation coefficients and mass attenuation coefficients of wood were determined theoretically and experimentally for thermal and cold neutrons. Experiments were carried out at the neutron imaging facilities at the Paul Scherrer Institute, Villigen (CH). For the calculation of theoretical attenuation coefficients, only the three main elemental components (carbon, oxygen and hydrogen) were taken into consideration. While hydrogen accounts only for 6% (by wt) of wood, over 90% of the attenuation can be attributed to this element. Nitrogen and other trace elements were estimated to have a negligible impact on the theoretical attenuation coefficient. For the experimental determination of the attenuation coefficients, samples from different European and tropical wood species were tested in order to examine the influence of density and extractives content. Experimental results show a very strong linear correlation between attenuation coefficient and wood density irrespective of the tested species and extractives content that play only a minor role. As neutrons are very susceptible to scattering, it is necessary to apply a scattering correction if a quantitative evaluation is intended.

Rebekah's 5p: A Case Study from Surface Analytics

Correspondence: m.petty@LSALtd.co.uk http://www.lsaltd.co.uk One day recently, one of my daughters, Rebekah, who was fi ve at the time, came to tell me that she had swallowed a fi ve-pence piece. I was not too concerned by this news. The fi ve-pence piece was quite small in comparison to Rebekah and I knew that both would part company within a day or two. However, I am a Yorkshire man. I was troubled by the potential loss of fi ve pence. So, with the aid of my son’s metal detector, we followed the progress of the fi ve pence through Rebekah. Our divinings indicated that the coin would reappear after about a day and a half. Sure enough, the coin emerged as predicted and was unscathed except for the fact that it had now changed colour. Rebekah’s fi ve-pence piece had turned a very deep and vivid blue. Intrigued by this transformation, I and my colleagues at LSA decided to try to fi nd out what changes had occurred to the coin on its travels through Rebekah. We began by taking an Auger electron spectrum of the surface of blue stain. It came as no surprise to fi nd traces of sulphur, chlorine, calcium, nitrogen and sodium along with substantial amounts of carbon, oxygen and copper. Carbon, oxygen, sulphur and chlorine are often found on air-exposed surfaces, whilst the calcium and sodium may be a residue from the soap and water used to wash the coin (normally samples are analysed as received, but in this case. . .). Interestingly, we did not detect any nickel on the surface as you might expect on a cupronickel-plated coin. The next stage in our investigation was to see how these elements varied with depth. By following the signals from the elements as we etched into the coin with an argon ion beam, we produced a composition depth profi le through the blue stain on Her Majesty’s cheek (see Fig. 1). The chlorine, calcium, nitrogen and sodium were only present at the very surface. Much to our surprise, as we etched into the surface the sulphur signal rose dramatically. The blue stain was composed of three distinct layers on top of the cupronickel plating. The outer two layers were chiefl y copper and sulphur, whilst the inner layer contained nickel and sulphur. In contrast, a control fi ve-pence piece from “petty” cash gave the composition depth profi le in Fig. 2. In this case, only a thin surface oxide was present. So, we can conclude that the anaerobic environment within Rebekah’s gut has produced a relatively thick sulphide multilayer on the surface of the coin. No children or animals were harmed in the performance of this experiment. But do not try this at home! Surface Analytics is Loughborough Surface Analysis Ltd (www.lsaltd.co.uk) and Midlands Surface Analysis (www. midsurfanalysis.co.uk) working in strategic alliance. We provide a surface chemical analysis and depth profi ling service. Areas of application include,

Assessing the environmental impact of ashes used in a landfill cover construction

Large amounts of construction materials will be needed in Europe in anticipation for capping landfills that will be closed due to the tightening up of landfill legislation. This study was conducted to assess the potential environmental impacts of using refuse derived fuel (RDF) and municipal solid waste incineration (MSWI) ashes as substitutes for natural materials in landfill cover designs. The leaching of substances from a full-scale landfill cover test area built with different fly and bottom ashes was evaluated based on laboratory tests and field monitoring. The water that drained off above the liner (drainage) and the water that percolated through the liner into the landfill (leachate) were contaminated with Cl(-), nitrogen and several trace elements (e.g., As, Cu, Mo, Ni and Se). The drainage from layers containing ash will probably require pre-treatment before discharge. The leachate quality from the ash cover is expected to have a minor influence on overall landfill leachate quality because the amounts generated from the ash covers were low, <3-30l (m(2)yr)(-1). Geochemical modelling indicated that precipitation of clay minerals and other secondary compounds in the ash liner was possible within 3 years after construction, which could contribute to the retention of trace elements in the liner in the long term. Hence, from an environmental view point, the placement of ashes in layers above the liner is more critical than within the liner.

Cross-section measurements of the N14(α,p)O17 and N14(α,α)N14 reactions between 3.5 and 6 MeV

The cross-section of the N14(α,p0)O17 reaction at angles of 90°, 135°, and 165° was measured for incident energies between 3.5 and 6.0 MeV simultaneously with the cross-section of the N14(α,α)N14 reaction at 165°. Interference between these two reactions at the angle of 165° and around 3.9 MeV was taken into account. The technique used is very powerful, thanks to the Ta450 nm/C target being implanted with a high dose of nitrogen. The N14(α,p0)O17 reaction exhibits some resonances allowing traces of nitrogen to be quantified. This reaction also offers an alternative to the N14(d,α)C12 and N14(H3e,p)O16 nuclear reactions for profiling nitrogen in the first few microns below the surface. Moreover, by using α-particles, Rutherford backscattering spectroscopy can be performed simultaneously with a good mass resolution to depth profile high Z elements in the sample. The sensitivity of these reactions (0.1%) has been tested by measuring the nitrogen traces in a titanium oxide film deposited on silicon. Depth profiling of nitrogen in a TiN layer on a silicon substrate was also performed. In addition, we publish for the first time some cross-sections values for the N14(α,p1)O17 reaction at 90° and 165°; this measurement is a challenging task.

A global sensitivity study of sulfur chemistry in a premixed methane flame model using HDMR

AbstractThe use of complex mechanisms is increasing within models describing a range of important chemical processes, including combustion. Parameters describing chemical reaction rates and thermodynamics can often be very uncertain. Highlighting the main parameters contributing to predictive uncertainty is an important part of model development. However, due to the computational cost of the models and their nonlinearity, traditional methods for sensitivity analysis are often not suitable. The high‐dimensional model representation (HDMR) method was developed to express the input–output relationship of a complex model with a high‐dimensional input space. A fully functional surrogate model can be constructed with low computational effort. First‐ and second‐order sensitivity indices can then be calculated in an automatic way, over large input parameter ranges. These provide an importance ranking for the input parameters. An extension to the existing set of HDMR tools is developed in this work, where the number of HMDR component functions can be reduced to explore large dimensional input spaces very efficiently. The HDMR tools are demonstrated for a case study of a one‐dimensional low‐pressure premixed methane flame model doped with trace sulfur and nitrogen species. Uncertainties in rate constants and thermodynamic data are considered, leading to a study of 176 input parameters. Using the new HDMR tools, the use of screening methods such as the Morris method, which aim to identify unimportant parameters beforehand, can generally be avoided. However, in certain cases, a combination of a screening method and HDMR is computationally more efficient than using HDMR alone. The final ranking of important parameters is shown to be critically dependent on the uncertainty ranges chosen due to the nonlinearity of the model. The study demonstrates that the proposed HDMR method provides a powerful tool for general application to global sensitivity analysis of complex chemical mechanisms. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 742–753, 2008