Anaerobic methane oxidation and aerobic methane production in an east African great lake (Lake Kivu)

We investigated CH₄ oxidation in the water column of Lake Kivu, a deep meromictic tropical lake with CH₄-rich anoxic deep waters. Depth profiles of dissolved gases (CH₄ and N₂O) and a diversity of potential electron acceptors for anaerobic CH₄ oxidation (NO₃^?, SO₄^2?, Fe and Mn oxides) were determined during six field campaigns between June 2011 and August 2014. Denitrification measurements based on stable isotope labelling experiments were performed twice. In addition, we quantified aerobic and anaerobic CH₄ oxidation, NO₃^? and SO₄^2? consumption rates, with and without the presence of an inhibitor of SO₄^2?-reducing bacteria activity. Aerobic CH₄ production was also measured in parallel incubations with the addition of an inhibitor of aerobic CH₄ oxidation. The maximum aerobic and anaerobic CH₄ oxidation rates were estimated to be 27?±?2 and 16?±?8?μmol/L/d, respectively. We observed a difference in the relative importance of aerobic and anaerobic CH₄ oxidation during the rainy and the dry season, with a greater role for aerobic oxidation during the dry season. Lower anaerobic CH₄ oxidation rates were measured in presence of molybdate in half of the measurements, suggesting the occurrence of linkage between SO₄^2? reduction and anaerobic CH₄ oxidation. NO₃^? consumption and dissolved Mn production rates were never high enough to sustain the measured anaerobic CH₄ oxidation, reinforcing the idea of a coupling between SO₄^2? reduction and CH₄ oxidation in the anoxic waters of Lake Kivu. Finally, significant rates (up to 0.37?μmol/L/d) of pelagic CH₄ production were also measured in oxygenated waters.     

Analytical model for the high-temperature behaviour of the subthreshold slope in MuGFETs

As MuGFETs are promising contenders for the end of the silicon Roadmap, their high-temperature behaviour needs to be addressed. In this work we investigate the variations of the subthreshold slope (SS) of double-gate devices and MuGFETs with intrinsic doping as a function of the temperature and fin width. Focus is placed on the superlinear behaviour of SS occurring above a certain temperature threshold. Numerical simulations are performed using Comsol Multiphysics^™ and a 1D analytical model is developed. The model, which includes the effect of film and gate oxide thickness, is shown to accurately fit the numerical data. A new definition for the subthreshold slope under high-temperature operation is proposed. The high-temperature subthreshold slope degradation is shown to increase with fin width.     

MCT technology challenges for mass production

Second generation infrared (IR) detectors are now mature at the production level. These detectors are mostly based on HgCdTe (MCT) materials technology. The main second generation detectors at the mass production level are the 288 4 long wave length for most of the European forward-looking infrared (FLIR) and the 480 6 long wave length for the U.S. Army SADA applications. As far as the 288 4 is concerned, SOFRADIR has delivered more than 3000 units already and the market is estimated to be 15,000 units at least! The market is also very large for SADA II units and SOFRADIR has produced them since the end of 1999. Thus, SOFRADIR produces large quantities of mercury cadmium telluride (MCT) detectors and has a unique experience for MCT detectors in mass production. MCT materials technology challenges for mass production concern the main following issues: Quality and reproducibility, MCT wafer size increase, array yield level increase, and the collective manufacturing approach. These issues are discussed in detail in this paper as well as future trends.     

A hierarchical approach for planning a multisensor multizone search for a moving target

This paper deals with a well-known problem in the general area of search theory: optimize the search resources sharing so as to maximize the probability of detection of a (moving) target. However, the problem we consider here considerably differs from the classical one. First, there is a bilevel search planning and we have to consider jointly discrete and continuous optimization problems. To this perspective original methods are proposed within a common framework. Furthermore, this framework is sufficiently general and versatile so as to be easily and successfully extended to the difficult problem of the multizone multisensor search planning for a Markovian target.     

RFID behavior study in enclosed marine container for real time temperature tracking

The performance of radio waves in open environments has been studied for years. In contrast, the behavior of Radio Frequency Identification (RFID) inside metal enclosed areas is not yet understood. This research project focuses on the 3-D mapping of RFID signal strength inside a 12 m refrigerated marine container instrumented with three different types of radio frequency (RF) emitters: 915 MHz reader; 2.45 GHz reader and 433 MHz RF transmitter. The main goal is to find a frequency/configuration that would allow real time reading of the temperature in a shipment of perishable products using RFID. Only one frequency and one antenna were used at a time. The RF transmitter antenna was mounted at two different places inside the container; at the top of the front wall (facing back) and on the ceiling in the middle of the container (facing down). The signal strength was acquired by a spectrum analyzer and its antenna was mounted on a small electric cart inside the container. The cart was programmed to move along the length of the container and stop repeatedly, allowing three automated measures per position. All data were analyzed in terms of power level and attenuation. The maps showed that the RFID antenna positioned at the front of the container delivered slightly better results than the one in the middle of the ceiling. The results showed a significantly higher performance at the 433 MHz level. This article was presented at Food Processing Automation Conference, American Society of Agricultural and Biological Engineering (ASABE), Providence, RI, June 28–29 2008.     

The effect of a scattering layer on the edge output of a luminescent solar concentrator

The effect of adding white scattering layers to the bottom side of luminescent solar concentrator waveguides is evaluated. It is determined that adding a rear scatterer separated from the waveguide by an air gap results in a large increase of energy output from the waveguides, and this enhancement persists over long (>30 cm) distances, although the magnitude of the enhancement decreases with distance. An attached scatterer resulted in the greatest improvement of light output for short (∼6 cm) distances, but actually reduced edge emissions over longer distances. We provide estimates for the relative contribution of dye-emitted light and scattered light to the total waveguide emission, as well as distinguishing between the contributions of direct and indirect scattering of light to the total output as a function of dye content of the waveguides.     

Electrical contact resistance between stainless steel bipolar plate and carbon felt in PEFC: A comprehensive study

Bipolar plate represents a key component of Proton Exchange Membrane Fuel Cell (PEFC) with several essential functions, among them the electric connection of elementary cells. Usually made of graphite, this component is studied worldwide in order to develop a commercially viable alternative: different ways have been being investigated, and to date, despite corrosion issues, stainless steel (SS) appears as a good candidate material, but its Electrical Contact Resistance (ECR) can reach unacceptable values when exposed to PEFC environment. This paper offers a comprehensive study of the parameters acting on ECR when using uncoated SS in PEFC: roughness, which influences the surface contact area with carbon baking, bulk composition of the alloy, which influences only partly the nature of passive films, and the composition and structure of passive films, strongly modified by surface treatments and ageing conditions.     

Formation of the Perovskite Phase in the PbMg1/3Nb2/3O3─PbTiO3 System

The reaction sequences during calcination of oxide mixtures were studied for the PbMg_1/3Nb_2/3O₃─PbTiO₃ (PMN-PT) system. The effect of reactivity and composition of the starting mixtures was investigated. In the present study, a B-site-deficient, cubic pyrochlore phase in the PbO-Nb₂O₅ system was formed at 500°C. The perovskite phase of PMN was formed at 7007deg;C through the diffusion of MgO into the pyrochlore phase. The lattice parameter of the pyrochlore phase decreased as this transformation to perovskite progressed.     

Arachidonic acid autoxidation in an aqueous media effect of α-tocopherol,cysteine and nucleic acids

The autoxidation of arachidonic acid dispersed in aqueous media was evaluated simultaneously with and without different agents, e.g., α-tocopherol at different concentrations, cysteine, DNA and RNA. The autoxidation rate of arachidonic acid was evaluated by quantitative gas liquid chromatography (GLC) determination of the unoxidized acid and by spectrophotometric measurement of conjugated dienes. α-Tocopherol exhibited a prooxidant activity at concentrations of 1.25 × 10⁻⁴ M and 1.25 × 10⁻⁵ M and a weak antioxidant activity at a concentration of 1.25 × 10⁻⁶ M. Cysteine showed antioxidant activity and greatly reduced the prooxidant activity of α-tocopherol. DNA and RNA had no effect in either case. α-Tocopherol oxidation was followed by high pressure liquid chromatography (HPLC). The prooxidant effect was accompanied by a rapid oxidation of α-tocopherol, except in the presence of cysteine, which prevented the oxidation of α-tocopherol.