Hydrogen isotopic enrichment: an indicator of biodegradation at a petroleum hydrocarbon contaminated field site

Compound-specific carbon and hydrogen isotope analysis was used to investigate biodegradation of benzene and ethylbenzene in contaminated groundwater at Dow Benelux BV industrial site. delta13C values for dissolved benzene and ethylbenzene in downgradient samples were enriched by up to 2+/-0.5 per thousand, in 13C, compared to the delta13C value of the source area samples. delta2H values for dissolved benzene and ethylbenzene in downgradient samples exhibited larger isotopic enrichments of up to 27+/-5 per thousand for benzene and up to 50+/-5 per thousand for ethylbenzene relative to the source area. The observed carbon and hydrogen isotopic fractionation in downgradient samples provides evidence of biodegradation of both benzene and ethylbenzene within the study area at Dow Benelux BV. The estimated extents of biodegradation of benzene derived from carbon and hydrogen isotopic compositions for each sample are in agreement, supporting the conclusion that biodegradation is the primary control on the observed differences in carbon and hydrogen isotope values. Combined carbon and hydrogen isotope analyses provides the ability to compare biodegradation in the field based on two different parameters, and hence provides a stronger basis for assessment of biodegradation of petroleum hydrocarbon contaminants.     

Barium Borosilicate Sealing Glasses Synthesized by a Sol–Gel Process: Chemical Interactions with a Stainless Steel and Gas‐Tightness of a SOFC

Several glasses synthesized by sol–gel route and based on the BaO–B₂O₃–X–Al₂O₃–SiO₂ (X = CaO, MgO) glass system have been investigated to evaluate their applicability as sealant for solid oxide fuel cell (SOFC). Chemical interactions with K41X stainless steel and hydrogen‐tightness of these materials were evaluated after operations at high temperatures over 1,000 h in air atmosphere. Formation of a new phase at the steel–glass interface and formation of porosity in the glass were observed and determined as critical problems over mid‐term operations. The role of MgO is important to obtain a gas‐tight sealing. Application of the glass paste without binder addition was performed in order to avoid possible residual porosity related problems. The best glass was finally used as sealant between anodic and cathodic compartments in complete SOFCs operated at 760 and at 800 °C. Open circuit voltages and power densities of the cells were recorded during the first hours of operation.     

Photonic bandgap fibre oscillators and amplifiers

In the search for ever higher output power or energy from fibre oscillators or amplifiers a nowadays mature technology relies on enlarging the fibre mode area. Broadening of the core diameter, all other things being equal, inevitably yields a multimode fibre, thereby dramatically limiting the device usefulness. Various strategies have been deployed to design and manufacture single transverse mode fibre oscillators and amplifiers, among which making use of the so-called photonic bandgap effect to restrict the modal population seems promising. Helped by efficient and reliable numerical tools the design of large mode area singlemode photonic bandgap fibres is presented. Two fibres with 20-μm and 40-μm core diameter, both of them heavily doped with Yb³⁺ ions, have been fabricated by the widespread modified chemical vapour deposition process and are shown to behave properly when used as the core element of either continuous wave oscillators or femtosecond amplifiers. Good output beam quality (M² parameter spanning from 1.12 to 1.5 for the set of fibres studied) and high slope efficiency of 80% in cw oscillation regime are demonstrated. Furthermore the 40-μm core diameter fibre is shown to be resilient to tight bending down to 7.5-cm radius. The stack-and-draw process makes it easy to tailor the outer cladding so that a large numerical aperture can be reached. Subsequently, from this air-clad fibre, 500 fs 47 W pulses at 35 MHz are obtained from a two-stage chirped pulse amplification system.     

Birefringence effect of optical fiber laser with intracore fiberBragg grating

The spectra of Nd³⁺- and Pr³⁺-doped fibre lasers utilizing an intracore Bragg grating reflector written at 1.08-μm Bragg wavelength and a dichroic mirror for cavity feedback have been investigated under 0.6-GHz resolution. Two oscillating frequencies corresponding to two orthogonal linear polarization states of laser emission were observed. The frequencies and orientations of the two linearly polarized emissions could be changed by varying the fiber birefringence with an inline polarization controller. A phenomenological model is proposed to explain the experimental results     

Spectrally narrowed amplified spontaneous emission source at 977 nm based on a single-mode ytterbium-doped fiber

We present an amplified spontaneous emission (ASE) source based on a single-mode ytterbium-doped fiber pumped by a Nd : YVO/sub 4/ laser emitting at 914 nm. The ASE is centered on 977 nm with a bandwidth of 3 nm. With a spectrally filtered reflection of the copropagating ASE, we have obtained a source of ASE with a bandwidth of 0.4 nm and a tunability of 7 nm. This source delivers an output power of 340 for 700 mW of pump power, with a slope efficiency of 50%.     

Severe methicillin-resistant Staphylococcus aureus infections. Emergence of resistance to fusidic acid or fosfomycin during treatment with continuous infusion of vancomycin

OBJECTIVES: To evaluate the development of resistance to fosfomycin or fucidic acid in severe infections caused by methicillin-resistant Staphylococcus aureus (MRSA) and to assess the relationship with serum levels of vancomycin METHODS: A retrospective study was performed in patients hospitalized in our intensive care unit during a 3-year period (1993-1995) who were treated for severe MRSA infection with continuous infusion vacomycin and fosfomycin or fucidic acid. We analyzed the development of resistance and serum levels of vancomycin. RESULTS: During this period, only 20 patients received continuous infusion vancomycin plus fucidic acid or fosfomycin. MSRA resistant to fucidic or fosfomycin developed in 9. Vancomycin serum levels were significantly lower in patients who developed resistance to focidic acid or fosfomycin, both during the first 5 days of treatment (16.68 +/- 1.07 micrograms/ml vs. 22.64 +/- 1.05 mg/ml, p < 0.01) and throughout treatment duration (17.29 +/- 1.07 micrograms/ml vs. 21.85 +/- 0.78 microgram/ml, p < 0.01). CONCLUSIONS: Our findings confirm that in spite of continuous vancomycin infusion at an initial rate of 2 g/24 h, Staphylococcus aureus resistance to fosfomycin or fucidic acid an develop during ongoing treatment. Vancomycin levels of at least 20 micrograms/ml should be obtained as rapidly as possible.     

Relationship Between Structure and Glass Transition Temperature in Low-silica Calcium Aluminosilicate Glasses: the Origin of the Anomaly at Low Silica Content

The anomalous behavior of the glass transition temperature ( T _g) in low silica calcium aluminosilicate glasses has been related to the structural modifications observed by neutron and X-ray diffraction. The diffraction data indicate that Al and Si are in tetrahedral sites and that Ca atoms are in distorted octahedral sites. By subtracting the correlation functions for glasses at constant SiO₂ or constant Al₂O₃ content, we have shown that Si and Al atoms are introduced in a different way within the glass structure. Si is present in various Q ⁿ sites, while Al resides in Q³ and Q⁴ sites for glasses with high CaO content and enters fully polymerized Q⁴ sites with increasing SiO₂ or Al₂O₃ content. The higher proportion of Al in Q³ positions at high CaO content yields a depolymerization of the network. The lower connectivity will contribute to a decrease of the viscosity, which may be at the origin of the decrease of T _g for glasses at low silica content.