Chemical dispersants can suppress the activity of natural oil-degrading microorganisms

Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences of the United States of America 112 (2015): 14900-14905, doi:10.1073/pnas.1507380112.During the Deepwater Horizon oil well blowout in the Gulf of Mexico, the application of 7 million liters of chemical dispersants aimed to stimulate microbial crude oil degradation by increasing the bioavailability of oil compounds. However, the effects of dispersants on oil biodegradation rates are debated. In laboratory experiments, we simulated environmental conditions comparable in the hydrocarbon-rich, 1100m deep, plume that formed during the Deepwater Horizon discharge. The presence of dispersant significantly altered the microbial community composition through selection for potential dispersant-degrading Colwellia, which also bloomed in situ in Gulf deep-waters during the discharge. In contrast, oil addition lacking dispersant stimulated growth of natural hydrocarbon-degrading Marinobacter. Dispersants did not enhance heterotrophic microbial activity or hydrocarbon oxidation rates. Extrapolating this comprehensive data set to real world scenarios questions whether dispersants stimulate microbial oil degradation in deep ocean waters and instead highlights that dispersants can exert a negative effect on microbial hydrocarbon degradation rates.This research was supported by a grant from BP/the Gulf of Mexico Research Initiative to support the "Ecosystem Impacts of Oil and Gas Inputs to the Gulf (ECOGIG)” consortium. PMM also acknowledges funding from the National Science Foundation (OCE-1057683)

Reflektierendes Kontaktschichtsystem für ein optoelektronisches Bauelement und Verfahren zu dessen Herstellung

A reflective contact layer system for an optoelectronic component (100) is specified, comprising: - a first p-doped nitride compound semiconductor layer (1), - a transparent conductive oxide layer (3), - a mirror layer (4), and - a second p-doped nitride compound semiconductor layer (2) arranged between the first p-doped nitride compound semiconductor layer (1) and the transparent conductive oxide layer (3), wherein the second p-doped nitride compound semiconductor layer (2) has N-face domains (22) at an interface (23) facing the transparent conductive oxide layer (3), and wherein the N-face domains (22) have an area proportion of at least 95 percent at the interface (23). Furthermore, a method for producing the contact layer system is specified

Ultraviolet laser ablation as technique for defect repair of GaN-based light-emitting diodes

Defect repair of GaN-based light-emitting diodes (LEDs) by ultraviolet laser micromachining is reported. Percussion and helical drilling in GaN by laser ablation were investigated using 248 nm nanosecond and 355 nm picosecond pulses. The influence of laser ablation including different laser parameters on electrical and optical properties of GaN-based LED chips was evaluated. The results for LEDs on sapphire with transparent conductive oxide p-type contact on top as well as for thin-film LEDs are reported. A reduction of leakage current by up to six orders in magnitude and homogeneous luminance distribution after proper laser defect treatment were achieved

Avalanche multiplication in AlGaN-based heterostructures for the ultraviolet spectral range

Al(x)Ga(1-x)N based avalanche photodiodes grown on sapphire substrate with Al-contents of x=0.65 and x=0.60 have been examined under back- and frontside illumination with respect to their avalanche gain properties. The photodetectors suitable for the solar-blind ultraviolet spectral regime show avalanche gain for voltages in excess of 30V reverse bias in the linear gain mode. Devices with a mesa diameter of 100 lm exhibit stable avalanche gain below the break through threshold voltage, exceeding a multiplication gain of 5500 at 84V reverse bias. A dark current below 1 pA can be found for reverse voltages up to 60 V

Design, fabrication and characterization of near milliwatt power RCLEDs emitting at 390 nm

International audienceWe report on the realization and first demonstration of CW near-milliwatt-power emission at λ = 390 nm from resonant-cavity light-emitting diode (RCLED) on GaN templates. The vertical cavity consists of a bottom AlGaN/GaN distributed Bragg reflector and a top dielectric SiO2/ZrO2 mirror enclosing a GaInN/GaN multiple-quantum-well active layer. RCLEDs with total optical output of about 600 μW at an injection current of 20 mA were achieved before packaging, taking account of current growth and processing considerations. Dislocations generated during the growth of the RCLED structure seem to be affecting the mean light output. This can be further improved by the use of high-quality low-dislocation-density GaN templates or freestanding GaN substrates

Chemical dispersants can suppress the activity of natural oil-degrading microorganisms

During the Deepwater Horizon oil well blowout in the Gulf of Mexico, the application of 7 million liters of chemical dispersants aimed to stimulate microbial crude oil degradation by increasing the bioavailability of oil compounds. However, the effects of dispersants on oil biodegradation rates are debated. In laboratory experiments, we simulated environmental conditions comparable to the hydrocarbon-rich, 1,100 m deep plume that formed during the Deepwater Horizon discharge. The presence of dispersant significantly altered the microbial community composition through selection for potential dispersant-degrading Colwellia, which also bloomed in situ in Gulf deep waters during the discharge. In contrast, oil addition to deepwater samples in the absence of dispersant stimulated growth of natural hydrocarbon-degrading Marinobacter. In these deepwater microcosm experiments, dispersants did not enhance heterotrophic microbial activity or hydrocarbon oxidation rates. An experiment with surface seawater from an anthropogenically derived oil slick corroborated the deepwater microcosm results as inhibition of hydrocarbon turnover was observed in the presence of dispersants, suggesting that the microcosm findings are broadly applicable across marine habitats. Extrapolating this comprehensive dataset to real world scenarios questions whether dispersants stimulate microbial oil degradation in deep ocean waters and instead highlights that dispersants can exert a negative effect on microbial hydrocarbon degradation rates