Seawater carbonate chemistry and combined mechanistic effects of CO2 and light on the N2-fixing cyanobacterium Trichodesmium IMS101, 2010

The marine diazotrophic cyanobacterium Trichodesmium responds to elevated atmospheric CO2 partial pressure (pCO2) with higher N2 fixation and growth rates. To unveil the underlying mechanisms, we examined the combined influence of pCO2(150 and 900 µatm) and light (50 and 200 µmol photons m-2 s-1) on TrichodesmiumIMS101. We expand on a complementary study that demonstrated that while elevated pCO2 enhanced N2 fixation and growth, oxygen evolution and carbon fixation increased mainly as a response to high light. Here, we investigated changes in the photosynthetic fluorescence parameters of photosystem II, in ratios of the photosynthetic units (photosystem I:photosystem II), and in the pool sizes of key proteins involved in the fixation of carbon and nitrogen as well as their subsequent assimilation. We show that the combined elevation in pCO2 and light controlled the operation of the CO2-concentrating mechanism and enhanced protein activity without increasing their pool size. Moreover, elevated pCO2 and high light decreased the amounts of several key proteins (NifH, PsbA, and PsaC), while amounts of AtpB and RbcL did not significantly change. Reduced investment in protein biosynthesis, without notably changing photosynthetic fluxes, could free up energy that can be reallocated to increase N2 fixation and growth at elevated pCO2 and light. We suggest that changes in the redox state of the photosynthetic electron transportchain and posttranslational regulation of key proteins mediate the high flexibility in resources and energy allocation in Trichodesmium. This strategy should enableTrichodesmium to flourish in future surface oceans characterized by elevated pCO2, higher temperatures, and high light.

Impact of N2 plasma power and duration on AlGaN/GaN HEMT

urface treatments have been recently shown to play an active role in electrical characteristics in AlGaN/GaN HEMTs, in particular during the passivation processing [1-4]. However, the responsible mechanisms are partially unknown and further studies are demanding. The effects of power and time N2 plasma pre-treatment prior to SiN deposition using PE-CVD (plasma enhanced chemical vapour deposition) on GaN and AlGaN/GaN HEMT have been investigated. The low power (60 W) plasma pre-treatment was found to improve the electronic characteristics in GaN based HEMT devices, independently of the time duration up to 20 min. In contrast, high power (150 and 210 W) plasma pretreatment showed detrimental effects in the electronic properties (Fig. 1), increasing the sheet resistance of the 2DEG, decreasing the 2DEG charge density in AlGaN/GaN HEMTs, transconductance reduction and decreasing the fT and fmax values up to 40% respect to the case using 60 W N2 plasma power. Although AFM (atomic force microscopy) results showed AlGaN and GaN surface roughness is not strongly affected by the N2-plasma, KFM (Kelvin force microscopy) surface analysis shows significant changes in the surface potential, trending to increase its values as the plasma power is higher. The whole results point at energetic ions inducing polarization-charge changes that affect dramatically to the 2-DEG charge density and the final characteristics of the HEMT devices. Therefore, we conclude that AlGaN surface is strongly sensitive to N2 plasma power conditions, which turn to be a key factor to achieve a good surface preparation prior to SiN passivation.

Valence photoionization of the N2 molecule in the region of the N 1s→Rydberg excitations

The intensities of the X and A valence photoelectron lines of N2 have been found to display Fano line shapes as a function of photon energy around the N 1s→ Rydberg excitations. The vibrational intensity distributions of these photoelectron lines change at the N 1s→3sσ and 3pπ resonances. These effects indicate interference between direct and resonant photoionization channels. Our numerical simulations reproduce quite well the experimental results.

Impact of N2 plasma power discharge on AlGaN/GaN HEMT performance

The effects of power and time conditions of in situ N2 plasma treatment, prior to silicon nitride (SiN) passivation, were investigated on an AlGaN/GaN high-electron mobility transistor (HEMT). These studies reveal that N2 plasma power is a critical parameter to control the SiN/AlGaN interface quality, which directly affects the 2-D electron gas density. Significant enhancement in the HEMT characteristics was observed by using a low power N2 plasma pretreatment. In contrast, a marked gradual reduction in the maximum drain-source current density (IDS max) and maximum transconductance (gm max), as well as in fT and fmax, was observed as the N2 plasma power increases (up to 40% decrease for 210 W). Different mechanisms were proposed to be dominant as a function of the discharge power range. A good correlation was observed between the device electrical characteristics and the surface assessment by atomic force microscopy and Kelvin force microscopy techniques.

Atraque discontinuo Nº2 en la explanada de inflamables del puerto de Barcelona

A lo largo de la historia, el Puerto de Barcelona ha seguido el mismo modelo en el crecimiento de sus infraestructuras, consistente en un incremento de la superficie portuaria mediante la formación de terminales portuarias en zonas de aguas abrigadas siendo éstas generadas mediante el desarrollo de grandes diques a lo largo de la costa. Las obras del presente proyecto tienen como fin la creación de la infraestructura necesaria para poder ubicar un nuevo atraque para buques que transporten petróleo en el denominado Muelle de Inflamables del Puerto de Barcelona. El objeto del proyecto es el diseño y definición a nivel constructivo de la infraestructura básica de un atraque que sirva como interfaz entre buque y tierra para la transferencia de productos refinados. Este terminal deberá dar servicio a buques trasportadores de graneles líquidos, de entre 180 y 300 m de eslora, y se ubicará en la cara noroeste del Muelle de Inflamables, a unos 335 m del Nou Contradie.