Abiotic release of nitrous acid (HONO) in equilibrium with soil nitrite (NO 2 - ) was suggested as an important contributor to the missing source of atmospheric HONO and hydroxyl radicals (OH). The ...role of total soil-derived HONO in the biogeochemical and atmospheric nitrogen cycles, however, has remained unknown. In laboratory experiments, we found that for nonacidic soils from arid and arable areas, reactive nitrogen emitted as HONO is comparable with emissions of nitric oxide (NO). We show that ammonia-oxidizing bacteria can directly release HONO in quantities larger than expected from the acid-base and Henry's law equilibria of the aqueous phase in soil. This component of the nitrogen cycle constitutes an additional loss term for fixed nitrogen in soils and a source for reactive nitrogen in the atmosphere.
The nitrogen dioxide (NO2) exchange between the atmosphere and needles of Picea abies L. (Norway Spruce) was studied under uncontrolled field conditions using a dynamic chamber system. This system ...allows measurements of the flux density of the reactive NO-NO2-O3 triad and additionally of the non-reactive trace gases CO2 and H2O. For the NO2 detection a highly NO2 specific blue light converter was used, which was coupled to chemiluminescence detection of the photolysis product NO. This NO2 converter excludes known interferences with other nitrogen compounds, which occur by using more unspecific NO2 converters. Photo-chemical reactions of NO, NO2, and O3 inside the dynamic chamber were considered for the determination of NO2 flux densities, NO2 deposition velocities, as well as NO2 compensation point concentrations. The calculations are based on a bi-variate weighted linear regression analysis (y- and x-errors considered). The NO2 deposition velocities for spruce, based on projected needle area, ranged between 0.07 and 0.42 mm s−1. The calculated NO2 compensation point concentrations ranged from 2.4 ± 9.63 to 29.0 ± 16.30 nmol m−3 (0.05–0.65 ppb) but the compensation point concentrations were all not significant in terms of compensation point concentration is unequal to zero. These data challenge the existence of a NO2 compensation point concentration for spruce. Our study resulted in lower values of NO2 gas exchange flux densities, NO2 deposition velocities and NO2 compensation point concentrations in comparison to most previous studies. It is essential to use a more specific NO2 analyzer than used in previous studies and to consider photo-chemical reactions between NO, NO2, and O3 inside the chamber.
We describe a dynamic chamber system to determine reactive trace gas exchange fluxes between plants and the atmosphere under laboratory and, with small modifications, also under field conditions. The ...system allows measurements of the flux density of the reactive NO-NO2-O3 triad and additionally of the non-reactive trace gases CO2 and H2O. The chambers are made of transparent and chemically inert wall material and do not disturb plant physiology. For NO2 detection we used a highly NO2 specific blue light converter coupled to chemiluminescence detection of the photolysis product, NO. Exchange flux densities derived from dynamic chamber measurements are based on very small concentration differences of NO2 (NO, O3) between inlet and outlet of the chamber. High accuracy and precision measurements are therefore required, and high instrument sensitivity (limit of detection) and the statistical significance of concentration differences are important for the determination of corresponding exchange flux densities, compensation point concentrations, and deposition velocities. The determination of NO2 concentrations at sub-ppb levels (<1 ppb) requires a highly sensitive NO/NO2 analyzer with a lower detection limit (3σ-definition) of 0.3 ppb or better. Deposition velocities and compensation point concentrations were determined by bi-variate weighted linear least-squares fitting regression analysis of the trace gas concentrations, measured at the inlet and outlet of the chamber. Performances of the dynamic chamber system and data analysis are demonstrated by studies of Picea abies L. (Norway Spruce) under field and laboratory conditions. Our laboratory data show that the quality selection criterion based on the use of only significant NO2 concentration differences has a considerable impact on the resulting compensation point concentrations yielding values closer to zero. The results of field experiments demonstrate the need to consider photo-chemical reactions of NO, NO2, and O3 inside the chamber for the correct determination of the exchange flux densities, deposition velocities, as well as compensation point concentrations. Under our field conditions NO2 deposition velocities would have been overestimated up to 80%, if NO2 photolysis has not been considered. We also quantified the photolysis component for some previous NO2 flux measurements. Neglecting photo-chemical reactions may have changed reported NO2 compensation point concentration by 10%. However, the effect on NO2 deposition velocity was much more intense, ranged between 50 and several hundreds percent. Our findings may have consequences for the results from previous studies and ongoing discussion of NO2 compensation point concentrations.
To investigate the energy, matter and reactive and non-reactive trace gas exchange between the atmosphere and a spruce forest in the German mountain region, two intensive measuring periods were ...conducted at the FLUXNET site DE-Bay (Waldstein-Weidenbrunnen) in September/October 2007 and June/July 2008. They were part of the project "ExchanGE processes in mountainous Regions" (EGER). Beyond a brief description of the experiment, the main focus of the paper concerns the coupling between the trunk space, the canopy and the above-canopy atmosphere. Therefore, relevant coherent structures were analyzed for different in- and above canopy layers, coupling between layers was classified according to already published procedures, and gradients and fluxes of meteorological quantities as well as concentrations of non-reactive and reactive trace compounds have been sorted along the coupling classes. Only in the case of a fully coupled system, it could be shown, that fluxes measured above the canopy are related to gradients between the canopy and the above-canopy atmosphere. Temporal changes of concentration differences between top of canopy and the forest floor, particularly those of reactive trace gases (NO, NO2, O3, and HONO) could only be interpreted on the basis of the coupling stage. Consequently, only concurrent and vertically resolved measurements of micrometeorological (turbulence) quantities and fluxes (gradients) of trace compounds will lead to a better understanding of the forest-atmosphere interaction.
Automated health monitoring of a pulsed power system Peters, C.; Huhman, B.; Breuninger, C. ...
2014 IEEE 41st International Conference on Plasma Sciences (ICOPS) held with 2014 IEEE International Conference on High-Power Particle Beams (BEAMS)
Conference Proceeding
The field of pulsed power has enjoyed widespread utilization, from industrial welding to high power microwave generation. In pulsed power, an energy storage device is charged to a specific voltage ...over a long time period. To achieve high peak power, the energy storage device is discharged over a small time duration, ranging from nanoseconds to microseconds, depending on the application. As the field matures from single-shot machines that fire only a few times a day to rep-rated operation with several shots per minute, the ability for operators to determine the operational state of the system on the fly is extremely limited. This paper discusses the application of Singular Value Decomposition (SVD) to real-time data output from Rogowski coils on a capacitor bank to determine the state of health between shots. The SVD pattern recognition system can be used to rapidly ascertain if the system should continue to operate, or if there is a potential problem developing somewhere in the system. This technique may lead to improving the operation of current and future pulsed power systems.
In this discussion, I examine the strategic planning experience of the Information Design and Development organization in DuPont External Affairs. It describes why we undertook our strategic planning ...initiative, the process we used, the logistics involved in preparing for and carrying
out the process, and the results of our work.
We must do strategic planning to ensure our survival as publications professionals in our organizations. A strategic plan looks ahead at least five years and encompasses all of the organization's ...activities. Most importantly, strategic planning requires a commitment to change. The articles
in this special issue provide examples of strategic planning techniques and their implementation.
A performance comparison of an interleaved boost converter (IBC) using Si and SiC diodes for photovoltaic (PV) energy conversion systems is presented in this paper. The performance attributes under ...investigation include the semiconductor device behavior, thermal requirement, system efficiency, and power density. The IBC is designed to sustain the dc-link voltage in the energy conversion system and to provide the maximum power point tracking in the PV system. Due to the absence of reverse recovery current in SiC Schottky diodes, low switching losses are generated in diodes and switches. This benefit results in a higher system efficiency and smaller cooling system design requirement. As a benefit, the volume and weight of the heatsink can be further reduced. Furthermore, behaviors of the power semiconductors, which will impact the performance in the system, are discussed in the paper. The validity of the analysis is confirmed experimentally with a 2.5-kW IBC prototype with relatively wide power and input voltage operating range. The overall performance of the IBC prototype using Si and SiC diodes is summarized in a table for easy comparison.
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