1,515 research outputs found
Biogeochemical controls and isotopic signatures of nitrous oxide production by a marine ammonia-oxidizing bacterium
No full textNitrous oxide (N2O)[N subscript 2 O] is a trace gas that contributes to the greenhouse effect and stratospheric ozone depletion. The N2O [N subscript 2 O] yield from nitrification (moles N2O-N [N subscript 2 O - N] produced per mole ammonium-N consumed) has been used to estimate marine N2O [N subscript 2 O] production rates from measured nitrification rates and global estimates of oceanic export production. However, the N2O [N subscript 2 O] yield from nitrification is not constant. Previous culture-based measurements indicate that N2O [N subscript 2 O] yield increases as oxygen (O2) [O subscript 2] concentration decreases and as nitrite (NO2−) [NO subscript 2 overscore] concentration increases. Here, we have measured yields of N2O [N subscript 2 O] from cultures of the marine β-proteobacterium [beta-proteobacterium] Nitrosomonas marina C-113a as they grew on low-ammonium (50 μM)[50 mu M] media. These yields, which were typically between 4 × 10−4 [10 superscript -4] and 7 × 10−4 [10 superscript -4] for cultures with cell densities between 2 × 102 [10 super script 2] and 2.1 × 104 [10 superscript 4] cells ml−1 [ml superscript -1], were lower than previous reports for ammonia-oxidizing bacteria. The observed impact of O2 [O subscript 2] concentration on yield was also smaller than previously reported under all conditions except at high starting cell densities (1.5 × 106 cells ml−1) [1.5 x 10 superscript 6 cells ml superscript -1], where 160-fold higher yields were observed at 0.5% O2 [O subscript 2](5.1 μM [mu M] dissolved O2 [O subscript 2]) compared with 20% O2 [O subscript 2] (203 μM [mu M] dissolved O2 O subscript 2]). At lower cell densities (2 × 102 [10 superscript 2] and 2.1 × 104 [10 superscript 4] cells ml−1 [ml superscript -1]), cultures grown under 0.5% O2 [O subscript 2] had yields that were only 1.25- to 1.73-fold higher than cultures grown under 20% O2 [O subscript 2]. Thus, previously reported many-fold increases in N2O [N subscript 2 O] yield with dropping O2 [O subscript 2] could be reproduced only at cell densities that far exceeded those of ammonia oxidizers in the ocean. The presence of excess NO2− [NO subscript 2 overscore] (up to 1 mM) in the growth medium also increased N2O [N subscript 2 O] yields by an average of 70% to 87% depending on O2 [O subscript 2] concentration. We made stable isotopic measurements on N2O [N subscript 2 O] from these cultures to identify the biochemical mechanisms behind variations in N2O [N subscript 2 O] yield. Based on measurements of δ15Nbulk [delta superscript 15 N superscript bulk], site preference (SP = δ15Nα−δ15Nβ [delta superscript 15 N superscript alpha - delta superscript 15 N superscript beta]), and δ18O [delta superscript 18 O] of N2O [N subscript 2 O] (δ18O-N2O [delta superscript 18 O - N subscript 2 O]), we estimate that nitrifier-denitrification produced between 11% and 26% of N2O [N subscript 2 O] from cultures grown under 20% O2 [O subscript 2] and 43% to 87% under 0.5% O2 [O subscript 2]. We also demonstrate that a positive correlation between SP and δ18O-N2O [delta superscript 18 O - N subscript 2 O] is expected when nitrifying bacteria produce N2O [N subscript 2 O]. A positive relationship between SP and δ18O-N2O [delta superscript 18 O - N subscript 2 O] has been observed in environmental N2O [N subscript 2 O] datasets, but until now, explanations for the observation invoked only denitrification. Such interpretations may overestimate the role of heterotrophic denitrification and underestimate the role of ammonia oxidation in environmental N2O [N subscript 2 O] production
The biogeochemistry of marine nitrous oxide
No full textSubmitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2011Atmospheric nitrous oxide N2O concentrations have been rising steadily for the past century
as a result of human activities. In particular, human perturbation of the nitrogen cycle has
increased the N2O production rates of the two major sources of this greenhouse gas, soil and
the ocean. Nitrification, and particularly ammonia oxidation, is one of the major processes
that produces N2O in the ocean. In this thesis, a series of stable isotopic methods have been
used to characterize the biogeochemical controls on N2O production by marine nitrification
as well as the natural abundance stable isotopic signatures of N2O produced by marine
nitrifiers. This thesis shows that in addition to chemical controls on N2O production rates
such as oxygen (O2) and nitrite (NO-2) concentrations, there are also biological controls
such as nitrifier cell abundances and coastal phytoplankton blooms that may influence N2O
production by ammonia oxidizers as well. Ammonia oxidizers can produce N2O through
two separate biochemical mechanisms that have unique isotopic signatures. Using culture-
based measurements of these signatures, we conclude that one of these pathways, nitrifier-
denitrification, may be a significant source of N2O produced in the South Atlantic Ocean
and possibly the global ocean.Funding for this work was provided by NSF/OCE 05-26277, the Andrew W. Mellon Founda-
tion Awards for Innovative Research, the Cecil H. and Ida M. Green Technology Innovation
Awards, and the W. M. Keck Foundation
Key factors in frame-building
No full textIn this article, the author focuses on the relationship between political actors and the mass media. The author uses media frames as dependent variables and investigates the factors that influence the presence and frequency of frames applied by journalists (the frames in “news media”). This has come to be known as frame building. The author argues that there are at least three important factors in frame building: power, the salience of the frames in the media input, and the multiplication effect of the minister. Using data from content analyses of campaign material and news media and from interviews with political actors, the author finds support that for frame presence, power is important. For frame frequency, the salience of the frames in the media input and the minister are crucial
New Stationary Frame Control Scheme for Three Phase PWM Rectifiers Under Unbalanced Voltage Dips Conditions
No full textA new stationary frame control scheme for three-phase pulsewidth-modulation (PWM) rectifiers operating under unbalanced voltage dips conditions is proposed in this paper. The proposed control scheme regulates the instantaneous active power at the converter poles to minimize the harmonics of the input currents and the output voltage ripple. This paper's novelty is the development of a new current-reference generator implemented directly in stationary reference frame. This allows using proportional sinusoidal signal integrator (P-SSI) controllers for simultaneous compensation of both positive and negative current sequence components. No phase-locked loop (PLL) strategies and coordinate transformations are needed for the proposed current-reference generator. Experimental results are presented for a 20-kV A alternative current (ac)/direct current (dc) converter prototype to demonstrate the effectiveness of the proposed control scheme. A comparison with two other existing control techniques is also performed. Fast dynamic performance with small dc-link voltage ripple and input sinusoidal currents are obtained with this control scheme, even under severe voltage dips operating condition
Multiple description video coding for stereoscopic 3D
No full textIn this paper, we propose an MDC schemes for stereoscopic 3D video. In the literature, MDC has previously been applied in 2D video but not so much in 3D video. The proposed algorithm enhances the error resilience of the 3D video using the combination of even and odd frame based MDC while retaining good temporal prediction efficiency for video over error-prone networks. Improvements are made to the original even and odd frame MDC scheme by adding a controllable amount of side information to improve frame interpolation at the decoder. The side information is also sent according to the video sequence motion for further improvement. The performance of the proposed algorithms is evaluated in error free and error prone environments especially for wireless channels. Simulation results show improved performance using the proposed MDC at high error rates compared to the single description coding (SDC) and the original even and odd frame MDC
Henri Matisse Drawing: An Eye-Hand Interaction Study Based on Archival Film.
No full textHenri Matisse (1869-1954) attached fundamental importance to his drawings, in particular to the famous Themes et Variations series. These were accomplished following a precise method, starting with arduous life studies and evolving into brilliant spontaneous drawings. A 1946 archival documentary film showing the artist drawing four portraits of his grandson Gerard was shot in such a way as to allow the present author to undertake a detailed eye-hand interaction analysis of the drawing process.
It was found that Matisse’s temporal working rhythm and use of motor memory resulted in a more direct approach than that used by most painters. Taken together with remarks the artist made throughout his lifetime, these results provide a cognitive interpretation of his drawing method
Scale, Frame and Language: Highway community center in the periphery of Rome
No full textThe periphery of Rome in its chaotic sprawl created a condition of extremes. Trough time the distinction between private and public space, between low density and high density became blurred generating a condition where different scales of space and time cross each other. This thesis develops a process where this condition of constant limit is premise. Through the understanding how an architectural object can mediate and transform the periphery, 6 disciplines are extrapolated in the research to be used as design tools. Zooming from top-down to bottom-up, the tools are continuously used to frame architectural space which is transformed and materialized with a an architectural language. Scale/Frame/Language is an abstract machine that emerges from the context to become a-contextual, it is a finite set of instructions that has infinite outcomes.Border ConditionPublic BuildingArchitectur
Thinking the unthinkable: managerialization of work related suicides as a framing process.
No full textManagerialism has been studied in many ways, including diffusion of management techniques notably in public sectors, management ideology or the colonization of everyday life by management thought. However, the process leading to managerialism, namely managerialization, has been largely unexplored in this literature. This article draws upon framing theory to better understand managerialization processes. The article offers two case studies that investigate following theoretical assumptions: (1) managerialization acts as a framing process on every kind of issue; (2) managerialization has framing process characteristics. Two frame analysis based on newspaper articles about work related suicide show that one of the identified frames has strong managerial characteristics and suggest that managerialization took place as a set of framing processes. Taken together, these studies provide insight to characterize the process of managerialization. Research implications and limitations are discussed in order to highlight directions for futher researchs.Work related suicide; Framing process; Frame analysis; Managerialism; Managerialization;
The Common Frame of Reference in Europe
No full textDiscusses the origins of the Draft Common Frame of Reference and assesses the need for further work in particular areas, taking as an example the subject of restitutionary damages for non-performance of a contract. Also assesses the possible relevance of the DCFR in work on African legal unity
Life as it should be: Tapping into the potentials of cross-fertilization in design
No full textToday's cities present new challenges, and ask for a different breed of designers. Who are these future designers; what are their responsibilities, values, and skills; and how do our design schools need to change in order to produce them? This book hypothesizes that interdisciplinary, intercultural education will be crucial for the preparation of the next generation of designers. It explores new models for design education, looking at the Next City joint studio as a first step.UrbanismArchitectur
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