Space shuttle high pressure auxiliary propulsion subsystem definition study Summary report

Space shuttle high pressure hydrogen oxygen auxiliary propulsion subsystem conceptual and design study summar

Timescales for the development of methanogenesis and free gas layers in recently-deposited sediments of Arkona Basin (Baltic Sea)

Arkona Basin (southwestern Baltic Sea) is a seasonally-hypoxic basin characterized by the presence of free methane gas in its youngest organic-rich muddy stratum. Through the use of reactive transport models, this study tracks the development of the methane geochemistry in Arkona Basin as this muddy sediment became deposited during the last 8 kyr. Four cores are modeled each pertaining to a unique geochemical scenario according to their respective contemporary geochemical profiles. Ultimately the thickness of the muddy sediment and the flux of particulate organic carbon are crucial in determining the advent of both methanogenesis and free methane gas, the timescales over which methanogenesis takes over as a dominant reaction pathway for organic matter degradation, and the timescales required for free methane gas to form

Why not marry them? History, essentialism and the condition of slave descendants among the southern Betsileo (Madagascar)

The thesis investigates the condition of slave descendants among the southern Betsileo of Madagascar. Unlike previous research, which has focused on the dependency of those slave descendants who stayed as share-croppers on their former masters’ land and on the discrimination against slave descent migrants, the present study focuses on a group of slave descendants, the Berosaiña, who own their land and have acquired autonomy and wealth. Based on fieldwork in a rural area south of Ambalavao, the thesis presents an ethnographic study of the ambivalent relations between the Berosaiña and their neighbours of free descent. It shows that the Berosaiña’s knowledge of local history and of their ancestor’s role in the region’s settlement is one of their key stakes in local politics, while the free descendants’ refusal to marry them is the most serious obstacle to their integration. A close study of slave descendants’ genealogies and of local marriage practices suggests that, although a few ‘unilateral’ marriages occurred, no ‘bilateral’ marriage between commoner descendants and the Berosaiña ever took place. After suggesting an explanation for the avoidance of marriage with the Berosaiña, the thesis proceeds by showing that the category ‘slaves’ is essentialized by commoner descendants. The essentialist construal of ‘slaves’, it is argued, is likely to have become entrenched only in the aftermath of the abolition of slavery, because the circumstances in which it occurred prevented a large number of freed slaves to be ritually cleansed and because a number of established cultural practices made it difficult for freed slaves to marry free people. Finally, the thesis analyses the peculiar predicament of the Berosaiña in light of the strict marriage avoidance observed by commoner descendants and of commoner descendants’ highly essentialized views about ‘slaves’

A cost-efficient biogeochemical model for estuaries: a case-study of a funnel-shaped system

The hydrodynamics exerts an important influence on the biogeochemical functioning of estuarine systems. Comparative studies have long recognized this tight coupling and, for instance, have attempted to correlate key estuarine biogeochemical processes to simple hydrodynamic properties, such as the residence time or the tidal forcing. Yet, these correlations fail to resolve the estuarine spatio-temporal variability and do not provide powerful means to disentangle the complex interplay of multiple reaction and transport processes. In this context, reaction-transport models (RTMs) are useful tools to resolve the variability inherent to the estuarine environment. They ideally complement field observations, because their integrative power provides the required extrapolation means for a system-scale analysis over the entire spectrum of changing forcing conditions, including the long-term response to land-use and climate changes. However, RTM simulations are associated with high computational costs, especially when the biogeochemical dynamics are to be resolved on a regional or global scale. Furthermore, specific data requirements, such as boundary conditions or bathymetric and geometric information may limit their applicability.Here, a generic one-dimensional RTM approach which relies on idealized geometries to support the estuarine physics is used to quantify the biogeochemical dynamics. The model is cost-efficient and requires only a limited number of readily available input data. The approach is applied to a case-study of a funnel-shaped estuary (The Scheldt, BE/NL) and is tested by comparing integrative measures of the estuarine biogeochemical functioning (e.g. Net Ecosystem Metabolism, integrated CO2 fluxes) with those derived from observations (Frankignoulle et al., 1996, 1998) and highly-resolved model simulations (Vanderborght et al., 2002; Arndt et al., 2009). The method provides a robust quantitative tool to carry sensitivity and uncertainty analyses and to investigate the estuarine biogeochemistry at the regional scale

Linking biogeochemistry to hydro-geometrical variability in tidal estuaries:a generic modeling approach

This study applies the Carbon-Generic Estuary Model (C-GEM) modeling platform to simulate the estuarine biogeochemical dynamics – in particular the air-water CO₂ exchange – in three idealized end-member systems covering the main features of tidal alluvial estuaries. C-GEM uses a generic biogeochemical reaction network and a unique set of model parameters extracted from a comprehensive literature survey to perform steady-state simulations representing average conditions for temperate estuaries worldwide. Climate and boundary conditions are extracted from published global databases (e.g. World Ocean Atlas, GLORICH) and catchment model outputs (GlobalNEWS2). The whole-system biogeochemical indicators Net Ecosystem Metabolism (NEM), C and N filtering capacities (FC_TC and FC_TN, respectively) and CO₂ gas exchanges (FCO₂) are calculated across the three end-member systems and are related to their main hydrodynamic and transport characteristics. A sensitivity analysis, which propagates the parameter uncertainties, is also carried out, followed by projections of changes in the biogeochemical indicators for the year 2050. <br><br> Results show that the average C filtering capacities for baseline conditions are 40, 30 and 22% for the marine, mixed and riverine estuary, respectively. This translates into a first-order, global CO₂ outgassing flux for tidal estuaries between 0.04 and 0.07 Pg C yr^&minus;1. N filtering capacities, calculated in similar fashion, range from 22% for the marine estuary to 18 and 15% for the mixed and the riverine estuary, respectively. Sensitivity analysis performed by varying the rate constants for aerobic degradation, denitrification and nitrification over the range of values reported in the literature significantly widens these ranges for both C and N. Simulations for the year 2050 indicate that all end-member estuaries will remain net heterotrophic and while the riverine and mixed systems will only marginally be affected by river load changes and increase in atmospheric <i>p</i>CO₂, the marine estuary is likely to become a significant CO₂ sink in its downstream section. In the decades to come, such change of behavior might strengthen the overall CO₂ sink of the estuary-coastal ocean continuum

Magnetic Anisotropy of Co2+ as Signature of Intrinsic Ferromagnetism in ZnO:Co

We report on the magnetic properties of thoroughly characterized Zn1-xCoxO epitaxial thin films, with low Co concentration, x=0.003-0.005. Magnetic and EPR measurements, combined with crystal field theory, reveal that isolated Co2+ ions in ZnO possess a strong single ion anisotropy which leads to an "easy plane" ferromagnetic state when the ferromagnetic Co-Co interaction is considered. We suggest that the peculiarities of the magnetization process of this state can be viewed as a signature of intrinsic ferromagnetism in ZnO:Co materials.Comment: 4 pages, 4 figure

Continental shelves as a variable but increasing global sink for atmospheric carbon dioxide

It has been speculated that the partial pressure of carbon dioxide (pCO2) in shelf waters may lag the rise in atmospheric CO2. Here, we show that this is the case across many shelf regions, implying a tendency for enhanced shelf uptake of atmospheric CO2. This result is based on analysis of long-term trends in the air–sea pCO2 gradient (ΔpCO2) using a global surface ocean pCO2 database spanning a period of up to 35 years. Using wintertime data only, we find that ΔpCO2 increased in 653 of the 825 0.5° cells for which a trend could be calculated, with 325 of these cells showing a significant increase in excess of +0.5 μatm yr−1 (p 2 during the last century

Towards a numerical simulation of direct manufacturing of thermoplastic parts by powder laser sintering COMPLAS XI

Direct manufacturing technology using Selective Laser Sintering (SLS) on thermoplastic powders allows obtaining final parts in a short time, with classical polymer density and a high flexibility of shape and evolution of parts. The physical base of this process is the coalescence of grains, which initiates the densification of powder during SLS. This study presents a 2D C-NEM simulation of the whole process. We firstly focus on the chosen method and its advantages. We present the simulation details and validate the modeling through a 2D infinite cylinders coalescence simulation. The mesh of the grain interface is continuously adapted to the local curvature to better capture the coalescence phenomenon. We are able to simulate the sintering of twelve particles laying on a support within some hours

Amplitude equations for Rayleigh-Benard convective rolls far from threshold

An extension of the amplitude method is proposed. An iterative algorithm is developed to build an amplitude equation model that is shown to provide precise quantitative results even far from the linear instability threshold. The method is applied to the study of stationary Rayleigh-Benard thermoconvective rolls in the nonlinear regime. In particular, the generation of second and third spatial harmonics is analyzed. Comparison with experimental results and direct numerical calculations is also made and a very good agreement is found.Peer reviewe

Modelling estuarine biogeochemical dynamics: from the local to the global scale

Estuaries act as strong carbon and nutrient filters and are relevant contributors to the atmospheric CO2 budget. They thus play an important, yet poorly constrained, role for global biogeochemical cycles and climate. This manuscript reviews recent developments in the modelling of estuarine biogeochemical dynamics. The first part provides an overview of the dominant physical and biogeochemical processes that control the transformations and fluxes of carbon and nutrients along the estuarine gradient. It highlights the tight links between estuarine geometry, hydrodynamics and scalar transport, as well as the role of transient and nonlinear dynamics. The most important biogeochemical processes are then discussed in the context of key biogeochemical indicators such as the net ecosystem metabolism (NEM), air–water CO2 fluxes, nutrient-filtering capacities and element budgets. In the second part of the paper, we illustrate, on the basis of local estuarine modelling studies, the power of reaction-transport models (RTMs) in understanding and quantifying estuarine biogeochemical dynamics. We show how a combination of RTM and high-resolution data can help disentangle the complex process interplay, which underlies the estuarine NEM, carbon and nutrient fluxes, and how such approaches can provide integrated assessments of the air–water CO2 fluxes along river–estuary–coastal zone continua. In addition, trends in estuarine biogeochemical dynamics across estuarine geometries and environmental scenario are explored, and the results are discussed in the context of improving the modelling of estuarine carbon and CO2 dynamics at regional and global scales