222 research outputs found
Torque measurements and flowvisualisations in a wide gap Taylor-Couette flow
No full textThe Torque acting on the inner cylinder in a differentially rotating Taylor-Couette flow is investigated. In the past a torque maximum has been found in the counter rotating regime. Using flow visualisations and LDA measurements a deeper look inside the flow in the vicinity of this maximum will be done
Experimental investigation of Taylor-Couette flow with radius ratio 0.1 to 0.3
No full textTurbulent flow of a very wide Taylor Couette flow (radius ratio 0.1 up to 0.3) is the scope of the present work. Flow visualisation shows the existing coherent structures. Laser Doppler Velocimetry is used to analyse the local velocity behaviour and understand the flow in this geometry
Measurements of small radius ratio turbulent Taylor-Couette flow
No full textIn Taylor-Couette flow, the radius ratio () is one of the key parameters of the system. For small , the asymmetry of the inner and outer boundary layer becomes more important, affecting the general flow structure and boundary layer characteristics. Using high-resolution particle image velocimetry we measure flow profiles for a radius ratio of 0.5 and Taylor number of up to . By measuring at varying heights, roll structures are characterized for two different rotation ratios of the inner and outer cylinder. In addition, we investigate how the turbulent bursts coming from the inner and outer cylinder affect the flow profiles. These results exemplify how curvature affects flow in strongly turbulent Taylor-Couette Flow
Ecosystem - atmosphere exchange of carbon dioxide in highly seasonal environments under the aspect of disturbance
No full textA framework for assessing the effects of shock events on livestock and environment in sub-Saharan Africa: The COVID-19 pandemic in Northern Kenya
No full textCONTEXT
Livestock are the primary source of greenhouse gas (GHG) emissions from agriculture in most African countries, but there is a paucity of baseline data and monitoring of GHG emissions from livestock in Africa, particularly for extreme or shock events. The COVID-19 pandemic represents a novels shock to livestock systems and may result in indirect effects on livestock emissions and other Sustainable Development Goals (SDGs). Due to the pandemic in 2020, extensive pastoralist livestock systems in Northern Kenya were subjected to restrictions on movement, increased costs of transportation, and closure of livestock markets.
OBJECTIVE
The objective of this study was to assess the indirect effects of the COVID-19 pandemic on GHG emissions from livestock systems in Northern Kenya using proxy data and a three-part framework based on changes in 1) herd size, 2) feed availability, and 3) livestock movement.
METHODS
We evaluated changes in GHG emissions from livestock systems in Northern Kenya due to the COVID-19 pandemic based on proxy data from crowd-sourced market data, household panel surveys, and remote sensing data on Normalized Difference Vegetation Index (NDVI). Proxy data were obtained before the pandemic in 2019 and after the pandemic in 2020 to compare between years and evaluate the indirect effects of the pandemic and associated restrictions on livestock GHG emissions using the three-part framework.
RESULTS AND CONCLUSIONS
Overall GHG emissions from livestock in Northern Kenya have decreased due to the pandemic and this was largely driven by reductions in herd size. This reduction in GHG emissions occurred despite an increase in GHG emissions from livestock associated with higher feed availability. Decreased livestock movement due to the pandemic contributed to reductions in GHG emissions from livestock, but such reductions were likely to be small due to limited need for livestock to travel longer distances under the prevailing conditions of high feed availability.
SIGNIFICANCE
This research shows that assessments of changes in GHG emissions from livestock systems due to shock events can be conducted successfully based on proxy data and the three-part framework developed here. We found that shock events, such as the COVID-19 pandemic, may lead to unexpected results with respect to the direction and magnitude of changes in livestock emissions depending on contextual factors and environmental conditions. Thus, we call for more spatially explicit and continued data collection to assess and monitor the consequences of shock events on GHG emissions from livestock and related SDGs in Africa
Estimating the storage term in eddy covariance measurements: The ICOS methodolog
No full textIn eddy covariance measurements, the storage flux represents the variation in time of the dry molar fraction of a given gas in the control volume representative of turbulent flux. Depending on the time scale considered, and on the height above ground of the measurements, it can either be a major component of the overall net ecosystem exchange or nearly negligible. Instrumental configuration and computational procedures must be optimized to measure this change at the time step used for the turbulent flux measurement. Three different configurations are suitable within the Integrated Carbon Observation System infrastructure for the storage flux determination: separate sampling, subsequent sampling and mixed sampling. These configurations have their own advantages and disadvantages, and must be carefully selected based on the specific features of the considered station. In this paper, guidelines about number and distribution of vertical and horizontal sampling points are given. Details about suitable instruments, sampling devices, and computational procedures for the quantification of the storage flux of different GHG gases are also provided
Eddy covariance raw data processing for CO2 and energy fluxes calculation at ICOS ecosystem stations
No full textThe eddy covariance is a powerful technique to
estimate the surface-atmosphere exchange of different scalars
at the ecosystem scale. The EC method is central to the ecosys tem component of the Integrated Carbon Observation System,
a monitoring network for greenhouse gases across the European
Continent. The data processing sequence applied to the collected
raw data is complex, and multiple robust options for the differ ent steps are often available. For Integrated Carbon Observation
System and similar networks, the standardisation of methods is
essential to avoid methodological biases and improve compara bility of the results. We introduce here the steps of the processing
chain applied to the eddy covariance data of Integrated Carbon
Observation System stations for the estimation of final CO2, water
and energy fluxes, including the calculation of their uncertain ties. The selected methods are discussed against valid alternative
options in terms of suitability and respective drawbacks and
advantages. The main challenge is to warrant standardised pro cessing for all stations in spite of the large differences in e.g.
ecosystem traits and site conditions. The main achievement of
the Integrated Carbon Observation System eddy covariance data
processing is making CO2 and energy flux results as comparable
and reliable as possible, given the current micrometeorological
understanding and the generally accepted state-of-the-art process ing metho
Severe below-maintenance feed intake increases methane yield from enteric fermentation in cattle
No full textDigesta passage and nutrient digestibility in Boran steers at low feed intake levels
No full textThe present study evaluated the effects of energetic undernutrition on liquid and solid digesta passage and on nutrient digestibility as well as their interdependencies. Using a 4 x 4 Latin square design, 12 growing Boran steers (183 ± 15.2 kg live weight) were allocated to four levels of metabolizable energy (ME) supply fixed at 100, 80, 60 and 40% of individual maintenance energy requirements (MER) during four experimental periods. Each period comprised three weeks of adaptation, two weeks of data collection and two weeks of recovery. Diets MER80, MER60 and MER40 only consisted of Rhodes grass hay (RGH), whereas diet MER100 contained (as fed) 83% RGH, 8% cotton seed meal and 9% sugarcane molasses. Feed intake differed between treatments (p < .001) and ranged from 40 ± 0.6 g dry matter (DM) per kg of metabolic weight (kg0.75) in MER40 to 81 ± 1.3 g DM in MER100. Digestibility of neutral and acid detergent fibre (NDF, ADF) was highest at MER80, whereas rumen retention time of liquid and solid digesta was longest at MER40. The correlation of rumen retention time of liquid and solid digesta with the digestibility of proximate diet components was weak but positive, whereas the correlation of liquid and solid rumen retention time with quantitative feed and nutrient intake was strong (p < .01) and negative. Our results suggest that tropical cattle are able to buffer a moderate energy deficit by prolonging rumen retention time of digesta and hence improve diet digestibility. Conversely, a severe energy deficit cannot be buffered by digestive adaptation mechanisms and will inevitably lead to productivity losses
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