14,492 research outputs found
Development and Analysis of the Automated Object Reentry Survival Analysis Tool Parametric Study Wrapper
The NASA Orbital Debris Program Office (ODPO) studies all aspects of spacecraft end-of-life and orbital debris measurement, modeling, and mitigation. The reentry safety group within the ODPO uses the Object Reentry Survival Analysis Tool (ORSAT) to calculate the casualty risk due to reentry of spacecraft and other types of orbital debris. ORSAT models spacecraft as a collection of fragments that break apart from the parent object at a pre-defined breakup altitude. It then calculates the trajectory and aero-heating of these fragments to determine which fragments are completely destroyed and which survive to the ground and pose a risk to human population. Because of the historically high computational cost of these calculations, many simplifying assumptions have been made in the traditional calculation and analysis process used by the ODPO, some of which have been shown by recent research by the ODPO and others to be incorrect. Improvements to the ORSAT code and advancements in computer technology have vastly decreased the programs processing time, and have allowed the ODPO to develop a capability for large-scale parametric studies and Monte Carlo reentry simulations that can aid in both the initial spacecraft design and provide more detailed and accurate risk analysis to spacecraft operators
Environment Agency review of methods for determining organic waste biodegradability and municipal waste diversion.
The Environment Agency is required to regulate
the landfilling of biodegradable organic wastes
and their diversion from landfilling. Simple, cost
effective, reliable and widely applicable methods
for the measurement of organic waste and its
biodegradability are needed for this activity. A
review of such methods was carried out in order to
select promising methods for an experimental
screening exercise. The review considered both
biological and non-biological methods including
simple methods that may provide a surrogate
measurement of waste biodegradability instead of
the time-consuming biological methods. The
biological methods selected for further evaluation
were the aerobic specific oxygen uptake rate
(SOUR) and dynamic respiration index (DRI)
tests, and the anaerobic biochemical methane
potential (BMP) test.
The non-biological methods selected for further
evaluation were dry matter (DM), loss on ignition
(LOI), total organic carbon (TOC), total nitrogen
(TN), water extractable dissolved organic carbon
(DOC), BOD and COD, the lignin and cellulose
content and the cellulase hydrolysis method.
These tests are being evaluated on a wide variety
of typical organic materials that might be found in
municipal solid waste (MSW) such as newspaper
corrugated paper, compost, kitchen waste
(vegetable and animal), garden wastes (grass and
twigs), nappies, cotton and wool textiles
An Easy to Use Repository for Comparing and Improving Machine Learning Algorithm Usage
The results from most machine learning experiments are used for a specific
purpose and then discarded. This results in a significant loss of information
and requires rerunning experiments to compare learning algorithms. This also
requires implementation of another algorithm for comparison, that may not
always be correctly implemented. By storing the results from previous
experiments, machine learning algorithms can be compared easily and the
knowledge gained from them can be used to improve their performance. The
purpose of this work is to provide easy access to previous experimental results
for learning and comparison. These stored results are comprehensive -- storing
the prediction for each test instance as well as the learning algorithm,
hyperparameters, and training set that were used. Previous results are
particularly important for meta-learning, which, in a broad sense, is the
process of learning from previous machine learning results such that the
learning process is improved. While other experiment databases do exist, one of
our focuses is on easy access to the data. We provide meta-learning data sets
that are ready to be downloaded for meta-learning experiments. In addition,
queries to the underlying database can be made if specific information is
desired. We also differ from previous experiment databases in that our
databases is designed at the instance level, where an instance is an example in
a data set. We store the predictions of a learning algorithm trained on a
specific training set for each instance in the test set. Data set level
information can then be obtained by aggregating the results from the instances.
The instance level information can be used for many tasks such as determining
the diversity of a classifier or algorithmically determining the optimal subset
of training instances for a learning algorithm.Comment: 7 pages, 1 figure, 6 table
Modelling the Fluid Mechanics of Cilia and Flagella in Reproduction and Development
Cilia and flagella are actively bending slender organelles, performing
functions such as motility, feeding and embryonic symmetry breaking. We review
the mechanics of viscous-dominated microscale flow, including time-reversal
symmetry, drag anisotropy of slender bodies, and wall effects. We focus on the
fundamental force singularity, higher order multipoles, and the method of
images, providing physical insight and forming a basis for computational
approaches. Two biological problems are then considered in more detail: (1)
left-right symmetry breaking flow in the node, a microscopic structure in
developing vertebrate embryos, and (2) motility of microswimmers through
non-Newtonian fluids. Our model of the embryonic node reveals how particle
transport associated with morphogenesis is modulated by the gradual emergence
of cilium posterior tilt. Our model of swimming makes use of force
distributions within a body-conforming finite element framework, allowing the
solution of nonlinear inertialess Carreau flow. We find that a three-sphere
model swimmer and a model sperm are similarly affected by shear-thinning; in
both cases swimming due to a prescribed beat is enhanced by shear-thinning,
with optimal Deborah number around 0.8. The sperm exhibits an almost perfect
linear relationship between velocity and the logarithm of the ratio of zero to
infinite shear viscosity, with shear-thickening hindering cell progress.Comment: 20 pages, 24 figure
Application of DR4 and BM100 Biodegradability tests to treated and untreated organic wastes
The aerobic DR4 and anaerobic BM100 biodegradability tests are currently
applied in England and Wales for monitoring the reduction in biological municipal waste
(BMW) achieved by mechanical biological treatment (MBT) plants (Environment Agency
2005). The protocol is applied only when outputs are landfilled and is based on estimating the
reduction in potential biogas production between the MBT input, municipal solid waste (MSW),
and all of the landfilled outputs, using the BM100 test. As this is a long term 100 day test the
more rapid 4 day DR4 test may also be applied as this has been shown to correlate with the
BM100 test. We have now applied the DR4 and BM100 tests to 132 organic waste samples
including untreated and treated BMW and specific organic wastes. The results indicate that the
correlation between the DR4 and BM100 tests has proved valid for mixed MSW derived BMW
wastes. However when both tests are applied to specific organic wastes such as turkey feathers,
cardboard packaging waste and pizza food wastes the correlation between the tests is less strong.
It is concluded that the use of the DR4 and BM100 test correlation is valid for its designed
application (monitoring MBT processes treating MSW derived mixed BMW), but that caution
should be exercised when applying both tests to specific single component organic wastes
Characterisation of untreated and treated biodegradable wastes
As part of a Defra sponsored project (WRT220), approximately 40 biodegradable
wastes were characterised according to biodegradability (DR4 and BM100), total PTE content,
C:N ratio and biochemical composition. Two leaching tests were employed; upflow percolation
test and a one step LS10 test; eluates were analysed for TOC, pH, electrical conductivity, PTEs
and a range of cations and anions. This paper contains a limited set of data for a selection of
untreated and treated waste types representing four waste treatment processes (composting,
MBT, MHT, anaerobic digestion). The DR4 and BM100 tests were found to be appropriate for a
wide range of waste types but where possible they should be used in conjunction with other
related tests. Longer-term MBT composting processes appeared to produce compost material
with reduced ammonium concentrations and extractability of some PTEs. Carbon content
(carbon analyzer - LECO) could be estimated as C = LOI/1.9 which is a routine operation. N
LECO values were approximately 12% greater than the equivalent N Kjeldahl values
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