Molecular and compound-specific stable isotope investigation of the fate of dung carbon in a temperate grassland soil
Concrete is regarded as a skeleton of aggregate particles of various sizes, almost
in direct contact with each other. The cement matrix acts as a filler and adhesive
enabling the structure to be able to carry tensile stresses.
A 2D circular rigid discrete element formulation based on the Discrete Element
Method has been adopted. Random assemblies of particles based on a given sieve
analysis can be generated enabling the simulation of the concrete structure at the
Contact models that are able to transmit moments through the contact plane
have been implemented, namely, a developed contact model adopting more than one
contact point at the contact plane. The steel reinforcement has been modelled with
1D beam finite elements or with 1D rigid discrete elements that interact with the
discrete rigid particles through contact interfaces. Softening has been introduced
into the microlevel constitutive equations.
The traditional DEM has been enhanced with a boundary wall driven by force algorithm,
an adaptive global damping algorithm and an arc-length control algorithm
increasing the range of applicability and the performance of the model.
The behavior of a double notched plain concrete specimen is investigated. Comparison
of results in terms of crack patterns and load displacement relationships up
to the peak load with both experimental and numerical results obtained using a
lattice beam element formulation showed good agreement.
The performance of the developed DEM model has also been evaluated for uniaxial
tension, uniaxial compression and tensile splitting tests. The developed model
showed good agreement in terms of peak strength, fracture localization and crack
Finally the interaction between the stiffness of the reinforcement normal to the
plane of cracking and the shear stiffness due to aggregate interlock is investigated.
Good comparisons in terms of shear force and shear displacement relationships for
a given crack width and reinforcement stiffness were obtained with known experimental
dataFirstly, I would like to thank my supervisors, Richard Evershed and Roland Bol for
supporting my metamorphosis from rusty biologist to fully-fledged Organic Geochemist. I
would especially like to thank Richard for his close support, mentorship and advice on the
biomolecular dimension that have been second to none, and for his kindness and
understanding following a particular long haul flight after misplacing both my purse and
work file en route!
Special thanks to Roland for his unbounding enthusiasm and deep knowledge of the
theoretical and practical side of carbon cycling in soil, even when sampling cow pats in
horizontal rain on Dartmoor in December! I couldn't have wished for a more idyllic place
for field work than IGER-NW. All of the staff were amazingly helpful and enthusiastic
(particularly Mel who always knew where everything and everybody was when you
needed them), so ready to share interest in soils and agricultural excreta that coffee breaks
were a joy! Regrettably the Foot and Mouth epidemic prevented me from organising
production of my own dung (no, really! ), so an enormous thank you is owed to Richard
Dewhurst and Roger Evans at IGER-Aberystwyth for the supply of 25 large buckets of
deep frozen cow dung. I would also like to acknowledge the valuable help and advice of
Dan Dhanoa with statistical analysis.
I was equally lucky to be part of a wonderful group known collectively as the OGU at
Bristol. It would be impossible to acknowledge all of the individuals that have contributed
to my training and support on a day-to-day basis. However, I would like to give special
thanks to Dr Rob and Staffy for their technical expertise on most aspects of geochemistry.
Thanks to Ian Bull for his training on lipid analysis, and respect for being able to recite the
elution order of dung sterols backwards. I must also schtop here and thank Bart van
Dongen for sharing his knowledge of off-line pyrolsyis and Nat for investigating its
reproducibility, and Andy Rawlins and Zoe Crossman for their expertise and guidance on
carbohydrates and PLFA analysis, respectively. Thanks also to John Webster and Mike
Kitcherside at UOB Vet. School for access to forage fibre analysis. Last, but my no means
least, thank you for the fantastic friendship of `the girls' Lorna, Anna, Claire E., Kate,
Bickers, Zoe, Susie and Erin without whom I would be a little bit greyer!
I would like to formally acknowledge funding for my PhD from BBSRC and IGER, and
the UOB Alumni Foundation, British Mass Spectrometry Society and British Soil Science
Society for travel awards.
Most importantly, I wish to acknowledge the enormous support and love of my darling
husband, Ben, who has put up with my ranting and raving for, well, longer than I care to
mention; a lesser man would have run for hills a long time ago! I also wish to thank my
fur baby Ted for making me laugh and chilling me out with long walkies when the going
got too tough! Thanks to my parents for their support and ridiculous pride in my
achievements, and for my brother, sister and non-work friends for tolerating my absentism
-I promise to make up for it!
And finally, some additional information on my favourite organic material:
In the 16th and 17th centuries, everything had to be transported by ship, and it was also before commercial
fertilizer's invention, so large shipments of manure were common. It was shipped dry, because in dryform it
weighed a lot less than when wet, but once water (at sea) hit it, it not only became heavier, but the process of
fermentation began again, of which a by-product is methane gas. As the stuff was stored below decks in
bundles, you can see what could (and did) happen. Methane began to build up below decks and the first time
someone came below at night with a lantern, BOOOOM! Several ships were destroyed in this
manner before it was determined what caused the explosions. After that, the bundles of manure were always
stamped with the term "Ship High In Transit" on them which meant for the sailors to stow it high enough off
the lower decks so that any water that came into the hold would not touch this volatile cargo and start the
production of methane. Thus evolved the term "S. H. I. T., " (Ship High In Transit) which has come down
through the centuries and is in use to this very day.