Ga(+) Focused Ion Beam-Scanning Electron Microscopes (FIB-SEM) have revolutionised the level of microstructural information that can be recovered in 3D by block face serial section tomography (SST), as well as enabling the site-specific removal of smaller regions for subsequent transmission electron microscope (TEM) examination. However, Ga(+) FIB material removal rates limit the volumes and depths that can be probed to dimensions in the tens of microns range. Emerging Xe(+) Plasma Focused Ion Beam-Scanning Electron Microscope (PFIB-SEM) systems promise faster removal rates. Here we examine the potential of the method for large volume serial section tomography as applied to bainitic steel and WC-Co hard metals. Our studies demonstrate that with careful control of milling parameters precise automated serial sectioning can be achieved with low levels of milling artefacts at removal rates some 60× faster. Volumes that are hundreds of microns in dimension have been collected using fully automated SST routines in feasible timescales (<24h) showing good grain orientation contrast and capturing microstructural features at the tens of nanometres to the tens of microns scale. Accompanying electron back scattered diffraction (EBSD) maps show high indexing rates suggesting low levels of surface damage. Further, under high current Ga(+) FIB milling WC-Co is prone to amorphisation of WC surface layers and phase transformation of the Co phase, neither of which have been observed at PFIB currents as high as 60nA at 30kV. Xe(+) PFIB dual beam microscopes promise to radically extend our capability for 3D tomography, 3D EDX, 3D EBSD as well as correlative tomography.
Aims Plant root system architecture adapts to the prevailing soil environment and the distribution of nutrients. Many species respond to localised regions of high nutrient supply, found in the vicinity of fertiliser granules, by elevating branching density in these areas. However, observation of these adaptations is frequently limited to plants cultured in idealised materials (e.g., hydrogels) which have a structure-less, homogenous matrix, which are spatially limited and in the case of rhizotron observation provide only 2D data that are not fully quantitative. Methods In this study, in vivo, time resolved, microfocus X-ray CT imaging (μCT) in 3D was used to visualise, quantify and assess root/fertiliser interactions of wheat plants in an agricultural soil during the entire plant life cycle. Two contrasting fertilisers [Triple superphosphate (TSP) and struvite (Crystal Green®)] were applied according to 3 different treatments, each providing an equivalent of 80 kg P 2 O 5 ha −1 (struvite only, TSP only and a 50:50 mixture) to each plant. μCT scans (60 μm spatial resolution) of the plant roots were obtained over 14 weeks.Results This is the first time that in situ root/soil/ fertiliser interactions have been visualised in 3D from plant germination through to maturity. Results show that lateral roots tend to pass within a few millimetres of the phosphorus (P) source. At this length scale, roots are able to access the P diffusing from the granule. Conclusions Quantitative analysis of root/fertiliser interactions has shown that rooting density correlates with granule volume-loss for a slow release, struvite fertiliser.
This paper proposes a variational approach to describe the evolution of
organization of complex systems from first principles, as increased efficiency
of physical action. Most simply stated, physical action is the product of the
energy and time necessary for motion. When complex systems are modeled as flow
networks, this efficiency is defined as a decrease of action for one element to
cross between two nodes, or endpoints of motion - a principle of least unit
action. We find a connection with another principle that of most total action,
or a tendency for increase of the total action of a system. This increase
provides more energy and time for minimization of the constraints to motion in
order to decrease unit action, and therefore to increase organization. Also,
with the decrease of unit action in a system, its capacity for total amount of
action increases. We present a model of positive feedback between action
efficiency and the total amount of action in a complex system, based on a
system of ordinary differential equations, which leads to an exponential growth
with time of each and a power law relation between the two. We present an
agreement of our model with data for core processing units of computers. This
approach can help to describe, measure, manage, design and predict future
behavior of complex systems to achieve the highest rates of self-organization
and robustness.Comment: 22 pages, 4 figures, 1 tabl
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