Purpose
Simultaneously interacting rhizosphere processes determine emergent plant behaviour, including growth, transpiration, nutrient uptake, soil carbon storage and transformation by ...microorganisms. However, these processes occur on multiple scales, challenging modelling of rhizosphere and plant behaviour. Current advances in modelling and experimental methods open the path to unravel the importance and interconnectedness of those processes across scales.
Methods
We present a series of case studies of state-of-the art simulations addressing this multi-scale, multi-process problem from a modelling point of view, as well as from the point of view of integrating newly available rhizosphere data and images.
Results
Each case study includes a model that links scales and experimental data to explain and predict spatial and temporal distribution of rhizosphere components. We exemplify the state-of-the-art modelling tools in this field: image-based modelling, pore-scale modelling, continuum scale modelling, and functional-structural plant modelling. We show how to link the pore scale to the continuum scale by homogenisation or by deriving effective physical parameters like viscosity from nano-scale chemical properties. Furthermore, we demonstrate ways of modelling the links between rhizodeposition and plant nutrient uptake or soil microbial activity.
Conclusion
Modelling allows to integrate new experimental data across different rhizosphere processes and scales and to explore more variables than is possible with experiments. Described models are tools to test hypotheses and consequently improve our mechanistic understanding of how rhizosphere processes impact plant-scale behaviour. Linking multiple scales and processes including the dynamics of root growth is the logical next step for future research.
The yeast
Saccharomyces cerevisiae
has a limited replicative lifespan. The cell mass at division is partitioned unequally between a larger, old parent cell and a smaller, new daughter cell. ...Industrial beer fermentations maintain and reuse yeast. At the end of fermentation a portion of the yeast is ‘cropped’ from the vessel for ‘serial repitching’. Harvesting yeast may select a population with an imbalance of young and aged individuals, but the output of any bioprocess is dependent on the physiology of each single cell in the population. Unlike continuous models, individual-based modelling is an approach that considers each microbe as an individual, a unique and discrete entity, with characteristics that change throughout its life. The aim of this contribution is to explore, by means of individual-based simulations, the effects of inoculum size and cell genealogical age on the dynamics of virtual yeast fermentation, focussing on: (1) the first stages of population growth, (2) the mean biomass evolution of the population, (3) the rate of glucose uptake and ethanol production, and (4) the biomass and genealogical age distributions. The ultimate goal is to integrate these results in order to make progress in the understanding of the composition of yeast populations and their temporal evolution in beer fermentations. Simulation results show that there is a clear influence of these initial features of the inocula on the subsequent growth dynamics. By contrasting both the individual and global properties of yeast cells and populations, we gain insight into the interrelation between these two types of data, which helps us to deal with the macroscopic behaviour observed in experimental research.
We applied electric particle analysis, light diffraction and flow cytometry to obtain information on the morphological changes during the stationary phase of Saccharomyces cerevisiae. The reported ...analyses of S. cerevisiae populations were obtained under two different conditions, aerobic and microaerophilic, at 27°C. The samples analysed were taken at between 20 and 50 h from the beginning of culture. To assist in the interpretation of the observed distributions a complexity index was used. The aerobically grown culture reached significantly greater cell density. Under these conditions, the cell density experienced a much lower reduction (3%) compared with the microaerophilic conditions (30%). Under aerobic conditions, the mean cell size determined by both electric particle analysis and light diffraction was lower and remained similar throughout the experiment. Under microaerophilic conditions, the mean cell size determined by electric particle analysis decreased slightly as the culture progressed through the stationary phase. Forward and side scatter distributions revealed two cell subpopulations under both growth conditions. However, in the aerobic growing culture the two subpopulations were more separated and hence easier to distinguish. The distributions obtained with the three experimental techniques were analysed using the complexity index. This analysis suggested that a complexity index is a good descriptor of the changes that take place in a yeast population in the stationary phase, and that it aids in the discussion and understanding of the implications of these distributions obtained by these experimental techniques.
This contribution reports on preliminary measurements of searches for squarks and gluinos at CDF and DØ detectors in p collisions at s√ 1.96 TeV using 1 fb-1 of data. The analyses are optimised for ...event topologies with multiple jets and large missing transverse energy in the final state. No excess with respect to the Standard Model predictions is observed and new limits on the gluino and squark masses are extracted in a mSUGRA scenario with R-parity conservation.
A
bstract
The results of a search for direct pair production of heavy top-quark partners in 4.7 fb
−1
of integrated luminosity from
pp
collisions at
TeV collected by the ATLAS detector at the LHC are ...reported. Heavy top-quark partners decaying into a top quark and a neutral non-interacting particle are searched for in events with two leptons in the final state. No excess above the Standard Model expectation is observed. Limits are placed on the mass of a supersymmetric scalar top and of a spin-1/2 top-quark partner. A spin-1/2 top-quark partner with a mass between 300 GeV and 480 GeV, decaying to a top quark and a neutral non-interacting particle lighter than 100 GeV, is excluded at 95% confidence level.
CDF and DO detectors have already collected 1.3 fb^{-1} of data delivered by the Tevatron collider at 1.96 TeV center-of-mass energy. We present here the various analyses that are currently testing ...the possibility of a supersymmetric extension of the Standard Model. No evidence for such processes have been found in luminosities that range from 300 to 800 pb^{-1} and different limits on the different supersymmetric models are set. Constraints coming from indirect searches are also presented.
A
bstract
An inclusive search for anomalous production of two prompt, isolated leptons with the same electric charge is presented. The search is performed in a data sample corresponding to 4.7 fb
−1
...of integrated luminosity collected in 2011 at
with the ATLAS detector at the LHC. Pairs of leptons (
e
±
e
±
,
e
±
μ
±
, and
μ
±
μ
±
) with large transverse momentum are selected, and the dilepton invariant mass distribution is examined for any deviation from the Standard Model expectation. No excess is found, and upper limits on the production cross section of like-sign lepton pairs from physics processes beyond the Standard Model are placed as a function of the dilepton invariant mass within a fiducial region close to the experimental selection criteria. The 95% confidence level upper limits on the cross section of anomalous
e
±
e
±
,
e
±
μ
±
, or
μ
±
μ
±
production range between 1.7 fb and 64 fb depending on the dilepton mass and flavour combination.
A
bstract
This paper describes measurements of the sum of the transverse energy of particles as a function of particle pseudorapidity,
η
, in proton-proton collisions at a centre-of-mass energy,
TeV ...using the ATLAS detector at the Large Hadron Collider. The measurements are performed in the region |
η
|
<
4
.
8 for two event classes: those requiring the presence of particles with a low transverse momentum and those requiring particles with a significant transverse momentum. In the second dataset measurements are made in the region transverse to the hard scatter. The distributions are compared to the predictions of various Monte Carlo event generators, which generally tend to underestimate the amount of transverse energy at high |
η
|.
A
bstract
A search for flavour changing neutral current (FCNC) processes in top-quark decays by the ATLAS Collaboration is presented. Data collected from
pp
collisions at the LHC at a centre-of-mass ...energy of
during 2011, corresponding to an integrated luminosity of 2.1 fb
−1
, were used. A search was performed for top-quark pair-production events, with one top quark decaying through the
t
→
Zq
FCNC (
q
=
u, c
) channel, and the other through the Standard Model dominant mode
t
→
W b
. Only the decays of the
Z
boson to charged leptons and leptonic
W
-boson decays were considered as signal. Consequently, the final-state topology is characterised by the presence of three isolated charged leptons, at least two jets and missing transverse momentum from the undetected neutrino. No evidence for an FCNC signal was found. An upper limit on the
t
→
Zq
branching ratio of BR(
t
→
Zq
)
<
0
.
73% is set at the 95% confidence level.
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