Interactions of N-Acylethanolamine Metabolism and Abscisic Acid Signaling in Arabidopsis Thaliana Seedlings

N-Acylethanolamines (NAEs) are endogenous plant lipids hydrolyzed by fatty acid amide hydrolase (FAAH). When wildtype Arabidopsis thaliana seeds were germinated and grown in exogenous NAE 12:0 (35 µM and above), growth was severely reduced in a concentration dependent manner. Wildtype A. thaliana seeds sown on exogenous abscisic acid (ABA) exhibited similar growth reduction to that seen with NAE treatment. AtFAAH knockouts grew and developed similarly to WT, but AtFAAH overexpressor lines show markedly enhanced sensitivity to ABA. When low levels of NAE and ABA, which have very little effect on growth alone, were combined, there was a dramatic reduction in seedling growth in all three genotypes, indicating a synergistic interaction between ABA and NAE. Notably, this synergistic arrest of seedling growth was partially reversed in the ABA insensitive (abi) mutant abi3-1, indicating that a functional ABA signaling pathway is required for the full synergistic effect. This synergistic growth arrest results in an increased accumulation of NAEs, but no concomitant increase in ABA levels. The combined NAE and ABA treatment induced a dose-dependent increase in ABI3 transcript levels, which was inversely related to growth. The ABA responsive genes AtHVA22B and RD29B also had increased expression in both NAE and ABA treatment. The abi3-1 mutant showed no expression of ABI3 and AtHVA22B, but RD29B expression remained similar to wildtype seedlings, suggesting an alternate mechanism for NAE and ABA interaction. Taken together, these data suggest that NAE metabolism acts through ABI3-dependent and independent pathways in the negative regulation of seedling development

Towards the Fully-coupled Numerical Modelling of Floating Wind Turbines

AbstractThe aim of this study is to model the interactions between fluids and solids using fully nonlinear models. Non- linearity is important in the context of floating wind turbines, for example, to model breaking waves impacting on the structure and the effect of the solid's elasticity. The fluid- and solid-dynamics equations are solved using two unstructured finite-element models, which are coupled at every time step. Importantly, the coupling ensures that the action-reaction principle is satisfied at a discrete level, independently of the order of representation of the discrete fields. To the authors’ knowledge, the present algorithm is novel in that it can simultaneously handle: (i) non- matching fluid and solid meshes, (ii) different polynomial orders of the basis functions on each mesh, and (iii) different fluid and solid time steps. First, results are shown for the flow past a fixed actuator-disk immersed in a uniform flow and representing a wind turbine. The present numerical results for the velocity deficit induced by the disk are shown to be in good agreement with the semi-analytical solution, for three values of thrust coefficients. The presence of a non-zero fluid viscosity in the numerical simulation affects wake recovery and fluid entrainment around the disk. Second, the dynamic response of a cylindrical pile is computed when placed at an interface between air and water. The results qualitatively demonstrate that the present models are applicable to the modelling of multiple fluids interacting with a floating solid. This work provides a first-step towards the fully coupled simulation of offshore wind turbines supported by a floating spar

Evidence for phenotypic bistability resulting from transcriptional interference of bvgAS in Bordetella bronchiseptica: Phenotypic bistability inBordetella

Bordetella species cause respiratory infections in mammals. Their master regulatory system BvgAS controls expression of at least three distinct phenotypic phases in response to environmental cues. The Bvg+ phase is necessary and sufficient for respiratory infection while the Bvg− phase is required for survival ex vivo. We obtained large colony variants (LCVs) from the lungs of mice infected with B. bronchiseptica strain RBX9, which contains an in-frame deletion mutation in fhaB, encoding filamentous hemagglutinin. RBX9 also yielded LCVs when switched from Bvg− phase conditions to Bvg+ phase conditions in vitro. We determined that LCVs are composed of both Bvg+ and Bvg− phase bacteria and that they result from defective bvgAS positive autoregulation. The LCV phenotype was linked to the presence of a divergent promoter 5′ to bvgAS, suggesting a previously undescribed mechanism of transcriptional interference that, in this case, leads to feedback-based bistability (FBM). Our results also indicate that a small proportion of RBX9 bacteria modulates to the Bvg− phase in vivo. In addition to providing insight into transcriptional interference and FBM, our data provide an example of an in-frame deletion mutation exerting a ‘polar’ effect on nearby genes

Few-body hydrodynamic interactions probed by optical trap pulling experiment

We study the hydrodynamic coupling of neighboring micro-beads placed in a dual optical trap setup allowing us to precisely control the degree of coupling and directly measure time-dependent trajectories of the entrained beads. Average experimental trajectories of a probe bead entrained by the motion of a neighboring scan bead are compared with theoretical computation, illustrating the role of viscous coupling and setting timescales for probe bead relaxation. The findings provide direct experimental corroborations of hydrodynamic coupling at larger, micron spatial scales and millisecond timescales, of relevance to hydrodynamic-assisted colloidal assembly as well as improving the resolution of optical tweezers. We repeat the experiments for three bead setups

Image Segmentation Using Frequency Locking of Coupled Oscillators

Synchronization of coupled oscillators is observed at multiple levels of neural systems, and has been shown to play an important function in visual perception. We propose a computing system based on locally coupled oscillator networks for image segmentation. The system can serve as the preprocessing front-end of an image processing pipeline where the common frequencies of clusters of oscillators reflect the segmentation results. To demonstrate the feasibility of our design, the system is simulated and tested on a human face image dataset and its performance is compared with traditional intensity threshold based algorithms. Our system shows both better performance and higher noise tolerance than traditional methods.Comment: 7 pages, 14 figures, the 51th Design Automation Conference 2014, Work in Progress Poster Sessio

Hydro-morphodynamics 2D modelling using a discontinuous Galerkin discretisation

The development of morphodynamic models to simulate sediment transport accurately is a challenging process that is becoming ever more important because of our increasing exploitation of the coastal zone, as well as sea-level rise and the potential increase in strength and frequency of storms due to a changing climate. Morphodynamic models are highly complex given the non-linear and coupled nature of the sediment transport problem. Here we implement a new depth-averaged coupled hydrodynamic and sediment transport model within the coastal ocean model Thetis, built using the code generating framework Firedrake which facilitates code flexibility and optimisation benefits. To the best of our knowledge, this represents the first full morphodynamic model including both bedload and suspended sediment transport which uses a discontinuous Galerkin based finite element discretisation. We implement new functionalities within Thetis extending its existing capacity to model scalar transport to modelling suspended sediment transport, incorporating within Thetis options to model bedload transport and bedlevel changes. We apply our model to problems with non-cohesive sediment and account for effects of gravity and helical flow by adding slope gradient terms and parametrising secondary currents. For validation purposes and in demonstrating model capability, we present results from test cases of a migrating trench and a meandering channel comparing against experimental data and the widely-used model Telemac-Mascaret

Hybridised multigrid preconditioners for a compatible finite element dynamical core

Compatible finite element discretisations for the atmospheric equations of motion have recently attracted considerable interest. Semi-implicit timestepping methods require the repeated solution of a large saddle-point system of linear equations. Preconditioning this system is challenging since the velocity mass matrix is non-diagonal, leading to a dense Schur complement. Hybridisable discretisations overcome this issue: weakly enforcing continuity of the velocity field with Lagrange multipliers leads to a sparse system of equations, which has a similar structure to the pressure Schur complement in traditional approaches. We describe how the hybridised sparse system can be preconditioned with a non-nested two-level preconditioner. To solve the coarse system, we use the multigrid pressure solver that is employed in the approximate Schur complement method previously proposed by the some of the authors. Our approach significantly reduces the number of solver iterations. The method shows excellent performance and scales to large numbers of cores in the Met Office next-generation climate- and weather prediction model LFRic.Comment: 24 pages, 13 figures, 5 tables; accepted for publication in Quarterly Journal of the Royal Meteorological Societ