Fully automated compound screening in Arabidopsis thaliana seedlings

High-throughput small molecule screenings in model plants are of great value to identify compounds that interfere with plant developmental processes. In academic research, the plant Arabidopsis thaliana is the most commonly used model organism for this purpose. However, compared to plant cellular systems, A. thaliana plants are less amenable to develop high-throughput screening assays. In this chapter, we describe a screening procedure that is compatible with liquid handling systems and increases the throughput of compound screenings in A. thaliana seedlings

Dynamics of Nonlinear Diffusion Processes

The purpose of this thesis is to analyze nonlinear diffusion processes. In particular, some of the results arrived at by Newman and Sagan in their 1981 paper Galactic Civilizations: Population Dynamics and Interstellar Diffusion, will be reproduced by different means. First, a thorough analysis of the linear diffusion equation will be performed in order to test a numerical algorithm that can solve the nonlinear diffusion equation and look at the processes of interest with sufficient accuracy. Once the algorithm is tested and shows good resolution it is used to solve the nonlinear equation. The post processing is then done to compare the numerical results with the analytical solution and then they are related to the results arrived at by Newman and Sagan. More precisely, the timescales over which these processes take place are of great interest. A study of the dynamics of these diffusion processes that take place will bring about a better understanding of the nature of nonlinear diffusion and some of its applications

Auxin and epigenetic regulation of SKP2B, an F-box that represses lateral root formation

In plants, lateral roots originate from pericycle founder cells that are specified at regular intervals along the main root. Here, we show that Arabidopsis (Arabidopsis thaliana) SKP2B (for S-Phase Kinase-Associated Protein2B), an F-box protein, negatively regulates cell cycle and lateral root formation as it represses meristematic and founder cell divisions. According to its function, SKP2B is expressed in founder cells, lateral root primordia and the root apical meristem. We identified a novel motif in the SKP2B promoter that is required for its specific root expression and auxin-dependent induction in the pericycle cells. Next to a transcriptional control by auxin, SKP2B expression is regulated by histone H3.1/H3.3 deposition in a CAF-dependent manner. The SKP2B promoter and the 59 end of the transcribed region are enriched in H3.3, which is associated with active chromatin states, over H3.1. Furthermore, the SKP2B promoter is also regulated by H3 acetylation in an auxin-and IAA14-dependent manner, reinforcing the idea that epigenetics represents an important regulatory mechanism during lateral root formation

CEP5 and XIP1/CEPR1 regulate lateral root initiation in Arabidopsis

Roots explore the soil for water and nutrients through the continuous production of lateral roots. Lateral roots are formed at regular distances in a steadily elongating organ, but how future sites for lateral root formation become established is not yet understood. Here, we identified C-TERMINALLY ENCODED PEPTIDE 5 (CEP5) as a novel, auxin-repressed and phloem pole-expressed signal assisting in the formation of lateral roots. In addition, based on genetic and expression data, we found evidence for the involvement of its proposed receptor, XYLEM INTERMIXED WITH PHLOEM 1 (XIP1)/CEP RECEPTOR 1 (CEPR1), during the process of lateral root initiation. In conclusion, we report here on the existence of a peptide ligand−receptor kinase interaction that impacts lateral root initiation. Our results represent an important step towards the understanding of the cellular communication implicated in the early phases of lateral root formation

Ovni-net : a flexible cluster interconnect for the new OVNI Real-time simulator

The original OVNI Real-time simulator employs one of the lowest latency network solutions available today. However, with the advent of the MATE solution scheme, a new, more flexible interconnect solution became necessary. Also, the current system is limited in bandwidth and tied into the IDE hard-disk interface. This technology is soon to disappear, in favor of serial ATA. The new system presented circumvents any of the normal PC standard ports and is build directly on top of the industry-standard PCI bus. Also, the parallel connections between the nodes are replaced by high-speed full-duplex serial links, allowing for a system of larger physical size with a more manageable wiring solution. These enhancements yield in an even lower latency while significantly boosting the throughput. It also allows the hardware to be used on non-PC platforms such as Sun, Apple, HP, and IBM workstations. A major change to accommodate the flexibility of MATE was the incorporation of an intelligent shared-memory hub, avoiding many of the latency issues introduced by switched packet network solutions. To further boost the performance, no microprocessors were used in the network system. Instead, the required intelligence was distributed throughout the system and implemented locally in logic. This allows for a highly parallel operation of the interconnect with an absolute minimum of overhead. The integration of the new interconnect system and the MATE solution scheme is now so tight that the network system itself became part of the solution algorithm. However, due to the highly modular design approach, and the extensive use of FPGA technology, the system can be modified at will. Very different solution schemes and enhancements such as hardware error control, digital and analog I/O, and other features can be implemented without electrical modifications, allowing the same physical hardware to be used in both a research and a production environment. The result is a economic, obsolescence proof, flexible, high-speed low-latency cluster interconnect system build around industry-standard components.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat

Temporal-spatial discretization and fractional latency techniques for wave propagation in heterogeneous media

This thesis presents the development of a novel, transient wave propagation simulator using time-decoupled transmission line models. The models are based on the electro-magnetic transient program (EMTP) power system transient analysis tools, extended to two dimensions. The new tool is targeted at acoustic wave propagation phenomena. The method, called TINA for transient insular nodal analysis, uses temporal interpolation and fractional latency to maintain synchronicity in heterogeneous media. The fractional latency method allows the model cells to operate at a local simulation time step which can be a non-integer ratio of the global simulation time step. This simplifies synchronicity and saves computation time and memory. Thévenin equivalents are used to interface the mesh cells and provide an abstraction of the cell content. Numerically, the method is of the transmission-line matrix (TLM) family. In the thesis, loss-less and distortion-less models are considered. The loss-less transmission line models are studied for their stability and numerical error, for which analytical expressions are derived based on the simulation parameters. A number of new relations were discovered and discussed. The TINA method is evaluated in 2D using acoustic experiments, and also a new method is proposed for obtaining impulse responses in time-domain simulation, based on a periodic, band-limited impulse signals.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat

Technical Assessment of Centralized and Localized Voltage Control Strategies in Low Voltage Networks

© 2016 Elsevier Ltd Both the electric power demand and the penetration of small-scale embedded generators (SSEGs) is rapidly increasing in LV distribution grids. These trends are expected to have significant effects on system performance, efficiency and reliability necessitating the adjustments to the current framework for power supply dispatch and delivery. This paper proposes hybrid voltage control schemes for LV distribution networks combining: (i) centralized control via the on-load tap-changer (OLTC) of secondary distribution transformers and (ii) localized control via both the real and reactive power management from single-phase PV inverters. Specific control algorithms are proposed for both the centralized and localized methods. All the possible operation sequences of the aforementioned methods are examined. The performance of the proposed approaches is investigated on four different test feeders considering the voltage magnitudes, the voltage unbalances, the total losses and the PV power utilization.publisher: Elsevier articletitle: Technical assessment of centralized and localized voltage control strategies in low voltage networks journaltitle: Sustainable Energy, Grids and Networks articlelink: http://dx.doi.org/10.1016/j.segan.2016.09.003 content_type: article copyright: © 2016 Elsevier Ltd. All rights reserved.status: publishe

Optimal Placement and Sizing of Active In-line Voltage Regulators in Flemish LV Distribution Grids

© 1972-2012 IEEE. Over the past few years, both the integration of small-scale embedded generators and the electric power consumption have been increased rapidly in the low-voltage (LV) distribution networks. These two trends are likely to result in a number of power quality issues such as voltage rise/drop and voltage unbalance. Regarding the mitigation of the voltage rise/drop effects, several utilities have already implemented the application of on-load tap changer (OLTC) in secondary distribution transformers. However, the voltage control via OLTC transformers might be infeasible in the case of radial feeders with both large number of branches and long distribution lines. This paper evaluates the performance of active in-line voltage regulators (IVRs) in LV grids. The study also investigates the optimal placement and sizing of active IVRs in Flemish LV networks. Concerning the OLTC control of the IVRs, an algorithm from a previous work is used. Finally, the influence on various power quality metrics is tested, when IVRs are incorporated into the system.status: publishe