The GAP in Fruit Development: Determining the Role of RanGAP in Arabidopsis Fruit Development

RanGAP is the activating protein for the small GTPase Ran, and is known to be involved in nucleocytoplasmic transport and mitotic cell division across kingdoms. Arabidopsis has two RanGAP proteins, RanGAP1 and RanGAP2, which share 63% amino acid homology. Both proteins contain two functional domains: a localization domain known as the WPP domain, which contains a conserved tryptophanproline- proline motif necessary for interaction with localization binding partners, and a GTPase activation (GAP) domain, which is responsible for Ran binding and activation. Double null mutants in the genes encoding RanGAP1 and RanGAP2 are lethal at an early stage of development. However, a homozygous mutant combining the RanGAP1 null allele and RanGAP2 knockdown allele, called short silique knockdown (SILK), exhibits a reduced fruit (silique) length phenotype. What role RanGAP plays in fruit development, however, is unknown. In order to determine its function, constructs containing wildtype RanGAP1 or mutant RanGAP1 with one or both functional domains mutated were inserted into SILK mutant plants. Their phenotypes were quantified by measuring fruit length and seed number to determine if the RanGAP1 transgene had rescued the short-fruit phenotype. RanGAP1 transgenes with mutations in the GAP domain did not rescue the SILK phenotype whereas mutants that maintained this function did, regardless of localization. These results indicate that it is the GAP function of RanGAP that is important in fruit development. Seed count, however, varied greatly among individual lines with the same transgene, indicating that seed development may depend on the location of the RanGAP1 insertion into the genome. Further analysis of silique cell types indicate that the length phenotype may be due to defects in the differentiation of the cells of the fruit itself. This work highlights the intersection between cell biological processes and developmental events, and shows the relevance of intracellular events to the understanding of whole-plant processes.National Science FoundationNo embargoAcademic Major: Plant Cellular and Molecular Biolog

Performance assessment of density and level-set topology optimisation methods for 3D heatsink design

In this paper, two most prevalent topological optimisation approaches namely Density and Level set method are applied to a three dimensional heatsink design problem. The relative performance of the two approaches are compared in terms of design quality, robustness and computational speed. The work is original as for the first time it demonstrates the relative advantages and disadvantages for each method when applied to a practical engineering problem. It is additionally novel in that it presents the design of a convectively cooled heatsink by solving full thermo-fluid equations for two different solid-fluid material sets. Further, results are validated using a separate CFD study with the optimised designs are compared against a standard pin-fin based heatsink design. The results show that the Density method demonstrates better performance in terms of robustness and computational speed, while Level-set method yields a better quality design

On the Application of Topology Optimisation Techniques to Thermal Management of Microelectronics Systems

In this paper, an autonomous thermal management design process based on a topological optimisation algorithm is presented. The numerical framework uses a finite element multiphysics solver to assess fluid flow and heat transfer, coupled with the Method of Moving Asymptotes approach for topology optimisation. The design framework is utilised to develop a copper heatsink for a simplified electronics package at two differing Reynolds numbers. In both cases, the final shape resembles a tree like structure rather than a more conventional fin structure

Optimizing the reliability of power electronics module isolation substrates

Optimal design of a power electronics module isolation substrate is assessed using a combination of finite element structural mechanics analysis and response surface optimisation technique. Primary failure modes in power electronics modules include the loss of structural integrity in the ceramic substrate materials due to stresses induced through thermal cycling. Analysis of the influence of ceramic substrate design parameters is undertaken using a design of experiments approach. Finite element analysis is used to determine the stress distribution for each design, and the results are used to construct a quadratic response surface function. A particle swarm optimisation algorithm is then used to determine the optimal substrate design. Analysis of response surface function gradients is used to perform sensitivity analysis and develop isolation substrate design rules. The influence of design uncertainties introduced through manufacturing tolerances is assessed using a Monte-Carlo algorithm, resulting in a stress distribution histogram. The probability of failure caused by the violation of design constraints has been analyzed. Six geometric design parameters are considered in this work and the most important design parameters have been identified. Overall analysis results can be used to enhance the design and reliability of the component

Modelling methodologies for quality assessment of 3D inkjet printed electronic products

Purpose of the Fraunhofer Direct Digital Manufacturing Conference is an intellectual exchange between researchers, enterprises and users of Additive Manufacturing technologies in order to gather the latest information about trends, progress, importance and the future potential of these technologies for industrial applications. The range of topics covers Product Development (incl. simulation, co-design, mass customization), Technologies (incl. bio-printing, hybrid processes, novel developments/visionary concepts, process chains for industrial production), Materials (incl. ceramics, bio-materials, multi-material approaches), Quality (incl. process/ part quality management) as well as further innovative and visionary approaches not fitting the range of topics above. Renowned international keynote speakers give insight into the latest trends and challenges in additive manufacturing in a variety of industry sectors, including biomedical, aerospace and automotive

Thermal-mechanical modelling of power electronic module packaging

In this paper the reliability of the isolation substrate and chip mountdown solder interconnect of power modules under thermal-mechanical loading has been analysed using a numerical modelling approach. The damage indicators such as the peel stress and the accumulated plastic work density in solder interconnect are calculated for a range of geometrical design parameters, and the effects of these parameters on the reliability are studied by using a combination of the finite element analysis (FEA) method and optimisation techniques. The sensitivities of the reliability of the isolation substrate and solder interconnect to the changes of the design parameters are obtained and optimal designs are studied using response surface approximation and gradient optimization metho

Numerical analysis of droplet deposition in inkjet printed electronics assembly

In this paper, a computational approach for the analysis of microscale droplet impact dynamics is presented. The approach is intended to support a condition based monitoring system to enhance quality and reliability of inkjet printed electronics components. The Smoothed Particle Hydrodynamics (SPH) approach of Lucy and Gingold and Monaghan has been used as the basis for the model, with the δ-SPH terms of Marrone et al used to improve handling of the dynamic impact events and the gradient correction terms of Belytschko used to improve the accuracy of interface dynamics. Model validation has been performed through comparison against a macroscale dam break problem and through a microscale analysis designed to determine accurate surface tension-pressure behaviour based on the Young-Laplace relation. The model is used to assess impact of a single drop on a uniform surface and the three dimensional formation of multi-drop layers

GAP activity, but not subcellular targeting, is required for Arabidopsis RanGAP cellular and developmental functions

The Ran GTPase activating protein (RanGAP) is important to Ran signaling involved in nucleocytoplasmic transport, spindle organization, and postmitotic nuclear assembly. Unlike vertebrate and yeast RanGAP, plant RanGAP has an N-terminal WPP domain, required for nuclear envelope association and several mitotic locations of Arabidopsis thaliana RanGAP1. A double null mutant of the two Arabidopsis RanGAP homologs is gametophyte lethal. Here, we created a series of mutants with various reductions in RanGAP levels by combining a RanGAP1 null allele with different RanGAP2 alleles. As RanGAP level decreases, the severity of developmental phenotypes increases, but nuclear import is unaffected. To dissect whether the GAP activity and/or the subcellular localization of RanGAP are responsible for the observed phenotypes, this series of rangap mutants were transformed with RanGAP1 variants carrying point mutations abolishing the GAP activity and/or the WPP-dependent subcellular localization. The data show that plant development is differentially affected by RanGAP mutant allele combinations of increasing severity and requires the GAP activity of RanGAP, while the subcellular positioning of RanGAP is dispensable. In addition, our results indicate that nucleocytoplasmic trafficking can tolerate both partial depletion of RanGAP and delocalization of RanGAP from the nuclear envelope

On variable frequency microwave processing of heterogeneous chip-on-board assemblies

Variable Frequency Microwave (VFM) processing of heterogeneous chip-on-board assemblies is assessed using a multiphysics modelling approach. The Frequency Agile Microwave Oven Bonding System (FAMOBS) is capable of rapidly processing individual packages on a Chip-On-Board (COB) assembly. This enables each package to be processed in an optimal manner, with temperature ramp rate, maximum temperature and process duration tailored to the specific package, a significant benefit in assemblies containing disparate package types. Such heterogeneous assemblies may contain components such as large power modules alongside smaller modules containing low thermal budget materials with highly disparate processing requirements. The analysis of two disparate packages has been assessed numerically to determine the applicability of the dual section microwave system to curing heterogeneous devices and to determine the influence of differing processing requirements of optimal process parameters

Experimental investigation of open-ended microwave oven assisted encapsulation process

An open ended microwave oven is presented with improved uniform heating, heating rates and power conversion efficiency. This next generation oven produces more uniform EM fields in the evanescent region forming part of the heating area of the oven. These fields are vital for the rapid and uniform heating of various electromagnetically lossy materials. A fibre optic temperature sensor and an IR pyrometer are used to measure in situ and in real-time the temperature of the curing materials. An automatic computer controlled closed feedback loop measures the temperature in the curing material and drives the microwave components to obtain predetermined curing temperature cycles for efficient curing. Uniform curing of the lossy encapsulants is achieved with this oven with typical cure cycle of 270 seconds with a ramp rate of 1oC/s and a hold period of 2 minutes. Differential scanning calorimeter based measurement for the pulsed microwave based curing of the polymer dielectric indicates a ~ 100% degree of cure