Role of sr on microstructure, mechanical properties, wear and corrosion behaviour of an al-mg2si-cu in-situ composite

The influence of Sr additions on the microstructure of primary and eutectic Mg2Si phases, wear and corrosion behaviour of Al–Mg2Si–Cu in-situ composite was investigated. The results showed that addition of 0.01 wt% Sr modified the primary Mg2Si morphology but exceeding this level of Sr induced a loss of modification as the primary phase morphology coarsened again. The Al–Mg2Si eutectic phase, on the other hand, still exhibited a refined structure even with higher levels of Sr additions. Thermal analysis results revealed that both modification of the primary Mg2Si and refinement of the eutectic Mg2Si are most likely related to nucleation and growth stages respectively. The results of 0.01 wt% Sr addition showed that the mean size and mean aspect ratio decreased by about 30% and 6% respectively, but the mean density increased by 185% respectively. The highest UTS, El%, impact toughness and hardness were measured at 101.57 MPa, 1.1%, 1.31 J and 81 VHN respectively. Fractography of tensile and impact specimens from the Sr-treated composite revealed that Mg2Si particles suffered cracking with few decohesion indicating higher ductility. The results of wear testing also showed that composites treated with Sr have higher wear resistance compared with those of without Sr. The highest resistance to wear was observed in the composite containing 0.01 wt %Sr which is likely the result of good dispersion of fine Mg2Si particles in the Al matrix. This fine morphology and uniform distribution of Mg2Si particles also contributed to better corrosion resistance by reducing the propagation of corrosion pits

A Model Analysis of Mechanisms for Radial Microtubular Patterns at Root Hair Initiation Sites

Plant cells have two main modes of growth generating anisotropic structures. Diffuse growth where whole cell walls extend in specific directions, guided by anisotropically positioned cellulose fibers, and tip growth, with inhomogeneous addition of new cell wall material at the tip of the structure. Cells are known to regulate these processes via molecular signals and the cytoskeleton. Mechanical stress has been proposed to provide an input to the positioning of the cellulose fibers via cortical microtubules in diffuse growth. In particular, a stress feedback model predicts a circumferential pattern of fibers surrounding apical tissues and growing primordia, guided by the anisotropic curvature in such tissues. In contrast, during the initiation of tip growing root hairs, a star-like radial pattern has recently been observed. Here, we use detailed finite element models to analyze how a change in mechanical properties at the root hair initiation site can lead to star-like stress patterns in order to understand whether a stress-based feedback model can also explain the microtubule patterns seen during root hair initiation. We show that two independent mechanisms, individually or combined, can be sufficient to generate radial patterns. In the first, new material is added locally at the position of the root hair. In the second, increased tension in the initiation area provides a mechanism. Finally, we describe how a molecular model of Rho-of-plant (ROP) GTPases activation driven by auxin can position a patch of activated ROP protein basally along a 2D root epidermal cell plasma membrane, paving the way for models where mechanical and molecular mechanisms cooperate in the initial placement and outgrowth of root hairs.This work was funded by the Knut and Alice Wallenberg Foundation via grant ShapeSystems (KAW 2012.0050) to MG and HJ, the Swedish Research Council (VR2013-4632) to HJ, and the Gatsby Charitable Foundation (GAT3395/PR4) to HJ

SLAM in Dynamic Environments: A Deep Learning Approach for Moving Object Tracking Using ML-RANSAC Algorithm

The important problem of Simultaneous Localization and Mapping (SLAM) in dynamic environments is less studied than the counterpart problem in static settings. In this paper, we present a solution for the feature-based SLAM problem in dynamic environments. We propose an algorithm that integrates SLAM with multi-target tracking (SLAMMTT) using a robust feature-tracking algorithm for dynamic environments. A novel implementation of RANdomSAmple Consensus (RANSAC) method referred to as multilevel-RANSAC (ML-RANSAC) within the Extended Kalman Filter (EKF) framework is applied for multi-target tracking (MTT). We also apply machine learning to detect features from the input data and to distinguish moving from stationary objects. The data stream from LIDAR and vision sensors are fused in real-time to detect objects and depth information. A practical experiment is designed to verify the performance of the algorithm in a dynamic environment. The unique feature of this algorithm is its ability to maintain tracking of features even when the observations are intermittent whereby many reported algorithms fail in such situations. Experimental validation indicates that the algorithm is able to perform consistent estimates in a fast and robust manner suggesting its feasibility for real-time applications

Optimal virtual water flows for improved food security in water-scarce countries

This is the final version. Available on open access from Nature Research via the DOI in this recordThe worsening water scarcity has imposed a significant stress on food production in many parts of the world. This stress becomes more critical when countries seek self-sufficiency. A literature review shows that food self-sufficiency has not been assessed as the main factor in determining the optimal cultivation patterns. However, food self-sufficiency is one of the main policies of these countries and requires the most attention and concentration. Previous works have focused on the virtual water trade to meet regional food demand and to calculate trade flows. The potential of the trade network can be exploited to improve the cropping pattern to ensure food and water security. To this end, and based on the research gaps mentioned, this study develops a method to link intra-country trade networks, food security, and total water footprints (WFs) to improve food security. The method is applied in Iran, a water-scarce country. The study shows that 781 × 106 m3 of water could be saved by creating a trade network. Results of the balanced trade network are input to a multi-objective optimization model to improve cropping patterns based on the objectives of achieving food security and preventing water crises. The method provides 400 management scenarios to improve cropping patterns considering 51 main crops in Iran. Results show a range of improvements in food security (19–45%) and a decrease in WFs (2–3%). The selected scenario for Iran would reduce the blue water footprint by 1207 × 106 m3, and reduce the cropland area by 19 × 103 ha. This methodology allows decision makers to develop policies that achieve food security under limited water resources in arid and semi-arid regions.Iran National Science FoundationCenter for International Scientific Studies and Collaboration (CISSC), Ministry of Science, Research and Technolog

Evolution of Nanocrystalline Structures Using High Energy Ball Milling of Quaternary Mg1.75Nb0.125C0.125NiMg_{1.75}Nb_{0.125}C_{0.125}Ni and Binary Mg2NiMg_2Ni

High energy ball milling of two initial quaternary and binary powder mixtures of $Mg_{1.75}Nb_{0.125}C_{0.125}Ni$ and $Mg_2Ni$ has been carried out in pure argon atmosphere for the synthesis of nanocrystalline powders based on $Mg_2Ni$ intermetallic compound. A planetary ball mill was employed using a ball to powder weight ratio of 20:1 for various milling time of 5, 10, 15, 20, 30 and 60 h. Characterization of the crystal structure of the milled products using X-ray diffractometry exhibited the formation of $Mg_2Ni$-based nanocrystallites after ≈ 5 h of milling for the both powder mixture. However, its volume fraction was greater in the case of quaternary powder mixture than that of binary one. In addition, an amorphous phase was detected in the milled products; its volume fraction showed increase by increasing milling time. The calculated mean crystallite size of $Mg_2Ni$ structure showed decrease by increasing the milling time following the Williamson-Hall procedure and was found to be ≈ 8 and 10 nm after 20 h of milling for the initial powder mixture of $Mg_{1.75}Nb_{0.125}C_{0.125}Ni$ and $Mg_2Ni$, respectively

A State-Space Approach to the Modelling and Control of the Neutral Leg of a Four Legs, Three-Phase Inverter

In this paper, a novel approach to determine the model of an ICNL (Independently Controlled Neutral Leg) is proposed. Based on this model, a cascaded control method is developed to provide a steady neutral point connection for a three-phase four-wire inverter and to balance the two DC capacitors voltages of a split DC-bus. Validation of the model is realised by simulations and the control has been tested by experiments. Results have shown good performance even with a high level of neutral current, which demonstrate the ability of the system to work within an unbalanced load or grid