Changes of Kondo effect in the junction with DIII-class topological and ss-wave superconductors

We discuss the change of the Kondo effect in the Josephson junction formed by the indirect coupling between a one-dimensional \emph{DIII}-class topological and s-wave superconductors via a quantum dot. By performing the Schrieffer-Wolff transformation, we find that the single-electron occupation in the quantum dot induces various correlation modes, such as the Kondo and singlet-triplet correlations between the quantum dot and the $s$-wave superconductor and the spin exchange correlation between the dot and Majorana doublet. Moreover, it plays a nontrivial role in modifying the Josephson effect, leading to the occurrence of anisotropic and high-order Kondo correlation. In addition, due to the quantum dot in the Kondo regime, extra spin exchange correlations contribute to the Josephson effect as well. Nevertheless, if the \emph{DIII}-class topological superconductor degenerates into \emph{D}-class because of the destruction of time-reversal invariance, all such terms will disappear completely. We believe that this work shows the fundamental difference between the \emph{D}- and \emph{DIII}-class topological superconductors.Comment: 10 pages, 3 figures. Any comment is welcom

Modular Design of an Educational Robotics Platform

The goal of this thesis is to design a modular educational robotics platform to improve the limitation of current educational robotics platforms, such as limited pins, single programming language, and single programming device. This platform uses an SPI bus for modularity and to solve the problem of limited pins on current educational robot platforms. A Raspberry Pi, which runs a 32bit Embedded Linux System, has been used to build the central control for this educational robotics platform to enable it to use different programming languages and to be programmed by different devices. The modules and libraries for stepper motors and IR sensors have been built for this robot, and the example projects, basic control, obstacle avoidance, and wall following, show that this educational robotics platform can be used as a platform for basic artificial intelligence design. This thesis also shows how to design a custom module, which enables users to design their own modules and put them into their robot projects

Dry Sliding Wear And Friction Behavior Of Silicon Carbide And Multi Wall Carbon Nanotubes Reinforced Magnesium Matrix Hybrid Composites

In order to optimize the functionality of magnesium, a modest attempt has been made to develop magnesium hybrid composites incorporating of synthesis micro and nano size fillers. Commercially pure magnesium (Mg) reinforced with (i) 10 wt.% micro-sized silicon carbide (SiC) particles (ii) combination of 10 wt.% micro-sized silicon carbide (SiC) particles and 1 wt.% multi-walled carbon nanotubes (MWCNTs), respectively, were synthesized via powder metallurgy route followed by hot extrusion. After the specimen preparation, microstructural characterization studies were conducted to determine the distribution of reinforcement, grain morphology, and presence of porosity by using Optical Microscope, Scanning Electron Microscope and Field Emission Scanning Electron Microscopy. Density and porosity measurements were carried out accordance with Archimedes’ principle. Micro-Vickers Test was also carried out to investigate the hardness of material. The dry sliding tests were performed using a pin-on-disc tester against a grey cast iron counterbody under two applied normal loads (5, 10, 20, 40 N) with four sliding speeds (0.5, 1.5, 3.5, 4.5 m/s) corresponding to a constant sliding distance of 5000 m to identify the wear rate and coefficient of friction of magnesium composite. The morphology of the worn pin surfaces and collected wear debris were examined using Scanning Electron Microscope. Throughout this work, reasonably uniform distribution of SiC particulates and MWCNTs in magnesium matrix were observed. Low porosity (below 2.0 %) was obtained which indicated the suitability of the processing parameters. The Vickers hardness of all the hierarchical magnesium composite configurations are significantly higher than the pure magnesium. Wear rate for both unreinforced magnesium and its composite increased with increasing load but the incorporation of micro and nano size fillers reduced the wear rate of magnesium particularly at loads of 5, 10, 20 N. The sliding speed increment induced higher wear on magnesium composites. However, at the highest load of 40 N, a crossover in wear rate was observed with the increased in sliding speeds, i.e., at sliding speed of 1.5 m/s the wear rate of the composite higher than unreinforced magnesium, but the incorporation of SiC and MWCNTs shifts to minimize the wear rate at sliding speeds of 3.5 and 4.5 m/s respectively. There is a small reduction in the coefficient of friction for Mg/SiC/MWCNTs composite as compared to Mg/SiC particularly at low loads of 5, 10, 20 N as the sliding speed increased but the change of coefficient of friction among different materials become insignificant at high load of 40 N. Five wear mechanisms mostly operated in combination namely abrasion, adhesion, oxidation, delamination and plastic deformation have been observed in various sliding conditions. Such modify hybrid approach may bring significant implications on application particularly in automotive and aviation sectors. These would become as another material option to further improve the fuel efficiency as well as service life of components