Safe navigation and human-robot interaction in assistant robotic applications

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Oxide Nanoelectronics

This thesis describes research performed on two types of complex oxide heterostructures. The first consists of ultrathin LaAlO3 films grown on SrTiO3 substrates. At the interface between these two insulating oxides, a quasi two dimensional electron gas may form under proper conditions. This interface has remarkable properties such as interfacial superconductivity, interfacial magnetism and a hysteretic voltage-controlled metal-insulator transition. We developed an Atomic Force Microscope (AFM) lithography technique which is capable of switching reversibly at room temperature this metal-insulator transition with nanometer scale spatial resolution. Based on this technique, conducting nanowires as thin as 2 nm and nanodots array with density up to 1014 inch-2 were written, probed and erased. Sketch-defined field effect transistors (SketchFET) with channel lengths as short as 2 nm were fabricated. These structures were characterized over a temperature range 15 K-300 K, revealing a complex energy landscape. Magnetotransport measurements performed at temperatures at and below 1 K reveal a variety of intriguing quantum phenomena, including integer and fractional quantum Hall states. The second material system consists of thin films of SrTiO3 grown directly on silicon. Although SrTiO3 is not ferroelectric at any temperature in bulk form, when strained to the silicon lattice it can become ferroelectric at and above room temperature. Temperature-dependent piezo force microscopy was performed to verify that those strain engineered films with certain thickness are indeed ferroelectric. Ultrafast optical experiments were carried out to measure lattice dynamics in these strained films. A coherent acoustic phonon mode was observed and studied as a function of film thickness and laser polarization. Using SrTiO3 grown on silicon-on-insulator structures, ferroelectric field effect transistors (FeFET) were fabricated and characterized at room temperature

Sen3Bot Net: a meta-sensors network to enable smart factories implementation

In the near future, an increasing number of mobile agents working closely with human operators is envisaged in smart factories. In industrial human-shared environments that employ traditional Automated Guided Vehicles, safety can be ensured thanks to the support provided by Autonomous Mobile Robots, acting as a net of meta-sensors. The localization and perception information of each meta-sensor is shared among all mobile platforms. In particular, the information about the dynamic detection of human presence is combined and uploaded in a shared map, increasing the awareness of the mobile robots about their surroundings in a specific working area. This paper proposes an architecture that integrates the meta-sensors with an existing net of Automated Guided Vehicles, with the aim of enhancing systems based on outdated mobile agents that seek for Industry 4.0 solutions without the necessity of a complete renewal. Simulations of test scenarios are provided in order to confirm the validity of the proposed architecture model

Light induced non-volatile switching of superconductivity in single layer FeSe on SrTiO3 substrate

The capability of controlling superconductivity by light is highly desirable for active quantum device applications. Since superconductors rarely exhibit strong photoresponses, and optically sensitive materials are often not superconducting, efficient coupling between these two characters can be very challenging in a single material. Here we show that, in FeSe/SrTiO3 heterostructures, the superconducting transition temperature in FeSe monolayer can be effectively raised by the interband photoexcitations in the SrTiO3substrate. Attributed to a light induced metastable polar distortion uniquely enabled by the FeSe/SrTiO3 interface, this effect only requires a less than 50 µW cm−2 continuous-wave light field. The fast optical generation of superconducting zero resistance state is non-volatile but can be rapidly reversed by applying voltage pulses to the back of SrTiO3substrate. The capability of switching FeSe repeatedly and reliably between normal and superconducting states demonstrate the great potential of making energy-efficient quantum optoelectronics at designed correlated interfaces

Fast Global Convergence of Natural Policy Gradient Methods with Entropy Regularization

Natural policy gradient (NPG) methods are among the most widely used policy optimization algorithms in contemporary reinforcement learning. This class of methods is often applied in conjunction with entropy regularization -- an algorithmic scheme that encourages exploration -- and is closely related to soft policy iteration and trust region policy optimization. Despite the empirical success, the theoretical underpinnings for NPG methods remain limited even for the tabular setting. This paper develops $\textit{non-asymptotic}$ convergence guarantees for entropy-regularized NPG methods under softmax parameterization, focusing on discounted Markov decision processes (MDPs). Assuming access to exact policy evaluation, we demonstrate that the algorithm converges linearly -- or even quadratically once it enters a local region around the optimal policy -- when computing optimal value functions of the regularized MDP. Moreover, the algorithm is provably stable vis-\`a-vis inexactness of policy evaluation. Our convergence results accommodate a wide range of learning rates, and shed light upon the role of entropy regularization in enabling fast convergence.Comment: v2 adds new proofs and improved results; accepted to Operations Researc