Funnel-based Reward Shaping for Signal Temporal Logic Tasks in Reinforcement Learning

Signal Temporal Logic (STL) is a powerful framework for describing the complex temporal and logical behaviour of the dynamical system. Numerous studies have attempted to employ reinforcement learning to learn a controller that enforces STL specifications; however, they have been unable to effectively tackle the challenges of ensuring robust satisfaction in continuous state space and maintaining tractability. In this paper, leveraging the concept of funnel functions, we propose a tractable reinforcement learning algorithm to learn a time-dependent policy for robust satisfaction of STL specification in continuous state space. We demonstrate the utility of our approach on several STL tasks using different environments.Comment: 8 pages, 10 figure

Funnel-based Reachability Control of Unknown Nonlinear Systems using Gaussian Processes

This paper aims to synthesize a reachability controller for an unknown dynamical system. We first learn the unknown system using Gaussian processes and the (probabilistic) guarantee on the learned model. Then we use the funnel-based controller synthesis approach using this approximated dynamical system to design the controller for a reachability specification. Finally, the merits of the proposed method are shown using a numerical example.Comment: Accepted in Indian Control Conference 202

Electron Beam-Induced Reduction of Cuprite

Cu-based materials are used in various industries, such as electronics, power generation, and catalysis. In particular, monolayered cuprous oxide (Cu2O) has potential applications in solar cells owing to its favorable electronic and magnetic properties. Atomically thin Cu2O samples derived from bulk cuprite were characterized by high-resolution transmission electron microscopy (HRTEM). Two voltages, 80 kV and 300 kV, were explored for in situ observations of the samples. The optimum electron beam parameters (300 kV, low-current beam) were used to prevent beam damage. The growth of novel crystal structures, identified as Cu, was observed in the samples exposed to isopropanol (IPA) and high temperatures. It is proposed that the exposure of the copper (I) oxide samples to IPA and temperature causes material nucleation, whereas the consequent exposure via e-beams generated from the electron beam promotes the growth of the nanosized Cu crystals

Effect of graphene coatings on the morphology of submillimeter thin copper wires after salt spray aging

Unprotected copper conductors are prone to oxidation and corrosion, especially when in contact with salt water or at high temperature. In this study, we compared commercially available coating with graphene oxide and plasma-enhanced chemical vapor deposition (PECVD) graphene coated wires in terms of antioxidation and anticorrosion protection. Samples were subjected to aging tests in a salt spray chamber. Thereafter, both the degree of coverage and surface protection were assessed by X-ray photoelectron spectroscopy measurements and scanning electron microscope images, which showed significant surface protection for both graphene coatings. Raman spectra obtained from the transferred coatings revealed their structural stability, which shows that it is possible to successfully use few atomic-layers-thick coatings to protect commercially available wires. Wire resistance tests performed at temperatures up to 320°C showed similar or better results for graphene coatings than for commercially coated wires. Additionally, images of the wires after high temperature tests showed high antioxidation protection for graphene coatings, especially for PECVD. The results of this study can be applied for further research on mechanical suitability of the coatings and wires themselves, especially after high-temperature CVD processes. Such studies may lead to novel Cu wire processing technologies.publishedVersio

Impact of MBE-grown (In,Ga)As/GaAs metamorphic buffers on excitonic and optical properties of single quantum dots with single-photon emission tuned to the telecom range

Tuning GaAs-based quantum emitters to telecom wavelengths makes it possible to use the existing mature technology for applications in, e.g., long-haul ultra-secure communication in the fiber networks. A promising method re-developed recently is to use a metamorphic InGaAs buffer that redshifts the emission by reducing strain. However, the impact of such a buffer causes also a simultaneous modification of other quantum dot properties. Knowledge of these effects is crucial for actual implementations of QD-based non-classical light sources for quantum communication schemes. Here, we thoroughly study single GaAs-based quantum dots grown by molecular-beam epitaxy on specially designed, digital-alloy InGaAs metamorphic buffers. With a set of structures varying in the buffer indium content and providing quantum dot emission through the telecom spectral range up to 1.6 $\mu$m, we analyze the impact of the buffer and its composition on QD structural and optical properties. We identify the mechanisms of quantum dot emission shift with varying buffer composition. We also look into the charge trapping processes and compare excitonic properties for different growth conditions with single-dot emission successfully shifted to both, the second and the third telecom windows.Comment: 20 pages, 9 figure

Prediction of magnesium-based bulk metallic glasses and their microstructural characterization

The development of advanced materials has resulted in the evolution of new class of materials called bulk metallic glasses...This thesis deals with efforts to meet two main challenges currently faced in the development of novel bulk metallic lass systems in genera, and Mg - based bulk metallic glasses in particular. Firstly, the development of a multifunctional optimization model, for selecting new Mg - based bulk metallic glass-forming compositions lighter than Al based on past research spanning over a decade. Secondly, understanding the challenges an artifacts associated with the transmission electron microscopy characterization of Mg₅₄Cu₂₈Ag₇Y₁₁ bulk metallic glasses and developing an artifact-free specimen preparation protocol for their microstructural characterization --Abstract, page iii

Electron Beam-Induced Reduction of Cuprite

Cu-based materials are used in various industries, such as electronics, power generation, and catalysis. In particular, monolayered cuprous oxide (Cu2O) has potential applications in solar cells owing to its favorable electronic and magnetic properties. Atomically thin Cu2O samples derived from bulk cuprite were characterized by high-resolution transmission electron microscopy (HRTEM). Two voltages, 80 kV and 300 kV, were explored for in situ observations of the samples. The optimum electron beam parameters (300 kV, low-current beam) were used to prevent beam damage. The growth of novel crystal structures, identified as Cu, was observed in the samples exposed to isopropanol (IPA) and high temperatures. It is proposed that the exposure of the copper (I) oxide samples to IPA and temperature causes material nucleation, whereas the consequent exposure via e-beams generated from the electron beam promotes the growth of the nanosized Cu crystals