Fast Second-order Cone Programming for Safe Mission Planning

This paper considers the problem of safe mission planning of dynamic systems operating under uncertain environments. Much of the prior work on achieving robust and safe control requires solving second-order cone programs (SOCP). Unfortunately, existing general purpose SOCP methods are often infeasible for real-time robotic tasks due to high memory and computational requirements imposed by existing general optimization methods. The key contribution of this paper is a fast and memory-efficient algorithm for SOCP that would enable robust and safe mission planning on-board robots in real-time. Our algorithm does not have any external dependency, can efficiently utilize warm start provided in safe planning settings, and in fact leads to significant speed up over standard optimization packages (like SDPT3) for even standard SOCP problems. For example, for a standard quadrotor problem, our method leads to speedup of 1000x over SDPT3 without any deterioration in the solution quality. Our method is based on two insights: a) SOCPs can be interpreted as optimizing a function over a polytope with infinite sides, b) a linear function can be efficiently optimized over this polytope. We combine the above observations with a novel utilization of Wolfe's algorithm to obtain an efficient optimization method that can be easily implemented on small embedded devices. In addition to the above mentioned algorithm, we also design a two-level sensing method based on Gaussian Process for complex obstacles with non-linear boundaries such as a cylinder

Approximate Capacities of Two-Dimensional Codes by Spatial Mixing

We apply several state-of-the-art techniques developed in recent advances of counting algorithms and statistical physics to study the spatial mixing property of the two-dimensional codes arising from local hard (independent set) constraints, including: hard-square, hard-hexagon, read/write isolated memory (RWIM), and non-attacking kings (NAK). For these constraints, the strong spatial mixing would imply the existence of polynomial-time approximation scheme (PTAS) for computing the capacity. It was previously known for the hard-square constraint the existence of strong spatial mixing and PTAS. We show the existence of strong spatial mixing for hard-hexagon and RWIM constraints by establishing the strong spatial mixing along self-avoiding walks, and consequently we give PTAS for computing the capacities of these codes. We also show that for the NAK constraint, the strong spatial mixing does not hold along self-avoiding walks

CO-SOLVENT ASSISTED SPRAY PYROLYSIS FOR THE PREPARATION OF METAL MICROPARTILCE

Metal and bimetallic particles play an important role in catalytic, medical and electronic applications. Various techniques have been developed for the preparation of metal particles, including vaporization techniques, sonochemical, polyol method, mechanical alloying and spray pyrolysis. Compared with the other preparation techniques, the spray pyrolysis process has the advantages of easy scale up in industry, tunable particle size and controllable particle composition. Sometimes hydrogen was used in the process to promote the formation of metallic phase in a lower temperature, but it also created a potential safety problem. In order to eliminate the use of hydrogen, a cosolvent assisted ultrasonic spray pyrolysis process was developed, and ethanol (ET) and ethylene glycol (EG) are used as the cosolvent. In this study, the cosolvent assisted ultrasonic spray pyrolysis process was used for the generation of various oxide free oxide particles, and the reaction mechanism was shown. In the first part of this study, properties of ultrasonic droplet generator were investigated. Precursor solutions were atomized by a 1.7 MHz ultrasonic nebulizer. The droplet size distribution and atomization rate were measured. Relationship between droplet diameters and the physical properties were revealed by statistic tools. Bimodal droplets distribution was observed during the experiment. Then copper particles were generated by the spray pyrolysis process. Copper nitrate aqueous solution was used as the precursor and either ET or EG was used as cosolvent. Oxide free particles were generated at temperature from 400 oC to 1000 oC. It was noticed that particles morphology and formation process was strong affected by the properties of the cosolvents. In the following study, the spray pyrolysis process was successfully used for the generation of AgNi, CuNi and AgCu bi-components particles. Various particle structures were observed, and the structures were mainly determined by the thermodynamic properties of the particles components. In the last part of this dissertation, efforts mainly focused on the mechanism of AgCu particle generation. Reaction intermediates were collected. Reaction process from nitrates to pure metal and the phase separation behavior between Cu and Ag was demonstrated