Field Theory of free Active Ornstein-Uhlenbeck Particles

We derive a Doi-Peliti field theory for free active Ornstein-Uhlenbeck particles, or, equivalently, free inertial Brownian particles, and present a way to diagonalise the Gaussian part of the action and calculate the propagator. Unlike previous course-grained approaches this formulation correctly tracks particle identity and yet can easily be expanded to include potentials and arbitrary reactions

Computational Approaches for Modeling Power Consumption on an Underwater Flapping Fin Propulsion System

The last few decades have led to the rise of research focused on propulsion and control systems for bio-inspired unmanned underwater vehicles (UUVs), which provide more maneuverable alternatives to traditional UUVs in underwater missions. Propulsive efficiency is of utmost importance for flapping-fin UUVs in order to extend their range and endurance for essential operations. To optimize for different gait performance metrics, we develop a non-dimensional figure of merit (FOM), derived from measures of propulsive efficiency, that is able to evaluate different fin designs and kinematics, and allow for comparison with other bio-inspired platforms. We create and train computational models using experimental data, and use these models to predict thrust and power under different fin operating states, providing efficiency profiles. We then use the developed FOM to analyze optimal gaits and compare the performance between different fin materials. These comparisons provide a better understanding of how fin materials affect our thrust generation and propulsive efficiency, allowing us to inform control systems and weight for efficiency on an inverse gait-selector model.Comment: 9 pages, 8 figures, conferenc

Platinum-paper micromotors: An urchin-like nanohybrid catalyst for green monopropellant bubble-thrusters

Platinum nanourchins supported on microfibrilated cellulose films (MFC) were fabricated and evaluated as hydrogen peroxide catalysts for small-scale, autonomous underwater vehicle (AUV) propulsion systems. The catalytic substrate was synthesized through the reduction of chloroplatinic acid to create a thick film of Pt coral-like microstructures coated with Pt urchin-like nanowires that are arrayed in three dimensions on a two-dimensional MFC film. This organic/inorganic nanohybrid displays high catalytic ability (reduced activation energy of 50-63% over conventional materials and 13-19% for similar Pt nanoparticle-based structures) during hydrogen peroxide (H2O2) decomposition as well as sufficient propulsive thrust (\u3e0.5 N) from reagent grade H2O2 (30% w/w) fuel within a small underwater reaction vessel. The results demonstrate that these layered nanohybrid sheets are robust and catalytically effective for green, H2O2-based micro-AUV propulsion where the storage and handling of highly explosive, toxic fuels are prohibitive due to size-requirements, cost limitations, and close person-to-machine contact

High Aspect Ratio Carbon Nanotube Membranes Decorated with Pt Nanoparticle Urchins for Micro Underwater Vehicle Propulsion via H2O2 Decomposition

The utility of unmanned micro underwater vehicles (MUVs) is paramount for exploring confined spaces, but their spatial agility is often impaired when maneuvers require burst-propulsion. Herein we develop high-aspect ratio (150:1), multiwalled carbon nanotube microarray membranes (CNT-MMs) for propulsive, MUV thrust generation by the decomposition of hydrogen peroxide (H2O2). The CNT-MMs are grown via chemical vapor deposition with diamond shaped pores (nominal diagonal dimensions of 4.5 × 9.0 μm) and subsequently decorated with urchin-like, platinum (Pt) nanoparticles via a facile, electroless, chemical deposition process. The Pt-CNT-MMs display robust, high catalytic ability with an effective activation energy of 26.96 kJ mol–1 capable of producing a thrust of 0.209 ± 0.049 N from 50% [w/w] H2O2 decomposition within a compact reaction chamber of eight Pt-CNT-MMs in series

Porous Wood Monoliths Decorated with Platinum Nano-Urchins as Catalysts for Underwater Micro-Vehicle Propulsion via H2O2 Decomposition

Porous carbon is becoming an important and promising high-surface area scaffold material for various energy-based applications including catalysis. Here we demonstrate the growth of urchin-like platinum nanoparticles (PtNPs) on carbon monoliths derived from basswood that work as catalysts for micro underwater vehicle (MUV) propulsion via H2O2 decomposition. The carbon monoliths were constructed of natural basswood that was carbonized in argon (Ar) and subjected to a subsequent CO2 activation process that rendered the material into a hardened 3D porous activated carbonized wood (ACW) with inner channel voids measuring 10-70 μm in diameter. The PtNP nanourchins (500 nm or less in total diameter, with individual nanospikes measuring 3-5 nm in diameter) form on the ACW via a facile electroless and template-free chemical deposition approach that utilized the reduction of chloroplatinic acid. The developed PtNP-ACW hybrid material exhibited higher catalytic efficiency as compared to previously reported platinum (Pt) catalysts with a low activation energy of 18.9 ± 2.5 kJ mol-1 for H2O2 decomposition. The catalyst also proved useful in an important energy application by its ability to rapidly decompose H2O2 fuel and generate O2 gas for propulsion of a 3D printed MUV prototype. The PtNP-ACW catalysts weighing only 0.14 g generated a propulsion thrust of 230 mN, which is sufficient to power MUVs. The natural wood derived carbon scaffolds significantly reduce the overall cost as compared to other carbon-based catalysts such as carbon nanotubes or graphene without reducing catalytic efficiency. Hence such catalysts act as a stepping stone for potential low cost and sustainable power for burst thrust operation of MUVs

Platinum Nanoparticle Decorated SiO2 Microfibers as Catalysts for Micro Unmanned Underwater Vehicle Propulsion

Micro unmanned underwater vehicles (UUVs) need to house propulsion mechanisms that are small in size but sufficiently powerful to deliver on-demand acceleration for tight radius turns, burst-driven docking maneuvers, and low-speed course corrections. Recently, small-scale hydrogen peroxide (H2O2) propulsion mechanisms have shown great promise in delivering pulsatile thrust for such acceleration needs. However, the need for robust, high surface area nanocatalysts that can be manufactured on a large scale for integration into micro UUV reaction chambers is still needed. In this report, a thermal/electrical insulator, silicon oxide (SiO2) microfibers, is used as a support for platinum nanoparticle (PtNP) catalysts. The mercapto-silanization of the SiO2 microfibers enables strong covalent attachment with PtNPs, and the resultant PtNP–SiO2 fibers act as a robust, high surface area catalyst for H2O2 decomposition. The PtNP–SiO2 catalysts are fitted inside a micro UUV reaction chamber for vehicular propulsion; the catalysts can propel a micro UUV for 5.9 m at a velocity of 1.18 m/s with 50 mL of 50% (w/w) H2O2. The concomitance of facile fabrication, economic and scalable processing, and high performance—including a reduction in H2O2 decomposition activation energy of 40–50% over conventional material catalysts—paves the way for using these nanostructured microfibers in modern, small-scale underwater vehicle propulsion systems

Platinum Nanoparticle Decorated SiO 2 Microfibers as Catalysts for Micro Unmanned Underwater Vehicle Propulsion

Micro unmanned underwater vehicles (UUVs) need to house propulsion mechanisms that are small in size but sufficiently powerful to deliver on-demand acceleration for tight radius turns, burst-driven docking maneuvers, and low-speed course corrections. Recently, small-scale hydrogen peroxide (H2O2) propulsion mechanisms have shown great promise in delivering pulsatile thrust for such acceleration needs. However, the need for robust, high surface area nanocatalysts that can be manufactured on a large scale for integration into micro UUV reaction chambers is still needed. In this report a thermal/electrical insulator, silicon oxide (SiO2) microfibers, are used as a support for platinum nanoparticle (PtNP) catalysts. The mercapto-silanization of the SiO2 microfibers enables strong covalent attachment with PtNPs and the resultant PtNP-SiO2 fibers act as a robust, high surface area catalyst for H2O2 decomposition. The PtNP-SiO2 catalysts are fitted inside a micro UUV reaction chamber for vehicular propulsion; the catalysts can propel a micro UUV for 5.9 meters at a velocity of 1.18 m/s with 50 mL of 50% (w/w) H2O2.The concomitance of facile fabrication, economic and scalable processing, and high performance —including a reduction in H2O2 decomposition activation energy of 40-50% over conventional material catalysts—paves the way for using these nanostructured microfibers in modern, small-scale underwater vehicle propulsion systems

Particle Entity in the Doi-Peliti and Response Field Formalisms

We introduce a procedure to test a theory for point particle entity, that is, whether said theory takes into account the discrete nature of the constituents of the system. We then identify the mechanism whereby particle entity is enforced in the context of two field-theoretic frameworks designed to incorporate the particle nature of the degrees of freedom, namely the Doi-Peliti field theory and the response field theory that derives from Dean's equation. While the Doi-Peliti field theory encodes the particle nature at a very fundamental level that is easily revealed, demonstrating the same for Dean's equation is more involved and results in a number of surprising diagrammatic identities. We derive those and discuss their implications. These results are particularly pertinent in the context of active matter, whose surprising and often counterintuitive phenomenology rests wholly on the particle nature of the agents and their degrees of freedom as particles

Data-Driven Machine Learning Models for a Multi-Objective Flapping Fin Unmanned Underwater Vehicle Control System

Flapping-fin unmanned underwater vehicle (UUV) propulsion systems provide high maneuverability for naval tasks such as surveillance and terrain exploration. Recent work has explored the use of time-series neural network surrogate models to predict thrust from vehicle design and fin kinematics. We develop a search-based inverse model that leverages a kinematics-to-thrust neural network model for control system design. Our inverse model finds a set of fin kinematics with the multi-objective goal of reaching a target thrust and creating a smooth kinematic transition between flapping cycles. We demonstrate how a control system integrating this inverse model can make online, cycle-to-cycle adjustments to prioritize different system objectives

Platinum-paper micromotors: An urchin-like nanohybrid catalyst for green monopropellant bubble-thrusters

Platinum nanourchins supported on microfibrilated cellulose films (MFC) were fabricated and evaluated as hydrogen peroxide catalysts for small-scale, autonomous underwater vehicle (AUV) propulsion systems. The catalytic substrate was synthesized through the reduction of chloroplatinic acid to create a thick film of Pt coral-like microstructures coated with Pt urchin-like nanowires that are arrayed in three dimensions on a two-dimensional MFC film. This organic/inorganic nanohybrid displays high catalytic ability (reduced activation energy of 50-63% over conventional materials and 13-19% for similar Pt nanoparticle-based structures) during hydrogen peroxide (H2O2) decomposition as well as sufficient propulsive thrust (>0.5 N) from reagent grade H2O2 (30% w/w) fuel within a small underwater reaction vessel. The results demonstrate that these layered nanohybrid sheets are robust and catalytically effective for green, H2O2-based micro-AUV propulsion where the storage and handling of highly explosive, toxic fuels are prohibitive due to size-requirements, cost limitations, and close person-to-machine contact.This article is from ACS Applied Materials and Interfaces 6 (2014): 17837, doi: 10.1021/am504525e. Posted with permission.</p