Arcjet Supplemental Diagnostics

This document proposes a new set of diagnostics designed to be implemented on the NASA Ames miniature Arcjet Research Chamber (mARC) for improved characterization of the flow. The diagnostics are grouped into three classes:higher cadence measurements, higher spatial resolution, and computer vision techniques for improved analysis of existing imaging. The goal is to better understand and quantify the following properties: flow statistics/uncertainty, temporal & spatial non-uniformity, flow temperature/enthalp

A comparison of two frameworks for kinematic hardening in hyperelasto-plasticity

In this work we compare two frameworks for thermodynamically consistent hyperelasto-plasticity with kinematic hardening. The first was formulated by Dettmer and Reese (2004), inspired by Lion (2000), and has been used to model sheet metal forming. The second, formulated by Wallin et al. (2003), has been used to model large shear strains and cyclic ratcheting behavior of pearlitic steel (Johansson et al. 2006). In this paper we show that these frameworks can result in equivalent models for certain choices of free energies. Furthermore, it is shown that the choices of free energy found in the literature only result in minor differences. These differences are discussed theoretically and investigated numerically

Groups with compact open subgroups and multiplier Hopf ∗^*-algebras

For a locally compact group $G$ we look at the group algebras $C_0(G)$ and $C_r^*(G)$, and we let $f\in C_0(G)$ act on $L^2(G)$ by the multiplication operator $M(f)$. We show among other things that the following properties are equivalent: 1. $G$ has a compact open subgroup. 2. One of the $C^*$-algebras has a dense multiplier Hopf $^*$-subalgebra (which turns out to be unique). 3. There are non-zero elements $a\in C_r^*(G)$ and $f\in C_0(G)$ such that $aM(f)$ has finite rank. 4. There are non-zero elements $a\in C_r^*(G)$ and $f\in C_0(G)$ such that $aM(f)=M(f)a$. If $G$ is abelian, these properties are equivalent to: 5. There is a non-zero continuous function with the property that both $f$ and $\hat f$ have compact support.Comment: 23 pages. Section 1 has been shortened and improved. To appear in Expositiones Mathematica

Safe Learning of Quadrotor Dynamics Using Barrier Certificates

To effectively control complex dynamical systems, accurate nonlinear models are typically needed. However, these models are not always known. In this paper, we present a data-driven approach based on Gaussian processes that learns models of quadrotors operating in partially unknown environments. What makes this challenging is that if the learning process is not carefully controlled, the system will go unstable, i.e., the quadcopter will crash. To this end, barrier certificates are employed for safe learning. The barrier certificates establish a non-conservative forward invariant safe region, in which high probability safety guarantees are provided based on the statistics of the Gaussian Process. A learning controller is designed to efficiently explore those uncertain states and expand the barrier certified safe region based on an adaptive sampling scheme. In addition, a recursive Gaussian Process prediction method is developed to learn the complex quadrotor dynamics in real-time. Simulation results are provided to demonstrate the effectiveness of the proposed approach.Comment: Submitted to ICRA 2018, 8 page

Calculation of Superdiffusion for the Chirikov-Taylor Model

It is widely known that the paradigmatic Chirikov-Taylor model presents enhanced diffusion for specific intervals of its stochasticity parameter due to islands of stability, which are elliptic orbits surrounding accelerator mode fixed points. In contrast with normal diffusion, its effect has never been analytically calculated. Here, we introduce a differential form for the Perron-Frobenius evolution operator in which normal diffusion and superdiffusion are treated separately through phases formed by angular wave numbers. The superdiffusion coefficient is then calculated analytically resulting in a Schloemilch series with an exponent $\beta=3/2$ for the divergences. Numerical simulations support our results.Comment: 4 pages, 2 figures (revised version

Method for Identifying Actors in a Knowledge Based Cluster

The objective of the paper is to develop a method through which we can identify the actors (industrial, institutional and individual) who are active in technology development in the same or similar knowledge fields. The paper is, thus, aimed to make a methodological contribution to the literature, which has emerged on the systemic nature of innovation. The method involves broadening out from a starting point in a specific patent class, which corresponds as closely as possibly to the technological area of interest, to a set of related patent classes by using co-classifications and citations. After close scrutiny of both patent classes and patents, the actors in the new classes, as well as in the original class, are then identified. We try out the method on radio wave antennas for communication technology in Sweden. We find a range of firms and other actors in a whole set of industries, which bear little relation to one another in an input-output sense. Although we can not ascertain the extent of linkages or relations between these actors, our hypothesis is that they constitute a cluster around radio wave antenna technology in Sweden.knowledge-based clusters, indicators, patents, similar and complementary technologies, horisontal linkages, knowledge spillovers, actors

Two-proton correlation function: a gentle introduction

The recent COSY-11 collaboration measurement of the two-proton correlation function in the pp -> ppeta reaction, reported at this meeting [1], arouse some interest in a simple theoretical description of the correlation function. In these notes we present a pedagogical introduction to the practical methods that can be used for calculating the correlation function.Comment: Prepared for the proceedings of the Symposium on Meson Physics at COSY-11 and WASA-at-COSY, Krakow, Poland, 17-22 June 200