11,703 research outputs found
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 ïŹrst 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 diïŹerences. These diïŹerences are discussed theoretically and investigated numerically
Groups with compact open subgroups and multiplier Hopf -algebras
For a locally compact group we look at the group algebras and
, and we let act on by the multiplication
operator . We show among other things that the following properties are
equivalent:
1. has a compact open subgroup.
2. One of the -algebras has a dense multiplier Hopf -subalgebra
(which turns out to be unique).
3. There are non-zero elements and such that
has finite rank.
4. There are non-zero elements and such that
.
If is abelian, these properties are equivalent to:
5. There is a non-zero continuous function with the property that both
and 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 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
- âŠ