The Flawed Greatness of Huckleberry Finn

spring 2013"Read an article by MU's Mark Twain scholar, who retires this year."Essay by Tom Quir

Computational Eulerian Hydrodynamics and Galilean Invariance

Eulerian hydrodynamical simulations are a powerful and popular tool for modeling fluids in astrophysical systems. In this work, we critically examine recent claims that these methods violate Galilean invariance of the Euler equations. We demonstrate that Eulerian hydrodynamics methods do converge to a Galilean-invariant solution, provided a well-defined convergent solution exists. Specifically, we show that numerical diffusion, resulting from diffusion-like terms in the discretized hydrodynamical equations solved by Eulerian methods, accounts for the effects previously identified as evidence for the Galilean non-invariance of these methods. These velocity-dependent diffusive terms lead to different results for different bulk velocities when the spatial resolution of the simulation is kept fixed, but their effect becomes negligible as the resolution of the simulation is increased to obtain a converged solution. In particular, we find that Kelvin-Helmholtz instabilities develop properly in realistic Eulerian calculations regardless of the bulk velocity provided the problem is simulated with sufficient resolution (a factor of 2-4 increase compared to the case without bulk flows for realistic velocities). Our results reiterate that high-resolution Eulerian methods can perform well and obtain a convergent solution, even in the presence of highly supersonic bulk flows.Comment: Version accepted by MNRAS Oct 2, 2009. Figures degraded. For high-resolution color figures and movies of the numerical simulations, please visit http://www.astro.caltech.edu/~brant/Site/Computational_Eulerian_Hydrodynamics_and_Galilean_Invariance.htm

IGRT/ART phantom with programmable independent rib cage and tumor motion

Abstract PURPOSE: This paper describes the design and experimental evaluation of the Methods and Advanced Equipment for Simulation and Treatment in Radiation Oncology (MAESTRO) thorax phantom, a new anthropomorphic moving ribcage combined with a 3D tumor positioning system to move target inserts within static lungs. METHODS: The new rib cage design is described and its motion is evaluated using Vicon Nexus, a commercial 3D motion tracking system. CT studies at inhale and exhale position are used to study the effect of rib motion and tissue equivalence. RESULTS: The 3D target positioning system and the rib cage have millimetre accuracy. Each axis of motion can reproduce given trajectories from files or individually programmed sinusoidal motion in terms of amplitude, period, and phase shift. The maximum rib motion ranges from 7 to 20 mm SI and from 0.3 to 3.7 mm AP with LR motion less than 1 mm. The repeatability between cycles is within 0.16 mm root mean square error. The agreement between CT electron and mass density for skin, ribcage, spine hard and inner bone as well as cartilage is within 3%. CONCLUSIONS: The MAESTRO phantom is a useful research tool that produces programmable 3D rib motions which can be synchronized with 3D internal target motion. The easily accessible static lungs enable the use of a wide range of inserts or can be filled with lung tissue equivalent and deformed using the target motion system.status: publishe

Joking: uses and abuses of humour in the election campaign

A brief analysis of the use of humour in the 2019 UK General Election campaign, comparing uses of humour by mainstream candidates with the long-established practice of positing marginal, joke candidates

The clever country as a cargo cult. by Tom Quirk, Tim Duncan & Richard De Lautour

tag=1 data=The clever country as a cargo cult. by Tom Quirk, Tim Duncan & Richard De Lautour. tag=2 data=Quirk, Tom%Duncan, Tim%De Lautour, Richard tag=3 data=Quadrant. tag=4 data=XXXIV tag=5 data=270/1 tag=6 data=October & November 1990 tag=8 data=EDUCATION tag=9 data=NATIONAL NEEDS AND HIGHER EDUCATION PARTS I & II tag=10 data=Australian politicians and their counterparts around the world think of reshaping the future by coupling business to technology, science and education. tag=11 data=1990/2/11 tag=12 data=409 tag=13 data=CABAustralian politicians and their counterparts around the world think of reshaping the future by coupling business to technology, science and education