An experimental study of low-velocity impacts into granular material in reduced gravity

In order to improve our understanding of landing on small bodies and of asteroid evolution, we use our novel drop tower facility \citep{sunday2016} to perform low-velocity (2 - 40 cm/s), shallow impact experiments of a 10 cm diameter aluminum sphere into quartz sand in low effective gravities (~0.2 - 1 m/s^2). Using in-situ accelerometers we measure the acceleration profile during the impacts and determine the peak accelerations, collision durations and maximum penetration depth. We find that the penetration depth scales linearly with the collision velocity but is independent of the effective gravity for the experimental range tested, and that the collision duration is independent of both the effective gravity and the collision velocity. No rebounds are observed in any of the experiments. Our low-gravity experimental results indicate that the transition from the quasi-static regime to the inertial regime occurs for impact energies two orders of magnitude smaller than in similar impact experiments under terrestrial gravity. The lower energy regime change may be due to the increased hydrodynamic drag of the surface material in our experiments, but may also support the notion that the quasi-static regime reduces as the effective gravity becomes lower

Morally Respectful Listening and its Epistemic Consequences

What does it mean to listen to someone respectfully, that is, insofar as they are due recognition respect? This paper addresses that question and gives the following answer: it is to listen in such a way that you are open to being surprised. A specific interpretation of this openness to surprise is then defended

A novel facility for reduced-gravity testing: A setup for studying low-velocity collisions into granular surfaces

This work presents an experimental design for studying low-velocity collisions into granular surfaces in low-gravity. In the experiment apparatus, reduced-gravity is simulated by releasing a free-falling projectile into a surface container with a downward acceleration less than that of Earth’s gravity. The acceleration of the surface is controlled through the use of an Atwood machine, or a system of pulleys and counterweights. The starting height of the surface container and the initial separation distance between the projectile and surface are variable and chosen to accommodate collision velocities up to 20 cm/s and effective accelerations of ∼0.1 to 1.0 m/s2. Accelerometers, placed on the surface container and inside the projectile, provide acceleration data, while high-speed cameras capture the collision and act as secondary data sources. The experiment is built into an existing 5.5 m drop tower frame and requires the custom design of all components, including the projectile, surface sample container, release mechanism, and deceleration system. Data from calibration tests verify the efficiency of the experiment’s deceleration system and provide a quantitative understanding of the performance of the Atwood system

« L’Art est l’imitation de la Nature »

Je tiens à dire tout d'abord à quel point nous sommes, John Bayley et moi, heureux d'être ici à Caen. C'est la première fois que nous nous rendons dans une université française et votre invitation nous a enchantés, touchés et honorés : ce sont des moments vraiment très agréables que nous passons. Mon point de départ est la citation : « L'Art imite la Nature » ou « L'Art est l'imitation de la Nature ». Or le philosophe Wittgenstein, à l'ombre duquel j'ai grandi quand j'étais étudiante, commenç..

The red and the green

331 p. ; 22 cm

Contra la aridez. Esbozo polémico

«Against Dryness», en: Existentialists and Mystics. Writings on Philosophy and Literature, Nuev York-Londres, Penguin, 1999, pp. 287-295. Originariamente publicado en Encounter, Enero 1961, pp. 16-20. La presente traducción es una reedición de la que Flora Botton-Burlá realizó para la compilación de Federico Patán: Raíces en la tierra. Irlanda en su ensayo literario, México D. F., Universidad Nacional Autónoma de México, 2005, pp. 159-171