다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Discrete particle simulation of particulate systems: A review of major applications and findings

During its approach to asteroid (101955) Bennu, NASA’s Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft surveyed Bennu’s immediate environment, photometric properties, and rotation state. Discovery of a dusty environment, a natural satellite, or unexpected asteroid characteristics would have had consequences for the mission’s safety and observation strategy. Here we show that spacecraft observations during this period were highly sensitive to satellites (sub-meter scale) but reveal none, although later navigational images indicate that further investigation is needed. We constrain average dust production in September 2018 from Bennu’s surface to an upper limit of 150 g s–1 averaged over 34 min. Bennu’s disk-integrated photometric phase function validates measurements from the pre-encounter astronomical campaign. We demonstrate that Bennu’s rotation rate is accelerating continuously at 3.63 ± 0.52 × 10–6 degrees day–2, likely due to the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect, with evolutionary implications.

/pdf/the-operational-environment-and-rotational-acceleration-of-25pb0r9b60.pdf

The operational environment and rotational acceleration of asteroid (101955) Bennu from OSIRIS-REx observations

Computer Methods in Applied Mechanics and Engineering

Dynamic fracture mechanics

Surface particle motions excited by a low velocity normal impact into a granular medium

Granular media are soft matter systems that exhibit some of the extreme behavior of complex fluids. Understanding of the natural formation of planetary bodies, landing on and exploring them, future engineering of structures beyond Earth and planetary defense all hinge on the ability to predict the complex mechanical behavior of granular matter. As we understand them, these behaviors are linked to the granular fluid to solid transition. In this white paper, we describe issues that emerge for granular systems under reduced gravity and their implications for basic science and space exploration. (Topical White Paper submitted to the NASA Biological and Physical Sciences in Space Decadal Survey 2023-2032)

Effects of reduced gravity on the granular fluid-solid transition: underexplored forces can dominate soft matter behaviors

Sanchez(Diego.Sanchez − lana@colorado.edu), Daniel J. Scheeres, CCAR, University of Colorado, Boulder, USA. Using a Soft-Sphere DEM code we simulate the reshaping and disruption of a self-gravitating 3D granular aggregate by increasing its spin rate. During the process, we monitor the evolution of the internal stresses in the aggregate to find its yield stress using the Von Mises and Maximum Stress yield criteria. In the simulations we either increase the number of particles or their density to increase the total mass of the aggregate and find an increment in the yield stress. In addition, once a reshaping spin rate (density dependent) has been reached, its further increase causes further reshape (ultimately fission) and a decrease in the spin rate itself.

/pdf/rotational-reshaping-and-yield-stress-of-rubble-pile-2ebac8cwtv.pdf

Paul Sánchez

Papers

Surface particle motions excited by a low velocity normal impact into a granular medium

Effects of reduced gravity on the granular fluid-solid transition: underexplored forces can dominate soft matter behaviors

Rotational Reshaping and Yield Stress of Rubble-Pile Asteroids