저작근 근전도에 관한 정상교합자와 ii급 부정교합자의 비교 연구

Exploring and identifying structure is even more important for multivariate data than univariate data, given the difficulties in graphically presenting multivariate data and the comparative lack of parametric models to represent it. Unfortunately, such exploration is also inherently more difficult.

Multivariate Density Estimation

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.

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

High-resolution gravity data obtained from the dual Gravity Recovery and Interior Laboratory (GRAIL) spacecraft show that the bulk density of the Moon's highlands crust is 2550 kilograms per cubic meter, substantially lower than generally assumed. When combined with remote sensing and sample data, this density implies an average crustal porosity of 12% to depths of at least a few kilometers. Lateral variations in crustal porosity correlate with the largest impact basins, whereas lateral variations in crustal density correlate with crustal composition. The low-bulk crustal density allows construction of a global crustal thickness model that satisfies the Apollo seismic constraints, and with an average crustal thickness between 34 and 43 kilometers, the bulk refractory element composition of the Moon is not required to be enriched with respect to that of Earth.

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The Crust of the Moon as Seen by GRAIL

Lunar sourcebook. A user's guide to the moon

The First Detailed Look at Asteroid Ryugu with Visible Multi-band Camera on Hayabusa2

Crater Degradation on Mercury: A Global Perspective

The shapes of asteroids are a product of their formation and evolution interplaying with their bulk properties. The OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security— Regolith Explorer) measured the shape of Bennu using stereophotoclinometry and laser altimetry. Bennu is found to be a highly porous rubble pile with a toplike shape. Bennu’s surface is dominated by boulders and craters. It exhibits a non-circular equatorial ridge and high-standing longitudinal ridges that, in some instances, span all latitudes. These structures suggest interior strength through friction or cohesive forces. Long surface lineaments and mass-wasting suggest recent activity by surface and, perhaps, interior processes. We report on global shape models that will undergo further improvements through the addition of higher resolution images and altimetric data. These results include global shape, spherical harmonic analysis, hypsometry, and a comparison to other asteroids – leading to additional insights into Bennu’s history.

New insights from (101955) Bennu's global digital terrain model

242 formation of an impact crater will provide new constraints on the collisional evolution of the asteroid belt. To first order, higher strain rates yield smaller fragment sizes. As Fig. 1 shows, the relationship is really more complex. As a first step toward better understanding the failure of geological materials at fairly moderate strain rates— more akin to what a planetary body typically encounters during a planetary-scale impact—we embarked on an experimental investigation to probe the response of a model geological material (single-crystal quartz) under uniaxial compression. Dynamic compression experiments were conducted using a Kolsky bar, which allowed a detailed history of the stress–time response on the microsecond time scale to be obtained. Ultra-high-speed photography recorded the evolution of damage and the propagation of cracks. Experiments also were done at quasi-static loading rates to further determine the effect of loading rate. Again, images detailing the evolution of the failure process were recorded. An increase in compressive strength was observed with increased loading rate. In specimens that were not loaded to (catastrophic) failure, significant crack growth was observed during the mechanical unloading of the specimen. The mechanism (or mechanisms) responsible for generating and propagating these “unloading cracks” is currently under investigation. A parallel modeling effort is in progress (Fig. 2). Impacts initiate dynamic fracturing on macroand micro-scales, and the resulting fragmentation can be related to strain rate. Dynamic fracture has been directly observed at low strain rates (~10 −2 to 10−3 s−1, during earthquakes) and at high strain rates (~105 to 106 s−1, during laboratory-scale hypervelocity impact experiments). On the basis of firstorder estimates of the strain rate in the event (approximate impact velocity/projectile diameter) and numerical results such as those shown, the strain rates encountered in a typical planetary-scale impact range from ~100 to 102 s−1. These intermediate values lie within a strain rate regime that can be observed with the Kolsky bar, but are not easy to observe during typical small-scale hypervelocity (<2 km/s) impact experiments. Combining our numerical simulations with new dynamic fragmentation models derived from Kolsky bar experiments, we have begun to Figure 1. Factors that contribute to the failure of materials on the basis of classical dynamic fracture mechanics. Most of the region cratered by a bolide actually undergoes moderate rather than high strain rates, which result in different mechanical and failure behaviors of the impacted body. The Dynamic Fracture of Rocky Bodies: Applications to Planetary Impact Problems

Olivier S. Barnouin

Papers

The First Detailed Look at Asteroid Ryugu with Visible Multi-band Camera on Hayabusa2

Crater Degradation on Mercury: A Global Perspective

New insights from (101955) Bennu's global digital terrain model

The Dynamic Fracture of Rocky Bodies: Applications to Planetary Impact Problems

Shape Model Construction of Bennu Using the OSIRIS-REx Laser Altimeter (OLA)