準包括的再構成法を用いたB→Xs gammaの精密測定

Tohoku University山本均課

Angular Momentum Exchange by Gravitational Torques and Infall in the Circumbinary Disk of the Protostellar System L1551 NE

We report the ALMA observation of the Class I binary protostellar system L1551 NE in the 0.9-mm continuum, C18O (3-2), and 13CO (3-2) lines at a ~1.6 times higher resolution and a ~6 times higher sensitivity than those of our previous SMA observations, which revealed a r ~300 AU-scale circumbinary disk in Keplerian rotation. The 0.9-mm continuum shows two opposing U-shaped brightenings in the circumbinary disk, and exhibits a depression between the circumbinary disk and the circumstellar disk of the primary protostar. The molecular lines trace non-axisymmetric deviations from Keplerian rotation in the circumbinary disk at higher velocities relative to the systemic velocity, where our previous SMA observations could not detect the lines. In addition, we detect inward motion along the minor axis of the circumbinary disk. To explain the newly-observed features, we performed a numerical simulation of gas orbits in a Roche potential tailored to the inferred properties of L1551 NE. The observed U-shaped dust features coincide with locations where gravitational torques from the central binary system are predicted to impart angular momentum to the circumbinary disk, producing shocks and hence density enhancements seen as a pair of spiral arms. The observed inward gas motion coincides with locations where angular momentum is predicted to be lowered by the gravitational torques. The good agreement between our observation and model indicates that gravitational torques from the binary stars constitute the primary driver for exchanging angular momentum so as to permit infall through the circumbinary disk of L1551 NE.Comment: 38 pages, 11 figures, accepted for publication in Ap

Evaluation of Adaptive Bone Remodeling after Total Hip Arthroplasty Using Finite Element Analysis

We compared equivalent stress and strain energy density (SED) to bone mineral density (BMD) in the femur after total hip arthroplasty (THA) using subject-specific finite element analysis (FEA). Equivalent stress and BMD were maintained in the distal femur after THA, whereas both decreased in the proximal femur. A significant correlation was observed between the rates of changes in BMD and equivalent stress before and after THA. Therefore, FEA can predict adaptive bone remodeling after mechanical loading changes. Additionally, we evaluated the effects of two different types of stem geometries (Zweymüller-type stem and fit-and-fill-type stem) on load distribution and BMD using the same method. Equivalent stress and BMD in the medial side of the proximal femur were significantly lower with the Zweymüller-type stem than with the fit-and-fill-type stem. Therefore, FEA can assess the effects of stem geometry on bone remodeling after THA. Moreover, we evaluated the effects of bone geometry on load distribution and BMD after THA. Equivalent stress in the medial side of the proximal femur was significantly lower in the stovepipe model implanted with large tapered wedge-type stems than in the champagne flute and intermediate models, and there was a significant loss of BMD in the stovepipe model. Therefore, a large tapered wedge-type stem and stovepipe femur may be associated with significant proximal BMD loss