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

In this review the theory and application of Smoothed particle hydrodynamics (SPH) since its inception in 1977 are discussed. Emphasis is placed on the strengths and weaknesses, the analogy with particle dynamics and the numerous areas where SPH has been successfully applied.

https://iopscience.iop.org/article/10.1088/0034-4885/68/8/R01/pdf

Smoothed particle hydrodynamics

The presence of a Jupiter-mass companion to the star 51 Pegasi is inferred from observations of periodic variations in the star's radial velocity. The companion lies only about eight million kilometres from the star, which would be well inside the orbit of Mercury in our Solar System. This object might be a gas-giant planet that has migrated to this location through orbital evolution, or from the radiative stripping of a brown dwarf.

A Jupiter-Mass Companion to a Solar-Type Star

Building on the legacy of the Sloan Digital Sky Survey (SDSS-I and II), SDSS-III is a program of four spectroscopic surveys on three scientific themes: dark energy and cosmological parameters, the history and structure of the Milky Way, and the population of giant planets around other stars. In keeping with SDSS tradition, SDSS-III will provide regular public releases of all its data, beginning with SDSS DR8 (which occurred in Jan 2011). This paper presents an overview of the four SDSS-III surveys. BOSS will measure redshifts of 1.5 million massive galaxies and Lya forest spectra of 150,000 quasars, using the BAO feature of large scale structure to obtain percent-level determinations of the distance scale and Hubble expansion rate at z 100 per resolution element), H-band (1.51-1.70 micron) spectra of 10^5 evolved, late-type stars, measuring separate abundances for ~15 elements per star and creating the first high-precision spectroscopic survey of all Galactic stellar populations (bulge, bar, disks, halo) with a uniform set of stellar tracers and spectral diagnostics. MARVELS will monitor radial velocities of more than 8000 FGK stars with the sensitivity and cadence (10-40 m/s, ~24 visits per star) needed to detect giant planets with periods up to two years, providing an unprecedented data set for understanding the formation and dynamical evolution of giant planet systems. (Abridged)

/pdf/sdss-iii-massive-spectroscopic-surveys-of-the-distant-513ci0j1ij.pdf

Sdss-iii: massive spectroscopic surveys of the distant universe, the milky way, and extra-solar planetary systems

Monthly Notices is one of the three largest general primary astronomical research publications. It is an international journal, published by the Royal Astronomical Society. This article 1 describes its publication policy and practice.

Monthly Notices of the Royal Astronomical Society

THE recent discovery1 and confirmation2 of a possible planetary companion orbiting the solar-type star 51 Pegasi represent a breakthrough in the search for extrasolar planetary systems. Analysis of systematic variations in the velocity of the star indicate that the mass of the companion is approximately that of Jupiter, and that it is travelling in a nearly circular orbit at a distance from the star of 0.05 AU (about seven stellar radii). Here we show that, if the companion is indeed a gas-giant planet, it is extremely unlikely to have formed at its present location. We suggest instead that the planet probably formed by gradual accretion of solids and capture of gas at a much larger distance from the star (∼5 AU), and that it subsequently migrated inwards through interactions with the remnants of the circumstellar disk. The planet's migration may have stopped in its present orbit as a result of tidal interactions with the star, or through truncation of the inner circumstellar disk by the stellar magnetosphere.

/pdf/orbital-migration-of-the-planetary-companion-of-51-pegasi-to-3tcylrxx6u.pdf

Orbital migration of the planetary companion of 51 Pegasi to its present location

Many asteroids and trans-neptunian objects have satellites: the tally stands at over 150 on http://tinyurlcom/dweqf
  The smallest of these binary systems are main-belt and near-Earth asteroids, but the environments of these two types of object are very different, making it difficult to work out a common mechanism to explain their formation Now Walsh et al present a model that fits the bill Properties of the observed main-belt and near-Earth asteroids with satellites are matched by simulations involving the slow spinup of a 'rubble pile' asteroid via the thermal YORP effect (where radiation from an irregular body exerts a net force on that body) The mass shed from the equator of a spinning body accretes into a satellite if the material consists of particles undergoing energy-dissipating collisions Binary asteroids are created by the slow spin up of a 'rubble pile' asteroid via the thermal YORP effect (where radiation from an irregularly shaped body exerts a net force on the body) The mass shed from the equator of a critically spinning body accretes into a satellite if the material is collisionally dissipative Asteroids with satellites are observed throughout the Solar System, from subkilometre near-Earth asteroid pairs to systems of large and distant bodies in the Kuiper belt The smallest and closest systems are found among the near-Earth and small inner main-belt asteroids, which typically have rapidly rotating primaries and close secondaries on circular orbits About 15 per cent of near-Earth and main-belt asteroids with diameters under 10 km have satellites1,2 The mechanism that forms such similar binaries in these two dynamically different populations was hitherto unclear Here we show that these binaries are created by the slow spinup of a ‘rubble pile’ asteroid by means of the thermal YORP (Yarkovsky–O’Keefe–Radzievskii–Paddack) effect We find that mass shed from the equator of a critically spinning body accretes into a satellite if the material is collisionally dissipative and the primary maintains a low equatorial elongation The satellite forms mostly from material originating near the primary’s surface and enters into a close, low-eccentricity orbit The properties of binaries produced by our model match those currently observed in the small near-Earth and main-belt asteroid populations, including 1999 KW4 (refs 3, 4)

http://www.asu.cas.cz/~asteroid/paris/material/128220_1_merged_1209050230.pdf

Rotational breakup as the origin of small binary asteroids

Numerical simulations of the collisional disruption of large asteroids show that although the parent body is totally shattered, subsequent gravitational reaccumulation leads to the formation of an entire family of large and small objects with dynamical properties similar to those of the parent body. Simulations were performed in two different collisional regimes representative of asteroid families such as Eunomia and Koronis. Our results indicate that all large family members must be made of gravitationally reaccumulated fragments; that the post-collision member size distribution and the orbital dispersion are steeper and smaller, respectively, than for the evolved families observed today; and that satellites form frequently around family members.

Collisions and gravitational reaccumulation: forming asteroid families and satellites.

https://www.astro.umd.edu/~dcr/reprints/richardson_icarus143,45.pdf

Direct Large-Scale N-Body Simulations of Planetesimal Dynamics

A large fraction of ~100 km class low-inclination objects in the classical Kuiper Belt (KB) are binaries with comparable masses and a wide separation of components. A favored model for their formation is that they were captured during the coagulation growth of bodies in the early KB. However, recent studies have suggested that large, 100 km objects can rapidly form in the protoplanetary disks when swarms of locally concentrated solids collapse under their own gravity. Here, we examine the possibility that KB binaries formed during gravitational collapse when the excess of angular momentum prevented the agglomeration of available mass into a solitary object. We find that this new mechanism provides a robust path toward the formation of KB binaries with observed properties, and can explain wide systems such as 2001 QW322 and multiples such as (47171) 1999 TC36. Notably, the gravitational collapse is capable of producing ~100% binary fraction for a wide range of the swarm's initial angular momentum values. The binary components have similar masses (~80% have a secondary-over-primary radius ratio >0.7) and their separation ranges from ~1000 to ~100,000 km. The binary orbits have eccentricities from e = 0 to ~1, with the majority having e < 0.6. The binary orbit inclinations with respect to the initial angular momentum of the swarm range from i = 0 to ~90°, with most cases having i < 50°. The total binary mass represents a characteristic fraction of the collapsing swarm's total initial mass, M tot, suggesting M tot equivalent to that of a radius ~100-250 km compact object. Our binary formation mechanism also implies that the primary and secondary components in each binary pair should have identical bulk composition, which is consistent with the current photometric data. We discuss the applicability of our results to the Pluto-Charon, Orcus-Vanth, (617) Patroclus-Menoetius, and (90) Antiope binary systems.

https://iopscience.iop.org/article/10.1088/0004-6256/140/3/785/pdf

Derek C. Richardson

Papers

Orbital migration of the planetary companion of 51 Pegasi to its present location

Rotational breakup as the origin of small binary asteroids

Collisions and gravitational reaccumulation: forming asteroid families and satellites.

Direct Large-Scale N-Body Simulations of Planetesimal Dynamics

Formation of kuiper belt binaries by gravitational collapse