The Experts below are selected from a list of 164952 Experts worldwide ranked by ideXlab platform
Gregory Laughlin - One of the best experts on this subject based on the ideXlab platform.
-
In Situ Formation and Dynamical Evolution of Hot Jupiter Systems
The Astrophysical Journal, 2016Co-Authors: Konstantin Batygin, Peter Bodenheimer, Gregory LaughlinAbstract:Hot Jupiters, giant extrasolar planets with orbital periods shorter than ~10 days, have long been thought to form at large radial distances, only to subsequently experience long-range inward migration. Here, we propose that in contrast with this picture, a substantial fraction of the hot Jupiter population formed in Situ via the core accretion process. We show that under conditions appropriate to the inner regions of protoplanetary disks, rapid gas accretion can be initiated by Super-Earth type planets, comprising 10-20 Earth masses of refractory composition material. An in Situ Formation scenario leads to testable consequences, including the expectation that hot Jupiters should frequently be accompanied by additional low-mass planets with periods shorter than ~100 days. Our calculations further demonstrate that dynamical interactions during the early stages of planetary systems' lifetimes should increase the inclinations of such companions, rendering transits rare. High-precision radial velocity monitoring provides the best prospect for their detection.
-
The minimum-mass extrasolar nebula: in Situ Formation of close-in super-Earths
Monthly Notices of the Royal Astronomical Society, 2013Co-Authors: Eugene Chiang, Gregory LaughlinAbstract:Close-in super-Earths, with radii R = 2-5 R_Earth and orbital periods P < 100 days, orbit more than half, and perhaps nearly all Sun-like stars in the universe. We use this omnipresent population to construct the minimum-mass extrasolar nebula (MMEN), the circumstellar disk of solar-composition solids and gas from which such planets formed, if they formed near their current locations and did not migrate. In a series of back-of-the-envelope calculations, we demonstrate how in-Situ Formation in the MMEN is fast, efficient, and can reproduce many of the observed properties of close-in super-Earths, including their gas-to-rock fractions. Testable predictions are discussed.
Tristan Guillot - One of the best experts on this subject based on the ideXlab platform.
-
A reassessment of the in Situ Formation of close-in super-Earths
Astronomy & Astrophysics, 2015Co-Authors: Masahiro Ogihara, Alessandro Morbidelli, Tristan GuillotAbstract:A large fraction of stars host one or multiple close-in super-Earth planets. There is an active debate about whether these planets formed in Situ or at greater distances from the central star and migrated to their current position. It has been shown that part of their observed properties (e.g., eccentricity distribution) can be reproduced by N-body simulations of in Situ Formation starting with a population of protoplanets of high masses and neglecting the effects of the disk gas. We plan to reassess the in Situ Formation of close-in super-Earths through more complete simulations. We performed N-body simulations of a population of small planetary embryos and planetesimals that include the effects of disk-planet interactions (e.g., eccentricity damping, type I migration). In addition, we also consider the accretion of a primitive atmosphere from a protoplanetary disk. We find that planetary embryos grow very quickly well before the gas dispersal, and thus undergo rapid inward migration, which means that one cannot neglect the effects of a gas disk when considering the in-Situ Formation of close-in super-Earths. Owing to their rapid inward migration, super-Earths reach a compact configuration near the disk's inner edge whose distribution of orbital parameters matches the observed close-in super-Earths population poorly. On the other hand, simulations including eccentricity damping, but no type I migration, reproduce the observed distributions better. Including the accretion of an atmosphere does not help reproduce the bulk architecture of observations. Interestingly, we find that the massive embryos can migrate inside the disk edge while capturing only a moderately massive hydrogen/helium atmosphere. By this process they avoid becoming giant planets. The bulk of close-in super-Earths cannot form in Situ, unless type I migration is suppressed in the entire disk inside 1 AU.
Sheng Lin-gibson - One of the best experts on this subject based on the ideXlab platform.
-
In Situ Formation of silver nanoparticles in photocrosslinking polymers
Journal of biomedical materials research. Part B Applied biomaterials, 2011Co-Authors: Ya-jun Cheng, Diana N. Zeiger, John A. Howarter, Xinran Zhang, Nancy J. Lin, Joseph M. Antonucci, Sheng Lin-gibsonAbstract:Nanocomposites of cross-linked methacrylate polymers with silver nanoparticles have been synthesized by coupling photoinitiated free radical polymerization of dimethacrylates with in Situ silver ion reduction. A polymerizable methacrylate bearing a secondary amino functional group was used to increase the solubility of the silver salt in the hydrophobic resin system. Fourier transform infrared spectroscopy (FTIR) revealed that the silver ion reduction had no significant effect on the degree of vinyl conversion of the methacrylate. X-ray photoelectron spectroscopy (XPS) measurements showed an increased silver concentration at the composite surface compared to the expected concentration based on the total amount of silver salt added. Furthermore, the surface silver concentration leveled off when the silver salt mass fractions were 0.08% or greater. Composites with low concentrations of silver salt (< 0.08% by mass) exhibited comparable mechanical properties to those containing no silver. Transmission electron microscopy (TEM) confirmed that the silver nanoparticles formed within the polymer matrix were nanocrystalline in nature and primarily ≈ 3 nm in diameter, with some large particle aggregates. Composites containing silver nanoparticles were shown to reduce bacterial colonization with as little as 0.03% (by mass) silver salt, while additional amounts of silver salt did not further decrease their surface colonization. With a substantial effect on bacterial growth and minimal effects on mechanical properties, the in Situ Formation of silver nanoparticles within methacrylate materials is a promising technique for synthesizing antibacterial nanocomposites for biomedical applications. © 2011 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2011.
Ricardo Antonio Francisco Machado - One of the best experts on this subject based on the ideXlab platform.
-
Low temperature in Situ Formation of cobalt in silicon nitride toward functional nitride nanocomposites †
Chemical Communications, 2021Co-Authors: Shotaro Tada, Maira Debarba Mallmann, Haruna Takagi, Junya Iihama, Norifumi Asakuma, Toru Asaka, Yusuke Daiko, Sawao Honda, Rafael Kenji Nishihora, Ricardo Antonio Francisco MachadoAbstract:This work highlights the first demonstration of a low-temperature in Situ Formation of Co nanocrystallites embedded within an amorphous silicon nitride matrix through careful control of the chemistry behind material design using perhydropolysilazane (PHPS) as a Si3N4 precursor further coordinated with CoCl2 and ammonia as a pyrolysis atmosphere. The Co nucleation was allowed to proceed at temperatures as low as 400 8C via thermal decomposition of Co2N pre-formed in Situ by the reaction of CoCl2 with the Si centers of PHPS at the early stage of pyrolysis (220-350 8C).
-
Low temperature in Situ Formation of cobalt in silicon nitride toward functional nitride nanocomposites.
Chemical communications (Cambridge England), 2021Co-Authors: Shotaro Tada, Maira Debarba Mallmann, Haruna Takagi, Junya Iihama, Norifumi Asakuma, Toru Asaka, Yusuke Daiko, Sawao Honda, Rafael Kenji Nishihora, Ricardo Antonio Francisco MachadoAbstract:This work highlights the first demonstration of a low-temperature in Situ Formation of Co nanocrystallites embedded within an amorphous silicon nitride matrix through careful control of the chemistry behind material design using perhydropolysilazane (PHPS) as a Si3N4 precursor further coordinated with CoCl2 and ammonia as a pyrolysis atmosphere. The Co nucleation was allowed to proceed at temperatures as low as 400 °C via thermal decomposition of Co2N pre-formed in Situ by the reaction of CoCl2 with the Si centers of PHPS at the early stage of pyrolysis (220–350 °C).
Shao Yanru - One of the best experts on this subject based on the ideXlab platform.
-
In Situ Formation of low interstitials Ti-TiC composites by gas-solid reaction
Journal of Alloys and Compounds, 2018Co-Authors: Ce Zhang, Zhimeng Guo, Fang Yang, Haiying Wang, Shao YanruAbstract:Abstract In this work, in Situ Formation of low interstitials Ti-TiC composites with a high relative density has been fabricated by the combination of TiH2-CH4 reaction and vacuum pressure-less sintering. During the gas-solid reaction, TiH2 reacted with CH4 to form TiC particles on the powder surface. As a consequence, low interstitials contents (O 10%) is important for following thermomechanical processing. In summary, the achievement of high performance Ti-TiC composites was attributed to the grain refinement, in-Situ TiC strengthening, as well as a solid solution strengthening of the O, N and C elements in the Ti matrix.
