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  • 1
    Online Resource
    Online Resource
    American Astronomical Society ; 2017
    In:  The Astronomical Journal Vol. 153, No. 6 ( 2017-05-31), p. 269-
    In: The Astronomical Journal, American Astronomical Society, Vol. 153, No. 6 ( 2017-05-31), p. 269-
    Type of Medium: Online Resource
    ISSN: 1538-3881
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2017
    detail.hit.zdb_id: 2207625-6
    detail.hit.zdb_id: 2003104-X
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  • 2
    Online Resource
    Online Resource
    Frontiers Media SA ; 2019
    In:  Frontiers in Astronomy and Space Sciences Vol. 6 ( 2019-5-22)
    In: Frontiers in Astronomy and Space Sciences, Frontiers Media SA, Vol. 6 ( 2019-5-22)
    Type of Medium: Online Resource
    ISSN: 2296-987X
    Language: Unknown
    Publisher: Frontiers Media SA
    Publication Date: 2019
    detail.hit.zdb_id: 2778829-5
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  • 3
    Online Resource
    Online Resource
    American Astronomical Society ; 2022
    In:  The Astrophysical Journal Vol. 926, No. 2 ( 2022-02-01), p. 197-
    In: The Astrophysical Journal, American Astronomical Society, Vol. 926, No. 2 ( 2022-02-01), p. 197-
    Abstract: Although it is accepted that perfect-merging is not a realistic outcome of collisions, some researchers state that perfect-merging simulations can still be considered as quantitatively reliable representations of the final stage of terrestrial planet formation. Citing the work of Kokubo & Genda, they argue that the differences between the final planets in simulations with perfect-merging and those where collisions are resolved accurately are small, and it is justified to use perfect-merging results as an acceptable approximation to realistic simulations. In this paper, we show that this argument does not stand. We demonstrate that when the mass lost during collisions is taken into account, the final masses of the planets will be so different from those obtained from perfect-merging that the latter cannot be used as an approximation. We carried out a large number of smooth particle hydrodynamics simulations of embryo–embryo collisions and determined the amount of the mass and water lost in each impact. We applied the results to collisions in a typical perfect-merging simulation and showed that even when the mass loss in each collision is as small as 10%, perfect-merging can, on average, overestimate the masses of the final planets by ∼35% and their water content by more than 18%. Our analysis demonstrates that, while perfect-merging simulations are still a powerful tool in proving concepts, they cannot be used to make predictions, draw quantitative conclusions (especially about the past history of a planetary system), or serve as a valid approximation to the simulations in which collisions are resolved accurately.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    RVK:
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2022
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
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  • 4
    Online Resource
    Online Resource
    Elsevier BV ; 2017
    In:  Planetary and Space Science Vol. 141 ( 2017-07), p. 35-44
    In: Planetary and Space Science, Elsevier BV, Vol. 141 ( 2017-07), p. 35-44
    Type of Medium: Online Resource
    ISSN: 0032-0633
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2017
    detail.hit.zdb_id: 2012795-9
    SSG: 16,12
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  • 5
    Online Resource
    Online Resource
    Oxford University Press (OUP) ; 2021
    In:  Monthly Notices of the Royal Astronomical Society Vol. 508, No. 4 ( 2021-11-02), p. 6013-6022
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), Vol. 508, No. 4 ( 2021-11-02), p. 6013-6022
    Abstract: The last phase of the formation of rocky planets is dominated by collisions among Moon- to Mars-sized planetary embryos. Simulations of this phase need to handle the difficulty of including the post-impact material without saturating the numerical integrator. A common approach is to include the collision-generated material by clustering it into few bodies with the same mass and uniformly scattering them around the collision point. However, this approach oversimplifies the properties of the collision material by neglecting features that can play important roles in the final structure and composition of the system. In this study, we present a statistical analysis of the orbital architecture, mass, and size distributions of the material generated through embryo–embryo collisions and show how they can be used to develop a model that can be directly incorporated into the numerical integrations. For instance, results of our analysis indicate that the masses of the fragments follow an exponential distribution with an exponent of −2.21 ± 0.17 over the range of 10−7 to 2 × 10−2 Earth-masses. The distribution of the post-impact velocities show that a large number of fragments are scattered towards the central star. The latter is a new finding that may be quite relevant to the delivery of material from the outer regions of the asteroid belt to the accretion zones of terrestrial planets. Finally, we present an analytical model for the 2D distribution of fragments that can be directly incorporated into numerical integrations.
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2021
    detail.hit.zdb_id: 2016084-7
    SSG: 16,12
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  • 6
    Online Resource
    Online Resource
    Cambridge University Press (CUP) ; 2014
    In:  Proceedings of the International Astronomical Union Vol. 9, No. S310 ( 2014-07), p. 138-141
    In: Proceedings of the International Astronomical Union, Cambridge University Press (CUP), Vol. 9, No. S310 ( 2014-07), p. 138-141
    Abstract: We investigate the outcome of collisions of Ceres-sized planetesimals composed of a rocky core and a shell of water ice. These collisions are not only relevant for explaining the formation of planetary embryos in early planetary systems, but also provide insight into the formation of asteroid families and possible water transport via colliding small bodies. Earlier studies show characteristic collision velocities exceeding the bodies' mutual escape velocity which—along with the distribution of the impact angles—cover the collision outcome regimes ‘partial accretion’, ‘erosion’, and ‘hit-and-run’ leading to different expected fragmentation scenarios. Existing collision simulations use bodies composed of strengthless material; we study the distribution of fragments and their water contents considering the full elasto-plastic continuum mechanics equations also including brittle failure and fragmentation.
    Type of Medium: Online Resource
    ISSN: 1743-9213 , 1743-9221
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2014
    detail.hit.zdb_id: 2170724-8
    SSG: 16,12
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  • 7
    Online Resource
    Online Resource
    Cambridge University Press (CUP) ; 2018
    In:  Proceedings of the International Astronomical Union Vol. 14, No. S345 ( 2018-08), p. 287-288
    In: Proceedings of the International Astronomical Union, Cambridge University Press (CUP), Vol. 14, No. S345 ( 2018-08), p. 287-288
    Abstract: Final water inventories of newly formed terrestrial planets are shaped by their collision history. A setting where volatiles are transported from beyond the snowline to habitable-zone planets suggests collisions of very dry with water-rich bodies. By means of smooth particle hydrodynamics (SPH) simulations we study water delivery in scenarios where a dry target is hit by a water-rich projectile, focusing on hit-and-run encounters with two large surviving bodies, which probably comprise about half of all similar-sized collisions (Genda et al. 2017).
    Type of Medium: Online Resource
    ISSN: 1743-9213 , 1743-9221
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2018
    detail.hit.zdb_id: 2170724-8
    SSG: 16,12
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  • 8
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 667 ( 2022-11), p. A51-
    Abstract: In the past 15 yr, the triaxial Schwarzschild orbit-superposition code developed by van den Bosch and van de Ven in Leiden has been widely applied to study the dynamics of galaxies. Recently, a bug was reported in the orbit calculation of this code, specifically in the mirroring procedure that is used to speed up the computation. We have fixed the incorrect mirroring in the DYNAMITE code, which is the publicly-released successor of the Leiden triaxial Schwarzschild code. In this study, we provide a thorough quantification of how this bug has affected the results of dynamical analyses performed with this code. We compare results obtained with the original and corrected versions of DYNAMITE, and discuss the differences in the phase-space distribution of a single orbit and in the global stellar orbit distribution, in the mass estimate of the central black hole in the highly triaxial galaxy PGC 46832, and in the measurement of intrinsic shape and enclosed mass for more than 50 galaxies. Focusing on the typical scientific applications of the Schwarzschild method, in all our tests we find that differences are negligible with respect to the statistical and systematic uncertainties. We conclude that previous results with the Leiden triaxial Schwarzschild code are not significantly affected by the incorrect mirroring.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    RVK:
    RVK:
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2022
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 9
    Online Resource
    Online Resource
    Institute for Operations Research and the Management Sciences (INFORMS) ; 2022
    In:  INFORMS Journal on Computing Vol. 34, No. 1 ( 2022-01), p. 20-38
    In: INFORMS Journal on Computing, Institute for Operations Research and the Management Sciences (INFORMS), Vol. 34, No. 1 ( 2022-01), p. 20-38
    Abstract: Many stochastic systems face a time-dependent demand. Especially in stochastic service systems, for example, in call centers, customers may leave the queue if their waiting time exceeds their personal patience. As discussed in the extant literature, it can be useful to use general distributions to model such customer patience. This paper analyzes the time-dependent performance of a multiserver queue with a nonhomogeneous Poisson arrival process with a time-dependent arrival rate, exponentially distributed processing times, and generally distributed time to abandon. Fast and accurate performance approximations are essential for decision support in such queueing systems, but the extant literature lacks appropriate methods for the setting we consider. To approximate time-dependent performance measures for small- and medium-sized systems, we develop a new stationary backlog-carryover (SBC) approach that allows for the analysis of underloaded and overloaded systems. Abandonments are considered in two steps of the algorithm: (i) in the approximation of the utilization as a reduced arrival stream and (ii) in the approximation of waiting-based performance measures with a stationary model for general abandonments. To improve the approximation quality, we discuss an adjustment to the interval lengths. We present a limit result that indicates convergence of the method for stationary parameters. The numerical study compares the approximation quality of different adjustments to the interval length. The new SBC approach is effective for instances with small numbers of time-dependent servers and gamma-distributed abandonment times with different coefficients of variation and for an empirical distribution of the abandonment times from real-world data obtained from a call center. A discrete-event simulation benchmark confirms that the SBC algorithm approximates the performance of the queueing system with abandonments very well for different parameter configurations. Summary of Contribution: The paper presents a fast and accurate numerical method to approximate the performance measures of a time‐dependent queueing system with generally distributed abandonments. The presented stationary backlog carryover approach with abandonment combines algorithmic ideas with stationary queueing models for generally distributed abandonment times. The reliability of the method is analyzed for transient systems and numerically studied with real‐world data.
    Type of Medium: Online Resource
    ISSN: 1091-9856 , 1526-5528
    RVK:
    Language: English
    Publisher: Institute for Operations Research and the Management Sciences (INFORMS)
    Publication Date: 2022
    detail.hit.zdb_id: 2070411-2
    detail.hit.zdb_id: 2004082-9
    SSG: 3,2
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  • 10
    Online Resource
    Online Resource
    American Astronomical Society ; 1996
    In:  The Astrophysical Journal Vol. 466 ( 1996-07), p. 122-
    In: The Astrophysical Journal, American Astronomical Society, Vol. 466 ( 1996-07), p. 122-
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    RVK:
    Language: English
    Publisher: American Astronomical Society
    Publication Date: 1996
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
    Location Call Number Limitation Availability
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