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  • 1
    Electronic Resource
    Electronic Resource
    Similarity solution of mixed convection over a horizontal moving plate (1997)
    Springer
    Heat and mass transfer 32 (1997), S. 199-206 
    Details
    ISSN: 1432-1181
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Zusammenfassung  Die Untersuchung bezieht sich auf den Wärme- und Stoffübergang bei Mischkonvektion über einer horizontalen Platte. Durch Anwendung der Translationsgruppen-Theorie auf die Grundgleichungen für Kontinuität, Impuls, Energie- und Diffusion wird gezeigt, daß eine Ähnlichkeitslösung dann existiert, wenn Temperatur und Konzentration an der Wand proportional zu x 4/(7-5n) sind und die Geschwindigkeit der bewegten Platte proportional zu x (3-n)/(7-5n) ist. Somit läßt sich das Problem in Abhängigkeit von Ähnlichkeitsparametern beschreiben. Die Ähnlichkeitsgleichungen wurden numerisch mittels eines Runge/Kutta-Schemas vierter Ordnung gelöst. Die numerischen Resultate für Pr=0.72 und verschiedene Werte der Parameter Sc, K 1, K 2 und K 3 zeigen deren Einfluß auf das Strömungsfeld sowie den Wärme- und Stoffübergang.
    Notes: Abstract  Investigation to the mixed convective heat and mass transfer over a horizontal plate has been carried out. By applying transformation group theory to analysis of the governing equations of continuity, momentum, energy and diffusion, we show the existence of similarity solution for the problem provided that the temperature and concentration at the wall are proportional to x 4/(7-5n) and that the moving speed of the plate is proportional to x (3-n)/(7-5n), and further obtain a similarity representation of the problem. The similarity equations have been solved numerically by a fourth-order Runge–Kutta scheme. The numerical results obtained for Pr=0.72 and various values of the parameters Sc, K 1, K 2 and K 3 reveals the influence of the parameters on the flow, heat and mass transfer behavior.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002310050112
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Similarity solution of mixed convection with diffusion and chemical reaction over a horizontal moving plate (1998)
    Springer
    Acta mechanica 126 (1998), S. 59-69 
    Details
    ISSN: 1619-6937
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The mixed convective heat and mass transfer over a horizontal plate has been investigated. A diffusion equation with a chemical reaction source term is taken into account. By applying transformation group theory to the analysis of the governing equations, we obtain a similarity solution of the problem in the case that the temperature and concentration at the wall and the moving speed of the plate are proportional to power distributions along the distance from the leading edge. Furthermore the similarity equations have been solved numerically by a fourth-order Runge-Kutta scheme. The numerical results obtained for various values of the Schmidt number, chemical reaction parameter and buoyancy parameters reveal the influence of the parameters on the flow, heat and mass transfer behavior.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01172799
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  • 3
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    Resonant Magnetopolaron Effects due to Interface Phonons inGaAs/AlGaAsMultiple Quantum Well Structures (1997)
    American Physical Society
    Details
    Publication Date: 1997-10-27
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society
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  • 4
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    Solid solubility in 1:13 phase of doping element for La(Fe,Si)13 alloys (2016)
    American Institute of Physics
    Details
    Publication Date: 2016-05-01
    Electronic ISSN: 2158-3226
    Topics: Physics
    Published by American Institute of Physics
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  • 5
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    Reliable brazing of SiBCN ceramic and TC4 alloy using AgCuTi filler with the assist of laser melting deposited FGM layers (2018)
    Springer
    Details
    Publication Date: 2018-10-19
    Print ISSN: 0022-2461
    Electronic ISSN: 1573-4803
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Springer
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  • 6
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    Hydrodynamics of embedded planets' first atmospheres - II. A rapid recycling of atmospheric gas (2015)
    Oxford University Press
    Details
    Publication Date: 2015-01-26
    Description: Following Paper I we investigate the properties of atmospheres that form around small protoplanets embedded in a protoplanetary disc by conducting hydrodynamical simulations. These are now extended to three dimensions, employing a spherical grid centred on the planet. Compression of gas is shown to reduce rotational motions. Contrasting the 2D case, no clear boundary demarcates bound atmospheric gas from disc material; instead, we find an open system where gas enters the Bondi sphere at high latitudes and leaves through the mid-plane regions, or, vice versa, when the disc gas rotates sub-Keplerian. The simulations do not converge to a time-independent solution; instead, the atmosphere is characterized by a time-varying velocity field. Of particular interest is the time-scale to replenish the atmosphere by nebular gas, t replenish . It is shown that the replenishment rate, M atm / t replenish , can be understood in terms of a modified Bondi accretion rate, ~ $R_\mathrm{Bondi}^2\rho _\mathrm{gas}v_\mathrm{Bondi}$ , where v Bondi is set by the Keplerian shear or the magnitude of the sub-Keplerian motion of the gas, whichever is larger. In the inner disc, the atmosphere of embedded protoplanets replenishes on a time-scale that is shorter than the Kelvin–Helmholtz contraction (or cooling) time-scale. As a result, atmospheric gas can no longer contract and the growth of these atmospheres terminates. Future work must confirm whether these findings continue to apply when the (thermodynamical) idealizations employed in this study are relaxed. But if shown to be broadly applicable, replenishment of atmospheric gas provides a natural explanation for the preponderance of gas-rich but rock-dominant planets like super-Earths and mini-Neptunes.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    Hydrodynamics of embedded planets' first atmospheres - I. A centrifugal growth barrier for 2D flows (2014)
    Oxford University Press
    Details
    Publication Date: 2014-11-16
    Description: In the core accretion paradigm of planet formation, gas giants only form a massive atmosphere after their progenitors exceeded a threshold mass: the critical core mass. Most (exo)planets, being smaller and rock/ice-dominated, never crossed this line. Nevertheless, they were massive enough to attract substantial amounts of gas from the disc, while their atmospheres remained in pressure-equilibrium with the disc. Our goal is to characterize the hydrodynamical properties of the atmospheres of such embedded planets and the implications for their (long-term) evolution. In this paper – the first in series – we start to investigate the properties of an isothermal and inviscid flow past a small, embedded planet by conducting local, 2D hydrodynamical simulations. Using the pluto code, we confirm that the flow is steady and bound. This steady outcome is most apparent for the log-polar grid (with the grid spacing proportional to the distance from the planet). For low-mass planets, Cartesian grids are somewhat less efficient as they have difficulty to follow the circular, large speeds in the deep atmosphere. Relating the amount of rotation to the gas fraction of the atmosphere, we find that more massive atmospheres rotate faster – a finding consistent with Kelvin's circulation theorem. Rotation therefore limits the amount of gas that planets can acquire from the nebula. Dependent on the Toomre-Q parameter of the circumstellar disc, the planet's atmosphere will reach Keplerian rotation before self-gravity starts to become important.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    Dust dynamics in 2D gravito-turbulent discs (2016)
    Oxford University Press
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    Publication Date: 2016-04-21
    Description: The dynamics of solid bodies in protoplanetary discs are subject to the properties of any underlying gas turbulence. Turbulence driven by disc self-gravity shows features distinct from those driven by the magnetorotational instability (MRI). We study the dynamics of solids in gravito-turbulent discs with two-dimensional (in the disc plane), hybrid (particle and gas) simulations. Gravito-turbulent discs can exhibit stronger gravitational stirring than MRI-active discs, resulting in greater radial diffusion and larger eccentricities and relative speeds for large particles (those with dimensionless stopping times t stop 〉 1, where is the orbital frequency). The agglomeration of large particles into planetesimals by pairwise collisions is therefore disfavoured in gravito-turbulent discs. However, the relative speeds of intermediate-size particles ( t stop ~ 1) are significantly reduced as such particles are collected by gas drag and gas gravity into coherent filament-like structures with densities high enough to trigger gravitational collapse. First-generation planetesimals may form via gravitational instability of dust in marginally gravitationally unstable gas discs.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    Energy level broadening control in quantum dots by interfacial doping (1999)
    Elsevier
    Details
    Publication Date: 1999-11-01
    Print ISSN: 0038-1098
    Electronic ISSN: 1879-2766
    Topics: Physics
    Published by Elsevier
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  • 10
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    Saturation of the magnetorotational instability in the unstratified shearing box with zero net flux: convergence in taller boxes (2016)
    Oxford University Press
    Details
    Publication Date: 2016-01-02
    Description: Previous studies of the non-linear regime of the magnetorotational instability in one particular type of shearing box model – unstratified with no net magnetic flux – find that without explicit dissipation (viscosity and resistivity) the saturation amplitude decreases with increasing numerical resolution. We show that this result is strongly dependent on the vertical aspect ratio of the computational domain L z / L x . When L z / L x 1, we recover previous results. However, when the vertical domain is extended L z / L x 2.5, we find the saturation level of the stress is greatly increased (giving a ratio of stress to pressure α 0.1), and moreover the results are independent of numerical resolution. Consistent with previous results, we find that saturation of the magnetorotational (MRI) in this regime is controlled by a cyclic dynamo which generates patches of strong toroidal field that switches sign on scales of L x in the vertical direction. We speculate that when L z / L x 1, the dynamo is inhibited by the small size of the vertical domain, leading to the puzzling dependence of saturation amplitude on resolution. We show that previous toy models developed to explain the MRI dynamo are consistent with our results, and that the cyclic pattern of toroidal fields observed in stratified shearing box simulations (leading to the so-called butterfly diagram) may also be related. In tall boxes the saturation amplitude is insensitive to whether or not explicit dissipation is included in the calculations, at least for large magnetic Reynolds and Prandtl number. Finally, we show MRI turbulence in tall domains has a smaller critical Pm c , and an extended lifetime compared to L z / L x 1 boxes.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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