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Dima Shalybkov - One of the best experts on this subject based on the ideXlab platform.

  • Hydrodynamic stability in accretion disks under the Combined Influence of shear and density stratification
    Astronomy & Astrophysics, 2002
    Co-Authors: Günther Rüdiger, R. Arlt, Dima Shalybkov
    Abstract:

    The hydrodynamic stability of accretion disks is considered. The particular question is whether the Combined action of a (stable) vertical density stratification and a (stable) radial dierential rotation gives rise to a new instability for nonax- isymmetric modes of disturbances. The existence of such an instability is not suggested by the well-known Solberg-Hoiland criterion. It is also not suggested by a local analysis for disturbances in general stratifications of entropy and angular momentum which is presented in our Sect. 2. This confirms the results of the Solberg-Hoiland criterion also for nonaxisymmetric modes within the frame of ideal hydrodynamics but only in the frame of a short-wave approximation for small m .A s anecessary condition for stability we find that only conservative external forces are allowed to Influence the stable disk. As magnetic forces are never conservative, linear disk instabilities should only exist in the magnetohydrodynamical regime which indeed contains the magnetorotational instability as a much-promising candidate. To overcome some of the used approximations in a numerical approach, the equations of the compressible adiabatic hydro- dynamics are integrated, imposing initial nonaxisymmetric velocity perturbations with m = 1t om = 200. Only solutions with decaying kinetic energy are found. The system always settles in a vertical equilibrium stratification according to pressure balance with the gravitational potential of the central object.

  • hydrodynamic stability in accretion disks under the Combined Influence of shear and density stratification
    arXiv: Astrophysics, 2002
    Co-Authors: Günther Rüdiger, R. Arlt, Dima Shalybkov
    Abstract:

    The hydrodynamic stability of accretion disks is considered. The particular question is whether the Combined action of a (stable) vertical density stratification and a (stable) radial differential rotation gives rise to a new instability for nonaxisymmetric modes of disturbances. The existence of such an instability is not suggested by the well-known Solberg-Hoiland criterion. It is also not suggested by a local analysis for disturbances in general stratifications of entropy and angular momentum which is presented in our Section 2 confirming the results of the Solberg-Hoiland criterion also for nonaxisymmetric modes within the frame of ideal hydrodynamics but only in the frame of a short-wave approximation for small m. As a necessary condition for stability we find that only conservative external forces are allowed to Influence the stable disk. As magnetic forces are never conservative, linear disk instabilities should only exist in the magnetohydrodynamical regime which indeed contains the magnetorotational instability as a much-promising candidate. To overcome some of the used approximations in a numerical approach,the equations of the compressible adiabatic hydrodynamics are integrated imposing initial nonaxisymmetric velocity perturbations with m=1 to m=200. Only solutions with decaying kinetic energy are found. The system always settles in a vertical equilibrium stratification according to pressure balance with the gravitational potential of the central object. keywords: accretion disks -- hydrodynamic instabilities -- turbulence

Günther Rüdiger - One of the best experts on this subject based on the ideXlab platform.

  • Hydrodynamic stability in accretion disks under the Combined Influence of shear and density stratification
    Astronomy & Astrophysics, 2002
    Co-Authors: Günther Rüdiger, R. Arlt, Dima Shalybkov
    Abstract:

    The hydrodynamic stability of accretion disks is considered. The particular question is whether the Combined action of a (stable) vertical density stratification and a (stable) radial dierential rotation gives rise to a new instability for nonax- isymmetric modes of disturbances. The existence of such an instability is not suggested by the well-known Solberg-Hoiland criterion. It is also not suggested by a local analysis for disturbances in general stratifications of entropy and angular momentum which is presented in our Sect. 2. This confirms the results of the Solberg-Hoiland criterion also for nonaxisymmetric modes within the frame of ideal hydrodynamics but only in the frame of a short-wave approximation for small m .A s anecessary condition for stability we find that only conservative external forces are allowed to Influence the stable disk. As magnetic forces are never conservative, linear disk instabilities should only exist in the magnetohydrodynamical regime which indeed contains the magnetorotational instability as a much-promising candidate. To overcome some of the used approximations in a numerical approach, the equations of the compressible adiabatic hydro- dynamics are integrated, imposing initial nonaxisymmetric velocity perturbations with m = 1t om = 200. Only solutions with decaying kinetic energy are found. The system always settles in a vertical equilibrium stratification according to pressure balance with the gravitational potential of the central object.

  • hydrodynamic stability in accretion disks under the Combined Influence of shear and density stratification
    arXiv: Astrophysics, 2002
    Co-Authors: Günther Rüdiger, R. Arlt, Dima Shalybkov
    Abstract:

    The hydrodynamic stability of accretion disks is considered. The particular question is whether the Combined action of a (stable) vertical density stratification and a (stable) radial differential rotation gives rise to a new instability for nonaxisymmetric modes of disturbances. The existence of such an instability is not suggested by the well-known Solberg-Hoiland criterion. It is also not suggested by a local analysis for disturbances in general stratifications of entropy and angular momentum which is presented in our Section 2 confirming the results of the Solberg-Hoiland criterion also for nonaxisymmetric modes within the frame of ideal hydrodynamics but only in the frame of a short-wave approximation for small m. As a necessary condition for stability we find that only conservative external forces are allowed to Influence the stable disk. As magnetic forces are never conservative, linear disk instabilities should only exist in the magnetohydrodynamical regime which indeed contains the magnetorotational instability as a much-promising candidate. To overcome some of the used approximations in a numerical approach,the equations of the compressible adiabatic hydrodynamics are integrated imposing initial nonaxisymmetric velocity perturbations with m=1 to m=200. Only solutions with decaying kinetic energy are found. The system always settles in a vertical equilibrium stratification according to pressure balance with the gravitational potential of the central object. keywords: accretion disks -- hydrodynamic instabilities -- turbulence

Menachem Elimelech - One of the best experts on this subject based on the ideXlab platform.

  • Combined Influence of natural organic matter nom and colloidal particles on nanofiltration membrane fouling
    Journal of Membrane Science, 2005
    Co-Authors: Menachem Elimelech
    Abstract:

    The Combined Influence of natural organic matter (NOM) and colloidal particles on the fouling of thin-film composite nanofiltration (NF) membranes is systematically investigated. Combined fouling is compared to the individual fouling behaviors (i.e., colloid or NOM alone) with respect to fouling mechanisms and the effect of concentration factor (or recovery). Results demonstrate that (1) “cake-enhanced osmotic pressure” (CEOP) is a key fouling mechanism for individual colloidal fouling, (2) NOM–calcium complexation is the dominant factor governing individual NOM fouling, and (3) Combined fouling is affected by both CEOP and NOM–calcium complexation. The extent of flux decline for Combined fouling, however, is less than what inferred from additivity of the individual contributions of colloidal and NOM fouling to flux decline. This observation implies that the contributions of the fouling mechanisms appear to be relatively less significant for Combined fouling compared to their separate Influences on individual colloidal and NOM fouling. An increase in colloidal stability in presence of NOM and the competition between colloids and NOM for calcium are likely explanations for this behavior. It is further shown that NF membrane salt rejection increases noticeably in case of Combined fouling compared to individual colloidal fouling due to the formation of an active rejecting layer by the accumulated NOM on the membrane surface. Results from Combined fouling runs involving EDTA treatment confirm that both CEOP and NOM–calcium complexation take place simultaneously.

Debra Lerner - One of the best experts on this subject based on the ideXlab platform.

Jinming Yu - One of the best experts on this subject based on the ideXlab platform.