164,114 research outputs found
Shear-dependent apparent slip on hydrophobic surfaces: The Mattress Model
Recent experiments (Zhu & Granick (2001) Phys. Rev. Lett. 87 096105) have
measured a large shear dependent fluid slip at partially wetting fluid-solid
surfaces. We present a simple model for such slip, motivated by the recent
observations of nanobubbles on hydrophobic surfaces. The model considers the
dynamic response of bubbles to change in hydrodynamic pressure due to the
oscillation of a solid surface. Both the compression and diffusion of gas in
the bubbles decrease the force on the oscillating surface by a ``leaking
mattress'' effect, thereby creating an apparent shear-dependent slip. With
bubbles similar to those observed by atomic force microscopy to date, the model
is found to lead to force decreases consistent with the experimental
measurements of Zhu & Granick
Conformally flat manifolds with nonnegative Ricci curvature
revised version, added reference to previous paper by S. Zhu on the same subjectInternational audienceWe show that complete conformally flat manifolds of dimension n>2 with nonnegative Ricci curvature enjoy nice rigidity properties: they are either flat, or locally isometric to a product of a sphere and a line, or are globally conformally equivalent to flat space or to a spherical spaceform. This extends previous works by Q.-M. Cheng, M.H. Noronha, B.-L. Chen and X.-P. Zhu, and S. Zhu
Comparing the Tsallis distribution with and without thermodynamical description in p+p collisions
We compare two types of Tsallis distribution, i.e., with and without
thermodynamical description, using the experimental data from the STAR, PHENIX,
ALICE and CMS Collaborations on the rapidity and energy dependence of the
transverse momentum spectra in p+p collisions. Both of them can give us the
similar fitting power to the particle spectra. We show that the Tsallis
distribution with thermodynamical description gives lower temperatures than the
ones without it. The extra factor (transverse mass) in the Tsallis
distribution with thermodynamical description plays an important role in the
discrepancies between the two types of Tsallis distribution. But for the heavy
particles, the choice to use the or (transverse energy) in the
Tsallis distribution becomes more crucial.Comment: 9 pages, 5 figure
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