9,697 research outputs found
Polarization of B -> VV: experimental status
The experimental status of the polarization measurements in B to charmless
vector-vector decays by both the Belle and Babar experiments is reviewed. The
results obtained in related vector-tensor, axial vector-vector, and axial
vector-axial vector modes are also given.Comment: 6 pages, 5 figures, Proceedings of CKM2010, the 6th International
Workshop on the CKM Unitarity Triangle, University of Warwick, UK, 6-10
September 201
Regularity criterion for 3D Navier-Stokes equations in terms of the direction of the velocity
In this short note, we give a link between the regularity of the solution
to the 3D Navier-Stokes equation, and the behavior of the direction of the
velocity . It is shown that the control of \Div (u/|u|) in a suitable
norm is enough to ensure global regularity. The result is
reminiscent of the criterion in terms of the direction of the vorticity,
introduced first by Constantin and Fefferman. But in this case the condition is
not on the vorticity, but on the velocity itself. The proof, based on very
standard methods, relies on a straightforward relation between the divergence
of the direction of the velocity and the growth of energy along streamlines.Comment: 6 page
Cell Adhesion: A surprising cohesive force
When an experimentalist or a biological mechanism applies an external force onto a cell chemically sticking to its substrate, a reacting "suction" force, due to the slow penetration of the surrounding fluid between the cell and the substrate, opposes to the dissociation. This force can overcome other known adhesive forces when the process is sufficiently violent (typically 10^5^ pN). Its maximal contribution to the total adhesive energy of the cell can then be estimated to 2 10^-3^ J/m2. The physical origin of this effect is quite simple, and it may be compared with that leaning a "suction-cup" against a bathroom wall. We address the consequences of this effect on (i) the separation energy, (ii) the motion of the fluid surrounding the cell, more especially, on the pumping of the fluid by moving cells, and (iii) the inhibition of cell motion
Delocalization due to correlations in two-dimensional disordered systems
We study the spectral statistics of interacting spinless fermions in a
two-dimensional disordered lattice. Within a full quantum treatment for small
few-particle-systems, we compute the low-energy many-body states numerically.
While at weak disorder the interactions reduce spectral correlations and lead
to localization, for the case of strong disorder we find that a moderate
Coulomb interaction has a delocalizing effect. In addition, we observe a
non-universal structure in the level-spacing distribution which we attribute to
a mechanism reinforcing spectral correlations taking place in small systems at
strong disorder.Comment: 6 pages, 4 figures, corrected typo
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