51,978 research outputs found
The Birkhoff theorem for unitary matrices of arbitrary dimensions
It was shown recently that Birkhoff's theorem for doubly stochastic matrices
can be extended to unitary matrices with equal line sums whenever the dimension
of the matrices is prime. We prove a generalization of the Birkhoff theorem for
unitary matrices with equal line sums for arbitrary dimension.Comment: This manuscript presents a proof for the general unitary birkhoff
theorem, conjectured in arXiv:1509.0862
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Paxillin facilitates timely neurite initiation on soft-substrate environments by interacting with the endocytic machinery.
Neurite initiation is the first step in neuronal development and occurs spontaneously in soft tissue environments. Although the mechanisms regulating the morphology of migratory cells on rigid substrates in cell culture are widely known, how soft environments modulate neurite initiation remains elusive. Using hydrogel cultures, pharmacologic inhibition, and genetic approaches, we reveal that paxillin-linked endocytosis and adhesion are components of a bistable switch controlling neurite initiation in a substrate modulus-dependent manner. On soft substrates, most paxillin binds to endocytic factors and facilitates vesicle invagination, elevating neuritogenic Rac1 activity and expression of genes encoding the endocytic machinery. By contrast, on rigid substrates, cells develop extensive adhesions, increase RhoA activity and sequester paxillin from the endocytic machinery, thereby delaying neurite initiation. Our results highlight paxillin as a core molecule in substrate modulus-controlled morphogenesis and define a mechanism whereby neuronal cells respond to environments exhibiting varying mechanical properties
Eta absorption by mesons
Using the chiral Lagrangian with hidden local
symmetry, we evaluate the cross sections for the absorption of eta meson () by pion (), rho (), omega (), kaon (), and kaon
star () in the tree-level approximation. With empirical masses and
coupling constants as well as reasonable values for the cutoff parameter in the
form factors at interaction vertices, we find that most cross sections are less
than 1 mb, except the reactions ,
, , and , which are a few mb, and the reactions and , which are more than 10 mb. Including these reactions in a kinetic model
based on a schematic hydrodynamic description of relativistic heavy ion
collisions, we find that the abundance of eta mesons likely reaches chemical
equilibrium with other hadrons in nuclear collisions at the Relativistic Heavy
Ion Collider.Comment: 29 pages, 10 figures, version to appear in Nucl. Phys.
Matrix Model in a Class of Time Dependent Supersymmetric Backgrounds
We discuss the matrix model in a class of 11D time dependent supersymmetric
backgrounds as obtained in hep-th/0508191 . We construct the matrix model
action through the matrix regularization of the membrane action in the
background. We show that the action is exact to all order of fermionic
coordinates. Furthermore We discuss the fuzzy sphere solutions in this
background.Comment: 16 pages, 4 figures; references added, modifications of some comments
in introduction, version to appear in PL
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