5,597 research outputs found
On coarse embeddability into -spaces and a conjecture of Dranishnikov
We show that the Hilbert space is coarsely embeddable into any for
. In particular, this yields new characterizations of
embeddability of separable metric spaces into the Hilbert space.Comment: 5 page
Aperiodic tilings of manifolds of intermediate growth
We give a homological construction of aperiodic tiles for certain open
Riemannian surfaces admitting actions of Grigorchuk groups of intermediate
growth.Comment: Accepted for publication in Groups, Geometry and Dynamic
The superconducting and magnetic states in RuSr2GdCu2O8, based on the magnetic, transport and magneto-caloric characteristics
The article discusses selected properties of the non- and superconducting
polycrystalline samples of RuSr2GdCu2O8 and comments the consequences of
introducing insignificant sub-stoichiometry of Ru into the nominal formula. The
magneto-resistive and the magnetic characteristics are interpreted in favour of
the formation of the intrinsically inhomogeneous superconducting phase, which
seems to be stabilized along with the structural modifications likely enhanced
with the modification of starting stoichiometry. The specific heat data reveals
the shift of temperature of the magnetic ordering T_{m}, suggesting the
dilution in magnetic sublattice of the Ru moments. The measurements of the
magnetic field dependences of the isothermal magnetocaloric coefficient M_{T}
show that there is no gain in magnetic entropy in a broad range of the accessed
fields and temperatures. Whereas the multi-component character of the probed
magnetic system precludes from concluding on the ground state for the Ru
ordering, the maximum in M_{T}(H) which occurs at weak magnetic fields for
temperature vicinity of T_{m} may reflect dominance of the ferromagnetic type
interactions with a constrained correlation range. The literature explored
models for the Ru magnetic ordering and possible phase separation in the
RuSr2GdCu2O8 are brought into the discussion.Comment: Most of the discussed results conform to the first author's
presentations given at XIV Polish National School for Superconductivity (XIV
KSN) in October 2009, and at M2S-IX Conference in September 2009. Submitted
to the proceedings of XIV KSN
Eilenberg swindles and higher large scale homology of products of trees
We show that uniformly finite homology of products of trees vanishes in
all degrees except degree , where it is infinite dimensional. Our method is
geometric and applies to several large scale homology theories, including
almost equivariant homology and controlled coarse homology. As an application
we determine group homology with -coefficients of lattices in
products of trees. We also show a characterization of amenability in terms of
1-homology and construct aperiodic tilings using higher homology.Comment: Final version, to appear in Groups, Geometry & Dynamic
Hilbert C*-modules and amenable actions
We study actions of discrete groups on Hilbert -modules induced from
topological actions on compact Hausdorff spaces. We show non-amenability of
actions of non-amenable and non-a-T-menable groups, provided there exists a
quasi-invariant probability measure which is sufficiently close to being
invariant.Comment: Final version, to appear in Studia Mathematic
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