463 research outputs found
Nonhyperbolic step skew-products: Ergodic approximation
We study transitive step skew-product maps modeled over a complete shift of
, , symbols whose fiber maps are defined on the circle and have
intermingled contracting and expanding regions. These dynamics are genuinely
nonhyperbolic and exhibit simultaneously ergodic measures with positive,
negative, and zero exponents.
We introduce a set of axioms for the fiber maps and study the dynamics of the
resulting skew-product. These axioms turn out to capture the key mechanisms of
the dynamics of nonhyperbolic robustly transitive maps with compact central
leaves.
Focusing on the nonhyperbolic ergodic measures (with zero fiber exponent) of
these systems, we prove that such measures are approximated in the weak
topology and in entropy by hyperbolic ones. We also prove that they are in the
intersection of the convex hulls of the measures with positive fiber exponent
and with negative fiber exponent. Our methods also allow us to perturb
hyperbolic measures. We can perturb a measure with negative exponent directly
to a measure with positive exponent (and vice-versa), however we lose some
amount of entropy in this process. The loss of entropy is determined by the
difference between the Lyapunov exponents of the measures.Comment: 43 pages, 5 figure
Non-factorial nodal complete intersection threefolds
We give a bound on the minimal number of singularities of a nodal projective
complete intersection threefold which contains a smooth complete intersection
surface that is not a Cartier divisor
Magnetic properties of Yb2Mo2O7 and Gd2Mo2O7 from rare earth Mossbauer measurements
Using 170-Yb and 155-Gd Mossbauer measurements down to 0.03K, we have
examined the semiconducting pyrochlore Yb2Mo2O7 where the Mo intra-sublattice
interaction is anti-ferromagnetic and the metallic pyrochlore Gd2Mo2O7 where
this interaction is ferromagnetic. Additional information was obtained from
susceptibility, magnetisation and 172-Yb perturbed angular correlation
measurements. The microscopic measurements evidence lattice disorder which is
important in Yb2Mo2O7 and modest in Gd2Mo2O7. Magnetic irreversibilities occur
at 17K in Yb2Mo2O7 and at 75K in Gd2Mo2O7 and below these temperatures the rare
earths carry magnetic moments which are induced through couplings with the Mo
sublattice. In Gd2Mo2O7, we observe the steady state Gd hyperfine populations
at 0.027K are out of thermal equilibrium, indicating that Gd and Mo spin
fluctuations persist at very low temperatures. Frustration is thus operative in
this essentially isotropic pyrochlore where the dominant Mo intra-sublattice
interaction is ferromagnetic.Comment: 9 pages, 9 figure
Relationship Between Periodontal Screening and Recording Index Scores and Need for Periodontal Access Surgery
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141032/1/jper1042.pd
On the Hausdorff dimension of invariant measures of weakly contracting on average measurable IFS
We consider measures which are invariant under a measurable iterated function
system with positive, place-dependent probabilities in a separable metric
space. We provide an upper bound of the Hausdorff dimension of such a measure
if it is ergodic. We also prove that it is ergodic iff the related skew product
is.Comment: 16 pages; to appear in Journal of Stat. Phy
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