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Spaces defined by the level function and their duals

Gord Sinnamon (1994)

Studia Mathematica

The classical level function construction of Halperin and Lorentz is extended to Lebesgue spaces with general measures. The construction is also carried farther. In particular, the level function is considered as a monotone map on its natural domain, a superspace of L p . These domains are shown to be Banach spaces which, although closely tied to L p spaces, are not reflexive. A related construction is given which characterizes their dual spaces.

Squaring a reverse AM-GM inequality

Minghua Lin (2013)

Studia Mathematica

Let A, B be positive operators on a Hilbert space with 0 < m ≤ A, B ≤ M. Then for every unital positive linear map Φ, Φ²((A + B)/2) ≤ K²(h)Φ²(A ♯ B), and Φ²((A+B)/2) ≤ K²(h)(Φ(A) ♯ Φ(B))², where A ♯ B is the geometric mean and K(h) = (h+1)²/(4h) with h = M/m.

Subadditive functions and partial converses of Minkowski's and Mulholland's inequalities

J. Matkowski, T. Świątkowski (1993)

Fundamenta Mathematicae

Let ϕ be an arbitrary bijection of + . We prove that if the two-place function ϕ - 1 [ ϕ ( s ) + ϕ ( t ) ] is subadditive in + 2 then ϕ must be a convex homeomorphism of + . This is a partial converse of Mulholland’s inequality. Some new properties of subadditive bijections of + are also given. We apply the above results to obtain several converses of Minkowski’s inequality.

Subelliptic Poincaré inequalities: the case p &lt; 1.

Stephen M. Buckley, Pekka Koskela, Guozhen Lu (1995)

Publicacions Matemàtiques

We obtain (weighted) Poincaré type inequalities for vector fields satisfying the Hörmander condition for p &lt; 1 under some assumptions on the subelliptic gradient of the function. Such inequalities hold on Boman domains associated with the underlying Carnot- Carathéodory metric. In particular, they remain true for solutions to certain classes of subelliptic equations. Our results complement the earlier results in these directions for p ≥ 1.

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