Wyniki wyszukiwania

1

Comparing gaussian and Rademacher cotype for operators on the space of continuous functions

100%

Junge M.

Studia Mathematica

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1996

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tom 118

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nr 2

101-115

EN

We prove an abstract comparison principle which translates gaussian cotype into Rademacher cotype conditions and vice versa. More precisely, let 2 < q < ∞ and T: C(K) → F a continuous linear operator. (1) T is of gaussian cotype q if and only if $(∑_k ((∥Tx_k∥_F)/(√log(k+1)))^q)^{1/q} ≤ c ∥ ∑_k ɛ_{k} x_{k} ∥_{L_{2}(C(K))}$, for all sequences $(x_k)_{k∈ℕ} ⊂ C(K)$ with $(∥Tx_k∥)_{k=1}^n$ decreasing. (2) T is of Rademacher cotype q if and only if $(∑_k (∥Tx_k∥_{F} √((log(k+1))^q) )^{1/q} ≤ c ∥∑_k g_{k}x_{k}∥_{L_2(C(K))}$, for all sequences $(x_k)_{k∈ℕ} ⊂ C(K)$ with $(∥Tx_k∥)_{k=1}^n$ decreasing. Our method allows a restriction to a fixed number of vectors and complements the corresponding results of Talagrand.

2

Best constants and asymptotics of Marcinkiewicz-Zygmund inequalities

64%

Defant A., Junge M.

Studia Mathematica

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1997

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tom 125

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nr 3

271-287

EN

We determine the set of all triples 1 ≤ p,q,r ≤ ∞ for which the so-called Marcinkiewicz-Zygmund inequality is satisfied: There exists a constant c≥ 0 such that for each bounded linear operator $T: L_q(μ) → L_p(ν)$, each n ∈ ℕ and functions $f_1,...,f_n ∈ L_q(μ)$, $( ʃ(∑^{n}_{k=1} |Tf_{k}|^r)^{p/r} dν)^{1/p} ≤ c∥T∥(ʃ(∑^{n}_{k=1} |f_k|^{r})^{q/r} dμ)^{1/q}$. This type of inequality includes as special cases well-known inequalities of Paley, Marcinkiewicz, Zygmund, Grothendieck, and Kwapień. If such a Marcinkiewicz-Zygmund inequality holds for a given triple (p,q,r), then we calculate the best constant c ≥ 0 (with the only exception: the important case 1 ≤ p < r = 2 < q ≤ ∞); if such an inequality does not hold, then we give asymptotically optimal estimates for the graduation of these constants in n. Two problems of Gasch and Maligranda from [9] are solved; as a by-product we obtain best constants of several important inequalities from the theory of summing operators.

3

Characterization of weak type by the entropy distribution of r-nuclear operators

64%

Defant M., Junge M.

Studia Mathematica

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1993

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tom 107

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nr 1

1-14

EN

The dual of a Banach space X is of weak type p if and only if the entropy numbers of an r-nuclear operator with values in a Banach space of weak type q belong to the Lorentz sequence space $ℓ_{s,r}$ with 1/s + 1/p + 1/q = 1 + 1/r (0 < r < 1, 1 ≤ p, q ≤ 2). It is enough to test this for Y = X*. This extends results of Carl, König and Kühn.

4

Volume ratios in $L_p$-spaces

64%

Gordon Y., Junge M.

Studia Mathematica

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1999

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tom 136

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nr 2

147-182

EN

There exists an absolute constant $c_0$ such that for any n-dimensional Banach space E there exists a k-dimensional subspace F ⊂ E with k≤ n/2 such that $inf_{ellipsoid ε ⊂ B_E} (vol(B_E)/vol(ε))^{1/n} ≤ c_0 inf_{zonoid Z ⊂ B_F} (vol(B_F)/vol(Z))^{1/k}$ . The concept of volume ratio with respect to $ℓ_p$-spaces is used to prove the following distance estimate for $2≤ q≤ p < ∞$: $sup_{F ⊂ ℓ_p, dim F=n} inf_{G ⊂ L_q, dim G=n} d(F,G) ∼_{c_{pq}} n^{(q/2)(1/q-1/p)}$.

5

On weak (r,2)-summing operators and weak Hilbert spaces

32%

Defant M., Junge M.

Studia Mathematica

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1990

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tom 96

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nr 3

203-217

Ograniczanie wyników

5 Studia Mathematica

5 Junge M.

2 Defant M.

1 Defant A.

1 Gordon Y.

1 1999

1 1997

1 1996

1 1993

1 1990

Comparing gaussian and Rademacher cotype for operators on the space of continuous functions

Best constants and asymptotics of Marcinkiewicz-Zygmund inequalities

Characterization of weak type by the entropy distribution of r-nuclear operators

Volume ratios in $L_p$-spaces

On weak (r,2)-summing operators and weak Hilbert spaces