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On the completeness of the system { t λ n log m n t } in C 0 ( E )

Xiangdong Yang — 2012

Czechoslovak Mathematical Journal

Let E = n = 1 I n be the union of infinitely many disjoint closed intervals where I n = [ a n , b n ] , 0 < a 1 < b 1 < a 2 < b 2 < < b n < , lim n b n = . Let α ( t ) be a nonnegative function and { λ n } n = 1 a sequence of distinct complex numbers. In this paper, a theorem on the completeness of the system { t λ n log m n t } in C 0 ( E ) is obtained where C 0 ( E ) is the weighted Banach space consists of complex functions continuous on E with f ( t ) e - α ( t ) vanishing at infinity.

A note on the number of zeros of polynomials in an annulus

Xiangdong YangCaifeng YiJin Tu — 2011

Annales Polonici Mathematici

Let p(z) be a polynomial of the form p ( z ) = j = 0 n a j z j , a j - 1 , 1 . We discuss a sufficient condition for the existence of zeros of p(z) in an annulus z ∈ ℂ: 1 - c < |z| < 1 + c, where c > 0 is an absolute constant. This condition is a combination of Carleman’s formula and Jensen’s formula, which is a new approach in the study of zeros of polynomials.

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