PDE実解析研究会

過去の記録 ~03/28次回の予定今後の予定 03/29~

開催情報 火曜日 10:30~11:30 数理科学研究科棟(駒場) 056号室
担当者 儀我美一、石毛和弘、三竹大寿、米田剛
セミナーURL http://coe.math.sci.hokudai.ac.jp/sympo/pde_ra/
目的 首都圏の偏微分方程式、実解析の研究をさらに活発にするために本研究会を東大で開催いたします。
偏微分方程式研究者と実解析研究者の討論がより日常的になることを目指しています。
そのため、講演がその分野の概観をもわかるような形になるよう配慮いたします。
また講演者との1対1の討論がしやすいように講演は火曜の午前とし、午後に討論用の場所を用意いたします。
この研究会を通して皆様に気楽に東大を訪問していただければ幸いです。
北海道大学のHPには、第1回(2004年9月29日)~第38回(2008年10月15日)の情報が掲載されております。

2016年04月27日(水)

15:00-16:00   数理科学研究科棟(駒場) 056号室
通常の曜日、時刻と異なります。
Elijah Liflyand 氏 (Bar-Ilan University, Israel)
Fourier transform versus Hilbert transform (English)
[ 講演概要 ]
We present several results in which the interplay between the Fourier transform and the Hilbert transform is of special form and importance.
1. In 50-s (Kahane, Izumi-Tsuchikura, Boas, etc.), the following problem in Fourier Analysis attracted much attention: Let $\{a_k\},$ $k=0,1,2...,$ be the sequence of the Fourier coefficients of the absolutely convergent sine (cosine) Fourier series of a function $f:\mathbb T=[-\pi,\pi)\to \mathbb C,$ that is $\sum |a_k|<\infty.$ Under which conditions on $\{a_k\}$ the re-expansion of $f(t)$ ($f(t)-f(0)$, respectively) in the cosine (sine) Fourier series will also be absolutely convergent?
We solve a similar problem for functions on the whole axis and their Fourier transforms. Generally, the re-expansion of a function with integrable cosine (sine) Fourier transform in the sine (cosine) Fourier transform is integrable if and only if not only the initial Fourier transform is integrable but also the Hilbert transform of the initial Fourier transform is integrable.
2. The following result is due to Hardy and Littlewood: If a (periodic) function $f$ and its conjugate $\widetilde f$ are both of bounded variation, their Fourier series converge absolutely.
We generalize the Hardy-Littlewood theorem (joint work with U. Stadtmüller) to the Fourier transform of a function on the real axis and its modified Hilbert transform. The initial Hardy-Littlewood theorem is a partial case of this extension, when the function is taken to be with compact support.
3. These and other problems are integrated parts of harmonic analysis of functions of bounded variation. We have found the maximal space for the integrability of the Fourier transform of a function of bounded variation. Along with those known earlier, various interesting new spaces appear in this study. Their inter-relations lead, in particular, to improvements of Hardy's inequality.
There are multidimensional generalizations of these results.
[ 参考URL ]
http://u.math.biu.ac.il/~liflyand/