标题： 与$L^2(\mathbb{R})$中某些翻译系统不相容的操作 显示英文标题

标题： Operations that are incompatible with certain systems of translates in $L^2(\mathbb{R})$

摘要： 我们说闭子空间$M$of$L^2(\mathbb{R})$有一个\emph{半正则a-平移的完整集合}，如果存在某些$a>0$，有限个函数$g_1,\dots,g_N$，某些子集$J_1,\dots,J_N$of$\mathbb{Z}$和某些有限子集$\{\alpha_{1j}\}_{j=1}^{K_1},\dots,\{\alpha_{Nj}\}_{j=1}^{K_N}$of$\mathbb{R}$，使得$$M={\overline{\text{span}}}\{g_i(\cdot-ak), ~g_i(\cdot-\alpha_{ij})\,|\,k\in J_i,1\leq j\leq K_i\,\}_{i=1}^N.$$ 这里$\cdot$表示一个通用变量。 在本文的前半部分，我们证明了一个闭子空间如果在调制下闭合，或者在缩放因子 $b$ 下闭合，且满足 $b\neq 0$ 和 $b^{-1}\notin \mathbb{Z}.$，则 $L^2(\mathbb{R})$ 的闭子空间不包含半正则 $a$-平移的完全集。我们还表明， $L^2(\mathbb{R})$ 的任何无限维闭子空间都不能同时在傅里叶变换下闭合，并且具有半正则 $a$-平移的完全集，当 $a^2\in \mathbb{Q}$ 时，而对于任何 $a>0$，都存在在反射下闭合并且具有半正则 $a$-平移的完全集的闭子空间。 In the second half, we prove that a closed subspace of $L^2(\mathbb{R})$ does not admit a frame formed by a system of translates if it contains a closed subspace that is closed under modulation and contains a nonzero function in $M^1(\mathbb{R})$. We also prove that no closed subspace of $L^2(\mathbb{R})$ can simultaneously be closed under modulation and admit a Schauder basis of translates generated by finitely many functions in $M^1(\mathbb{R}).$ In addition, we present related results concerning the incompatibility between being closed under Fourier transform and the existence of frames or Schauder bases of translates in closed subspaces of $L^2(\mathbb{R})$. All results in this half can be extended to $L^2(\mathbb{R}^d)$ for any $d>1.$ 显示英文摘要

摘要： We say that a closed subspace $M$ of $L^2(\mathbb{R})$ admits a \emph{complete set of semi-regular a-translates} if there exist some $a>0$, finitely many functions $g_1,\dots,g_N$, some subsets $J_1,\dots,J_N$ of $\mathbb{Z}$ and some finite subsets $\{\alpha_{1j}\}_{j=1}^{K_1},\dots,\{\alpha_{Nj}\}_{j=1}^{K_N}$ of $\mathbb{R}$ such that $$M={\overline{\text{span}}}\{g_i(\cdot-ak), ~g_i(\cdot-\alpha_{ij})\,|\,k\in J_i,1\leq j\leq K_i\,\}_{i=1}^N.$$ Here $\cdot$ denotes a generic variable. In the first half of this paper, we prove that a closed subspace of $L^2(\mathbb{R})$ does not admit a complete set of semi-regular $a$-translates if it is closed under modulation or if it is closed under dilation with respect to a scaling factor $b$ satisfying $b\neq 0$ and $b^{-1}\notin \mathbb{Z}.$ We also show that no infinite-dimensional closed subspace of $L^2(\mathbb{R})$ can simultaneously be closed under Fourier transform and admit a complete set of semi-regular $a$-translates with $a^2\in \mathbb{Q}$, whereas for any $a>0$, there do exist closed subspaces that are closed under reflection and admit a complete set of semi-regular $a$-translates. In the second half, we prove that a closed subspace of $L^2(\mathbb{R})$ does not admit a frame formed by a system of translates if it contains a closed subspace that is closed under modulation and contains a nonzero function in $M^1(\mathbb{R})$. We also prove that no closed subspace of $L^2(\mathbb{R})$ can simultaneously be closed under modulation and admit a Schauder basis of translates generated by finitely many functions in $M^1(\mathbb{R}).$ In addition, we present related results concerning the incompatibility between being closed under Fourier transform and the existence of frames or Schauder bases of translates in closed subspaces of $L^2(\mathbb{R})$. All results in this half can be extended to $L^2(\mathbb{R}^d)$ for any $d>1.$