侯晓阳,许 毅,陈 伟
(1.温州商学院基础部,浙江温州 325035;2.温州大学数理与电子信息工程学院,浙江温州 325035)
若n=0,则就是加权复合算子,如果再有u(z)≡1,则为复合算子Cφ.
Madigan K和Matheson A在文[2]中研究了Bloch空间和小Bloch空间上复合算子Cφ的有界性和紧性问题;LouZ[3]研究了不同权Bloch型空间之间的复合算子Cφ,对于H∞空间上的加权复合算子uCφ的有关结论,可见文[4-8]及相应文献;Stevic[9-10]和刘永民等[11]等研究了混合范数空间和Bloch空间,以及Hardy空间上的加权微分复合算子的有界性和紧性问题.文献[12]研究了单位圆盘上从BMOA空间到Bloch型空间的加权微分复合算子的有界性和紧性,得到:
当α=1时,即为上述定理A,定理B;当n=1,时,则算子,可得文[13]主要结论:
定理的证明主要采用待定系数法确定检验函数,本文出现的字母C表示与变量z,w等无关的常数,为方便起见,不同的地方可以表示不同的常数.
引理1 对任意正整数n,f∈Bα,存在常数C(只与权值α有关),使得
引理1可见文[14]定理5的证明过程,下面的紧性判断引理见文[15]定理3.11,取X=Bα,Y=Bβ,类似证明可得.
定理1的证明:充分性.若条件(1)(2)成立,结合引理1,可得:
综合(8)和(9)可知(1)式成立.
定理2的证明:充分性.对Bα中的任意有界序列,有fk在D的紧子集上一致收敛于0,由引理2,只需证明.以下不妨设
由条件(3)和(4),∀ε>0,当时,有:
结合(10)和(11)式,以及引理1,可得:
当|z|≤r<1时,有:
即fk(z)在D的紧子集上一致收敛于0.故由引理2,结合式(14)式得到:
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