کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
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4604057 | 1337413 | 2015 | 8 صفحه PDF | دانلود رایگان |
We prove the following variant of Marstrand's theorem about projections of cartesian products of sets:Let K1,…,KnK1,…,Kn be Borel subsets of Rm1,…,RmnRm1,…,Rmn respectively, and π:Rm1×…×Rmn→Rkπ:Rm1×…×Rmn→Rk be a surjective linear map. We setm:=min{∑i∈IdimH(Ki)+dimπ(⨁i∈IcRmi),I⊂{1,…,n},I≠∅}. Consider the space Λm={(t,O),t∈R,O∈SO(m)} with the natural measure and set Λ=Λm1×…×ΛmnΛ=Λm1×…×Λmn. For every λ=(t1,O1,…,tn,On)∈Λλ=(t1,O1,…,tn,On)∈Λ and every x=(x1,…,xn)∈Rm1×…×Rmnx=(x1,…,xn)∈Rm1×…×Rmn we define πλ(x)=π(t1O1x1,…,tnOnxn)πλ(x)=π(t1O1x1,…,tnOnxn). Then we haveTheorem. (i)If m>km>k, then πλ(K1×…×Kn)πλ(K1×…×Kn)has positive k-dimensional Lebesgue measure for almost every λ∈Λλ∈Λ.(ii)If m⩽km⩽kand dimH(K1×…×Kn)=dimH(K1)+…+dimH(Kn)dimH(K1×…×Kn)=dimH(K1)+…+dimH(Kn), then dimH(πλ(K1×…×Kn))=mdimH(πλ(K1×…×Kn))=mfor almost every λ∈Λλ∈Λ.
Journal: Annales de l'Institut Henri Poincare (C) Non Linear Analysis - Volume 32, Issue 4, July–August 2015, Pages 833–840