C^(*)-Isomorphisms Associated with Two Projections on a Hilbert C^(*)-Module

Motivated by two norm equations used to characterize the Friedrichs angle,this paper studies C^(*)-isomorphisms associated with two projections by introducing the matched triple and the semi-harmonious pair of projections.A triple(P,Q,H)is said to be matched if is a Hilbert C^(*)-module,P and Q are projections on H such that their infimum P∧Q exists as an element of L(H),where L(H)denotes the set of all adjointable operators on H.The C^(*)-sub algebras of L(H)generated by elements in{P-P∧Q,Q-P∧Q,I}and{P,Q,P∧Q,I}are denoted by i(P,Q,H)and o(P,Q,H),respectively.It is proved that each faithful representation(π,X)of o(P,Q,H)can induce a faithful representation(π,X)of i(P,Q,H)such that π~(P−P∧Q)=π(P)−π(P)∧π(Q),π~(Q−P∧Q)=π(Q)−π(P)∧π(Q)..When(P,Q)is semi-harmonious,that is,R(P+Q) and R(2I−P−Q) are both orthogonally complemented in H,it is shown that i(P,Q,H)and i(I-Q,I-P,H)are unitarily equivalent via a unitary operator in L(H).A counterexample is constructed,which shows that the same may be not true when(P,Q)fails to be semi-harmonious.Likewise,a counterexample is constructed such that(P,Q)is semi-harmonious,whereas(P,I-Q)is not semi-harmonious.Some additional examples indicating new phenomena of adjointable operators acting on Hilbert C^(*)-modules are also provided.

On Maps Preserving Unitarily Invariant Norms of the Spectral Geometric Mean

We consider maps on positive definite cones of von Neumann algebras preserving unitarily invariant norms of the spectral geometric means. The main results concern Jordan *-isomorphisms between C*-algebras, and show that they are characterized by the preservation of unitarily invariant norms of those operations.

THE ■■-LEMMA UNDER SURJECTIVE MAPS

We consider the ■■-lemma for complex manifolds under surjective holomorphic maps.Furthermore,using Deligne-Griffiths-Morgan-Sullivan’s theorem,we prove that a product compact complex manifold satisfies the ■■-lemma if and only if all of its components do as well.

A Characterization of *-Automorphism on B(H)

Let H be a Hilbert space and A be a standard ＊-subalgebra of B（H）. We show that a bijective map Ф ： A →A preserves the Lie-skew product AB - BA＊ if and only if there is a unitary or conjugate unitary operator U ∈A（H） such that Ф（A） = UAU＊ for all A ∈ A, that is, Фis a linear ＊ -isomorphism or a conjugate linear ＊-isomorphism.