When products of selfadjoints are normal

When are the products of normal operators normal ?

Given two normal operators A and B on a Hilbert space it is known that, in general, AB is not normal. The question on characterizing those pairs of normal operators for which their products are normal has been solved for finite dimensional spaces by F.R. Gantmaher and M.G. Krein in 1930, and for compact normal operators by N.A. Wiegmann in 1949. Actually, in the afore mentioned cases, the norma...

On Normal Subgroups Which Are Direct Products

Now that the classification of finite simple groups is complete, it is logical to look at the extension problem. An important special case to consider is when M is a minimal normal subgroup of G and both G/M and M are known groups. If M is abelian, various techniques have been used to derive information about G. Indeed, almost the entire theory of finite solvable groups can be said to rest upon...

Are Biosimilars Identical to the Reference Products?

Testing for Monopoly Power when Products are Differentiated in Quality

Testing for Monopoly Power when Products are Differentiated in Quality by Frank Verboven This paper proposes a reduced form approach to identify the presence of monopoly power in oligopolies characterized by vertical product differentiation. In a fairly general model I derive an explicit solution for the reduced form pricing equations under the hypothesis that firms behave collusively. The cent...

Are Sale Signs Less Effective When More Products Have Them?

We analyze data from a variety of sources, including historical data from a women’s clothing catalog, a field study in that catalog, survey responses to catalog stimuli, and grocery store data for frozen juice, toothpaste, and tuna. The analysis yields three conclusions. First, sale signs are less effective at increasing demand when more items have them. Second, total category sales are maximiz...