Ernest Michael

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Let us quickly recall the definitions of the terms which are used in the statement of Theorem 1, and which will be used throughout this paper. Let X be a topological space. A collection <R of subsets of X is called open (resp. closed) if every element of "R. is open (resp. closed) in X. A covering of X is a collection of subsets of X whose union is X;(More)
The following result, and a closely related one, is proved: If u : X + Y is an open, perfect surjection, with X metrizable and with dim X = 0 or dim Y = 0, then there exists a perfect surjection h : Y x S + X such that u 0 h = riTy (where S in the Cantor set and rTTy : Y x S + Y is the projection). If moreover, u-‘(y) is homeomorphic to S for all YE Y, then(More)
Due to its advantages over other configurations, sideband-separating receivers are usually preferred for radio astronomy, particularly in the presence of high atmospheric noise. However, even with all the advances that have been made in recent years in the field of receiver technology, one of the most important figures of merit for this kind of receiver,(More)
Proof. Let 11 and V be countable bases for X and Y, respectively, and let 3 have as sub-base the collection of sets {fCC(X, Y) \f(U) C V), with UCM and VCÜ. Then 3 certainly has a countable base. Clearly 3 also makes (/, x)—>/(x) jointly continuous, and hence [l, p. 223] is finer than the compact-open topology. Finally, every subset of C(X, Y) is certainly(More)
We report on the results of our monitoring program of the X-ray remnant of supernova 1987A with the Chandra X-Ray Observatory. We have performed two new observations during the Chandra Cycle 3 period, bringing the total to six monitoring observations over the past three years. These six observations provide a detailed time history of the birth of a new(More)
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