The galactic center compact radio source Sgr A was discovered on 13 and 15 February 1974 by Bruce Balick and Robert L. Brown using the Green Bank 35 km radio link interferometer (Balick & Brown 1974). We discuss other observations of this source in the years 1965-1985. Early VLBI observations are described. The name Sgr A was first used by Robert L. Brown (1982) and has become the accepted name...

Let M be a compact Minimal hypersurface of the unit sphere S. In this paper we use a constant vector field on R to characterize the Clifford hypersurfaces S (√ l n ) × S mn ) , l + m = n, in S. We also study compact minimal Einstein hypersurfaces of dimension greater than two in the unit sphere and obtain a lower bound for first nonzero eigenvalue λ1 of its Laplacian operator.

We characterize well-founded algebraic lattices by means of forbidden subsemilattices of the join-semilattice made of their compact elements. More specifically, we show that an algebraic lattice L is well-founded if and only if K(L), the join-semilattice of compact elements of L, is well-founded and contains neither [ω], nor Ω(ω∗) as a join-subsemilattice. As an immediate corollary, we get that...

in this paper, a complete description concerning linear operators of banach spaces with range in lipschitz algebras $lip_al(x)$ is provided. necessary and sufficient conditions are established to ensure boundedness and (weak) compactness of these operators. finally, a lower bound for the essential norm of such operators is obtained.

the purpose of this paper is to introduce the concept of pairwise f-closedness in bitopological spaces. this space contains both of pairwise strongcompactness and pairwise s-closedness and contained in pairwise quasi h-closedness. the characteristics and relationships concerning this new class ofspaces with other corresponding types are established. moreover, several ofits basic and important p...

We show that many invariant subspaces M for d-shifts (S1, . . . , Sd) of finite rank have the property that the orthogonal projection PM onto M satisfies PMSk − SkPM ∈ L, 1 ≤ k ≤ d for every p > 2d, L denoting the Schatten-von Neumann class of all compact operators having p-summable singular value lists. In such cases, the d tuple of operators T̄ = (T1, . . . , Td) obtained by compressing (S1, ....

We study compact finite difference methods for the Schrödinger-Poisson equation in a bounded domain and establish their optimal error estimates under proper regularity assumptions on wave function ψ and external potential V(x). The CrankNicolson compact finite difference method and the semi-implicit compact finite difference method are both of order O(h4+τ2) in discrete l2 ,H1 and l norms with ...

A locally compact group G is compact if and only if L(G) is an ideal in L(G), and the Fourier algebra A(G) of G is an ideal in A(G)∗∗ if and only if G is discrete. On the other hand, G is discrete if and only if C0(G) is an ideal in C0(G)∗∗. We show that these assertions are special cases of results on locally compact quantum groups in the sense of J. Kustermans and S. Vaes. In particular, a vo...

In their paper on fibrations with singularities Montgomery and Samelson showed that if a compact connected Lie group acts differentiably and effectively on a sphere and if there is one stationary point, then the remaining orbits cannot all be of the same dimension [2]. In our note we will examine transformation groups in which all orbits have the same dimension. As a corollary, we shall extend ...

There are many examples known of compact continua no two of whose simple links intersect, even though uncountably many of the links are nondegenerate. On page 346 of his Foundations of point set theory [ l] , R. L. Moore has given an example of a compact continuum which is the sum of an uncountable collection of nondegenerate simple links, only a countable number of which intersect. In view of ...