High-quality Zn 0.85 Cd 0.15 Se/ZnSe single quantum wells (SQWs) have been fabricated on GaAs(110) crystal surfaces which were obtained by cleaving GaAs(100) wafers in ultra high vacuum (UHV). The growth interruption was found to prevent the growth of high-quality quantum well structures. The (110)-oriented SQWs grown under appropriate conditions show a very sharp photoluminescence spectrum whose full width at half-maximum (FWHM) is as small as 4.9 meV. The sample showed a strong in-plane polarization angle dependence of the emission intensity, due to the compressive strain in the well layer. The ratio of maximum to minimum values of the polarized PL intensity was 1.6.

We study the notion of α-covering map with respect to certain subsets in metric spaces. Generalizing results from [1] we use this notion to give some coincidence theorems for pairs of single-valued and multivalued maps one of which is relatively α-covering while the other satisfies the Lipschitz condition. These assertions extend some classical contraction map principles. We define the notion of α-covering multimap at a point and give conditions under which the covering property of a multimap at each interior point of a set implies that it is covering on the whole set. As applications we consider the solvability of a system of inclusions and the existence of a positive trajectory for a semilinear feedback control system. (2000). Primary 54H25; Secondary 47H04, 47H10, 47J05, 49J24, 54E40. Mathematics Subject Classification

Gel'man, Obukhovs kii UDC 517.988.52The present paper is a survey of the contemporary state of art in the theory of multivalued mappings. In it one considers different forms of continuity of multivalued mappings, one investigates differentiable and measurable multivalued mappings, one considers single-valued continuous approximations and sections of multivalued mappings, one studies fixed points of multivalued mappings and other questions of this theory. One gives references to the literature regarding applications to the theory of games, mathematical economics, the theory of differential inclusions and generalized dynamical systems. The paper contains an extensive bibliography.

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