Electronic structure of non-centrosymmetric AgCd2GaS4 and AgCd2GaSe4 single crystals

X-ray photoelectron core-level and valence-band spectra for pristine and Ar⁺-ion irradiated (0 0 1) surfaces of AgCd₂GaS₄ and AgCd₂GaSe₄ single crystals grown, respectively, by the Bridgman method and the method of direct crystallization have been measured in the present work. The X-ray photoelectron spectroscopy (XPS) results reveal high chemical stability of (0 0 1) surfaces of AgCd₂GaS₄ and AgCd₂GaSe₄ single crystals. Electronic structure of AgCd₂GaS₄ has been calculated employing the full potential linearized augmented plane wave method. For the AgCd₂GaS₄ compound, the X-ray emission bands representing the energy distribution of the valence Ag d-, Cd d-, Ga p- and S p-like states were recorded and compared on a common energy scale with the XPS valence-band spectrum. The theoretical and experimental data regarding the occupation of the valence band of AgCd₂GaS₄ were found to be in excellent agreement to each other. Second harmonic generation (SHG) efficiency of AgCd₂GaS₄ by using the 320 ns CO laser at 5.5 μm has been recorded within the temperature range 80–300 K. Substantial increase of the photoinduced SHG which in turn is substantially dependent on the temperature has been detected for the AgCd₂GaS₄ compound.     

Weakly infinite-dimensional spaces modulo simplicial complexes

The classes of spaces

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-wid and ?-wid are introduced for the class

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of finite simplicial complexes and the class ? of compact polyhedra. If

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, then

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-wid = wid, ?-wid = S-wid. It is proved that S-wid ? ?-wid and ?-wid = S-? _τ -wid for any triangulation τ of the class ?.

     

Preparation and X-ray structures of Cu(I), Ni(II), and Pd(II) (N,S) complexes of the monoanion [(tBuN)(S)P(mu-N(t)Bu)2P(S)(NH(t)Bu)]- and a Pt(II) (S,S') complex of the dianion [((t)BuN)(S)P(mu-N(t)Bu)2P(S)(N(t)Bu)]2-

The metathetical reactions of the lithium derivative of the monoanion [((t)BuN)(S)P(mu-N(t)Bu)(2)P(S)(NH(t)Bu)](-) (L) with CuCl/PPh(3), NiCl(2)(PEt(3))(2), PdCl(2)L'(2) (L' = PhCN, PPh(3)), and PtCl(2)(PEt(3))(2) produced the complexes (PPh(3))CuL (5), NiL(2) (6), PdCl(L)(PPh(3)) (7), PdL(2) (8), and Pt(PEt(3))(2)[((t)BuN)(S)P(mu-N(t)Bu)(2)P(S)(N(t)Bu)] (9). The X-ray structures of 5, 6, and 8 reveal a N,S-coordination for the chelating monoanion L with the metal centers in trigonal planar, tetrahedral, and square planar environments, respectively. By contrast, the dianionic ligand in the square planar Pt(II) complex 9 is S,S'-chelated to the metal center. (31)P NMR spectra readily distinguish between the N,S and S,S' bonding modes, and, on that basis, N,S chelation is inferred for the Pd(II) complex 7. Crystal data: 5, monoclinic, P2(1)/c, a = 19.175(4) A, b = 20.331(4) A, c = 10.017(6) A, beta = 91.79(3) degrees, V = 3903(2) A(3), and Z = 4; 6, orthorhombic, Pbcn, a = 14.298(5) A, b = 15.333(5) A, c = 24.378(5) A, beta = 90.000(5) degrees, V = 5344(3) A(3), and Z = 4; 8, monoclinic, P2(1)/n, a = 13.975(3) A, b = 14.283(3) A, c = 15.255(4) A, beta = 116.565(18) degrees, V = 2723.5(11) A(3), and Z = 2; 9, monoclinic, P2(1)/n, a = 12.479(6) A, b = 21.782(7) A, c = 17.048(5) A, beta = 100.30(3) degrees, V = 4559(3) A(3), and Z = 4.     

On iterates of fully closed absolutes

In this article we give a sufficient condition for a space X to have the fully closed absolute faX with the property fa(faX)=faX. An example of a compact space X such that the canonical mapping fa(α+1)X→fa(α)X (where α is a given ordinal) is not a homeomorphism is constructed. Also we give an example of a compact space X such that the canonical mapping faX→X is not a homeomorphism but for which there exists a homeomorphism faX→X.     

Certain classes of weakly infinite-dimensional spaces and topological games

In [V.V. Fedorchuk, Questions on weakly infinite-dimensional spaces, in: E.M. Pearl (Ed.), Open Problems in Topology II, Elsevier, Amsterdam, 2007, pp. 637-645; V.V. Fedorchuk, Weakly infinite-dimensional spaces, Russian Math. Surveys 42 (2) (2007) 1-52] classes w-m-C of weakly infinite-dimensional spaces, 2?m?∞, were introduced. We prove that all of them coincide with the class wid of all weakly infinite-dimensional spaces in the Alexandroff sense. We show also that transfinite dimensions dimwm, introduced in [V.V. Fedorchuk, Questions on weakly infinite-dimensional spaces, in: E.M. Pearl (Ed.), Open Problems in Topology II, Elsevier, Amsterdam, 2007, pp. 637-645; V.V. Fedorchuk, Weakly infinite-dimensional spaces, Russian Math. Surveys 42 (2) (2007) 1-52], coincide with dimension dimw2=dim, where dim is the transfinite dimension invented by Borst [P. Borst, Classification of weakly infinite-dimensional spaces. I. A transfinite extension of the covering dimension, Fund. Math. 130 (1) (1988) 1-25]. Some topological games which are related to countable-dimensional spaces, to C-spaces, and some other subclasses of weakly infinite-dimensional spaces are discussed.     

Peculiarities of Formation of Intermolecular Polycomplexes Based on Polyacrylamide,Poly(vinyl alcohol) and Poly(ethylene oxide)

The phenomenon of self-assembly of aggregates formed by relatively short chains of poly(vinyl alcohol) (PVA) on the long macromolecules of polyacrylamide (PAA) in aqueous medium are discussed. PVA and PAA form intermolecular polycomplexes (InterPC) of a constant composition independently on a ratio of polymer components. The complex formation between high-molecular-weight PAA and relatively low-molecular-weight poly(ethylene oxide) (PEO) are considered also. PEO with M ⩽ 4·10⁴ g.mol⁻¹ weakly interacts with PAA. The polymer-polymer interaction can be intensified when the part of amide groups (∼20 mol %) on PAA chain to transform into the carboxylic groups. InterPCs formed by PEO and initial or modified PAA have associative structure with friable packing of the polymer segments. They are stabilized by the hydrogen bond system.     

Covariant functors in categories of topological spaces

This survey is devoted to the properties of certain concrete covariant functors-normal and almost normal functors-in the category of compacta, as well as the algebraic theory of covariant functors, and the connections between the theory of functors with absolute extensors and manifolds.Translated from Itogi Nauki i Tekhniki, Seriya Algebra, Topologiya, Geometriya, Vol. 28, pp. 47–95, 1990.