General features of single-spin asymmetry in inclusive pion production in fixed-target experiments

Physics of Atomic Nuclei - The results of various experiments that measured a single-spin asymmetry in inclusive pion production are analyzed in the energy range between 13 and 200 GeV. The...     

Resonant Phenomena in Slowly Irregular Rectangular Waveguides

A waveguide with a rectangular cross section of size and orientation slowly changing along the length of the waveguide is considered. Methods of the canonical perturbation theory are used to describe the ray dynamics in the waveguide. As the size and orientation of the cross section slowly change along the ray trajectory, certain resonance conditions may be satisfied. The phenomena of scattering on resonance and capture into resonance is studied. These phenomena lead to destruction of the adiabatic invariance in the system. Bibliography: 12 titles.__________Published in Zapiski Nauchnykh Seminarov POMI, Vol. 300, 2003, pp. 173–179     

Magnetic field effects on the localization of electromagnetic waves in random 1D systems which are almost periodic

The effects of an externally applied magnetic field on the Anderson localization of electromagnetic waves in an alternating layered system of vacuum and semiconducting slabs are studied. Specifically, a waveguide formed from perfectly conducting parallel plates which contain between them an array of vacuum and n-type semiconductor slabs is examined in the presence of an external static magnetic field applied parallel to both the plates and the slab surfaces. The widths of the slabs in the array are random but with a randomness such that the array of slabs is almost periodic, and we study only electromagnetic modes which propagate perpendicular to the slab surfaces. The localization length is obtained by studying the reflection and transmission properties of a finite array of slabs in the limit that it becomes semi-infinite. Two types of system are treated: (i) a reciprocal system which exhibits a localization length that does not depend on the sign of the applied magnetic field, and (ii) a non-reciprocal system which exhibits a localization length that depends on the sign of the applied magnetic field.     

The high‐pressure form of cadmium vanadate,CdV2O6

The crystal structure of a new high‐pressure modification of cadmium divanadium hexaoxide, CdV₂O₆, was refined from X‐ray single‐crystal data. It contains zigzag chains of edge‐sharing VO₆ octahedra. Octahedra in adjacent chains share corners and form corrugated layers. Octahedrally coordinated Cd atoms, which lie on twofold axes, are situated between the layers. The columbite‐like structure results in a strong distortion of the CdO₆ octahedra which may be stabilized only at high pressure.     

Generalized double affine Hecke algebras of rank 1 and quantized del Pezzo surfaces

Let D be a simply laced Dynkin diagram of rank r whose affinization has the shape of a star (i.e., D₄,E₆,E₇,E₈). To such a diagram one can attach a group G whose generators correspond to the legs of the affinization, have orders equal to the leg lengths plus 1, and the product of the generators is 1. The group G is then a 2-dimensional crystallographic group: G=Z??Z², where ? is 2, 3, 4, and 6, respectively. In this paper, we define a flat deformation H(t,q) of the group algebra C[G] of this group, by replacing the relations saying that the generators have prescribed orders by their deformations, saying that the generators satisfy monic polynomial equations of these orders with arbitrary roots (which are deformation parameters). The algebra H(t,q) for D₄ is the Cherednik algebra of type C^∨C₁, which was studied by Noumi, Sahi, and Stokman, and controls Askey-Wilson polynomials. We prove that H(t,q) is the universal deformation of the twisted group algebra of G, and that this deformation is compatible with certain filtrations on C[G]. We also show that if q is a root of unity, then for generic t the algebra H(t,q) is an Azumaya algebra, and its center is the function algebra on an affine del Pezzo surface. For generic q, the spherical subalgebra eH(t,q)e provides a quantization of such surfaces. We also discuss connections of H(t,q) with preprojective algebras and Painlevé VI.     

Mechanism of phase transitions in the (NH4)2WO2F4 ferroelastic

Precision studies of the thermophysical properties and structure of an (NH₄)₂WO₂F₄ crystal have been performed. It was established reliably that there is a sequence of two phase transitions at T ₁ = 201 K and T ₂ = 160 K characterized by wedging out of an intermediate phase with an increase in pressure. The role of tetrahedral and octahedral ionic groups in the mechanism of the structural transitions was determined.     

Magnetic and transport properties of double distorted perovskites CaCuMn6O12 and CaCu2Mn5O12

Magnetic and transport properties of double distorted perovskites CaCuMn₆O₁₂ and CaCu₂Mn₅O₁₂ are studied in a range 2–300 K. The leading role in magnetism of these compounds belongs to antiferromagnetic exchange interaction of Cu²⁺ in square coordination with Mn³⁺/Mn⁴⁺ in octahedral coordination. The values of saturation magnetization indicate that Mn³⁺ ions in square coordination are coupled ferromagnetically with Mn³⁺/Mn⁴⁺ in octahedral coordination. The colossal magnetoresistance in the pellet samples is due assumingly to intergranular spin-polarized tunneling of current carriers.     

Application of Horner–Emmons Olefination to the Crown-Ether Derivatives

An effective synthetic approach to the preparation of a new crown-ether vinylogs involving the Horner–Emmons olefination of carbonyl precursors with the use of C₂- and C₅-phosphonates was proposed. The effects of the conjugation chain length and the nature of the terminal polar functions in the phosphonate reagent on the yield and process stereoselectivity were discussed.     

Ion-Bearing Propellers: Alkali Metal Complexes of Tris(2-alkoxyphenyl)amine Ionophores

NMR spectroscopic studies reveal that binding of Na(+) by tris(2-methoxyphenyl)amine (3) brings two of these tripod ethers together about the metal ion; the related double-tripod-ether ionophore 1,2-bis[2-(bis(2-methoxyphenyl)amino)phenoxy]ethane (4), in which two triarylamines are covalently attached, binds LiI, LiBPh(4), NaI, NaBPh(4), and KB(4-ClPh)(4). Dynamic NMR puts lower limits on binding free energies of 4 for Na(+) (71.8 kJ mol(-)(1)) and K(+) (66.8 kJ mol(-)(1)) ions. X-ray studies of 3(2).NaBPh(4), 4.NaBPh(4), 4.NaB(4-ClPh)(4), and 4.KB(4-ClPh)(4).CH(3)NO(2) show eight-coordinate M(+) ions bound between crystallographically independent, homochiral triarylamine tripod ethers in structures reminiscent of alkali metal [2.2.2] cryptates. Complexes crystallize as follows: 3(2).NaBPh(4), monoclinic, P2(1)/c, Z = 4, a = 10.701(3) ?, b = 37.593(3) ?, c = 13.774(2) ?, and beta = 98.24(2) degrees; 4.NaBPh(4), triclinic, P&onemacr;, Z = 2, a = 12.157(1) ?, b = 14.811(1) ?, c = 15.860(2) ?, alpha = 105.400(8) degrees, beta = 91.594(9) degrees, and gamma = 95.354(8) degrees; 4.NaB(4-ClPh)(4), monoclinic, P2(1)/n, Z = 4, a = 13.652(5) ?, b = 18.75(1) ?, c = 22.805(5) ?, and beta = 92.21(5) degrees; 4.KB(4-ClPh)(4).CH(3)NO(2), monoclinic, Pn, Z = 2, a = 13.663(4) ?, b = 12.228(3) ?, c = 18.712(8) ?, and beta = 91.45(3) degrees. They show variable N-M-N angles; 3(2).NaBPh(4) is surprisingly bent ( angleN-Na-N = 154.5 degrees ), while the 4.M(+) complexes are normal: nearly linear for Na(+) ( angleN-Na-N = 178.6, 178.1 degrees ) and again bent with the larger K(+) ( angleN-K-N = 164.5 degrees ). Finally, free 4 is structurally similar to 3; it crystallizes in the triclinic space group P&onemacr;, with Z = 2, a = 8.068(1) ?, b = 14.599(2) ?, c = 16.475(3) ?, alpha = 115.43(1) degrees, beta = 92.51(1) degrees, and gamma = 90.40(1) degrees.