Induced smectic C* phases

Induced ferroelectric S*_C phases are formed by non-chiral S_C host phases doped with chiral dipolar guest molecules. In those mixtures the spontaneous polarization P_s and the tilt angle Θ has been investigated as a function of the mole fraction x_G of the chiral dopant. In most cases the reduced polarization P₀ = P_S/ sin Θ has been found to depend linearly on x_G. The polarization power which is defined by δ_P=(∂P₀/∂x_G)ΔT is discussed in terms of the molecular structure of the chiral dopants. There are systems in which P₀(x_G) deviates positively from linearity. This behaviour can be understood by considering a local field correction to P₀. By assuming a local field of Lorentz type a theoretical relation for P₀(x_G) has been derived which explains the experimental results. The effect of a local field is considerable if the transverse dipole moment and the polarizability of the chiral dopant are large.     

Synthesis of 4H-pyrans by O-cyclization of 1,5-diketones

Substituted 4H-pyrans were obtained in high preparative yields by the reaction of 1,5-diketones with acetic anhydride and boron trifluoride etherate in diethyl ether. It is assumed that the heterocyclization of 1,5-diketones includes a step involving the formation and transformations of an acyloxy carbonium ion.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 320–322, March, 1992.     

Nitroazines. 20. Simple syntheses of nitropyrazolopyridines from aliphatic nitrosynthons and aminopyrazoles

Two variants of a synthesis for nitropyrazolopyridines from aminopyrazoles and two- or three-carbon nitrosynthons are examined.For Communication 19 see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1560–1564, November, 1992.     

On a new class of function systems of Faber-Schauder type

In this paper, we introduce a new class of function systems generalizing the classical Faber-Schauder system. Under the condition that the generating sequence is bounded, we show that systems of such a class constitute bases in the space of continuous functions and prove some properties of series expansions of functions in these systems.     

Mg 2p shallow core-level and local atomic structure of i-ZnMgRE quasicrystals

We present a detailed analysis of the Mg 2p shallow core-levels measured on icosahedral single-grain ZnMgY, ZnMgHo, and ZnMgEr quasicrystals during a photoelectron microscopy study. The synchrotron radiation photoemission measurements were performed on in situ cleaved samples at a pressure of 10⁻¹⁰ mbar and at low temperature, typically 90-150 K. The Mg 2p photoemission lines are essentially broadened as compared to those of the Mg 2p spin-orbit doublet recorded on the Zn₂Mg crystalline Laves phase. The broadening is associated to the coordination shifts of the Mg 2p level due to the inequivalent magnesium sites in the quasicrystalline lattice. The coordination shifts are calculated on the basis of i-ZnMg(Ho, Y) atomic structure data, recently determined from the pair distribution function analysis. The coordination shifts obtained are up to 0.2 eV. The Mg 2p experimental spectral intensity is nicely reproduced by a superposition of coordination-shifted Mg 2p spin-orbit doublets.     

Taylor-Galerkin algorithms for viscoelastic flow: Application to a model problem

Coupled and decoupled Taylor-Galerkin algorithms are considered for viscoelastic flow and a model problem—transient startup Poiseuille flow in a channel under a fixed pressure gradient. All algorithms reproduce the steady-state solutions and are stable at high elasticity numbers (E). For a fixed mesh, the coupled and decoupled versions (TGC and TGD) give exceptional time-accuracy at low elasticity numbers [to within O(1%) at E = 1] and reasonable accuracy at high elasticity numbers [to within O(10%) at E = 10, 100]. By definition, the decoupled false-transient scheme (TGF), which uses different time scales for velocity and stress time stepping, provides a poor transient history. Where the main requirement is to compute a steady-state algorithm efficiency is crucial. The TGF scheme attains a steady state between six to eight times faster than does the TGC scheme, and the latter is over twice as fast as the TGD form. © 1994 John Wiley & Sons, Inc.