When is the mean self-consistent?

We study the conditions under which the sample mean is self-consistent, and therefore an optimal predictor, for an arbitrary observation in the sample.     

Studies of thin smectic C films by X-ray reflectivity

The smectic order in thin and ultra thin films (150–600Å) of the chiral ferroelectric liquid crystal mixture ZLI-3654 is studied using the X-ray reflectivity technique. The spin cast films on various substrates (float glass, Si wafer, polymer coated glass, etc.) order spontaneously with smectic layering parallel to the substrate surface. A simple model which assumes a sinusoidal density modulation can describe well the experimental reflectivity profiles. The X-ray reflectivity provides a method to evaluate the phases of the structure factor. We demonstrate, for the first time, that is possible to extract the molecular tilt angle, , in ferroelectric liquid crystals from X-ray reflectivity measurements of ultra thin films. The temperature dependence of the tilt angle in the smectic C^* phase are almost independent of the film thickness (down to 200 Å) and are similar to those in the bulk.     

Anomalous behavior in the low temperature properties of UPd3

The low temperature specific heat of the hexagonal intermetallic compound UPd₃ reveals a contribution from low lying crystal field levels. In annealed or single crystal samples, sharp phase transitions are observed at temperatures of 6 and 7 K respectively. Correlation with resistivity, susceptibility and X-ray measurements in this temperature range indicate that the collective phenomenon is probably due to the electric quadrupole interaction between the U⁴⁺ ions.     

Nuclear magnetic resonance study of HfV2Hx and ZrV2Hx (0 ⩽ x ⩽ 4.2) hydrides

A proton NMR spin echo study of the system HfV₂H_x and ZrV₂H_x (0 ? x ? 4.5) hydrides are reported. The T₁ spin lattice relaxation rate enables us to extract the activation energy for diffusion, E_a, as well as the attempt frequency v₀; both depend strongly on the hydrogen concentration. The existence of a correlation between E_a and v₀ in these and other hydride systems yield the temperature dependence of the activation energy.     

Magnetostriction of dilute rare-earth bismuthides: The effect of non-S-state ions versus “S-state” ions

Shape magnetostriction measurements along the [001] direction were carried out for dilute rare-earth bismuthides; LaBi: R (R = Ce, Sm, Gd, Tb, Er) and the antimonide LaSb: Gd. The magnetostriction of LaBi: Ce and LaBi: Sm reveal the “reverse magnetostriction” phenomenon, enabling us to extract an overall crystalline field splitting of 12 K for the former compound. The magnetostriction of LaBi: Gd and LaSb: Gd which are significantly larger than that of the “pure” hosts, can be explained by a modified version of a model previously suggested by us. The fitting procedure yields magnetoelastic coupling constants for LaSb: Gd and LaBi: Gd which has the correct sign and magnitude according to existing theories.     

Isolation of short-lived isotopes of lanthanum and indium by β-diketonates sublimation

Trace amounts of lanthanum hexafluoroacetylacetonate and indium acetylacetonate were isolated by combination of methods, which includes synthesis of volatile elements -diketonates by nucleophilic ligands exchange and fractional sublimation. This method is useful for produce isotope generators.     

Compact self-dual Hermitian surfaces

In this paper, we obtain a classification (up to conformal equivalence) of the compact self-dual Hermitian surfaces. As an application, we prove that every compact Hermitian surface of pointwise constant holomorphic sectional curvature with respect to either the Riemannian or the Hermitian connection is Kähler.

     

Surface forms of unsaturated hydrocarbons and their transformations on group VIII metals

IR-spectroscopic and kinetic studies of the surface forms of unsaturated hydrocarbons and their catalytic transformations on group VIII metals have been carried out. Data on the nature and properties of surface compounds in hydrogenation and hydrocracking reactions have been obtained, yielding the sequence of selectivities in these processes.

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- VIII . , .

     

ESR and conductivity studies of doped polyacetylene

Low temperature ESR spectra of cis-rich and trans-rich polyacetylene, lightly doped with pentafluorides (AsF₅, SbF₅) exhibit two clearly distinguishable ESR lines. Detailed studies of these two lines as a function of temperature, doping concentration and microwave power indicate that one of these lines originates from localized spins, the other from conduction electrons. The concentration of the localized spins, generally speaking, decreases with doping. The Pauli-like susceptibility associated with the conduction electrons changes from 1.5×10^–7 to 15×10^–7 emu·cm³/mole for various doping levels and correlates with the conductivity of the same samples. The longitudinal relaxation time of the localized spins in doped trans-rich was found to beT ₁100 s at low temperatures, consistent with values of others in undoped trans rich. The temperature dependence of the homogeneous transverse relaxationT ₂ of the localized spins in doped trans-rich polyacetylene is similar to that of undoped trans polyacetylene. These facts show that the localized spins originate from undoped regions of the doped polyacetylene, perhaps due to inhomogenous doping. Our results are consistent with either formation of metallic islands, or, probably more, with impurity band conduction in strongly disordered semiconductors.