Ab initio studies of the para- and antiferroelectric structures and local polarized configurations in NH4H2PO4

A study of differently polarized structures relevant to the H-bonded antiferroelectric (AFE) compound NH(4)H(2)PO(4) (ADP) is performed by first-principles calculations in the framework of the density functional theory. The calculated structures for the AFE and paraelectric (PE) phases are found in general good agreement with the available experimental data. We study the energetics and relative stability of different polarized clusters embedded in a PE matrix of ADP. We find that local ferroelectric and AFE clusters are stable and may coexist in the PE phase, which explains the coexistence of both type of microregions determined by electron spin probe measurements above the AFE-PE transition temperature. The dependency with the O-H···O bridge length of the energy barrier heights for proton transfer is studied for coordinated proton displacements along the bridges within clusters of different sizes. This dependency may have implications for the geometric isotopic effects on T(c). We analyze Mulliken orbital and bond populations which confirm the existence of a charge flow within the NH(4)(+) ion, an essential fact for the stabilization of the AFE phase over other possible polarized structures. This charge transfer is correlated with the optimization of the N-H···O bridges and with distortions of the NH(4)(+) group.     

Influence of initial deflections on the stability of composite cylindrical shells interacting with a fluid flow

Composite cylindrical shells interacting with an internal fluid flow are analyzed for stability. It is assumed that the shells have small initial geometrical imperfections. The effect of axisymmetric and nonaxisymmetric initial deflections on the critical speeds of the fluid, which cause static (divergent) or dynamic (flutter) loss of stability, is studied     

Bounded law of the iterated logarithm for multidimensional martingales normalized by matrices

We investigate a bounded law of the iterated logarithm for matrix-normalized weighted sums of martingale differences in R ^d . We consider the normalization of matrices inverse to the covariance matrices of these sums by square roots. This result is used for the proof of the bounded law of the iterated logarithm for martingales with arbitrary matrix normalization. __________ Translated from Ukrains’kyi Matematychnyi Zhurnal, Vol. 58, No. 7, pp. 1006–1008, July, 2006.     

First results for the measurement of double-electron capture of 106Cd in the experiment TGV II

Present status of the experiment TGV II which is devoted to the measurement of double-beta decay of ¹⁰⁶Cd is given. The low background spectrometer TGV II is installed in the Modane Underground Laboratory and has been running from February 2005 with approx 10 grams of ¹⁰⁶Cd enriched at 75%. After an analysis of 3736 hours of experimental data the new improved half-life limit for 2νEC/EC decay of ¹⁰⁶Cd (0 _g.s. ⁺ → 0 _g.s. ⁺ ) is given as T ₁ ^2/2ν > 4.8 × 10¹⁹ years (90% CL). The search for 2νEC/EC decay of ¹⁰⁶Cd to the excited states of ¹⁰⁶Pd allows to determine the limits of the half-lives T ₁ ^2/2ν (0 _g.s. ⁺ → 2 ₁ ⁺ ) > 3.9 × 10¹⁹ years (90% CL) and T ₁ ^2/2ν (0 _g.s. ⁺ → 0 ₁ ⁺ ) > 5.8 × 10¹⁹ years (90% CL). Presented by I. Štekl at the Workshop on calculation of double-beta-decay matrix elements (MEDEX’05), Corfu, Greece, September 26–29, 2005.     

Unusual dependence of the effectiveness of spectral sensitization of the photoconductivity of polycrystalline ZnO on the dye concentration in a mixed monolayer on a semiconductor surface

A nonmonotonic, oscillatory dependence of the effectiveness of spectral sensitization of the photoconductivity of polycrystalline ZnO on the dye concentration in n-octadecylamine and stearic acid monolayers, transferred to the surface of a semiconductor by the Langmuir-Blodgett method, has been observed experimentally. The observed effect is completely different from the monotonic increase of the photocurrent with a peak at some dye concentration in certain films adsorbed on a semiconductor surface from a solution and in films deposited in vacuum. To explain the results, a simple model describing the balance of monomers and dimers of the dye is examined. The solution of the problem is an oscillatory decaying function of the monomer concentration as the total dye concentration in the monolayer increases. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 3, 174–177 (10 August 1996)     

The determination of electron mean free paths in solids by depth and angular dependences of inelastically scattered electron spectra

A technique is presented of electron mean free path determination in solids using the spectra of backscattered electrons. The mean free path without energy loss (λ₀) in Ge, and the mean free paths for excitation of volume (λ_v) and surface (λ_s) plasmons in Al, are determined in the electron energy range E₀ = 0.1–10 kev. The depth d_s of surface plasmon localization is estimated for Al.     

Glass electrode measurements of sodium in albumin solutions

Measurements of the sodium level of albumin solutions and their ultrafiltrates were made with commercially available sodium-sensitive glass electrodes. The potential of the electrode was found to vary considerably with the depth of immersion. The potentials of albumin solutions which were allowed to remain at room temperature or higher for any length of time were found to increase, and in time gave unrealistic levels of sodium activity. An albumin solution stored in a refrigerator for a month did not show this effect. The sodium levels of albumin solutions as determined by the electrode were lower than the flame photometric values for the same solutions.