Nanoclusters based on pentagondodecahedra with shells in the form of <Emphasis Type="Italic">D</Emphasis>32, <Emphasis Type="Italic">D</Emphasis>42, and <Emphasis Type="Italic">D</Emphasis>50 deltahedra in crystal structures of intermetallic compounds

The TOPOS software package has been used to form a database of intermetallic compounds containing pentagondodecahedral d clusters (528 crystal structures of intermetallic compounds, 111 topological types, and 47 space symmetry groups). On the whole, 606 atomic d configurations have been selected which are described by 14 point symmetry groups. Examples of nanoclusters are presented which are precursors of the crystal structures of intermetallic compounds with the outer shell in the form of deltahedra D, which are formed above dodecahedra. These nanoclusters are identified in the automatic mode of structural data processing: D32 (K₈In₆Ge₄₀, Cs₃₀Na₃Sn₁₆₂), D ₄₂ (Ru₃Be₁₇, Y₃Cd₁₈, Ca₃(Cd₁₇Al)), and D ₅₀ (Yb₃Zn₁₈, Ce₃(Au₁₄Sn₃), Pr₃Cd₁₈, Eu₄Cd₂₅), where 32, 42, and 50 are the numbers of atoms in the shell. Similar deltahedra were found previously in icosahedral nanoclusters (precursors of intermetallic compounds). Structures with the dodecahedral nanocluster precursors containing D42 and D50 deltahedra are approximants of MCd_5.7 (M = Yb or Ca) quasicrystals and belong to the family of MCd₆ (M = Ce, Pr, Nd, Sm, Eu, Gd, Dy, Yb, Y, or Ca).     

Iterative reduction of the Dirichlet problem to the Neumann problem

An iteration procedure for reduction of the Dirichlet boundary-value problem to the Neumann problem is suggested. Estimates of the rate of convergence are established.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 47, No. 3, pp. 362–369, March, 1995.This paper was supported by the Foundation for Fundamental Research of the Ukrainian State Committee on Science and Technology and by the American Mathematical Society.     

Bestimmung von Spurenverunreinigungen (Al, Ca, Cr, Cu, Mg, Mn, Ni, Pb) in Reinstplatin durch Flammen-AAS

Ohne Zusammenfassung

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Determination of traces of contaminants (Al, Ca, Cr, Cu, Mg, Mn, Ni, Pb) in high-purity platinum by flame-AAS

     

Spatial correlation of hydroacoustic signals in a biaxial underwater sound channel

In the hydrological conditions of a biaxial sound channel, the cross-correlation between acoustic signals received at points spatially separated (from 10 to 63 km) along the sound propagation track is investigated. The signals are received by a narrow-beam array scanning in the vertical plane. The beam width is ～2° at the mean frequency (1 kHz) of a pseudo-noise signal. It is noted that, as the distance between the points of reception increases, the correlation decreases. This is mainly caused by the effect of the multipath propagation with an incomplete resolution of signals in arrival angles, rather than by changes in the “water” signal spectrum due to the attenuation.     

The domain decomposition method for parabolic transmission problems

An estimate of the rate of convergence is given for the domain decomposition method for the second-order parabolic transmission problem. A brief discussion of the method and some of its applications are presented.     

Crystal structure of di-(L-serine) phosphate monohydrate [C3O3NH7]2H3PO4H2O

The crystal structure of di-(L-serine) phosphate monohydrate [C₃O₃NH₇]₂H₃PO₄H₂O is determined by single-crystal x-ray diffraction. The intensities of x-ray reflections are measured at temperatures of 295 and 203 K. The crystal structure is refined using two sets of intensities. It is established that, in the structure, symmetrically nonequivalent molecules of L-serine occur in two forms, namely, the monoprotonated positively charged molecule CH₂(OH)CH(NH₃)⁺COOH and the zwitterion CH₂(OH)CH(NH₃)⁺COO^?, which are linked with each other and with the H₂PO ^?₄ ion through a hydrogen-bond system involving water molecules.

     

Crystal structure of <Emphasis Type="Italic">L</Emphasis>-serine phosphate

The crystal structure of L-serine phosphate (C₃O₃NH₇ · H₃PO₄) is determined by single-crystal X-ray diffraction. The unit cell parameters are as follows: a = 9.134(5) Å, b = 9.489(5) Å, c = 4.615(5) Å, γ = 99.54(5)°, space group P2₁, and Z = 2. The amino group of serine is protonated by a hydrogen atom of the phosphoric acid. The H₂PO ₄ ^1? ions are linked by hydrogen bonds into infinite ribbons aligned along the twofold screw axes. The ribbons form layers alternating with layers of serine molecules, which are directly linked by hydrogen bonds.