Isotope-geochemical and mineralogical-petrographic characteristics of the pergamon altar marble

Abstract We report preliminary results of our provenance study of marble from the Telephos Frieze of the Pergamon altar. The emphasis here is on the stable isotope geochemistry of marble. The obtained δ(13)C values (2.4 to 3.5‰) vary insignificantly. However, the δ(18)O values give two clusters. The isotopically light marbles (close to -9.5‰) derive from panels 1-8 and the heavy marbles (-3.5 to -1.0‰) derive from panels 11-50. Mineralogical, petrographic and geochemical investigations (accessory minerals, grain size distribution, rare earth elements) further refined the marble characteristics. In spite of certain differences observed (grain size distributions, isotopy and contents of certain elements) for the two marble groups, the present data support a common provenance. So far, east Aegean islands and the Marmara region are favored.     

Effect of three-body forces on the lattice dynamics of noble metals

A simple method to generate an effective electron-ion interaction pseudopotential from the energy wave number characteristic obtained by first principles calculations has been suggested. This effective potential has been used, in third order perturbation, to study the effect of three-body forces on the lattice dynamics of noble metals. It is found that three-body forces, in these metals, do play an important role. The inclusion of such three-body forces appreciably improves the agreement between the experimental and theoretical phonon dispersion curves.     

Influence of the Non‐holonomic Constraints on the Legged and Wheeled Vehicle ALDURO

The aim of this paper is to examine the influence of non‐holonomic constraints (the wheel‐ground contact) on the manoeuvrability of the walking vehicle ALDURO. A simplified two‐wheeled rigid model is developed. For this model classification into cases with two and with three degrees of freedom is made, and a geometric condition for the latter is found.     

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Ohne Zusammenfassung     

Glas

Analytical and Bioanalytical Chemistry -     

On the Crystal Structure of a Previously Unknown Anhydrous Zinc Hydroxide Sulfate

Anhydrous zinc hydroxide sulfates are promising precursors for the preparation of pigments and ZnO nanomaterials. The crystal structure of one such compound 5[Zn(OH)₂] · 2[ZnSO₄] was determined from high resolution laboratory X‐ray powder diffraction data by use of a combination of charge flipping, 18 simulated annealing, 26 and difference Fourier analysis. The material crystallizes in the space group P$\bar{1}$ with the lattice parameters of a = 5.4559(2) Å, b = 8.0528(3) Å, c = 8.9275(3) Å, α = 112.697(2)°, β = 85.219(3)°, γ = 95.441(3)°, and a volume of V = 359.76(2) ų. The basic crystal structure consists of brucite type Zn(OH)₂ layers where every sixth octahedral site is vacant. Tetrahedrally coordinated zinc ions are located above and below these vacancies and consecutive layers are bridged by sulfate molecules. The composition of this layered structure can be written as [Zn₅^VI□(OH)₄ · Zn₂^IV(OH)₆ · (SO₄)₂]. Its thermal decomposition was studied by X‐ray powder diffraction and thermal analysis.     

Dimensionality effects in void-induced explosive sensitivity

The dimensionality of defects in high explosives controls their heat generation and the expansion of deflagrations from them. We compare the behaviour of spherical voids in three dimensions to that of circular voids in two dimensions. The behaviour is qualitatively similar, but the additional focusing along the extra transverse dimension significantly reduces the piston velocity needed to initiate reactions. However, the reactions do not grow as well in three dimensions, so detonations require larger piston velocities. Pressure exponents are seen to be similar to those for the two-dimensional system.     

Synthesis of a 2'-Se-uridine phosphoramidite and its incorporation into oligonucleotides for structural study

[chemical reaction: see text]. We report here the synthesis of the 5'-[benzhydryloxybis(trimethylsilyloxy)]silyl-2'-methylseleno-2'-deoxyuridine phosphoramidite and its incorporation into oligonucleotides by solid-phase synthesis. The coupling yield of this phosphoramidite into oligonucleotides is higher than 99%. We also demonstrate that this 2'-methylselenophosphoramidite is compatible with the 5'-silyl-2'-ACE chemistry, for longer Se-RNA solid-phase synthesis. Our preliminary NMR study on the synthesized 2'-Se-DNA has revealed a U(Se)-A base pair and a duplex structure formation when its complementary strand was present.     

Predicting EXAFS signals from shock compressed iron by use of molecular dynamics simulations

Simulated EXAFS signals from ab initio models and configurational averaging of molecular dynamics (MD) data are compared for α-Fe, and configurationally averaged MD EXAFS signals are compared with experimental data for iron shock compressed to pressures above the α–ε transition pressure. It is shown that molecular dynamics potentials and ab initio models capable of recreating similar vibrational density of states lead to EXAFS signals in good mutual agreement. The effects of the classical nature of the phonon distribution in the MD and the anharmonicity of the potential give rise to noticeable differences between ab initio models and configurational averaging of MD data. However, the greatest influence on the spectra is the form of the potential itself. We discuss the importance of these effects in simulating EXAFS spectra for shock compressed polycrystalline iron. It is shown that EXAFS is an insensitive probe for determining the nature of the close packed product phase in this system.     

Direct observation of the alpha-epsilon transition in shock-compressed iron via nanosecond x-ray diffraction

In situ x-ray diffraction studies of iron under shock conditions confirm unambiguously a phase change from the bcc (alpha) to hcp (epsilon) structure. Previous identification of this transition in shock-loaded iron has been inferred from the correlation between shock-wave-profile analyses and static high-pressure x-ray measurements. This correlation is intrinsically limited because dynamic loading can markedly affect the structural modifications of solids. The in situ measurements are consistent with a uniaxial collapse along the [001] direction and shuffling of alternate (110) planes of atoms, and are in good agreement with large-scale nonequilibrium molecular dynamics simulations.