Mechanical properties and structural characteristics of plastically deformed peridotites

The paper reports on experimental study of peridotites with different average grain sizes. It is shown that coarse-crystalline peridotite undergoes multiple bulk fracture along all large fragments, whereas fracture of fine-crystalline peridotite is localized in the centre and develops in a direction close to the compression axis with the only slight deflection toward maximum tangential stresses in the upper and lower parts in which the strain localization zone is bifurcated. It is found that by the onset of fracture, the lateral to axial strain ratio for the coarse- and fine-crystalline specimens is 1.36 and 0.76, respectively.     

Morphology of hybrid polystyrene-block-poly(ethylene oxide) micelles: analytical ultracentrifugation and SANS studies

Morphology and structure of aqueous block copolymer solutions based on polystyrene-block-poly(ethylene oxide) (PS-b-PEO) of two different compositions, a cationic surfactant, cetyl pyridinium chloride (CPC), and either platinic acid (H2PtCl6.6H2O) or Pt nanoparticles were studied using a combination of analytical ultracentrifugation (AUC), transmission electron microscopy (TEM), and small angle neutron scattering (SANS). These studies combining methods contributing supplemental and analogous structural information allowed us to comprehensively characterize the complex hybrid systems and to discover an isotope effect when H2O was replaced with D2O. In particular, TEM shows formation of both micelles and larger aggregates after incorporation of platinic acid, yet the amount of aggregates depends on the H2PtCl6.6H2O concentration. AUC reveals the presence of micelles and micellar clusters in the PS-b-PEO block copolymers solution and even larger (supermicellar) aggregates in hybrids (with CPC). Conversely, SANS applied to D2O solutions of the similar species indicates that micelles are spherical and no other micellar species are found in block copolymer solutions. To reconcile the SANS and AUC data, we carried out AUC examination of the corresponding D2O block copolymer solutions. These measurements demonstrate a pronounced isotope effect on micelle aggregation and micelle size, i.e., no micelle aggregation in D2O solutions, revealing good agreement of AUC and SANS data.     

Small-angle X-ray scattering study of the structure of self-organized polymer matrices and formation of imbedded metal nanoparticles

The structures of self-organizing polymer matrices based on collapsed gels and polyoctadecylsiloxanes have been studied by the methods of conventional and anomalous X-ray small-angle scattering with the use of the laboratory and synchrotron sources of X-ray radiation. The process of formation of metal nanoparticles in such matrices is also studied, their size distributions are calculated, and the models of localization of these particles in the polymer matrices are suggested. It is shown that growth of metal particles is controlled by the structure of the polymer network and is limited by the dimensions of its cells. The electron-density profiles of polycondensed octadecylsiloxane matrices are also calculated.     

Improvement of the fractional uncertainty of a neutral-atom calcium optical frequency standard to 2×10-14

We have investigated the two major effects that limit the accuracy of an optical frequency standard based on laser-cooled neutral calcium atoms, i.e. the residual Doppler shift and atomic collisions. A new correction method was applied to reduce the contribution of the residual Doppler effect to the total fractional uncertainty to 1×10^-14. Measurements of the shift of the clock transition frequency due to cold collisions allowed us to reduce their contribution to 4×10^-15. With these improvements we have reduced the total fractional frequency uncertainty of the standard by nearly an order of magnitude to 2×10^-14. Received: 9 August 2002 / Revised version: 16 November 2002 / Published online: 26 February 2003 RID="*" ID="*"Permanent address: Russian Academy of Sciences, P.N. Lebedev Physical Institute, Samara Branch, Novo-Sadovaya st. 221, Samara 443011, Russia RID="**" ID="**"Corresponding author. Fax: +49-531/592-4305, E-mail: uwe.sterr@ptb.de