Gradual Cerium Valence Change in the Solid Solution CeRu1–xPdxAl (x = 0.1–0.9)

The solid solution CeRu_1–xPd_xAl was synthesized for x = 0.1–0.9 from the elements by arc‐melting and subsequent annealing and characterized by powder X‐ray diffraction. All members crystallize in the orthorhombic LaNiAl type structure, space group Pnma. The lattice parameters range from a = 718–722, b = 412–426, and c = 1588–1620 pm, but no linear change of the lattice parameters was found. Magnetic measurements reveal intermediate cerium valences, which change to more trivalent cerium with increasing Pd content. The susceptibility data was interpreted by either the Inter‐Configuration Fluctuation (ICF) model or the Curie‐Weiss law.     

Synchrotron SAX and WAX diffraction study of a hydrated very long-chain, dendritic amphiphile + DPPC mixture

The tri-headed anionic dendritic amphiphile, 4-(2-carboxyethyl)-4-[(icosyloxycarbonyl)amino]heptanedioic acid (3CCb20), forms mixed aggregates with dipalmitoylphosphatidylcholine (DPPC) in excess water at 3CCb20:DPPC = 0.91:1 molar ratio. On heating, these mixed aggregates transform into fluid bilayers stacked in the liquid crystalline lamellar L phase at about 40 °C. This phase transition and the microstructure of 3CCb20 + DPPC aggregates were studied with small- and wide-angle synchrotron X-ray diffraction. The ability of 3CCb20 to solubilize solidlike lipid bilayers could contribute to the antimicrobial activities of 3CCb20, including its anti-HIV activity.     

Smoothed aggregation multigrid for incompressible flows

We discuss the advantages of using algebraic multigrid based on smoothed aggregation for solving indefinite linear problems. The ingredients of smoothed aggregation are used to construct a black-box monolithic multigrid method with indefinite coarse problems. Although we discuss some techniques for enforcing the uniform inf-sup stability on all coarse levels, numerical experiments suggest that it is not strictly necessary. The proposed multigrid preconditioner shows robust behaviour for different time-step parameters and even for very elongated geometries, where other techniques based on h -independent preconditioners of the pressure Schur complement lose their efficiency. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Measuring neutron-star properties via gravitational waves from neutron-star mergers

We demonstrate by a large set of merger simulations for symmetric binary neutron stars (NSs) that there is a tight correlation between the frequency peak of the postmerger gravitational-wave (GW) emission and the physical properties of the nuclear equation of state (EoS), e.g., expressed by the radius of the maximum-mass Tolman-Oppenheimer-Volkhoff configuration. Therefore, a single measurement of the peak frequency of the postmerger GW signal will constrain the NS EoS significantly. For optimistic merger-rate estimates a corresponding detection with Advanced LIGO is expected to happen within an operation time of roughly a year.     

Suppression of self-induced flavor conversion in the supernova accretion phase

Self-induced flavor conversions of supernova (SN) neutrinos can strongly modify the flavor-dependent fluxes. We perform a linearized flavor stability analysis with accretion-phase matter profiles of a 15M[symbol: see text] spherically symmetric model and corresponding neutrino fluxes. We use realistic energy and angle distributions, the latter deviating strongly from quasi-isotropic emission, thus accounting for both multiangle and multienergy effects. For our matter and neutrino density profile we always find stable conditions: flavor conversions are limited to the usual Mikheyev-Smirnov-Wolfenstein effect. In this case one may distinguish the neutrino mass hierarchy in a SN neutrino signal if the mixing angle θ13 is as large as suggested by recent experiments.     

Decoration of nitrogen vacancies by oxygen atoms in boron nitride nanotubes

Decoration of nitrogen vacancies by oxygen atoms has been studied by near-edge X-ray absorption fine structure (NEXAFS) around B K-edge in several boron nitride (BN) structures, including bamboo-like and multi-walled BN nanotubes. Breaking of B-N bonds and formation of nitrogen vacancies under low-energy ion bombardment reduces oxidation resistance of BN structures and promotes an efficient oxygen-healing mechanism, in full agreement with some recent theoretical predictions. The formation of mixed O-B-N and B-O bonds is clearly identified by well-resolved peaks in NEXAFS spectra of excited boron atoms.     

Evaluation of laboratory powder X-ray micro-diffraction for applications in the fields of cultural heritage and forensic science

The uniqueness and limited amounts of forensic samples and samples from objects of cultural heritage together with the complexity of their composition requires the application of a wide range of micro-analytical methods, which are non-destructive to the samples, because these must be preserved for potential late revision. Laboratory powder X-ray micro-diffraction (micro-XRD) is a very effective non-destructive technique for direct phase analysis of samples smaller than 1 mm containing crystal constituents. It compliments optical and electron microscopy with elemental micro-analysis, especially in cases of complicated mixtures containing phases with similar chemical composition. However, modification of X-ray diffraction to the micro-scale together with its application for very heterogeneous real samples leads to deviations from the standard procedure. Knowledge of both the limits and the phenomena which can arise during the analysis is crucial for the meaningful and proper application of the method. We evaluated basic limits of micro-XRD equipped with a mono-capillary with an exit diameter of 0.1 mm, for example the size of irradiated area, appropriate grain size, and detection limits allowing identification of given phases. We tested the reliability and accuracy of quantitative phase analysis based on micro-XRD data in comparison with conventional XRD (reflection and transmission), carrying out experiments with two-phase model mixtures simulating historic colour layers. Furthermore, we demonstrate the wide use of micro-XRD for investigation of various types of micro-samples (contact traces, powder traps, colour layers) and we show how to enhance data quality by proper choice of experiment geometry and conditions.     

Hardness of approximation for orthogonal rectangle packing and covering problems

Bansal and Sviridenko [N. Bansal, M. Sviridenko, New approximability and inapproximability results for 2-dimensional bin packing, in: Proceedings of the 15th Annual ACM–SIAM Symposium on Discrete Algorithms, SODA, 2004, pp. 189–196] proved that there is no asymptotic PTAS for 2-dimensional Orthogonal Bin Packing (without rotations), unless P=NP. We show that similar approximation hardness results hold for several 2- and 3-dimensional rectangle packing and covering problems even if rotations by ninety degrees are allowed. Moreover, for some of these problems we provide explicit lower bounds on asymptotic approximation ratio of any polynomial time approximation algorithm. Our hardness results apply to the most studied case of 2-dimensional problems with unit square bins, and for 3-dimensional strip packing and covering problems with a strip of unit square base.     

Crocoite PbCrO4 and mimetite Pb5(AsO4)3Cl: rare minerals in highly degraded mediaeval murals in Northern Bohemia

Mural paintings of exceptional quality, which can be discerned in spite of their extensive mechanical damage and colour fading, have been uncovered in the church of St. Gallus in Kuřívody, Northern Bohemia, dated to the second half of the 13th century. Materials research with particular use of portable X‐ray fluorescence, Raman micro‐spectroscopy and powder X‐ray micro‐diffraction revealed the presence of rare pigments. In Kuřívody, it is only a second identification of intentionally used yellow mineral crocoite (PbCrO₄) in European art. Its identification is facilitated by providing a very good Raman scattering, even when present in small amounts in fragmentarily preserved colour layers. Light yellow mimetite (Pb₅(AsO₄)₃Cl) was never before mentioned as intentionally used pigment in Europe. Its finding in Kuřívody, however, corresponds more likely with undesirable physical–chemical conditions causing its formation by alteration of orpiment (As₂S₃) and minium (Pb₃O₄). Obtained results highlight the importance of Raman spectroscopy for direct identification of mineral pigments in low concentrations, which may be crucial for interpreting cultural heritage objects in historical context. By materials, the almost forgotten paintings in Kuřívody can be seen as outstanding and rare example of ancient artistic tradition that has spread to Europe from Mediterranean in early Middle Ages. After all, mineral crocoite was already used by ancient Egyptians to paint sarcophagi and degraded orpiment decorates the walls of the Nefertari's tomb in Thebes. Copyright © 2014 John Wiley & Sons, Ltd.