Sandpiles with bistable automata rules: towards a minimal model of pedestal formation and structure

A sandpile with two stable and two unstable ranges of slopes is presented as a minimal model for the study of H-mode pedestal formation and dynamics. Pedestals are observed to form and expand inward with increasing deposition. Transport bifurcation is not critical to pedestal formation, though the pedestal structure obtained with a second, hard stability boundary is qualitatively different from that found in standard sandpiles. Nonperiodic particle ejection events are observed, but do not initiate pedestal collapse. Pedestal formation alters the spectrum of transport avalanches.     

Electrical transport and magnetic ordering in R 2Ti3Ge4 (R=Dy, Ho and Er) compounds

New R ₂Ti₃Ge₄ (R=Dy, Ho and Er) intermetallic compounds have been synthesized and characterized by X-ray diffraction and low temperature ac magnetic susceptibility, electrical resistivity and thermoelectric power measurements were carried out. The compounds crystallize in the parent, Sm₅Ge₄-type orthorhombic structure (space group Pnma) and lanthanide contraction is observed as one moves along the rare-earth series. The changeover from paramagnetic to antiferromagnetic phase happens at low temperatures and the ordering temperature scales with the de Gennes factor. The electrical resistivity is metallic with a negative curvature above 100 K. Thermopower displays a weak maximum at temperatures less than 50 K signifying the possible phonon and magnon drag effects.     

Thermotropic phase transitions in model membranes of the outer skin layer based on ceramide 6

The lipid intercellular matrix stratum corneum of the outer skin layer is a multilayer membrane consisting of a complex mixture of different lipids: ceramides, fatty acids, cholesterol, and its derivatives. The basis of the multilayer membrane is the lipid bilayer, i.e., a two-dimensional liquid crystal. Currently, it is known that the main way of substance penetration through the skin is the lipid matrix. The complexity of the actual biological system does not allow reliable direct study of its properties; therefore, system modeling is often used. Phase transitions in the lipid system whose composition simulates the native lipid matrix are studied by the X-ray synchrotron radiation diffraction method.     

Block SSOR preconditionings for high-order 3D FE systems. III: Incomplete BSSOR preconditionings based on p-partitionings

This paper considers the construction of high quality IBSSOR preconditionings for p-adaptive hierarchical high-order 3D FE systems. Instead of the commonly-adopted domain decomposition approach to the selection of a block partitioning underlying the corresponding block SSOR preconditioning, we introduce the so-called p-partitionings based on subdividing the degrees of freedom in accordance with the levels of p-refinement. A theoretical analysis of IBSSOR preconditionings is presented. The results of numerical experiments with 3D FE systems arising from the hierarchical approximations of order p, 3 ≤ p ≤ 5, of the 3D equilibrium equations for linear elastic orthotropic materials show that the IBSSOR preconditionings suggested are more efficient than the IBSSOR preconditionings based on domain decomposition partitionings. Moreover, we demonstrate that the new preconditionings are more reliable when solving extremely ill-conditioned 3D FE systems. © 1997 John Wiley & Sons, Ltd.     

Elastic properties of the Ta–V system: bcc Ta0.33V0.67 and C15 TaV2

Resonant ultrasound spectroscopy was used to measure the elastic constants of bcc Ta_0.33V_0.67 over the temperature range 3.5–300?K; the results were compared to earlier measurements on C15 TaV₂. The temperature dependence of the polycrystalline shear modulus is completely different in the two phases; that of the bcc phase decreases with temperature whereas that of the C15 phases increases in an anomalous fashion. This difference is consistent with a model involving doubly-degenerate levels at the X point of the Brillouin zone in the C15 phase with the Fermi level lying near the doubly degenerate level. This model accounted for the unusual behaviour of the C15 phase. Debye temperatures were determined from the ultrasonic measurements: 295?K for the C15 phase and 315?K for the bcc phase.     

Synchrotron X-ray diffraction study of the structure of oral stratum corneum model lipid membranes

Membranes modeling the lipid fraction of the mucous membrane of the human oral cavity have been studied by X-ray synchrotron diffraction. Ternary systems, composed of a mixture of sphingomyelin, dipalmitoylphosphatidylcholine, and dipalmitoylphosphatidylethanolamine with component weight ratios of 1: 2: 2 and 1: 2: 1, have lamellar structures in the gel phase at the physiological temperature (37°C). An inverted hexagonal phase is formed in the system with 40% dipalmitoylphosphatidylethanolamine in the temperature range of 60–70°C. This phase coexists with the liquid-crystalline lamellar phase in a narrow temperature range and completely surpresses the lamellar phase with an increase in temperature to 80°C. Multi-component oral stratum corneum membranes are characterized by several lamellar phases at 20–37°C and the coexistence of one or several lamellar phases with inverted hexagonal phase at 80–90°C.