Gradient‐based nodal limiters for artificial diffusion operators in finite element schemes for transport equations

This paper presents new linearity‐preserving nodal limiters for enforcing discrete maximum principles in continuous (linear or bilinear) finite element approximations to transport problems with steep fronts. In the process of algebraic flux correction, the oscillatory antidiffusive part of a high‐order base discretization is decomposed into a set of internodal fluxes and constrained to be local extremum dim inishing. The proposed nodal limiter functions are designed to be continuous and satisfy the principle of linearity preservation that implies the preservation of second‐order accuracy in smooth regions. The use of limited nodal gradients makes it possible to circumvent angle conditions and guarantee that the discrete maximum principle holds on arbitrary meshes. A numerical study is performed for linear convection and anisotropic diffusion problems on uniform and distorted meshes in two space dimensions. Copyright © 2017 John Wiley & Sons, Ltd.     

Shock wave bifurcation in convergent–divergent channels of rectangular cross section

This work addresses two- and three-dimensional turbulent flow in simple channels, modeling the air intakes of rectangular cross section. Flow regimes with a supersonic free stream and supersonic velocities at the throat or immediately downstream of the throat are considered. Bifurcations of the shock wave arising ahead of the cowl are studied numerically. Solutions of the Reynolds-averaged Navier–Stokes equations are obtained with a finite-volume solver of second-order accuracy on fine computational meshes. The solutions reveal jumps of the shock leg position with variations of the free-stream Mach number. The dependence of the shock position on the cowl slope and streamwise location of the throat is examined.     

Effect of transition metal ions on partial ethane oxidation in an electrochemical system

Transition metal ions (Fe²⁺ and Cu²⁺) have been found to enhance the rate of ethane partial oxidation in a gas-liquid electrochemical reactor under mild conditions (363 K, atmospheric pressure). The effect is discussed in terms of a radical-chain mechanism involving OH radicals.     

Possible galactic sources of ultrahigh-energy cosmic rays and a strategy for their detection via gravitational lensing

If decays of superheavy relic particles in the galactic halo are responsible for ultrahigh-energy cosmic rays, these particles must be clustered to account for small-scale anisotropy in the AGASA data. We show that the masses of such clusters are large enough for them to gravitationally lens stars and galaxies in the background. We propose a general strategy that can be used to detect such clusters via gravitational lensing, or to rule out the hypothesis of decaying relic particles as the origin of highest energy cosmic rays.     

Color centres and polymorphism in pure WO3 and mixed (1−x)WO3−y·xReO2 powders

The relationship between structural transformations and colour centres creation is discussed for deeply coloured hydrogen tungsten bronzes and for pure WO₃ powders, acquiring less intense colour after mechanical treatments of variable duration. A comparative study on coloration is made also for mixed compounds (1−x)WO_3−y·xReO₂, where an evidence of a resonance effect for a particular Raman band at 970 cm⁻¹, attributed to the color centres, is observed. Besides, it is found that even moderate milling treatments result in a quite different structural evolution of tungsten trioxide upon cooling. Paper presented at the 6th Euroconference on Solid State Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999.     

Biomolecular component analysis of cultured cell nucleoli by Raman microspectrometry

Distinct cellular domains, such as structure–function compartments of the cell nucleus and cytoplasmic organelles, are responsible for numerous macromolecular processes essential for cell functions. Spectroscopic analysis of specific cellular domains opens a way for noninvasive characterization of their molecular content and monitoring of their function. Confocal Raman spectroscopy was employed here for characterization of the complex molecular organization of major structure–function compartment of the cell nucleus, the nucleolus. The Raman spectra obtained in the nucleoli were processed by biomolecular component analysis (BCA). BCA was used to determine the contribution of each major type of macromolecules (proteins, DNA, RNA and lipids) to the complex molecular composition of nucleoli. A notable cell‐to‐cell variability in the macromolecular composition of nucleolus was found. At the same time, we observed a correlation between the concentrations of major types of biomolecules in this nuclear compartment. In particular, the averaged concentration of RNA increases along with increase in protein concentration, while an inverse dependence between the concentrations of RNA and DNA was found. Variations in the nucleolar concentrations of lipids were also noticed. Manifestations in spectral variations of proteins for individual nucleoli, shown by BCA, are discussed and interpreted. We also compared utility of BCA and principal component analysis for biomolecular studies and conclude that BCA is a more powerful and informative technique for studies of macromolecular composition and its variations in specific subcellular domains. Copyright © 2012 John Wiley & Sons, Ltd.     

The cyclolinear polyorganosiloxanes - a new class of mesomorphic polymers

The paper summarizes the recent achievements concerning the influence of the chemical structure and rigidity of cyclolinear polyorganosiloxane chains on the glassy, crystalline and mesophase behaviour with a special emphasis on the temperature range of mesophase stability and some thermal, X-ray and optical characteristics of their mesophase state. The packing of macromolecules in the mesophase state is suggested.