Cavitation bubble dynamics in non‐Newtonian fluids

Cavitation phenomena play important roles in many areas of science and engineering. The most interesting effect of the non‐Newtonian properties of the liquid is the reduction of cavitation damage and noise. This article reviews experimental and theoretical efforts to understand such phenomena. Two major areas of research are described, namely the dynamics of cavitation bubbles oscillating in a liquid of infinite extent, and the behavior of bubbles collapsing near rigid walls. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers     

Error estimation in the approximation of the solution of nonlinear fuzzy Fredholm integral equations

Using a fixed point technique, the sequence of successive approximations and a recent quadrature formula for fuzzy-number-valued functions, it is constructed a numerical method for the solution of nonlinear fuzzy Fredholm integral equations. Moreover, the error estimate of the method and a criterion to stop the corresponding algorithm are given.     

Chemical oxidation of residual carbon from ZnAl2O4 powders prepared by combustion synthesis

The removal of carbon residue from ZnAl₂O₄ nanopowders by annealing at 500–800 °C leads to a decrease of specific surface area from 228.1 m²/g to 47.6 m²/g. At the same time, the average crystallite size increased from 5.1 nm to 14.9 nm. In order to overcome these drawbacks, a new solution for removing the carbon residue has been suggested: chemical oxidation using hydrogen peroxide. In terms of carbon removal, a H₂O₂ treatment for 8 h at 107 °C proved to be equivalent to a heat treatment of 1 h at 600 °C. The benefits of chemical oxidation over thermal oxidation were obvious. The specific surface area was much larger (188.1 m²/g) in the case of the powder treated with H₂O₂. The average crystallite size (5.8 nm) of ZnAl₂O₄ powder treated with H₂O₂ was smaller than the crystallite size (8.2 nm) of the ZnAl₂O₄ powder annealed at 600 °C.     

Computing global and diffuse solar hourly irradiation on clear sky. Review and testing of 54 models

Fifty-four broad band models for computation of global and diffuse irradiance on horizontal surface are shortly presented and tested. The input data for these models consist of surface meteorological data, atmospheric column integrated data and data derived from satellite measurements. The testing procedure is performed for two meteorological stations in Romania (South-Eastern Europe). The testing procedure consists of forty-two stages intended to provide information about the sensitivity of the models to various sets of input data. There is no model to be ranked “the best” for all sets of input data. Very simple models as well as more complex models may belong to the category of “good models”. The best models for solar global radiation computation are, on equal-footing, ESRA3, Ineichen, METSTAT and REST2 (version 81). The second best models are, on equal-footing, Bird, CEM and Paulescu & Schlett. The best models for solar diffuse radiation computation are, on equal-footing, ASHRAE2005 and King. The second best model is MAC model. The best models for computation of both global and diffuse radiation are, on equal-footing, ASHRAE 1972, Biga, Ineichen and REST2 (version 81). The second best is Paulescu & Schlett model.     

Some Polyamides,Polyesters, and Polyurethanes Containing AZO Groups

The paper discusses the synthesis of the N,N,′-azobis(formamidopropionic) acid (AFP), along with some characteristics determined from NMR spectrum, differential thermal analysis, and DSC. The behavior of AFP acid—as well as of its analogue, N,N′-azobis(formamidoacetic) acid (AFA)—has been studied in the reaction with aromatic diamine and with bis(glycol)terephthalate, leading to azopolymers of the azopolyamide, or azopolyester, type. On employing N,N′-bis(β-hydroxyethyl) azobis-formamide (HEAF) as the azo bifunctional compound in the reaction with diphenylmethane diisocyanate, a polyurethane possessing azo groups was obtained. The structure of the azopolymers has been spectroscopically confirmed.     

A REGULARITY FOR CYCLIC CONJUGATION IN ACENAPHYHYLENE,FLUORANTHENE AND THEIR CONGENERS

Acenaphthylene, fluoranthene and their congeners are compounds that, in view of their chemical and physical properties, belong among benzenoid hydrocarbons. However, because of the presence of a five-membered ring, in all chemical-graph-theoretical considerations of benzenoid systems, these species have been disregarded. Continuing our recent studies of the title compounds, we report here on a peculiar characteristic of the pattern of their cyclic conjugation, named “the phenyl-cyclopentadienyl rule” (PCP rule): if a benzene ring is connected with the (unique) five-membered ring by exactly one carbon-carbon bond (which we refer to as a PCP constellation), then the cyclic conjugation in the five-membered ring significantly increases. If there are several PCP constellations, then the intensity of cyclic conjugation is additionally increased.     

PARTITIONING OF π-ELECTRONS IN RINGS OF POLYCYCLIC conjugated HYDROCARBONS. PART 1: CATACONDENSED BENZENOIDS

Recently a novel view on Kekulé valence structures (or resonance structures) was reported in which their standard geometrical representation was replaced by a numerical representation obtained by assigning π-electrons associated with CC double bonds to individual benzenoid rings. In the present article, we examine in more detail the partitioning of π-electrons to benzenoid rings for cata-condensed benzenoid hydrocarbons. For special families of cata-condensed benzenoids, we offer formulas which allow one to obtain the average π-electron ring content for individual benzenoid rings of polycyclic conjugated hydrocarbons. We also show that the average π-electron ring content for individual benzenoid rings can be calculated from Pauling bond orders without a need to examine all Kekulé resonance structures of a molecule.