On the Easy Use of Scientific Computing Services for Large Scale Linear Algebra and Parallel Decision Making with the P-Grade Portal

Scientific research is becoming increasingly dependent on the large-scale analysis of data using distributed computing infrastructures (Grid, cloud, GPU, etc.). Scientific computing (Petitet et al. 1999) aims at constructing mathematical models and numerical solution techniques for solving problems arising in science and engineering. In this paper, we describe the services of an integrated portal based on the P-Grade (Parallel Grid Run-time and Application Development Environment) portal (http://www.p-grade.hu) that enables the solution of large-scale linear systems of equations using direct solvers, makes easier the use of parallel block iterative algorithm and provides an interface for parallel decision making algorithms. The ultimate goal is to develop a single sign on integrated multi-service environment providing an easy access to different kind of mathematical calculations and algorithms to be performed on hybrid distributed computing infrastructures combining the benefits of large clusters, Grid or cloud, when needed.     

The influence of delayed light curing on the degree of conversion and polymerization contraction stress in dual-cured resin luting agents

The aim of the study was to assess the effect of delayed photo-initiation on the polymerization contraction stress (PCS) and degree of conversion (DC) of a dual-cure resin-luting agent. Thirty-five disk (6 mm × 1 mm) samples (n = 10 each group) of dual cure resin luting agent for PCS assessment were fabricated and polymerized using two illuminated quartz rods. Based on the delay in photo-initiation, 30 disks were divided among six groups [group A-0 min (min) delay, group B-2 min, group C-4 min, group D-6 min, group E-8 min and group F-10 min]. A non-photoinitiated group (group G – chemical cure – n = 5) was included as control. The PCS for all specimens was assessed using a Tensometer. For DC evaluation thirty-five specimens were divided into seven groups with delays in photo-initiation (group H-0 min, group I-2 min, group J-4 min, group K-6 min, group L-8 min and group M-10 min, group N-chemical cure). DC was assessed using attenuated total reflectance spectroscopic technique. Statistical comparison among groups was performed using analysis of variance (α = 0.05). The maximum and minimum PCS and DC values with delayed photo-initiation was observed in group-C (3.34 MPa) & group-F (2.44 MPa); and group-M (0.78 MPa) and group-H (0.55 MPa) respectively. Chemically cured samples showed the least PCS (group-G, 1.94) and DC (group-N, 0.53) values in their respective categories. PCS significantly decreased with delayed photo-initiation. A significant increase in DC was noticed when photo-initiation was delayed in the dual cure resin luting agent.     

Novel chemical methods for the infiltration of opal particles with electrically conductive polyaniline polymers

Chemical methods for successfully coating opal particles with electrically conducting polyaniline (PANi) polymers were studied. Two different routes were proven successful. First was the in situ chemical doping reaction of PANi with dodecylbenzenesulfonic acid (DBSA) and camphorsulfonic acid dopants. The other method was placement of opal particles in a low concentration of a conducting PANi/DBSA solution in chloroform. Ultraviolet analyses of opal samples showed typical spectra for doped PANi with delocalized polarons. The electrical resistance of coated opal was measured to be 0.75 × 10³ Ω. Morphological studies of the fractured surface by scanning electron microscopy indicated successful coating. Cyclic voltammetry studies confirmed the percolating behavior of infiltrated PANi. Also, a selective electroactive behavior toward the type of dopant was observed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 788–793, 2002     

Investigation of the tribochemical and physico-mechanical processes in sliding of mineral-filled formaldehyde copolymer composites against steel

The effect of the treatment of the mineral fillers travertine, bentonite and tuff by organic lubricating materials on the structure and tribological properties of polymer composites was studied. The composites were made with these fillers and the formaldehyde based copolymer. They exhibited higher wear-resistance, improved strength properties and decreased coefficient of friction. The thermo-gravimetric, thermo-mechanical and sol-gel analyses indicated higher thermostability and improved elastic-viscous properties of the composites. The electron paramagnetic resonance spectroscopy confirmed the formation of intermolecular chemical bonds between polymer chains, which contributed to the increase in stiffness of the filled composite as a consequence of the formation of reticular structure. The analysis of transfer films formed on steel counterfaces by secondary-ion mass-spectrometry indicated thermo- and tribocracking of composites because of the depolymerization of polymer chain and the formation of low-molecular fractions. The modified mineral fillers contributed to the decrease in the rate of tribodestruction of basic copolymer chain by retarding the active oxidation of friction surfaces. Because of these processes, the increase in wear-resistance and the decrease in the coefficient of friction were obtained.     

Degradation of fullerene C60 by human myeloperoxidase and some reaction products

Abstract

The biodegradation of the fullerene molecule C₆₀ under the action of the human myeloperoxidase enzyme accompanied by a complete loss of the topology of the fullerene core. Analysis of this reaction mixture using UV and FTIR spectroscopy, chromatographic and mass spectrometry methods showed that the degradation proceeds without the formation of significant amounts of hydroxylated compounds. Among other intermediate compounds aromatic compounds were detected.     

Roasting of the sulfide-zinc concentrate with predominant obtaining of sulfate roast for effective leaching

Roasting the sulfide-zinc concentrate with a high silver content is investigated by thermogravimetric and differential thermal analyses in the mode of polythermal heating. It is shown that roasting at 630 ± 10°C makes it possible to obtain mostly sulfate roast, which is most suitable for the effective recovery of zinc and other components.     

2D simulation of generation of difference-frequency radiation by few-cycle laser pulse in thin crystal of GaAs

We present the results of theoretical study of generation of difference frequency radiation in interaction of few-cycle laser pulse with a GaAs thin crystal. 2D numerical time-integration of system of nonlinear Maxwell equations for the TE_y mode has been performed by the finite-difference method. We consider the interaction of linearly-polarized pulse having the central wavelength of 1.98 ??m, duration of 17.16 fs and the electric field amplitude E _x0,max = 100 MV/m, propagating along the normal to the ??110?? plane in the 14.74 ??m-thickness GaAs crystal. The beam waist of initial linearly polarized pulse varies from 5.94 ??m to 9.9 ??m. The process of generation of difference frequency radiation (DFR) pulses arising at the output of nonlinear crystal via spectral filtration of formed supercontinuum is studied. The dependence of difference frequency generation efficiency on the beam waist is examined.     

Undoped polyaniline–surfactant complex for corrosion prevention

Due to the strict regulations on the usage of heavy metals as the additives in the coating industries, the search for effective organic corrosion inhibitors in replacement of metal additives has become essential. Electrically conducting polymers have been shown to be effective for corrosion prevention, but the poor solubility of these intractable polymers has been a problem. We have explored a polyaniline–4-dodecylphenol complex (PANi–DDPh) to improve the dissolution, and it has been shown to be an effective organic corrosion inhibitor. With the surfactant, DDPh, PANi could be diluted into the coatings, and the properties of the coatings were affected. An emeraldine base (EB) form of PANi was also found to be oxidized by the hardener. The oxidized form of polyaniline provides improved corrosion protection of metals than that of emeraldine base since the value of the standard electrode potential for the oxidized form of PANi is higher than that of EB. Additionally, the surfactant improves the wet adhesion property between the coating and the metal surface. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2849–2856, 1999     

Concomitant processes in the redox switching of polyaniline

It is shown for the first time that the redox switching of polyaniline (PANI) under voltammetric conditions is accompanied by the following processes: oxidation of PANI by atmospheric oxygen in the range of low potentials (E < 0.2 V); reduction with addition of aniline (post-polymerization) at E > 0.2(5) V, which in the range 0.2(5) < E < 0.5 V compensates entirely for the oxidation over the timescale of the cyclic voltammogram. These processes determine: (a) the existence of the emeraldine (conducting) state in a potential window (instead of at a defined potential); (b) the fundamental asymmetry in the redox behaviour of PANI; (c) the difference in the rates of the oxidation and reduction transients and (d) the dependence of the electrochemical activity of PANI on the pH of the medium.     

Liquid–liquid phase separation and crystallization of polydisperse isotactic polypropylene solutions

Phase diagrams were calculated based on Flory-Huggins solution thermodynamics to investigate the effects of polydispersity of polymer molecules and interaction parameter on the phase equilibria of crystallizable polymer solutions. The polydispersity was modeled with blends of two monodisperse polymers differing in chain lengths as a simplification. It was found that a longer chain length component could be separated easily to a polymer-rich phase by liquid demixing, but a shorter chain length component might exist at relatively constant concentration in each phase on fractionation. The influence of polydispersity on the liquid–solid phase equilibrium was small, and the phase boundary could be moved significantly in the region of low concentration of polymer by a small change of temperature. Liquid–liquid phase separation was more sensitive to the interaction between polymer and solvent than liquid–solid phase transition. Numerical calculations showed that the temperature at which liquid–liquid phase separation was coupled with liquid–solid phase equilibrium increased with a lower concentration of the polymer due to polydispersity of polymer chain lengths, and this phenomenon was observed at a lower temperature with more favorable interaction. The results were consistent with the experimental observations of isotactic polypropylene solutions. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 849–857, 1998