A Theoretical Study on Nitrourea and its Tautomers

In the present study, nitrourea and its possible tautomers have been subjected to theoretical analysis by performing Hartree-Fock and also density functional theory (DFT) calculations. The optimized geometries, vibrational frequencies, and some thermodynamical values for the presently considered species have been obtained in their ground states.     

Process modification of a wire‐welding plant for efficient sulphate removal

Sulphate removal by chemical precipitation from the wastewater of a wire‐welding facility was investigated. Sulphate was precipitated by using limestone and a small amount of lime. Firstly, the relationship between the ionic strength of wastewater and sulphate removal efficiency was established. A kinetic study of sulphate precipitation was also conducted. Finally, modification of plating process was proposed to achieve the highest sulphate removal. According to the suggested modification, the sulphate concentration of final discharge could be down to 425 mg/L. Hence, if wire‐welding facilities modify their systems so that the wastewater is treated at the highest level of sulphate contents, the removal efficiency will be the highest, i.e. lesser amounts of sulphate will be discharged into sewage systems.     

The Electrochemical Generation of Ozone: A Review

This article reviews work on the electrochemical generation of ozone from the original studies by Schönbein in the early 1800s to the present day, and is intended for specialists and nonspecialists in the field of electrochemistry. The experimental techniques employed to study the mechanism of electrochemical ozone generation are described, as is the most commonly quoted mechanism and the experimental evidence for the mechanism is summarized and discussed. The types of electrochemical cells employed are described, and the effects of temperature, anode type and composition, current density and electrolyte composition and pH are discussed.     

Effects of cavity disinfectants on bond strength of an etch-and-rinse adhesive to water- or ethanol-saturated sound and caries-affected dentin

Objective: To evaluate the effect of cavity disinfectants on the immediate microtensile bond strength (μTBS) of an etch-and-rinse adhesive to water- and ethanol-saturated sound and caries-affected dentin (CAD). Material and Methods: Thirty-six human molars were sectioned to expose 1/3 of the mid-coronal dentin surface. Sound (n = 18) and CAD (n = 18) specimens were divided into six groups each (n = 3): one positive control (sound), one negative control (CAD), and five experimental groups each. In the control group, dentin surfaces were bonded using an etch-and-rinse adhesive with a traditional water-wet bonding technique. In the experimental groups, ozone was applied before etching and chlorhexidine after etching. In the ethanol-wet bonding groups, acid-etched dentin surfaces were treated with ethanol. Following adhesive application and composite buildups, bonded specimens were sectioned to form sticks. Failure modes were analyzed using a stereomicroscope. Results: The water-wet bonded sound control group yielded the highest μTBS among all groups (p < 0.001). The lowest μTBS values were observed in the ozone groups (p < 0.05). The ethanol-wet bonded CAD group exhibited a higher μTBS than the water-wet bonded negative controls. Although compared to the positive control, chlorhexidine decreased the μTBS (p < 0.05), an increase with no significant difference was observed in the negative control (p > 0.05). Conclusions: The μTBS values of CAD were lower than those of sound dentin. Ethanol-wet bonding improved the μTBS of CAD. Ozone application reduced the μTBS in both sound and CAD; chlorhexidine improved the immediate μTBS after etching in CAD.     

Computational studies on nitratoethylnitramine (NENA), its tautomers and charged forms

An energetic material, nitratoethylnitramine (NENA), its tautomers and also its charged forms are considered quantum chemically, using various basis sets at the levels of ab initio and density functional theories (DFT). NENA has been found to be sensitive to negative charge development, resulting in rupture of ONO(2) bond. Also conformational and molecular dynamics (MD) studies have been performed on NENA. Various geometrical parameters, energies and infrared spectra have been obtained and discussed. Also, calculations indicate that s-cis conformation of NENA is slightly more stable than the s-trans and the tautomers of it have very comparable total energy values to NENA. On the other hand, on the basis of homolytic bond dissociation energies (BDE) for ONO(2) bond in the structures, it is clear that the presence of the tautomers in the bulk of NENA somewhat should decrease its sensitivity.     

Biofilm formation by Staphylococcus aureus strains and their control by selected phytochemicals

Biofilm formation by 30 Staphylococcus aureus dairy isolates and their control by phytochemicals were investigated. The majority of strains were biofilm positive by phenotypic analysis. The nuc and icaA genes were present in 30 and 27 strains, respectively. In addition, 13 strains were positive for all nuc, clfA, fnbA and icaA genes. The antimicrobial and antibiofilm activities of citral, cinnamaldehyde, eugenol, farnesol, limonene and terpinen‐4‐ol were also evaluated for seven strains. It was shown that the use of farnesol, cinnamaldehyde or terpinen‐4‐ol at a concentration of 2 mg/mL could be at least 80% effective on S. aureus strains and their biofilms.     

Fabrication of calix[4]pyrrole nanofilms at the glassy carbon surface and their characterization by spectroscopic, optic and electrochemical methods

meso-Octamethylcalix[4]pyrrole (CP) and meso-heptaethylcalix[4]pyrrole-meso-4-aminophenyl (4APCP) modified glassy carbon (GC) electrodes were prepared by the electrochemical oxidation in acetonitrile solution. Binding of the calix[4]pyrroles with the glassy carbon surface was investigated that it is through the etheric linkage revealed from the reflection-absorption infrared spectroscopy (RAIRS). Surface films of CP and 4APCP were investigated by cyclic voltammetry (CV), ellipsometry, X-ray photoelectron spectroscopy, RAIRS and the contact angle measurements. The thicknesses of the films were determined by ellipsometry which confirmed that the film was multilayer and homogeneous over the surface. Ellipsometric measurements also provided that the CP and 4APCP film thicknesses were 2.49 nm and 4.58 nm for 6 CV cycle modification, corresponding to 66 μF/cm² and 106 μF/cm² capacitances obtained by CV. The wetting behavior was examined by contact angle measurements and found that the hydrophobicity of the GC-4APCP surface was higher than that of GC-CP, probably due to the aromatic meso substituent present in the former.     

Fracture characteristics of high impact polystyrene under impact fatigue loadings

This study analyses the impact properties of high impact polystyrene (HIPS). HIPS is one of the well-known toughened polymers. The high toughness is given by the rubbery phase. The impact fatigue behavior of HIPS was studied with a Ceast pendulum type tester (Resil 25). The fracture mechanisms were examined with a scanning electron microscopy. The nature of crack initiation and propagation was investigated for small impact angles and three different spans. The impact angles of charpy hammer were chosen as 5°, 10°, 15°, 20°, and 25°. The fracture characteristics varied with the impact angle, the number of impacts, and the distance between supports. The rate of crack propagation was high at higher impact angles with lower endurance, and low at lower impact angles with higher endurance.     

Innovation zur Bestimmung der Erdstoff‐Geokunststoff‐Wechselwirkung – Pullout‐, Scher‐ und Reibungsversuche

Innovation for the determination of the soil‐geosynthetic interaction – pullout‐, shear‐ and friction tests. The use of the economical and ecological construction material “geosynthetic” plays a rapidly increasing role in a variety of civil engineering, mining and environmental protection applications. Geosynthetics captured their own place as construction material due to their diversity and their specific characteristics. The applications of geosynthetics are many‐sided. In the form of geotextiles, geogrids, geomembranes and related products, they make technically simple and low‐priced alternative solution concepts possible. For the stability analysis of geosynthetic constructions knowledge of the friction behaviour in the geosynthetic interfaces is essential. For the assessment of the main failure mechanisms of a geosynthetic reinforced construction shear‐ and friction tests are usually performed as well as now also Pullout tests. In the following, a novel experimental apparatus for the examination of the interaction behaviour of soil‐geosynthetic compound systems capable of performing both pullout and direct shear tests is described. In comparison with known geosynthetic testing practice, the novel testing apparatus offers the special advantage that a wide range of innovative shear and pullout test procedures can be carried out in the same device with negligible influence of test device configurations on friction test results.