Effects of photoaging on the tribological properties of engineering plastics

Ball‐on‐disk tests were performed to investigate the effects of photoaging on the tribological properties of engineering plastics under dry sliding. Results exhibit that different molecular structures of plastics result in different aging morphologies, and ultra high molecular weight polyethylene has better resistance to photoaging than polyformaldehyde (POM). However, POM has better wear resistance before and after the photoaging. Marked increase of the width and depth of wear tracks is observed after aging. Analysis of worn surface has revealed that photoaging significantly affects the wear mechanism of ultra high molecular weight polyethylene and POM. Although the major wear mechanism before the aging of materials is identified as plastic deformation and adhesive wear, it becomes quite complicated when the materials experienced photoaging. Such complex wear mechanism hence deteriorates the tribological performance of the engineering plastics. Copyright © 2014 John Wiley & Sons, Ltd.     

Design,synthesis, antitubercular and antibacterial activities of pyrrolo[3,2-b]pyridine-3-carboxamide linked 2-methoxypyridine derivatives and in silico docking studies

Abstract

A novel series pyrrolo[3,2-b]pyridine-3-carboxamide linked 2-methoxypyridine derivatives have been designed, synthesized and confirmed by FT-IR, ¹H NMR, ¹³C NMR, ¹⁹F NMR, MS, and elemental analysis. The synthesized compounds were screened for their antitubercular activity using microplate alamar blue assay method and antibacterial activity. Among the tested compounds, 4- fluorophenyl (8m), 4- chlorophenyl (8n) and 4-methoxyphenyl (8i) showed potent anti-TB activity (3.12?µg/mL) in comparison with reference drug, Pyrazinamide ((3.12?µg/mL). In addition, all compounds were docked into DprE1 (PDB code: 4KW5) to explore their binding interactions at the active site. The compounds exhibited essential key interactions as that of reported DprE1 inhibitors and hence, the synthesized compounds may be considered as molecular scaffolds for antitubercular activity. Compounds, 4-chlorophenyl (8n) and 4-flurophenyl (8m) showed significant antibacterial activity against Escherichia coli and Staphylococcus aureus strains. In silico prediction of toxicities, druglikeness and drug score profiles of the tested compounds are promising.     

Kinetics and Mechanism of the Oxidation of Some Aldoses by Cerium(IV)

Abstract

The kinetics of oxidation of some aldoses by cerium(IV) have been studied spectrophotometrically in sulphuric acid medium. The reactions are second order; first order with respect to both cerium(IV) and aldose concentration. The reaction rate decreases with increase in sulphuric acid concentration. The mechanisms for the reactions are discussed.     

Application of potentiometric stripping analysis with constant inverse current for determining soluble lead in human teeth

A method for the determination of soluble lead in human teeth by potentiometric stripping analysis with constant inverse current in the analytic step (PSA-i_R), is described. The metal ions were concentrated as their amalgams on the glassy carbon surface of a working electrode that was previously coated with a thin mercury film and then stripped by a suitable oxidant. This paper examined effect of various factors on the PSA-i_R results including the electrolysis potential, the solution stirring rate, and the constant inverse current. Quantitative analysis was carried out by both standard addition and calibration curve methods; a good linearity was obtained in the concentration range from 5 to 25 μg/dm³. A detection limit of 0.64 μg/dm³ was obtained, with a 5.21% coefficient of variation. Results obtained for teeth were not significantly different from these obtained by flameless atomic absorption spectrophotometry (FAAS).     

Refractive Indices and Dielectric Studies of Three Phenylcyclohexane Liquid Crystals in the Nematic Phase

The refractive indices n_e, n_o and densities and the dielectric primittivities ε_∥ and ε_⊥ of three P-cyano-P-alkylcyclohexanes (PHC-3, PCH-5, PCH-7) have been measured at different temperatures. The order parameters calculated by using Neugebauer and Vuks' methods were comparable. A comparison of order parameters of the PCH with the corresponding alkylcyanobiphenyls at reduced temperatures τ (= T-T_NI/T_NI) shows that the replacement of a phenyl ring with a cyclohexyl ring decreases the order parameter appreciably. The experimental values of dielectric permittivities ε_⊥ in each of the PCHs are found to be less than half of the ε_⊥-value calculated from Maier and Meier equations using the polarizability and the order parameter obtained from refactive index measurements. This was explained as due to short range antiparallel ordering of strongly polar molecules in the nematic phase, as proposed by Chandrasekhar and Madhusudan, which was not taken into consideration in Maier and Meiers' theory     

A k-Sample Test for Functional Data Based on Generalized Maximum Mean Discrepancy

Lithuanian Mathematical Journal - In this paper, we deal with the problem of testing the equality of k probability distributions. We introduce a generalization of the maximum mean discrepancy that...     

Diagnostics-based Approach to Vibration Surveillance during High Speed Milling of Flexible Details

The paper concerns vibration surveillance during ball end milling of curved flexible details and considering assurance of parameters of a modal subsystem. Here is explained dynamic analysis of non-stationary vibrating system, from which are separated subsystems: modal, structural and connective. Minimising vibration level by matching the spindle speed to optimal phase shift has been employed. Two alternatives of the approach have been developed. The first one is based on generalised condition of optimum spindle speed and relates to diagnosis of chatter vibration with only one detected frequency. The second approach concerns a few harmonic components having different frequencies. Obtained results of production experiments proved a meaning of the approaches. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)