Materials Literature
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The electric properties of an air gap between a hemisphere-rod covered with 3 mm thick silicone rubber and plane metal electrode have been examined. Observation of discharge activity and measurement of the discharge current have been made under impulse voltage stress. When applying an impulse voltage close to the ince…
In view of interest in the emulsion polymerization of octamethylcyclosiloxane, (D4), the stability of droplets of monomer D4 against Ostwald ripening was studied and shown to obey the LSW theory at room temperature. The emulsifier was sodium dodecyl benzylsulfonate and the mixture was initially sonicated for a few min…
Dibenzodioxadiselenafulvalene (DBOSF) was prepared and the cis and trans isomers were separated. X-ray crystallographic analysis revealed the presence of Se- - -H and O- - -H hydrogen bonds in both crystals. The electrochemical properties of cis- and trans-DBOSFs together with dibenzotetraoxafulvalene (DBTOF) and cis-…
Bacterial adhesion is an important initiating step of microbial contamination in the paper and board industry. The adhesion process results from interactions between the cell surface, the liquid, and the fibers. In this context, we determined the cellulose pulp surface energy to better understand these interactions. A…
Since a few decades, the pulsed electro acoustic (PEA) method is used for measuring space charge in insulating materials. Through the years, the PEA method has been mainly applied on flat homogeneous dielectrics. However, this technique has been recently used on multi-layer dielectrics as well. In this case, particula…
Behaviors of insulation system are strongly affected by frequency of the system voltages. In addition to power-frequency voltage, the insulation system could be also exposed to a voltage with frequency on the order of kHz due to application of new HV devices. Insulation failures under HF voltages occur not only becaus…
Abstract Polarized Raman and IR spectra were obtained for NaBi(WO 4 ) 2 crystal at ambient temperature. Assignment of the observed bands to the respective internal and external phonons was proposed on the basis of lattice dynamics calculations. The spectra showed also the appearance of additional Raman and IR bands wh…
This paper demonstrates the use of a dielectric spectroscopy technique for monitoring the effect of different ageing: ultra violet radiation (UV), thermal, water immersion, humidity and water boiling on silicone rubber, ethylene-propylene diene monomer (EPDM) and alloy of SIR-EPDM (50/50 wt%). The measurement of diele…
Real insulation systems are often heterogeneous and sometimes non-linear. In this paper we discuss the application of dielectric frequency response methods to a number of such practically important systems. Important examples of composite insulation systems are the oil/cellulose insulation of power transformers and th…
Abstract Graft copolymers consisting of amorphous main chain, poly(methyl methacrylate) (PMMA), or poly(methyl acrylate) (PMAc), and crystalline side chains, poly(ethylene glycol) (PEG), have been prepared by copolymerization of PEG macromonomers with methyl methacrylate or methyl acrylate (MMA x or MAC x , respective…
Derivatives of bufogenin isolated from the skin of the Chinese toad, Bufo bufo gargarizans Cantor ("Ch'an Su"), and several semisynthetic derivatives of 20beta,21beta-epoxy-resibufogenin (13) have been evaluated for interleukin-6 (IL-6) antagonistic activity due to their growth-inhibitory activities on IL-6-dependent…
Six new triterpenoid saponins were isolated as methyl or butyl esters from an n-BuOH extract of the roots of Symplocos chinensis. Their structures were established as symplocososides A (1), B (2), C (3), D (4), E (5), and F (6), by extensive 1D and 2D NMR as well as HR-MS analysis and chemical methods. Compounds 1, 3,…
Abstract Three oxamido‐bridged tetranuclear complexes with the formulae [(LCu)Cu(LCuSCN) 2 ]·H 2 O ( 1 ), [(LCu)Mn(LCuSCN) 2 ]·1.38CH 3 OH ( 2 ) and {(LCu)Mn[LCuN(CN) 2 ] 2 }·0.75DMF·0.25H 2 O ( 3 ) (where H 2 L = 2,3‐dioxo‐5,6:15,16‐dibenzo‐1,4,8,13‐tetraazacylotetradeca‐7,13‐diene) have been prepared and characteris…
Here we show that electrochemical equilibrium voltage curves of amorphous WO3 and TiO2 coatings exhibit fine structure in striking agreement with the density of states in the conduction bands, as obtained by ab initio calculations for the crystalline counterparts. We suggest that localization of the band states is ess…
The present paper reports about the results of a study of mechanical, thermal, dynamic mechanical and electrical properties of polymeric insulators. Silicone rubber, ethylene-propylene-diene monomer (EPDM) and alloys of silicon-EPDM are known polymers for use as high voltage insulators. The result of dynamical mechani…
Born in 1985, the PEA technique consists in detecting acoustic waves generated by space charges when they are subjected to an impulse of electric field. Its principle is relatively simple to understand and its use is very flexible. Compared to other techniques as LIPP (Laser Induced Pressure Pulse) method and TSM (The…
Abstract Banana pseudostem fiber which is a lignocellulosic material, relatively inexpensive, and abundantly available was assessed in terms of its fiber‐matrix adhesion and dispersion in composites. Different types of adhesives were used. The mechanical and water absorption properties were investigated. Overall, for…
Abstract The recovery properties of dry and water saturated polyamide 6 (PA6) and its copolymer PA6/66 (ratio 4:1 by mol) were studied at elevated temperatures above the glass‐transition temperature in uniaxial tensile tests. The data yield critical points along the true stress–strain curves at which the differential…
Abstract We performed temperature‐dependent Raman scattering studies on K 0.2 Na 0.8 NbO 3 ceramics and compared the results with those for NaNbO 3 . The wavenumbers associated with NbO 6 vibrations suggest the existence of two phase transitions, as occurs with pure NaNbO 3 ceramics. Although the disorder on the Na/K…
Decarboxylation of orotidine 5'-monophosphate (Omp) to uridine 5'-monophosphate by orotidine 5'-monophosphate decarboxylase (ODCase) is currently the object of vivid debate. Here, we clarify its enzymatic activity with long time scale classical molecular dynamics and hybrid ab initio Car-Parrinello/molecular mechanics…