Tricholoroisocyanuric Acid as a Useful Reagent in Microwave‐assisted Aromatization of 1,3,5‐Trisubstituted 2‐Pyrazolines

An efficient aromatization of 1,3,5‐trisubstituted 2‐pyrazolines to their corresponding pyrazoles has been performed by tricholoroisocyanuric acid [TCCA] under microwave irradiation in excellent yields. It has been observed that the reactions occur more rapidly under microwave irradiation conditions, and the amount of the reagent TCCA consumed is considerably reduced to afford better yields when compared with conventional thermal conditions at the same temperature.     

Mild Oxidation of 1,3,5‐Trisubstituted Pyrazolines with N‐Bromo‐sulphonamides

1,3,5‐Trisubstituted pyrazolines to pyrazoles are carried out efficiently in the presence of new reagents N,N,N′, N′‐tetrabromo‐benzene‐1,3‐disulfonylamine [TBBDA] and N,N′‐dibromo‐N,N′‐1,2‐ethanediylbis‐(p‐toluenesulphonamide) [BNBTS] in solvent‐free conditions with catalytic amounts of SiO₂ under microwave irradiation in high yields.     

A novel life management model consists of chemical aging model and electrical-thermal aging model for power transformers using a new activation energy calculation method

Power transformers aging is investigated by a chemical aging model and an electrical-thermal aging model. In the chemical aging model, oil and cellulose chemical status are considered, but transformer load is not considered, while in the electrical-thermal model, only the effects of load and hotspot temperature are considered. The primary purpose of this paper is to combine both aging models to achieve a transformer life management model that considers the effect of all chemical parameters and the transformer load current simultaneously. Combining one chemical and one electrical-thermal aging model to reach a life management model for the transformer means that the remaining life of the transformer is first estimated using the chemical aging model by the provided equations for pre-exponential factor and activation energy in this paper. For this estimation, after conducting scientific studies, including experimental studies and computation on measurement results, an empirical mathematical equation will be presented to calculate the activation energy. Then using the presented equation, the remaining life will be estimated more accurately. Then, in the next step, this estimated life will be used in the electrical-thermal aging model and finally, a hotspot temperature will be calculated for the transformer. Finally, using the proposed hotspot temperature value and presented equations in this paper, a load current will be determined, which is recommended that the transformer load should not exceed that value. Finally, the proposed equation for activation energy calculation and the presented life management model validation will be verified using some transformers measurement results.

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Linear time optimal approaches for reverse obnoxious center location problems on networks

This paper is concerned with a reverse obnoxious (undesirable) center location problem on networks in which the aim is to modify the edge lengths within an associated budget such that a predetermined facility location on the underlying network becomes as far as possible from the existing customer points under the new edge lengths. Exact combinatorial algorithms with linear time complexities are developed for the problem under the weighted rectilinear norm and the weighted Hamming distance. Furthermore, it is shown that the problem with integer decision variables can also be solved in linear time.     

Evidence for electron‐based ion generation in radio‐frequency ionization

Radio‐frequency ionization (RFI) is a novel ionization method coupled to mass spectrometry (MS) for analysis of semi‐volatile and volatile organic compounds (VOCs). Despite the demonstrated capabilities of RFI MS for VOC analysis in both positive‐ and negative‐ion modes, mechanism of RFI is not completely understood. Improved understanding of the ion generation process in RFI should expand its utility in MS. Here, we studied the possibility of electron emission in RFI using both direct charged particle current measurements and indirect electron detection in a 9.4‐T Fourier transform‐ion cyclotron resonance (FT‐ICR) mass spectrometer. We show that RF‐generated electrons can be trapped in the ICR cell and, subsequently, reacted with neutral hexafluorobenzene (C₆F₆) molecules to generate C₆F₆^●?. Intensity of observed C₆F₆^●? species correlated with the number of trapped electrons and decreased as a function of electron quenching period. We also measured the electron attachment rate constant of hexafluorobenzene using a post‐RF electron trapping experiment. Measured electron attachment rate constant of hexafluorobenzene (1.19 (±0.53) × 10^?9 cm³ molecule^?1 s^?1) for post‐RF FT‐ICR MS agreed with the previously reported value (1.60 (±0.30) × 10^?9 cm³ molecule^?1 s^?1) from low‐pressure ICR MS measurements. Experimental results from direct and indirect electron measurements suggest that RFI process involves RF‐generated electrons under ultrahigh vacuum conditions. Copyright © 2015 John Wiley & Sons, Ltd.     

A characterization of the finite simple group L<Subscript>16</Subscript>(2) by its prime graph

In this paper as the main result we prove that the projective special linear group L ₁₆(2) is uniquely determined by its prime graph. In fact we give a positive answer to an open problem arose in Zavarnitsin (Algebra Logic 43(4), 220–231, 2006) and we obtain a first example of a finite group with connected prime graph which is uniquely determined by its prime graph. This research was in part supported by a grant from IPM (No. 86200023).