br Method The initial geometry optimizations of all

Method The initial geometry optimizations of all the structures leading to AG-14361 minima were achieved by using MM2 method followed by semi-empirical PM3 self-consistent fields molecular orbital (SCF MO) method [26,27] at the restricted level [28,29]. Subsequent optimizations were achieved at Hartree-Fock level using various basis sets. Then, geometry optimizations were managed within the framework of density functional theory (DFT, B3LYP) [30,31] finally at the levels of 6–31++G (d,p) (restricted closed-shell) or CC-PVTZ [28,32]. The exchange term of B3LYP consists of hybrid Hartree–Fock and local spin density (LSD) exchange functions with Becke\'s gradient correlation to LSD exchange [31,33]. The correlation term of B3LYP consists of the Vosko, Wilk, Nusair (VWN3) local correlation functional [34] and Lee, Yang, Parr (LYP) correlation correction functional [35]. The vibrational analyses were also done. The total electronic energies are corrected for the zero point vibrational energy (ZPE). The normal mode analysis for each structure yielded no imaginary frequencies for the 3N−6 vibrational degrees of freedom, where N is the number of atoms in the system. This indicates that the structure of each molecule corresponds to at least a local minimum on the potential energy surface. All these calculations were done by using the Spartan 06 package program [36].
Results and discussion A nitramine type explosive, known as simply DINGU, is constitutionally cis-1,4-dinitroglycoluril [25]. However, it should have also trans form which has not been synthesized yet. In addition to that either cis or trans forms of dinitroglycoluril should have other isomers which possess the nitramine group at different positions of the bicyclic system. In the present study, trans-dinitroglycoluril skeleton is considered in which three isomers exist arising from positional variations of the nitramine groups and they are indicated by capital letters as A,B and C.
Conclusion Within the constraints of level of calculations performed presently, trans-dinitroglycoluril isomers exhibit highly structure-dependent properties that is the location of the nitramine group dictates various geometrical, physical and quantum chemical properties. Both in the vacuum and water the isomer having the nitramine groups farthest away from each other (isomer-C) is the most stable one. It is also true for the 1,3-tautomers considered. As for the protonated isomers, O-protonated ones are overall more stable than their N-protonated isomers and also the former ones are more stable than their respective N-protonated counterparts. The interaction of the isomers with proton in vacuum causes tertiary CH bond to cleave from relatively less stable isomers, A and B, but the most stable isomers (C) remains intact. All these results might provide some insight for researchers interested in trans-dinitroglycoluril isomers.
Introduction Aluminum alloy 6061-T6 is widely utilized in aircraft, defence, automobiles and marine areas due to their good strength, light weight and better corrosion properties. But, they exhibits inferior tribological properties in extensive usage [1]. Aluminum matrix composites (AMCs) which are produced by reinforcing Aluminum alloys with particles like SiC, Al2O3 and TiB2 etc., are the new generation materials. These AMCs exhibit higher properties than parent alloy such as stiffness, improved tribological characteristics and high strength. Further these properties can be enhanced by using nano scale ceramic materials [2–4]. Distribution of nano reinforcement particles on Al alloy surface and its control is complex to achieve in conventional surface modification methods [4,5]. Earlier researches [6,7] reported that thermal spraying and laser beam techniques were utilized to prepare surface composites, in which it degrades the properties due to creation of unfavorable phases. These techniques operate at higher temperatures and impossible to avoid the reaction between the reinforcements and the matrix, which forms detrimental phase. A process can be employed which is operated at a below melting temperature of the matrix for the fabrication of surface composites which can be avoided the above mentioned problems. Considering these problems, Friction stir processing (FSP) is the best technique suited for preparation of surface composites and surface modification. In FSP, a rotating tool with the shoulder and pin is plunge onto the surface of a material, which creates frictional heat and dynamic mixing of material area underneath of the tool and it results to incorporate and/or disperse the reinforcement particles in the matrix material such as Aluminum alloys, Magnesium alloys and Copper alloys [8–12]. This investigation is aimed to fabricate the nano Titanium Boride (TiB2) particle reinforced 6061-T6 Al alloy surface nano-composites by using FSP. Extended to study, influence of volume percentage of nano sized TiB2 (average size is 35 nm) reinforcement particles on microstructural characterization, mechanical and tribological behaviour of 6061-T6 Al alloy based nano surface-composites prepared via FSP.