Vibrations of single- and double-walled carbon nanotubes with layerwise boundary conditions: A molecular dynamics study

In the present work, the vibration characteristics of single- and double-walled carbon nanotubes under various layerwise boundary conditions at different lengths are investigated. This is accomplished by the use of molecular dynamics simulations based on the Tersoff-Brenner and Lennard-Jones potential energy functions. The effects of initial tensile and compressive strains on the resonant frequency of carbon nanotubes are also taken into consideration. From the results generated, it is observed that the natural frequency of carbon nanotubes is strongly dependent on their boundary conditions especially when tubes are shorter in length. The natural frequency and its dependence on tube end conditions reduce by increasing the tube length. The natural frequency of DWCNTs lies between those of the constituent inner and outer SWCNTs and is nearer to those of the outer one. It is further observed that the natural frequency is highly sensitive to tensile and compressive strains. The frequency shift occurring in the presence of small initial strains is positive for tensile strains and negative for compressive strains. The results obtained provide valuable information for calibrating the small scaling parameter of the nonlocal models for the vibration problem of carbon nanotubes.     

聚 (4-乙烯基吡啶硝酸盐)、硅硫酸和溴化铵催化氧化硫化物生成亚砜

 A new catalytic procedure for the chemoselective oxidation of sulfides to sulfoxides was studied. A variety of aliphatic and aromatic sulfides were subjected to sulfoxidation by combining poly(4-vinyl pyridinium nitrate), silica sulfuric acid (SiO₂-OSO₃H), and catalytic amounts of ammonium bromide in CH₂Cl₂ in the presence of a few drops of water at room temperature. Excellent yields were obtained.     

Hetero-cope rearrangements of nitrosobutenes. DFT studies of thermal and acid-catalyzed reactions

[Structure: see text] Density functional theory studies of the hetero-Cope reactions of 4-nitroso-1-butenes and nitrosobicyclo[2.2.2]hexenes are reported. The reactions proceed via concerted mechanisms. The electron-withdrawing methoxycarbonyl group alpha- to the nitroso group decreases the activation barrier. Lewis acids such as SbF5 and TiCl4 accelerate the reactions, as has been found experimentally by Zakarian and Lu.     

Domino synthesis of novel series of 4-substituted 5-thioxo-1,2,4-triazolidin-3-one derivatives

The efficient synthesis of 4-substituted 5-thioxo-1,2,4-triazolidin-3-one derivatives (4-substituted thiourazoles) via domino combination of thiophosgene, aliphatic or aromatic amines, and ethyl carbazate is presented.     

Heat transfer analysis of energy and exergy improvement in water-tube boiler in steam generation process

Journal of Thermal Analysis and Calorimetry - Steam generation is an essential process in steel production. Saturated steam is used in the cold-rolling mills of sample steel company to raise the...     

Polyvinylpolypyrrolidonium tribromide as new and metal-free catalyst for the formylation and trimethylsilylation of hydroxyl group

Trimethylsilylation of alcohols was achieved using 1,1,1,3,3,3-hexamethyldisilazane(HMDS) as silylating agent,in the presence of polyvinylpolypyrrolidonium tribromide in acetonitrile at room temperature.Also a variety of alcohols were converted into alkyl formates by ethyl formate and a catalytic amount of polyvinylpolypyrrolidonium tribromide under solvent free conditions at room temperature.     

Poly(4-vinylpyridinium tribromide) as metal-free and recoverable oxidizing agent for the selective oxidation of alcohols, and oxidative deprotection of trimethylsily ethers

Poly(4-vinylpyridinium tribromide) was found to be an efficient oxidizing polymer for the chemoselective oxidation of a wide range of alcohols into aldehydes and ketones. In addition it was used for the oxidative deprotection of trimethylsilyl ethers into alcohols or carbonyl compounds depending on the structure of trimethylsilyl ether.     

Synthesis of new zirconium complex supported on MCM‐41 and its application as an efficient catalyst for synthesis of sulfides and the oxidation of sulfur containing compounds

In the present work, we report synthesis of new zirconium complex supported on mesoporous silica by anchoring of adenine on the wall of functionalized MCM‐41, then reacted with ZrOCl₂. The resultant MCM‐41‐Adenine‐Zr was characterized by FT‐IR, XRD, TEM, SEM, TGA, EDX, ICP and BET techniques. It was exhibited that the MCM‐41‐Adenine‐Zr can be used as an efficient and thermally stable nanocatalyst for the oxidation of sulfides, oxidative coupling of thiols and synthesis of sulfides. Moreover, this heterogeneous catalyst can be easily recovered from the reaction mixture by simple filtration and reused for several consecutive cycles without noticeable change in its catalytic activity.