Density functional study on the functionalization of BN nanotubes with nitramide

Chemical functionalization of a boron nitride nanotube (BNNT) with nitramide molecule (H₂NNO₂) has been investigated using density functional theory. It was found that the molecule prefers to be adsorbed and dissociated on a diagonal B-N bond of the tube surface so that the -NH₂ and -NO₂ groups are attached on B and N atoms, releasing energy of 0.50 eV. The results show that the functionalized BNNT is more soluble than the pristine one which may render the chemical modification process to be an effective way for purification of the BNNTs. Depending on the cleavage behavior of nitramide on the tube, HOMO/LUMO gap of the system can be either decreased or increased while the chemically modified BNNT is still a semiconductor. Furthermore, the chemical functionalization results in hindered field emission in the tube by raising the potential barrier of the electron emission.     

The ab initio study and NBO analysis of the solvent dielectric constant effects and the implicit water molecules on the structural stability of the 1-(6-chloroquinoxalin-2-yl)-2-(4-(trifluoromethyl)-2,6-dinitrophenyl) hydrazine

Ab initio molecular orbital (MO) and density functional theory (DFT) methods were used to analyze the structure and the relative stability of 1-(6-chloroquinoxalin-2-yl)-2-(4-(trifluoromethyl)-2,6-dinitrophenyl) hydrazine in gas phase and the different solvent media. The effects of solvent dielectric constant and the implicit water molecules were investigated on the structural stability and intramolecular interactions. All used methods revealed that by the increase of solvent dielectric constant, the relative stability of the considered compound increase. Hence, the most stable structure is perceived in aqueous solution. Furthermore, natural bond orbital (NBO) analysis demonstrated that in the presence of implicit water molecules, the lone pair electrons of nitrogen have the most contribution in the resonance interactions of the aromatic rings and their stability. These facts may be the probable reasons behind the structural stability of the considered structure in the water solution based on energetic data and NBO analysis at the microscopic level.     

NMR imaging of polyethylene pipes

¹H nuclear magnetic resonance (NMR) imaging techniques have been used to image the extrusion aid (EA) in polyethylene (PE) pipe samples. The resulting two-dimensional images show the distribution of EA within the pipe. EA is found to be uniformly distributed in a normal pipe. Examples of degraded pipes, due to exposure to extreme conditions, show migration of EA to the pipes' wall surfaces. NMR images of a normal pipe and two examples of damaged pipes are presented. The imaging technique and the results are discussed. © 1995 John Wiley & Sons, Inc.     

TiCl3OTf-[bmim]Br: a novel and efficient catalyst system for chemoselective one-pot synthesis of thioamides from arylaldoximes

The combination of TiCl₃OTf with 1-butyl-3-methylimidazolium bromide is found to be an efficient and novel catalytic system for chemoselective one-pot transformation of arylaldoximes to their corresponding thioamides in high to excellent yields.     

Local nonglobal minima for solving large-scale extended trust-region subproblems

We study large-scale extended trust-region subproblems (eTRS) i.e., the minimization of a general quadratic function subject to a norm constraint, known as the trust-region subproblem (TRS) but with an additional linear inequality constraint. It is well known that strong duality holds for the TRS  and that there are efficient algorithms for solving large-scale TRS  problems. It is also known that there can exist at most one local non-global minimizer (LNGM) for TRS. We combine this with known characterizations for strong duality for eTRS  and, in particular, connect this with the so-called hard case for TRS. We begin with a recent characterization of the minimum for the TRS  via a generalized eigenvalue problem and extend this result to the LNGM. We then use this to derive an efficient algorithm that finds the global minimum for eTRS  by solving at most three generalized eigenvalue problems.     

On self-regular IPMs

Primal-dual interior-point methods (IPMs) have shown their power in solving large classes of optimization problems. However, at present there is still a gap between the practical behavior of these algorithms and their theoretical worst-case complexity results, with respect to the strategies of updating the duality gap parameter in the algorithm. The so-called small-update IPMs enjoy the best known theoretical worst-case iteration bound, but work very poorly in practice. To the contrary, the so-called large-update IPMs have superior practical performance but with relatively weaker theoretical results. In this paper we discuss the new algorithmic variants and improved complexity results with respect to the new family of Self-Regular proximity based IPMs for Linear Optimization problems, and their generalizations to Conic and Semidefinite Optimization This research was supported by the MITACS project “New IPMs and Software for Convex Conic-Linear Optimization and Their Application to Solve VLSI Circuit Layout Problems”, by an NSERC discovery grant, and the CRC program. The first author would also like to thank the Iranian Ministry of Science, Research and Technology for supporting his research.     

Sub-100 nm structuring of indium-tin-oxide thin films by sub-15 femtosecond pulsed near-infrared laser light

In magnetron sputtered indium-tin-oxide thin films of varying oxygen content, nanostructures were formed using tightly focused high-repetition rate near-infrared sub-15 femtosecond pulsed laser light. At radiant exposure well beyond the ablation threshold, cuts of 280-350 nm in width were generated. Illumination close to the ablation threshold resulted in periodic cuts of typically 20 nm in width at periodicities between 50 nm and 180 nm, as well as single sub-20 nm cuts. Subthreshold exposure, in combination with hydrochloric acid etching, yielded nanowires of 50 nm minimum lateral dimensions.     

Density functional study on the sensing properties of nano-sized BeO tube toward H2S

Using density functional calculations, we have investigated the adsorption of a H₂S molecule on the pristine and Si-doped BeO nanotubes (BeONT). It was found that the H₂S molecule is physically adsorbed on the pristine BeONT with adsorption energies ranging from 3.0 to 4.2 kcal/mol. Substituting a Be or O atom of the tube by Si increases the adsorption energy to 6.9–17.2 kcal/mol. We found that substituting an O atom by Si makes the electronic properties of the BeONT strongly sensitive to the H₂S molecule. Therefore, the process of Si doping provides a good strategy for improving the sensitivity of BeONT to toxic H₂S, which cannot be trapped and detected by the pristine BeONT. Also, the emitted electron current density from the Si_O–BeONT will be significantly increased after the H₂S adsorption.     

Selective Sensing Characteristics of Ca Doped BeO Nano-sized Tube toward H20 and NH3

By means of density functional calculations, the structural and electronic properties of chemical modification of pristine and Ca-doped BeO nanotubes were investigated with NH3 and H20 molecules. It was found that the NH3 and H20 molecules can be adsorbed on the Be atom of the tube sidewall with the adsorption energies of about 36.1 and 39.0 kcal/mol, respectively. Density of states analysis shows that the electronic properties of the BeONT are slightly changed after the adsorption processes. Substitution of a Be atom in the tube surface with a Ca atom increases the adsorption energies by about 7.4 and 14.7 kcal/mol for NH3 and H20, respectively. Unlike the pristine tube, the electronic properties of Ca-doped BeONT are sensitive to NH3 and H20 molecules. Also, the Ca-doped tube is much more sensitive to H20 molecule than NH3 one.