Direct measurement of the nitrogen content by XPS in self‐passivated TaNx thin films

The nitrogen content in tantalum nitride (TaN_x) thin films, where x indicates that TaN_x is not generally stoechiometric, can be measured directly by XPS. This is the purpose of the present study. However, the XPS spectra of TaN_x present electron energy loss spectroscopy (EELS) peaks that lead to a complex peak fitting, particularly for self‐passivated thin films. A complete peak fitting procedure based upon Tougaard's background, the Doniach‐Sunjic Function and EELS peaks, is presented. It is applied to two self‐passivated TaN_x thin films elaborated by reactive sputtering and presenting a different nitrogen content. The physical properties of these surfaces are interpreted in terms of Ta 4f_7/2 chemical states directly dependent on the nitrogen content. The main results are discussed and improvements are proposed to the method. Copyright © 2008 John Wiley & Sons, Ltd.     

Molecular dynamics simulation of aqueous solutions of 26-unit segments of p(NIPAAm) and of p(NIPAAm) "doped" with amino acid based comonomers

We have performed 75-ns molecular dynamics (MD) simulations of aqueous solutions of a 26-unit NIPAAm oligomer at two temperatures, 302 and 315 K, below and above the experimentally determined lower critical solution temperature (LCST) of p(NIPAAm). We have been able to show that at 315 K the oligomer assumes a compact form, while it keeps a more extended form at 302 K. A similar behavior has been demonstrated for a similar NIPAAm oligomer, where two units had been substituted by methacryloyl- l-valine (MAVA) comonomers, one of them being charged and one neutral. For another analogous oligomer, where the same units had been substituted by methacryloyl- l-leucine (MALEU) comonomers, no transition from the extended to the more compact conformation has been found within the same simulation time. Statistical analysis of the trajectories indicates that this transition is related to the dynamics of the oligomer backbone, and to the formation of intramolecular hydrogen bonds and water-bridges between distant units of the solute. In the MAVA case, we have also evidenced an important role of the neutral MAVA comonomer in stabilizing the compact coiled structure. In the MALEU case, the corresponding comonomer is not equally efficacious and, possibly, is even hindering the readjustment of the oligomer backbone. Finally the self-diffusion coefficient of water molecules surrounding the oligomers at the two temperatures for selected relevant times is observed to characteristically depend on the distance from the solute molecules.     

An efficient synthesis of hydropyrido[1,2-a]indole-6(7H)-ones via an In(III)-catalyzed tandem cyclopropane ring-opening/Friedel-Crafts alkylation sequence

An efficient Lewis acid-catalyzed cyclopropane ring-opening/Friedel-Crafts alkylation sequence of methyl 1-(1H-indole-carbonyl)-1-cyclopropanecarboxylates is reported. The protocol affords functionalized hydropyrido[1,2-a]indole-6(7H)-ones in up to 99% yield.     

Convenient and improved protocols for the hydrogenation of esters using Ru catalysts derived from (P,P), (P,N,N) and (P,N,O) ligands

An improved protocol where a pre-cursor, [Ru(Cl)(2)(NBD)(Py)(2)], is treated with ligands to form [RuCl(2)(bidentate ligand)(diamine)] pre-catalysts for ester hydrogenation is reported. This family of catalysts, as well as a range of ruthenium complexes of tridentate P^N^X (X = NR(2), OH) ligands have been investigated in the hydrogenation of aromatic esters. A range of aromatic esters can be hydrogenated in high yields at temperatures between 30 °C and 100 °C.     

HEAT TRANSFER TO DISPERSED SWIRL FLOW OF HIGH-PRESSURE WATER WITH LOW WALL SUPERHEAT

Heat transfer was studied to two-phase flow in the post-CHF dispersed flow regime under swirl conditions. Data were used for post-CHF water flow at high pressure, 15.9 MPa, inside a vertical tube with twisted-tape inserts. Data used were obtained under test conditions typical of heat exchanger operation with low wall superheats of 5-40°C. The mass flux range of the data was 910-1878 kg/m2 s, and three tape-twist ratios were used: 2.55, 5.03, and 7.52. The low wall superheat and the relatively high mass fluxes resulted in higher than predicted drop-wall heat transfer. The only existing heat transfer correlation for this flow situation was modified to include this heat exchanger parameter range.     

Cooperative Metal Binding and Helical Folding in Model Peptides of Treble‐Clef Zinc Fingers

Synergy in zinc fingers : The comparison between peptide folding and metal binding properties of two model peptides of treble‐clef zinc fingers presenting high affinities for zinc and cobalt reveals a cooperative effect: the metal folds the peptide into a α‐helix, which in turn strengthens the metal core.

     

Experimental investigation of subcooled flow boiling of a 50/50 ethylene glycol/water mixture in finned rectangular aluminum channels

Subcooled flow boiling heat transfer experiments were performed with a 50/50 ethylene glycol/water mixture in a finned aluminum channel. The channel represented a hybrid electric vehicle power electronic cold plate receiving a 50/50 mixture from the radiator at 105°C and 2 atmospheres. Experiments used a range of mixture flow rates and both top- and bottom-heating situations. Boiling curves were generated, and subcooled flow boiling heat transfer coefficients were determined including the test channel fin effects. Subcooled flow boiling heat transfer coefficients showed a 25–30% increase compared to single-phase convection.     

Beta-decay branching ratios of 62Ga

Beta-decay branching ratios of ⁶²Ga have been measured at the IGISOL facility of the Accelerator Laboratory of the University of Jyv?skyl?. ⁶²Ga is one of the heavier T _z = 0 , 0⁺ → 0⁺ β -emitting nuclides used to determine the vector coupling constant of the weak interaction and the V_ud quark-mixing matrix element. For part of the experimental studies presented here, the JYFLTRAP facility has been employed to prepare isotopically pure beams of ⁶²Ga . The branching ratio obtained, BR = 99.893(24) %, for the super-allowed branch is in agreement with previous measurements and allows to determine the ft value and the universal Ft value for the super-allowed β -decay of ⁶²Ga .