Thermodynamic method to two dimensional stagnation flow and heat transfer

The purpose of this paper is to develop a variational technique, using the variational principle of non-equilibrium thermodynamics for the solution of laminar stagnation point flow and heat transfer in two dimensions. The governing principle of dissipative processes is formulated for the problem and then using the boundary conditions of the system the elementary trial functions of third degree are assumed for the flow and temperature fields in the vicinity of the wall. The viscous and thermal boundary layer thicknesses, the skin friction and the rate of heat transfer from the wall to the fluid are obtained. It is found that these new approximate results are quite close to the exact known ones. These results are better than those of the Kármán-Pohlhausen technique.The authors are thankful to the referee for his valuable suggestions.     

Thermal conductivity of NbSe3

The thermal conductivity, κ, of NbSe₃ has been measured by novel self-heating techniques that allowed the electric field dependence of κ to also be measured. Measurements were made from 35 K to room temperature. Above the charge density wave transitions, the phonon thermal conductivity is 4–7 times the electron thermal conductivity, and it rises smoothly below the transitions, indicating that phonon-phonon scattering predominates. Phonon mean free parths have been estimated at 187 A° at 60 K and 60 A° at 150 K. No clear anomalies were observed at the phase transitions, giving upper limits to changes in the phonon mean free path. No field dependence of κ was observed.     

Reactions of phosphorus fluorides and ortho-carborane ditertiary aminophosphines

Fluorophosphine bidentate ligands containing o-carborane as backbone can be prepared by the reaction of the lithium-o-carboranes and PF₂X derivatives to give only two species: the unsymmetrical (C₆H₅)₂P[B₁₀H₁₀C₂]PF₂ and the cyclic FP[B₁₀H₁₀C₂]₂PF, both in low yield. However, exchange of F and NMe₂ groups by use of PF₅ or PF₃ provides a facile way to produce several new fluorophosphines.Phosphorus pentafluoride forms solid adducts with the o-phosphino derivatives (C₆H₅)₂P[B₁₀H₁₀C₂]P(NMe₂)₂, (Me₂N)₂P[B₁₀H₁₀C₂]P(NMe₂)₂ and (C₆H₅)₂P[B₁₀H₁₀C₂]H. All the adducts contain a phosphorus-phosphorus bond as evidenced from i.r., NMR and stoichiometry. The stability of the adducts reflects the strength of the PP bond formed upon complexation. When suspensions or solutions of the adducts are heated they exchange F and NMe₂ groups and no redox occurs. The products (C₆H₅)₂P[B₁₀H₁₀C₂]P(F)NMe₂(I) and Me₂N(F)P[B₁₀H₁₀C₂]P(F)NMe₂(II) react further with PF₅ giving (C₆H₅)₂P[B₁₀H₁₀C₂]PF₂(III) and F₂P[B₁₀H₁₀C₂]PF₂(IV).The precursors also react with phosphorus trifluoride to produce only (I) and (Me₂N)₂P[B₁₀H₁₀C₂]P(F)NMe₂(V) regardless of the reaction conditions. All the products I–V have been identified by ¹H, ¹⁹F, and ³¹P NMR and i.r. spectroscopy, mass spectrometry, and elemental analysis. The NMR spectra of the novel (IV) have been analysed as X₂AA¹X¹₂ spin system.     

Laminar swirling flow in an annulus with porous walls

Flow of an incompressible viscous fluid under constant pressure gradient in a porous annulus is considered, with surface mass transfer, both in the radial and circumferential directions. Expressions for the fully developed velocities are then obtained. With these fully developed velocities on a section of the annulus, on which the origin of co-ordinates lies, the downstream decay of the swirl velocity is analysed, subject to the condition that the velocities on the boundaries are now purely radial. The perturbations in the axial and radial velocities, caused by the decaying swirl, are also determined. It is observed that the decay of the swirl velocity is faster for suction at the inner boundary and injection at the outer andvice versa.     

Synthesis and intramolecular nitrile oxide cycloaddition of 3,5'-ether-linked pseudooligosaccharide derivatives: an approach to chiral macrooxacycles

3,5'-ether-linked pseudooligopentose derivatives were synthesized for the first time from readily available carbohydrate precursors. The 1,2-isopropylidene-protected ether-linked oligopentoses are potentially important as precursors of novel RNA analogues. Intramolecular cycloaddition of the nitrile oxides prepared from these derivatives led to the diastereoselective formation of chiral isoxazolines fused to 10-16-membered oxacycles. The stereochemistry of some of these isoxazolines was established by X-ray diffraction and NOESY analysis.