A note on the interaction of unsteady flow with an acoustic liner

The effects of a mean grazing flow on the energy exchanges involved in the interaction of a bias-flow acoustic liner with, respectively, incident sound and boundary layer turbulence are contrasted. The analysis of model problems which make use of a line vortex to simulate large scale, unsteady boundary layer structures indicates that, whereas acoustic waves may be effectively attenuated, dissipation caused by “jetting” in the apertures of the liner can result in a net transfer of energy from the mean flow to the turbulence in the boundary layer.     

Synthesis of 3-aryl-4-isothiazolecarboxylates

A short, convenient route to 3-aryl-4-isothiazolecarboxylates is described in which aryl Grig-nard reagents are added to the magnesium etiolate of ethyl cyanoacetete, and the resultant β-aminocinnamates are converted via a Vilsmeier-Haack reaction, thiation, and oxidation to the isothiazolecarboxylates.     

A density functional study of oxygen activation by unsaturated complexes [M(bipy)(2)](2+), M = Cr and Fe

Density functional theory is used to probe the reaction of O(2) with the unsaturated transition-metal fragments [M(bipy)(2)](2+), M = Cr, Fe. In both cases, calculations indicate that the O(2) molecule is initially trapped as an eta(2)-bound superoxide ion, where the unpaired electron in the out-of-plane pi orbital of O(2) is weakly coupled to those on the trivalent metal ion. In the chromium case, a cis-dioxo Cr(VI) complex is found to be significantly more stable than the superoxo species. The two minima are, however, separated by a large barrier, along with a change in spin state. For the iron analogue, the relative energies of the two minima are reversed, the superoxo complex being the global minimum. The energetics of the O(2) activation processes are consistent with previously reported mass spectrometric experiments, where an adduct, [M(bipy)(2)(O(2))](2+), was detected only for chromium.     

Photoreactivity of ETS-10

Irradiation of H-ETS-10 in the presence of adsorbed methanol or ethene causes photoreduction of Ti(IV) to Ti(III); photoreduction does not occur for Na, K-ETS-10, but a photoinduced polymerization of ethene is observed.     

Pressure transients generated when high-speed trains pass in a tunnel

An analysis is made of the pressure transients generated when two high-speed trains meet in a tunnel. Safe operation at speeds exceeding about 300 km/h usually demands that the hydraulicblockage produced by a train should be small. The problem canthen be formulated in terms of the scattering of the potentialflow near field of each train by the moving surface of theother train, and this permits the derivation of closed formrepresentations of the unsteady pressure in the special caseof ‘snub nosed’ trains in a tunnel of semicircularcross-section. This solution is used to devise a general procedurefor calculating pressure transients generated by trains ofarbitrary nose profiles in tunnels of arbitrary cross-sectionalshape in terms of a knowledge of the local incompressible potentialflow produced by each train travelling separately in the tunnel.Numerical results indicate that at train Mach numbers exceeding0.25the amplitudes of the pressure transients generated bymeeting trains will typically exceed about 25 per cent of theamplitude of the compression wave produced when a train entersor leaves the tunnel. Received 12 April, 1999. Revised 13 March, 2000.     

Is perfection ever attainable? Strong coupling effects in the Perfect Echo

The Perfect Echo sequence, originally proposed in the late 1980s, has recently been popularised with many applications in the field of small-molecule proton NMR spectroscopy. The Perfect Echo refocuses all homonuclear J-couplings for AX spin systems and refocuses magnetization in-phase for more complex weakly coupled spin systems, albeit with some intensity reduction. In contrast to suggestions in previous publications, spectra acquired in our laboratory showed that the Perfect Echo caused intensity distortions in strongly coupled systems where the chemical shift difference between the coupled spins was not large compared to the J-coupling. This paper reports experimental observations and theoretical analysis of strongly coupled spins to confirm the distortions are real and that they originate principally from transfer of magnetization caused by the final inversion pulse of the Perfect Echo. The intensity changes are not large, but because of them, identifications of coupling partners based on resonance intensities (“roofing”) can no longer be relied on when the Perfect Echo is used. However, theory and experiment confirm that adding an orthogonal excitation pulse at the end of the Perfect Echo greatly reduces the distortions.     

Dechanneling of MeV protons in tungsten

Abstract

A systematic investigation of the dechanneling of protons in tungsten has been completed for the <111> axial direction and also for the (110) plane. Measurements at room temperature have been made at energies of 0.5, 2.0, 3.5, 8.0 and 12.0 MeV; at 2.0 MeV, the effect of target temperature has been investigated over the range 77–873°K. In the axial case, the dechanneling rate increases strongly with the vibrational amplitude _ρ, but not as strongly as the ρ² dependence reported by the Catania group (Refs. 4–7) for silicon and germanium. Also, unlike silicon and germanium, the tungsten axial data exhibit practically no energy dependence and so cannot be fitted by the zρ²/E scaling parameter suggested by the Catania group. On the other hand, the planar dechanneling data in tungsten exhibit the predicted (E ^?1)dependence and relatively littie temperature dependence, in good agreement with previous work.     

Stimuli-Responsive Cycloaurated “OFF-ON” Switchable Anion Transporters

Anion transporters have shown potential application as anti-cancer agents that function by disrupting homeostasis and triggering cell death. In this research article we report switchable anion transport by gold complexes of anion transporters that are “switched on” in situ in the presence of the reducing agent GSH by decomplexation of gold. GSH is found in higher concentrations in tumors than in healthy tissue and hence this approach offers a strategy to target these systems to tumors.