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.     

The genetically optimized tunnel-entrance hood

A numerical procedure is investigated for optimizing the design of tunnel-entrance hoods used for controlling the compression wave generated when a high-speed train enters a tunnel. Long hoods are required for long tunnels and train speeds exceeding about 350 km/h. The hood must minimize the maximum pressure gradient across the compression wave-front by taking advantage of the pressure-release provided by open windows distributed along one or both of its walls. The compression wave produced by the train can be evaluated by means of a rapid computational scheme devised and validated against experiment. Optimization is achieved by representing a possible distribution of windows by a binary string. The individuals in an initial, random population of such strings are allowed to ‘mate’ and evolve by ‘natural selection’ through several generations towards an optimal configuration by application of a genetic algorithm. The genetically fittest hood is associated with the minimum possible maximum pressure gradient for prescribed values of the train speed and hood dimensions. The algorithm yields an optimal design from among a theoretically unlimited number of possibilities; it can also supply near-optimal, smoothly varying window distributions (or optimize the variation in width of a long slit-like window in the hood wall) satisfying additional constraints imposed by the designer.     

Einen elektrischen Widerstands-Tiegel-Ofen aus Magnesia

Ohne Zusammenfassung