Sum-free sets and Ramsey numbers

In this note we obtain new lower bounds for the Ramsey numbers R(5, 5) and R(5, 6). The method is based on computational results of partitioning the integers into sum-free sets. We obtain R(5, 5)?42 and R(5, 6)?53.     

Planar laser-induced fluorescence imaging of carbon monoxide using vibrational (infrared) transitions

We report a new imaging diagnostic suitable for measurements of infrared-active molecules, namely infrared planar laser-induced fluorescence (IR PLIF), in which a tunable infrared source is used to excite vibrational transitions in molecules and vibrational fluorescence is collected by an infrared camera. A nanosecond-pulse Nd:YAG-pumped KTP/KTA OPO/OPA system is used to generate 12 mJ of tunable output near 2.35 μm which excites the 2ν band of carbon monoxide (CO); fluorescence resulting from excited CO is collected at 4.7 μm by using an InSb focal plane array. Quantitative, high-SNR PLIF imaging of gas-phase CO is demonstrated at a 10-Hz acquisition rate with a minimum detection limit of 1350 ppm at 300 K. Received: 30 July 1999 / Published online: 16 September 1999     

Using external coils to correct field errors in tokamaks

Non axisymmetric correction coils can be highly effective at canceling the low order magnetic islands generated by magnetic field errors. Correction coil currents which, by themselves, mould produce an island of the same size and opposite phase as the error field, will result in cancelled magnetic islands. In computing the magnetic island sizes and toroidal phases of perturbations, the use of a straight-cylinder approximation can cause substantial error. An n=1 error with arbitrary phase can be corrected at a single resonant surface with one set of four correction coils. Correcting higher n harmonics requires more coils toroidally. Correcting same-n errors at more than one rational surface requires more correction coil sets     

Evidence for the importance of trapped particle resonances for resistive wall mode stability in high beta tokamak plasmas

Active measurements of the plasma stability in tokamak plasmas reveal the importance of kinetic resonances for resistive wall mode stability. The rotation dependence of the magnetic plasma response to externally applied quasistatic n=1 magnetic fields clearly shows the signatures of an interaction between the resistive wall mode and the precession and bounce motions of trapped thermal ions, as predicted by a perturbative model of plasma stability including kinetic effects. The identification of the stabilization mechanism is an essential step towards quantitative predictions for the prospects of "passive" resistive wall mode stabilization, i.e., without the use of an "active" feedback system, in fusion-alpha heated plasmas.     

Optimization of a tracer-based PLIF diagnostic for simultaneous imaging of EGR and temperature in IC engines

A tracer-based planar laser-induced fluorescence (TB-PLIF) imaging diagnostic using 3-pentanone has been optimized for use in IC engines. The diagnostic utilizes dual-wavelength excitation of 3-pentanone in the ultraviolet to make simultaneous measurements of exhaust gas residual mole fraction and temperature. A merit function based optimization of the diagnostic precision was performed which allowed for selection of optimal excitation wavelengths for the conditions of interest. Optimized system performance was validated in a motored optical engine over a wide range of in-cylinder temperatures and pressures. In-cylinder results verify the utility of the uncertainty estimates. Differences in magnitude between the estimated and measured precision were determined to be due to errors in parameter values used in the calculations. The observed 2.1% temperature precision at a temperature of 600 K was compared with previous TB-PLIF temperature measurements and shown to be approximately a factor of 2 better than previous results.